Discovery of small molecule inhibitors of Plasmodium falciparum apicoplast DNA polymerase

Malaria is caused by infection with protozoan parasites of the Plasmodium genus, which is part of the phylum Apicomplexa. Most organisms in this phylum contain a relic plastid called the apicoplast. The apicoplast genome is replicated by a single DNA polymerase (apPOL), which is an attractive target for anti-malarial drugs. We screened small-molecule libraries (206,504 compounds) using a fluorescence-based high-throughput DNA polymerase assay. Dose/response analysis and counter-screening identified 186 specific apPOL inhibitors. Toxicity screening against human HepaRG human cells removed 84 compounds and the remaining were subjected to parasite killing assays using chloroquine resistant P. falciparum parasites. Nine compounds were potent inhibitors of parasite growth and may serve as lead compounds in efforts to discover novel malaria drugs.     

An image-based assay for high throughput screening of Giardia lamblia

Giardia lamblia is a protozoan parasite that causes widespread gastrointestinal illness. Drugs to treat giardiasis are limited, but efforts to discover new anti-giardial compounds are constrained by the lack of a facile system for cell culture and inhibitor testing. We achieved robust and reproducible growth of G. lamblia in 384-well tissue culture plates in a modified TYI-S-33 medium. A high throughput assay for the screening of potential anti-giardial compounds was developed utilizing the WB strain of G. lamblia and automated optical detection of parasites after growth with tested inhibitors. We screened a library of 1600 known bioactive molecules and identified 12 compounds that inhibited growth of G. lamblia at low- or sub-micromolar concentrations. Our high throughput assay should facilitate evaluation of available chemical libraries for novel drugs to treat giardiasis.     

Anti-leishmanial activity of disubstituted purines and related pyrazolo[4,3-d]pyrimidines

We report here results of screening directed to finding new anti-leishmanial drugs among 2,6-disubstituted purines and corresponding 3,7-disubstituted pyrazolo[4,3-d]pyrimidines. These compounds have previously been shown to moderately inhibit human cyclin-dependent kinases. Since some compounds reduced viability of axenic amastigotes of Leishmania donovani, we screened them for interaction with recombinant leishmanial cdc-2 related protein kinase (CRK3/CYC6), an important cell cycle regulator of the parasitic protozoan. Eighteen pairs of corresponding isomers were tested for viability of amastigotes and for inhibition of CRK3/CYC6 kinase activity. Some compounds (9A, 12A and 13A) show activity against amastigotes with EC₅₀ in a range 1.5-12.4 μM. Structure-activity relationships for the tested compounds are discussed and related to the lipophilicity of the compounds.     

Synthesis of 2-,4,-6-, and/or 7-substituted quinoline derivatives as human dihydroorotate dehydrogenase (hDHODH) inhibitors and anticancer agents: 3D QSAR-assisted design

Following our research for human dihydroorotate dehydrogenase (hDHODH) inhibitors as anticancer agents, herein we describe 3D QSAR-based design, synthesis and in vitro screening of 2-,4,-6-, and/or 7-substituted quinoline derivatives as hDHODH inhibitors and anticancer agents. We have designed 2-,4,-6-, and/or 7-substituted quinoline derivatives and predicted their hDHODH inhibitory activity based on 3D QSAR study on 45 substituted quinoline derivatives as hDHODH inhibitors, and also predicted toxicity. Designed compounds were docked into the binding site of hDHODH. Designed compounds which showed good predictive activity, no toxicity, and good docking score were selected for the synthesis, and in vitro screening as hDHODH inhibitors in an enzyme inhibition assay, and anticancer agents in MTT assay against cancer cell lines (HT-29 and MDA-MB-231). Synthesized compounds 7 and 14 demonstrated IC₅₀ value of 1.56?µM and 1.22?µM, against hDHODH, respectively, and these are our lead compounds for the development of new hDHODH inhibitors and anticancer agents.     

