A Phase 1 Study with the Novel B-Cell Lymphoma 2 (Bcl-2) Inhibitor Bgb-11417 As Monotherapy or in Combination with Zanubrutinib (ZANU) in Patients (Pts) with CLL/SLL: Preliminary Data

Abstract

Background/introduction: The effectiveness of Bcl-2 inhibitors as a treatment for chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) was established by the approval of venetoclax in pts with CLL/SLL across all lines of therapy. However, the related adverse events (AEs) and emergence of BCL2 mutations, resulting in resistance, can limit the utility of venetoclax. BGB-11417 is a highly selective Bcl-2 inhibitor with potency >10 times that of venetoclax in biochemical assays. BGB-11417 monotherapy is tolerable, with no maximum tolerated dose (MTD) reached after dose escalation through all planned doses to 640 mg once daily (QD) in pts with non-Hodgkin lymphoma (EHA 2022. Abstract P687). The combination of Bcl-2 and Bruton tyrosine kinase (BTK) inhibitors is tolerable with synergistic activity in CLL and mantle cell lymphoma (MCL) (J Clin Oncol 2019;37:2722-9; N Engl J Med 2019;380:2095-103; EHA 2020. Abstract S158; N Engl J Med 2018;378:1211-23). ZANU, a next-generation BTK inhibitor, has shown favorable activity and safety in pts with CLL/SLL (EHA 2021. Abstract LB1900) and Waldenström macroglobulinemia (Blood. 2020;136(18):2038-2050). BGB-11417-101 is an ongoing first-in-human phase 1/1b dose-escalation/expansion study (NCT04277637). Pts with various B-cell malignancies were enrolled; data from CLL/SLL cohorts are presented here. Methods: In separate monotherapy and combination therapy cohorts, pts received escalating doses of BGB-11417 (40, 80, 160, 320, or 640 mg QD) with a ramp-up to the intended target dose to minimize risk of tumor lysis syndrome (TLS). In combination therapy cohorts, pts received ZANU (320 mg QD or 160 mg twice daily) beginning 8-12 weeks before BGB-11417. Dose-limiting toxicity for each cohort was evaluated by a Bayesian logistic regression model during dose ramp-up through day 21 at the intended dose. AEs were reported per Common Terminology Criteria for AEs v5.0. Minimal residual disease (MRD) was assessed by a European Research Initiative on CLL flow cytometry assay. Results: As of May 15 2022, 50 pts with CLL received treatment: 6 monotherapy (all relapsed/refractory [R/R]) and 44 combination (22 R/R; 22 treatment naïve [TN]). The monotherapy CLL cohort received BGB-11417 doses up to 160 mg. Based on emerging safety data from other cohorts, pts in combination cohorts with R/R CLL received BGB-11417 up to 640 mg and pts with TN CLL received up to 320 mg (data include 8 pts in ZANU pretreatment not yet dosed with BGB-11417). MTD has not yet been reached for any CLL cohort, with dose escalation ongoing. Median follow-up was 11.5 mo (range 8.5-18.3) for monotherapy and 5.8 mo (range 0.2-10.5) for combination. Treatment-emergent AEs (TEAEs) across all doses are listed in the Table. With monotherapy, cytopenias were the most common TEAEs (≥50%), with 33% grade ≥3. With combination, contusion, neutropenia, and low-grade gastrointestinal toxicity were the most common TEAEs (≥22.7%); neutropenia was the most common grade ≥3 TEAE (11.4%) with 5 pts. No pts discontinued monotherapy treatment, and 1 pt discontinued combination treatment (disease progression; Richter transformation). Only 1 high-risk pt with CLL on monotherapy had laboratory TLS that resolved with no intervention (overall laboratory TLS ≤2%). No clinical TLS was reported. Diarrhea was mostly grade 1 and grade ≥3 was not seen. Although efficacy data are early, most pts with CLL/SLL had notable reductions in absolute lymphocyte count (ALC) with responses seen at doses as low as 1 mg (Figure), consistent with improved potency of BGB-11417 vs venetoclax. Four responses (66%, partial response [PR] or better) and 32 responses (72.7%, PR with lymphocytosis or better) were observed with mono- and combination therapy, respectively. MRD data are early: among 4 MRD evaluable pts at 160 mg, 3 pts (2 monotherapy; 1 combination) had a peripheral blood CLL count <10-4 at 24 weeks after BGB-11417 initiation. Conclusion: These preliminary data show BGB-11417, alone or in combination with ZANU, was well-tolerated in most patients. Grade ≥3 neutropenia was uncommon and manageable. Efficacy is supported by the rapid reduction in ALC during ramp-up, and early response data are promising. TLS rates are low; the prophylactic measures and ramp-up schedule seem to adequately mitigate TLS across all dose levels tested. Mature MRD data are forthcoming, and venetoclax-treated CLL/SLL cohorts will soon be open for enrollment. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal