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Supplementary methods and figure legends

Supplementary Figures S1-S2, Supplementary Methods, and Supplementary Tables S1-S8.

Purpose: Acalabrutinib (ACP-196) is a novel, potent, and highly selective Bruton tyrosine kinase (BTK) inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. We sought to evaluate the antitumor effects of acalabrutinib treatment in two established mouse models of chronic lymphocytic leukemia (CLL).Experimental Design: Two distinct mouse models were used, the TCL1 adoptive transfer model where leukemic cells from Eμ-TCL1 transgenic mice are transplanted into C57BL/6 mice, and the human NSG primary CLL xenograft model. Mice received either vehicle or acalabrutinib formulated into the drinking water.Results: Utilizing biochemical assays, we demonstrate that acalabrutinib is a highly selective BTK inhibitor as compared with ibrutinib. In the human CLL NSG xenograft model, treatment with acalabrutinib demonstrated on-target effects, including decreased phosphorylation of PLCγ2, ERK, and significant inhibition of CLL cell proliferation. Furthermore, tumor burden in the spleen of the mice treated with acalabrutinib was significantly decreased compared with vehicle-treated mice. Similarly, in the TCL1 adoptive transfer model, decreased phosphorylation of BTK, PLCγ2, and S6 was observed. Most notably, treatment with acalabrutinib resulted in a significant increase in survival compared with mice receiving vehicle.Conclusions: Treatment with acalabrutinib potently inhibits BTK in vivo, leading to on-target decreases in the activation of key signaling molecules (including BTK, PLCγ2, S6, and ERK). In two complementary mouse models of CLL, acalabrutinib significantly reduced tumor burden and increased survival compared with vehicle treatment. Overall, acalabrutinib showed increased BTK selectivity compared with ibrutinib while demonstrating significant antitumor efficacy in vivo on par with ibrutinib. Clin Cancer Res; 23(11); 2831–41. ©2016 AACR.

Purpose: Complete response to induction chemotherapy is observed in ∼60% of patients with newly diagnosed non-M3 acute myelogenous leukemia (AML). However, no methods exist to predict with high accuracy at the individual patient level the response to standard AML induction therapy.Experimental Design: We applied single-cell network profiling (SCNP) using flow cytometry, a tool that allows a comprehensive functional assessment of intracellular signaling pathways in heterogeneous tissues, to two training cohorts of AML samples (n = 34 and 88) to predict the likelihood of response to induction chemotherapy.Results: In the first study, univariate analysis identified multiple signaling “nodes” (readouts of modulated intracellular signaling proteins) that correlated with response (i.e., AUCROC ≥ 0.66; P ≤ 0.05) at a level greater than age. After accounting for age, similar findings were observed in the second study. For patients Conclusions: These data emphasize the value of performing quantitative SCNP under modulated conditions as a basis for the development of tests highly predictive for response to induction chemotherapy. SCNP provides information distinct from other known prognostic factors such as age, secondary AML, cytogenetics, and molecular alterations and is potentially combinable with the latter to improve clinical decision making. Independent validation studies are warranted. Clin Cancer Res; 16(14); 3721–33. ©2010 AACR.

Supplementary Table S1. Kinase selectivity of acalabrutinib as assessed by DiscoveRX KinomeScan screening.

Supplementary Figures 1-4

Purpose: Targeting the B-cell receptor (BCR) pathway with inhibitors of Bruton tyrosine kinase (BTK) and PI3Kδ is highly effective for the treatment of chronic lymphocytic leukemia (CLL). However, deep remissions are uncommon, and drug resistance with single-agent therapy can occur. In vitro studies support the effectiveness of combing PI3Kδ and BTK inhibitors.Experimental Design: As CLL proliferation and survival depends on the microenvironment, we used murine models to assess the efficacy of the BTK inhibitor acalabrutinib combined with the PI3Kδ inhibitor ACP-319 in vivo. We compared single-agent with combination therapy in TCL1-192 cell–injected mice, a model of aggressive CLL.Results: We found significantly larger reductions in tumor burden in the peripheral blood and spleen of combination-treated mice. Although single-agent therapy improved survival compared with control mice by a few days, combination therapy extended survival by over 2 weeks compared with either single agent. The combination reduced tumor proliferation, NF-κB signaling, and expression of BCL-xL and MCL-1 more potently than single-agent therapy.Conclusions: The combination of acalabrutinib and ACP-319 was superior to single-agent treatment in a murine CLL model, warranting further investigation of this combination in clinical studies. Clin Cancer Res; 23(19); 5814–23. ©2017 AACR.

Supplementary Figure S5: Acalabrutinib demonstrates similar changes in proliferation and tumor burden in the CLL xenograft mouse model as ibrutinib.

Supplementary Figure S1: Acalabrutinib is a more potent BCR-inhibitor than ibrutinib in vivo at 1mg/kg and 3mg/kg. Supplementary Figure S2: In vivo gating strategy for murine cells. Supplementary Figure S3: In vivo acalabrutinib treatment inhibits BCR signal transduction similarly to ibrutinib. Supplementary Figure S4: In vitro gating strategy for patient MNCs.

Inhibition of the B-cell receptor pathway, and specifically of Bruton tyrosine kinase (BTK), is a leading therapeutic strategy in B-cell malignancies, including chronic lymphocytic leukemia (CLL). Target occupancy is a measure of covalent binding to BTK and has been applied as a pharmacodynamic parameter in clinical studies of BTK inhibitors. However, the kinetics of de novo BTK synthesis, which determines occupancy, and the relationship between occupancy, pathway inhibition and clinical outcomes remain undefined. This randomized phase 2 study investigated the safety, efficacy, and pharmacodynamics of a selective BTK inhibitor acalabrutinib at 100 mg twice daily (BID) or 200 mg once daily (QD) in 48 patients with relapsed/refractory or high-risk treatment-naïve CLL. Acalabrutinib was well tolerated and yielded an overall response rate (ORR) of partial response or better of 95.8% (95% confidence interval [CI], 78.9-99.9) and an estimated progression-free survival (PFS) rate at 24 months of 91.5% (95% CI, 70.0-97.8) with BID dosing and an ORR of 79.2% (95% CI, 57.9-92.9) and an estimated PFS rate at 24 months of 87.2% (95% CI, 57.2-96.7) with QD dosing. BTK resynthesis was faster in patients with CLL than in healthy volunteers. BID dosing maintained higher BTK occupancy and achieved more potent pathway inhibition compared with QD dosing. Small increments in occupancy attained by BID dosing relative to QD dosing compounded over time to augment downstream biological effects. The impact of BTK occupancy on long-term clinical outcomes remains to be determined. This trial was registered at www.clinicaltrials.gov as #NCT02337829.

Bruton tyrosine kinase (BTK) is an important target in oncology and (auto)immunity. Various BTK inhibitors have been approved or are currently in clinical development. A novel BTK inhibitor series was developed starting with a quinazoline core. Moving from a quinazoline to a quinoline core provided a handle for selectivity for BTK over EGFR and resulted in the identification of potent and selective BTK inhibitors with good potency in human whole blood assay. Furthermore, proof of concept of this series for BTK inhibition was shown in an in vivo mouse model using one of the compounds identified.

Therapeutic targeting of Bruton tyrosine kinase (BTK) has dramatically improved survival outcomes for patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Acalabrutinib is an oral, highly selective BTK inhibitor that allows for twice-daily dosing due to its selectivity. In this phase 1b/2 study, 134 patients with relapsed/refractory CLL or SLL (median age, 66 years [range, 42-85 years]; median prior therapies, 2 [range, 1-13]) received acalabrutinib 100 mg twice daily for a median of 41 months (range, 0.2-58 months). Median trough BTK occupancy at steady state was 97%. Most adverse events (AEs) were mild or moderate, and were most commonly diarrhea (52%) and headache (51%). Grade ≥3 AEs (occurring in ≥5% of patients) were neutropenia (14%), pneumonia (11%), hypertension (7%), anemia (7%), and diarrhea (5%). Atrial fibrillation and major bleeding AEs (all grades) occurred in 7% and 5% of patients, respectively. Most patients (56%) remain on treatment; the primary reasons for discontinuation were progressive disease (21%) and AEs (11%). The overall response rate, including partial response with lymphocytosis, with acalabrutinib was 94%; responses were similar regardless of genomic features (presence of del(11)(q22.3), del(17)(p13.1), complex karyotype, or immunoglobulin variable region heavy chain mutation status). Median duration of response and progression-free survival (PFS) have not been reached; the estimated 45-month PFS was 62% (95% confidence interval, 51% to 71%). BTK mutation was detected in 6 of 9 patients (67%) at relapse. This updated and expanded study confirms the efficacy, durability of response, and long-term safety of acalabrutinib, justifying its further investigation in previously untreated and treated patients with CLL/SLL. This trial was registered at www.clinicaltrials.gov as #NCT02029443.

Purpose: Targeting the B-cell receptor (BCR) pathway with inhibitors of Bruton tyrosine kinase (BTK) and PI3Kδ is highly effective for the treatment of chronic lymphocytic leukemia (CLL). However, deep remissions are uncommon, and drug resistance with single-agent therapy can occur. In vitro studies support the effectiveness of combing PI3Kδ and BTK inhibitors. Experimental Design: As CLL proliferation and survival depends on the microenvironment, we used murine models to assess the efficacy of the BTK inhibitor acalabrutinib combined with the PI3Kδ inhibitor ACP-319 in vivo. We compared single-agent with combination therapy in TCL1-192 cell–injected mice, a model of aggressive CLL. Results: We found significantly larger reductions in tumor burden in the peripheral blood and spleen of combination-treated mice. Although single-agent therapy improved survival compared with control mice by a few days, combination therapy extended survival by over 2 weeks compared with either single agent. The combination reduced tumor proliferation, NF-κB signaling, and expression of BCL-xL and MCL-1 more potently than single-agent therapy. Conclusions: The combination of acalabrutinib and ACP-319 was superior to single-agent treatment in a murine CLL model, warranting further investigation of this combination in clinical studies. Clin Cancer Res; 23(19); 5814–23. ©2017 AACR.

International audience; BACKGROUND:Bruton tyrosine kinase is a clinically validated target in mantle cell lymphoma. Acalabrutinib (ACP-196) is a highly selective, potent Bruton tyrosine kinase inhibitor developed to minimise off-target activity.METHODS:In this open-label, phase 2 study, oral acalabrutinib (100 mg twice per day) was given to patients with relapsed or refractory mantle cell lymphoma, until disease progression or unacceptable toxicity. The primary endpoint was overall response assessed according to the Lugano classification, and safety analyses were done in all participants. This trial is registered with ClinicalTrials.gov, number NCT02213926.FINDINGS:From March 12, 2015, to Jan 5, 2016, 124 patients with relapsed or refractory mantle cell lymphoma were enrolled and all patients received treatment; median age 68 years. Patients received a median of two (IQR 1-2) previous therapies. At a median follow-up of 15·2 months, 100 (81%) patients achieved an overall response and 49 (40%) patients achieved a complete response. The Kaplan-Meier estimated medians for duration of response, progression-free survival, and overall survival were not reached; the 12-month rates were 72% (95% CI 62-80), 67% (58-75), and 87% (79-92%), respectively. The most common adverse events were primarily grade 1 or 2 and were headache (47 [38%]), diarrhoea (38 [31%]), fatigue (34 [27%]), and myalgia (26 [21%]). The most common grade 3 or worse adverse events were neutropenia (13 [10%]), anaemia (11 [9%]), and pneumonia (six [5%]). There were no cases of atrial fibrillation and one case of grade 3 or worse haemorrhage. The median duration of treatment was 13·8 months. Treatment was discontinued in 54 (44%) patients, primarily due to progressive disease (39 [31%]) and adverse events (seven [6%]).INTERPRETATION:Acalabrutinib treatment provided a high rate of durable responses and a favourable safety profile in patients with relapsed or refractory mantle cell lymphoma. These findings suggest an important role for acalabrutinib in the treatment of this disease population.FUNDING:Acerta Pharma, a member of the AstraZeneca Group.Copyright © 2017 Elsevier Ltd. All rights reserved.

