Chloroquine-resistant W2 Strain Research Articles

Towards development of new antimalarial compounds through in silico and in vitro assays

Malaria is one of most widespread infectious disease in world. The antimalarial therapy presents a series of limitations, such as toxicity and the emergence of resistance, which makes the search for new drugs urgent. Thus, it becomes necessary to explore essential and exclusive therapeutic targets of the parasite to achieve selective inhibition. Enoyl-ACP reductase is an enzyme of the type II fatty acid biosynthetic pathway and is responsible for the rate-limiting step in the fatty acid elongation cycle. In this work, we use hierarchical virtual screening and drug repositioning strategies to prioritize compounds for phenotypic assays and molecular dynamics studies. The molecules were tested against chloroquine-resistant W2 strain of Plasmodium falciparum (EC50 between 330.05 and 13.92 µM). Nitrofurantoin was the best antimalarial activity at low micromolar range (EC50 = 13.92 µM). However, a hit compound against malaria must have a biological activity value below 1 µM. A large number of molecules present problems with permeability in biological membranes and reaching an effective concentration in their target's microenvironment. Nitrofurantoin derivatives with inclusions of groups which confer increased lipid solubility (methyl groups, halogens and substituted and unsubstituted aromatic rings) have been proposed. These derivatives were pulled through the lipid bilayer in molecular dynamics simulations. Molecules 14, 18 and 21 presented lower free energy values than nitrofurantoin when crossing the lipid bilayer.

A Study of the Antimalarial Activity of Combined Plant Extracts Traditionally Used in Kenya

Introduction: Due to resistance and cost of current antimalarial drugs in use, there is need to continue searching for effective and affordable treatment for this disease. Traditional medicinal plants have been focused on as source of such drugs.
 Methodology: For this study, combined crude extracts from six plants used in Kenya were tested in vitro against chloroquine resistant Plasmodium falciparum W2 strain using the [3H] hypoxanthine uptake assay and in vivo using Plasmodium berghei on mice. Cytotoxicity tests were done using the MTT based colorimetric assay on Vero 199 and selectivity index used to assess safety of the extracts with the best activity.
 Results: In vitro results with combinations involving Zanthoxylum chalybeum with four of the extracts indicated activity below IC50 10µg/ml. A combination of S. pinnata and Toddalia asiatica extracts exhibited the best activity in vivo having a parasite growth suppression of 81.3% at a dose of 500mg/kg. S. pinnata and T.asiatica combination had CC50 values of 102.93±5.96µg/ml and >1000µg/ml with selectivity indices of 9.52 and 15.24 respectively, indicating good therapeutic potential due to their safety margins.
 Conclusion: The results obtained from both in vitro and in vivo tests support the use of the plants selected in traditional treatment of malaria. A combination of methanol fruit extract of T. asiatica and methanol whole plant extract of S. pinnata showed promising parasite growth suppression against P. berghei that was comparable with Artemether and was synergistic on in vitro testing against chloroquine- resistant W2 strain of P. falciparum.

In Vitro Antimalarial Activity of Inhibitors of the Human GTPase Rac1.

ABSTRACTMalaria accounts for millions of cases and thousands of deaths every year. In the absence of an effective vaccine, drugs are still the most important tool in the fight against the disease. Plasmodium parasites developed resistance to all classes of known antimalarial drugs. Thus, the search for antimalarial drugs with novel mechanisms of action is compelling. The human GTPase Rac1 plays a role in parasite invasion of the host cell in many intracellular pathogens. Also, in Plasmodium falciparum, the involvement of Rac1 during both the invasion process and parasite intracellular development was suggested. The aim of this work is to test a panel of Rac1 inhibitors as potential antimalarial drugs. Fourteen commercially available or newly synthesized inhibitors of Rac1 were tested for antimalarial activity. Among these, EHop-016 was the most effective against P. falciparum in vitro, with nanomolar 50% inhibitory concentrations (IC50s) (138.8 ± 16.0 nM on the chloroquine-sensitive D10 strain and 321.5 ± 28.5 nM on the chloroquine-resistant W2 strain) and a selectivity index of 37.8. EHop-016 did not inhibit parasite invasion of red blood cells but affected parasite growth inside them. Among the tested Rac1 inhibitors, EHop-016 showed promising activity that raises attention to this class of molecules as potential antimalarials and deserves further investigation.

