Resistance of the human O6-alkylguanine-DNA alkyltransferase containing arginine at codon 160 to inactivation by O6-benzylguanine

Suvarchala Edara, Sreenivas Kanugula, Karina Goodtzova, Anthony E. Pegg

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Abstract

Inactivation of O6-alkylguanine-DNA alkyltransferase by O6-benzyl- guanine renders tumor cells more sensitive to killing by methylating and chloroethylating agents, and O6-benzylguanine is currently undergoing clinical trials for development as an agent to enhance chemotherapy. It has been reported recently that a polymorphism in the human O6-alkylguanine-DNA alkyltransferase gene exists, with about 15% of the population studied having arginine at codon 160 instead of glycine (Y. Imai et al., Carcinogenesis (Lond.), 16: 2441-2445, 1995). We have studied the effects of mutations of this glycine to arginine, tryptophan, or alanine on the interaction of human alkyltransferase with O6-benzylguanine using direct determination of the amount of activity remaining after incubation with various concentrations of the inhibitor and measurement of the rate of production of [8-3H]guanine from O6-benzyl[8-3H]guanine as assays. These mutations had little effect on the alkyltransferase activity in repairing O6-methylguanine in methylated DNA. Alteration of glycine 160 to tryptophan or alanine slightly increased the sensitivity to O6-benzylguanine (by up to 4-fold). However, alteration of glycine 160 to arginine drastically reduced the inactivation by O6- benzylguanine with at least a 20-fold increase in the ED50 value and a similar reduction in the production of guanine whether inactivation was carried out in the absence or presence of DNA. These results raise the possibility that a subpopulation of patients may be resistant to O6- benzylguanine and that higher doses or additional alkyltransferase inhibitors capable of inactivating this form of the alkyltransferase will be necessary.

Original languageEnglish (US)
Pages (from-to)5571-5575
Number of pages5
JournalCancer Research
Volume56
Issue number24
StatePublished - Dec 15 1996

All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research

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