Mechanisms of Resistance to Noncovalent Bruton's Tyrosine Kinase Inhibitors

BackgroundCovalent (irreversible) Bruton's tyrosine kinase (BTK) inhibitors have transformed the treatment of multiple B-cell cancers, especially chronic lymphocytic leukemia (CLL). However, resistance can arise through multiple mechanisms, including acquired mutations in BTK at residue C481, the binding site of covalent BTK inhibitors. Noncovalent (reversible) BTK inhibitors overcome this mechanism and other sources of resistance, but the mechanisms of resistance to these therapies are currently not well understood.MethodsWe performed genomic analyses of pretreatment specimens as well as specimens obtained at the time of disease progression from patients with CLL who had been treated with the noncovalent BTK inhibitor pirtobrutinib. Structural modeling, BTK-binding assays, and cell-based assays were conducted to study mutations that confer resistance to noncovalent BTK inhibitors.ResultsAmong 55 treated patients, we identified 9 patients with relapsed or refractory CLL and acquired mechanisms of genetic resistance to pirtobrutinib. We found mutations (V416L, A428D, M437R, T474I, and L528W) that were clustered in the kinase domain of BTK and that conferred resistance to both noncovalent BTK inhibitors and certain covalent BTK inhibitors. Mutations in BTK or phospholipase C gamma 2 (PLCγ2), a signaling molecule and downstream substrate of BTK, were found in all 9 patients. Transcriptional activation reflecting B-cell-receptor signaling persisted despite continued therapy with noncovalent BTK inhibitors.ConclusionsResistance to noncovalent BTK inhibitors arose through on-target BTK mutations and downstream PLCγ2 mutations that allowed escape from BTK inhibition. A proportion of these mutations also conferred resistance across clinically approved covalent BTK inhibitors. These data suggested new mechanisms of genomic escape from established covalent and novel noncovalent BTK inhibitors. (Funded by the American Society of Hematology and others.)

Adverse Events, Patterns of Tumor Lysis Syndrome Prophylaxis and Management, and Dosing Patterns in a Large Cohort of Venetoclax Treated CLL Patients in Community and Academic Settings

