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To achieve malaria eradication, new preventative agents that act differently to front-line treatment drugs are needed. To identify potential chemoprevention starting points we screened a sub-set of the CSIRO Australia Compound Collection for compounds with slow-action in vitro activity against Plasmodium falciparum. This work identified N , N -dialkyl-5-alkylsulfonyl-1,3,4-oxadiazol-2-amines as a new antiplasmodial chemotype (e.g., 1 96 h IC 50 550 nM; 3 96 h IC 50 160 nM) with a different action to delayed-death slow-action drugs. A series of analogues were synthesized from thiotetrazoles and carbomoyl derivatives using Huisgen 1,3,4-oxadiazole synthesis followed by oxidation of the resultant thioethers to target sulfones. Structure activity relationship analysis of analogues identified compounds with potent and selective in vitro activity against drug-sensitive and multi-drug resistant Plasmodium parasites (e.g., 31 and 32 96 h IC 50 <40 nM; SI > 2500). Subsequent studies in mice with compound 1 , which had the best microsomal stability of the compounds assessed (T 1/2 >255 min), demonstrated rapid clearance and poor oral in vivo efficacy in a P. berghei murine malaria model. These data indicate that while N , N -dialkyl-5-alkylsulfonyl-1,3,4-oxadiazol-2-amines are a novel class of slow-acting antiplasmodial agents, the further development of this chemotype for malaria chemoprophylaxis will require pharmacokinetic profile improvements. [Display omitted] • New drugs are needed to achieve malaria eradication. • Novel 1,3,4-oxadiazoles with activity against malaria parasites were identified. • In vivo studies indicated that pharmacokinetic improvements are needed. [ABSTRACT FROM AUTHOR]

Malaria is caused by infection with Plasmodium parasites and results in significant health and economic impacts. Malaria eradication is hampered by parasite resistance to current drugs and the lack of a widely effective vaccine. Compounds that target epigenetic regulatory proteins, such as histone deacetylases (HDACs), may lead to new therapeutic agents with a different mechanism of action, thereby avoiding resistance mechanisms to current antimalarial drugs. The anticancer HDAC inhibitor AR-42, as its racemate (rac- AR-42), and 36 analogues were investigated for in vitro activity against P. falciparum. Rac- AR-42 and selected compounds were assessed for cytotoxicity against human cells, histone hyperacetylation, human HDAC1 inhibition and oral activity in a murine malaria model. Rac- AR-42 was tested for ex vivo asexual and in vitro exoerythrocytic stage activity against P. berghei murine malaria parasites. Rac- AR-42 and 13 achiral analogues were potent inhibitors of asexual intraerythrocytic stage P. falciparum 3D7 growth in vitro (IC 50 5–50 nM), with four of these compounds having >50-fold selectivity for P. falciparum versus human cells (selectivity index 56–118). Rac- AR-42 induced in situ hyperacetylation of P. falciparum histone H4, consistent with Pf HDAC(s) inhibition. Furthermore, rac- AR-42 potently inhibited P. berghei infected erythrocyte growth ex vivo (IC 50 40 nM) and P. berghei exoerythrocytic forms in hepatocytes (IC 50 1 nM). Oral administration of rac- AR-42 and two achiral analogues inhibited P. berghei growth in mice, with rac- AR-42 (50 mg/kg/day single dose for four days) curing all infections. These findings demonstrate curative properties for HDAC inhibitors in the oral treatment of experimental mouse malaria. [Display omitted] • HDAC inhibitors r ac- AR-42 and 13 analogues inhibit P. falciparum growth in vitro. • Rac- AR-42 inhibits P. berghei exoerythrocytic forms in hepatocytes (IC 50 1 nM). • Rac- AR-42 causes in situ hyperacetylation of P. falciparum histone H4. • Rac- AR-42 cures P. berghei infected mice with oral dosing. [ABSTRACT FROM AUTHOR]

