Isothermal microcalorimetry, a new tool to monitor drug action against Trypanosoma brucei and Plasmodium falciparum

Antiprotozoal Structure-Activity Relationships of Synthetic Leucinostatin Derivatives and Elucidation of their Mode of Action

Leucinostatin A is one of the most potent antiprotozoal compounds ever described, but little was known on structure-activity relationships (SAR). We used Trypanosoma brucei as a protozoal model organism to test synthetically modified derivatives, resulting in simplified but equally active compounds 2 (ZHAWOC6025) and 4 (ZHAWOC6027), which were subsequently modified in all regions of the molecule to gain an in-depth SAR understanding. The antiprotozoal SAR matched SAR in phospholipid liposomes, where membrane integrity, leaking, and dynamics were studied. The mode of action is discussed based on a structure-activity analysis of derivatives in efficacy, ultrastructural studies in T. brucei, and artificial membrane models, mimicking membrane stability and membrane potential. The main site of antiprotozoal action of natural and synthetic leucinostatins lies in the destabilization of the inner mitochondrial membrane, as demonstrated by ultrastructural analysis, electron microscopy and mitochondrial staining. Long-time sublethal exposure of T. brucei (200 passages) and siRNA screening of 12'000 mutants showed no signs of resistance development to the synthetic derivatives.

Non-invasive monitoring of drug action: A new live in vitro assay design for Chagas' disease drug discovery

New assay designs are needed to improve the predictive value of the Trypanosoma cruzi in vitro tests used as part of the Chagas' disease drug development pipeline. Here, we employed a green fluorescent protein (eGFP)-expressing parasite line and live high-content imaging to monitor the growth of T. cruzi amastigotes in mouse embryonic fibroblasts. A novel assay design allowed us to follow parasite numbers over 6 days, in four-hour intervals, while occupying the microscope for only 24 hours per biological replicate. Dose-response curves were calculated for each time point after addition of test compounds, revealing how EC50 values first decreased over the time of drug exposure, and then leveled off. However, we observed that parasite numbers could vary, even in the untreated controls, and at different sites in the same well, which caused variability in the EC50 values. To overcome this, we established that fold change in parasite number per hour is a more robust and informative measure of drug activity. This was calculated based on an exponential growth model for every biological sample. The net fold change per hour is the result of parasite replication, differentiation, and death. The calculation of this fold change enabled us to determine the tipping point of drug action, i.e. the time point when the death rate of the parasites exceeded the growth rate and the fold change dropped below 1, depending on the drug concentration and exposure time. This revealed specific pharmacodynamic profiles of the benchmark drugs benznidazole and posaconazole.

Chagas' disease, caused by Trypanosoma cruzi, is a chronic debilitating infection occurring mostly in Latin America. There is an urgent need for new, well tolerated drugs. However, the latest therapeutic candidates have yielded disappointing outcomes in clinical trials, despite promising preclinical results. This demands new and more predictive in vitro assays. To address this, we have developed an assay design that enables the growth of T. cruzi intracellular forms to be monitored in real time, under drug pressure, for 6 days post-infection. This allowed us to establish the tipping point of drug action, when the death rate of the parasites exceeded the growth rate. The resulting pharmacodynamics profiles can provide robust and informative details on anti-chagasic candidates, as demonstrated for the benchmark drugs benznidazole and posaconazole.

In Vitro Drug Efficacy Testing Against Trypanosoma brucei

The recent endorsement of fexinidazole by the European Medicines Agency for the treatment of human African trypanosomiasis has demonstrated the high predictive value of cell-based assays for parasite chemotherapy. Here we describe three in vitro drug susceptibility tests with Trypanosoma brucei that have served as the basis for the identification of fexinidazole as a promising lead: (1) a standard assay with end-point measurement to determine drug efficacy; (2) a wash-out assay to test for reversibility and speed of drug action; (3) isothermal microcalorimetry for real-time measurement of onset of drug action and time to kill. Together, these assays allow to estimate pharmacodynamic parameters in vitro and to devise appropriate treatment regimens for subsequent in vivo experiments.

