An assessment of progress in the use of alternatives in toxicity testing since the publication of the report of the second FRAME Toxicity Committee (1991)

Prediction of metabolism-induced hepatotoxicity on three-dimensional hepatic cell culture and enzyme microarrays

Human liver contains various oxidative and conjugative enzymes that can convert nontoxic parent compounds to toxic metabolites or, conversely, toxic parent compounds to nontoxic metabolites. Unlike primary hepatocytes, which contain myriad drug-metabolizing enzymes (DMEs), but are difficult to culture and maintain physiological levels of DMEs, immortalized hepatic cell lines used in predictive toxicity assays are easy to culture, but lack the ability to metabolize compounds. To address this limitation and predict metabolism-induced hepatotoxicity in high-throughput, we developed an advanced miniaturized three-dimensional (3D) cell culture array (DataChip 2.0) and an advanced metabolizing enzyme microarray (MetaChip 2.0). The DataChip is a functionalized micropillar chip that supports the Hep3B human hepatoma cell line in a 3D microarray format. The MetaChip is a microwell chip containing immobilized DMEs found in the human liver. As a proof of concept for generating compound metabolites in situ on the chip and rapidly assessing their toxicity, 22 model compounds were dispensed into the MetaChip and sandwiched with the DataChip. The IC₅₀ values obtained from the chip platform were correlated with rat LD₅₀ values, human C _max values, and drug-induced liver injury categories to predict adverse drug reactions in vivo. As a result, the platform had 100% sensitivity, 86% specificity, and 93% overall predictivity at optimum cutoffs of IC₅₀ and C _max values. Therefore, the DataChip/MetaChip platform could be used as a high-throughput, early stage, microscale alternative to conventional in vitro multi-well plate platforms and provide a rapid and inexpensive assessment of metabolism-induced toxicity at early phases of drug development.

Engineering tissue alternatives to animals: applying tissue engineering to basic research and safety testing

The focus for the rapid progress in the field of tissue engineering has been the clinical potential of the technology to repair, replace, maintain or enhance the function of a particular tissue or organ. However, tissue engineering has much wider applicability in basic research and safety testing, which is often not recognized owing to the clinical focus of tissue engineers. Using examples from a recent National Centre for the Replacement, Refinement and Reduction of Animals in Research/Biotechnology and Biological Sciences Research Council symposium, which brought together tissue engineers and scientists from other research communities, this review highlights the potential of tissue engineering to provide scientifically robust alternatives to animals to address basic research questions and improve drug and chemical development in the pharmaceutical and chemical industries.

Assessing risk to humans from chemical exposure by using non-animal test data

The use of data from non-animal toxicity methods in risk assessment has mainly been limited to hazard identification and for elucidating mechanisms of toxicity. However, there is a need to extend the use of in vitro tests to hazard characterisation and risk assessment. This might be feasible by: (a) increased use of human cells of different types; (b) better maintenance of differentiated cells in culture for long periods; (c) use of genetically-engineered cells with useful characteristics; (d) development of complex organotypic cell systems; (e) development of co-cultures of different cell types; and (f) development of techniques for long term culturing, repeat dosing and assessment of recovery. Also, it will be necessary to obtain more information on the differences between cells in culture and in situ in tissues, and on the effects of dosing in vitro and in vivo, to develop realistic and meaningful uncertainty factors to allow in vitro information to be used for risk assessment in its own right, and in conjunction with animal data. These issues and a suggested proposal for using in vitro data in risk assessment are discussed.