A review on potential therapeutic targets for the treatment of leishmaniasis

Comprehensive insights into leishmaniasis: From etiopathogenesis to a novel therapeutic approach

Leishmaniasis is a vector-borne disease caused by protozoan parasites of the genus Leishmania and is transmitted through the bites of infected sandflies. The disease is characterized by a variety of clinical manifestations, from small skin blemishes to large deformable ulcers, classified as cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL) and disseminated cutaneous leishmaniasis (DCL), as well as severe systemic infections (Kala-Azar or visceral leishmaniasis [VL]), affecting the spleen and liver, along with atypical forms such as lupoid leishmaniasis. As one of the world's most neglected tropical diseases, leishmaniasis threatens more than 1 billion people globally, with 12 million currently affected and <1.3 million new cases reported annually. This review provides comprehensive insights into the etiopathogenesis of leishmaniasis and explores the complex life cycle of parasites and their interactions with host immune responses. A systematic literature search was conducted across databases such as PubMed, Google Scholar, and Scopus via keywords such as "Leishmaniasis," "etiopathogenesis," "cutaneous leishmaniasis," "visceral leishmaniasis," and "Novel therapeutic approaches." Relevant studies published after 2015 were critically analyzed to present the current understanding of the disease mechanisms involved. It also highlights the current treatment landscape, emphasizing the emergence of drug resistance and the need for novel therapeutic approaches. Recent advancements in drug delivery systems, such as nanoparticle formulations, have shown promise for enhancing treatment efficacy and reducing toxicity. Additionally, integrated control measures, such as vector management and public education, are crucial for mitigating disease spread. This overview underscores the urgent need for continued research and innovation to combat this neglected tropical disease effectively.

RNA interference in protozoan parasites and its application

RNA interference (RNAi) is a biological process in which RNA molecules are involved in sequence-specific suppression of gene expression, via small RNA triggers derived from double-stranded RNA that can target specific genes; it is a natural process that plays a role in both the regulation of protein synthesis and in immunity. Discovery of RNAi by Fire and Mello in 1998 had a profound impact on unraveling novel aspects of eukaryotic biology. RNA interference (RNAi) has proven to be an immensely useful tool for studying gene function and validation of potential drug targets in almost all organisms. A great advance in parasitic protozoa was achieved by the experimental demonstration of RNAi in Trypanosoma brucei, and in other protists such as Leishmania braziliensis, Entamoeba histolytica and Giardia lamblia/intestinalis. These organisms exhibit numerous differences beyond the core 'dicer' and 'slicer' activities, thereby expanding knowledge of the evolutionary diversification of this pathway in eukaryotes. When present, RNAi has led to new technologies for engineering powerful and facile knockdowns in gene expression, revolutionizing biomedical research and opening clinical potentialities. In this review, we discuss the distribution of RNAi pathways, their biological roles, and experimental applications in protozoan parasites.

Anti-Parasitics with a Triple Threat: Targeting Parasite Enzymes, the Proton Motive Force, and Host Cell-Mediated Killing

We investigated the effects of the tuberculosis drug candidate SQ109 (8a) and of its analog MeSQ109 (8b) against Leishmania mexicana in promastigote and amastigote forms and against host cell macrophages finding potent activity (1.7 nM) for MeSQ109 against the intracellular forms, as well as low toxicity (∼61 μM) to host cells, resulting in a selectivity index of ∼36,000. We then investigated the mechanism of action of MeSQ109, finding that it targeted parasite mitochondria, collapsing the proton motive force, as well as targeting acidocalcisomes, rapidly increasing the intracellular Ca2+ concentration. Using an E. coli inverted membrane vesicle assay, we investigated the pH gradient collapse for SQ109 and 17 analogs, finding that there was a significant correlation (on average, R = 0.67, p = 0.008) between pH gradient collapse and cell growth inhibition in Trypanosoma brucei, T. cruzi, L. donovani, and Plasmodium falciparum. We also investigated pH gradient collapse with other antileishmanial agents: azoles, antimonials, benzofurans, amphotericin B, and miltefosine. The enhanced activity against intracellular trypanosomatids is seen with Leishmania spp. grown in macrophages but not with Trypanosoma cruzi in epithelial cells and is proposed to be due in part to host-based killing, based on the recent observation that SQ109 is known to convert macrophages to a pro-inflammatory (M1) phenotype.