Several small-molecule Bruton tyrosine kinase (BTK) inhibitors are in development for B cell malignancies and autoimmune disorders, each characterized by distinct potency and selectivity patterns. Herein we describe the pharmacologic characterization of BTK inhibitor acalabrutinib [compound 1, ACP-196 (4-[8-amino-3-[(2S)-1-but-2-ynoylpyrrolidin-2-yl]imidazo[1,5-a]pyrazin-1-yl]-N-(2-pyridyl)benzamide)]. Acalabrutinib possesses a reactive butynamide group that binds covalently to Cys481 in BTK. Relative to the other BTK inhibitors described here, the reduced intrinsic reactivity of acalabrutinib helps to limit inhibition of off-target kinases having cysteine-mediated covalent binding potential. Acalabrutinib demonstrated higher biochemical and cellular selectivity than ibrutinib and spebrutinib (compounds 2 and 3, respectively). Importantly, off-target kinases, such as epidermal growth factor receptor (EGFR) and interleukin 2-inducible T cell kinase (ITK), were not inhibited. Determination of the inhibitory potential of anti-immunoglobulin M-induced CD69 expression in human peripheral blood mononuclear cells and whole blood demonstrated that acalabrutinib is a potent functional BTK inhibitor. In vivo evaluation in mice revealed that acalabrutinib is more potent than ibrutinib and spebrutinib. Preclinical and clinical studies showed that the level and duration of BTK occupancy correlates with in vivo efficacy. Evaluation of the pharmacokinetic properties of acalabrutinib in healthy adult volunteers demonstrated rapid absorption and fast elimination. In these healthy individuals, a single oral dose of 100 mg showed approximately 99% median target coverage at 3 and 12 hours and around 90% at 24 hours in peripheral B cells. In conclusion, acalabrutinib is a BTK inhibitor with key pharmacologic differentiators versus ibrutinib and spebrutinib and is currently being evaluated in clinical trials.

Ribosomal biogenesis involves the processing of pre-ribosomal RNA. A deficiency of some ribosomal proteins (RPs) impairs processing and causes Diamond Blackfan anemia (DBA), which is associated with anemia, congenital malformations and cancer. p53 mediates many features of DBA, but the mechanism of p53 activation remains unclear. Another hallmark of DBA is the upregulation of adenosine deaminase (ADA), indicating changes in nucleotide metabolism. In RP-deficient zebrafish, we found activation of both nucleotide catabolism and biosynthesis, which is consistent with the need to break and replace the faulty ribosomal RNA. We also found upregulation of deoxynucleotide triphosphate (dNTP) synthesis – a typical response to replication stress and DNA damage. Both RP-deficient zebrafish and human hematopoietic cells showed activation of the ATR/ATM-CHK1/CHK2/p53 pathway. Other features of RP deficiency included an imbalanced dNTP pool, ATP depletion and AMPK activation. Replication stress and DNA damage in cultured cells in non-DBA models can be decreased by exogenous nucleosides. Therefore, we treated RP-deficient zebrafish embryos with exogenous nucleosides and observed decreased activation of p53 and AMPK, reduced apoptosis, and rescue of hematopoiesis. Our data suggest that the DNA damage response contributes to p53 activation in cellular and zebrafish models of DBA. Furthermore, the rescue of RP-deficient zebrafish with exogenous nucleosides suggests that nucleoside supplements could be beneficial in the treatment of DBA.

Background: Acalabrutinib (ACP-196) is a highly selective, potent Bruton tyrosine kinase (BTK) inhibitor developed to minimize off-target activity. Acalabrutinib monotherapy shows promising safety and efficacy in CLL (Ghia et al 2019). However, a few patients (pts) develop resistance to acalabrutinib. A known mechanism of covalent BTK inhibitor resistance is acquired mutations in BTK (particularly Cys481) and its downstream target PLCg2. Alternate mechanisms and the contribution of the CLL microenvironment to acquired resistance remain to be elucidated. In this study, we performed cell surface phenotyping, intracellular signaling, and RNA-seq analyses on samples from 39 pts with relapsed/refractory or treatment-naive CLL from the ACE-CL-001 clinical trial (NCT02029443) to identify novel mechanisms of acalabrutinib resistance with focus on the CLL microenvironment. Methods : Pts were divided into 2 groups: those who continued to respond to treatment (non-progressed, NP, n=23) and those who developed progressive disease (progressed, PD, n=16) within 36 months of starting acalabrutinib. Blood mononuclear cells (PBMCs) were analyzed after 6 months of acalabrutinib therapy (100 mg twice a day) for the first (NP) group of patients, or at the time of progression for the second (PD) group of patients and compared with pre-treatment baseline. Expression of cell surface markers, including CD49d, CD38, and CD79b, was evaluated by flow cytometry. A 30% positive cut-off was used to identify pts that express high levels of CD49d, an α-chain of the VLA-4 integrin (Tissino, et al 2018), CD38, and CD79b. Intracellular flow cytometry was used to measure cell proliferation via Ki-67 staining. RNA-seq was used to measure changes in gene expression. Results: Cell surface phenotyping showed higher expression of CD49d (p Conclusions: High surface expression of CD49d (VLA-4) and CD79b prior to and after therapy correlates with acalabrutinib resistance in pts with CLL. Targeting CD49d may prove an effective strategy to overcome acalabrutinib resistance in CD49d high pts. Disclosures Bibikova: Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Law:Acerta Pharma: Employment; AstraZeneca: Equity Ownership. Clevenger:Acerta Pharma: Employment; AstraZeneca: Equity Ownership. Cheung:AstraZeneca: Equity Ownership; Acerta Pharma: Employment, Equity Ownership. De Jesus:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Gulrajani:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Yamaguchi:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Do:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Burke:AstraZeneca: Employment, Equity Ownership. Brock:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Munugalavadla:Gilead Sciences: Equity Ownership; AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Frigault:Acerta Pharma: Employment; AstraZeneca: Employment, Equity Ownership. Byrd:Acerta: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Genentech: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; BeiGene: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S; Novartis: Other: Travel Expenses, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S. Furman:Acerta Pharma: Consultancy; AstraZeneca: Consultancy; Incyte: Consultancy; Janssen: Consultancy; Beigene: Consultancy; Oncotracker: Consultancy; Pharmacyclics: Consultancy; Sunesis: Consultancy; TG Therapeutics: Consultancy; Verastem: Consultancy; Genentech: Consultancy; Abbvie: Consultancy. Brown:Catapult Therapeutics: Consultancy; AbbVie: Consultancy; Genentech/Roche: Consultancy; Acerta Pharma: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy; Janssen: Honoraria; Teva: Honoraria; AstraZeneca: Consultancy; Octapharma: Consultancy; Invectys: Other: Data safety monitoring board; Morphosys: Other: Data safety monitoring board; Dynamo Therapeutics: Consultancy; BeiGene: Consultancy; TG Therapeutics: Consultancy; Sunesis: Consultancy; Loxo: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Juno/Celgene: Consultancy; Gilead: Consultancy, Research Funding; Verastem: Consultancy, Research Funding; Sun Pharmaceuticals: Research Funding; Novartis: Consultancy. Covey:AstraZeneca: Equity Ownership; Acerta Pharma: Employment, Equity Ownership.

