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Background: Richter transformation usually presents as an aggressive diffuse large B-cell lymphoma, occurs in up to 10% of patients with chronic lymphocytic leukaemia, has no approved therapies, and is associated with a poor prognosis. Pirtobrutinib has shown promising efficacy and tolerability in patients with relapsed or refractory B-cell malignancies, including those who progress on covalent Bruton tyrosine kinase (BTK) inhibitors. This study aims to report the safety and activity of pirtobrutinib monotherapy in a subgroup of patients with Richter transformation from the multicentre, open-label, phase 1/2 BRUIN study., Methods: This analysis included adult patients (aged ≥18 years) with histologically confirmed Richter transformation, an Eastern Cooperative Oncology Group performance status score of 0-2, and no limit of previous therapies, with patients receiving first-line treatment added in a protocol amendment (version 9.0, Dec 15, 2021). Pirtobrutinib 200 mg was administered orally once a day in 28-day cycles. The primary endpoint of phase 1 of the BRUIN trial as a whole, which has been previously reported, was to establish the recommended phase 2 dose for pirtobrutinib monotherapy and the phase 2 primary endpoint was overall response rate. Safety and activity were measured in all patients who received at least one dose of pirtobrutinib monotherapy. This BRUIN phase 1/2 trial was registered with ClinicalTrials.gov and is closed to enrolment (NCT03740529)., Findings: Between Dec 26, 2019, and July 22, 2022, 82 patients were enrolled, of whom five were enrolled during phase 1 and 77 during phase 2. All but one patient received a starting dose of 200 mg pirtobrutinib once a day as the recommended phase 2 dose. The remaining patient received 150 mg pirtobrutinib once a day, which was not escalated to 200 mg. The median age of patients was 67 years (IQR 59-72). 55 (67%) of 82 patients were male and 27 (33%) were female. Most patients were White (65 [79%] of 82). 74 (90%) of 82 patients received at least one previous Richter transformation-directed therapy. Most patients (61 [74%] of 82) had received previous covalent BTK inhibitor therapy for chronic lymphocytic leukaemia or Richter transformation. The overall response rate was 50·0% (95% CI 38·7-61·3). 11 (13%) of 82 patients had a complete response and 30 (37%) of 82 patients had a partial response. Eight patients with ongoing response electively discontinued pirtobrutinib to undergo stem-cell transplantation. The most common grade 3 or worse adverse event was neutropenia (n=19). There were no treatment-related deaths., Interpretation: Pirtobrutinib shows promising safety and activity among patients with Richter transformation, most of whom received previous Richter transformation-directed therapy, including covalent BTK inhibitors. These data suggest that further investigation is warranted of pirtobrutinib as a treatment option for patients with relapsed or refractory Richter transformation after treatment with a covalent BTK inhibitor., Funding: Loxo Oncology., Competing Interests: Declaration of interests WGW reports research funding from Numab Therapeutics, Loxo Oncology–Lilly, Janssens Biotech, NIH P30 CA016672/MDACC Cancer Center Support Grant, GlaxoSmithKline, AbbVie, Cyclacel, Nurix Therapeutics, Juno Therapeutics, Bristol Myers Squibb (Juno & Celgene), AstraZeneca–Acerta Pharma Miragen, Oncternal Therapeutics, Janssens Biotech, Accutar Biotechnology, Sunesis, KITE Pharma, Gilead Sciences, Genentech, Pharmacyclics, GlaxoSmithKline–Novartis; consultancy fees from AbbVie, Cyclacel Nurix Therapeutics, Bristol Myers Squibb (Juno & Celgene), AstraZeneca–Acerta Pharma; a non-relevant financial relationship with the National Comprehensive Cancer Network; support from the National Institutes of Health and National Cancer Institute under award number P30 CA016672; and use of MDACC Cancer Center Support Grant shared resources. NNS reports consultancy fees from Umoja, Janssen, Bristol Myers Squibb–Juno, LOXO Oncology–Lilly, TG