A trio of quinoline-isoniazid-phthalimide with promising antiplasmodial potential: Synthesis, in-vitro evaluation and heme-polymerization inhibition studies

Quinoline-isoniazid-phthalimide triads have been synthesised to assess their antiplasmodial efficacy and cytotoxicity against chloroquine-resistant W2 strain of P. falciparum and Vero cells, respectively. Most of the synthesized compounds displayed IC50 in lower nM range and appeared to be approximately five to twelve fold more active than chloroquine. Heme-binding studies were also carried out to delineate the mode of action. The promising compounds with IC50s in range of 11–30 nM and selectivity index >2800, may act as promising template for the design of new antiplasmodials.

Synthesis and antiplasmodial evaluation of 1H-1,2,3-triazole grafted 4-aminoquinoline-benzoxaborole hybrids and benzoxaborole analogues

A library of 1H-1,2,3-triazole-tethered 4-aminoquinoline-benzoxaborole hybrids as well as aryl substituted benzoxaborole analogues was synthesized and screened for their anti-plasmodial efficacy against both chloroquine-susceptibility 3D7 and chloroquine-resistant W2 strains of P. falciparum. The inclusion of quinoline core among the synthesized analogues resulted in substantial enhancement of anti-plasmodial activities. Further, the spacer of a flexible alkyl chain is marginally preferred over piperazyl-ethyl in inhibiting growth of P. falciparum. The most potent 4-aminoquinoline-benzoxaborole conjugate with ethyl as spacer exhibited IC50 values of 4.15 and 3.78 μM against 3D7 CQ-susceptible and W2 CQ-resistant strains of P. falciparum with lower cross resistance with Chloroquine. There was no difference in anti-plasmodial activities between the CQ-susceptible 3D7 and CQ-resistant W2 strains of P. falciparum for the benzoxaborole derivatives lacking a quinoline core.

In Vivo Antiplasmodial Activity of Terminalia mantaly Stem Bark Aqueous Extract in Mice Infected by Plasmodium berghei.

Background Terminalia mantaly is used in Cameroon traditional medicine to treat malaria and related symptoms. However, its antiplasmodial efficacy is still to be established. Objectives The present study is aimed at evaluating the in vitro and in vivo antiplasmodial activity and the oral acute toxicity of the Terminalia mantaly extracts. Materials and Methods Extracts were prepared from leaves and stem bark of T. mantaly, by maceration in distilled water, methanol, ethanol, dichloromethane (DCM), and hexane. All extracts were initially screened in vitro against the chloroquine-resistant strain W2 of P. falciparum to confirm its in vitro activity, and the most potent one was assessed in malaria mouse model at three concentrations (100, 200, and 400 mg/kg/bw). Biochemical, hematological, and histological parameters were also determined. Results Overall, 7 extracts showed in vitro antiplasmodial activity with IC50 ranging from 0.809 μg/mL to 5.886 μg/mL. The aqueous extract from the stem bark of T. mantaly (Tmsbw) was the most potent (IC50 = 0.809 μg/mL) and was further assessed for acute toxicity and efficacy in Plasmodium berghei-infected mice. Tmsbw was safe in mice with a median lethal dose (LD50) higher than 2000 mg/kg of body weight. It also exerted a good antimalarial efficacy in vivo with ED50 of 69.50 mg/kg and had no significant effect on biochemical, hematological, and histological parameters. Conclusion The results suggest that the stem bark extract of T. mantaly possesses antimalarial activity.

