1. Experimental Therapeutics Program, Taussig Cancer Center, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, U.S.A.
2. Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
3. Department of Surgical Oncology, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612, U.S.A.
4. Genome Integrity Group, Institute of Molecular Medicine, ICRF Laboratories, Oxford, U.K.