therapeutic, Novartis, Seattle Genetics, Gilead–Kite, Incyte, AbbVie, Lilly Oncology, and Miltenyi Biotec; research funding from Miltenyi Biotec and Lilly Oncology; having stock options in a privately-held company with Tundra Therapeutics; and travel support from Epizyme and Miltenyi Biotec. CYC reports consultancy fees, honoraria, and having an advisory role for Roche, Janssen, Gilead, AstraZenecca, Eli Lilly, BeiGene, AbbVie, Menarini, Daizai, and Genmab, and research funding from Roche, MSD, Eli Lilly, Bristol Myers Squibb, and AbbVie. DL reports consultancy fees from Kite, BeiGene, Roche, Eli Lilly, and Janssen and membership on an entity's board of directors or advisory committees with Kite, BeiGene, Roche, Eli Lilly, and Janssen. MSH reports consultancy fees and honoraria from Pharmacyclics. CCC reports consultancy fees from LOXO Oncology–Eli Lilly, BeiGene, AstraZeneca, Genentech, AbbVie, Octapharma, Allogene, Janssen, TG Therapeutics, MEI Pharma, and Mingsight; honoraria from LOXO Oncology–Eli Lilly, BeiGene, AstraZeneca, Genentech, AbbVie; research funding paid to an institution from LOXO Oncology–Eli Lilly, AbbVie, and CarnaBio; membership on an entity's board of directors or advisory committees with BeiGene, AstraZeneca, Genentech, and AbbVie; being an equity holder in a publicly-traded company with Bluebird Bio, Geron, and Pfizer; and receiving travel support from LOXO Oncology–Eli Lilly. NL reports consultancy fees from Genentech, Pharmacyclics, BeiGene, AstraZeneca, AbbVie, Adaptive Biotechnologies, Janssen, and research funding from Genentech, TG Therapeutics, BeiGene, AstraZeneca, AbbVie, MingSight, LOXO Oncology–Eli Lilly, Oncternal, and Octapharma. SM reports consultancy fees from AstraZeneca, Juno–Bristol Myers Squibb, AbbVie, Genentech, Janssen Pharmaceuticals, BeiGene; membership on a board of directors or advisory committee with AstraZeneca, Juno–Bristol Myers Squibb, Janssen Pharmaceuticals, Eli Lilly, Loxo Oncology, and BeiGene; research funding from AstraZeneca, Juno–Bristol Myers Squibb, AbbVie, Janssen Pharmaceuticals, Eli Lilly–Loxo Oncology, BeiGene; and speakers bureau with AstraZeneca, Eli Lilly–Loxo Oncology, and BeiGene. DJ reports research funding from Seagen, Trillium Pharmaceuticals, Regeneron Pharmaceuticals, MEI Pharma, Loxo Oncology, Debio Pharma, ATARA Biotherapeutics, AstraZeneca and membership on a board of directors or advisory committees with Affimed and Daiichi Sankyo. TM reports consultancy fees from BeiGene, Alexion, Sobi, Roche, AstraZeneca, Janssen, and AbbVie; honoraria from BeiGene, Alexion, Sobi, Roche, AstraZeneca, Janssen, and AbbVie; membership on a board of directors or advisory committees on BeiGene, Alexion, Sobi, Roche, AstraZeneca, Janssen, Abbvie; research Funding from Janssen, AbbVie; and speakers bureau for BeiGene, Alexion, Sobi, Roche, AstraZeneca, Janssen, and AbbVie. YW reports research funding from Incyte, InnoCare, LOXO Oncology, Eli Lilly, MorphoSys, Novartis, Genentech, Genmab, and AbbVie; membership on an advisory board with Eli Lilly, LOXO Oncology, TG Therapeutics, Incyte, InnoCare, Kite, Jansen, BeiGene, AstraZeneca, and Genmab; consultancy fees from Innocare and AbbVie; and honoraria from Kite. TAE reports membership on an entity's Board of Directors or advisory committees from Loxo Oncology, Incyte, BeiGene, AstraZeneca, KITE, AbbVie, Roche, Gilead, Secura Bio; speakers bureau from Loxo Oncology, Eli Lilly, Incyte, BeiGene, AstraZeneca, KITE, AbbVie, Loxo Oncology, Roche, Medscape, Janssen, Gilead, PeerView; research funding from BeiGene and AstraZeneca; consultancy fees from Eli Lilly, Incyte, Beigene, Autolus, AstraZeneca, KITE, AbbVie, Loxo Oncology, Roche, Janssen, and Gilead; and honoraria from Eli Lilly, BeiGene, AstraZeneca, KITE, AbbVie, Loxo Oncology, Roche, Janssen, and Gilead. JMR reports consultancy fees from Pharmacyclics, Jannsen, Genentech, GenMab, AstraZeneca, Morphosys, ADC Therapeutics, Epizyme, BeiGene, and AbbVie; research funding from Pharmacyclics, Velosbio, Loxo Oncology, Acerta, Oncternal Pharmaceuticals, Epizyme, and AbbVie; and