Interaction of A₃ adenosine receptor ligands with the human multidrug transporter ABCG2

Various adenosine receptor nucleoside-like ligands were found to modulate ATP hydrolysis by the multidrug transporter ABCG2. Both ribose-containing and rigidified (N)-methanocarba nucleosides (C2-, N⁶- and 5'-modified), as well as adenines (C2-, N⁶-, and deaza modified), were included. 57 compounds out of 63 tested either stimulated (50) or inhibited (7) basal ATPase activity. Structure-activity analysis showed a separation of adenosine receptor and ABCG2 activities. The 7-deaza modification had favorable effects in both (N)-methanocarba nucleosides and adenines. Adenine 37c (MRS7608) and (N)-methanocarba 7-deaza-5'-ethyl ester 60 (MRS7343) were found to be potent stimulators of ABCG2 ATPase activity with EC₅₀ values of 13.2 ± 1.7 and 13.2 ± 2.2 nM, respectively. Both had affinity in the micromolar range for A₃ adenosine receptor and lacked the 5'-amide agonist-enabling group (37c was reported as a weak A₃ antagonist, K_i 6.82 microM). Compound 60 significantly inhibited ABCG2 substrate transport (IC₅₀ 0.44 microM). Docking simulations predicted the interaction of 60 with 21 residues in the drug-binding pocket of ABCG2.