Design,synthesis and biological evaluation of aryl pyrimidine derivatives as potential leishmanicidal agents

A series of substituted aryl pyrimidine derivatives was synthesized and evaluated in vitro for their antileishmanial potential against intracellular amastigotes of Leishmania donovani using reporter gene luciferase assay. Among all, 8 compounds showed promising IC₅₀ values ranging from 0.5 to 12.9 μM. Selectivity indices (S.I.) of all these compounds are far better than reference drugs, sodium stibogluconate (SSG) and miltefosine. On the basis of good S.I., compounds were further screened for their in vivo antileishmanial activity against L. donovani/hamster model. Compounds 2d, 4a and 4b have shown significant inhibition of parasitic multiplication that is 88.4%, 78.1% and 78.2%, respectively at a daily dose of 50 mg/kg × 5 days, when administered intraperitoneally. Compound 2d is most promising one, which may provide a new lead that could be exploited as a new antileishmanial agent.     

A host-parasite list of the protozoan and helminth parasites of New Guinea animals

Ewers W. H. 1973. A host-parasite list of the protozoan and helminth parasites of New Guinea animals. International Journal for Parasitology, 3: 89–110. This paper provides a hostparasite list for protozoan and helminth parasites recorded from native animals of New Guinea. The synonomy of both hosts and parasites are given together with references to the literature of each species of parasite.     

Design,synthesis and exploring the quantitative structure–activity relationship of some antioxidant flavonoid analogues

A series of flavonoid analogues were synthesized and screened for the in vitro antioxidant activity through their ability to quench 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical. The activity of these compounds, measured in comparison to the well-known standard antioxidants (29–32), their precursors (38–42) and other bioactive moieties (38–42) resembling partially the flavone skeleton was analyzed further to develop Quantitative Structure–Activity Relationship (QSAR) models using the Genetic Function Approximation (GFA) technique. Based on the essential structural requirements predicted by the QSAR models, some analogues were designed, synthesized and tested for activity. The predicted and experimental activities of these compounds were well correlated. Flavone analogue 20 was found to be the most potent antioxidant.     

Agrochemicals against Malaria,Sleeping Sickness,Leishmaniasis and Chagas Disease

In tropical regions, protozoan parasites can cause severe diseases with malaria, leishmaniasis, sleeping sickness, and Chagas disease standing in the forefront. Many of the drugs currently being used to treat these diseases have been developed more than 50 years ago and can cause severe adverse effects. Above all, resistance to existing drugs is widespread and has become a serious problem threatening the success of control measures. In order to identify new antiprotozoal agents, more than 600 commercial agrochemicals have been tested on the pathogens causing the above mentioned diseases. For all of the pathogens, compounds were identified with similar or even higher activities than the currently used drugs in applied in vitro assays. Furthermore, in vivo activity was observed for the fungicide/oomyceticide azoxystrobin, and the insecticide hydramethylnon in the Plasmodium berghei mouse model, and for the oomyceticide zoxamide in the Trypanosoma brucei rhodesiense STIB900 mouse model, respectively.     

Design,synthesis, biological evaluation,QSAR analysis and molecular modelling of new thiazol-benzimidazoles as EGFR inhibitors

Heterocyclic rings such as thiazole and benzimidazole are considered as privileged structures, since they constitute several FDA-approved drugs for cancer treatment. In this work, a new set of 2-(2-(substituted) hydrazinyl)-4-(1-methyl-1H-benzo[d]imidazol-2-yl) thiazoles 4a-q were designed as epidermal growth factor receptor (EGFR) inhibitors and synthesized using concise synthetic methods. The new target compounds have been evaluated in vitro for their suppression activity against EGFR TK. Compounds 4n, 4h, 4i, 4a and 4d exhibited significant potency in comparison with erlotinib which served as a reference drug (IC50, 71.67–152.59 nM; IC50 erlotinib, 152.59 nM). Furthermore, MTT assay revealed that compounds 4j, 4a, 4f, 4h, 4n produced the most promising cytotoxic potency against the human breast cancer cell line (MCF-7) (IC50; 5.96–11.91 µM; IC50 erlotinib; 4.15 µM). Compound 4a showed promising activity as EGFR TK inhibitor as well as anti-breast cancer agent. In addition, 4a induced apoptotic effect and cell cycle arrest at G2/M phase preventing the mitotic cycle in MCF-7 cells. Moreover, 4a upregulated the oncogenic parameters; caspase-3, p53, Bax/Bcl-2 as well as it inhibited the level of PARP-1 enzyme. QSAR study was carried out for the new derivatives and it revealed the goodness of the models. Furthermore, molecular docking studies represented the binding modes of the promising compounds in the active pocket of EGFR.     

