|Inclusion Criteria:||1) Signed informed consent.|
2) Age 18 years or more.
3) Histologically diagnosed acute myeloid leukemia (AML) or acute lymphocytic leukemia (ALL) by WHO classification.
4) Refractory or relapsed disease (requiring at least 5% leukemic blasts in the bone marrow, regardless of the presence of other features such as new or recurrent dysplastic changes or extramedullary disease) according to the following definitions: AML - Relapsed (defined as >/=5% leukemic blasts in the bone marrow) after receiving 1prior induction regimen, (i.e., first relapse); - Refractory (defined as >/=5% leukemic blasts in the bone marrow) to not more than 1 prior induction regimen (i.e., up to 1 induction failure). ALL - Relapsed/refractory (defined as >/=5% leukemic blasts in the bone marrow) after receiving 1 or more prior induction regimens (i.e., any number of relapses)
5) ECOG performance status of 0-2.
6) At least 2 weeks from administration of prior anti-leukemia therapy unless subject has progressed while receiving targeted therapy on a continuous daily dosing schedule.
7) No remaining clinically significant toxicities from prior chemotherapy of grade 2 or greater.
8) Women of child-bearing potential (i.e., women who are pre-menopausal or not surgically sterile) must be willing to use an acceptable contraceptive method (abstinence, oral contraceptive or double barrier device) for the duration of the study and for 30 days following the last dose of study drug, and must have a negative urine or serum pregnancy test within 2 weeks prior to beginning treatment on this trial.
9) Sexually active men must be willing to use an acceptable contraceptive method for the duration of time on study and for 30 days following the last dose of study drug.
10) Clinical laboratory values within the following ranges unless considered due to leukemic organ involvement: - Serum creatinine </=2.0 mg/dl. - Total bilirubin </=1.5X the upper limits of normal unless considered due to Gilbert's syndrome; - Alanine iminotransferase (ALT), or aspartate aminotransferase (AST) </=3X the upper limit of normal.
11) Willingness to provide at least one pre-PR104 leukemia sample (e.g., bone marrow or peripheral blood) that contains greater than or equal to 5% leukemic blasts for analysis of AKR1C3 (if peripheral blood samples demonstrates less than 5% leukemic blasts, must be willing to undergo a bone marrow.)