Single linear regression analysis was used to characterise the relationship between cytotoxicity in a variety of mammalian cell culture systems and acute oral toxicity (LD50) in experimental animals. The following results were obtained. Firstly, in a cytotoxicity assay using the calf aortic endothelial cell line BKEz-7, IC50 values determined for 44 chemicals in culture showed significant correlation with the oral LD50 values for rat and mouse (computed correlation coefficient r = 0.546). After eliminating three chemicals that were characterised by extreme lethality indices (LI = IC50/LD50), the correlation coefficient of the remaining 41 chemicals increased to a value of r=0.728. By using the linear regression model for these 41 chemicals, the oral LD50 for rat and mouse can be predicted correctly from the IC50 values for 83% of substances from a variety of chemical substance classes within a range of approximately one order of magnitude of dosage unit of LD50 for rat and mouse. Secondly, the mean IC50 values (IC50xBAR) determined as the geometrical mean of two or more IC50 values per substance, which were generated in a wide spectrum of mammalian cell lines and collected in a "Registry of Cytotoxicity" (RC), gave similar results (r = 0.644). Likewise, with the aid of this method, the oral LD50 for rat and mouse can be predicted for 74% of non-selected chemicals from structurally-different classes in the same dosage range, e.g., 1-25 millimoles per kg body weight. The prediction of LD50 values from in vitro cytotoxicity data may permit the calculation of a more precise dose range-finding and offers a new way for reducing the number of animals in acute toxicity testing.
