Teratogenicity of valproic acid derivatives: Evaluation of structure-activity relationships using the embryonic stem cell test

The embryonic stem cell test (EST) which is based on the morphometric measurement of cardiomyocyte differentiation and cytotoxicity parameters represents a validated method for the detection and classification of compounds according to their teratogenic potency. However, more work is required to assess its applicability domainand to improve its predictive capacity before gaining regulatory acceptance. We picked valproic acid (VPA) as a model compound to evaluate the suitability of the EST for distinguishing between developmental toxicity potencies of substances with closely related structures. Here we investigated six closely related analogues of VPA whose teratogenic potential has been previously determined in the NMRI exencephaly mouse model. Determining the concentration of VPA and of each of its six derivatives at which half maximal inhibition of differentiation occurs in the EST revealed a similar ranking as found previously. Distinct embryotoxicities in vivo of stereoisomers which differ only in their spatial configuration were reproduced by the EST. Similarly, an increased potency in vivo correlating with longer chain length of the congener was evident as higher toxicity in the EST. Our data demonstrate that the EST is capable of differentiating among closely related molecules accordingto their embryotoxic potency. As toxicological endpoints, both differentiation and cytotoxicity in vitro have to be considered to assess teratogenicity comparable to in vivo results. In conclusion, all substances were ranked in the same order and in full accordance to data obtained in the NMRI exencephaly mouse model.