title: Antitumor quinol PMX464 is a cytocidal anti-trypanosomal inhibitor targeting trypanothione metabolism.
abstract: Better drugs are urgently needed for the treatment of African sleeping sickness. We tested a series of promising anticancer agents belonging to the 4-substituted 4-hydroxycyclohexa-2,5-dienones class ("quinols") and identified several with potent trypanocidal activity (EC(50) < 100 nM). In mammalian cells, quinols are proposed to inhibit the thioredoxin/thioredoxin reductase system, which is absent from trypanosomes. Studies with the prototypical 4-benzothiazole-substituted quinol, PMX464, established that PMX464 is rapidly cytocidal, similar to the arsenical drug, melarsen oxide. Cell lysis by PMX464 was accelerated by addition of sublethal concentrations of glucose oxidase implicating oxidant defenses in the mechanism of action. Whole cells treated with PMX464 showed a loss of trypanothione (T(SH)(2)), a unique dithiol in trypanosomes, and tryparedoxin peroxidase (TryP), a 2-Cys peroxiredoxin similar to mammalian thioredoxin peroxidase. Enzyme assays revealed that T(SH)(2), TryP, and a glutathione peroxidase-like tryparedoxin-dependent peroxidase were inhibited in time- and concentration-dependent manners. The inhibitory activities of various quinol analogues against these targets showed a good correlation with growth inhibition of Trypanosoma brucei. The monothiols glutathione and L-cysteine bound in a 2:1 ratio with PMX464 with K(d) values of 6 and 27 μM, respectively, whereas T(SH)(2) bound more tightly in a 1:1 ratio with a K(d) value of 430 nM. Overexpression of trypanothione synthetase in T. brucei decreased sensitivity to PMX464 indicating that the key metabolite T(SH)(2) is a target for quinols. Thus, the quinol pharmacophore represents a novel lead structure for the development of a new drug against African sleeping sickness.
authors.affiliation: From the Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH and.
authors.forename: Janine
authors.initials: J
authors.lastname: König
authors.affiliation: From the Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH and.
authors.forename: Susan
authors.initials: S
authors.lastname: Wyllie
authors.affiliation: the Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Wells
authors.affiliation: the Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Malcolm F
authors.initials: MF
authors.lastname: Stevens
authors.affiliation: From the Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH and.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Wyatt
authors.affiliation: From the Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH and. Electronic address: a.h.fairlamb@dundee.ac.uk.
authors.forename: Alan H
authors.initials: AH
authors.lastname: Fairlamb
mesh_terms: D019732:Amide Synthases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D052160:Benzothiazoles / Q000494:pharmacology*; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000031:analogs & derivatives / Q000235:genetics / Q000378:metabolism; D006873:Hydroquinones / Q000494:pharmacology*; D015800:Protozoan Proteins / Q000378:metabolism; D013095:Spermidine / Q000031:analogs & derivatives / Q000378:metabolism; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014344:Trypanocidal Agents / Q000494:pharmacology*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*; D014352:Trypanosomiasis / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D052160:Benzothiazoles; D006873:Hydroquinones; C554438:PMX 464; D015800:Protozoan Proteins; D014344:Trypanocidal Agents; C114110:tryparedoxin; D013879:Thioredoxins; C044809:trypanothione; D019732:Amide Synthases; C064407:trypanothione synthetase; D005978:Glutathione; D003545:Cysteine; D013095:Spermidine