A comparison of relative abundance, activity factor and inhibitory monoclonal antibody approaches in the characterization of human CYP enzymology.

Aims: The objective of this study was to evaluate the potential uses of relative abundance, relative activity approaches and inhibitory monoclonal antibodies (mAbs) in the characterization of CYP enzymology in early drug discovery.

Methods: Intrinsic clearance estimates for the oxidation of ethoxyresorufin (a selective probe of CYP1A2 activity), tolbutamide (CYP2C9), S-mephenytoin (CYPC19), dextromethorphan (CYP2D6) and testosterone (CYP3A4) were used to determine relative activity factors (RAFs). CLint values were determined for the metabolism of 14 drugs in human liver microsomes (HLM) and for these major CYPs. The relative contribution of each individual CYP to the oxidation of each drug was then assessed using relative abundance and activity techniques in addition to inhibitory mAbs.

Results: Relative abundance and activity methods as well as inhibitory mAbs qualitatively assigned the same CYP isoform as predominantly responsible for the clearance of each drug by HLM. Metabolism catalysed by CYP1A2, 2C9, 2D6 and 3A4 was also predicted to be quantitatively similar using both abundance and activity techniques. However, the relative contribution of the polymorphic CYP2C19 appeared to be over-estimated approximately two-fold using recombinant CYP compared with that from the HLM and mAb approach.

Conclusions: All three methods investigated in this study appear suitable for use in the characterization of the CYP metabolism of new chemical entities produced during early drug discovery.