Antitrypanosomal Agents Research Articles

Discovery of a quinoline-based phenyl sulfone derivative as an antitrypanosomal agent

A series of natural products-based phenyl sulfone derivative and their property-based analogues were investigated as potential growth inhibitors of Trypanosoma brucei. Trypanosoma brucei is a kinetoplastid protozoan parasite that causes trypanosomiasis. In this work, we found that nopol- and quinoline-based phenyl sulfone derivative were the most active and selective for T. brucei, and they were not reactive towards the active thiol of T. brucei’s cysteine protease rhodesain. A thiol reactive variant of the quinoline-based phenyl sulfone was subsequently investigated and found to be a moderate inhibitor of rhodesain. The quinoline-based compound that is not reactive towards rhodesain can serve a template for phenotypic-based lead discovery while its thiol-active congener can serve as template for structure-based investigation of new antitrypanosomal agents.

Efforts To Access the Potent Antitrypanosomal Marine Natural Product Janadolide: Synthesis of Des-tert-butyl Janadolide and Its Biological Evaluation.

To identify novel antitrypanosomal agents based on Janadolide, a potent macrocyclic polyketide–peptide hybrid, a macrolactonization strategy was explored. We prepared des-tert-butyl Janadolide and evaluated its antitrypanosomal activity. Our findings suggest that the tert-butyl group is necessary for the desired bioactivity.

Trypanothione reductase inhibition and anti-leishmanial activity of all-hydrocarbon stapled α-helical peptides with improved proteolytic stability

Trypanothione reductase (TryR) is a well-established target in the search for novel antitrypanosomal and antileishmanial agents. We have previously identified linear and lactam-bridged 13-residue peptides derived from an α-helical region making up part of the dimeric interface of Leishmania infantum TryR (Li-TryR) which prevent trypanothione reduction by disrupting enzyme dimerization. We now show that i,i + 4 side-chain cross-linking with an all-hydrocarbon staple stabilizes the helical structure of these peptides and significantly improves their resistance to protease cleavage relative to previous linear and cyclic lactam analogues. Interestingly, replacement of the amide bridge by the hydrocarbon staple at the same cyclization positions generates derivatives (2 and 3) that similarly inhibit oxidoreductase activity of the enzyme but unexpectedly stabilize the TryR homodimer. The most proteolytically stable peptide 2 covalently linked to oligoarginines displayed potent in vitro leishmanicidal activity against L. infantum parasites.

Sesquiterpene Lactones from Vernonia cinerascens Sch. Bip. and Their in Vitro Antitrypanosomal Activity.

In the endeavor to obtain new antitrypanosomal agents, particularly sesquiterpene lactones, from Kenyan plants of the family Asteraceae, Vernonia cinerascens Sch. Bip. was investigated. Bioactivity-guided fractionation and isolation in conjunction with LC/MS-based dereplication has led to the identification of vernodalol (1) and isolation of vernodalin (2), 11β,13-dihydrovernodalin (3), 11β,13-dihydrovernolide (4), vernolide (5), 11β,13-dihydrohydroxyvernolide (6), hydroxyvernolide (7), and a new germacrolide type sesquiterpene lactone vernocinerascolide (8) from the dichloromethane extract of V. cinerascens leaves. Compounds 3–8 were characterized by extensive analysis of their 1D and 2D NMR spectroscopic and HR/MS spectrometric data. All the compounds were evaluated for their in vitro biological activity against bloodstream forms of Trypanosoma brucei rhodesiense and for cytotoxicity against the mammalian cell line L6. Vernodalin (2) was the most active compound with an IC50 value of 0.16 µM and a selectivity index of 35. Its closely related congener 11β,13-dihydrovernodalin (3) registered an IC50 value of 1.1 µM and a selectivity index of 4.2.

Synthesis, characterization and in vitro antitrypanosomal activities of new carboxamides bearing quinoline moiety.

