PMID: 8603405Apr 1, 1996Paper

Point mutations in human O6-alkylguanine-DNA alkyltransferase prevent the sensitization by O6-benzylguanine to killing by N,N'-bis (2-chloroethyl)-N-nitrosourea

Cancer Research
Natalia A Loktionova, A E Pegg

Abstract

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. Transfection with plasmids expressing mutants of the AGT in which either proline140 is converted to alanine or glycine156 is converted to alanine also gave rise to CHO cells resistant to BCNU, but these mutations rendered the expressed AGT less sensitive to O6-benzylguanine, and O6-benzylguanine was therefore much less effective in restoring sensitivity to BCNU. The G156A mutation provided the greater amount of resistance to O6-benzylguanine, and the CHO cells expressing this mutant AGT were not effectively killed by the O6-benzylguanine plus BCNU combination. CHO cells expressing the mutant AGTs were also much less sensitive than those expressing the control protein with respect to loss of AGT activity and enhancement of killing by BCNU in response to the more potent AGT inhibitor, 2,4-diamino-6-benzyloxy-5-nitrosopyrimidine. Although these results...Continue Reading

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