Special Issue "Drug Discovery and Development for Tropical Diseases (TDs)"

A special issue of Pharmaceuticals (ISSN 1424-8247). This special issue belongs to the section "Medicinal Chemistry".

Deadline for manuscript submissions: closed (31 December 2021).

Special Issue Editor

Dr. Christophe Dardonville
E-Mail Website
Guest Editor
1. Instituto de Química Médica—CSIC, Madrid, Spain
2. Medicinal Chemistry Institute—Spanish Council for Scientific Research, Madrid, Spain
Interests: medicinal chemistry; design and synthesis of antiparasitic agents for neglected tropical diseases (trypanosomiasis, leishmaniasis, malaria); cationic compounds; DNA binding study; pKa measurement
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Tropical diseases (TDs) cause immense human suffering and death. They represent a huge socioeconomic and life-threatening burden in less-developed countries. In the last 20 years, a great effort has been made by the international scientific community to tackle this problem and discover new safe and effective drugs against TDs, including the most neglected tropical diseases (NTDs) (https://www.who.int/teams/control-of-neglected-tropical-diseases). In this this Special Issue, we would like to provide a picture of the recent discoveries in the field of drug discovery for TDs. We will acknowledge research papers which topic includes, but is not restricted to, the design, synthesis, in vitro/in vivo evaluation, and development of new compounds for TDs, including promising chemotherapeutic targets to combat these diseases. Review articles outlining recent developments in the field are also welcome.

This special issue covers (but is not restricted to) the Tropical Diseases listed below:

  • Buruli ulcer
  • Chagas disease (American trypanosomiasis) 
  • Dengue      
  • Dracunculiasis (Guinea-worm disease)    
  • Echinococcosis   
  • Foodborne trematode infections    
  • Human African trypanosomiasis (sleeping sickness)
  • Leishmaniasis·       
  • Leprosy (Hansen's disease)
  • Lymphatic filariasis (Elephantiasis)  
  • Malaria
  • Mycetoma, chromoblastomycosis, and other deep mycoses
  • Onchocerciasis (river blindness)
  • Rabies      
  • Scabies and other ectoparasitoses  
  • Schistosomiasis (Bilharzia)
  • Soil-transmitted helminthiases
  • Snakebite envenoming
  • Taeniasis and cisticercosis
  • Trachoma
  • Yaws (Endemic treponematoses)

Dr. Christophe Dardonville
Guest Editor

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Keywords

  • Tropical diseases (TDs)
  • Neglected tropical diseases (NTDs)
  • Drug discovery
  • Medicinal chemistry
  • Drug synthesis
  • SAR studies
  • in vitro/in vivo activity
  • Chemotherapeutic targets

Published Papers (16 papers)

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Research

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Article
First In Silico Screening of Insect Molecules for Identification of Novel Anti-Parasitic Compounds
Pharmaceuticals 2022, 15(2), 119; https://0-doi-org.brum.beds.ac.uk/10.3390/ph15020119 - 19 Jan 2022
Viewed by 43
Abstract
Schistosomiasis is a neglected tropical disease caused by blood flukes of the genus Schistosoma. In silico screenings of compounds for the identification of novel anti-parasitic drug candidates have received considerable attention in recent years, including the screening of natural compounds. For the [...] Read more.
