The Drugs of Sleeping Sickness: Their Mechanisms of Action and Resistance, and a Brief History

Identification of Innovative Folate Inhibitors Leveraging the Amino Dihydrotriazine Motif from Cycloguanil for Their Potential as Anti-Trypanosoma brucei Agents

Folate enzymes, namely, dihydrofolate reductase (DHFR) and pteridine reductase (PTR1) are acknowledged targets for the development of antiparasitic agents against Trypanosomiasis and Leishmaniasis. Based on the amino dihydrotriazine motif of the drug Cycloguanil (Cyc), a known inhibitor of both folate enzymes, we have identified two novel series of inhibitors, the 2-amino triazino benzimidazoles (1) and 2-guanidino benzimidazoles (2), as their open ring analogues. Enzymatic screening was carried out against PTR1, DHFR, and thymidylate synthase (TS). The crystal structures of TbDHFR and TbPTR1 in complex with selected compounds experienced in both cases a substrate-like binding mode and allowed the rationalization of the main chemical features supporting the inhibitor ability to target folate enzymes. Biological evaluation of both series was performed against T. brucei and L. infantum and the toxicity against THP-1 human macrophages. Notably, the 5,6-dimethyl-2-guanidinobenzimidazole 2g resulted to be the most potent (Ki = 9 nM) and highly selective TbDHFR inhibitor, 6000-fold over TbPTR1 and 394-fold over hDHFR. The 5,6-dimethyl tricyclic analogue 1g, despite showing a lower potency and selectivity profile than 2g, shared a comparable antiparasitic activity against T. brucei in the low micromolar domain. The dichloro-substituted 2-guanidino benzimidazoles 2c and 2d revealed their potent and broad-spectrum antitrypanosomatid activity affecting the growth of T. brucei and L. infantum parasites. Therefore, both chemotypes could represent promising templates that could be valorized for further drug development.

The activities of suaveolol and other compounds from Hyptis suaveolens and Momordica charantia against the aetiological agents of African trypanosomiasis, leishmaniasis and malaria

African trypanosomiasis and malaria are among the most severe health challenges to humans and livestock in Africa and new drugs are needed. Leaves of Hyptis suaveolens Kuntze (Lamiaceae) and Momordica charantia L. (Cucurbitaceae) were extracted with hexane, ethyl acetate, and then methanol, and subjected to silica gel column chromatography. Structures of six isolated compounds were elucidated through NMR and HR-EIMS spectrometry. Callistrisic acid, dehydroabietinol, suaveolic acid, suaveolol, and a mixture of suaveolol and suaveolic acid (SSA) were obtained from H. suaveolens, while karavilagenin D and momordicin I acetate were obtained from M. charantia. The isolated biomolecules were tested against trypomastigotes of Trypanosoma brucei brucei and T. congolense, and against Plasmodium falciparum. The most promising EC50 values were obtained for the purified suaveolol fraction, at 2.71 ± 0.36 μg/mL, and SSA, exhibiting an EC50 of 1.56 ± 0.17 μg/mL against T. b. brucei trypomastigotes. Suaveolic acid had low activity against T. b. brucei but displayed moderate activity against T. congolense trypomastigotes at 11.1 ± 0.5 μg/mL. Suaveolol and SSA were also tested against T. evansi, T. equiperdum, Leishmania major and L. mexicana but the antileishmanial activity was low. Neither of the active compounds, nor the mixture of the two, displayed any cytotoxic effect on human foreskin fibroblast (HFF) cells at even the highest concentration tested, being 200 μg/mL. We conclude that suaveolol and its mixture possessed significant and selective trypanocidal activity.

Structural insights into drug transport by an aquaglyceroporin

Pentamidine and melarsoprol are primary drugs used to treat the lethal human sleeping sickness caused by the parasite Trypanosoma brucei. Cross-resistance to these two drugs has recently been linked to aquaglyceroporin 2 of the trypanosome (TbAQP2). TbAQP2 is the first member of the aquaporin family described as capable of drug transport; however, the underlying mechanism remains unclear. Here, we present cryo-electron microscopy structures of TbAQP2 bound to pentamidine or melarsoprol. Our structural studies, together with the molecular dynamic simulations, reveal the mechanisms shaping substrate specificity and drug permeation. Multiple amino acids in TbAQP2, near the extracellular entrance and inside the pore, create an expanded conducting tunnel, sterically and energetically allowing the permeation of pentamidine and melarsoprol. Our study elucidates the mechanism of drug transport by TbAQP2, providing valuable insights to inform the design of drugs against trypanosomiasis.

Tractable Quinolone Hydrazides Exhibiting Sub-Micromolar and Broad Spectrum Antitrypanosomal Activities

Nagana and Human African Trypanosomiasis (HAT), caused by (sub)species of Trypanosoma, are diseases that impede human and animal health, and economic growth in Africa. The few drugs available have drawbacks including suboptimal efficacy, adverse effects, drug resistance, and difficult routes of administration. New drugs are needed. A series of 20 novel quinolone compounds with affordable synthetic routes was made and evaluated in vitro against Trypanosoma brucei and HEK293 cells. Of the 20 compounds, 12 had sub-micromolar potencies against the parasite (EC50 values=0.051-0.57 μM), and most were non-toxic to HEK293 cells (CC50 values>5 μM). Two of the most potent compounds presented sub-micromolar activities against other trypanosome (sub)species (T. cruzi and T. b. rhodesiense). Although aqueous solubility is poor, both compounds possess good logD values (2-3), and either robust or poor microsomal stability profiles. These varying attributes will be addressed in future reports.

A structure-based virtual high-throughput screening, molecular docking, molecular dynamics and MM/PBSA study identified novel putative drug-like dual inhibitors of trypanosomal cruzain and rhodesain cysteine proteases

Virtual screening a collection of ~ 25,000 ChemBridge molecule collection identified two nitrogenous heterocyclic molecules, 12 and 15, with potential dual inhibitory properties against trypanosomal cruzain and rhodesain cysteine proteases. Similarity search in DrugBank found the two virtual hits with novel chemical structures with unreported anti-trypanosomal activities. Investigations into the binding mechanism by molecular dynamics simulations for 100 ns revealed the molecules were able to occupy the binding sites and stabilise the protease complexes. Binding affinities calculated using the MM/PBSA method for the last 20 ns showed that the virtual hits have comparable binding affinities to other known inhibitors from literature suggesting both molecules as promising scaffolds with dual cruzain and rhodesain inhibition properties, i.e. 12 has predicted ΔGbind values of - 38.1 and - 38.2 kcal/mol to cruzain and rhodesain, respectively, and 15 has predicted ΔGbind values of - 34.4 and - 25.8 kcal/mol to rhodesain. Per residue binding free energy decomposition studies and visual inspection at 100 ns snapshots revealed hydrogen bonding and non-polar attractions with important amino acid residues that contributed to the ΔGbind values. The interactions are similar to those previously reported in the literature. The overall ADMET predictions for the two molecules were favourable for drug development with acceptable pharmacokinetic profiles and adequate oral bioavailability.

Synthesis and Biophysical and Biological Studies of N-Phenylbenzamide Derivatives Targeting Kinetoplastid Parasites

The AT-rich mitochondrial DNA (kDNA) of trypanosomatid parasites is a target of DNA minor groove binders. We report the synthesis, antiprotozoal screening, and SAR studies of three series of analogues of the known antiprotozoal kDNA binder 2-((4-(4-((4,5-dihydro-1H-imidazol-3-ium-2-yl)amino)benzamido)phenyl)amino)-4,5-dihydro-1H-imidazol-3-ium (1a). Bis(2-aminoimidazolines) (1) and bis(2-aminobenzimidazoles) (2) showed micromolar range activity against Trypanosoma brucei, whereas bisarylimidamides (3) were submicromolar inhibitors of T. brucei, Trypanosoma cruzi, and Leishmania donovani. None of the compounds showed relevant activity against the urogenital, nonkinetoplastid parasite Trichomonas vaginalis. We show that series 1 and 3 bind strongly and selectively to the minor groove of AT DNA, whereas series 2 also binds by intercalation. The measured pKa indicated different ionization states at pH 7.4, which correlated with the DNA binding affinities (ΔTm) for series 2 and 3. Compound 3a, which was active and selective against the three parasites and displayed adequate metabolic stability, is a fine candidate for in vivo studies.

