Drug sensitivity of Leishmania species: some unresolved problems

Evidence of Guanidines Potential against Leishmania (Viannia) braziliensis: Exploring In Vitro Effectiveness, Toxicities and of Innate Immunity Response Effects

Leishmaniasis is a complex group of infectious and parasitic diseases that afflict many thousands of individuals across five continents. Leishmaniasis treatment remains a challenge because it relies on drugsknown for their high toxicity and limited efficacy, making itimperative to identify new molecules that offer greater effectiveness and safety. This study sought to explore the impact of seven synthetic guanidine derivatives (LQOF-G1, LQOF-G2, LQOF-G6, LQOF-G7, LQOF-G32, LQOF-G35 and LQOF-G36) onthe parasite Leishmania (Viannia) braziliensis and in vitro macrophage infection by this parasite, as well as cytotoxic approaches in vitro models of mammalian host cells and tissues. The synthesized compounds showed purity ≥ 99.65% and effectively inhibited parasite growth. LQOF-G1 proved the most potent, yielding the best half-maximal inhibitory concentration (IC50) values against promastigotes (4.62 μmol/L), axenic amastigotes (4.27 μmol/L), and intracellular amastigotes (3.65 μmol/L). Notably, the antileishmanial activity of LQOF-G1, LQOF-G2, and LQOF-G6 was related to immunomodulatory effects, evidenced by alterations in TNF-α, IL-12, IL-10, nitric oxide (NO), and reactive oxygen species (ROS) levels in the supernatant of culture macrophages infected with L. (V.) braziliensis and coincubated with these compounds. LQOF-G2 and LQOF-G36 compounds exhibited vasodilator and spasmolytic effects at higher concentrations (≥100 μmol/L). Generally, LQOF-G1, LQOF-G2, and LQOF-G32 compounds were found to be nontoxic to assessed organs and cells. No toxic effects were observed in human cell lines, such as HEK-293, CaCo-2 and A549, at concentrations ≥ 500 μmol/L. Collectively, data have shown unequivocal evidence of the effectiveness of these compounds against L. (V.) braziliensis parasite, one of the causative agents of Tegumentary Leishmaniasis and Mucocutaneous Leishmaniasis in America.

Design, synthesis and biological evaluation of antiparasitic dinitroaniline-ether phospholipid hybrids

A series of nine novel ether phospholipid-dinitroaniline hybrids were synthesized in an effort to deliver more potent antiparasitic agents with improved safety profile compared to miltefosine. The compounds were evaluated for their in vitro antiparasitic activity against L. infantum, L.donovani, L. amazonensis, L. major and L. tropica promastigotes, L. infantum and L. donovani intracellular amastigotes, Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the oligomethylene spacer between the dinitroaniline moiety and the phosphate group, the length of the side chain substituent on the dinitroaniline and the choline or homocholine head group were found to affect both the activity and toxicity of the hybrids. The early ADMET profile of the derivatives did not reveal major liabilities. Hybrid 3, bearing an 11-carbon oligomethylene spacer, a butyl side chain and a choline head group, was the most potent analogue of the series. It exhibited a broad spectrum antiparasitic profile against the promastigotes of New and Old World Leishmania spp., against intracellular amastigotes of two L. infantum strains and L. donovani, against T. brucei and against T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes. The early toxicity studies revealed that hybrid 3 showed a safe toxicological profile while its cytotoxicity concentration (CC50) against THP-1 macrophages being >100 μM. Computational analysis of binding sites and docking indicated that the interaction of hybrid 3 with trypanosomatid α-tubulin may contribute to its mechanism of action. Furthermore, compound 3 was found to interfere with the cell cycle in T. cruzi epimastigotes, while ultrastructural studies using SEM and TEM in T. cruzi showed that compound 3 affects cellular processes that result in changes in the Golgi complex, the mitochondria and the parasite's plasma membrane. The snapshot pharmacokinetic studies showed low levels of 3 after 24 h following oral administration of 100 mg/Kg, while, its homocholine congener compound 9 presented a better pharmacokinetic profile.

Review on the Drug Intolerance and Vaccine Development for the Leishmaniasis

Leishmaniasis is one of the Neglected Tropical Diseases (NTDs), a zoonotic disease of vector-borne nature that is caused by a protozoan parasite Leishmania. This parasite is transmitted by the vector sandfly into the human via a bite. Visceral leishmaniasis (VL), also called kala-azar, is the most fatal among the types of leishmaniasis, with high mortality mostly spread in the East Africa and South Asia regions. WHO report stated that approximately 3.3 million disabilities occur every year due to the disease along with approximately 50,000 annual deaths. The real matter of concern is that there is no particular effective medicine/vaccine available against leishmaniasis to date except a few approved drugs and chemotherapy for the infected patient. The current selection of small compounds was constrained, and their growing drug resistance had been a major worry. Additionally, the serious side effects on humans of the available therapy or drugs have made it essential to discover efficient and low-cost methods to speed up the development of new drugs against leishmaniasis. Ideally, the vaccine could be a low risk and effective alternative for both CL and VL and elicit long-lasting immunity against the disease. There are a number of vaccine candidates at various stages of clinical development and preclinical stage. However, none has successfully passed all clinical trials. But, the successful development and approval of commercially available vaccines for dogs against canine leishmaniasis (CanL) provides evidence that it can be possible for humans in distant future. In the present article, the approaches used for the development of vaccines for leishmaniasis are discussed and the progress being made is briefly reviewed.