honoraria from SeaGen. MM reports consultancy from Bayer, ADC therapeutics, Epizyme, Genentech, F Hoffmann-La Roche, and Incyte; research funding from BeiGene, Janssen, F Hoffmann-La Roche– Genentech, Celgene–Bristol Myers Squibb, and Incyte; and speakers bureau with ADC therapeutics, BeiGene, and Kite–Gilead. CT reports honoraria from Loxo Oncolgy. WJ reports consultancy fees from AbbVie, AstraZeneca, BeiGene, Eli Lilly, Pfizer, Roche, SOBI, and Takeda and research funding from AbbVie, AstraZeneca, Bayer, BeiGene, Celgene, Janssen, Eli Lilly, Roche, SOBIm, and Takeda. KI reports honoraria from Eli Lilly, SymBio Pharmaceuticals, Meiji Seika, Nihon Kayaku, Takeda, AstraZeneca, Janssen, Genmab, MSD, Pfizer, AbbVie, Ono Pharmaceuticals, Daiichi Sankyo, Novartis, Bristol Myers Squibb, Chugai Pharma, and Kyowa Kirin; consultancy fees from Takeda, AstraZeneca, Genmab, AbbVie, Otsuka, Eisai, Ono Pharmaceuticals, Nippon Shinyaku, Mitsubishi Tanabe Pharma, and Zenyaku Kogyo; and research funding from AstraZeneca, Genmab, MSD, Pfizer, AbbVie, Otsuka, Eisai, Regeneron, Loxo Oncology, BeiGene, Daiichi Sankyo, Yakult, Novartis, Bristol Myers Squibb, Incyte, Astellas Amgen, Chugai Pharma, Kyowa Kirin. AA reports membership on a board of directors or advisory committees with Genentech, Eli Lilly and Company, Amgen, TG Therapeutics, Incyte, BeiGene, Epizyme, Janssen, and SeaGen; research funding from Eli Lilly, Incyte, and BeiGene; and honoraria from Dr Reddy. MP reports consulting fees from Kura, Accutar, Mitsubishi; participating on a data safety monitoring board or advisory board with lema, Nurix, Daiichi, Kura, and Janssen; leadership with ION Pharma; honoraria from Janssen Oncology; and participating in a consulting or advisory role with Olema Pharmaceuticals, Daiichi Sankyo–UCB Japan, Kura Oncology, Accutar Biotech, and Kura. JFS reports honoraria from Hoffmann-La Roche, AbbVie, AstraZeneca, Janssen, Bristol Myers Squibb, Gilead, and BeiGene; consultancy fees from Hoffmann-La Roche, TG Therapeutics, Bristol Myers Squibb; participating on a data safety monitoring board or advisory board with Genor Bio, Hoffmann-La Roche, AbbVie, AstraZeneca, Janssen, Bristol Myers Squibb, Gilead, and BeiGene; speakers bureau with Hoffmann-La Roche, AbbVie, and BeiGene; and research funding from F Hoffmann-La Roche and AbbVie. JAW reports consultancy from Newave, Loxo Oncology, BeiGene, AstraZeneca, AbbVie, Janssen, and Pharmacyclics and research funding from Schrodinger, Morphosys, Karyopharm, Janssen, and Pharmacyclics. PAT reports consultancy and honoraria from AbbVie, Adaptive Biotechnologies, Ascentage AstraZeneca, BeiGene, Genentech, Genmab, Janssen, Lilly, Merck, Pharmacyclics; speakers bureau from AbbVie, Adaptive Biotechnologies, AstraZeneca, Janssen, and Merck; research funding from AbbVie, Pharmacyclics, Genentech, Lilly, and Adaptive Biotechnologies; and travel support from Merck. PA is a current employee of and equity holder in Eli Lilly. CH reports being an equity holder in Eli Lilly and Foundation Medicine and travel support from Eli Lilly. SCM reports current employment with, being an equity holder in, and travel support from Eli Lilly. NM reports being a current equity holder in Eli Lilly and current employment with Loxo Oncology. BN, CW, BCN, and DET reports current employment with and current equity holder in Eli Lilly. ASR reports current employment with and being equity holder in Eli Lilly and consultancy work with Telios Pharma. HL reports current employment with Loxo Oncology. LER reports serving as a consultant for AbbVie, Ascentage, AstraZeneca, BeiGene, Janssen, Loxo Oncology, Pharmacyclics, Pfizer, and TG Therapeutics; membership of a data safety monitoring committee for Ascentage; serving as a CME speaker for DAVA, Curio, Medscape, and PeerView; holding minority ownership interest in Abbott Laboratories; having received travel support from LOXO Oncology; and having received research funding (paid to the institution) from Adaptive Biotechnologies, AstraZeneca, Genentech, AbbVie, Pfizer, Loxo Oncology, Aptose Biosciences, Dren Bio, and Qilu Puget Sound Biotherapeutics. PG reports consultancy, fees, honoraria, and research funding from Janssen, Eli Lilly–Loxo Oncology, MSD, Roche, AbbVie, BMS, BeiGene, and AstraZeneca., (Copyright © 2024 Elsevier Ltd. All rights reserved, including those for text and data mining, AI training, and similar technologies.)

