Drug used in the treatment of sleeping sickness (human African trypanosomiasis: HAT)

Synthesis and biological evaluation of orally active anti-Trypanosoma agents

In previous studies, we developed anti-trypanosome tubulin inhibitors with promising in vitro selectivity and activity against Human African Trypanosomiasis (HAT). However, for such agents, oral activity is crucial. This study focused on further optimizing these compounds to enhance their ligand efficiency, aiming to reduce bulkiness and hydrophobicity, which should improve solubility and, consequently, oral bioavailability. Using Trypanosoma brucei brucei cells as the parasite model and human normal kidney cells and mouse macrophage cells as the host model, we evaluated 30 new analogs synthesized through combinatorial chemistry. These analogs have fewer aromatic moieties and lower molecular weights than their predecessors. Several new analogs demonstrated IC50s in the low micromolar range, effectively inhibiting trypanosome cell growth without harming mammalian cells at the same concentration. We conducted a detailed structure-activity relationship (SAR) analysis and a docking study to assess the compounds' binding affinity to trypanosome tubulin homolog. The results revealed a correlation between binding energy and anti-Trypanosoma activity. Importantly, compound 7 displayed significant oral activity, effectively inhibiting trypanosome cell proliferation in mice.

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.

Targeting Cysteine Proteases and their Inhibitors to Combat Trypanosomiasis

BACKGROUND

Trypanosomiasis, caused by protozoan parasites of the Trypanosoma genus, remains a significant health burden in several regions of the world. Cysteine proteases play a crucial role in the pathogenesis of Trypanosoma parasites and have emerged as potential therapeutic targets for the development of novel antiparasitic drugs.

INTRODUCTION

This review article aims to provide a comprehensive overview of the role of cysteine proteases in trypanosomiasis and their potential as therapeutic targets. We discuss the biological significance of cysteine proteases in Trypanosoma parasites and their involvement in essential processes, such as host immune evasion, cell invasion, and nutrient acquisition.

METHODS

A comprehensive literature search was conducted to identify relevant studies and research articles on the role of cysteine proteases and their inhibitors in trypanosomiasis. The selected studies were critically analyzed to extract key findings and provide a comprehensive overview of the topic.

RESULTS

Cysteine proteases, such as cruzipain, TbCatB and TbCatL, have been identified as promising therapeutic targets due to their essential roles in Trypanosoma pathogenesis. Several small molecule inhibitors and peptidomimetics have been developed to target these proteases and have shown promising activity in preclinical studies.

CONCLUSION

Targeting cysteine proteases and their inhibitors holds great potential for the development of novel antiparasitic drugs against trypanosomiasis. The identification of potent and selective cysteine protease inhibitors could significantly contribute to the combat against trypanosomiasis and improve the prospects for the treatment of this neglected tropical disease.

Thiazolidin-4-one-based derivatives - Efficient tools for designing antiprotozoal agents. A review of the last decade

Thiazolidin-4-one derivatives have a wide range of therapeutic implementations and clinical significance for medicinal chemistry. This heterocyclic ring has been reported to possess a variety of biological activities, including antiprotozoal activities that have inspired scientists to integrate this scaffold with different pharmacophoric fragments to design novel and effective antiprotozoal compounds. There are reviews describing thiazolidin-4-ones small molecules as good candidates with a single type of antiprotozoal activity, but none of these show collected news associated with the antiprotozoal activity of thiazolidin-4-ones and their SAR analysis from the last decade. In this review we are focusing on the antitoxoplasmic, anti-trypanosomal, antimalarial, antileishmanial, and antiamoebic activity of these derivatives, we attempt to summarize and analyze the recent developments with regard to the antiprotozoal potential of 4-TZD covering the structure-activity relationship and main molecular targets. The importance of various structural modifications at C2, N3, and C5 of the thiazolidine-4-one core has also been discussed in this review. We hope that all information concluded in this review can be useful for other researchers in constructing new effective antiprotozoal agents.

