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.

Antiplasmodial Activity of Hydroalcoholic Extract from Jucá (Libidibia ferrea) Pods

Malaria is an infectious and parasitic disease caused by protozoa of the genus Plasmodium, which affects millions of people in tropical and subtropical areas. Recently, there have been multiple reports of drug resistance in Plasmodium populations, leading to the search for potential new active compounds against the parasite. Thus, we aimed to evaluate the in vitro antiplasmodial activity and cytotoxicity of the hydroalcoholic extract of Jucá (Libidibia ferrea) in serial concentrations. Jucá was used in the form of a freeze-dried hydroalcoholic extract. For the cytotoxicity assay, the(3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) method with the WI-26VA4 human cell line was used. For the antiplasmodial activity, Plasmodium falciparum synchronized cultures were treated with serial concentrations (0.2 to 50 μg/mL) of the Jucá extract. In terms of the chemical composition of the Jucá extract, gas chromatography coupled to mass spectrometry measurements revealed the main compounds as ellagic acid, valoneic acid dilactone, gallotannin, and gallic acid. The Jucá hydroalcoholic extract did not show cytotoxic activity per MTT, with an IC₅₀ value greater than 100 µg/mL. Regarding the antiplasmodial activity, the Jucá extract presented an IC₅₀ of 11.10 µg/mL with a selective index of nine. Because of its antiplasmodial activity at the tested concentrations and low toxicity, the Jucá extract is presented as a candidate for herbal medicine in the treatment of malaria. To the best of our knowledge, this is the first report of antiplasmodial activity in Jucá.

Antiplasmodial activity of coumarins isolated from Polygala boliviensis: in vitro and in silico studies

Polygala boliviensis is found in the Brazilian semiarid region. This specie is little chemically and biologically studied. Polygala spp. have different metabolites, especially coumarins. Studies indicate that coumarins have antimalarial potential, denoting the importance of researching new active compounds from plants, since the resistance of Plasmodium strains to conventional therapy has increased. The present study aimed to evaluate the antiplasmodial activity of auraptene and poligalen against a chloroquine-resistant strain of Plasmodium falciparum. Coumarins were isolated from P. boliviensis by open column chromatography and identified by Nuclear Magnetic Resonance Spectroscopy. A cytotoxicity assay was carried out using MTT test, and the in vitro antiplasmodial activity was evaluated using the W2 strain. The antiplasmodial activity results found were IC50=0.171 ± 0.016 for auraptene and 0.164 ± 0.012 for poligalen; the selectivity indexes were 78.71 and 609.76, respectively. Inverse virtual screening in the BRAMMT database by OCTOPUS 1.2 was applied to coumarins to find potential P. falciparum targets and showed higher affinity energy of auraptene for purine nucleoside phosphorylase (PfPNP) and of poligalen for dihydroorotate dehydrogenase (PfDHODH). Molecular Dynamics studies (MD and MM-GBSA) approach were applied to calculate binding energies against selected P. falciparum targets and showed that all coumarins were stable at the binding site during simulations. Furthermore, energies were favorable for complexation. This is the first report of auraptene in P. boliviensis species and of in vitro antiplasmodial activity of auraptene and poligalen. In silico studies indicated that the mechanism of action of coumarins is the inhibition of PfPNP and PfDHODH.Communicated by Ramaswamy H. Sarma.

Rational-Based Discovery of Novel β-Carboline Derivatives as Potential Antimalarials: From In Silico Identification of Novel Targets to Inhibition of Experimental Cerebral Malaria