Bis-6-amidino-benzothiazole Derivative that Cures Experimental Stage 1 African Trypanosomiasis with a Single Dose

We designed and synthesized a series of symmetric bis-6-amidino-benzothiazole derivatives with aliphatic central units and evaluated their efficacy against bloodstream forms of the African trypanosome Trypanosoma brucei. Of these, a dicationic benzothiazole compound (9a) exhibited sub-nanomolar in vitro potency with remarkable selectivity over mammalian cells (>26,000-fold). Unsubstituted 5-amidine groups and a cyclohexyl spacer were the crucial determinants of trypanocidal activity. In all cases, mice treated with a single dose of 20 mg kg-1 were cured of stage 1 trypanosomiasis. The compound displayed a favorable in vitro ADME profile, with the exception of low membrane permeability. However, we found evidence that uptake by T. brucei is mediated by endocytosis, a process that results in lysosomal sequestration. The compound was also active in low nanomolar concentrations against cultured asexual forms of the malaria parasite Plasmodium falciparum. Therefore, 9a has exquisite cross-species efficacy and represents a lead compound with considerable therapeutic potential.

Discovery of 5-Phenylpyrazolopyrimidinone Analogs as Potent Antitrypanosomal Agents with In Vivo Efficacy

Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei, is one of the neglected tropical diseases with a continuing need for new medication. We here describe the discovery of 5-phenylpyrazolopyrimidinone analogs as a novel series of phenotypic antitrypanosomal agents. The most potent compound, 30 (NPD-2975), has an in vitro IC50 of 70 nM against T. b. brucei with no apparent toxicity against human MRC-5 lung fibroblasts. Showing good physicochemical properties, low toxicity potential, acceptable metabolic stability, and other pharmacokinetic features, 30 was further evaluated in an acute mouse model of T. b. brucei infection. After oral dosing at 50 mg/kg twice per day for five consecutive days, all infected mice were cured. Given its good drug-like properties and high in vivo antitrypanosomal potential, the 5-phenylpyrazolopyrimidinone analog 30 represents a promising lead for future drug development to treat HAT.

Tackling Sleeping Sickness: Current and Promising Therapeutics and Treatment Strategies

Human African trypanosomiasis is a neglected tropical disease caused by the extracellular protozoan parasite Trypanosoma brucei, and targeted for eradication by 2030. The COVID-19 pandemic contributed to the lengthening of the proposed time frame for eliminating human African trypanosomiasis as control programs were interrupted. Armed with extensive antigenic variation and the depletion of the B cell population during an infectious cycle, attempts to develop a vaccine have remained unachievable. With the absence of a vaccine, control of the disease has relied heavily on intensive screening measures and the use of drugs. The chemotherapeutics previously available for disease management were plagued by issues such as toxicity, resistance, and difficulty in administration. The approval of the latest and first oral drug, fexinidazole, is a major chemotherapeutic achievement for the treatment of human African trypanosomiasis in the past few decades. Timely and accurate diagnosis is essential for effective treatment, while poor compliance and resistance remain outstanding challenges. Drug discovery is on-going, and herein we review the recent advances in anti-trypanosomal drug discovery, including novel potential drug targets. The numerous challenges associated with disease eradication will also be addressed.

Novel Lipophilic Hydroxamates Based on Spirocarbocyclic Hydantoin Scaffolds with Potent Antiviral and Trypanocidal Activity

Flaviviridae infections, such as those caused by hepatitis C (HCV) and dengue viruses (DENVs), represent global health risks. Infected people are in danger of developing chronic liver failure or hemorrhagic fever, both of which can be fatal if not treated. The tropical parasites Trypanosoma brucei and Trypanosoma cruzi cause enormous socioeconomic burdens in Sub-Saharan Africa and Latin America. Anti-HCV chemotherapy has severe adverse effects and is expensive, whereas dengue has no clinically authorized treatment. Antiparasitic medicines are often toxic and difficult to administer, and treatment failures are widely reported. There is an urgent need for new chemotherapies. Based on our previous research, we have undertaken structural modification of lead compound V with the goal of producing derivatives with both antiviral and trypanocidal activity. The novel spirocarbocyclic-substituted hydantoin analogs were designed, synthesized, and tested for antiviral activity against three HCV genotypes (1b, 3a, 4a), DENV, yellow fever virus (YFV), and two trypanosome species (T. brucei, T. cruzi). The optimization was successful and led to compounds with significant antiviral and trypanocidal activity and exceptional selectivity. Several modifications were made to further investigate the structure-activity relationships (SARs) and confirm the critical role of lipophilicity and conformational degrees of freedom.

Cysteine Proteases as Validated Targets for the Treatment of Neglected and Poverty-Related Parasitic Diseases

Neglected tropical diseases (NTDs) include 20 diverse infections mainly prevalent in tropical areas that mostly affect disadvantaged communities and women and children [...].

Dipeptide Nitrile CD34 with Curcumin: A New Improved Combination Strategy to Synergistically Inhibit Rhodesain of Trypanosoma brucei rhodesiense

Rhodesain is the main cysteine protease of Trypanosoma brucei rhodesiense, the parasite causing the acute lethal form of Human African Trypanosomiasis. Starting from the dipeptide nitrile CD24, the further introduction of a fluorine atom in the meta position of the phenyl ring spanning in the P3 site and the switch of the P2 leucine with a phenylalanine led to CD34, a synthetic inhibitor that shows a nanomolar binding affinity towards rhodesain (K_i = 27 nM) and an improved target selectivity with respect to the parent dipeptide nitrile CD24. In the present work, following the Chou and Talalay method, we carried out a combination study of CD34 with curcumin, a nutraceutical obtained from Curcuma longa L. Starting from an affected fraction (f_a) of rhodesain inhibition of 0.5 (i.e., the IC₅₀), we observed an initial moderate synergistic action, which became a synergism for f_a values ranging from 0.6 to 0.7 (i.e., 60-70% inhibition of the trypanosomal protease). Interestingly, at 80-90% inhibition of rhodesain proteolytic activity, we observed a strong synergism, resulting in 100% enzyme inhibition. Overall, in addition to the improved target selectivity of CD34 with respect to CD24, the combination of CD34 + curcumin resulted in an increased synergistic action with respect to CD24 + curcumin, thus suggesting that it is desirable to use CD34 and curcumin in combination.

Influence of amino acid size at the P3 position of N-Cbz-tripeptide Michael acceptors targeting falcipain-2 and rhodesain for the treatment of malaria and human african trypanosomiasis

In recent decades, several structure-activity relationship (SAR) studies provided potent inhibitors of the cysteine proteases falcipain-2 (FP-2) and rhodesain (RD) from Plasmodium falciparum and Trypanosoma brucei rhodesiense, respectively. Whilst the roles of the warhead and residues targeting the P1 and P2 pockets of the proteases were extensively investigated, the roles of the amino acids occupying the S3 pocket were not widely assessed. Herein we report the synthesis and biological evaluation of a set of novel Michael acceptors bearing amino acids of increasing size at the P3 site (1a-g/2a-g, SPR20-SPR33) against FP-2, RD, P. falciparum, and T. brucei. Overall, the Michael acceptors bearing small amino acids at the P3 site exhibited the most potent inhibitory properties towards FP-2. In contrast, analogues with bulky residues at the P3 position were very potent rhodesain inhibitors. In cell based assays, single-digit micromolar EC₅₀ values against the two protozoa were observed. These findings can be a starting point for the development of peptide-based FP-2 and RD inhibitors.

