Inclusion Criteria:

          -  Has signed the Informed Consent (ICF) and is able to comply with protocol
             requirements.

          -  Has adequate organ function according to study protocol guidelines.

          -  Age ≥18 years at the time of signing the informed consent form.

          -  Documented diagnosis of myelodysplastic syndrome (MDS), MDS/ myeloproliferative
             neoplasm (MPN), chronic myelomonocytic leukemia (CMML) or oligoblastic AML (20-30%
             myeloblasts) by World Health Organization (WHO) criteria.

          -  Documentation of a TP53 gene mutation by NGS based on central or local evaluation.

          -  For TP53 mutant patients with lower risk MDS (i.e., low or intermediate-1 risk by the
             International Prognostic Scoring System (IPSS)) and isolated deletion of 5q (del(5q)),
             failure of prior treatment with at least 4 full cycles of lenalidomide defined as no
             response to treatment, loss of response at any time point, progressive disease, or
             intolerance to therapy.

          -  An Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1, or 2 is
             required.

          -  If of childbearing potential, negative pre-treatment urine or serum pregnancy test.

          -  If of childbearing potential, willing to use an effective form of contraception such
             as hormonal birth control, intrauterine device or double barrier method during
             chemotherapy treatment and for at least six months thereafter.

        Exclusion Criteria:

          -  Known history of HIV or active hepatitis B or active hepatitis C infection (testing
             not mandatory).

          -  Has any of the following cardiac abnormalities (as determined by treating MD): a.
             Symptomatic congestive heart failure; b. Myocardial infarction less than or equal to 6
             months prior to enrollment; c. Unstable angina pectoris; d. Serious uncontrolled
             cardiac arrhythmia; e. QTc ≥ 470 msec

          -  Concomitant malignancies or previous malignancies with less than a 1-year disease free
             interval at the time of signing consent. Potential participants with adequately
             resected basal or squamous cell carcinoma of the skin, or adequately resected
             carcinoma in situ (e.g., cervix) may enroll irrespective of the time of diagnosis.

          -  Use of cytotoxic chemotherapeutic agents, or experimental agents (agents that are not
             commercially available) for the treatment of MDS, MDS/MPN, CMML or AML within 14 days
             of the first day of study drug treatment.

          -  No concurrent use of erythroid stimulating agents, G-CSF, GM-CSF is allowed during
             study except in cases of febrile neutropenia where G-CSF can be used for short term.
             Growth factors must be stopped 14 days prior to study.

          -  Women who are pregnant or breastfeeding.