Involvement of everolimus‑induced ABCB1 downregulation in drug‑drug interactions

Everolimus is an oral mammalian target of rapamycin (mTOR) inhibitor used in cancer chemotherapy and transplantation. Due to its therapeutic properties, everolimus has been used long-term in clinical practice. Drug interactions with everolimus during gastrointestinal absorption can alter the oral bioavailability of everolimus and/or concomitant drugs. However, the effects of everolimus on gastrointestinal absorption remain unknown. The present study assessed the impact of continuous exposure to everolimus on expression and function of the ATP-binding cassette (ABC) transporter ABCB1 and ABCG2 using a Caco-2 intestinal cell model. Caco-2 subline, Caco/EV, was established by continuously exposing Caco-2 cells to 1 µM everolimus. Cell viability was evaluated using WST-1 assay. mRNA levels were measured by reverse transcription-quantitative PCR. Transport activity of ABCB1 was evaluated through the cellular accumulation of Rhodamin 123, a substrate for ABCB1. The half-maximal inhibitory concentration (IC₅₀) values for everolimus in Caco-2 and Caco/EV cells were 0.31 and 4.33 µM, respectively, indicating 14-fold resistance in Caco/EV cells. Sensitivity to paclitaxel and 7-ethyl-10-hydroxycamptothecin, which are substrates for ABCB1 and ABCG2, respectively, was enhanced in Caco/EV, but not in Caco-2 cells. The IC₅₀ values of cisplatin were comparable in both cell lines. Furthermore, mRNA expression levels of ABCB1 and ABCG2 were lower in Caco/EV cells than in Caco-2 cells, and the cellular accumulation of Rhodamine 123 was significantly higher in Caco/EV cells. These findings demonstrated that continuous exposure to everolimus suppressed the expression and function of ABCB1 and ABCG2, suggesting potential drug-drug interactions via the suppression of ABCB1 and ABCG2 in the intestinal tract.