Pincer Complexes Derived from Tridentate Schiff Bases for Their Use as Antimicrobial Metallopharmaceuticals

Within the current challenges in medicinal chemistry, the development of new and better therapeutic agents effective against infectious diseases produced by bacteria, fungi, viruses, and parasites stands out. With chemotherapy as one of the main strategies against these diseases focusing on the administration of organic and inorganic drugs, the latter is generally based on the synergistic effect produced by the formation of metal complexes with biologically active organic compounds. In this sense, Schiff bases (SBs) represent and ideal ligand scaffold since they have demonstrated a broad spectrum of antitumor, antiviral, antimicrobial, and anti-inflammatory activities, among others. In addition, SBs are synthesized in an easy manner from one-step condensation reactions, being thus suitable for facile structural modifications, having the imine group as a coordination point found in most of their metal complexes, and promoting chelation when other donor atoms are three, four, or five bonds apart. However, despite the wide variety of metal complexes found in the literature using this type of ligands, only a handful of them include on their structures tridentate SBs ligands and their biological evaluation has been explored. Hence, this review summarizes the most important antimicrobial activity results reported this far for pincer-type complexes (main group and d-block) derived from SBs tridentate ligands.

Identification of Prazosin as a Potential Flagellum Attachment Zone 1(FAZ1) Inhibitor for the Treatment of Human African Trypanosomiasis

Human African trypanosomiasis (HAT) remains a health threat to sub-Saharan Africa. The current treatments suffer from drug resistance and life-threatening side effects, making drug discovery for HAT still important. A high-throughput screening of the library of pharmaceutically active compounds identified prazosin, an α-adrenoceptor antagonist, that showed selective activity toward Trypanosoma brucei brucei. Furthermore, a series of prazosin analogues were examined, and overall, the new analogues had improved activity and selectivity. To elucidate the binding partner, a biotin-conjugated probe was synthesized, and a protein pulldown assay combined with a proteomic analysis identified the flagellum attachment zone 1 (FAZ1) filament as an interacting partner. Additionally, prazosin treatment resulted in dysfunction of the flagellum of trypanosome cells, which is indicative of a FAZ1 irregularity. We also examined the drug distribution by utilizing immunofluorescence with a designed fluorescent analogue that showed partial colocalization with FAZ1. With the activity of the prazosin analogues, a structure-activity relationship (SAR) was summarized for future lead optimization. Our findings provide a new group of FAZ1 inhibitors as novel antitrypanosomal agents.

Human neuronal signaling and communication assays to assess functional neurotoxicity

Prediction of drug toxicity on the human nervous system still relies mainly on animal experiments. Here, we developed an alternative system allowing assessment of complex signaling in both individual human neurons and on the network level. The LUHMES cultures used for our approach can be cultured in 384-well plates with high reproducibility. We established here high-throughput quantification of free intracellular Ca2+ concentrations [Ca2+]i as broadly applicable surrogate of neuronal activity and verified the main processes by patch clamp recordings. Initially, we characterized the expression pattern of many neuronal signaling components and selected the purinergic receptors to demonstrate the applicability of the [Ca2+]i signals for quantitative characterization of agonist and antagonist responses on classical ionotropic neurotransmitter receptors. This included receptor sub-typing and the characterization of the anti-parasitic drug suramin as modulator of the cellular response to ATP. To exemplify potential studies on ion channels, we characterized voltage-gated sodium channels and their inhibition by tetrodotoxin, saxitoxin and lidocaine, as well as their opening by the plant alkaloid veratridine and the food-relevant marine biotoxin ciguatoxin. Even broader applicability of [Ca2+]i quantification as an end point was demonstrated by measurements of dopamine transporter activity based on the membrane potential-changing activity of this neurotransmitter carrier. The substrates dopamine or amphetamine triggered [Ca2+]i oscillations that were synchronized over the entire culture dish. We identified compounds that modified these oscillations by interfering with various ion channels. Thus, this new test system allows multiple types of neuronal signaling, within and between cells, to be assessed, quantified and characterized for their potential disturbance.

Application of Dithiocarbamates as Potential New Antitrypanosomatids-Drugs: Approach Chemistry, Functional and Biological

Dithiocarbamates represent a class of compounds that were evaluated in different biomedical applications because of their chemical versatility. For this reason, several pharmacological activities have already been attributed to these compounds, such as antiparasitic, antiviral, antifungal activities, among others. Therefore, compounds that are based on dithiocarbamates have been evaluated in different in vivo and in vitro models as potential new antimicrobials. Thus, the purpose of this review is to present the possibilities of using dithiocarbamate compounds as potential new antitrypanosomatids-drugs, which could be used for the pharmacological control of Chagas disease, leishmaniasis, and African trypanosomiasis.

