Chemico-Biological Interactions 192 (2011) 65–71 Contents lists available at ScienceDirect Chemico-Biological Interactions journal homepage: www.elsevier.com/locate/chembioint Risk assessment and mitigation strategies for reactive metabolites in drug discovery and development Richard A. Thompson a,* , Emre M. Isin a , Yan Li b , Richard Weaver c , Lars Weidolf d , Ian Wilson e , Alf Claesson f , Ken Page g , Hugues Dolgos a , J. Gerry Kenna h a Discovery DMPK, AstraZeneca R&D Mölndal, SE-413 83 Mölndal, Sweden b Discovery DMPK, AstraZeneca R&D Wilmington, Wilmington, DE, USA c Discovery DMPK, AstraZeneca R&D Charnwood, Loughborough, Leics, UK d Clinical Pharmacology & DMPK, AstraZeneca R&D Mölndal, Mölndal Sweden e Clinical Pharmacology & DMPK, AstraZeneca R&D Alderley Park, Macclesfield, Cheshire, UK f Medicinal Chemistry, AstraZeneca R&D Södertälje, Sodertalje, Sweden g Discovery DMPK, AstraZeneca R&D Alderley Park, Macclesfield, Cheshire, UK h Safety Assessment UK, AstraZeneca R&D Alderley Park, Macclesfield, Cheshire, UK article info Article history: Available online 11 November 2010 Keywords: Reactive metabolite Adverse drug reaction Hepatotoxicity abstract Drug toxicity is a leading cause of attrition of candidate drugs during drug development as well as of withdrawal of drugs post-licensing due to adverse drug reactions in man. These adverse drug reactions cause a broad range of clinically severe conditions including both highly reproducible and dose dependent toxicities as well as relatively infrequent and idiosyncratic adverse events. The underlying risk factors can be split into two groups: (1) drug-related and (2) patient-related. The drug-related risk factors include metabolic factors that determine the propensity of a molecule to form toxic reactive metabolites (RMs), and the RM and non-RM mediated mechanisms which cause cell and tissue injury. Patient related risk factors may vary markedly between individuals, and encompass genetic and non-genetic processes, e.g. environmental, that influence the disposition of drugs and their metabolites, the nature of the adverse responses elicited and the resulting biological consequences. We describe a new strategy, which builds upon the strategies used currently within numerous phar- maceutical companies to avoid and minimize RM formation during drug discovery, and that is intended to reduce the likelihood that candidate drugs will cause toxicity in the human population. The new strat- egy addresses drug-related safety hazards, but not patient-related risk factors. A common target organ of toxicity is the liver and to decrease the likelihood that candidate drugs will cause liver toxicity (both non- idiosyncratic and idiosyncratic), we propose use of an in vitro Hepatic Liability Panel alongside in vitro methods for the detection of RMs. This will enable design and selection of compounds in discovery that have reduced propensity to cause liver toxicity. In vitro Hepatic Liability is assessed using toxicity assays that quantify: CYP 450 dependent and CYP 450 independent cell toxicity; mitochondrial impairment; and inhibition of the Bile Salt Export Pump. Prior to progression into development, a Hepatotoxicity Hazard Matrix combines data from the Hepatic Liability Panel with the Estimated RM Body Burden. The latter is defined as the level of covalent binding of radiolabelled drug to human hepatocyte proteins in vitro adjusted for the predicted human dose. We exemplify the potential value of this approach by consideration of the thiazolidinedione class of drugs. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Discovery and development of innovative new medicines is essential to address unmet medical need, yet is a high risk activ- ity. The costs of drug discovery and development are substantial and increasing due to the great expense incurred in running large * Corresponding author. Tel.: +46 31 776 25 67; fax: +46 31 776 38 67. E-mail address: richard.thompson@astrazeneca.com (R.A. Thompson). clinical trials to prove efficacy and safety. However, the likelihood of success is low because of the high rate of attrition of candidate drugs throughout all stages of preclinical and clinical development. One of the most important causes of attrition is toxicity [1]. For many compounds, toxicity is evident during preclinical Safety Test- ing in Preclinical Species and results in compound termination prior to clinical progression, or restricted levels of exposure in humans which reduces the likelihood that clinical efficacy can be achieved [2]. However, numerous candidate drugs do not cause toxicity in preclinical species, even though they cause adverse effects in man. 0009-2797/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cbi.2010.11.002