Analysis of the in vivo nitrosation capacity of the larvae used in the wing somatic mutation and recombination test of Drosophila melanogaster.

The in vivo nitrosation capacity of third-instar larvae of Drosophila melanogaster was assessed using the wing somatic mutation and recombination test (SMART). Larvate derived from two different crosses, the standard cross (ST) and the high bioactivation cross (HB) both involving the recessive wing cell markers multiple wing hairs (mwh) and flare (flr3), were used. The HB cross is characterised by an increased cytochrome P450-dependent bioactivation capacity for promutagens and procarcinogens. The larvae were treated either with methyl urea, sodium nitrite or its combination. N-Nitrosomethylurea was used as a positive control. The wings of the resulting flies were analysed for the occurrence of mutant spots produced by various types of mutational events or by mitotic recombination. Methyl urea is negative in the ST and the HB cross, whereas sodium nitrite is weakly genotoxic in both crosses. However, the combination of both compounds produces highly increased frequencies of mutations and recombinations predominantly in the HB cross. The genotoxic effects produced by the combined treatments were considerably increased when mashed potatoes or an agar-yeast medium were used for the treatment instead of the standard instant medium. Treatment of larvae with the mixture resulting from the in vitro reaction of nitrosation precursors also resulted in high frequencies of induced spots comparable to those recorded with the potent genotoxin N-nitrosomethylurea. Further experiments showed that the genotoxic effect resulting from the in vivo exposure to nitrosation precursors can be reduced by co-treatment with catechin, a known nitrosation inhibitor. The present study demonstrates that the wing spot test is well suited for the determination of genotoxicity produced by in vivo nitrosation processes and for the study of their modulation by individual compounds or dietary complex mixtures.

Dietary garlic suppresses DNA adducts caused by N-nitroso compounds.

The present studies examined the impact of a processed garlic powder on the in vivo occurrence of DNA adducts caused by N-nitroso compounds (NOC) in rats. Addition of 2% garlic powder to diets containing aminopyrine and sodium nitrite (each at 600 mg/kg) reduced the occurrence of both 7-N-methyldeoxyguanosine (7-N-mG) and 6-O-methyldeoxyguanosine (6-O-mG) adducts to rat liver DNA by approximately 55%; and over 80% when 4% garlic was provided. Dietary supplementation with garlic powder (2 and 4%) also reduced the occurrence of 7-N-mG and 6-O-mG adducts by approximately 40 and 60% respectively, in rats intubated with N-nitrosodimethylamine (150 mg/kg body wt). The quantity of 7-N-mG and 6-O-mG adducts in mammary tissue of rats given intravenous N-methyl-N-nitrosourea (50 mg/kg body wt) was reduced over 50% in rats fed 2% garlic compared to controls. The depression in the occurrence of these adducts was approximately 70% when dietary garlic was increased to 4%. These experiments suggest the reduction in DNA adducts caused by processed garlic powder likely reflects a depression in the formation of NOC from precursors and changes in the bioactivation and/or denitrosation of NOC.

Ellagic acid embryoprotection in vitro: distribution and effects on DNA adduct formation.

Ellagic acid (EA) is a naturally occurring plant phenol that was recently demonstrated to protect cultured rat embryos from the embryotoxic effects of N-methyl-N-nitrosourea (MNU). The teratogenic mechanism of action of MNU, as well as other methylating agents, is debated: both cell death and mutation have been proposed. In some model systems, EA has been reported to selectively decrease the mutagenic DNA adduct O6-methylguanine (O6MG) when compared to the cytotoxic DNA adduct N7-methylguanine (N7MG). The present study was initiated to determine 1) the distribution of 14C-EA and 3H-MNU in the rat whole embryo culture model system and 2) the effects of EA on MNU-induced DNA adduct formation in this model system. 14C-EA (50 microM for 2 hr, known embryoprotective concentration; no MNU added) was used to demonstrate access of EA to the embryo within the 2 hr exposure period. The majority of EA (99.5%) remained in the media while tissue concentrations of 57.0 and 47.9 pmol/mg were attained in the yolk sacs and embryos, respectively. Similarly, MNU (75 microM for 1 hr, known effective concentration; no EA added) was distributed between the media, yolk sacs, and embryos at 99.7%, 73.7 and 112.9 pmol/mg, respectively. When non-radiolabeled EA (50 microM for 2 hr) was used to protect embryos prior to exposure to 3H-MNU (75 microM for 1 hr), the distribution of MNU in the model system was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

[14Co-dimetinur distribution in mice in relation to the stage of the development of tumor process]. / Raspredelenie 14Co-dimetinura v organizme myshei v zavisimosti ot stadii razvitiia opukholevogo protsessa.

Pharmacokinetics of the antitumour agent 14CO-dimetinur (100 mg/kg) after oral administration to the intact mice and those with solid leukemia P 388 is characterized by its rapid delivery to organs and tumours with the achievement of maximum radioactivity 5 hours later and the further gradually decline during 4 days. The increased accumulation of the 14CO-products in kidneys and their retarded output from the brain and lungs against a background of the relatively equal distribution of radioactivity between other tested organs have been established. The same level of carbamoylated products in large tumours (the 16th day after leukemia transplantation) as well as in small tumours (the 9th day after inoculation) is in agreement with the conservation of the initial marked inhibitory effect of the drug against advanced tumours.

