Role of O-6-alkylguanine-DNA alkyltransferase in the resistance of mouse spermatogenic cells to O-6-alkylating agents

The O-6-alkylguanine-DNA alkyltransferase inactivator O-6-benzylguanine was administered to BALB/c mice either alone or before exposure to 1,3-bis(2-c hloroethyl) l-nitrosourea to study the role of the DNA repair protein O-6-a lkylguanine-DNA alkyltransferase in the protection of the testis against an ti-cancer O-6-alkylating agents. Exposure of the mice to 1,3-bis(2-chloroet hyl)-1-nitrosourea or O-6-benzylguanine alone did not produce any marked te sticular toxicity at the times studied. Testicular O-6-alkylguanine-DNA alk yltransferase concentrations were assayed between 0 and 240 min after O-6-b enzylguanine treatment and were shown to be > 95% depleted 15 min after tre atment with O-6-benzylguanine and remained at > 95% at all the times assaye d. Histological examination, the reduction in testicular mass and the induc tion of spermatogenic cell apoptosis showed that this depletion significant ly potentiated 1,3-bis(2-chloroethyl)-1-nitrosourea-induced testicular dama ge after treatment. Major histological damage was apparent 42 days after tr eatment, demonstrating that the stem spermatogonia were significantly affec ted by the combination. These results demonstrate that O-6-alkylguanine-DNA alkyltransferase plays a significant role in protecting the spermatogenic cells from damage caused by DNA alkylation and indicate that the observed t oxicity may result from damage to stem spermatogonia.