Background: Targeted inhibition of Bruton tyrosine kinase (BTK) has improved clinical outcomes for patients with chronic lymphocytic leukemia (CLL). Acalabrutinib is a highly selective, covalent BTK inhibitor. A recently completed phase 3 trial showed acalabrutinib improved progression-free survival (PFS) vs idelalisib or bendamustine + rituximab in relapsed/refractory (R/R) CLL patients (ASCEND: Ghia et al. EHA 2019;273259:LB2606). This is an updated analysis with extended follow-up of a phase 1-2 multicenter study (NCT02029443) in patients with R/R CLL/small lymphocytic lymphoma (SLL), to demonstrate the durability of response and long-term tolerability of acalabrutinib. Methods: Patients with CLL or SLL were eligible if they were R/R after ≥1 prior treatment. Eligible patients were ≥18 years of age with an Eastern Cooperative Oncology Group performance status (ECOG PS) ≤2. Oral acalabrutinib 100 mg was administered twice daily. All patients were treated until progressive disease or unacceptable toxicity occurred. Study endpoints included overall response rate (ORR), PFS, duration of response (DOR) and safety, with post hoc analysis of event-free survival (EFS). Response rates were based on the International Workshop on Chronic Lymphocytic Leukemia 2008 criteria (Hallek et al., 2008) with modification for lymphocytosis (Cheson et al., 2012). Nine patients had longitudinal peripheral blood mononuclear cell samples from pre-treatment baseline, during treatment and at progression analyzed for whole exome sequencing, to assess acquired mechanisms of treatment resistance. Results: In total, 134 patients with R/R CLL/SLL received ≥ 1 dose of acalabrutinib. The median age was 66 years (range, 42-85 years). Baseline characteristics included ECOG PS ≤1 (97%), bulky lymph nodes ≥5 cm (39%), unmutated immunoglobulin heavy chain variable region (IGHV; 73%), chromosome 17p13.1 deletion (23%), chromosome 11q22.3 deletion (18%), and complex karyotype (≥3 abnormalities; 35%). The median number of prior therapies was 2 (range, 1-13). Patients received acalabrutinib for a median of 41 months (range, 0.2-58 months). Most adverse events (AEs) were mild to moderate, and most commonly were diarrhea (52%), headache (46%), and upper respiratory tract infection (36%). Grade ≥3 AEs occurred in 66% of patients; most commonly (≥5% of patients) neutropenia (14%), pneumonia (11%), hypertension (7%), anemia (7%) and diarrhea (5%). AEs of interest included atrial fibrillation (7% all grades; 3% Grade ≥3) and major bleeding events (5% all grades; 3% Grade ≥3). Most patients (56%) remained on treatment. The most common reasons for discontinuing treatment were progressive disease (21%) and AEs (11%). AEs leading to discontinuation occurring in ≥1 patient included pneumonia (4 events), anemia, neutropenia, and thrombocytopenia (2 events each). The ORR (partial response with lymphocytosis or above) was 94% (95% confidence interval [CI]: 89-97%); with 4% of patients having complete response, 84% having partial response and 6% having partial response with lymphocytosis (Table). The median DOR, PFS and EFS were not reached; the estimated 42-month DOR was 61% (95% CI: 49-71%), PFS was 68% (95% CI: 59-76%) and EFS was 64% (95% CI: 54-71%). Responses were similar regardless of genomic features, including unmutated IGHV, chromosomal deletions and complex karyotype (Table). Upon relapse during acalabrutinib treatment, whole exome sequencing detected BTK mutations in 6 of 9 (67%) tested patients that were not detectable at baseline. Of the 6 patients with detectable BTK C481X mutations, 4 had expansion to high allele frequency of the BTK mutation at progression (up to 58%). In a longitudinal analysis of patients who had a sample after 6 months of treatment, the BTK mutation was not detectable. No PLCG2 gene mutations were detected using exome analysis in the 9 patients analyzed. Conclusions: These updated results confirm the earlier reports of acalabrutinib efficacy for the treatment of CLL and provide additional data on DOR and long-term tolerability. Reported AEs indicate a tolerable and consistent safety profile, with a low rate of major bleeding events. Genomic profiling in a small subset of patients indicated that acquired mutation of BTK was the most frequent mechanism of acalabrutinib resistance. Disclosures Furman: Genentech: Consultancy. Wierda:Loxo Oncology Inc.: Research Funding; Janssen: Research Funding; Xencor: Research Funding; Cyclcel: Research Funding; Oncternal Therapeutics Inc.: Research Funding; Miragen: Research Funding; Sunesis: Research Funding; KITE pharma: Research Funding; Juno Therapeutics: Research Funding; Gilead Sciences: Research Funding; Acerta Pharma Inc: Research Funding; Pharmacyclics LLC: Research Funding; Genentech: Research Funding; AbbVie: Research Funding; GSK/Novartis: Research Funding. Schuh:Roche: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Gilead: Consultancy, Honoraria. Devereux:Servier: Speakers Bureau; Roche: Consultancy, Other: Travel expenses, Speakers Bureau; GlaxoSmithKline: Consultancy; Gilead: Consultancy, Honoraria, Other: Travel expenses, Speakers Bureau; MSD: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Other: Travel expenses, Speakers Bureau. Brown:Pfizer: Consultancy; Sun: Research Funding; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Teva: Honoraria; Sunesis: Consultancy; Pharmacyclics: Consultancy; Morphosys: Other: Data safety monitoring boards ; Sun Pharmaceuticals, Inc: Research Funding; Acerta Pharma: Consultancy; AstraZeneca: Consultancy; BeiGene: Consultancy; Catapult Therapeutics: Consultancy; Dynamo Therapeutics: Consultancy; Genentech/Roche: Consultancy; Gilead: Consultancy, Research Funding; Invectys: Other: other; Janssen: Honoraria; Kite: Consultancy, Research Funding; Loxo: Consultancy, Research Funding; Novartis: Consultancy; Octapharma: Consultancy. Hillmen:AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Expenses, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Expenses, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding; Roche: Research Funding; Gilead: Research Funding; Apellis: Research Funding; Acerta: Membership on an entity's Board of Directors or advisory committees. Martin:Karyopharm: Consultancy; Teneobio: Consultancy; Celgene: Consultancy; I-MAB: Consultancy; Sandoz: Consultancy; Janssen: Consultancy. Awan:Sunesis: Consultancy; AstraZeneca: Consultancy, Speakers Bureau; Innate Pharma: Research Funding; Gilead: Consultancy; Janssen: Consultancy; Abbvie: Consultancy, Speakers Bureau; Pharmacyclics: Consultancy, Research Funding. Stephens:Acerta: Research Funding; Gilead: Research Funding; Karyopharm: Research Funding. Ghia:Sunesis: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; ArQule: Consultancy, Honoraria; BeiGene: Consultancy, Honoraria; Dynamo: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Juno/Celgene: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Acerta/AstraZeneca: Consultancy, Honoraria; Pharmacyclics LLC, an AbbVie Company: Consultancy. Barrientos:Bayer: Consultancy; AstraZeneca: Consultancy; AbbVie: Consultancy, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; Genentech: Consultancy; Gilead: Consultancy; Janssen: Honoraria; Sandoz: Consultancy; Oncternal Therapeutics: Research Funding. Pagel:AstraZeneca: Consultancy; Gilead Sciences: Consultancy; Pharmacyclics: Consultancy. Woyach:Janssen: Consultancy, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; AbbVie: Research Funding; Karyopharm: Research Funding; Loxo: Research Funding; Morphosys: Research Funding; Verastem: Research Funding. Burke:AstraZeneca: Employment, Equity Ownership. Covey:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Gulrajani:AstraZeneca: Equity Ownership; Acerta Pharma: Employment, Equity Ownership. Hamdy:Acerta Pharma: Employment, Equity Ownership. Izumi:Acerta Pharma: Employment, Equity Ownership. Frigault:Acerta Pharma: Employment; AstraZeneca: Employment, Equity Ownership. Patel:Acerta Pharma: Employment, Equity Ownership. Rothbaum:Acerta Pharma: Employment, Equity Ownership. Wang:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. O'Brien:Eisai: Consultancy; Celgene: Consultancy; TG Therapeutics: Consultancy, Research Funding; Sunesis: Consultancy, Research Funding; GlaxoSmithKline: Consultancy; Gilead: Consultancy, Research Funding; Verastem: Consultancy; Vaniam Group LLC: Consultancy; Astellas: Consultancy; Pfizer: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Acerta: Research Funding; Alexion: Consultancy; Amgen: Consultancy; Aptose Biosciences, Inc: Consultancy; Regeneron: Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; Janssen: Consultancy, Honoraria; Kite: Research Funding. Byrd:Ohio State University: Patents & Royalties: OSU-2S; BeiGene: Research Funding; Acerta: Research Funding; Genentech: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; Novartis: Other: Travel Expenses, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Genentech: Research Funding; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau. OffLabel Disclosure: This is a Phase 1/2 investigational study of acalabrutinib in chronic lymphocytic leukemia

Chronic Lymphocytic Leukemia (CLL) is the predominant hematologic malignancy in the U.S. BTK inhibitors (BTKi) demonstrate prolonged survival compared to standard chemotherapy, but they also show notable toxicity, including increased risk for infections. While BTKi have shown both immunosuppressive and -stimulatory effects, the overall effect on T cells (TC), including tumor-reactive TC, is not well understood. Because non-BTK TEC-family and homologous kinases have critical roles in immune cells, we tested whether differentially specific BTKi have differing immunomodulatory effects. We treated mice with ibrutinib or acalabrutinib in vivo and analyzed their immune cell repertoire. Mass cytometry revealed that acalabrutinib, but not ibrutinib, increased the number of NK cells and myeloid cells in spleens and tumors of A20-lymphoma bearing mice, while both BTKi increased TC numbers in A20 tumors. Ibrutinib inhibited the activation of CD8 TC and NK cells isolated from BTKi-treated mice and their ability to lyse tumor cells ex vivo, while acalabrutinib improved CD8 TC-mediated cytolysis. A20 tumor growth was not influenced by BTKi in vivo, but ibrutinib inhibited the ability of transferred, antigen-specific TC to induce tumor regression. To translate our findings, we tested the effect of BTKi on immunogenicity of primary human CLL/MCL cells and their ability to stimulate TC. Ibrutinib inhibited upregulation of activation markers on tumor cells to a higher extent than acalabrutinib. Similarly, only ibrutinib inhibited autologous TC activation after co-culture with tumor cells and superantigen. In conclusion, ibrutinib, but not acalabrutinib inhibits the activation and function of anti-tumor T and NK cells in vivo and in vitro.

The aim of this study was to assess the feasibility of applying the single cell network profiling (SCNP) assay to the examination of signaling networks in epithelial cancer cells, using bladder washings from 29 bladder cancer (BC) and 15 nonbladder cancer (NC) subjects. This report describes the methods we developed to detect rare epithelial cells (within the cells we collected from bladder washings), distinguish cancer cells from normal epithelial cells, and reproducibly quantify signaling within these low frequency cancer cells. Specifically, antibodies against CD45, cytokeratin, EpCAM, and cleaved-PARP (cPARP) were used to differentiate nonapoptotic epithelial cells from leukocytes, while measurements of DNA content to determine aneuploidy (DAPI stain) allowed for distinction between tumor and normal epithelial cells. Signaling activity in the PI3K and MAPK pathways was assessed by measuring intracellular levels of p-AKT and p-ERK at baseline and in response to pathway modulation; 66% (N = 19) of BC samples and 27% (N = 4) of NC samples met the "evaluable" criteria, i.e., at least 400,000 total cells available upon sample receipt with >2% of cells showing an epithelial phenotype. The majority of epithelial cells detected in BC samples were nonapoptotic and all signaling data were generated from identified cPARP negative cells. In four of 19 BC samples but in none of the NC specimens, SCNP assay identified epithelial cancer cells with a quantifiable increase in epidermal growth factor-induced p-AKT and p-ERK levels. Furthermore, preincubation with the PI3K inhibitor GDC-0941 reduced or completely inhibited basal and epidermal growth factor-induced p-AKT but, as expected, had no effect on p-ERK levels. This study demonstrates the feasibility of applying SCNP assay using multiparametric flow cytometry to the functional characterization of rare, bladder cancer cells collected from bladder washing. Following assay standardization, this method could potentially serve as a tool for disease characterization and drug development in bladder cancer and other solid tumors.

Purpose: Acalabrutinib (ACP-196) is a novel, potent, and highly selective Bruton tyrosine kinase (BTK) inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. We sought to evaluate the antitumor effects of acalabrutinib treatment in two established mouse models of chronic lymphocytic leukemia (CLL). Experimental Design: Two distinct mouse models were used, the TCL1 adoptive transfer model where leukemic cells from Eμ-TCL1 transgenic mice are transplanted into C57BL/6 mice, and the human NSG primary CLL xenograft model. Mice received either vehicle or acalabrutinib formulated into the drinking water. Results: Utilizing biochemical assays, we demonstrate that acalabrutinib is a highly selective BTK inhibitor as compared with ibrutinib. In the human CLL NSG xenograft model, treatment with acalabrutinib demonstrated on-target effects, including decreased phosphorylation of PLCγ2, ERK, and significant inhibition of CLL cell proliferation. Furthermore, tumor burden in the spleen of the mice treated with acalabrutinib was significantly decreased compared with vehicle-treated mice. Similarly, in the TCL1 adoptive transfer model, decreased phosphorylation of BTK, PLCγ2, and S6 was observed. Most notably, treatment with acalabrutinib resulted in a significant increase in survival compared with mice receiving vehicle. Conclusions: Treatment with acalabrutinib potently inhibits BTK in vivo, leading to on-target decreases in the activation of key signaling molecules (including BTK, PLCγ2, S6, and ERK). In two complementary mouse models of CLL, acalabrutinib significantly reduced tumor burden and increased survival compared with vehicle treatment. Overall, acalabrutinib showed increased BTK selectivity compared with ibrutinib while demonstrating significant antitumor efficacy in vivo on par with ibrutinib. Clin Cancer Res; 23(11); 2831–41. ©2016 AACR.

Acalabrutinib (ACP-196) is a second-generation inhibitor of Bruton agammaglobulinemia tyrosine kinase (BTK) with increased target selectivity and potency compared to ibrutinib. In this study, we evaluated acalabrutinib in spontaneously occurring canine lymphoma, a model of B-cell malignancy similar to human diffuse large B-cell lymphoma (DLBCL). First, we demonstrated that acalabrutinib potently inhibited BTK activity and downstream effectors in CLBL1, a canine B-cell lymphoma cell line, and primary canine lymphoma cells. Acalabrutinib also inhibited proliferation in CLBL1 cells. Twenty dogs were enrolled in the clinical trial and treated with acalabrutinib at dosages of 2.5 to 20mg/kg every 12 or 24 hours. Acalabrutinib was generally well tolerated, with adverse events consisting primarily of grade 1 or 2 anorexia, weight loss, vomiting, diarrhea and lethargy. Overall response rate (ORR) was 25% (5/20) with a median progression free survival (PFS) of 22.5 days. Clinical benefit was observed in 30% (6/20) of dogs. These findings suggest that acalabrutinib is safe and exhibits activity in canine B-cell lymphoma patients and support the use of canine lymphoma as a relevant model for human non-Hodgkin lymphoma (NHL).

