Peroxide derivatives as SARS-CoV-2 entry inhibitors

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the ongoing coronavirus disease 2019 (COVID-19) pandemic. Host cell invasion is mediated by the interaction of the viral spike protein (S) with human angiotensin-converting enzyme 2 (ACE2) through the receptor-binding domain (RBD). In this work, bio-layer interferometry (BLI) was used to screen a series of fifty-two peroxides, including aminoperoxides and bridged 1,2,4 - trioxolanes (ozonides), with the aim of identifying small molecules that interfere with the RBD-ACE2 interaction. We found that two compounds, compound 21 and 29, exhibit the activity to inhibit RBD-ACE2. They are further demonstrated to inhibit SARS-CoV-2 cell entry, as shown in pseudovirus assay and experiment with authentic SARS-CoV-2. A comprehensive in silico analysis was carried out to study the physicochemical and pharmacokinetic properties, revealing that both compounds have good physicochemical properties as well as good bioavailability. Our results highlight the potential of small molecules targeting RBD inhibitors as potential therapeutic drugs for COVID-19.

Synthesis, docking studies and biological evaluation of 1H-1,2,3-triazole-7-chloroquinoline derivatives against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a single-stranded enveloped positive RNA virus and the cause of the ongoing coronavirus disease 2019 (COVID-19) pandemic. Chloroquine (CQ), an antimalarial drug, was reported to be active against several viruses including coronaviruses. The mechanism of host cell invasion by SARS-CoV-2 involves the interaction of angiotensin-converting enzyme (ACE2) with receptor-binding domain (RBD) of spike protein (S). The main protease (Mpro/3CLpro) is an attractive drug target due to its vital function in regulation of polyprotein translated from viral RNA. In this study, a series of novel quinoline-triazole hybrid compounds was synthesized and subjected to evaluations on their cytotoxicity, interactions with different variants of RBD in SARS-CoV-2 and with 3CLpro enzyme by experimental and computational techniques to identify their ability of counteracting viral infection. The results of bio-layer interferometry showed that quinoline derivative 11 has good interaction with delta plus and omicron RBD variants (KD = 3.46 × 10-5 and 6.38 × 10-5 M) while derivative 1 is the best binder for recent variant omicron (KD = 26.9 µM) among the series. Potent compounds 1-4 and 11 also demonstrated a suppressive effect on 3CLpro activity in a non-dose-dependent manner. Further docking study revealed that these compounds interacted within the same area of RBD, while no correlation was found for 3CLpro. Furthermore, the molecular dynamics simulations were carried out to assess the conformational stability of docked complexes for preliminary verification.

Chemo-/Regio-Selective Synthesis of Novel Functionalized Spiro[pyrrolidine-2,3'-oxindoles] under Microwave Irradiation and Their Anticancer Activity

A novel series of nitrostyrene-based spirooxindoles were synthesized via the reaction of substituted isatins 1a-b, a number of α-amino acids 2a-e and (E)-2-aryl-1-nitroethenes 3a-e in a chemo/regio-selective manner using [3+2] cycloaddition (Huisgen) reaction under microwave irradiation conditions. The structure elucidation of all the synthesized spirooxindoles were done using 1H and 13C NMR and HRMS spectral analysis. The single crystal X-ray crystallographic study of compound 4l was used to assign the stereochemical arrangements of the groups around the pyrrolidine ring in spiro[pyrrolidine-2,3'-oxindoles] skeleton. The in vitro anticancer activity of spiro[pyrrolidine-2,3'-oxindoles] analogs 4a-w against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines shows promising results. Out of the 23 synthesized spiro[pyrrolidine-2,3'-oxindoles], while five compounds (4c, 4f, 4m, 4q, 4t) (IC50 = 34.99-47.92 µM; SI = 0.96-2.43) displayed significant in vitro anticancer activity against human lung (A549) cancer cell lines, six compounds (4c, 4f, 4k, 4m, 4q, 4t) (IC50 = 41.56-86.53 µM; SI = 0.49-0.99) displayed promising in vitro anticancer activity against human liver (HepG2) cancer cell lines. In the case of lung (A549) cancer cell lines, these compounds were recognized to be more efficient and selective than standard reference artemisinin (IC50 = 100 µM) and chloroquine (IC50 = 100 µM; SI: 0.03). However, none of them were found to be active as compared to artesunic acid [IC50 = 9.85 µM; SI = 0.76 against lung (A549) cancer cell line and IC50 = 4.09 µM; SI = 2.01 against liver (HepG2) cancer cell line].

Next generation of boron neutron capture therapy (BNCT) agents for cancer treatment

Boron neutron capture therapy (BNCT) is one of the most promising treatments among neutron capture therapies due to its long-term clinical application and unequivocally obtained success during clinical trials. Boron drug and neutron play an equivalent crucial role in BNCT. Nevertheless, current clinically used l-boronophenylalanine (BPA) and sodium borocaptate (BSH) suffer from large uptake dose and low blood to tumor selectivity, and that initiated overwhelm screening of next generation of BNCT agents. Various boron agents, such as small molecules and macro/nano-vehicles, have been explored with better success. In this featured article, different types of agents are rationally analyzed and compared, and the feasible targets are shared to present a perspective view for the future of BNCT in cancer treatment. This review aims at summarizing the current knowledge of a variety of boron compounds, reported recently, for the application of BCNT.

Natural-Product-Inspired Microwave-Assisted Synthesis of Novel Spirooxindoles as Antileishmanial Agents: Synthesis, Stereochemical Assignment, Bioevaluation, SAR, and Molecular Docking Studies

Leishmaniasis is a neglected tropical disease, and there is an emerging need for the development of effective drugs to treat it. To identify novel compounds with antileishmanial properties, a novel series of functionalized spiro[indoline-3,2'-pyrrolidin]-2-one/spiro[indoline-3,3'-pyrrolizin]-2-one 23a-f, 24a-f, and 25a-g were prepared from natural-product-inspired pharmaceutically privileged bioactive sub-structures, i.e., isatins 20a-h, various substituted chalcones 21a-f, and 22a-c amino acids, via 1,3-dipolar cycloaddition reactions in MeOH at 80 °C using a microwave-assisted approach. Compared to traditional methods, microwave-assisted synthesis produces higher yields and better quality, and it takes less time. We report here the in vitro antileishmanial activity against Leishmania donovani and SAR studies. The analogues 24a, 24e, 24f, and 25d were found to be the most active compounds of the series and showed IC₅₀ values of 2.43 µM, 0.96 µM, 1.62 µM, and 3.55 µM, respectively, compared to the standard reference drug Amphotericin B (IC₅₀ = 0.060 µM). All compounds were assessed for Leishmania DNA topoisomerase type IB inhibition activity using the standard drug Camptothecin, and 24a, 24e, 24f, and 25d showed potential results. In order to further validate the experimental results and gain a deeper understanding of the binding manner of such compounds, molecular docking studies were also performed. The stereochemistry of the novel functionalized spirooxindole derivatives was confirmed by single-crystal X-ray crystallography studies.