Malaria is an infectious disease widespread in underdeveloped tropical regions. The most severe form of infection is caused by Plasmodium falciparum, which can lead to development of cerebral malaria (CM) and is responsible for deaths and significant neurocognitive sequelae throughout life. In this context and considering the emergence and spread of drug-resistant P. falciparum isolates, the search for new antimalarial candidates becomes urgent. β-carbolines alkaloids are good candidates since a wide range of biological activity for these compounds has been reported. Herein, we designed 20 chemical entities and performed an in silico virtual screening against a pool of P. falciparum molecular targets, the Brazilian Malaria Molecular Targets (BRAMMT). Seven structures showed potential to interact with PfFNR, PfPK7, PfGrx1, and PfATP6, being synthesized and evaluated for in vitro antiplasmodial activity. Among them, compounds 3−6 and 10 inhibited the growth of the W2 strain at µM concentrations, with low cytotoxicity against the human cell line. In silico physicochemical and pharmacokinetic properties were found to be favorable for oral administration. The compound 10 provided the best results against CM, with important values of parasite growth inhibition on the 5th day post-infection for both curative (67.9%) and suppressive (82%) assays. Furthermore, this compound was able to elongate mice survival and protect them against the development of the experimental model of CM (>65%). Compound 10 also induced reduction of the NO level, possibly by interaction with iNOS. Therefore, this alkaloid showed promising activity for the treatment of malaria and was able to prevent the development of experimental cerebral malaria (ECM), probably by reducing NO synthesis.

In vitro and in silico assessment of new beta amino ketones with antiplasmodial activity

BACKGROUND

Based on the current need for new drugs against malaria, our study evaluated eight beta amino ketones in silico and in vitro for potential antimalarial activity.

METHODS

Using the Brazilian Malaria Molecular Targets (BraMMT) and OCTOPUS® software programs, the pattern of interactions of beta-amino ketones was described against different proteins of P. falciparum and screened to evaluate their physicochemical properties. The in vitro antiplasmodial activities of the compounds were evaluated using a SYBR Green-based assay. In parallel, in vitro cytotoxic data were obtained using the MTT assay.

RESULTS

Among the eight compounds, compound 1 was the most active and selective against P. falciparum (IC50 = 0.98 µM; SI > 60). Six targets were identified in BraMMT that interact with compounds exhibiting a stronger binding energy than the crystallographic ligand: P. falciparum triophosphate phosphoglycolate complex (1LYX), P. falciparum reductase (2OK8), PfPK7 (2PML), P. falciparum glutaredoxin (4N0Z), PfATP6, and PfHT.

CONCLUSIONS

The physicochemical properties of compound 1 were compatible with the set of criteria established by the Lipinski rule and demonstrated its potential as a drug prototype for antiplasmodial activity.

COVID-19 Vaccines: Bioethical Consideration

The COVID-19 pandemic produced immeasurable impacts on the economy, education, and socialization, besides the loss of millions of lives. Thus, there has been an accelerated development of an unprecedented number of COVID-19 vaccine candidates to control the pandemic. The World Health Organization’s emergency use authorization of COVID-19 vaccines still in clinical trial allowed immunizing the population. This paper presents a perspective of the bioethical precepts of autonomy, non-maleficence, beneficence, and justice in the emergency use of COVID-19 vaccines. Furthermore, it emphasizes the importance of surveillance at all stages of vaccine development to detect adverse effects and ensure compliance with bioethical precepts.

COVID-19 pandemic: multilevel dental technical guidelines based on new scientific evidence

The COVID-19 pandemic imposed restrictive measures on dentistry in different regions of the world, ranging from stoppage of care to only permission for urgent and emergency dental services. Thus, new biosafety guidelines for resuming activities, whether in single dental offices, large clinics or dental education activities, are urgently required. In this sense, herein, guidelines that incorporate common points of the main protocols found in the literature for the resumption of dental activities at their different levels, whether in the scope of care or education, are presented. Furthermore, we present the incorporation of measures that allow an increase in the level of biosafety, such as the control of the dental team, the inclusion in the history of conjunctivitis as a possible alert for COVID-19, and the use of the pulse oximeter to assess the risk of silent hypoxemia, which may indicate a complication of COVID-19. In addition, new perspectives for directing research and innovation for biosafety in dentistry are discussed.