In vitro Multistage Malaria Transmission Blocking Activity of Selected Malaria Box Compounds.

PurposeContinuous efforts into the discovery and development of new antimalarials are required to face the emerging resistance of the parasite to available treatments. Thus, new effective drugs, ideally able to inhibit the Plasmodium life-cycle stages that cause the disease as well as those responsible for its transmission, are needed. Eight compounds from the Medicines for Malaria Venture (MMV) Malaria Box, potentially interfering with the parasite polyamine biosynthesis were selected and assessed in vitro for activity against malaria transmissible stages, namely mature gametocytes and early sporogonic stages.MethodsCompound activity against asexual blood stages of chloroquine-sensitive 3D7 and chloroquine-resistant W2 strains of Plasmodium falciparum was tested measuring the parasite lactate dehydrogenase activity. The gametocytocidal effect was determined against the P. falciparum 3D7elo1-pfs16-CBG99 strain with a luminescent method. The murine P. berghei CTRP.GFP strain was employed to assess compounds activities against early sporogonic stage development in an in vitro assay simulating mosquito midgut conditions.ResultsAmong the eight tested molecules, MMV000642, MMV000662 and MMV006429, containing a 1,2,3,4-tetrahydroisoquinoline-4-carboxamide chemical skeleton substituted at N-2, C-3 and C-4, displayed multi-stage activity. Activity against asexual blood stages of both strains was confirmed with values of IC50 (50% inhibitory concentration) in the range of 0.07–0.13 µM. They were also active against mature stage V gametocytes with IC50 values below 5 µM (range: 3.43–4.42 µM). These molecules exhibited moderate effects on early sporogonic stage development, displaying IC50 values between 20 and 40 µM.ConclusionGiven the multi-stage, transmission-blocking profiles of MMV000642, MMV000662, MMV006429, and their chemical characteristics, these compounds can be considered worthy for further optimisation toward a TCP5 or TCP6 target product profile proposed by MMV for transmission-blocking antimalarials.

Design, synthesis, heme binding and density functional theory studies of isoindoline-dione-4-aminoquinolines as potential antiplasmodials.

Aim:WHO Malaria report 2017 estimated 216 million cases of malaria and 445,000 deaths worldwide, with 91% of deaths affecting the African region.Results/methodology:Microwave promoted the synthesis of cycloalkyl amine substituted isoindoline-1,3-dione-4-aminoquinolines was urbanized for evaluating their antiplasmodial activities. Compound with the optimum combination of propyl chain length and hydroxyethyl piperazine proved to be the most potent among the synthesized scaffolds against chloroquine-resistant W2 strain of Plasmodium falciparum with an IC50 value of 0.006 μM. Heme-binding along with density functional theory studies were further carried out in order to delineate the mechanism of action of the most active compound.Conclusion:The synthesized scaffold can act as a therapeutic template for further synthetic modifications toward the search for a new antimalarial agent.

Synthesis, anti-plasmodial and cytotoxic evaluation of 1H-1,2,3-triazole/acyl hydrazide integrated tetrahydro-β-carboline-4-aminoquinoline conjugates

A series of 1H-1,2,3-triazole/acylhydrazide-tethered tetrahydro-β-carboline-4-aminoquinoline conjugates was synthesized with an aim to study their anti-plasmodial structure-activity relationship. The presence of 1H-1,2,3-triazole-core along with a flexible alkyl chain length on aminoquinoline core has favourable influence on the anti-plasmodial activity against Chloroquine-resistant W2 strain of P. falciparum while the introduction of hydrazine core not only diminished the activities but also resulted in increased cytotoxicity against mammalian Vero cells.

Antiplasmodial activity and cytotoxicity, isolation of active alkaloids, and dereplication of Xylopia sericea leaves ethanol extract by UPLC-DAD-ESI-MS/MS.