Introduction: Venetoclax (Ven), an oral BCL2 inhibitor, is approved for the treatment (tx) of relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL). Ven is generally well tolerated, and side effects observed in clinical trials have been consistent with other CLL tx. Clinical trials using the approved dose escalation schedule report negligible rates of clinical tumor lysis syndrome (TLS). We aimed to understand rates of select adverse events (AEs) including cytopenias, infections, and TLS in CLL patients (pts) treated with Ven in community and academic settings. To do so, we examined 297 pts with CLL who received Ven, either alone or paired, in this multicenter, international study. Methods: We conducted a retrospective cohort study of Ven treated pts with CLL across at 15 academic (n=169) and 51 community (n=128) centers outside of the clinical trial setting. This study represents a collaboration between US centers, CLL Collaborative Study of Real World Evidence (CORE), and UK CLL Forum. Demographics, baseline disease characteristics, Ven dosing, TLS risk (per FDA Ven label) and prophylaxis, and AEs were collected. Lab vs. clinical TLS was defined by Howard criteria. PFS was estimated by Kaplan Meier methodology. All comparisons were descriptive. Results: Of the 297 pts examined, median age at Ven initiation was 67 (range 37-91). The group was 69% male, 96% had R/R CLL, and 45% had del17p. Baseline characteristics stratified by practice setting are included in Table 1. 80% received Ven as monotherapy while 20% received it paired with another agent (anti-CD20 mAb (75%), ibrutinib (8.5%), other (16.5%)). All pts were treated outside of clinical trials. During dose escalation, 81% achieved a 400 mg dose and 65% maintained 400 mg following escalation (cyp3A4 use unknown). TLS risk was low in 40%, intermediate (int) in 32%, and high risk in 28%. CT scan prior to Ven initiation was performed in 62%. At least one hospitalization occurred for 56% of low, 80% of int, and 88% of high risk pts (63% of the total cohort). Table 1 describes the distribution of TLS risk and frequency of hospitalizations in academic, community centers. TLS prophylactic measures were available for a subset of pts. Allopurinol was used for 91% (n=68/75) of low, 93% (n=52/56) of int, and 94% (n=29/31) of pts at high risk for TLS. Rasburicase was used for 27% (n=28/102) of low, 42% (n=34/81) of int, and 72% (n=57/79) of high risk pts. Normal saline was used in 85% (n=62/73) of low, 88% (n=49/56) of int, and 97% (n=30/31) of high risk pts. TLS occurred in 8.4% of pts (n=25/297). Three lab and 2 clinical events occurred in low risk pts, 7 lab and 3 clinical events in int risk pts, and 7 lab and 3 clinical events in high risk pts. Of pts with TLS, 1 has discontinued Ven. Of pts with clinical TLS, all were hospitalized, received allopurinol and normal saline, and 28% received rasburicase. 72% with TLS had creatinine clearance \u3c80 mg/mL vs. 44% who did not have TLS (p=0.02). One int risk pt received hemodialysis. One death from TLS (previously reported) was observed in a pt hospitalized with rapid disease progression and tx-related neutropenia re-challenged with 400 mg Ven after dose interruption without dose escalation. Select AEs were neutropenia (ANC\u3c1000) 39.6%, thrombocytopenia (plt \u3c100) 29.2%, infection 25%, neutropenic fever 7.9%, and diarrhea (\u3e7 stools/day) 6.9%. For the subset who received Ven paired, AEs were not increased: 35% neutropenia, 29% thrombocytopenia, 22% infection, 6.3% neutropenic fever, and 6.4% diarrhea. TLS was observed in 3.4% of pts who received Ven paired vs. 9.3% who received Ven monotherapy. 29% pts required ≥1 dose reduction and 32% had ≥1 dose interruption. Median length of dose interruption was 7 days (range 1 - 132). 22 pts (7.4%) discontinued Ven due to an AE. PFS was similar in pts with ≥1 dose interruption vs. 0, pts who required dose interruption ≥8 days vs. \u3c8 days, and pts who achieved a stable Ven dose of \u3c400 mg vs. 400 mg (Figure 1). Conclusions: Ven was well tolerated in this cohort; AE rates were similar to those reported in clinical trials. Both academic and community sites employed TLS prophylaxis consistent with FDA/EMA recommendations resulting in a small proportion of clinical TLS events (\u3c3%). Of note, Ven paired with another agent did not appear to result in increased rates of AEs and TLS events. Dose reduction and interruptions were consistent with clinical experience with other novel agents though these did not appear to impact PFS

