title: Role of O6-methylguanine-DNA methyltransferase in protecting from alkylating agent-induced toxicity and mutations in mice.
abstract: The DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) protects from toxicity and mutations incurred following alkylating agents by removing O(6)-alkylguanine lesions. Using Mgmt-/- mice, we examined MGMT's role in protecting from in vivo mutations induced by three different alkylating agents, temozolomide (TMZ), 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) and cyclophosphamide. Mutant frequencies were determined in the hypoxanthine-guanine phosphoribosyltransferase gene of splenic T-lymphocytes from C57BL/6 mice (Mgmt+/+ and Mgmt-/-) following TMZ, BCNU or cyclophosphamide. Following TMZ, the mutation frequency was significantly greater in Mgmt-/- mice (5.5 and 9.8 x 10(-6) for 7 and 10 mg/kg TMZ, respectively) compared with vehicle-treated mice (1.0 x 10(-6), P <or= 0.05). In contrast, TMZ-induced mutations were not increased over vehicle in Mgmt+/+ mice. The mutation frequency of mice treated with BCNU (7.5 mg/kg) was the same regardless of Mgmt status. Similarly, pretreatment of Mgmt+/+ mice with 30 mg/kg O(6)-benzylguanine, a potent inactivator of MGMT, prior to BCNU (15 mg/kg) did not result in significantly more mutations than mice treated with BCNU alone. Following cyclophosphamide, mutation frequencies significantly increased from 1.8 x 10(-6) in control-treated mice to 12.9 x 10(-6) in Mgmt+/+ and 18.1 x 10(-6) in Mgmt-/- mice, although the difference in Mgmt-/- compared with Mgmt+/+ was not significant. Acrolein and chloroacetaldehyde, metabolites of cyclophosphamide, were not mutagenic in Mgmt+/+ and Mgmt-/- mice. These results demonstrate that MGMT significantly protects against in vivo TMZ-induced mutations and that MGMT deficiency does not result in greater mutation frequency following cyclophosphamide or BCNU compared with wild-type mice.
authors.affiliation: Committee on Cancer Biology, The University of Chicago, 5841 S. Maryland Avenue, Chicago, IL 60637, USA.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Hansen
authors.forename: Ramamoorthy
authors.initials: R
authors.lastname: Nagasubramanian
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Delaney
authors.forename: Leona D
authors.initials: LD
authors.lastname: Samson
authors.forename: M Eileen
authors.initials: ME
authors.lastname: Dolan
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity*; D000818:Animals; D002330:Carmustine / Q000633:toxicity; D045744:Cell Line, Tumor; D003520:Cyclophosphamide / Q000633:toxicity; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000633:toxicity; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009152:Mutagenicity Tests; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000077204:Temozolomide; D014162:Transfection
chemical_list: D000477:Alkylating Agents; C064976:O(6)-benzylguanine; D006147:Guanine; D003606:Dacarbazine; D003520:Cyclophosphamide; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine; D000077204:Temozolomide