Background Irreversible inhibition of Bruton's tyrosine kinase (BTK) by ibrutinib represents an important therapeutic advance for the treatment of chronic lymphocytic leukemia (CLL). However, ibrutinib also irreversibly inhibits alternative kinase targets, which potentially compromises its therapeutic index. Acalabrutinib (ACP-196) is a more selective, irreversible BTK inhibitor that is specifically designed to improve on the safety and efficacy of first-generation BTK inhibitors. Methods In this uncontrolled, phase 1-2, multicenter study, we administered oral acalabrutinib to 61 patients who had relapsed CLL to assess the safety, efficacy, pharmacokinetics, and pharmacodynamics of acalabrutinib. Patients were treated with acalabrutinib at a dose of 100 to 400 mg once daily in the dose-escalation (phase 1) portion of the study and 100 mg twice daily in the expansion (phase 2) portion. Results The median age of the patients was 62 years, and patients had received a median of three previous therapies for CLL; 31% had chromosome 17p13.1 deletion, and 75% had unmutated immunoglobulin heavy-chain variable genes. No dose-limiting toxic effects occurred during the dose-escalation portion of the study. The most common adverse events observed were headache (in 43% of the patients), diarrhea (in 39%), and increased weight (in 26%). Most adverse events were of grade 1 or 2. At a median follow-up of 14.3 months, the overall response rate was 95%, including 85% with a partial response and 10% with a partial response with lymphocytosis; the remaining 5% of patients had stable disease. Among patients with chromosome 17p13.1 deletion, the overall response rate was 100%. No cases of Richter's transformation (CLL that has evolved into large-cell lymphoma) and only one case of CLL progression have occurred. Conclusions In this study, the selective BTK inhibitor acalabrutinib had promising safety and efficacy profiles in patients with relapsed CLL, including those with chromosome 17p13.1 deletion. (Funded by the Acerta Pharma and others; ClinicalTrials.gov number, NCT02029443 .).

Background: Bruton tyrosine kinase (BTK) is a critical component of B-cell receptor signaling and a validated target for CLL. Acalabrutinib is a highly selective, potent, covalent BTK inhibitor, which has shown promising efficacy and safety in patients with CLL, including high-risk patients. We present preliminary efficacy, safety, and pharmacodynamic results from an ongoing single-center, open-label, phase 2 study of acalabrutinib monotherapy in patients with R/R and high-risk, TN CLL. Methods: Patients with R/R or high-risk (chromosome 17p deletion [del17p] or mutation in TP53 or NOTCH1) TN CLL/small lymphocytic lymphoma (SLL) who met International Workshop on Chronic Lymphocytic Leukemia (IWCLL) 2008 criteria for treatment and had an Eastern Cooperative Oncology Group performance status ≤2 were eligible. Patients who had prior BTK inhibitor therapy were excluded. Patients were randomized to receive oral acalabrutinib 100 mg twice daily (BID) or 200 mg daily (QD) until progressive disease or unacceptable toxicity. The primary endpoint was investigator-assessed overall response rate (ORR) by IWCLL 2008 criteria with modification for lymphocytosis. Secondary endpoints included safety and BTK occupancy. BTK occupancy was measured with a biotin-tagged analogue probe in peripheral blood cells at drug trough time points after 3 days of dosing and after 1, 6, and 12 mo of treatment. BTK occupancy in lymph node samples was measured at drug trough time points after 3 days of dosing. Results: Forty-six patients were enrolled and treated (100 mg BID, n=22; 200 mg QD, n=24). The median age was 64 years (range, 45-83), and 35% (16/46) were TN. Approximately 39% of patients (25% of TN) had bulky lymph nodes ≥5 cm, 37% (50% of TN) had Rai stage III-IV disease at baseline, 76% (88% of TN) had unmutatedIGHV, 21% (40% of TN) had del(17p), 21% (23% of TN) had TP53 mutation, and 47% (54% of TN) had NOTCH1 mutation. As of April 13, 2018, the median time on study for all treated patients was 20 mo (range 1-39), with 89% (41/46) remaining on acalabrutinib. Two patients (9%) in the BID group and 3 patients (13%) in the QD group discontinued treatment due to an adverse event (AE; n=1), progressive disease (n=1), and other reasons (n=3). The patient who discontinued due to progressive disease (BID group) achieved partial response at 2 mo and developed Richter transformation at 6 mo. The ORR was 90% (95% CI: 76, 97) for efficacy evaluable patients (N=39), defined per protocol as patients who had ≥ 6 mo of acalabrutinib (Table). ORR was 95% (75, 100) and 84% (60, 97) for the BID and QD group, respectively. For the intent-to-treat population (N=46), ORR was 80% (66, 91). Most AEs were grade 1/2 and did not require dose delays or modifications. The most common AEs (all grades; >25%) were headache (63%), contusion (50%), diarrhea (43%), upper respiratory tract infection (43%), arthralgia (33%), influenza-like illness (28%), maculo-papular rash (28%), myalgia (26%), and nausea (26%). Grade 3/4 AEs occurred in 33% (15/46) of patients (BID, 27% [6/22]; QD, 38% [9/24]), most commonly (>10%) infections (13%; urinary tract infection, lung infection, hepatitis B reactivation, which led to treatment discontinuation and fatal hepatic failure after 10 mo of treatment, and an invasive pulmonary aspergillosis at 2 mo in the setting of prolonged neutropenia and recent systemic corticosteroid use that led to treatment discontinuation) and neutropenia (11%). Approximately 33% (15/46) of patients (BID, 23% [5/22]; QD, 42% [10/24]) reported serious AEs (all grades), most commonly (>5%) lung infection (7%). No atrial fibrillation was reported, and one grade 1 atrial flutter occurred (BID). On day 4 of cycle 1, median trough BTK occupancy was significantly higher for the BID group versus the QD group in the peripheral blood (95% vs 87%; P Conclusion: Acalabrutinib monotherapy produced high ORR in R/R and high-risk TN CLL, with an acceptable safety profile. The study was not designed to detect a statistically significant difference in clinical outcomes between the dosing groups. Near complete target coverage (>95%) was more rapidly achieved with 100 mg BID than 200 mg QD dosing in the lymph node and peripheral blood. Disclosures Nierman: National Institutes of Health: Employment. Covey:Acerta Pharma: Employment; AstraZeneca: Equity Ownership. Hamdy:Acerta Pharma: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: various patents for ACP-196. Izumi:Acerta Pharma: Employment, Equity Ownership, Patents & Royalties: Acerta Pharma, various patents for ACP-196. Liu:Acerta Pharma: Employment. Patel:Acerta Pharma: Employment, Equity Ownership. Wiestner:Pharmacyclics LLC, an AbbVie Company: Research Funding.

Background: Bruton tyrosine kinase (BTK) is a validated target for B-cell malignancies. The BTK inhibitor ibrutinib was approved in chronic lymphocytic leukemia, mantle cell lymphoma (MCL), and Waldenstrom macroglobulinemia. Acalabrutinib is a potent, highly selective, covalent BTK inhibitor with minimal off-target activity; it received accelerated FDA approval in October 2017 for the treatment of patients with MCL having ≥1 prior therapy. In addition to the approved covalent BTK inhibitors ibrutinib and acalabrutinib, clinical data in B-cell malignancies are available for spebrutinib (CC-292), tirabrutinib (ONO/GS-4059) and zanubrutinib (BGB-3111). We performed biochemical and cellular profiling of these 5 BTK inhibitors, investigating potency and selectivity. Methods: Two biochemical kinase assays assessed BTK inhibitor potency, with IC50 determination at a fixed time point (IMAP; Molecular Devices) or over time (LanthaScreen; Invitrogen); the latter was used to calculate binding kinetics. Kinome profiling was performed at a single dose (1 µM) using KINOMEscan (Eurofins DiscoverX). IC50 determinations were made using kinases with a Cys in the same position as the Cys481 residue in BTK, using assays developed in house (using IMAP and LanthaScreen) or at Thermo Fisher Scientific (Z'-LYTE) with IC50 determination at a fixed time point. On-target inhibition of BTK in cellular assays was evaluated using B-cell receptor-mediated activation of CD69 expression on peripheral B cells using human peripheral blood mononuclear cells (hPBMCs) or human whole blood (hWB). Off-target inhibition of epidermal growth factor receptor (EGFR) was evaluated in a cellular assay examining the effect of EGF-induced EGFR phosphorylation in A431 cells. Off-target inhibition of ITK and/or TXK was evaluated using T-cell receptor (TCR)-mediated activation of interleukin-2 expression in Jurkat T cells and CD25 cell surface expression using primary human peripheral T cells. Results: Based on biochemical binding kinetics, ibrutinib and zanubrutinib were the most potent BTK inhibitors (Table 1), followed by spebrutinib; acalabrutinib and tirabrutinib had comparable potency. Differences in potency were largely driven by differences in inactivation rates. However, differences in biochemical potency were lost (in part) in cellular assays using hPBMCs or hWB. EC50 values in hWB were Differences in overall kinase selectivity were observed among the BTK inhibitors (Figure 1; KINOMEscan). Acalabrutinib had the lowest hit rate; 1.5% of human wild-type kinases were inhibited >65% at 1 µM (excluding BTK). Kinase hit rate was also low for tirabrutinb (2.3%), whereas ibrutinib (9.4%), zanubrutinib (4.3%), and spebrutinib (8.3%) had higher hit rates. Acalabrutinib had a high selectivity for BTK over kinases with a Cys in the same position as the Cys481 residue in BTK (Table 2). Similar results were observed for tirabrutinib, whereas ibrutinib, spebrutinib and zanubrutinib were less selective in this panel of kinases with potential for off-target covalent binding by BTK inhibitors (Table 2). Acalabrutinib also had a higher selectivity for BTK over Src-family kinases than the other BTK inhibitors tested. Acalabrutinib and tirabrutinib had EC50 values >10 µM in the cellular assay of off-target inhibition of EGFR; ibrutinib, zanubrutinib, and spebrutinib had EC50 values of 0.07, 0.39, and 4.7 µM, respectively. No off-target inhibition was observed for acalabrutinib or tirabrutinib on TCR-mediated activation of T cells up to 10 µM. Ibrutinib, zanubrutinib, and spebrutinib had EC50 values Conclusion: BTK inhibitors in clinical development for B-cell malignancies had differing potency in biochemical assays, but these differences were lost (in part) in cellular assays, particularly in hWB. Among the BTK inhibitors tested, the greatest differentiation was observed in kinase selectivity profiles; acalabrutinib and tirabrutinib had the highest kinase selectivity. Disclosures Kaptein: Covaluation Pharma BV: Employment, Equity Ownership; Acerta Pharma BV: Consultancy, Equity Ownership; Apo-T BV: Consultancy. de Bruin:Acerta Pharma: Employment. Emmelot-van Hoek:Acerta Pharma: Employment. van de Kar:Acerta Pharma: Employment. de Jong:Acerta Pharma: Employment. Gulrajani:Acerta Pharma: Employment, Equity Ownership. Demont:Acerta Pharma: Employment. Covey:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Mittag:Acerta Pharma: Employment, Equity Ownership. Barf:Covaluation Holding BV: Employment, Equity Ownership; Acerta Pharma BV: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Inhibitors of B-cell receptor (BCR) signaling, in particular of Bruton tyrosine kinase (BTK), are effective in patients with chronic lymphocytic leukemia (CLL). Acalabrutinib is a highly selective, covalent BTK inhibitor with rapid absorption and fast elimination (Barf et al., J Pharmacol Exp Ther 2017; 363:240-252). In a previous clinical trial of patients with relapsed/refractory CLL, acalabrutinib therapy was well tolerated and efficacious and had high target occupancy (Byrd et al., N Engl J Med 2016; 374:323-21). Here, we report on BTK occupancy, BTK resynthesis rates, and the relationship between BTK occupancy and BCR signaling in patients with CLL enrolled in a single center, phase 2 study of acalabrutinib monotherapy (NCT02337829). Patients were randomized to receive either 200 mg of acalabrutinib once daily (QD) or 100 mg twice daily (BID). The percentage of BTK bound by acalabrutinib (target occupancy) was measured with the aid of a biotin-tagged analogue probe. After 3 days of dosing, the median BTK occupancy in peripheral blood at peak (4 hours postdose) was 99% in both dosing groups (n=21 per group). However, at the drug trough time points (12 hours for BID; 24 hours for QD), median occupancy was greater in the BID than QD group (95% vs 87%, respectively; P As acalabrutinib binds covalently to BTK, reactivation of the pathway requires de novo synthesis of BTK. We estimated the rate of BTK synthesis in vivo by measuring the accumulation of free BTK (% unbound by acalabrutinib) in serial blood samples taken 4, 12, 24, 36, and 48 hours postdose during a preplanned dose interruption on days 4 and 5. BTK was synthesized at a median rate of 13.4% per day, which was highly variable (fast vs slow) across patients (Figure). Interestingly, we found the median BTK de novo synthesis rate to be roughly twice as fast as observed in B cells from healthy volunteers (P We next correlated BTK occupancy levels and activity of BCR signaling in 10 representative patients. On Day 3, four hours after receiving the drug, significant reductions were observed in phospho-BTK (P=0.05), pNF-κB (P=0.03), and CD69 expression (P=0.001) compared with pretreatment. Next, we evaluated the change in BCR signaling from trough (for each dose group) to 36 (BID) or 48 (QD) hours after dosing (i.e., during the short window of drug withholding). A trend for increased signaling was driven by individual patients with low occupancy (≲70%). To mimic microenvironmental activation, we stimulated overnight with anti-IgM, all the peripheral blood samples collected during drug withholding (4 to 48 hours postdose). We found that upon BCR activation, B-CLL cells showed the ability to reactivate BCR signaling as measured by an increase in CD69 expression. Moreover, the extent of reactivation in BCR signaling positively correlated with the percentage of free BTK (R=0.73; P=0.0001). In conclusion, higher target coverage was achieved when acalabrutinib was administered 100 mg BID compared with 200 mg QD. Given that BTK de novo synthesis rates do vary across patients with CLL, and that reactivation of BCR signaling correlates with lower occupancy (higher free BTK), BID dosing provides the highest target coverage for a greater number of patients. This work was supported by the Intramural Research Program of National Heart, Lung, and Blood Institute, the National Institutes of Health, and Acerta Pharma. We thank our patients for donating blood and tissue samples to make this research possible. Figure. Figure. Disclosures Cheung: Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Gulrajani:Acerta Pharma: Employment, Equity Ownership. Davies-Hill:NIH/NCI: Employment. Izumi:Acerta Pharma: Employment, Equity Ownership, Patents & Royalties: Acerta Pharma, various patents for ACP-196. Covey:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Wiestner:Pharmacyclics LLC, an AbbVie Company: Research Funding.

