Integrated in vitro-in silico models for predicting in vivo developmental toxicity : facilitating non-animal based safety assessment

In chemical safety assessment, information on adverse effects after repeated dose and chronic exposure to low levels of hazardous compounds is essential for estimating human risks. At present, this information is almost solely obtained by performing animal experiments. Therefore, suitable methods to reduce, refine or replace (3Rs) repeated dose animal testing are urgently needed. At present, in vitro toxicity assays are able to screen compounds for toxicity, but since these tests result in in vitro concentration-response curves, whereas for the safety assessment of chemicals for human in vivo dose-response curves are needed, it is important that in vitro concentration-response curves can be translated to in vivo dose-response curves. The goal of the present project is to extrapolate in vitro concentration-response curves to in vivo dose-response curves with the help of physiologically based kinetic (PBK) models that describe the in vivo absorption, distribution, metabolism and excretion (ADME) processes. This is achieved by using the concentration-response curves, acquired in an appropriate in vitro toxicity test, as internal concentrations in the model, in order to calculate the in vivo dose levels that are needed to reach the internal (toxic) concentrations, by using the PBK-model. The predicted dose-response curves thus obtained can be used to determine safe exposure levels in chemical safety assessment. The endpoint used in the present study is developmental toxicity. The in vitro toxicity assay used is the differentiation assay of the embryonic stem cell test (EST). With the use of a rat PBK model, predicted dose-response curves for in vivo developmental toxicity for the rat are acquired, which are compared with experimental literature data on the in vivo developmental toxicity of these compounds in the rat. To obtain the dose-response curves for in vivo developmental toxicity in human, PBK-models describing the in vivo kinetics in human are used. The combined in vitro-in silico approach described is used for compounds belonging to the chemical class of glycol ethers or the chemical class of retinoids. This enables evaluation of whether the combined in vitro - in silico approach is able to predict dose-response curves for in vivo developmental toxicity for compounds belonging to the same chemical class, but with differences in toxic potency. The results of the research reveal the feasibility of translating in vitro concentration-response curves to in vivo dose-response curves using PBK modeling. This finding shows the possibility of using in vitro toxicity data in chemical risk assessment, which will, if applied in risk assessment, highly contribute to the 3Rs.