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DNA-repair studies on cytostatic drugs
171 and of catalysts, such as thiocyanate as well as the role of biotransformation were studied. The results with a series of secondary and tertiary amines (aliphatic and cyclic) combined with nitrite showed that nitrosation reactions occur in vitro and in vivo. Various amine types induced different patterns of response. Because of these qualitative and mainly quantitative differences, it is not justified to prefer only one 'nitrosation model' for the detection of nitrosated amines.
17 Belisario, M.A., F. De Lorenzo and E. De Marinis 1, I1 Istituto di Chimica Biologica, 2a Fac. di Medicina e Chirurgia and 1Ente Farmacologico Italiano, S.p.A., Naples (Italy) Activation in vivo of 5-nitroimidazoles Metronidazole (Flagyl), a widely used drug for treating Trichomonas vaginalis infections, exhibits a mutagenic action on bacteria and a carcinogenic effect on mice. It is presumed that the genetic activity is dependent upon its ability to be enzymatically reduced to hydroxylamino or amino derivatives, as no mutagenic activity has been found on TA100 Frl, a nitroreductase-deficient strain of Salmonella typhimurium. In vitro incubation of this strain with metronidazole in the presence of rat-liver microsomal preparation partially restores the mutagenic activity (Rosenkranz, Biochem. Biophys. Res. Commun., 66 (1975) 520). In vivo activation of metronidazole has been proved by p.o. administration of a single dose (800 mg/kg) of the drug to 250 g male rats. The sterilized 24-h urines have been assayed in the Ames test with TA100 Frl and its parent strain TA100. In both cases mutagenic activity was observed, thus showing that partial activation of metronidazole occurs in rat metabolism. The same results have been obtained with dimetridazole, a metronidazole analogue. It has been reported, however, that no mutagenic activity is found in urines of patients therapeutically treated with this drug. Such differences might depend either on different metabolic activation among rats and man or on the higher amount of drug used in rats as compared with the therapeutic doses used in man.
18 Benigni, R., E. Falcone, A. Calcagnile, A. Giuliani and E. Dogliotti, Istituto Superiore di Sanita, Rome (Italy) DNA-repair studies on cytostatic drugs w e have examined the ability to induce UDS of a number of cytostatic drugs, representing different classes: alkylating agents (thiotepa, cyclophosphamide), antitumor antibiotics (bleomycin, adriamycin, actinomycin D), antimetabolites
172
(methotrexate, 6-mercaptopurine) and spindle poisons (vincristine). These chemotherapeutic agents act by different mechanisms and express lethality according to the cycle phase; besides, data are known about their carcinogenicity in vivo, transformation ability and clastogenicity in vitro, mutagenicity and induction of SCEs. We have studied the UDS induction in MRC-5 cells, a normal human cell line, in proliferating as well as in quiescent cultures, by autoradiographic analysis of [3H]TdR incorporation. Our results show that the antimetabolites and vincristine do not provoke UDS (they evidently do not interact with DNA); the alkylating agents thiotepa and cyclophosphamide damage DNA in S-phase cells; adriamycin and actinomycin D, which are known to exert an S-phase-specific action, in fact induce UDS only in proliferating cultures; bleomycin, which is known to act especially in G 2- and M-phase cells, exerts a more relevant DNA-damaging action in quiescent cultures (higher proportion of G 2-phase cells) than in proliferating ones. Furthermore, UDS data parallel the results from carcinogenicity studies. Work partially granted by the E.E.C. (Contract No. 177-77-1 ENV I).