The prevention and treatment of malaria requires a multi-pronged approach, including the development of drugs that have novel modes of action. Histone deacetylases (HDACs), enzymes involved in post-translational protein modification, are potential new drug targets for malaria. However, the lack of recombinant P. falciparum HDACs and suitable activity assays, has made the investigation of compounds designed to target these enzymes challenging. Current approaches are indirect and include assessing total deacetylase activity and protein hyperacetylation via Western blot. These approaches either do not allow differential compound effects to be determined or suffer from low throughput. Here we investigated dot blot and ELISA methods as new, higher throughput assays to detect histone lysine acetylation changes in P. falciparum parasites. As the ELISA method was found to be superior to the dot blot assay using the control HDAC inhibitor vorinostat, it was used to evaluate the histone H3 and H4 lysine acetylation changes mediated by a panel of six HDAC inhibitors that were shown to inhibit P. falciparum deacetylase activity. Vorinostat, panobinostat, trichostatin A, romidepsin and entinostat all caused an ~3-fold increase in histone H4 acetylation using a tetra-acetyl lysine antibody. Tubastatin A, the only human HDAC6-specific inhibitor tested, also caused H4 hyperacetylation, but to a lesser extent than the other compounds. Further investigation revealed that all compounds, except tubastatin A, caused hyperacetylation of the individual N-terminal H4 lysines 5, 8, 12 and 16. These data indicate that tubastatin A impacts P. falciparum H4 acetylation differently to the other HDAC inhibitors tested. In contrast, all compounds caused hyperacetylation of histone H3. In summary, the ELISA developed in this study provides a higher throughput approach to assessing differential effects of antiplasmodial compounds on histone acetylation levels and is therefore a useful new tool in the investigation of HDAC inhibitors for malaria. Image 1 • P. falciparum histone lysine acetylation was compared using dot blot and ELISA. • ELISA was more reproducible than dot blot in acetylation assays. • ELISA was used to assess acetylation changes induced by anti-cancer HDAC inhibitors. • Tubastatin A showed a different histone H4 acetylation profile to other compounds. • This new method will facilitate the study of HDAC inhibitors for malaria. [ABSTRACT FROM AUTHOR]

Bromodomain-containing proteins (BDPs) are involved in the regulation of eukaryotic gene expression. Compounds that bind and/or inhibit BDPs are of interest as tools to better understand epigenetic regulation, and as possible drug leads for different diseases, including malaria. In this study, we assessed the activity of 42 compounds demonstrated or predicted (using virtual screening of a pharmacophore model) to bind/inhibit eukaryotic BDPs for activity against Plasmodium falciparum malaria parasites. In silico docking studies indicated that all compounds are predicted to participate in a typical hydrogen bond interaction with the conserved asparagine (Asn1436) of the P. falciparum histone acetyltransferase ( Pf GCN5) bromodomain and a conserved water molecule. Only one compound (the dimethylisoxazole SGC-CBP30; a selective inhibitor of CREBBP (CBP) and EP300 bromodomains) is also predicted to have a salt-bridge between the morpholine nitrogen and Glu1389. When tested for in vitro activity against asynchronous asexual stage P. falciparum Dd2 parasites, all compounds displayed 50% growth inhibitory concentrations (IC 50 ) >10 μM. Further testing of the three most potent compounds using synchronous parasites for 72 h showed that SGC-CBP30 was the most active (IC 50 3.2 μM). In vitro cytotoxicity assays showed that SGC-CBP30 has ∼7-fold better selectivity for the parasites versus a human cell line (HEK 293). Together these data provide a possible starting point for future investigation of these, or related compounds, as tools to understand epigenetic regulation or as potential new drug leads. [ABSTRACT FROM AUTHOR]

In the past decade there has been a significant reduction in deaths due to malaria, in part due to the success of the gold standard antimalarial treatment - artemisinin combination therapies (ACTs). However the potential threat of ACT failure and the lack of a broadly effective malaria vaccine are driving efforts to discover new chemical entities (NCEs) to target this disease. The primary sulfonamide (PS) moiety is a component of several clinical drugs, including those for treatment of kidney disease, glaucoma and epilepsy, however this chemotype has not yet been exploited for malaria. In this study 31 PS compounds sourced from the GlaxoSmithKline (GSK) Tres Cantos antimalarial set (TCAMS) were investigated for their ability to selectively inhibit the in vitro growth of Plasmodium falciparum asexual stage malaria parasites. Of these, 14 compounds were found to have submicromolar activity (IC 50 0.16–0.89 μM) and a modest selectivity index (SI) for the parasite versus human cells (SI > 12 to >43). As the PS moiety is known to inhibit carbonic anhydrase (CA) enzymes from many organisms, the PS compounds were assessed for recombinant P. falciparum CA ( Pf CA) mediated inhibition of CO 2 hydration. The Pf CA inhibition activity did not correlate with antiplasmodial potency. Furthermore, no significant difference in IC 50 was observed for P. falciparum versus P. knowlesi (P > 0.05), a Plasmodium species that is not known to contain an annotated Pf CA gene. Together these data suggest that the asexual intraerythrocytic stage antiplasmodial activity of the PS compounds examined in this study is likely unrelated to Pf CA inhibition. [ABSTRACT FROM AUTHOR]

