Voacamine alters Leishmania ultrastructure and kills parasite by poisoning unusual bi-subunit topoisomerase IB

DNA topoisomerases as a drug target in Leishmaniasis: Structural and mechanistic insights

Leishmaniasis, caused by a protozoan parasite, is among humanity's costliest banes, owing to the high mortality and morbidity ratio in poverty-stricken areas. To date, no vaccine is available for the complete cure of the disease. Current chemotherapy is expensive, has undesirable side effects, and faces drug resistance limitations and toxicity concerns. The substantial differences in homology between leishmanial DNA topoisomerase IB compared with the human counterparts provided a new lead in the study of the structural determinants that can be targeted. Several research groups explored this molecular target, trying to fill the therapeutic gap, and came forward with various anti-leishmanial scaffolds. This article is a comprehensive review of knowledge about topoisomerases as an anti-leishmanial drug target and their inhibitors collected over the years. In addition to information on molecular targets and reported scaffolds, the review details the structure-activity relationship of described compounds with leishmanial Topoisomerase IB. Moreover, the work also includes information about the structure of the inhibitors, showing common interacting residues with leishmanial topoisomerases that drive their mode of action towards them. Finally, in search of topoisomerase inhibitors at the stage of clinical trials, we have listed all the drugs that have been in clinical trials against leishmaniasis.

Exploration of Antileishmanial Compounds Derived from Natural Sources

AIMS

Leishmaniasis is a deadly tropical disease that is neglected in many countries. World Health Organization, along with a few other countries, has been working together to protect against these parasites. Many novel drugs from the past few years have been discovered and subjected against leishmaniasis, which have been effective but they are quite expensive for lower-class people. Some drugs showed no effect on the patients, and the longer use of these medicines has made resistance against these deadly parasites. Researchers have been working for better medication by using natural products from medicinal plants (oils, secondary metabolites, plant extracts) and other alternatives to find active compounds as an alternative to the current synthetic drugs.

MATERIALS AND METHODS

To find more potential natural products to treat Leishmania spp, a study has been conducted and reported many plant metabolites and other natural alternatives from plants and their extracts. Selected research papers with few term words such as natural products, plant metabolites, Leishmaniasis, in vivo, in vitro, and treatment against leishmaniasis; in the Google Scholar, PubMed, and Science Direct databases with selected research papers published between 2015 and 2021 have been chosen for further analysis has been included in this report which has examined either in vivo or in vitro analysis.

RESULTS

This paper reported more than 20 novel natural compounds in 20 research papers that have been identified which report a leishmanicidal activity and shows an action against promastigote, axenic, and intracellular amastigote forms.

CONCLUSION

Medicinal plants, along with a few plant parts and extracts, have been reported as a possible novel anti-leishmanial medication. These medicinal plants are considered nontoxic to Host cells. Leishmaniasis treatments will draw on the isolated compounds as a source further and these compounds compete with those already offered in clinics.

Molecular-level strategic goals and repressors in Leishmaniasis - Integrated data to accelerate target-based heterocyclic scaffolds

Leishmaniasis is a complex of neglected tropical diseases caused by various species of leishmanial parasites that primarily affect the world's poorest people. A limited number of standard medications are available for this disease that has been used for several decades, these drugs have many drawbacks such as resistance, higher cost, and patient compliance, making it difficult to reach the poor. The search for novel chemical entities to treat leishmaniasis has led to target-based scaffold research. Among several identified potential molecular targets, enzymes involved in the purine salvage pathway include polyamine biosynthetic process, such as arginase, ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase, trypanothione reductase as well as enzymes in the DNA cell cycle, such as DNA topoisomerases I and II plays vital role in the life cycle survival of leishmanial parasite. This review mainly focuses on various heterocyclic scaffolds, and their specific inhibitory targets against leishmaniasis, particularly those from the polyamine biosynthesis pathway and DNA topoisomerases with estimated activity studies of various heterocyclic analogs in terms of their IC₅₀ or EC₅₀ value, reported molecular docking analysis from available published literatures.