In Vitro Antiparasitic Activities of Monovalent Ionophore Compounds for Human and Canine Leishmaniases

The leishmaniases are vector-borne parasitic diseases affecting humans and animals, with high mortality rates in endemic countries. Infected dogs represent the main reservoir of infection. Disease control is mainly based on chemotherapy, which, at present, shows serious drawbacks both in humans and dogs. Therefore, the discovery or repurposing of new treatments is mandatory. Here, three monovalent ionophores (salinomycin, monensin, nigericin) were tested against promastigotes of Leishmania (L.) infantum, Leishmania tropica, and Leishmania braziliensis, and against amastigotes of L. infantum within human and, for the first time, canine macrophages. All three drugs were leishmanicidal against all Leishmania spp. promastigotes with IC50 values between 7.98 and 0.23 µM. Monensin and nigericin showed IC50 values < 1 µM, whereas salinomycin was the least active compound (IC50 > 4 µM). Notably, the ionophores killed L. infantum amastigotes within human THP-1 cells with IC50 values ranging from 1.67 to 1.93 µM, but they only reduced by 27−37% the parasite burden in L. infantum-infected canine macrophages, showing a host-specific efficacy. Moreover, a selective higher toxicity against canine macrophages was observed. Overall, repurposed ionophores have the potential to be further investigated as anti-Leishmania agents, but different drug options may be required to tackle human or canine leishmaniases.

Anti-malarial effect of a combination of risedronate and azithromycin against Plasmodium yoelii nigeriensis infection in Swiss mice

Combination therapy is used to retard the selection of malaria parasite strains resistant to individual components of a combination of drugs. This approach has proved to be a success in the combination of sulphadoxine and pyrimethamine, which targets two different steps in the folate pathway of malaria parasites. However, after the success of this therapeutic combination, the efficacy of other combinations of drugs that target different enzymes in a particular metabolic pathway has, apparently, not been reported. In the current study, the antimalarial effect of a combination of risedronate (RIS), which is known for its anti-osteoporosis activity, and azithromycin (AZT) was investigated. Peter's suppression test was carried out on mice infected with 1 × 10⁷P. yoelii infected erythrocytes. Drug efficacy was analyzed by comparing the percent reduction in parasitaemia on day 4 post-infection. RIS was observed to be a blood schizonticidal agent against P. yoelii infection which showed ED₅₀ 7.0 (4.04-12.13) mg/kg/day x 4. Normalized isobologram showed additive action between RIS 1 mg/kg/day x 4 and AZT 10 mg/kg/day x 4, and antagonistic action for the rest of the combinations (RIS 1 + AZT 20, RIS 1 + AZT 40, RIS 5 + AZT 10, RIS 5 + AZT 20, RIS 5 + AZT 40, RIS 10 + AZT 10, RIS 10 + AZT 20 and RIS 10 + AZT 40 mg/kg/day x 4). Furthermore, a combination of RIS with AZT showed inferior efficacy as compared to AZT treatment alone. This antagonistic interaction may be due to the high accumulation of AZT in WBCs, which will reduce its serum bio-availability, whereas RIS has anti-parasitic activity by increasing WBCs.

Tackling Drug Resistance and Other Causes of Treatment Failure in Leishmaniasis

Leishmaniasis is a tropical infectious disease caused by the protozoan Leishmania parasite. The disease is transmitted by female sand flies and, depending on the infecting parasite species, causes either cutaneous (stigmatizing skin lesions), mucocutaneous (destruction of mucous membranes of nose, mouth and throat) or visceral disease (a potentially fatal infection of liver, spleen and bone marrow). Although more than 1 million new cases occur annually, chemotherapeutic options are limited and their efficacy is jeopardized by increasing treatment failure rates and growing drug resistance. To delay the emergence of resistance to existing and new drugs, elucidating the currently unknown causes of variable drug efficacy (related to parasite susceptibility, host immunity and drug pharmacokinetics) and improved use of genotypic and phenotypic tools to define, measure and monitor resistance in the field are critical. This review highlights recent progress in our understanding of drug action and resistance in Leishmania, ongoing challenges (including setbacks related to the COVID-19 pandemic) and provides an overview of possible strategies to tackle this public health challenge.

Potential of Piper spp. as a source of new compounds for the leishmaniases treatment

Current treatment guidelines for leishmaniasis is based on chemotherapy with drugs that show a set of limitations such as high cost, toxicity, difficult route of administration, and lack of efficacy in endemic areas. In this context, phytopharmaceutical products and herbal medicines emerge as promising alternatives for developing new treatment against leishmaniasis. This review discusses the perspectives of leishmaniasis treatment based on natural products and phytotherapy highlighting the Piper genus, especially P. aduncun and P. mollicomum Kunth covering the period of 1998 to 2020. Leishmanicidal activity of pure compounds of Piper spp. [3-(3,4,5-trimethoxyphenyl) propanoic acid, 3-chlorosintenpyridone, 2'-hydroxy-3',4',6'-trimethoxy-chalcone, cardamonin, conocarpan, cubebin, eupomatenoid, flavokavain B, ( +)-(7R,8S)-epoxy-5,6-didehydrokavain, N-[7-(3',4'-methylenedioxypheny l-2(E),4(E)-heptadienoyl-pyrrolidine, N-[7-(3',4'-methylenedioxyphenyl)-2(Z),4(Z)-heptadienoyl-pyrrolidine, piperovatine, pellitorine, and piplartine (piperlongumine)] were proved against the promastigote and amastigote forms of parasite related with cutaneous (L. (L.) amazonensis, L. (V.) braziliensis, and L. (V.) guyanensis) and visceral (L. (L.) donovani, L. (L.) chagasi, and L. (L.) infantum). We also discussed the perspective of leishmaniasis treatment, considering the potential synergism between different promising species of Piper, presenting some interesting interaction possibilities for future studies between plants. Finally, the necessary steps for technological development of phytomedicines and herbal medicines with the desirable quality requirements for medicines are highlighted. The data presented here highlight the use of Piper spp. as source of pharmacological compounds that can lead to effective, safe, and inexpensive treatments for leishmaniasis.

