Efficacy and safety of acoziborole in patients with human African trypanosomiasis caused by Trypanosoma brucei gambiense: a multicentre, open-label, single-arm, phase 2/3 trial

New WHO guidelines for treating rhodesiense human African trypanosomiasis: expanded indications for fexinidazole and pentamidine

Human African trypanosomiasis is a neglected tropical disease that is usually fatal without treatment. WHO has revised its rhodesiense human African trypanosomiasis treatment guidelines on the basis of an independent systematic literature review and following the GRADE methodology. This Review reports on the decision-making process and summarises the new recommendations and their potential implications for health-care professionals and policy makers. Due to data scarcity, all recommendations are conditional and based on very low certainty of evidence. Fexinidazole replaces suramin and melarsoprol as the first-line therapy in individuals aged 6 years and older with a bodyweight of 20 kg or more. As fexinidazole is effective in both stages of rhodesiense human African trypanosomiasis, a lumbar puncture for staging is no longer required. In settings in which first-choice drugs are not readily available, immediate interim treatment with pentamidine is suggested. The introduction of oral fexinidazole represents an advancement in the management of rhodesiense human African trypanosomiasis considering the life-threatening adverse reactions individuals can have to melarsoprol. However, children below the age or weight limits remain ineligible for treatment with fexinidazole.

Hydrazinated geraniol derivatives as potential broad-spectrum antiprotozoal agents

Geraniol, a primary component of several essential oils, has been associated with broad-spectrum antiprotozoal activities, although moderate to weak. This study primarily concentrated on the synthesis of hydrazinated geraniol derivatives as potential antiprotozoal agents. The synthesised compounds were tested in vitro against different parasitic protozoans of clinical relevance, including Trypanosoma brucei brucei, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania infantum. Compounds 6, 8, 13, 14 and 15 demonstrated low micromolar activity against the different parasites. Compounds 8, 13, 14 and 15 had the highest efficacy against Trypanosoma brucei rhodesiense, as indicated by their respective IC50 values of 0.74, 0.56, 1.26 and 1.00 µM. Compounds 6, 14 and 15 displayed the best activity against Trypanosoma brucei brucei, with IC50 values of 1.49, 1.48 and 1.85 µM, respectively. The activity of compounds 6, 14 and 15 also extended to intracellular Trypanosoma cruzi, with IC50 values of 5.14, 6.30 and 4.90 µM, respectively. Compound 6, with an IC50 value of 11.73 µM, and compound 14, with an IC50 value of 8.14 µM, demonstrated some modest antileishmanial activity.

Pass the boron: benzoxaboroles as antiparasite drugs

The development of new drug modalities has been facilitated recently by the introduction of boron as a component of organic compounds, and specifically within a benzoxaborale scaffold. This has enabled exploration of new chemical space and the development of effective compounds targeting a broad range of morbidities, including infections by protozoa, fungi, worms, and bacteria. Most notable is the recent demonstration of a single oral dose cure using acoziborole against African trypanosomiasis. Common and species-/structure-specific interactions between benzoxaboroles and parasite species have emerged and provide vital insights into the mechanisms of cidality, as well as potential challenges in terms of resistance and/or side effects. Here, we discuss the literature specific to benzoxaborole studies in parasitic protists and consider unanswered questions concerning this important new drug class.

Fexinidazole optimization: enhancing anti-leishmanial profile, metabolic stability and hERG safety

The lack of adequate anti-leishmanial therapies has led to the continued suffering of millions of people from developing nations. Moreover, optimism for a therapeutic intervention by fexinidazole was dashed due to the inability to maintain cures and control unwanted side effects. To solve these shortcomings, the structural elements of fexinidazole responsible for anti-leishmanial activity and toxicities were explored. Accordingly, a systematic analog design approach was taken for the synthesis of 24 novel analogs. We established the structural features important for activity and identified modifications that improved the hERG receptor safety and liver microsomal metabolic stability. Compared to fexinidazole, the S-configured imidazolooxazole analog 51 exhibited 25-fold greater potency against miltefosine resistant L. donovani amastigotes, greater metabolic stability and little hERG receptor inhibition. Replacement of the toxicophore nitro group for a cyano group resulted in a complete loss of anti-leishmanial activity. The SAR findings should be useful in the further development of this important class of anti-leishmanial agents.