Combining computational and experimental evidence on the activity of antimalarial drugs on papain-like protease of SARS-CoV-2: A repurposing study

The development of inhibitors that target the papain-like protease (PLpro) has the potential to counteract the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the agent causing coronavirus disease 2019 (COVID-19). Based on a consideration of its several downstream effects, interfering with PLpro would both revert immune suppression exerted by the virus and inhibit viral replication. By following a repurposing strategy, the current study evaluates the potential of antimalarial drugs as PLpro inhibitors, and thereby the possibility of their use for treatment of SARS-CoV-2 infection. Computational tools were employed for structural analysis, molecular docking, and molecular dynamics simulations to screen antimalarial drugs against PLpro, and in silico data were validated by in vitro experiments. Virtual screening highlighted amodiaquine and methylene blue as the best candidates, and these findings were complemented by the in vitro results that indicated amodiaquine as a μM PLpro deubiquitinase inhibitor. The results of this study demonstrate that the computational workflow adopted here can correctly identify active compounds. Thus, the highlighted antimalarial drugs represent a starting point for the development of new PLpro inhibitors through structural optimization.

Antimalarial and antitumour activities of the steroidal quinone-methide celastrol and its combinations with artemiside, artemisone and methylene blue

Artemisinin, isolated from the traditional Chinese medicinal plant qīng hāo 青蒿 (Artemisia annua) and its derivatives are used for treatment of malaria. With treatment failures now being recorded for the derivatives and companion drugs used in artemisinin combination therapies new drug combinations are urgently required. The amino-artemisinins artemiside and artemisone display optimal efficacies in vitro against asexual and sexual blood stages of the malaria parasite Plasmodium falciparum and are active against tumour cell lines. In continuing the evolution of combinations of the amino-artemisinins with new drugs, we examine the triterpenoid quinone methide celastrol isolated from the traditional Chinese medicinal plant léi gōng téng 雷公藤 (Tripterygium wilfordii). This compound is redox active, and has attracted considerable attention because of potent biological activities against manifold targets. We report that celastrol displays good IC₅₀ activities ranging from 0.50–0.82 µM against drug-sensitive and resistant asexual blood stage Pf, and 1.16 and 0.28 µM respectively against immature and late stage Pf NF54 gametocytes. The combinations of celastrol with each of artemisone and methylene blue against asexual blood stage Pf are additive. Given that celastrol displays promising antitumour properties, we examined its activities alone and in combinations with amino-artemisinins against human liver HepG2 and other cell lines. IC₅₀ values of the amino-artemisinins and celastrol against HepG2 cancer cells ranged from 0.55–0.94 µM. Whereas the amino-artemisinins displayed notable selectivities (SI > 171) with respect to normal human hepatocytes, in contrast, celastrol displayed no selectivity (SI < 1). The combinations of celastrol with artemiside or artemisone against HepG2 cells are synergistic. Given the promise of celastrol, judiciously designed formulations or structural modifications are recommended for mitigating its toxicity.

Antimalarial and anticancer activity evaluation of bridged ozonides, aminoperoxides and tetraoxanes

Bridged aminoperoxides, for the first time, were investigated for the in vitro antimalarial activity against the chloroquine-resistant Plasmodium falciparum strain K1 and for their cytotoxic activities against immortalized human normal liver (LO2) and lung (BEAS-2B) cell lines as well as human liver (HepG2) and lung (A549) cancer cell lines. Aminoperoxides exhibit good cytotoxicity against lung A549 cancer cells line. Synthetic ozonides were shown to have high activity against the chloroquine-resistant P. falciparum . A cyclic voltammetry study of peroxides was performed, and most of the compounds did not show a direct correlation in oxidative capacity-activity. Peroxides were analyzed for ROS production to understand their mechanism of action. However, none of the compounds has an impact on ROS generation, suggesting that ozonides induce apoptosis in HepG2 cells through ROS - independent dysfunction pathway.

Exploring SARS-CoV-2 Delta variant spike protein receptor-binding domain (RBD) as a target for tanshinones and antimalarials

The interaction of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor-binding domain (RBD) of spike protein with angiotensin-converting enzyme 2 (ACE2) mediates cell invasion. While this interaction mechanism is conserved, the RBD is affected by amino acid mutations in variants such as Delta and Omicron, resulting in enhanced transmissibility and altered ligand binding. Tanshinones are currently investigated as multi-target antiviral agents, but the studies were limited to the original SARS-CoV-2. This study aims at investigating the interaction of tanshinones with the Delta RBD. Chloroquine, methylene blue and pyronaridine, antimalarials previously identified as SARS-CoV-2 RBD binders, were studied for reference. Docking indicated the best scores for tanshinones, while bio-layer interferometry and molecular dynamics highlighted methylene blue as the best Delta RBD binder, although with decreased affinity with respect to the original strain.

Biological Evaluation in Resistant Cancer Cells and Study of Mechanism of Action of Arylvinyl-1,2,4-Trioxanes

1,2,4-trioxane is a pharmacophore, which possesses a wide spectrum of biological activities, including anticancer effects. In this study, the cytotoxic effect and anticancer mechanism of action of a set of 10 selected peroxides were investigated on five phenotypically different cancer cell lines (A549, A2780, HCT8, MCF7, and SGC7901) and their corresponding drug-resistant cancer cell lines. Among all peroxides, only 7 and 8 showed a better P-glycoprotein (P-gp) inhibitory effect at a concentration of 100 nM. These in vitro results were further validated by in silico docking and molecular dynamic (MD) studies, where compounds 7 and 8 exhibited docking scores of −7.089 and −8.196 kcal/mol, respectively, and remained generally stable in 100 ns during MD simulation. Further experiments revealed that peroxides 7 and 8 showed no significant effect on ROS accumulations and caspase-3 activity in A549 cells. Peroxides 7 and 8 were also found to decrease cell membrane potential. In addition, peroxides 7 and 8 were demonstrated to oxidize a flavin cofactor, possibly elucidating its mechanism of action. In conclusion, apoptosis induced by 1,2,4-trioxane was shown to undergo via a ROS- and caspase-3-independent pathway with hyperpolarization of cell membrane potential.

Functionalized Boron Nanoparticles as Potential Promising Antimalarial Agents

Boron nanoparticles (BNPs), functionalized with hydroxyl groups, were synthesized in situ by a cascade process, followed by bromination and hydrolyzation reactions. These functionalized BNPs, (B _m (OH) _n ), were characterized using ¹H and ¹¹B NMR spectra, Fourier-transform infrared (FT-IR) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray photoelectron spectroscopy (XPS) methods. These nanoparticles were also evaluated in vitro for their antimalarial activity against Plasmodium falciparum (3D7 strain) with an IC₅₀ value of 0.0021 μM and showed low toxicity to Uppsala 87 malignant glioma (U87MG) cell lines, malignant melanoma A375 cell lines, KB human oral cancer cell lines, rat cortical neuron cell lines, and rat fibroblast-like synoviocyte (FLS) cell lines.

