 The initial dose finding phase of the study will provide estimates of the activity and toxicity of PR104 in subjects with refractoryrelapsed AML, and determine the optimal individualized dose to give each subject based on hisher covariates prior CR duration, prior number of salvage therapies, age. Once a potentially beneficial dose has been determined, an expanded cohort of subjects with AML or ALL will receive PR104 at a uniform dose. This information will prove valuable in defining the future clinical development of PR104, and in determining if PR104 has sufficient activity and acceptable safety in AML to warrant future phase II or phase III studies in this indication. 