Potent In Vitro Antiproliferative Synergism of Combinations of Ergosterol Biosynthesis Inhibitors against Leishmania amazonensis

Buparvaquone Induces Ultrastructural and Physiological Alterations Leading to Mitochondrial Dysfunction and Caspase-Independent Apoptotic Cell Death in Leishmania donovani

Leishmaniasis is a neglected tropical disease (endemic in 99 countries) caused by parasitic protozoa of the genus Leishmania. As treatment options are limited, there is an unmet need for new drugs. The hydroxynaphthoquinone class of compounds demonstrates broad-spectrum activity against protozoan parasites. Buparvaquone (BPQ), a member of this class, is the only drug licensed for the treatment of theileriosis. BPQ has shown promising antileishmanial activity but its mode of action is largely unknown. The aim of this study was to evaluate the ultrastructural and physiological effects of BPQ for elucidating the mechanisms underlying the in vitro antiproliferative activity in Leishmania donovani. Transmission and scanning electron microscopy analyses of BPQ-treated parasites revealed ultrastructural effects characteristic of apoptosis-like cell death, which include alterations in the nucleus, mitochondrion, kinetoplast, flagella, and the flagellar pocket. Using flow cytometry, laser scanning confocal microscopy, and fluorometry, we found that BPQ induced caspase-independent apoptosis-like cell death by losing plasma membrane phospholipid asymmetry and cell cycle arrest at sub-G0/G1 phase. Depolarization of the mitochondrial membrane leads to the generation of oxidative stress and impaired ATP synthesis followed by disruption of intracellular calcium homeostasis. Collectively, these findings provide valuable mechanistic insights and demonstrate BPQ's potential for development as an antileishmanial agent.

Profiling Novel Quinuclidine-Based Derivatives as Potential Anticholinesterase Drugs: Enzyme Inhibition and Effects on Cell Viability

The cholinergic system, relying on the neurotransmitter acetylcholine (ACh), plays a significant role in muscle contraction, cognition, and autonomic nervous system regulation. The enzymes acetylcholinesterase, AChE, and butyrylcholinesterase, BChE, responsible for hydrolyzing ACh, can fine-tune the cholinergic system's activity and are, therefore, excellent pharmacological targets to address a range of medical conditions. We designed, synthesized, and profiled 14 N-alkyl quaternary quinuclidines as inhibitors of human AChE and BChE and analyzed their impact on cell viability to assess their safety in the context of application as potential therapeutics. Our results showed that all of the 14 tested quinuclidines inhibited both AChE and BChE in the micromolar range (Ki = 0.26 - 156.2 μM). The highest inhibition potency was observed for two bisquaternary derivatives, 7 (1,1'-(decano)bis(3-hydroxyquinuclidinium bromide)) and 14 (1,1'-(decano)bis(3-hydroxyiminoquinuclidinium bromide)). The cytotoxic effect within 7-200 μM was observed only for monoquaternary quinuclidine derivatives, especially those with the C12-C16 alkyl chain. Further analysis revealed a time-independent mechanism of action, significant LDH release, and a decrease in the cells' mitochondrial membrane potential. Taking all results into consideration, we can confirm that a quinuclidine core presents a good scaffold for cholinesterase binding and that two bisquaternary quinuclidine derivatives could be considered as candidates worth further investigations as drugs acting in the cholinergic system. On the other hand, specific cell-related effects probably triggered by the free long alkyl chain in monoquaternary quinuclidine derivatives should not be neglected in future N-alkyl quaternary quinuclidine derivative structure refinements. Such an effect and their potential to interact with other specific targets, as indicated by a pharmacophore model, open up a new perspective for future investigations of these compounds' scaffold in the treatment of specific conditions and diseases other than cholinergic system-linked disorders.

