Leishmania major protein disulfide isomerase as a drug target: enzymatic and functional characterization

Drug Discovery for Cutaneous Leishmaniasis: A Review of Developments in the Past 15 Years

Leishmaniasis is a group of vector-borne, parasitic diseases caused by over 20 species of the protozoan Leishmania spp. The three major disease classifications, cutaneous, visceral, and mucocutaneous, have a range of clinical manifestations from self-healing skin lesions to hepatosplenomegaly and mucosal membrane damage to fatality. As a neglected tropical disease, leishmaniasis represents a major international health challenge, with nearly 350 million people living at risk of infection a year. The current chemotherapeutics used to treat leishmaniasis have harsh side effects, prolonged and costly treatment regimens, as well as emerging drug resistance, and are predominantly used for the treatment of visceral leishmaniasis. There is an undeniable need for the identification and development of novel chemotherapeutics targeting cutaneous leishmaniasis (CL), largely ignored by concerted drug development efforts. CL is mostly non-lethal and the most common presentation of this disease, with nearly 1 million new cases reported annually. Recognizing this unaddressed need, substantial yet fragmented progress in early drug discovery efforts for CL has occurred in the past 15 years and was outlined in this review. However, further work needs to be carried out to advance early discovery candidates towards the clinic. Importantly, there is a paucity of investment in the translation and development of therapies for CL, limiting the emergence of viable solutions to deal with this serious and complex international health problem.

The potential role of protein disulfide isomerases (PDIs) during parasitic infections: a focus on Leishmania spp

Leishmaniasis is a group of vector-borne diseases caused by intracellular protozoan parasites belonging to the genus Leishmania. Leishmania parasites can employ different and numerous sophisticated strategies, including modulating host proteins, cell signaling, and cell responses by parasite proteins, to change the infected host conditions to favor the parasite persistence and induce pathogenesis. In this sense, protein disulfide isomerases (PDIs) have been described as crucial proteins that can be modulated during leishmaniasis and affect the pathogenesis process. The effect of modulated PDIs can be investigated in both aspects, parasite PDIs and infected host cell PDIs, during infection. The information concerning PDIs is not sufficient in parasitology; however, this study aimed to provide data regarding the biological functions of such crucial proteins in parasites with a focus on Leishmania spp. and their relevant effects on the pathogenesis process. Although there are no clinical trial vaccines and therapeutic approaches, highlighting this information might be fruitful for the development of novel strategies based on PDIs for the management of parasitic diseases, especially leishmaniasis.

An insight into differential protein abundance throughout Leishmania donovani promastigote growth and differentiation

Leishmania donovani causes anthroponotic visceral leishmaniasis, responsible for about 50,000 annual deaths worldwide. Current therapies have considerable side effects. Drug resistance has been reported and no vaccine is available nowadays. The development of undifferentiated promastigotes in the sand fly vector's gut leads to the promastigote form that is highly infective to the mammalian host. Fully differentiated promastigotes play a crucial role in the initial stages of mammalian host infection before internalization in the host phagocytic cell. Therefore, the study of protein levels in the promastigote stage is relevant for disease control, and proteomics analysis is an ideal source of vaccine candidate discovery. This study aims to get insight into the protein levels during the differentiation process of promastigotes by 2DE-MALDI-TOF/TOF. This partial proteome analysis has led to the identification of 75 proteins increased in at least one of the L. donovani promastigote differentiation and growth phases. This study has revealed the differential abundance of said proteins during growth and differentiation. According to previous studies, some are directly involved in parasite survival or are immunostimulatory. The parasite survival-related proteins are ascorbate peroxidase; cystathionine β synthase; an elongation factor 1β paralog; elongation factor 2; endoribonuclease L-PSP; an iron superoxide dismutase paralog; GDP-mannose pyrophosphorylase; several heat shock proteins-HSP70, HSP83-17, mHSP70-rel, HSP110; methylthioadenosine phosphorylase; two thiol-dependent reductase 1 paralogs; transitional endoplasmic reticulum ATPase; and the AhpC thioredoxin paralog. The confirmed immunostimulatory proteins are the heat shock proteins, enolase, and protein kinase C receptor analog. The potential immunostimulatory molecules according to findings in patogenic bacteria are fructose-1,6-diphophate aldolase, dihydrolipoamide acetyltransferase, isocitrate dehydrogenase, pyruvate dehydrogenase E1α and E1β subunits, and triosephosphate isomerase. These proteins may become disease control candidates through future intra-vector control methods or vaccines.

