Development of New Leishmanicidal Compounds via Bioconjugation of Antimicrobial Peptides and Antileishmanial Guanidines

Leishmaniasis refers to a collection of diseases caused by protozoa from the Leishmania genus. These diseases, along with other parasitic afflictions, pose a significant public health issue, particularly given the escalating number of at-risk patients. This group includes immunocompromised individuals and those residing in impoverished conditions. The treatment of leishmaniasis is crucial, particularly in light of the mortality rate associated with nontreatment, which stands at 20-30,000 deaths per year globally. However, the therapeutic options currently available are limited, often ineffective, and potentially toxic. Consequently, the pursuit of new therapeutic alternatives is warranted. This study aims to design, synthesize, and evaluate the leishmanicidal activity of antimicrobial peptides functionalized with guanidine compounds and identify those with enhanced potency and selectivity against the parasite. Accordingly, three bioconjugates were obtained by using the solid-phase peptide synthesis protocol. Each proved to be more potent against intracellular amastigotes than their respective peptide or guanidine compounds alone and demonstrated higher selectivity to the parasites than to the host cells. Thus, the conjugation strategy employed with these compounds effectively contributes to the development of new molecules with leishmanicidal activity.

Antileishmanial activity of tetra-cationic porphyrins with peripheral Pt(II) and Pd(II) complexes mediated by photodynamic therapy approaches

Leishmaniasis is a seriously neglected disease that impacts more than one billion people in endemic areas of the globe. Several drawbacks are associated with the currently existing drugs for the treatment as low effectiveness, toxicity, and the emergence of resistant strains that demonstrates the importance of looking for novel therapeutic alternatives. Photodynamic therapy (PDT) is a promising novel alternative for cutaneous leishmaniasis treatment because its topical application avoids potential side effects generally associated with oral/parenteral application. A light-sensitive compound known as photosensitizer (PS) interacts with light and molecular oxygen to generate reactive oxygen species (ROS), which promote cell death by oxidative stress through PDT approaches. Here, for the first time, we demonstrate the antileishmanial effect of tetra-cationic porphyrins with peripheral Pt(II)- and Pd(II)-polypyridyl complexes using PDT. The isomeric tetra-cationic porphyrins in the meta positions, 3-PtTPyP, and 3-PdTPyP, exhibited the highest antiparasitic activity against promastigote (IC_50-pro = 41.8 nM and 46.1 nM, respectively) and intracellular amastigote forms (IC_50-ama = 27.6 nM and 38.8 nM, respectively) of L. amazonensis under white light irradiation (72 J cm^-2) with high selectivity (SI > 50) for both forms of parasites regarding mammalian cells. In addition, these PS induced the cell death of parasites principally by a necrotic process in the presence of white light by mitochondrial and acidic compartments accumulation. This study showed that porphyrins 3-PtTPyP and 3-PdTPyP displayed a promising antileishmanial-PDT activity with potential application for cutaneous leishmaniasis treatment.

Novel Selective and Low-Toxic Inhibitor of LmCPB2.8ΔCTE (CPB) One Important Cysteine Protease for Leishmania Virulence

Leishmaniasis is a highly prevalent, yet neglected disease caused by protozoan parasites of the genus Leishmania. In the search for newer, safer, and more effective antileishmanial compounds, we herein present a study of the mode of action in addition to a detailed structural and biological characterization of LQOF-G6 [N-benzoyl-N'-benzyl-N″-(4-tertbutylphenyl)guanidine]. X-ray crystallography and extensive NMR experiments revealed that LQOF-G6 nearly exclusively adopts the Z conformation stabilized by an intramolecular hydrogen bond. The investigated guanidine showed selective inhibitory activity on Leishmania major cysteine protease LmCPB2.8ΔCTE (CPB) with ~73% inhibition and an IC50-CPB of 6.0 µM. This compound did not show any activity against the mammalian homologues cathepsin L and B. LQOF-G6 has been found to be nontoxic toward both organs and several cell lines, and no signs of hepatotoxicity or nephrotoxicity were observed from the analysis of biochemical clinical plasma markers in the treated mice. Docking simulations and experimental NMR measurements showed a clear contribution of the conformational parameters to the strength of the binding in the active site of the enzyme, and thus fit the differences in the inhibition values of LQOF-G6 compared to the other guanidines. Furthermore, the resulting data render LQOF-G6 suitable for further development as an antileishmanial drug.