Novel Pyrido[2',1':2,3]imidazo[4,5-c]quinoline Derivative Selectively Poisons Leishmania donovani Bisubunit Topoisomerase 1 to Inhibit the Antimony-Resistant Leishmania Infection in Vivo

The unique bisubunit structure of Leishmania donovani topoisomerase 1B (LdTop1) is a potential drug target in the parasites unlike the monomeric Top1 from its human host counterpart. Here, we report the design, synthesis, and validation of a chimeric pyrido[2',1':2,3]imidazo[4,5-c]quinoline derivative (C17) as a novel antileishmanial agent that poisons topoisomerase 1-DNA covalent complexes (LdTop1cc) inside the parasites and inhibits Top1 religation activity both in the drug sensitive and antimony-resistant L. donovani clinical isolates. Importantly, the human Top1 is not sensitive to C17. Further, C17 overcomes the chemical instability of camptothecin (CPT) by generating persistent LdTop1cc-induced DNA breaks inside the parasites even after 12 h of drug removal. Intraperitoneal administration of C17 results in marked reduction of the Leishmania amastigotes from the infected spleen and liver of BALB/c mice. C17 confers a host protective immune-response up-regulating the Th1 cytokines facilitating parasite clearance which can be exploited for treating drug-resistant leishmaniasis.

Demystifying the potential of inhibitors targeting DNA topoisomerases in unicellular protozoan parasites

DNA topoisomerases are a group of enzymes omnipresent in all organisms. They maintain the DNA topology during replication, repair, recombination, and transcription. However, the structure of topoisomerase in protozoan parasites differs significantly from that of human topoisomerases; thus, this enzyme acts as a crucial target in drug development against parasitic diseases. Although the therapeutic potential of drugs targeting the parasitic topoisomerase is well known, to manage the shortcomings of currently available therapeutics and the emergence of drug resistance, the discovery of novel antiparasitic molecules is an urgent need. In this review, we describe various investigational and repurposed topoisomerase inhibitors developed against protozoan parasites over the past few years. Teaser: Fatal parasitic diseases are an increasing cause for concern; here, we provide a compilation of different inhibitors targeting DNA topoisomerases, enzymes that are essential for, and unique to, protozoan parasites; therefore, inhibitors are efficient and have few adverse effects.

Holanamine, a Steroidal Alkaloid from the Bark of Holarrhena pubescens Wall. ex G. Don Inhibits the Growth of Leishmania donovani by Targeting DNA Topoisomerase 1B

Leishmaniasis is a group of neglected tropical diseases (NTDs) caused by about 20 species of obligate intracellular protozoan parasites of the genus Leishmania, which occurs in cutaneous, mucocutaneous, and visceral forms. Many researchers have sought to utilize natural products for novel and effective treatments to combat many infectious diseases, including leishmaniasis. Holarrhena pubescens Wall. ex G. Don (Apocynaceae) bark is a rich source of bioactive steroidal alkaloids. The total alkaloidal extract (IC₅₀ 6.12 ± 0.117 μg/mL), and the isolated alkaloid, holanamine, showed significant antileishmanial activity (IC₅₀ 2.66 ± 0.112 μM against AG83 and 3.80 ± 0.126 μM against BHU-575) against the Leishmania donovani parasite, better than miltefosine (IC₅₀ 19.61 ± 0.093 μM against AG83 and 23.20 ± 0.094 μM against BHU-575). Holanamine inhibited the L. donovani topoisomerase 1B (LdToP1B) in a non-competitive manner (IC₅₀ 2.81 ± 0.105 μM), indicating that it interacts with the free enzyme and enzyme-DNA complex without inhibiting human topoisomerase. Hydrogen bonding and hydrophobic interactions of holanamine with the N-terminal and hinge region of the large subunit of LTop1B is responsible for its potent antileishmanial activity, as shown by docking studies. Treatment with holanamine causes apoptotic-like cell death by generating cellular and mitochondrial reactive oxygen species, disrupting the mitochondrial membrane potential and inducing ultrastructural alterations in the promastigotes. Holanamine effectively clears intracellular amastigotes but minimally affects host macrophages with no significant cytotoxicity in HEK 293 and L929 cell lines. Thus, our studies show that holanamine can further be used to develop effective antileishmanial agents against evolving drug-resistant parasites.

