Introduction of Imatinib medication has improved treatment of chronic myeloid leukemia (CML), but early relapses and resistant disease prevent many patients from being cured. The frequency of resistance to current Imatinib therapy is 15-20%, increasing to 40% in patients with advanced phase disease. Research has now shown that this is due to the inability of current agents to eradicate the blood cancer stem cells which then maintain the potential for relapse. There is thus an urgent need to develop new therapies that target other critical proteins active in CML blood cancer stem cells so that these critical cells can be eliminated. One candidate target is AHI-1, a newly discovered cancer-causing gene we identified that is involved in murine (mouse) blood cancer (leukemia) development and displays abnormal expression in CML blood cancer stem cells. Interestingly, we have recently found that AHI-1 plays a major role in abnormal blood cancer stem cell activity and resistance to Imatinib therapy in both mouse models and in blood cancer stem cells from CML patients, a strong indicator that AHI-1 is likely to be an important new cancer-causing gene involved in development of leukemia and drug resistance and that developing new drugs that inhibit its abnormal functions in blood cancer stem cells will be a more effective treatment option for CML patients. The present proposal will explore and solve the protein structure of key parts of the AHI-1 protein and identify the proteins with which it interacts in the development of leukemia and drug resistance in CML blood cancer stem cells. New inhibitors will be identified and discovered based on the structure of the AHI-1 protein using cutting-edge technologies, resulting in the development of molecularly targeted cancer therapies that will be more effective and have fewer side effects than currently used therapies.