Anti-malarial activity of geldanamycin derivatives in mice infected with Plasmodium yoelii

Backbone-enabled modification of peptides with benzoquinone via palladium-catalyzed δ-C(sp2)-H functionalization

Backbone-enabled site-selective modification of peptides with benzoquinone via Pd-catalyzed δ-C(sp2)-H functionalization has been achieved. The amide groups of peptides serve as internal directional groups, facilitating C-H functionalization through a kinetically less favored six-membered palladacycle. This methodology presents novel opportunities for the late-stage site-selective diversification of peptides.

Identification of Plasmodium falciparum heat shock 90 inhibitors via molecular docking

A virtual screen was performed to identify anti-malarial compounds targeting Plasmodium falciparum heat shock 90 protein by applying a series of drug-like and commercial availability filters to compounds in the ZINC database, resulting in a virtual library of more than 13 million candidates. The goal of the virtual screen was to identify novel compounds which could serve as a starting point for the development of antimalarials with a mode of action different from anything currently used in the clinic. The screen targeted the ATP binding pocket of the highly conserved Plasmodium heat shock 90 protein, as this protein is critical to the survival of the parasite and has several significant structural differences from the human homolog. The top twelve compounds from the virtual screen were tested in vitro, with all twelve showing no antiproliferative activity against the human fibroblast cell line and three compounds exhibiting single digit or better micromolar antiproliferative activity against the chloroquine-sensitive P. falciparum 3D7 strain.

Antimalarial application of quinones: A recent update

Atovaquone belongs to a naphthoquinone class of drugs and is used in combination with proguanil (Malarone) for the treatment of acute, uncomplicated malaria caused by Plasmodium falciparum (including chloroquine-resistant P. falciparum/P. vivax). Numerous quinone-derived compounds have attracted considerable attention in the last few decades due to their potential in antimalarial drug discovery. Several semi-synthetic derivatives of natural quinones, synthetic quinones (naphtho-/benzo-quinone, anthraquinones, thiazinoquinones), and quinone-based hybrids were explored for their in vitro and in vivo antimalarial activities. A careful literature survey revealed that this topic has not been compiled as a review article so far. Therefore, we herein summarise the recent discovery (the year 2009-2020) of quinone based antimalarial compounds in chronological order. This compilation would be very useful towards the exploration of novel quinone-derived compounds against malarial parasites with promising efficacy and lesser side effects.

Proteomic analysis of Plasmodium falciparum histone deacetylase 1 complex proteins

Plasmodium falciparum histone deacetylases (PfHDACs) are an important class of epigenetic regulators that alter protein lysine acetylation, contributing to regulation of gene expression and normal parasite growth and development. PfHDACs are therefore under investigation as drug targets for malaria. Despite this, our understanding of the biological roles of these enzymes is only just beginning to emerge. In higher eukaryotes, HDACs function as part of multi-protein complexes and act on both histone and non-histone substrates. Here, we present a proteomics analysis of PfHDAC1 immunoprecipitates, identifying 26 putative P. falciparum complex proteins in trophozoite-stage asexual intraerythrocytic parasites. The co-migration of two of these (P. falciparum heat shock proteins 70-1 and 90) with PfHDAC1 was validated using Blue Native PAGE combined with Western blot. These data provide a snapshot of possible PfHDAC1 interactions and a starting point for future studies focused on elucidating the broader function of PfHDACs in Plasmodium parasites.

Hexaricins, Pradimicin-like Polyketides from a Marine Sediment-Derived Streptosporangium sp. and Their Antioxidant Effects

Seven pradimicin-like polyketides were isolated from the dichloromethane extract of the marine sediment-derived Streptosporangium sp. CGMCC 4.7309, including five new hexaricins, D-H (1-5), and known hexaricins A (6) and C (7). Their structures were determined by HRESIMS, 1D and 2D NMR, and other spectroscopic analyses. The absolute configurations of compounds 1-5 were determined on the basis of circular dichroism and specific rotation data. All isolated compounds 1-7 were tested for their antioxidant capacities by DPPH^• scavenging, ^•OH scavenging, and ^•O₂̅ scavenging assays. Compounds 3 and 4 displayed stronger antioxidant activities than the positive control ( tert-butylhydroquinone). The relationship between structure and antioxidant activity is discussed. These compounds could be effective natural antioxidants with considerable pharmaceutical value.

