2-Hexadecynoic acid inhibits plasmodial FAS-II enzymes and arrests erythrocytic and liver stage Plasmodium infections

Acetylenic fatty acids are known to display several biological activities, but their antimalarial activity has remained unexplored. In this study, we synthesized the 2-, 5-, 6-, and 9-hexadecynoic acids (HDAs) and evaluated their in vitro activity against erythrocytic (blood) stages of Plasmodium falciparum and liver stages of Plasmodium yoelii infections. Since the type II fatty acid biosynthesis pathway (PfFAS-II) has recently been shown to be indispensable for liver stage malaria parasites, the inhibitory potential of the HDAs against multiple P. falciparum FAS-II (PfFAS-II) elongation enzymes was also evaluated. The highest antiplasmodial activity against blood stages of P. falciparum was displayed by 5-HDA (IC₅₀ value 6.6 μg/ml), whereas the 2-HDA was the only acid arresting the growth of liver stage P. yoelii infection, in both flow cytometric assay (IC₅₀ value 2-HDA 15.3 μg/ml, control drug atovaquone 2.5 ng/ml) and immunofluorescence analysis (IC₅₀ 2-HDA 4.88 μg/ml, control drug atovaquone 0.37 ng/ml). 2-HDA showed the best inhibitory activity against the PfFAS-II enzymes PfFabI and PfFabZ with IC₅₀ values of 0.38 and 0.58 μg/ml (IC₅₀ control drugs 14 and 30 ng/ml), respectively. Enzyme kinetics and molecular modeling studies revealed valuable insights into the binding mechanism of 2-HDA on the target enzymes. All HDAs showed in vitro activity against Trypanosoma brucei rhodesiense (IC₅₀ values 3.7–31.7 μg/ml), Trypanosoma cruzi (only 2-HDA, IC₅₀ 20.2 μg/ml), and Leishmania donovani (IC₅₀ values 4.1–13.4 μg/ml) with generally low or no significant toxicity on mammalian cells. This is the first study to indicate therapeutic potential of HDAs against various parasitic protozoa. It also points out that the malarial liver stage growth inhibitory effect of the 2-HDA may be promoted via PfFAS-II enzymes. The lack of cytotoxicity, lipophilic nature, and calculated pharmacokinetic properties suggests that 2-HDA could be a useful compound to study the interaction of fatty acids with these key P. falciparum enzymes.     

Kojic acid derived hydroxypyridinone–chloroquine hybrids: Synthesis,crystal structure,antiplasmodial activity and β-haematin inhibition

Aminochloroquinoline–kojic acid hybrids were synthesized and evaluated for β-haematin inhibition and antiplasmodial activity against drug resistant (K1) and sensitive (3D7) strains of Plasmodium falciparum. Compound 7j was the most potent compound in both strains (IC₅₀^3D7 = 0.004 μM; IC₅₀^K1 = 0.03 μM) and had the best β-haematin inhibition activity (0.07 IC₅₀ equiv vs 1.91 IC₅₀ equiv for chloroquine). One compound 8c was found to be equipotent in both strains (IC₅₀ = 0.04 μM).     

Glabridin induces oxidative stress mediated apoptosis like cell death of malaria parasite Plasmodium falciparum

Plants are known as the source of novel agents for developing new antimalarial drugs. Glabridin is a polyphenolic flavonoid, a main constituent in the roots of Glycyrrhiza glabra possesses various biological activities. However, its anti-plasmodial activity is unexplored. In the present work, it is for the first time demonstrated that glabridin inhibits Plasmodium falciparum growth in vitro with an IC₅₀ 23.9 ± 0.43 μM. Glabridin showed poor cytotoxicity in vitro with an IC₅₀ 246.6 ± 0.88 μM against Vero cell line and good selectivity index (9.6). In erythrocytic cycle, trophozoite stage was found to be most sensitive to glabridin. In silico study showed that glabridin inhibits Pf LDH enzyme activity by acting on NADH binding site. Glabridin induced oxidative stress by the generation of reactive oxygen and nitrogen species. Glabridin could induce apoptosis in parasite as evidenced by the depolarization of mitochondrial membrane potential (Δψ_m), activation of caspase like proteases and DNA fragmentation. These results indicate that glabridin exhibits antiplasmodial activity and is suitable for developing antimalarial agent from a cheap and sustainable source.     