COVID-19 and Diarylamidines: The Parasitic Connection

As emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants (Omicron) continue to outpace and negate combinatorial vaccines and monoclonal antibody therapies targeting the spike protein (S) receptor binding domain (RBD), the appetite for developing similar COVID-19 treatments has significantly diminished, with the attention of the scientific community switching to long COVID treatments. However, treatments that reduce the risk of "post-COVID-19 syndrome" and associated sequelae remain in their infancy, particularly as no established criteria for diagnosis currently exist. Thus, alternative therapies that reduce infection and prevent the broad range of symptoms associated with 'post-COVID-19 syndrome' require investigation. This review begins with an overview of the parasitic-diarylamidine connection, followed by the renin-angiotensin system (RAS) and associated angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSSR2) involved in SARS-CoV-2 infection. Subsequently, the ability of diarylamidines to inhibit S-protein binding and various membrane serine proteases associated with SARS-CoV-2 and parasitic infections are discussed. Finally, the roles of diarylamidines (primarily DIZE) in vaccine efficacy, epigenetics, and the potential amelioration of long COVID sequelae are highlighted.

Further Investigations of Nitroheterocyclic Compounds as Potential Antikinetoplastid Drug Candidates

Due to the lack of specific vaccines, management of the trypanosomatid-caused neglected tropical diseases (sleeping sickness, Chagas disease and leishmaniasis) relies exclusively on pharmacological treatments. Current drugs against them are scarce, old and exhibit disadvantages, such as adverse effects, parenteral administration, chemical instability and high costs which are often unaffordable for endemic low-income countries. Discoveries of new pharmacological entities for the treatment of these diseases are scarce, since most of the big pharmaceutical companies find this market unattractive. In order to fill the pipeline of compounds and replace existing ones, highly translatable drug screening platforms have been developed in the last two decades. Thousands of molecules have been tested, including nitroheterocyclic compounds, such as benznidazole and nifurtimox, which had already provided potent and effective effects against Chagas disease. More recently, fexinidazole has been added as a new drug against African trypanosomiasis. Despite the success of nitroheterocycles, they had been discarded from drug discovery campaigns due to their mutagenic potential, but now they represent a promising source of inspiration for oral drugs that can replace those currently on the market. The examples provided by the trypanocidal activity of fexinidazole and the promising efficacy of the derivative DNDi-0690 against leishmaniasis seem to open a new window of opportunity for these compounds that were discovered in the 1960s. In this review, we show the current uses of nitroheterocycles and the novel derived molecules that are being synthesized against these neglected diseases.

Cloning and Characterization of Trypanosoma congolense and T. vivax Nucleoside Transporters Reveal the Potential of P1-Type Carriers for the Discovery of Broad-Spectrum Nucleoside-Based Therapeutics against Animal African Trypanosomiasis

African Animal Trypanosomiasis (AAT), caused predominantly by Trypanosoma brucei brucei, T. vivax and T. congolense, is a fatal livestock disease throughout Sub-Saharan Africa. Treatment options are very limited and threatened by resistance. Tubercidin (7-deazaadenosine) analogs have shown activity against individual parasites but viable chemotherapy must be active against all three species. Divergence in sensitivity to nucleoside antimetabolites could be caused by differences in nucleoside transporters. Having previously characterized the T. brucei nucleoside carriers, we here report the functional expression and characterization of the main adenosine transporters of T. vivax (TvxNT3) and T. congolense (TcoAT1/NT10), in a Leishmania mexicana cell line ('SUPKO') lacking adenosine uptake. Both carriers were similar to the T. brucei P1-type transporters and bind adenosine mostly through interactions with N3, N7 and 3'-OH. Expression of TvxNT3 and TcoAT1 sensitized SUPKO cells to various 7-substituted tubercidins and other nucleoside analogs although tubercidin itself is a poor substrate for P1-type transporters. Individual nucleoside EC₅₀s were similar for T. b. brucei, T. congolense, T. evansi and T. equiperdum but correlated less well with T. vivax. However, multiple nucleosides including 7-halogentubercidines displayed pEC50>7 for all species and, based on transporter and anti-parasite SAR analyses, we conclude that nucleoside chemotherapy for AAT is viable.

The Activity of Red Nigerian Propolis and Some of Its Components against Trypanosoma brucei and Trypanosoma congolense

Propolis is a resin that is gathered by bees from exudates produced by various plants. Its exact chemical composition depends on the plants available near the hive. Bees use propolis to coat the surfaces of the hive, where it acts as an anti-infective. Regardless of the chemical composition of propolis, it is always anti-protozoal, probably because protozoan parasites, particularly Lotmarium passim, are widespread in bee populations. The protozoa Trypanosoma brucei and T. congolense cause disease in humans and/or animals. The existing drugs for treating these diseases are old and resistance is an increasingly severe problem. The many types of propolis present a rich source of anti-trypanosomal compounds-from a material gathered by bees in an environmentally friendly way. In the current work, red Nigerian propolis from Rivers State, Nigeria was tested against T. brucei and T. congolense and found to be highly active (EC₅₀ 1.66 and 4.00 µg/mL, respectively). Four isoflavonoids, vestitol, neovestitol, 7-methylvestitol and medicarpin, were isolated from the propolis. The isolated compounds were also tested against T. brucei and T. congolense, and vestitol displayed the highest activity at 3.86 and 4.36 µg/mL, respectively. Activities against drug-resistant forms of T. brucei and T. congolense were similar to those against wild type.

Clinically relevant benzoxaboroles inhibit mRNA processing in Trypanosoma brucei

OBJECTIVE

The cleavage and polyadenylation endonuclease CPSF73 is thought to be the target of the anti-trypanosomal benzoxaboroles AN7973, acoziborole and AN11736. We previously showed that AN7973 inhibits mRNA processing. We here investigated whether the drug candidates acoziborole (for human sleeping sickness) and AN11736 (for nagana in cattle) have the same effect. We also affinity purified tagged CPSF73 from parasites without, or after, AN7973 treatment, and analysed differentially co-purified proteins by mass spectrometry.

RESULTS

AN11736 and acoziborole both inhibited mRNA processing, as demonstrated by decreased levels of spliced mRNAs and accumulation of di- and tri-cistronic mRNAs from the alpha-beta tubulin locus. Treating the cells with AN7973 for 30 min. did not significantly affect the proteins that copurified with CPSF73.

Fexinidazole for Human African Trypanosomiasis, the Fruit of a Successful Public-Private Partnership

After 100 years of chemotherapy with impractical and toxic drugs, an oral cure for human African trypanosomiasis (HAT) is available: Fexinidazole. In this case, we review the history of drug discovery for HAT with special emphasis on the discovery, pre-clinical development, and operational challenges of the clinical trials of fexinidazole. The screening of the Drugs for Neglected Diseases initiative (DNDi) HAT-library by the Swiss TPH had singled out fexinidazole, originally developed by Hoechst (now Sanofi), as the most promising of a series of over 800 nitroimidazoles and related molecules. In cell culture, fexinidazole has an IC50 of around 1 µM against Trypanosoma brucei and is more than 100-fold less toxic to mammalian cells. In the mouse model, fexinidazole cures both the first, haemolymphatic, and the second, meningoencephalitic stage of the infection, the latter at 100 mg/kg twice daily for 5 days. In patients, the clinical trials managed by DNDi and supported by Swiss TPH mainly conducted in the Democratic Republic of the Congo demonstrated that oral fexinidazole is safe and effective for use against first- and early second-stage sleeping sickness. Based on the positive opinion issued by the European Medicines Agency in 2018, the WHO has released new interim guidelines for the treatment of HAT including fexinidazole as the new therapy for first-stage and non-severe second-stage sleeping sickness caused by Trypanosoma brucei gambiense (gHAT). This greatly facilitates the diagnosis and treatment algorithm for gHAT, increasing the attainable coverage and paving the way towards the envisaged goal of zero transmission by 2030.

