SELLAS Life Sciences Group, Inc. announces the preliminary data from Phase 2a trial of SLS009, a highly selective CDK9 inhibitor, in relapsed/refractory acute myeloid leukemia (r/r AML) and successful filing of a provisional patent application around the ASXL1 mutation and SLS009, including all CDK9 inhibitor drugs. ASXL1 mutations are associated with poor prognosis in all myeloid diseases, owing to the reduced response to the current treatment options. SELLAS has observed a high rate of responses in patients with myelodysplasia-related molecular mutations, as defined by the World Health Organization (WHO).

Among all myelodysplasia-related mutations, those in the ASXL1 gene accounted for most responders across all dose cohorts. SELLAS has now expanded the ongoing Phase 2 r/r AML study to include two additional cohorts, one with ASXL1 mutated AML patients and one with patients with myelodysplasia-related molecular abnormalities other than ASXL1. Study highlights: As of April 19, 2024 data cutoff, a 57% overall response rate has been achieved thus far, in the selected optimal dose regimen of 30 mg BIW, far surpassing the targeted 20% rate.

4/4 (100%) r/r AML patients with ASXL1 truncating mutations at the selected dose level achieved an overall response (CR/CRi/MLFS) and are alive. 5/8 (63%) of r/r AML patients, across all dose levels, with ASXL1 truncating mutations treated with SLS009 achieved an overall response. A review of the mutational status of the patient in the Phase 1 trial with SLS009 monotherapy, who achieved a CR lasting 8+ months, revealed that the patient also harbored an ASXL1 mutation.

The ASXL1 mutation is found in both hematological malignancies as well as solid tumors. All patients in the study are diagnosed with AML refractory to or relapsed after venetoclax-containing regimens. Enrollment and treatment will be focused on the participants in the expansion cohort receiving 30 mg BIW dose and diagnosed with the ASXL1 mutation.

SELLAS intends to initiate discussions with the U.S. Food and Drug Administration (FDA) about the potential for an accelerated approval pathway with SLS009 in the ASXL1 molecularly defined r/r AML population as well as in patients harboring this mutation in other indications. The Phase 2a 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 aza/ven at two dose levels, 45 and 60 mg. In the 60 mg dose cohort patients were randomized into either a 60 mg dose once per week or a 30 mg dose two times per week.

The target response rate at the optimal dose level is 20% with a target median survival over 3 months. In addition, the study aims to identify biomarkers for the target patient population and enrichment for further trials.