Model System Identifies Kinetic Driver of Hsp90 Inhibitor Activity against African Trypanosomes and Plasmodium falciparum

Hsp90 inhibitors, well studied in the laboratory and clinic for antitumor indications, have promising activity against protozoan pathogens, including Trypanosoma brucei which causes African sleeping sickness, and the malaria parasite, Plasmodium falciparum To progress these experimental drugs toward clinical use, we adapted an in vitro dynamic hollow-fiber system and deployed artificial pharmacokinetics to discover the driver of their activity: either concentration or time. The activities of compounds from three major classes of Hsp90 inhibitors in development were evaluated against trypanosomes. In all circumstances, the activities of the tested Hsp90 inhibitors were concentration driven. By optimally deploying the drug to match its kinetic driver, the efficacy of a given dose was improved up to 5-fold, and maximal efficacy was achieved with a significantly lower drug exposure. The superiority of concentration-driven regimens was evident in vitro over several logs of drug exposure and was predictive of efficacy in a mouse model of African trypanosomiasis. In studies with P. falciparum, antimalarial activity was similarly concentration driven. This experimental strategy offers an expedient and versatile translational tool to assess the impact of pharmacokinetics on antiprotozoal activity. Knowing kinetic governance early in drug development provides an additional metric for judging lead compounds and allows the incisive design of animal efficacy studies.

HSQC-TOCSY Fingerprinting-Directed Discovery of Antiplasmodial Polyketides from the Marine Ascidian-Derived Streptomyces sp. (USC-16018)

Chemical investigations on the fermentation extract obtained from an ascidian-derived Streptomyces sp. (USC-16018) yielded a new ansamycin polyketide, herbimycin G (1), as well as a known macrocyclic polyketide, elaiophylin (2), and four known diketopiperazines (3–6). The structures of the compounds were elucidated based on 1D/2D NMR and MS data. The absolute configuration of 1 was established by comparison of experimental and predicted electronic circular dichroism (ECD) data. Antiplasmodial activities were tested for the natural products against chloroquine sensitive (3D7) and chloroquine resistant (Dd2) Plasmodium falciparum strains; the two polyketides (1–2) demonstrated an inhibition of >75% against both parasite strains and while 2 was highly cytotoxic, herbimycin G (1) showed no cytotoxicity and good predicted water solubility.

HSQC-TOCSY Fingerprinting for Prioritization of Polyketide- and Peptide-Producing Microbial Isolates

Microbial products are a promising source for drug leads as a result of their unique structural diversity. However, reisolation of already known natural products significantly hampers the discovery process, and it is therefore important to incorporate effective microbial isolate selection and dereplication protocols early in microbial natural product studies. We have developed a systematic approach for prioritization of microbial isolates for natural product discovery based on heteronuclear single-quantum correlation-total correlation spectroscopy (HSQC-TOCSY) nuclear magnetic resonance profiles in combination with antiplasmodial activity of extracts. The HSQC-TOCSY experiments allowed for unfractionated microbial extracts containing polyketide and peptidic natural products to be rapidly identified. Here, we highlight how this approach was used to prioritize extracts derived from a library of 119 ascidian-associated actinomycetes that possess a higher potential to produce bioactive polyketides and peptides.

Identification of Hsp90 Inhibitors with Anti-Plasmodium Activity

Malaria remains a global health burden partly due to Plasmodium parasite resistance to first-line therapeutics. The molecular chaperone heat shock protein 90 (Hsp90) has emerged as an essential protein for blood-stage Plasmodium parasites, but details about its function during malaria's elusive liver stage are unclear. We used target-based screens to identify compounds that bind to Plasmodium falciparum and human Hsp90, which revealed insights into chemotypes with species-selective binding. Using cell-based malaria assays, we demonstrate that all identified Hsp90-binding compounds are liver- and blood-stage Plasmodium inhibitors. Additionally, the Hsp90 inhibitor SNX-0723 in combination with the phosphatidylinositol 3-kinase inhibitor PIK-75 synergistically reduces the liver-stage parasite load. Time course inhibition studies with the Hsp90 inhibitors and expression analysis support a role for Plasmodium Hsp90 in late-liver-stage parasite development. Our results suggest that Plasmodium Hsp90 is essential to liver- and blood-stage parasite infections and highlight an attractive route for development of species-selective PfHsp90 inhibitors that may act synergistically in combination therapies to prevent and treat malaria.

