Abstract 1258: Preclinical characterization of LOXO-338, a novel, oral and selective BCL2 inhibitor

BCL2 is an important therapeutic target in various hematologic malignancies. Venetoclax is the only FDA-approved BCL2 inhibitor, indicated for use in CLL/SLL and acute myeloid leukemia (AML). LOXO-338 is a novel, oral BCL2 inhibitor, designed to achieve selectivity over BCL-xL (Lin S, et al. AACR, 2019), to avoid dose-limiting thrombocytopenia associated with BCL-xL inhibition. Here, we present updated LOXO-338 preclinical characterization of its potency in biophysical and cellular assays, selectivity for BCL2 over other BCL2 family members, and efficacy in murine tumor growth models to support its advancement into human clinical trials. In homogeneous time resolved fluorescence (HTRF) assays measuring the molecular interactions of BCL2 and other BCL2 family members to BAK, LOXO-338 preferentially inhibited the BCL2/BAK interaction with an IC50 value of 4.5 nM; whereas the interactions between BCLxL/BAK, and MCL1/BAK were inhibited by LOXO-338 with IC50 values of 49.6 nM and >10,000 nM, respectively. In cellular immunoprecipitation assays, LOXO-338 showed dose-dependent inhibition of BCL2/BIM interactions in RS4;11 cells (acute lymphoblastic leukemia (ALL) cell line) at concentrations ranging from 30-3000 nM and no inhibition of MCL-1/NOXA interactions in Karpas 299 cells (anaplastic large cell lymphoma cell line) at 3000 nM, the highest concentration tested. Using high-content imaging to measure the effects of LOXO-338 on cellular proliferation we determined LOXO-338 inhibited proliferation of RS4;11 cells with an IC50 value of 2 nM, whereas the IC50 values for the BCL2 independent cell lines H146 (small cell lung cancer (SCLC) cell line), Daudi (Burkitt9s lymphoma cell line), and KMS11 (multiple myeloma cell line) cells were greater than 2000 nM. Anti-proliferative effects of LOXO-338 on a panel of cancer cell lines derived from different tissues were assessed using CCK-8 assays. LOXO-338 inhibited the proliferation of cell lines derived from follicular lymphoma (FL), diffuse large B-cell lymphoma, AML, and ALL with IC50 values ranging from 7 nM to 78 nM. In murine tumor xenograft models using FL, AML, and ALL cell lines, LOXO-338 administered once daily demonstrated dose-dependent tumor growth inhibition. LOXO-338 was well-tolerated by the tumor-bearing mice and no significant weight loss of the mice was observed in the studies. The antitumor potency of LOXO-338 is similar to comparable doses of venetoclax in these models. Novel preclinical combination data and comparative profiles to venetoclax will be presented. This preclinical profile of LOXO-338 supports its nomination as a novel BCL2 inhibitor clinical candidate. A first-in-human Phase 1 clinical trial is planned for 2021. Citation Format: Barbara Brandhuber, Karin Ku, Maria J. Lallena, Carmen Baquero, Regina Choy, Kevin Ebata, Sophie Shu Lin, Lihua Jiang, Yanxin Liu, Xiangling Chen, Liguang Lou. Preclinical characterization of LOXO-338, a novel, oral and selective BCL2 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1258.