Acute myeloid leukemia is a malignant disorder characterized by the rapid, uncontrolled proliferation of malignant clonal hematopoietic stem cells that accumulate as immature, undifferentiated cells (blasts) in the bone marrow and circulation. APG-115 is a potent and orally active small-molecule MDM2 inhibitor, it binds to MDM2 protein and shows potent cell growth inhibitory activity in vitro with low nanomolar potencies in a subset of human cancer cell lines. APG-115 has demonstrated its strong antitumor activities with either daily or less frequent dosing-schedules in the acute leukemia xenograft models. This is a phase 1b, open-label, three-stages study that will initially evaluate the safety and PK/PD profile of APG-115 as a single agent, followed by a combination of APG-115 + azacytidine or cytarabine in R/R AML or MDS subjects. Patients will continue treatment for maximally 6 cycles or until progression of disease or unacceptable toxicity is observed or administrative discontinuation whichever occurs first. Patients who continue to be benefit after 6 cycles' treatment will receive additional cycles of treatment until progression of disease, unacceptable toxicity is observed or administrative discontinuation. (As long as it is proven safe).