Aberrant signal transduction through the B cell receptor (BCR) plays a critical role in the pathogenesis of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). BCR-dependent signaling is necessary for the growth and survival of neoplastic cells, making inhibition of down-stream pathways a logical therapeutic strategy. Indeed, selective inhibitors against Bruton's tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) have been shown to induce high rates of response in CLL and other B cell lymphomas. In particular, the development of BTK inhibitors revolutionized the treatment approach to CLL, demonstrating long-term efficacy. While BTK inhibitors are widely used for multiple lines of treatment, PI3K inhibitors are much less commonly utilized, mainly due to toxicities. CLL remains an incurable disease and effective treatment options after relapse or development of TKI resistance are greatly needed. This review provides an overview of BCR signaling, a summary of the current therapeutic landscape, and a discussion of the ongoing trials targeting BCR-associated kinases., Competing Interests: Declaration of competing interest JTP has no conflicts of interest to disclose. JAW consults for Abbvie, AstraZeneca, Beigene, Genentech, Janssen, Loxo/Lilly, Merck, Newave, and Pharmacyclics, and research funding from Abbvie, Janssen, and Schrodinger., (Copyright © 2024. Published by Elsevier Inc.)

Background: Patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) have poor outcomes after the failure of covalent Bruton's tyrosine kinase (BTK) inhibitor treatment, and new therapeutic options are needed. Pirtobrutinib, a highly selective, noncovalent (reversible) BTK inhibitor, was designed to reestablish BTK inhibition., Methods: We conducted a phase 1-2 trial in which patients with relapsed or refractory B-cell cancers received pirtobrutinib. Here, we report efficacy results among patients with CLL or SLL who had previously received a BTK inhibitor as well as safety results among all the patients with CLL or SLL. The primary end point was an overall response (partial response or better) as assessed by independent review. Secondary end points included progression-free survival and safety., Results: A total of 317 patients with CLL or SLL received pirtobrutinib, including 247 who had previously received a BTK inhibitor. Among these 247 patients, the median number of previous lines of therapy was 3 (range, 1 to 11), and 100 patients (40.5%) had also received a B-cell lymphoma 2 (BCL2) inhibitor such as venetoclax. The percentage of patients with an overall response to pirtobrutinib was 73.3% (95% confidence interval [CI], 67.3 to 78.7), and the percentage was 82.2% (95% CI, 76.8 to 86.7) when partial response with lymphocytosis was included. The median progression-free survival was 19.6 months (95% CI, 16.9 to 22.1). Among all 317 patients with CLL or SLL who received pirtobrutinib, the most common adverse events were infections (in 71.0%), bleeding (in 42.6%), and neutropenia (in 32.5%). At a median duration of treatment of 16.5 months (range, 0.2 to 39.9), some adverse events that are typically associated with BTK inhibitors occurred relatively infrequently, including hypertension (in 14.2% of patients), atrial fibrillation or flutter (in 3.8%), and major hemorrhage (in 2.2%). Only 9 of 317 patients (2.8%) discontinued pirtobrutinib owing to a treatment-related adverse event., Conclusions: In this trial, pirtobrutinib showed efficacy in patients with heavily pretreated CLL or SLL who had received a covalent BTK inhibitor. The most common adverse events were infections, bleeding, and neutropenia. (Funded by Loxo Oncology; BRUIN ClinicalTrials.gov number, NCT03740529.)., (Copyright © 2023 Massachusetts Medical Society.)