Identification and characterization of the antiplasmodial activity of Hsp90 inhibitors

Background

The recent reduction in mortality due to malaria is being threatened by the appearance of Plasmodium falciparum parasites that are resistant to artemisinin in Southeast Asia. To limit the impact of resistant parasites and their spread across the world, there is a need to validate anti-malarial drug targets and identify new leads that will serve as foundations for future drug development programmes targeting malaria. Towards that end, the antiplasmodial potential of several Hsp90 inhibitors was characterized. Because, the Hsp90 chaperone has been suggested as a good drug target against multiple parasitic infections including malaria.

Results

Chemically diverse sets of Hsp90 inhibitors, evaluated in clinical trials as anti-cancer agents, were tested against the malaria parasite. Most of the compounds showed strong antiplasmodial activity in growth inhibition assays against chloroquine sensitive and resistant strains. There was a good agreement between the compound in vitro anti-parasitic activity and their affinity against the Plasmodium chaperone. The two most potent Hsp90 inhibitors also showed cytocidal activity against two P. falciparum strains. Their antiplasmodial activity affected all parasite forms during the malaria blood cycle. However, the compounds activity against the parasite showed no synergy when combined with anti-malarial drugs, like chloroquine or DHA.

Discussion

The Hsp90 inhibitors anti-parasitic activity correlates with their affinity to their predicted target the P. falciparum chaperone Hsp90. However, the most effective compounds also showed high affinity for a close homologue, Grp94. This association points to a mode of action for Hsp90 inhibitors that correlate compound efficacy with multi-target engagement. Besides their ability to limit parasite replication, two compounds also significantly impacted P. falciparum viability in vitro. Finally, a structural analysis suggests that the best hit represents a promising scaffold to develop parasite specific leads according.

Conclusion

The results shown that Hsp90 inhibitors are lethal against the malaria parasite. The correlation between biochemical and in vitro data strongly supports Hsp90 as a drug target against the malaria parasite. Furthermore, at least one Hsp90 inhibitor developed as anticancer therapeutics could serve as starting point to generate P. falciparum-specific lead compounds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1940-7) contains supplementary material, which is available to authorized users.

In vitro and in vivo anti-malarial activity of novel harmine-analog heat shock protein 90 inhibitors: a possible partner for artemisinin

Background

The emergence of artemisinin-resistant Plasmodium falciparum strains poses a serious challenge to the control of malaria. This necessitates the development of new anti-malarial drugs. Previous studies have shown that the natural beta-carboline alkaloid harmine is a promising anti-malarial agent targeting the P. falciparum heat-shock protein 90 (PfHsp90). The aim of this study was to test the anti-malarial activity of harmine analogues.

Methods

Forty-two harmine analogues were synthesized and the binding of these analogues to P. falciparum heat shock protein 90 was investigated. The in vitro anti-malarial activity of two of the analogues, 17A and 21A, was evaluated using a 72-h growth inhibition assay. The in vivo anti-malarial activity was tested in Plasmodium berghei infection of BALB/c mice. The potential of 21A for a combination treatment with artemisinin was evaluated using in vivo combination study with dihydro-artemisinin in BALB/c mice. Cytotoxicity of the harmine analogues was tested in vitro using HepG2 and HeLa cell lines.

Results

17A and 21A bound to PfHsp90 with average IC₅₀ values of 12.2 ± 2.3 and 23.1 ± 8.8 µM, respectively. They also inhibited the P. falciparum W2 strain with average IC₅₀ values of 4.2 ± 1.3 and 5.7 ± 1.7 µM, respectively. In vivo, three daily injections of P. berghei-infected BALB/c mice with 100 mg/kg of either 17A or 21A showed significant reduction in parasitaemia with a 51.5 and 56.1% reduction, respectively. Mice treated with 17A and 21A showed a median survival time of 11 and 14 days, respectively, while the vehicle control mice survived a median of only 8.5 days. A dose-ranging experiment with 21A showed that the compound has a dose-dependent anti-malarial effect. Furthermore, treatment of infected mice with a combination of 21A and dihydroartemisinin (DHA) showed a dramatic reduction in parasitaemia compared to treatment with DHA alone.

Conclusion

A novel and non-toxic harmine analogue has been synthesized which binds to PfHsp90 protein, inhibits P. falciparum in vitro at micromolar concentration, reduces parasitaemia and prolongs survival of P. berghei-infected mice with an additive anti-malarial effect when combined with DHA.

