Trypanocidal activity of marine natural products

Synthesis and Evaluation of Marine-Inspired Compounds Result in Hybrids with Antitrypanosomal and Antileishmanial Activities

Natural products are a very rich source for obtaining new compounds with therapeutic potential. In the search for new antiparasitic and antimicrobial agents, molecular hybrids were designed based on the structures of antimicrobial marine quinazolinones and eugenol, a natural phenolic compound. Following reports of the therapeutic potential of quinazolinones and eugenol derivatives, it was expected that the union of these pharmacophores could generate biologically relevant substances. The designed compounds were obtained by classical synthetic procedures and were characterized by routine spectrometric techniques. Nine intermediates and final products were then evaluated in vitro against Trypanosoma brucei and Leishmania infantum. Antifungal and antibacterial activity were also evaluated. Six compounds (9b, 9c, 9d, 10b, 10c, and 14) showed mild activity against T. brucei with IC50 in the range of 11.17-31.68 μM. Additionally, intermediate 9c showed anti-Leishmania activity (IC50 7.54 μM) and was six times less cytotoxic against THP-1 cells. In conclusion, novel derivatives with a simple quinazolinone scaffold showing selectivity against parasites without antibacterial and antifungal activities were disclosed, paving the way for new antitrypanosomal agents.

Piplartine-Inspired 3,4,5-Trimethoxycinnamates: Trypanocidal, Mechanism of Action, and In Silico Evaluation

Chagas disease (CD) is one of the main neglected tropical diseases that promote relevant socioeconomic impacts in several countries. The therapeutic options for the treatment of CD are limited, and parasite resistance has been reported. Piplartine is a phenylpropanoid imide that has diverse biological activities, including trypanocidal action. Thus, the objective of the present work was to prepare a collection of thirteen esters analogous to piplartine (1-13) and evaluate their trypanocidal activity against Trypanosoma cruzi. Of the tested analogues, compound 11 ((E)-furan-2-ylmethyl 3-(3,4,5-trimethoxyphenyl)acrylate) showed good activity with IC₅₀ values = 28.21 ± 5.34 μM and 47.02 ± 8.70 μM, against the epimastigote and trypomastigote forms, respectively. In addition, it showed a high rate of selectivity to the parasite. The trypanocidal mechanism of action occurs through the induction of oxidative stress and mitochondrial damage. In addition, scanning electron microscopy showed the formation of pores and leakage of cytoplasmic content. Molecular docking indicated that 11 probably produces a trypanocidal effect through a multi-target mechanism, including affinity with proteins CRK1, MPK13, GSK3B, AKR, UCE-1, and UCE-2, which are important for the survival of the parasite. Therefore, the results suggest chemical characteristics that can serve for the development of new trypanocidal prototypes for researching drugs against Chagas disease.

Bulbiferamide, an Antitrypanosomal Hexapeptide Cyclized via an N-Acylindole Linkage from a Marine Obligate Microbulbifer

UV absorption spectroscopy-guided fractionation of the culture extract of a marine obligate bacterium of the genus Microbulbifer yielded a novel cyclic hexapeptide, bulbiferamide (1). NMR spectroscopic and mass spectrometric analyses revealed the structure of 1 to be a cyclic tetrapeptide appending a ureido-bridged two amino acid unit. Notably, Trp is a junction residue, forming on one hand a very rare N-aminoacylated indole linkage for cyclization and on the other hand connecting the ureido-containing tail structure, which is an unprecedented way of configuring peptides. The component amino acids were determined to be l by the advanced Marfey's method. Compound 1 displayed growth inhibitory activity against Trypanosoma cruzi epimastigotes with an IC₅₀ value of 4.1 μM, comparable to the currently approved drug benznidazole, while it was not cytotoxic to P388 murine leukemia cells at 100 μM.

Antimicrobial Peptides (AMPs): Potential Therapeutic Strategy against Trypanosomiases?

Trypanosomiases are a group of tropical diseases that have devastating health and socio-economic effects worldwide. In humans, these diseases are caused by the pathogenic kinetoplastids Trypanosoma brucei, causing African trypanosomiasis or sleeping sickness, and Trypanosoma cruzi, causing American trypanosomiasis or Chagas disease. Currently, these diseases lack effective treatment. This is attributed to the high toxicity and limited trypanocidal activity of registered drugs, as well as resistance development and difficulties in their administration. All this has prompted the search for new compounds that can serve as the basis for the development of treatment of these diseases. Antimicrobial peptides (AMPs) are small peptides synthesized by both prokaryotes and (unicellular and multicellular) eukaryotes, where they fulfill functions related to competition strategy with other organisms and immune defense. These AMPs can bind and induce perturbation in cell membranes, leading to permeation of molecules, alteration of morphology, disruption of cellular homeostasis, and activation of cell death. These peptides have activity against various pathogenic microorganisms, including parasitic protists. Therefore, they are being considered for new therapeutic strategies to treat some parasitic diseases. In this review, we analyze AMPs as therapeutic alternatives for the treatment of trypanosomiases, emphasizing their possible application as possible candidates for the development of future natural anti-trypanosome drugs.

