Replacement of in vivo acute oral toxicity studies by in vitro cytotoxicity methods: Opportunities, limits and regulatory status

The development of a new medicinal product is a long and costly process in particular due to the regulatory requirements for quality, safety and efficacy. There is a common interest to increase the efficiency of drug development and to provide new, better quality medicinal products much faster to the public. One possible way to economize time and costs, as well as to consider animal protection issues, is to introduce new alternative methods into non-clinical toxicity testing. Currently, animal tests are mandatory for the evaluation of acute toxicity of chemicals and new drugs. The replacement of the in vivo tests by alternative in vitro assays would offer the opportunity to screen and assess numerous compounds at the same time, to predict acute oral toxicity and thus accelerate drug development. Moreover, the substitution of in vivo tests by in vitro methods shows a proactive pursuit of ethical and animal welfare issues. Importantly, the implementation of in vitro assays for acute oral toxicity would require the establishment of common test guidelines across the EU, USA and Japan, i.e., the regions of ICH (International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use). Presently, alternative in vitro tests are being investigated internationally. Yet, in order to achieve regulatory acceptance and implementation of in vitro assays, convincing results from validation studies are required. In this review, we discuss the current regulatory status of acute oral toxicity testing and point out achievements of alternative methods. We describe the application of in vitro tests, correlating in vitro with in vivo data. The use of in vitro data to predict in vivo acute oral toxicity is analyzed using the Registry of Cytotoxicity, an official independent database. We have then analyzed opportunities and drawbacks for future implementation of in vitro test methods, with particular focus on industrial use.