Mechanism of Erastin-Induced Ferroptosis in MDA-MB-231 Human Breast Cancer Cells: Evidence for a Critical Role of Protein Disulfide Isomerase

Ferroptosis is a form of regulated cell death resulting predominantly from catastrophic accumulation of lipid reactive oxygen species (ROS). While the antioxidant systems that counter ferroptosis have been well characterized, the mechanism underlying ferroptosis-associated accumulation of lipid ROS remains unclear. In this study, we demonstrated that protein disulfide isomerase (PDI) is a novel mediator of ferroptosis, which is responsible for the accumulation of lipid ROS and ultimately ferroptosis in MDA-MB-231 human breast cancer cells. Treatment with erastin led to a significant increase in inducible nitric oxide synthase (iNOS)-mediated nitric oxide production, which contributes to the accumulation of the death-inducing cellular lipid ROS. Small interfering RNA (siRNA)-mediated PDI knockdown or pharmacological inhibition of PDI’s isomerase activity with cystamine strongly suppressed iNOS dimerization and its catalytic activation, subsequently prevented lipid ROS accumulation, and conferred strong protection against erastin-induced ferroptosis. Remarkably, PDI knockdown in MDA-MB-231 cells also largely abrogated the protective effect of cystamine against erastin-induced ferroptotic cell death. Together, these experimental observations demonstrate a noncanonical role of PDI in ferroptosis, which may serve as a potential therapeutic target for ferroptosis-related diseases.

A computer-aided approach to identify novel Leishmania major protein disulfide isomerase inhibitors for treatment of leishmaniasis

Leishmaniasis is an infectious disease caused by parasites of the genus Leishmania and transmitted by the bite of a sand fly. To date, most available drugs for treatment are toxic and beyond the economic means of those affected by the disease. Protein disulfide isomerase (PDI) is a chaperone protein that plays a major role in the folding of newly synthesized proteins, specifically assisting in disulfide bond formation, breakage, or rearrangement in all non-native proteins. In previous work, we demonstrated that Leishmania major PDI (LmPDI) has an essential role in pathogen virulence. Furthermore, inhibition of LmPDI further blocked parasite infection in macrophages. In this study, we utilized a computer-aided approach to design a series of LmPDI inhibitors. Fragment-based virtual screening allowed for the understanding of the inhibitors' modes of action on LmPDI active sites. The generated compounds obtained after multiple rounds of virtual screening were synthesized and significantly inhibited target LmPDI reductase activity and were shown to decrease in vitro parasite growth in human monocyte-derived macrophages. This novel cheminformatics and synthetic approach led to the identification of a new series of compounds that might be optimized into novel drugs, likely more specific and less toxic for the treatment of leishmaniasis.

Potential therapeutic targets shared between leishmaniasis and cancer

The association of leishmaniasis and malignancies in human and animal models has been highlighted in recent years. The misdiagnosis of coexistence of leishmaniasis and cancer and the use of common drugs in the treatment of such diseases prompt us to further survey the molecular biology of Leishmania parasites and cancer cells. The information regarding common expressed proteins, as possible therapeutic targets, in Leishmania parasites and cancer cells is scarce. Therefore, the current study reviews proteins, and investigates the regulation and functions of several key proteins in Leishmania parasites and cancer cells. The up- and down-regulations of such proteins were mostly related to survival, development, pathogenicity, metabolic pathways and vital signalling in Leishmania parasites and cancer cells. The presence of common expressed proteins in Leishmania parasites and cancer cells reveals valuable information regarding the possible shared mechanisms of pathogenicity and opportunities for therapeutic targeting in leishmaniasis and cancers in the future.