Emerging compounds and therapeutic strategies to treat infections from Trypanosoma brucei: an overhaul of the last 5-years patents

INTRODUCTION

Human African Trypanosomiasis is a neglected disease caused by infection from parasites belonging to the Trypanosoma brucei species. Only six drugs are currently available and employed depending on the stage of the infection: pentamidine, suramin, melarsoprol, eflornithine, nifurtimox, and fexinidazole. Joint research projects were launched in an attempt to find new therapeutic options for this severe and often lethal disease.

AREAS COVERED

After a brief description of the recent literature on the parasite and the disease, we searched for patents dealing with the proposal of new anti-trypanosomiasis agents and, following the PRISMA guidelines, we filtered the results to those published from 2018onwards returning suitable entries, which represent the contemporary landscape of compounds/strategies against Trypanosoma brucei. In addition, some relevant publications from the overall scientific literature were also discussed.

EXPERT OPINION

This review comprehensively covers and analyzes the most recent advances not only in the discovery of new inhibitors and their structure-activity relationships but also in the assessment of innovative biological targets opening new scenarios in the MedChem field. Lastly, also new vaccines and formulations recently patented were described. However, natural and synthetic compounds were analyzed in terms of inhibitory activity and selective toxicity against human cells.

RE, Marín-Villa M. In Silico, In Vitro, and Pharmacokinetic Studies of UBMC-4, a Potential Novel Compound for Treating against Trypanosoma cruzi

The lack of therapeutic alternatives for the treatment of Chagas disease, a neglected disease, drives the discovery of new drugs with trypanocidal activity. Consequently, we conducted in vitro studies using UBMC-4, a potential Trypanosoma cruzi AKT-like pleckstrin homology (PH) domain inhibitory compound found using bioinformatics tools. The half effective concentration (EC50) on intracellular amastigotes was determined at 1.85 ± 1 μM showing low cytotoxicity (LC50) > 40 μM on human cell lines tested. In order to study the lethal effect caused by the compound on epimastigotes, morphological changes were assessed by scanning and transmission electron microscopy. Progressive alterations such as flagellum inactivation, cell size reduction, nuclear structure alteration, condensation of chromatin towards the nuclear periphery, vacuole formation, and mitochondrial swelling with kinetoplast integrity loss were evidenced. In addition, apoptosis-like markers in T. cruzi were assessed by flow cytometry, demonstrating that the effect of UBMC-4 on T. cruzi AKT-like kinase reduced the tolerance to nutritional stress-triggered, apoptosis-like events, including DNA fragmentation, mitochondrial damage, and loss of plasma membrane integrity. After this, UBMC-4 was formulated for oral administration and pharmacokinetics were analyzed in a mouse model. Finally, upon oral administration of 200 mg/kg in mice, we found that a UBMC-4 plasma concentration remaining in circulation beyond 24 h after administration is well described by the two-compartment model. We conclude that UBMC-4 has an effective trypanocidal activity in vitro at low concentrations and this effect is evident in T. cruzi cell structures. In mice, UBMC-4 was well absorbed and reached plasma concentrations higher than the EC50, showing features that would aid in developing a new drug to treat Chagas disease.

Benznidazole, itraconazole, and their combination for the treatment of chronic experimental Chagas disease in dogs