Malaria, schistosomiasis and leishmaniases are among the most prevalent tropical parasitic diseases and each requires new innovative treatments. Targeting essential parasite pathways, such as those that regulate gene expression and cell cycle progression, is a key strategy for discovering new drug leads. In this study, four clinically approved anti-cancer drugs (Vorinostat, Belinostat, Panobinostat and Romidepsin) that target histone/lysine deacetylase enzymes were examined for in vitro activity against Plasmodium knowlesi , Schistosoma mansoni , Leishmania amazonensis and L. donovani parasites and two for in vivo activity in a mouse malaria model. All four compounds were potent inhibitors of P. knowlesi malaria parasites (IC 50 9–370 nM), with belinostat, panobinostat and vorinostat having 8–45 fold selectivity for the parasite over human neonatal foreskin fibroblast (NFF) or human embryonic kidney (HEK 293) cells, while romidepsin was not selective. Each of the HDAC inhibitor drugs caused hyperacetylation of P. knowlesi histone H4. None of the drugs was active against Leishmania amastigote or promastigote parasites (IC 50 > 20 μM) or S. mansoni schistosomula (IC 50 > 10 μM), however romidepsin inhibited S. mansoni adult worm parings and egg production (IC 50 ∼10 μM). Modest in vivo activity was observed in P. berghei infected mice dosed orally with vorinostat or panobinostat (25 mg/kg twice daily for four days), with a significant reduction in parasitemia observed on days 4–7 and 4–10 after infection (P < 0.05), respectively. [ABSTRACT FROM AUTHOR]

Giardia duodenalis is an intestinal parasite that causes giardiasis, a widespread human gastrointestinal disease. Treatment of giardiasis relies on a small arsenal of compounds that can suffer from limitations including side-effects, variable treatment efficacy and parasite drug resistance. Thus new anti- Giardia drug leads are required. The search for new compounds with anti- Giardia activity currently depends on assays that can be labour-intensive, expensive and restricted to measuring activity at a single time-point. Here we describe a new in vitro assay to assess anti- Giardia activity. This image-based assay utilizes the Perkin-Elmer Operetta ® and permits automated assessment of parasite growth at multiple time points without cell-staining. Using this new approach, we assessed the “Malaria Box” compound set for anti- Giardia activity. Three compounds with sub-μM activity (IC 50 0.6–0.9 μM) were identified as potential starting points for giardiasis drug discovery. [ABSTRACT FROM AUTHOR]

Histone deacetylase (HDAC) enzymes work together with histone acetyltransferases (HATs) to reversibly acetylate both histone and non-histone proteins. As a result, these enzymes are involved in regulating chromatin structure and gene expression as well as other important cellular processes. HDACs are validated drug targets for some types of cancer, with four HDAC inhibitors clinically approved. However, they are also showing promise as novel drug targets for other indications, including malaria and other parasitic diseases. In this study the in vitro activity of four anti-cancer HDAC inhibitors was examined against parasites that cause malaria and trypanosomiasis. Three of these inhibitors, suberoylanilide hydroxamic acid (SAHA; vorinostat ® ), romidepsin (Istodax ® ) and belinostat (Beleodaq ® ), are clinically approved for the treatment of T-cell lymphoma, while the fourth, panobinostat, has recently been approved for combination therapy use in certain patients with multiple myeloma. All HDAC inhibitors were found to inhibit the growth of asexual-stage Plasmodium falciparum malaria parasites in the nanomolar range (IC 50 10–200 nM), while only romidepsin was active at sub-μM concentrations against bloodstream form Trypanosoma brucei brucei parasites (IC 50 35 nM). The compounds were found to have some selectivity for malaria parasites compared with mammalian cells, but were not selective for trypanosome parasites versus mammalian cells. All compounds caused hyperacetylation of histone and non-histone proteins in P. falciparum asexual stage parasites and inhibited deacetylase activity in P. falciparum nuclear extracts in addition to recombinant Pf HDAC1 activity. P. falciparum histone hyperacetylation data indicate that HDAC inhibitors may differentially affect the acetylation profiles of histone H3 and H4. [ABSTRACT FROM AUTHOR]

