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

The purpose of the study is to assess the safety, pharmacokinetics, and preliminary efficacy of AMX-883 monotherapy in participants with acute myeloid leukaemia (AML) and high-risk myelodysplastic syndrome (MDS) and in combination with anticancer agents 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 for at least 120 days, or 27 weeks (applicable to the United Kingdom \[UK\] only), after last dose, 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 (\