A comparative analysis of secreted protein disulfide isomerases from the tropical co-endemic parasites Schistosoma mansoni and Leishmania major

The human parasites Schistosoma mansoni and Leishmania major are co-endemic and a major threat to human health. Though displaying different tissue tropisms, they excrete/secrete similar subsets of intracellular proteins that, interacting with the host extracellular matrix (ECM), help the parasites invading the host. We selected one of the most abundant proteins found in the secretomes of both parasites, protein disulfide isomerase (PDI), and performed a comparative screening with surface plasmon resonance imaging (SPRi), looking for ECM binding partners. Both PDIs bind heparan sulfate; none of them binds collagens; each of them binds further ECM components, possibly linked to the different tropisms. We investigated by small-angle X-ray scattering both PDIs structures and those of a few complexes with host partners, in order to better understand the differences within this conserved family fold. Furthermore, we highlighted a previously undisclosed moonlighting behaviour of both PDIs, namely a concentration-dependent switch of function from thiol-oxidoreductase to holdase. Finally, we have tried to exploit the differences to look for possible compounds able to interfere with the redox activity of both PDI.

An immunoproteomic approach to identifying immunoreactive proteins in Leishmania infantum amastigotes using sera of dogs infected with canine visceral leishmaniasis

Visceral leishmaniasis (VL), the most severe form of leishmaniasis, is caused by Leishmania donovani and Leishmania infantum. The infected dogs with canine visceral leishmaniasis (CVL) are important reservoirs for VL in humans, so the diagnosis, treatment and vaccination of the infected dogs will ultimately decrease the rate of human VL. Proteomics and immunoproteomics techniques have facilitated the introduction of novel drug, vaccine and diagnostic targets. Our immunoproteomic study was conducted to identify new immunoreactive proteins in amastigote form of L. infantum. The strain of L. infantum (MCAN/IR/07/Moheb-gh) was obtained from CVL-infected dogs. J774 macrophage cells were infected with the L. infantum promastigotes. The infected macrophages were ruptured, and pure amastigotes were extracted from the macrophages. After protein extraction, two-dimensional gel electrophoresis was employed for protein separation followed by Western blotting. Western blotting was performed, using symptomatic and asymptomatic sera of the infected dogs with CVL. Thirteen repeatable immunoreactive spots were identified by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Some, including prohibitin, ornithine aminotransferase, annexin A4, and apolipoprotein A-I, have been critically involved in metabolic pathways, survival, and pathogenicity of Leishmania parasites. Further investigations are required to confirm our identified immunoreactive proteins as a biomarker for CVL.

High Throughput and Computational Repurposing for Neglected Diseases

Purpose

Neglected tropical diseases (NTDs) represent are a heterogeneous group of communicable diseases that are found within the poorest populations of the world. There are 23 NTDs that have been prioritized by the World Health Organization, which are endemic in 149 countries and affect more than 1.4 billion people, costing these developing economies billions of dollars annually. The NTDs result from four different causative pathogens: protozoa, bacteria, helminth and virus. The majority of the diseases lack effective treatments. Therefore, new therapeutics for NTDs are desperately needed.

Methods

We describe various high throughput screening and computational approaches that have been performed in recent years. We have collated the molecules identified in these studies and calculated molecular properties.

Results

Numerous global repurposing efforts have yielded some promising compounds for various neglected tropical diseases. These compounds when analyzed as one would expect appear drug-like. Several large datasets are also now in the public domain and this enables machine learning models to be constructed that then facilitate the discovery of new molecules for these pathogens.

Conclusions

In the space of a few years many groups have either performed experimental or computational repurposing high throughput screens against neglected diseases. These have identified compounds which in many cases are already approved drugs. Such approaches perhaps offer a more efficient way to develop treatments which are generally not a focus for global pharmaceutical companies because of the economics or the lack of a viable market. Other diseases could perhaps benefit from these repurposing approaches.

Electronic supplementary material

The online version of this article (10.1007/s11095-018-2558-3) contains supplementary material, which is available to authorized users.

Emerging therapeutic targets for treatment of leishmaniasis

INTRODUCTION

Parasitic diseases that pose a threat to human life include leishmaniasis - caused by protozoan parasite Leishmania species. Existing drugs have limitations due to deleterious side effects like teratogenicity, high cost and drug resistance. This calls for the need to have an insight into therapeutic aspects of disease. Areas covered: We have identified different drug targets via. molecular, imuunological, metabolic as well as by system biology approaches. We bring these promising drug targets into light so that they can be explored to their maximum. In an effort to bridge the gaps between existing knowledge and prospects of drug discovery, we have compiled interesting studies on drug targets, thereby paving the way for establishment of better therapeutic aspects. Expert opinion: Advancements in technology shed light on many unexplored pathways. Further probing of well established pathways led to the discovery of new drug targets. This review is a comprehensive report on current and emerging drug targets, with emphasis on several metabolic targets, organellar biochemistry, salvage pathways, epigenetics, kinome and more. Identification of new targets can contribute significantly towards strengthening the pipeline for disease elimination.