Pharmacophore Identification and Structure-Activity Relationship Analysis of a Series of Substituted Azaindoles as Inhibitors of Trypanosoma brucei

Human African trypanosomiasis is among the World Health Organization's designated neglected tropical diseases. Repurposing strategies are often employed in academic drug discovery programs due to financial limitations, and in this instance, we used human kinase inhibitor chemotypes to identify substituted 4-aminoazaindoles, exemplified by 1. Structure-activity and structure-property relationship analysis, informed by cheminformatics, identified 4s as a potent inhibitor of Trypanosoma brucei growth. While 4s appeared to be fast acting and cidal in the in vitro assays, it failed to cure a murine model of infection. Preliminary efforts to identify the potential mechanism of action of the series pointed to arginine kinase, though, as we demonstrate, this does not appear to be the sole target of our compounds. This comprehensive approach to drug discovery, encompassing cheminformatics, structure-potency and structure-property analysis, and pharmacophore identification, highlights our multipronged efforts to identify novel lead compounds for this deadly disease.

Modelling timelines to elimination of sleeping sickness in the Democratic Republic of Congo, accounting for possible cryptic human and animal transmission

BACKGROUND

Sleeping sickness (gambiense human African trypanosomiasis, gHAT) is a vector-borne disease targeted for global elimination of transmission (EoT) by 2030. There are, however, unknowns that have the potential to hinder the achievement and measurement of this goal. These include asymptomatic gHAT infections (inclusive of the potential to self-cure or harbour skin-only infections) and whether gHAT infection in animals can contribute to the transmission cycle in humans.

METHODS

Using modelling, we explore how cryptic (undetected) transmission impacts the monitoring of progress towards and the achievement of the EoT goal. We have developed gHAT models that include either asymptomatic or animal transmission, and compare these to a baseline gHAT model without either of these transmission routes, to explore the potential role of cryptic infections on the EoT goal. Each model was independently calibrated to five different health zones in the Democratic Republic of the Congo (DRC) using available historical human case data for 2000-2020 (obtained from the World Health Organization's HAT Atlas). We applied a novel Bayesian sequential updating approach for the asymptomatic model to enable us to combine statistical information about this type of transmission from each health zone.

RESULTS

Our results suggest that, when matched to past case data, we estimated similar numbers of new human infections between model variants, although human infections were slightly higher in the models with cryptic infections. We simulated the continuation of screen-confirm-and-treat interventions, and found that forward projections from the animal and asymptomatic transmission models produced lower probabilities of EoT than the baseline model; however, cryptic infections did not prevent EoT from being achieved eventually under this approach.

CONCLUSIONS

This study is the first to simulate an (as-yet-to-be available) screen-and-treat strategy and found that removing a parasitological confirmation step was predicted to have a more noticeable benefit to transmission reduction under the asymptomatic model compared with the others. Our simulations suggest vector control could greatly impact all transmission routes in all models, although this resource-intensive intervention should be carefully prioritised.

Prevalence of dermal trypanosomes in suspected and confirmed cases of gambiense human African trypanosomiasis in Guinea

The skin is an anatomical reservoir for African trypanosomes, yet the prevalence of extravascular parasite carriage in the population at risk of gambiense Human African Trypanosomiasis (gHAT) remains unclear. Here, we conducted a prospective observational cohort study in the HAT foci of Forecariah and Boffa, Republic of Guinea. Of the 18,916 subjects serologically screened for gHAT, 96 were enrolled into our study. At enrolment and follow-up visits, participants underwent a dermatological examination and had blood samples and superficial skin snip biopsies taken for examination by molecular and immuno-histological methods. In seropositive individuals, dermatological symptoms were significantly more frequent as compared to seronegative controls. Trypanosoma brucei DNA was detected in the blood of 67% of confirmed cases (22/33) and 9% of unconfirmed seropositive individuals (3/32). However, parasites were detected in the extravascular dermis of up to 71% of confirmed cases (25/35) and 41% of unconfirmed seropositive individuals (13/32) by PCR and/or immuno-histochemistry. Six to twelve months after treatment, trypanosome detection in the skin dropped to 17% of confirmed cases (5/30), whereas up to 25% of unconfirmed, hence untreated, seropositive individuals (4/16) were still found positive. Dermal trypanosomes were observed in subjects from both transmission foci, however, the occurrence of pruritus and the PCR positivity rates were significantly higher in unconfirmed seropositive individuals in Forecariah. The lower sensitivity of superficial skin snip biopsies appeared critical for detecting trypanosomes in the basal dermis. These results are discussed in the context of the planned elimination of gHAT.