3-nitroimidazo[1,2-b]pyridazine as a novel scaffold for antiparasitics with sub-nanomolar anti-Giardia lamblia activity

As there is a continuous need for novel anti-infectives, the present study aimed to fuse two modes of action into a novel 3-nitroimidazo[1,2-b]pyridazine scaffold to improve antiparasitic efficacy. For this purpose, we combined known structural elements of phosphodiesterase inhibitors, a target recently proposed for Trypanosoma brucei and Giardia lamblia, with a nitroimidazole scaffold to generate nitrosative stress. The compounds were evaluated in vitro against a panel of protozoal parasites, namely Giardia lamblia, Trypanosoma brucei, T. cruzi, Leishmania infantum and Plasmodium falciparum and for cytotoxicity on MRC-5 cells. Interestingly, selective sub-nanomolar activity was obtained against G. lamblia, and by testing several analogues with and without the nitro group, it was shown that the presence of a nitro group, but not PDE inhibition, is responsible for the low IC₅₀ values of these novel compounds. Adding the favourable drug-like properties (low molecular weight, cLogP (1.2–4.1) and low polar surface area), the key compounds from the 3-nitroimidazo[1,2-b]pyridazine series can be considered as valuable hits for further anti-giardiasis drug exploration and development.

•

Analogues fusing a nitroimidazole moiety and a PDE inhibitor scaffold were prepared.

•

These compounds were tested in vitro against a panel of protozoal parasites.

•

Against Giardia lamblia, sub-nanomolar IC₅₀ values were determined.

•

PDE inhibition provided no significant contribution to the anti-Giardia potency.

•

High potency with drug-like properties warrants further study of this hit series.

Development of Urea-Bond-Containing Michael Acceptors as Antitrypanosomal Agents Targeting Rhodesain

Human African Trypanosomiasis (HAT) is a neglected tropical disease widespread in sub-Saharan Africa. Rhodesain, a cysteine protease of Trypanosoma brucei rhodesiense, has been identified as a valid target for the development of anti-HAT agents. Herein, we report a series of urea-bond-containing Michael acceptors, which were demonstrated to be potent rhodesain inhibitors with K_i values ranging from 0.15 to 2.51 nM, and five of them showed comparable k_2nd values to that of K11777, a potent antitrypanosomal agent. Moreover, most of the urea derivatives exhibited single-digit micromolar activity against the protozoa, and the presence of substituents at the P3 position appears to be essential for the antitrypanosomal effect. Replacement of Phe with Leu at the P2 site kept unchanged the inhibitory properties. Compound 7 (SPR7) showed the best compromise in terms of rhodesain inhibition, selectivity, and antiparasitic activity, thus representing a new lead compound for future SAR studies.

Current Treatments to Control African Trypanosomiasis and One Health Perspective

Human African Trypanosomiasis (HAT, sleeping sickness) and Animal African Trypanosomiasis (AAT) are neglected tropical diseases generally caused by the same etiological agent, Trypanosoma brucei. Despite important advances in the reduction or disappearance of HAT cases, AAT represents a risky reservoir of the infections. There is a strong need to control AAT, as is claimed by the European Commission in a recent document on the reservation of antimicrobials for human use. Control of AAT is considered part of the One Health approach established by the FAO program against African Trypanosomiasis. Under the umbrella of the One Health concepts, in this work, by analyzing the pharmacological properties of the therapeutic options against Trypanosoma brucei spp., we underline the need for clearer and more defined guidelines in the employment of drugs designed for HAT and AAT. Essential requirements are addressed to meet the challenge of drug use and drug resistance development. This approach shall avoid inter-species cross-resistance phenomena and retain drugs therapeutic activity.

Probing Adamantane Arylhydroxamic Acids against Trypanosoma brucei and Trypanosoma cruzi

In this work, we present the synthesis and the anti-trypanosomal activity of the 2-(4-(adamant-1-yl)phenyl)-N-hydroxyarylamides, 1a,b and the 2-(4-(adamant-1-yl)phenoxy)-N-hydroxyacetamide, 1c. The 4-(adamant-1-yl)phenyl- and 4-(adamant-1-yl)phenoxy- moieties, which are endowed with promising drug-like properties, are functionalized at the side chain termini as hydroxamic acids. The phenoxy acetohydroxamic derivative, 1c, shows the most interesting profile in terms of activity and toxicity against trypanosomes and merits further investigation.

Development and Introduction of Fexinidazole into the Global Human African Trypanosomiasis Program

In this article, the authors show the strategy used to streamline the introduction of fexinidazole, the first all oral treatment of human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense. The dose range was determined in phase 1 studies and a significant food effect was observed, which was tested with field-adapted meals. The pharmacokinetic profile required definition of a higher loading dosage for the first 4 days and administration of the daily dose together with a typical local meal to optimize product absorption and rapidly achieve drug steady state. This allowed for a combined phase II/III pivotal study directly after phase I trials. Partnerships with highly engaged actors from endemic country control programs and international research institutions started early through the HAT platform, building on an agreed target product profile (TPP), establishing a regulatory plan early and transparently including endemic countries in the research and data flow. A key element that enabled a quick start to access activities was preparing for World Health Organization guidelines early and starting the process prior to registration. Distribution plans were identified and supply was established from the start, by taking advantage of the existing supply agreement between the producers of all HAT drugs (Sanofi and Bayer) and the WHO. Pharmacovigilance and phase 4 studies were nested into wider implementation activities. Targeted sequential introduction into national programs was prioritized, based on medical need and epidemiologically updated information.

Population Pharmacodynamic Modeling of Eflornithine-Based Treatments Against Late-Stage Gambiense Human African Trypanosomiasis and Efficacy Predictions of L-eflornithine-Based Therapy

Eflornithine is a recommended treatment against late-stage gambiense human African trypanosomiasis, a neglected tropical disease. Standard dosing of eflornithine consists of repeated intravenous infusions of a racemic mixture of L- and D-eflornithine. Data from three clinical studies, (i) eflornithine intravenous monotherapy, (ii) nifurtimox-eflornithine combination therapy, and (iii) eflornithine oral monotherapy, were pooled and analyzed using a time-to-event pharmacodynamic modeling approach, supported by in vitro activity data of the individual enantiomers. Our aim was to assess (i) the efficacy of the eflornithine regimens in a time-to-event analysis and (ii) the feasibility of an L-eflornithine-based therapy integrating clinical and preclinical data. A pharmacodynamic time-to-event model was used to estimate the total dose of eflornithine, associated with 50% reduction in baseline hazard, when administered as monotherapy or in the nifurtimox-eflornithine combination therapy. The estimated total doses were 159, 60 and 291 g for intravenous eflornithine monotherapy, nifurtimox-eflornithine combination therapy and oral eflornithine monotherapy, respectively. Simulations suggested that L-eflornithine achieves a higher predicted median survival, compared to when racemate is administered, as treatment against late-stage gambiense human African trypanosomiasis. Our findings showed that oral L-eflornithine-based monotherapy would not result in adequate efficacy, even at high dose, and warrants further investigations to assess the potential of oral L-eflornithine-based treatment in combination with other treatments such as nifurtimox. An all-oral eflornithine-based regimen would provide easier access to treatment and reduce burden on patients and healthcare systems in gambiense human African trypanosomiasis endemic areas. Graphical abstract.

Trypanosoma brucei: Metabolomics for analysis of cellular metabolism and drug discovery

BACKGROUND

Trypanosoma brucei is the causative agent of Human African Trypanosomiasis (also known as sleeping sickness), a disease causing serious neurological disorders and fatal if left untreated. Due to its lethal pathogenicity, a variety of treatments have been developed over the years, but which have some important limitations such as acute toxicity and parasite resistance. Metabolomics is an innovative tool used to better understand the parasite's cellular metabolism, and identify new potential targets, modes of action and resistance mechanisms. The metabolomic approach is mainly associated with robust analytical techniques, such as NMR and Mass Spectrometry. Applying these tools to the trypanosome parasite is, thus, useful for providing new insights into the sleeping sickness pathology and guidance towards innovative treatments.

