title: Subtle changes in endochin-like quinolone structure alter the site of inhibition within the cytochrome bc1 complex of Plasmodium falciparum.
abstract: The cytochrome bc1 complex (cyt bc1) is the third component of the mitochondrial electron transport chain and is the target of several potent antimalarial compounds, including the naphthoquinone atovaquone (ATV) and the 4(1H)-quinolone ELQ-300. Mechanistically, cyt bc1 facilitates the transfer of electrons from ubiquinol to cytochrome c and contains both oxidative (Qo) and reductive (Qi) catalytic sites that are amenable to small-molecule inhibition. Although many antimalarial compounds, including ATV, effectively target the Qo site, it has been challenging to design selective Qi site inhibitors with the ability to circumvent clinical ATV resistance, and little is known about how chemical structure contributes to site selectivity within cyt bc1. Here, we used the proposed Qi site inhibitor ELQ-300 to generate a drug-resistant Plasmodium falciparum clone containing an I22L mutation at the Qi region of cyt b. Using this D1 clone and the Y268S Qo mutant strain, P. falciparum Tm90-C2B, we created a structure-activity map of Qi versus Qo site selectivity for a series of endochin-like 4(1H)-quinolones (ELQs). We found that Qi site inhibition was associated with compounds containing 6-position halogens or aryl 3-position side chains, while Qo site inhibition was favored by 5,7-dihalogen groups or 7-position substituents. In addition to identifying ELQ-300 as a preferential Qi site inhibitor, our data suggest that the 4(1H)-quinolone scaffold is compatible with binding to either site of cyt bc1 and that minor chemical changes can influence Qo or Qi site inhibition by the ELQs.
authors.affiliation: Departments of Physiology and Pharmacology, Molecular Microbiology, and Immunology, Oregon Health & Science University, Portland, Oregon, USA stickles@ohsu.edu riscoem@ohsu.edu.
authors.forename: Allison M
authors.identifier: http://orcid.org/0000-0002-5006-3611
authors.initials: AM
authors.lastname: Stickles
authors.affiliation: Department of Microbiology and Immunology, Columbia University Medical Center, New York, New York, USA.
authors.forename: Mariana Justino
authors.initials: MJ
authors.lastname: de Almeida
authors.affiliation: Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Morrisey
authors.affiliation: VA Medical Center, Portland, Oregon, USA.
authors.forename: Kayla A
authors.initials: KA
authors.lastname: Sheridan
authors.affiliation: VA Medical Center, Portland, Oregon, USA.
authors.forename: Isaac P
authors.initials: IP
authors.lastname: Forquer
authors.affiliation: VA Medical Center, Portland, Oregon, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Nilsen
authors.affiliation: VA Medical Center, Portland, Oregon, USA.
authors.forename: Rolf W
authors.initials: RW
authors.lastname: Winter
authors.affiliation: Medicines for Malaria Venture, Geneva, Switzerland.
authors.forename: Jeremy N
authors.initials: JN
authors.lastname: Burrows
authors.affiliation: Department of Microbiology and Immunology, Columbia University Medical Center, New York, New York, USA Division of Infectious Diseases, Department of Medicine, Columbia University Medical Center, New York, New York, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Fidock
authors.affiliation: Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
authors.forename: Akhil B
authors.initials: AB
authors.lastname: Vaidya
authors.affiliation: Departments of Physiology and Pharmacology, Molecular Microbiology, and Immunology, Oregon Health & Science University, Portland, Oregon, USA VA Medical Center, Portland, Oregon, USA stickles@ohsu.edu riscoem@ohsu.edu.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Riscoe
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D045303:Cytochromes b / Q000235:genetics / Q000378:metabolism; D004351:Drug Resistance; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors* / Q000235:genetics; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D015363:Quinolones / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: C000601913:6-Chloro-7-methoxy-2-methyl-3-(4-(4-(trifluoromethoxy)phenoxy)phenyl)quinolin-4(1H)-one; D000962:Antimalarials; D015363:Quinolones; D045303:Cytochromes b; D014450:Electron Transport Complex III