Cardiac involvement in Chagas disease and African trypanosomiasis

Trypanosomiases are diseases caused by various species of protozoan parasite in the genus Trypanosoma, each presenting with distinct clinical manifestations and prognoses. Infections can affect multiple organs, with Trypanosoma cruzi predominantly affecting the heart and digestive system, leading to American trypanosomiasis or Chagas disease, and Trypanosoma brucei primarily causing a disease of the central nervous system known as human African trypanosomiasis or sleeping sickness. In this Review, we discuss the effects of these infections on the heart, with particular emphasis on Chagas disease, which continues to be a leading cause of cardiomyopathy in Latin America. The epidemiology of Chagas disease has changed substantially since 1990 owing to the emigration of over 30 million Latin American citizens, primarily to Europe and the USA. This movement of people has led to the global dissemination of individuals infected with T. cruzi. Therefore, cardiologists worldwide must familiarize themselves with Chagas disease and the severe, chronic manifestation - Chagas cardiomyopathy - because of the expanded prevalence of this disease beyond traditional endemic regions.

Specificity of serological screening tests and reference laboratory tests to diagnose gambiense human African trypanosomiasis: a prospective clinical performance study

BACKGROUND

Serological screening tests play a crucial role to diagnose gambiense human African trypanosomiasis (gHAT). Presently, they preselect individuals for microscopic confirmation, but in future "screen and treat" strategies they will identify individuals for treatment. Variability in reported specificities, the development of new rapid diagnostic tests (RDT) and the hypothesis that malaria infection may decrease RDT specificity led us to evaluate the specificity of 5 gHAT screening tests.

METHODS

During active screening, venous blood samples from 1095 individuals from Côte d'Ivoire and Guinea were tested consecutively with commercial (CATT, HAT Sero-K-SeT, Abbott Bioline HAT 2.0) and prototype (DCN HAT RDT, HAT Sero-K-SeT 2.0) gHAT screening tests and with a malaria RDT. Individuals with ≥ 1 positive gHAT screening test underwent microscopy and further immunological (trypanolysis with T.b. gambiense LiTat 1.3, 1.5 and 1.6; indirect ELISA/T.b. gambiense; T.b. gambiense inhibition ELISA with T.b. gambiense LiTat 1.3 and 1.5 VSG) and molecular reference laboratory tests (PCR TBRN3, 18S and TgsGP; SHERLOCK 18S Tids, 7SL Zoon, and TgsGP; Trypanozoon S2-RT-qPCR 18S2, 177T, GPI-PLC and TgsGP in multiplex; RT-qPCR DT8, DT9 and TgsGP in multiplex). Microscopic trypanosome detection confirmed gHAT, while other individuals were considered gHAT free. Differences in fractions between groups were assessed by Chi square and differences in specificity between 2 tests on the same individuals by McNemar.

RESULTS

One gHAT case was diagnosed. Overall test specificities (n = 1094) were: CATT 98.9% (95% CI: 98.1-99.4%); HAT Sero-K-SeT 86.7% (95% CI: 84.5-88.5%); Bioline HAT 2.0 82.1% (95% CI: 79.7-84.2%); DCN HAT RDT 78.2% (95% CI: 75.7-80.6%); and HAT Sero-K-SeT 2.0 78.4% (95% CI: 75.9-80.8%). In malaria positives, gHAT screening tests appeared less specific, but the difference was significant only in Guinea for Abbott Bioline HAT 2.0 (P = 0.03) and HAT Sero-K-Set 2.0 (P = 0.0006). The specificities of immunological and molecular laboratory tests in gHAT seropositives were 98.7-100% (n = 399) and 93.0-100% (n = 302), respectively. Among 44 reference laboratory test positives, only the confirmed gHAT patient and one screening test seropositive combined immunological and molecular reference laboratory test positivity.

CONCLUSIONS

Although a minor effect of malaria cannot be excluded, gHAT RDT specificities are far below the 95% minimal specificity stipulated by the WHO target product profile for a simple diagnostic tool to identify individuals eligible for treatment. Unless specificity is improved, an RDT-based "screen and treat" strategy would result in massive overtreatment. In view of their inconsistent results, additional comparative evaluations of the diagnostic performance of reference laboratory tests are indicated for better identifying, among screening test positives, those at increased suspicion for gHAT.

TRIAL REGISTRATION

The trial was retrospectively registered under NCT05466630 in clinicaltrials.gov on July 15 2022.