Synthesis and Coordination Properties of a Water-Soluble Material by Cross-Linking Low Molecular Weight Polyethyleneimine with Armed Cyclotriveratrilene

In this study, a full organic and water-soluble material was synthesized by coupling low molecular weight polyethylenimine (PEI-800) with cyclotriveratrilene (CTV). The water-soluble cross-linked polymer contains hydrophobic holes with a high coordination capability towards different organic drug molecules. The coordinating capability towards hydrophilic drugs (doxorubicin, gatifloxacin and sinomenine) and hydrophobic drugs (camptothecin and celastrol) was analyzed in an aqueous medium by using NMR, UV-Vis and emission spectroscopies. The coordination of drug molecules with the armed CTV unit through hydrophobic interactions was observed. In particular, celastrol exhibited more ionic interactions with the PEI moiety of the hosting system. In the case of doxorubicin, the host-guest detachment was induced by the addition of ammonium chloride, suggesting that the intracellular environment can facilitate the release of the drug molecules.

A Drug Repurposing Approach for Antimalarials Interfering with SARS-CoV-2 Spike Protein Receptor Binding Domain (RBD) and Human Angiotensin-Converting Enzyme 2 (ACE2)

Host cell invasion by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is mediated by the interaction of the viral spike protein (S) with human angiotensin-converting enzyme 2 (ACE2) through the receptor-binding domain (RBD). In this work, computational and experimental techniques were combined to screen antimalarial compounds from different chemical classes, with the aim of identifying small molecules interfering with the RBD-ACE2 interaction and, consequently, with cell invasion. Docking studies showed that the compounds interfere with the same region of the RBD, but different interaction patterns were noted for ACE2. Virtual screening indicated pyronaridine as the most promising RBD and ACE2 ligand, and molecular dynamics simulations confirmed the stability of the predicted complex with the RBD. Bio-layer interferometry showed that artemisone and methylene blue have a strong binding affinity for RBD (KD = 0.363 and 0.226 μM). Pyronaridine also binds RBD and ACE2 in vitro (KD = 56.8 and 51.3 μM). Overall, these three compounds inhibit the binding of RBD to ACE2 in the μM range, supporting the in silico data.

Cytotoxicity of isoflavones from Millettia dura

The first phytochemical investigation of the flowers of Millettia dura resulted in the isolation of seven isoflavones, a flavonol and a chalcone. Eleven isoflavones and a flavonol isolated from various plant parts from this plant were tested for cytotoxicity against a panel of cell lines, and six of these showed good activity with IC₅₀ values of 6-14 μM. Durmillone was the most active with IC₅₀ values of 6.6 μM against A549 adenocarcinomic human alveolar basal epithelial cancer cell line with low cytotoxicity against the non-cancerous cell lines BEAS-2B (IC₅₀ = 58.4 μM), LO2 hepatocytes (IC₅₀ 78.7 μM) and CCD19Lu fibroblasts (IC₅₀ >100 μM).

Novel halogenated arylvinyl-1,2,4 trioxanes as potent antiplasmodial as well as anticancer agents: Synthesis, bioevaluation, structure-activity relationship and in-silico studies

Herein, we have synthesized a series of lipophilic, halogenated-arylvinyl-1,2,4-trioxanes 8a-g (28 compounds) and assessed for their in vitro anti-plasmodial activity in Plasmodium falciparum culture using SYBRgreen-I fluorescence assay against chloroquine-resistant Pf INDO and artemisinin-resistant Pf Cam 3.1^R539T (MRA-1240) strains. Alongside, the cell cytotoxic potential of 8a-g has also been determined against the HEK293 cell line in vitro. Out of twenty-eight halogenated-arylvinyl-1,2,4-trioxanes; ten analogues (8a₂, 8a₄, 8b₂, 8b₄, 8d₄, 8e₁, 8e₂, 8e_4,8f₂, and 8g₄) have shown potent in vitro antiplasmodial activity with IC₅₀ < 27 nM (IC₅₀ range = 4.48-26.58 nM). Also, the selectivity index (SI) for these ten analogues were found in the range of 72.00-3972.50 which indicates their selective potential towards Plasmodium cells. Results of the cell cycle stage specificity with two of the most potent compounds 8a₄ {(IC₅₀ = 4.48 nM; SI = 3972.50) more potent than chloroquine (IC₅₀ = 546 nM; SI = 36.64) and artesunate (IC₅₀ = 6.6 nM; SI = 4333.33)} and 8e₂ (IC₅₀ = 9.69 nM; SI = 1348) against Pf INDO indicated all three stages to be the target of the action of 8e₂ while only rings and trophozoites appeared to be targeted by 8a₄. Ring stage survival assay against artemisinin-resistant Pf Cam 3.1^R539T indicated that 8a₄ may be well suited to replace artemisinin from current ACTs which are experiencing in vivo delayed parasite clearance. With intraperitoneal (i.p.) and oral (p.o.) route at the dose of 50 mg/kg/day × 4 days; 8a₄ has also shown 100% suppression of parasitemia in P. berghei ANKA infected Balb C mice. Further, the in vitro anticancer activity of 8a-g performed against human lung (A549) and liver (HepG2) cancer cell lines as also against immortalized normal lung (BEAS-2B) and liver (LO2) cell lines has revealed that most of the derivatives are endowed also with promising anticancer activity (IC₅₀ = 0.69-15 μM; SI = 1.02-20.61) in comparison with standard drugs such as chloroquine (IC₅₀ = 100 μM; SI = 0.03), artemisinin (IC₅₀ = 100 μM), and artesunic acid (IC₅₀ = 9.85 μM; SI = 0.76), respectively. All the derivatives have shown moderate anticancer activity against liver (HepG2) cancer cell lines. Arylvinyl-1,2,4-trioxanes 8f₂ (IC₅₀ = 0.69 μM; SI = 16.66), the most active compound of the series, has shown ∼145 fold more cytotoxic potential with higher selectivity in comparison to reference drugs chloroquine (IC₅₀ = 100 μM; SI = 0.03) and artemisinin (IC₅₀ = 100 μM), respectively against the lung (A549) cancer cell line. Finally, the in-silico docking studies of the potent halogenated 1,2,4-trioxanes along with reference drug molecules against epidermal growth factor receptor (EGFR; PDB ID: 1M17) have demonstrated the strong virtual interaction.

Synthesis, computational docking and biological evaluation of celastrol derivatives as dual inhibitors of SERCA and P-glycoprotein in cancer therapy

A series of eleven celastrol derivatives was designed, synthesized, and evaluated for their in vitro cytotoxic activities against six human cancer cell lines (A549, HepG2, HepAD38, PC3, DLD-1 Bax-Bak WT and DKO) and three human normal cells (LO₂, BEAS-2B, CCD19Lu). To our knowledge, six derivatives were the first example of dipeptide celastrol derivatives. Among them, compound 3 was the most promising derivative, as it exhibited a remarkable anti-proliferative activity and improved selectivity in liver cancer HepAD38 versus human normal hepatocytes, LO₂. Compound 6 showed higher selectivity in liver cancer cells against human normal lung fibroblasts, CCD19Lu cell line. The Ca²⁺ mobilizations of 3 and 6 were also evaluated in the presence and absence of thapsigargin to demonstrate their inhibitory effects on SERCA. Derivatives 3 and 6 were found to induce apoptosis on LO₂, HepG2 and HepAD38 cells. The potential docking poses of all synthesized celastrol dipeptides and other known inhibitors were proposed by molecular docking. Finally, 3 inhibited P-gp-mediated drug efflux with greater efficiency than inhibitor verapamil in A549 lung cancer cells. Therefore, celastrol-dipeptide derivatives are potent drug candidates for the treatment of drug-resistant cancer.