The reported toxicities of current antitrypanosomal drugs and the emergence of drug resistant trypanosomes underscore the need for the development of new antitrypanosomal agents. We report herein the synthesis and antitrypanosomal activity of 24 new amide derivatives of 3-aminoquinoline, bearing substituted benzenesulphonamide. Nine of the new derivatives showed comparable antitrypanosomal activities at IC50 range of 1–6 nM (melarsoprol 5 nM). Compound 11n and 11v are more promising antitrypanosomal agents with IC50 1.0 nM than the rest of the reported derivatives. The novel compounds showed satisfactory predicted physico-chemical properties including oral bioavailability, permeability and transport properties.

Development of Predictive QSAR Models of 4-Thiazolidinones Antitrypanosomal Activity Using Modern Machine Learning Algorithms.

This paper presents novel QSAR models for the prediction of antitrypanosomal activity among thiazolidines and related heterocycles. The performance of four machine learning algorithms: Random Forest regression, Stochastic gradient boosting, Multivariate adaptive regression splines and Gaussian processes regression have been studied in order to reach better levels of predictivity. The results for Random Forest and Gaussian processes regression are comparable and outperform other studied methods. The preliminary descriptor selection with Boruta method improved the outcome of machine learning methods. The two novel QSAR-models developed with Random Forest and Gaussian processes regression algorithms have good predictive ability, which was proved by the external evaluation of the test set with corresponding Q2ext =0.812 and Q2ext =0.830. The obtained models can be used further for in silico screening of virtual libraries in the same chemical domain in order to find new antitrypanosomal agents. Thorough analysis of descriptors influence in the QSAR models and interpretation of their chemical meaning allows to highlight a number of structure-activity relationships. The presence of phenyl rings with electron-withdrawing atoms or groups in para-position, increased number of aromatic rings, high branching but short chains, high HOMO energy, and the introduction of 1-substituted 2-indolyl fragment into the molecular structure have been recognized as trypanocidal activity prerequisites.

Benzoic Acid Derivatives with Trypanocidal Activity: Enzymatic Analysis and Molecular Docking Studies toward Trans-Sialidase.

Chagas, or American trypanosomiasis, remains an important public health problem in developing countries. In the last decade, trans-sialidase has become a pharmacological target for new anti-Chagas drugs. In this work, the aims were to design and find a new series of benzoic acid derivatives as trans-sialidase (TS) inhibitors and anti-trypanosomal agents. Three compounds (14, 18, and 19) sharing a para-aminobenzoic acid moiety showed more potent trypanocidal activity than the commercially available drugs nifurtimox and benznidazole in both strains: the lysis concentration of 50% of the population (LC50) was <0.15 µM on the NINOA strain, and LC50 < 0.22 µM on the INC-5 strain. Additionally, compound 18 showed a moderate inhibition (47%) on the trans-sialidase enzyme and a binding model similar to DANA (pattern A).

A Schmidt rearrangement-mediated synthesis of novel tetrahydro-benzo[1,4]diazepin-5-ones as potential anticancer and antiprotozoal agents

Novel tetrahydro-5H-benzo[e][1,4]diazepin-5-ones, several of them, containing the quinoline pharmacophore, were synthesized via a Schmidt rearrangement from their corresponding 1,2,3,4-tetrahydro-4-quinolones mediated by the NaN3/H2SO4 reaction conditions. Twelve of the obtained compounds were in vitro screened by the US National Cancer Institute (NCI) for their ability to inhibit 60 different human tumor cell lines, where compound 24a presented a remarkable activity against 58 of the 60 cancer cell lines, with the most important GI50 values ranging from 0.047 to 8.16 μM and LC50 values ranging from 9.4 to > 100 μM. Additionally, some of them were evaluated as antimalarial, antitrypanosomal and antileishmanial agents. The best antimalarial response was observed for compound 22g with an EC50 = 13.61 μg/mL for Plasmodium falciparum, while compound 24d exhibited high activity against Trypanosoma cruzi. and Leishmania (V) panamensis with EC50 = 2.78 μg/mL and 3.35 μg/mL respectively.