Design, Synthesis and Antiparasitic Evaluation of Click Phospholipids

A library of seventeen novel ether phospholipid analogues, containing 5-membered heterocyclic rings (1,2,3-triazolyl, isoxazolyl, 1,3,4-oxadiazolyl and 1,2,4-oxadiazolyl) in the lipid portion were designed and synthesized aiming to identify optimised miltefosine analogues. The compounds were evaluated for their in vitro antiparasitic activity against Leishmania infantum and Leishmania donovani intracellular amastigotes, against Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the substituents of the heterocyclic ring (tail) and the oligomethylene spacer between the head group and the heterocyclic ring was found to affect the activity and toxicity of these compounds leading to a significantly improved understanding of their structure-activity relationships. The early ADMET profile of the new derivatives did not reveal major liabilities for the potent compounds. The 1,2,3-triazole derivative 27 substituted by a decyl tail, an undecyl spacer and a choline head group exhibited broad spectrum antiparasitic activity. It possessed low micromolar activity against the intracellular amastigotes of two L. infantum strains and T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes, while its cytotoxicity concentration (CC50) against THP-1 macrophages ranged between 50 and 100 μM. Altogether, our work paves the way for the development of improved ether phospholipid derivatives to control neglected tropical diseases.

In Silico Insights into the Mechanism of Action of Epoxy-α-Lapachone and Epoxymethyl-Lawsone in Leishmania spp

Epoxy-α-lapachone (Lap) and Epoxymethyl-lawsone (Law) are oxiranes derived from Lapachol and have been shown to be promising drugs for Leishmaniases treatment. Although, it is known the action spectrum of both compounds affect the Leishmania spp. multiplication, there are gaps in the molecular binding details of target enzymes related to the parasite’s physiology. Molecular docking assays simulations were performed using DockThor server to predict the preferred orientation of both compounds to form stable complexes with key enzymes of metabolic pathway, electron transport chain, and lipids metabolism of Leishmania spp. This study showed the hit rates of both compounds interacting with lanosterol C-14 demethylase (−8.4 kcal/mol to −7.4 kcal/mol), cytochrome c (−10.2 kcal/mol to −8.8 kcal/mol), and glyceraldehyde-3-phosphate dehydrogenase (−8.5 kcal/mol to −7.5 kcal/mol) according to Leishmania spp. and assessed compounds. The set of molecular evidence reinforces the potential of both compounds as multi-target drugs for interrupt the network interactions between parasite enzymes, which can lead to a better efficacy of drugs for the treatment of leishmaniases.

Molecular Identification of Parasites Causing Cutaneous Leishmaniasis in Panama

Isolates from 475 cutaneous leishmaniasis (CL) patients from three endemic regions were studied by three typing techniques. The molecular analysis from lesion scrapings based on hsp70 PCR-RFLP showed that 78.1% (371/475) restriction patterns corresponded to Leishmania (Viannia) panamensis, 19% (90/475) to Leishmania (Viannia) guyanensis, and 3.0% (14/475) to Leishmania (Viannia) braziliensis. Promastigotes isolated by culture from lesions of 228 patients (48.0%, 228/475) were identified by multi-locus enzyme electrophoresis. Of them, 95.2% (217/228) were typified as L. (V.) panamensis, 1.3% (3/228) as L. (V.) guyanensis, 2.2% (5/228) as L. (V.) braziliensis, and 1.3% (3/228) as hybrids (L. [V.] braziliensis/L. [V.] panamensis). However, a partial sequencing analysis of the hsp70 gene from 77 selected samples showed 16.9% (13/77) typified as L. (V.) panamensis, 68.8% (53/77) as Leishmania (V.) sp., 1, 3.9% (3/77) as L. (V.) guyanensis, 1.3% (1/77) as L. (V.) braziliensis outlier, 2.6% (2/77) as Leishmania (Viannia) naiffi, 2.6% as (2/77) Leishmania (V.) sp., and 2 and 3.9% (3/77) hybrid isolates of L. (V.) braziliensis/L. (V.) guyanensis. These results confirm L. (V.) panamensis as the predominant species and cause of CL lesions in Panama and that L. (V.) guyanensis, L. (V.) braziliensis, and L. (V.) naiffi are circulating to a lower degree. Furthermore, the determination of parasite isolates belonging to atypical clusters and hybrid isolates suggests the circulation of genetic variants with important implications for the epidemiology and clinical follow-up of CL in Panama. No evidence of the existence of parasites of the Leishmania (Leishmania) mexicana complex in Panamanian territory was found in this study.

Colombian Contributions Fighting Leishmaniasis: A Systematic Review on Antileishmanials Combined with Chemoinformatics Analysis

Leishmaniasis is a parasitic morbid/fatal disease caused by Leishmania protozoa. Twelve million people worldwide are appraised to be currently infected, including ca. two million infections each year, and 350 million people in 88 countries are at risk of becoming infected. In Colombia, cutaneous leishmaniasis (CL) is a public health problem in some tropical areas. Therapeutics is based on traditional antileishmanial drugs, but this practice has several drawbacks for patients. Thus, the search for new antileishmanial agents is a serious need, but the lack of adequately funded research programs on drug discovery has hampered its progress. Some Colombian researchers have conducted different research projects focused on the assessment of the antileishmanial activity of naturally occurring and synthetic compounds against promastigotes and/or amastigotes. Results of such studies have separately demonstrated important hits and reasonable potential, but a holistic view of them is lacking. Hence, we present the outcome from a systematic review of the literature (under PRISMA guidelines) on those Colombian studies investigating antileishmanials during the last thirty-two years. In order to combine the general efforts aiming at finding a lead against Leishmania panamensis (one of the most studied and incident parasites in Colombia causing CL) and to recognize structural features of representative compounds, fingerprint-based analyses using conventional machine learning algorithms and clustering methods are shown. Abstraction from such a meta-description led to describe some function-determining molecular features and simplify the clustering of plausible isofunctional hits. This systematic review indicated that the Colombian efforts for the antileishmanials discovery are increasingly intensified, though improvements in the followed pathways must be definitively pursued. In this context, a brief discussion about scope, strengths and limitations of such advances and relationships is addressed.

