Evidence for the Interaction of A3 Adenosine Receptor Agonists at the Drug-Binding Site(s) of Human P-glycoprotein (ABCB1)

P-glycoprotein (P-gp) is a multidrug transporter that is expressed on the luminal surface of epithelial cells in the kidney, intestine, bile-canalicular membrane in the liver, blood-brain barrier, and adrenal gland. This transporter uses energy of ATP hydrolysis to efflux from cells a variety of structurally dissimilar hydrophobic and amphipathic compounds, including anticancer drugs. In this regard, understanding the interaction with P-gp of drug entities in development is important and highly recommended in current US Food and Drug Administration guidelines. Here we tested the P-gp interaction of some A 3 adenosine receptor agonists that are being developed for the treatment of chronic diseases, including rheumatoid arthritis, psoriasis, chronic pain, and hepatocellular carcinoma. Biochemical assays of the ATPase activity of P-gp and by photolabeling P-gp with its transport substrate [ 125 I]-iodoarylazidoprazosin led to the identification of rigidified (N)-methanocarba nucleosides (i.e., compound 3 as a stimulator and compound 8 as a partial inhibitor of P-gp ATPase activity). Compound 8 significantly inhibited boron-dipyrromethene (BODIPY)-verapamil transport mediated by human P-gp (IC 50 2.4 ± 0.6 µ M); however, the BODIPY-conjugated derivative of 8 (compound 24 ) was not transported by P-gp. In silico docking of compounds 3 and 8 was performed using the recently solved atomic structure of paclitaxel (Taxol)-bound human P-gp. Molecular modeling studies revealed that both compounds 3 and 8 bind in the same region of the drug-binding pocket as Taxol. Thus, this study indicates that nucleoside derivatives can exhibit varied modulatory effects on P-gp activity, depending on structural functionalization. SIGNIFICANCE STATEMENT: Certain A 3 adenosine receptor agonists are being developed for the treatment of chronic diseases. The goal of this study was to test the interaction of these agonists with the human multidrug resistance-linked transporter P-glycoprotein (P-gp). ATPase and photolabeling assays demonstrated that compounds with rigidified (N)-methanocarba nucleosides inhibit the activity of P-gp; however, a fluorescent derivative of one of the compounds was not transported by P-gp. Furthermore, molecular docking studies revealed that the binding site for these compounds overlaps with the site for paclitaxel in the drug-binding pocket. These results suggest that nucleoside derivatives, depending on structural functionalization, can modulate the function of P-gp.