Can the in vivo maximum tolerated dose be predicted using in vitro techniques? A working hypothesis

By Shrivastava, R. - John, G.W. - Rispat, G. - Chevalier, A. - Massingham, R.

All new chemical entities synthesised in our laboratories have routinely been subjected to in vitro toxicity tests. Out of curiosity, we established a working hypothesis in which the in vitro data could be empirically transformed to predict the in vivo four-week standard maximum tolerated dose (MTD) studies in rats and dogs. As a first step to verifying this hypothesis, we report here the findings of an in vitro cytotoxicity study of 25 compounds randomly selected from our files, possessing a wide range of pharmacological activities and for which data from standard four-week MTD studies were available. Single blind in vitro toxicity studies in three carefully selected types of primary and cell line cultures were carried out. In vitro CT50 (concentration inducing 50% cell death) and CT100 (concentration inducing 100% cell death) values were obtained for each of the three cell types and, using empirical assumptions, these results were used to predict the MTD in vivo in the rat and dog. The actual in vivo threshold and toxic doses were obtained from the MTD study reports. The in vivo toxicity values predicted from the in vitro toxicity results with this series of 25 compounds showed a better than 80% correlation with the actual in vivo results obtained in the MTD studies. Whether or not in vitro cytotoxicity predictions are ultimately found to be directly and consistently related to the MTD in vivo for all pharmacological classes of compounds will require many additional studies, but it is hoped that these results will stimulate the necessary research effort required to answer this question.