IRAG working group 4. Cell cytotoxicity assays. Interagency Regulatory Alternatives Group

Twenty-seven data sets from 12 cellular cytotoxicity assays, intended to predict ocular irritation, were submitted to the Interagency Regulatory Alternatives Group (IRAG) for review. These data consisted of paired in vivo (Draize) and in vitro responses to individual chemicals and formulations. In vivo data consisted of individual tissue scores so that the predictive value of the in vitro assay could be assessed for each tissue response normally measured in the standard Draize assay. Data were compiled and evaluated according to the IRAG Guidelines Document. The Pearson's linear correlation coefficient was used as the first step in assessing the relationship between the in vitro and in vivo responses. The majority of the data sets represented the study of surfactant-based materials. In many cases, there was good correlation between the in vitro scores and the in vivo tissue responses. Most pronounced were the particularly good correlations between the in vitro scores and conjunctival redness scores across most of the assays. Based on the data submitted, a number of the cell cytotoxicity assays show considerable promise as screens for ocular irritancy. None of the submitters recommended that their cell cytotoxicity assay be used as a sole replacement for in vivo assessment. For almost all of these assays, the materials being tested should be water-soluble/miscible. The toxicity of products with reserve acidity or alkalinity or with high reactivity may be underestimated. A given user may prefer certain assays depending on the types of materials to be tested, the expected range of toxicities and the resources available. The cell cytotoxicity assays can serve as a valuable component of a tiered or battery testing program. As with any assay, a sufficient number of replicate values, concurrent positive and negative controls, and a strict adherence to assay acceptance criteria are essential to produce credible data.