AIM OF REVIEW

The present review aims to comprehensively describe the T. brucei biology and identify targets for new or commercialized antitrypanosomal drugs. Recent metabolomic applications to provide a deeper knowledge about the mechanisms of action of drugs or potential drugs against T. brucei are highlighted. Additionally, the advantages of metabolomics, alone or combined with other methods, are discussed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Compared to other parasites, only few studies employing metabolomics have to date been reported on Trypanosoma brucei. Published metabolic studies, treatments and modes of action are discussed. The main interest is to evaluate the metabolomics contribution to the understanding of T. brucei's metabolism.

An Update on African Trypanocide Pharmaceutics and Resistance

African trypanosomiasis is associated with Trypanosoma evansi, T. vivax, T. congolense, and T. brucei pathogens in African animal trypanosomiasis (AAT) while T. b gambiense and T. b rhodesiense are responsible for chronic and acute human African trypanosomiasis (HAT), respectively. Suramin sodium suppresses ATP generation during the glycolytic pathway and is ineffective against T. vivax and T. congolense infections. Resistance to suramin is associated with pathogen altered transport proteins. Melarsoprol binds irreversibly with pyruvate kinase protein sulfhydryl groups and neutralizes enzymes which interrupts the trypanosome ATP generation. Melarsoprol resistance is associated with the adenine-adenosine transporter, P2, due to point mutations within this transporter. Eflornithine is used in combination with nifurtimox. Resistance to eflornithine is caused by the deletion or mutation of TbAAT6 gene which encodes the transmembrane amino acid transporter that delivers eflornithine into the cell, thus loss of transporter protein results in eflornithine resistance. Nifurtimox alone is regarded as a poor trypanocide, however, it is effective in melarsoprol-resistant gHAT patients. Resistance is associated with loss of a single copy of the genes encoding for nitroreductase enzymes. Fexinidazole is recommended for first-stage and non-severe second-stage illnesses in gHAT and resistance is associated with trypanosome bacterial nitroreductases which reduce fexinidazole. In AAT, quinapyramine sulfate interferes with DNA synthesis and suppression of cytoplasmic ribosomal activity in the mitochondria. Quinapyramine sulfate resistance is due to variations in the potential of the parasite's mitochondrial membrane. Pentamidines create cross-links between two adenines at 4–5 pairs apart in adenine-thymine-rich portions of Trypanosoma DNA. It also suppresses type II topoisomerase in the mitochondria of Trypanosoma parasites. Pentamidine resistance is due to loss of mitochondria transport proteins P2 and HAPT1. Diamidines are most effective against Trypanosome brucei group and act via the P2/TbAT1 transporters. Diminazene aceturate resistance is due to mutations that alter the activity of P2, TeDR40 (T. b. evansi). Isometamidium chloride is primarily employed in the early stages of trypanosomiasis and resistance is associated with diminazene resistance. Phenanthridine (homidium bromide, also known as ethidium bromide) acts by a breakdown of the kinetoplast network and homidium resistance is comparable to isometamidium. In humans, the development of resistance and adverse side effects against monotherapies has led to the adoption of nifurtimox-eflornithine combination therapy. Current efforts to develop new prodrug combinations of nifurtimox and eflornithine and nitroimidazole fexinidazole as well as benzoxaborole SCYX-7158 (AN5568) for HAT are in progress while little comparable progress has been done for the development of novel therapies to address trypanocide resistance in AAT.

Differences in Transporters Rather than Drug Targets Are the Principal Determinants of the Different Innate Sensitivities of Trypanosoma congolense and Trypanozoon Subgenus Trypanosomes to Diamidines and Melaminophenyl Arsenicals

The animal trypanosomiases are infections in a wide range of (domesticated) animals with any species of African trypanosome, such as Trypanosoma brucei, T. evansi, T. congolense, T. equiperdum and T. vivax. Symptoms differ between host and infective species and stage of infection and are treated with a small set of decades-old trypanocides. A complication is that not all trypanosome species are equally sensitive to all drugs and the reasons are at best partially understood. Here, we investigate whether drug transporters, mostly identified in T. b. brucei, determine the different drug sensitivities. We report that homologues of the aminopurine transporter TbAT1 and the aquaporin TbAQP2 are absent in T. congolense, while their introduction greatly sensitises this species to diamidine (pentamidine, diminazene) and melaminophenyl (melarsomine) drugs. Accumulation of these drugs in the transgenic lines was much more rapid. T. congolense is also inherently less sensitive to suramin than T. brucei, despite accumulating it faster. Expression of a proposed suramin transporter, located in T. brucei lysosomes, in T. congolense, did not alter its suramin sensitivity. We conclude that for several of the most important classes of trypanocides the presence of specific transporters, rather than drug targets, is the determining factor of drug efficacy.

The Antiprotozoal Activity of Papua New Guinea Propolis and Its Triterpenes

Profiling a propolis sample from Papua New Guinea (PNG) using high-resolution mass spectrometry indicated that it contained several triterpenoids. Further fractionation by column chromatography and medium-pressure liquid chromatography (MPLC) followed by nuclear magnetic resonance spectroscopy (NMR) identified 12 triterpenoids. Five of these were obtained pure and the others as mixtures of two or three compounds. The compounds identified were: mangiferonic acid, ambonic acid, isomangiferolic acid, ambolic acid, 27-hydroxyisomangiferolic acid, cycloartenol, cycloeucalenol, 24-methylenecycloartenol, 20-hydroxybetulin, betulin, betulinic acid and madecassic acid. The fractions from the propolis and the purified compounds were tested in vitro against Crithidia fasciculata, Trypanosoma congolense, drug-resistant Trypanosoma congolense, Trypanosoma b. brucei and multidrug-resistant Trypanosoma b. brucei (B48). They were also assayed for their toxicity against U947 cells. The compounds and fractions displayed moderate to high activity against parasitic protozoa but only low cytotoxicity against the mammalian cells. The most active isolated compound, 20-hydroxybetulin, was found to be trypanostatic when different concentrations were tested against T. b. brucei growth.

Fragment-Based Drug Discovery for Trypanosoma brucei Glycosylphosphatidylinositol-Specific Phospholipase C through Biochemical and WaterLOGSY-NMR Methods

Glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) of Trypanosoma brucei, the causative protozoan parasite of African trypanosomiasis, is a membrane-bound enzyme essential for antigenic variation, because it catalyses the release of the membrane-bound form of variable surface glycoproteins. Here, we performed a fragment-based drug discovery of TbGPI-PLC inhibitors using a combination of enzymatic inhibition assay and water-ligand observed via gradient spectroscopy (WaterLOGSY) NMR experiment. The TbGPI-PLC was cloned and over-expressed using an Escherichia coli expression system followed by purification using three-phase partitioning and gel filtration. Subsequently, the inhibitory activity of 873 fragment compounds against the recombinant TbGPI-PLC led to the identification of 66 primary hits. These primary hits were subjected to the WaterLOGSY NMR experiment where 10 fragment hits were confirmed to directly bind to the TbGPI-PLC. These included benzothiazole, chlorobenzene, imidazole, indole, pyrazol and quinolinone derivatives. Molecular docking simulation indicated that six of them share a common binding site, which corresponds to the catalytic pocket. The present study identified chemically diverse fragment hits that could directly bind and inhibit the TbGPI-PLC activity which constructed a framework for fragment optimisation or linking towards the design of novel drugs for African trypanosomiasis.