Targeting the intersubunit cavity of Plasmodium falciparum glutathione reductase by a novel natural inhibitor: Computational and experimental evidence

Glutathione reductase (GR), a homodimeric FAD-dependent disulfide reductase, is essential for redox homeostasis of the malaria parasite Plasmodium falciparum and has been proposed as an antimalarial drug target. In this study we performed a virtual screening against PfGR, using the structures of about 170,000 natural compounds. Analysis of the two top-scoring molecules, TTB and EPB, indicated that these ligands are likely to interact with the homodimer intersubunit cavity of PfGR with high binding energy scores of −9.67 and −9.60 kcal/mol, respectively. Both compounds had a lower affinity for human GR due to differences in structure and electrostatic properties. In order to assess the putative interactions in motion, molecular dynamics simulations were carried out for 30 ns, resulting in TTB being more dynamically and structurally favored than EPB. A closely related compound MDPI 21618 was tested on recombinant PfGR and hGR, resulting in IC₅₀ values of 11.3 ± 2.5 μM and 10.2 ± 1.7 μM, respectively. Kinetic characterization of MDPI 21618 on PfGR revealed a mixed-type inhibition with respect to glutathione disulfide (K_i = 9.7 ± 2.3 μM) and an uncompetitive inhibition with respect to NADPH. Furthermore, MDPI 21618 was found to inhibit the growth of the chloroquine-sensitive P. falciparum strain 3D7 with an IC₅₀ of 3.2 ± 1.9 μM and the chloroquine-resistant Dd2 strain with an IC₅₀ of 3.2 + 1.6 μM. In drug combination assays with chloroquine, artemisinin, or mefloquine MDPI 21618 showed an antagonistic action, which might suggest partially overlapping routes of action. This study further substantiates research on PfGR as a potential antimalarial drug target.     

Synthesis and biological evaluation of new bis-indolone-N-oxides

A series of bis-indolone-N-oxides, 1a–f, was prepared from bis(ethynyl)benzenes and o-halonitroaryls and studied for their in vitro antiplasmodial activities against Plasmodium falciparum and representative strains of bacteria and candida as well as for their cytotoxicity against a human tumor cell line (MCF7). They did not cause any haemolysis (300 μg mL⁻¹). Of the synthesized bis-indolones, compound 1a had the most potent antiplasmodial activity (IC₅₀ = 0.763 μmol L⁻¹ on the FcB1 strain) with a selectivity index (CC₅₀ MCF7/IC₅₀ FcB1) of 35.6. No potency against the tested microbial strains was observed.     

Antiplasmodial and leishmanicidal activity of biflavonoids from Indian Selaginella bryopteris

A series of eleven biflavonoids containing amentoflavone and hinokiflavone derivatives from the Indian medicinal herb Selaginella bryopteris has been investigated for their antiprotozoal activity using in vitro assays against the K1 strain of Plasmodium falciparum, Leishmania donovani, Trypanosoma brucei rhodesiense and Trypanosoma cruzi. The highest antiprotozoal activity was displayed by 7,4′,7″-tri-O-methylamentoflavone which exhibited an IC₅₀ of 0.26 μM. This compound showed no significant cytotoxicity (IC₅₀ > 150 μM) evaluated using L-6 cells. The strongest activity against Leishmania was detected for 2,3-dihydrohinokiflavone (IC₅₀ = 1.6 μM), whereas for Trypanosoma no significant activity was observed (IC₅₀ > 12.5 μg/mL for the extract). To evaluate the in vivo activity against Plasmodium of the most active compound, trimethylated amentoflavones were obtained by partial synthesis starting from amentoflavone. The synthesized mixture of trimethylated amentoflavones did not show activity in the Plasmodium berghei mouse model against female NMRI mice at 50 mg/kg.     

