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Background Glioblastoma (GBM) has a devastating median survival of only one year. Treatment includes resection, radiation therapy, and temozolomide (TMZ); however, the latter increased median survival by only 2.5 months in the pivotal study. A desperate need remains to find an effective treatment. Methods We used the Connectivity Map (CMap) bioinformatic tool to identify candidates for repurposing based on GBM’s specific genetic profile. CMap identified histone deacetylase (HDAC) inhibitors as top candidates. In addition, Gene Expression Profiling Interactive Analysis (GEPIA) identified HDAC1 and HDAC2 as the most upregulated and HDAC11 as the most downregulated HDACs. We selected PCI-24781/abexinostat due to its specificity against HDAC1 and HDAC2, but not HDAC11, and blood-brain barrier permeability. Results We tested PCI-24781 using in vitro human and mouse GBM syngeneic cell lines, an in vivo murine orthograft, and a genetically engineered mouse model for GBM (PEPG - PTENflox/+; EGFRvIII+; p16Flox/− & GFAP Cre +). PCI-24781 significantly inhibited tumor growth and downregulated DNA repair machinery (BRCA1, CHK1, RAD51, and O6-methylguanine-DNA- methyltransferase (MGMT)), increasing DNA double-strand breaks and causing apoptosis in the GBM cell lines, including an MGMT expressing cell line in vitro. Further, PCI-24781 decreased tumor burden in a PEPG GBM mouse model. Notably, TMZ + PCI increased survival in orthotopic murine models compared to TMZ + vorinostat, a pan-HDAC inhibitor that proved unsuccessful in clinical trials. Conclusion PCI-24781 is a novel GBM-signature specific HDAC inhibitor that works synergistically with TMZ to enhance TMZ efficacy and improve GBM survival. These promising MGMT-agnostic results warrant clinical evaluation.

PURPOSE: Belinostat is a second-generation histone deacetylase inhibitor (HDI) predominantly metabolized by UGT1A1-mediated glucuronidation. Two common polymorphisms (UGT1A1*28 and UGT1A1*60) were previously associated with impaired drug clearance and thrombocytopenia risk, likely form increased drug exposure. This latter phenomenon has been observed with other HDIs such as abexinostat, panobinostat, romidepsin, and vorinostat. It was the intention of this brief report to expand a population pharmacokinetic (PPK) model to include a pharmacodynamic (PD) model describing the change in platelet levels in patients with cancer administered belinostat as a 48-h continuous intravenous infusion, along with cisplatin and etoposide. METHODS: The PPK/PD model developed here introduced an additional rate constant to a commonly used mechanistic myelo-suppression model to better describe the maturation of megakaryocytes into platelets before degradation and a feedback mechanism. The model employed a proportional error model to describe the observed circulating platelet data. RESULTS: Several covariates were explored, including sex, body weight, UGT1A1 genotype status, liver, and kidney function, but none significantly improved the model. Platelet levels rebounded to baseline within 21 days, before the next cycle of therapy. Simulations predicted that higher belinostat drug exposure does cause lower thrombocyte nadirs compared to lower belinostat levels. However, platelet levels rebound by the start of the next belinostat cycle. CONCLUSIONS: This model suggests a q3week schedule allows for sufficient platelet recovery before the next belinostat infusion is optimal.

// Eric Deutsch 1, 2, 3 , Elizabeth Cohen-Jonathan Moyal 4 , Vanesa Gregorc 5 , Paolo Andrea Zucali 6 , Jean Menard 7 , Jean-Charles Soria 8 , Ioana Kloos 9 , Jeff Hsu 10 , Ying Luan 10 , Emily Liu 10 , Remus Vezan 10 , Thorsten Graef 10 , Sofia Rivera 1, 2, 3 1 Department of Radiation Oncology, Gustave-Roussy Cancer Campus, Villejuif, France 2 INSERM 1030 Molecular Radiotherapy, Villejuif, France 3 Faculte de Medecine, Universite Paris-Sud, Universite Paris-Saclay, Le Kremlin-Bicetre, France 4 Department of Radiation Oncology, Institut Claudius Regaud, Toulouse, France 5 Department of Medical Oncology, Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale San Raffaele, Milan, Italy 6 Department of Medical Oncology and Haematology, Humanitas Cancer Center, IRCCS, Rozzano, Italy 7 Department of Radiation Oncology, Hopital Saint-Louis, Paris, France 8 DITEP (Departement d’Innovations Therapeutiques et Essais Precoces), Gustave Roussy Cancer Campus, Villejuif, France 9 Institut de Recherches Internationales Servier, Clinical Pharmacokinetics, Suresnes, France 10 Pharmacyclics LLC, an AbbVie Company, Sunnyvale, CA, USA Correspondence to: Eric Deutsch, email: eric.deutsch@gustaveroussy.fr Keywords: abexinostat, histone deacetylase inhibitor, radiotherapy, solid tumors, brain lesions Received: July 28, 2016 Accepted: November 14, 2016 Published: December 24, 2016 ABSTRACT Current treatments for advanced solid tumors tend to be only palliative. Although radiotherapy is administered with a curative intent, radioresistance and dose-limiting toxicities pose limitations to treatment. Abexinostat, an oral pan-histone deacetylase inhibitor, demonstrated enhanced sensitivity to radiation in various solid tumor cell lines. We conducted an exploratory, phase 1, dose-escalation study of abexinostat in combination with standard hypofractionated radiotherapy in patients with advanced solid tumors treated in a palliative setting. Among 58 treated patients, the median age was 61.5 years (range, 20-82); 47% of the patients had M1 stage disease, and 95% had received previous chemotherapy alone or chemotherapy in combination with surgery and/or radiotherapy. The recommended phase 2 dose was determined to be 90 mg/m 2 (140 mg). Of the 51 patients evaluable for response, best overall response was 8% (1 complete response [CR], 3 partial responses [PRs]), and best loco-regional response was 12% (1 CR and 5 PRs) at a median follow-up of 16 weeks. Of note, patients with target or non-target brain lesions showed encouraging responses, with 1 patient achieving a best loco-regional response of CR. Treatment-emergent grade ≥3 adverse events (AEs) were few, with most common being thrombocytopenia (17%), lymphopenia (12%), and hypokalemia (7%). Six patients (10%) discontinued treatment due to AEs. No grade ≥3 prolongation of the QTc interval was observed, with no treatment discontinuations due to this AE. Oral abexinostat combined with radiotherapy was well tolerated in patients with advanced solid tumors. The combination may have potential for treatment of patients with brain lesions.

Histone deacetylase (HDAC) inhibitor abexinostat is under investigation for the treatment of various cancers. Epigenetic changes including aberrant HDAC activity are associated with cancers, including myelodysplastic syndromes (MDS), acute myeloid leukemia (AML), and acute lymphoblastic leukemia (ALL). In this phase 1 dose-escalation study, 17 patients with relapsed/refractory higher-risk MDS, AML, or ALL received oral abexinostat (60, 80 [starting dose], 100, or 120 mg) twice daily (bid) on Days 1-14 of 21-day cycles. The most common treatment-related grade ≥3 adverse events were thrombocytopenia (29%) and neutropenia (24%), none of which led to discontinuation. Maximum-tolerated dose was not reached. Of 12 evaluable patients, best response was stable disease in 1 patient. This study was closed due to limited clinical benefit. Future development of oral abexinostat 100 mg bid in patients with MDS, AML, or ALL should focus on combination regimens. ISRCTN registry: 99680465.

Cancer cells contain significant alterations in their epigenomic landscape, which several enzyme families reversibly contribute to. One class of epigenetic modifying enzymes is that of histone deacetylases (HDAC), which are receiving considerable scrutiny clinically as a therapeutic target in many cancers. The underlying rationale is that inhibiting HDACs will reverse dysregulated target gene expression by modulating functional histone (or other) acetylation marks. This perspective will discuss a recent paper by Markozashvili and co-workers which appeared in Gene, which indicates that the mechanisms by which HDAC inhibitors (HDACis) alter the epigenetic landscape include widespread alternative effects beyond simply controlling regional epigenetic marks. HDACs are involved in many processes/diseases, and it is not surprising that HDACis have considerable off-target effects, and thus a major effort is being directed toward identification of inhibitors which are selective for HDAC isoforms often uniquely implicated in various cancers. This Perspective will also discuss some representative work with inhibitors targeting individual HDAC classes or isoforms. At present, it is not really clear that isoform-specific HDACis will avoid non-selective effects on other unrecognized activities of HDACs.

