Reduction of BCNU toxicity to lung cells by high-level expression of O-6-methylguanine-DNA methyltransferase

1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) is an important cause of pulmon ary toxicity. BCNU alkylates DNA at the O-6 position of guanine. O-6-methyl guanine-DNA methyltransferase (MGMT) is a DNA repair protein that removes a lkyl groups from the O-6 position of guanine. To determine whether overexpr ession of MGMT in a lung cell reduces BCNU toxicity, the MGMT gene was tran sfected into A549 cells, a lung epithelial cell line. Transfected A549 cell populations demonstrated high levels of MGMT RNA, MGMT protein, and DNA re pair activity. The overexpression of MGMT in lung epithelial cells provided protection from the cytotoxic effects of BCNU. Control A549 cells incubate d with 100 muM BCNU had a cell survival rate of 12.5 +/- 1.2%; however, A54 9 cells overexpressing MGMT had a survival rate of 71.8 +/- 2.7% (P < 0.001 ). We also demonstrated successful transfection of MGMT into human pulmonar y artery endothelial cells and a primary culture of rat type II alveolar ep ithelial cells with overexpression of MGMT, resulting in significant protec tion from BCNU toxicity. These data suggest that overexpression of DNA repa ir proteins such as MGMT in lung cells may protect the lung cells from cyto toxic effects of cancer chemotherapy drugs such as BCNU.