Synthesis and anti-parasitic activity of a novel quinolinone–chalcone series

A series of novel quinolinone–chalcone hybrids and analogues were designed, synthesized and their biological activity against the mammalian stages of Trypanosoma brucei and Leishmania infantum evaluated. Promising molecular scaffolds with significant microbicidal activity and low cytotoxicity were identified. Quinolinone–chalcone 10 exhibited anti-parasitic properties against both organisms, being the most potent anti-L. infantum agent of the entire series (IC₅₀ value of 1.3 ± 0.1 μM). Compounds 4 and 11 showed potency toward the intracellular, amastigote stage of L. infantum (IC₅₀ values of 2.1 ± 0.6 and 3.1 ± 1.05 μM, respectively). Promising trypanocidal compounds include 5 and 10 (IC₅₀ values of 2.6 ± 0.1 and 3.3 ± 0.1 μM, respectively) as well as 6 and 9 (both having IC₅₀ values of <5 μM). Chemical modifications on the quinolinone–chalcone scaffold were performed on selected compounds in order to investigate the influence of these structural features on antiparasitic activity.     

Pyrazole-based arylalkyne cathepsin S inhibitors. Part II: Optimization of cellular potency

Basic lipophilic substituents dramatically improved the cellular potency of a previously disclosed series of pyrazole-based arylalkyne cathepsin S inhibitors. The incorporation of substituted benzylamines in the para position of the arylalkyne maintained enzymatic activity (hCatS IC₅₀ = 80–420 nM) and imparted cellular potency (IC₅₀ = 0.8–4.0 μM). Further refinement of the morpholine portion of the pharmacophore enabled the identification of bicyclic piperidines with enhanced affinity for CatS (IC₅₀ = 10–30 nM) and sub-micromolar cellular potency (JY Ii IC₅₀ = 200–720 nM).     

Earthworm-mediated synthesis of silver nanoparticles: A potent tool against hepatocellular carcinoma,Plasmodium falciparum parasites and malaria mosquitoes

The development of parasites and pathogens resistant to synthetic drugs highlighted the needing of novel, eco-friendly and effective control approaches. Recently, metal nanoparticles have been proposed as highly effective tools towards cancer cells and Plasmodium parasites. In this study, we synthesized silver nanoparticles (EW–AgNP) using Eudrilus eugeniae earthworms as reducing and stabilizing agents. EW–AgNP showed plasmon resonance reduction in UV–vis spectrophotometry, the functional groups involved in the reduction were studied by FTIR spectroscopy, while particle size and shape was analyzed by FESEM. The effect of EW–AgNP on in vitro HepG2 cell proliferation was measured using MTT assays. Apoptosis assessed by flow cytometry showed diminished endurance of HepG2 cells and cytotoxicity in a dose-dependent manner. EW–AgNP were toxic to Anopheles stephensi larvae and pupae, LC₅₀ were 4.8 ppm (I), 5.8 ppm (II), 6.9 ppm (III), 8.5 ppm (IV), and 15.5 ppm (pupae). The antiplasmodial activity of EW–AgNP was evaluated against CQ-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. EW–AgNP IC₅₀ were 49.3 μg/ml (CQ-s) and 55.5 μg/ml (CQ-r), while chloroquine IC₅₀ were 81.5 μg/ml (CQ-s) and 86.5 μg/ml (CQ-r). EW–AgNP showed a valuable antibiotic potential against important pathogenic bacteria and fungi. Concerning non-target effects of EW–AgNP against mosquito natural enemies, the predation efficiency of the mosquitofish Gambusia affinis towards the II and II instar larvae of A. stephensi was 68.50% (II) and 47.00% (III), respectively. In EW–AgNP-contaminated environments, predation was boosted to 89.25% (II) and 70.75% (III), respectively. Overall, this research highlighted the EW–AgNP potential against hepatocellular carcinoma, Plasmodium parasites and mosquito vectors, with little detrimental effects on mosquito natural enemies.     