Insights into agar and secondary metabolite pathways from the genome of the red alga Gracilaria domingensis (Rhodophyta, Gracilariales)

Gracilariales is a clade of florideophycean red macroalgae known for being the main source of agar. We present a de novo genome assembly and annotation of Gracilaria domingensis, an agarophyte alga with flattened thallus widely distributed along Central and South American Atlantic intertidal zones. In addition to structural analysis, an organizational comparison was done with other Rhodophyta genomes. The nuclear genome has 78 Mbp, with 11,437 predicted coding genes, 4,075 of which did not have hits in sequence databases. We also predicted 1,567 noncoding RNAs, distributed in 14 classes. The plastid and mitochondrion genome structures were also obtained. Genes related to agar synthesis were identified. Genes for type II galactose sulfurylases could not be found. Genes related to ascorbate synthesis were found. These results suggest an intricate connection of cell wall polysaccharide synthesis and the redox systems through the use of L-galactose in Rhodophyta. The genome of G. domingensis should be valuable to phycological and aquacultural research, as it is the first tropical and Western Atlantic red macroalgal genome to be sequenced.

Design, synthesis and biological evaluation of N-oxide derivatives with potent in vivo antileishmanial activity

Leishmaniasis is a neglected disease that affects 12 million people living mainly in developing countries. Herein, 24 new N-oxide-containing compounds were synthesized followed by in vitro and in vivo evaluation of their antileishmanial activity. Compound 4f, a furoxan derivative, was particularly remarkable in this regard, with EC₅₀ value of 3.6 μM against L. infantum amastigote forms and CC₅₀ value superior to 500 μM against murine peritoneal macrophages. In vitro studies suggested that 4f may act by a dual effect, by releasing nitric oxide after biotransformation and by inhibiting cysteine protease CPB (IC₅₀: 4.5 μM). In vivo studies using an acute model of infection showed that compound 4f at 7.7 mg/Kg reduced ~90% of parasite burden in the liver and spleen of L. infantum-infected BALB/c mice. Altogether, these outcomes highlight furoxan 4f as a promising compound for further evaluation as an antileishmanial agent.

Baccharis trimera (Less.) DC leaf derivatives and eupatorin activities against Leishmania amazonensis

Natural products have been largely explored as treatments for leishmaniasis, neglected diseases with few toxic therapeutic options, as scaffolds for the development of new drugs. Herein, derivatives from the aerial parts of Baccharis trimera (Less.) DC (extract and its fractions) were evaluated against Leishmania amazonensis and macrophage cells. The ethyl acetate extract was fractionated by solid-phase extraction, resulting in eight fractions (F1-F8). Fractions F3-4 were further separated into 149 subfractions; subfraction 148 (IC_50-PRO = 1.56 ± 0.1 μg mL^-1) was selected for purification and constituent(s) characterization by high-performance liquid chromatography, as well as ¹H and ¹³C nuclear magnetic resonance spectroscopy. The flavonoid eupatorin (3',5-dihydroxy-4',6,7-trimethoxyflavone) was identified. This compound was 3.7 times more effective against intracellular amastigotes (IC_50-AMA = 1.6 ± 0.1 μM) than amphotericin B and presented low cytotoxicity (CC₅₀ > 100 μM), being almost 62 times more selective for the parasite, showing great potential in drug development for cutaneous leishmaniasis treatment.

Antimicrobial activity of RP-1 peptide conjugate with ferrocene group

Parasitic diseases are a neglected and serious problem, especially in underdeveloped countries. Among the major parasitic diseases, Leishmaniasis figures as an urgent challenge due to its high incidence and severity. At the same time, the indiscriminate use of antibiotics by the population is increasing together with resistance to medicines. To address this problem, new antibiotic-like molecules that directly kill or inhibit the growth of microorganisms are necessary, where antimicrobial peptides (AMPs) can be of great help. In this work, the ferrocene molecule, one active compound with low levels of in vivo toxicity, was coupled to the N-terminus of the RP1 peptide (derived from the human chemokine CXCL4), aiming to evaluate how this change modifies the structure, biological activity, and toxicity of the peptide. The peptide and the conjugate were synthesized using the solid phase peptide synthesis (SPPS). Circular dichroism assays in PBS showed that the RP1 peptide and its conjugate had a typical spectrum for disordered structures. The Fc-RP1 presented anti-amastigote activity against Leishmania amazonensis (IC₅₀ = 0.25 μmol L^–1). In comparison with amphotericin B, a second-line drug approved for leishmaniasis treatment, (IC₅₀ = 0.63 μmol L^-1), Fc-RP1 was more active and showed a 2.5-fold higher selectivity index. The RP1 peptide presented a MIC of 4.3 μmol L^-1 against S. agalactiae, whilst Fc-RP1 was four times more active (MIC = 0.96 μmol L^-1), indicating that ferrocene improved the antimicrobial activity against Gram-positive bacteria. The Fc-RP1 peptide also decreased the minimum inhibitory concentration (MIC) in the assays against E. faecalis (MIC = 7.9 μmol L^-1), E. coli (MIC = 3.9 μmol L^-1) and S. aureus (MIC = 3.9 μmol L^-1). The cytotoxicity of the compounds was tested against HaCaT cells, and no significant activity at the highest concentration tested (500 μg. mL^-1) was observed, showing the high potential of this new compound as a possible new drug. The coupling of ferrocene also increased the vesicle permeabilization of the peptide, showing a direct relation between high peptide concentration and high carboxyfluorescein release, which indicates the action mechanism by pore formation on the vesicles. Several studies have shown that ferrocene destabilizes cell membranes through lipid peroxidation, leading to cell lysis. It is noteworthy that the Fc-RP1 peptide synthesized here is a prototype of a bioconjugation strategy, but it still is a compound with great biological activity against neglected and fish diseases.

