Megazol combined with suramin: a chemotherapy regimen which reversed the CNS pathology in a model of human African trypanosomiasis in mice

Although 60 million people are exposed to human African trypanosomiasis, drug companies have not been interested in developing new drugs due to the lack of financial reward. No new drugs will be available for several years. A clearer understanding of the distribution of existing drugs into the brains of sleeping sickness patients is needed if we are to use the treatments that are available more safely and effectively. This proposal addresses this issue by using established animal models. Using in situ brain perfusion and isolated incubated choroid plexus techniques, we investigated the distribution of [

Section: Discussionmentioning

confidence: 99%

Section: H]suramin Would Be Unlikely To Treat the Second Or Cns Stagementioning

confidence: 99%

Distribution of Suramin, an Antitrypanosomal Drug, across the Blood-Brain and Blood-Cerebrospinal Fluid Interfaces in Wild-Type and P-Glycoprotein Transporter-Deficient Mice

Sanderson

Khan

Thomas

2007

“…The World Health Organization and Bayer are currently engaged in efforts to extend the license for nifurtimox for routine use against human African trypanosomiasis (7). A nitroimidazole, megazol, has recently received attention for its potent trypanocidal activity (9,17), although toxicity issues (34) have stifled further development. Reports of novel trypanocidal nitroheterocycles continue to appear (8,30), which emphasizes the fact that trypanosomes are particularly sensitive to this class of compound.…”

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confidence: 99%

Trypanocidal Activity of Melamine-Based Nitroheterocycles

Stewart

Bueno

Baliani

et al. 2004

A series of nitroheterocyclic compounds were designed with linkages to melamine or benzamidine groups that are known substrates of the P2 aminopurine and other transporters in African trypanosomes of the brucei group. Several compounds showed in vitro trypanotoxicity with 50% inhibitory concentrations in the submicromolar range. Although most compounds interacted with the P2 transporter, as judged by their ability to inhibit adenosine transport via this carrier, uptake through this route was not necessary for activity since TbAT1-null mutant parasites, deficient in this transporter, retained sensitivity to these drugs. One compound, a melamine-linked nitrofuran, also showed pronounced activity against parasites in mice. Studies into the mode of action of this compound indicated that neither reductive, nor oxidative, stress were related to its trypanocidal activity ruling out a genotoxic effect in T. brucei, distinguishing it from some other, mammalian cell toxic, trypanocidal nitroheterocycles.

“…One compound with promise is megazol (5,12,13,18), a nitroheterocyclic compound that forms a nitro radical anion upon reduction (31). Megazol appears to enter Trypanosoma brucei via passive diffusion (3), but little is known about its mode of action.…”

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confidence: 99%

Activity of Megazol, a Trypanocidal Nitroimidazole, Is Associated with DNA Damage

Enanga

Ariyanayagam

Stewart

et al. 2003

DNA damage associated with the trypanocidal activity of megazol [2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazole] was shown in experiments in which DNA repair-deficient RAD51؊/؊ Trypanosoma brucei mutants were found to be hypersensitive to the drug. Parasites resistant to megazol were selected and showed modest cross-resistance to other trypanocides, although neither drug efflux nor changes to intracellular thiols correlated with resistance.New drugs are urgently required for treatment of human African trypanosomiasis (22). One compound with promise is megazol (5, 12, 13, 18), a nitroheterocyclic compound that forms a nitro radical anion upon reduction (31). Megazol appears to enter Trypanosoma brucei via passive diffusion (3), but little is known about its mode of action. We determined the effect of megazol in assays that measured oxidative and reductive stress. We also selected parasites resistant to megazol in order to assess cellular changes associated with resistance.Bloodstream forms (17) and procyclic forms (6) of T. brucei brucei (strain 427) were cultivated by using standard techniques. Assays measuring drug sensitivity were carried out to determine the drug concentration producing a 50% decrease in cell proliferation (IC 50 ) and the resistance factor (average ratio of the IC 50 for a resistant clone to the IC 50 for a wild-type clone). The Alamar Blue test (28) was used for bloodstream forms, while cell counting by using an improved Neubauer chamber was required for procyclics. For procyclic cells the IC 50 of megazol was 0.28 Ϯ 0.01 M, and for bloodstream forms the IC 50 was 0.15 Ϯ 0.02 M.To induce megazol resistance in vitro, trypanosomes were exposed to drug concentrations that doubled every 2 weeks, starting at 0.008 and 0.01 M for bloodstream forms and procyclics, respectively. After 6 months of cultivation, procyclic and bloodstream forms that tolerated 10 and 1 M megazol, respectively, were cloned by limiting dilution.The IC 50 for the cloned, resistant, procyclic line was 29.24 Ϯ 3.2 M (105-fold-reduced sensitivity), while the IC 50 for the bloodstream form line was 3.2 Ϯ 0.48 M (21-fold-reduced sensitivity).Cross-resistance to megazol and other trypanocides was also studied (Table 1). Moderate levels of cross-resistance to two nitroheterocyclic trypanocides, the nitrofuran nifurtimox and the nitroimidazole benznidazole, were detected. Significant, albeit low-level, cross-resistance to the melaminophenyl arsenical compounds cymelarsan, melarsen oxide, and melarsoprol, the diamidine compounds pentamidine and berenil, and suramin was also observed.Verapamil (20), PAK-104P (7), and two phenothiazine derivatives (prochlorperazine and trifluoperazine) (14) all inhibit cellular extrusion pumps but, when used at 5 M, failed to reverse megazol resistance in T. brucei. Efflux pumps are thus unlikely to play a significant role in the megazol resistance characterized here.It was recently shown that megazol exposure reduces trypanothione levels in Trypanosoma cruzi (23). Bloodstream form T. b...