Purpose: Additional targeted therapeutics are needed for the treatment of lymphoma. Abexinostat is an oral pan-histone deacetylase inhibitor (HDACi) displaying potent activity in preclinical models. We conducted a multicenter phase I/II study (N = 55) with single-agent abexinostat in relapsed/refractory lymphoma. Experimental Design: In phase I, 25 heavily pretreated patients with any lymphoma subtype received oral abexinostat ranging from 30 to 60 mg/m2 twice daily 5 days/week for 3 weeks or 7 days/week given every other week. Phase II evaluated abexinostat at the maximum tolerated dose in 30 patients with relapsed/refractory follicular lymphoma or mantle cell lymphoma. Results: The recommended phase II dose was 45 mg/m2 twice daily (90 mg/m2 total), 7 days/week given every other week. Of the 30 follicular lymphoma and mantle cell lymphoma patients enrolled in phase II, 25 (14 follicular lymphoma, 11 mantle cell lymphoma) were response-evaluable. Tumor size was reduced in 86% of follicular lymphoma patients with an investigator-assessed ORR of 64.3% for evaluable patients [intent-to-treat (ITT) ORR 56.3%]. Median duration of response was not reached, and median progression-free survival (PFS) was 20.5 months (1.2–22.3+). Of responding follicular lymphoma patients, 89% were on study/drug >8 months. In mantle cell lymphoma, the ORR was 27.3% for evaluable patients (ITT ORR 21.4%), and median PFS was 3.9 months (range, 0.1–11.5). Grade 3–4 treatment-related adverse events (phase II) with ≥10% incidence were thrombocytopenia (20%), fatigue (16.7%), and neutropenia (13.3%) with rare QTc prolongation and no deaths. Conclusions: The pan-HDACi, abexinostat, was overall well tolerated and had significant clinical activity in follicular lymphoma, including highly durable responses in this multiply relapsed patient population. Clin Cancer Res; 22(5); 1059–66. ©2015 AACR.

Introduction Several inhibitors of histone deacetylase have been shown to enhance chemotherapy induced apoptosis and reduce sarcoma tumor volume in preclinical models. We sought to determine the MTD, PK/PD, safety and toxicity of the histone deacetylase inhibitor (HDACi) abexinostat (PCI-24781) when administered with doxorubicin in patients with metastatic sarcomas.

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Despite prominent role of radiotherapy in lung cancer management, there is an urgent need for strategies increasing therapeutic efficacy. Reversible epigenetic changes are promising targets for combination strategies using HDAC inhibitors (HDACi). Here we evaluated on two NSCLC cell lines, the antitumor effect of abexinostat, a novel pan HDACi combined with irradiation in vitro in normoxia and hypoxia, by clonogenic assays, demonstrating that abexinostat enhances radiosensitivity in a time dependent way with mean SER10 between 1.6 and 2.5 for A549 and H460. We found, by immunofluorescence staining, flow cytometry assays and western blotting, in abexinostat treated cells, increasing radio-induced caspase dependent apoptosis and persistent DNA double-strand breaks associated with decreased DNA damage signalling and repair. Interestingly, we demonstrated on nude mice xenografts that abexinostat potentiates tumor growth delay in combined modality treatments associating not only abexinostat and irradiation but also when adding cisplatin. Altogether, our data demonstrate in vitro and in vivo anti-tumor effect potentiation by abexinostat combined with irradiation in NSCLC. Moreover, our work suggests for the first time to our knowledge promising triple combination opportunities with HDACi, irradiation and cisplatin which deserves further investigations and could be of major interest in the treatment of NSCLC.

Purpose This phase I trial evaluated epigenetic modulation of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor by using a histone deacetylase abexinostat in combination with pazopanib to enhance response and reverse resistance. Patients and Methods Pazopanib was administered once a day on days 1 to 28 and abexinostat was administered orally twice a day on days 1 to 5, 8 to 12, and 15 to 19 (schedule A) or on days 1 to 4, 8 to 11, and 15 to 18 (schedule B). Dose escalation (3 + 3 design) in all solid tumors was followed by dose expansion in renal cell carcinoma (RCC). Results Fifty-one patients with RCC (N = 22) were enrolled, including 30 (59%) with one or more lines of prior VEGF-targeting therapy. Five dose-limiting toxicities, including fatigue (n = 2), thrombocytopenia (n = 2), and elevated AST/ALT (n = 1), were observed with schedule A; one dose-limiting toxicity was observed (elevated AST/ALT) was observed with schedule B. Grade ≥ 3 related adverse events included fatigue (16%), thrombocytopenia (16%), and neutropenia (10%). The recommended phase II dose was established as abexinostat 45 mg/m2 twice a day administered per schedule B plus pazopanib 800 mg/d. Objective response rate was 21% overall and 27% in the RCC subset. Median duration of response was 9.1 months (1.2 to > 49 months). Eight patients (16%) had durable control of disease for > 12 months. Durable tumor regressions were observed in seven (70%) of 10 patients with pazopanib-refractory disease, including one patients with RCC with ongoing response > 3.5 years. Peripheral blood histone acetylation and HDAC2 gene expression were associated with durable response to treatment. Conclusion Abexinostat is well tolerated in combination with pazopanib, allowing prolonged exposure and promising durable responses in pazopanib- and other VEGF inhibitor-refractory tumors, which supports epigenetically mediated reversal of treatment resistance.

International audience; Histone deacetylase inhibitors are members of a class of epigenetic drugs that have proven activity in T-cell malignancies, but little is known about their efficacy in B-cell lymphomas. Abexinostat is an orally available hydroxamate-containing histone deacetylase inhibitor that differs from approved inhibitors; its unique pharmacokinetic profile and oral dosing schedule, twice daily four hours apart, allows for continuous exposure at concentrations required to efficiently kill tumor cells. In this phase II study, patients with relapsed/refractory non-Hodgkin lymphoma or chronic lymphocytic leukemia received oral abexinostat at 80 mg BID for 14 days of a 21-day cycle and continued until progressive disease or unacceptable toxicity. A total of 100 patients with B-cell malignancies and T-cell lymphomas were enrolled between October 2011 and July 2014. All patients received at least one dose of study drug. Primary reasons for discontinuation included progressive disease (56%) and adverse events (25%). Grade 3 or over adverse events and any serious adverse events were reported in 88% and 73% of patients, respectively. The most frequently reported grade 3 or over treatment-emergent related adverse events were thrombocytopenia (80%), neutropenia (27%), and anemia (12%). Among the 87 patients evaluable for efficacy, overall response rate was 28% (complete response 5%), with highest responses observed in patients with follicular lymphoma (overall response rate 56%), T-cell lymphoma (overall response rate 40%), and diffuse large B-cell lymphoma (overall response rate 31%). Further investigation of the safety and efficacy of abexinostat in follicular lymphoma, T-cell lymphoma, and diffuse large B-cell lymphoma implementing a less dose-intense week-on-week-off schedule is warranted. (Trial registered at: EudraCT-2009-013691-47).

3022 Background: We previously reported the initial phase 1b study results of PAZ + ABX, a potent pan-HDAC inhibitor, demonstrating acceptable toxicity profile and encouraging anti-tumor activity (Aggarwal et al. JCO 2017). We report the long-term follow up of exceptional responders and additional correlative analyses associated with clinical outcomes. Methods: Key efficacy endpoints included objective response rate and duration of response. Peripheral blood histone acetylation, HDAC expression, and plasma VEGF levels were analyzed and associated with clinical outcomes. Results: 51 pts (RCC subset; N = 22) were enrolled between June 2012 and October 2015. 10 pts (20%) had experienced disease progression on prior PAZ; 59% had received any prior VEGF-targeting therapy. 9 evaluable pts (18%) (N = 6 RCC; 2 thyroid; 1 mesothelioma) achieved partial tumor response (PR), of which 6 had prior progression on VEGF-targeting therapy. 7/10 (70%) of pts with prior disease progression on PAZ monotherapy had reduction in tumor burden on study. The median duration of response was 9.1 months (range 1.2 to 70+), and clinical benefit rate (PR or stable disease > 6 months) was 33%. Five treatment-refractory pts achieved durable PRs lasting for > 2 years duration, and one previously PAZ-refractory patient with RCC remains on treatment with ongoing PR for > 6 years. Higher HDAC2 expression was associated with prolonged progression-free survival (median PFS 5.9 vs. 3.5 months, log-rank p = 0.02). Induction of histone acetylation on ABX lead-in treatment was associated with subsequent time to progression (p = 0.002). On-treatment plasma VEGF levels were inversely correlated with PBMC histone acetylation (p = 0.02). Conclusions: Markedly durable responses with PAZ + ABX are achievable, including in pts with PAZ- and VEGF-refractory RCC and other solid tumor malignancies. Host factors including HDAC expression and acetylation status may identify those most likely to benefit. A randomized phase 3 study is underway of PAZ + ABX as a first- or second-line therapy in pts with locally advanced or metastatic RCC (RENAVIV; NCT03592472). Clinical trial information: NCT01543763.