Zinc(II)-Sterol Hydrazone Complex as a Potent Anti-Leishmania Agent: Synthesis, Characterization, and Insight into Its Mechanism of Antiparasitic Action

Searching for new alternatives for treating leishmaniasis, we present the synthesis, characterization, and biological evaluation against Leishmania amazonensis of the new ZnCl2(H3)2 complex. H3 is 22-hydrazone-imidazoline-2-yl-chol-5-ene-3β-ol, a well-known bioactive molecule functioning as a sterol Δ24-sterol methyl transferase (24-SMT) inhibitor. The ZnCl2(H3)2 complex was characterized by infrared, UV-vis, molar conductance measurements, elemental analysis, mass spectrometry, and NMR experiments. The biological results showed that the free ligand H3 and ZnCl2(H3)2 significantly inhibited the growth of promastigotes and intracellular amastigotes. The IC50 values found for H3 and ZnCl2(H3)2 were 5.2 µM and 2.5 µM for promastigotes, and 543 nM and 32 nM for intracellular amastigotes, respectively. Thus, the ZnCl2(H3)2 complex proved to be seventeen times more potent than the free ligand H3 against the intracellular amastigote, the clinically relevant stage. Furthermore, cytotoxicity assays and determination of selectivity index (SI) revealed that ZnCl2(H3)2 (CC50 = 5 μΜ, SI = 156) is more selective than H3 (CC50 = 10 μΜ, SI = 20). Furthermore, as H3 is a specific inhibitor of the 24-SMT, free sterol analysis was performed. The results showed that H3 was not only able to induce depletion of endogenous parasite sterols (episterol and 5-dehydroepisterol) and their replacement by 24-desalkyl sterols (cholesta-5,7,24-trien-3β-ol and cholesta-7,24-dien-3β-ol) but also its zinc derivative resulting in a loss of cell viability. Using electron microscopy, studies on the fine ultrastructure of the parasites showed significant differences between the control cells and parasites treated with H3 and ZnCl2(H3)2. The inhibitors induced membrane wrinkle, mitochondrial injury, and abnormal chromatin condensation changes that are more intense in the cells treated with ZnCl2(H3)2.

Leishmanicidal and cytotoxic activity of essential oil from the fruit peel of Myrciaria floribunda (H. West ex Willd.) O. Berg: Molecular docking and molecular dynamics simulations of its major constituent onto Leishmania enzyme targets

Cutaneous Leishmaniasis (CL) is a neglected disease characterized by highest morbidity rates worldwide. The available treatment for CL has several limitations including serious side effects and resistance to the treatment. Herein we aimed to evaluate the activity of essential oil from the peel of Myrciaria floribunda fruits (MfEO) on Leishmania amazonensis. The cytotoxic potential of MfEO on host mammalian cells was evaluated by MTT. The in vitro leishmanicidal effects of MfEO were investigated on the promastigote and intracellular amastigote forms. The ultrastructural changes induced by MfEO were evaluated by Scanning Electron Microscopy (SEM). The molecular docking of the major compounds δ-Cadinene, γ-Cadinene, γ-Muurolene, α-Selinene, α-Muurolene and (E)-Caryophyllene onto the enzymes trypanothione reductase (TreR) and sterol 14-alpha demethylase (C14DM) were performed. Our results showed that MfEO presented moderate cytotoxicity for Vero cells and macrophages. The MfEO inhibited the growth of promastigote and the survival of intracellular amastigotes, in a dose- and time- dependent way. The MfEO presented high selectivity towards amastigote forms, being 44.1 times more toxic for this form than to macrophages. Molecular docking analysis showed that the major compounds of MfEO interact with Leishmania enzymes and that δ-Cadinene (δ-CAD) presented favorable affinity energy values over TreR and C14DM enzymes, when compared with the other major constituents. Molecular dynamics (MD) simulation studies revealed a stable binding of δ-CAD with lowest binding free energy values in MMGBSA assay. Our results suggested that δ-CAD may be a potent inhibitor of TreR and C14DM enzymes. Communicated by Ramaswamy H. Sarma.

