Cryo-EM structures reveal distinct mechanisms of inhibition of the human multidrug transporter ABCB1

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 42; pp. 26245 - 26253
• Main Authors: Nosol, Kamil, Romane, Ksenija, Irobalieva, Rossitza N., Alam, Amer, Kowal, Julia, Fujita, Naoya, Locher, Kaspar P.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 20.10.2020
• Subjects: Acridines - metabolism; Antibodies, Monoclonal - metabolism; Antineoplastic Agents, Phytogenic - metabolism; ATP Binding Cassette Transporter, Subfamily B - antagonists & inhibitors; ATP Binding Cassette Transporter, Subfamily B - chemistry; ATP Binding Cassette Transporter, Subfamily B - metabolism; Biological Sciences; Biophysics and Computational Biology; Cell Proliferation; Cryoelectron Microscopy - methods; Drug Resistance, Multiple; Extrusion; HEK293 Cells; Humans; Inhibitors; Models, Molecular; Monoclonal antibodies; Multidrug resistance; Phenylalanine; Protein Binding; Protein Conformation; Substrate inhibition; Tetrahydroisoquinolines - metabolism; Therapeutic applications; Vincristine; Vincristine - metabolism; P-glycoprotein; ABCB1; ABC transporter; single-particle cryoelectron microscopy; structure
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.2010264117

ABCB1 detoxifies cells by exporting diverse xenobiotic compounds, thereby limiting drug disposition and contributing to multidrug resistance in cancer cells. Multiple small-molecule inhibitors and inhibitory antibodies have been developed for therapeutic applications, but the structural basis of their activity is insufficiently understood. We determined cryo-EM structures of nanodisc-reconstituted, human ABCB1 in complex with the Fab fragment of the inhibitory, monoclonal antibody MRK16 and bound to a substrate (the antitumor drug vincristine) or to the potent inhibitors elacridar, tariquidar, or zosuquidar. We found that inhibitors bound in pairs, with one molecule lodged in the central drug-binding pocket and a second extending into a phenylalanine-rich cavity that we termed the “access tunnel.” This finding explains how inhibitors can act as substrates at low concentration, but interfere with the early steps of the peristaltic extrusion mechanism at higher concentration. Our structural data will also help the development of more potent and selective ABCB1 inhibitors.