Antileishmanial activity of 4-phenyl-1-[2-(phthalimido-2-yl)ethyl]-1H-1,2,3-triazole (PT4) derivative on Leishmania amazonensis and Leishmania braziliensis: In silico ADMET, in vitro activity, docking and molecular dynamic simulations

Organic compounds obtained by click chemistry reactions have demonstrated a broad spectrum of biological activities being widely applied for the development of molecules against pathogens of medical and veterinary importance. Cutaneous leishmaniasis (CL), caused by intracellular protozoa parasite of genus Leishmania, comprises a complex of clinical manifestations that affect the skin and mucous membranes. The available drugs for the treatment are toxic and costly, with long periods of treatment, and the emergence of resistant strains has been reported. In this study we investigated the in vitro effects of a phthalimide-1,2,3-triazole derivative, the 4-Phenyl-1-[2-(phthalimido-2-yl)ethyl]-1H-1,2,3-triazole (PT4) obtained by click chemistry, on mammalian cells and on L. amazonensis and L. braziliensis, the causative agents of CL in Brazil. In silico ADMET evaluation of PT4 showed that this molecule has good pharmacokinetic properties with no violation of Lipinski's rules. The in vitro assays showed that PT4 was more selective for both Leishmania species than to mammalian cells. This compound also presented low cytotoxicity to mammalian cells with CC₅₀ > 500 μM. Treatment of promastigote forms with different concentrations of PT4 resulted in ultrastructural alterations, such as plasma membrane wrinkling, shortening of cell body, increased cell volume and cell rupture. The molecular dynamic simulations showed that PT4 interacts with Lanosterol 14 α-demethylase from Leishmania, an essential enzyme of lipid synthesis pathway in this parasite. Our results demonstrated PT4 was effective against both species of Leishmania. PT4 caused a decrease of mitochondrial membrane potential and increased production of reactive oxygen species, which may lead to parasite death. Taken together, our results pointed PT4 as promissing therapeutic agent against CL.

A Multi-Species Phenotypic Screening Assay for Leishmaniasis Drug Discovery Shows That Active Compounds Display a High Degree of Species-Specificity

High genetic and phenotypic variability between Leishmania species and strains within species make the development of broad-spectrum antileishmanial drugs challenging. Thus, screening panels consisting of several diverse Leishmania species can be useful in enabling compound prioritization based on their spectrum of activity. In this study, a robust and reproducible high content assay was developed, and 1280 small molecules were simultaneously screened against clinically relevant cutaneous and visceral species: L. amazonensis, L. braziliensis, and L. donovani. The assay is based on THP-1 macrophages infected with stationary phase promastigotes and posterior evaluation of both compound antileishmanial activity and host cell toxicity. The profile of compound activity was species-specific, and out of 51 active compounds, only 14 presented broad-spectrum activity against the three species, with activities ranging from 52% to 100%. Notably, the compounds CB1954, Clomipramine, Maprotiline, Protriptyline, and ML-9 presented pan-leishmanial activity, with efficacy greater than 70%. The results highlight the reduced number of compound classes with pan-leishmanial activity that might be available from diversity libraries, emphasizing the need to screen active compounds against a panel of species and strains. The assay reported here can be adapted to virtually any Leishmania species without the need for genetic modification of parasites, providing the basis for the discovery of broad spectrum anti-leishmanial agents.

The current drug discovery landscape for trypanosomiasis and leishmaniasis: Challenges and strategies to identify drug targets

Human trypanosomiasis and leishmaniasis are vector-borne neglected tropical diseases caused by infection with the protozoan parasites Trypanosoma spp. and Leishmania spp., respectively. Once restricted to endemic areas, these diseases are now distributed worldwide due to human migration, climate change, and anthropogenic disturbance, causing significant health and economic burden globally. The current chemotherapy used to treat these diseases has limited efficacy, and drug resistance is spreading. Hence, new drugs are urgently needed. Phenotypic compound screenings have prevailed as the leading method to discover new drug candidates against these diseases. However, the publication of the complete genome sequences of multiple strains, advances in the application of CRISPR/Cas9 technology, and in vivo bioluminescence-based imaging have set the stage for advancing target-based drug discovery. This review analyses the limitations of the narrow pool of available drugs presently used for treating these diseases. It describes the current drug-based clinical trials highlighting the most promising leads. Furthermore, the review presents a focused discussion on the most important biological and pharmacological challenges that target-based drug discovery programs must overcome to advance drug candidates. Finally, it examines the advantages and limitations of modern research tools designed to identify and validate essential genes as drug targets, including genomic editing applications and in vivo imaging.

Antiproliferative effect of a benzofuran derivate based on the structure of amiodarone on Leishmania donovani affecting mitochondria, acidocalcisomes and intracellular Ca2+ homeostasis

Leishmaniasis is a parasitic disease representing an important problem of public health. Visceral leishmaniasis, resulting from infection with Leishmania donovani, causes considerable mortality and morbidity in the poorest region of the word. At present there is no current effective treatment, since the approved, drugs are expensive and are not free of undesirable side effects. Therefore, there is a need for the identification of new drugs. In this context, the parasite Ca²⁺ regulatory mechanisms in which mitochondria and acidocalcisomes are involved have been postulated as important targets for several trypanocidal drugs. Thus, amiodarone and dronedarone, common human antiarrythmics, exert its known action on these parasites through the disruption of the intracellular Ca²⁺ homeostasis. AMIODER is a benzofuran derivate based on the structure of amiodarone that recently demonstrates a significant effect on Trypanosoma cruzi. We now report the effect of AMIODER on Leishmania donovani demonstrating that it inhibit the growth of promastigotes and also of amastigotes inside macrophages, the clinically relevant stage of the parasite, obtaining IC₅₀ values significantly lower than those reported for T. cruzi. We also show that this compound disrupted Ca²⁺ homeostasis in L. donovani, through its action on two organelles involved in the intracellular Ca²⁺ regulation and on the bioenergetics of the parasite. AMIODER totally collapsed the electrochemical membrane potential of the unique giant mitochondrion and simultaneously induced the alkalinization of acidocalcisomes, driving together to a large increase in the intracellular Ca²⁺ concentration of the parasite as the main mechanism of action of this benzofurane derivative.