Complex karyotype, defined as ≥3 cytogenetic abnormalities, is prognostic of survival in patients treated with ibrutinib or venetoclax in relapsed/refractory (RR) chronic lymphocytic leukemia (CLL). Recent studies re-evaluating this dichotomous variable have shown that higher numbers of cytogenetic abnormalities (ie, ≥5) have a worse overall survival in patients treated with chemoimmunotherapy. We sought to determine if increasing karyotypic complexity, treated as a continuous variable, was prognostic of survival for patients treated with ibrutinib for CLL. We conducted a retrospective analysis of all patients with CLL treated with single-agent ibrutinib or in combination with an anti-CD20 antibody at our institution. We included 456 patients with both treatment-naive and RR disease. Median number of prior therapies was 2 (range, 0-13), 30% of patients had presence of del(17p), and 75% expressed unmutated IGHV. Fifty percent had ≥3 cytogenetic abnormalities, including 30% with ≥5. In a multivariable analysis, increasing karyotypic complexity was an independent predictor of shorter progression-free survival (hazard ratio, 1.07; 95% confidence interval, 1.04-1.10; P < .0001) and overall survival (hazard ratio, 1.09; 95% confidence interval, 1.05-1.12; P < .0001). Furthermore, we found that presence of clonal evolution determined by cytogenetic analysis at progression was prognostic of subsequent survival (P = .02). This solidifies karyotypic complexity as an important prognostic factor for patients with CLL treated with ibrutinib. Further research should consider sequential karyotypic analysis as a determination of risk of progression and death in patients with CLL., (© 2021 by The American Society of Hematology.)

Background: Covalent Bruton's tyrosine kinase (BTK) inhibitors are efficacious in multiple B-cell malignancies, but patients discontinue these agents due to resistance and intolerance. We evaluated the safety and efficacy of pirtobrutinib (working name; formerly known as LOXO-305), a highly selective, reversible BTK inhibitor, in these patients., Methods: Patients with previously treated B-cell malignancies were enrolled in a first-in-human, multicentre, open-label, phase 1/2 trial of the BTK inhibitor pirtobrutinib. The primary endpoint was the maximum tolerated dose (phase 1) and overall response rate (ORR; phase 2). This trial is registered with ClinicalTrials.gov, NCT03740529., Findings: 323 patients were treated with pirtobrutinib across seven dose levels (25 mg, 50 mg, 100 mg, 150 mg, 200 mg, 250 mg, and 300 mg once per day) with linear dose-proportional exposures. No dose-limiting toxicities were observed and the maximum tolerated dose was not reached. The recommended phase 2 dose was 200 mg daily. Adverse events in at least 10% of 323 patients were fatigue (65 [20%]), diarrhoea (55 [17%]), and contusion (42 [13%]). The most common adverse event of grade 3 or higher was neutropenia (32 [10%]). There was no correlation between pirtobrutinib exposure and the frequency of grade 3 treatment-related adverse events. Grade 3 atrial fibrillation or flutter was not observed, and grade 3 haemorrhage was observed in one patient in the setting of mechanical trauma. Five (1%) patients discontinued treatment due to a treatment-related adverse event. In 121 efficacy evaluable patients with chronic lymphocytic leukaemia (CLL) or small lymphocytic lymphoma (SLL) treated with a previous covalent BTK inhibitor (median previous lines of treatment 4), the ORR with pirtobrutinib was 62% (95% CI 53-71). The ORR was similar in CLL patients with previous covalent BTK inhibitor resistance (53 [67%] of 79), covalent BTK inhibitor intolerance (22 [52%] of 42), BTK C481-mutant (17 [71%] of 24) and BTK wild-type (43 [66%] of 65) disease. In 52 efficacy evaluable patients with mantle