Worldwide Examination of Patients with CLL Hospitalized for COVID-19

Introduction: Patients (pts) with CLL may be at particular risk of severe COVID-19 given advanced age and immune dysregulation. Two large series with limited follow-up have reported outcomes for pts with CLL and COVID-19 (Scarfò, et al. Leukemia 2020; Mato, et al. Blood 2020). To provide maximal clarity on outcomes for pts with CLL and COVID-19, we partnered in a worldwide effort to describe the clinical experience and validate predictors of survival, including potential treatment effects. Methods: This international collaboration represents a partnership between investigators at 141 centers. Data are presented in two cohorts. Cohort 1 (Co1) includes pts captured through efforts by European Research Initiative on CLL (ERIC), Italian CAMPUS CLL Program, and Grupo Español de Leucemia Linfática Crónica. The validation cohort, Cohort 2 (Co2), includes pts from US (66%), UK (23%), EU (7%), and other countries (4%). There is no overlap in cases between cohorts. CLL pts were included if COVID-19 was diagnosed by PCR detection of SARS-CoV-2 and they required inpatient hospitalization. Data were collected retrospectively 2/2020 - 5/2020 using standardized case report forms. Baseline characteristics, preexisting comorbidities (including cumulative illness rating scale (CIRS) score ≥6 vs. \u3c6), CLL treatment history, details regarding COVID-19 course, management, and therapy, and vital status were collected. The primary endpoint of this study was to estimate the case fatality rate (CFR), defined as the proportion of pts who died among all pts hospitalized with COVID-19. Chi-squared test was used to compare frequencies; univariable and multivariable analyses utilized Cox regression. Predictors of inferior OS in both Co1 and Co2 were included in multivariable analyses. Kaplan-Meier method was used to estimate overall survival (OS) from time of COVID-19 diagnosis (dx). Results: 411 hospitalized, COVID-19 positive CLL pts were analyzed (Co1 n=281, Co2 n=130). Table 1 describes baseline characteristics. At COVID-19 dx, median age was 72 in Co1 (range 37-94) and 68 in Co2 (range 41-98); 31% (Co1) and 45% (Co2) had CIRS ≥6. In Co1, 48% were treatment-naïve and 26% were receiving CLL-directed therapy at COVID-19 dx (66% BTKi ± anti-CD20, 19% Venetoclax ± anti-CD20, 9.6% chemo/chemoimmunotherapy (CIT), 1.4% PI3Ki, 4% other). In Co2, 36% were never treated and 49% were receiving CLL-directed therapy (65% BTKi ± anti-CD20, 19% Venetoclax ± anti-CD20, 9.4% multi-novel agent combinations, 1.6% CIT, 1.6% PI3Ki, 1.6% anti-CD20 monotherapy, 1.6% other). Most pts receiving CLL-directed therapy had it held at COVID-19 diagnosis (93% in Co1 and 81% in Co2). Frequency of most COVID-19 symptoms/laboratory abnormalities were similar in the two cohorts including fever (88% in both), lymphocytosis (ALC ≥30 x 109/L; 27% vs. 21%), and lymphocytopenia (ALC \u3c 1.0 x 109/L; 18% vs. 28%), while others varied between Co1 and Co2 (p\u3c0.0001), including cough (61% vs. 93%), dyspnea (60% vs. 84%), fatigue (13% vs. 77%). Median follow-up was 24 days (range 2-86) in Co1 and 17 days (1-43) in Co2. CFRs were similar in Co1 and Co2, 30% and 34% (p=0.45). 54% and 43% were discharged while 16% and 23% remained admitted at last follow-up in Co1 and Co2, respectively. The proportion of pts requiring supplemental oxygen was similar (89% vs. 92%) while rate of ICU admission was higher in Co2 (20% vs. 48%, p\u3c0.0001). Figure 1 depicts OS in each cohort. Univariable analyses demonstrated that age and CIRS ≥6 significantly predicted inferior OS in both cohorts, while only age remained an independent predictor of inferior OS in multivariable analyses (Table 2). Prior treatment for CLL (vs. observation) predicted inferior OS in Co1 but not Co2. Conclusions: In the largest cancer dx-specific cohort reported, pts with CLL hospitalized for COVID-19 had a CFR of 30-34%. Advanced patient age at COVID-19 diagnosis was an independent predictor of OS in two large cohorts. This CFR will serve as a benchmark for mortality for future outcomes studies, including therapeutic interventions for COVID-19 in this population. The effect of CLL treatment on OS was inconsistent across cohorts; COVID-19 may be severe regardless of treatment status. While there were no significant differences in distribution of current lines of therapy between cohorts, prior chemo exposure was more common in Co1 vs. Co2, which may account for difference in OS. Extended follow-up will be presented

A First-in-Human Phase 1 Study of Oral LOXO-338, a Selective BCL2 Inhibitor, in Patients with Advanced Hematologic Malignancies (Trial in Progress)