Schistosomiasis is a neglected tropical disease caused by blood flukes of the genus Schistosoma. In silico screenings of compounds for the identification of novel anti-parasitic drug candidates have received considerable attention in recent years, including the screening of natural compounds. For the first time, we investigated molecules from insects, a rather neglected source in drug discovery, in an in silico screening approach to find novel antischistosomal compounds. Based on the Dictionary of Natural Products (DNP), we created a library of 1327 insect compounds suitable for molecular docking. A structure-based virtual screening against the crystal structure of a known druggable target in Schistosoma mansoni, the thioredoxin glutathione reductase (SmTGR), was performed. The top ten compounds predominantly originated from beetles and were predicted to interact particularly with amino acids in the doorstop pocket of SmTGR. For one compound from a jewel beetle, buprestin H, we tested and confirmed antischistosomal activity against adult and juvenile parasites in vitro. At concentrations with anti-parasitic activity, we could also exclude any unspecific cytotoxic activity against human HepG2 cells. This study highlights the potential of insect molecules for the identification of novel antischistosomal compounds. Our library of insect-derived molecules could serve not only as basis for future in silico screenings against additional target proteins of schistosomes, but also of other parasites. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Repurposing the Trypanosomatidic GSK Kinetobox for the Inhibition of Parasitic Pteridine and Dihydrofolate Reductases
Pharmaceuticals 2021, 14(12), 1246; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14121246 - 30 Nov 2021
Viewed by 478
Abstract
Three open-source anti-kinetoplastid chemical boxes derived from a whole-cell phenotypic screening by GlaxoSmithKline (Tres Cantos Anti-Kinetoplastid Screening, TCAKS) were exploited for the discovery of a novel core structure inspiring new treatments of parasitic diseases targeting the trypansosmatidic pteridine reductase 1 (PTR1) and dihydrofolate [...] Read more.
Three open-source anti-kinetoplastid chemical boxes derived from a whole-cell phenotypic screening by GlaxoSmithKline (Tres Cantos Anti-Kinetoplastid Screening, TCAKS) were exploited for the discovery of a novel core structure inspiring new treatments of parasitic diseases targeting the trypansosmatidic pteridine reductase 1 (PTR1) and dihydrofolate reductase (DHFR) enzymes. In total, 592 compounds were tested through medium-throughput screening assays. A subset of 14 compounds successfully inhibited the enzyme activity in the low micromolar range of at least one of the enzymes from both Trypanosoma brucei and Lesihmania major parasites (pan-inhibitors), or from both PTR1 and DHFR-TS of the same parasite (dual inhibitors). Molecular docking studies of the protein–ligand interaction focused on new scaffolds not reproducing the well-known antifolate core clearly explaining the experimental data. TCMDC-143249, classified as a benzenesulfonamide derivative by the QikProp descriptor tool, showed selective inhibition of PTR1 and growth inhibition of the kinetoplastid parasites in the 5 μM range. In our work, we enlarged the biological profile of the GSK Kinetobox and identified new core structures inhibiting selectively PTR1, effective against the kinetoplastid infectious protozoans. In perspective, we foresee the development of selective PTR1 and DHFR inhibitors for studies of drug combinations. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Discovery of New Chemical Tools against Leishmania amazonensis via the MMV Pathogen Box
Pharmaceuticals 2021, 14(12), 1219; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14121219 - 24 Nov 2021
Viewed by 462
Abstract
The protozoan parasite Leishmania causes a spectrum of diseases and there are over 1 million infections each year. Current treatments are toxic, expensive, and difficult to administer, and resistance to them is emerging. In this study, we screened the antileishmanial activity of the [...] Read more.
The protozoan parasite Leishmania causes a spectrum of diseases and there are over 1 million infections each year. Current treatments are toxic, expensive, and difficult to administer, and resistance to them is emerging. In this study, we screened the antileishmanial activity of the Pathogen Box compounds from the Medicine for Malaria Venture against Leishmania amazonensis, and compared their structures and cytotoxicity. The compounds MMV676388 (3), MMV690103 (5), MMV022029 (7), MMV022478 (9) and MMV021013 (10) exerted a significant dose-dependent inhibition effect on the proliferation of L. amazonensis promastigotes and intracellular amastigotes. Moreover, studies on the mechanism of cell death showed that compounds 3 and 5 induced an apoptotic process while the compounds 7, 9 and 10 seem to induce an autophagic mechanism. The present findings underline the potential of these five molecules as novel therapeutic leishmanicidal agents. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Antiparasitic Effect of Stilbene and Terphenyl Compounds against Trypanosoma cruzi Parasites
Pharmaceuticals 2021, 14(11), 1199; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14111199 - 22 Nov 2021
Viewed by 409
Abstract
Background: Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite Trypanosoma cruzi. No progress in the treatment of this pathology has been made since Nifurtimox was introduced more than fifty years ago, and this [...] Read more.
