DNA methylating agents such as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are potent carcinogens; their carcinogenic effect is mainly due to the effect of production of O6-methylguanine (O6 MeG) on DNA. O6 MeG is not only mutagenic but also toxic to the cell because Mer-/Mex- cells unable to remove O6 MeG are very sensitive to killing by MNNG. It has been proposed that repeated futile mismatch...

Chinese hamster ovary (CHO) cells lack O6-alkylguanine-DNA alkyltransferase (AGT) activity and are sensitive to killing by N,N'-bis (2-chloroethyl)-N-nitrosourea (BCNU). Transfection of these cells with a plasmid leading to the production of wild-type human AGT rendered them resistant to BCNU but this resistance could be overcome by treatment with O6-benzylguanine, an AGT inhibitor. Transfectio...

The effects of treatment of mice with O6-benzylguanine (O6-BeG) on the levels of O6-alkylguanine-DNA alkyltransferase (ATase) in the hematopoietic compartment and on the in vivo sensitivity of hematopoietic progenitor cells to the toxic and clastogenic effects of the antitumor agents 1,3-bis(2-chloroethyl)-nitrosourea (BCNU) and temozolomide were studied. When the overall effects of BCNU alone ...

Local delivery of carmustine (BCNU) via biodegradable polymers prolongs survival against experimental brain tumors and in human clinical trials. O6-benzylguanine (O6-BG), a potent inhibitor of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase (AGT), has been shown to reduce nitrosourea resistance and, thus, enhance the efficacy of systemic BCNU therapy in a variety of tumor models. I...

Human cell extracts perform an aberrant form of DNA synthesis on methylated plasmids [1], which represents processing of O6-methylguanine (O6-meG). Here, we show that extracts of colorectal carcinoma cells with defects in the mismatch repair proteins that normally correct replication errors do not carry out this synthesis. hMSH2-defective LoVo cell extracts (hMSH for human MutS homologue) perfo...

The activity of O6-methylguanine-DNA methyltransferase was determined in fibroblast cultures from 45 patients with lung cancer, 39 patients with cutaneous malignant melanoma, and 29 healthy controls. This enzyme is a critical parameter for the capacity to repair O6-methylguanine (O6-mGua) adducts in DNA, and a decreased activity might therefore be responsible for an enhanced susceptibility to c...

The human DNA repair protein O6-methylguanine DNA methyltransferase (MGMT) dealkylates mutagenic O6-alkylguanine lesions within DNA in an irreversible reaction which results in inactivation of the protein. MGMT also provides resistance of tumours to alkylating agents used in cancer chemotherapy and its inactivation is therefore of particular clinical importance. We describe a post-DNA synthesis...

Single residues of O6-methylguanine (O6-meG) were introduced into the first or second position of codon 12 (GGC; positions 12G1 or 12G2, respectively) or the first position of codon 13 (GGT; position 13G1) of the human Ha-ras oncogene in phage M13-based vectors. After transformation of E.coli, higher mutant plaque frequencies (MPF) were observed at 12G1 and 13G1 than at 12G2 if O6-alkylguanine-...

Incubation of O6-[3H]ethylguanine-containing DNA with a rat liver chromatin fraction resulted in a decrease in the O6-ethylguanine content of the DNA. Analysis of the products of this reaction showed that the ethyl group had been transferred from the O6-ethylguanine to a protein acceptor. When the incubation mixture was separated on a cesium chloride gradient, the radioactivity removed from O6-...