Abstract Background: B-cell lymphoma 2 (BCL2) is a key regulator of apoptosis and provides protection from cell death in many hematological malignancies. The BCL2 inhibitor venetoclax is approved for the treatment of CLL/SLL and acute myeloid leukemia and has activity in other lymphoid malignancies. LOXO-338 is a novel, orally bioavailable small molecule inhibitor of BCL2, designed to achieve selectivity over BCL-xL and thus avoid dose-limiting thrombocytopenia associated with BCL-xL inhibition. In preclinical studies, LOXO-338 showed a favorable pharmacological profile, selectively inhibited BCL2, and was well-tolerated in vivo. LOXO-338 also demonstrated dose-dependent tumor growth inhibition in various murine xenograft models, and showed improved efficacy in combination with pirtobrutinib, a highly selective, non-covalent BTK inhibitor (Brandhuber et al. Cancer Res 2021; 81, 13 Supplement, 1258). Study Design and Methods: LOXO-BCL-20001 is an open-label, multi-center, first-in-human Phase 1 study of oral LOXO-338 in patients with advanced hematologic malignancies who have received standard therapy. The study will be conducted in 2 parts. Part 1 will evaluate LOXO-338 as monotherapy, and will explore different dosing strategies. Part 2 will evaluate LOXO-338 in combination with pirtobrutinib. The dose escalation portion of the study in Part 1 will follow an i3+3 design. Each cycle will be 28 days (4 weeks). Eligible patients include those with CLL/SLL, mantle cell lymphoma (MCL), and Waldenstrӧm macroglobulinemia (WM) who have already received standard therapy. Patients with other B-cell non-Hodgkin lymphomas (NHLs) who failed standard therapy or, in the opinion of the investigator, have no known available options to provide benefit for the patient's condition, are also eligible. Patients must have recovered from prior treatment-related adverse events. Patients with active or suspected Richter transformation, transformed low grade lymphoma, Burkitt or Burkitt-like lymphoma, and multiple myeloma (MM) are eligible in dose-expansion. Key exclusion criteria include history of CNS involvement, stem cell transplant or CAR-T therapy <60 days, concurrent anticancer therapy, and clinically significant cardiovascular disease. The primary objective of Part 1 is to determine the maximum tolerated dose (MTD)/ recommended Phase 2 dose (RP2D) of oral LOXO-338 in patients who were previously treated for CLL/SLL and other B-cell NHLs. Key secondary objectives include determining the safety and tolerability, and pharmacokinetic properties of LOXO-338. Antitumor activity will be evaluated based on overall response rate (ORR), progression-free survival (PFS), time to progression (TTP) and duration of response (DOR) based on disease-specific response criteria per investigator assessment. Key objectives of part 2 are to determine the safety profile and tolerability, PK properties, and anti-tumor activity of LOXO-338 in combination with pirtobrutinib. Disclosures Alencar: Seattle Genetics: Consultancy; Kite Pharma: Consultancy; Karyopharm: Consultancy; Janssen: Consultancy; Incyte: Consultancy; Epizyme: Consultancy; Celgene: Consultancy; BeiGene: Consultancy; Amgen: Consultancy. Roeker: AbbVie, AstraZeneca, Janssen, LOXO, Pharmacyclics, TG Therapeutics, Vaniam Group, Verastem: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy, Research Funding; Loxo Oncology: Consultancy; TG Therapeutics: Consultancy; Abbot Laboratories: Current equity holder in publicly-traded company. Hoffmann: TG Therapeutics: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pharmcyclics: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; celgene: Consultancy, Honoraria. Guru Murthy: Cancerexpertnow: Honoraria; Guidepoint: Consultancy; Techspert: Consultancy; Qessential: Consultancy; Cardinal Health Inc.: Honoraria; TG therapeutics: Other: Advisory board. Patel: Loxo Oncology at Lilly: Current Employment, Current equity holder in publicly-traded company. Ku: Loxo Oncology at Lilly: Current Employment, Current holder of stock options in a privately-held company. Pauff: Loxo Oncology at Lilly: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company. Eyre: Incyte: Consultancy; Loxo Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Beigene: Honoraria, Research Funding; Roche: Consultancy, Honoraria; Gilead/KITE: Honoraria, Other: Travel support for conferences, Research Funding, Speakers Bureau; Secura Bio: Consultancy, Honoraria; Janssen: Honoraria; Abbvie: Consultancy, Honoraria, Other: Travel to conferences; AstraZeneca: Honoraria, Research Funding. Jurczak: Celtrion: Research Funding; Celgene: Research Funding; Debbiopharm: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Loxo Oncology: Membership on an entity's Board of Directors or advisory committees; Sandoz: Membership on an entity's Board of Directors or advisory committees; BeiGene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Research Funding; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Epizyme: Research Funding; Incyte: Research Funding; Merck: Research Funding; Takeda: Research Funding; TG Therapeutics: Research Funding. OffLabel Disclosure: LOXO-338 is a novel, orally bioavailable small molecule inhibitor of BCL2 for advanced hematologic malignancies

The efficacy and safety of venetoclax therapy in elderly patients with relapsed, refractory chronic lymphocytic leukaemia.

Elderly chronic lymphocytic leukaemia (CLL) patients treated outside of trials have notably greater toxicity with the Bruton\u27s tyrosine kinase inhibitor ibrutinib compared to younger patients. It is not known whether the same holds true for the B-cell lymphoma 2 inhibitor venetoclax. We provide a comprehensive analysis of key safety measures and efficacy in 342 patients comparing age categories ≥75 andrelapsed, refractory non-trial setting. We demonstrate that venetoclax has equivalent efficacy and safety in relapsed/refractory CLL patients who are elderly, the majority of whom are previous ibrutinib-exposed and therefore may otherwise have few clear therapeutic options