Treatment for Chagas disease has limited efficacy in the chronic phase. We evaluated benznidazole (BZ) and itraconazole (ITZ) individually and in association in dogs 16 months after infection with a BZ-resistant Trypanosoma cruzi strain. Four study groups (20 animals) were evaluated and treated for 60 days with BZ, ITZ, or BZ + ITZ, and maintained in parallel to control group infected and not treated (INT). All dogs were evaluated in the first, sixth, 12th, 18th and 24th months of study. Polymerase chain reaction (PCR) was negative in 2 of 3 animals in the BZ + ITZ group, 2 of 5 in the BZ group, and 4 of 5 in the ITZ group. Hemoculture performed in the 24th month was negative in all groups. Enzyme-linked immunoassay remained reactive in all treated animals. Echocardiography differentiated treated animals from control animals. Quantitative PCR analysis of cardiac tissue was negative in the BZ + ITZ and BZ groups, positive in 2 of 5 dogs in the ITZ group and in 2 of 3 dogs in the control group, but negative in colon tissue in all groups. Inflammation was significantly reduced in the right atrium and left ventricle of dogs treated with BZ + ITZ and BZ compared with those receiving ITZ alone. Fibrosis was absent in most dogs treated with BZ + ITZ, mild in those treated with BZ or ITZ alone, and intense in the control group. Parasitological and histopathological evaluations showed that BZ + ITZ treatment improved or stabilized the clinical condition of the dogs.

Presence of short and cyclic peptides in Acacia and Ziziphus honeys may potentiate their medicinal values

Acacia honey is characterized by high nutritional, antioxidant, antibacterial and immuno-modulatory values. This work investigated the presence of short and cyclic peptides in Acacia and Ziziphus honey samples. Acacia honey samples (Acacia tortilis and Acacia hamulosa) and three Ziziphus honeys (Ziziphus spina-christi) were screened for their short and cyclic peptide contents using the LC-MS and the chemical structure databases. Moreover, the total protein content was determined using the Bradford method. The A. tortilis honey contained three short peptides; HWCC, DSST, and ECH, and the A. hamulosa honey sample contained five short peptides and one cyclic peptide. The short peptides of the A. hamulosa honey were Ac-GMGHG-OH (Ac-MGGHG-OH), Boc-R(Aloc)2-C(Pal)-OH, H-C (1)-NEt2·H-C (1)-NEt2, APAP (AAPP), and GAFQ (deamino-2-pyrid-4-yl-glycyl-dl-alanyl-dl-norvalyl-dl-asparagine). The cyclic peptide of the A. hamulosa honey was cyclo[Aad-RGD-d-F] (cyclo[Aad-Arg-Gly-Asp-d-Phe]). The Ziziphus honey was characterized by the presence of either Almiramide B or Auristatin-6-AQ. A. tortilis, A. hamulosa, and Ziziphus honeys are characterized by the presence of short and cyclic peptides which may contribute to their medicinal values.

In vitro screening of novel anti-Babesia gibsoni drugs from natural products

Babesia gibsoni is a tick-transmitted intraerythrocytic apicomplexan parasite that causes babesiosis in dogs. Due to the strong side effects and lack of efficacy of current drugs, novel drugs against B. gibsoni are urgently needed. Natural products as a source for new drugs is a good choice for screening drugs against B. gibsoni. The current study focuses on identifying novel potential drugs from natural products against B. gibsoniin vitro. Parasite inhibition was verified using a SYBR green I-based fluorescence assay. A total of 502 natural product compounds were screened for anti-B. gibsoni activity in vitro. Twenty-four compounds showed high growth inhibition (>80%) on B. gibsoni and 5 plant-derived compounds were selected for further study. The half-maximal inhibitory concentration (IC₅₀) values of lycorine (LY), vincristine sulfate (VS), emetine·2HCl (EME), harringtonine (HT) and cephaeline·HBr (CEP) were 784.4 ± 3.3, 643.0 ± 2.8, 253.1 ± 1.4, 23.4 ± 1.2, and 108.1 ± 4.3 nM, respectively. The Madin-Darby canine kidney (MDCK) cell line was used to assess cytotoxicity of hit compounds. All compounds showed minimal toxicity to the MDCK cells. The effects of hit compounds combined with diminazene aceturate (DA) on B. gibsoni were further evaluated in vitro. VS, EME, HT or CEP combined with DA showed synergistic effects against B. gibsoni, whereas LY combined with DA showed an antagonistic effect against B. gibsoni. The results obtained in this study indicate that LY, VS, EME, HT and CEP are promising compounds for B. gibsoni treatment.

