Inclusion Criteria:

          1. Patients with a diagnosis of histologically confirmed relapsed or refractory (R/R)
             acute myeloid leukemia by WHO classification or relapsed/progressed high/very high
             risk MDS (score≥4.5) according to IPSS-R risk stratification

          2. Age >/= 18 years.

          3. Adequate organ function

          4. Subject must have a projected life expectancy of at least 12 weeks.

          5. ECOG performance status of 0-1.

          6. Patient must have the ability to understand the requirements of the study and signed
             informed consent. A signed informed consent by the patient or his legally authorized
             representative is required prior to their enrollment on the protocol.

          7. Subject has a white blood cell count< 50 × 109/L. Note: Hydroxyurea is permitted to
             meet this criterion.

        Exclusion Criteria:

          1. Subject has acute promyelocytic leukemia.

          2. Patients must not have had leukemia biotherapy 12 weeks prior to starting
             investigational drug, or less than 5 half-lives small molecular targeted drug therapy,
             or 28 days any anti-cancer therapy (whichever is longer)

          3. Uncontrolled intercurrent illness including, but not limited to active uncontrolled
             infection, symptomatic congestive heart failure (NYHA Class III or IV), unstable
             angina pectoris, clinically significant cardiac arrhythmia, or psychiatric
             illness/social situations that would limit compliance with study requirements.

          4. Active infection requiring systemic antibiotic/antifungal medication, known clinically
             active hepatitis B or C, or HIV infection.

          5. Participants who have received allogeneic HSCT, or autologous HSCT within 12 months.

          6. Patients with active, uncontrolled CNS leukemia will not be eligible.

          7. Any prior systemic MDM2-p53 inhibitor treatment

          8. Any other condition or circumstance that would, in the opinion of the investigator,
             make the patient unsuitable for participation in the study.

          9. Subject has a history of other malignancies within 5 years prior to study entry, with
             the exception of:

               -  Adequately treated in situ carcinoma of the cervix uteri or carcinoma in situ of
                  breast;

               -  Basal cell carcinoma of the skin or localized squamous cell carcinoma of the
                  skin;

               -  Previous malignancy confined and surgically resected (or treated with other
                  modalities) with curative intention: requires discussion with sponsor.