Evaluation of an in vitro cytotoxicity assay for specific groups of chemicals.

The FRAME KB cytotoxicity assay is an ill vitro test for basal cytotoxicity which measures the sub-lethal inhibition of cell growth by toxic substances. Exponentially growing 3T3-Ll mouse fibroblasts are exposed to a range of concentrations of a test substance for 72 hours, then relative cell number is estimated by the protein/kenacid blue dye-binding method. The assay was evaluated for its ability to predict parameters of in vivo acute lethal potency. In vivo/in vitro comparisons were performed for a set of miscellaneous chemicals and for a set of metal compounds. The degree of correlation was closer for the metal compounds than for the unrelated set, in the in vitro/mouse i.p. LDso comparison. The cytotoxicity assay was more useful than metal "softness" (a physico-chemical parameter) for predicting metal compound toxicity ill vivo. An investigation of the ill vitro toxicities of a group of commercial chemicals and formulations revealed very poor ill vivo/in vitro correlations. Some were toxic to the 3T3-Ll cells, yet of very low toxicity to rats. This was partly due to the poor solubility of some of the substances, which probably caused their virtual non-toxicity to rats by oral dosage. Chemical volatility is another methodological problem for ill vitro assays. A simple modification of the FRAME KB cytotoxicity assay was successfully developed in order to prevent the underestimation of the cytotoxicities of volatile liquids. The assay also demonstrated potential use for providing data for the safety assessment of surfactants and toiletry formulations. It is emphasised that the FRAME KB cytotoxicity assay should never be used in isolation, but as part of a battery of tests chosen for a particular type of toxicity and/or type of chemical or formulation. The F9 embryonal carCInoma cell line was evaluated for its potential usefulness in in vitro toxicity testing. F9 cells were induced to differentiate morphologically and biochemically, and it was found that cells in different stages of differentiation did not respond in the same way to toxic chemicals.