Design,synthesis and anticonvulsant properties of new N-Mannich bases derived from 3-phenylpyrrolidine-2,5-diones

The synthesis and anticonvulsant properties of new N-Mannich bases of 3-phenyl- (9a–d), 3-(2-chlorophenyl)- (10a–d), 3-(3-chlorophenyl)- (11a–d) and 3-(4-chlorophenyl)-pyrrolidine-2,5-diones (12a–d) were described. The key synthetic strategies involve the formation of 3-substituted pyrrolidine-2,5-diones (5–8), and then aminoalkylation reaction (Mannich-type) with formaldehyde and corresponding secondary amines, which let to obtain the final compounds 9a–d, 10a–d, 11a–d and 12a–d in good yields. Initial anticonvulsant screening was performed in mice (ip) using the maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) seizures tests. The most effective compounds in mice were tested after oral administration in rats. The acute neurological toxicity was determined applying the minimal motor impairment rotarod test. The in vivo results revealed that numerous compounds were effective especially in the MES test (model of human tonic-clonic seizures). The most active in the MES seizures in rats was 1-[(4-benzyl-1-piperidyl)methyl]-3-(2-chlorophenyl)pyrrolidine-2,5-dione (10c) which showed ED₅₀ value of 37.64 mg/kg. It should be stressed that this molecule along with 9a, 9d and 10d showed protection in the psychomotor seizure test (6-Hz), which is known as an animal model of therapy-resistant epilepsy. Furthermore compounds 9a, 9d and 10d were also tested in the pilocarpine-induced status prevention (PISP) test to assess their potential effectiveness in status epilepticus. For the most promising molecule 9d an influence on human CYP3A4 isoform of P-450 cytochrome was studied in vitro.     

A novel achiral seco-cyclopropylpyrido[e]indolone (CPyI) analog of CC-1065 and the duocarmycins: Synthesis,DNA interactions,in vivo anticancer and anti-parasitic evaluation

The synthesis of an achiral seco-hydroxy-aza-CBI-TMI analog (8) of the duocarmycins is reported. Its specificity for the DNA minor groove of AT-rich sequences and covalent bonding to adenine-N3 was ascertained by a thermal cleavage assay. Compound 8 was found to be cytotoxic in the nanomolar range against murine and human cancer cells. It was further demonstrated that compound 8 was active against murine melanoma (B16-F0) grown in C57BL/6 mice. Compound 8 was also shown to inhibit the growth of the protozoan parasites Leishmania donovani, Leishmania mexicana, Trypanosoma brucei, and Plasmodium falciparum in culture.     

Ligand based design and synthesis of pyrazole based derivatives as selective COX-2 inhibitors

The design and synthesis of novel pyrazole based derivatives has been carried out using the ligand based approach like pharmacophore and QSAR modelling of reported pyrazoles from the available literature to investigate the chemical features that are essential for the design of selective and potent COX-2 inhibitors. Both pharmacophore and QSAR models with good statistical parameters were selected for the design of the lead molecule. Also by exploiting the chemical structures of selective and marketed COX-2 inhibitors, celecoxib and SC-558 were used in designing the molecules which are used in the treatment of inflammation and related disorders. The therapeutic action of the Non-Steroidal Anti-inflammatory Agents (NSAIDs) is based primarily on the COX-2 inhibition. With this background we have synthesized some azomethine derivatives of 3-methyl-1-substituted-4-phenyl-6-[{(1E)-phenylmethylene}amino]-1,4-dihydro pyrano[2,3-c]pyrazole-5-carbonitrile 6(a-o) and were characterized by ¹HNMR, ¹³CNMR and Mass spectral techniques. All the synthesized pyrazole derivatives were tested for in vitro membrane stability property in both COX-1 & COX-2 inhibition studies and in vivo anti-inflammatory activity by carrageenan induced rat paw edema model. Among them, compound 6k showed very good activity by in vivo anti-inflammatory activity with 0.8575 mmol/kg as ED₅₀. Similarly compounds 6m, 6o, 6i and 6h exhibited comparable anti-inflammatory activity to standard drugs. Also the active compounds were further screened for ulcerogenic activity and were found be safer with less ulcer index compared to the marketed drugs like aspirin, ibuprofen and celecoxib.     

