1. Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Dipartimento di Biochimica “G. Moruzzi”, Università di Bologna, Via Irnerio 48, 40126 Bologna, Italy, and Developmental Therapeutics Program, Information Technology Branch, Division of Cancer Treatment and Diagnosis, National Cancer Institute, 6130 Executive Boulevard, Room 8008, Rockville, Maryland, 20892-7444