Visceral leishmaniasis is a protozoan disease associated with high fatality rate in developing countries. Although the drug pipeline is constantly improving, available treatments are costly and live-threatening side effects are not uncommon. Moreover, an approved vaccine against human leishmaniasis does not exist yet. Using whole antigens from Leishmania donovani promastigotes (LdAg), we investigated the protective potential of a novel adjuvant-free vaccine strategy. Immunization of mice with LdAg via the intradermal or the intranasal route prior to infection decreases the parasitic burden in primary affected internal organs, including the liver, spleen, and bone marrow. Interestingly, the intranasal route is more efficient than the intradermal route, leading to better parasite clearance and remarkable induction of adaptive immune cells, notably the helper and cytotoxic T cells. In vitro restimulation experiments with Leishmania antigens led to significant IFN-γ secretion by splenocytes; therefore, exemplifying specificity of the adaptive immune response. To improve mucosal delivery and the immunogenic aspects of our vaccine strategy, we used polysaccharide-based nanoparticles (NP) that carry the antigens. The NP-LdAg formulation is remarkably taken up by dendritic cells and induces their maturation in vitro, as revealed by the increased expression of CD80, CD86 and MHC II. Intranasal immunization with NP-LdAg does not improve the parasite clearance in our experimental timeline; however, it does increase the percentage of effector and memory T helper cells in the spleen, suggesting a potential induction of long-term memory. Altogether, this study provides a simple and cost-effective vaccine strategy against visceral leishmaniasis based on LdAg administration via the intranasal route, which could be applicable to other parasitic diseases. Visceral leishmaniasis is a neglected tropical disease caused by specific species of Leishmania parasites that affect internal organs including spleen, liver, and bone marrow. The infective stage called promastigote, is transmitted into the host skin via sandfly bites. Visceral leishmaniasis is usually associated with high mortality rate in poor and developing countries, lacking proper health assistance. Moreover, treatments are expensive while no approved vaccines exist to prevent infection and avoid disease outbreaks. This study suggests an affordable and adjuvant-free vaccine formulation made from the total lysate of promastigotes. Vaccine administration via the intranasal route, ensures a remarkable clearance of Leishmania parasites from the internal organs of infected experimental mice. In particular, intranasal route known to be not invasive, is efficient in inducing adequate immune response against the infective form of the parasite. Further studies are now required to improve this prophylactic vaccine and provide therefore the basis for a promising translational approach.

Hydrazone compounds represent an important area of research that includes, among others, synthetic approaches and biological studies. A series of 17 hydrazones have been synthesized by mechanochemical means. The fragments chosen were phenolic and furanyl aldehydes coupled with 12 heterocyclic hydrazines or hydrazinamides. All compounds can be obtained quantitatively when operating on a planetary ball mill and a maximum reaction time of 180 min (6 cycles of 30 min each). Complete spectroscopic analyses of hydrazones revealed eight compounds (3–5, 8–11, 16) present in one geometric form, six compounds (1, 2, 13–15) present in two isomeric forms, and three compounds (6, 7, 12) where one rotation is restricted giving rise to two different forms. The single crystal X-ray structure of one of the hydrazones bearing the isoniazid fragment (8) indicates a crystal lattice consisting of two symmetry-independent molecules with different geometries. All compounds obtained were tested for anti-infectious and antibacterial activities. Four compounds (1, 3, 5 and 8) showed good activity against Mycobacterium tuberculosis, and one (7) was very potent against Staphylococcus aureus. Most interesting, this series of compounds displayed very promising antileishmanial activity. Among all, compound 9 exhibited an IC₅₀ value of 0.3 µM on the Leishmania donovani intramacrophage amastigote in vitro model and a good selectivity index, better than miltefosine, making it worth evaluating in vivo.

Chalcones are polyphenols that belong to the flavonoids family, known for their broad pharmacological properties. They have thus attracted the attention of chemists for their obtention and potential activities. In our study, a library of compounds from 2′-hydroxychalcone’s family was first synthesized. A one-step mechanochemical synthesis via Claisen–Schmidt condensation reaction under ball mill conditions was studied, first in a model reaction between a 5′-fluoro-2′-hydroxyacetophenone and 3,4-dimethoxybenzaldehyde. The reaction was optimized in terms of catalysts, ratio of reagents, reaction time, and influence of additives. Among all assays, we retained the best one, which gave the highest yield of 96% when operating in the presence of 1 + 1 eq. of substituted benzaldehyde and 2 eq. of KOH under two grinding cycles of 30 min. Thus, this protocol was adopted for the synthesis of the selected library of 2′-hydroxychalcones derivatives. The biological activities of 17 compounds were then assessed against Plasmodium falciparum, Leishmania donovani parasite development, as well as IGR-39 melanoma cell lines by inhibiting their viability and proliferation. Compounds 6 and 11 are the most potent against L. donovani, exhibiting IC₅₀ values of 2.33 µM and 2.82 µM, respectively, better than the reference drug Miltefosine (3.66 µM). Compound 15 presented the most interesting antimalarial activity against the 3D7 strain, with IC₅₀ = 3.21 µM. Finally, chalcone 12 gave the best result against IGR-39 melanoma cell lines, with an IC₅₀ value of 12 µM better than the reference drug Dacarbazine (IC₅₀ = 25 µM).

