Alternative testing in drug research and development-The validation issue

Neurotoxicity of Seven MEIC Chemicals Evaluated in Organotypic Cultures of Chick Embryonic Dorsal Root Ganglia

The neurotoxic effects of seven selected Multicenter Evaluation of In Vitro Cytotoxicity programme chemicals (methanol, ethanol, isopropanol, sodium chloride, potassium chloride, iron [II] sulphate and chloroform) were evaluated in organotypic cultures of chick embryonic dorsal root ganglia (DRG), maintained in a soft agar culture medium. Two growth parameters of neurite outgrowth from the ganglia — the mean radial length of neurites and the area of neurite outgrowth — were used to evaluate the toxicities of the chemicals. Dose-dependent decreases of both parameters were observed in all experiments. IC50 values (the concentration causing 50% inhibition of growth) were calculated from the dose-response curves established at three time-points during culture, i.e. 24, 48 and 72 hours. The lowest toxic effect was observed in cultures exposed to methanol (the IC50 ranging from 580mM to 1020mM). The highest toxic effect was observed in cultures exposed to iron (II) sulphate (the IC50 ranging from 1.2mM to 1.7mM). The results of other recent experiments suggest that organotypic cultures of DRG can be used during in vitro studies on target organ toxicity within the peripheral nervous system. Moreover, these cultures preserve the internal organisation of the tissue, maintain intercellular contacts, and thus reflect the in vitro situation, more precisely than other cell cultures.

Biostatistical Methods for the Validation of Alternative Methods for In Vitro Toxicity Testing

Statistical methods for the validation of toxicological in vitro test assays are developed and applied. Validation is performed either in comparison with in vivo assays or in comparison with other in vitro assays of established validity. Biostatistical methods are presented which are of potential use and benefit for the validation of alternative methods for the risk assessment of chemicals, providing at least an equivalent level of protection through in vitro toxicity testing to that obtained through the use of current in vivo methods. Characteristic indices are developed and determined. Qualitative outcomes are characterised by the rates of false-positive and false-negative predictions, sensitivity and specificity, and predictive values. Quantitative outcomes are characterised by regression coefficients derived from predictive models. The receiver operating characteristics (ROC) technique, applicable when a continuum of cut-off values is considered, is discussed in detail, in relation to its use for statistical modelling and statistical inference. The methods presented are examined for their use for the proof of safety and for toxicity detection and testing. We emphasise that the final validation of toxicity testing is human toxicity, and that the in vivo test itself is only a predictor with an inherent uncertainty. Therefore, the validation of the in vitro test has to account for the vagueness and uncertainty of the "gold standard" in vivo test. We address model selection and model validation, and a four-step scheme is proposed for the conduct of validation studies. Gaps and research needs are formulated to improve the validation of alternative methods for in vitro toxicity testing.

Defining the role of ECVAM in the development, validation and acceptance of alternative tests and testing strategies

The background to the establishment of the European Centre for the Validation of Alternative Methods (ECVAM) is reviewed, and the main events at the opening of the Centre and an ECVAM symposium on practical aspects of validation are summarized. Finally, recommendations made to ECVAM for consideration in developing the Centre's strategy are listed.

Dialogue and collaboration with ECVAM: the view of the EFPIA

An evaluation is presented of past experience of dialogue and collaboration of ECVAM with the European Federation of Pharmaceutical Industries and Associations (EFPIA) over the last nine years. Lessons learnt from the viewpoint of EFPIA company representatives are given. Also, proposals for the future ECVAM approach are made, such as support for other research areas for new methods to be validated, giving realistic statements to ECVAM's EU and external customers, and being open to any new technology development that might help in opening and establishing new alternative avenues. Finally, the need for proper publications on the implementation of alternatives is recommended, for example, through the existing national platforms and their umbrella organisation, ecopa.

Cytotoxicity of prodigiosin and benznidazole on V79 cells

The cytotoxicity of prodigiosin, an antibiotic and potential trypanocide produced by Serratia marcescens, and Benznidazole, a trypanocidal drug, were assayed on V79 fibroblast cell line. Three independent endpoints for cytotoxicity were evaluated; namely, the nucleic acid content (NAC), MTT reduction and neutral red uptake (NRU). IC(50) values of 1-20 microM were obtained for prodigiosin in the NRU, MTT and NAC tests. Prodigiosin had greater trypanocidal activity (IC(50)=5 microM) than Nifurtimox (IC(50)=150 microM) a known trypanocide drug used in Chagas' disease therapy. Benznidazole was less toxic (IC(50)=2000 microM) than prodigiosin (IC(50)=1-20 microM) in V79 cells based on the MTT and NAC assays. Benznidazole stimulated the NRU until 2 mM. Indeed, the cell viability measured with the NRU was higher at all concentrations of benznidazole tested than that measured by MTT reduction and NAC assays.