Transporter-enzyme interactions: implications for predicting drug-drug interactions from in vitro data

Area of Science:

• Pharmacology
• Drug Metabolism
• Drug Interactions

Background:

• Predicting in vivo drug-drug interactions from in vitro studies is vital for drug development.
• The interplay between metabolic enzymes and transporters can affect in vivo-in vitro relationships.
• Intestinal P-glycoprotein (P-gp) efflux reduces bioavailability of CYP3A4 substrates.

Purpose of the Study:

• To investigate the interplay between P-gp and CYP3A4 at the intestinal membrane.
• To determine the impact of enzyme-transporter interactions on drug metabolism and bioavailability.
• To explore the inverse interactive effect of P-gp and CYP3A4 in the liver.

Main Methods:

• Utilized CYP3A4 transfected Caco-2 cells to determine bidirectional extraction ratios for dual P-gp/CYP3A4 substrates (K77, sirolimus) and CYP3A4-only substrates (midazolam, felodipine).
• Conducted studies under control conditions, with a P-gp inhibitor (GG918), and with a dual inhibitor (cyclosporine).
• Performed in vivo rat intestinal and liver perfusion studies with K77 and tacrolimus, using inhibitors of CYP3A4, P-gp, or both.

Main Results:

• The interplay between P-gp and CYP3A4 at the apical intestinal membrane increased drug metabolism opportunity.
• Bidirectional extraction ratios were determined for dual and single substrates.
• In vivo rat studies supported the hypothesis of an opposite interactive effect in the liver due to inverse P-gp and CYP3A4 orientation.

Conclusions:

• Demonstrated that enzyme-transporter interactions significantly influence drug metabolism and bioavailability.
• Results provide a template for predicting enzyme-transporter interactions in the intestine and liver.
• Highlights the importance of considering both enzymes and transporters for accurate in vivo drug interaction predictions.