Background: Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite Trypanosoma cruzi. No progress in the treatment of this pathology has been made since Nifurtimox was introduced more than fifty years ago, and this drug is considered very aggressive and may cause several adverse effects. This drug currently has severe limitations, including a high frequency of undesirable side effects and limited efficacy and availability, so research to discover new drugs for the treatment of Chagas disease is imperative. Many drugs available on the market are natural products as found in nature or compounds designed based on the structure and activity of these natural products. Methods: This study evaluated the in vitro antiparasitic activity of a series of previously synthesized stilbene and terphenyl compounds in T. cruzi epimastigotes and intracellular amastigotes. The action of the most selective compounds was investigated by flow cytometric analysis to evaluate the mechanism of cell death. The ability to induce apoptosis or caspase-1 inflammasomes was assayed in macrophages infected with T. cruzi after treatment, comparing it with that of Nifurtimox. Results: The stilbene ST18 was the most potent compound of the series. It was slightly less active than Nifurtimox in epimastigotes but most active in intracellular amastigotes. Compared to Nifurtimox, it was markedly less cytotoxic when tested in vitro on normal cells. ST18 was able to induce a marked increase in parasites positive for Annexin V and monodansylcadaverine. Moreover, ST18 induced the activation, in infected macrophages, of caspase-1, a conserved enzyme that plays a major role in controlling parasitemia, host survival and the onset of the adaptive immune response in Trypanosoma infection. Conclusions: The antiparasitic activity of ST18 together with its ability to activate caspase-1 in infected macrophages and its low toxicity toward normal cells makes this compound interesting for further clinical investigation. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Synthesis, Molecular Docking, and Antimalarial Activity of Hybrid 4-Aminoquinoline-pyrano[2,3-c]pyrazole Derivatives
Pharmaceuticals 2021, 14(11), 1174; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14111174 - 17 Nov 2021
Viewed by 493
Abstract
Widespread resistance of Plasmodium falciparum to current artemisinin-based combination therapies necessitate the discovery of new medicines. Pharmacophoric hybridization has become an alternative for drug resistance that lowers the risk of drug–drug adverse interactions. In this study, we synthesized a new series of hybrids [...] Read more.
Widespread resistance of Plasmodium falciparum to current artemisinin-based combination therapies necessitate the discovery of new medicines. Pharmacophoric hybridization has become an alternative for drug resistance that lowers the risk of drug–drug adverse interactions. In this study, we synthesized a new series of hybrids by covalently linking the scaffolds of pyrano[2,3-c]pyrazole with 4-aminoquinoline via an ethyl linker. All synthesized hybrid molecules were evaluated through in vitro screenings against chloroquine-resistant (K1) and -sensitive (3D7) P. falciparum strains, respectively. Data from in vitro assessments showed that hybrid 4b displayed significant antiplasmodial activities against the 3D7 strain (EC50 = 0.0130 ± 0.0002 μM) and the K1 strain (EC50 = 0.02 ± 0.01 μM), with low cytotoxic effect against Vero mammalian cells. The high selectivity index value on the 3D7 strain (SI > 1000) and the K1 strain (SI > 800) and the low resistance index value from compound 4b suggested that the pharmacological effects of this compound were due to selective inhibition on the 3D7 and K1 strains. Molecular docking analysis also showed that 4b recorded the highest binding energy on P. falciparum lactate dehydrogenase. Thus, P. falciparum lactate dehydrogenase is considered a potential molecular target for the synthesized compound. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Synthesis and Structure-Activity Relationships of New 2-Phenoxybenzamides with Antiplasmodial Activity
Pharmaceuticals 2021, 14(11), 1109; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14111109 - 30 Oct 2021
Viewed by 459
Abstract
The 2-phenoxybenzamide 1 from the Medicines for Malaria Venture Malaria Box Project has shown promising multi-stage activity against different strains of P. falciparum. It was successfully synthesized via a retrosynthetic approach. Subsequently, twenty-one new derivatives were prepared and tested for their in [...] Read more.