Benzylamines as highly potent inhibitors of the sterol biosynthesis pathway in Leishmania amazonensis leading to oxidative stress and ultrastructural alterations

Leishmaniasis is a neglected disease caused by protozoan parasites of the Leishmania genus. Benzylamines are a class of compounds selectively designed to inhibit the squalene synthase (SQS) that catalyzes the first committed reaction on the sterol biosynthesis pathway. Herein, we studied seven new benzylamines (SBC 37–43) against Leishmania amazonensis. After the first screening of cell viability, two inhibitors (SBC 39 and SBC 40) were selected. Against intracellular amastigotes, SBC 39 and SBC 40 presented selectivity indexes of 117.7 and 180, respectively, indicating high selectivity. Analysis of the sterol composition revealed a depletion of endogenous 24-alkylated sterols such as episterol and 5-dehydroepisterol, with a concomitant accumulation of fecosterol, implying a disturbance in cellular lipid content. This result suggests a blockade of de novo sterol synthesis at the level of SQS and C-5 desaturase. Furthermore, physiological analysis and electron microscopy revealed three main alterations: (1) in the mitochondrion; (2) the presence of lipid bodies and autophagosomes; and (3) the appearance of projections in the plasma membrane. In conclusion, our results support the notion that benzylamines have a potent effect against Leishmania amazonensis and should be an exciting novel pharmaceutical lead for developing new chemotherapeutic alternatives to treat leishmaniasis.

Unravelling the myth surrounding sterol biosynthesis as plausible target for drug design against leishmaniasis

The mortality rate of leishmaniasis is increasing at an alarming rate and is currently second to malaria amongst the other neglected tropical diseases. Unfortunately, many governments and key stakeholders are not investing enough in the development of new therapeutic interventions. The available treatment options targeting different pathways of the parasite have seen inefficiencies, drug resistance, and toxic side effects coupled with longer treatment durations. Numerous studies to understand the biochemistry of leishmaniasis and its pathogenesis have identified druggable targets including ornithine decarboxylase, trypanothione reductase, and pteridine reductase, which are relevant for the survival and growth of the parasites. Another plausible target is the sterol biosynthetic pathway; however, this has not been fully investigated. Sterol biosynthesis is essential for the survival of the Leishmania species because its inhibition could lead to the death of the parasites. This review seeks to evaluate how critical the enzymes involved in sterol biosynthetic pathway are to the survival of the leishmania parasite. The review also highlights both synthetic and natural product compounds with their IC50 values against selected enzymes. Finally, recent advancements in drug design strategies targeting the sterol biosynthesis pathway of Leishmania are discussed.

Synthesis and biological activity of novel 4-aminoquinoline/1,2,3-triazole hybrids against Leishmania amazonensis

Quinoline and 1,2,3-triazoles are well-known nitrogen-based heterocycles presenting diverse pharmacological properties, although their antileishmanial activity is still poorly exploited. As an effort to contribute with studies involving these interesting chemical groups, in the present study, a series of compounds derived from 4-aminoquinoline and 1,2,3-triazole were synthetized and biological studies using L. amazonensis species were performed. The results pointed that the derivative 4, a hybrid of 4-aminoquinoline/1,2,3-triazole exhibited the best antileishmanial action, with inhibitory concentration (IC₅₀) values of ~1 µM against intramacrophage amastigotes of L. amazonensis , and being 16-fold more active to parasites than to the host cell. The mechanism of action of derivative 4 suggest a multi-target action on Leishmania parasites, since the treatment of L. amazonensis promastigotes caused mitochondrial membrane depolarization, accumulation of ROS products, plasma membrane permeabilization, increase in neutral lipids, exposure of phosphatidylserine to the cell surface, changes in the cell cycle and DNA fragmentation. The results suggest that the antileishmanial effect of this compound is primarily altering critical biochemical processes for the correct functioning of organelles and macromolecules of parasites, with consequent cell death by processes related to apoptosis-like and necrosis. No up-regulation of reactive oxygen and nitrogen intermediates was promoted by derivative 4 on L. amazonensis -infected macrophages, suggesting a mechanism of action independent from the activation of the host cell. In conclusion, data suggest that derivative 4 presents selective antileishmanial effect, which is associated with multi-target action, and can be considered for future studies for the treatment against disease.