TPS681 Background: Abexinostat is a pan-histone deacetylase (HDAC) inhibitor that has shown promising activity in prior pre-clinical studies and early phase clinical trials. A phase 1b study of pazopanib plus abexinostat (Aggarwal et al. J Clin Oncol 2017) demonstrated strikingly durable responses in patients (pts) with clear cell renal cell carcinoma (RCC), including one patient with previously refractory disease with ongoing response for > 5 years’ duration. Induction of histone acetylation in peripheral blood mononuclear cells (PBMCs) was associated with durable treatment response. We hypothesize that the addition of abexinostat to pazopanib will significantly improve outcomes in patients with clear cell RCC. Methods: RENAVIV is a global, randomized, double-blind, placebo-controlled, two arm phase 3 study of pazopanib plus abexinostat versus pazopanib plus placebo, in pts with locally advanced or metastatic RCC with clear cell component. Up to one prior line of immunotherapy is allowed. Prior VEGF-targeting tyrosine kinase inhibitor treatment is prohibited. Stratification factors include: 1) Prior immunotherapy (yes/no) and 2) prognostic group (good, intermediate, poor). Pts randomized to pazopanib + placebo have the option of crossing over to receive pazopanib plus abexinostat at the time of disease progression. The primary endpoint is PFS by independent review committee. Secondary endpoints include PFS by investigator assessment, overall survival, safety, objective response rate (ORR), duration of response, patient-reported quality of life, and outcomes in cross-over population. Planned correlative studies include association between histone acetylation and HDAC expression in PBMCs with clinical outcomes. The total planned accrual is 413 pts, estimated to provide 90% power to detect a hazard ratio of 0.67 in the comparison of PFS between experimental versus control arms, with an overall two-sided type I error rate of 0.025. A pre-specified minimum of 50% of patients are required to have received prior immunotherapy. The first patient was enrolled in October 2018. Clinical trial information: NCT03592472.

Background: Around 20% of patients initially diagnosed with local stage breast cancer will develop metastatic breast cancer, with an about 23% median 5-year survival rate from diagnosis. Patients whose tumors express ER and PR (ER+, PR+) are frequently treated with antiestrogens and aromatase inhibitors (AI). Primary and secondary resistances to hormone therapy lead to tumor progression and shorten survival expectancy. In preclinical models, treatment of ER+ breast cancer cells with HDAC inhibitors leads to transcriptional down regulation and post-translation modification of the ER. This treatment reverses tamoxifen-induced ER stabilization, followed by induction of pro-apoptotic genes and apoptotic cell death. Epigenetic modulation of ER signaling by HDAC inhibitor represents a novel strategy to reverse hormonal resistance. Abexinostat is a hydroxamate-based pan-HDAC inhibitor of class I/II, in phase I/II clinical trials. Abexinostat inhibits tumor growth in a panel of commonly used ER+ breast cancer cell lines including ATCC and NCI. Abexinostat potentiates the anti-tumor activity of tamoxifen in vitro in ER+ breast cancer cells, by down-regulation of ER protein expression and its pro-growth response genes (PgR, Cyclin D). It abrogates AKT cell signaling by directly down-regulating AKT1 at the transcriptional and post-translational level. Furthermore, cell death is induced by activating the apoptotic program. Study design: phase I dose-finding of abexinostat for 4 consecutive days each week of a 3-week cycle given in combination with daily tamoxifen at 20 mg. Dose levels of abexinostat, 120, 140 and 160 mg bid, of 3 to 6 patients will be explored. Two dose de-escalation levels (100/80 mg) are allowed depending on toxicity. Dose-Limiting Toxicities assessment will be done at the end of cycle 2. Once the Maximum Tolerated Dose is determined up to 20 additional patients will be treated at the recommended dose in a confirmatory cohort. Main eligibility criteria: Female≥ 18 years with histologically confirmed primary adenocarcinoma of the breast; ER+ (IHC≥ 10%), HER2- tumors. Patients must have had tumor progression on an AI administered for advanced/metastatic disease OR recurrence while on or within 12 months of completion of adjuvant AI, OR recurrence within 12 months of adjuvant tamoxifen completion and must have had up to 3 prior chemotherapy regimens in metastatic/advanced setting. Patients must have progressive tumor measurable or evaluable (RECIST criteria version 1.1). Main objectives: Primary: to assess the safety and the tolerability of the combination treatment and to determine a recommended Phase II dose. Secondary: to determine the pharmacokinetic profile of both the drugs in combination and metabolites; to measure tumor response to the combination; to measure drug target inhibition by assessing acetylation state of histones proteins, HbF level and HDAC2 expression in peripheral blood mononuclear cells and in peripheral blood samples; to assess circulating tumor cells; to analyze biomarkers on tissue sample and pharmacogenomic of genes implicated in the metabolism of combination (optional). Status: Study opened in September 2012, currently recruiting. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT1-4-05.

Abexinostat, an oral pan-histone deacetylase inhibitor (HDACi), was evaluated in patients with advanced solid tumours in two single agent phase I studies (PCYC-402 and CL1-78454-002). In PCYC-402 study testing four different administration schedules, the maximum tolerated dose (MTD) was established at 75 mg/m(2) BID (twice daily) and the recommended dose at 60 mg/m(2) BID regardless of the schedule tested. The dose limiting toxicity (DLT), consistently observed across all these schedules, was reversible thrombocytopenia. The CL1-78454-002 study was initially investigating an additional schedule of 14 days on/7 days off. While testing two first cohorts, thrombocytopenia was observed without reaching DLT. To address this issue, a pharmacokinetic/pharmacodynamic (PK/PD) model was used to predict the optimal schedule allowing higher doses with minimal thrombocytopenia. Several administration schedules were simulated using this model. A 4 days on/3 days off schedule was associated with the smallest platelet decrease. Accordingly, the CL1-78454-002 study was amended. After reaching MTD1 (75 mg/m(2) BID) with the initial schedule, subsequent cohorts received abexinostat on a revised schedule of 4 days on/3 days off, starting at one dose level below MTD1 (60 mg/m(2) BID). As expected, the dose-escalation continued for two more dose levels beyond MTD1. The MTD2 reached for this optimised schedule was 105 mg/m(2) BID and the recommended dose 90 mg/m(2) BID. In conclusion, early understanding of toxicities and PK determination allowed us to build a PK/PD model of thrombocytopenia, which predicted the optimal administration schedule. This optimised schedule is currently used in the trials in solid tumours with abexinostat.

Histone deacetylase inhibitors (HDACi) have been actively explored as anti-cancer agents due to their ability to prevent deacetylation of histones, resulting in uncoiling of chromatin and stimulation of a range of genes associated in the regulation of cell survival, proliferation, differentiation and apoptosis. During the past several years, many HDACi have entered pre-clinical or clinical research as anti-cancer agents with satisfying results. Out of these, more than 8 novel hydroxamic acid based HDACi i.e., belinostat, abexinostat, SB939, resminostat, givinostat, quisinostat, pentobinostat, CUDC-101 are in clinical trials and one of the drug vorinostat (SAHA) has been approved by US FDA for cutaneous T-cell lymphoma (CTCL). It is clear from the plethora of new molecules and the encouraging results from clinical trials that this class of HDAC inhibitors hold a great deal of promise for the treatment of a variety of cancers. In this review, we classified the hydroxamic acid based HDACi on the basis of their structural features into saturated, unsaturated, branched, un-branched and 5, 6-membered cyclic ring linker present between zinc binding group and connecting unit. The present article enlists reports on hydroxamic acid based HDACi designed and developed using concepts of medicinal chemistry, demonstrating that hydroxamate derivatives represent a versatile class of compounds leading to novel imaging and therapeutic agents. This article will also provide a complete insight into various structural modifications required for optimum anticancer activity.

A population pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the thrombocytopenia (dose-limiting toxicity) of abexinostat, a new histone deacetylase inhibitor. An optimal administration schedule of the drug was determined using a simulation-based approach. Early PK and PK/PD data were analysed using a sequential population modeling approach (NONMEM 7), allowing for the description of a PK profile and platelet-count decrease after abexinostat administration with various administration schedules. Simulations of platelet count with several administration schedules over 3-week treatment cycles (ASC) and over a day (ASD) were computed to define the optimal schedule that limits the depth of thrombocytopenia. An intermediate PK/PD model accurately described the data. The administration of abexinostat during the first 4 days of each week in a 3-week cycle resulted in fewer adverse events (with no influence of ASD on platelet count profiles), and corresponded to the optimal treatment schedule. This administration schedule was clinically evaluated in a phase I clinical trial and allowed for the definition of a new maximum tolerated dose (MTD), leading to a nearly 30% higher dose-intensity than that of another previously tested schedule. Lastly, a final model was built using all of the available data. The final model, characterizing the dose-effect and the dose-toxicity relationships, provides a useful modeling tool for clinical drug development.