Parasitic diseases have an enormous health, social and economic impact and are a particular problem in tropical regions of the world. Diseases caused by protozoa and helminths, such as malaria and schistosomiasis, are the cause of most parasite related morbidity and mortality, with an estimated 1.1 million combined deaths annually. The global burden of these diseases is exacerbated by the lack of licensed vaccines, making safe and effective drugs vital to their prevention and treatment. Unfortunately, where drugs are available, their usefulness is being increasingly threatened by parasite drug resistance. The need for new drugs drives antiparasitic drug discovery research globally and requires a range of innovative strategies to ensure a sustainable pipeline of lead compounds. In this review we discuss one of these approaches, drug repurposing or repositioning, with a focus on major human parasitic protozoan diseases such as malaria, trypanosomiasis, toxoplasmosis, cryptosporidiosis and leishmaniasis. [ABSTRACT FROM AUTHOR]

Abstract: Despite the urgent need for effective antimalarial drugs with novel modes of action no new chemical class of antimalarial drug has been approved for use since 1996. To address this, we have used a rational approach to investigate compounds comprising the primary benzene sulfonamide fragment as a potential new antimalarial chemotype. We report the in vitro activity against Plasmodium falciparum drug sensitive (3D7) and resistant (Dd2) parasites for a panel of fourteen primary benzene sulfonamide compounds. Our findings provide a platform to support the further evaluation of primary benzene sulfonamides as a new antimalarial chemotype, including the identification of the target of these compounds in the parasite. [Copyright &y& Elsevier]

Abstract: As part of a research program aimed at discovering new antimalarial leads from Australian macrofungi a unique fungi-derived prefractionated library was screened against a chloroquine-sensitive Plasmodium falciparum line (3D7) using a radiometric growth inhibition assay. A library fraction derived from a Cortinarius species displayed promising antimalarial activity. UV-guided fractionation on the CH2Cl2/MeOH extract from this fungus resulted in the isolation of four known compounds: (1S,3R)-austrocortirubin (1), (1S,3S)-austrocortirubin (2), 1-deoxyaustrocortirubin (3), and austrocortinin (4). Compound 2 was used as a natural product scaffold in the parallel solution-phase synthesis of a small library of N-substituted tetrahydroanthraquinones (5–15). All compounds (1–15) were tested in vitro against P. falciparum 3D7 parasites and (1S,3S)-austrocortirubin (2), the major fungal constituent, was shown to be the most active compound with an IC50 of 1.9μM. This compound displayed moderate cytotoxicity against neonatal foreskin fibroblast (NFF) cells with an IC50 of 15.6μM. [Copyright &y& Elsevier]

Abstract: Malaria is the most lethal parasite-mediated tropical infectious disease, killing 1–2 million people each year. An emerging drug target is the enzyme Plasmodium falciparum histone deacetylase 1 (PfHDAC1). We report 26 compounds designed to bind the zinc and exterior surface around the entrance to the active site of PfHDAC1, 16 displaying potent in vitro antimalarial activity (IC50 <100nM) against P. falciparum. Selected compounds were shown to cause hyperacetylation of P. falciparum histones and be >10-fold more cytotoxic towards P. falciparum than a normal human cell type (NFF). Twenty-two inhibitors feature cinnamic acid derivatives or non-steroidal anti-inflammatory drugs (NSAIDs) as HDAC-binding components. A homology model of PfHDAC1 enzyme gives new insights to interactions likely made by some of these inhibitors. Results support PfHDAC1 as a promising new antimalarial drug target. [Copyright &y& Elsevier]

