Targeted Atomic Nano-Generators (Actinium-225-Labeled Humanized Anti-CD33 Monoclonal Antibody HuM195) in Patients With Advanced Myeloid Malignancies

The purpose of this study is to find a safe dose of actinium-225 when it is labeled to HuM195. This will be done with a "phase I trial," in which a preset schedule of doses gets more powerful for each new group of patients as the trial progresses. If too many serious side effects are seen with a certain dose, no one will be treated with a higher dose, and some additional patients may be treated with a lower dose to make sure that this dose is safe. The starting dose of actinium-225 in this study is less than doses that are known to be safe in animals. Antibodies are proteins that are produced by the immune system and help the body to fight foreign substances, such as bacteria or viruses. HuM195 was made by putting human leukemia cells into mice. Most of the mouse parts of this antibody were replaced with human parts. Only the part of the antibody that binds to the leukemia cells was kept from the mouse. HuM195 attaches to leukemia cells but does not attach to most normal cells. It can kill small amounts of disease by identifying the leukemia cells as "foreign." HuM195 has worked less well against large amounts of leukemia since the normal immune cells needed to kill leukemia cells are lowered in most patients with leukemia.