Unmasking the dynamic interplay between efflux transporters and metabolic enzymes

Int J Pharm. 2004 Jun 11;277(1-2):3-9. doi: 10.1016/j.ijpharm.2002.12.002.


Drug efflux by intestinal P-glycoprotein (P-gp) is known to decrease the bioavailability of many CYP3A4 substrates. We have demonstrated that the interplay between P-gp and CYP3A4 at the apical intestinal membrane can increase the opportunity for drug metabolism by determining bidirectional extraction ratios across CYP3A4-transfected Caco-2 cells for two dual P-gp/CYP3A4 substrates, K77 (an experimental cysteine protease inhibitor) and sirolimus, as well as two negative control, CYP3A4 only substrates, midazolam and felodipine. Studies were carried out under control conditions, with a P-gp inhibitor (GG918) and with a dual inhibitor (cyclosporine). Measurement of intracellular concentration changes is an important component in calculating the extraction ratios. We hypothesize that the inverse orientation of P-gp and CYP3A4 in the liver will result in an opposite interactive effect in that organ. In vivo rat intestinal perfusion studies with K77 and rat liver perfusion studies with tacrolimus under control conditions and with inhibitors of CYP3A4 (troleandomycin), P-gp (GG918) and both CYP3A4/P-gp (cyclosporine) lend support to our hypotheses. These results serve as a template for predicting enzyme-transporter (both absorptive and efflux) interactions in the intestine and the liver.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism
  • ATP-Binding Cassette Transporters / metabolism*
  • Animals
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme System / metabolism*
  • Humans
  • Organ Specificity / physiology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • ATP-Binding Cassette Transporters
  • Cytochrome P-450 Enzyme System
  • CYP3A protein, human
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human