Acarbose presents in vitro and in vivo antileishmanial activity against Leishmania infantum and is a promising therapeutic candidate against visceral leishmaniasis

Treatment against visceral leishmaniasis (VL) is mainly hampered by drug toxicity, long treatment regimens and/or high costs. Thus, the identification of novel and low-cost antileishmanial agents is urgent. Acarbose (ACA) is a specific inhibitor of glucosidase-like proteins, which has been used for treating diabetes. In the present study, we show that this molecule also presents in vitro and in vivo specific antileishmanial activity against Leishmania infantum. Results showed an in vitro direct action against L. infantum promastigotes and amastigotes, and low toxicity to mammalian cells. In addition, in vivo experiments performed using free ACA or incorporated in a Pluronic^® F127-based polymeric micelle system called ACA/Mic proved effective for the treatment of L. infantum-infected BALB/c mice. Treated animals presented significant reductions in the parasite load in their spleens, livers, bone marrows and draining lymph nodes when compared to the controls, as well as the development of antileishmanial Th1-type humoral and cellular responses based on high levels of IFN-γ, IL-12, TNF-α, GM-CSF, nitrite and IgG2a isotype antibodies. In addition, ACA or ACA-treated animals suffered from low organ toxicity. Treatment with ACA/Mic outperformed treatments using either Miltefosine or free ACA based on parasitological and immunological evaluations performed one and 15 days post-therapy. In conclusion, data suggest that the ACA/Mic is a potential therapeutic agent against L. infantum and merits further consideration for VL treatment.

Furan derivatives impair proliferation and affect ultrastructural organization of Trypanosoma cruzi and Leishmania amazonensis

Chagas disease and leishmaniasis are neglected diseases caused by parasites of the Trypanosomatidae family and together they affect millions of people in the five continents. The treatment of Chagas disease is based on benznidazole, whereas for leishmaniasis few drugs are available, such as amphotericin B and miltefosine. In both cases, the current treatment is not entirely efficient due to toxicity or side effects. Encouraged by the need to discover valid targets and new treatment options, we evaluated 8 furan compounds against Trypanosoma cruzi and Leishmania amazonensis, considering their effects against proliferation, infection, and ultrastructure. Many of them were able to impair T. cruzi and L. amazonensis proliferation, as well as cause ultrastructural alterations, such as Golgi apparatus disorganization, autophagosome formation, and mitochondrial swelling. Taken together, the results obtained so far make these compounds eligible for further steps of chemotherapy study.

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.

In Vitro Effect of Pitavastatin and Its Synergistic Activity with Isavuconazole against Acanthamoeba castellanii

Acanthamoeba keratitis (AK) can occur in healthy individuals wearing contact lenses and it is a painful, blinding infection of the cornea caused by a free-living ameba Acanthamoeba. Current treatment for AK relies on a combination of chlorhexidine, propamidine isethionate, and polyhexamethylene biguanide. However, the current regimen includes an aggressive disinfectant and in 10% of cases recurrent infection ensues. Therefore, development of efficient and safe drugs is a critical unmet need to avert blindness. Acanthamoeba sterol biosynthesis includes two essential enzymes HMG-CoA reductase (HMGR) and sterol 14-demethylase (CYP51), and we earlier identified a CYP51 inhibitor isavuconazole that demonstrated nanomolar potency against A. castellanii trophozoites. In this study, we investigated the effect of well-tolerated HMGR inhibitors and identified pitavastatin that is active against trophozoites of three different clinical strains of A.castellanii. Pitavastatin demonstrated an EC₅₀ of 0.5 to 1.9 µM, depending on strains. Combination of pitavastatin and isavuconazole is synergistic and led to 2- to 9-fold dose reduction for pitavastatin and 11- to 4000-fold dose reduction for isavuconazole to achieve 97% of growth inhibition. Pitavastatin, either alone or in combination with isavuconazole, may lead to repurposing for the treatment of Acanthamoeba keratitis.