Delayed administration of suramin attenuates peritoneal fibrosis in rats

BACKGROUND

Peritoneal fibrosis is the most common complication of peritoneal dialysis, but there is currently no effective treatment. We previously reported that suramin pretreatment prevents the development of peritoneal fibrosis in a rat model of peritoneal fibrosis induced by chlorhexidine gluconate (CG). Here, we further examined the effectiveness of delayed administration of suramin on peritoneal fibrosis and the mechanism (s) involved in this process.

METHODS

In the rat model of peritoneal fibrosis induced by CG, suramin or saline was administered at day 21 and 28. All rats were then sacrificed to collect peritoneal tissues for Western blot analysis and histological staining at day 35.

RESULTS

Our results demonstrated that delayed administration of suramin starting at 21 days following CG injection can ameliorate peritoneal damage, with greater efficacy after two injections. Suramin also reduced the expression of α-smooth muscle actin, Collagen 1, and Fibronectin and suppressed phosphorylation of Smad-3, epidermal growth factor receptor (EGFR), signal transducers, activator of transcription 3 (STAT3) as well as extracellular signal-regulated kinases 1/2 (ERK 1/2) in the peritoneum injured with CG. Moreover, delayed administration of suramin inhibited overproduction of transforming growth factor-β1(TGF-β1) and expression of several pro-inflammatory cytokines, including monocyte chemoattractant protein-1, tumor necrosis factor-α, interleukin-1, and interleukin-6.

CONCLUSIONS

Our results indicated that suramin can attenuate progression of peritoneal fibrosis by a mechanism involving inhibition of the TGF-β1/Smad3 and EGFR signaling pathways as well as suppression of multiple proinflammatory cytokines. Thus, suramin may have the potential to offer an effective treatment for peritoneal fibrosis.

Nanoscale 3D temperature gradient measurement based on fluorescence spectral characteristics of the CdTe quantum dot probe

The existing quantum dot temperature measurement techniques can only measure the planar temperature in the cell but fails in 3D temperature investigation. We present a novel method of measuring the 3D temperature field on nano scale, combining fluorescence spectral characteristics of the CdTe quantum dot probe with optical spatial positioning. Based on dual-helix point spread function, a 3D temperature optical measurement system with a resolution of 0.625 °C is established, providing a new perspective of 3D temperature measurement inside the cell. We thus offer an original research tool for further revealing the evolution process of secretions in cell metabolism.

The activity of Artemisia spp. and their constituents against Trypanosomiasis

BACKGROUND

Trypanosomiasis belongs to the neglected tropical diseases. Although standard therapies are available, the safety and efficacy of current synthetic drugs are limited due to the development of drug resistance and adverse side effects.

PURPOSE

Artemisia annua and artemisinin are not only active against Plasmodia, but also other protozoa. Therefore, we reviewed the literature on species of the genus Artemisia and their phytochemicals regarding their activity against trypanosomes.

STUDY DESIGN

A PubMed search for "Artemisia/Artemisinin and Trypanosoma" has been conducted for literature until December 2017.

RESULTS

Interestingly, not only A. annua L. and its active principle, artemisinin revealed inhibitory activity towards trypanosomes. Other Artemisia species (A. absinthium, A. abyssinica, A. afra, A. douglasia, A. elegantissima, A. maciverae, A. mexicana, and A. roxburghiana) also inhibited T. brucei, T. cruzi, or T. congolense. The plants contained numerous chemical constituents including 3',4'-dihydroxybonanzin, apigenin, betulinic acid, bonanzin, dehydroleucodine, dihydroluteolin, dracunculin and bis-dracunculin, helenalin, nepetin, scoparol, scopoletin, stigmasterol, (Z)-p‑hydroxy cinnamic acid, β-sitosterol and others. In addition to artemisinin from A. annua, artemether and artesunate, further novel artemisinin derivatives and nanotechnological preparations may also be useful to combat Trypanosoma infections.

CONCLUSION

There are numerous results reporting on the anti-trypanosomal activity the genus Artemisia, artemisinin and its derivatives and other phytochemicals from Artemisia species. This field of research is, however, still in its infancy and more intensive research is required to explore the full potential of diverse Artemisia species and their chemical ingredients for eradication of trypanosomal infections.

