Discovery of Pyxinol Amide Derivatives Bearing Amino Acid Residues as Nonsubstrate Allosteric Inhibitors of P-Glycoprotein-Mediated Multidrug Resistance

Nonsubstrateallosteric inhibitors of P-glycoprotein (Pgp), whichare considered promising modulators for overcoming multidrug resistance(MDR), are relatively unknown. Herein, we designed and synthesizedamino acids bearing amide derivatives of pyxinol, the main ginsenosidemetabolite produced by the human liver, and examined their MDR reversalabilities. A potential nonsubstrate inhibitor (7a) wasidentified to undergo high-affinity binding to the putative allostericsite of Pgp at the nucleotide-binding domains. Subsequent assays confirmedthat 7a (25 mu M) was able to suppress both basaland verapamil-stimulated Pgp-ATPase activities (inhibition rates of87 and 60%, respectively) and could not be pumped out by Pgp, indicatingthat it was a rare nonsubstrate allosteric inhibitor. Moreover, 7a interfered with Pgp-mediated Rhodamine123 efflux whileexhibiting high selectivity for Pgp. Notably, 7a alsomarkedly enhanced the therapeutic efficacy of paclitaxel, with a tumorinhibition ratio of 58.1%, when used to treat nude mice bearing KBVxenograft tumors.

Automated summary

In this study, nonsubstrate allosteric inhibitors of P-glycoprotein (Pgp) were designed and synthesized. A potential nonsubstrate inhibitor (7a) was found to bind to the allosteric site of Pgp with high affinity and inhibit its ATPase activity. It also interfered with Pgp-mediated efflux and enhanced the therapeutic efficacy of paclitaxel in vivo.