Voacamine is a novel inhibitor of EGFR exerting oncogenic activity against colorectal cancer through the mitochondrial pathway

Colorectal cancer (CRC), among the most aggressive and prevailing neoplasms, is primarily treated with chemotherapy. Voacamine (VOA), a novel bisindole natural product, possesses a variety of conspicuous pharmacological activities. Within the current research, we evaluated in vitro and in vivo the anticancer efficacy of VOA against CRC and its potential mechanisms. Our results illustrated that VOA concentrationdependently suppressed the proliferation and migration of CT26 and HCT116 cells as correspondingly indicated by IC₅₀ values of 1.38 ± 0.09 μM and 4.10 ± 0.14 μM. Furthermore, treatment of VOA also suppressed tumor cell colony formation, escalated the late-stage apoptosis rate of tumor cells, and evoked cell cycle of CT26 and HCT116 cells arrest inhibition in G2-M and G0-G1 phases, respectively. Meanwhile, VOA markedly disrupted the mitochondrial membrane potential eliciting mitochondrial dysfunction, decreased ATP production, and intermediated an enhanced accumulation of intracellular reactive oxygen species with a concentration-dependent pattern, accompanied by elevated expression levels of pro-apoptotic related protein Bax, Cyt-C, cleaved caspases 3/8/9 and by diminished Bcl-2, Bid, PRAP and caspases 3/8/9 expression. Further mechanistic studies revealed VOA treatment suppressed the EGFR/PI3K/Akt pathway with the evidence of the decreased phosphorylation proteins of EGFR, PI3K, Akt, and downstream proteins of p-mTOR, p-NF-kB, and p-P70S6. Additionally, molecular dynamics simulations further displayed VOA could enter the EGFR pocket followed by multiple mutual interaction effects. Interestingly, the EGFR activator (NSC228155) could slack the inhibitory capability of VOA on the EGFR/PI3K/Akt pathway as well as VOA-induced impairment of mitochondrial function. Finally, administration of VOA (15, 30 mg/kg every 2 days, i.p., for 16 days) in CT26 syngeneic mice dose-dependently suppressed the neoplastic development without appreciable organ toxicities. Taken together, our study demonstrated that VOA may be a prospective therapeutic agent for the treatment of CRC.

Type II DNA Topoisomerases in trypanosomatid and apicomplexan parasites

Diseases caused by trypanosomatid parasites have no commercially available vaccines for human application. Treatment modalities completely rely on chemotherapeutics strategies that often exhibit clinical drawbacks, like host toxicity, side effects and treatment failure for drug resistance. These, in many instances, are costly, making them unaffordable for certain groups of beneficiaries. To find reasonable solutions, researchers are attempting to identify and validate new drug targets that would offer parasite specificity. DNA topoisomerases in parasites present a consolidated class of drug targets due to their multiple structural and functional differences with host homologs. Type II DNA topoisomerases in these parasites, in particular, have been attracting interest of scientific community attributable to their pivotal role in the replication of the atypical DNA. In this article, we present a detailed review of structural and functional features of type II DNA topoisomerases of clinically-relevant trypanosomatid and apicomplexan parasites. Also, we provide up-to-date information on different molecules that target these enzymes. Altogether, the review will largely help in understanding the rationale for exploiting type II DNA topoisomerases in these groups of parasites as drug targets.

Discovery of 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-one derivatives as possible antileishmanial agents

A series of uniquely functionalized 2,3,-dihydro-1H-pyyrolo[3,4-b]quinolin-1-one derivatives were synthesized in one to two steps by utilizing a post-Ugi modification strategy and were evaluated for antileishmanial efficacy against visceral leishmaniasis (VL). Among the library compounds, compound 5m exhibited potential in vitro antileishmanial activity (CC50 = 65.11 μM, SI = 7.79, anti-amastigote IC50 = 8.36 μM). In vivo antileishmanial evaluation of 5m demonstrated 56.2% inhibition in liver and 61.1% inhibition in spleen parasite burden in infected Balb/c mice (12.5 mg kg-1, i.p.). In vitro pharmacokinetic study ascertained the stability of 5m in both simulated gastric fluid and simulated intestinal fluid. All the active compounds passed the PAINS filter and showed no toxicity in in silico predictions.

