Additional Study Information: The goal of this research study is to find the safest highest dose of SL-401 that can be given to patients with AML or BPDCN. This study will also look at how SL-401 stops or slows leukemia or BPDCN growth and how SL-401 enters and leaves the body. This study will also look at certain proteins in the blood and bone marrow and how the amounts of them might change after receiving SL-401, or might be related to how well SL-401 does or does not function against the cancer. SL-401 is an investigational medication. This means that SL-401 is still being studied. It also means that the United States Food and Drug Administration (also called the FDA) does not allow it to be sold in the United States for the treatment of patients. The FDA allows SL-401 to be used only in research studies.