The effect of the biflavonoid 2″,3″-dihydroochnaflavone on Trypanosoma cruzi Y strain

Trypanosoma cruzi is the causative agent of Chagas disease which affects 8 million people in Latin America. The parasite possesses high capacity to evade host immune system and the available drugs to treat Chagas disease present low efficacy combined to serious side effects to patients. Therefore, the identification of alternative therapeutics is essential. Brazilian flora exhibits an immense diversity of metabolites with great potential to be developed into new drugs. We investigated the action of 2″,3″-dihydroochnaflavone a biflavonoid extracted from Luxemburgia nobilis Eichler ex Engl. (Ochnaceae) against T. cruzi (Y strain). Our experiments showed that this compound is effective against parasite epimastigote forms, presenting IC₅₀ value of (2.5 ± 0.1) μM after 96 h of treatment. Ultrastructure alterations were also detected in treated epimastigotes especially mitochondrial enlargement at the kinetoplast region. At the concentration of 30 μM, the compound killed (61.6 ± 3.37)% of the parasite in its amastigote form. In addition, at the same concentration, the compound killed all trypamastigotes growing within murine macrophages after 7-9 days of infection. Nonetheless, the biflavonoid concentrations were harmless to murine enriched population of lymphocytes and peritoneal macrophages. These results indicate that 2″,3″- dihydroochnaflavone presents activity against T. cruzi.

Synthesis, docking study and inhibitory activity of 2,6-diketopiperazines derived from α-amino acids on HDAC8

Diketopiperazines (DKPs) have been regarded as an important scaffold from the viewpoint of synthesis due to their biological properties for the treatment of several diseases, including cancer. In this work, two novel series of enantiomeric 2,6-DKPs derived from α-amino acids were synthesized through nucleophilic substitution and intramolecular cyclization reactions. All the compounds were docked against histone deacetylase 8 (HDAC8), which is a promising target for the development of anticancer drugs. These compounds bound into the active site of HDAC8 in a similar way to Trichostatin A (TSA), which is an HDAC8 inhibitor. This study showed that the conformation of the 2,6-DKP ring, stereochemistry, and the type of substituent on the chiral center had an important role in the binding modes. The Gibbs free energies and dissociation constants values of HDAC8-ligand complexes showed that compounds (S)-4hBn, (S)-4m, (R)-4h, and (R)-4m were more stable and affine towards HDAC8 than TSA. The inhibitory activities of 4a, (S)-4h, (S)- and (R)-4(g, l, m) were evaluated in vitro on HDAC8. It was found that compounds (R)-4g (IC₅₀ = 21.54 nM) and (R)-4m (IC₅₀ = 10.81 nM) exhibited better inhibitory activities than TSA (IC₅₀ = 28.32 nM). These results suggested that 2,6-DKPs derivatives may be promising anticancer agents for further biological studies.

Recent Advances in the Discovery of Novel Antiprotozoal Agents

Parasitic diseases have serious health, social, and economic impacts, especially in the tropical regions of the world. Diseases caused by protozoan parasites are responsible for considerable mortality and morbidity, affecting more than 500 million people worldwide. Globally, the burden of protozoan diseases is increasing and is been exacerbated because of a lack of effective medication due to the drug resistance and toxicity of current antiprotozoal agents. These limitations have prompted many researchers to search for new drugs against protozoan parasites. In this review, we have compiled the latest information (2012-2017) on the structures and pharmacological activities of newly developed organic compounds against five major protozoan diseases, giardiasis, leishmaniasis, malaria, trichomoniasis, and trypanosomiasis, with the aim of showing recent advances in the discovery of new antiprotozoal drugs.

Therapeutic Interventions for Countering Leishmaniasis and Chagas's Disease: From Traditional Sources to Nanotechnological Systems

The incidence of neglected diseases in tropical countries, such as Leishmaniasis and Chagas's disease, is attributed to a set of biological and ecological factors associated with the socioeconomic context of developing countries and with a significant burden to health care systems. Both Leishmaniasis and Chagas's disease are caused by different protozoa and develop diverse symptoms, which depend on the specific species infecting man. Currently available drugs to treat these disorders have limited therapeutic outcomes, frequently due to microorganisms' drug resistance. In recent years, significant efforts have been made towards the development of innovative drug delivery systems aiming to improve bioavailability and pharmacokinetic profiles of classical drug therapy. This paper discusses the key facts of Leishmaniasis and Chagas's disease, the currently available pharmacological therapies and the new drug delivery systems for conventional drugs.

Prospect of natural products in glioma: A novel avenue in glioma management

Glioma is one of the most perplexing cancers because of its infiltrating nature, molecular signaling, and location in central nervous system. Blood-brain barrier acts as a natural barrier to the glioma making it difficult to access by conventional chemotherapy. Clinicians are using natural compounds or their derivatives for several diseases including different cancers. However, the feasibility of using natural compounds in glioma is not explored in details. Natural compounds can act over a wide variety of signaling pathways such as survival and metabolic pathways and induce cell death. Some of the natural agents have additional benefits of crossing biological barriers such as blood-brain barrier with ease having few or no impact on the surrounding healthy cells. All of these benefits make natural compounds a prospective candidate for the glioma management. This article evaluates the benefits of using natural compounds for glioma therapy and their possible mechanism of actions. We have discussed the natural compounds assessed currently for glioma therapy and proposed a few novel natural compounds with potential antiglioma effect based on their mechanism of action.