Characterization of long-term responders in a phase I trial evaluating the role of epigenetic modulation of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor by using a histone deacetylase abexinostat in combination with pazopanib to enhance response and reverse resistance. Patients and Methods: Pazopanib was administered once a day on days 1 to 28 and abexinostat was administered orally twice a day on days 1 to 5, 8 to 12, and 15 to 19 (schedule A) or on days 1 to 4, 8 to 11, and 15 to 18 (schedule B). Dose escalation (3 + 3 design) in all solid tumors was followed by dose expansion in renal cell carcinoma (RCC). Histone acetylation and HDAC2 expression were correlated long-term responders, >1y). Results: Fifty-one patients including RCC (N = 22) were enrolled, including 30 (59%) with one or more lines of prior VEGF-targeting therapy. Toxicities and PK studies were reported previously. 7 pts had response > 23 months (23-60+), including 5/22 patients with RCC, and one patient with medullary thyroid and thymic neurondocrine cancer. Long-term response was associated with high HDAC2 expression in PBMCs, increased histone acetylation, and modulation of VEGF level. Conclusion: Epigenetic modulation with HDAC inhibitors is strongly dependent on host factors to promote long-term benefit to abexinostat and pazopanib in pretreated patients. Citation Format: Rahul Aggarwal, Nela Pawlowsk, Jennifer Grabowsky, Armand Harb, Kamran Abri-Lavasani, Scott Thomas, Pamela N. Munster. Long-term responders to epigenetic modulators: abexinostat and pazopanib [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A173.

International audience; Background We determined the safety, pharmacokinetics, pharmacodynamics, and antitumour activity of abexinostat in B-cell lymphoma or chronic lymphocytic leukaemia. Patients and methods Thirty-five patients received oral abexinostat 30, 45, or 60 mg/m(2) bid in a 3 + 3 design in three 21-day schedules: 14 days on treatment in schedule 1 (D1-14); 10 days in schedule 2 (D1-5 and D8-12); and 12 days in schedule 3 (D1-4, D8-11, and D15-18). Safety, tumour response, plasma concentration, and histone H3 acetylation were measured. Results Two dose-limiting toxicities occurred in each schedule (one grade 3 febrile neutropenia; five grade 4 thrombocytopenia) at 60 mg/m(2) bid (maximal tolerated dose). The recommended dose was 45 mg/m(2) bid; schedule 1 was considered optimal. Non-haematological drug-related toxicities included grade 1 or 2 diarrhoea (43%), nausea (23%), and vomiting (11%); haematological toxicities included thrombocytopenia (31% grade 3, and 26% grade 4), which remained manageable and reversible on withdrawal. Of 29 evaluable patients, there were 2 complete and 6 partial responses; median duration of response was 14.6 months (range 3-16.5 months) (1 cycle is equivalent to 0.75 months). There was no evidence for nonlinear pharmacokinetics. There was a correlation between dose and histone acetylation. Conclusion Abexinostat has manageable toxicity and induced some durable complete and partial responses in B-cell lymphoma or chronic lymphocytic leukaemia. Our results suggest most favourable responses in patients with follicular lymphoma, though further research would be needed to confirm this finding.

In this study, we investigated the cytotoxic effects of a broad-spectrum histone deacetylase (HDAC) inhibitor, PCI-24781, alone and in combination with the proteasome inhibitor bortezomib in neuroblastoma cell lines. The combination was shown to induce synergistic cytotoxity involving the formation of reactive oxygen species. The cleavage of caspase-3 and PARP, as determined by western blotting, indicated that cell death was primarily due to apoptosis. Xenograft mouse models indicated increased survival among animals treated with this combination. The Notch signaling pathway and MYCN gene expression were quantified by reverse transcription-polymerase chain reaction (PCR) in cells treated with PCI-24781 and bortezomib, alone and in combination. Notch pathway expression increased in response to an HDAC inhibitor. NFKB1 and MYCN were both significantly down regulated. Our results suggest that PCI-24781 and bortezomib are synergistic in neuroblastoma cell lines and may be a new therapeutic strategy for this disease.

Several publications have suggested that histone deacetylase inhibitors (HDACis) could reverse the repression of estrogen receptor alpha (ERα) in triple-negative breast cancer (TNBC) cell lines, leading to the induction of a functional protein. Using different HDACis, vorinostat, panobinostat, and abexinostat, we therefore investigated this hypothesis in various human TNBC cell lines and patient-derived xenografts (PDXs). We used three human TNBC cell lines and three PDXs. We analyzed the in vitro toxicity of the compounds, their effects on the hormone receptors and hormone-related genes and protein expression both in vitro and in vivo models. We then explored intra-tumor histone H3 acetylation under abexinostat in xenograft models. Despite major cytotoxicity of all tested HDAC inhibitors and repression of deactylation-dependent CCND1 gene, neither ERα nor ERβ, ESR1 or ESR2 genes respectively, were re-expressed in vitro. In vivo, after administration of abexinostat for three consecutive days, we did not observe any induction of ESR1 or ESR1-related genes and ERα protein expression by RT-qPCR and immunohistochemical methods in PDXs. This observation was concomitant to the fact that in vivo administration of abexinostat increased intra-tumor histone H3 acetylation. These observations do not allow us to confirm previous studies which suggested that HDACis are able to convert ER-negative (ER−) tumors to ER-positive (ER+) tumors, and that a combination of HDAC inhibitors and hormone therapy could be proposed in the management of TNBC patients.

Background In the clinical development of oncology drugs, the recommended dose is usually determined using a 3 + 3 dose-escalation study design. However, this phase I design does not always adequately describe dose-toxicity relationships. Methods 125 patients, with either solid tumours or lymphoma, were included in the study and 1217 platelet counts were available over three treatment cycles. The data was used to build a population pharmacokinetic/pharmacodynamic (PKPD) model using a sequential modeling approach. Model-derived Recommended Doses (MDRD) of abexinostat (a Histone Deacetylase Inhibitor) were determined from simulations of different administration schedules, and the higher bound for the probability of reaching these MDRD with a 3 + 3 design were obtained. Results The PKPD model developed adequately described platelet kinetics in both patient populations with the inclusion of two platelet baseline counts and a disease progression component for patients with lymphoma. Simulation results demonstrated that abexinostat administration during the first 4 days of each week in a 3-week cycle led to a higher MDRD compared to the other administration schedules tested, with a maximum probability of 40 % of reaching these MDRDs using a 3 + 3 design. Conclusions The PKPD model was able to predict thrombocytopenia following abexinostat administration in both patient populations. A model-based approach to determine the recommended dose in phase I trials is preferable due to the imprecision of the 3 + 3 design.

EBV-related nasopharyngeal carcinomas (NPCs) still raise serious therapeutic problems. The therapeutic potential of the histone-deacetylase (HDAC) inhibitor Abexinostat was investigated using 5 preclinical NPC models including 2 patient-derived xenografts (C15 and C17). The cytotoxicity of Abexinostat used either alone or in combination with cis-platin or irradiation was assessed in vitro by MTT and clonogenic assays using 2 EBV-negative (CNE1 and HONE1) and 3 EBV-positive NPC models (C15, C17 and C666-1). Subsequently, the 3 EBV-positive models were used under the form of xenografts to assess the impact of systemic treatments by Abexinostat or combinations of Abexinostat with cis-platin or irradiation. Several cell proteins known to be affected by HDAC inhibitors and the small viral non-coding RNA EBER1 were investigated in the treated tumors. Synergistic cytotoxic effects of Abexinostat combined with cis-platin or irradiation were demonstrated in vitro for each NPC model. When using xenografts, Abexinostat by itself (12.5 mg/kg, BID, 4 days a week for 3 weeks) had significant anti-tumor effects against C17. Cooperative effects with cis-platin (2 mg/kg, IP, at days 3, 10 and 17) and irradiation (1 Gy) were observed for the C15 and C17 xenografts. Simultaneously two types of biological alterations were induced in the tumor tissue, especially in the C17 model: a depletion of the DNA-repair protein RAD51 and a stronger in situ detection of the small viral RNA EBER1. Overall, these results support implementation of phase I/II clinical trials of Abexinostat for the treatment of NPC. A depletion of RAD51 is likely to contribute to the cooperation of Abexinostat with DNA damaging agents. Reduction of RAD51 combined to enhanced detection of EBER 1 might be helpful for early assessment of tumor response.

Purpose: Cancer stem cells (CSC) are the tumorigenic cell population that has been shown to sustain tumor growth and to resist conventional therapies. The purpose of this study was to evaluate the potential of histone deacetylase inhibitors (HDACi) as anti-CSC therapies. Experimental Design: We evaluated the effect of the HDACi compound abexinostat on CSCs from 16 breast cancer cell lines (BCL) using ALDEFLUOR assay and tumorsphere formation. We performed gene expression profiling to identify biomarkers predicting drug response to abexinostat. Then, we used patient-derived xenograft (PDX) to confirm, in vivo, abexinostat treatment effect on breast CSCs according to the identified biomarkers. Results: We identified two drug-response profiles to abexinostat in BCLs. Abexinostat induced CSC differentiation in low-dose sensitive BCLs, whereas it did not have any effect on the CSC population from high-dose sensitive BCLs. Using gene expression profiling, we identified the long noncoding RNA Xist (X-inactive specific transcript) as a biomarker predicting BCL response to HDACi. We validated that low Xist expression predicts drug response in PDXs associated with a significant reduction of the breast CSC population. Conclusions: Our study opens promising perspectives for the use of HDACi as a differentiation therapy targeting the breast CSCs and identified a biomarker to select patients with breast cancer susceptible to responding to this treatment. Clin Cancer Res; 19(23); 6520–31. ©2013 AACR.

