title: Increased cytotoxicity of 1-(2-chloroethyl)-1-nitroso-3(4-methyl)-cyclohexylurea by pretreatment with O6-methylguanine in resistant but not in sensitive human melanoma cells.
abstract: Cells from a resistant ("Gr II") and a sensitive ("Str") human melanoma xenograft were incubated in vitro with O6-methylguanine for 2 h, subsequently treated with 1-(2-chloroethyl)-1-nitroso-3(4-methyl)-cyclohexylurea (MeCCNU) for 1 h and then plated in soft agar. In the resistant cells the O6-methylguanine pretreatment (2 mM) yielded an increase in sensitivity towards MeCCNU by a factor of 7.5. In the sensitive melanoma cells pretreatment with O6-methylguanine did not increase cytotoxicity. Human bone marrow cells from three normal donors were similarly pretreated with O6-methylguanine and MeCCNU. There was a clear increase in MeCCNU-induced cytotoxicity. We conclude, that while O6-methylguanine does potentiate the action of MeCCNU in resistant melanoma cells, the therapeutic usefulness of this treatment strategy may be limited.
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000187:drug effects; D001854:Bone Marrow Cells; D002455:Cell Division / Q000187:drug effects; D003114:Colony-Forming Units Assay; D003432:Cross-Linking Reagents; D004351:Drug Resistance; D004357:Drug Synergism; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008545:Melanoma / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009607:Nitrosourea Compounds / Q000494:pharmacology*; D012673:Semustine / Q000494:pharmacology*; D014183:Transplantation, Heterologous; D014410:Tumor Stem Cell Assay
chemical_list: D003432:Cross-Linking Reagents; D009607:Nitrosourea Compounds; D012673:Semustine; D006147:Guanine; C008449:O-(6)-methylguanine