Abstract

Translational and ADME Sciences Leadership Group (TALG) Induction Working Group (IWG) presents an analysis on the time-course for cytochrome P450 induction in primary human hepatocytes. Induction of CYP1A2, CYP2B6, and CYP3A4 was evaluated by seven IWG laboratories following incubation with prototypical inducers (omeprazole, phenobarbital, rifampicin, and efavirenz) for 6 to 72 hours. The effect of incubation duration and model-fitting approaches on induction parameters (E_max and EC₅₀) and drug-drug interaction (DDI) risk assessment was determined. Despite variability in induction response across hepatocyte donors, the following recommendations are proposed: i) 48 hours should be the primary time point for in vitro assessment of induction, based on mRNA level or activity, with no further benefit from 72 hours, ii) when using mRNA, 24 hour incubations provide reliable assessment of induction and DDI risk, iii) if validated using prototypical inducers (>10-fold induction), 12-hour incubations may provide an estimate of induction potential including characterization as negative if < 2-fold induction of mRNA and no concentration-dependence, iv) atypical dose-response ('bell-shaped') curves can be addressed by removing points outside an established confidence interval and %CV, v) when maximum fold induction is well-defined, the choice of non-linear regression model has limited impact on estimated induction parameters, vi) when the maximum-fold induction is not well-defined, conservative DDI risk assessment can be obtained using sigmoidal-3-parameter fit or constraining logistic 3/4 parameter fits to the maximum observed fold induction, vii) preliminary data suggest initial slope of the fold induction curve can be used to estimate E_max/EC₅₀ and for induction risk assessment.

Significance Statement Regulatory agencies have provided inconsistent guidance on the optimum length of time to evaluate CYP induction in human hepatocytes, with the EMA recommending 72 h and the FDA suggesting 48 to 72 h. The IWG analyzed a large dataset generated by 7 member companies and determined that induction response and drug-drug risk assessment determined after 48 h incubations was representative of 72 h incubations. Additional recommendations are provided on model-fitting techniques for induction parameter estimation and addressing atypical concentration-response curves.