СИНТЕЗ ТА ДОСЛІДЖЕННЯ АНТИТРИПАНОСОМНОЇ АКТИВНОСТІ НОВИХ 5-ІЛІДЕН-2-(1,3,4-ТІАДІАЗОЛ-2-ІЛ)ІМІНОТІАЗОЛІДИН-4-ОНІВ

Мета роботи. На основі реакцій гетероциклізації та Кньовенагеля здійснити синтез нових тіадіазоло-2-імінотіазолідин-4-онів та їх 5-ариліденпохідних для скринінгу антитрипаносомної активності.Матеріали і методи. Органічний синтез, спектроскопія ЯМР, елементний аналіз, фармакологічний скринінг.Результати й обговорення. Циклізацією N-(1,3,4-тіадіазол-2-іл)заміщених 2-хлороацетамідів під дією амонію тіоціанату в середовищі ацетону синтезовано серію нових похідних 2-імінотіазолідин-4-ону. Наявність метиленактивної групи в положенні 5 тіазолідинового циклу отриманих 2-(1,3,4-тіадіазол-2-іл)імінотіазолідин-4-онів дозволила провести їх подальшу модифікацію в умовах реакції Кньовенагеля з різноманітними арил(гетерил)карбальдегідами, ізатином або похідними коричного альдегіду з утворенням серій відповідних 5-арил(гетерил)іліден- та 5-ізатин(3-фенілпропен)іліденпохідних як потенційних антитрипаносомних агентів. Структуру синтезованих сполук підтверджено елементним аналізом та спектроскопією ПМР.Висновки. Результати скринінгу антитрипаносомної активності in vitro синтезованих сполук на штамі Trypanosoma brucei gambiense (TBG) дозволили ідентифікувати чотири високоактивні сполуки, які зі значеннями IC50 в межах 7,3-12,8 мкМ володіли суттєвим трипаноцидним ефектом.

Binding of triazole-linked galactosyl arylsulfonamides to galectin-3 affects Trypanosoma cruzi cell invasion

The synthesis of the O-3 triazole-linked galactosyl arylsulfonamides 1–7 as potential inhibitors of Trypanosoma cruzi cell invasion is described. These target compounds were synthesized by Cu(I)-catalysed azide-alkyne cycloaddition reaction (‘click chemistry’) between different azide arylsulfonamides and the alkyne-based sugar 3-O-propynyl-βGalOMe. Inhibition assays of T. cruzi cell invasion with compounds 1–7 showed reduced values of infection index (∼20) for compounds 3 and 5, bearing the corresponding 5-methylisoxazole and 2,4-dimethoxypyrimidine groups, which also presented higher binding affinities to galectin-3 (EC50 17–18 μM) in Corning Epic label-free assays. In agreement with experimental results, the assessment of the theoretical binding of compounds 1–7 to galectin-3 by MM/PBSA method displayed higher affinities for compounds 3 (−9.7 kcal/mol) and 5 (−11.1 kcal/mol). Overall, these achievements highlight compounds 3 and 5 as potential T. cruzi cell invasion blockers by means of a galectin-3 binding-related mechanism, revealing galectin-3 as an important host target for design of novel anti-trypanosomal agents.

Lipophilic conformationally constrained spiro carbocyclic 2,6-diketopiperazine-1-acetohydroxamic acid analogues as trypanocidal and leishmanicidal agents: An extended SAR study.

We have previously described a number of lipophilic conformationally constrained spiro carbocyclic 2,6-diketopiperazine (2,6-DKP)-1-acetohydroxamic acids as potent antitrypanosomal agents. In this report, we extend the SAR analysis in this class of compounds with respect to in vitro growth inhibition of Trypanosoma and Leishmania parasites. Introduction of bulky hydrophobic substituents at the vicinal position of the basic nitrogen atom in the spiro carbocyclic 2,6-DKP ring system can provide analogues which are potently active against bloodstream form Trypanosomabrucei and exhibit significant activities toward Trypanosoma cruzi epimastogotes and Leishmania infantum promastigotes and intracellular amastigotes. In particular, compounds possessing a benzyl or 4-chlorobenzyl substituent were found to be the most active growth inhibitors, with activities in the low nanomolar and low micromolar ranges for T.brucei and L.infantum, respectively. The benzyl-substituted (S)-enantiomer was the most potent derivative against T.brucei (IC50 =6.8nm), T.cruzi (IC50 =0.21μm), and L.infantum promastigotes (IC50 =2.67μm) and intracellular amastigotes (IC50 =2.60μm). Moreover, the (R)-chiral benzyl-substituted derivative and its racemic counterpart displayed significant activities against L.donovani. Importantly, the active compounds show high selectivity in comparison with two mammalian cell lines.