Second-generation pterocarpanquinones: synthesis and antileishmanial activity

Background

Despite the development of new therapies for leishmaniasis, among the 200 countries or territories reporting to the WHO, 87 were identified as endemic for Tegumentary Leishmaniasis and 75 as endemic for Visceral Leishmaniasis. The identification of antileishmanial drug candidates is essential to fill the drug discovery pipeline for leishmaniasis. In the hit molecule LQB-118 selected, the first generation of pterocarpanquinones was effective and safe against experimental visceral and cutaneous leishmaniasis via oral delivery. In this paper, we report the synthesis and antileishmanial activity of the second generation of pterocarpanoquinones.

Methods

The second generation of pterocarpanquinones 2a-f was prepared through a palladium-catalyzed oxyarylation of dihydronaphtalen and chromens with iodolawsone, easily prepared by iodination of lawsone. The spectrum of antileishmanial activity was evaluated in promastigotes and intracellular amastigotes of L. amazonensis, L. braziliensis, and L. infantum. Toxicity was assessed in peritoneal macrophages and selective index calculated by CC₅₀/IC₅₀. Oxidative stress was measured by intracellular ROS levels and mitochondrial membrane potential in treated cells.

Results

In this work, we answered two pertinent questions about the structure of the first-generation pterocarpanquinones: the configuration and positions of rings B (pyran) and C (furan) and the presence of oxygen in the B ring. When rings B and C are exchanged, we noted an improvement of the activity against promastigotes and amastigotes of L. amazonensis and promastigotes of L. infantum. As to the oxygen in ring B of the new generation, we observed that the oxygenated compound 2b is approximately twice as active against L. braziliensis promastigotes than its deoxy derivative 2a. Another modification that improved the activity was the addition of the methylenedioxy group. A variation in the susceptibility among species was evident in the clinically relevant form of the parasite, the intracellular amastigote. L. amazonensis was the species most susceptible to novel derivatives, whilst L. infantum was resistant to most of them. The pterocarpanoquinones (2b and 2c) that possess the oxygen atom in ring B showed induction of increased ROS production.

Conclusions

The data presented indicate that the pterocarpanoquinones are promising compounds for the development of new leishmanicidal agents.

Screening a Natural Product-Based Library against Kinetoplastid Parasites

Kinetoplastid parasites cause vector-borne parasitic diseases including leishmaniasis, human African trypanosomiasis (HAT) and Chagas disease. These Neglected Tropical Diseases (NTDs) impact on some of the world's lowest socioeconomic communities. Current treatments for these diseases cause severe toxicity and have limited efficacy, highlighting the need to identify new treatments. In this study, the Davis open access natural product-based library was screened against kinetoplastids (Leishmania donovani DD8, Trypanosoma brucei brucei and Trypanosoma cruzi) using phenotypic assays. The aim of this study was to identify hit compounds, with a focus on improved efficacy, selectivity and potential to target several kinetoplastid parasites. The IC50 values of the natural products were obtained for L. donovani DD8, T. b. brucei and T. cruzi in addition to cytotoxicity against the mammalian cell lines, HEK-293, 3T3 and THP-1 cell lines were determined to ascertain parasite selectivity. Thirty-one compounds were identified with IC50 values of ≤ 10 µM against the kinetoplastid parasites tested. Lissoclinotoxin E (1) was the only compound identified with activity across all three investigated parasites, exhibiting IC50 values < 5 µM. In this study, natural products with the potential to be new chemical starting points for drug discovery efforts for kinetoplastid diseases were identified.

Insights into the structural patterns of the antileishmanial activity of bi- and tricyclic N-heterocycles

The influence of various structural patterns in a series of novel bi- and tricyclic N-heterocycles on the activity against Leishmania major and Leishmania panamensis has been studied and compounds that are active in the low micromolar region have been identified. Both quinolines and tetrahydrooxazinoindoles (TOI) proved to have significant antileishmanial activities, while substituted indoles were inactive. We have also showed that a chloroquine analogue induces Leishmania killing by modulating macrophage activation.

Concurrent visual diagnosis and susceptibility profiling of the first line drug against visceral leishmaniasis by plasmonic detection of PCR amplified genetic biomarker

Visceral form of leishmaniasis (also known as Kala-azar) is a fatal neglected tropical disease affecting 95 countries worldwide. Recently, substantial proportion of resistance related treatment failure cases have been reported against its first line drug, sodium-antimony gluconate (SAG). We report an easy, fast, sensitive and cheap visual diagnosis and SAG susceptibility profiling for this disease based on recently recognized genetic biomarker and gold nanoparticle based plasmonic detection phenomenon. This is a non-gel, non-culture based detection technique, which can be used as simultaneous high throughput detection and SAG-susceptibility profiling in Leishmania endemic resource stringent countries.

Antileishmanial Activity of Compounds Derived from the Medicines for Malaria Venture Open Access Box Against Intracellular Leishmania major Amastigotes

Leishmaniasis is a complex tropical disease caused by kinetoplastid parasitic protozoa of the genus Leishmania and is transmitted by the sand fly insect vector. Cutaneous leishmaniasis (CL) is the most common form of this disease, and CL infections often result in serious skin lesions and scars. CL remains a public health problem in many endemic countries worldwide because of the absence of effective, safe, and cost-effective drugs for treatment. One of the strategies we chose to use to find novel chemical entities worthy of further development as antileishmanials involved screening synthetic and natural products libraries. In our study, we developed a Leishmania major intracellular amastigote assay that uses the activity of luciferase as a measure of parasite proliferation and used this assay to screen a collection of 400 compounds obtained from Medicines for Malaria Venture (MMV) for their antileishmanial activity. Our results showed that 14 compounds identified by MMV as antimalarial drugs have antileishmanial activity and can potentially be optimized for CL drug development.