Intracellular activation of cytotoxic agents: kinetic models for methylnitrosoureas and N-methyl-N'-nitro-N-nitrosoguanidine in cell culture.

The cytotoxic activity of N-methyl-N-nitrosourea (MNU), streptozotocin, and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was determined in cell culture by using a P388 cell growth rate inhibition assay. These agents appear to have very different activities when inhibition is related to the agent concentration in the culture medium: ED50(C0) = 40 microM for MNNG to 875 microM for streptozotocin. The mechanism of action of these three agents involves conversion to the active methanediazonium ion and subsequent methylation of cellular macromolecules. As a consequence, the rates of conversion of the parent agent to the methylating species in the medium and within the cell are important parameters that also need to be considered to reach a more detailed understanding of the mechanism of action. In order to do this, a kinetic model has been developed to calculate the concentration of drug that is converted to active methylating species within the cell during the assay incubation period. The use of cell culture kinetic models was extended from simple compounds activated through solvolytic reactions (nitrosoureas) to an agent that undergoes selective intracellular activation (MNNG). By use of measured values for initial drug concentration, incubation time, and cell volume, as well as extracellular and intracellular chemical activation rate constants, the intracellular concentration, [P4], which represents the cumulative intracellular reaction products formed during the incubation period, was calculated and related to cytotoxicity. All three agents showed an ED50[P4] between 140 and 180 microM, and for MNNG, this ED50 was independent of extracellular sulfhydryl concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

[The pharmacokinetics of the antitumor preparation of dimetinur]. / Farmakokinetika protivoopukholevogo preparata dimetinur.

The pharmacological disposition of 1,3-dimethyl-1-nitrosourea (dimetinur) in intact rats and animals with Walker carcinosarcoma, glioma 2211, colon adenocarcinoma was studied by the colorimetric assay using an oral drug dose of 100 mg/kg. Computer analysis of data was based on a single-compartment model using the area under the concentration-time curve (S) and the intact drug half-life (t1/2) as main pharmacokinetic parameters. The highest level of the drug (S) was observed in tumour and brain tissues on an equality with drug distribution between blood, spleen, kidney and lungs. The half-life of the dimetinur removal from blood exceeds the known values for certain active NAM type. The antitumour activity of the drug against the studied tumours correlates positively with pharmacokinetic parameters for the tumours (S and 1/tmax).

[Ames test study of the effect of 2nd-phase biotransformation reactions on the level of mutagenic action of a number of chemical compounds]. / Issledovanie v teste Eimsa vliianiia reaktsii vtoroi fazy biotransformatsii na uroven' mutagennogo deistviia riada khimicheskikh soedinenii.

Introduction of cosubstrates for reactions of conjugation with the reduced glutathione, glucuronic acid and sulphate is shown to modify (increase or decrease) the level of mutagenic effect of thiophosphamide, nitrosomethylurea and DDDTDP on S. typhimurium TA 1950 or TA 1534.

[Pharmacokinetics of nitrosomethylurea in oncologic patients]. / Farmakokinetika nitrozometilmocheviny u onkologicheskikh bol'nykh.

Kinetics of blood-nitrosomethylurea (NMU) was studied in 68 patients with lung cancer, malignant melanoma and lymphoma who had received NMU-based combination chemotherapy. The results were used for computing main pharmacokinetic parameters such as logarithm of calculated initial concentration, time of half-elimination from blood, area under the kinetic curve of concentration, volume of distribution in the body and clearance. All those values were shown to significantly differ with individual patients. A longer retention of the drug in blood flow (as evidenced by increased time of half-elimination and area under kinetic curve matched by decreased volume of distribution and clearance) was registered in responders than in non-responders, the difference sometimes reaching statistical significance.

Uptake and binding of 1-methyl-1-nitrosourea (MNU) and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) by the isolated guinea pig pancreas.

1-Methyl-1-nitrosourea (MNU) and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) are carcinogens which methylate nucleic acids and proteins and covalently modify proteins by carbamoylation (MNU) or guanidination (MNNG). Using MNU and MNNG labeled with carbon-14 in the individual carbon positions, the above reactions were quantitated in the isolated guinea pig pancreas, an organ susceptible to tumorigenesis by MNU. Freshly prepared pancreatic lobules were incubated with the labeled drugs (0.03, 0.3 and 1.0 mM) for one hour at 37 degrees C. Alkylated purines from hydrolyzed DNA were separated on Sephadex G10 and acid-soluble nuclear proteins were extracted and separated on polyacrylamide gels. Total uptake of all four labels into lobules was linear with concentration. Acid insoluble radioactivity also increased linearly except for MNNG methylation which plateaued between 0.3 and 1.0 mM. 7-Methylguanine formation by both compounds was approximately ten fold greater than 06-methylation. However, DNA modification by MNU exceeded that by MNNG, especially at the higher drug concentrations. No carbamoylation or guanidination of DNA was detected. Total binding (methylation plus carbamoylation/guanidination) to acid-extractable chromatin proteins was equivalent to DNA modification on a molar basis (approximately 0.35 and 0.08 pmol/microg for exposure to 1.0 mM MNU and MNNG, respectively). All histones were labeled by all drug preparations, with H2A being the principal site of methylation and H2B, H3 and H1 being the major targets of carbamoylation and guanidination. H4 was the least modified histone. Drug binding to cytoplasmic organelles also occurred. These results show a broad spectrum of nuclear and cytoplasmic modification of pancreatic cells by MNU and, to a smaller extent, MNNG.