Diglycosyl diselenides alter redox homeostasis and glucose consumption of infective African trypanosomes

With the aim to develop compounds able to target multiple metabolic pathways and, thus, to lower the chances of drug resistance, we investigated the anti-trypanosomal activity and selectivity of a series of symmetric diglycosyl diselenides and disulfides. Of 18 compounds tested the fully acetylated forms of di-β-D-glucopyranosyl and di-β-D-galactopyranosyl diselenides (13 and 15, respectively) displayed strong growth inhibition against the bloodstream stage of African trypanosomes (EC50 0.54 μM for 13 and 1.49 μM for 15) although with rather low selectivity (SI < 10 assayed with murine macrophages). Nonacetylated versions of the same sugar diselenides proved to be, however, much less efficient or completely inactive to suppress trypanosome growth. Significantly, the galactosyl (15), and to a minor extent the glucosyl (13), derivative inhibited glucose catabolism but not its uptake. Both compounds induced redox unbalance in the pathogen. In vitro NMR analysis indicated that diglycosyl diselenides react with glutathione, under physiological conditions, via formation of selenenylsulfide bonds. Our results suggest that non-specific cellular targets as well as actors of the glucose and the redox metabolism of the parasite may be affected. These molecules are therefore promising leads for the development of novel multitarget antitrypanosomal agents.

Development of Novel Peptide-Based Michael Acceptors Targeting Rhodesain and Falcipain-2 for the Treatment of Neglected Tropical Diseases (NTDs).

This paper describes the development of a class of peptide-based inhibitors as novel antitrypanosomal and antimalarial agents. The inhibitors are based on a characteristic peptide sequence for the inhibition of the cysteine proteases rhodesain of Trypanosoma brucei rhodesiense and falcipain-2 of Plasmodium falciparum. We exploited the reactivity of novel unsaturated electrophilic functions such as vinyl-sulfones, -ketones, -esters, and -nitriles. The Michael acceptors inhibited both rhodesain and falcipain-2, at nanomolar and micromolar levels, respectively. In particular, the vinyl ketone 3b has emerged as a potent rhodesain inhibitor (k2nd = 67 × 106 M-1 min-1), endowed with a picomolar binding affinity (Ki = 38 pM), coupled with a single-digit micromolar activity against Trypanosoma brucei brucei (EC50 = 2.97 μM), thus being considered as a novel lead compound for the discovery of novel effective antitrypanosomal agents.

In silico molecular docking studies of new potential 4-phthalazinyl-hydrazones on selected Trypanosoma cruzi and Leishmania enzyme targets

Recently, a series of 4-phthalazinyl-hydrazones under its E-configuration have exhibited excellent in vitro antichagasic and antileishmanial profiles. Preliminary assays on both parasites suggested that the most active derivatives act through oxidative and nitrosative stress mechanisms; however, their exact mode of actions as anti-trypanosomal and anti-leishmanial agents have not been completely elucidated. This motivated to perform a molecular docking study on essential trypanosomatid enzymes such as superoxide dismutase (SOD), trypanothione reductase (TryR), cysteine-protease (CP) and pteridine reductase 1 (PTR1). In addition, to understand the experimental results of nitric oxide production obtained for infected macrophages with Leishmania parasite, a molecular docking was evaluated on nitric oxide synthase (iNOS) enzyme of Rattus norvegicus. Both diastereomers (E and Z) of the 4-phthalazinyl-hydrazones were docked on the mentioned targets. In general, molecular docking on T. cruzi enzymes revealed that the E-diastereomers exhibited lower binding energies than Z-diastereomers on the Fe-SOD and CP enzymes, while Z-diastereomers showed lower docking energies than E-isomers on TryR enzyme. For the Leishmania docking studies, the Z-isomers exhibited the best binding affinities on the PTR1 and iNOS enzymes, while the TryR enzyme showed a minor dependence with the stereoselectivity of the tested phthalazines. However, either the structural information of the ligand-enzyme complexes or the experimental data suggest that the significant antitrypanosomatid activity of the most active derivatives is not associated to the inhibition of the SOD, CP and PTR1 enzymes, while the TryR inhibition and nitric oxide generation in host cells emerge as interesting antitrypanosomatid therapeutic targets.

