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Substituent effects on the genotoxicity of 4-nitrostilbene derivatives
B H Hooberman1, M D Brezzell, S K Das
1College of Pharmacy, University of Michigan, Ann Arbor 48109-1065.
Abstract:
4-Nitrostilbene and twelve of its derivatives (eleven E-stilbenes and two Z-stilbenes) were examined for possible quantitative structure-activity relationships of their in vitro and in vivo genotoxicity. Relative mutagenicity was studied with and without S9 activation in Salmonella strains TA98 and TA100, as well as in the nitroreductase deficient strains TA98/NR and TA100/NR. Chromosomal aberrations in the bone-marrow cells of mice following intraperitoneal administration of the nitrostilbenes were observed as an indicator of in vivo genotoxicity. All of the compounds were active in TA98 and TA100 without S9 activation, with the exception of 4-amino-4'-nitrostilbene in TA100. Mutagenic activity was greatly reduced or eliminated in the NR strains, which is consistent with metabolic activation of the compounds by bacterial reductase. The presence of S9 lowered the activity of most of the nitrostilbenes presumedly by enzymatic detoxication. Hammet values of substituents, partition coefficients and frontier orbital energies (ELUMO and EHOMO) were studied for correlations with mutagenicity of the eleven E-stilbenes. Correlations could be established between mutagenicity in TA98 without S9 activation and the Hammet values. The same mutagenicity could also be correlated to ELUMO. Rationales for these correlations include the concept that electron-withdrawing groups which lower ELUMO should facilitate the reduction of the nitro group, leading to the proximate mutagen hydroxylamine. The correlations are also explained by the concept that electron-withdrawing groups should help stabilize the hydroxylamine intermediate and make the ultimate mutagenic species, the nitrenium ions, more reactive toward DNA. The relationship between mutagenicity and electronic effects of substituent groups found in vitro could not be extended to the in vivo results. However, except for the dinitrostilbenes, where insolubility prevented their testing, all the nitrostilbenes produced a statistically significant increase in chromosomal aberrations compared to the negative solvent control.
Insights
This study investigated the genotoxicity of 4-nitrostilbene derivatives, finding that mutagenic activity in bacterial assays correlated with electronic properties, but not in vivo chromosomal damage.
Area of Science:
- Toxicology
- Medicinal Chemistry
- Structure-Activity Relationships
Background:
- Nitrostilbenes are a class of compounds with potential genotoxic activity.
- Understanding structure-activity relationships is crucial for predicting and mitigating chemical toxicity.
- In vitro and in vivo genotoxicity assays provide complementary data on a compound's safety profile.
Purpose of the Study:
- To investigate the in vitro and in vivo genotoxicity of 4-nitrostilbene and its derivatives.
- To explore quantitative structure-activity relationships (QSAR) between chemical properties and genotoxic effects.
- To elucidate the role of metabolic activation and detoxification pathways in nitrostilbene genotoxicity.
Main Methods:
- In vitro mutagenicity testing using Salmonella strains (TA98, TA100) with and without S9 activation and nitroreductase-deficient strains (TA98/NR, TA100/NR).
- In vivo genotoxicity assessment via chromosomal aberration analysis in mouse bone-marrow cells.
- Quantitative structure-activity relationship analysis using Hammett values, partition coefficients, and frontier orbital energies (ELUMO, EHOMO).
Main Results:
- All tested nitrostilbenes showed mutagenicity in TA98 and TA100 without S9 activation, with reduced activity in NR strains, indicating bacterial nitroreductase involvement.
- S9 activation generally decreased mutagenicity, suggesting enzymatic detoxification.
- Correlations were found between in vitro mutagenicity (TA98, no S9) and Hammett values/ELUMO, supporting electronic effects in metabolic activation and DNA interaction.
- In vivo chromosomal aberration assays showed significant genotoxicity for most nitrostilbenes, but these results did not correlate with in vitro findings.
Conclusions:
- Bacterial nitroreductase is key for nitrostilbene mutagenicity in vitro.
- Electronic properties of substituents influence in vitro genotoxicity through modulation of metabolic activation and reactive intermediate stability.
- In vitro structure-activity relationships do not fully predict in vivo genotoxicity, highlighting the complexity of toxicological mechanisms.