The 2-phenoxybenzamide 1 from the Medicines for Malaria Venture Malaria Box Project has shown promising multi-stage activity against different strains of P. falciparum. It was successfully synthesized via a retrosynthetic approach. Subsequently, twenty-one new derivatives were prepared and tested for their in vitro activity against blood stages of the NF54 strain of P. falciparum. Several insights into structure-activity relationships were revealed. The antiplasmodial activity and cytotoxicity of compounds strongly depended on the substitution pattern of the anilino partial structure as well as on the size of substituents. The diaryl ether partial structure had further impacts on the activity. Additionally, several physicochemical and pharmacokinetic parameters were calculated (log P, log D7.4 and ligand efficiency) or determined experimentally (passive permeability and CYP3A4 inhibition). The tert-butyl-4-{4-[2-(4-fluorophenoxy)-3-(trifluoromethyl)benzamido]phenyl}piperazine-1-carboxylate possesses high antiplasmodial activity against P. falciparum NF54 (PfNF54 IC50 = 0.2690 µM) and very low cytotoxicity (L-6 cells IC50 = 124.0 µM) resulting in an excellent selectivity index of 460. Compared to the lead structure 1 the antiplasmodial activity was improved as well as the physicochemical and some pharmacokinetic parameters. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Antikinetoplastid Activity of Sesquiterpenes Isolated from the Zoanthid Palythoa aff. clavata
Pharmaceuticals 2021, 14(11), 1095; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14111095 - 28 Oct 2021
Viewed by 513
Abstract
Leishmaniasis and Chagas disease are neglected tropical diseases that cause problems in developing countries. The causative agents, Leishmania spp. and Trypanosoma cruzi, produce a clinical picture that can be fatal for the patient, such as Chagas heart disease, visceral leishmaniasis and megacolon, [...] Read more.
Leishmaniasis and Chagas disease are neglected tropical diseases that cause problems in developing countries. The causative agents, Leishmania spp. and Trypanosoma cruzi, produce a clinical picture that can be fatal for the patient, such as Chagas heart disease, visceral leishmaniasis and megacolon, among others. Current treatments for these diseases are not very effective and highly toxic, since they require very prolonged treatments. The development of innovative, effective and safe drugs to fight infections caused by these parasites remains a challenge. For this reason, in recent years, there has been an increase in the search for new therapies. In this study, the antikinetoplastid activity of 13 sesquiterpene lactones obtained from Palythoa aff. clavata was screened against L. amazonensis, L. donovani and T. cruzi. The results revealed that the sesquiterpene lactones anhydroartemorin (2), cis,trans-costunolide-14-acetate (3) and 4-hydroxyarbusculin A (11) were the most selective against the kinetoplastid species studied. These molecules seem to induce the mechanisms involved in an apoptotic-like death or programmed cell death (PCD) in the kinetoplastids, and since they do not cause necrosis, the inflammatory events associated with this type of cell death will not be triggered. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Small Molecule–Peptide Conjugates as Dimerization Inhibitors of Leishmania infantum Trypanothione Disulfide Reductase
Pharmaceuticals 2021, 14(7), 689; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14070689 - 17 Jul 2021
Viewed by 986
Abstract
Trypanothione disulfide reductase (TryR) is an essential homodimeric enzyme of trypanosomatid parasites that has been validated as a drug target to fight human infections. Using peptides and peptidomimetics, we previously obtained proof of concept that disrupting protein–protein interactions at the dimer interface of [...] Read more.