Does Prolactin treatment trigger imunoendocrine alterations during experimental T. cruzi infection?

Prolactin (PRL) is a pleiotropic polypeptide hormone produced by the anterior pituitary gland and negatively controlled by dopamine. Some researchers have associated the immune regulatory functions of PRL with some infectious diseases like Toxoplasma gondii and T. cruzi. This work aimed to analyze the possible immuno-modulatory effects of this hormone through the subcutaneous administration of PRL during the experimental Chagas disease. On the 14th day post-infection (dpi), PRL triggered increased percentages of NK cells in treated infected animals as compared to the infected and untreated ones. For early and late apoptosis, our results showed that in chronically infected groups, PRL counteracted splenocyte apoptosis as revealed by the reduced percentages of both, early and late apoptosis. Reduced percentages of spleen CD4⁺ and CD8⁺ T cells were detected in infected PRL treated rats (60 days post-infection). Concerning to B cells, a significant increased percentage of these cells was found for all PRL treated infected animals (14th dpi), but no statistically significant alteration was observed on the 60th days post-infection. Furthermore, PRL treatment triggered a significant increase in the percentage of CD4⁺ T lymphocytes IFN-γ producers, while on the 60th dpi, a reduced percentage of IFN-γ in these cells was observed in prolactin-treated rats compared to infected and untreated ones. Enhanced serum IL-12 levels were detected in infected and PRL treated subjects (60th dpi). Only on 7th day post-infection, the flow cytometric analysis of CFSE-stained CD3⁺ T cells showed an enhanced proliferation of polyclonal stimulated T cells in PRL-treated and infected animals. In this study, we demonstrated that PRL can influence many aspects of the immune response during the experimental Chagas' disease, and this substance could be used as a supporting trial along with the conventional drug treatment.

Therapeutic Potential of Iridoid Derivatives: Patent Review

Iridoids belong to a family of monoterpenoids comprising the cyclopentan[c]-pyran system; this class of compounds offers a wide range of biological effects, namely antileishmanial, anticancer, antiplasmodial, and anti-inflammatory potency. To date, a large number of biologically active iridoid derivatives have been reported from various plant families, including Rubiaceae, Plantaginaceae, Scrophulariaceae, and Verbenaceae. Furthermore, iridoids have the potential to form conjugates with other anticancer, antidiabetic, antileishmanial, and antimalarial drugs which synergistically have the potential to increase their effects. Additionally, future research should focus on the synthesis of halo analogs as well as preparing homo dimers or heterodimers of iridoids, since these might quite conceivably possess an increased bioactivity.

Spiralyde A, an Antikinetoplastid Dolabellane from the Brown Alga Dictyota spiralis

Bioassay-guided fractionation of the antikinetoplastid extract of the brown alga Dictyota spiralis has led to the isolation of spiralyde A (1), a new dolabellane aldehyde, along with other five known related diterpenes (2⁻6). Their structures were determined by HRESIMS, 1D and 2D NMR spectroscopy, and comparison with data reported in the literature. The antiparasitic activity of all compounds was evaluated. Spiralyde A (1) and the known compound 3,4-epoxy-7,18-dolabelladiene (2) were the most active compounds against Leishmania amazonensis and Trypanosoma cruzi. Spiralyde A (1) was the most potent compound, comparable to benznidazole, the reference drug for trypanocidal activity.

Active Natural Product Scaffolds against Trypanosomatid Parasites: A Review

Neglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in countries in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date and expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. Natural products have long been a source of potent, structurally diverse bioactive molecules. Herein are reviewed natural products with reported trypanocidal activity, which have been clustered based on core structural similarities, to aid the future discovery of new trypanocidal core motifs with potential routes to synthetically accessible natural product cores suggested.

Germacranolide-type sesquiterpene lactones from Smallanthus sonchifolius with promising activity against Leishmania mexicana and Trypanosoma cruzi

Background

Leishmaniasis and Chagas disease are life-threatening illnesses caused by the protozoan parasites Leishmania spp. and Trypanosoma cruzi, respectively. They are known as “neglected diseases” due to the lack of effective drug treatments and the scarcity of research work devoted to them. Therefore, the development of novel and effective drugs is an important and urgent need. Natural products are an important source of bioactive molecules for the development of new drugs. In this study, we evaluated the activity of enhydrin, uvedalin and polymatin B, three sesquiterpene lactones (STLs) isolated from Smallanthus sonchifolius, on Leishmania mexicana (MNYC/BZ/62/M) and Trypanosoma cruzi (Dm28c). In addition, the in vivo trypanocidal activity of enhydrin and uvedalin and the effects of these STLs on parasites’ ultrastructure were evaluated.