A thermostable alkaliphilic protein-disulfide isomerase from Bacillus subtilis DR8806: cloning, expression, biochemical characterization and molecular dynamics simulation

Disulfide bonds are among the most important factors related to correct folding of the proteins. Protein disulfide isomerase (PDI) is the enzyme responsible for the correct formation and isomerization of these bonds. It is rarely studied so far and none of them showed industrial properties. In this study, the gene encoding for a putative PDI from Bacillus subtilis DR8806 was identified, cloned and expressed in Escherichia coli. It was encoded a 23.26kDa protein. The enzyme was purified by GST affinity chromatography with a specific activity of 1227u/mg. It was active and stable over a wide range of temperature (20-85°C) and pH (4.5-10) with an optimum at 65°C and pH 5.5. Its activity was enhanced by Mn²⁺ and Co²⁺ while Ag⁺ and Zn²⁺ decreased it. Some of the known PDI inhibitors such as Tocinoic acid and Bactiracin did not affect its activity. In-silico analysis shows the five amino acids changes in the protein sequence regarding to the consensus sequence of PDIs, have a positive impact toward the protein thermal stability. This was further confirmed by molecular dynamics simulations. By considering the overall results, the enzyme might be a potential candidate for applications in the respective industries.

Protein disulfide isomerase a multifunctional protein with multiple physiological roles

Protein disulfide isomerase (PDI), is a member of the thioredoxin superfamily of redox proteins. PDI has three catalytic activities including, thiol-disulfide oxireductase, disulfide isomerase and redox-dependent chaperone. Originally, PDI was identified in the lumen of the endoplasmic reticulum and subsequently detected at additional locations, such as cell surfaces and the cytosol. This review will provide an overview of the recent advances in relating the structural features of PDI to its multiple catalytic roles as well as its physiological and pathophysiological functions related to redox regulation and protein folding.

Molecular characterization and analysis of a novel protein disulfide isomerase-like protein of Eimeria tenella

Protein disulfide isomerase (PDI) and PDI-like proteins are members of the thioredoxin superfamily. They contain thioredoxin-like domains and catalyze the physiological oxidation, reduction and isomerization of protein disulfide bonds, which are involved in cell function and development in prokaryotes and eukaryotes. In this study, EtPDIL, a novel PDI-like gene of Eimeria tenella, was cloned using rapid amplification of cDNA ends (RACE) according to the expressed sequence tag (EST). The EtPDIL cDNA contained 1129 nucleotides encoding 216 amino acids. The deduced EtPDIL protein belonged to thioredoxin-like superfamily and had a single predicted thioredoxin domain with a non-classical thioredoxin-like motif (SXXC). BLAST analysis showed that the EtPDIL protein was 55–59% identical to PDI-like proteins of other apicomplexan parasites. The transcript and protein levels of EtPDIL at different development stages were investigated by real-time quantitative PCR and western blot. The messenger RNA and protein levels of EtPDIL were higher in sporulated oocysts than in unsporulated oocysts, sporozoites or merozoites. Protein expression was barely detectable in unsporulated oocysts. Western blots showed that rabbit antiserum against recombinant EtPDIL recognized only a native 24 kDa protein from parasites. Immunolocalization with EtPDIL antibody showed that EtPDIL had a disperse distribution in the cytoplasm of whole sporozoites and merozoites. After sporozoites were incubated in complete medium, EtPDIL protein concentrated at the anterior of the sporozoites and appeared on the surface of parasites. Specific staining was more intense and mainly located on the parasite surface after merozoites released from mature schizonts invaded DF-1 cells. After development of parasites in DF-1 cells, staining intensified in trophozoites, immature schizonts and mature schizonts. Antibody inhibition of EtPDIL function reduced the ability of E. tenella to invade DF-1 cells. These results suggested that EtPDIL might be involved in sporulation in external environments and in host cell adhesion, invasion and development of E. tenella.

