Anthony J. Galati

Dose-related inhibition by dietary phenethyl isothiocyanate of esophageal tumorigenesis and DNA methylation induced by N-nitrosomethylbenzylamine in rats

The purpose of this investigation was to establish a dose response for the effects of dietary phenethyl isothiocyanate (PEITC) on N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis and DNA methylation. Groups of 13-27 rats were randomly assigned to AIN-76A diets containing 0, 0.325, 0.75, 1.5 or 3.0 mumol PEITC/g. Two weeks later, rats were administered NMBA subcutaneously at a dose of 0.5 mg/kg once a week for 15 weeks. Animals were maintained on control or experimental diets for an additional 8 weeks and were terminated at week 25 of the experiment. No significant effects on weight gain or food intake were noted for any of the experimental diets when compared with control values. Animals receiving only NMBA developed 9.3 +/- 0.9 tumors/rat, with an incidence of 100%. Dietary PEITC at concentrations of 0.75, 1.5 and 3.0 mumol/g inhibited NMBA-induced esophageal tumor multiplicity by 39%, 90% and 100%, respectively. Esophageal tumor incidence in these groups was reduced by 0%, 40% and 100%, respectively. The 0.325 mumol/g PEITC diet did not significantly affect NMBA-induced esophageal tumorigenesis. These results indicate that the minimum inhibitory dietary concentration of PEITC is between 0.325 and 0.75 mumol/g. Groups of 20 rats were assigned to diets containing 0-3.0 mumol PEITC/g for two weeks as described above, and then sacrificed 24 hours after administration of [3H-methyl]NMBA. The esophageal DNA was isolated, purified, hydrolyzed, and analyzed by HPLC. PEITC inhibited DNA methylation in a dose-dependent manner, as was found in the tumor bioassay. The inhibition of tumor incidence was highly correlated with the percentage inhibition of either 7-methylguanine or O6-methylguanine. These latter results suggest that the inhibitory activity of PEITC in this model is manifested, at least in part, during the functional equivalent of tumor initiation.

Sister-chromatid exchanges in human bronchial epithelial cells.

One method of assessing the genotoxic effects of exposure to environmental agents is by determining the frequency of sister chromatid exchanges in exposed cells. In the present study, a procedure for observing sister chromatid exchanges in adult human bronchial epithelial cells exposed to a carcinogen has been developed. Using this procedure, the frequencies of sister chromatid exchanges in untreated cells from two individuals were found to be 5.1 +/- 1.8 and 6.5 +/- 1.4 per metaphase (mean +/- SD). Cells from the first individual exposed to 7,12-dimethylbenz[a]anthracene at 0.5, 1 and 2 mug/ml had 7.8 +/- 2.2, 13 +/- 3.1, 18.7 +/- 3.7 sister chromatid exchanges per metaphase, respectively. This method is likely to be particularly useful for observing sister chromatid exchanges in cells that have a relatively slow growth rate in the presence of bromodeoxyuridine and for which preparation of a large number of metaphase chromosomes is difficult. In addition, the procedure provides a means of assessing genotoxic effects in the lung by examining the direct effects of pollutants on the chromosomes of the target cells for human lung cancer.

Relationship Between Tumorigenic Potency, Ki-ras Codon 12 Mutations, and DNA Adducts Induced by Cyclopenta[cd]pyrene

Abstract Cyclopenta[cd]pyrene (CPP) was examined for its lung tumorigenic activity in strain A/J mice, for the formation and persistence of CPP-induced DNA adducts in lung tissue, and for its induction of mutations in the Ki−ras oncogene from CPP-induced tumors. CPP displayed high tumorigenic activity, inducing 97.7 lung adenomas/mouse at 200 mg/kg. Ki−ras codon 12 mutations in the DNA of induced tumors were: GGT→CGT (50%); GGT→KTT (15%); GGT→TGT (25%); GGT→GAT (10%). All DNA adducts in the lungs of CPP-treated mice were CPP−3,4−oxide derived and most were CPP−3,4−oxide−2′−deoxyguanosine adducts. CPP is highly tumorigenic in the strain A/J mouse lung adenoma model, being 5 times more active than benzo[a]pyrene. The increased activity of CPP may be related to the unique induction of the GGT→CGT, Ki−ras codon 12 mutation.