Discovery, Development, Inventions and Patent Review of Fexinidazole: The First All-Oral Therapy for Human African Trypanosomiasis

Human African trypanosomiasis (HAT or ‘sleeping sickness’) is a neglected tropical disease. If untreated, it is always fatal and leads to death. A few treatments are available for HAT, but most of them require a skilled professional, which increases the financial burden on the patient. Recently, fexinidazole (FEX) has been approved by the European Medicine Agency (EMA) and the United States Food and Drug Administration (USFDA) as the first all-oral therapy for the treatment of stage-1 (hemolymphatic) as well as stage-2 (meningoencephalitic) of HAT. Before the FEX approval, there were separate treatments for stage-1 and stage-2 of HAT. This study reviews the discovery, development timeline, inventions, and patent literature of FEX. It was first approved by EMA and USFDA in 2018 and 2021, respectively. FEX was also added to the World Health Organization’s list of essential drugs in 2019. The patent literature search revealed many types of patents/patent applications (compound, salt, process, method of treatment, drug combinations, and compositions) related to FEX, which have been summarized in this article. The authors foresee a great scope to develop more inventions based on FEX (novel salts, polymorphs, drug conjugates, cyclodextrin complex, etc.) for the treatment of many protozoal diseases (Leishmaniasis and Chagas disease), inflammatory diseases, and other microbial infections. New combinations of FEX with other treatments of HAT may also provide fruitful results. This review might be useful to the scientists working on the HAT and other neglected diseases to develop novel inventions and innovations of therapeutic relevance.

The Transporter-Mediated Cellular Uptake and Efflux of Pharmaceutical Drugs and Biotechnology Products: How and Why Phospholipid Bilayer Transport Is Negligible in Real Biomembranes

Over the years, my colleagues and I have come to realise that the likelihood of pharmaceutical drugs being able to diffuse through whatever unhindered phospholipid bilayer may exist in intact biological membranes in vivo is vanishingly low. This is because (i) most real biomembranes are mostly protein, not lipid, (ii) unlike purely lipid bilayers that can form transient aqueous channels, the high concentrations of proteins serve to stop such activity, (iii) natural evolution long ago selected against transport methods that just let any undesirable products enter a cell, (iv) transporters have now been identified for all kinds of molecules (even water) that were once thought not to require them, (v) many experiments show a massive variation in the uptake of drugs between different cells, tissues, and organisms, that cannot be explained if lipid bilayer transport is significant or if efflux were the only differentiator, and (vi) many experiments that manipulate the expression level of individual transporters as an independent variable demonstrate their role in drug and nutrient uptake (including in cytotoxicity or adverse drug reactions). This makes such transporters valuable both as a means of targeting drugs (not least anti-infectives) to selected cells or tissues and also as drug targets. The same considerations apply to the exploitation of substrate uptake and product efflux transporters in biotechnology. We are also beginning to recognise that transporters are more promiscuous, and antiporter activity is much more widespread, than had been realised, and that such processes are adaptive (i.e., were selected by natural evolution). The purpose of the present review is to summarise the above, and to rehearse and update readers on recent developments. These developments lead us to retain and indeed to strengthen our contention that for transmembrane pharmaceutical drug transport "phospholipid bilayer transport is negligible".

Synthesis, antiproliferative and antitrypanosomal activities, and DNA binding of novel 6-amidino-2-arylbenzothiazoles

A series of 6-amidinobenzothiazoles, linked via phenoxymethylene or directly to the 1,2,3-triazole ring with a p-substituted phenyl or benzyl moiety, were synthesised and evaluated in vitro against four human tumour cell lines and the protozoan parasite Trypanosoma brucei. The influence of the type of amidino substituent and phenoxymethylene linker on antiproliferative and antitrypanosomal activities was observed, showing that the imidazoline moiety had a major impact on both activities. Benzothiazole imidazoline 14a, which was directly connected to N-1-phenyl-1,2,3-triazole, had the most potent growth-inhibitory effect (IC₅₀ = 0.25 µM) on colorectal adenocarcinoma (SW620), while benzothiazole imidazoline 11b, containing a phenoxymethylene linker, exhibited the best antitrypanosomal potency (IC₉₀ = 0.12 µM). DNA binding assays showed a non-covalent interaction of 6-amidinobenzothiazole ligands, indicating both minor groove binding and intercalation modes of DNA interaction. Our findings encourage further development of novel structurally related 6-amidino-2-arylbenzothiazoles to obtain more selective anticancer and anti-HAT agents.

AQPX-cluster aquaporins and aquaglyceroporins are asymmetrically distributed in trypanosomes

Major Intrinsic Proteins (MIPs) are membrane channels that permeate water and other small solutes. Some trypanosomatid MIPs mediate the uptake of antiparasitic compounds, placing them as potential drug targets. However, a thorough study of the diversity of these channels is still missing. Here we place trypanosomatid channels in the sequence-function space of the large MIP superfamily through a sequence similarity network. This analysis exposes that trypanosomatid aquaporins integrate a distant cluster from the currently defined MIP families, here named aquaporin X (AQPX). Our phylogenetic analyses reveal that trypanosomatid MIPs distribute exclusively between aquaglyceroporin (GLP) and AQPX, being the AQPX family expanded in the Metakinetoplastina common ancestor before the origin of the parasitic order Trypanosomatida. Synteny analysis shows how African trypanosomes specifically lost AQPXs, whereas American trypanosomes specifically lost GLPs. AQPXs diverge from already described MIPs on crucial residues. Together, our results expose the diversity of trypanosomatid MIPs and will aid further functional, structural, and physiological research needed to face the potentiality of the AQPXs as gateways for trypanocidal drugs.

Direct, Late-Stage Mono-N-arylation of Pentamidine: Method Development, Mechanistic Insight, and Expedient Access to Novel Antiparastitics against Diamidine-Resistant Parasites

A selective mono‐N‐arylation strategy of amidines under Chan‐Lam conditions is described. During the reaction optimization phase, the isolation of a mononuclear Cu(II) complex provided unique mechanistic insight into the operation of Chan‐Lam mono‐N‐arylation. The scope of the process is demonstrated, and then applied to access the first mono‐N‐arylated analogues of pentamidine. Sub‐micromolar activity against kinetoplastid parasites was observed for several analogues with no cross‐resistance in pentamidine and diminazene‐resistant trypanosome strains and against Leishmania mexicana. A fluorescent mono‐N‐arylated pentamidine analogue revealed rapid cellular uptake, accumulating in parasite nuclei and the kinetoplasts. The DNA binding capability of the mono‐N‐arylated pentamidine series was confirmed by UV‐melt measurements using AT‐rich DNA. This work highlights the potential to use Chan‐Lam mono‐N‐arylation to develop therapeutic leads against diamidine‐resistant trypanosomiasis and leishmaniasis.

Divergent metabolism between Trypanosoma congolense and Trypanosoma brucei results in differential sensitivity to metabolic inhibition

Animal African Trypanosomiasis (AAT) is a debilitating livestock disease prevalent across sub-Saharan Africa, a main cause of which is the protozoan parasite Trypanosoma congolense. In comparison to the well-studied T. brucei, there is a major paucity of knowledge regarding the biology of T. congolense. Here, we use a combination of omics technologies and novel genetic tools to characterise core metabolism in T. congolense mammalian-infective bloodstream-form parasites, and test whether metabolic differences compared to T. brucei impact upon sensitivity to metabolic inhibition. Like the bloodstream stage of T. brucei, glycolysis plays a major part in T. congolense energy metabolism. However, the rate of glucose uptake is significantly lower in bloodstream stage T. congolense, with cells remaining viable when cultured in concentrations as low as 2 mM. Instead of pyruvate, the primary glycolytic endpoints are succinate, malate and acetate. Transcriptomics analysis showed higher levels of transcripts associated with the mitochondrial pyruvate dehydrogenase complex, acetate generation, and the glycosomal succinate shunt in T. congolense, compared to T. brucei. Stable-isotope labelling of glucose enabled the comparison of carbon usage between T. brucei and T. congolense, highlighting differences in nucleotide and saturated fatty acid metabolism. To validate the metabolic similarities and differences, both species were treated with metabolic inhibitors, confirming that electron transport chain activity is not essential in T. congolense. However, the parasite exhibits increased sensitivity to inhibition of mitochondrial pyruvate import, compared to T. brucei. Strikingly, T. congolense exhibited significant resistance to inhibitors of fatty acid synthesis, including a 780-fold higher EC50 for the lipase and fatty acid synthase inhibitor Orlistat, compared to T. brucei. These data highlight that bloodstream form T. congolense diverges from T. brucei in key areas of metabolism, with several features that are intermediate between bloodstream- and insect-stage T. brucei. These results have implications for drug development, mechanisms of drug resistance and host-pathogen interactions.