Activity of alkaloids from Aspidosperma nitidum against Leishmania (Leishmania) amazonensis

This study evaluated the morphological changes caused by fractions and subfractions, obtained from barks of Aspidosperna nitidum, against L. (L.) amazonensis promastigotes. The ethanolic extract (EE) obtained through the maceration of trunk barks was subjected to an acid-base partition, resulting the neutral (FN) and the alkaloid (FA) fractions, and fractionation under reflux, yielded hexane (FrHEX), dichloromethane (FrDCL), ethyl acetate (FrACoET), and methanol (FrMEOH) fractions. The FA was fractionated and three subfractions (SF5-6, SF8, and SF9) were obtained and analyzed by HPLC-DAD and 1H NMR. The antipromastigote activity of all samples was evaluated by MTT, after that, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the active fractions were performed. Chromatographic analyzes suggest the presence of alkaloids in EE, FN, FA, and FrDCL. The fractionation of FA led to the isolation of the indole alkaloid dihydrocorynantheol (SF8 fractions). The SF5-6, dihydrocorynantheol and SF-9 samples were active against promastigotes, while FrDCL was moderately active. The SEM analysis revealed cell rounding and changes in the flagellum of the parasites. In the TEM analysis, the treated promastigotes showed changes in flagellar pocket and kinetoplast, and presence of lipid inclusions. These results suggest that alkaloids isolated from A. nitidum are promising as leishmanicidal.

Activation of mitochondrial-associated apoptosis signaling pathway and inhibition of PI3K/Akt/mTOR signaling pathway by voacamine suppress breast cancer progression

BACKGROUND

Breast cancer is one of the malignant tumors with the highest morbidity and mortality rate. Numerous efficient anti-breast cancer drugs are being derived from the development of natural products. Voacamine (VOA), a bisindole alkaloid isolated from Voacanga africana Stapf, possesses various pharmacological and biological activities.

PURPOSE

In this study, we investigated the efficacy of VOA against breast cancer cells and elucidated the underlying mechanisms in vitro and in vivo.

METHODS

Human breast cancer cell line MCF-7 and mouse breast cancer cell line 4T1 were used to study the underlying anti-cancer mechanisms of VOA. The proliferation was detected by MTT, colony formation, cell proliferation and wound-healing migration assays. Flow cytometry was utilized to determine the level of reactive oxygen species (ROS) cell-cycle, apoptosis and mitochondrial membrane potential. The target proteins were analyzed by Western blot. Molecular docking was performed and scored by AutoDock. Subcutaneous cancer models in mice were established to evaluate the anticancer effects in vivo.

RESULT

Our results demonstrated that VOA selectively suppressed breast cancer MCF-7 and 4T1 cells proliferation with IC50 values of 0.99 and 1.48 μM, and significantly inhibited the migration and colony formation of tumor cells. Furthermore, the cell cycle was arrested in the S phase with the decreased expression levels of CDK2, Cyclin A and Cyclin E. Additionally, exposure to VOA dose-dependently brought about dose-dependently the loss of mitochondrial membrane potential (Δψm) and amassment of reactive oxygen species (ROS), resulting in the initiation of the intrinsic apoptotic pathway. Western blot analysis unveiled that VOA significantly activated mitochondrial-associated apoptosis and obviously suppress the PI3K/Akt/mTOR pathway via modulation of related protein expression levels in both tumor cell lines. In tumor-bearing mouse models, administration of VOA dose-dependently inhibited the tumor growth without causing apparent toxicities.

