Nitroaromatic pro-drug activation and resistance in the African trypanosome

  • Antoaneta Y. Sokolova

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    Sleeping sickness, caused by Trypanosoma brucei, is a deadly disease that affects some of the poorest countries in sub-Saharan Africa. Although the disease prevalence is declining, strengthening of the current control efforts, including introduction of more adequate chemotherapeutic options, is needed to prevent the re-emergence of yet another epidemic. Nitroaromatic compounds, such as nifurtimox (in combination with eflornithine) and fexinidazole (in clinical trials), have been recently introduced for the treatment of the second stage of sleeping sickness. These compounds are believed to act as pro-drugs that require intracellular enzymatic activation for antimicrobial activity. Here, the role of the bacterial-like nitroreductase TbNTR as a nitrodrug activating enzyme is examined through overexpression and knock-out studies in T. brucei. Multiple attempts to purify soluble recombinant TbNTR from E. coli were unsuccessful, because the recombinant protein was found to be membrane associated. In keeping with the role of TbNTR in nitrodrug activation, loss of an NTR gene copy in T. brucei was found to be one, but not the only, mechanism that may lead to nitrodrug resistance. Furthermore, in the bloodstream form of T. brucei, resistance was relatively easy to select for nifurtimox, with no concurrent loss of virulence and at clinically relevant levels. More worryingly, nifurtimox resistance led to a decreased sensitivity of these parasites to other nitroaromatic compounds, including a high level of cross-resistance to fexinidazole. Conversely, generation of fexinidazole resistance resulted in cross-resistance to nifurtimox. Should these findings translate to the field, emerging nitrodrug resistance could reverse all recent advances in the treatment of sleeping sickness, made since the introduction of eflornithine 20 years ago. Therefore, all efforts should be made to ensure nitroaromatic drugs are used only in drug combination therapies against sleeping sickness, in order to protect them from emerging resistance.
    Date of Award2011
    Original languageEnglish
    Awarding Institution
    • University of Dundee
    SponsorsBiotechnology and Biological Sciences Research Council & Wellcome Trust
    SupervisorAlan Fairlamb (Supervisor)

    Keywords

    • Sleeping sickness
    • African trypanosomiasis
    • Trypanosome
    • Trypanosoma brucei
    • Trypanosomiasis
    • Resistance
    • Pro-drug
    • Nitroaromatic
    • Nitroheterocyclic
    • Nifurtimox
    • Fexinidazole
    • Nitroreductase
    • NTR
    • Recombinant expression
    • Protein

    Cite this

    Nitroaromatic pro-drug activation and resistance in the African trypanosome
    Sokolova, A. Y. (Author). 2011

    Student thesis: Doctoral ThesisDoctor of Philosophy