To assess the antiplasmodial activity of the ethanol extract of Xylopia sericea leaves, Annonaceae, often associated with antimalarial use and to perform a bioguided isolation of active compounds. Dereplication of ethanol extract by the UPLC-DAD-ESI-MS/MS technique allowed the identification of the major constituents, isolation and identification of alkaloids. The antiplasmodial and cytotoxic activity of the extract, fractions and isolated compounds was evaluated against the chloroquine-resistant W2 strain Plasmodium falciparum and HepG2 cells, respectively. Ethanol extract showed high reduction of parasitemia as well as moderate cytotoxicity (86.5±3.0% growth inhibition at 50μg/ml and CC50 72.1±5.1μg/ml, respectively). A total of eight flavonoids were identified, and two aporphine alkaloids, anonaine and O-methylmoschatoline, were isolated. Anonaine disclosed significant antiplasmodial effect and moderate cytotoxicity (IC50 23.2±2.7μg/ml, CC50 38.3±2.3μg/ml, SI 1.6) while O-methylmoschatoline was not active against P.falciparum and showed a low cytotoxicity (33.5±1.9% growth inhibition at 50μg/ml, CC50 274.4±0.5μg/ml). Characterization of Xylopia sericea leaves ethanol extract by UPLC-DAD-ESI-MS/MS as well as its antiplasmodial activity and the occurrence of anonaine and O-methylmoschatoline in this Xylopia species are reported by the first time.

In vitro evaluation of chloroquine-loaded and heparin surface-functionalized solid lipid nanoparticles

BackgroundUse of chloroquine, an otherwise safe and relatively affordable anti-malarial drug, was discontinued due to widespread prevalence of resistant parasites. Many entrant anti-malarial drugs for treatment of chloroquine resistant malaria raises the concerns of cost and safety among other challenges. Innovative ways of circumventing chloroquine resistance is of paramount importance. Such may include nanoparticulate delivery strategies and targeting. This study evaluated physicochemical properties and in vitro antiplasmodial activity of chloroquine encapsulated heparin functionalized solid lipid nanoparticles (CQ-Hep-SLNs) and non-heparin functionalized SLNs (CQ-SLN) against Plasmodium falciparum.MethodsThe modified double-emulsion solvent evaporation technique was used to prepare the nanoparticles. HPLC/UV was used to determine the in vitro drug release. The semi-automated micro-dilution technique was adapted in assessing the in vitro antiplasmodial activity to give drug concentration capable of inhibiting 50% of the P. falciparum (IC50), as a function of antiplasmodial efficacy.ResultsPrepared nanoparticles were below 500 nm in size with % drug loading (%DL) between 21 and 25% and encapsulation efficiency (%EE) of 78–90%. The drug-loaded SLN exhibited a biphasic drug release profile at pH 7.4, with an initial burst release during the first 24 h followed by sustained release in both formulations. Nanoformulated CQ-SLN (4.72 ± 0.14 ng/mL) and CQ-Hep-SLN (2.41 ± 0.27 ng/mL), showed enhanced in vitro antiplasmodial activities against chloroquine sensitive (D6) strain of P. falciparum, albeit with no activity against the chloroquine resistant W2 strain, compared to free CQ standard (5.81 ± 0.18 ng/mL).ConclusionsThese findings suggest that the nanoformulated drugs displayed enhanced anti-malarial activities against chloroquine sensitive (D6) strains of P. falciparum compared to the free CQ standard. There is some form of potential dual synergistic effect of CQ-loaded heparinized solid lipid nanoparticles (Hep-SLN), meaning that combining heparin and CQ in SLNs has beneficial effects, including potential for specific targeting of parasitized red blood cells as afforded by heparin. Thus, the study has produced SLNs nanoparticles that have superior in vitro activities than CQ on CQ-sensitive parasites.

Evaluation of Triazole and Isoxazole Derivatives as Potential Anti-infective Agents.

