RT Journal Article
SR Electronic
T1 Inactivation of <em>O</em><sup>6</sup>-Methylguanine-DNA Methyltransferase and Sensitization of Human Tumor Cells to Killing by Chloroethylnitrosourea by <em>O</em><sup>6</sup>-Methylguanine as a Free Base
JF Cancer Research
JO Cancer Res
FD American Association for Cancer Research
SP 1663
OP 1668
VO 46
IS 4 Part 1
A1 Yarosh, Daniel B.
A1 Hurst-Calderone, Susan
A1 Babich, Michael A.
A1 Day, Rufus S.
YR 1986
UL http://cancerres.aacrjournals.org/content/46/4_Part_1/1663.abstract
AB Human fibroblasts and tumor cells with constitutive levels of the DNA repair protein O6-methylguanine-DNA methyltransferase were incubated with mm concentrations of the free base O6-methylguanine for up to 24 h. This treatment depleted the cells of their transferase activity, and sensitized the cells to killing by the antineoplastic drug 1-[2-chloroethyl]-1-nitrosourea. Cells constitutively lacking the methyltransferase were not sensitized to cell killing. Cell free extracts incubated with O6-methylguanine also lost methyltransferase activity. Other alkylpurines, such as O6-methylguanosine, S6-methylthioguanine, O6-ethylguanine, and 3-methyladenine, did not have this effect on extracts of human tumor cells, while O6-methylguanosine and O6-methylguanine inactivated purified methyltransferase from Escherichia coli. The data suggest that the free base O6-methylguanine is probably a substrate for the methyltransferase. Calculation of the second order rate constants for free base versus O6-methylguanine in DNA, and experiments in which the free base was mixed with DNA containing O6-methylguanine before reaction with methyltransferase, indicated that the base in DNA is about 4 × 107 better as a substrate than is the free base. These results demonstrate that DNA repair capacity of tumor cells can be diminished without DNA damage, and suggest a method for increasing the efficiency of chemotherapy. ©1986 American Association for Cancer Research.