Diverse Functions of Tim50, a Component of the Mitochondrial Inner Membrane Protein Translocase

Mitochondria are essential in eukaryotes. Besides producing 80% of total cellular ATP, mitochondria are involved in various cellular functions such as apoptosis, inflammation, innate immunity, stress tolerance, and Ca2+ homeostasis. Mitochondria are also the site for many critical metabolic pathways and are integrated into the signaling network to maintain cellular homeostasis under stress. Mitochondria require hundreds of proteins to perform all these functions. Since the mitochondrial genome only encodes a handful of proteins, most mitochondrial proteins are imported from the cytosol via receptor/translocase complexes on the mitochondrial outer and inner membranes known as TOMs and TIMs. Many of the subunits of these protein complexes are essential for cell survival in model yeast and other unicellular eukaryotes. Defects in the mitochondrial import machineries are also associated with various metabolic, developmental, and neurodegenerative disorders in multicellular organisms. In addition to their canonical functions, these protein translocases also help maintain mitochondrial structure and dynamics, lipid metabolism, and stress response. This review focuses on the role of Tim50, the receptor component of one of the TIM complexes, in different cellular functions, with an emphasis on the Tim50 homologue in parasitic protozoan Trypanosoma brucei.

A Small Molecule Inhibitor of Pex3-Pex19 Interaction Disrupts Glycosome Biogenesis and Causes Lethality in Trypanosoma brucei

Trypanosomatid parasites, including Trypanosoma and Leishmania, are infectious zoonotic agents for a number of severe diseases such as African sleeping sickness and American trypanosomiasis (Chagas disease) that affect millions of people, mostly in the emergent world. The glycosome is a specialized member of the peroxisome family of organelles found in trypanosomatids. These organelles compartmentalize essential enzymes of the glycolytic pathway, making them a prime target for drugs that can kill these organisms by interfering with either their biochemical functions or their formation. Glycosome biogenesis, like peroxisome biogenesis, is controlled by a group of proteins called peroxins (Pex). Pex3 is an early acting peroxin that docks Pex19, the receptor for peroxisomal membrane proteins, to initiate biogenesis of peroxisomes from the endoplasmic reticulum. Identification of Pex3 as the essential master regulator of glycosome biogenesis has implications in developing small molecule inhibitors that can impede Pex3–Pex19 interaction. Low amino acid sequence conservation between trypanosomatid Pex3 and human Pex3 (HsPex3) would aid in the identification of small molecule inhibitors that selectively interfere with the trypanosomatid Pex3–Pex19 interaction. We tested a library of pharmacologically active compounds in a modified yeast two-hybrid assay and identified a compound that preferentially inhibited the interaction of Trypanosoma brucei Pex3 and Pex19 versus HsPex3 and Pex19. Addition of this compound to either the insect or bloodstream form of T. brucei disrupted glycosome biogenesis, leading to mislocalization of glycosomal enzymes to the cytosol and lethality for the parasite. Our results show that preferential disruption of trypanosomal Pex3 function by small molecule inhibitors could help in the accelerated development of drugs for the treatment of trypanosomiases.

Identifying SARS-CoV-2 antiviral compounds by screening for small molecule inhibitors of nsp12/7/8 RNA-dependent RNA polymerase

The coronavirus disease 2019 (COVID-19) global pandemic has turned into the largest public health and economic crisis in recent history impacting virtually all sectors of society. There is a need for effective therapeutics to battle the ongoing pandemic. Repurposing existing drugs with known pharmacological safety profiles is a fast and cost-effective approach to identify novel treatments. The COVID-19 etiologic agent is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a single-stranded positive-sense RNA virus. Coronaviruses rely on the enzymatic activity of the replication–transcription complex (RTC) to multiply inside host cells. The RTC core catalytic component is the RNA-dependent RNA polymerase (RdRp) holoenzyme. The RdRp is one of the key druggable targets for CoVs due to its essential role in viral replication, high degree of sequence and structural conservation and the lack of homologues in human cells. Here, we have expressed, purified and biochemically characterised active SARS-CoV-2 RdRp complexes. We developed a novel fluorescence resonance energy transfer-based strand displacement assay for monitoring SARS-CoV-2 RdRp activity suitable for a high-throughput format. As part of a larger research project to identify inhibitors for all the enzymatic activities encoded by SARS-CoV-2, we used this assay to screen a custom chemical library of over 5000 approved and investigational compounds for novel SARS-CoV-2 RdRp inhibitors. We identified three novel compounds (GSK-650394, C646 and BH3I-1) and confirmed suramin and suramin-like compounds as in vitro SARS-CoV-2 RdRp activity inhibitors. We also characterised the antiviral efficacy of these drugs in cell-based assays that we developed to monitor SARS-CoV-2 growth.

Parasitic sirtuin 2 as an opportunity in drug discovery

Infections caused by protozoans remain a public health issue, especially in tropical countries. Serious adverse events, lack of efficacy at the different stages of the infection and routes of administration that have a negative impact on treatment adherence are some of the problems with currently available therapy against these diseases. Here we describe an epigenetic target, sirtuin 2 and its related proteins, that is promising given the results in phenotypic assays and in vivo models against Sir2 of Plasmodium falciparum, Leishmania donovani, Leishmania infantum, Schistosoma mansoni, Trypanosoma brucei and Trypanosoma cruzi parasites. The results we present highlight how this target can be extensively explored and how its inhibitors might be employed in the clinic.

Activity of Compounds from Temperate Propolis against Trypanosoma brucei and Leishmania mexicana

Ethanolic extracts of samples of temperate zone propolis, four from the UK and one from Poland, were tested against three Trypanosoma brucei strains and displayed EC₅₀ values < 20 µg/mL. The extracts were fractionated, from which 12 compounds and one two-component mixture were isolated, and characterized by NMR and high-resolution mass spectrometry, as 3-acetoxypinobanksin, tectochrysin, kaempferol, pinocembrin, 4′-methoxykaempferol, galangin, chrysin, apigenin, pinostrobin, cinnamic acid, coumaric acid, cinnamyl ester/coumaric acid benzyl ester (mixture), 4′,7-dimethoxykaempferol, and naringenin 4′,7-dimethyl ether. The isolated compounds were tested against drug-sensitive and drug-resistant strains of T. brucei and Leishmania mexicana, with the highest activities ≤ 15 µM. The most active compounds against T. brucei were naringenin 4′,7 dimethyl ether and 4′methoxy kaempferol with activity of 15–20 µM against the three T. brucei strains. The most active compounds against L. mexicana were 4′,7-dimethoxykaempferol and the coumaric acid ester mixture, with EC₅₀ values of 12.9 ± 3.7 µM and 13.1 ± 1.0 µM. No loss of activity was found with the diamidine- and arsenical-resistant or phenanthridine-resistant T. brucei strains, or the miltefosine-resistant L. mexicana strain; no clear structure activity relationship was observed for the isolated compounds. Temperate propolis yields multiple compounds with anti-kinetoplastid activity.

