Relationships between structure and mutagenic activity of environmental chemicals

Influence of structural and functional modifications of selected genotoxic carcinogens on metabolism and mutagenicity - a review

Alterations in molecular structure are responsible for the differential biological response(s) of a chemical inside a biosystem. Structural and functional parameters that govern a chemical's metabolic course and determine its ultimate outcome in terms of mutagenic/carcinogenic potential are extensively reviewed here. A large number of environmentally-significant organic chemicals are addressed under one or more broadly classified groups each representing one or more characteristic structural feature. Numerous examples are cited to illustrate the influence of key structural and functional parameters on the metabolism and DNA adduction properties of different chemicals. It is hoped that, in the event of limited experimental data on a chemical's bioactivity, such knowledge of the likely roles played by key molecular features should provide preliminary information regarding its bioactivation, detoxification and/or mutagenic potential and aid the process of screening and prioritising chemicals for further testing.

Extended quantitative structure-activity relationships for 80 aromatic and heterocyclic amines: structural, electronic, and hydropathic factors affecting mutagenic potency

The mutagenic/carcinogenic heterocyclic amines formed during the cooking of protein foods have been determined to be probable or possible human carcinogens. As part of a comprehensive study of the food mutagens, our laboratory has produced a series of quantitative structure-activity relationships (QSARs) of aromatic and heterocyclic amines, to attempt to elucidate the mechanisms of mutagenesis/carcinogenesis. Amines are genotoxically active only after activation by a series of reactions converting the parent compound to an electrophilic derivative, which is postulated to be a nitrenium ion that covalently binds to and damages DNA. An important agent in this conversion is cytochrome P450. In this report we develop a QSAR for 80 amines of diverse structure and a range of 10 orders of magnitude in mutagenic potency. New structural factors and quantum chemical ab initio and Hückel calculations are included. The results are interpreted to show that a main determinant of mutagenic potency is the extent of the aromatic pi-electron system. Small contributions are made by both the dipole moment and the calculated stability of the nitrenium ion. Multiple linear regression models account for nearly two-thirds of the variance in potency, leaving room for additional unknown factors. The role of cytochrome P450 1A in amine toxification is supported, and further theoretical and experimental research on its reaction mechanisms and modeling of its active site are proposed.

Base-pair mutation caused by four nitro-group containing aromatic amines in Salmonella typhimurium TA100, TA104, TA4001 and TA4006

Among p-phenylenediamine, benzidine and the analogues we previously tested, only the nitro-group containing 2-nitro-p-phenylenediamine, 3-nitro-o-phenylenediamine, 4-nitro-o-phenylenediamine and 4,4'-dinitro-2-biphenylamine caused base-pair reversion in the histidine locus of Salmonella typhimurium TA100. In order to determine the types of mutations involved, such as transversion or transition, these four nitro-group containing compounds were tested with S. typhimurium strains TA100, TA104, TA4001 and TA4006. Dose-mutagenicity relationships occurred with TA100 and TA104. However, the majority of revertants from TA100 and TA104 were insensitive to inhibition by histidine analogue, DL-1,2,4-triazole-3-alanine. These results suggested that the occurrence of histidine revertants was predominantly induced by base-pair (point) mutations and not by suppressor gene mutations. The CG-TA transition and CG-AT transversion are the major types of mutation induced by all these compounds in TA100. The TA-AT transversion also contributed to the mutagenicity of 4-nitro-o-phenylenediamine and 4,4'-dinitro-2-biphenylamine in TA104. These nitro-group containing compounds showed no mutagenicity in TA4001, but induced CG-GC transversion in TA4006.

Mutagenicity of structurally related phenylazo-3-pyridines in Salmonella typhimurium

