Dolan ME, Roy SK, Garbiras BJ, Helft P, Paras P, Chae MY, Moschel RC, Pegg AE. O6-alkylguanine-DNA alkyltransferase inactivation by ester prodrugs of O6-benzylguanine derivatives and their rate of hydrolysis by cellular esterases. Biochem Pharmacol. 1998 May 15; 55(10):1701-9.