Evaluation of mRNA and Enzyme Activity

Recent guidance from the FDA and EMA advocates the use of human hepatocytes as the test system for evaluating cytochrome P450 induction potential. Both agencies indicate that use of hepatocytes that have been prequalified for response to known clinical inducers and non-inducers are acceptable and/or preferred for certain model applications. In addition, the use of mRNA alone is suggested as the necessary endpoint to evaluate induction response (except in cases where enzyme stabilization is suspected as a mechanism). However, the applicability of using prequalified hepatocytes as the test system, and the use of mRNA alone as a response endpoint, has not been widely demonstrated. To this end, we have examined the induction response from a set of 20 compounds, including established clinical inducers and non-inducers of CYP3A4/5, in cryopreserved hepatocytes from three donors. The endpoint examined was CYP3A4 mRNA, typically over 8 concentration points in an effort to enable calculation of EC50 and Emax. Results were used to determine relative induction scores (RIS) and R3 values that may classify a drug candidate as a potential clinical inducer. The results and merits of these and other parameters for evaluating the induction potential of drug candidates will be discussed.

Mar 13 2013

47 mins