In vitro mutagenic activity of 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (DTIC) in eukaryotic and prokaryotic cells

Research on the anti-tumour effect of steroid lactam alkylator (NSC-294859) in comparison with conventional chemotherapeutics in malignant melanoma

Evidence indicating that hybrid steroid compounds of anti-cancer agents produce reduced toxicity, significantly lower than the cytotoxic components alone, and increased anti-cancer activity has prompted the design and development of such steroids, mostly alkylating esters. We investigated the in-vitro and in-vivo activity of a homo-aza-steroidal alkylating ester (HASE), in comparison with dacarbazine (DTIC), cisplatin (CPDD), carmustine (BCNU) and semustine (MeCCNU), in the treatment of malignant melanoma. Cytotoxicity was assessed in vitro by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using a panel of six human malignant melanoma cell lines, with or without the presence of rat liver microsome assay. B16 melanoma-bearing mice were used to evaluate in vivo the anti-tumour activity of the tested compounds. In all cases of in-vitro screening, HASE displayed a significantly higher (P<0.0001) cytostatic and cytotoxic effect than DTIC, BCNU and MeCCNU, but produced significantly lower (P<0.0001) activity than CPDD. HASE exhibited a significantly smaller range than CPDD between concentration levels that produced growth arrest and those that induced a cytotoxic effect against melanoma cells in vitro. The anti-tumour activity of HASE in B16 melanoma-bearing mice, as determined by tumour growth rate inhibition (<42%) and percentage survival prolongation (treated versus control, 167%), was significantly superior (P<0.001) to that achieved by DTIC, BCNU and MeCCNU and was equal to that of CPDD. HASE exhibited a toxicity similar to that of DTIC, BCNU and MeCCNU, but significantly lower than that of CPDD. It can be concluded that HASE displays significant in-vitro and in-vivo activity in the treatment of melanoma.

Toxicity, mutation frequency and mutation spectrum induced by dacarbazine in CHO cells expressing different levels of O(6)-methylguanine-DNA methyltransferase

The toxicity and mutagenicity (including the mutation spectrum induced) of dacarbazine, a methylating cytostatic drug, was examined in CHO cells expressing different levels of the repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT). Expression of low or high levels of a transfected human MGMT gene under the control of the metallothionein promoter protected the cells against dacarbazine-induced toxicity and mutagenesis. In the absence of MGMT expression, the mutation spectrum in the HPRT locus was dominated by GC-->AT transitions (mostly found at 5'Pu-G sequences), while there were also a few AT-->GC transitions. Expression MGMT was associated with a substantial decrease of GC-->AT mutations, suggesting that these mutations arose primarily via O(6)-methylguanine. These data illustrate the important role of the latter lesion in the drug's mutagenic and cytotoxic activity.

Nurses' and pharmacists' exposure to antineoplastic drugs: findings from industrial hygiene scans and urine mutagenicity tests

Data from 83 nurses and pharmacists handling antineoplastic drugs and 35 nurse/pharmacist controls who participated in a national study of antineoplastic drug-handling risks were examined to investigate antineoplastic drug exposure. Measures of external exposure included self-completion drug logs and industrial hygiene scans conducted in clinical settings. Internal exposure was measured by urine mutagenicity tests on end-of-week 24-hour urine specimens. To control for potential confounders, the staff was asked to complete food and hobby diaries and to avoid identified mutagenic substances for 1 week before collection of 24-hour urine samples. On the scans of the drug handlers, 13% showed one or more spots of drug contamination on gloved and ungloved hands, gowns, or shoes. Of the 24-hour urine samples, 15% were mutagenic for Salmonella typhimurium: Rates did not differ significantly for drug handlers and controls. Among nurses who both prepared and administered antineoplastics, those with positive mutagenicity tests handled more doses of the drugs, used less skin protection, and had more skin contact with the drugs than those with negative tests. Nurses who only administered the drugs and had positive mutagenicity tests handled fewer doses of drugs than those with negative tests, but they also reported less use of protection and more skin contact. For both groups of nurses, skin contact with antineoplastics was associated with positive mutagenicity test results (p < 0.01).

Effects of an inducer and an inhibitor of hepatic metabolism on the antitumor action of dimethyltriazenes

To investigate the role of monomethyltriazenes as the active metabolites of antitumor dimethyltriazenes, the in vivo simultaneous treatment with an inducer (phenobarbital, PB) or an inhibitor (carbon tetrachloride, CCl4) of hepatic drug metabolism was examined in mice bearing Lewis lung carcinoma. Treatment with PB or CCl4 with the dosage and schedules employed proved to be effective in markedly modifying the N-demethylation of the three dimethyltriazenes tested, as had been determined in vitro. No unambiguous increase by PB, or decrease by CCl4, which might theoretically be expected if metabolic conversion to monomethyltriazenes was involved, was observed for the antitumor and antimetastatic activity of dimethyltriazenes. At the same time, a difference was noted between the effects on primary tumors and those on metastases. These data support the view that generalizations on the relevance of monomethyltriazenes as the active metabolites responsible for the antitumor and antimetastatic activity of dimethyltriazenes may not be valid.

In vivo metabolism and reaction with DNA of the cytostatic agent, 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC)

The cytostatic drug dacarbazine [DTIC, 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide] is strongly carcinogenic in rats. Bioactivation of DTIC yields a methylating intermediate but the extent of interaction with cellular macromolecules has not previously been reported. Following a single i.p. injection of [14C-methyl]DTIC, exhalation of 14CO2 occurred with a t1/2 max of approximately 2 hr (0.95 mg/kg) and 2.5 hr (95 mg/kg). Of the total radioactivity administered, 8.5% was exhaled as 14CO2; 54% was excreted via the urine, predominantly as unchanged DTIC. In liver, kidney and lung, formation of 7-[14C]methylguanine in DNA and RNA was directly proportional with dose. DNA methylation by a single dose of DTIC (9.8 mg/kg; 5 hr survival time) was highest in liver (35 mumoles 7-methylguanine/mole guanine), followed by kidney (25 mumoles) and lung (20 mumoles). The remainder tissues showed 7-methylguanine concentrations approximately 50% of those in liver DNA, with the exception of the brain which had a very low extent of DNA modification (approximately 1 mumole/mole guanine). At the specific radioactivity used (48 mCi/mmole), the promutagenic base O6-methylguanine was only detectable in liver, kidney, lung, and stomach DNA (0.6-0.8 mumoles/mole guanine). Autoradiographic studies revealed a diffuse distribution of reaction products in rat liver. In contrast, N-nitrosodimethylamine and related carcinogens known to be bioactivated by the hepatic cytochrome P-450 system show a predominantly centrilobular distribution. This difference may be due to the greater stability of proximate carcinogens generated by alpha-C hydroxylation at one of the methyl groups of DTIC.

Mutagenic activity of the dacarbazine analog p-(3,3-dimethyl-1-triazeno)benzoic acid potassium salt in bacterial cells

The mutagenic activity of the antimetastatic agent p-(3,3-dimethyl-1-triazeno)benzoic acid potassium salt (DM-COOK) was studied in procaryotic cells and compared with that of dacarbazine (DTIC) which is clinically used in the management of human neoplasms. The results indicated that DM-COOK has a very low mutagenic activity on the Salmonella typhimurium strains tested, while it is more effective in inducing trp+ revertants in E. coli B strains. The magnitude of these effects was always less pronounced than that displayed by DTIC. The mutagenic activity of DM-COOK appeared to be independent from the addition of a metabolic activating system and had a different pattern from that displayed by MM-COOK. It is therefore unlikely that DM-COOK acts through conversion into the monomethyl derivative.