Trypanothione disulfide reductase (TryR) is an essential homodimeric enzyme of trypanosomatid parasites that has been validated as a drug target to fight human infections. Using peptides and peptidomimetics, we previously obtained proof of concept that disrupting protein–protein interactions at the dimer interface of Leishmania infantum TryR (LiTryR) offered an innovative and so far unexploited opportunity for the development of novel antileishmanial agents. Now, we show that linking our previous peptide prototype TRL38 to selected hydrophobic moieties provides a novel series of small-molecule–peptide conjugates that behave as good inhibitors of both LiTryR activity and dimerization. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Novel Purine Chemotypes with Activity against Plasmodium falciparum and Trypanosoma cruzi
Pharmaceuticals 2021, 14(7), 638; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14070638 - 01 Jul 2021
Cited by 1 | Viewed by 1311
Abstract
Malaria and Chagas disease, caused by Plasmodium spp. and Trypanosoma cruzi parasites, remain important global health problems. Available treatments for those diseases present several limitations, such as lack of efficacy, toxic side effects, and drug resistance. Thus, new drugs are urgently needed. The [...] Read more.
Malaria and Chagas disease, caused by Plasmodium spp. and Trypanosoma cruzi parasites, remain important global health problems. Available treatments for those diseases present several limitations, such as lack of efficacy, toxic side effects, and drug resistance. Thus, new drugs are urgently needed. The discovery of new drugs may be benefited by considering the significant biological differences between hosts and parasites. One of the most striking differences is found in the purine metabolism, because most of the parasites are incapable of de novo purine biosynthesis. Herein, we have analyzed the in vitro anti-P. falciparum and anti-T. cruzi activity of a collection of 81 purine derivatives and pyrimidine analogs. We firstly used a primary screening at three fixed concentrations (100, 10, and 1 µM) and progressed those compounds that kept the growth of the parasites < 30% at 100 µM to dose–response assays. Then, we performed two different cytotoxicity assays on Vero cells and human HepG2 cells. Finally, compounds specifically active against T. cruzi were tested against intracellular amastigote forms. Purines 33 (IC50 = 19.19 µM) and 76 (IC50 = 18.27 µM) were the most potent against P. falciparum. On the other hand, 6D (IC50 = 3.78 µM) and 34 (IC50 = 4.24 µM) were identified as hit purines against T. cruzi amastigotes. Moreover, an in silico docking study revealed that P. falciparum and T. cruzi hypoxanthine guanine phosphoribosyltransferase enzymes could be the potential targets of those compounds. Our study identified two novel, purine-based chemotypes that could be further optimized to generate potent and diversified anti-parasitic drugs against both parasites. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Evidence of Pyrimethamine and Cycloguanil Analogues as Dual Inhibitors of Trypanosoma brucei Pteridine Reductase and Dihydrofolate Reductase
Pharmaceuticals 2021, 14(7), 636; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14070636 - 30 Jun 2021
Cited by 1 | Viewed by 952
Abstract
Trypanosoma and Leishmania parasites are the etiological agents of various threatening neglected tropical diseases (NTDs), including human African trypanosomiasis (HAT), Chagas disease, and various types of leishmaniasis. Recently, meaningful progresses in the treatment of HAT, due to Trypanosoma brucei (Tb), have [...] Read more.