Isothermal microcalorimetry - A quantitative method to monitor Trypanosoma congolense growth and growth inhibition by trypanocidal drugs in real time

Trypanosoma congolense is a protozoan parasite that is transmitted by tsetse flies, causing African Animal Trypanosomiasis, also known as Nagana, in sub-Saharan Africa. Nagana is a fatal disease of livestock that causes severe economic losses. Two drugs are available, diminazene and isometamidium, yet successful treatment is jeopardized by drug resistant T. congolense. Isothermal microcalorimetry is a highly sensitive tool that can be used to study growth of the extracellular T. congolense parasites or to study parasite growth inhibition after the addition of antitrypanosomal drugs. Time of drug action and time to kill can be quantified in a simple way by real time heat flow measurements. We established a robust protocol for the microcalorimetric studies of T. congolense and developed mathematical computations in R to calculate different parameters related to growth and the kinetics of drug action. We demonstrate the feasibility and benefit of the method exemplary with the two standard drugs, diminazene aceturate and isometamidium chloride. The method and the mathematical approach can be translated to study other pathogenic or non-pathogenic cells if they are metabolically active and grow under axenic conditions.

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Isothermal microcalorimetry enables heat flow measurement of T. congolense in real-time.

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Heat flow measurements correlate with number of viable cells.

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Growth and drug-induced growth inhibition can be deducted from heat flow curves.

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Pharmacodynamic drug action parameters can be computed from heat flow curves.

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This method is a valuable tool in the drug discovery process against T. congolense.

Beyond immune escape: a variant surface glycoprotein causes suramin resistance in Trypanosoma brucei

Suramin is one of the first drugs developed in a medicinal chemistry program (Bayer, 1916), and it is still the treatment of choice for the hemolymphatic stage of African sleeping sickness caused by Trypanosoma brucei rhodesiense. Cellular uptake of suramin occurs by endocytosis, and reverse genetic studies with T. b. brucei have linked downregulation of the endocytic pathway to suramin resistance. Here we show that forward selection for suramin resistance in T. brucei spp. cultures is fast, highly reproducible and linked to antigenic variation. Bloodstream-form trypanosomes are covered by a dense coat of variant surface glycoprotein (VSG), which protects them from their mammalian hosts' immune defenses. Each T. brucei genome contains over 2000 different VSG genes, but only one is expressed at a time. An expression switch to one particular VSG, termed VSG^Sur , correlated with suramin resistance. Reintroduction of the originally expressed VSG gene in resistant T. brucei restored suramin susceptibility. This is the first report of a link between antigenic variation and drug resistance in African trypanosomes.

Evaluation of the Antibacterial Effects of Flavonoid Combination from the Leaves of Dracontomelon dao by Microcalorimetry and the Quadratic Rotary Combination Design

Skin infectious disease is a common public health problem due to the emergence of drug-resistant bacteria caused by the antibiotic misuse. Dracontomelon dao (Blanco) Merr. et Rolfe, a traditional Chinese medicine, has been used for the treatment of various skin infectious diseases over 1000 of years. Previous reports have demonstrated that the leaves of D. dao present favorable antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtitles. The flavonoids are the main components of the ethyl acetate extract of D. dao leaf. However, the correlation between flavonoids and antibacterial activities is yet to be determined. In this study, the combined antibacterial activities of these flavonoids were investigated. Three samples with the different concentrations of flavonoids (S1–S3) were obtained. By microcalorimetric measurements, the results showed that the IC₅₀ value of S2 was lower than those of S1 and S3. The contents of main flavonoids (including Luteolin, L-Epicatechin, Cianidanol, and Quercetin) in S1–S3 were various, confirmed by the method of the Ultra High Performance Liquid Chromatography (UPLC). Based on the method of quadratic general rotary unitized design, the antibacterial effect of single flavonoid, and the potential synergistic effects between Luteolin and Quercetin, Luteolin and Cianidanol were calculated, which were also proved by microcalorimetric analysis. The antibacterial activities of main flavonoids were Luteolin > Cianidanol > Quercetin > L-Epicatechin. Meanwhile, the synergistic effects of Luteolin and Cianidanol (P_L+C = 1.425), Quercetin and Luteolin (P_L+Q = 1.129) on anti-microbial activity were validated. Finally, we found that the contents of Luteolin, L-Epicatechin, Cianidanol, Quercetin were 1061.00–1061.00, 189.14–262.86, 15,990.33–16,973.62, 6799.67–7662.64 ng·ml⁻¹ respectively, with the antibacterial rate over 60.00%. In conclusion, this study could provide reference for quality evaluation and pharmacodynamics research of D. dao.