Methods

The inhibitory effect of the three STLs on the growth of L. mexicana amastigotes and promastigotes as well as T. cruzi epimastigotes was evaluated in vitro. The changes produced by the STLs on the ultrastructure of parasites were examined by transmission electron microscopy (TEM). Enhydrin and uvedalin were also studied in a murine model of acute T. cruzi infection (RA strain). Serum activities of the hepatic enzymes alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase were used as biochemical markers of hepatotoxicity.

Results

The three compounds exhibited leishmanicidal activity on both parasite forms with IC₅₀ values of 0.42–0.54 μg/ml for promastigotes and 0.85–1.64 μg/ml for intracellular amastigotes. Similar results were observed on T. cruzi epimastigotes (IC₅₀ 0.35–0.60 μg/ml). The TEM evaluation showed marked ultrastructural alterations, such as an intense vacuolization and mitochondrial swelling in both L. mexicana promastigotes and T. cruzi epimastigotes exposed to the STLs. In the in vivo study, enhydrin and uvedalin displayed a significant decrease in circulating parasites (50–71%) and no signs of hepatotoxicity were detected.

Conclusions

Enhydrin, uvedalin and polymatin B possess significant leishmanicidal and trypanocidal activity on different parasite stages. These results show that these compounds may provide valuable leads for the development of new drugs against these neglected parasitic diseases.

Screening a Natural Product-Based Library against Kinetoplastid Parasites

Kinetoplastid parasites cause vector-borne parasitic diseases including leishmaniasis, human African trypanosomiasis (HAT) and Chagas disease. These Neglected Tropical Diseases (NTDs) impact on some of the world's lowest socioeconomic communities. Current treatments for these diseases cause severe toxicity and have limited efficacy, highlighting the need to identify new treatments. In this study, the Davis open access natural product-based library was screened against kinetoplastids (Leishmania donovani DD8, Trypanosoma brucei brucei and Trypanosoma cruzi) using phenotypic assays. The aim of this study was to identify hit compounds, with a focus on improved efficacy, selectivity and potential to target several kinetoplastid parasites. The IC50 values of the natural products were obtained for L. donovani DD8, T. b. brucei and T. cruzi in addition to cytotoxicity against the mammalian cell lines, HEK-293, 3T3 and THP-1 cell lines were determined to ascertain parasite selectivity. Thirty-one compounds were identified with IC50 values of ≤ 10 µM against the kinetoplastid parasites tested. Lissoclinotoxin E (1) was the only compound identified with activity across all three investigated parasites, exhibiting IC50 values < 5 µM. In this study, natural products with the potential to be new chemical starting points for drug discovery efforts for kinetoplastid diseases were identified.

Marine Pharmacology in 2012-2013: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis, and Antiviral Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The peer-reviewed marine pharmacology literature from 2012 to 2013 was systematically reviewed, consistent with the 1998–2011 reviews of this series. Marine pharmacology research from 2012 to 2013, conducted by scientists from 42 countries in addition to the United States, reported findings on the preclinical pharmacology of 257 marine compounds. The preclinical pharmacology of compounds isolated from marine organisms revealed antibacterial, antifungal, antiprotozoal, antituberculosis, antiviral and anthelmitic pharmacological activities for 113 marine natural products. In addition, 75 marine compounds were reported to have antidiabetic and anti-inflammatory activities and affect the immune and nervous system. Finally, 69 marine compounds were shown to display miscellaneous mechanisms of action which could contribute to novel pharmacological classes. Thus, in 2012–2013, the preclinical marine natural product pharmacology pipeline provided novel pharmacology and lead compounds to the clinical marine pharmaceutical pipeline, and contributed significantly to potentially novel therapeutic approaches to several global disease categories.