Chondroitin sulfate (CS) A is a key receptor for adhesion of Plasmodium falciparum-infected erythrocytes (lEs) in the placenta and can also mediate adhesion to microvascular endothelial cells. lEs that adhere to CSA express var2csa-type genes, which encode specific variants of the IE surface antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1). We report direct binding of native PfEMP1, isolated from lEs and encoded by var2csa, to immobilized CSA. Binding of PfEMP1 was dependent on 4-O-sulfated disaccharides and glucuronic acid rather than iduronic acid, consistent with the specificity of intact lEs, Using immobilized CS oligosaccharides as neoglycolipid probes, the minimum chain length for direct binding of PfEMP1 was eight monosaccharide units. Similarly for IE adhesion to placental tissue there was a requirement for 4-O-sulfated GalNAc and glucuronic acid mixed with non-sulfated disaccharides; 6-O-sulfation interfered with the interaction between placental CSA and lEs. The minimum chain length for maximal inhibition of adhesion was 10 monosaccharide residues. Partially 4-O-sulfated CS oligosaccharides (45-55% sulfation) were highly effective inhibitors of placental adhesion (IC50, 0.15 µg/ml) and may have potential for therapeutic development. We used defined P. falciparum isolates expressing different variants of var2csa in adhesion assays and found that there were isolate-specific differences in the preferred structural motifs for adhesion to CSA that correlated with polymorphisms in PfEMP1 encoded by var2csa-type genes. This may influence sites of IE sequestration or parasite virulence. These findings have significant implications for understanding the pathogenesis and biology of malaria, particularly during pregnancy, and the development of targeted interventions. [ABSTRACT FROM AUTHOR]

Abstract: Antiretroviral protease inhibitors were assessed in vitro for their activity against Giardia duodenalis and Trichomonas vaginalis. Kaletra® (a co-formulation of ritonavir and lopinavir) was the most effective overall, with 50% effective drug concentrations (EC50) of 1.1–2.7μM (ritonavir concentration) against G. duodenalis and 6.8–8μM against metronidazole-sensitive and clinically metronidazole-resistant T. vaginalis. Minimal inhibitory concentrations were 2–2.5μM and 10–50μM for G. duodenalis and T. vaginalis, respectively. Within the range of human plasma concentrations for ritonavir, only G. duodenalis was inhibited. Lopinavir alone was less inhibitory than ritonavir but was associated with a blockage in cytokinesis of G. duodenalis trophozoites. Saquinavir was not effective. These findings are significant considering the association between human immunodeficiency virus and T. vaginalis, and between G. duodenalis and homosexual behaviour. [Copyright &y& Elsevier]

Abstract: 7-Methoxyflavenes and 5,7,8-trimethoxyflavenes were found to undergo stereoselective acid-catalyzed rearrangement to generate the benzopyrano[4,3-b]benzopyran ring system present in the natural product, dependensin. Dependensin and its analogs were subjected to antimalarial growth inhibition assays against Plasmodium falciparum and found to have IC50 values ranging between 1.9 and 3.9μM. [Copyright &y& Elsevier]

Abstract Malaria drug discovery has shifted from a focus on targeting asexual blood stage parasites, to the development of drugs that can also target exo-erythrocytic forms and/or gametocytes in order to prevent malaria and/or parasite transmission. In this work, we aimed to develop parasite-selective histone deacetylase inhibitors (HDACi) with activity against the disease-causing asexual blood stages of Plasmodium malaria parasites as well as with causal prophylactic and/or transmission blocking properties. An optimized one-pot, multi-component protocol via a sequential Ugi four-component reaction and hydroxylaminolysis was used for the preparation of a panel of peptoid-based HDACi. Several compounds displayed potent activity against drug-sensitive and drug-resistant P. falciparum asexual blood stages, high parasite-selectivity and submicromolar activity against exo-erythrocytic forms of P. berghei. Our optimization study resulted in the discovery of the hit compound 1u which combines high activity against asexual blood stage parasites (Pf 3D7 IC 50 : 4 nM; Pf Dd2 IC 50 : 1 nM) and P. berghei exo-erythrocytic forms (Pb EEF IC 50 : 25 nM) with promising parasite-specific activity (SI Pf 3D7/HepG2: 2496, SI Pf Dd2/HepG2: 9990, and SI Pb EEF/HepG2: 400). Graphical abstract Image 1 Highlights • Novel HDACi were synthesized using a one-pot multi-component protocol. • All compounds showed nanomolar activity against asexual blood stage parasites. • Selected compounds were shown to hyperacetylate P. falciparum histones. • Compound 1u revealed potent and selective activity against exo-erythrocytic forms. • This series of HDACi represents a valuable starting point for further optimization. [ABSTRACT FROM AUTHOR]

