Antitumor Quinol PMX464 Is a Cytocidal Anti-trypanosomal Inhibitor Targeting Trypanothione Metabolism

Janine Konig, Susan Wyllie, Geoffrey Wells, Malcolm F. Stevens, Paul G. Wyatt, Alan H. Fairlamb

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    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 (EC50 < 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 mu M, 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.

    Original languageEnglish
    Pages (from-to)8523-8533
    Number of pages11
    JournalJournal of Biological Chemistry
    Volume286
    Issue number10
    DOIs
    Publication statusPublished - 11 Mar 2011

    Keywords

    • REDOX-SENSITIVE OLIGOMERIZATION
    • CANCER CELL-LINES
    • TRYPANOSOMA-BRUCEI
    • TRYPAREDOXIN PEROXIDASES
    • CRITHIDIA-FASCICULATA
    • AFRICAN TRYPANOSOMES
    • CRYSTAL-STRUCTURE
    • MOLECULAR CHARACTERIZATION
    • SUBSTRATE-SPECIFICITY
    • THIOREDOXIN INHIBITOR

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