(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.