title: Creation of human alkyltransferases resistant to O6-benzylguanine.
abstract: O6-benzylguanine (BG), an inhibitor of O6-alkylguanine-DNA alkyltransferase, is being tested clinically for its ability to chemosensitize tumors to alkylating agents. Although this drug may increase the killing of tumors that express high levels of alkyltransferase, it would also be expected to reduce the already low alkyltransferase levels of hematopoietic stem cells and, thus, exacerbate the dose-limiting side effect of myelosuppression. One way to overcome this problem would be to transduce hematopoietic stem cells with a gene encoding a BG-resistant alkyltransferase prior to BG/alkylation treatment. We used the technique of random mutagenesis followed by positive genetic selection to create such a mutant gene. A pool of 6.5 x 10(6) human alkyltransferases that were randomly mutated at six amino acids near the alkyl-accepting cysteine was transformed into alkyltransferase-deficient Escherichia coli. Five mutants were selected based on their ability to provide the bacteria with resistance to both N-methyl-N'-nitro-N-nitrosoguanidine and BG. One mutant, V139F/P140R/L142M, not only had the highest BG resistance (50% inhibitory concentration, >500 microM) but also offered E. coli the best protection from N-methyl-N'-nitro-N-nitrosoguanidine and, thus, is a promising gene therapy candidate.
authors.affiliation: The Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology, University of Washington, Seattle 98195-7705, USA.
authors.forename: F C
authors.initials: FC
authors.lastname: Christians
authors.forename: B J
authors.initials: BJ
authors.lastname: Dawson
authors.forename: M M
authors.initials: MM
authors.lastname: Coates
authors.forename: L A
authors.initials: LA
authors.lastname: Loeb
mesh_terms: D001665:Binding Sites; D002273:Carcinogens / Q000494:pharmacology; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D008780:Methyltransferases / Q000037:antagonists & inhibitors* / Q000235:genetics*; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase; D014170:Transformation, Genetic
chemical_list: D002273:Carcinogens; D004791:Enzyme Inhibitors; C064976:O(6)-benzylguanine; D008769:Methylnitronitrosoguanidine; D006147:Guanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase