Inclusion Criteria:

- Relapsed/refractory leukemias including acute non-lymphocytic leukemia (AML), acute
lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), and chronic
myelogenous leukemia in blastic phase (CML-BP) for which no standard therapies are
anticipated to result in a durable remission; or poor-risk myelodysplasia (MDS)
patients to include refractory anemia with excess blasts (RAEB) or excess blasts in
transformation (RAEBT) and chronic myelomonocytic leukemia (CMML) who are either
relapsed/refractory or who refuse/are not eligible for frontline therapy.

- Only patients with refractory ALL or CML in lymphoid blastic phase are eligible for
phase II.

- ECOG performance status 0 - 2.

- Adequate organ function and bone marrow reserve.

- At least 4 weeks must have elapsed from the time of major surgery.

- Use of appropriate contraceptive method.

- Signed patient informed consent.

Exclusion Criteria:

- Known human immunodeficiency virus (HIV).

- Active heart disease including myocardial infarction within previous 3 months,
symptomatic coronary artery disease, arrhythmias not controlled by medication, or
uncontrolled congestive heart failure.

- Patients receiving any other standard or investigational treatment for their leukemia
other than corticosteriods, hydroxyurea, and 6-mercaptopurine.

- Any medical condition which, in the opinion of the investigator, places the patient
at an unacceptably high risk for toxicities.