Inhibition of Plasmodium falciparum Hsp90 Contributes to the Antimalarial Activities of Aminoalcohol-carbazoles

Malaria caused by the protozoan parasite Plasmodium falciparum (Pf) remains a major public health problem throughout the developing world. One molecular target that should receive more attention is the molecular chaperone Hsp90. It is essential and highly conserved in all eukaryotes, including in protozoan parasites. We have identified an amino-alcohol carbazole (N-CBZ) as a PfHsp90-selective inhibitor by virtually docking a large set of antimalarial compounds, previously found in a phenotypic screen, into a PfHsp90-specific pocket. By correlating the ability of 30 additional N-CBZ derivatives to bind directly to PfHsp90 with their Pf-inhibitory activity, we found that these types of compounds are more likely to inhibit Pf growth if they bind PfHsp90. For plausible targets such as PfHsp90, our workflow may help identifying the molecular target for compounds found by screening large chemical libraries for a desired biological effect and, conversely, ensuring biological effectiveness for compounds affecting a particular target.

Chemotherapeutic potential of 17-AAG against cutaneous leishmaniasis caused by Leishmania (Viannia) braziliensis

BACKGROUND

Leishmaniasis remains a worldwide public health problem. The limited therapeutic options, drug toxicity and reports of resistance, reinforce the need for the development of new treatment options. Previously, we showed that 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), a Heat Shock Protein 90 (HSP90)-specific inhibitor, reduces L. (L.) amazonensis infection in vitro. Herein, we expand the current knowledge on the leishmanicidal activity of 17-AAG against cutaneous leishmaniasis, employing an experimental model of infection with L. (V.) braziliensis.

METHODOLOGY/PRINCIPAL FINDINGS

Exposure of axenic L. (V.) braziliensis promastigotes to 17-AAG resulted in direct dose-dependent parasite killing. These results were extended to L. (V.) braziliensis-infected macrophages, an effect that was dissociated from the production of nitric oxide (NO), superoxide (O(-2)) or inflammatory mediators such as TNF-α, IL-6 and MCP-1. The leishmanicidal effect was then demonstrated in vivo, employing BALB/c mice infected with L. braziliensis. In this model, 17-AAG treatment resulted in smaller skin lesions and parasite counts were also significantly reduced. Lastly, 17-AAG showed a similar effect to amphotericin B regarding the ability to reduce parasite viability.

CONCLUSION/SIGNIFICANCE

17-AAG effectively inhibited the growth of L. braziliensis, both in vitro and in vivo. Given the chronicity of L. (V.) braziliensis infection and its association with mucocutaneous leishmaniasis, 17-AAG can be envisaged as a new chemotherapeutic alternative for cutaneous Leishmaniasis.

Mouse studies on inhibitors of Plasmodium falciparum Hsp90: progress and challenges

This review highlights studies conducted in murine models to evaluate the efficacy of compounds targeting Heat shock protein (Hsp) 90 of malaria. Both advances achieved and limitations that exist are highlighted.

A review of recent patents on the protozoan parasite HSP90 as a drug target

Diseases caused by protozoan parasites are still an important health problem. These parasites can cause a wide spectrum of diseases, some of which are severe and have high morbidity or mortality if untreated. Since they are still uncontrolled, it is important to find novel drug targets and develop new therapies to decrease their remarkable social and economic impact on human societies. In the past years, human HSP90 has become an interesting drug target that has led to a large number of investigations both at state organizations and pharmaceutical companies, followed by clinical trials. The finding that HSP90 has important biological roles in some protozoan parasites like Plasmodium spp, Toxoplasma gondii and trypanosomatids has allowed the expansion of the results obtained in human cancer to these infections. This review summarizes the latest important findings showing protozoan HSP90 as a drug target and presents three patents targeting T. gondii, P. falciparum and trypanosomatids HSP90.

Differences in conformational dynamics between Plasmodium falciparum and human Hsp90 orthologues enable the structure-based discovery of pathogen-selective inhibitors

The high sequence conservation of druggable pockets of closely related proteins can make it challenging to develop selective inhibitors. We designed a new drug discovery approach that exploits both the static and dynamic differences of two orthologues. We applied it, as a proof of concept, to identify compounds that discriminate between the molecular chaperone Hsp90 of the protozoan pathogen Plasmodium falciparum (Pf) and that of its human host. We found that the ATP-binding pocket has a Pf-specific extension, whose sequence lining is identical in human Hsp90 but which differs by tertiary structure and dynamics. Using these insights for a structure-based drug screen, we discovered novel 7-azaindole compounds that exclusively bind the recombinant N-terminal domain of PfHsp90 but not of human Hsp90 nor of a PfHsp90 mutant with "human-like" dynamics. Moreover, these compounds preferentially inhibit the growth of yeast complemented by PfHsp90 and block the growth of Pf in culture.