A Study of BTX-A51 in People With Relapsed or Refractory Acute Myeloid Leukemia or High-Risk Myelodysplastic Syndrome

This is an open-label, dose escalation study to evaluate the safety, toxicity, and pharmacokinetics (PK) as well as preliminary efficacy of BTX-A51 capsules in participants with relapsed or refractory acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS). The study will be done in three parts. Part 1a (Monotherapy Dose Escalation) of this study is designed to determine the dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of orally administered BTX-A51 in up to 35 participants who are evaluable for toxicity. Once the MTD is determined, it is planned that an additional 15 participants will be enrolled in Part 1b (Monotherapy Cohort Expansion) of this study for additional experience with safety and efficacy, and to determine the recommended Phase 2 dose (RP2D) which may or may not be different from the MTD. After determination of MTD and RP2D from Part 1a, Part 1c (Azacitidine Combination Dose Escalation) will enroll up to 30 participants. Continued treatment will be available under this study protocol for up to eight 28-day cycles (Continued Treatment Phase) if the Investigator judges the benefit outweighs the risk. Once BTX-A51 treatment has completed, participants will be contacted by telephone every 3 months for up to 2 years after their last treatment for survival status and anticancer therapy (Overall Survival Follow-up).