Bruton tyrosine kinase (BTK) is an essential kinase in the B-cell receptor (BCR) signalling pathway. Acalabrutinib is a potent and highly selective irreversible BTK inhibitor that received accelerated approval by FDA for the treatment of Relapsed/Refractory Mantle Cell Lymphoma. It is proposed to be combined with the Ataxia telangiectasia and Rad3-related (ATR) kinase inhibitor AZD6738, in a Phase I/II proof of concept clinical trial to assess safety and efficacy in patients with B-cell malignancies. ATR is a key regulator of DNA replication, repair and cell cycle checkpoints. The Activated B-Cell (ABC) subtype of Diffuse Large B-Cell Lymphoma (DLBCL) is associated with chronic active BCR signalling, and given our previous identification of sensitivity to AZD6738 in ABC-DLBCL cell lines, we hypothesised that combination with acalabrutinib may have additional therapeutic benefit. Here we report preliminary data to support combination efficacy in models of ABC-type DLBCL. The growth inhibitory and cell kill effect of AZD6738 and acalabrutinib in combination was assessed in 3 ABC and 4 GCB DLBCL cell lines. Combination activity and cell kill was detected specifically in the ABC-type TMD8 cell line. Using flow cytometry, we show that the cell kill effects of the drug combination were dependent on dose and schedule. Single agent treatment with 5 nM acalabrutinib or 0.5 µM AZD6738 for 72 h, caused cell death in 12% and 17% of cells respectively. The equivalent doses given in combination for 72 h induced cell death in 39% of cells, indicative of a greater than additive effect. Cell killing was increased with longer co-exposure to the combination, shown by an increase in cell death from 18% at 24 h, to 30% at 48 h. Acalabrutinib is dosed on a BID schedule, thus we tested whether its activity in combination with AZD6738 was affected by pre- or post-addition of acalabrutinib. A 24 h pre-treatment of cells with acalabrutinib, followed by the combination of AZD6738 and acalabrutinib for 48 h resulted in 20% cell death, whereas 48 h combination treatment followed by 24 h acalabrutinib monotherapy caused a similar 27% increase in death, suggesting that combination efficacy is not dependent on sequence of drug administration. Furthermore, the mRNA expression of BTK target genes in ABC-DLBCL cell lines was modulated by acalabrutinib, however there was no additional modulation to this pathway by the combination with AZD6738, suggesting the two agents kill cells through different mechanisms of action. In the TMD8 xenograft mouse model, daily dosing of AZD6738 (25 mg/kg) with twice daily dosing of acalabrutinib (20 mg/kg) was well tolerated and resulted in complete and durable tumor regressions (8/8 tumors), whereas single agent treatments resulted in tumor growth delay. Collectively, our preliminary data support a rationale for combining BTK and ATR inhibitors for an effective and alternative treatment option in ABC-DLBCL. Citation Format: Lucy A. Young, Oona Delpuech, Brandon Willis, Alexandra Bussey, Zena Wilson, Michelle Dupont, Carlos Grajales, Andrew Bloecher, Todd Covey, Kate Wills, Alan Lau, Simon J. Hollingsworth. Preclinical efficacy of the ATR inhibitor AZD6738 in combination with the BTK inhibitor acalabrutinib in ABC-DLBCL models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-263.

Throughout life, the hematopoietic system requires a supportive microenvironment that allows for the maintenance and differentiation of hematopoietic stem cells (HSC). To understand the cellular interactions and molecules that provide these functions, investigators have previously established stromal cell lines from the late gestational stage and adult murine hematopoietic microenvironments. However, the stromal cell microenvironment that supports the emergence, expansion and maintenance of HSCs during mid-gestational stages has been largely unexplored. Since several tissues within the mouse embryo are known to harbor HSCs (i.e. aortagonads-mesonephros, yolk sac, liver), we generated numerous stromal cell clones from these mid-gestational sites. Owing to the limited cell numbers, isolations were performed with tissues from transgenic embryos containing the ts SV40 Tag gene (tsA58) under the transcriptional control of constitutive and ubiquitously expressing promoters. We report here that the growth and cloning efficiency of embryonic cells (with the exception of the aorta) is increased in the presence of the tsA58 transgene. Furthermore, our results show that the large panel of stromal clones isolated from the different embryonal subregions exhibit heterogeneity in their ability to promote murine and human hematopoietic differentiation. Despite our findings of heterogeneity in hematopoietic growth factor gene expression profiles, high-level expression of some factors may influence hematopoietic differentiation. Interestingly, a few of these stromal clones express a recently described chordin-like protein, which is an inhibitor of bone morphogenic proteins and is preferentially expressed in cells of the mesenchymal lineage.

INTRODUCTION: Recent advances in the treatment of CLL focus on targeting the B-cell receptor (BCR) pathway, which is strongly upregulated in CLL. The BTK inhibitor ibrutinib and the PI3Kä inhibitor idelalisib, both targeting the BCR pathway, are approved for clinical use based on significant survival benefit in clinical trials. In vitro studies have shown synergy for combined PI3Kä and BTK inhibition (Griner, PNAS, 2014). Since CLL propagation relies on the microenvironment, in vivo models are needed for better testing of new drug combinations. We tested two new inhibitors of the BCR pathway, the BTK inhibitor ACP-196 and the PI3Kä inhibitor ACP-319 as single agents and in combination using the murine TCL1-192 allograft model of aggressive, BCR driven CLL. METHODS: TCL1-192 cells were injected into SCID mice and drug was given through the drinking water with vehicle, ACP-196, ACP-319 or a combination of the two drugs at a concentration of 0.15 mg/mL of each drug. Blood was analyzed weekly by flow cytometry and at the end of the study spleens were weighed and analyzed by flow cytometry. RESULTS: Tumor burden in the blood significantly decreased with both single agent and combination treatment compared to vehicle, and with single agent compared to combination, P < 0.05, P < 0.0001 and P < 0.0075, respectively. Combination treatment also resulted in significantly lower spleen weights when compared to spleens from mice treated with single agents or vehicle. Both single agent and combination treatment led to decreased phosphorylation of PLCã2, NFêB and ERK, molecules downstream in the BCR pathway, P < 0.05 compared to vehicle treated mice. Phosphorylation of PLCã2 and NFêB was further decreased with combination treatment compared to single agent treatment. Both single agent and combination treatment greatly enhanced survival of the mice compared to vehicle treatment with a median survival from treatment start of 17 days (vehicle), 23 days (single agent) and 40 days (combination), P < 0.0001 for single agent vs to combination treatment. CONCLUSION: We here show that a combination of ACP-196 (BTK inhibitor) and ACP-319 (PI3Kä inhibitor) is superior to single agent treatment in the murine TCL1-192 model of aggressive, BCR-driven CLL. Survival was significantly increased by combination treatment and the tumor burden was significantly reduced compared to both single agent mice and vehicle treated mice. The on-target effects were validated by reduced phosphorylation of PLCã2 and NFêB. Thus, evaluation of combination treatment with ACP-196 and ACP-319 in clinical trials is warranted. Citation Format: Helena I. Mora-Jensen, Carsten U. Niemann, Michael Gulrajani, Fanny Krantz, Todd Covey, Brian J. Lannutti, Adrian Wiestner, Sarah EM Herman. The combination of ACP-196 and ACP-319 leads to increased survival in the TCL1-192 CLL mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4797.