Picrasin K,a new quassinoid from Quassia amara L. (Simaroubaceae)

A new quassinoid Picrasin K 1 was isolated from a decoction made of Quassia amara leaves, traditionally used in French Guyana to treat malaria. The structure and relative stereochemistry of 1 was determined through extensive NMR analysis. Picrasin K showed a low activity against Plasmodium falciparum in vitro (IC₅₀ = 8 μM), and a similar low activity on human cancerous cells line (IC₅₀ = 7 μM on MCF-7 cells line).     

Synthesis and SAR study of 4,5-diaryl-1H-imidazole-2(3H)-thione derivatives,as potent 15-lipoxygenase inhibitors

A series of 4,5-diaryl-1H-imidazole-2(3H)-thione was synthesized and their inhibitory potency against soybean 15-lipoxygenase and free radical scavenging activities were determined. Compound 11 showed the best IC₅₀ for 15-LOX inhibition (IC₅₀ = 4.7 μM) and free radical scavenging activity (IC₅₀ = 14 μM). Methylation of SH at C₂ position of imidazole has dramatically decreased the 15-LOX inhibition and radical scavenging activity as it can be observed in the inactive compound 14 (IC₅₀ >250 μM). Structure activity similarity (SAS) showed that the most important chemical modification in this series was methylation of SH group and Docking studies revealed a proper orientation for SH group towards Fe core of the 15-LOX active site. Therefore it was concluded that iron chelating could be a possible mechanism for enzyme inhibition in this series of compounds.     

Hybrid fluorescent conjugates of COX-2 inhibitors: Search for a COX-2 isozyme imaging cancer biomarker

The observation that the cyclooxygenase-2 (COX-2) isozyme is over-expressed in multiple types of cancer, relative to that in adjacent non-cancerous tissue, prompted this investigation to prepare a group of hybrid fluorescent conjugates wherein the COX inhibitors ibuprofen, (S)-naproxen, acetyl salicylic acid, a chlororofecoxib analog and celecoxib were coupled via a linker group to an acridone, dansyl or rhodamine B fluorophore. Within this group of compounds, the ibuprofen-acridone conjugate (10) showed potent and selective COX-2 inhibition (COX-2 IC₅₀ = 0.67 μM; SI = 110.6), but its fluorescence emission (λ_em = 417, 440 nm) was not suitable for fluorescent imaging of cancer cells that over-express the COX-2 isozyme. In comparison, the celecoxib-dansyl conjugate (25) showed a slightly lower COX-2 potency and selectivity (COX-2 IC₅₀ = 1.1 μM; SI > 90) than the conjugate 10, and it possesses a better fluorescence emission (λ_em = 500 nm). Ultimately, a celecoxib-rhodamine B conjugate (28) that exhibited moderate COX-2 potency and selectivity (COX-2 IC₅₀ = 3.9 μM; SI > 25) having the best fluorescence emission (λ_em = 580 nm) emerged as the most promising biomarker for fluorescence imaging using a colon cancer cell line that over-expresses the COX-2 isozyme.     

Synthesis and α-glucosidase inhibitory activity evaluation of N-substituted aminomethyl-β-d-glucopyranosides

A series of N-substituted 1-aminomethyl-β-d-glucopyranoside derivatives was prepared. These novel synthetic compounds were assessed in vitro for inhibitory activity against yeast α-glucosidase and both rat intestinal α-glucosidases maltase and sucrase. Most of the compounds displayed α-glucosidase inhibitory activity, with IC₅₀ values covering the wide range from 2.3 μM to 2.0 mM. Compounds 19a (IC₅₀ = 2.3 μM) and 19b (IC₅₀ = 5.6 μM) were identified as the most potent inhibitors for yeast α-glucosidase, while compounds 16 (IC₅₀ = 7.7 and 15.6 μM) and 19e (IC₅₀ = 5.1 and 10.4 μM) were the strongest inhibitors of rat intestinal maltase and sucrase. Analysis of the kinetics of enzyme inhibition indicated that 19e inhibited maltase and sucrase in a competitive manner. The results suggest that the aminomethyl-β-d-glucopyranoside moiety can mimic the substrates of α-glucosidase in the enzyme catalytic site, leading to competitive enzyme inhibition. Moreover, the nature of the N-substituent has considerable influence on inhibitory potency.     