Development of a liquid chromatographic method for the quantification of paromomycin. Application to in vitro release and ex vivo permeation studies

We have developed a reversed phase high performance liquid chromatography pulsed amperometric detection (RPHPLC-PAD) method for the determination of paromomycin. It is sensitive, repeatable, and selective without the pretreatment step. Trifluoroacetic acid-water was utilized as the eluent and detected by PAD under NaOH alkaline conditions. The paromomycin detection limit (S/N=3.3) was 2μgmL(-1) and the quantification limit (S/N=10) was 6μgmL(-1). Coefficients of linear regression were higher than 0.99 for concentrations between 6.25 and 200μgmL(-1). The intra and inter-day precision (RSD) was less than 6.5%. The average recoveries were 97.53-102.01%. The proposed HPLC-PAD method presented advantageous performance characteristics and it can be considered suitable for the evaluation of paromomycin loaded nanogel formulation in ex vivo permeation and in vitro release studies.

Development and validation of four Leishmania species constitutively expressing GFP protein. A model for drug discovery and disease pathogenesis studies

Green fluorescent protein (GFP)-parasite transfectants have been widely used as a tool for studying disease pathogenesis in several protozoan models and their application in drug screening assays has increased rapidly. In the past decade, the expression of GFP has been established in several Leishmania species, mostly for in vitro studies. The current work reports generation of four transgenic parasites constitutively expressing GFP (Leishmania mexicana, Leishmania aethiopica, Leishmania tropica and Leishmania major) and their validation as a representative model of infection. This is the first report where stable expression of GFP has been achieved in L. aethiopica and L. tropica. Integration of GFP was accomplished through homologous recombination of the expression construct, pRib1.2αNEOαGFP downstream of the 18S rRNA promoter in all species. A homogeneous and high level expression of GFP was detected in both the promastigote and the intracellular amastigote stages. All transgenic species showed the same growth pattern, ability to infect mammalian host cells and sensitivity to reference drugs as their wild type counterparts. All four transgenic Leishmania are confirmed as models for in vitro and possibly in vivo infections and represent an ideal tool for medium throughput testing of compound libraries.

(Post-) Genomic approaches to tackle drug resistance in Leishmania

Leishmaniasis, like other neglected diseases is characterized by a small arsenal of drugs for its control. To safeguard the efficacy of current drugs and guide the development of new ones it is thus of utmost importance to acquire a deep understanding of the phenomenon of drug resistance and its link with treatment outcome. We discuss here how (post-)genomic approaches may contribute to this purpose. We highlight the need for a clear definition of the phenotypes under consideration: innate and acquired resistance versus treatment failure. We provide a recent update of our knowledge on the Leishmania genome structure and dynamics, and compare the contribution of targeted and untargeted methods for the understanding of drug resistance and show their limits. We also present the main assays allowing the experimental validation of the genes putatively involved in drug resistance. The importance of analysing information downstream of the genome is stressed and further illustrated by recent metabolomics findings. Finally, the attention is called onto the challenges for implementing the acquired knowledge to the benefit of the patients and the population at risk.

Primary oral Penicillium marneffei infection diagnosed by PCR-based molecular identification and transmission electron microscopic observation from formalin-fixed paraffin-embedded tissues

We report a case of primary oral Penicillium marneffei infection in a 39-year-old man without HIV infection. Although fungal culture was negative, the patient was finally confirmed to have P. marneffei infection by PCR-based molecular identification and transmission electron microscopic observation from formalin-fixed, paraffin-embedded tissues. The patient was cured with taking itraconazole for 3 months.

Genetic markers for SSG resistance in Leishmania donovani and SSG treatment failure in visceral leishmaniasis patients of the Indian subcontinent

The current standard to assess pentavalent antimonial (SSG) susceptibility of Leishmania is a laborious in vitro assay of which the result has little clinical value because SSG-resistant parasites are also found in SSG-cured patients. Candidate genetic markers for clinically relevant SSG-resistant parasites identified by full genome sequencing were here validated on a larger set of clinical strains. We show that 3 genomic locations suffice to specifically detect the SSG-resistant parasites found only in patients experiencing SSG treatment failure. This finding allows the development of rapid assays to monitor the emergence and spread of clinically relevant SSG-resistant Leishmania parasites.

Improvement of the green fluorescent protein reporter system in Leishmania spp. for the in vitro and in vivo screening of antileishmanial drugs

Development of new therapeutic approaches for leishmaniasis treatment requires new high throughput screening methodologies for the antileishmanial activity of the new compounds both in vitro and in vivo. Reporter genes as the GFP have become one of the most promissory and widely used tools for drug screening in several models, since it offers live imaging, high sensibility, specificity and flexibility; additionally, the use of GFP as a reporter gene in screening assays eliminates all the drawbacks presented in conventional assays and also those technical problems found using other reporter genes. The utility of the GFP as a reporter gene in drug screening assays with Leishmania parasites depends on the homogeneity and stability of the GFP transfected strains. Stable expression of the GFP in the Old World Leishmania species has been demonstrated using integration vectors; however, no reports exist yet about the success of this methodology in the New World species. Here we report the generation of New World Leishmania strains expressing the GFP protein from an integration vector, which replaces one copy of the 18S RNA in the chromosome with the GFP coding sequence by homologous recombination. We also prove that the expression of the integrated GFP is stable and homogeneous in the transfected parasites after months in culture without selective pressure or during its use in hamster infection assays. The fluorescent strains are useful for in vitro, ex vivo and in vivo drug screening assays since no considerable variations in virulence or infectivity where seen attributable to the genetic manipulation during both in vitro and in vivo infection experiments. The platform described here for drug testing assays based on the use of stable fluorescent Leishmania strains coupled to flow cytometry and fluorescent microscopy is more sensitive, more specific and faster than conventional assays used normally for the evaluation of compounds with potential antileishmanial activity.

