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) according
             to the World Health Organization classification and, with respect to MDS, that is high
             risk; participants must have refractory or relapsed disease and be ineligible for or
             have exhausted standard therapeutic options that would otherwise be likely to provide
             clinical benefit

          -  Eastern Cooperative Oncology Group performance status ≤ 2 and life expectancy of ≥ 6
             weeks

          -  Adequate organ function (Grade 1 serum creatinine; Grade 1 total bilirubin; aspartate
             aminotransferase and/or alanine transaminase ≤ 2 × ULN)

          -  Females of childbearing age must not be pregnant at time of Screening/beginning of
             treatment and agree to either abstain from sexual intercourse or use highly effective
             methods 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 barrier
             method of birth control during and after the study (up to 3 months after last dose of
             study 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 the
             start 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-host
             disease 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 to
             Screening

          -  Immediate life-threatening severe complications of leukemia such as uncontrolled
             bleeding, pneumonia with hypoxia or shock, and/or disseminated intravascular
             coagulation

          -  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 the
             ingestion or gastrointestinal absorption of drugs administered orally

          -  Any other concurrent medical condition or disease that is likely to interfere with
             study procedures or results, or that, in the opinion of the Investigator, would
             constitute a hazard for participating in this study

          -  If female, pregnant or breastfeeding