Imaging Assays to Detect DNA Damage in Trypanosome Parasites Using γH2A

Diseases caused by trypanosomatid parasites remain a significant unmet medical need for millions of people globally. Trypanosomatid parasites such as Trypanosoma cruzi and subspecies of Trypanosoma brucei cause Chagas disease and human African trypanosomiasis (HAT), respectively. Although efforts to find novel treatments have been successful for HAT, Chagas disease is still treated with decades-old therapies that suffer from long treatment durations and severe safety concerns. We recently described the identification and characterization of the cyanotriazole compound class that kills trypanosomes, in vitro and in vivo, by selective inhibition of the trypanosome nuclear topoisomerase II enzyme. To evaluate whether inhibition of the topoisomerase II enzyme led to parasite death due to lethal double-strand DNA breaks, we developed assays for detecting DNA damage in both intracellular amastigotes of T. cruzi and bloodstream-form T. brucei by using the canonical DNA damage marker γH2A. Herein, this article describes the protocols for detecting DNA damage using an immunofluorescence assessment of γH2A by microscopy in trypanosome parasites. Key features • Immunofluorescence-based assay to detect the γH2A response in T. brucei and T. cruzi parasites. • Robust DNA damage pathway-based cellular assays to evaluate topoisomerase II poisons' ability to cause DNA damage. • A 384-well plate-based T. cruzi protocol allows high-resolution and high-throughput evaluation of compounds that cause DNA damage by measuring γH2A in intracellular parasites. • This assay could be modifiable for evaluation of DNA damage responses in various intracellular and extracellular eukaryotic pathogens.

Aminopyridines in the development of drug candidates against protozoan neglected tropical diseases

Neglected tropical diseases (NTDs) pose a major threat in tropical zones for impoverished populations. Difficulty of access, adverse effects or low efficacy limit the use of current therapeutic options. Therefore, development of new drugs against NTDs is a necessity. Compounds containing an aminopyridine (AP) moiety are of great interest for the design of new anti-NTD drugs due to their intrinsic properties compared with their closest chemical structures. Currently, over 40 compounds with an AP moiety are on the market, but none is used against NTDs despite active research on APs. The aim of this review is to present the medicinal chemistry work carried out with these scaffolds, against protozoan NTDs: Trypanosoma cruzi, Trypanosoma brucei or Leishmania spp.

The evolving spectrum of human African trypanosomiasis

Human African trypanosomiasis (HAT), or sleeping sickness, continues to be a major threat to human health in 36 countries throughout sub-Saharan Africa with up to 60 million people at risk. Over the last decade, there have been several advances in this area, some of which are discussed in this overview. Due to the concerted efforts of several bodies, including better identification and treatment of cases and improved tsetse fly vector control, the number of cases of HAT has declined dramatically. The clinical heterogeneity of HAT has also been increasingly recognized, and the disease, while usually fatal if untreated or inadequately treated, does not always have a uniformly fatal outcome. Improved methods of HAT diagnosis have now been developed including rapid diagnostic tests. Novel drug treatment of HAT has also been developed, notably nifurtimox-eflornithine combination therapy (NECT) for late-stage Trypanosoma brucei gambiense, oral fexinidazole for early and the early component of the late-stage of T.b. gambiense, and the new oral compounds of the oxaborole group, which have shown considerable promise in field trials. Advances in HAT neuropathogenesis have been steady, though largely incremental, with a particular focus on the role of the blood-brain barrier in parasite entry into the central nervous system and the relevant importance of both innate and adaptive immunity. While the World Health Organization goal of elimination of HAT as a public health problem by 2020 has probably been achieved, it remains to be seen whether the second more ambitious goal of interruption of transmission of HAT by 2030 will be attained.

Discovery of 1,3,4-Oxadiazole Derivatives as Broad-Spectrum Antiparasitic Agents

Vector-borne parasitic diseases (VBPDs) pose a significant threat to public health on a global scale. Collectively, Human African Trypanosomiasis (HAT), Leishmaniasis, and Malaria threaten millions of people, particularly in developing countries. Climate change might alter the transmission and spread of VBPDs, leading to a global burden of these diseases. Thus, novel agents are urgently needed to expand therapeutic options and limit the spread of drug-resistant parasites. Herein, we report the development of broad-spectrum antiparasitic agents by screening a known library of antileishmanial and antimalarial compounds toward Trypanosoma brucei (T. brucei) and identifying a 1,3,4-oxadiazole derivative (19) as anti-T. brucei hit with predicted blood-brain barrier permeability. Subsequently, extensive structure-activity-relationship studies around the lipophilic tail of 19 led to a potent antitrypanosomal and antimalarial compound (27), with moderate potency also toward Leishmania infantum (L. infantum) and Leishmania tropica. In addition, we discovered a pan-active antiparasitic molecule (24), showing low-micromolar IC50s toward T. brucei and Leishmania spp. promastigotes and amastigotes, and nanomolar IC50 against Plasmodium falciparum, together with high selectivity for the parasites over mammalian cells (THP-1). Early ADME-toxicity assays were used to assess the safety profile of the compounds. Overall, we characterized 24 and 27, bearing the 1,3,4-oxadiazole privileged scaffold, as broad-spectrum low-toxicity agents for the treatment of VBPDs. An alkyne-substituted chemical probe (30) was synthesized and will be utilized in proteomics experiments aimed at deconvoluting the mechanism of action in the T. brucei parasite.

