Hop‐derived prenylflavonoids are substrates and inhibitors of the efflux transporter breast cancer resistance protein (BCRP/ABCG2)

SCOPE: Hops (Humulus lupulus L.) produce unique prenylflavonoids that exhibit interesting bioactivities. This study investigates the interactions between selected prenylflavonoids and breast cancer resistance protein (BCRP/ABCG2), an efflux transporter important for xenobiotic bioavailability and multidrug resistance (MDR). METHODS AND RESULTS: ABCG2‐inhibitory activity of xanthohumol (XN), isoxanthohumol (IX), 6‐prenylnaringenin (6‐PN), 8‐prenylnaringenin (8‐PN), and 6,8‐diprenylnarigenin (6,8‐diPN) was evaluated using mitoxantrone accumulation and vesicular transport assays. XN, IX, and 8‐PN were tested for a substrate‐type relationship with ABCG2 using ATPase and bidirectional transport assays. The prenylflavonoids exhibited significant ABCG2‐inhibitory activities in mitoxantrone accumulation and vesicular transport assays. In the ATPase assay, XN, IX, and 8‐PN inhibited baseline and sulfasalazine‐stimulated ATPase activities with IC₅₀of 2.16–27.0 μM. IX and 8‐PNalso displayed bell‐shaped activation curves in Ko143‐suppressed membranes, indicating a substrate‐type relationship. For IX, efflux ratios of 1.25 ± 0.21 and 9.18 ± 0.56 were observed in wild type and ABCG2‐overexpressing MDCKII cell monolayers, respectively. The latter was reduced to 1.25 ± 0.15 in the presence of the ABCG2‐specific inhibitor Ko143, demonstrating an ABCG2‐mediated efflux of IX. Additionally, evidence was shown for the involvement of ABCG2 in the efflux of 8‐PN and/or its sulfate conjugate. CONCLUSION: Prenylflavonoids are potent inhibitors of ABCG2 and therefore implicated in ABCG2‐mediated food/herb‐drug interactions and MDR. ABCG2‐mediated efflux of prenylflavonoids may represent one mechanism that regulates prenylflavonoid bioavailability.