{"id":2918,"date":"2026-08-22T15:50:14","date_gmt":"2026-08-22T14:50:14","guid":{"rendered":"https:\/\/seamlessbio.de\/?page_id=2918"},"modified":"2026-08-23T00:53:45","modified_gmt":"2026-08-22T23:53:45","slug":"what-is-p-glycoprotein-pgp","status":"publish","type":"page","link":"https:\/\/seamlessbio.de\/de\/what-is-p-glycoprotein-pgp\/","title":{"rendered":"What is P-glycoprotein (P-gp \/ MDR1)?"},"content":{"rendered":"\t\t
\n\t\t\t\t
\n \t\t
\n\t\t\t\t\t\n\n
\n

Quick Definition<\/p>\n

What is P-glycoprotein (P-gp \/ MDR1 \/ ABCB1)?:<\/strong> P-glycoprotein (P-gp), also known as MDR1 or ABCB1, is an ABC efflux transporter that pumps a wide range of drugs and xenobiotics out of cells. It is expressed in the intestinal epithelium, blood-brain barrier, liver (canalicular membrane), kidneys, and tumour cells. P-gp is one of the two most clinically important drug transporters \u2014 mandatory testing for all new drug candidates under FDA, EMA, and ICH M12 guidance.<\/p>\n<\/div>\n\n

Why does P-gp matter for drug development?<\/h2>\n

P-gp at the intestinal epithelium acts as a gatekeeper \u2014 pumping orally administered drugs back into the gut lumen, reducing bioavailability. A drug that is a P-gp substrate will have lower and more variable oral bioavailability, especially when co-administered with P-gp inhibitors. At the blood-brain barrier, P-gp limits CNS penetration \u2014 relevant for CNS-targeted drugs (where P-gp substrates fail to reach therapeutic concentrations) and for safety (where non-CNS drugs unexpectedly penetrate the BBB when P-gp is inhibited).<\/p>\n\n

P-gp and multidrug resistance<\/h2>\n

P-gp was originally identified as the mechanism of multidrug resistance in cancer cells \u2014 tumour cells overexpressing P-gp pump out chemotherapy agents (vincristine, doxorubicin, paclitaxel), rendering them resistant to treatment. This is still a major challenge in oncology and drives development of P-gp inhibitors as chemosensitisers.<\/p>\n\n

P-gp inhibition testing<\/h2>\n

For inhibitor IC50 determination \u2014 particularly for high-permeability compounds where cell-based efflux ratios are compressed \u2014 the vesicular transport assay with inside-out P-gp membrane vesicles provides permeability-independent IC50 values suitable for regulatory DDI cutoff calculations.<\/p>\n\n

Key Facts<\/h2>\n