Knockout Transporter Cell Lines to Assess Substrate Potential Towards Efflux Transporters.

Area of Science:

• Pharmacology
• Molecular Biology
• Drug Metabolism

Background:

• Efflux transporters, including P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance transporter 2 (MRP2), significantly influence drug absorption, distribution, and excretion.
• Current bidirectional cell assays for evaluating drug interactions with these transporters are limited by the lack of selective substrates/inhibitors and the co-expression of multiple transporters in cell lines.

Purpose of the Study:

• To evaluate an in vitro efflux cell assay using knockout (KO) cell lines to specifically assess the roles of P-gp, BCRP, and MRP2 in drug transport.
• To determine the efflux ratios (ER) of known substrates for P-gp, BCRP, MRP2, and mixed substrates in wild-type and KO cell lines.

Main Methods:

• Utilized wild-type C2BBe1 cells and corresponding KO cell lines lacking P-gp, BCRP, or MRP2 expression.
• Determined efflux ratios (ER) for model substrates: digoxin and paclitaxel (P-gp), prazosin and rosuvastatin (BCRP), etoposide and olmesartan (MRP2), and methotrexate and mitoxantrone (mixed substrates).

Main Results:

• ER for P-gp substrates (digoxin, paclitaxel) decreased to <2 in P-gp KO cells.
• ER for BCRP substrates (prazosin, rosuvastatin) decreased to <3 and <2, respectively, in BCRP KO cells.
• ER for MRP2 substrates (etoposide, olmesartan) decreased to <2 in MRP2 KO cells. Mixed substrate ERs also decreased in single- and double-KO cells.

Conclusions:

• Knockout cell lines provide a more accurate method for interpreting complex drug-transporter interactions, reducing reliance on non-selective inhibitors or substrates.
• These KO models are valuable for assessing drug affinities to specific efflux transporters, particularly for drugs interacting with multiple transporter systems.