Presumptive tests.

The necessary characteristics of presumptive tests are that they require no more than weeks or months to perform; the-results from such tests be highly reproducible; the significance of test results be validated by empirical correlation; they be capable of being coupled to appropriate metabolic activation systems; they circumvent the requirement that the intact animal (or a similarly limited condition) serve as the statistical unit of the experiment. Currently, most but not all presumptive tests utilize individual cells, either microbial or mammalian cells in tissue culture, which are grown, treated, and analyzed in vitro. There are three major categories of presumptive tests which have been considered useful as predictors of carcinogenesis or mutagenesis. The first category includes those tests which assess the potential of a substance and/or its metabolite to damage and/or interact with DNA. The rationale for tests of this type is that DNA is known to be the principal target molecule for mutagenesis and that a common feature of carcinogens is their ability to form electrophiles and to react with molecules such as DNA to form new covalent bonds. Among the tests which measure either directly or indirectly damage to DNA are: liquid and thin-layer chromatography of the constituent nucleotides of DNA; use of isotopically labeled reactants; repair-replication of DNA. The next category of presumptive tests are the mutational assay systems in bacteria (such as the Ames test), other microbial organisms and mammalian cells in tissue culture. These tests also reflect whether damage to DNA has occurred by interaction with a chemical or its metabolic product. This entire category can be subdivided into two major classes: those tests responding only to highly specific chemical changes on the DNA (e.g., specific base-substitution); and those which are to