Hydroxamate-based histone deacetylase inhibitors (Hb-HDACIs), such as vorinostat, belinostat and panobinostat, have been previously shown to have a wide range of activity in hematologic malignancies such as cutaneous T-cell lymphoma and multiple myeloma. Recent data show that they synergize with a variety of cytotoxic and molecular targeted agents in many different solid tumors, including breast, prostate, pancreatic, lung and ovarian cancer. Hb-HDACIs have a quite good toxicity profile and are now being tested in phase I and II clinical trials in solid tumors with promising results in selected neoplasms, such as hepatocarcinoma. This review will focus on their clinical activity and safety in patients with advanced solid neoplasms.

Background: PAZ is a tyrosine kinase inhibitor of VEGFR, PDGFR, and c-KIT approved for use in renal cell carcinoma (RCC). ABX is a potent pan-HDAC inhibitor (HDACi). Pre-clinical models suggest that HDACi-mediated epigenetic modulation of VEGF expression prevents PAZ resistance and potentiates efficacy. We therefore designed a Phase I clinical trial combining ABX with PAZ in pts with advanced solid tumors with an expansion cohort in RCC. Methods: The primary endpoint was the maximal tolerated dose (MTD) of PAZ plus ABX. Secondary endpoints included pharmacokinetics (PK) and efficacy. PAZ was dosed days 1-28 and ABX days 1-5, 8-12, and 15-19 of 28-day cycle (schedule A) with at a starting dose of 400 mg/day and 45 mg/m2 orally twice daily respectively. An alternate ABX dosing schedule days 1-4, 8-11, and 15-18 was investigated (schedule B) due to toxicity of Schedule A. Results: 52 patients (pts) (RCC; N = 23) with advanced solid tumors were enrolled (N = 22 schedule A; N = 30 schedule B). There were six dose-limiting toxicities including fatigue (N = 2), thrombocytopenia (N = 2), and elevated AST/ALT (N = 2). The most common grade ? 3 related adverse events observed were fatigue (13%), thrombocytopenia (12%), and diarrhea (10%). The MTD was PAZ 800 mg/day + ABX 45 mg/m2 BID on schedule B. 8 evaluable pts (19%) (N = 6 RCC; 2 thyroid; median number of prior lines of therapy = 3) achieved partial tumor response (PR), with median duration of response of 9.2 months (1-33.2+). 7/9 (78%) of pts with prior disease progression on PAZ monotherapy had reduction in tumor burden on study. 15 out of 48 evaluable pts (31%) experienced stable disease or better for ? 6 months, and two previously PAZ-refractory pts with PRs remain on study for > 20 and 37 mos respectively. PK analyses did not reveal drug-drug interaction. Degree of histone acetylation and metabolomic profile are being evaluated. Conclusion: The combination of PAZ + ABX was well tolerated and durable tumor control (> 3 yrs) was observed in RCC and thyroid cancer. Tumor regressions observed in majority of PAZ-refractory tumors preliminarily support the potential of ABX to reverse therapeutic resistance. A randomized phase 2 study with cross-over design is planned to further evaluate the combination of PAZ + HDACi. Citation Format: Rahul Aggarwal, Scott Thomas, Jennifer Grabowsky, Armand Harb, Jim Leng, Anne Reinert, Ilaria Mastroserio, Thach-Giao Truong, Pamela N. Munster. Abexinostat (ABX) as a means to reverse pazopanib (PAZ) resistance: a phase I study in advanced solid tumor malignancies. [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 CT016.

4551Background: Renal cell carcinoma (RCC) exhibits somatic alterations in genes controlling hypoxia and chromatin states including VHL. Analysis of circulating cell-free DNA (cfDNA) as a means to ...

2519Background: PAZ is a tyrosine kinase inhibitor of VEGFR approved for use in renal cell carcinoma (RCC). ABX is a potent pan-HDAC inhibitor (HDACi). Pre-clinical models suggest that HDACi-mediated epigenetic modulation of VEGF expression prevents PAZ resistance and potentiates efficacy. We therefore designed a Phase I clinical trial combining ABX with PAZ in pts with advanced solid tumors with an expansion cohort in RCC. Methods: The primary endpoint was the maximal tolerated dose (MTD) of PAZ plus ABX. Secondary endpoints included pharmacokinetics (PK) and efficacy. PAZ was dosed days 1-28 and ABX days 1-5, 8-12, and 15-19 of 28-day cycle (schedule A) with at a starting dose of 400 mg/day and 45 mg/m2orally twice daily respectively. An alternate ABX dosing schedule days 1-4, 8-11, and 15-18 was investigated (schedule B) due to toxicity of Schedule A. Results: 52 patients (pts) (RCC; N = 23) with advanced solid tumors were enrolled (N = 22 schedule A; N = 30 schedule B). There were six dose-limiting to...

Acute myeloid leukemia (AML) is a highly heterogeneous disease primarily affecting the elderly. Despite considerable progress in understanding the biology of AML, the prognosis of the majority of patients still remains poor due to lack of progress in improving therapy over the past 3 decades, thus creating the need to identify new pharmacological strategies. Bruton's Tyrosine Kinase (BTK) has been demonstrated to be functionally important in a variety of hematological malignancies and several groups have recently shown that BTK is highly expressed and constitutively active in AML cell lines and in a subset of AML patients. Moreover, treatment with ibrutinib, a covalent irreversible inhibitor of BTK, can reduce proliferation, blast adhesion to bone marrow stromal cells and migration of both AML cell lines and primary AML blasts. Validation of this target also occurred with shRNA experiments confirming the specificity of BTK for growth inhibition of AML. Dysregulation of microRNA (miRNA) expression contributes to the pathogenesis of numerous human malignancies including AML, where multiple miRNAs have been associated with specific cytogenetic and molecular subsets of the disease. Using a target prediction algorithm we identified several miRNAs as potential regulators of BTK (miR-147b, miR-210-3p, miR-425-5p, miR-1253, miR-4269, miR-4667-3p). We performed 3′UTR luciferase reporter assays in the AML cell line OCI-AML3 and found that relative luciferase activities were significantly decreased (20-30%) in cells transfected with miR-147b, miR-425-5p, miR-4269 and miR-4667-3p mimics. Flow cytometry and western blotting analysis confirmed that BTK protein expression was significantly down-regulated by all the predicted miRs except miR-1253. Previous data from our lab have shown that histone deacetylase (HDAC) 1 and 2 become recruited to multiple microRNA promoters, including the ones targeting BTK. To determine the consequence of HDAC inhibition on BTK signaling, we exposed primary blasts from 14 AML patients to 10nM of the pan-deacetylase inhibitor panobinostat (LBH589) for 48h. Our results showed that panobinostat induced a 2-23 fold increase in the expression miR-147b, miR-210-3p, miR-425-5p, and miR-4667-3p in most of the patients and a time-dependent depletion of total BTK protein and downstream BTK signaling (phospho- and total ERK and phospho- and total AKT) in about half of them. BTK protein at 24h directly correlated with BTK and HDAC1 mRNA expression at 24h and miR-210 induction at 24h inversely correlated with BTK mRNA levels at 24h. Moreover, 2 days of incubation with 10nM panobinostat is able to induce robust cell death in AML primary samples (9.6-92% apoptosis). We hypothesized that HDAC inhibitors would cooperate with kinase inhibitors of BTK to synergistically abolish BTK signaling and induce death in AML cells. Therefore, we treated OCI-AML3 and MV4-11 cell lines with 0.40 µM abexinostat, 1 µM ibrutinib for 2h alone followed by washout, or a combination of 0.40 µM abexinostat with 1 µM ibrutinib for 2h, and viability was measured at 48h. The combination of abexinostat and ibrutinib induced greater than additive cytotoxicity compared to either abexinostat or ibrutinib alone. Exposure to ibrutinib alone for 2h followed by washout inhibited the kinase activity of BTK (measured by the auto-phosphorylation on Y223) but did not affect total BTK protein. However, the combination of abexinostat and ibrutinib showed both loss of BTK kinase and decrease in total BTK protein, in addition to attenuation of BTK signaling, thus confirming the dual targeting of BTK via independent mechanisms. Our results provide the rationale for the clinical evaluation of ibrutininb in combination with histone deacetylase inhibitors in AML patients. Disclosures No relevant conflicts of interest to declare.

