Additional Study Information: You are being asked to participate in this study because you have acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL) or leukemia of mixed lineage (the leukemia cells cannot be classified as AML or ALL or where both types of AML and ALL cells are present). Because you have already received standard therapy that is no longer helping, or there is no standard of care for your type of leukemia at this point in your care, you are eligible to participate in a study such as this that involves an experimental drug. It is up to you and your study doctor to decide on whether to take part. DSP-5336 is an experimental drug. It means that Regulatory Agencies like the Food and Drug Administration (FDA) have not approved the sale of DSP-5336 for use in patients, including in people with AML, ALL or leukemia of mixed lineage. The purpose of this study is to evaluate how safe DSP-5336 is at different doses and to find a recommended dose that is safe for further study. This study will also gain information about how your body processes the study drug over time.