cell lymphoma (MCL) previously treated with covalent BTK inhibitors, the ORR was 52% (95% CI 38-66). Of 117 patients with CLL, SLL, or MCL who responded, all but eight remain progression-free to date., Interpretation: Pirtobrutinib was safe and active in multiple B-cell malignancies, including patients previously treated with covalent BTK inhibitors. Pirtobrutinib might address a growing unmet need for alternative therapies for these patients., Funding: Loxo Oncology., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Chronic lymphocytic leukemia (CLL) is associated with perturbed immune function and increased risk for second primary malignancies (SPM). Ibrutinib and acalabrutinib (BTKi) are effective therapies for CLL resulting in partial restoration of immune function. The incidence of and risk factors for SPM in CLL patients receiving BTKi are not yet characterized. We retrospectively determined the incidence of SPM in CLL patients treated with ibrutinib or acalabrutinib at our institution between 2009 and 2017, assessed for association between baseline characteristics and SPM incidence, and compared the observed to expected cancer incidence among age, sex, and year matched controls without CLL. After a median of 44 months follow-up, 64/691 patients (9%) were diagnosed with SPM (excluding non-melanoma skin cancer [NMSC]). The 3-year cumulative incidence rate was 16% for NMSC and 7% for other SPM. On multivariable analysis, smoking was associated with increased SPM risk (HR 2.8 [95% CI: 1.6-4.8]) and higher baseline CD8 count was associated with lower SPM risk (HR 0.9 for 2-fold increase [95% CI: 0.8-0.9]). The observed over expected rate of SPM was 2.2 [95% CI: 1.7-2.9]. CLL patients treated with BTKi remain at increased risk for SPM, and secondary cancer detection is an important consideration in this population.

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., (© 2020 by The American Society of Hematology.)

Ibrutinib, a once-daily oral inhibitor of Bruton's tyrosine kinase, is approved in the United States and Europe for treatment of patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). The phase 3 RESONATE study showed improved efficacy of single-agent ibrutinib over ofatumumab in patients with relapsed/refractory CLL/SLL, including those with high-risk features. Here we report the final analysis from RESONATE with median follow-up on study of 65.3 months (range, 0.3-71.6) in the ibrutinib arm. Median progression-free survival (PFS) remained significantly longer for patients randomized to ibrutinib vs ofatumumab (44.1 vs 8.1 months; hazard ratio [HR]: 0.148; 95% confidence interval [CI]: 0.113-0.196; P˂.001). The PFS benefit with ibrutinib vs ofatumumab was preserved in the genomic high-risk population with del(17p), TP53 mutation, del(11q), and/or unmutated IGHV status (median PFS 44.1 vs 8.0 months; HR: 0.110; 95% CI: 0.080-0.152), which represented 82% of patients. Overall response rate with ibrutinib was 91% (complete response/complete response with incomplete bone marrow recovery, 11%). Overall survival, censored for crossover, was better with ibrutinib than ofatumumab (HR: 0.639; 95% CI: 0.418-0.975). With up to 71 months (median 41 months) of ibrutinib therapy, the safety profile remained consistent with prior reports; cumulatively, all-grade (grade ≥3) hypertension and atrial fibrillation occurred in 21% (9%) and 12% (6%) of patients, respectively. Only 16% discontinued ibrutinib because of adverse events (AEs). These long-term results confirm the robust efficacy of ibrutinib in relapsed/refractory CLL/SLL irrespective of high-risk clinical or genomic features, with no unexpected AEs. This trial is registered at www.clinicaltrials.gov (NCT01578707)., (© 2019 The Authors. American Journal of Hematology published by Wiley Periodicals, Inc.)

