The practical application of three validated in vitro embryotoxicity tests. The report and recommendations of an ECVAM/ZEBET workshop (ECVAM workshop 57).

In line with the recommendations of an ECVAM workshop on reproductive toxicity, held in 1994 (1), ECVAM initiated and funded a validation study of three in vitro embryotoxicity tests. In two of these assays, pregnant laboratory animals are used to obtain embryonic tissue — either primary embryonic cells in the mouse micromass (MM) test or embryos in the rat whole embryo culture (WEC) test. In contrast, in the embryonic stem cell test (EST) a permanent mouse embryonic stem cell line is used. The main objectives of the validation study were to assess the performance of the three in vitro tests in discriminating between non-embryotoxic, weak embryotoxic and strong embryotoxic compounds. All three in vitro embryotoxicity tests proved to be applicable to testing a diverse group of chemicals with different embryotoxic potentials (2). The results obtained in the blind trial of the definitive phase of the ECVAM validation study were reproducible, both within and among laboratories, and the concordances between the embryotoxic potentials derived from the in vitro data and from the in vivo data were good for the EST and the WEC test (with one prediction model [PM]), and sufficient for the MM test and the WEC test (with another PM), according to the performance criteria defined by the Management Team (MT) before the formal validation study (2). The ECVAM Scientific Advisory Committee (ESAC) concluded from the results that the three in vitro embryotoxicity tests had been sufficiently validated and could be applied to the assessment of the embryotoxic potential of drugs and other chemicals (3). Furthermore, the ESAC recommended the setting up of a workshop with the aim of producing a guidance document on the applicability of the three scientifically valid test methods in the context of reproductive toxicity testing. ECVAM, therefore, held a second embryotoxicity workshop on 28–30 January 2003, in Ispra, Italy, to further evaluate the practical applications of the three in vitro embryotoxicity tests.