Introduction: Histone deacetylase (HDAC) inhibitors, by blocking HDAC enzymes, can regulate acetylation states of histones and other non-histone proteins. Hyperacetylation of histones in cells can cause transcriptional activation of tumor suppressor genes, as well as genes involved in cell cycle control, cell division, and apoptosis, resulting in antitumor activity. Currently, 3 HDAC inhibitors (HDACi), vorinostat, romidepsin, and belinostat, are approved for the treatment of relapsed or refractory peripheral or cutaneous T-cell lymphoma (T-CL). HDACi in development also show promising results in B-cell malignancies and solid tumors. Abexinostat, an orally available hydroxamate-containing HDACi with good tolerability, differs from approved HDACi due to its unique pharmacokinetic profile and oral dosing schedule, twice daily 4 hours apart, which allows for continuous exposure at concentrations required for efficient tumor cell killing (Mitsiades, et al. Blood. 2003; unpublished data). Abexinostat may, therefore, offer an active and potentially less-toxic treatment option for cancer with a wider therapeutic index than other HDACi in development. Abexinostat showed manageable toxicity and durable responses, including some complete responses (CR), particularly in patients (pts) with relapsed/refractory follicular lymphoma (FL) (Evens ICML 2013; Morschhauser, Invest New Drugs, 2015). Methods: In this phase 2 trial, pts aged ≥18 years with relapsed/refractory NHL or CLL received oral abexinostat at 80 mg BID for 14 days of a 21-day cycle and continued until progressive disease or unacceptable toxicity. The 80 mg BID dose, which corresponds to the recommended phase 2 dose of 45 mg/m2 BID, was identified in phase 1 of the study (Morschhauser, Invest New Drugs, 2015). The primary endpoint was overall response rate (ORR); secondary endpoints included overall survival, progression-free survival, time to tumor progression, duration of response, disease-free survival, and time to treatment failure. Results: A total of 100 pts (median age, 66.5 years; 52% >65 years; 55% male) were enrolled between Oct 2011 and Jul 2014, including 16 with CLL, 17 with diffuse large B-cell lymphoma (DLBCL), 18 with FL, 16 with mantle cell lymphoma (MCL), 18 with T-CL, and 15 with marginal zone lymphoma (MZL) or other NHL subtypes. The median number of prior regimens across all lymphoma subtypes was 3 (range, 1-11) with a median of 4.5 prior regimens (range, 1-11) for FL pts. All pts received at least one dose of study drug; 55% discontinued due to progressive disease and 25% due to adverse events. Seven pts remain on treatment. Among the 87 pts evaluable for efficacy, ORR was 28% (CR, 5%). Responses by histology are shown in the table. Highest responses were observed in FL, T-CL, and DLBCL with ORRs of 56%, 40%, and 31% and median durations of response of 26.0 weeks (range, 0.1-90.4), 32.1 weeks (range, 6.3-51.3), and 8.1 weeks (range, 3.1-59.0), respectively. Grade ≥3 adverse events (AEs) and any serious AEs (SAEs) were reported in 86% and 46% of pts, respectively. The most frequently reported grade ≥3 treatment-emergent AEs were thrombocytopenia (80%), neutropenia (27%), and anemia (22%). The incidence of any-grade diarrhea was 47% (grade ≥3, 3%). The most commonly reported SAEs included thrombocytopenia (15%), anemia (7%), and pneumonia (6%). The most frequent toxicities that led to discontinuation included hematologic events, such as thrombocytopenia and neutropenia. Gastrointestinal toxicities leading to discontinuation were infrequent with 1 episode of vomiting being reported. Conclusions: Abexinostat has a manageable toxicity profile in pts with various NHL subtypes that is similar to other HDACi and comparable to other single-agent therapies currently in development. Promising efficacy was observed with abexinostat, especially in FL, T-CL, and DLBCL, with an ORR ≥30% in these subtypes, consistent with the results of an independent study of abexinostat in lymphomas that used a week-on-week-off schedule (Evens ICML 2013). Further investigation of the safety and efficacy of abexinostat in these indications implementing the less dose-intense interval on a week-on-week-off schedule is planned. Table. Response With Abexinostat by Tumor Type Tumor type ORR, % (CR, %) Overall (N=87) 28% (5%) FL (n=16) 56% (6%) T-CL (n=15) 40% (7%) DLBCL (n=16) 31% (6%) MCL (n=13) 15% (8%) MZL/other (n=13) 15% (0%) CLL (n=14) 0% (0%) Disclosures Ribrag: Pharmamar: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Off Label Use: abexinostat in NHL and CLL. Coiffier:CELLTRION, Inc.: Consultancy, Honoraria. Luan:Pharmacyclics LLC, an AbbVie Company: Employment. Graef:AbbVie: Equity Ownership; Pharmacyclics LLC, an AbbVie Company: Employment, Membership on an entity's Board of Directors or advisory committees. Morschhauser:Genentech Inc./Roche: Other: Advisory boards.

The acetylation of DNA can modulate the expression of genes involved in the development and progression of malignancies. Histone deacetylase (HDACs) inhibitors are clinically active and well tolerated in the treatment of a wide variety of tumors. HDACs inhibitors can sensitize cell response to ionizing radiation, potentially reducing treatment doses and side effects. OBJECTIVES: To assess the potential radiosensitizer effect of abexinostat (PCI-24781), a new and potent pan-HDAC inhibitor in two pediatric glioblastoma cell-lines (SF188 and KNS42). METHODS: The effect of PCI-24781 on proliferation rates, clonogenic capacity and apoptosis were compared prior and following cell irradiation. The clonogenic assay was performed without irradiation (48h of incubation) at the doses of 0.25, 0.5, 1 and 2uM of PCI-24781. The clonogenic assay combined with irradiation was performed at 48h using the inhibitor IC30 for each cell-line in combination with irradiation doses of 0.5, 1, 2 and 4Gy. For cell proliferation assays, the intervals of 24h, 48h, 72h and 96h at the doses of 0.5, 1, 2, 4, 8 and 16uM of PCI-24781 were selected for study. Apoptosis were evaluated at 48h-cultures at the doses of 2, 4, 8 and 16uM. RESULTS: The HDAC inhibitor repressed cell proliferation, displaying a more significant effect at 48h in the dose of 2uM (p < 0.05). PCI-24781 also induced apoptosis (p < 0,05); the percentage of cell death for SF188 and KNS42 (at 16uM) was 40% and 55% respectively. Cells demonstrated massive decrease in colony formation with PCI-24781; this effect was more pronounced when drug was combined with irradiation (p < 0.001). CONCLUSION: These data demonstrate potential radiosensitizer and antiproliferative effects of PCI- 24781 on pediatric glioblastoma cell-lines. This study will now focus on key proteins responsible for the double-strand breaks repair caused by irradiation, trying to elucidate epigenetic pathways potentially involved in the therapy with PCI-24781. Financial Support: Fapesp (process no. 2013/15891-8).

been linked to more aggressive disease and poor clinical outcomes. HER2 is particularly reliant on the chaperoning activity of heat shock protein 90 (HSP90) for its stability and function. Pharmacological blockade of HSP90 results in cellular depletion and loss of its client proteins, in turn providing a means to simultaneously disrupt multiple oncogenic pathways. Ganetespib is a clinically advanced small molecule inhibitor of HSP90. Here, we have evaluated the antitumor activity and efficacy of ganetespib, both as a single agent and in combination with clinically approved drugs, in models of human gastric cancer. Material and Methods: Cell viability was determined by CellTiterGlo. The anticancer effect of ganetespib as single agent or coupled with other chemotherapeutic agents was examined via immunoblot, immunofluorescence, flow cytometry and xenograft models in SCID mice. Results: Ganetespib demonstrated potent in vitro cytotoxic activity in a panel of 22 gastric cancer cell lines in vitro, with an average IC50 value 20 nM. The panel included 3 HER2-overexpressing (HER2+) lines and antiproliferative activity was independent of p53 status. At the molecular level, ganetespib treatment promoted destabilization of multiple HSP90 client proteins and effectors, including HER2, EGFR, IGF-IR, cMET, cKit, P-AKT, P-ERK1/2 and a number of cell cycle modulators, which ultimately resulted in apoptosis. These effects of ganetespib were durable, with kinetic analysis showing client suppression was maintained for over 48 hours following a 1 hour drug exposure. Combinations of ganetespib with chemotherapeutic agents (doxorubicin, docetaxel, cisplatin) as well as the dual HER2/EGFR kinase inhibitor lapatinib promoted significant increases in total cell death in comparison to monotherapy. Synergistic effects were also observed when ganetespib was combined with the PI3K/mTOR inhibitor BEZ235, due in part to ganetespibs’ ability to overcome the rebound in AKT activity that arises from PI3K/mTOR inhibition. The combinatorial benefit observed in vitro translated to improved efficacy in vivo, where combinations of ganetespib with capecitabine or docetaxel induced tumor regressions in NCI-N87 xenografts. Conclusions: Taken together, these data highlight the potent antitumor activity of ganetespib for gastric cancer cells, including HER2+ lines, both in vitro and in animal models. The findings support the potential therapeutic value of ganetespib, particularly in combination with standardof-care agents, for the treatment of patients with gastric cancer.

e17059 Background: Non-keratinizing nasopharyngeal carcinoma (NPC) is associated with the Epstein-Barr Virus (EBV), and sensitive to chemotherapy and radiotherapy. Cisplatin-based combination therapy is the most effective treatment for metastatic NPC. Abexinostat, a pan-HDAC inhibitor, exhibited synergistic effects in combination with cisplatin in NPC tumor cell lines, either EBV-positive or negative. A phase I dose-escalation study was performed to determine the maximal tolerated dose, dose-limiting toxicities (DLTs) of abexinostat with a fixed dose of cisplatin in patients with relapsed or refractory advanced NPC. Methods: Abexinostat was administered BID on days 1-4 and 8-11 of a 21-day cycles. Cisplatin dose (75mg/m2) was given on day 3. Abexinostat treatment started 2 days before to induce biological modifications in tumor cells prior to chemotherapy to maximize the synergistic effect. Since toxicities related to cisplatin are cumulative, dose-dependent and may be irreversible, the combination was li...