Diminazene resistance in Trypanosoma congolense is not caused by reduced transport capacity but associated with reduced mitochondrial membrane potential

Trypanosoma congolense is a principal agent causing livestock trypanosomiasis in Africa, costing developing economies billions of dollars and undermining food security. Only the diamidine diminazene and the phenanthridine isometamidium are regularly used, and resistance is widespread but poorly understood. We induced stable diminazene resistance in T. congolense strain IL3000 in vitro. There was no cross-resistance with the phenanthridine drugs, melaminophenyl arsenicals, oxaborole trypanocides, or with diamidine trypanocides, except the close analogs DB829 and DB75. Fluorescence microscopy showed that accumulation of DB75 was inhibited by folate. Uptake of [³ H]-diminazene was slow with low affinity and partly but reciprocally inhibited by folate and by competing diamidines. Expression of T. congolense folate transporters in diminazene-resistant Trypanosoma brucei brucei significantly sensitized the cells to diminazene and DB829, but not to oxaborole AN7973. However, [³ H]-diminazene transport studies, whole-genome sequencing, and RNA-seq found no major changes in diminazene uptake, folate transporter sequence, or expression. Instead, all resistant clones displayed a moderate reduction in the mitochondrial membrane potential Ψm. We conclude that diminazene uptake in T. congolense proceed via multiple low affinity mechanisms including folate transporters; while resistance is associated with a reduction in Ψm it is unclear whether this is the primary cause of the resistance.

Two New Antiprotozoal Diterpenes From the Roots of Acacia nilotica

The powdered roots of the medicinal plant Acacia nilotica were extracted with hexane and ethyl acetate, and the extracts were subjected to column chromatography for the isolation of potentially bioactive compounds and their screening against kinetoplastid pathogens. NMR and HREI mass spectrometric analyses identified two new diterpenes, characterized as 16, 19-dihydroxycassa-12-en-15-one (Sandynone, 1) and (5S, 7R, 8R, 9R, 10S, 13Z, 17S)-7,8:7,17:16,17-triepoxy-7,8-seco-cassa-13-ene (niloticane B, 2). The previously reported (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-diene-7,17-diol (3), (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol-17-al (4), and (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol (5) a, mixture of stigmasterol (6a) and sitosterol (6b), and lupeol (7) were also isolated. Several column fractions displayed significant activity against a panel of Trypanosoma and Leishmania spp., and from the most active fraction, compound 4 was isolated with high purity. The compound displayed high activity, particularly against T. brucei, T. evansi, and L. mexicana (0.88-11.7 µM) but only a modest effect against human embryonic kidney cells and no cross-resistance with the commonly used melaminophenyl arsenical and diamidine classes of trypanocides. The effect of compound 4 against L. mexicana promastigotes was irreversible after a 5-h exposure, leading to the sterilization of the culture between 24 and 48 h.

Synthesis and Antitrypanosomal Activity of 6-Substituted 7-Methyl-7-deazapurine Nucleosides

Human African Trypanosomiasis caused by Trypanosoma brucei species is one of the most damaging neglected tropical diseases. While the number of newly diagnosed cases per year is record low, there is still high interest in the development of new antitrypanosomal agents in case of resistance to currently used drugs and their combinations, and to replace drugs with serious side effects. We report a series of 7-methyl-7-deazapurine (5-methyl-pyrrolo[2,3-d]pyrimidine) ribonucleosides bearing alkyl, methylsulfanyl, methylamino, or diverse alkoxy groups at position 6 that was prepared through glycosylation of 6-chloro-7-methyl-7-deazapurine followed by nucleophilic substitutions or cross-coupling reactions at position 6 and deprotection. Most of the title nucleosides displayed significant activity against Trypanosoma brucei brucei and T. b. gambiense at submicromolar or nanomolar concentrations and low cytotoxicity and thus represent promising candidates for further development.

Evaluation of trypanocidal properties of ferrocenyl and cyrhetrenyl N-acylhydrazones with pendant 5-nitrofuryl group

Four N-acylhydrazones of general formulae [R¹-C(O)-NH-N=C(R²)(5-nitrofuryl)] with (R¹ = ferrocenyl or cyrhetrenyl and R² = H or Me) are synthesized and characterized in solution and in the solid-state. Comparative studies of their stability in solution under different experimental conditions and their electrochemical properties are reported. NMR studies reveal that the four compounds are stable in DMSO‑d₆ and complementary UV-Vis studies confirm that they also exhibit high stability in mixtures DMSO:H₂O at 37 °C. Electrochemical studies show that the half-wave potential of the nitro group of the N-acylhydrazones is smaller than that of the standard drug nifurtimox and the reduction process follows a self-protonation mechanism. In vitro studies on the antiparasitic activities of the four complexes and the nifurtimox against Trypanosoma cruzi and Trypanosoma brucei reveal that: i) the N-acylhydrazones have a potent inhibitory growth activity against both parasites [EC₅₀ in the low micromolar (in T. cruzi) or even in the nanomolar (in T. brucei) range] and ii) cyrhetrenyl derivatives are more effective than their ferrocenyl analogs. Parallel studies on the L₆ rat skeletal myoblast cell line have also been conducted, and the selectivity indexes determined. Three of the four N-acylhydrazones showed higher selectivity towards T. brucei than the standard drug nifurtimox. Additional studies suggest that the organometallic compounds are bioactivated by type I nitroreductase enzymes.

Antitrypanosomal and Antileishmanial Activity of Chalcones and Flavanones from Polygonum salicifolium

Trypanosomiasis and leishmaniasis are a group of neglected parasitic diseases caused by several species of parasites belonging to the family Trypansomatida. The present study investigated the antitrypanosomal and antileishmanial activity of chalcones and flavanones from Polygonum salicifolium, which grows in the wetlands of Iraq. The phytochemical evaluation of the plant yielded two chalcones, 2′,4′-dimethoxy-6′-hydroxychalcone and 2′,5′-dimethoxy-4′,6′-dihydroxychalcone, and two flavanones, 5,7-dimethoxyflavanone and 5,8-dimethoxy-7-hydroxyflavanone. The chalcones showed a good antitrypanosomal and antileishmanial activity while the flavanones were inactive. The EC₅₀ values for 2′,4′-dimethoxy-6′-hydroxychalcone against Trypanosoma brucei brucei (0.5 μg/mL), T. congolense (2.5 μg/mL), and Leishmania mexicana (5.2 μg/mL) indicated it was the most active of the compounds. None of the compounds displayed any toxicity against a human cell line, even at 100 µg/mL, or cross-resistance with first line clinical trypanocides, such as diamidines and melaminophenyl arsenicals. Taken together, our study provides significant data in relation to the activity of chalcones and flavanones from P. salicifolium against both parasites in vitro. Further future research is suggested in order to investigate the mode of action of the extracted chalcones against the parasites.

Cost of a new method of active screening for human African trypanosomiasis in the Democratic Republic of the Congo

BACKGROUND

Human African trypanosomiases caused by the Trypanosoma brucei gambiense parasite is a lethal disease targeted for eradication. One of the main disease control strategies is active case-finding through outreach campaigns. In 2014, a new method for active screening was developed with mini, motorcycle-based, teams. This study compares the cost of two active case-finding approaches, namely the traditional mobile teams and mini mobile teams, in the two health districts of the Democratic Republic of the Congo.

METHODS

The financial and economic costs of both approaches were estimated from a health care provider perspective. Cost and operational data were collected for 12 months for 1 traditional team and 3 mini teams. The cost per person screened and diagnosed was calculated and univariate sensitivity analysis was conducted to identify the main cost drivers.

RESULTS

During the study period in total 264,630 people were screened, and 23 HAT cases detected. The cost per person screened was lower for a mini team than for a traditional team in the study setting (US$1.86 versus US$2.08). A comparable result was found in a scenario analysis, assuming both teams would operate in a similar setting, with the cost per person screened by a mini team 15% lower than the cost per person screened by a traditional team (1.86 $ vs 2.14$). The main explanations for this lower cost are that mini teams work with fewer human resources, cheaper means of transportation and do not perform the Capillary Tube Centrifugation test or card agglutination test dilutions.

DISCUSSION

Active HAT screening with mini mobile teams has a lower cost and could be a cost-effective alternative for active case-finding. Further research is needed to determine if mini mobile teams have similar or better yields than traditional mobile teams in terms of detections and cases successfully treated.