1. Contribution from Departments of Internal Medicine, Pharmacology and Medicinal Chemistry and Comprehensive Cancer Center, Life Sciences Institute, and Biological Chemistry, Biophysics Research Division, University of Michigan, 1500 E. Medical Center Drive, Ann Arbor, Michigan 48109, Lombardi Cancer Center, Georgetown University Medical Center, Washington DC 20007, and Laboratory of Medicinal Chemistry, National Cancer InstituteFrederick, NIH, Frederick, Maryland 21702