The treatment of major human parasitic infections is dependent on drugs that are plagued by issues of drug resistance. New chemotherapeutics with novel mechanisms of action (MOA) are desperately needed to combat multi-drug-resistant parasites. Although widespread screening strategies are identifying potential new hits for development against most major human parasitic diseases, in many cases such efforts are hindered by limited MOA data. Although MOA data are not essential for drug development, they can facilitate compound triage and provide a mechanism to combat drug resistance. Here we describe and discuss methods currently used to identify the targets of antiparasitic compounds, which could circumvent this bottleneck and facilitate the development of new antiparasitic drugs. [ABSTRACT FROM AUTHOR]

Bioassay-guided fractionation of an antimalarial DCM/MeOH extract derived from the Australian rainforest fungus Entonaema sp. resulted in the isolation of three new isoindolinone derivatives, entonalactams A–C ( 1 – 3 ), along with the known natural products 3-methoxy-5-methylbenzene-1,2-diol ( 4 ), daldinal B ( 5 ), and ergosta-4,6,8(14),22-tetraen-3-one ( 6 ). The chemical structures of the new secondary metabolites were determined following extensive 1D/2D NMR and MS data analysis. A single crystal X-ray structure for entonalactam A ( 1 ) confirmed the NMR-based structure assignment. Entonalactams A–C ( 1–3 ) were all determined to be racemic based on chiro-optical data. All secondary metabolites were tested in vitro against Plasmodium falciparum malaria parasites, and ergosta-4,6,8(14),22-tetraen-3-one ( 6 ) was identified as the most active compound with 66% inhibition at 50 μM. [ABSTRACT FROM AUTHOR]

The η-carbonic anhydrases (CAs, EC 4.2.1.1) were recently discovered as the sixth genetic class of this metalloenzyme superfamily, and are so far known only in protozoa, including various Plasmodium species, the causative agents of malaria. We report here an inhibition study of the η-CA from Plasmodium falciparum ( Pf CA) against a panel of sulfonamides and one sulfamate compound, some of which are clinically used. The strongest inhibitors identified were ethoxzolamide and sulthiame, with K I s of 131–132 nM, followed by acetazolamide, methazolamide and hydrochlorothiazide ( K I s of 153–198 nM). Brinzolamide, topiramate, zonisamide, indisulam, valdecoxib and celecoxib also showed significant inhibitory action against Pf CA, with K I s ranging from 217 to 308 nM. An interesting observation was that the more efficient Pf CA inhibitors are representative of several scaffolds and chemical classes, including benzene sulfonamides, monocyclic/bicyclic heterocyclic sulfonamides and compounds with a more complex scaffold (i.e., the sugar sulfamate derivative, topiramate, and the coxibs, celecoxib and valdecoxib). A comprehensive inhibition study of small molecules for η-CAs is needed as a first step towards assessing Pf CA as a druggable target. The present work identifies the first known η-CA inhibitors and provides a platform for the development of next generation novel Pf CA inhibitors. [ABSTRACT FROM AUTHOR]

The genome of the protozoan parasite Plasmodium falciparum , the causative agent of the most lethal type of human malaria, contains a single gene annotated as encoding a carbonic anhydrase (CAs, EC 4.2.1.1) thought to belong to the α-class, Pf CA. Here we demonstrate the kinetic properties of Pf CA for the CO 2 hydration reaction, as well as an inhibition study of this enzyme with inorganic and complex anions and other molecules known to interact with zinc proteins, including sulfamide, sulfamic acid, and phenylboronic/arsonic acids, detecting several low micromolar inhibitors. A closer examination of the sequence of this and the CAs from other Plasmodium spp., as well as a phylogenetic analysis, revealed that these protozoa encode for a yet undisclosed, new genetic family of CAs termed the η-CA class. The main features of the η-CAs are described in this report. [ABSTRACT FROM AUTHOR]

