Cell proliferation, migration and CAM-dependent neurite outgrowth as developmental in vitro endpoints for screening teratogenic potential: Application to valproic acid and related analogues of varying potency

The in vivo teratogenic potential of valproic acid (VPA) and related teratogenic and non-teratogenic analogues has been correlated with their effects on specific in vitro endpoints of cell proliferation, migration and CAM-dependent neurite outgrowth, as these events are common to crucial epochs of development. The (+/-)-2-n-propyl-4-pentynoic acid [(+/-)-4-yn-VPA] and S-2-n-propyl-4-pentynoic acid [S(-)-4-yn-VPA] analogues increased the incidence of neural tube defects in mouse embryos exposed to a single dose, whereas the E-2-n-propyl-2-pentenoic acid (E-2-en-VPA) analogue and R-2-n-propyl-4-pentynoic acid [R(+)-4-yn-VPA] enantiomer were without effect. VPA and related analogues tested exerted comparable G1 phase antiproliferative effects in C6 glioma and limb bud cells in a dose range of 0-3 mM; however, their relative potency did not correlate with in vivo teratogenicity. In contrast, VPA and all teratogenic analogues, at 3 mM, inhibited neuronal cell aggregation and limb bud chondrocyte differentiation in a manner that exhibited a reasonable correlation with their in vivo teratogenicity. The teratogenic S(-)-4-yn-VPA and non-teratogenic R(+)-4-yn-VPA enantiomers exhibited a differential inhibition of primary neurone outgrowth of neurites stimulated by cell adhesion molecules [L1 and N-cadherin (NCAD)]. Half-maximal inhibition was observed at approximately 150 mu M for the teratogenic S(-)-4-yn-VPA enantiomer, but not the non-teratogenic R(+)-4-yn-VPA form. These results suggest that in vitro perturbations of differentiation are likely to provide the greatest discriminatory power for in vivo teratogenicity. (C) 1998 Elsevier Science Ltd. All rights reserved.