1. Contribution from the Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724, Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona 85721, Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, Arizona 85724, and BIO5 Collaborative Research Institute, 1657 East Helen Street, Tucson, Arizona 85721