Synthesis,screening and docking analysis of hispolon analogs as potential antitubercular agents

A series of 20 hispolons/dihydrohispolons were synthesized and characterized by spectral data. These compounds were subjected to in vitro antitubercular activity screening against Mycobacterium tuberculosis (H37Rv) strain. The synthesized compounds showed varied antitubercular activity ranging from 100 to 1.6 μg/mL. Among the screened compounds, four compounds (H1, H2, H3 and H15) have shown moderate activity with MIC 25 μg/mL. Potent activities were observed for the dihydrohispolon derivative H14 (MIC 1.6 μg/mL) followed by H13 (6.25 μg/mL) and H17 (12.5 μg/mL), H19 (3.125 μg/ML). Docking simulations gave good insights on the possible interactions between the tested compounds and β-keto acyl synthase enzyme (mtbFabH). Drug-inhibitor combination studies showed no synergism with the drugs targeting mycolic acid biosynthesis (isoniazid, ethambutol and thiolactomycin, a specific inhibitor of KAS-B enzyme) but showed significant synergism with other drugs including rifampicin and ciprofloxacin ascertaining the drug target for hispolons as inhibition of mycolic acid biosynthesis, probably via mtbFabH.     

Alpha-glucosidase inhibitors from Nervilia concolor,Tecoma stans,and Bouea macrophylla

Tecoma stans (L.) Juss. Ex Kunth is widely used in folk medicine. In ethnomedicine, it is applied as a cardioprotective, hepatoprotective, antiarthritic, antinociceptive, anti-inflammatory, and antimicrobial. The aqueous extract is considered antidiabetic, and is used as a traditional remedy in Mexico. More than 120 chemical constituents have been identified in its leaves, barks, and roots. However, less is known about the phytochemical properties of T. stans flower extracts. The herbal plant Nervilia concolor (Blume) Schltr. is native to Vietnam, and is used in traditional Chinese medicine to treat diseases such as bronchitis, stomatitis, acute pneumonia, and laryngitis. Only two previous reports have addressed the chemical content of this plant. Bouea macrophylla Griff., commonly known as marian plum or plum mango, is a tropical plant that is used to treat a range of illnesses. Phytochemical analysis of B. macrophylla suggests the presence of volatile components and flavonoids. However, existing data have been obtained from screening without isolation. As part of our ongoing search for alpha-glucosidase inhibitors from Vietnamese medicinal plants, we conducted bioactive-guided isolation of the whole plant N. concolor, the flowers of T. stans, and the leaves of B. macrophylla. We isolated and structurally elucidated five known compounds from T. stans: ursolic acid (TS1), 3-oxours-12-en-28-oic acid (TS2), chrysoeriol (TS3), ferulic acid (TS4), and tecomine (TS5). Three known compounds were isolated from Nervilia concolor: astragalin (NC1), isoquercitrin (NC2), and caffeic acid (NC3). From B. macrophylla, betullinic acid (BM1), methyl gallate (BM2), and 3-O-galloyl gallic acid methyl ester (BM3) were isolated. All compounds showed promising alpha-glucosidase inhibition, with IC₅₀ values ranging from 1.4 to 143.3 µM. The kinetics of enzyme inhibition showed BM3 to be a competitive-type inhibitor. An in silico molecular docking model confirmed that compounds NC1, NC2, and BM3 were potential inhibitors of the α-glucosidase enzyme. Molecular dynamics simulations were carried out with compound BM3 demonstrating the best docking model during simulation up to 100 ns to explore the stability of the complex ligand–protein.     

Benzochromenes from the roots of Bourreria pulchra

Two new benzochromenes, (6,6-dimethyl-2-methoxy-6H-benzo[c]chromen-9-yl)methanol (1), and 2-methoxy-6,6-dimethyl-6H-benzo[c]chromen-9-carbaldehyde (2), together with several already known metabolites, were isolated from the root extract of Bourreria pulchra (Boraginaceae). The structures of 1 and 2 were established on the basis of their spectroscopic data. Both were assayed for in vitro antiprotozoan activity, and especially 1 was found to possess significant activity against Leishmania mexicana and Trypanosoma cruzi parasites (IC₅₀ 4.6 μg/mL and 7.5 μg/mL, respectively).     