New applications of squalene synthase inhibitors: Membrane cholesterol as a therapeutic target

Squalene synthase (SQS) inhibitors, mostly known as antihyperlipidemic agents for controlling blood cholesterol levels, have been increasingly used to study alterations of the cholesterol content in cell membranes. As such, SQS inhibitors have been demonstrated to control cellular activities related to cancer cell proliferation and migration, neuron degeneration, and parasite growth. While the mechanisms behind the effects of cellular cholesterol are still being revealed in detail, the evidence for SQS as a therapeutic target for several seemingly unrelated diseases is increasing. SQS inhibitors may be the next promising candidates targeting the three remaining primary therapeutic areas, beyond cardiovascular disease, which still need to be addressed; their application as anticancer, antimicrobial, and antineurodegenerative agents appears promising for new drug discovery projects underway.

Synthesis and trypanocidal activity of novel pyridinyl-1,3,4-thiadiazole derivatives

Herein, we present the design, synthesis and trypanocidal evaluation of sixteen new 1,3,4-thiadiazole derivatives from N-aminobenzyl or N-arylhydrazone series. All derivatives were assayed against the trypomastigote form of Trypanosoma cruzi, showing IC₅₀ values ranging from 3 to 226 μM, and a better trypanocidal profile was demonstrated for the 1,3,4-thiadiazole-N-arylhydrazones (3a-g). In this series, the 2-pyridinyl fragment bound to the imine subunit of the hydrazine moiety presented pharmacophoric behavior for trypanocidal activity. Compounds 2a, 11a and 3e presented remarkable activity and excellent selectivity indexes. Compound 2a was also active against the intracellular amastigote form of T. cruzi. Moreover, its corresponding hydrochloride, compound 11a, showed the most promising profile, producing phenotypic changes similar to those caused by posaconazole, a well-known inhibitor of sterol biosynthesis. Thus, 1,3,4-thiadiazole derivative 11a could be considered a good prototype for the development of new drug candidates for Chagas disease therapy.

Synthesis and Biological Activity of Novel Zinc-Itraconazole Complexes in Protozoan Parasites and Sporothrix spp

The new complexes Zn(ITZ)₂Cl₂ (1) and Zn(ITZ)₂(OH)₂ (2) were synthetized by a reaction of itraconazole with their respective zinc salts under reflux. These Zn-ITZ complexes were characterized by elemental analyses, molar conductivity, mass spectrometry, ¹H and ¹³C{¹H} nuclear magnetic resonance, and UV-vis and infrared spectroscopies. The antiparasitic and antifungal activity of Zn-ITZ complexes was evaluated against three protozoans of medical importance, namely, Leishmania amazonensis, Trypanosoma cruzi, and Toxoplasma gondii, and two fungi, namely, Sporothrix brasiliensis and Sporothrix schenckii The Zn-ITZ complexes exhibited a broad spectrum of action, with antiparasitic and antifungal activity in low concentrations. The strategy of combining zinc with ITZ was efficient to enhance ITZ activity since Zn-ITZ-complexes were more active than the azole alone. This study opens perspectives for future applications of these Zn-ITZ complexes in the treatment of parasitic diseases and sporotrichosis.

Enabling Heterologous Synthesis of Lupulones in the Yeast Saccharomyces cerevisiae

Lupulones, naturally produced by glandular trichomes of hop (Humulus lupulus), are prenylated phloroglucinol derivatives that contribute the bitter flavor of beer and demonstrate antimicrobial and anticancer activities. It is appealing to develop microbial cell factories such that lupulones may be produced via fermentation technology in lieu of extraction from limited plant resources. In this study, the yeast Saccharomyces cerevisiae transformants harboring a synthetic lupulone pathway that consisted of five genes from hop were constructed. The transformants accumulated several precursors but failed to accumulate lupulones. Overexpression of 3-hydroxy-3-methyl glutaryl co-enzyme A reductase, the key enzyme in precursor formation in the mevalonate pathway, also failed to achieve a detectable level of lupulones. To decrease the consumption of the precursors, the ergosterol biosynthesis pathway was chemically downregulated by a small molecule ketoconazole, leading to successful production of lupulones. Our study demonstrated a combination of molecular biology and chemical biology to regulate the metabolism for heterologous production of lupulones. The strategy may be valuable for future engineering microbial process for other prenylated natural products.