Corilagin prevents SARS-CoV-2 infection by targeting RBD-ACE2 binding

BACKGROUND

The outbreak of coronavirus (SARS-CoV-2) disease caused more than 100,000,000 people get infected and over 2,200,000 people being killed worldwide. However, the current developed vaccines or drugs may be not effective in preventing the pandemic of COVID-19 due to the mutations of coronavirus and the severe side effects of the newly developed vaccines. Chinese herbal medicines and their active components play important antiviral activities. Corilagin exhibited antiviral effect on human immunodeficiency virus (HIV), hepatitis C virus (HCV) and Epstein-Barr virus (EBV). However, whether it blocks the interaction between SARS-CoV-2 RBD and hACE2 has not been elucidated.

PURPOSE

To characterize an active compound, corilagin derived from Phyllanthus urinaria as potential SARS-CoV-2 entry inhibitors for its possible preventive application in daily anti-virus hygienic products.

METHODS

Computational docking coupled with bio-layer interferometry, BLI were adopted to screen more than 1800 natural compounds for the identification of SARS-CoV-2 spike-RBD inhibitors. Corilagin was confirmed to have a strong binding affinity with SARS-CoV-2-RBD or human ACE2 (hACE2) protein by the BLI, ELISA and immunocytochemistry (ICC) assay. Furthermore, the inhibitory effect of viral infection of corilagin was assessed by in vitro pseudovirus system. Finally, the toxicity of corilagin was examined by using MTT assay and maximal tolerated dose (MTD) studies in C57BL/6 mice.

RESULTS

Corilagin preferentially binds to a pocket that contains residues Cys 336 to Phe 374 of spike-RBD with a relatively low binding energy of -9.4 kcal/mol. BLI assay further confirmed that corilagin exhibits a relatively strong binding affinity to SARS-CoV-2-RBD and hACE2 protein. In addition, corilagin dose-dependently blocks SARS-CoV-2-RBD binding and abolishes the infectious property of RBD-pseudotyped lentivirus in hACE2 overexpressing HEK293 cells, which mimicked the entry of SARS-CoV-2 virus in human host cells. Finally, in vivo studies revealed that up to 300 mg/kg/day of corilagin was safe in C57BL/6 mice. Our findings suggest that corilagin could be a safe and potential antiviral agent against the COVID-19 acting through the blockade of the fusion of SARS-CoV-2 spike-RBD to hACE2 receptors.

CONCLUSION

Corilagin could be considered as a safe and environmental friendly anti-SARS-CoV-2 agent for its potential preventive application in daily anti-virus hygienic products.

A new benzophenone, and the antiplasmodial activities of the constituents of Securidaca longipedunculata fresen (Polygalaceae)

Extracts from Securidaca longipedunculata showed antiplasmodial activities against reference clones and clinical isolates using SYBR Green I method. A new benzophenone, 2,3,4,5-tetramethoxybenzophenone (1) was isolated and characterized along with seven known compounds: 4-hydroxy-2,3-dimethoxybenzophenone (2); 3-hydroxy-5-methoxybiphenyl (3), methyl-2-hydroxy-6-methoxybenzoate (4), benzyl-2-hydroxy-6-methoxybenzoate (5), 2-hydroxy-6-methoxybenzoic acid (6), 2,4,5-trimethoxybenzophenone (7) and 2-methoxy-3,4-methylenedioxybenzophenone (8). Compounds 1 and 2 showed ex vivo antiplasmodial activities (IC₅₀ 28.8 μM and 18.6 μM, respectively); while 5 and 8 showed in vivo activities (IC₅₀ 19.7 μM and 14.5 μM, respectively) against D6 strain. In a cytotoxicity assay, all the extracts (with an exception of the MeOH extract of the leaves) and pure compounds were not toxic to the normal LO2 and BEAS cell-lines, while the methanol roots extract (IC₅₀ 66.4 µg/mL against A549, and 77.4 µg/mL against HepG2), compounds 6 (IC₅₀ 22.2 µM against A549) and 7 (IC₅₀ 45.2 µM against HepG2) were weakly active against cancerous cell-lines.

Computational and experimental insights on the interaction of artemisinin, dihydroartemisinin and chloroquine with SARS-CoV-2 spike protein receptor-binding domain (RBD)

The mechanism of host cell invasion of severe acute respiratory syndrome coronavirus-2 SARS-CoV-2 is connected with the interaction of spike protein (S) with angiotensin-converting enzyme 2 (ACE2) through receptor-binding domain (RBD). Small molecules targeting this assembly are being investigated as drug candidates to contrast SARS-CoV-2. In this context, chloroquine, an antimalarial agent proposed as a repurposed drug to treat coronavirus disease-19 (COVID-19), was hypothesized to bind RBD among its other mechanisms. Similarly, artemisinin and its derivatives are being studied as potential antiviral agents. In this work, we investigated the interaction of artemisinin, its metabolite dihydroartemisinin and chloroquine with RBD by means of computational tools and in vitro. Docking studies showed that the compounds interfere with the same region of the protein and molecular dynamics (MD) simulations demonstrated the stability of the predicted complexes. Bio-layer interferometry showed that chloroquine dose-dependently binds RBD (KD = 35.9 µM) more efficiently than artemisinins.

Antileishmanial and cytotoxic activity of secondary metabolites from Taberneamontana ventricosa and two aloe species

In this study, the antileishmanial and cytotoxic activities of secondary metabolites isolated from Tabernaemontana ventricosa Hochst. ex A. DC., Aloe tororoana Reynolds, and Aloe schweinfurthii var. labworana Reynolds were investigated. Overall, nineteen known compounds were isolated from the three plant species. The compounds were characterized based on their spectroscopic data. Voacristine and aloenin were the most active compounds against promastigotes of antimony-sensitive Leishmania donovani (IC₅₀ 11 ± 5.2 μM and 26 ± 6.5 µM, respectively) with low toxicity against RAW264.7, murine monocyte/macrophage-like cells. The in silico docking evaluation and in vitro NO generation assay also substantially support the antileishmanial effects of these compounds. In a cytotoxicity assay against cancer and normal cell lines, ursolic acid highly inhibited proliferation of lung cancer cells, A549 (IC₅₀ 6.61 ± 0.7 μM) while voacristine was moderately active against human liver cancer cells, HepG2 (IC₅₀ 23.0 ± 0.0 μM). All other compounds were inactive against the test parasites and cell lines.

Antiplasmodial and antileishmanial flavonoids from Mundulea sericea

Five known compounds (1-5) were isolated from the extract of Mundulea sericea leaves. Similar investigation of the roots of this plant afforded an additional three known compounds (6-8). The structures were elucidated using NMR spectroscopic and mass spectrometric analyses. The absolute configuration of 1 was established using ECD spectroscopy. In an antiplasmodial activity assay, compound 1 showed good activity with an IC₅₀ of 2.0 μM against chloroquine-resistant W2, and 6.6 μM against the chloroquine-sensitive 3D7 strains of Plasmodium falciparum. Some of the compounds were also tested for antileishmanial activity. Dehydrolupinifolinol (2) and sericetin (5) were active against drug-sensitive Leishmania donovani (MHOM/IN/83/AG83) with IC₅₀ values of 9.0 and 5.0 μM, respectively. In a cytotoxicity assay, lupinifolin (3) showed significant activity on BEAS-2B (IC₅₀ 4.9 μM) and HePG2 (IC₅₀ 10.8 μM) human cell lines. All the other compounds showed low cytotoxicity (IC₅₀ > 30 μM) against human lung adenocarcinoma cells (A549), human liver cancer cells (HepG2), lung/bronchus cells (epithelial virus transformed) (BEAS-2B) and immortal human hepatocytes (LO2).