Antifungal potential of marine natural products

Fungal diseases represent an increasing threat to human health worldwide which in some cases might be associated with substantial morbidity and mortality. However, only few antifungal drugs are currently available for the treatment of life-threatening fungal infections. Furthermore, plant diseases caused by fungal pathogens represent a worldwide economic problem for the agriculture industry. The marine environment continues to provide structurally diverse and biologically active secondary metabolites, several of which have inspired the development of new classes of therapeutic agents. Among these secondary metabolites, several compounds with noteworthy antifungal activities have been isolated from marine microorganisms, invertebrates, and algae. During the last fifteen years, around 65% of marine natural products possessing antifungal activities have been isolated from sponges and bacteria. This review gives an overview of natural products from diverse marine organisms that have shown in vitro and/or in vivo potential as antifungal agents, with their mechanism of action whenever applicable. The natural products literature is covered from January 2000 until June 2015, and we are reporting the chemical structures together with their biological activities, as well as the isolation source.

Secondary metabolites extracted from marine sponge associated Comamonas testosteroni and Citrobacter freundii as potential antimicrobials against MDR pathogens and hypothetical leads for VP40 matrix protein of Ebola virus: an in vitro and in silico investigation

The current study explores therapeutic potential of metabolites extracted from marine sponge (Cliona sp.)-associated bacteria against MDR pathogens and predicts the binding prospective of probable lead molecules against VP40 target of Ebola virus. The metabolite-producing bacteria were characterized by agar overlay assay and as per the protocols in Bergey's manual of determinative bacteriology. The antibacterial activities of extracted metabolites were tested against clinical pathogens by well-diffusion assay. The selected metabolite producers were characterized by 16S rDNA sequencing. Chemical screening and Fourier Transform Infrared (FTIR) analysis for selected compounds were performed. The probable lead molecules present in the metabolites were hypothesized based on proximate analysis, FTIR data, and literature survey. The drug-like properties and binding potential of lead molecules against VP40 target of Ebola virus were hypothesized by computational virtual screening and molecular docking. The current study demonstrated that clear zones around bacterial colonies in agar overlay assay. Antibiotic sensitivity profiling demonstrated that the clinical isolates were multi-drug resistant, however; most of them showed sensitivity to secondary metabolites (MIC-15 μl/well). The proximate and FTIR analysis suggested that probable metabolites belonged to alkaloids with O-H, C-H, C=O, and N-H groups. 16S rDNA characterization of selected metabolite producers demonstrated that 96% and 99% sequence identity to Comamonas testosteroni and Citrobacter freundii, respectively. The docking studies suggested that molecules such as Gymnastatin, Sorbicillactone, Marizomib, and Daryamide can designed as probable lead candidates against VP40 target of Ebola virus.

Genome-Directed Lead Discovery: Biosynthesis, Structure Elucidation, and Biological Evaluation of Two Families of Polyene Macrolactams against Trypanosoma brucei

Marine natural products are an important source of lead compounds against many pathogenic targets. Herein, we report the discovery of lobosamides A-C from a marine actinobacterium, Micromonospora sp., representing three new members of a small but growing family of bacterially produced polyene macrolactams. The lobosamides display growth inhibitory activity against the protozoan parasite Trypanosoma brucei (lobosamide A IC50 = 0.8 μM), the causative agent of human African trypanosomiasis (HAT). The biosynthetic gene cluster of the lobosamides was sequenced and suggests a conserved cluster organization among the 26-membered macrolactams. While determination of the relative and absolute configurations of many members of this family is lacking, the absolute configurations of the lobosamides were deduced using a combination of chemical modification, detailed spectroscopic analysis, and bioinformatics. We implemented a "molecules-to-genes-to-molecules" approach to determine the prevalence of similar clusters in other bacteria, which led to the discovery of two additional macrolactams, mirilactams A and B from Actinosynnema mirum. These additional analogs have allowed us to identify specific structure-activity relationships that contribute to the antitrypanosomal activity of this class. This approach illustrates the power of combining chemical analysis and genomics in the discovery and characterization of natural products as new lead compounds for neglected disease targets.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Anti-Protozoal Activities of Cembrane-Type Diterpenes from Vietnamese Soft Corals