Purpose of Review: While the Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib has revolutionized the treatment of chronic lymphocytic leukemia (CLL), current limitations include off-target toxicities and the development of resistance. In this review, we summarize the emerging data for alternative BTKi., Recent Findings: Second-generation BTKi include acalabrutinib, zanubrutinib, and tirabrutinib which offer greater BTK selectivity. While these agents may limit off-target toxicity, they do not overcome common mechanisms of ibrutinib resistance. Reversible BTKi including vecabrutinib and LOXO-305 inhibit BTK in the presence of C481S mutation, and non-selective reversible BTKi, including ARQ-531, may retain activity despite mutations within PLCG2. Early-phase studies are underway to establish the clinical efficacy and toxicity of these agents. A randomized trial of ibrutinib versus acalabrutinib is ongoing, and acalabrutinib may be an option for ibrutinib-intolerant patients. Results from ongoing trials of alternate BTKi will help to define their role in CLL therapy as single agents or in combination therapy.

Targeted inhibition of Bruton tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has improved outcomes for patients with hematologic malignancies, including chronic lymphocytic leukemia (CLL). Here, we describe preclinical investigations of ARQ 531, a potent, reversible inhibitor of BTK with additional activity against Src family kinases and kinases related to ERK signaling. We hypothesized that targeting additional kinases would improve global inhibition of signaling pathways, producing more robust responses. In vitro treatment of patient CLL cells with ARQ 531 decreases BTK-mediated functions including B-cell receptor (BCR) signaling, viability, migration, CD40 and CD86 expression, and NF-κB gene transcription. In vivo , ARQ 531 was found to increase survival over ibrutinib in a murine Eμ-TCL1 engraftment model of CLL and a murine Eμ-MYC/TCL1 engraftment model resembling Richter transformation. Additionally, ARQ 531 inhibits CLL cell survival and suppresses BCR-mediated activation of C481S BTK and PLCγ2 mutants, which facilitate clinical resistance to ibrutinib. Significance: This study characterizes a rationally designed kinase inhibitor with efficacy in models recapitulating the most common mechanisms of acquired resistance to ibrutinib. Reversible BTK inhibition is a promising strategy to combat progressive CLL, and multikinase inhibition demonstrates superior efficacy to targeted ibrutinib therapy in the setting of Richter transformation. Cancer Discov; 8(10); 1300-15. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1195 ., (©2018 American Association for Cancer Research.)

Inhibition of Bruton's tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has emerged as a transformative treatment option for patients with chronic lymphocytic leukemia (CLL) and other B-cell malignancies, yet >80% of CLL patients develop resistance due to a cysteine to serine mutation at the site covalently bound by ibrutinib (C481S). Currently, an effective treatment option for C481S patients exhibiting relapse to ibrutinib does not exist, and these patients have poor outcomes. To address this, we have developed a PROteolysis TArgeting Chimera (PROTAC) that induces degradation of both wild-type and C481S mutant BTK. We selected a lead PROTAC, MT-802, from several candidates on the basis of its potency to induce BTK knockdown. MT-802 recruits BTK to the cereblon E3 ubiquitin ligase complex to trigger BTK ubiquitination and degradation via the proteasome. MT-802 binds fewer off-target kinases than ibrutinib does and retains an equivalent potency (>99% degradation at nanomolar concentrations) against wild-type and C481S BTK. In cells isolated from CLL patients with the C481S mutation, MT-802 is able to reduce the pool of active, phosphorylated BTK whereas ibrutinib cannot. Collectively, these data provide a basis for further preclinical study of BTK PROTACs as a novel strategy for treatment of C481S mutant CLL.

Ibrutinib represents a therapeutic advance in chronic lymphocytic leukemia (CLL) but as monotherapy produces few complete remissions in previously treated patients. Anti-CD20 antibodies have improved response and progression-free survival (PFS) when combined with chemotherapy. We evaluated the safety and activity of adding ofatumumab to ibrutinib in 3 different administration sequences. Patients with CLL/small lymphocytic lymphoma (SLL), prolymphocytic leukemia, or Richter's transformation who failed ≥2 prior therapies were enrolled. Patients received ibrutinib 420 mg daily and 12 doses of ofatumumab 300/2000 mg in 3 schedules: ibrutinib lead-in (group 1; n = 27), concurrent start (group 2; n = 20), or ofatumumab lead-in (group 3; n = 24). Seventy-one patients were treated; most had high-risk disease including del(17)(p13.1) (44%) or del(11)(q22.3) (31%). The most frequent adverse events (any grade) were diarrhea (70%), infusion-related reaction (45%), and peripheral sensory neuropathy (44%). Overall response rates in CLL/SLL patients (n = 66) were 100%, 79%, and 71% in groups 1, 2, and 3, respectively. Estimated 12-month PFSs for all patients were 89%, 85%, and 75%, respectively. Four patients in group 3 progressed prior to receiving ibrutinib. This study demonstrates the tolerability and clinical activity of this combination with quicker time to best response than single-agent ibrutinib and with durable responses. This trial was registered at www.clinicaltrials.gov as #NCT01217749., (© 2015 by The American Society of Hematology.)