A new approach to chemotherapy: drug-induced differentiation kills African trypanosomes

Human African trypanosomiasis (sleeping sickness) is a neglected tropical disease caused by Trypanosoma brucei spp. The parasites are transmitted by tsetse flies and adapt to their different hosts and environments by undergoing a series of developmental changes. During differentiation, the trypanosome alters its protein coat. Bloodstream form trypanosomes in humans have a coat of variant surface glycoprotein (VSG) that shields them from the immune system. The procyclic form, the first life-cycle stage to develop in the tsetse fly, replaces the VSG coat by procyclins; these proteins do not protect the parasite from lysis by serum components. Our study exploits the parasite-specific process of differentiation from bloodstream to procyclic forms to screen for potential drug candidates. Using transgenic trypanosomes with a reporter gene in a procyclin locus, we established a whole-cell assay for differentiation in a medium-throughput format. We screened 7,495 drug-like compounds and identified 28 hits that induced expression of the reporter and loss of VSG at concentrations in the low micromolar range. Small molecules that induce differentiation to procyclic forms could facilitate studies on the regulation of differentiation as well as serving as scaffolds for medicinal chemistry for new treatments for sleeping sickness.

Susceptibility testing of Mycobacterium abscessus by isothermal microcalorimetry

We evaluated a new method for susceptibility testing of a rapidly growing mycobacterium using real-time measurement of heat (microcalorimetry). MICs of 2 clinical Mycobacterium abscessus isolates were determined by microbroth dilution and E-test. For microcalorimetry, Middlebrook-7H10 agar+10% oleic acid-albumin-dextrose-catalase, containing amikacin, clarithromycin, linezolid, and ciprofloxacin was inoculated with ~10(5)CFU/mL. Heat production was measured at 37°C for 72h. Minimal heat inhibition concentration (MHIC) was defined as the lowest antibiotic concentration inhibiting growth-related heat production. Growth of M. abscessus was detected after a median of 16.5h (range, 8.5-26.9h). Heat detection was proportionally delayed with increasing concentration of antibiotics. MHICs for the tested strains were 16 to >16mg/L for amikacin, >8mg/L for clarithromycin, 4 to >16mg/L for ciprofloxacin, 24 to >32mg/L for linezolid. MHICs were in agreement within two 2-fold dilutions with conventional MICs. Microcalorimetry may accelerate antimicrobial susceptibility testing in mycobacteria and provide additional real-time information on the drug effect.

Heterochromatin protein 1 secures survival and transmission of malaria parasites

Clonally variant expression of surface antigens allows the malaria parasite Plasmodium falciparum to evade immune recognition during blood stage infection and secure malaria transmission. We demonstrate that heterochromatin protein 1 (HP1), an evolutionary conserved regulator of heritable gene silencing, controls expression of numerous P. falciparum virulence genes as well as differentiation into the sexual forms that transmit to mosquitoes. Conditional depletion of P. falciparum HP1 (PfHP1) prevents mitotic proliferation of blood stage parasites and disrupts mutually exclusive expression and antigenic variation of the major virulence factor PfEMP1. Additionally, PfHP1-dependent regulation of PfAP2-G, a transcription factor required for gametocyte conversion, controls the switch from asexual proliferation to sexual differentiation, providing insight into the epigenetic mechanisms underlying gametocyte commitment. These findings show that PfHP1 is centrally involved in clonally variant gene expression and sexual differentiation in P. falciparum and have major implications for developing antidisease and transmission-blocking interventions against malaria.

