Phase 1 Open-label Study of AMX-883 Alone in Participants With AML and High-risk MDS and in Combination in Participants With AML

Inclusion Criteria: * Participants with relapsed or refractory AML who have failed all available standard therapies or relapsed or refractory high-risk MDS with BM blasts 10-19% * Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 * Adequate washout from prior therapies * Adequate kidney and liver function * Female participants of childbearing potential must use highly effective contraception, and male participants must agree to use barrier contraception and avoid sperm donation for at least 120 days after last dose * If enrolled in M1B: Participant must have no documented contraindication to treatment with posaconazole before start of treatment Exclusion Criteria: * Diagnosis of acute promyelocytic leukaemia or chronic myelogenous leukaemia in blast crisis * Clinically active central nervous system (CNS) leukaemia * Receiving immunosuppressive therapy post HSCT * History of another malignancy that is active, progressing, or has required systemic treatment within the past 2 years * Presence of \>Grade 1 active graft versus host disease within 4 weeks prior to C1D1 * Significant cardiovascular disease * Family history of sudden cardiac death before 40 years of age or a family history of long QT syndrome * Clinically significant electrolyte imbalances (e.g., hypokalaemia, hypomagnesaemia, hypocalcaemia) that may contribute to QT interval prolongation * Clinically significant bradycardia (\<50 beats per minute) that is symptomatic or causes haemodynamic insta…