Contribution of epidermal growth factor (EGF) in the treatment of cutaneous leishmaniasis caused by Leishmania major in BALB/c mice

Cutaneous leishmaniasis (CL) is a tropical disease that can cause chronic lesions and leave life-long scars, leading to social stigmatization and psychological disorders. Using growth factors and immunomodulatory agents that could accelerate wound healing and reduce the scar is highly demanded. Epidermal growth factor (EGF) plays an essential role in wound healing. It stimulates the proliferation of keratocytes and fibroblasts, and promotes re-epithelialization. Here, the effect of EGF in combination with Glucantime and nano-liposomal Amphotericin B (SinaAmpholeish) on the healing process of CL in BALB/c mice was investigated. Seventy-two mice were infected with Leishmania major parasites and randomly divided into eight treatment groups after the appearance of the lesion. The treatment was continued for five weeks, and lesion sizes were measured weekly. Parasite load was determined in the skin biopsies using qPCR. We found that subcutaneous injection of EGF at 4.5 μg/kg, combined with each of the two antileishmanial drugs, significantly reduced the wound size and parasite load; however, EGF at 1.5 μg/kg failed to be effective. Besides, the wound size and parasite loads were significantly lower in the SinaAmfoleish groups compared to the Glucantime groups. Among the treatment groups, EGF 4.5 μg/kg combined with SinaAmpholeish exhibited the most significant reduction in wound size and parasitic load. Our results suggest that EGF can potentiate the wound healing effect of antileishmanial drugs. Further studies are warranted to explore the beneficial effects of combining EGF with antileishmanial drugs in patients with cutaneous leishmaniasis in order to accelerate wound healing and reduce the scar.

A Novel Sesterterpenoid, Petrosaspongin and γ-Lactone Sesterterpenoids with Leishmanicidal Activity from Okinawan Marine Invertebrates

Leishmaniasis is a major public health problem, especially affecting vulnerable populations in tropical and subtropical regions. The disease is endemic in 90 countries, and with millions of people at risk, it is seen as one of the ten most neglected tropical diseases. Current treatments face challenges such as high toxicity, side effects, cost, and growing drug resistance. There is an urgent need for safer, affordable treatments, especially for cutaneous leishmaniasis (CL), the most common form. Marine invertebrates have long been resources for discovering bioactive compounds such as sesterterpenoids. Using bioassay-guided fractionations against cutaneous-type leishmaniasis promastigotes, we identified a novel furanosesterterpenoid, petrosaspongin from Okinawan marine sponges and a nudibranch, along with eight known sesterterpenoids, hippospongins and manoalides. The elucidated structure of petrosaspongin features a β-substituted furane ring, a tetronic acid, and a conjugated triene. The sesterterpenoids with a γ-butenolide group exhibited leishmanicidal activity against Leishmania major promastigotes, with IC50 values ranging from 0.69 to 53 μM. The structure-activity relationship and molecular docking simulation suggest that γ-lactone is a key functional group for leishmanicidal activity. These findings contribute to the ongoing search for more effective treatments against CL.

Uncovering the Mechanism of Action of Antiprotozoal Agents: A Survey on Photoaffinity Labeling Strategy

Plasmodium, Leishmania, and Trypanosoma parasites are responsible for infectious diseases threatening millions of people worldwide. Despite more recent efforts devoted to the search for new antiprotozoal agents, efficacy, safety, and resistance issues still hinder the development of suited therapeutic options. The lack of robustly validated targets and the complexity of parasite's diseases have made phenotypic screening a preferential drug discovery strategy for the identification of new chemical entities. However, via this approach, no information on biological target(s) and mechanisms of action of compounds are provided. Among the target deconvolution strategies useful to fill this gap, photoaffinity labeling (PAL) has emerged as one of most suited to enable investigation in a complex cellular environment. More recently, PAL has been exploited to unravel the molecular basis of bioactive compounds' function in live parasites, allowing elucidation of the mechanism of action of both approved drugs and new chemical entities. Besides highlighting new potential drug targets, PAL can provide valuable information on efficacy and liabilities of small molecules at the molecular level, which could be exploited to greatly facilitate the rational optimization of compounds in terms of potency and safety. In this review, we will report the most recent studies that have leveraged PAL to disclose the biological targets and mechanism of action of phenotypically active compounds targeting kinetoplastid diseases (i.e., human African trypanosomiasis, leishmaniasis, and Chagas disease) and malaria. Moreover, we will comment on potential perspectives that this innovative approach can provide in aiding the discovery and development of new antiprotozoal drugs.

Bisindole Compounds-Synthesis and Medicinal Properties

The indole nucleus stands out as a pharmacophore, among other aromatic heterocyclic compounds with remarkable therapeutic properties, such as benzimidazole, pyridine, quinoline, benzothiazole, and others. Moreover, a series of recent studies refer to strategies for the synthesis of bisindole derivatives, with various medicinal properties, such as antimicrobial, antiviral, anticancer, anti-Alzheimer, anti-inflammatory, antioxidant, antidiabetic, etc. Also, a series of natural bisindole compounds are mentioned in the literature for their various biological properties and as a starting point in the synthesis of other related bisindoles. Drawing from these data, we have proposed in this review to provide an overview of the synthesis techniques and medicinal qualities of the bisindolic compounds that have been mentioned in recent literature from 2010 to 2024 as well as their numerous uses in the chemistry of materials, nanomaterials, dyes, polymers, and corrosion inhibitors.