Synthesis of 9-anilinoacridine triazines as new class of hybrid antimalarial agents

There is challenge and urgency to synthesize cost-effective chemotherapeutic agents for treatment of malaria after the widespread development of resistance to CQ. In the present study, we synthesized a new series of hybrid 9-anilinoacridine triazines using the cheap chemicals 6,9-dichloro-2-methoxy acridine and cyanuric chloride. The series of new hybrid 9-anilinoacridine triazines were evaluated in vitro for their antimalarial activity against CQ-sensitive 3D7 strain of Plasmodium falciparum and their cytotoxicity were determined on VERO cell line. Of the evaluated compounds, two compounds 17 (IC₅₀ = 4.21 nM) and 22 (IC₅₀ = 4.27 nM) displayed two times higher potency than CQ (IC₅₀ = 8.15 nM). Most of the compounds showed fairly high selectivity index. The compounds 13 and 29 displayed >96.59% and 98.73% suppression, respectively, orally against N-67 strain of Plasmodium yoelii in swiss mice at dose 100 mg/kg for four days.     

Selective inhibition of human acetylcholinesterase by xanthine derivatives: In vitro inhibition and molecular modeling investigations

The commonly used beverage and psychostimulant caffeine is known to inhibit human acetylcholinesterase enzyme. This pharmacological activity of caffeine is partly responsible for its cognition enhancing properties. However, the exact mechanisms of its binding to human cholinesterases (acetyl and butyrylcholinesterase; hAChE and hBuChE) are not well known. In this study, we investigated the cholinesterase inhibition by the xanthine derivatives caffeine, pentoxifylline, and propentofylline. Among them, propentofylline was the most potent AChE inhibitor (hAChE IC₅₀ = 6.40 μM). The hAChE inhibitory potency was of the order: caffeine (hAChE IC₅₀ = 7.25 μM) < pentoxifylline (hAChE IC₅₀ = 6.60 μM) ? propentofylline (hAChE IC₅₀ = 6.40 μM). These compounds were less potent relative to the reference agent donepezil (hAChE IC₅₀ = 0.04 μM). Moreover, they all exhibited selective inhibition of hAChE with no inhibition of hBuChE (IC₅₀ > 50 μM) relative to the reference agent donepezil (hBuChE IC₅₀ = 13.60 μM). Molecular modeling investigations indicate that caffeine binds primarily in the catalytic site (Ser203, Glu334 and His447) region of hAChE whereas pentoxifylline and propentofylline are able to bind to both the catalytic site and peripheral anionic site due to their increased bulk/size, thereby exhibiting superior AChE inhibition relative to caffeine. In contrast, their lack of hBuChE inhibition is due to a larger binding site and lack of key aromatic amino acids. In summary, our study has important implications in the development of novel caffeine derivatives as selective AChE inhibitors with potential application as cognitive enhancers and to treat various forms of dementia.     

3-Oxo-14α,15α-epoxyschizozygine: A new schizozygane indoline alkaloid from Schizozygia coffaeoides

The stem bark extract of Schizozygia coffaeoides (Apocynaceae) showed moderate antiplasmodial activity (IC₅₀ = 8–12 μg/mL) against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Chromatographic separation of the extract led to the isolation of a new schizozygane indoline alkaloid, named 3-oxo-14α,15α-epoxyschizozygine. In addition, two dimeric anthraquinones, cassiamin A and cassiamin B, were identified for the first time in the family Apocynaceae. The structures of the isolated compounds were deduced on the basis of spectroscopic evidence. The schizozygane indole alkaloids showed good to moderate antiplasmodial activities (IC₅₀ = 13–52 μМ).     

Design and synthesis of new potent anticancer pyrazoles with high FLT3 kinase inhibitory selectivity

A new series of 1H- and 2H-pyrazole derivatives (35 final compounds) has been designed and synthesized in this study. A selected group (13 compounds) was then tested over a panel of 60 cancer cell lines at a single dose concentration of 10 μM. At this concentration, six compounds have showed moderate to strong mean inhibitions, and were further tested at five-dose testing mode to determine their IC₅₀ over the 60 cell lines. The IC₅₀ values of the tested compounds indicated high potency (as for compound 10f) as well as high efficacy (as for compound 11e). Accordingly, compound 10f was then tested at a single dose concentration of 10 μM over a panel of 54 kinases to determine its kinase inhibitory profile. The compound has showed good selectivity towards FLT3 kinase, associated with a moderate potency, with an IC₅₀ value of 1.74 μM.     