Substitution-Induced Mechanistic Switching in SNAr-Warheads for Cysteine Proteases

The aim of this study was to investigate the transition from non-covalent reversible over covalent reversible to covalent irreversible inhibition of cysteine proteases by making delicate structural changes to the warhead scaffold. To this end, dipeptidic rhodesain inhibitors with different N-terminal electrophilic arenes as warheads relying on the SNAr mechanism were synthesized and investigated. Strong structure-activity relationships of the inhibition potency, the degree of covalency, and the reversibility of binding on the arene substitution pattern were found. The studies were complemented and substantiated by molecular docking and quantum-mechanical calculations of model systems. Furthermore, the improvement in the membrane permeability of peptide esters in comparison to their corresponding carboxylic acids was exemplified.

Discovery of an orally active nitrothiophene-based antitrypanosomal agent

Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei gambiense and rhodesiense, is a parasitic disease endemic to sub-Saharan Africa. Untreated cases of HAT can be severely debilitating and fatal. Although the number of reported cases has decreased progressively over the last decade, the number of effective and easily administered medications is very limited. In this work, we report the antitrypanosomal activity of a series of potent compounds. A subset of molecules in the series are highly selective for trypanosomes and are metabolically stable. One of the compounds, (E)-N-(4-(methylamino)-4-oxobut-2-en-1-yl)-5-nitrothiophene-2-carboxamide (10), selectively inhibited the growth of T. b. brucei, T. b. gambiense and T. b. rhodesiense, have excellent oral bioavailability and was effective in treating acute infection of HAT in mouse models. Based on its excellent bioavailability, compound 10 and its analogs are candidates for lead optimization and pre-clinical investigations.

High-throughput screening of compounds targeting RNA editing in Trypanosoma brucei: Novel molecular scaffolds with broad trypanocidal effects

Mitochondrial uridine insertion/deletion RNA editing, catalyzed by a multiprotein complex (editosome), is essential for gene expression in trypanosomes and Leishmania parasites. As this process is absent in the human host, a drug targeting this mechanism promises high selectivity and reduced toxicity. Here, we successfully miniaturized our FRET-based full-round RNA editing assay, which replicates the complete RNA editing process, adapting it into a 1536-well format. Leveraging this assay, we screened over 100,000 compounds against purified editosomes derived from Trypanosoma brucei, identifying seven confirmed primary hits. We sourced and evaluated various analogs to enhance the inhibitory and parasiticidal effects of these primary hits. In combination with secondary assays, our compounds marked inhibition of essential catalytic activities, including the RNA editing ligase and interactions of editosome proteins. Although the primary hits did not exhibit any growth inhibitory effect on parasites, we describe eight analog compounds capable of effectively killing T. brucei and/or Leishmania donovani parasites within a low micromolar concentration. Whether parasite killing is - at least in part - due to inhibition of RNA editing in vivo remains to be assessed. Our findings introduce novel molecular scaffolds with the potential for broad antitrypanosomal effects.

Drug Discovery Efforts to Identify Novel Treatments for Neglected Tropical Diseases - Cysteine Protease Inhibitors

BACKGROUND

Neglected tropical diseases are a severe burden for mankind, affecting an increasing number of people around the globe. Many of those diseases are caused by protozoan parasites in which cysteine proteases play a key role in the parasite's pathogenesis.

OBJECTIVE

In this review article, we summarize the drug discovery efforts of the research community from 2017 - 2022 with a special focus on the optimization of small molecule cysteine protease inhibitors in terms of selectivity profiles or drug-like properties as well as in vivo studies. The cysteine proteases evaluated by this methodology include Cathepsin B1 from Schistosoma mansoni, papain, cruzain, falcipain, and rhodesain.

