1. School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, U.K., Laboratory of Medicinal Chemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, School of Biological Sciences, Queen’s University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, U.K., and Department of Pharmaceutical Sciences and Cancer Center, School of Pharmacy, University of Colorado and Health Sciences Center, Denver, Colorado 80220