2575 Background: Preclinical data indicate that abexinostat enhances sensitivity to DNA-damaging agents, such as doxorubicin, particularly when administered 48h before infusion. A phase I dose-esca...

2560 Background: PAZ is a tyrosine kinase inhibitor of VEGFR, PDGFR, and C-KIT approved for use in renal cell carcinoma (RCC) and soft tissue sarcoma (STS). ABX is a potent pan-HDAC inhibitor (HDAC...

Abexinostat is a pan histone deacetylase inhibitor (HDACi) that demonstrates efficacy in malignancy treatment. Like other HDACi, this drug induces a profound thrombocytopenia whose mechanism is only partially understood. We have analyzed its effect at doses reached in patient plasma on in vitro megakaryopoiesis derived from human CD34(+) cells. When added at day 0 in culture, abexinostat inhibited CFU-MK growth, megakaryocyte (MK) proliferation and differentiation. These effects required only a short incubation period. Decreased proliferation was due to induction of apoptosis and was not related to a defect in TPO/MPL/JAK2/STAT signaling. When added later (day 8), the compound induced a dose-dependent decrease (up to 10-fold) in proplatelet (PPT) formation. Gene profiling from MK revealed a silencing in the expression of DNA repair genes with a marked RAD51 decrease at protein level. DNA double-strand breaks were increased as attested by elevated γH2AX phosphorylation level. Moreover, ATM was phosphorylated leading to p53 stabilization and increased BAX and p21 expression. The use of a p53 shRNA rescued apoptosis, and only partially the defect in PPT formation. These results suggest that HDACi induces a thrombocytopenia by a p53-dependent mechanism along MK differentiation and a p53-dependent and -independent mechanism for PPT formation.

Epstein-Barr virus (EBV) related nasopharyngeal carcinoma (NPC) is the third leading cause of virus-related human malignancy. On average, NPCs are more radiosensitive and chemosensitive than other head and neck tumors. However, local relapse and distant organ metastases still raise serious therapeutic problems. The aim of this study was to investigate the potential of the novel pan-HDAC inhibitor Abexinostat (S78454) for the treatment of NPC. Three types of EBV-positive NPC cells have been used as targets for in vitro and in vivo treatments. C666-1 and C17 cells were first xenotransplanted from the patients to nude mice and, in a second stage, adapted to permanent in vitro culture. In contrast, C15 cells are still propagated exclusively as xenografts; however, they can be used in short term culture assays. S78454 was applied to these cells either alone or in combination with cis-platinum. All three types of NPC cells - C666-1, C15 and C17 - were sensitive to the cytotoxic effects of Abexinostat with IC50 of 220, 150 and 200 nM, respectively. Combined treatment of Abexinostat with cis-platinum resulted in a synergistic effect with Bliss additivism index of 34, 33 and 19, respectively. In the next step, we used xenografted NPC cells for in vivo assessment of Abexinostat. Tumor-bearing mice were treated for 3 weeks. The compound was administered by intra-peritoneal injections, twice a day; 4 days a week, at a dose of 12.5 mg/Kg. Cis-platinum (2mg/Kg) was delivered once a week. In these experimental conditions, cis-platinum had no effect on tumor growth when used as a single agent. In contrast, Abexinostat by itself induced a significant decrease in tumor growth. This clinical effect was accompanied by a substantial decrease in the concentrations of Rad 51 and Rad 23B proteins in xenografted NPC cells for all 3 tumor lines. An increase in the concentration of acetylated tubulin was observed for only one type of xenografted NPC (C666-1). A strong synergistic anti-tumor effect was obtained when Abexinostat was combined with cis-platinum. It was manifested clinically by a spectacular inhibition of tumor growth and at histological examination by extensive areas of fibroblast proliferation segmenting and pushing residual tumor areas. These results support implementation of phase I/II clinical trials of Abexinostat for the treatment of NPC, especially in association with cis-platinum. The fact that Abexinostat was active against NPC xenografts at a relatively low dose (25mg/kg/day) suggests that it might have a better therapeutic index in NPC patients than in patients bearing other types of carcinomas. Down-regulation of Rad51 in tumor cells seems to be more consistent that the increase in acetylated tubulin. Additional investigations will be required to determine whether this change is predictive of a long term favourable tumor response to Abexinostat. Citation Format: Benjamin Vérillaud, Mélanie Gressette, Anne-Sophie Jimenez, Hélène Lelièvre, Kwok-Wai Lo, Anne Jacquet-Bescond, Laurence Kraus-Berthier, Stéphane Depil, Pierre Busson. Treatment of EBV-positive nasopharyngeal carcinoma xenografts with the HDAC-inhibitor Abexinostat: synergy with cis-platinum. [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 1013. doi:10.1158/1538-7445.AM2013-1013

Intro/Objective: Several inhibitors of histone deacetylase have been shown to enhance chemotherapy induced apoptosis and reduce sarcoma tumor burden in preclinical models. We sought to determine the MTD, PK/PD, safety and toxicity of the histone deacetylase inhibitor (HDACi) abexinostat when administered with doxorubicin in patients with metastatic sarcomas. Methods: Participants were enrolled in a standard 3x3 dose escalation phase I study design. Abexinostat was administered on days 1-5 with 75 mg/m2 of doxorubicin administered on day 4 of every 21 day cycle until disease progression, drug intolerance, or a cumulative lifetime dose of 450 mg/m2 of doxorubicin was reached. GCSF support was provided at physician discretion on Arm A or provided to all participants in Arm B. 3-6 subjects were administered abexinostat at doses of 15, 30, 45, and 60 mg/m2 BID. All patients without progressive disease after receiving a cumulative lifetime dose of 450 mg/m2 of doxorubicin continued with abexinostat as a single agent until disease progression. Results: 22 participants (10 with prior doxorubicin therapy) were enrolled (6 in Arm A, 14 in Arm B), 20 were evaluable for DLT, and 17 were evaluable for radiologic response. In Arm A, participants were administered abexinostat at 30 or 15 mg/m2 BID. DLTs of grade 3 and 4 ANC were observed in two out of three participants dosed at 30 mg/m2 BID. Neither of these patients received GCSF prophylaxis. In Arm B, participants were administered abexinostat at 30, 45, or 60 mg/m2 BID, all with mandated GCSF support. Two DLTs were observed on the 60 mg/m2 BID dose (grade 3 infection and grade 4 thrombocytopenia). The pharmacokinetics of abexinostat was not affected by doxorubicin. HDAC activity, as measured by histone acetylation in PBMC, was maximally inhibited at 30mg/m2 BID. In the 17 participants evaluable for radiologic response there was 1 PR, 11 SD, and 5 PD as best response, with 7 participants completing 5 cycles or more. 3 of those participants remain in SD as their last disease status when this abstract was submitted. 4 participants who continued on monotherapy remained in SD for a median of 9.8 weeks after completing doxorubicin. The most common toxicities were fatigue, thrombocytopenia, and anemia (see Table 1). No study related deaths were observed. Conclusion: The MTD for abexinostat is 45 mg/m2 BID when administered on days 1-5 when doxorubicin is given at 75 mg/m2 on day 4 of a 3-week cycle and GCSF support is provided. Toxicities were manageable and tumor responses were seen. Additional studies are needed to further define the specific contributions of HDAC inhibition for patients receiving doxorubicin to treat metastatic sarcoma. Grade Type 1 2 3 4 Totals Fatigue 13 6 0 0 19 Platelets 10 3 1 2 16 Hemoglobin 11 4 1 0 16 Nausea 13 1 0 0 14 Neutrophils 4 1 4 3 12 Leukocytes 6 3 3 0 12 Diarrhea w/o prior colostomy 7 3 1 0 11 Hyperglycemia 7 1 1 0 9 QTc interval 7 2 0 0 9 Alopecia 1 5 1 0 7 Hypophosphatemia 3 4 0 0 7 Constipation 5 2 0 0 7 Extremity/limb pain 6 1 0 0 7 Anorexia 7 0 0 0 7 Lymphopenia 0 2 4 0 6 Pain: other 5 1 0 0 6 Hypomagnesemia 4 1 0 0 5 Hyponatremia 5 0 0 0 5 Taste disturbance 5 0 0 0 5 Citation Format: Edwin Choy, Sriram Balasubramanian, James Butrynski, Jeffrey Morgan, Mint Sirisawad, Chitra Mani, Suzanne George, Andrew Wagner, David Harmon, Yael Rubinstein, Zhenfeng Duan, Francis Hornicek, George Demetri. Phase I dose escalation study of abexinostat and doxorubicin in patients with metastatic sarcomas. [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 LB-167. doi:10.1158/1538-7445.AM2013-LB-167

