Purpose: The purpose of this study was to determine the dynamic parameter (EC50) of flavonoids apigenin, biochanin A, chrysin, genistein, kaempferol, hesperetin, naringenin, and silymarin for breast cancer resistance protein (BCRP) inhibition when used alone, and to evaluate their potential interactions (additive, synergistic, or antagonistic) with regards to BCRP inhibition when used in multiple-flavonoid combinations.
Methods: The effects of flavonoids on BCRP-mediated transport were examined by evaluating their effects on mitoxantrone accumulation and cytotoxicity in MCF-7 MX100 cells overexpressing BCRP. The EC50 values of these flavonoids for increasing mitoxantrone accumulation were estimated using a Hill equation. The potential interactions among multiple flavonoids with regard to BCRP inhibition were assessed by isobologram and Berenbaum's interaction index methods.
Results: The EC50 values of these flavonoids for increasing mitoxantrone accumulation ranged from 0.39+/-0.13 microM to 33.7+/-2.78 microM. Quantitative analysis of the combined effects of multiple flavonoids on mitoxantrone accumulation indicated that these flavonoids act additively in inhibiting BCRP when given as 2-, 3-, 5-, or 8-flavonoid combinations with equimolar concentrations of all constituents. The results of the mitoxantrone cytotoxicity studies were consistent with these findings.
Conclusions: The additive effects of multiple flavonoids for BCRP inhibition suggests that prediction of BCRP-mediated food (herbal product)-drug interactions should also take into consideration the presence of multiple flavonoids and provides a rationale for using "flavonoid cocktails" as a potential approach for multidrug resistance reversal in cancer treatment.