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

Inclusion Criteria:

• Demonstration of understanding and voluntarily signing of an informed consent form
• Age ≥ 18 years
• Diagnosis of acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) accordingto the World Health Organization classification and, with respect to MDS, that is highrisk; participants must have refractory or relapsed disease and be ineligible for orhave exhausted standard therapeutic options that would otherwise be likely to provideclinical benefit
• Eastern Cooperative Oncology Group performance status ≤ 2 and life expectancy of ≥ 6weeks
• Adequate organ function (Grade 1 serum creatinine; Grade 1 total bilirubin; aspartateaminotransferase and/or alanine transaminase ≤ 2 × ULN)
• Females of childbearing age must not be pregnant at time of Screening/beginning oftreatment and agree to either abstain from sexual intercourse or use highly effectivemethods of contraception (for up to 3 months after last dose of study drug)
• Males sexually active with a woman of childbearing age must agree to use barriermethod of birth control during and after the study (up to 3 months after last dose ofstudy drug)

Exclusion Criteria:

• Diagnosis of acute promyelocytic leukemia
• White blood cell count > 20 x 10^9/L
• Receipt of cancer chemotherapy (other than hydroxyurea) within 2 weeks prior to thestart of study drug
• In participants who have undergone autologous or allogeneic stem cell transplantation:transplantation within the 3 months prior to Screening; active graft-versus-hostdisease requiring anything other than topical corticosteroids and budesonide;treatment with systemic immunosuppressive medications including high-dose steroids (≥ 20 mg prednisolone or equivalent per day), or calcineurin inhibitors (e.g.,cyclosporine, tacrolimus) for at least 1 week prior to Screening, and sirolimus,mycophenylate mofetil, azathioprine, or ruxolitinib for at least 2 weeks prior toScreening
• Immediate life-threatening severe complications of leukemia such as uncontrolledbleeding, pneumonia with hypoxia or shock, and/or disseminated intravascularcoagulation
• Persistent toxicities from prior treatment of Grade 2 or higher
• Active uncontrolled systemic fungal, bacterial, mycobacterial, or viral infection
• Clinically significant cardiac disease
• Known dysphagia, short-gut syndrome, gastroparesis, or other conditions that limit theingestion or gastrointestinal absorption of drugs administered orally
• Any other concurrent medical condition or disease that is likely to interfere withstudy procedures or results, or that, in the opinion of the Investigator, wouldconstitute a hazard for participating in this study
• If female, pregnant or breastfeeding