Background: Signaling through the B-cell receptor (BCR) results in cell survival and proliferation, and this pathway is critical for the progression of many B-cell malignancies, such a chronic lymphocytic leukemia (CLL). BTK, a TEC family kinase, is essential to the BCR signaling cascade. The recent approval of the first-in-class BTK inhibitor for the treatment certain B-cell malignancies, ibrutinib, has validated BTK as a clinical target. ACP-196 is a novel, second generation inhibitor of BTK with an IC50of 3 nM against purified BTK and EC50 of 8 nM in a human whole-blood CD69 B-cell activation assay. In vivo, oral administration of ACP-196 inhibits BCR-induced CD69 expression in murine splenic lymphocytes with an ED50 of 1.3 mg/kg compared with 2.9 mg/kg for ibrutinib. ACP-196 also has improved target specificity over ibrutinib with 323-,94-, 19- and 9-fold selectivity over the other TEC kinase familymembers (ITK, TXK, BMX, and TEC, respectively) and no activity against EGFR (Covey AACR, 2015). TXK and ITK are critical for T-cell receptor activation and development. ITK is also necessary for natural killer (NK)-cell mediated antibody dependent cell cytotoxicity (ADCC), which is important for the efficacy of monoclonal antibody therapy, eg, obinutuzumab. Additionally, therapeutic blockade of EGFR signaling is employed for treatment of epithelial cancers and is associated with adverse events, such as diarrhea and skin rash. Here, we describe results from signaling and functional assays to further elucidate the differential effects of ACP-196 on primary CLL cells compared with T-cells, NK-cells and epithelial cells. Methods: CLL patient samples were evaluated for pathway activation in the presence and absence of ACP-196 using phospho-protein immunoblotting. Helper T-cell (Th) skewing assays were performed using purified naive CD4+ T-cells from C57BL/6, Itk knock out (KO) and Itk/Txk double KO mice in the presence ACP-196 or ibrutinib. CD8+ T-cell activity was assessed by cytolytic activity (CTL) assays using T-cells isolated from C57BL/6 mice. The CTL response was initiated with various effector:T-cell ratios using C57BL/6 T-cells and murine BALB/c lymphoblasts. To evaluate NK-cell ADCC function, standard chromium release assays were done using purified NK-cells isolated from healthy volunteer peripheral blood mononuclear cells and cultured with obinutuzumab-coated (10 µg/mL) CLL cells in the presence and absence of ACP-196. Immunoblotting of H460 lung cancer cells for phospho-EGFR was used to evaluate the effect of ACP-196 on EGFR signaling. Results: ACP-196 treatment of primary human CLL cells showed a dose-dependent (0.01μM-1μM) decrease in p-BTK (Y223), p-ERK (T202/Y204) and p-AKT (T308) and p-IκB-α (S32), without impact on total protein levels. These findings demonstrate ACP-196 inhibits autophosphorylation of BTK as well as down-stream effectors of BCR signaling. Phospho-protein immunoblotting of primary human T-cells and Jurkat cells showed that ACP-196 does not inhibit T-cell receptor signaling molecules downstream of ITK and TXK such as IκBα, NFAT, or JunB. In in vitro helper T cell skewing assays, ACP-196, unlike ibrutinib, showed no effect on differentiation of Th subsets (Th1/Th2/Th17) or regulatory T cells (Tregs). The effect of ibrutinib on Th and Treg differentiation was similar to that observed in cells from Itk KO and Itk/Txk KO mice. In addition, ACP-196 had no effect on CD8+ T-cell viability or cytotoxicity as compared with ibrutinib-treated CD8+ T cells (46% and 36% reduction, respectively). In the in vitro ADCC assay, ACP-196 had no effect on NK cell function (chromium release of 34.8% vs 39.6% for the vehicle control). Lastly, at clinically relevant concentrations ACP-196 did not attenuate autophosphorylation of EGFR in H460 lung epithelial cells demonstrating no effect of ACP-196 on EGFR signaling. Conclusions: ACP-196 selectively inhibits BTK and BCR signaling at pharmacologic concentrations without off-target effects on T-cells, NK-cells and lung epithelial cells. ACP-196 is currently in Phase 3 trials for the treatment of CLL (ClinicalTrials.gov NCT0247568 and NCT02477696). This work was supported by the NIH NCI R01CA197870 and Acerta Pharma. Disclosures Gulrajani: Acerta Pharma: Employment. Covey:Acerta Pharma BV: Employment, Equity Ownership, Patents & Royalties. Kaptein:Acerta Pharma: Employment. Van Lith:Acerta Pharma: Employment. Izumi:Acerta Pharma: Employment. Hamdy:Acerta Pharma BV: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Ulrich:Acerta Pharma: Employment. Lannutti:Acerta Pharma: Employment. Johnson:Acerta Pharma: Research Funding.

Introduction: BTK is involved in B-cell receptor (BCR) signal transduction and is an established target for the treatment of chronic lymphocytic leukemia (CLL) (Byrd, NEJM, 2013). ACP-196 is a novel, potent second generation BTK inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. IC50determinations on nine kinases with a cysteine in the same position as BTK showed ACP-196 to be more selective than the first-in-class BTK inhibitor, ibrutinib (Covey, AACR, 2015). We present data evaluating the anti-tumor effects of ACP-196 in established murine models of CLL. Methods: Two distinct murine models were used for these studies. In the TCL1 adoptive transfer model, leukemic cells from Eμ-TCL1 transgenic mice were transplanted into C57BL/6 mice, resulting in a CD5+/CD19+ leukemia with peripheral blood, spleen and nodal involvement. ACP-196 treatment in drinking water (0.16 mg/mL) commenced when recipient mice had > 10% CD5+/CD19+ leukocytes in the peripheral blood. Mice were followed for survival. Separate cohorts were sacrificed for pharmacodynamic analyses after 1 and 4 weeks of treatment. In the second model, NSG mice received primary human CLL cells. The xenografted human CLL cells have comparable tumor biology (including active BCR signaling) to activated human lymph node resident CLL cells (Herman, Leukemia, 2013). PBMCs harvested from CLL patients were adoptively transferred at 1 x 108 cells per mouse. ACP-196 was initiated on day -1 (at the time of busulfan priming) at multiple doses ranging from 0.006 to 0.3 mg/mL in drinking water. Results: In the TCL1 model, treatment with ACP-196 showed > 90% BTK occupancy of BTK after 1 and 4 weeks of therapy. ACP-196 inhibited BCR signaling as shown by decreased autophosphorylation of BTK and reduction in surface expression of the BCR activation markers CD86 and CD69. After 1 week of ACP-196 inhibited BCR signaling as shown by a 6-fold reduction of autophosphorylation of BTK in the presence of anti-IgM, and surface expression of the BCR activation markers CD69 and CD86 were decreased by 47% and 57% respectively. Inhibition of BTK and downstream BCR activation was maintained through at least day 28 of treatment. Most notably, ACP-196 treatment resulted in a significant increase in survival compared with mice receiving vehicle (median 81 vs 59 days, respectively; P =0.02). In the NSG xenograft model, ACP-196 at the times examined did not cause a significant treatment-induced lymphocytosis in the patients evaluated (n=6). After 4 weeks of treatment with ACP-196, the NSG mice were sacrificed, and BCR signaling activity and tumor burden in the spleen were evaluated. ACP-196 treatment showed decreases in phosphorylation of PLCγ2 and ERK (P Conclusions: ACP-196 is a potent inhibitor of BTK as measured by inhibition of BCR activity, reduced tumor proliferation and increased survival. Overall, ACP-196 showed statistically significant efficacy in two murine models of CLL and is currently in Phase 3 trials for treatment-naive (ClinicalTrials.gov NCT0247568) and previously treated high-risk CLL (ClinicalTrials.gov NCT02477696). This work was supported by the Intramural Research Program of NHLBI, NIH, R01CA197870, K23 CA178183-02, and Acerta Pharma. Disclosures Gulrajani: Acerta Pharma: Employment. Krantz:Acerta Pharma: Employment. Covey:Acerta Pharma BV: Employment, Equity Ownership, Patents & Royalties. Lannutti:Acerta Pharma: Employment. Izumi:Acerta Pharma: Employment, Equity Ownership, Patents & Royalties. Ulrich:Acerta Pharma: Employment. Byrd:Acerta Pharma BV: Research Funding. Wiestner:Pharmacyclics: Research Funding. Johnson:Acerta Pharma: Research Funding.

Introduction Btk is a kinase involved in B-cell receptor (BCR) signal transduction and a critical target in chronic lymphocytic leukemia (CLL). ACP-196-a potent, second generation Btk inhibitor that is more selective than the first-in-class Btk inhibitor, ibrutinib (Covey AACR2015)-has demonstrated antitumor activity in preclinical CLL models (Niemann AACR2014). Here, we present preliminary data from patients with relapsed/refractory (R/R) CLL/small lymphocytic lymphoma (SLL) enrolled in an ongoing Phase 1/2 study of single-agent ACP-196 (ClinicalTrials.gov NCT02029443). Methods and Patients This first-in-human study was designed to evaluate the safety, maximum tolerated dose, pharmacokinetics, pharmacodynamics and efficacy of orally administered ACP-196 in patients with R/R CLL/SLL. Patients were continuously treated with ACP-196 at dosages ranging from 100 to 400 mg once daily (QD) as part of the dose-escalation portion of the study (4 cohorts of 6-8 patients per cohort), and 100 mg twice daily (BID) and 200 mg QD as part of the expansion portion of the study (2 cohorts). Of note, CLL patients with any degree of pancytopenia and prior exposure to PI3K inhibitors were allowed. CLL responses were investigator assessed per IWCLL criteria (modified Hallek 2008). SLL responses were investigator assessed per IWG criteria (Cheson 2007). Patients had a median age of 62 years (range 44-84), bulky lymph nodes ≥ 5 cm (47%) and median of 3 prior therapies (1-13). High-risk prognostic factors included del(17)(p13.1) 31% (18/58), del(11)(q22.3) 29% (17/58) and unmutated IGVH genes 75% (38/51). Results Results are presented through 01 June 2015 for the first 61 R/R patients, including 60 evaluable for response. The median time on study (N=61) was 10.3 (0.5-15.9) months. ACP-196 has been well tolerated with 93% (57/61) of patients continuing on study drug. Of the 4 patients who discontinued, 1 patient each discontinued due to withdrawal of consent, physician decision, unrelated AE (pre-existing, active autoimmune hemolytic anemia) and related AE (Grade 3 dyspnea). To date, no dose-related effect has been observed in frequency or severity of AEs or serious adverse events. No dose-limiting toxicities have occurred, and most AEs were Grade ≤ 2. The most common Grade 1/2 AEs (≥ 15%) were headache (39%), diarrhea (33%) and URI (16%). Grade 3/4 AEs that occurred in ≥ 3 patients were anemia (7%), pneumonia (7%) and hypertension (5%). No major hemorrhage (including subdural hematomas), atrial fibrillation, tumor lysis syndrome or pneumonitis have occurred suggesting an improved safety profile compared with other BCR and BCL-2-targeted therapies. Clinical activity has been observed in patients with R/R CLL/SLL at all doses evaluated. All patients experienced rapid reductions in lymphadenopathy. Treatment-related lymphocytosis (defined as ≥ 50% increase from baseline and above absolute lymphocyte count [ALC] of 5 K/µL) occurred in 61% (37/61) of patients and resolved in 81% (31/37) of these patients. In general, lymphocytosis peaked at a median of 3 weeks and resolved by a median of 19 weeks (range 1 to 58 weeks). The rapid decrease in lymphadenopathy and treatment-related lymphocytosis along with concurrent improvement in baseline cytopenias has led to a high proportion of partial responses (PRs) early in treatment (Figure 1). Best overall response rate including PR and PR with lymphocytosis (PR+L) was 93% (PR=70%, PR+L=23%, SD=7%, PD=0%). For patients with del(17)(p13.1), the response rate was 100% (PR=72%, PR+L=28%). In the 4 patients with prior idelalisib therapy, the response rate also was 100% (PR=75%, PR+L=25%). To date, no disease progression or Richter's transformation has occurred (Figure 2). Pharmacokinetic results showed exposure of ACP-196 was dose proportional with no drug accumulation. At dosages as low as 100 mg QD, pharmacodynamic results showed low intra-patient variability, high Btk occupancy (> 90% over 24 hr) and high phospho-Btk inhibition (> 90% over 24 hr). Conclusion ACP-196 is a highly potent and selective oral Btk inhibitor with a favorable safety profile. Responses occur early in treatment with no disease progression to date either in heavily pretreated patients or those with high-risk prognosis factors. ACP-196 is currently in Phase 3 trials for TN (ClinicalTrials.gov NCT0247568) and R/R high-risk CLL (ClinicalTrials.gov NCT02477696). Disclosures Byrd: Acerta Pharma BV: Research Funding. Jones:Acerta Pharma BV: Research Funding. O'Brien:Acerta Pharma BV: Research Funding. Schuh:Acerta Pharma BV: Research Funding. Hillmen:Abbvie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Acerta Pharma BV: Research Funding; Gilead: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Janssen: Honoraria, Research Funding. Stephens:Immunomedics: Research Funding; Acerta Pharma BV: Research Funding. Ghia:Pharmacyclics: Consultancy; Janssen: Consultancy; Adaptive: Consultancy; Acerta Pharma BV: Research Funding; Gilead: Consultancy, Research Funding, Speakers Bureau; GSK: Research Funding; Roche: Consultancy, Research Funding; AbbVie: Consultancy. Devereux:Acerta Pharma BV: Research Funding. Chaves:Acerta Pharma BV: Research Funding. Barrientos:Acerta Pharma BV: Research Funding. Wang:Acerta Pharma BV: Employment, Equity Ownership. Huang:Acerta Pharma BV: Employment, Equity Ownership. Covey:Acerta Pharma BV: Employment, Equity Ownership, Patents & Royalties. Navarro:Acerta Pharma BV: Employment, Equity Ownership. Rothbaum:Acerta Pharma BV: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Izumi:Acerta Pharma: Employment, Equity Ownership, Patents & Royalties. Hamdy:Acerta Pharma BV: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Furman:Gilead: Consultancy; Acerta Pharma BV: Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Honoraria, Speakers Bureau.

