Inclusion Criteria:

- Confirmed diagnosis of acute myeloid leukemia (AML), any subtype except acute
promyelocytic leukemia (APL), by the World Health Organization (WHO) criteria, or
high risk MDS with blasts between 10 and 20% in the bone marrow.

- No prior AML chemotherapy except hydroxyurea.

- Leukemic blast count <30x10^9/L at the start of therapy. Prior cytoreduction with
hydroxyurea (maximum 14 days) is permitted.

- Participant is not a candidate for aggressive induction based on at least one of the
following: adverse-risk cytogenetics (complete or partial deletion of 5 or 7, complex
[>3] cytogenetic abnormalities, inv3, 11q23 abnormalities); secondary AML (antecedent
hematologic disorder or therapy-related AML); comorbid medical illnesses precluding
standard induction therapy; participant's refusal of standard induction therapy.

- Confirmed low MGMT expression (MGMT: beta-actin ≤0.2), as evaluated by Western blot,
or weak MGMT expression defined as > 0.2 and ≤2.5 if promoter is methylated, upon
Sponsor approval.

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

- Use of medically approved contraception in fertile males and females.

- Negative urine or serum pregnancy test for women of childbearing potential (72 hours
prior to Baseline).

Exclusion Criteria:

- Serum bilirubin >2 times the upper limit of normal (ULN), or serum aspartate
aminotransferase/ alanine aminotransferase >5 times ULN.

- Serum creatinine >200 umol/L.

- History of other malignancies within 1 year prior to study entry, with the exception
of localized nonmelanomatous skin cancer or cervical cancer in situ.

- Presence of active uncontrolled infection.

- Known human immunodeficiency virus (HIV) infection.

- Any medical condition that may interfere with protocol evaluation or oral medication
intake.

- Prior chemotherapy other than hydroxyurea.