2,6-Diaryl-4H-tetrahydro-thiopyran-4-ones and corresponding sulfoxide and sulfone derivatives were designed to lower the major toxicity of their parent anti-kinetoplatidal diarylideneacetones through a prodrug effect. Novel diastereoselective methodologies were developed and generalized from diarylideneacetones and 2,6-diaryl-4H-tetrahydro-thiopyran-4-ones to allow the introduction of a wide substitution profile and to prepare the related S-oxides. The in vitro biological activity and selectivity of diarylideneacetones, 2,6-diaryl-4H-tetrahydro-thiopyran-4-ones, and their S-sulfoxide and sulfone metabolites were evaluated against Trypanosoma brucei brucei, Trypanosoma cruzi, and various Leishmania species in comparison with their cytotoxicity against human fibroblasts hMRC-5. The data revealed that the sulfides, sulfoxides, and sulfones, in which the Michael acceptor sites are temporarily masked, are less toxic against mammal cells while the anti-trypanosomal potency was maintained against T. b. brucei, T. cruzi, L. infantum, and L. donovani, thus confirming the validity of the prodrug strategy. The mechanism of action is proposed to be due to the involvement of diarylideneacetones in cascades of redox reactions involving the trypanothione system. After Michael addition of the dithiol to the double bonds, resulting in an elongated polymer, the latter—upon S-oxidation, followed by syn-eliminations—fragments, under continuous release of reactive oxygen species and sulfenic/sulfonic species, causing the death of the trypanosomal parasites in the micromolar or submicromolar range with high selectivity indexes.

Leishmaniasis chemotherapy faces significant challenges, including high costs, severe side effects, and the emergence of drug-resistant parasites, demanding global efforts to identify novel antileishmanial agents. Pentavalent antimony (Sb^V), the primary treatment for over 78 years, suffers from reduced efficacy and high toxicity, underscoring the urgent need for alternatives. We have synthesized metalloporphyrins with potent antileishmanial properties, including the Sb^V-porphyrin complex (Sb^VT4MPP). Sb^VT4MPP exhibited high potency against both Sb-sensitive and Sb-resistant Leishmania spp. with IC₅₀ as low as 0.05 and 0.12 µM, respectively, for amastigotes and promastigotes; 170-fold more effective than Sb^V and with a 28-37-fold selectivity index, highlighting the importance of host cells on drug activity. Sterol profiling of L. infantum revealed that Sb^VT4MPP ablated ergosterol production while accumulating cholestane-based sterols (e.g., cholesta-5,7,22-trien-3β-ol). Additional sterols appeared exclusively under Sb^VT4MPP treatment, accompanied by upregulated erg6, encoding sterol-C-24 methyltransferase (SMT), a key enzyme in sterol biosynthesis. Overexpression of ERG6 reduced Sb^VT4MPP potency, increasing the IC₅₀ by 2.5-fold, confirming ERG6's role in its mode of action. Disruption of ergosterol biosynthesis was indirectly confirmed through hypoosmotic shock assays, which indicated increased membrane fluidity in Sb^VT4MPP-treated Leishmania. In vivo studies revealed a 96 % reduction in parasite load, highlighting Sb^VT4MPP's efficacy in visceral leishmaniasis model. Since ERG6 is absent in mammals, it represents a selective and promising pharmacological target. Our findings position Sb^VT4MPP as a novel chemical entity with potent in vitro and in vivo antileishmanial efficacy, providing mechanistic insights and warranting further preclinical investigation as a promising drug candidate for leishmaniasis treatment.

Background: Drug development for leishmaniases treatment follows a very selective process in order to propose drug candidates that possess all the qualities that meet the strict specifications of the pharmaceutical industry. Drug resistance is a limiting factor that can impact the lifespan of a marketed drug. It is now essential that the risk of drug resistance be evaluated at the early stage of in vitro studies to discard a lead compound that could quickly generate drug resistance once available on the market. Objectives: This article aims to estimate the risk of drug resistance emergence for a promising drug candidate at the in vitro early stage of drug development. Methods: A sequential method is proposed to study some of the phenotypic characteristics and parameters of resistant parasites such as time to achieve maximal resistance during stepwise drug pressure, resistance amplitude, stability, fitness, and infectivity both in vitro and in vivo. Results: Some examples with drugs in clinical use and former drug candidates are given. Conclusions: This method providing an evaluation of the risk of drug resistance from an in vitro model of Leishmania donovani be extrapolated to other Leishmania species.