Studies were conducted to explore structure-activity relationships for 4'-N,N-dimethylamino-1'-phenylazo-3-pyridine and nine structurally related compounds in Salmonella typhimurium tester strains TA1535, TA100, TA1537, TA1538, TA98. Each compound was tested for mutagenicity at five or more concentrations that varied from 10-5000 micrograms/plate. We used the standard plate test and the investigations were carried out both in the absence and presence of Aroclor-1254-induced rat-liver homogenate and the components of the NADPH-generating system. Negative response was observed for 4'-N,N-dimethylamino-1'-phenylazo-3-pyridine and five of its analogues (4'-N,N-diethylamino-1' phenylazo-3-pyridine; 4'-N,N-di-(beta-hydroxyethylamino)-1' phenylazo-3-pyridine; 4'-N-methylamino sulfonic acid-1'-phenylazo-3-pyridine; 4'-N,N-dimethylamino-6'-acetamido-1' phenylazo-3-pyridine, and 4'-N,N-di-(beta-hydroxyethylamino)-6'-methyl-l' phenylazo-3-pyridine). When S9 induced by Aroclor-1254 was present, the compound 4'-N,N-dimethylamino-6-methoxy-1' phenylazo-3-pyridine exhibited mutagenic activity in the two strains TA1538 and TA98. The compound 4',6'-diamino-3-methyl-1'-phenylazo-3-pyridine was also mutagenic, both in the presence and in the absence of S9 mix. The two compounds 4'-N,N-dimethylamino-6-butoxy-1'-phenylazo-3-pyridine and 4'N,N-di-(beta-hydroxyethylamino)-1'-phenylazo-3-[6-N,N-di-(beta- hydroxyethylamino) pyridine were either weakly mutagenic or nonmutagenic. On the basis of these data, it is concluded that the mutagenicity of phenylazo-3-pyridines, like monocyclic aromatic amines and azo dyes, is influenced by the nature of the substituent chemical groups and their positions in the molecular structure of the compounds.

Quantitative structure-mutagenic activity relationships of triazino indole derivatives

The mutagenicity of 3-(4'-benzylidenamino)-5H-1,2,3-triazin[5,4-b]-indol-4-one derivatives, new compounds with considerable platelet antiaggregating activity, was assayed with the Ames test using the Salmonella typhimurium strains TA97, TA98, TA100 and TA102. The adaptive least-squares method (ALS method) was used to carry out a quantitative structure-activity relationship (QSAR) analysis. Three equations, based on 10 congeners, were found for strains TA97, TA98 and TA100. The results suggest that lipophilicity of the substituent decreases the mutagenicity of the series.

A comparative study of mutagenic and SOS-inducing activity of biphenyls, phenanthrenequinones and fluorenones

A total of 23 chemicals--biphenyls, phenanthrenequinones and fluorenones--were tested for mutagenicity towards Salmonella typhimurium strains TA1538, TA1535 and TA98. SOS-inducing activity of the same chemicals was studied in terms of the SOS-inducing potency in Escherichia coli PQ37, using an automated instrument controlled by a dedicated computer program for the SOS Chromotest. Of the 23 chemicals studied 14 induced His+ revertants in S. typhimurium TA1538 hisD305 (-1 frameshift); none induced His+ reversions in TA1535 (base-pair substitution). The mutagenicity of the chemicals in S. typhimurium TA98 (pKM 101) was lower than in TA1538. There was a close correlation between mutagenicity and SOS-inducing activity of fluorenones and phenanthrenequinones. None of the biphenyls tested induced SOS response and this property does not depend upon the mutagenic activity of the chemicals. SOS Chromotest is particularly valid in detecting chemicals which give rise to base-pair substitutions through SOS induction. If positive results are obtained, the Salmonella assay may be omitted. However, this test cannot replace the Ames test especially for the primary screening of mutagenicity of chemicals with unknown structure.

The effect of alkoxy substituents on the mutagenicity of some aminoazobenzene dyes and their reductive-cleavage products

15 aminoazobenzene dyes and 7 of their reductive-cleavage products were examined in the Salmonella/microsome assay with strains TA98, TA100, TA1535, TA1537 and TA1538. Dyes tested included 5 derivatives of 4-aminoazobenzene with different alkoxy substituents (-OCH3, -OCH2CH3, -OCH2CH2 CH3, -OCH2CH2CH2CH3 or -OCH2CH2OH) in the 8-position as well as the corresponding derivatives of 4-[(4-aminophenyl)azo]-N,N-diethylaniline and 4-[(4-aminophenyl)azo]-N,N-bis(2-hydroxyethyl)aniline. In general, as the size of the substituent ortho to the primary amino group of the dyes was increased, the mutagenicity decreased. A similar trend was observed for the reductive-cleavage products. The results from the latter aspect of this study suggest that the mutagenicity of aminoazobenzene dyes can not be accounted for solely from the properties of their reductive-cleavage products.