Importance: The Bruton tyrosine kinase (BTK) inhibitor ibrutinib is effective in patients with chronic lymphocytic leukemia (CLL). Reasons for discontinuing therapy with this drug and outcomes following discontinuation have not been evaluated outside of clinical trials with relatively short follow-up., Objective: To determine features associated with discontinuation of ibrutinib therapy and outcomes., Design, Setting, and Participants: A total of 308 patients participating in 4 sequential trials of ibrutinib at The Ohio State University Comprehensive Cancer Center were included. These clinical trials accrued patients included in this analysis from May 2010 until April 2014, and data were locked in June 2014., Main Outcomes and Measures: Patients were evaluated for time to therapy discontinuation, reasons for discontinuation, and survival following discontinuation. For patients who discontinued therapy because of disease progression, targeted deep sequencing was performed in samples at baseline and time of relapse., Results: With a median follow-up of 20 months, 232 patients remained on therapy, 31 had discontinued because of disease progression, and 45 had discontinued for other reasons. Disease progression includes Richter's transformation (RT) or progressive CLL. Richter's transformation appeared to occur early and CLL progressions later (cumulative incidence at 12 months, 4.5% [95% CI, 2.0%-7.0%] and 0.3% [95% CI, 0%-1.0%], respectively). Median survival following RT was 3.5 months (95% CI, 0.3-6.0 months) and 17.6 months (95% CI, 4.7 months-"not reached") following CLL progression. Sequencing on peripheral blood from 8 patients with RT revealed 2 with mutations in BTK, and a lymph node sample showed no mutations in BTK or PLCG2. Deep sequencing on 11 patients with CLL progression revealed BTK or PLCG2 mutations in all. These mutations were not identified before treatment in any patient., Conclusions and Relevance: This single-institution experience with ibrutinib confirms it to be an effective therapy and identifies, for the first time, baseline factors associated with ibrutinib therapy discontinuation. Outcomes data show poor prognosis after discontinuation, especially for those patients with RT. Finally, sequencing data confirm initial reports associating mutations in BTK and PLCG2 with progression and clearly show that CLL progressions are associated with these mutations, while RT is likely not., Trial Registrations: clinicaltrials.gov Identifiers:NCT01105247, NCT01217749, NCT01589302, and NCT01578707.

Targeting B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) has been successful with durable remissions observed with several targeted therapeutics. Protein kinase C-β (PKC-β) is immediately downstream of BCR and has been shown to be essential to CLL cell survival and proliferation in vivo. We therefore evaluated sotrastaurin (AEB071), an orally administered potent PKC inhibitor, on CLL cell survival both in vitro and in vivo. AEB071 shows selective cytotoxicity against B-CLL cells in a dose-dependent manner. Additionally, AEB071 attenuates BCR-mediated survival pathways, inhibits CpG-induced survival and proliferation of CLL cells in vitro, and effectively blocks microenvironment-mediated survival signaling pathways in primary CLL cells. Furthermore, AEB071 alters β-catenin expression, resulting in decreased downstream transcriptional genes as c-Myc, Cyclin D1, and CD44. Lastly, our preliminary in vivo studies indicate beneficial antitumor properties of AEB071 in CLL. Taken together, our results indicate that targeting PKC-β has the potential to disrupt signaling from the microenvironment contributing to CLL cell survival and potentially drug resistance. Future efforts targeting PKC with the PKC inhibitor AEB071 as monotherapy in clinical trials of relapsed and refractory CLL patients are warranted., (© 2014 by The American Society of Hematology.)