Enzymatic chokepoints and synergistic drug targets in the sterol biosynthesis pathway of Naegleria fowleri

Naegleria fowleri is a free-living amoeba that can also act as an opportunistic pathogen causing severe brain infection, primary amebic meningoencephalitis (PAM), in humans. The high mortality rate of PAM (exceeding 97%) is attributed to (i) delayed diagnosis, (ii) lack of safe and effective anti-N. fowleri drugs, and (iii) difficulty of delivering drugs to the brain. Our work addresses identification of new molecular targets that may link anti-Naegleria drug discovery to the existing pharmacopeia of brain-penetrant drugs. Using inhibitors with known mechanism of action as molecular probes, we mapped the sterol biosynthesis pathway of N. fowleri by GC-MS analysis of metabolites. Based on this analysis, we chemically validated two enzymes downstream to CYP51, sterol C24-methyltransferase (SMT, ERG6) and sterol Δ8-Δ7 -isomerase (ERG2), as potential therapeutic drug targets in N. fowleri. The sterol biosynthetic cascade in N. fowleri displayed a mixture of canonical features peculiar to different domains of life: lower eukaryotes, plants and vertebrates. In addition to the cycloartenol→ergosterol biosynthetic route, a route leading to de novo cholesterol biosynthesis emerged. Isotopic labeling of the de novo-synthesized sterols by feeding N. gruberi trophozoites on the U13C-glucose-containing growth medium identified an exogenous origin of cholesterol, while 7-dehydrocholesterol (7DHC) had enriched 13C-content, suggesting a dual origin of this metabolite both from de novo biosynthesis and metabolism of scavenged cholesterol. Sterol homeostasis in Naegleria may be orchestrated over the course of its life-cycle by a "switch" between ergosterol and cholesterol biosynthesis. By demonstrating the growth inhibition and synergistic effects of the sterol biosynthesis inhibitors, we validated new, potentially druggable, molecular targets in N. fowleri. The similarity of the Naegleria sterol Δ8-Δ7 -isomerase to the human non-opioid σ1 receptor, implicated in human CNS conditions such as addiction, amnesia, pain and depression, provides an incentive to assess structurally diverse small-molecule brain-penetrant drugs targeting the human receptor for anti-Naegleria activity.

Isobenzofuranone derivative JVPH3, an inhibitor of L. donovani topoisomerase II, disrupts mitochondrial architecture in trypanosomatid parasites

Kinetoplast DNA (kDNA) bearing unusual mitochondrion of trypanosomatid parasites offers a new paradigm in chemotherapy modality. Topoisomerase II of Leishmania donovani (LdTopII), a key enzyme associated with kDNA replication, is emerging as a potential drug target. However, mode of action of LdTopII targeted compounds in the parasites at sub-cellular level remains largely unknown. Previously, we reported that an isobenzofuranone derivative, namely 3,5-bis(4-chlorophenyl)-7-hydroxyisobenzofuran-1(3H)-one (JVPH3), targets LdTopII and induces apoptosis-like cell death in L. donovani. Here, we elucidate the phenotypic changes and the events occurring at sub-cellular level caused by JVPH3 in L. donovani. In addition, we have evaluated the cytotoxicity and ultrastructural alterations caused by JVPH3 in two brazilian trypanosomatid pathogens viz. L. amazonensis and Trypanosoma cruzi. Despite killing these parasites, JVPH3 caused significantly different phenotypes in L. donovani and L. amazonensis. More than 90% population of parasites showed altered morphology. Mitochondrion was a major target organelle subsequently causing kinetoplast network disorganization in Leishmania. Altered mitochondrial architecture was evident in 75–80% Leishmania population being investigated. Quantification of mitochondrial function using JC-1 fluorophore to measure a possible mitochondrial membrane depolarization further confirmed the mitochondrion as an essential target of the JVPH3 corroborating with the phenotype observed by electron microscopy. However, the impact of JVPH3 was lesser on T. cruzi than Leishmania. The molecule caused mitochondrial alteration in 40% population of the epimastigotes being investigated. To our knowledge, this is the first report to evaluate the proliferation pattern and ultrastructural alterations caused in Brazilian kinetoplastid pathogens by a synthetic LdTopII inhibitor previously established to have promising in vivo activity against Indian strain of L. donovani.

