C-isoprenylation of flavonoids enhances binding affinity toward P-glycoprotein and modulation of cancer cell chemoresistance

Previous studies have shown that flavones bind to P-glycoprotein (Pgp) with higher affinity than isoflavones, flavanones, and glycosylated derivatives . In the present work, a series of C- or O-substituted hydrophobic derivati ves of chrysin were synthesized to further investigate structural requireme nts of the A ring toward Pgp modulation. Increasing hydrophobicity at eithe r position 6, 8, or 7 increased the affinity of in vitro binding to a purif ied cytosolic domain of Pgp, but only benzyl and 3,3-dimethylallyl C-substi tution produced a high maximal quenching of the protein intrinsic fluoresce nce. Inhibition of membrane Pgp within leukemic cells, characterized by int racellular drug accumulation, was specifically produced by isoprenylated de rivatives, with 8-(3,3-dimethylallyl)chrysin being even more efficient than the commonly used cyclosporin A.