The purpose of Part 1 (Dose Escalation) of the study is to assess the safety and tolerability, and to identify the recommended Phase 2 dose\[s\] (RP2D\[s\]) in participants with relapsed or refractory (R/R) acute myeloid leukemia (AML) (that is a type of blood cancer that has come back after treatment/or has stopped responding to treatment) or R/R higher-risk type of myelodysplastic neoplasms (MDS, type of blood cancer). The purpose of Part 2 (Cohort Expansion) is to further assess the safety, tolerability and efficacy in participants with R/R AML or higher-risk types of MDS.