Recent progress in drug targets and inhibitors towards combating leishmaniasis

Lesihmaniasis is one of the major neglected tropical disease caused by the parasite of the genus Leishmania. The disease has more than one clinical forms and the visceral form is considered fatal. With the lack of potential vaccine, chemotherapy is the major treatment source considered for the control of the disease in the infected people. Drugs including amphotericin B and miltefosine are widely used for the treatment, however, development of resistance by the parasite towards the administered drug and high-toxicity of the drug are of major concern. Hence, more attention has been shown on identifying new targets, effective inhibitors, and better drug delivery system against the disease. This review deals with recent studies on drug targets and exploring their essentiality for the survival of Leishmania. Further, new inhibitors for those targets, novel anti-leishmanial peptides and vaccines against leishmaniasis were discussed. We believe that this pool of information will ease the researchers to gain knowledge and help in choosing right targets and design of new inhibitors against Leishmaniasis.

Antileishmanial Efficacy and Pharmacokinetics of DB766-Azole Combinations

Given the limitations of current antileishmanial drugs and the utility of oral combination therapy for other infections, developing an oral combination against visceral leishmaniasis should be a high priority. In vitro combination studies with DB766 and antifungal azoles against intracellular Leishmania donovani showed that posaconazole and ketoconazole, but not fluconazole, enhanced DB766 potency. Pharmacokinetic analysis of DB766-azole combinations in uninfected Swiss Webster mice revealed that DB766 exposure was increased by higher posaconazole and ketoconazole doses, while DB766 decreased ketoconazole exposure. In L. donovani-infected BALB/c mice, DB766-posaconazole combinations given orally for 5 days were more effective than DB766 or posaconazole alone. For example, 81% ± 1% (means ± standard errors) inhibition of liver parasite burden was observed for 37.5 mg/kg of body weight DB766 plus 15 mg/kg posaconazole, while 37.5 mg/kg DB766 and 15 mg/kg posaconazole administered as monotherapy gave 40% ± 5% and 21% ± 3% inhibition, respectively. Combination index (CI) analysis indicated that synergy or moderate synergy was observed in six of nine combined dose groups, while the other three were nearly additive. Liver concentrations of DB766 and posaconazole increased in almost all combination groups compared to monotherapy groups, although many increases were not statistically significant. For DB766-ketoconazole combinations evaluated in this model, two were antagonistic, one displayed synergy, and one was nearly additive. These data indicate that the efficacy of DB766-posaconazole and DB766-ketoconazole combinations in vivo is influenced in part by the pharmacokinetics of the combination, and that the former combination deserves further consideration in developing new treatment strategies against visceral leishmaniasis.

CYP51 is an essential drug target for the treatment of primary amoebic meningoencephalitis (PAM)

