DNA base adducts in urine andwhite blood cells of cancer patients receiving combination chemotherapies which include N-methyl-N-nitrosourea.

Abstract Urinary 3-methyladenine (3-MeAde) excretion andlymphocyte DNA adduct formation was studied in 15 patients receiving methylnitrosourea (MNU) at several dose levels (250 mg, 300 mg and600 mg total dose, 143-385 mg m(-2)) as part of various combination chemotherapies for advanced tumours (malignant melanoma, lymphoblastic lymphosarcorna andHodgkin's disease). Urinary 3-MeAde levels were significantly increased over background in patients at all dose levels (p < 0.001) andthe increases were dose-dependent (r = 0.77, p < 0.01). There were large interindividual variations in the excretion of 3-MeAde at each dose of MNU. In a subset of patients, N7-methyl-2-deoxyguanosine (7-MedG) andO(6)-methyl-2'-deoxyguanosine (O(6)-WedG) levels in DNA from blood leucocytes showed dose-dependent increases, however there were no simple relationships between urinary methylated DNA bases andleucocyte DNA adducts. Levels of adducts in leucocyte DNA (7-MedG, < 17-217 µmol mol(-1) dG; O(6)-WedG, < 1.6-35 µmol mol(-1) dG) were comparable with those reported for other methylating chemotherapeutic drugs. Leucocyte DNA andurinary methyl adducts may be useful markers of individual responses to treatment with methylating drugs.

Alkylation and oxidative-DNA damage repair activity in blood leukocytes of smokers and non-smokers.

The levels of 3 DNA repair enzymes involved in alkylation and oxidative DNA damage repair in human peripheral blood leukocytes were measured in 20 smokers and 17 non-smokers. No differences in O6-alkylguanine-DNA-alkyltransferase (AGT) activity were found between the 2 groups and the AGT distribution within the population appeared to be unimodal. In contrast, the mean activities of both the methylpurine (MeP)- and the 2-6-diamino-4-hydroxy-5N formamidopyrimidine (FaPy)-DNA glycosylases were higher in the smokers, although only the difference between the MeP-DNA glycosylase means was statistically significant. The standard deviations of these 2 enzymes were also higher in the smokers. The MeP-DNA glycosylase activity showed a bimodal distribution when all subjects were considered. This may in part be due to the smoking habit; 83% of the subjects with enzyme activities higher than 500 fmoles/mg protein were current smokers, whilst 85% of the non-smokers had lower enzyme activities. However, if the smokers were considered separately, a bimodal distribution of this enzyme activity could still be observed. No strong correlation was observed between enzyme activity and age, although the slopes of the regression lines of enzyme activity on age were all negative. The relationship between enzyme activities was studied by bivariate distribution and a strong correlation was only found between the MeP-DNA glycosylase and the FaPy-glycosylase, with the highest values of both enzyme activities being observed in the smokers and the lowest in the non-smokers. Our results suggest that the activity of certain DNA repair enzymes can be modulated by environmental exposure.

Individual levels of activity of O6-alkylguanine-DNA alkyltransferase in monkey gastric mucosa during chronic exposure to a gastrocarcinogen N-ethyl-N'-nitro-N-nitrosoguanidine.

The activity of a DNA repair enzyme, O6-alkylguanine-DNA alkyltransferase (AGT), was studied in gastric mucosa of 15 Macaca fascicularis monkeys before and during chronic oral exposure to the ethylating carcinogen N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) in order to investigate possible causes of inter-individual differences in susceptibility to its gastrocarcinogenic effect. A wide range of AGT activity (307-1903 fmol/mg protein, mean 695) was found before treatment and it decreased during the first year of exposure (means 627, 479 and 452 fmol/mg protein respectively at 6, 12 and 18 months after the beginning of the experiment). The carcinogenesis study is under way and to date four monkeys with low initial AGT level in gastric mucosa died of gastric cancer. The relevance of AGT level measurement for prediction of individual susceptibility to ENNG is discussed.

Biomarkers of individual susceptibility to carcinogens: application for biological monitoring.

In order to develop new markers of individual susceptibility to various human carcinogens, we studied some parameters of formation and metabolism of carcinogens, as well as DNA adducts formation and DNA repair in animals and humans. Following an i.p. administration of benzo(a)pyrene (BP) to the rats, levels of urinary excretion of BP-7,8-diol correlated with tumour latency. A high correlation was found between excretion of this metabolite and BP-DNA adducts level in the liver. Healthy smokers excreted higher quantities of BP-7,8-diol, than smoking lung cancer patients, thus confirming the suggestion on existence of cancer-prone phenotype. N-nitroso compounds formed most efficiently in stomach juice of children with superficial gastritis who therefore could be at high risk of stomach cancer. N-ethyl-N'-nitro-N-nitrosoguanidine induced stomach cancer earlier in monkeys with a low level of DNA repair enzyme, O6-alkylguanine-DNA alkyltransferase (AGT) in gastric mucosa. Overall, these markers can be helpful in predicting individual susceptibility to carcinogens.

[The individual characteristics of the activity of the DNA-repair enzyme O(6)-alkylguanine-DNA alkyltransferase in the stomach of monkeys exposed to the gastric carcinogen N-ethyl-N1-nitro-N-nitrosoguanidine]. / Individual'nye osobennosti aktivnosti fermenta reparatsii DNK O(6)-alkilguanin-DNK alkiltransferazy zheludka obez'ian, podvergnutykh vozdeistviiu gastrokantserogena N-étil-N1-nitro-N-nitrozoguanidina.

Variations in the activity of a DNA repair enzyme 0(6)-alkylgianine-DNA alkyltransferase (AGT) were studied in gastric mucosa samples obtained from 15 M. fascicularis monkeys chronically exposed to a gastrocarcinogen N-ethyl-N'-nitro-N-nitrosoguanidine. Marked interindividual difference in the enzyme activity before and in the course of the exposure was observed. The value of AGT activity assay to predict individual susceptibility to alkylating carcinogens is discussed.