Polyoxovanadates as new P-glycoprotein inhibitors: insights into the mechanism of inhibition.

A promising strategy to overcome multidrug resistance is the use of inhibitors of ABC drug transporters. For this reason, we evaluated the polyoxovanadates (POVs) [V10 O28 ]6- (V10 ), [H6 V14 O38 (PO4 )]5- (V14 ), [V15 O36 Cl]6- (V15 ) and [V18 O42 I]7- (V18 ) as inhibitors of three major multidrug resistance-linked ABC transporters: P-glycoprotein (P-gp), ABCG2 and MRP1. All of the POVs selectively inhibited P-gp. V10 and V18 were the two most promising compounds, with IC50 values of transport inhibition of 25.4 and 22.7 µm, respectively. Both compounds inhibited P-gp ATPase activity, with the same IC50 value of 1.26 µm. V10 and V18 triggered different conformational changes in the P-gp protein with time-dependent inhibition, which was confirmed using the synthesized salt of V10 with rhodamine B, RhoB-V10 . The hydrophilic nature of POVs supports the hypothesis that these compounds target an unusual ligand-binding site, opening new possibilities in the development of potent modulators of ABC transporters.