title: Stereoselective inhibition of serotonin transporters by antimalarial compounds.
abstract: The serotonin (5-HT) transporter (SERT) is an integral membrane protein that functions to reuptake 5-HT released into the synapse following neurotransmission. This role serves an important regulatory mechanism in neuronal homeostasis. Previous studies have demonstrated that several clinically important antimalarial compounds inhibit serotonin (5-hydroxytryptamine, 5-HT) reuptake. In this study, we examined the details of antimalarial inhibition of 5-HT transport in both Drosophila (dSERT) and human SERT (hSERT) using electrophysiologic, biochemical and computational approaches. We found that the cinchona alkaloids quinidine and cinchonine, which have identical stereochemistry about carbons 8 and 9, exhibited the greatest inhibition of dSERT and hSERT transporter function whereas quinine and cinchonidine, enantiomers of quinidine and cinchonine, respectively, were weaker inhibitors of dSERT and hSERT. Furthermore, SERT mutations known to decrease the binding affinity of many antidepressants affected the cinchona alkaloids in a stereo-specific manner where the similar inhibitory profiles for quinine and cinchonidine (8S,9R) were distinct from quinidine and cinchonine (8R,9S). Small molecule docking studies with hSERT homology models predict that quinine and cinchonidine bind to the central 5-HT binding site (S1) whereas quinidine and cinchonine bind to the S2 site. Taken together, the data presented here support binding of cinchona alkaloids to two different sites on SERT defined by their stereochemistry which implies separate modes of transporter inhibition. Notably, the most potent antimalarial inhibitors of SERT appear to preferentially bind to the S2 site. Our findings provide important insight related to how this class of drugs can modulate the serotonergic system as well as identify compounds that may discriminate between the S1 and S2 binding sites and serve as lead compounds for novel SERT inhibitors.
authors.affiliation: Department of Biology, Augsburg College, 2211 Riverside Ave S, Minneapolis, MN 55454, United States. Electronic address: beckmanm@augsburg.edu.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Beckman
authors.affiliation: Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, 501 North Columbia Road, Room 1700, Grand Forks, ND 58203, United States.
authors.forename: Akula Bala
authors.initials: AB
authors.lastname: Pramod
authors.affiliation: Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, 501 North Columbia Road, Room 1700, Grand Forks, ND 58203, United States.
authors.forename: Danielle
authors.initials: D
authors.lastname: Perley
authors.affiliation: Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, 501 North Columbia Road, Room 1700, Grand Forks, ND 58203, United States. Electronic address: keith.henry@med.und.edu.
authors.forename: L Keith
authors.initials: LK
authors.lastname: Henry
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D002930:Cinchona Alkaloids / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D018075:RNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D012702:Serotonin Antagonists / Q000494:pharmacology*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000187:drug effects*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D000962:Antimalarials; D002930:Cinchona Alkaloids; D018075:RNA, Complementary; D012702:Serotonin Antagonists; D050486:Serotonin Plasma Membrane Transport Proteins
keywords: Antagonist; Antimalarial agents; Serotonin; Serotonin transporter; Structure–function