Repurposing of the Open Access Malaria Box for Kinetoplastid Diseases Identifies Novel Active Scaffolds against Trypanosomatids

Phenotypic screening had successfully been used for hit generation, especially in the field of neglected diseases, in which feeding the drug pipeline with new chemotypes remains a constant challenge. Here, we catalyze drug discovery research using a publicly available screening tool to boost drug discovery. The Malaria Box, assembled by the Medicines for Malaria Venture, is a structurally diverse set of 200 druglike and 200 probelike compounds distilled from more than 20,000 antimalarial hits from corporate and academic libraries. Repurposing such compounds has already identified new scaffolds against cryptosporidiosis and schistosomiasis. In addition to initiating new hit-to-lead activities, screening the Malaria Box against a plethora of other parasites would enable the community to better understand the similarities and differences between them. We describe the screening of the Malaria Box and triaging of the identified hits against kinetoplastids responsible for human African trypanosomiasis (Trypanosoma brucei), Chagas disease (Trypanosoma cruzi), and visceral leishmaniasis (Leishmania donovani and Leishmania infantum). The in vitro and in vivo profiling of the most promising active compounds with respect to efficacy, toxicity, pharmacokinetics, and complementary druggable properties are presented and a collaborative model used as a way to accelerate the discovery process discussed.

In vitro and in vivo evaluation of 28DAP010, a novel diamidine for treatment of second-stage African sleeping sickness

African sleeping sickness is a neglected tropical disease transmitted by tsetse flies. New and better drugs are still needed especially for its second stage, which is fatal if untreated. 28DAP010, a dipyridylbenzene analogue of DB829, is the second simple diamidine found to cure mice with central nervous system infections by a parenteral route of administration. 28DAP010 showed efficacy similar to that of DB829 in dose-response studies in mouse models of first- and second-stage African sleeping sickness. The in vitro time to kill, determined by microcalorimetry, and the parasite clearance time in mice were shorter for 28DAP010 than for DB829. No cross-resistance was observed between 28DAP010 and pentamidine on the tested Trypanosoma brucei gambiense isolates from melarsoprol-refractory patients. 28DAP010 is the second promising preclinical candidate among the diamidines for the treatment of second-stage African sleeping sickness.

[Areas of application of isothermal microcalorimetry in urology: an overview]

Isothermal microcalorimetry (IMC) is a nonspecific analytical tool for measurement of heat. With sensitivity in the order of 0.2 μW, IMC can detect very small amounts of heat produced by only a small number of microorganisms or eukaryotic cells. This report is intended to introduce IMC to the urological audience and to give an overview about the past, present and future of this cutting edge technology in the urological context.

Activities of fluconazole, caspofungin, anidulafungin, and amphotericin B on planktonic and biofilm Candida species determined by microcalorimetry

We investigated the activities of fluconazole, caspofungin, anidulafungin, and amphotericin B against Candida species in planktonic form and biofilms using a highly sensitive assay measuring growth-related heat production (microcalorimetry). C. albicans, C. glabrata, C. krusei, and C. parapsilosis were tested, and MICs were determined by the broth microdilution method. The antifungal activities were determined by isothermal microcalorimetry at 37°C in RPMI 1640. For planktonic Candida, heat flow was measured in the presence of antifungal dilutions for 24 h. Candida biofilm was formed on porous glass beads for 24 h and exposed to serial dilutions of antifungals for 24 h, and heat flow was measured for 48 h. The minimum heat inhibitory concentration (MHIC) was defined as the lowest antifungal concentration reducing the heat flow peak by ≥50% (≥90% for amphotericin B) at 24 h for planktonic Candida and at 48 h for Candida biofilms (measured also at 24 h). Fluconazole (planktonic MHICs, 0.25 to >512 μg/ml) and amphotericin B (planktonic MHICs, 0.25 to 1 μg/ml) showed higher MHICs than anidulafungin (planktonic MHICs, 0.015 to 0.5 μg/ml) and caspofungin (planktonic MHICs, 0.125 to 0.5 μg/ml). Against Candida species in biofilms, fluconazole's activity was reduced by >1,000-fold compared to its activity against the planktonic counterparts, whereas echinocandins and amphotericin B mainly preserved their activities. Fluconazole induced growth of planktonic C. krusei at sub-MICs. At high concentrations of caspofungin (>4 μg/ml), paradoxical growth of planktonic C. albicans and C. glabrata was observed. Microcalorimetry enabled real-time evaluation of antifungal activities against planktonic and biofilm Candida organisms. It can be used in the future to evaluate new antifungals and antifungal combinations and to study resistant strains.

