Exploring flavonoids as potent SLC46A3 inhibitors: Insights from the structural characteristics of flavonoid-SLC46A3 interactions.

SLC46A3, a transporter for lysosomal steroid conjugates and bile acids, plays a pivotal role in the pharmacological effects of noncleavable antibody-drug conjugates using maytansine as a payload. SLC46A3 may exert negative effects on various phenomena, including copper homeostasis, mitochondrial function in the liver, and the uptake of lipid-based nanoparticles (NPs) in tumor cells. Consequently, inhibiting SLC46A3 may be a promising strategy for treating hepatic disease or enhancing lipid NP delivery to tumor cells, although the underlying mechanisms remain unknown. This study investigates flavonoids, the largest subgroup of polyphenols characterized by a simple C6-C3-C6 structure, as potential SLC46A3 inhibitors and provides insights into the structural requirements for flavonoid-SLC46A3 interactions. Screening revealed several flavonoids, including dihydrochalcones, flavonols, isoflavones, flavanones, and flavones, as effective inhibitors of 5-carboxyfluorescein (5-CF) uptake in MDCKII (Mardin-Darby canine kidney type II) cells stably expressing a mutant SLC46A3 localized to the plasma membrane. Notably, apigenin and luteolin exhibited marked 5-CF uptake inhibition, with IC₅₀ values of 10.8 and 8.7 µM, respectively. Additionally, 4',7-dihydroxyflavone significantly inhibited 5-CF uptake, exhibiting an IC₅₀ value of 9.3 µM, whereas acacetin and genkwanin possessing methoxy group substitutions for the hydroxy group at the 4'- or 7-position of apigenin, respectively, did not affect the uptake. Luteolin's inhibition mechanism was found to be of a mixed type involving increased K_m and decreased V_max. These findings emphasize the importance of hydroxy groups at 4'- and 7-positions in flavone-SLC46A3 interactions.