METHODS

Exhaustive literature searches were performed using the keywords "Cysteine Proteases" and "Neglected Tropical Diseases" including the years 2017 - 2022. Overall, approximately 3'000 scientific papers were retrieved, which were filtered using specific keywords enabling the focus on drug discovery efforts.

RESULTS AND CONCLUSION

Potent and selective cysteine protease inhibitors to treat neglected tropical diseases were identified, which progressed to pharmacokinetic and in vivo efficacy studies. As far as the authors are aware of, none of those inhibitors reached the stage of active clinical development. Either the inhibitor's potency or pharmacokinetic properties or safety profile or a combination thereof prevented further development of the compounds. More efforts with particular emphasis on optimizing pharmacokinetic and safety properties are needed, potentially by collaborations of academic and industrial research groups with complementary expertise. Furthermore, new warheads reacting with the catalytic cysteine should be exploited to advance the research field in order to make a meaningful impact on society.

Human African Trypanosomiasis (Sleeping Sickness)-Epidemiology, Clinical Manifestations, Diagnosis, Treatment, and Prevention

Purpose of Review

Human African Trypanosomiasis (HAT), also known as sleeping sickness, is a vector-borne parasitic neglected tropical disease (NTD) endemic in sub-Saharan Africa. This review aims to enhance our understanding of HAT and provide valuable insights to combat this significant public health issue by synthesizing the latest research and evidence.

Recent Findings

HAT has reached a historical < 1000 cases in 2018. In patients without neurologic symptoms and signs, the likelihood of a severe meningoencephalitic stage is deemed low, obviating the need for a lumbar puncture to guide treatment decisions using fexinidazole.

Summary

Both forms of the disease, gambiense HAT (gHAT) and rhodesiense HAT (rHAT), have specific epidemiology, risk factors, diagnosis, and treatment. Disease management still requires a high index of suspicion, infectious disease expertise, and specialized medical care. Essential stakeholders in health policy are critical to accomplishing the elimination goals of the NTD roadmap for 2021-2030.

Therapeutic Potential of Marine-Derived Cyclic Peptides as Antiparasitic Agents

Parasitic diseases still compromise human health. Some of the currently available therapeutic drugs have limitations considering their adverse effects, questionable efficacy, and long treatment, which have encouraged drug resistance. There is an urgent need to find new, safe, effective, and affordable antiparasitic drugs. Marine-derived cyclic peptides have been increasingly screened as candidates for developing new drugs. Therefore, in this review, a systematic analysis of the scientific literature was performed and 25 marine-derived cyclic peptides with antiparasitic activity (1-25) were found. Antimalarial activity is the most reported (51%), followed by antileishmanial (27%) and antitrypanosomal (20%) activities. Some compounds showed promising antiparasitic activity at the nM scale, being active against various parasites. The mechanisms of action and targets for some of the compounds have been investigated, revealing different strategies against parasites.

Structure-Activity Relationships, Tolerability and Efficacy of Microtubule-Active 1,2,4-Triazolo[1,5-a]pyrimidines as Potential Candidates to Treat Human African Trypanosomiasis

Tubulin and microtubules (MTs) are potential protein targets to treat parasitic infections and our previous studies have shown that the triazolopyrimidine (TPD) class of MT-active compounds hold promise as antitrypanosomal agents. MT-targeting TPDs include structurally related but functionally diverse congeners that interact with mammalian tubulin at either one or two distinct interfacial binding sites; namely, the seventh and vinca sites, which are found within or between α,β-tubulin heterodimers, respectively. Evaluation of the activity of 123 TPD congeners against cultured Trypanosoma brucei enabled a robust quantitative structure-activity relationship (QSAR) model and the prioritization of two congeners for in vivo pharmacokinetics (PK), tolerability and efficacy studies. Treatment of T. brucei-infected mice with tolerable doses of TPDs significantly decreased blood parasitemia within 24 h. Further, two once-weekly doses at 10 mg/kg of a candidate TPD significantly extended the survival of infected mice relative to infected animals treated with vehicle. Further optimization of dosing and/or the dosing schedule of these CNS-active TPDs may provide alternative treatments for human African trypanosomiasis.

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.

