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

Following previous observations that <i>N</i>⁶-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 <i>N</i>⁶-benzyl derivative <b>16</b> (MRS8288) as a dual inhibitor, with IC₅₀ 1.0 and 1.4 μM, respectively. Compound <b>30</b> (MRS8431) inhibited ABCG2-ATPase activity with IC₅₀ 160 ± 9 nM, while compound <b>40</b> (MRS8432) stimulated it potently with EC₅₀ 7.5 ± 2 nM. Selected (N)-methanocarba nucleosides, notably <b>16</b>, <b>30</b>, and <b>40</b>, inhibited ABCG2-mediated substrate transport, with marginal effects on the activity of P-gp and were not transported by ABCG2. Compound <b>30</b>, but not <b>16</b> or <b>40</b>, sensitized ABCG2-expressing HEK-293-R5 cells to mitoxantrone. Distinct docking modes of compounds <b>30</b> and <b>40</b> 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.