Structure-activity relationships for carcinogens with different modes of action.

The application of structure-activity concepts to the elucidation of the action of chemical carcinogens may proceed by two approaches: the hypothesis and the knowledge-based approaches. The former, exemplified by the 'structural alerts' devised by Ashby and associates, derives from the recognition of the electrophilic nature of carcinogens that damage DNA. The latter approach does not assume an a priori mechanism of action but derives information from the establishment of relationships between structural features and carcinogenicity. Indeed, the 'structural alerts' of Ashby et al. are recognized by such an approach; however, if structural features are associated with the activity of 'nongenotoxic' carcinogens, they would also be recognized by the knowledge-based approach. Obviously, the recognition of new (nonelectrophilic) structural features associated with carcinogenicity will lead to testable hypotheses.