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

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.