Leishmania strains causing self-healing cutaneous leishmaniasis have greater susceptibility towards oxidative stress

The survival of Leishmania parasites within macrophages is influenced by generation of free radicals. To establish whether generation of free radicals influenced chemotherapeutic response, promastigotes from isolates causing self-healing or delayed/non-self-healing cutaneous leishmaniasis (CL) or visceral leishmaniasis (VL) were evaluated for their susceptibility to nitric oxide (NO), antimony and miltefosine. In a self-healing CL strain of Leishmania major (5ASKH), susceptibility to NO and antimony was higher than other species. Likewise, a Leishmania amazonensis strain, M2269, showed greater susceptibility to NO and antimony than other species but no such correlation was observed with miltefosine. Additionally, 5ASKH and M2269 showed poorer free radical scavenging capacity as also their thiol levels were lower than species causing VL. Collectively, our study suggests that self-healing isolates tend to be more susceptible to oxidative stress.

Recent advances in leishmaniasis treatment

About 1.5 million new cases of cutaneous leishmaniasis and 500,000 new cases of visceral leishmaniasis occur each year around the world. For over half a century, the clinical forms of the disease have been treated almost exclusively with pentavalent antimonial compounds. In this review, we describe the arsenal available for treating Leishmania infections, as well as recent advances from research on plants and synthetic compounds as source drugs for treating the disease. We also review some new drug-delivery systems for the development of novel chemotherapeutics. We observe that the pharmaceutical industry should employ its modern technologies, which could lead to better use of plants and their extracts, as well as to the development of synthetic and semi-synthetic compounds. New studies have highlighted some biopharmaceutical technologies in the design of the delivery strategy, such as nanoparticles, liposomes, cochleates, and non-specific lipid transfer proteins. These observations serve as a basis to indicate novel routes for the development and design of effective anti-Leishmania drugs.

Chemistry, cytotoxicity and antileishmanial activity of the essential oil from Piper auritum

Leishmaniasis is one of the most important parasitic infections, but current treatments are unsatisfactory due to their toxicity, cost and resistance. Therefore, the development of new antileishmanial compounds is imperative. Many people who live in endemic areas use plants as an alternative to treat the disease. In this paper, we characterised the essential oil from Piper auritum, evaluated its cytotoxicity and determined its antileishmanial activity. The chromatogram obtained by gas chromatography revealed 60 peaks and we found that safrole was the most abundant compound, composing 87% of the oil. The oil was active against the promastigotes of Leishmania major, Leishmania mexicana, Leishmania braziliensis and Leishmania donovani with a favourable selectivity index against peritoneal macrophages from BALB/c mice. The Piper-oil inhibited the growing of intracellular amastigotes of L. donovani with an IC50 value of 22.3 +/- 1.8 microg/mL. This study demonstrates the usefulness of the essential oils as a promising alternative to treat leishmaniasis.

Heat-shock protein 70 PCR-RFLP: a universal simple tool for Leishmania species discrimination in the New and Old World

Introduction. Species typing in leishmaniasis gains importance in diagnostics, epidemiology, and clinical studies. A restriction fragment length polymorphism (RFLP) assay of PCR amplicons from a partial heat-shock protein 70 gene (hsp70) had been described for the New World, allowing identification of some species. Methods. Based on an initial in silico analysis of 51 hsp70 sequences, most of which we recently determined in the frame of a phylogenetic study, species-specific restriction sites were identified. These were tested by PCR-RFLP on 139 strains from 14 species, thereby documenting both inter- and intra-species variability. Results. Our assay could identify Leishmania infantum, L. donovani, L. tropica, L. aethiopica, L. major, L. lainsoni, L. naiffi, L. braziliensis, L. peruviana, L. guyanensis, and L. panamensis by applying 2 subsequent digests. L. mexicana, L. amazonensis, and L. garnhami did not generate species-specific restriction fragment patterns. Conclusion. Currently no assay is available for global Leishmania species discrimination. We present a universal PCR-RFLP method allowing identification of most medically relevant Old and New World Leishmania species on the basis of a single PCR, obviating the need to perform separate PCRs. The technique is simple to perform and can be implemented in all settings where PCR is available.

Antileishmanial high-throughput drug screening reveals drug candidates with new scaffolds

Drugs currently available for leishmaniasis treatment often show parasite resistance, highly toxic side effects and prohibitive costs commonly incompatible with patients from the tropical endemic countries. In this sense, there is an urgent need for new drugs as a treatment solution for this neglected disease. Here we show the development and implementation of an automated high-throughput viability screening assay for the discovery of new drugs against Leishmania. Assay validation was done with Leishmania promastigote forms, including the screening of 4,000 compounds with known pharmacological properties. In an attempt to find new compounds with leishmanicidal properties, 26,500 structurally diverse chemical compounds were screened. A cut-off of 70% growth inhibition in the primary screening led to the identification of 567 active compounds. Cellular toxicity and selectivity were responsible for the exclusion of 78% of the pre-selected compounds. The activity of the remaining 124 compounds was confirmed against the intramacrophagic amastigote form of the parasite. In vitro microsomal stability and cytochrome P450 (CYP) inhibition of the two most active compounds from this screening effort were assessed to obtain preliminary information on their metabolism in the host. The HTS approach employed here resulted in the discovery of two new antileishmanial compounds, bringing promising candidates to the leishmaniasis drug discovery pipeline.

Every year, more than 2 million people worldwide suffer from leishmaniasis, a neglected tropical disease present in 88 countries. The disease is caused by the single-celled protozoan parasite species of the genus Leishmania, which is transmitted to humans by the bite of the sandfly. The disease manifests itself in a broad range of symptoms, and its most virulent form, named visceral leishmaniasis, is lethal if not treated. Most of the few available treatments for leishmaniasis were developed decades ago and are often toxic, sometimes even leading to the patient's death. Furthermore, the parasite is developing resistance to available drugs, making the discovery and development of new antileishmanials an urgent need. To tackle this problem, the authors of this study employed the use of high-throughput technologies to screen a large library of small, synthetic molecules for their ability to interfere with the viability of Leishmania parasites. This study resulted in the discovery of two novel compounds with leishmanicidal properties and promising drug-like properties, bringing new candidates to the leishmaniasis drug discovery pipeline.