Trypanosoma and Leishmania parasites are the etiological agents of various threatening neglected tropical diseases (NTDs), including human African trypanosomiasis (HAT), Chagas disease, and various types of leishmaniasis. Recently, meaningful progresses in the treatment of HAT, due to Trypanosoma brucei (Tb), have been achieved by the introduction of fexinidazole and the combination therapy eflornithine–nifurtimox. Nevertheless, due to drug resistance issues and the exitance of animal reservoirs, the development of new NTD treatments is still required. For this purpose, we explored the combined targeting of two key folate enzymes, dihydrofolate reductase (DHFR) and pteridine reductase 1 (PTR1). We formerly showed that the TbDHFR inhibitor cycloguanil (CYC) also targets TbPTR1, although with reduced affinity. Here, we explored a small library of CYC analogues to understand how their substitution pattern affects the inhibition of both TbPTR1 and TbDHFR. Some novel structural features responsible for an improved, but preferential, ability of CYC analogues to target TbPTR1 were disclosed. Furthermore, we showed that the known drug pyrimethamine (PYR) effectively targets both enzymes, also unveiling its binding mode to TbPTR1. The structural comparison between PYR and CYC binding modes to TbPTR1 and TbDHFR provided key insights for the future design of dual inhibitors for HAT therapy. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Cell Death and Transcriptional Responses Induced in Larvae of the Nematode Haemonchus contortus by Toxins/Toxicants with Broad Phylogenetic Efficacy
Pharmaceuticals 2021, 14(7), 598; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14070598 - 22 Jun 2021
Viewed by 831
Abstract
Establishing methods to investigate treatments that induce cell death in parasitic nematodes will promote experimental approaches to elucidate mechanisms and to identify prospective anthelmintics capable of inducing this outcome. Here, we extended recent progress on a method to monitor cell death and to [...] Read more.
Establishing methods to investigate treatments that induce cell death in parasitic nematodes will promote experimental approaches to elucidate mechanisms and to identify prospective anthelmintics capable of inducing this outcome. Here, we extended recent progress on a method to monitor cell death and to identify small molecule inhibitors in Ascaris suum to Haemonchus contortus, a phylogenetically distant parasitic nematode of significance for both human and agricultural animal health. We utilized a diverse group of small molecule inhibitors referred to as nematode intestinal toxins/toxicants (NITs) coupled with motility, cytological and cell death assays to resolve gross effects on motility and individual cells and organ systems of two H. contortus larval stages in culture. Early transcriptional response evaluation identified NIT-responsive genes and pathways. The scope of death among cells in larvae varied among NITs but shared patterns with A. suum, despite the approach having some limitations due to characteristics of H. contortus larvae. Gene response patterns varied among NITs tested and provided information on the cell targets and pathways affected. Experimental NIT assays provide tools capable of inducing cell death in larval stages of parasitic nematodes, and can resolve many individual cells and organ systems in which cell death can be induced. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Enantioselective Interactions of Anti-Infective 8-Aminoquinoline Therapeutics with Human Monoamine Oxidases A and B
Pharmaceuticals 2021, 14(5), 398; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14050398 - 22 Apr 2021
Viewed by 636
Abstract
8-Aminoquinolines (8-AQs) are an important class of anti-infective therapeutics. The monoamine oxidases (MAOs) play a key role in metabolism of 8-AQs. A major role for MAO-A in metabolism of primaquine (PQ), the prototypical 8-AQ antimalarial, has been demonstrated. These investigations were further extended [...] Read more.