The advent of modulated multiparameter phosphoflow cytometry allows insight into the complexity of signal transduction networks in distinct cell subsets within a complex tissue sample. The application of this technology to hematopoietic malignancies can reveal pathogenic signaling profiles in intact tumor cells. Here, we review recent studies demonstrating the advantages and utility of this technology to inform the biological characterization of tumor cells and its applications to clinical medicine and drug development. Further, we discuss standardization and quality control approaches necessary for the adoption of this technique into clinical flow cytometry laboratories.

BACKGROUND:Single cell network profiling (SCNP) utilizing flow cytometry measures alterations in intracellular signaling responses. Here SCNP was used to characterize Acute Myeloid Leukemia (AML) disease subtypes based on survival, DNA damage response and apoptosis pathways. METHODOLOGY AND PRINCIPAL FINDINGS:Thirty four diagnostic non-M3 AML samples from patients with known clinical outcome were treated with a panel of myeloid growth factors and cytokines, as well as with apoptosis-inducing agents. Analysis of induced Jak/Stat and PI3K pathway responses in blasts from individual patient samples identified subgroups with distinct signaling profiles that were not seen in the absence of a modulator. In vitro exposure of patient samples to etoposide, a DNA damaging agent, revealed three distinct "DNA damage response (DDR)/apoptosis" profiles: 1) AML blasts with a defective DDR and failure to undergo apoptosis; 2) AML blasts with proficient DDR and failure to undergo apoptosis; 3) AML blasts with proficiency in both DDR and apoptosis pathways. Notably, AML samples from clinical responders fell within the "DDR/apoptosis" proficient profile and, as well, had low PI3K and Jak/Stat signaling responses. In contrast, samples from clinical non responders had variable signaling profiles often with in vitro apoptotic failure and elevated PI3K pathway activity. Individual patient samples often harbored multiple, distinct, leukemia-associated cell populations identifiable by their surface marker expression, functional performance of signaling pathway in the face of cytokine or growth factor stimulation, as well as their response to apoptosis-inducing agents. CONCLUSIONS AND SIGNIFICANCE:Characterizing and tracking changes in intracellular pathway profiles in cell subpopulations both at baseline and under therapeutic pressure will likely have important clinical applications, potentially informing the selection of beneficial targeted agents, used either alone or in combination with chemotherapy.

Purpose: Complete response to induction chemotherapy is observed in ∼60% of patients with newly diagnosed non-M3 acute myelogenous leukemia (AML). However, no methods exist to predict with high accuracy at the individual patient level the response to standard AML induction therapy. Experimental Design: We applied single-cell network profiling (SCNP) using flow cytometry, a tool that allows a comprehensive functional assessment of intracellular signaling pathways in heterogeneous tissues, to two training cohorts of AML samples (n = 34 and 88) to predict the likelihood of response to induction chemotherapy. Results: In the first study, univariate analysis identified multiple signaling “nodes” (readouts of modulated intracellular signaling proteins) that correlated with response (i.e., AUCROC ≥ 0.66; P ≤ 0.05) at a level greater than age. After accounting for age, similar findings were observed in the second study. For patients Conclusions: These data emphasize the value of performing quantitative SCNP under modulated conditions as a basis for the development of tests highly predictive for response to induction chemotherapy. SCNP provides information distinct from other known prognostic factors such as age, secondary AML, cytogenetics, and molecular alterations and is potentially combinable with the latter to improve clinical decision making. Independent validation studies are warranted. Clin Cancer Res; 16(14); 3721–33. ©2010 AACR.

Autoimmune diseases are complex and heterogeneous in nature and show varying responses to therapeutic treatment. A more accurate biological characterization of individual patients would assist in disease classification, prognosis, and treatment decisions. This characterization ideally would incorporate cellular, biochemical, and molecular information that contribute to the inflammatory state. The advent of single-cell network profiling (SCNP) using phospho-flow multiparametric flow cytometry allows insight into the complexity of signaling networks in various cell types. Here, we describe the potential of SCNP to inform on the biological characterization of autoimmune disease, the application in clinical medicine, and the utility in drug development.

Measuring target coverage of small molecule inhibitors is paramount-first, for selection of molecules to progress through the drug development process and second, once a candidate drug moves to clinical testing, for guiding dose/schedule selection. Single cell network profiling (SCNP) using multiparameter flow cytometry can measure compound effects on multiple signaling cascades in a cell-type-specific manner. We applied SCNP to a panel of compounds with reported inhibitory effects on Jak/Stat signaling using a novel system where modulation of multiple signaling cascades are simultaneously measured in discrete cell subsets in whole (ie, unfractionated) blood. Jak2 vs. Jak3 selectivity as well as "off-target" effects on other cell signaling pathways were measured using a combination of cytokines that target different white blood cell subsets, namely GM-CSF (monocytes/granulocytes), IL-2 (T cells), and CD40L (B cells). The compounds were then rank-ordered by potency and selectivity against the different pathways tested. Notably, SCNP performed in whole unfractionated blood compared to fractionated peripheral blood mononuclear cells (PBMC) from the same donors revealed potency loss for all compounds, with one exception. These studies show that SCNP can be used to efficiently measure a drug candidate's potency and selectivity in a physiologically relevant environment (eg, whole blood) and that robust IC(50) are attainable from rare subpopulations (100 cells). The ability to generate in vitro IC(50) measurements in whole blood can be used not only for the preclinical selection of lead molecules, but also to determine the target plasma concentration for clinical studies and to measure target coverage after drug administration in early phase clinical trials. Knowledge of the compound plasma concentration necessary to achieve biochemical coverage permits rational design of clinical trials based on biologically active dose vs. the traditional maximum tolerated dose (MTD) design, which is better suited for cytotoxic, nontargeted drugs.

Ibrutinib, a first generation Btk inhibitor, is approved for the treatment of CLL and mantle cell lymphoma; known toxicities include atrial fibrillation, diarrhea, rash, arthralgia and bleeding events (1). Recent reports show ibrutinib's off target effects may negatively impact its potential for combined therapy with anti-CD20 antibodies (2,3). Here we describe the pharmacologic characterization of ACP-196 a potent, novel second generation Btk inhibitor, which binds covalently to Cys481 with improved selectivity and in vivo target coverage. Compared to ibrutinib and CC-292, ACP-196 demonstrated higher selectivity for Btk when profiled against a panel of 395 non-mutant kinases (1 μM) in a competitive binding assay. IC50 determinations on 9 kinases with a Cys in the same position as Btk showed ACP-196 to be the most selective. The improved selectivity is related to the reduced intrinsic reactivity of ACP-196's electrophile. Importantly, unlike ibrutinib, ACP-196 did not inhibit EGFR, Itk or Txk. Phosphoflow assays on EGFR expressing cell lines confirmed ibrutinib's EGFR inhibition (EC50: 47-66 nM) with no inhibition observed for ACP-196 at 10 μM. These data may explain the ibrutinib-related incidence of diarrhea and rash. Ibrutinib's potency on Itk and Txk may explain why it interferes with cell-mediated anti-tumor activities of therapeutic CD20 antibodies and immune-mediated killing in the tumor microenvironment (2,3). In human whole blood, ACP-196 and ibrutinib showed robust and equipotent inhibitory activity on B-cell receptor induced responses in the low nM range, whereas CC-292 was 10-20 fold less potent. In vivo, oral administration of ACP-196 in mice resulted in dose-dependent inhibition of anti-IgM-induced CD86 expression in CD19+ splenocytes with an ED50 of 0.34 mg/kg compared to 0.91 mg/kg for ibrutinib. A similar model was used to compare the duration of Btk inhibition after a single oral dose of 25 mg/kg. ACP-196 and ibrutinib inhibited CD86 expression >90% at 3h and ∼50% at 24h postdose. In contrast, CC-292 inhibited ∼50% at 3h and ∼20% at 24h postdose. An ELISA based Btk target occupancy assay was developed to measure target coverage in preclinical and clinical studies. In healthy volunteers, ACP-196 at an oral dose of 100 mg QD showed >90% target coverage over a 24h period. Btk occupancy and regulation of the PD markers (CD69 and CD86) correlated with PK parameters for exposure. In CLL patients, after 7 days of dosing with ACP-196 at 200 mg QD, 94% Btk target occupancy was observed compared with ∼80% reported for ibrutinib at 420 mg QD (4). In conclusion, ACP-196 is a novel Btk inhibitor with key pharmacologic differentiators versus ibrutinib and CC-292. ACP-196 is currently being evaluated in clinical trials. 1. IMBRUVICA package insert 2014 2. Rajasekaran Blood 2014 Abstr # 3118 3. Da Roit Haematologica 2014 4. Byrd NEJM 2013 Citation Format: Todd Covey, Tjeerd Barf, Michael Gulrajani, Fanny Krantz, Bart van Lith, Elena Bibikova, Bas van de Kar, Edwin de Zwart, Ahmed Hamdy, Raquel Izumi, Allard Kaptein. ACP-196: a novel covalent Bruton's tyrosine kinase (Btk) inhibitor with improved selectivity and in vivo target coverage in chronic lymphocytic leukemia (CLL) patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2596. doi:10.1158/1538-7445.AM2015-2596