A series of isoxazole and triazole derivatives, with interesting bioactive scaffolds, were examined for their in vitro antibacterial, antifungal, and antiprotozoal activities. These compounds exhibited antitrypanosomal activity comparable to difluoromethylornithine (DMFO), a drug used in the treatment of human African trypanosomiasis. Isoxazole analogues 1, 3 and 4, and triazole derivatives 16, 17, 28, 37, 40 and 42 showed the highest antitrypanosomal activity with IC50 values of 17.89, 1.82, 10.38, 10.26, 11.77, 9.29, 3.93, 2.11, and 0.93 μM, respectively. Compounds 40 and 42 showed the most potent activity against Leishmania donovani amastigotes with IC50 values of 18.28 and 10.54 μM, respectively. Compound 42 showed the most potent activity against Leishmania donovani macrophage internalized amastigotes with an IC50 value of 8.32 μM. Conjugate triazoles 40-43 displayed potential antimalarial activity against chloroquine-resistant W2 and chloroquine sensitive D6 Plasmodium falciparum strains (IC50 value range from 0.58 to 8.36 μM). Compound 37 showed antibacterial activity against Staphylococcus aureus, MRSA and Mycobacterium intracellulare with IC50 values of 15.53, 14.22 and 47.45 μM, respectively. None of the compounds exhibited antifungal activity.

Piperazine-linked 4-aminoquinoline-chalcone/ferrocenyl-chalcone conjugates: Synthesis and antiplasmodial evaluation.

A series of piperazine-linked 4-aminoquinoline-chalcone/ferrocenyl-chalcone conjugates were prepared with a view to evaluate their activities against Plasmodium falciparum. The synthesized conjugates had in vitro IC50 values from 0.41 to 2.38μm against chloroquine-resistant and mefloquine-sensitive W2 strain of P.falciparum. The submicromolar activities of most of the synthesized conjugates suggest that such molecular frameworks can act as therapeutic templates for the design and synthesis of new antimalarials.

Docking, synthesis and antimalarial activity of novel 4-anilinoquinoline derivatives

A series of 4-anilinoquinoline triazine derivatives were designed, synthesized and screened for in vivo antimalarial activity against a chloroquine-sensitive strain of Plasmodium berghei. The compounds were further subjected to in vitro antimalarial activity against chloroquine-resistant W2 strain of Plasmodium falciparum and β-haematin inhibition studies. All the compounds exhibited in vivo antimalarial activity better than that shown by the standard drug, chloroquine. Twelve out of fifteen compounds showed better inhibition than that of chloroquine against chloroquine-resistant W2 strain of Plasmodium falciparum. Ten compounds showed β-haematin inhibition, better than that of chloroquine, with IC50 values in the range of 18–25µM. One compound, 3k, was found to be better than artemisinin against W2 strain of Plasmodium falciparum and also displayed the best β-haematin inhibitory activity, thereby becoming eligible to be explored as a potential lead for antimalarial chemotherapy.

4-Aminoquinoline-ferrocenyl-chalcone conjugates: Synthesis and anti-plasmodial evaluation

A series of aliphatic and aromatic substituted 1H-1,2,3-triazole-tethered 4-amino-quinoline-ferrocenylchalcone conjugates has been synthesized and evaluated for anti-plasmodial activity. The conjugates with flexible aliphatic (aminoethanol or aminopropanol) substituents on the quinoline ring showed better anti-plasmodial activities compared to those with cyclic (piperazine or aminophenol) substituents. The conjugate 17j was the most potent and non-cytotoxic, with an IC50 value of 0.37 μM against the chloroquine-resistant W2 strain of Plasmodium falciparum.

Antiplasmodial activity of selected medicinal plants used to treat malaria in Ghana.

