BPS2026 – Structures of P-glycoprotein bound to cis- and trans-flupentixol reveal the mechanism of modulation of inhibition

Human ABCB1 (P-glycoprotein, P-gp) is an ABC transporter known to function at various physiological barriers, protecting vital organs from a wide variety of toxic xenobiotics. Overexpression of P-gp in cancer cells can lead to multidrug resistance (MDR) in cancer patients undergoing chemotherapy. The hallmark of P-gp function is its substrate polyspecificity, capable of recognizing and transporting structurally diverse compounds ranging in size from ∼200 to 4,000 Da. Effective inhibition of P-gp function in cancer has been an area of intensive research. Allosteric modulators are a class of P-gp inhibitors, such as the antipsychotic drug cis-(Z)-flupentixol, that were shown biochemically to be able to regulate substrate binding affinity, whereas its geometric isomer trans-(E)-flupentixol lacks this ability. The structural basis of these phenomena remains elusive. 1 Using cryo-EM, we determined the structures of murine ABCB1 (mP-gp) in complex with either cis-(Z)-flupentixol or trans-(E)-flupentixol, in the presence or absence of the substrate prazosin. The structure of mP-gp with bound cis-(Z)-flupentixol reveals a single bound drug. Similarly, trans-(E)-flupentixol occupies a site that is different from that of cis-(Z)-flupentixol binding site. Most interestingly, the structure of mP-gp in the presence of both cis-(Z)-flupentixol and prazosin revealed additional density adjacent to flupentixol, which can be modeled as prazosin. Importantly, there are multiple points of interactions between the two ligands and considerable conformational changes in the binding environment, providing a mechanistic explanation for the stimulated prazosin labeling in the presence of cis-(Z)-flupentixol. These findings are consistent with P-gp having a flexible substrate-binding surface and offer structural insights into cooperative binding of P-gp substrates and modulators. 1 Ford et al., 1990, Cancer Res, 1748; Dey et al., 1997, PNAS , 10594; Dey et al., 1999 Biochem , 6630.