Phase 1 clinical trial of S64315, an intravenous MCL1 inhibitor, in patients with myeloid malignancies

Preclinical data support myeloid cell leukemia 1 (MCL1) inhibition in the treatment of acute myeloid leukemia (AML). Patients with relapsed/refractory myelodysplastic syndrome (n = 1) or AML (n = 32) or older patients with untreated AML ineligible to receive intensive chemotherapy (n = 5) were treated in this phase 1 study of S64315, an MCL1 inhibitor (NCT02979366). Seven dose levels (50, 100, 200, 250, 300, 400, and 500 mg) were tested. The most common toxicities were nausea and vomiting, diarrhea, and increased transaminases and troponin levels. Seven patients experienced dose-limiting toxicities (DLTs), including increased cardiac biomarkers (n = 3), grade 3 increased transaminases with hyperbilirubinemia (n = 2), and decreased cardiac ejection (n = 1). Three DLTs occurred at the 500-mg dose, which was intolerable; a maximum tolerated dose was not determined since fewer than six patients were treated at doses between 100 and 400 mg. Exposure to S64315 increased in a dose-dependent manner between 50 and 500 mg. There were no objective responses to therapy.