The present and future synthetic strategies of structural modifications of sinomenine

This review summarizes the modifications of sinomenine, a hot compound derived from herbal plants, which possesses diverse biological activities and low cytotoxicity.

Semi-synthetic isoflavones as BACE-1 inhibitors against Alzheimer's disease

BACE-1 is considered to be one of the targets for prevention and treatment of Alzheimer's disease (AD). We here report a novel class of semi-synthetic derivatives of prenylated isoflavones, obtained from the derivatization of natural flavonoids from Maclura pomifera. In vitro anti-AD effect of the synthesized compounds were evaluated via human recombinant BACE-1 inhibition assay. Compound 7, 8 and 13 were found to be the most active candidates which demonstrates good correlation between the computational docking and pharmacokinetic predictions. Moreover, cytotoxic studies demonstrated that the compounds are not toxic against normal and cancer cell lines. Among these three compounds, compound 7 enhance the activity of P-glycoprotein (P-gp) on A549 cancer cells and increases the activity of P-gp ATPase with a possible role on the efflux of amyloid-β across the blood- brain barrier. In conclusion, the present findings may pave the way for the discovery of a novel class of compounds to prevent and/or treat AD.

A Method for Rapid Screening of Anilide-Containing AMPK Modulators Based on Computational Docking and Biological Validation

Adenosine 5'-monophsphate-activated protein kinase (AMPK) is a crucial energy sensor for maintaining cellular homeostasis. Targeting AMPK may provide an alternative approach in treatment of various diseases like cancer, diabetes, and neurodegenerations. Accordingly, novel AMPK activators are frequently identified from natural products in recent years. However, most of such AMPK activators are interacting with AMPK in an indirect manner, which may cause off-target effects. Therefore, the search of novel direct AMPK modulators is inevitable and effective screening methods are needed. In this report, a rapid and straightforward method combining the use of in silico and in vitro techniques was established for selecting and categorizing huge amount of compounds from chemical library for targeting AMPK modulators. A new class of direct AMPK modulator have been discovered which are anilides or anilide-like compounds. In total 1,360,000 compounds were virtually screened and 17 compounds were selected after biological assays. Lipinski's rule of five assessment suggested that, 13 out of the 17 compounds are demonstrating optimal bioavailability. Proton acceptors constituting the structure of these compounds and hydrogen bonds with AMPK in the binding site appeared to be the important factors determining the efficacy of these compounds.

Novel Peroxides as Promising Anticancer Agents with Unexpected Depressed Antimalarial Activity

Twenty six peroxides belonging to bridged 1,2,4,5-tetraoxanes, bridged 1,2,4-trioxolanes (ozonides), and tricyclic monoperoxides were evaluated for their in vitro antimalarial activity against Plasmodium falciparum (3D7) and for their cytotoxic activities against immortalized human normal fibroblast (CCD19Lu), liver (LO₂ ), and lung (BEAS-2B) cell lines as well as human liver (HepG2) and lung (A549) cancer-cell lines. Synthetic ozonides were shown to have the highest cytotoxicity on HepG2 (IC₅₀ =0.19-0.59 μm), and some of these compounds selectively targeted liver cancer (selectivity index values for compounds 13 a and 14 a are 20 and 28, respectively) at levels that, in some cases, were higher than those of paclitaxel, artemisinin, and artesunic acid. In contrast some ozonides showed only moderate antimalarial activity against the chloroquine-sensitive 3D7 strain of P. falciparum (IC₅₀ from 2.76 to 24.2 μm; 12 b, IC₅₀ =2.76 μm; 13 a, IC₅₀ =20.14 μm; 14 a, IC₅₀ =6.32 μm). These results suggest that these derivatives have divergent mechanisms of action against cancer cells and malaria-infected cells. A cyclic voltammetry study of the peroxides was performed, but most of the compounds did not show direct correlation in oxidative capacity-activity. Our findings offer a new source of antimalarial and anticancer agents through structural modification of peroxide compounds.

N-Desmethyldauricine Induces Autophagic Cell Death in Apoptosis-Defective Cells via Ca2+ Mobilization

Resistance of cancer cells to chemotherapy remains a significant problem in oncology. Mechanisms regulating programmed cell death, including apoptosis, autophagy or necrosis, in the treatment of cancers have been extensively investigated over the last few decades. Autophagy is now emerging as an important pathway in regulating cell death or survival in cancer therapy. Recent studies demonstrated variety of natural small-molecules could induce autophagic cell death in apoptosis-resistant cancer cells, therefore, discovery of novel autophagic enhancers from natural products could be a promising strategy for treatment of chemotherapy-resistant cancer. By computational virtual docking analysis, biochemical assays, and advanced live-cell imaging techniques, we have identified N-desmethyldauricine (LP-4), isolated from rhizoma of Menispermum dauricum DC as a novel inducer of autophagy. LP-4 was shown to induce autophagy via the Ulk-1-PERK and Ca²⁺/Calmodulin-dependent protein kinase kinase β (CaMKKβ)-AMPK-mTOR signaling cascades, via mobilizing calcium release through inhibition of SERCA, and importantly, lead to autophagic cell death in a panel of cancer cells, apoptosis-defective and apoptosis-resistant cells. Taken together, this study provides detailed insights into the cytotoxic mechanism of a novel autophagic compound that targeting the apoptosis resistant cancer cells, and new implication on drug discovery from natural products for drug resistant cancer therapy.

Reactivity of decafluorobenzophenone and decafluoroazobenzene towards aromatic diamines: a practical entry to donor–acceptor systems

A series of Donor–Accepting–Donor (D–A–D) and Accepting–Donor–Accepting (A–D–A) compounds have been prepared and employed in the synthesis of oligomers potentially useful in optoelectronic applications.