CONCLUSION

These findings revealed the novel properties of VOA in promoting apoptosis of breast cancer cells by activating mitochondrial-associated apoptosis signaling pathway and inhibiting PI3K/Akt/mTOR signaling pathway and significantly decreasing tumor size without detecting appreciable toxicity. In summary, the present results demonstrated VOA could be an encouraging drug candidate to cure breast cancer, exhibiting an effective method to exploit unique drugs from natural components.

TDP1 knockout Leishmania donovani accumulate topoisomerase 1-linked DNA damage and are hypersensitive to clinically used antileishmanial drugs

Leishmania donovani, a unicellular protozoan parasite, causes a wide range of human diseases including fatal visceral leishmaniasis. Tyrosyl DNA-phosphodiesterase 1 (TDP1) hydrolyzes the phosphodiester bond between DNA 3'-end and a tyrosyl moiety of trapped topoisomerase I-DNA covalent complexes (Top1cc). We have previously shown Leishmania harbors a TDP1 gene (LdTDP1), however, the biological role of TDP1 remains largely unknown. In the present study, we have generated TDP1 knockout L. donovani (LdTDP1^-/- ) promastigotes and have shown that LdTDP1^-/- parasites are deficient in 3'-phosphodiesterase activities and were hypersensitive to Top1-poison like camptothecin (CPT), DNA alkylation agent like methyl methanesulfonate, and oxidative DNA lesions generated by hydrogen peroxide but were not sensitive to etoposide. We also detected elevated levels of CPT-induced reactive oxygen species triggering cell cycle arrest and cell death in LdTDP1^-/- promastigotes. LdTDP1^-/- promastigotes accumulate a significant change in the membrane morphology with the accumulation of membrane pores, which is associated with oxidative stress and lipid peroxidation. To our surprise, we detected that LdTDP1^-/- parasites were hypersensitive to antileishmanial drugs like amphotericin B and miltefosine, which could be rescued by complementation of wild-type TDP1 gene in the LdTDP1^-/- parasites. Notably, multidrug-resistant L. donovani clinical isolates showed a marked reduction in TDP1 expression and were sensitive to Top1 poisons. Taken together, our study provides a new role of LdTDP1 in protecting L. donovani parasites from oxidative stress-induced DNA damage and resistance to amphotericin B and miltefosine.

Iboga Inspired N-Indolylethyl-Substituted Isoquinuclidines as a Bioactive Scaffold: Chemoenzymatic Synthesis and Characterization as GDNF Releasers and Antitrypanosoma Agents

The first stage of the drug discovery process involves the identification of small compounds with biological activity. Iboga alkaloids are monoterpene indole alkaloids (MIAs) containing a fused isoquinuclidine-tetrahydroazepine ring. Both the natural products and the iboga-inspired synthetic analogs have shown a wide variety of biological activities. Herein, we describe the chemoenzymatic preparation of a small library of novel N-indolylethyl-substituted isoquinuclidines as iboga-inspired compounds, using toluene as a starting material and an imine Diels-Alder reaction as the key step in the synthesis. The new iboga series was investigated for its potential to promote the release of glial cell line-derived neurotrophic factor (GDNF) by C6 glioma cells, and to inhibit the growth of infective trypanosomes. GDNF is a neurotrophic factor widely recognized by its crucial role in development, survival, maintenance, and protection of dopaminergic neuronal circuitries affected in several neurological and psychiatric pathologies. Four compounds of the series showed promising activity as GDNF releasers, and a leading structure (compound 11) was identified for further studies. The same four compounds impaired the growth of bloodstream Trypanosoma brucei brucei (EC₅₀ 1-8 μM) and two of them (compounds 6 and 14) showed a good selectivity index.

