Transfer and expression of human O6-methylguanine-DNA methyltransferase cDNA confers resistance of Mer- HeLa MR cells to 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosoure a.

Previous studies have demonstrated that O6-methylguanine-DNA methyltransferase (MGMT) is a major contributor to tumor cellular resistance toward chloroethylnitrosoureas. To further clarify the effect of MGMT gene expression on cellular chemosensitivity to 1-(4-amino-2-methyl-5-pyrimidinyl)-3-(2-chloroethyl)-3-nitrosourea (ACNU) in human cells, a repair-deficient human tumor cell line (HeLa MR) was transfected with a human MGMT expression vector (pSV2MGMT-neo). Multiple unique transfectants were isolated which exhibited variable levels of MGMT mRNA by Northern hybridization analysis. Vector-transfected controls were generated simultaneously. Transfectants expressing high levels of MGMT activity showed an increased resistance to ACNU-induced cytotoxicity. Furthermore, the levels of the protective effect against ACNU correlated generally with the levels of introduced MGMT expression. This study further provided direct evidence of MGMT contribution to ACNU resistance in human tumor cells. Based on the results presented here, we also discussed the perspective of the clinical utility of MGMT cDNA transfer and expression.