Considerations on the mechanism of action of artemisinin antimalarials: part 1--the 'carbon radical' and 'heme' hypotheses

The isolation of artemisinin from the traditional medicinal herb qīng hāo (Artemisia annua), its characterization as a peroxide and preparation of the derivatives dihydroartemisinin, artemether and artesunate in the 1970s and 1980s by Chinese scientists under the umbrella of Project 523 collectively represents one of the great events in medicine in the latter third of the 20(th) Century. Artemisinins have become the most important component of chemotherapy of malaria: although used initially in monotherapy, they are now used in combination therapies or ACTs with longer half-life quinolines or arylmethanols. Nevertheless, the recent emergence of artemisinin-tolerant strains of the malaria parasite as reflected in increased clearance times of parasitaemia in patients treated with ACTs represents the greatest threat to control of malaria since resistance to chloroquine was first reported over 55 years ago. Importantly, the event brings into sharp focus the realization that relatively little is precisely understood, as opposed to widely assumed, for the mechanism of drug action of artemisinins and their synthetic peroxide analogues. Thus, we review here their antimalarial activities, the use of artemisinins in combination therapies, drug-drug interactions with the quinolines and arylmethanols, and metabolism of the artemisinins and synthetic peroxides. The mechanism of action of quinolines and arylmethanols, in particular their ability to induce redistribution of heme into the parasite cytosol, is also highlighted. This collective information is then used as a counterpoint to screen the validity of two of the prevailing hypotheses of drug action of artemisinins and synthetic peroxides, namely i. 'the C-radical hypothesis' wherein the peroxide undergoes 'bioactivation' by ferrous iron to generate C-radicals that are held to be the cytotoxic agents and ii. the 'heme hypothesis' wherein ferrous heme may generate either the same type of 'cytotoxic' C-radical, or the peroxide forms heme adducts that apparently inherit the exquisite cytotoxicities of the parent peroxide in one way or another. In a subsequent review, we screen the third and fourth hypotheses: the SERCA hypothesis wherein artemisinins modulate operation of the malaria parasite sarcoendo plasmic reticulum calcium pump SERCA Ca(2+)-ATPase ATP6 and the co-factor hypothesis wherein artemisinins act as oxidant drugs through rapidly oxidizing reduced conjugates of flavin cofactors, or those of flavin cofactor precursors such as riboflavin, and other susceptible endogenous substrates that play a role in maintaining intraparasitic redox homeostasis. For the C-radical hypothesis, details of in vitro chemical studies in the context of established chemistry of C-radicals and their ability to react with radical trapping agents such as nitroso compounds, cyclic nitrones, persistent nitroxyl radicals and atmospheric oxygen (dioxygen) are summarized. Overall, there is no correlation between antimalarial activities and abilities of the derived C-radicals to react with trapping agents in a chemical flask. This applies in particular to the reactions of C-radicals from artemisinins and steroidal tetraoxanes with the trapping agents vis-a-vis those from adamantyl capped systems. In an intraparasitic medium, it is not possible to intercept C-radicals either through use of a vast excess of a nitroxyl radical or dioxygen. The lack of correlation of antimalarial activities also applies to the Fe(2+)-mediated decomposition of artemisinins and synthetic peroxides, where literature data taken as indicating otherwise are critically assessed. The antagonism to antimalarial activities of artemisinins exerted by desferrioxamine (DFO) and related Fe(3+)-chelating agents is due to formation of stable chelates with bioavailable Fe(3+) that shuts down redox cycling through Fe(2+) and the subsequent generation of reactive oxygen species (ROS) via the Fenton reaction. The generation of ROS by Fe(2+) complements the action of artemisinins, to be discussed in Part 2; there is no need to posit a reaction of Fe(2+) with the artemisinins to account for their antimalarial activity. The ability of artemisinins and synthetic peroxides to elicit membrane damage is examined in the light of established processes of autoxidation. The oxidant character of the intraparasitic environment is incompatible with the reducing conditions required for generation of C-radicals, and in contrast to the expectation raised by the C-radical hypothesis, and indeed by the heme hypothesis outlined below, antimalarial activities of artemisinins are enhanced under higher partial pressures of dioxygen. Structure-activity data from a wide variety of artemisinins and synthetic peroxides cannot be accommodated within the bounds of the C-radical hypothesis. Finally, the antimalarial Cradical construct sharply contrasts with that of the potently antitumour-active ene-diyne antibiotics such as neocarzinostatin. In an iron-free process, these compounds generate highly reactive aryl C-radicals that abstract H atoms from deoxyribose units in DNA to generate alkyl C-radicals. The last do react with dioxygen in a normal intracellular environment to initiate DNA strand cleavage. Overall, it must be concluded that the C-radical hypothesis as the basis for antimalarial activities of artemisinins and synthetic peroxides is untenable. Heme has been intensively studied as an 'activator' of artemisinins and other antimalarial peroxides, and indeed the hypothesis seemingly has become firmly embedded in the underlying brickwork of the scientific edifice. The locus of activity of the peroxides interacting with the heme is considered to be the parasite digestive vacuole. The basis for the nanomolar activities of artemisinins and synthetic peroxides is variously ascribed to heme-Fe(2+)-mediated generation of C-radicals from the peroxides, formation of heme-artemisinin adducts that are held either to engage in redox cycling with concomitant generation of ROS or to inhibit formation of hemozoin. In the last case, just like the aminoquinolines and arylmethanols, the peroxides are not the active agents, but exert their parasiticidal effects through allowing the build-up of free heme-Fe(3+), the ultimate cytotoxic entity. We assess the literature relating to generation of heme by hemoglobin digestion, and the stage at which this process becomes significant in the intraerythrocytic parasite. The claims of production of heme and conversion into hemozoin occurring in a lipid environment may have to be put aside based on recent literature data that indicates crystallization of hemozoin must take place an aqueous interface; association of lipids with the heme/hemozoin is likely to be a reflection of attractive van der Waals interactions involving the hydrophobic surface of the heme or hemozoin aggregates. In addition, the observation leading to the claim that hemozoin manufacture commences at the mid-ring stage cannot be independently verified. That the quinoline and arylmethanol antimalarials have essentially no activities on the ring stage parasites and exert greatest efficacy at the trophozoite stage where heme production is maximal is consistent with this. Conversely, artemisinins, and indeed redox active drugs such as methylene blue and others, are highly active against early ring stage parasites. Thus, there is a prominent disconnect between stage specificities of artemisinins vis-a-vis those of 4-aminoquinolines and arylmethanols suggesting that heme is not the target of the former class of drug. Further, the ability of the Fe(3+) chelate DFO to antagonize antimalarial activities of artemisinins, but not the activities of 4-aminoquinolines, cannot be explained by involvement of heme as a target for artemisinins. We critically examine the basis for formation of products obtained from reaction of heme with artemisinins and synthetic peroxides under conditions ranging from biomimetic - reactions employing catalytic reagents under aqueous or semi-aqueous conditions - to those conducted under highly reducing and eminently artificial conditions, usually in the solvent dimethyl sulfoxide (DMSO) that both forms well characterized complexes with heme-Fe(2+) and actually assists in driving single electron transfer processes. It is noted that alkylated products tend to form in high yields under the last conditions, and this aspect is readily explained. Irrespective of product yields obtained under various conditions, an overarching correlation between facility of the reaction of the peroxide with heme and their antimalarial activities does not exist. The is underscored by the reproducible outcomes of reactions conducted under biomimetic conditions indicating adducts cannot form in physiologically meaningful concentrations and that heme is a recalcitrant reaction partner to artemisinins in general. Again, as in the case of the C-radical hypothesis, structure-activity data from a wide variety of artemisinins and synthetic peroxides is difficult to reconcile with the heme hypothesis. This applies in particular to dimeric and trimeric artemisinin derivatives where the ascribing of biological activity to reactions of the derived radicals or to the vastly encumbered artemisinin-heme adducts is physically unrealistic. Finally, the facile metabolism and induction of metabolism of the current clinically used artemisinins by members of the CYP superfamily - heme proteins that require an intimate interaction of the heme with the artemisinin for metabolism to occur - is incompatible with the oft-cited proclivity of the peroxide to associate via complex formation with heme as a prelude to its 'activation' as an antimalarial agent within the malaria parasite. (ABSTRACT TRUNCATED)

Antiplasmodial and anti-inflammatory activities of Canthium henriquesianum (K. Schum), a plant used in traditional medicine in Burkina Faso

ETHNOPHARMACOLOGICAL RELEVANCE

Canthium henriquesianum (K. Schum) is traditionally used in Burkina Faso for the treatment of malaria, but has not been properly investigated, yet. The aim of this study was to characterize in vitro the antiplasmodial and the anti-inflammatory activity of extracts from Canthium henriquesianum (K. Schum). In parallel, extracts of Gardenia sokotensis (Hutch) and Vernonia colorata (Willd), also traditionally used together in Burkina Faso and already reported with antimalarial activity, were compared.