Promotion of quality standard of herbal medicine by constituent removing and adding

To identify major active constituents and measure their levels in a typical medicinal herb-Rhizoma coptidis, we applied the concept of removing and adding, taking inspiration from functional genetic methods. As this herb has bacteriostatic properties and is used to treat bacterial diarrhea, we examined the effects of individual constituents (berberine, palmatine, coptisine, epiberberine, jateorrhizine and columbamine) on the growth of Shigella dysenteriae with microcalorimetry. The removing and adding procedures revealed that berberine and coptisine were the main antibacterial constituents of R. coptidis, with bacteriostatic activities of 54.10% and 39.75%, respectively. The relative levels of berberine and coptisine in R. coptidis were 8.08%-31.92% and 4.05%-14.45%, respectively. On the basis of whole effect, the method of constituents removing and adding, coupled with a bioassay, is a useful strategy to identify the active constituents and measure their levels in herbal medicines, which may provide reference to other natural products.

Trypanosoma brucei adenine-phosphoribosyltransferases mediate adenine salvage and aminopurinol susceptibility but not adenine toxicity

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African trypanosomes possess two distinct adenine phosphoribosyltransferases.

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Trypanosoma brucei TbAPRT1 is cytosolic, TbAPRT2 localizes to the glycosome.

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Aprt1,2 null mutants are viable but do not incorporate adenine into nucleotides.

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Aprt1,2 null mutants are resistant to aminopurinol but still sensitive to adenine.

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Aminopurinol is a trypanocide with submicromolar activity against T. brucei.

African trypanosomes, like all obligate parasitic protozoa, cannot synthesize purines de novo and import purines from their hosts to build nucleic acids. The purine salvage pathways of Trypanosoma brucei being redundant, none of the involved enzymes is likely to be essential. Nevertheless they can be of pharmacological interest due to their role in activation of purine nucleobase or nucleoside analogues, which only become toxic when converted to nucleotides. Aminopurine antimetabolites, in particular, are potent trypanocides and even adenine itself is toxic to trypanosomes at elevated concentrations. Here we report on the T. brucei adenine phosphoribosyltransferases TbAPRT1 and TbAPRT2, encoded by the two genes Tb927.7.1780 and Tb927.7.1790, located in tandem on chromosome seven. The duplication is syntenic in all available Trypanosoma genomes but not in Leishmania. While TbAPRT1 is cytosolic, TbAPRT2 possesses a glycosomal targeting signal and co-localizes with the glycosomal marker aldolase. Interestingly, the distribution of glycosomal targeting signals among trypanosomatid adenine phosphoribosyltransferases is not consistent with their phylogeny, indicating that the acquisition of adenine salvage to the glycosome happened after the radiation of Trypanosoma. Double null mutant T. brucei Δtbaprt1,2 exhibited no growth phenotype but no longer incorporated exogenous adenine into the nucleotide pool. This, however, did not reduce their sensitivity to adenine. The Δtbaprt1,2 trypanosomes were resistant to the adenine isomer aminopurinol, indicating that it is activated by phosphoribosyl transfer. Aminopurinol was about 1000-fold more toxic to bloodstream-form T. brucei than the corresponding hypoxanthine isomer allopurinol. Aminopurinol uptake was not dependent on the aminopurine permease P2 that has been implicated in drug resistance.

In vivo imaging of trypanosome-brain interactions and development of a rapid screening test for drugs against CNS stage trypanosomiasis

HUMAN AFRICAN TRYPANOSOMIASIS (HAT) MANIFESTS IN TWO STAGES OF DISEASE: firstly, haemolymphatic, and secondly, an encephalitic phase involving the central nervous system (CNS). New drugs to treat the second-stage disease are urgently needed, yet testing of novel drug candidates is a slow process because the established animal model relies on detecting parasitemia in the blood as late as 180 days after treatment. To expedite compound screening, we have modified the GVR35 strain of Trypanosoma brucei brucei to express luciferase, and have monitored parasite distribution in infected mice following treatment with trypanocidal compounds using serial, non-invasive, bioluminescence imaging. Parasites were detected in the brains of infected mice following treatment with diminazene, a drug which cures stage 1 but not stage 2 disease. Intravital multi-photon microscopy revealed that trypanosomes enter the brain meninges as early as day 5 post-infection but can be killed by diminazene, whereas those that cross the blood-brain barrier and enter the parenchyma by day 21 survived treatment and later caused bloodstream recrudescence. In contrast, all bioluminescent parasites were permanently eliminated by treatment with melarsoprol and DB829, compounds known to cure stage 2 disease. We show that this use of imaging reduces by two thirds the time taken to assess drug efficacy and provides a dual-modal imaging platform for monitoring trypanosome infection in different areas of the brain.

