Sellas Life Sciences meets all primary endpoints in Phase 2 trial of SLS009

SELLAS Life Sciences (SLS) Group announced that is has met all primary endpoints in its Phase 2 trial of SLS009, a highly selective CDK9 inhibitor, in relapsed/refractory acute myeloid leukemia. The Phase 2 clinical trial of SLS009 is an open-label, single-arm, multi-center study designed to evaluate the safety, tolerability, and efficacy of SLS009 in combination with venetoclax and azacitidine at two dose levels, 45 mg and 60 mg. In the 60 mg dose cohort, patients were treated with either a 60 mg dose once per week or a 30 mg dose two times per week. The trial was expanded to include ASXL1-mutated AML patients as well as patients with myelodysplasia-related cytogenetic abnormalities other than ASXL1 mutations. The target response rate for this Phase 2 trial, at the optimal dose level, was at least 20% and a target median survival of at least 3 months. The primary endpoint for the trial was overall response rate, and key secondary endpoints included overall survival, safety, and tolerability. The trial met all endpoints, demonstrating strong efficacy and favorable safety and tolerability with robust anti-tumor activity. Based on these data, the Company plans to advance SLS009 into a randomized trial that will expand into the newly diagnosed AML populations where earlier intervention may enhance therapeutic outcomes, as well as patients refractory to venetoclax and azacitidine, with the study to support a potential New Drug Application with the FDA. Patients Characteristics:: 54 evaluable r/r AML patients who previously failed venetoclax-based therapies were enrolled and treated with SLS009, and venetoclax/azacitidine; patients were enrolled across all five cohorts. Among the 54 treated patients, 47 had AML MR and 23 had ASXL1 mutations. 47 out of 54 had AML MR. Among AML MR patients,17 had myelomonocytic/myelomonoblastic subtype of AML, representing 31% of all patients. All patients had adverse risk cytogenetics except one patient who had intermediate risk cytogenetics. The median age of all patients was 69. Median number of prior lines of therapy was 2. Efficacy: The results exceeded the pre-specified ORR threshold of 20%, demonstrating robust clinical activity and supporting advancement into late-stage development. The ORR in all evaluable patients was 33% across all cohorts and dose levels and 40% for the 30mg BIW dose level. At the 30 mg BIW dose, among AML MR patients, the ORR was 44%. The highest efficacy was observed among patients with ASXL1 mutations, with an ORR of 50% at 30 mg BIW dose levels and M4/M5 patients with 50% ORR. The mOS surpassed the historical benchmark of best available therapy of 2.4 months for patients who received one prior line of therapy and 1.8 months for those who received more than one prior line of therapy. The mOS for patients treated with 30mg BIW, with a median of 1 prior line of therapy, was 8.8 months, while the mOS in AML MR patients reached 8.9 months vs. 2.4 months with best available therapy. The mOS for cohorts with a median of 2 prior lines of therapies was 4.1 months vs.1.8 months with best available therapy. Safety: The addition of SLS009 to the venetoclax/azacitidine regimen was well tolerated and did not result in increased toxicities compared to ven/aza alone. No dose-limiting toxicities were observed across all dose levels. Following a productive end of Phase 2 meeting, the FDA recommended that SELLAS proceeds into a trial to include newly diagnosed, first-line AML patients eligible for venetoclax/azacitidine therapy, where the agency believes clinical benefit might be greatest. The randomized 80-patient trial is currently in preparation and is expected to begin enrollment by Q1 2026. The trial will include two groups: Predictive biomarker cohort: Newly diagnosed patients unlikely to benefit from standard aza/ven therapy based on molecular profiling. Early resistance cohort: Patients who initiate treatment with aza/ven but demonstrate confirmed lack of any response after two treatment cycles.