1. Patients must have pathologically-confirmed acute leukemia, refractory or relapsed after standard therapy for the disease or for which conventional systemic chemotherapy is not reliably effective or no effective therapy is available Phase II Only: Patient must have histologically or pathologically confirmed diagnosis of AML based on WHO classification that is refractory after standard therapy, or for which conventional systemic chemotherapy is not reliably effective, or no effective therapy is available. Patients aged 60 years or older with newly diagnosed AML who are not eligible for, or who refuse, standard care are also eligible.