Pancreatic ductal adenocarcinoma exists in a complex desmoplastic microenvironment that provides stromal support for tumor growth and conceals the tumor from immune surveillance. Tumor-associated stroma comprises a mix of fibroblasts, immunosuppressive T regulatory cells (Tregs), myeloid suppressive monocytes (MDSCs) and tumor-associated macrophages (TAMs) that promote tumor growth and restrain immune-mediated tumor cell killing. The targeting of immune infiltrates may impair stromal support and enhance immune-mediated killing of pancreatic cancer cells. Bruton's tyrosine kinase (Btk) is a nonreceptor enzyme in the Tec kinase family expressed among cells of hematopoietic origin including B cells, myeloid cells, mast cells and platelets, but not T cells, where it regulates multiple cellular processes. Here we describe an unexpected finding of ACP-196, a potent, novel, second generation Btk inhibitor with improved selectivity and target coverage that binds covalently to a cysteine residue (Cys481) in the front position of the ATP-binding pocket. In an orthotopic mouse model of pancreatic cancer, KPC derived pancreatic cancer cells (KrasG12D; Trp53R172H; Pdx1-Cre) were injected into the pancreases. Vehicle, single agent ACP-196 (15 mg/kg/BID, gavage), single agent gemcitabine (50 mg/kg, IV) and combination ACP-196 with gemcitabine were evaluated for efficacy. By 4 weeks of treatment, mice in the vehicle group showed signs of health deterioration and all mice were euthanized, tumors were collected and measured. Relative to the vehicle treatment, ACP-196 monotherapy resulted in a >2-fold reduction in tumor growth compared with less than a 2-fold reduction with gemcitabine alone. The combination of ACP-196 and gemcitabine resulted in a further reduction in tumor growth when compared to each single agent. Interestingly, analysis of tumor tissues showed that single agent ACP-196 inhibited immunosuppressive populations of TAMs and MDSCs. Surprisingly, Treg populations were also reduced with a robust expansion of CD8+ T cells in the tumors. None of these effects were observed with gemcitabine alone. Although Btk is not expressed in T cells, this finding maybe the result of inhibiting the MDSC and TAM populations within the tumor microenvironment, a mechanism of action which is currently under investigation. Taken together, these data identify Btk as a novel target for modulating tumor immune escape and suggest that pharmacologic targeting of suppressive myeloid cells by ACP-196 induces therapeutic benefit. ACP-196 is currently being evaluated in clinical trials including frontline and salvage pancreatic cancer. Citation Format: Brian J. Lannutti, Michael Gulrajani, Fanny Krantz, Elena Bibikova, Todd Covey, Katti Jessen, Wayne Rothbaum, David M. Johnson, Roger Ulrich. ACP-196, an orally bioavailable covalent selective inhibitor of Btk, modulates the innate tumor microenvironment, exhibits antitumor efficacy and enhances gemcitabine activity in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 408. doi:10.1158/1538-7445.AM2015-408

Although previous studies have investigated the role of IL-27/WSX-1 interactions in the regulation of Th1 responses, little is known about their role in regulating Th2-type responses. Studies presented in this work identify a direct role for IL-27/WSX-1 interactions in the negative regulation of type 2 responses independent of effects on type 1 cytokines. WSX-1−/− mice infected with the gastrointestinal helminth Trichuris muris displayed accelerated expulsion of parasites and the development of exaggerated goblet cell hyperplasia and mastocytosis in the gut due to increased production of Th2 cytokines. Enhanced mast cell activity in the absence of WSX-1 was consistent with the ability of wild-type mast cells to express this receptor. In addition, IL-27 directly suppressed CD4+ T cell proliferation and Th2 cytokine production. Together, these studies identify a novel role for IL-27/WSX-1 in limiting innate and adaptive components of type 2 immunity at mucosal sites.

Diamond-Blackfan Anemia (DBA) is a rare childhood bone marrow failure disorder, characterized by the presence of red cell aplasia, congenital abnormalities, and increased levels of adenosine deaminase (ADA). Haploinsufficiency of ribosomal proteins (RPs) due to mutations in RPS19 and RPL11 occurs approximately 25% and 5% of DBA patients, respectively. The pathogenesis of DBA has been associated with activation of p53, but the mechanism of how this leads to the erythroid defect in DBA patients is not well understood. To understand the molecular pathways leading to DBA, we used previously published zebrafish models of RPS19 and RPL11 deficiency, in addition to primary human fetal liver CD34+ cells transduced with RPS19 shRNA to evaluate signaling pathways upstream of p53. One of the earliest responses to RP deficiency was upregulation of rrm1, a subunit of ribonucleotide reductase (RNR), responsible for de novosynthesis of dNTPs. Since ADA expression is increased in DBA and ADA is involved in nucleotide catabolism, we hypothesized that RP deficient zebrafish and primary human fetal liver CD34+ cells have defects in nucleotide metabolism, which result in replication stress and activation of p53 through the ATR/ATM/Chk1/2 pathways. Several genes involved in de novo nucleotide synthesis, nucleotide catabolism, and purine salvage are upregulated in RPL11 and RPS19 deficient zebrafish, including rrm1 (2-7 fold), ada (2.8 fold), xdh (2.3 fold), and hprt1 (3-fold). In contrast, genes involved in pyrimidine salvage, such as tk1 and dck were downregulated in RP deficient zebrafish (0.4 and 0.8 fold, respectively). RP deficient zebrafish also had imbalanced dNTP pools, with increased dTTP and decreased dCTP levels compared to controls. To test whether these alterations in nucleotide metabolism lead to replication stress, we evaluated DNA damage and stress-induced proteins in primary human fetal liver CD34+ cells transduced with RPS19 shRNA and found increased phosphorylation of p53 (Ser15 and Ser37), ATM (Ser1981), 53BP1 (Ser1778), Chk1 (Ser345), and Chk2 (Thr68), indicating activation of the ATR/ATM/Chk1/2/p53 pathway in RP deficient cells. To rescue the RP-deficient zebrafish, we treated them with a mixture of exogenous nucleosides. Nucleoside treatment decreased p53 expression, restored rrm1, ada, tk1, and dck to normal levels, decreased number of apoptotic cells, and increased the number of Gata1-expressing cells in RP deficient zebrafish. Our data suggest that defective nucleotide metabolism contributes to p53 upregulation in DBA, and that nucleoside supplements alleviate replication stress and may prove beneficial for patients with DBA. Disclosures: No relevant conflicts of interest to declare.

Background: SCNP is a multiparametric flow cytometry-based assay that quantitatively and simultaneously measures, at the single cell level, both extracellular surface markers and activation levels of intracellular signaling proteins in response to modulation. SCNP has been successfully applied to hematologic malignancies in both prognostic and predictive analyses. Previous work using bladder washes from bladder cancer patients (pts) established the feasibility of applying SCNP to the functional characterization of epithelial cell signaling and response to modulation and targeted kinase inhibition in non-conventional samples. Objectives: Assess the feasibility of applying SCNP to detect and functionally characterize epithelial cells, including sensitivity to targeted kinase inhibition, in pleural effusion (PE) samples from NSCLC pts. Methods: PE from confirmed NSCLC pts (n=4) were collected at the NSUH and shipped overnight to Nodality for processing on day of receipt. Antibodies to CD45, CytoKeratin (CK), EpCAM, and cPARP were used to differentiate non-apoptotic epithelial cells from leukocytes. DNA aneuploidy was evaluated using the lymphoid population in the patient samples as a diploid G0/G1 reference. Signaling in PI3K and MAPK pathways was quantified through measurement of p-AKT and p-ERK levels at baseline and after in vitro exposure to EGF +/- PI3K inhibitor GDC-0941. The epithelial bladder carcinoma cell line HT-1376 was used as a positive control for epithelial phenotypic staining and EGF-induced signaling. Results: In 3 of 4 PE samples, epithelial cells (DAPI+, CD45-, CK+, and EpCAM+) were identified (range 0.35% to 15.87% of all nucleated cells). Epithelial cells had a DNA index >1.3, indicating aneuploidy and therefore tumor origin. The majority of epithelial cells were cPARP negative (>80%) and suitable for SCNP analysis. In all 3 samples with epithelial cells: 1) EGF modulation induced increased p-AKT and p-ERK; 2) Pre-treatment with GDC-0941 inhibited EGF induced p-AKT but not p-ERK; 3) Constitutive activation of the PI3K pathway in the tumor epithelial cells was suggested by reduction in p-AKT levels compared to basal (no EGF exposure) following GDC-0941 treatment. Conclusion: This study demonstrates the feasibility of applying SCNP to the functional characterization of PE samples from NSCLC pts. Ongoing analyses will expand upon these data, including both additional NSCLC PE samples and the evaluation of compounds targeting alternative signaling pathways relevant to NSCLC (eg: MAPK, EGFR). The feasibility of extending such SCNP analyses to other solid tumor indications, using alternative tissue sources and circulating tumor cells, is under further investigation for both prognostic and response predictive utility. [S.Z. Fields and H. Raftopoulos are senior co-authors.] Citation Format: Matt Westfall, Rachael Hawtin, Todd Covey, Michael Gulrajani, Michelle Atallah, Michelle Cholankeril, Reena Vora, Alessandra Cesano, Scott Z. Fields, Haralambos Raftopoulos. Quantitative measurements of EGFR pathway signaling and modulation in pleural effusion samples from non-small cell lung cancer (NSCLC) patients using single cell network profiling (SCNP). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3523. doi:10.1158/1538-7445.AM2013-3523

Background: SCNP is a multiparametric flow cytometry-based assay that simultaneously provides measurements, at the single cell level, of extracellular surface markers and quantitative changes in the activation levels of intracellular signaling proteins in response to extracellular modulators (Kornblau et al. Clin Cancer Res 2010). Studies in hematologic malignancies have shown the value of quantitatively measuring single cell signaling networks under modulated conditions as a basis for the development of prognostic and predictive tests. The aim of this study was to assess the feasibility of applying SCNP to the examination of signaling networks in an epithelial cancer, using bladder washings as a BC sample source and EGF +/− the PI3K inhibitor GDC-0941 as modulators. Method: Bladder washes from non-cancer (NC) patients (pts) (n=8) and confirmed/suspected BC pts (n=20) were collected using standard practice and shipped overnight on ice for processing within 24 hours. Antibodies against CD45, CytoKeratin (CK), EpCam, and cleaved-PARP (cPARP) were used to differentiate non-apoptotic epithelial cells from leukocytes, while measurements of DNA aneuploidy (DAPI stain) allowed for distinction between tumor and normal epithelial cells. Signaling activity in the PI3K and MAPK pathways was assessed by measuring intracellular levels of p-AKT and p-ERK both at baseline and in response to pathway modulation. Upon delivery cells were pelleted, counted and incubated for 1 hr at 37°C. GDC-0941 (200nM) or vehicle control was added for 1 hr prior to stimulation with EGF (5 min) or vehicle control. After cell fixation and permeabilization, samples were stained with fluorophore-conjugated antibodies/DAPI cocktail, and data acquired using multi-parametric flow cytometry. The epithelial bladder carcinoma cell line HT-1376 was used as a control for the epithelial phenotype and EGF signaling. DNA index was determined using the lymphoid population in the pt samples as a diploid G0/G1 reference. Results: 50% (N=10) of BC samples and 25% (N=2) of NC samples met the “evaluable” criteria i.e., at least 400,000 total cells upon sample receipt and >2% of cells acquired containing an epithelial phenotype (DAPI+, CD45Low, CK+, and EpCam+). The majority of epithelial cells detected in BC samples were non-apoptotic (i.e. >77% cPARPneg) and therefore suitable for functional pathway analysis. In 3/10 BC samples a quantifiable increase in EGF-induced p-AKT and p-ERK signaling was identified (2–3 fold over baseline) and was preventable by GDC-0941 pre-incubation, whereas no EGF-induced signaling was observed in the NC specimens. Conclusion: This study demonstrates the feasibility of applying SCNP, using multi-parametric flow cytometry, to the functional characterization of BC. Ongoing studies are currently focused on correlation of the individual patient in vitro network signaling profile with clinical outcome to develop prognostic and predictive tools for improved BC management to inform treatment options. The feasibility of extending such SCNP analyses to other solid tumor indications, using alternative tissue sources is also under investigation, e.g., using circulating tumor cells or cells obtained from body fluids such as pleural effusions, ascites. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C92.