This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ayi, T.-C. Articles by Li, B. F. L. Search for Related Content PubMed PubMed Citation Articles by Ayi, T.-C. Articles by Li, B. F. L.

A Method for Simultaneous Identification of Human Active and Active-site Alkylated O⁶-Methylguanine-DNA Methyltransferase and Its Possible Application for Monitoring Human Exposure to Alkylating Carcinogens¹

Chemical Carcinogenesis Laboratory, Institute of Molecular and Cell Biology [T-C. A., H-K. O., B. F. L. L.], and Department of Surgery, National University Hospital [T. K-Y. L.], National University of Singapore, 10 Kent Ridge Crescent, Singapore 0511, Republic of Singapore

Cells resist the major mutagenic effects of alkylating agents by the action of O⁶-methylguanine-DNA methyltransferase (MGMT), which transfers the alkyl (R) group of O⁶-alkylguanine, produced in DNA by these chemicals, to a cysteine residue in its active site (formation of R-MGMT). We demonstrate that cellular R-MGMT (which represents a record or memory within the cells exposed to these chemicals) can be assayed by its sensitivity toward proteolysis by protease V8. The possible use of this assay for monitoring exposure to alkylating carcinogens was investigated by using cultured cells and a preliminary study with the use of human blood from normal subjects and patients undergoing chemotherapy. Cultured cell experiments show that R-MGMT is sufficiently stable for the monitoring purpose and its level bears a dose-response relationship to the concentrations of the alkylating agent used. Interestingly, experiments with blood from patients undergoing chemotherapy show a gradual formation of R-MGMT in 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and an induced MGMT deficiency in cyclophosphamidetreated patients. The use of this methodology, which allows for the possible quantification of active MGMT (cellular DNA repair capacity) and R-MGMT (recent exposure) simultaneously, in monitoring human exposure to alkylating carcinogens is discussed.

¹ This research is funded by the National University of Singapore.

² To whom requests for reprints should be addressed.

Received 12/15/93. Accepted 5/ 9/94.

This article has been cited by other articles:

				M. Xu-Welliver and A. E. Pegg Degradation of the alkylated form of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase Carcinogenesis, May 1, 2002; 23(5): 823 - 830. [Abstract] [Full Text] [PDF]

				A. K. C. Teo, H. K. Oh, R. B. Ali, and B. F. L. Li The Modified Human DNA Repair Enzyme O6-Methylguanine-DNA Methyltransferase Is a Negative Regulator of Estrogen Receptor-Mediated Transcription upon Alkylation DNA Damage Mol. Cell. Biol., October 15, 2001; 21(20): 7105 - 7114. [Abstract] [Full Text] [PDF]

				L. P. Encell and L. A. Loeb Enhanced in vivo repair of O4-methylthymine by a mutant human DNA alkyltransferase Carcinogenesis, July 1, 2000; 21(7): 1397 - 1402. [Abstract] [Full Text] [PDF]

				S. Edara, S. Kanugula, and A. E. Pegg Expression of the inactive C145A mutant human O6-alkylguanine-DNA alkyltransferase in E.coli increases cell killing and mutations by N-methyl-N'-nitro-N-nitrosoguanidine Carcinogenesis, January 1, 1999; 20(1): 103 - 108. [Abstract] [Full Text] [PDF]