Anti-trypanosomal activity of cationic N-heterocyclic carbene gold(I) complexes

Two gold(I) N-heterocyclic carbene complexes 1a and 1b were tested for their anti-trypanosomal activity against Trypanosoma brucei parasites. Both gold compounds exhibited excellent anti-trypanosomal activity (IC50=0.9–3.0nM). The effects of the gold complexes 1a and 1b on the T. b. brucei cytoskeleton were evaluated. Rapid detachment of the flagellum from the cell body occurred after treatment with the gold complexes. In addition, a quick and complete degeneration of the parasitic cytoskeleton was induced by the gold complexes, only the microtubules of the detached flagellum remained intact. Both gold compounds 1a and 1b feature selective anti-trypanosomal agents and were distinctly more active against T. b. brucei cells than against human HeLa cells. Thus, the gold complexes 1a and 1b feature promising drug candidates for the treatment of trypanosome infections such as sleeping sickness (human African Trypanosomiasis caused by Trypanosoma brucei parasites).

Trypanosuppresive effects of ellagic acid and amelioration of the trypanosome-associated pathological features coupled with inhibitory effects on trypanosomal sialidase in vitro and in silico

BackgroundThe search for novel antitrypanosomal agents had previously led to the isolation of ellagic acid as a bioactive antitrypanosomal compound using in vitro studies. However, it is not known whether this compound will elicit antitrypanosomal activity in in vivo condition which is usually the next step in the drug discovery process. PurposeHerein, we investigated the in vivo activity of ellagic acid against bloodstream form of Trypanosoma congolense and its ameliorative effects on trypanosome-induced anemia and organ damage as well as inhibitory effects on trypanosomal sialidase. MethodsRats were infected with T. congolense and were treated with 100 and 200mg/kg body weight (BW) of ellagic acid for fourteen days. The levels of parasitemia, packed cell volume and biochemical parameters were measured. Subsequently, T. congolense sialidase was partially purified on DEAE cellulose column and the mode of inhibition of ellagic acid on the T. congolense sialidase determined. Molecular docking study was also conducted to determine the mode of interaction of the ellagic acid to the catalytic domain of T. rangeli sialidase. ResultsAt a dose of 100 and 200mg/kg (BW), ellagic acid demonstrated significant (P < 0.05) trypanosuppressive effect for most of the 24 days experimental period. Further, the ellagic acid significantly (P < 0.05) ameliorated the trypanosome-induced anemia, hepatic and renal damages as well as hepatomegaly, splenomegaly and renal hypertrophy. The trypanosome-associated free serum sialic acid upsurge alongside the accompanied membrane bound sialic acid reduction were also significantly (P < 0.05) prevented by the ellagic acid treatment. The T. congolense sialidase was purified to a fold of 6.6 with a yield of 83.8%. The enzyme had a KM and Vmax of 70.12mg/ml and 0.04µmol/min respectively, and was inhibited in a non-competitive pattern by ellagic acid with an inhibition binding constant of 1986.75μM. However, in molecular docking study, ellagic acid formed hydrogen bonding interaction with major residues R39, R318, and W124 at the active site of T. rangeli sialidase with a predicted binding free energy of -25.584kcal/mol. ConclusionWe concluded that ellagic acid possesses trypanosuppressive effects and could ameliorate the trypanosome-induced pathological alterations.

