1. Cancer Research U.K. Experimental Cancer Chemotherapy Research Group, Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham, NG7 2RD, U.K.; Max-Delbrück-Center for Molecular Medicine Berlin-Buch, Robert-Rössle-Strasse 10, Postfach 74 02 38, 13092 Berlin, Germany; and Aston Pharmacy School, Aston University, Birmingham, B4 7ET, U.K.