Primary Amoebic Meningoencephalitis (PAM) is caused by Naegleria fowleri, a free-living amoeba that occasionally infects humans. While considered "rare" (but likely underreported) the high mortality rate and lack of established success in treatment makes PAM a particularly devastating infection. In the absence of economic inducements to invest in development of anti-PAM drugs by the pharmaceutical industry, anti-PAM drug discovery largely relies on drug 'repurposing'-a cost effective strategy to apply known drugs for treatment of rare or neglected diseases. Similar to fungi, N. fowleri has an essential requirement for ergosterol, a building block of plasma and cell membranes. Disruption of sterol biosynthesis by small-molecule inhibitors is a validated interventional strategy against fungal pathogens of medical and agricultural importance. The N. fowleri genome encodes the sterol 14-demethylase (CYP51) target sharing ~35% sequence identity to fungal orthologues. The similarity of targets raises the possibility of repurposing anti-mycotic drugs and optimization of their usage for the treatment of PAM. In this work, we (i) systematically assessed the impact of anti-fungal azole drugs, known as conazoles, on sterol biosynthesis and viability of cultured N. fowleri trophozotes, (ii) identified the endogenous CYP51 substrate by mass spectrometry analysis of N. fowleri lipids, and (iii) analyzed the interactions between the recombinant CYP51 target and conazoles by UV-vis spectroscopy and x-ray crystallography. Collectively, the target-based and parasite-based data obtained in these studies validated CYP51 as a potentially 'druggable' target in N. fowleri, and conazole drugs as the candidates for assessment in the animal model of PAM.

Antileishmanial Activity of Ezetimibe: Inhibition of Sterol Biosynthesis, In Vitro Synergy with Azoles, and Efficacy in Experimental Cutaneous Leishmaniasis

Leishmaniasis affects mainly low-income populations in tropical regions. Radical innovation in drug discovery is time-consuming and expensive, imposing severe restrictions on the ability to launch new chemical entities for the treatment of neglected diseases. Drug repositioning is an attractive strategy for addressing a specific demand more easily. In this project, we have evaluated the antileishmanial activities of 30 drugs currently in clinical use for various morbidities. Ezetimibe, clinically used to reduce intestinal cholesterol absorption in dyslipidemic patients, killed Leishmania amazonensis promastigotes with a 50% inhibitory concentration (IC₅₀) of 30 μM. Morphological analysis revealed that ezetimibe caused the parasites to become rounded, with multiple nuclei and flagella. Analysis by gas chromatography (GC)-mass spectrometry (MS) showed that promastigotes treated with ezetimibe had smaller amounts of C-14-demethylated sterols, and accumulated more cholesterol and lanosterol, than untreated promastigotes. We then evaluated the combination of ezetimibe with well-known antileishmanial azoles. The fractional inhibitory concentration index (FICI) indicated synergy when ezetimibe was combined with ketoconazole or miconazole. The activity of ezetimibe against intracellular amastigotes was confirmed, with an IC₅₀ of 20 μM, and ezetimibe reduced the IC₉₀s of ketoconazole and miconazole from 11.3 and 11.5 μM to 4.14 and 8.25 μM, respectively. Subsequently, we confirmed the activity of ezetimibe in vivo, showing that it decreased lesion development and parasite loads in murine cutaneous leishmaniasis. We concluded that ezetimibe has promising antileishmanial activity and should be considered in combination with azoles in further preclinical and clinical studies.

Synthesis and pharmacological evaluation of mono-arylimidamides as antileishmanial agents

Arylimidamide (AIA) compounds containing two pyridylimidamide terminal groups (bis-AIAs) possess outstanding in vitro antileishmanial activity, and the frontrunner bis-AIA DB766 (2,5-bis[2-(2-isopropoxy)-4-(2-pyridylimino)aminophenyl]furan) is active in visceral leishmaniasis models when given orally. Eighteen compounds containing a single pyridylimidamide terminal group (mono-AIAs) were synthesized and evaluated for their antileishmanial potential. Six of these compounds exhibited sub-micromolar potency against both intracellular Leishmania donovani and Leishmania amazonensis amastigotes, and three of these compounds also displayed selectivity indexes of 25 or greater for the parasites compared to a J774 macrophage cell line. When given orally at a dose of 100 mg/kg/day for five days, compound 1b (N-(3-isopropoxy-4-(5-phenylfuran-2-yl)phenyl)picolinimidamide methanesulfonate) reduced liver parasitemia by 46% in L. donovani-infected mice. Mono-AIAs are thus a new class of candidate molecules for antileishmanial drug development.