DIFFERENTIAL EFFECT OF ACETYLTRANSFERASE EXPRESSION ON THE GENOTOXICITY OF HETEROCYCLIC AMINES IN CHO CELLS

We earlier developed the Chinese hamster ovary UV5P3 cell line that ex presses cytochrome P4501A2 and lacks nucleotide excision repair for st udying metabolism and mutagenicity of heterocyclic amines. The Chinese hamster ovary UV5P3 cells are approximately 50-fold more sensitive to the cooked food mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyrid ine (PhIP) than 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), another genotoxic compound found in cooked food, with respect to cytotoxicity and mutation induction at the adenine phosphoribosyltransferase (aprt) locus. To test the hypothesis that the important missing activity in our CHO system for IQ genotoxicity was acetyltransferase, we transfect ed the UV5P3 cells with cDNA plasmids of either the human NAT2 N-acety ltransferase gene or a bacterial O-acetyltransferase gene. Functionall y transformed clones were determined by the differential cytotoxicity assay using IQ, and confirmed by measuring the enzyme activity with is oniazid as substrate. Two clones designated 5P3NAT2 and 5P3YG (express ing human and bacterial transferases, respectively) were characterized . Both cell lines were sensitive to killing by IQ at concentrations as low as 4 ng/ml. Based on the D-37 value, the dose that reduced the su rvival to 37% relative to untreated controls, the acetyltransferase ex pressing lines Showed similar to 1000-fold increase in sensitivity to the killing effects of IQ over the parental UV5P3 cell line. The same dramatic change in sensitivity was also seen in mutation response at t he aprt locus and with chromosomal aberrations and sister chromatid ex changes. In contrast, these cell lines showed cytotoxicity to PhIP sim ilar to that of the parental line UV5P3. These results suggest that Ph IP does not require acetyltransferase for metabolic activation leading to genotoxicity in these cells. These new cell lines constitute a sen sitive cell system for assessing genotoxicity of compounds requiring m etabolic activation by both P4501A2 and acetyltransferase, as well as for studying the molecular processes by which DNA damage can lead to m utation and cancer.