Expanding the Role of Boron in New Drug Chemotypes: Properties, Chemistry, Pharmaceutical Potential of Hemiboronic Naphthoids

New chemotypes and bioisosteres can open a new chemical space in drug discovery and help meet an urgent demand for novel agents to fight infections and other diseases. With the aim of identifying new boron-containing drug chemotypes, this article details a comprehensive evaluation of the pseudoaromatic hemiboronic naphthoids, benzoxaza- and benzodiazaborines. Relevant physical properties in aqueous media (acidity, solubility, log P, and stability) of prototypic members of four subclasses were determined. Both scaffolds are amenable to common reactions used in drug discovery, such as chemoselective Suzuki-Miyaura, Chan-Lam, and amidation reactions. Small model libraries were prepared to assess the scope of these transformations, and the entire collection was screened for antifungal (Candida albicans) and antibacterial activity (MRSA, Escherichia coli), unveiling promising benzoxazaborines with low micromolar minimum inhibitory concentration values. Select DMPK assays of representative compounds suggest promising drug-like behavior for all four subclasses. Moreover, several drug isosteres were evaluated for anti-inflammatory and anticancer activity as appropriate.

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.

Cyanotriazoles are selective topoisomerase II poisons that rapidly cure trypanosome infections

Millions who live in Latin America and sub-Saharan Africa are at risk of trypanosomatid infections, which cause Chagas disease and human African trypanosomiasis (HAT). Improved HAT treatments are available, but Chagas disease therapies rely on two nitroheterocycles, which suffer from lengthy drug regimens and safety concerns that cause frequent treatment discontinuation. We performed phenotypic screening against trypanosomes and identified a class of cyanotriazoles (CTs) with potent trypanocidal activity both in vitro and in mouse models of Chagas disease and HAT. Cryo-electron microscopy approaches confirmed that CT compounds acted through selective, irreversible inhibition of trypanosomal topoisomerase II by stabilizing double-stranded DNA:enzyme cleavage complexes. These findings suggest a potential approach toward successful therapeutics for the treatment of Chagas disease.

State-of-the-Art in the Drug Discovery Pathway for Chagas Disease: A Framework for Drug Development and Target Validation

Chagas disease is the most important protozoan infection in the Americas, and constitutes a significant public health concern throughout the world. Development of new medications against its etiologic agent, Trypanosoma cruzi, has been traditionally slow and difficult, lagging in comparison with diseases caused by other kinetoplastid parasites. Among the factors that explain this are the incompletely understood mechanisms of pathogenesis of T. cruzi infection and its complex set of interactions with the host in the chronic stage of the disease. These demand the performance of a variety of in vitro and in vivo assays as part of any drug development effort. In this review, we discuss recent breakthroughs in the understanding of the parasite's life cycle and their implications in the search for new chemotherapeutics. For this, we present a framework to guide drug discovery efforts against Chagas disease, considering state-of-the-art preclinical models and recently developed tools for the identification and validation of molecular targets.

The critical role of mode of action studies in kinetoplastid drug discovery

Understanding the target and mode of action of compounds identified by phenotypic screening can greatly facilitate the process of drug discovery and development. Here, we outline the tools currently available for target identification against the neglected tropical diseases, human African trypanosomiasis, visceral leishmaniasis and Chagas' disease. We provide examples how these tools can be used to identify and triage undesirable mechanisms, to identify potential toxic liabilities in patients and to manage a balanced portfolio of target-based campaigns. We review the primary targets of drugs that are currently in clinical development that were initially identified via phenotypic screening, and whose modes of action affect protein turnover, RNA trans-splicing or signalling in these protozoan parasites.

Performance of clinical signs and symptoms, rapid and reference laboratory diagnostic tests for diagnosis of human African trypanosomiasis by passive screening in Guinea: a prospective diagnostic accuracy study

BACKGROUND

Passive diagnosis of human African trypanosomiasis (HAT) at the health facility level is a major component of HAT control in Guinea. We examined which clinical signs and symptoms are associated with HAT, and assessed the performance of selected clinical presentations, of rapid diagnostic tests (RDT), and of reference laboratory tests on dried blood spots (DBS) for diagnosing HAT in Guinea.

METHOD

The study took place in 14 health facilities in Guinea, where 2345 clinical suspects were tested with RDTs (HAT Sero-K-Set, rHAT Sero-Strip, and SD Bioline HAT). Seropositives underwent parasitological examination (reference test) to confirm HAT and their DBS were tested in indirect enzyme-linked immunoassay (ELISA)/Trypanosoma brucei gambiense, trypanolysis, Loopamp Trypanosoma brucei Detection kit (LAMP) and m18S quantitative PCR (qPCR). Multivariable regression analysis assessed association of clinical presentation with HAT. Sensitivity, specificity, positive and negative predictive values of key clinical presentations, of the RDTs and of the DBS tests for HAT diagnosis were determined.