In-vitro and in-vivo studies on a topical formulation of sitamaquine dihydrochloride for cutaneous leishmaniasis

The efficacy of topical formulations of the 8-aminoquinoline, sitamaquine dihydrochloride, in both in-vitro and in in-vivo models of cutaneous leishmaniasis is reported. In-vitro parasite assays confirmed that sitamaquine dihydrochloride was active against a range of Leishmania species that cause either cutaneous or visceral leishmaniasis, with ED50 values against amastigotes over the range of 2.9 to 19.0μM. A range of topical sitamaquine dihydrochloride formulations (anhydrous gel, emulsions) were developed for studies on experimental cutaneous leishmaniasis using only topically acceptable excipients orthose currently undergoing regulatory approval. An uptake study into murine skin confirmed in-vitro skin penetration and retention. Several formulations were tested in-vivo against Leishmania major cutaneous lesions in BALB/c mice. None of the sitamaquine dihydrochloride formulations tested appeared to either slow lesion progression or reduce parasite burden.

In vitroactivity of an essential oil againstLeishmania donovani

The in vitro antileishmanial effect of the essential oil from Chenopodium ambrosioides against Leishmania donovani was investigated. The product showed significant activity against promastigotes and amastigotes, with a 50% effective concentration of 4.45 and 5.1 microg/mL, respectively. The essential oil caused an irreversible inhibition of the growth of promastigotes after a treatment with 100 or 10 microg/mL for 1 or 24 h, respectively. The phagocytic activity of the macrophages was preserved at a concentration toxic to the parasite. The essential oil from C. ambrosioides may be a potential candidate drug to development a new agent to combat this parasitic disease.

Use of PCR-restriction fragment length polymorphism analysis to identify the main new world Leishmania species and analyze their taxonomic properties and polymorphism by application of the assay to clinical samples

At least 13 characterized Leishmania species are known to infect humans in South America. Five of these parasites are transmitted in the sylvatic ecotopes of the whole French Guianan territory and responsible for cutaneous leishmaniasis. For the diagnosis of cutaneous leishmaniasis, restriction fragment length polymorphism (RFLP) analyses have shown promising results. Thus, the end of the small subunit and internal transcribed spacer 1 of the rRNA genes were sequenced and targeted by PCR-RFLP analysis in the 10 main New World (NW) Leishmania species from the two subgenera. Then, the procedure was tested on 40 samples from patients with cutaneous leishmaniasis, and its results were compared with those of conventional methods. (i) The results of this simple genus-specific method were in agreement with those of previous isoenzyme analyses. (ii) This method distinguished the most medically relevant Leishmania species with only one enzyme (RsaI). (iii) This method could be performed directly on human biopsy specimens (sensitivity of 85.7%). Performing NW Leishmania species typing rapidly and easily in the field constitutes a very valuable improvement for detection of Leishmania spp. Revealing great diversity with several enzymes, this method could also be useful for taxonomic, ecological, and epidemiological studies in space and time.

Itraconazole in the treatment of New World mucocutaneous leishmaniasis

BACKGROUND

A well-tolerated oral drug is required for the treatment of mucocutaneous leishmaniasis (MCL). Current parenteral treatment regimens with pentavalent antimonials are associated with marked toxicity and significant rates of relapse.

AIM

To evaluate the efficacy and tolerability of high-dose itraconazole for the treatment of MCL.

METHODS

An uncontrolled treatment study was performed in 13 Ecuadorian patients with MCL. Each patient received a daily dosage of 400 mg of itraconazole for a minimum of 3 months.

RESULTS

All 13 subjects responded to itraconazole during the first month of treatment, but by 12 months after treatment the complete resolution of MCL lesions was observed in only three (23%) subjects. No adverse effects of treatment were reported. Response to treatment was associated with a short evolution of the disease and mild to moderate disease severity.

CONCLUSION

Prolonged and high-dose treatment regimens with itraconazole are not effective for the treatment of the majority of patients with MCL.

Leishmaniose visceral no Brasil: quadro atual, desafios e perspectivas

No Brasil, a importância da leishmaniose visceral reside não somente na sua alta incidência e ampla distribuição, mas também na possibilidade de assumir formas graves e letais quando associada ao quadro de má nutrição e infecções concomitantes. A crescente urbanização da doença ocorrida nos últimos 20 anos coloca em pauta a discussão das estratégias de controle empregadas. Neste artigo foram analisados os principais aspectos biológicos, ambientais e sociais que influenciaram no processo de expansão e urbanização dos focos da doença. Os métodos disponíveis para o diagnóstico e tratamento não apresentam a eficácia e aplicabilidade desejadas, embora avanços promissores tenham sido alcançados com as pesquisas de novos testes diagnósticos e drogas terapêuticas. As medidas de controle da doença até agora implementadas foram incapazes de eliminar a transmissão e impedir a ocorrência de novas epidemias. É feita uma breve análise destas medidas e dos desafios a serem enfrentados. A prevenção da doença nos cães através da imunoprofilaxia aparece como uma alternativa para o controle. Uma nova vacina para cães, já testada em campo, está sendo industrializada e será comercializada no Brasil a partir de 2004. Apesar da existência de inúmeros estudos sobre a leishmaniose visceral humana e canina, muitas lacunas ainda precisam ser preenchidas.

In vitro assays for evaluation of drug activity against Leishmania spp

Leishmania is a parasitic protozoan which causes severe disease in humans and dogs. Screening of new compounds against leishmaniasis is particularly needed to determine the toxicity of some existing drugs and the appearance of drug-resistant strains. Reliable and simple in vitro models are required for large-scale initial screenings. In this review different methods for in vitro evaluation of drug activity against Leishmania spp. are summarized.