Compared Antileishmanial Activity of Clomiphene and Tamoxifen

Drug repositioning is an efficient strategy to search for new treatment alternatives that is especially valuable for neglected parasitic diseases such as leishmaniasis. Tamoxifen and raloxifene are selective estrogen receptor modulators (SERMs) that have shown antileishmanial activity. Clomiphene is a SERM structurally similar to tamoxifen, whose antileishmanial potential is unknown. That is why the objective of the present work was to evaluate its antileishmanial activity in vitro and in vivo in comparison with tamoxifen. The inhibitory effect against promastigotes of L. amazonensis, L. major, and L. mexicana was evaluated for both compounds, as well as the cytotoxicity against mouse peritoneal macrophages, the growth inhibitory activity in intracellular amastigotes of L. mexicana, and the in vivo activity in mice experimentally infected with L. mexicana. Clomiphene was about twice as active as tamoxifen against both promastigotes and intracellular amastigotes, with IC50 values of 1.7-3.3 µM for clomiphene and 2.9-6.4 µM for tamoxifen against all three species of promastigotes and 2.8 ± 0.2 µM and 3.7 ± 0.3 µM, respectively, against L. mexicana amastigotes. Clomiphene structurally affected several parasite organelles in a concentration-dependent fashion, leading to the death of both promastigotes and intracellular amastigotes. Interestingly, the macrophage host cell did not appear damaged by any of the clomiphene concentrations tested. With oral administration at 20 mg/kg for 14 days, both compounds showed similar effects in terms of reducing the growth of the lesions, as well as the weight of the lesions and the parasite load at the end of the follow-up period. The results showed the potential of SERMs as antileishmanial drugs and support further testing of clomiphene and other compounds of this pharmacological group.

Efficacy of Diterpene Polyalthic Acid Combined with Amphotericin B against Leishmania amazonensis In Vitro

Background/Objectives: Leishmaniasis, a neglected disease caused by Leishmania spp. including L. amazonensis, urgently requires new treatments. Polyalthic acid (PA), a natural diterpene from Copaifera spp., has previously demonstrated significant antiparasitic potential. This study evaluated the leishmanicidal effects of polyalthic acid (PA), alone and with amphotericin B (AmpB), on L. amazonensis promastigote and amastigote forms. Results: PA showed significant activity against promastigotes, with 50% effective concentration (EC50) values of 2.01 μM at 24 h and an EC50 of 3.22 μM against amastigotes after 48 h. The PA and AmpB combination exhibited a synergistic effect on both forms without inducing cytotoxicity or hemolysis. Morphological changes in promastigotes, including vacuole formation and cell rounding, were more pronounced with the combination. Conclusions: These findings suggest that PA and AmpB together could form a promising new treatment strategy against Leishmania infections, offering enhanced efficacy without added toxicity.

Understanding American tegumentary leishmaniasis in urban Montes Claros, Brazil: insights from clinical, immunological and therapeutic investigations

The challenge of American tegumentary leishmaniasis (ATL) continues in Brazil, presenting a persistent public health issue despite initiatives aimed at public outreach, vector control and health education. To gain a deeper understanding of this disease, a study was conducted in an endemic region located in the northern region of the state of Minas Gerais, Brazil. The study monitored 30 resident patients diagnosed with ATL, using serum samples from 6 healthy individuals as controls. The localized cutaneous form of the disease was found to be predominant, with lesions appearing on various parts of the body and the majority of the affected individuals being male. The study found significantly higher levels of IgG anti-α-Gal antibodies in ATL-infected patients compared to healthy individuals. Treatment of 19 patients with meglumine antimoniate resulted in limited improvement in symptoms for most. Nonetheless, the study found that 12 patients who completed treatment with epithelialization of the lesions showed a significant decrease in IgG anti-α-Gal antibodies, indicating potential applications of this antibody in the diagnosis and monitoring of the disease. The study also identified Leishmania species in 7 analysed patients, revealing 6 cases infected by Leishmania braziliensis and 1 by L. infantum, with a significant difference in the anti-α-Gal responses. The findings of the study emphasize the urgent need for the development of human vaccines and innovative treatment strategies adapted to the diversity of Leishmania species causing cutaneous leishmaniasis and individual patient responses to improve the clinical management of ATL in Brazil and similar endemic regions.

Acrylonitrile derivatives: In vitro activity and mechanism of cell death induction against Trypanosoma cruzi and Leishmania amazonensis

Leishmaniasis and Chagas disease are parasitic infections that affect millions of people worldwide, producing thousands of deaths per year. The current treatments against these pathologies are not totally effective and produce some side effects in the patients. Acrylonitrile derivatives are a group of compounds that have shown activity against these two diseases. In this work, four novels synthetic acrylonitriles were evaluated against the intracellular form and extracellular forms of L. amazonensis and T. cruzi. The compounds 2 and 3 demonstrate to have good selectivity indexes against both parasites, specifically the compound 3 against the amastigote form (SI = 6 against L. amazonensis and SI = 7.4 against T. cruzi). In addition, the parasites treated with these two compounds demonstrate to produce a programmed cell death, since they were positive for the events studied related to this type of death, including chromatin condensation, accumulation of reactive oxygen species and alteration of the mitochondrial membrane potential. In conclusion, this work confirms that acrylonitriles is a source of possible new compounds against kinetoplastids, however, more studies are needed to corroborate this activity.