8-Aminoquinolines (8-AQs) are an important class of anti-infective therapeutics. The monoamine oxidases (MAOs) play a key role in metabolism of 8-AQs. A major role for MAO-A in metabolism of primaquine (PQ), the prototypical 8-AQ antimalarial, has been demonstrated. These investigations were further extended to characterize the enantioselective interactions of PQ and NPC1161 (8-[(4-amino-1-methylbutyl) amino]-5-[3, 4-dichlorophenoxy]-6-methoxy-4-methylquinoline) with human MAO-A and -B. NPC1161B, the (R)-(−) enantiomer with outstanding potential for malaria radical cure, treatment of visceral leishmaniasis and pneumocystis pneumonia infections is poised for clinical development. PQ showed moderate inhibition of human MAO-A and -B. Racemic PQ and (R)-(−)-PQ both showed marginally greater (1.2- and 1.6-fold, respectively) inhibition of MAO-A as compared to MAO-B. However, (S)-(+)-PQ showed a reverse selectivity with greater inhibition of MAO-B than MAO-A. Racemic NPC1161 was a strong inhibitor of MAOs with 3.7-fold selectivity against MAO-B compared to MAO-A. The (S)-(+) enantiomer (NPC1161A) was a better inhibitor of MAO-A and -B compared to the (R)-(−) enantiomer (NPC1161B), with more than 10-fold selectivity for inhibition of MAO-B over MAO-A. The enantioselective interaction of NPC1161 and strong binding of NPC1161A with MAO-B was further confirmed by enzyme-inhibitor binding and computational docking analyses. Differential interactions of PQ and NPC1161 enantiomers with human MAOs may contribute to the enantioselective pharmacodynamics and toxicity of anti-infective 8-AQs therapeutics. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Absence of Association between Methylene Blue Reduced Susceptibility and Polymorphisms in 12 Genes Involved in Antimalarial Drug Resistance in African Plasmodium falciparum
Pharmaceuticals 2021, 14(4), 351; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14040351 - 09 Apr 2021
Cited by 1 | Viewed by 657
Abstract
Half the human population is exposed to malaria. Plasmodium falciparum antimalarial drug resistance monitoring and development of new drugs are major issues related to the control of malaria. Methylene blue (MB), the oldest synthetic antimalarial, is again a promising drug after the break [...] Read more.
Half the human population is exposed to malaria. Plasmodium falciparum antimalarial drug resistance monitoring and development of new drugs are major issues related to the control of malaria. Methylene blue (MB), the oldest synthetic antimalarial, is again a promising drug after the break of its use as an antimalarial drug for more than 80 years and a potential partner for triple combination. Very few data are available on the involvement of polymorphisms on genes known to be associated with standard antimalarial drugs and parasite in vitro susceptibility to MB (cross-resistance). In this context, MB susceptibility was evaluated against 482 isolates of imported malaria from Africa by HRP2-based ELISA chemosusceptibility assay. A total of 12 genes involved in antimalarial drug resistance (Pfcrt, Pfdhfr, Pfmdr1, Pfmdr5, Pfmdr6, PfK13, Pfubq, Pfcarl, Pfugt, Pfact, Pfcoronin, and copy number of Pfpm2) were sequenced by Sanger method and quantitative PCR. On the Pfmdr1 gene, the mutation 86Y combined with 184F led to more susceptible isolates to MB (8.0 nM vs. 11.6 nM, p = 0.03). Concerning Pfmdr6, the isolates bearing 12 Asn repetitions were more susceptible to MB (4.6 nM vs. 11.6 nM, p = 0.005). None of the polymorphisms previously described as involved in antimalarial drug resistance was shown to be associated with reduced susceptibility to MB. Some genes (particularly PfK13, Pfugt, Pfact, Pfpm2) did not present enough genetic variability to draw conclusions about their involvement in reduced susceptibility to MB. None of the polymorphisms analyzed by multiple correspondence analysis (MCA) had an impact on the MB susceptibility of the samples successfully included in the analysis. It seems that there is no in vitro cross-resistance between MB and commonly used antimalarial drugs. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Article
Synthesis, Biological Activity and In Silico Pharmacokinetic Prediction of a New 2-Thioxo-Imidazoldidin-4-One of Primaquine
Pharmaceuticals 2021, 14(3), 196; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14030196 - 27 Feb 2021
Viewed by 754
Abstract
The discovery of novel antiparasitic drugs for neglected tropical diseases (NTDs) constitutes a global urgency and requires a range of innovative strategies to ensure a sustainable pipeline of lead compounds. Thus far, primaquine (PQ) is the only transmission-blocking antimalarial that is clinically available, [...] Read more.
