Interstrain differences of in vitro metabolic stability and impact on early drug discovery

With the extensive use of different strains of mice and rats in in vivo efficacy models, lack of relevant metabolic clearance data among strains has been a concern. Metabolic clearance is an important parameter impacting drug discovery, and it is often used as a compound selection filter. Metabolically stable compounds are often preferred, and will have a better chance to achieve the desired exposure in vivo. The present study examined strain differences in mouse and rat, using 96 compounds which spanned a wide range of intrinsic clearances. The in vitro clearances were determined using liver microsomes from commonly used strains of mouse (BALB/c, C57BL/6J, and CD-1) and of rat (Sprague-Dawley, Fischer, and Wistar Han). There were few discrepancies in the interpretation of the in vitro intrinsic clearance results within species for the 96 compounds tested in mouse and rat liver microsomes. This data gives us confidence that the phase I hepatic clearance can be determined using only one strain of mouse or rat liver microsomes.