The Potential of Traditional Knowledge to Develop Effective Medicines for the Treatment of Leishmaniasis

Leishmaniasis is a neglected tropical disease that affects people living in tropical and subtropical areas of the world. There are few therapeutic options for treating this infectious disease, and available drugs induce severe side effects in patients. Different communities have limited access to hospital facilities, as well as classical treatment of leishmaniasis; therefore, they use local natural products as alternative medicines to treat this infectious disease. The present work performed a bibliographic survey worldwide to record plants used by traditional communities to treat leishmaniasis, as well as the uses and peculiarities associated with each plant, which can guide future studies regarding the characterization of new drugs to treat leishmaniasis. A bibliographic survey performed in the PubMed and Scopus databases retrieved 294 articles related to traditional knowledge, medicinal plants and leishmaniasis; however, only 20 were selected based on the traditional use of plants to treat leishmaniasis. Considering such studies, 378 quotes referring to 292 plants (216 species and 76 genera) that have been used to treat leishmaniasis were recorded, which could be grouped into 89 different families. A broad discussion has been presented regarding the most frequent families, including Fabaceae (27 quotes), Araceae (23), Solanaceae and Asteraceae (22 each). Among the available data in the 378 quotes, it was observed that the parts of the plants most frequently used in local medicine were leaves (42.3% of recipes), applied topically (74.6%) and fresh poultices (17.2%). The contribution of Latin America to studies enrolling ethnopharmacological indications to treat leishmaniasis was evident. Of the 292 plants registered, 79 were tested against Leishmania sp. Future studies on leishmanicidal activity could be guided by the 292 plants presented in this study, mainly the five species Carica papaya L. (Caricaceae), Cedrela odorata L. (Meliaceae), Copaifera paupera (Herzog) Dwyer (Fabaceae), Musa × paradisiaca L. (Musaceae), and Nicotiana tabacum L. (Solanaceae), since they are the most frequently cited in articles and by traditional communities.

Green Approach: ''A Forwarding Step for Curing Leishmaniasis-A Neglected Tropical Disease''

The present review focuses on a dreaded vector-mediated leishmaniasis, with the existing therapeutic approaches including a variety of drugs along with their limitations, the treatment with natural compounds, and different types of metal/metal oxide nanoparticles (NPs). As evidenced, various metallic NPs, comprising silver, silver oxide, gold, zinc oxide, titanium, lead oxide, etc., played a curative role to treat leishmaniasis, are also presented. Keeping in view the advance success of vaccines against the prevalent dreaded diseases in the past and the present scenario, efforts are also being made to develop vaccines based on these NP formulations.

Furan derivatives impair proliferation and affect ultrastructural organization of Trypanosoma cruzi and Leishmania amazonensis

Chagas disease and leishmaniasis are neglected diseases caused by parasites of the Trypanosomatidae family and together they affect millions of people in the five continents. The treatment of Chagas disease is based on benznidazole, whereas for leishmaniasis few drugs are available, such as amphotericin B and miltefosine. In both cases, the current treatment is not entirely efficient due to toxicity or side effects. Encouraged by the need to discover valid targets and new treatment options, we evaluated 8 furan compounds against Trypanosoma cruzi and Leishmania amazonensis, considering their effects against proliferation, infection, and ultrastructure. Many of them were able to impair T. cruzi and L. amazonensis proliferation, as well as cause ultrastructural alterations, such as Golgi apparatus disorganization, autophagosome formation, and mitochondrial swelling. Taken together, the results obtained so far make these compounds eligible for further steps of chemotherapy study.

Amino acid-derived defense metabolites from plants: A potential source to facilitate novel antimicrobial development

For millennia, humanity has relied on plants for its medicines, and modern pharmacology continues to reexamine and mine plant metabolites for novel compounds and to guide improvements in biological activity, bioavailability, and chemical stability. The critical problem of antibiotic resistance and increasing exposure to viral and parasitic diseases has spurred renewed interest into drug treatments for infectious diseases. In this context, an urgent revival of natural product discovery is globally underway with special attention directed toward the numerous and chemically diverse plant defensive compounds such as phytoalexins and phytoanticipins that combat herbivores, microbial pathogens, or competing plants. Moreover, advancements in “omics,” chemistry, and heterologous expression systems have facilitated the purification and characterization of plant metabolites and the identification of possible therapeutic targets. In this review, we describe several important amino acid–derived classes of plant defensive compounds, including antimicrobial peptides (e.g., defensins, thionins, and knottins), alkaloids, nonproteogenic amino acids, and phenylpropanoids as potential drug leads, examining their mechanisms of action, therapeutic targets, and structure–function relationships. Given their potent antibacterial, antifungal, antiparasitic, and antiviral properties, which can be superior to existing drugs, phytoalexins and phytoanticipins are an excellent resource to facilitate the rational design and development of antimicrobial drugs.

