title: Potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)-induced cytotoxicity in 9L cells by pretreatment with 6-thioguanine.
abstract: 9L Rat brain tumor cells were treated with 0.2 microM 6-thioguanine for 48 hr, which produced a 40% cell kill, a small (15%) inhibition of cell growth, and an accumulation of cells in S-phase. Maximum incorporation of [14C]6-thioguanine into cellular DNA occurred after 24 hr of incubation; 70% of the label was incorporated into DNA as 6-thio-2'-deoxyguanosine. Pretreatment of 9L cells for 48 hr with 0.2 microM 6-thioguanine potentiated the cytotoxicity of 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) by 50% with a dose enhancement ratio of 1.5, and caused a 30% increase in the number of BCNU-induced sister chromatid exchanges (SCEs) and a 50% increase in DNA crosslinks formed, compared to treatment with BCNU alone. Used as a single agent, 6-thioguanine induced a significant number of SCEs. Results suggest that these effects may be related to the increased formation of DNA crosslinks, possibly as the result of the formation of S6-(2-chloroethyl)-6-thioguanine in cellular DNA.
mesh_terms: D000818:Animals; D001932:Brain Neoplasms; D002330:Carmustine / Q000633:toxicity*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003432:Cross-Linking Reagents; D004273:DNA, Neoplasm / Q000378:metabolism; D004357:Drug Synergism; D051381:Rats; D012854:Sister Chromatid Exchange / Q000187:drug effects; D013866:Thioguanine / Q000378:metabolism / Q000633:toxicity*
chemical_list: D003432:Cross-Linking Reagents; D004273:DNA, Neoplasm; D013866:Thioguanine; D002330:Carmustine