1. Institute for Cognitive and Computational Sciences and Department of Pharmacology, Georgetown University Medical Center, 3970 Reservoir Road Northwest, Washington, DC 20007-2197, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fengling Lu, Shanghai 200032, China, Molecular Mechanisms of Tumor Promotion Section, Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, Bethesda, Maryland 20892