RESULTS

The HAT prevalence, as confirmed parasitologically, was 2.0% (48/2345, 95% CI: 1.5-2.7%). Odds ratios (OR) for HAT were increased for participants with swollen lymph nodes (OR = 96.7, 95% CI: 20.7-452.0), important weight loss (OR = 20.4, 95% CI: 7.05-58.9), severe itching (OR = 45.9, 95% CI: 7.3-288.7) or motor disorders (OR = 4.5, 95% CI: 0.89-22.5). Presence of at least one of these clinical presentations was 75.6% (95% CI: 73.8-77.4%) specific and 97.9% (95% CI: 88.9-99.9%) sensitive for HAT. HAT Sero-K-Set, rHAT Sero-Strip, and SD Bioline HAT were respectively 97.5% (95% CI: 96.8-98.1%), 99.4% (95% CI: 99.0-99.7%) and 97.9% (95% CI: 97.2-98.4%) specific, and 100% (95% CI: 92.5-100.0%), 59.6% (95% CI: 44.3-73.3%) and 93.8% (95% CI: 82.8-98.7%) sensitive for HAT. The RDT's positive and negative predictive values ranged from 45.2-66.7% and 99.2-100% respectively. All DBS tests had specificities ≥ 92.9%. While LAMP and m18S qPCR sensitivities were below 50%, trypanolysis and ELISA/T.b. gambiense had sensitivities of 85.3% (95% CI: 68.9-95.0%) and 67.6% (95% CI: 49.5-82.6%).

CONCLUSIONS

Presence of swollen lymph nodes, important weight loss, severe itching or motor disorders are simple but accurate clinical criteria for HAT referral in HAT endemic areas in Guinea. Diagnostic performances of HAT Sero-K-Set and SD Bioline HAT are sufficient for referring positives to microscopy. Trypanolysis on DBS may discriminate HAT patients from false RDT positives. Trial registration The trial was registered under NCT03356665 in clinicaltrials.gov (November 29, 2017, retrospectively registered https://clinicaltrials.gov/ct2/show/NCT03356665 ).

Emerging compounds and therapeutic strategies to treat infections from Trypanosoma brucei: an overhaul of the last 5-years patents

INTRODUCTION

Human African Trypanosomiasis is a neglected disease caused by infection from parasites belonging to the Trypanosoma brucei species. Only six drugs are currently available and employed depending on the stage of the infection: pentamidine, suramin, melarsoprol, eflornithine, nifurtimox, and fexinidazole. Joint research projects were launched in an attempt to find new therapeutic options for this severe and often lethal disease.

AREAS COVERED

After a brief description of the recent literature on the parasite and the disease, we searched for patents dealing with the proposal of new anti-trypanosomiasis agents and, following the PRISMA guidelines, we filtered the results to those published from 2018onwards returning suitable entries, which represent the contemporary landscape of compounds/strategies against Trypanosoma brucei. In addition, some relevant publications from the overall scientific literature were also discussed.

EXPERT OPINION

This review comprehensively covers and analyzes the most recent advances not only in the discovery of new inhibitors and their structure-activity relationships but also in the assessment of innovative biological targets opening new scenarios in the MedChem field. Lastly, also new vaccines and formulations recently patented were described. However, natural and synthetic compounds were analyzed in terms of inhibitory activity and selective toxicity against human cells.

Structure-Activity Relationships, Tolerability and Efficacy of Microtubule-Active 1,2,4-Triazolo[1,5- a ]pyrimidines as Potential Candidates to Treat Human African Trypanosomiasis

Tubulin and microtubules (MTs) are potential protein targets to treat parasitic infections and our previous studies have shown that the triazolopyrimidine (TPD) class of MT- active compounds hold promise as antitrypanosomal agents. MT-targeting TPDs include structurally related but functionally diverse congeners that interact with mammalian tubulin at either one or two distinct interfacial binding sites; namely, the seventh and vinca sites, which are found within or between α,β-tubulin heterodimers, respectively. Evaluation of the activity of 123 TPD congeners against cultured Trypanosoma brucei enabled a robust quantitative structure-activity relationship (QSAR) model and the prioritization of two congeners for in vivo pharmacokinetics (PK), tolerability and efficacy studies. Treatment of T. brucei -infected mice with tolerable doses of TPDs 3 and 4 significantly decreased blood parasitemia within 24 h. Further, two once-weekly doses of 4 at 10 mg/kg significantly extended the survival of infected mice relative to infected animals treated with vehicle. Further optimization of dosing and/or the dosing schedule of these CNS-active TPDs may provide alternative treatments for human African trypanosomiasis.