Table 9.

P-gp modulation activities of quercetin derivatives 88–91 in MES-SA/Dx5 cell line [118].

Compound	R1	R2	IC50 (µM) 1
88		H	0.41
89		H	0.14
90			0.78
91			0.71

¹ IC₅₀—Defined as the concentration of derivative needed to produce 50% P-gp protein function inhibition. Lower IC₅₀ values mean stronger P-gp protein inhibitors.