The discovery of novel antiparasitic drugs for neglected tropical diseases (NTDs) constitutes a global urgency and requires a range of innovative strategies to ensure a sustainable pipeline of lead compounds. Thus far, primaquine (PQ) is the only transmission-blocking antimalarial that is clinically available, displaying marked activity against gametocytes of all causative species of human malaria (Plasmodium spp.). Chagas disease, caused by Trypanosoma cruzi, is another PQ-sensitive illness besides malaria. One of the major drawbacks of PQ is its metabolism into carboxyprimaquine (CPQ), which is less active than the parent drug. In this study, we developed different synthetic pathways to confer N-protection to PQ through introduction of thioxo-imidazolidin-4-one. The introduction of this group prevents the formation of CPQ, counteracting one major drawback of the parent drug. After that, we evaluated the potential biological activity of the novel 2-thioxo-imidazolidin-4-one derivative of PQ, which showed relevant in vitro activity against Trypanosoma cruzi (IC50 1.4 μM) compared to PQ (IC50 1.7 μM) and the reference drug benznidazole (IC50 1.6 μM). Noting its acceptable pharmacokinetic profile, this PQ conjugate may be a potential scaffold for novel drug exploration against Chagas disease. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Review

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Review
Histone Deacetylase (HDAC) Inhibitors for the Treatment of Schistosomiasis
Pharmaceuticals 2022, 15(1), 80; https://0-doi-org.brum.beds.ac.uk/10.3390/ph15010080 - 10 Jan 2022
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Abstract
Schistosomiasis is a major neglected parasitic disease that affects more than 240 million people worldwide and for which the control strategy consists of mass treatment with the only available drug, praziquantel. Schistosomes display morphologically distinct stages during their life cycle and the transformations [...] Read more.
Schistosomiasis is a major neglected parasitic disease that affects more than 240 million people worldwide and for which the control strategy consists of mass treatment with the only available drug, praziquantel. Schistosomes display morphologically distinct stages during their life cycle and the transformations between stages are controlled by epigenetic mechanisms. The targeting of epigenetic actors might therefore represent the parasites’ Achilles’ heel. Specifically, histone deacetylases have been recently characterized as drug targets for the treatment of schistosomiasis. This review focuses on the recent development of inhibitors for schistosome histone deacetylases. In particular, advances in the development of inhibitors of Schistosoma mansoni histone deacetylase 8 have indicated that targeting this enzyme is a promising approach for the treatment of this infection. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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Review
Discovery and Development of Inhibitors of the Plasmodial FNT-Type Lactate Transporter as Novel Antimalarials
Pharmaceuticals 2021, 14(11), 1191; https://0-doi-org.brum.beds.ac.uk/10.3390/ph14111191 - 20 Nov 2021
Viewed by 473
Abstract
Plasmodium spp. malaria parasites in the blood stage draw energy from anaerobic glycolysis when multiplying in erythrocytes. They tap the ample glucose supply of the infected host using the erythrocyte glucose transporter 1, GLUT1, and a hexose transporter, HT, of the parasite’s plasma [...] Read more.
Plasmodium spp. malaria parasites in the blood stage draw energy from anaerobic glycolysis when multiplying in erythrocytes. They tap the ample glucose supply of the infected host using the erythrocyte glucose transporter 1, GLUT1, and a hexose transporter, HT, of the parasite’s plasma membrane. Per glucose molecule, two lactate anions and two protons are generated as waste that need to be released rapidly from the parasite to prevent blockage of the energy metabolism and acidification of the cytoplasm. Recently, the missing Plasmodium lactate/H+ cotransporter was identified as a member of the exclusively microbial formate–nitrite transporter family, FNT. Screening of an antimalarial compound selection with unknown targets led to the discovery of specific and potent FNT-inhibitors, i.e., pentafluoro-3-hydroxy-pent-2-en-1-ones. Here, we summarize the discovery and further development of this novel class of antimalarials, their modes of binding and action, circumvention of a putative resistance mutation of the FNT target protein, and suitability for in vivo studies using animal malaria models. Full article
(This article belongs to the Special Issue Drug Discovery and Development for Tropical Diseases (TDs))
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