Modulation of\nABCG2 Transporter Activity by Ko143\nDerivatives

ABCG2 is a multidrug transporter that protects tissues\nfrom xenobiotics,\naffects drug pharmacokinetics, and contributes to multidrug resistance\nof cancer cells. Here, we present tetracyclic fumitremorgin C analog\nKo143 derivatives, evaluate their <i>in vitro</i> modulation\nof purified ABCG2, and report four high-resolution cryo-EM structures\nand computational analyses to elucidate their interactions with ABCG2.\nWe found that Ko143 derivatives that are based on a ring-opened scaffold\nno longer inhibit ABCG2-mediated transport activity. In contrast,\nclosed-ring, tetracyclic analogs were highly potent inhibitors. Strikingly,\nthe least potent of these compounds, MZ82, bound deeper into the central\nABCG2 cavity than the other inhibitors and it led to partial closure\nof the transmembrane domains and increased flexibility of the nucleotide-binding\ndomains. Minor structural modifications can thus convert a potent\ninhibitor into a compound that induces conformational changes in ABCG2\nsimilar to those observed during binding of a substrate. Molecular\ndynamics simulations and free energy binding calculations further\nsupported the correlation between reduced potency and distinct binding\npose of the compounds. We introduce the highly potent inhibitor AZ99\nthat may exhibit improved <i>in vivo</i> stability.