MATERIALS AND METHODS

Plant extracts were tested in vitro for antimalarial activity against chloroquine susceptible (D10) and resistant (W2) strains of Plasmodium falciparum using the lactate dehydrogenase assay. Cell cytotoxicity was assessed on human dermal fibroblast (HDF) by the MTT assay. The selectivity index (SI) was used as the ratio of the activity against the parasites compared to the toxicity of the plant extract against HDF. In vitro cytokine production was assessed by ELISA technique.

RESULTS

Canthium henriquesianum aqueous extract had a moderate antimalarial activity (IC50<50 µg/ml) with a good selectivity index (SI=HDF/D10>7). Canthium henriquesianum diisopropyl ether extract was the most potent inhibitor of parasite growth with an IC50 9.5 µg/ml on W2 and 8.8 µg/ml on D10 and limited toxicity (SI>2). Gardenia sokotensis and Vernonia colorata aqueous extracts were shown to be significantly less active (IC50≥50 µg/ml) with substantial toxicity. In addition, when the production of IL-1β and TNFα by lipopolysaccharide (LPS) or hemozoin (malaria pigment) stimulated human THP-1 monocytes was assayed, it was found that the extract of Canthium henriquesianum induced a dose-dependent inhibition of IL-1β, but not of TNFα production, thus confirming its traditional use as antipyretic. By NMR analysis, the chromone was identified as the mostly represented compound in the diisopropyl ether extract of Canthium henriquesianum. Chromone however, was less active as antimalarial than the crude extract and it did not inhibit cytokine production at not toxic doses, indicating that other molecules in the total extracts contribute to the antiplasmodial and anti-inflammatory activity.

CONCLUSION

Canthium henriquesianum seems to possess antimalarial activity in vitro and the ability to inhibit the production of the pyrogenic cytokine IL-1β.

Interactions between artemisinins and other antimalarial drugs in relation to the cofactor model--a unifying proposal for drug action

Artemisinins are proposed to act in the malaria parasite cytosol by oxidizing dihydroflavin cofactors of redox-active flavoenzymes, and under aerobic conditions by inducing their autoxidation. Perturbation of redox homeostasis coupled with the generation of reactive oxygen species (ROS) ensues. Ascorbic acid-methylene blue (MB), N-benzyl-1,4-dihydronicotinamide (BNAH)-MB, BNAH-lumiflavine, BNAH-riboflavin (RF), and NADPH-FAD-E. coli flavin reductase (Fre) systems at pH 7.4 generate leucomethylene blue (LMB) and reduced flavins that are rapidly oxidized in situ by artemisinins. These oxidations are inhibited by the 4-aminoquinolines piperaquine (PPQ), chloroquine (CQ), and others. In contrast, the arylmethanols lumefantrine, mefloquine (MFQ), and quinine (QN) have little or no effect. Inhibition correlates with the antagonism exerted by 4-aminoquinolines on the antimalarial activities of MB, RF, and artemisinins. Lack of inhibition correlates with the additivity/synergism between the arylmethanols and artemisinins. We propose association via π complex formation between the 4-aminoquinolines and LMB or the dihydroflavins; this hinders hydride transfer from the reduced conjugates to the artemisinins. The arylmethanols have a decreased tendency to form π complexes, and so exert no effect. The parallel between chemical reactivity and antagonism or additivity/synergism draws attention to the mechanism of action of all drugs described herein. CQ and QN inhibit the formation of hemozoin in the parasite digestive vacuole (DV). The buildup of heme-Fe(III) results in an enhanced efflux from the DV into the cytosol. In addition, the lipophilic heme-Fe(III) complexes of CQ and QN that form in the DV are proposed to diffuse across the DV membrane. At the higher pH of the cytosol, the complexes decompose to liberate heme-Fe(III) . The quinoline or arylmethanol reenters the DV, and so transfers more heme-Fe(III) out of the DV. In this way, the 4-aminoquinolines and arylmethanols exert antimalarial activities by enhancing heme-Fe(III) and thence free Fe(III) concentrations in the cytosol. The iron species enter into redox cycles through reduction of Fe(III) to Fe(II) largely mediated by reduced flavin cofactors and likely also by NAD(P)H-Fre. Generation of ROS through oxidation of Fe(II) by oxygen will also result. The cytotoxicities of artemisinins are thereby reinforced by the iron. Other aspects of drug action are emphasized. In the cytosol or DV, association by π complex formation between pairs of lipophilic drugs must adversely influence the pharmacokinetics of each drug. This explains the antagonism between PPQ and MFQ, for example. The basis for the antimalarial activity of RF mirrors that of MB, wherein it participates in redox cycling that involves flavoenzymes or Fre, resulting in attrition of NAD(P)H. The generation of ROS by artemisinins and ensuing Fenton chemistry accommodate the ability of artemisinins to induce membrane damage and to affect the parasite SERCA PfATP6 Ca(2+) transporter. Thus, the effect exerted by artemisinins is more likely a downstream event involving ROS that will also be modulated by mutations in PfATP6. Such mutations attenuate, but cannot abrogate, antimalarial activities of artemisinins. Overall, parasite resistance to artemisinins arises through enhancement of antioxidant defense mechanisms.

A partial convergence in action of methylene blue and artemisinins: antagonism with chloroquine, a reversal with verapamil, and an insight into the antimalarial activity of chloroquine

Artemisinins rapidly oxidize leucomethylene blue (LMB) to methylene blue (MB); they also oxidize dihydroflavins such as the reduced conjugates RFH₂ of riboflavin (RF), and FADH₂ of the cofactor flavin adenine dinucleotide (FAD), to the corresponding flavins. Like the artemisinins, MB oxidizes FADH₂, but unlike artemisinins, it also oxidizes NAD(P)H. Like MB, artemisinins are implicated in the perturbation of redox balance in the malaria parasite by interfering with parasite flavoenzyme disulfide reductases. The oxidation of LMB by artemisinin is inhibited by chloroquine (CQ), an inhibition that is abruptly reversed by verapamil (VP). CQ also inhibits artemisinin-mediated oxidation of RFH₂ generated from N-benzyl-1,4-dihydronicotinamide (BNAH)-RF, or FADH₂ generated from NADPH or NADPH-Fre, an effect that is also modulated by verapamil. The inhibition likely proceeds by the association of LMB or dihydroflavin with CQ, possibly involving donor-acceptor or π complexes that hinder oxidation by artemisinin. VP competitively associates with CQ, liberating LMB or dihydroflavin from their respective CQ complexes. The observations explain the antagonism between CQ-MB and CQ-artemisinins in vitro, and are reconcilable with CQ perturbing intraparasitic redox homeostasis. They further suggest that a VP-CQ complex is a means by which VP reverses CQ resistance, wherein such a complex is not accessible to the putative CQ-resistance transporter (PfCRT).