Abstract 55 Background: Abexinostat (PCI-24781) is a novel oral pan-HDACi that has previously demonstrated potent preclinical activity in lymphoma cell lines and animal models (Evens et al, Clin Ca Res 2009) as well as a tolerable safety profile in phase I solid tumor clinical studies (Undevia et al, ASCO 2008). In a phase I single-agent clinical trial in patients (pts) with multiply relapsed/refractory lymphoma and leukemia, anti-tumor activity was noted in FL and MCL; 4/4 FL pts showed durable clinical benefit with median time on treatment of >8 months; 1 of 2 MCL pts had a complete remission (CR) and remains on treatment for >3 years. Based on these encouraging single-agent abexinostat data, a phase II extension study was completed in relapsed/refractory FL and MCL. Methods: The primary objective of this phase II study was objective response rate (ORR, complete [CR] and partial remission [PR]), while reduction in tumor size (CR + PR + stable disease) and safety were also examined. Abexinostat was given orally twice daily at 45mg/m2 on a 4-week cycle for 7 days/week every other week, which is the previously established dose and schedule identified in the phase I study. For pharmacodynamic correlative analyses, tubulin and histone acetylation were measured in peripheral blood mononuclear cells (PBMCs) at pre-dose and 4 hours after the first dose of abexinostat. Results: A total of 30 pts were enrolled (n=16 FL and n=14 MCL pts) of which 25 were response-evaluable. The median age was 67 years (36–81) and the median prior therapies were 3 (1–5), 77% of which were rituximab-containing and one-third (33%) had undergone prior autologous stem cell transplant (31% FL, 36% MCL). The ORR in all pts was 48% (12/25). A reduction in tumor size was observed in 86% (12/14) of FL pts, while the ORR in FL was 64% (9/14); the FL intent-to-treat ORR was 56%. With a median follow-up of 10.3 months (1.2–20.9), the progression-free probability was 86% in FL pts. Furthermore, the median duration of response (DOR) in FL pts has not been reached, as 5 responders remain on study. Notably, 4 FL pts were on treatment for over 16 months. Among MCL pts, reduction in tumor size was noted in 27% (3/11), while the ORR was similar at 27% (3/11). The median progression-free survival (PFS) in MCL pts was 4 months (1–12), while the DOR in the 3 responding patients were 2+, 3, and 6+ months. Therapy was overall well tolerated. The most common treatment-related adverse events (AEs) of any grade (> 20% incidence) include: nausea (60%), fatigue (57%), diarrhea (50%), thrombocytopenia (37%), vomiting (30%), anemia (27%), decreased appetite (23%), dysgeusia (20%) and neutropenia (20%). The most common grade 3/4 related AEs (> 5% incidence) were thrombocytopenia (17%), neutropenia (13%), fatigue (13%), and anemia (7%). There were no deaths reported on the study. Pharmacodynamic analyses revealed that a majority of pts had increased tubulin acetylation in PBMCs, however this finding did not correlate with response or toxicity. Conclusion: In this phase II study, the novel pan-HDACi, abexinostat, was clinically active and overall well tolerated in relapsed/refractory B-cell lymphoma. The safety profile was consistent with this class of agents with Disclosures: Off Label Use: PCI24781 is not FDA approved; it is an investigational agent. Plasencia:Pharmacyclics: Employment, Equity Ownership. Sirisawad:Pharmacyclics: Employment, Equity Ownership. Yue:Pharmacyclics: Employment, Equity Ownership. Luan:Pharmacyclics: Employment, Equity Ownership. Siek:Pharmacyclics: Employment, Equity Ownership. Zhou:Pharmacyclics: Consultancy. Balasubramanian:Pharmacyclics: Employment, Equity Ownership.

Abstract 3643 Background. Abexinostat is a new hydroxymate-based pan-HDAC inhibitor of class I and II that induces apoptosis and cell cycle arrest in various human tumor cell lines and inhibits tumor growth in several lymphoma xenograft models. Aim. The primary objective of the Phase I was to assess the safety profile and to determine the recommended Phase 2 dose (RP2D) as well as the optimal administration schedule of abexinostat in patients with refractory or relapsed lymphoma or chronic lymphocytic leukemia. The secondary objectives included assessment of pharmacokinetic and pharmacodynamic profiles and preliminary antitumor activity. Methods. Eligibility criteria included ECOG ≤ 1 and adequate hematological, renal and hepatic functions. This study used a 3+3 cohort expansion design to reach the RP2D. Three different 3-week schedules of abexinostat were tested: schedule 1 (S1) with 14 days of treatment (day 1 – day 14); schedule 2 (S2) with 10 days of treatment (day 1 – day 5 and day 8 – day 12); schedule 3 (S3) with 12 days of treatment (day 1 – day 4, day 8 – day 11 and day 15 – day 18). The schedules were evaluated at different dose levels of abexinostat b.i.d. (4 h apart): S1 at 30 mg/m2, and all 3 schedules at both 45 mg/m2 and 60 mg/m2. The following were considered DLTs if they occurred in cycle 1: ≥ grade 3 non-hematologic toxicity, prolongation of QTc interval and febrile neutropenia; grade 4 neutropenia or thrombocytopenia; and next cycle postponed by > 1 week. Results. A total of 35 patients were included. The median age was 61 (21–83). The sex ratio M/F was 22/13. The median number of prior therapies was 5 (2–11). Lymphoma subtypes were Hodgkin's lymphoma (HL) (n=11), follicular lymphoma (FL) (n=7), diffuse large B-cell lymphoma (DLBCL) (n=6), chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) (n=4), marginal zone B-cell lymphoma (MZL) (n=3), mantle cell lymphoma (MCL) (n=3) and peripheral T-cell lymphoma (n=1). One DLT (thrombocytopenia) was observed in S2 at 45 mg/m2. At 60 mg/m2, 2 DLTs were observed in each schedule: thrombocytopenia in S1 and S2 (2 each), thrombocytopenia and febrile neutropenia (1 each) in S3. Grade 3 and 4 toxicities were exclusively hematologic: thrombocytopenia (G3: 31.4% patients, G4: 25.7% patients), neutropenia (G3: 11.4% patients, G4: 5.7% patients), febrile neutropenia (G3: 2.9% patients, G4: 2.9% patients), anemia (G3: 2.9% patients, G4: 2.9% patients) and leukopenia (G3: 2.9% patients). The other frequent drug-related adverse events were grade 1 and 2: asthenia (34.3% patients), gastro-intestinal disorders (60% patients) and dry skin (17.1% patients). No prolonged QTc intervals were observed in any schedule. A dose reduction occurred in 28.6% patients in S1, 33.3% in S2 and 37.5% in S3. S1 was selected for Phase 2 since it allowed a full week for platelets recovery, a longer drug exposure than S2 and a safety profile similar to the 2 other schedules. Cmax was reached after each administration with median tmax between 0.5 h and 1 h for each schedule and at each dose level. The median apparent terminal elimination half-life was around 4 h. These results are consistent with the limited accumulation of abexinostat with these dose regimens. There is no evidence of time dependent pharmacokinetics. No correlations have been demonstrated so far between histones H3 acetylation in peripheral blood mononuclear cells and PK parameters or clinical activity. Eight out of 29 (27.5%) evaluable patients achieved objective response: 2 complete responses (2 FL) and 6 partial responses (1 FL, 1 CLL, 1 MZL and 3 HL). At the time of data cut off, all but 1 (HL) responses were ongoing between cycle 6 and cycle 22 (median 13.5 cycles). One stable disease (1 MZL) was observed and was still ongoing after cycle 9. Nineteen patients withdrew for progressive disease, including 9 patients who withdrew after at least 2 cycles (4 HL, 2 DLBCL, 1 MCL, 1 MZL and 1 FL). Conclusion. Abexinostat is well tolerated and demonstrates promising durable responses (including CRs) in indolent lymphomas and Hodgkin's lymphoma patients. Enrollment in the Phase II part of the study is ongoing following S1 (3-week cycles – 14 days of treatment) at the RP2D (45 mg/m2b.i.d.). Disclosures: Terriou: Servier: Honoraria; Pfizer: Consultancy; Amgen: Honoraria; GSK: Honoraria. Coiffier:Servier: Honoraria; Celgene: Consultancy, Honoraria, Research Funding. Kloos:Institut de recherches internationales Servier: Employment. Tavernier:Institut de recherches internationales Servier: Employment. Depil:Institut de recherches Internationales Servier: Employment. Ribrag:Servier: Membership on an entity's Board of Directors or advisory committees, Research Funding; astrazeneca: Membership on an entity's Board of Directors or advisory committees; takeda: Membership on an entity's Board of Directors or advisory committees; bayer: Research Funding; sanofi: Research Funding.