Disclosed are prodrugs of inactivators of O6-alkylguanine-DNA alkyltransferase (AGT). The prodrugs are cleavable by the β-glucuronidase enzyme, which is either administered to the patient or produced by necrotic tumor cells. The prodrugs are represented by the formula A-B-C, wherein A is a glucuronosyl residue linked through its 1-oxygen to the phenyl ring of B; B is a benzyloxycarbonyl group, optionally ring-substituted with one or more electron withdrawing groups; and C is an inactivator of AGT, e.g., a substituted or unsubstituted O6-benzylguanine or O6-benzyl-2′-deoxyguanosine. Also disclosed are additional inactivators of AGT, pharmaceutical compositions comprising an inactivator or prodrug and a pharmaceutically acceptable carrier, and a method of use of the inactivator or prodrug in enhancing the chemotherapeutic treatment of tumor cells in a mammal, e.g., a human, with an antineoplastic alkylating agent that causes cytotoxic lesions at the O6-position of guanine.