(N)-Methanocarba Adenosine Derivatives as Dual Modulators of P-Glycoprotein and ABCG2 Transporters

Following previous observations that N⁶-elongated (N)-methanocarba adenosine derivatives modulate efflux pump activity associated with multidrug resistance (MDR) in tumors, we synthesized and characterized 34 nucleoside analogues. Effects on ATPase activity of both ABCG2 and P-glycoprotein identified m-substituted N⁶-benzyl derivative 16 (MRS8288) as a dual inhibitor, with IC₅₀ 1.0 and 1.4 μM, respectively. Compound 30 (MRS8431) inhibited ABCG2-ATPase activity with IC₅₀ 160 ± 9 nM, while compound 40 (MRS8432) stimulated it potently with EC₅₀ 7.5 ± 2 nM. Selected (N)-methanocarba nucleosides, notably 16, 30, and 40, inhibited ABCG2-mediated substrate transport, with marginal effects on the activity of P-gp and were not transported by ABCG2. Compound 30, but not 16 or 40, sensitized ABCG2-expressing HEK-293-R5 cells to mitoxantrone. Distinct docking modes of compounds 30 and 40 to ABCG2 predict the structural determinants for the inhibition of ATPase. These results reveal novel rigid, extended nucleoside inhibitors of ABC transporters with varied activities that attenuate MDR in cells.