Abstract: In this work we investigated the antiplasmodial activity of a series of HDAC inhibitors containing an alkoxyamide connecting-unit linker region. HDAC inhibitor 1a (LMK235), previously shown to be a novel and specific inhibitor of human HDAC4 and 5, was used as a starting point to rapidly construct a mini-library of HDAC inhibitors using a straightforward solid-phase supported synthesis. Several of these novel HDAC inhibitors were found to have potent in vitro activity against asexual stage Plasmodium falciparum malaria parasites. Representative compounds were shown to hyperacetylate P. falciparum histones and to inhibit deacetylase activity of recombinant PfHDAC1 and P. falciparum nuclear extracts. All compounds were also screened in vitro for activity against Plasmodium berghei exo-erythrocytic stages and selected compounds were further tested against late stage (IV and V) P. falciparum gametocytes. Of note, some compounds showed nanomolar activity against all three life cycle stages tested (asexual, exo-erythrocytic and gametocyte stages) and several compounds displayed significantly increased parasite selectivity compared to the reference HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). These data suggest that it may be possible to develop HDAC inhibitors that target multiple malaria parasite life cycle stages. [Copyright &y& Elsevier]

Abstract: An antimalarial medicinal plant Picrorhiza scrophulariiflora was chemically investigated as part of our ongoing research in traditional chinese medicines (TCM). Mass directed fractionation of the active part of the crude extract led to the isolation of ten main components, three new compounds (1–3) and seven known compounds (4–10). Compound 10 inhibited the growth of the Plasmodium falciparum 3D7 malarial parasite line, with an IC50 value of 8.3μM. This compound accounted for ∼95% of P. falciparum growth inhibitory activity in the crude extract confirming, for this TCM, that a single compound was responsible for the antimalarial activity. [Copyright &y& Elsevier]

Abstract: Bioassay-guided fractionation of an antimalarial extract derived from the fungus Ramaria subaurantiaca afforded the known polyamine alkaloid, pistillarin. Nine pistillarin analogues were synthesised via EDC-mediated chemistry and these compounds along with the previously reported natural product polyamines, ianthelliformisamines A–C and spermatinamine, were evaluated against Plasmodium falciparum (3D7) parasites and a normal human cell line to determine parasite-specific activity. Spermatinamine (IC50 0.23μM) and pistillarin (IC50 1.9μM) were the two most potent antimalarials identified during these studies. [Copyright &y& Elsevier]

Abstract: Azadipeptide nitriles—novel cysteine protease inhibitors—display structure-dependent antimalarial activity against both chloroquine-sensitive and chloroquine-resistant lines of cultured Plasmodium falciparum malaria parasites. Inhibition of parasite’s hemoglobin-degrading cysteine proteases was also investigated, revealing the azadipeptide nitriles as potent inhibitors of falcipain-2 and -3. A correlation between the cysteine protease-inhibiting activity and the antimalarial potential of the compounds was observed. These first generation azadipeptide nitriles represent a promising new class of compounds for antimalarial drug development. [Copyright &y& Elsevier]

Histone deacetylases (HDACs) have been identified as emerging antiplasmodial drug targets. In this work, we report on the synthesis, structure-activity relationships, metabolic stability and in vivo efficacy of new peptoid-based HDAC inhibitors with dual-stage antiplasmodial activity. A mini library of HDAC inhibitors was synthesized using a one-pot, multi-component protocol or submonomer pathways. The screening of the target compounds for their activity against asexual blood stage parasites, human cell cytotoxicity, liver stage parasites, and selected human HDAC isoforms provided important structure-activity relationship data. The most promising HDAC inhibitor from this series, compound 3n , demonstrated potent activity against drug-sensitive and drug-resistant asexual stage P. falciparum parasites and was selective for the parasite versus human cells (Pf 3D7 IC 50 0.016 μM; SIHepG2/ Pf 3D7 573; Pf Dd2 IC 50 0.002 μM; SIHepG2/ Pf Dd2 4580) combined with activity against P. berghei exoerythrocytic liver stages (Pb EEF IC 50 0.48 μM). While compound 3n displayed high stability in human (Cl int 5 μL/min/mg) and mouse (Cl int 6 μL/min/mg) liver microsomes, only modest oral in vivo efficacy was observed in P. berghei infected mice. Together these data provide a foundation for future work to improve the properties of these dual-stage inhibitors as drug leads for malaria. Image 1 • Novel HDACi were synthesized using a one-pot multi-component protocol. • Selected compounds show potent activity against asexual P. falciparum parasites. • Selected compounds show dual-stage activity for asexual and liver stage parasites. • Selected compounds increased asexual P. falciparum histone H4 acetylation. • One compound has high microsomal stability and modest in vivo activity in mice. [ABSTRACT FROM AUTHOR]