Antimalarial and cytotoxic activities of chiral triamines

Chiral triamine antimalarial compounds have been identified following the screening of mixture-based positional scanning libraries made up of 31,320 compounds against P. falciparum. The library, namely N-methyl triamine (TPI 762) was generated following exhaustive reduction of resin-bound acylated dipeptides. Using the PSCL approach, individual compounds were rapidly identified which were only 10 times less active than the standard drugs chloroquine (CQ) and Artemisinin (Artes).     

Design,synthesis, evaluation and QSAR analysis of N1-substituted norcymserine derivatives as selective butyrylcholinesterase inhibitors

We synthesized a series of N¹-substituted norcymserine derivatives 7a–p and evaluated their anti-cholinesterase activities. In vitro evaluation showed that the pyridinylethyl derivatives 7m–o and the piperidinylethyl derivative 7p improved the anti-butyrylcholinesterase activity by approximately threefold compared to N¹-phenethylnorcymserine (PEC, 2). A quantitative structure-activity relationship (QSAR) study indicated that logS might be a key feature of the improved compounds.     

Design,synthesis and anticonvulsant activity of new hybrid compounds derived from N-phenyl-2-(2,5-dioxopyrrolidin-1-yl)-propanamides and -butanamides

The focused library of 21 new N-phenyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide, 2-(3-methyl-2,5-dioxopyrrolidin-1-yl)propanamide, and 2-(2,5-dioxopyrrolidin-1-yl)butanamide derivatives as potential new hybrid anticonvulsant agents was synthesized. These hybrid molecules were obtained as close analogs of previously described N-benzyl derivatives and fuse the chemical fragments of clinically relevant antiepileptic drugs such as ethosuximide, levetiracetam, and lacosamide. The initial anticonvulsant screening was performed in mice (ip) using the ‘classical’ maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) tests, as well as in the six-Hertz (6 Hz) model of pharmacoresistant limbic seizures. Applying the rotarod test, the acute neurological toxicity was determined. The broad spectra of activity across the preclinical seizure models in mice (ip) displayed compounds 4, 5, 11, and 19. The most favorable anticonvulsant properties demonstrated 4 (ED₅₀ MES = 96.9 mg/kg, ED₅₀ scPTZ = 75.4 mg/kg, ED₅₀ 6 Hz = 44.3 mg/kg) which showed TD₅₀ = 335.8 mg/kg in the rotarod test that yielded satisfying protective indexes (PI MES = 3.5, PI scPTZ = 4.4, PI 6 Hz = 7.6). Consequently, compound 4 revealed comparable or better safety profile than model antiepileptic drugs (AEDs): ethosuximide, lacosamide, and valproic acid. In the in vitro assays, compound 4 was observed as relatively effective binder to the neuronal voltage-sensitive sodium and diltiazem site of L-type calcium channels.     

In vitro assessment of 3-alkoxy-5-nitroindazole-derived ethylamines and related compounds as potential antileishmanial drugs

Leishmaniasis is a widespread neglected tropical disease complex that is responsible of one million new cases per year. Current treatments are outdated and pose many problems that new drugs need to overcome. With the goal of developing new, safe, and affordable drugs, we have studied the in vitro activity of 12 different 5-nitroindazole derivatives that showed previous activity against different strains of Trypanosoma cruzi in a previous work. T. cruzi belongs to the same family as Leishmania spp., and treatments for the disease it produces also needs renewal. Among the derivatives tested, compounds 1, 2, 9, 10, 11, and 12 showed low J774.2 macrophage toxicity, while their effect against both intracellular and extracellular forms of the studied parasites was higher than the ones found for the reference drug Meglumine Antimoniate (Glucantime®). In addition, their Fe-SOD inhibitory effect, the infection rates, metabolite alteration, and mitochondrial membrane potential of the parasites treated with the selected drugs were studied in order to gain insights into the action mechanism, and the results of these tests were more promising than those found with glucantime, as the leishmanicidal effect of these new drug candidates was higher. The promising results are encouraging to test these derivatives in more complex studies, such as in vivo studies and other experiments that could find out the exact mechanism of action.