Synthesis of proline derived benzenesulfonamides: A potent anti-Trypanosoma brucei gambiense agent

Thousands of death in Africa and other developing nations are still attributed to trypanosomiasis. Excessive sleep has been associated with increased inflammation. We report herein, the synthesis, antitrypanosomal and anti-inflammatory activities of eight new carboxamide derivatives bearing substituted benzenesulfonamides. The base promoted reactions of l-proline and L-4-hydroxyproline with substituted benzenesulfonyl chlorides gave the benzenesulfonamides (11a-h) in excellent yields. Boric acid mediated amidation of the benzenesulfonamides (11a-h) and p-aminobenzoic acid (12) gave the new carboxamides (13a-h) in excellent yields. The new carboxamides were tested for their antitrypanosomal and anti-inflammatory activities against Trypanosome brucei gambiense and inhibition of carrageenan-induced rat paw edema. Compound 13f was the most potent antitrypanosomal agent with an IC50 value of 2 nM as against 5 nM for melarsoprol; whereas compound 13a was the most potent anti-inflammatory agent with percentage inhibition of carrageenan-induced rat paw edema of 58, 60, 67 and 84% after 0.5 h, 1 h, 2 h and 3 h administration respectively. The structure-activity relationship study revealed that substitution at the para position in the benzenesulfonamide ring increased both the antitrypanosomal and anti-inflammatory activities. The 4-hydroxyprolines (13a-d) showed higher anti-inflammatory activity than the prolines (13e-h). In contrast, the prolines (13e-h) had higher antitrypanosomal activities than the 4-hydroxyprolines. The link between excessive sleep and inflammation makes the report of this class of compounds possessing both antitrypanosomal and anti-inflammatory activity worthwhile. The pharmacokinetic studies showed that the compounds would not pose oral bioavailability, transport and permeability problems.

Design and Synthesis of Brain Penetrant Trypanocidal N-Myristoyltransferase Inhibitors

N-Myristoyltransferase (NMT) represents a promising drug target within the parasitic protozoa Trypanosoma brucei (T. brucei), the causative agent for human African trypanosomiasis (HAT) or sleeping sickness. We have previously validated T. brucei NMT as a promising druggable target for the treatment of HAT in both stages 1 and 2 of the disease. We report on the use of the previously reported DDD85646 (1) as a starting point for the design of a class of potent, brain penetrant inhibitors of T. brucei NMT.

Efficacy and Safety of Pafuramidine versus Pentamidine Maleate for Treatment of First Stage Sleeping Sickness in a Randomized, Comparator-Controlled, International Phase 3 Clinical Trial

Background

Sleeping sickness (human African trypanosomiasis [HAT]) is a neglected tropical disease with limited treatment options that currently require parenteral administration. In previous studies, orally administered pafuramidine was well tolerated in healthy patients (for up to 21 days) and stage 1 HAT patients (for up to 10 days), and demonstrated efficacy comparable to pentamidine.

Methods

This was a Phase 3, multi-center, randomized, open-label, parallel-group, active control study where 273 male and female patients with first stage Trypanosoma brucei gambiense HAT were treated at six sites: one trypanosomiasis reference center in Angola, one hospital in South Sudan, and four hospitals in the Democratic Republic of the Congo between August 2005 and September 2009 to support the registration of pafuramidine for treatment of first stage HAT in collaboration with the United States Food and Drug Administration. Patients were treated with either 100 mg of pafuramidine orally twice a day for 10 days or 4 mg/kg pentamidine intramuscularly once daily for 7 days to assess the efficacy and safety of pafuramidine versus pentamidine. Pregnant and lactating women as well as adolescents were included.

The primary efficacy endpoint was the combined rate of clinical and parasitological cure at 12 months. The primary safety outcome was the frequency and severity of adverse events. The study was registered on the International Clinical Trials Registry Platform at www.clinicaltrials.gov with the number ISRCTN85534673.

Findings/Conclusions

The overall cure rate at 12 months was 89% in the pafuramidine group and 95% in the pentamidine group; pafuramidine was non-inferior to pentamidine as the upper bound of the 95% confidence interval did not exceed 15%. The safety profile of pafuramidine was superior to pentamidine; however, 3 patients in the pafuramidine group had glomerulonephritis or nephropathy approximately 8 weeks post-treatment. Two of these events were judged as possibly related to pafuramidine. Despite good tolerability observed in preceding studies, the development program for pafuramidine was discontinued due to delayed post-treatment toxicity.