Pharmacokinetics, Trypanosoma brucei gambiense efficacy, and time of drug action of DB829, a preclinical candidate for treatment of second-stage human African trypanosomiasis

Human African trypanosomiasis (HAT, also called sleeping sickness), a neglected tropical disease endemic to sub-Saharan Africa, is caused by the parasites Trypanosoma brucei gambiense and T. brucei rhodesiense. Current drugs against this disease have significant limitations, including toxicity, increasing resistance, and/or a complicated parenteral treatment regimen. DB829 is a novel aza-diamidine that demonstrated excellent efficacy in mice infected with T. b. rhodesiense or T. b. brucei parasites. The current study examined the pharmacokinetics, in vitro and in vivo activity against T. b. gambiense, and time of drug action of DB829 in comparison to pentamidine. DB829 showed outstanding in vivo efficacy in mice infected with parasites of T. b. gambiense strains, despite having higher in vitro 50% inhibitory concentrations (IC50s) than against T. b. rhodesiense strain STIB900. A single dose of DB829 administered intraperitoneally (5 mg/kg of body weight) cured all mice infected with different T. b. gambiense strains. No cross-resistance was observed between DB829 and pentamidine in T. b. gambiense strains isolated from melarsoprol-refractory patients. Compared to pentamidine, DB829 showed a greater systemic exposure when administered intraperitoneally, partially contributing to its improved efficacy. Isothermal microcalorimetry and in vivo time-to-kill studies revealed that DB829 is a slower-acting trypanocidal compound than pentamidine. A single dose of DB829 (20 mg/kg) administered intraperitoneally clears parasites from mouse blood within 2 to 5 days. In summary, DB829 is a promising preclinical candidate for the treatment of first- and second-stage HAT caused by both Trypanosoma brucei subspecies.

Isothermal microcalorimetry to study the activity of triclabendazole and its metabolites on juvenile and adult Fasciola hepatica

Isothermal microcalorimetry (IMC) is an analytical tool that continuously measures the heat flow generated by chemical, physical or biological processes. We have demonstrated that IMC is a useful tool to analyze drug effects on helminths, including adult Fasciola hepatica. Here, we used IMC to examine the activity of triclabendazole and its metabolites triclabendazole sulphone and triclabendazole sulphoxide on juvenile and adult F. hepatica. Worms (one adult or 2-3 juveniles) were placed in 4 or 20 ml glass ampoules containing RPMI 1640 and the test compound (25-100 μg/ml) and the heat flow and motility of worms was examined with TAM48 and TAMIII isothermal microcalorimetry instruments. IMC was found to be precisely document drug effects on juvenile F. hepatica and confirmed the pronounced effect of the benzimidazole derivatives on the motor activity of F. hepatica. Juvenile F. hepatica incubated with 100 μg/ml triclabendazole, triclabendazole sulphone and triclabendazole sulphoxide showed no movements 8.3, 35 and 6h post-incubation (all p<0.001). The metabolic heat of triclabendazole sulphoxide treated worms (100 μg/ml) was reduced by 50% and 76% 24 and 120 h post-incubation, respectively. Limitations of calorimetric measurements were observed using adult F. hepatica as only three worms could be measured simultaneously and also control worms showed a considerable decrease in heat flow. Adult F. hepatica exposed to triclabendazole, triclabendazole sulphone and triclabendazole sulphoxide showed no movements after 31 (p=0.009), 49 (p>0.05) and 88 (p>0.05)h. In conclusion, IMC is useful to document drug effects on juvenile F. hepatica and since rapid technological developments in this field are occurring IMC might also hold promise to study adult F. hepatica in the near future.