Recent University of Edinburgh spin out, FibromEd Products Limited, and biotechnology company Kirkstall Limited, have been awarded funding from the NC3Rs CRACK IT Solutions programme. The award supports work to improve methods to detect potential drug toxicity in humans and aims to reduce the reliance on animal use in drug safety studies. Dr David Hay, FibromEd Products Limited, explains how.
Bringing a new drug to market is a rocky road. Not only is it estimated to take over 12 years, but the price tag can run up to US $2 billion. During drug development, liver toxicity is the second most common cause of drug failure, so more predictive assays are urgently required to develop safer and more cost-effective medicines.
The potential of drugs to induce liver toxicity is currently assessed in a step wise manner. Initial screens are carried out in isolated liver cell models from a variety of species including rats, dogs and non-human primates. The most promising candidate drugs then progress to regulatory animal toxicology studies before entering clinical development. However, the high incidence of liver toxicity observed during preclinical and clinical development has called into question the utility of the currently used preclinical models and provided a driver for the development of potentially more relevant human cell-based assays. A major bottleneck is the routine supply of good-quality primary human hepatocytes from the desired genetic background. The efficient differentiation of stem cells to liver cells (hepatocytes) offers a way around this, promising a limitless supply of human cells for testing.
Encouragingly, at FibromEd, our recent data shows that stem-cell derived hepatocytes (Figure 1) perform on par with current gold standard assays (Medine et al 2013; Szkolnicka et al 2014). They may well serve as a partial or full replacement for primary cells from a number of species in safety screening in the future. Furthermore, by providing a potentially more physiologically relevant prescreen, only the best candidate drugs will enter regulatory in vivo studies, further reducing the number of animals used in the development of the drug. While these observations are very exciting, there is a requirement to incorporate other elements of human physiology into the design of improved non-animal methods. Key examples being:
- Three-dimensional cell culture
- Provision of a stable environment
- Exposure to blood flow.
Only certain cell types tolerate direct fluid flow – epithelial cells (skin, blood vessels, intestine) and the non-adherent (or floating) cells of the immune system. All other cells are in the regime of interstitial flow – the flow of fluid between tissues and capillaries and a key physiological stimulus that tissues are exposed to in the body.
It’s therefore important that cells are cultured in an environment that mimics the body as closely as possible, with a sufficient flow of nutrients and realistic gradients of oxygen tension. For an in vitro approach to give accurate and reliable drug metabolism or toxicity data, these extracellular environment features need to be present. This is now well documented, so represents an important target for further technological development.
In pursuit of this we have teamed up with Kirkstall Limited, experts in creating a physiologically relevant environment for culturing cells in vitro. Our collaborative research project aims to supply normal levels of blood flow to hepatocytes for predictive toxicology studies. It’s important to note that the expression of key genes involved in human drug metabolism is increased when exposed to blood flow, promising better drug metabolism in the future. Building on a recent collaboration with the pharmaceutical company Bristol-Myers Squib, we will use compounds, with known mechanisms of action, to assess the utility of our in vitro models and optimise them for industrial application.
In the short term, utilising our new approach has the potential to reduce animal use by removing the need for primary animal liver cell cultures and by screening out compounds earlier on that would otherwise fail in later animal studies due to unforeseen liver toxicity. In the long term, and with further validation, our approach has the potential in some instances to completely replace animal use in studies to determine liver toxicity.
Dagmara Szkolnicka, Sarah L. Farnworth, Baltasar Lucendo-Villarin, Christopher Storck, Wenli Zhou, John P. Iredale, Oliver Flint, & David C. Hay (2014). Accurate Prediction of Drug-Induced Liver Injury Using Stem Cell-Derived Populations Stem Cells Translational Medicine DOI: 10.5966/sctm.2013-0146
Claire N. Medinea, Baltasar Lucendo-Villarin, Christopher Storck, Faye Wang, Dagmara Szkolnicka, Ferdous Khan, Salvatore Pernagallo, James R. Black, Howard M. Marriage, James A. Ross, Mark Bradley, John P. Iredale, Oliver Flint, & David C. Hay (2013). Developing high-fidelity hepatotoxicity models from pluripotent stem cells Stem Cells Translational Medicine DOI: 10.5966/sctm.2012-0138