title: Benzo[b]quinolizinium Derivatives Have a Strong Antimalarial Activity and Inhibit Indoleamine Dioxygenase.
abstract: The heme-containing enzymes indoleamine 2,3-dioxygenase-1 (IDO-1) and IDO-2 catalyze the conversion of the essential amino acid tryptophan into kynurenine. Metabolites of the kynurenine pathway and IDO itself are involved in immunity and the pathology of several diseases, having either immunoregulatory or antimicrobial effects. IDO-1 plays a central role in the pathogenesis of cerebral malaria, which is the most severe and often fatal neurological complication of infection with Plasmodium falciparum. Mouse models are usually used to study the underlying pathophysiology. In this study, we screened a natural compound library against mouse IDO-1 and identified 8-aminobenzo[b]quinolizinium (compound 2c) to be an inhibitor of IDO-1 with potency at nanomolar concentrations (50% inhibitory concentration, 164 nM). Twenty-one structurally modified derivatives of compound 2c were synthesized for structure-activity relationship analyses. The compounds were found to be selective for IDO-1 over IDO-2. We therefore compared the roles of prominent amino acids in the catalytic mechanisms of the two isoenzymes via homology modeling, site-directed mutagenesis, and kinetic analyses. Notably, methionine 385 of IDO-2 was identified to interfere with the entrance of l-tryptophan to the active site of the enzyme, which explains the selectivity of the inhibitors. Most interestingly, several benzo[b]quinolizinium derivatives (6 compounds with 50% effective concentration values between 2.1 and 6.7 nM) were found to be highly effective against P. falciparum 3D7 blood stages in cell culture with a mechanism independent of IDO-1 inhibition. We believe that the class of compounds presented here has unique characteristics; it combines the inhibition of mammalian IDO-1 with strong antiparasitic activity, two features that offer potential for drug development.
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany.
authors.forename: Esther
authors.initials: E
authors.lastname: Jortzik
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Zocher
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Isernhagen
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany.
authors.forename: Boniface M
authors.initials: BM
authors.lastname: Mailu
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rahlfs
authors.affiliation: Department of Woman's and Child's Health, University of Padova, Padua, Italy.
authors.forename: Giampietro
authors.initials: G
authors.lastname: Viola
authors.affiliation: Swiss Tropical and Public Health Institute and University of Basel, Basel, Switzerland.
authors.forename: Sergio
authors.initials: S
authors.lastname: Wittlin
authors.affiliation: Molecular Immunopathology Unit, University of Sydney, Sydney, NSW, Australia.
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Hunt
authors.affiliation: Department of Chemistry and Biology, University of Siegen, Siegen, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Ihmels
authors.affiliation: Biochemistry and Molecular Biology, Justus Liebig University, Giessen, Germany katja.becker@uni-giessen.de.
authors.forename: Katja
authors.initials: K
authors.lastname: Becker
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004912:Erythrocytes / Q000187:drug effects / Q000469:parasitology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007737:Kynurenine / Q000378:metabolism; D008288:Malaria / Q000188:drug therapy* / Q000469:parasitology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010962:Plasmodium berghei / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D010963:Plasmodium falciparum / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D011807:Quinolizines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000962:Antimalarials; C583637:IDO1 protein, mouse; C586429:IDO2 protein, mouse; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D011807:Quinolizines; D011994:Recombinant Proteins; D007737:Kynurenine; D014364:Tryptophan