A Brief Review of Drug Discovery Research for Human African Trypanosomiasis.

Human African Trypanosomiasis (HAT), a neglected disease endemic in Sub- Saharan Africa, is usually fatal if left untreated. It is caused by the parasite Trypanosoma brucei, and is spread by the tsetse fly. The drugs currently available to treat HAT are few, and limited in efficacy. Furthermore, resistance towards these drugs is beginning to grow. In the last 25 years, only one advance has been made into HAT treatment and consequently, there is an increasing need for new drugs to be sought that are able to effectively treat this disease. This review provides a brief overview of drug discovery research for HAT, focusing on research published in the last four years, identifying new molecules with the potential to be developed into anti-HAT agents. The methods of drug discovery have been grouped into three key areas; new molecules inspired by known antitrypanosomal agents, target-based screening, and phenotypic screening.

Synthesis and biological evaluation of selective tubulin inhibitors as anti-trypanosomal agents

African trypanosomiasis is still a threat to human health due to the severe side-effects of current drugs. We identified selective tubulin inhibitors that showed the promise to the treatment of this disease, which was based on the tubulin protein structural difference between mammalian and trypanosome cells. Further lead optimization was performed in the current study to improve the efficiency of the drug candidates. We used Trypanosoma brucei brucei cells as the parasite model, and human normal kidney cells and mouse macrophage cells as the host model to evaluate the compounds. One new analog showed great potency with an IC50 of 70nM to inhibit the growth of trypanosome cells and did not affect the viability of mammalian cells. Western blot analyses reveal that the compound decreased tubulin polymerization in T. brucei cells. A detailed structure activity relationship (SAR) was summarized that will be used to guide future lead optimization.

Aryl- or heteroaryl-based hydrazinylphthalazine derivatives as new potential antitrypanosomal agents

A series of twenty phthalazinyl-hydrazones were synthesized and tested as potential anti-Trypanosoma cruzi agents. The phthalazines containing 5-nitroheteroaryl moiety 3l and 3m displayed an excellent in vitro antitrypanosomal profile, exhibiting low micromolar EC50 values against proliferative epimastigote of T. cruzi and minimal toxicity toward Vero cells. These derivatives were more potent than the reference drug benznidazole against the epimastigote stage of the parasite. Structure-property analysis indicates that the highly conjugated 5-nitroheteroaryl moiety connected to the phthalazin scaffold play an important role in the antichagasic activity of these phthalazines. The decrease on the mitochondrial dehydrogenase activity and significant ROS production found for the parasites treated with 3l and 3m suggest that both nitro-derivatives can act through an oxidative stress mechanism.

Ferrocenyl and cyrhetrenyl azines containing a 5-nitroheterocyclic moiety: Synthesis, structural characterization, electrochemistry and evaluation as anti-Trypanosoma cruzi agents

The synthesis of unsymmetrical ferrocenyl and cyrhetrenyl azines [(η5-C5H4)-CR=N-N=CH-2-C4H2X-5-NO2]M (M=Re(CO)3, Fe(η5-C5H5); R = H, CH3, X = O, S) has led to the development of new derivatives of 5-nitroheterocycles as potential anti-trypanosomal agents. The structures of compounds have been confirmed using conventional spectroscopic techniques (FT-IR, 1H and 13C NMR), mass spectrometry, including single-crystal X-ray diffraction analysis of compounds 2NT and 4NT. Based on the chemical shifts of the iminic carbons (C6, C7) and the reduction potential of the nitro group (E1/2 NO2), an extensive π-conjugation of the azine bridge (-C(R)=N-N=CH-) was observed along with a correlation between the opposing electronic effects of the cyrhetrenyl and ferrocenyl fragments. It was established that the existence of an electron-withdrawing group (cyrhetrene) could facilitate the generation of radical species (RNO2 to RNO2−) through the azine bridge. The organometallic azines were evaluated for anti-trypanosomal activity in vitro against the epimastigote form of the Dm28c strain of T. cruzi, yielding IC50 values in the low micromolar range.