Effects of Leishmania major clones showing different levels of virulence on infectivity, differentiation and maturation of human dendritic cells

Leishmania parasites and dendritic cell interactions (DCs) play an essential role in initiating and directing T cell responses and influence disease evolution. These interactions may vary depending on Leishmania species and strains. To evaluate the correlation between Leishmania major (Lm) virulence and in-vitro human DC response, we compared the ability of high (HV) and low virulent (LV) Lm clones to invade, modulate cytokine production and interfere with differentiation of DCs. Clones derived from HV and LV (HVΔlmpdi and LVΔlmpdi), and deleted for the gene coding for a Lm protein disulphide isomerase (LmPDI), probably involved in parasite natural pathogenicity, were also used. Unlike LV, which fails to invade DCs in half the donors, HV promastigotes were associated with a significant increase of the infected cells percentage and parasite burden. A significant decrease of both parameters was observed in HVΔlmpdi-infected DCs, compared to wild-type cells. Whatever Lm virulence, DC differentiation was accompanied by a significant decrease in CD1a expression. Lm clones decreased interleukin (IL)-12p70 production similarly during lipopolysaccharide (LPS)-induced maturation of DCs. LPS stimulation was associated with a weak increase in tumour necrosis factor (TNF)-α and IL-10 productions in HV-, HVΔlmpdi- and LVΔlmpdi-infected DCs. These results indicate that there is a significant variability in the capacity of Lm clones to infect human DCs which depends upon their virulence, probably involving LmPDI protein. However, independently of their virulence, Lm clones were able to down-regulate CD1a expression during DC differentiation and IL-12p70 production during DC maturation, which may favour their survival.

Molecular characterization and immunolocalization of a protein disulfide isomerase from Angiostrongylus cantonensis

Protein disulfide isomerases (PDIs), belonging to the thioredoxin superfamily, are oxidoreductases that catalyze the formation, reduction, and isomerization of disulfide bonds among cysteine residues of proteins. In this study, we report the cloning and characterization of a cDNA encoding a protein disulfide isomerase (AcPDI) from a cDNA library of fourth-stage larvae of Angiostrongylus cantonensis. The deduced amino acid sequence contains two thioredoxin domains and exhibits high identity to the homologues from other species. Quantitative real-time PCR (qRT-PCR) was performed at the third-stage larvae, fourth-stage larvae, and adult stage of A. cantonensis, and the results revealed that the AcPDI mRNA, while expressed at all three stages, is expressed at a significantly higher level in female adult worms. Results of immunohistochemical studies indicated that the AcPDI expression was specifically localized in the tegument and uterus wall of female adult worms. Biochemical analysis showed that recombinant AcPDI was biologically active in vitro and exhibited the typical biochemical functions of PDIs: oxidase/isomerase and reductase activities. Collectively, these results implied that AcPDI may be a female-enriched protein and associated with the reproductive development of A. cantonensis. In addition, considering its biochemical properties, AcPDI may be involved in the formation of the cuticle of A. cantonensis.

A high-throughput turbidometric assay for screening inhibitors of Leishmania major protein disulfide isomerase

The use of a high-throughput technique to perform a pilot screen for Leishmania major protein disulfide isomerase (LmPDI) inhibitors identification is reported. In eukaryotic cells, protein disulfide isomerase (PDI) plays a crucial role in protein folding by catalyzing the rearrangement of disulfide bonds in substrate proteins following their synthesis. LmPDI displays similar domain structure organization and functional properties to other PDI family members and is involved in Leishmania virulence. The authors used a method based on the enzyme-catalyzed reduction of insulin in the presence of dithiothreitol. The screen of a small library of 1920 compounds was performed in a 384-well format and led to the identification of 27 compounds with inhibitory activity against LmPDI. The authors further tested the cytotoxicity of these compounds using Jurkat cells as well as their effect on Leishmania donovani amastigotes using high-content analysis. Results show hexachlorophene and a mixture of theaflavin monogallates inhibit Leishmania multiplication in infected macrophages derived from THP-1 cells, although the inhibitory effect on LmPDI enzymatic activity does not necessarily correlate with the antileishmanial activity.