Based on our previous finding that certain cembranoid diterpenes possess selective toxicity against protozoan pathogens of tropical diseases such as Trypanosoma and Plasmodium, we have subjected a series of 34 cembranes isolated from soft corals living in the Vietnamese sea to an in vitro screening for anti-protozoal activity against Trypanosoma brucei rhodesiense (Tbr), T. cruzi (Tc), Leishmania donovani (Ld), and Plasmodium falciparum (Pf). Twelve of the tested compounds displayed significant activity against at least one of the parasites. Specifically, 7S,8S-epoxy-1,3,11-cembratriene-16-oic methyl ester (1), (1R,4R,2E,7E,11E)-cembra-2,7,11-trien-4-ol (2), crassumol D (12), crassumol E (13), and (1S,2E,4S,6E,8S,11S)-2,6,12(20)-cembrantriene-4,8,11-triol (16) from Lobophytum crassum, L. laevigatum, and Sinularia maxima showed the highest level of inhibitory activity against T. b. rhodesiense, with IC₅₀ values of about 1 µM or less. Lobocrasol A (6) and lobocrasol C (8) from L. crassum and L. laevigatum exhibited particularly significant inhibitory effects on L. donovani with IC₅₀ values < 0.2 µM. The best antiplasmodial effect was exerted by laevigatol A (10), with an IC₅₀ value of about 3.0 µM. The cytotoxicity of the active compounds on L6 rat skeletal myoblast cell was also assessed and found to be insignificant in all cases. This is the first report on anti-protozoal activity of these compounds, and points out the potential of the soft corals in discovery of new anti-protozoal lead compounds.

Evaluation of the in vitro trypanocidal activity of methylated flavonoid constituents of Vitex simplicifolia leaves

Background

Trypanosomiasis is a neglected tropical disease with complex clinical manifestations, tedious diagnosis, and difficult treatments. The drugs available for the treatment of this endemic disease are old, expensive, and associated with other problems including safety and drug resistant parasites. Therefore, there is an urgent need for the development of new, effective, cheap, and safe drugs for its treatment. Plants are potentially rich sources of leads for new drugs against trypanosomiasis.

Vitex simplicifolia (Verbenaceae) is used traditionally for the treatment of tooth ache, edema, skin diseases, gout and trypanosomiasis in Nigeria. In a preliminary study, the methanol extract of Vitex simplicifolia was shown to exhibit a pronounced trypanocidal activity against T. b. rhodesiense.

The present study was undertaken to investigate the active component responsible for the acclaimed activity of the leaves of Vitex simplicifolia in the traditional treatment of trypanosomiasis in Nigeria and other African countries. Our investigations aim at assessing the plant as a new source of potential trypanocidal compounds.

Methods

The crude extracts were prepared from the dried leaves using methanol, successive extraction with hexane, dichloromethane, ethylacetate and butanol was also done. The ethylacetate fraction was further fractionated and compounds isolated using preparative chromatographic technique and their structures were elucidated by NMR, mass spectrometry and comparison with literature data. Trypanocidal activities and cytotoxicity, using rat skeletal myoblast (L6) cells were investigated and their selectivity indices were determined.

Results

The chromatographic separations of the methanol extracts gave rise to seven compounds. The isolated compounds 2, 3, 6 and 7 exhibited promising trypanocidal activity with IC₅₀ values ranging from 4.7-12.3 μg/ml and cytotoxicity in the range of 1.58- 46.20 μg/ml. Compound 6, however, showed the most selective trypanocidal activity with a selectivity index of 9.8. This is the first report of trypanocidal activity of flavonoids from this plant genus.

Conclusions

The isolated compounds from Vitex simplicifolia exhibited noteworthy trypanocidal activities and hence may provide a source of new antitrypanosomal agents. These results also support the traditional use of Vitex simplicifolia in the treatment of trypanosomiasis. This is the first report of trypanocidal effect of flavonoids from this plant genus.

The in vitro biological activity of the Brazilian brown seaweed Dictyota mertensii against Leishmania amazonensis

Seaweeds present a wide variety of interesting bioactive molecules. In the present work we evaluated the biological activity of the dichloromethane/methanol (2:1) extract (DME) from the brown seaweed Dictyota mertensii against Leishmania amazonensis and its cytotoxic potential on mammalian cells. The extract showed significant inhibitory effect on the growth of promastigote forms (IC50=71.60 μg/mL) and low toxicity against mammalian cells (CC50=233.10 μg/mL). The DME was also efficient in inhibiting the infection in macrophages, with CC50 of 81.4 μg/mL and significantly decreased the survival of amastigote forms within these cells. The selectivity index showed that DME was more toxic to both promastigote (SI=3.25) and amastigote (SI=2.86) forms than to macrophages. Increased NO production was observed in treated macrophages suggesting that besides acting directly on the parasites, the DME also shows an immunomodulatory effect on macrophages. Drastic ultrastructural alterations consistent with loss of viability and cell death were observed in treated parasites. Confocal microscopy and cytometry analyzes showed no significant impairment of plasma membrane integrity, whereas an intense depolarization of mitochondrial membrane could be observed by using propidium iodide and rhodamine 123 staining, respectively. The low toxicity to mammalian cells and the effective activity against promastigotes and amastigotes, point to the use of DME as a promising agent for the treatment of cutaneous leishmaniasis.