Exploration of 2-benzylbenzimidazole scaffold as novel inhibitor of NF-κB

For finding the novel inhibitor of nuclear factor κB activity, a series of benzimidazole derivatives were rationally designed, synthesized and systematically studied for their in vitro activities against LPS induced NF-κB inhibition in RAW 264.7 cells using the SEAP assay based on the flexible chalcone JSH ((E)-1-(2-hydroxy-6-(isopentyloxy)phenyl)-3-(4-hydroxy phenyl)prop-2-en-1-one) which was previously reported. Although most of the benzimidazole derivatives showed strong inhibitory activity in low micromolar potency, 2-(4-methoxybenzyl)-1H-benzo[d]imidazole (3m; IC₅₀ = 1.7 μM) and 2-(2-methoxybenzyl)-1H-benzo[d]imidazole (3n; IC₅₀ = 2.4 μM) showed the best inhibition. The structure activity relationship revealed that 2-benzylbenzimidazole scaffold with hydrogen bonding acceptor on phenyl ring appears as a pharmacophore.     

Synthesis and cyclooxygenase inhibition of various (aryl-1,2,3-triazole-1-yl)-methanesulfonylphenyl derivatives

A series of 1,4- and 1,5-diaryl substituted 1,2,3-triazoles was synthesized by either Cu(I)-catalyzed or Ru(II)-catalyzed 1,3-dipolar cycloaddition reactions between 1-azido-4-methane-sulfonylbenzene 9 and a panel of various para-substituted phenyl acetylenes (4-H, 4-Me, 4-OMe, 4-NMe₂, 4-Cl, 4-F). All compounds were used in in vitro cyclooxygenase (COX) assays to determine the combined electronic and steric effects upon COX-1 and COX-2 inhibitory potency and selectivity. Structure-activity relationship studies showed that compounds having a vicinal diaryl substitution pattern showed more potent COX-2 inhibition (IC₅₀ = 0.03–0.36 μM) compared to their corresponding 1,3-diaryl-substituted counterparts (IC₅₀ = 0.15 to >10.0 μM). In both series, compounds possessing an electron-withdrawing group (Cl and F) at the para-position of one of the aryl rings displayed higher COX-2 inhibition potency and selectivity as determined for compounds containing electron-donating groups (Me, OMe, NMe₂). The obtained data show, that the central carbocyclic or heterocyclic ring system as found in many COX-2 inhibitors can be replaced by a central 1,2,3-triazole unit without losing COX-2 inhibition potency and selectivity. The high COX-2 inhibition potency of some 1,2,3-triazoles having a vicinal diaryl substitution pattern along with their ease in synthesis through versatile Ru(II)-catalyzed click chemistry make this class of compounds interesting candidates for further design and synthesis of highly selective and potent COX-2 inhibitors.     

The anthraquinone emodin inhibits the non-exported FIKK kinase from Plasmodium falciparum

The FIKK family of kinases is unique to parasites of the Apicomplexan order, which includes all malaria parasites. Plasmodium falciparum, the most virulent form of human malaria, has a family of 19 FIKK kinases, most of which are exported into the host red blood cell during malaria infection. Here, we confirm that FIKK 8 is a non-exported member of the FIKK kinase family. Through expression and purification of the recombinant kinase domain, we establish that emodin is a relatively high-affinity (IC₅₀ = 2 μM) inhibitor of PfFk8. Closely related anthraquinones do not inhibit PfFk8, suggesting that the particular substitution pattern of emodin is critical to the inhibitory pharmacophore. This first report of a P. falciparum FIKK kinase inhibitor lays the groundwork for developing specific inhibitors of the various members of the FIKK kinase family in order to probe their physiological function.