The use of medicinal plants for the treatment of diseases including malaria is commonplace in Ghanaian traditional medicine, though the therapeutic claims for most plants remain unvalidated. Antiplasmodial activity of the aqueous extracts and successively obtained petroleum ether, ethyl acetate and methanol fractions of the whole Phyllanthus fraternus plant, the leaves of Tectona grandis, Terminalia ivorensis and Bambusa vulgaris, and roots of Senna siamea were studied against Plasmodium falciparum chloroquine-sensitive 3D7 and chloroquine-resistant W2 strains. The aqueous extracts were assessed against human umbilical vein endothelial cells (HUVECs) for cytotoxicity, and the organic solvent fractions against human O(+) erythrocytes for haemolytic effect. Both extracts and fractions demonstrated antiplasmodial activity to varied extents. The aqueous extract of T. ivorensis was the most active (3D7, IC50 0.64 ± 0.14; and W2, IC50 10.52 ± 3.55μg/mL), and together with P. fraternus displayed cytotoxicity (CC50 6.25 ± 0.40 and 31.11 ± 3.31μg/mL, respectively). The aqueous extracts were generally selective for 3D7 strain of P. falciparum (selectivity indexes (SIs) ≥3.48) but only that of S. siamea was selective for the W2 strain (SI > 2.1). The organic solvent fractions also displayed antiplasmodial activity with the methanol fractions of P. fraternus and T. grandis, and the fractions of B. vulgaris showing activity with IC50 below 1μg/mL against P. falciparum 3D7 strain; some fractions showed haemolytic effect but with low to high selectivity indexes (SI ≥ 4). The results while justifying the traditional use of the plant materials in the treatment of malaria, however, suggest their cautious use.

Novel squaramides with in vitro liver stage antiplasmodial activity

A structure–activity relationship study was performed with ten 8-aminoquinoline-squaramides compounds active against liver stage malaria parasites, using human hepatoma cells (Huh7) infected by Plasmodium berghei parasites. In addition, their blood-schizontocidal activity was assessed against chloroquine-resistant W2 strain Plasmodium falciparum. Compound 3 was 7.3-fold more potent than the positive control primaquine against liver-stage parasites, illustrating the importance of the squarate moiety to activity.

Glycosyl hydroperoxides: A new class of potential antimalarial agents

Motivated by the antimalarial properties observed in organic peroxides, an extensive series of glycosyl hydroperoxides was prepared with the aim of identifying new bioactive molecules. Selected compounds were tested against a Plasmodium falciparum culture (chloroquine-susceptible strain D10 and chloroquine-resistant strain W2). Screening results indicated that the factors critical for antimalarial activity were the presence of a hydroperoxide moiety and solubility in water at pH 5.0. Moreover, the ability to inhibit β-hematin formation in vitro has been evaluated (BHIA Assay).

Investigation into novel thiophene- and furan-based 4-amino-7-chloroquinolines afforded antimalarials that cure mice

We herein report the design and synthesis of a novel series of thiophene- and furan-based aminoquinoline derivatives which were found to be potent antimalarials and inhibitors of β-hematin polymerization. Tested compounds were 3–71 times more potent in vitro than CQ against chloroquine-resistant (CQR) W2 strain with benzonitrile 30 being as active as mefloquine (MFQ), and almost all synthesized aminoquinolines (22/27) were more potent than MFQ against multidrug-resistant (MDR) strain C235. In vivo experiments revealed that compound 28 showed clearance with recrudescence at 40mg/kg/day, while 5/5 mice survived in Thompson test at 160mg/kg/day.

β-amino-alcohol tethered 4-aminoquinoline-isatin conjugates: Synthesis and antimalarial evaluation

A series of β-amino alcohol tethered 4-aminoquinoline-isatin conjugates were synthesized with the aim of probing their antimalarial structure activity relationship. Two of the most active conjugates (11b and 11f) exhibited antimalarial efficacy comparable to that of chloroquine, with IC50 values of 11.8 and 13.5 nM, respectively against chloroquine resistant W2 strain of Plasmodium falciparum and are devoid of any cytotoxicity.