Synthesis and evaluation of novel prenylated chalcone derivatives as anti-leishmanial and anti-trypanosomal compounds

Chalcones form a class of compounds that belong to the flavonoid family and are widely distributed in plants. Their simple structure and the ease of preparation make chalcones attractive scaffolds for the synthesis of a large number of derivatives enabling the evaluation of the effects of different functional groups on biological activities. In this Letter, we report the successful synthesis of a series of novel prenylated chalcones via Claisen-Schmidt condensation and the evaluation of their effect on the viability of the Trypanosomatidae parasites Leishmania amazonensis, Leishmania infantum and Trypanosoma cruzi.

Antiprotozoal activity of quinonemethide triterpenes from Maytenus ilicifolia (Celastraceae)

The present study describes the leishmanicidal and trypanocidal activities of two quinonemethide triterpenes, maytenin (1) and pristimerin (2), isolated from Maytenus ilicifolia root barks (Celastraceae). The compounds were effective against the Trypanosomatidae Leishmania amazonensis and Leishmania chagasi and Trypanosoma cruzi, etiologic agents of leishmaniasis and Chagas' disease, respectively. The quinonemethide triterpenes 1 and 2 exhibited a marked in vitro leishmanicidal activity against promastigotes and amastigotes with 50% inhibitory concentration (IC(50)) values of less than 0.88 nM. Both compounds showed IC(50) lower than 0.3 nM against Trypanosoma cruzi epimastigotes. The selectivity indexes (SI) based on BALB/c macrophages for L. amazonensis and L. chagasi were 243.65 and 46.61 for (1) and 193.63 and 23.85 for (2) indicating that both compounds presented high selectivity for Leishmania sp. The data here presented suggests that these compounds should be considered in the development of new and more potent drugs for the treatment of leishmaniasis and Chagas' disease.

Octenol as attractant to Nyssomyia neivai (Diptera:Psychodidae:Phlebotominae) in the field

The kairomone octenol is known as attractive to hematophagous Diptera such as mosquitoes, tsetse flies, and midges. There is little evidence that traps baited with octenol are also effective in attracting phlebotomine sand flies. The present report evaluated octenol in modified Centers for Disease Control and Prevention (CDC) traps in two experiments: 1) modified CDC trap without light and 2) modified CDC trap with light. The traps were baited with octenol at concentrations of 0.5, 27, and 43 mg/h in Rincão locality, São Paulo, Brazil. Traps without octenol were used as controls. The sand fly Nyssomyia neivai (Pinto) (= Lutzomyia neivai) (Diptera: Psychodidae: Phlebotominae) was the prevalent species (99.9%) in both experiments. The results of the experiments showed that traps baited with octenol at 27 and 43 mg/h caught significantly more N. neivai than control and octenol at 0.5 mg/h with and without light. This is the first report that shows that octenol itself is attractive to N. neivai and associated with light traps significantly increases the catches.

Isolation and isoenzyme characterization of Leishmania (Viannia) braziliensis from a case of human cutaneous leishmaniasis in northeast centre of the state of São Paulo

The diagnosis of human cutaneous leishmaniasis in small towns is sometimes made without the species identification of the Leishmania, even in areas without previous epidemiological surveys. Here we report the isolation of a Leishmania strain from a patient of Rincão, state of São Paulo, that was identified by isoenzyme characterization as L. (Viannia) braziliensis. Sand fly collections were made in the area where the patient live in order to investigate the likely vector species.

Terbinafine resistance mediated by salicylate 1-monooxygenase in Aspergillus nidulans

Resistance to antifungal agents is a recurring and growing problem among patients with systemic fungal infections. UV-induced Aspergillus nidulans mutants resistant to terbinafine have been identified, and we report here the characterization of one such gene. A sib-selected, 6.6-kb genomic DNA fragment encodes a salicylate 1-monooxygenase (salA), and a fatty acid synthase subunit (fasC) confers terbinafine resistance upon transformation of a sensitive strain. Subfragments carrying salA but not fasC confer terbinafine resistance. salA is present as a single-copy gene on chromosome VI and encodes a protein of 473 amino acids that is homologous to salicylate 1-monooxygenase, a well-characterized naphthalene-degrading enzyme in bacteria. salA transcript accumulation analysis showed terbinafine-dependent induction in the wild type and the UV-induced mutant Terb7, as well as overexpression in a strain containing the salA subgenomic DNA fragment, probably due to the multicopy effect caused by the transformation event. Additional naphthalene degradation enzyme-coding genes are present in fungal genomes, suggesting that resistance could follow degradation of the naphthalene ring contained in terbinafine.