Repurposing topical triclosan for cutaneous leishmaniasis: Preclinical efficacy in a murine Leishmania (L.) amazonensis model

Leishmaniasis remains an important neglected tropical infection caused by the protozoan Leishmania and affects 12 million people in 98 countries. The treatment is limited with severe adverse effects. In the search for new therapies, the drug repositioning and combination therapy have been successfully applied to neglected diseases. The aim of the present study was to evaluate the in vitro and in vivo anti-Leishmania (Leishmania) amazonensis potential of triclosan, an approved topical antimicrobial agent used for surgical procedures. in vitro phenotypic studies of drug-treated parasites were performed to evaluate the lethal action of triclosan, accompanied by an isobolographic ex-vivo analysis with the association of triclosan and miltefosine. The results showed that triclosan has activity against L. (L.) amazonensis intracellular amastigotes, with a 50% inhibitory concentration of 16 μM. By using fluorescent probes and transmission electron microscopy, a pore-forming activity of triclosan toward the parasite plasma membrane was demonstrated, leading to depolarization of the mitochondrial membrane potential and reduction of the reactive oxygen species levels in the extracellular promastigotes. The in vitro interaction between triclosan and miltefosine in the combination therapy assay was classified as additive against intracellular amastigotes. Leishmania-infected mice were treated with topical triclosan (1% base cream for 14 consecutive days), and showed 89% reduction in the parasite burden. The obtained results contribute to the investigation of new alternatives for the treatment of cutaneous leishmaniasis and suggest that the coadministration of triclosan and miltefosine should be investigated in animal models.

Stress-responsive Entamoeba topoisomerase II: a potential antiamoebic target

Topoisomerases, the ubiquitous enzymes involved in all DNA processes across the biological world, are targets for various anticancer and antimicrobial agents. In Entamoeba histolytica, the causative agent of amebiasis, we found one of seven unexplored putative topoisomerases to be highly upregulated during heat shock and oxidative stress, and also during the late hours of encystation. Further analysis revealed the upregulated enzyme to be a eukaryotic type IIA topoisomerase (TopoII) with demonstrable activity in vitro. This enzyme is localized to newly forming nuclei during encystation. Gene silencing of the TopoII reduces viability and encystation efficiency. Notable susceptibility of Entamoeba TopoII to prokaryotic topoisomerase inhibitors opens up the possibility for exploring this enzyme as a new antiamoebic target.

Influence of lipid composition on the ability of liposome loaded voacamine to improve the reversion of doxorubicin resistant osteosarcoma cells

The plant alkaloid voacamine (VOA) displays many interesting pharmacological activities thus, considering its scarce solubility in water, its encapsulation into liposome formulations for its delivery is an important goal. Different cationic liposome formulations containing a phospholipid, cholesterol and one of two diasteromeric cationic surfactants resulted able to maintain a stable transmembrane difference in ammonium sulfate concentration and/or pH gradient and to accumulate VOA in their internal aqueous bulk. The fluidity of the lipid bilayer affects both the ability to maintain a stable imbalance of protons and/or ammonium ions across the membrane and the entrapment efficiency. It was shown that VOA loaded into liposomes is more efficient than the free alkaloid to revert resistance of osteosarcoma cells resistant to doxorubicin to an extent depending on their composition.