19 Bennicelli, C., P. Zanacchi, A. Camoirano and S. De Flora, Institute of Hygiene, School of Medicine, University of Genoa (Italy)
Differential mutagenicity of 3 4-substituted quinoline N-oxides 4-Amino (Dr. M. Nagao), 4-hydroxylamino and 4-nitroquinoline N-oxides (IIT Research Institute) induced an intense mutagenic response in the Ames test, with maximum activity towards strain TA100. Differences were observed in the spectrum of sensitive strains, mutagenic potency and metabolic behaviour (Aroclor-treated rat-liver $9). Mutagenicity of the amino derivative (reverting TA100/98/1538 and weakly TA1537/1535) was further enhanced by $9 mix (potency: 0.38 rev./nmole). The hydroxylamino (TA 100/98/1538) and the nitro derivative (TA 100/98/1538/ 1537/1535) were very potent (56 and 2880 rev./nmole, resp.), but their mutagenicity was markedly decreased by $9 mix. The nitro derivative is the most potent mutagen out of 120 chemicals tested so far in this laboratory (overall 9 × 1 0 6 : 1 range of potency). The results obtained show the importance of some chemical groups in influencing the mutagenic response in S. typhimurium. 0
NH 2
0
HNOH
0
NO:
17 Belisario, M.A., F. De Lorenzo and E. De Marinis 1, I1 Istituto di Chimica Biologica, 2a Fac. di Medicina e Chirurgia and 1Ente Farmacologico Italiano, S.p.A., Naples (Italy) Activation in vivo of 5-nitroimidazoles Metronidazole (Flagyl), a widely used drug for treating Trichomonas vaginalis infections, exhibits a mutagenic action on bacteria and a carcinogenic effect on mice. It is presumed that the genetic activity is dependent upon its ability to be enzymatically reduced to hydroxylamino or amino derivatives, as no mutagenic activity has been found on TA100 Frl, a nitroreductase-deficient strain of Salmonella typhimurium. In vitro incubation of this strain with metronidazole in the presence of rat-liver microsomal preparation partially restores the mutagenic activity (Rosenkranz, Biochem. Biophys. Res. Commun., 66 (1975) 520). In vivo activation of metronidazole has been proved by p.o. administration of a single dose (800 mg/kg) of the drug to 250 g male rats. The sterilized 24-h urines have been assayed in the Ames test with TA100 Frl and its parent strain TA100. In both cases mutagenic activity was observed, thus showing that partial activation of metronidazole occurs in rat metabolism. The same results have been obtained with dimetridazole, a metronidazole analogue. It has been reported, however, that no mutagenic activity is found in urines of patients therapeutically treated with this drug. Such differences might depend either on different metabolic activation among rats and man or on the higher amount of drug used in rats as compared with the therapeutic doses used in man.
18 Benigni, R., E. Falcone, A. Calcagnile, A. Giuliani and E. Dogliotti, Istituto Superiore di Sanita, Rome (Italy) DNA-repair studies on cytostatic drugs w e have examined the ability to induce UDS of a number of cytostatic drugs, representing different classes: alkylating agents (thiotepa, cyclophosphamide), antitumor antibiotics (bleomycin, adriamycin, actinomycin D), antimetabolites
172
(methotrexate, 6-mercaptopurine) and spindle poisons (vincristine). These chemotherapeutic agents act by different mechanisms and express lethality according to the cycle phase; besides, data are known about their carcinogenicity in vivo, transformation ability and clastogenicity in vitro, mutagenicity and induction of SCEs. We have studied the UDS induction in MRC-5 cells, a normal human cell line, in proliferating as well as in quiescent cultures, by autoradiographic analysis of [3H]TdR incorporation. Our results show that the antimetabolites and vincristine do not provoke UDS (they evidently do not interact with DNA); the alkylating agents thiotepa and cyclophosphamide damage DNA in S-phase cells; adriamycin and actinomycin D, which are known to exert an S-phase-specific action, in fact induce UDS only in proliferating cultures; bleomycin, which is known to act especially in G 2- and M-phase cells, exerts a more relevant DNA-damaging action in quiescent cultures (higher proportion of G 2-phase cells) than in proliferating ones. Furthermore, UDS data parallel the results from carcinogenicity studies. Work partially granted by the E.E.C. (Contract No. 177-77-1 ENV I).
19 Bennicelli, C., P. Zanacchi, A. Camoirano and S. De Flora, Institute of Hygiene, School of Medicine, University of Genoa (Italy)
Differential mutagenicity of 3 4-substituted quinoline N-oxides 4-Amino (Dr. M. Nagao), 4-hydroxylamino and 4-nitroquinoline N-oxides (IIT Research Institute) induced an intense mutagenic response in the Ames test, with maximum activity towards strain TA100. Differences were observed in the spectrum of sensitive strains, mutagenic potency and metabolic behaviour (Aroclor-treated rat-liver $9). Mutagenicity of the amino derivative (reverting TA100/98/1538 and weakly TA1537/1535) was further enhanced by $9 mix (potency: 0.38 rev./nmole). The hydroxylamino (TA 100/98/1538) and the nitro derivative (TA 100/98/1538/ 1537/1535) were very potent (56 and 2880 rev./nmole, resp.), but their mutagenicity was markedly decreased by $9 mix. The nitro derivative is the most potent mutagen out of 120 chemicals tested so far in this laboratory (overall 9 × 1 0 6 : 1 range of potency). The results obtained show the importance of some chemical groups in influencing the mutagenic response in S. typhimurium. 0
NH 2
0
HNOH
0
NO: