Progress and problems in evaluating and validating alternative assays in toxicology

Various techniques have been proposed and subsequently developed as potential replacements for whole-animal topical toxicology assays. Comparisons of in vitro and in vivo endpoints, the solubility of test agents, solvent effects, interactions between components of complex test samples and the standardization of data presentation are factors that influence not only individual laboratory results but interlaboratory reproducibility and the acceptance of newly developed alternative methods. Representative alternative test systems for evaluating topical toxicity are discussed. Examples of problems, data and solutions based on the authors' experience and on experience in other laboratories are reviewed. Specific problems in choosing endpoints, comparing results, recognizing responses of different types of target cell, evaluating the influences of support media in culture and interpreting published animal-based data are included.