Sleeping sickness, or human African trypanosomiasis (HAT), is a neglected tropical disease. Because only 2 treatment options are available to treat persons with stage 1 disease, and both require parenteral administration, oral drugs would be of great benefit to the affected population. In this Phase 3, multi-center, randomized, open-label, parallel-group study, we compared oral pafuramidine with intramuscular pentamidine in persons in sub-Sahara Africa with first stage HAT. At 12 months, the overall cure rates (combined clinical and parasitological cure) were similar: 89% in the pafuramidine group and 95% in the pentamidine group. At 24 months, the cure rates continued to be high: 84% and 89%, respectively. Pafuramidine’s safety profile was superior to the comparator drug, and it was consistent with the overall safety profile seen in previous Phase 2 studies. Upon further analysis, however, a renal safety issue was identified as being possibly related to pafuramidine and further clinical development was halted. Nevertheless, the clinical studies conducted in the pafuramidine development program provide a model for future studies in rural Africa.

Treatment and follow-up of the first case of human trypanosomiasis caused by Trypanosoma evansi in India

The first reported human case of trypanosomiasis caused by Trypanosoma evansi was treated using suramin. Patient follow-up indicates that the drug and specific regimen used were well tolerated. Clinical, serological and parasitological investigations at 6 months indicate complete cure of the patient. Suramin should be considered in the treatment of other cases of human T. evansi infection, if they occur.

Effect of melarsoprol treatment on circulating IL-10 and TNF-alpha levels in human African trypanosomiasis

The pathogenesis of human African trypanosomiasis (HAT) has been the object of considerable research interest but has remained incompletely understood. The importance of cytokines in the pathophysiology of this protozoan infection is now widely recognized, but the full spectrum of cytokines involved has yet to be determined. In the present investigation we compared the plasma concentrations of TNF-alpha and IL-10 in normal African controls and patients suffering from advanced meningocephalic (late-stage) Trypanosomiasis brucei (T.b.) gambiense infections, before and after treatment with the arsenical trypanocide melarsoprol. We found that patients with late-stage T. b. gambiense exhibit chronically elevated circulating levels of both of these cytokines, and that these levels quickly decline following melarsoprol treatment. These findings confirm that TNF-alpha is involved in the immunopathogenesis of late-stage African trypanosomiasis and suggest that IL-10 may also play an important regulatory role in this disease.

Efficacy of anticancer alkylphosphocholines in Trypanosoma brucei subspecies

Tetradecylphosphocholine (TPC), hexadecylphosphocholine (HPC), hexadecylphospho(N-N-N-trimethyl)hexanolamine (HPC6), octadecylphosphocholine (OPC), and octadecyl-[2-(N-methylpiperidinio)ethyl]-phosphate (OMPEP) were investigated for antitrypanosomal activity in vitro and in vivo. OMPEP showed the best trypanocidal efficacy in vitro; it was superior to the model compound HPC and comparable to the reference compound alpha-DFMO. HPC showed moderate activity in vivo in terms of increased life expectancy (up to 35% in the acute NMRI-mouse model or 49% if combined with phenylbutazone) and increased packed cell volume, if administered daily. However, HPC and the other alkylphosphocholines failed to prolong survival time of treated mice if given intermittently. Phenylbutazone had no own trypanocidal effect but increased the efficacy of alkylphosphocholines in vitro and in vivo: the combination of HPC and phenylbutazone acted apparently synergistic.

Effect of megazol on Trypanosoma brucei brucei acute and subacute infections in Swiss mice

Human African trypanosomiasis (HAT) or sleeping sickness is a major public health problem in 36 sub-Saharan African countries and is caused by Trypanosoma brucei gambiense and T. b. rhodesiense. About 25,000 new cases of the disease are reported annually, and around 50 million people are classed as at risk of contracting the disease. Until now; the only effective drug available for treatment of advanced HAT was the trypanocide melarsoprol. The mortality rate of melarsoprol treated patients is 1-5%. Megazol is a nitroimidazole derivative shown to be effective in vitro against T. b. brucei with an EC50 of 0.01 micrograms.ml-1. When this compound was tested for its in vivo activity in T. b. brucei infected Swiss mice, it was shown to cure the acute disease. However, megazol alone did not cause cure of mice carrying a subacute infection with involvement of the central nervous system (CNS). Combined suramin and megazol treatment did prove effective and the mice were shown to have remission without further relapse from the CNS. The study of three megazol derivatives is also described here. Substitution of a bromine, methyl or trifluoromethyl moiety at the 4 position of the imidazole ring abolished trypanocidal activity both in vivo and in vitro. Intermediates of megazol synthesis (imidazole sulfoxide and imidazole sulfone) were also tested, but were shown not to be active. It is thought that megazol trypanocidal effect may be due to the triggering of radical production by the compound, which have toxic effects on the trypanosomes metabolism. In depth study of megazol is needed to fully elucidate its pharmacokinetics and to precisely pin down its mode of action.