Enhanced Solubility of Alkaloids by Complexation with Polycarboxylic Materials for Controlled Release Formulations: Case of Peschiera fuchsiaefolia

Malaria is a major public health problem with hundreds of thousands of deaths yearly. Extracts of Peschiera fuchsiaefolia (Pf), an Apocynaceae family plant, are used as malaria treatment by several populations. Artemisinin is another effective largely used antimalarial agent but susceptible to generate resistant forms of Plasmodium. To reduce the risk of new resistant strains' appearance, the WHO recommended artemisinin-based combination therapy (ACT) with another bioactive agent, ensuring a long duration of antiplasmodial activity. Pf alkaloids are good candidates for ACT, but their solubility is very low. This research was aimed to improve the solubility of Pf alkaloids by complexation via their amine groups with carboxylate groups of carboxymethylstarch (CMS), an excipient used to formulate oral dosage forms for controlled drug release. It was found that when complexed as CMS-Pf, the solubility of Pf is increased (four to five times in function of dissolution medium). A new specific and faster approach to evaluate the solubility was proposed, measuring the effective saturation concentration of the compound of interest via one of its specific capacities, i.e., absorption capacity at a specific wavelength or antioxidant properties. This approach is more convenient for solubility evaluation of various active agents from complexes or crude extracts, or in heterogeneous samples. Also, the storage stability was markedly improved from 1 week for Pf co-processed with maltodextrin (MD/Pf) to several months for CMS-Pf (in similar controlled temperature and humidity conditions). The co-processing as MD/Pf or complexation as CMS-Pf affected physical properties but not the biological (i.e., antioxidant) activity of Pf.

DNA Topoisomerases in Unicellular Pathogens: Structure, Function, and Druggability

All organisms, including unicellular pathogens, compulsorily possess DNA topoisomerases for successful nucleic acid metabolism. But particular subtypes of topoisomerases exist, in all prokaryotes and in some unicellular eukaryotes, that are absent in higher eukaryotes. Moreover, topoisomerases from pathogenic members of a niche possess some unique molecular architecture and functionalities completely distinct from their nonpathogenic colleagues. This review will highlight the unique attributes associated with the structures and functions of topoisomerases from the unicellular pathogens, with special reference to bacteria and protozoan parasites. It will also summarise the progress made in the domain pertaining to the druggability of these topoisomerases, upon which a future platform for therapeutic development can be successfully constructed.

Isobenzofuranone derivative JVPH3, an inhibitor of L. donovani topoisomerase II, disrupts mitochondrial architecture in trypanosomatid parasites

Kinetoplast DNA (kDNA) bearing unusual mitochondrion of trypanosomatid parasites offers a new paradigm in chemotherapy modality. Topoisomerase II of Leishmania donovani (LdTopII), a key enzyme associated with kDNA replication, is emerging as a potential drug target. However, mode of action of LdTopII targeted compounds in the parasites at sub-cellular level remains largely unknown. Previously, we reported that an isobenzofuranone derivative, namely 3,5-bis(4-chlorophenyl)-7-hydroxyisobenzofuran-1(3H)-one (JVPH3), targets LdTopII and induces apoptosis-like cell death in L. donovani. Here, we elucidate the phenotypic changes and the events occurring at sub-cellular level caused by JVPH3 in L. donovani. In addition, we have evaluated the cytotoxicity and ultrastructural alterations caused by JVPH3 in two brazilian trypanosomatid pathogens viz. L. amazonensis and Trypanosoma cruzi. Despite killing these parasites, JVPH3 caused significantly different phenotypes in L. donovani and L. amazonensis. More than 90% population of parasites showed altered morphology. Mitochondrion was a major target organelle subsequently causing kinetoplast network disorganization in Leishmania. Altered mitochondrial architecture was evident in 75–80% Leishmania population being investigated. Quantification of mitochondrial function using JC-1 fluorophore to measure a possible mitochondrial membrane depolarization further confirmed the mitochondrion as an essential target of the JVPH3 corroborating with the phenotype observed by electron microscopy. However, the impact of JVPH3 was lesser on T. cruzi than Leishmania. The molecule caused mitochondrial alteration in 40% population of the epimastigotes being investigated. To our knowledge, this is the first report to evaluate the proliferation pattern and ultrastructural alterations caused in Brazilian kinetoplastid pathogens by a synthetic LdTopII inhibitor previously established to have promising in vivo activity against Indian strain of L. donovani.