Facile oxidation of leucomethylene blue and dihydroflavins by artemisinins: relationship with flavoenzyme function and antimalarial mechanism of action

The antimalarial drug methylene blue (MB) affects the redox behaviour of parasite flavin-dependent disulfide reductases such as glutathione reductase (GR) that control oxidative stress in the malaria parasite. The reduced flavin adenine dinucleotide cofactor FADH(2) initiates reduction to leucomethylene blue (LMB), which is oxidised by oxygen to generate reactive oxygen species (ROS) and MB. MB then acts as a subversive substrate for NADPH normally required to regenerate FADH(2) for enzyme function. The synergism between MB and the peroxidic antimalarial artemisinin derivative artesunate suggests that artemisinins have a complementary mode of action. We find that artemisinins are transformed by LMB generated from MB and ascorbic acid (AA) or N-benzyldihydronicotinamide (BNAH) in situ in aqueous buffer at physiological pH into single electron transfer (SET) rearrangement products or two-electron reduction products, the latter of which dominates with BNAH. Neither AA nor BNAH alone affects the artemisinins. The AA-MB SET reactions are enhanced under aerobic conditions, and the major products obtained here are structurally closely related to one such product already reported to form in an intracellular medium. A ketyl arising via SET with the artemisinin is invoked to explain their formation. Dihydroflavins generated from riboflavin (RF) and FAD by pretreatment with sodium dithionite are rapidly oxidised by artemisinin to the parent flavins. When catalytic amounts of RF, FAD, and other flavins are reduced in situ by excess BNAH or NAD(P)H in the presence of the artemisinins in the aqueous buffer, they are rapidly oxidised to the parent flavins with concomitant formation of two-electron reduction products from the artemisinins; regeneration of the reduced flavin by excess reductant maintains a catalytic cycle until the artemisinin is consumed. In preliminary experiments, we show that NADPH consumption in yeast GR with redox behaviour similar to that of parasite GR is enhanced by artemisinins, especially under aerobic conditions. Recombinant human GR is not affected. Artemisinins thus may act as antimalarial drugs by perturbing the redox balance within the malaria parasite, both by oxidising FADH(2) in parasite GR or other parasite flavoenzymes, and by initiating autoxidation of the dihydroflavin by oxygen with generation of ROS. Reduction of the artemisinin is proposed to occur via hydride transfer from LMB or the dihydroflavin to O1 of the peroxide. This hitherto unrecorded reactivity profile conforms with known structure-activity relationships of artemisinins, is consistent with their known ability to generate ROS in vivo, and explains the synergism between artemisinins and redox-active antimalarial drugs such as MB and doxorubicin. As the artemisinins appear to be relatively inert towards human GR, a putative model that accounts for the selective potency of artemisinins towards the malaria parasite also becomes apparent. Decisively, ferrous iron or carbon-centered free radicals cannot be involved, and the reactivity described herein reconciles disparate observations that are incompatible with the ferrous iron-carbon radical hypothesis for antimalarial mechanism of action. Finally, the urgent enquiry into the emerging resistance of the malaria parasite to artemisinins may now in one part address the possibilities either of structural changes taking place in parasite flavoenzymes that render the flavin cofactor less accessible to artemisinins or of an enhancement in the ability to use intra-erythrocytic human disulfide reductases required for maintenance of parasite redox balance.

Old and new targets for innovative antimalarial compounds: the different strategies of the Italian Malaria Network

Clinical treatment-failures to affordable drugs encouraged new investigation for discovery and development of new prophylactic and therapeutic interventions against malaria. The Drug Discovery Cluster (DDcl) of the Italian Malaria Network gathers several highly integrated and complementary laboratories from different Italian Institutions to identify, synthesise, screen in vitro and in vivo new antimalarial molecules directed against the intraerythrocytic stage of P. falciparum parasites and/or with transmission blocking activity to select lead compounds for further development. Complementary research activities, both in vitro and in the clinics, aim at investigating the pathogenetic mechanisms of severe malaria anaemia and the different manifestations of the disease in malaria-HIV co-infected patients to identify new therapies and improve survival.

Human parvovirus B19 infection mimicking systemic lupus erythematosus in an adult patient

We report a case of widespread immune activation with moderate cytopenia during acute infection with human parvovirus B19 in an adult female patient, in whom five criteria for the diagnosis of systemic lupus erythematosus were present at disease onset. Our case is unusual due to the presence of a cutaneous rash mimicking leukocytoclastic vasculitis at presentation, moderate leukopenia with thrombocytopenia and the presence of a broad array of autoantibodies. Diagnosis was established on the grounds of serological tests confirming recent infection with human parvovirus B19; spontaneous regression of clinical and laboratory abnormalities was observed within 16 weeks, ruling out classic systemic lupus erythematosus. We conclude by proposing that human parvovirus B19 infection should be included in the differential diagnosis of lupus-like syndromes in adult patients.

Effects of reduced preload on diastolic filling in essential hypertensive patients with increased left ventricular mass

Doppler-derived indices of diastolic filling are widely used in the routine evaluation of essential hypertensives. However, these indices are affected by loading conditions and systolic performance. This study aimed at monitoring the transmitral flow pattern and indices of left ventricular systolic function during acute nonpharmacological isolated reduction of preload in essential hypertensives with left ventricular hypertrophy. Nine essential hypertensive patients with left ventricular hypertrophy and nine age- and sex-matched normotensive controls underwent echocardiographic and Doppler evaluation of both systolic function and diastolic filling indices at baseline and during lower body suction at -40 mm Hg. Lower body suction caused a similar decrease in end-diastolic volume index, stroke volume index, and midwall fractional shortening in the normotensives and hypertensives. Circumferential end-systolic stress was unaffected in both groups. Acceleration time of early diastolic filling and isovolumic relaxation time increased in the normotensives but not in the hypertensives. Deceleration time of early diastolic filling increased in both groups. The ratio of peak velocities during early filling and at atrial contraction decreased in the normotensives, whereas it was unchanged in the hypertensives; this was due to the fact that early filling velocity decreased in both groups, whereas peak velocity at atrial contraction decreased only in the hypertensives. We conclude that Doppler-derived diastolic filling indices are not affected by a reduction of preload in essential hypertensives with left ventricular hypertrophy.

Imipramine in alopecia areata. A double-blind, placebo-controlled study

Alopecia areata (AA) is a dermatologic disease whose onset is significantly associated to life events. Its course may often be characterized by high levels of anxiety and depression. These observations suggested a rationale for using an antidepressant in AA. Thirteen patients were enrolled in a double-blind, placebo-controlled study of efficacy of imipramine in alopecia. After six months clinically significant hair regrowth occurred in 5 of the 7 patients on imipramine, whereas no response was observed in the placebo group. An improvement in psychic symptomatology was present in both groups. Our preliminary results indicate the potential efficacy of imipramine in patients with AA, not acting directly through a reduction of anxiety or depression.