Potent and selective antiplasmodial activity of marine sponges from Bahia state, Brazil

This study evaluated the in vitro antiplasmodial and cytotoxic effects of 26 extracts from nine marine sponges collected in Salvador, Bahia state, Brazil. All assayed extracts were found to be potently active against Plasmodium falciparum W2 strain, with IC₅₀ values ranging from 0.28 to 22.34 μg mL^-1, and weakly cytotoxic against the human cell line WI-26-VA4 with CC₅₀ values > 89 μg mL^-1, thus displaying selectivity indices (SI) equal or higher than 17. Interestingly, some SI values exceeded 1,000. The highly potent and selective antiplasmodial activity of the assessed marine sponges is reported for the first time in this study.

Use of wide-field optical fluorescence for visualization of oral biofilm in a patient with peri-implant mucositis: a new approach

Peri-implant diseases, caused by bacteria from biofilm related to dental implants, are one of the main causes of late loss of implants. In this sense, peri-implant diseases are divided into peri-implant mucositis, when it affects only the soft tissues, and peri-implantitis, when there is a bone involvement, which can lead to the failure of dental implant therapy. Thus, biofilm removal is essential for peri-implant health, allowing long-term success in implant therapy. To improve the visualization of oral biofilm, which is usually transparent or colorless, disclosing agents have been routinely used. However, disclosing agents have allergenic potential and can cause staining extrinsically in restorative and prosthetic materials, leading to aesthetic impairment. Thus, the use of fluorescence has been studied as an alternative for visualization of oral biofilm. Therefore, this report describes the use of wide-field optical fluorescence for visualization of oral biofilm associated with implants and teeth, in a routine appointment and follow-up of a partially edentulous patient with peri-implant mucositis. In addition, this report showed wide-field optical fluorescence can be used in a clinical routine of care of patients with dental implants. In this sense, wide-field optical fluorescence allowed easy and immediate visualization of the mature oral biofilm for its adequate removal, evaluation of the quality of restoration to sealing of screw access-hole of implant and identification of cariogenic lesions, without risk of allergic reactions or staining of prostheses and restorations.

A novel antiplasmodial compound: integration of in silico and in vitro assays

Malaria is a disease caused by Plasmodium genus. which P. falciparum is responsible for the most severe form of the disease, cerebral malaria. In 2018, 405,000 people died of malaria. Antimalarial drugs have serious adverse effects and limited efficacy due to multidrug-resistant strains. One way to overcome these limitations is the use of computational approaches for prioritizing candidates to phenotypic assays and/or in vitro assays against validated targets. Plasmodium falciparum Enoyl-ACP reductase (PfENR) is noteworthy because it catalyzes the rate-limiting step of the biosynthetic pathway of fatty acid. Thus, the study aimed to identify potential PfENR inhibitors by ligand (2D molecular similarity and pharmacophore models) and structure-based virtual screening (molecular docking). 2D similarity-based virtual screening using Tanimoto Index (> 0.45) selected 29,236 molecules from natural products subset available in ZINC database (n = 181,603). Next, 10 pharmacophore models for PfENR inhibitors were generated and evaluated based on the internal statistical parameters from GALAHAD™ and ROC/AUC curve. These parameters selected a suitable pharmacophore model with one hydrophobic center and two hydrogen bond acceptors. The alignment of the filtered molecules on best pharmacophore model resulted in the selection of 10,977 molecules. These molecules were directed to the docking-based virtual screening by AutoDock Vina 1.1.2 program. These strategies selected one compound to phenotypic assays against parasite. ZINC630259 showed EC₅₀ = 0.12 ± 0.018 µM in antiplasmodial assays and selective index similar to other antimalarial drugs. Finally, MM/PBSA method showed stability of molecule within PfENR binding site (ΔG_binding=-57.337 kJ/mol).Communicated by Ramaswamy H. Sarma.

In vitro and in vivo antiplasmodial activity of novel quinoline derivative compounds by molecular hybridization

Chloroquine (CQ) has been the main treatment for malaria in regions where there are no resistant strains. Molecular hybridization techniques have been used as a tool in the search for new drugs and was implemented in the present study in an attempt to produce compound candidates to treat malarial infections by CQ-resistant strains. Two groups of molecules were produced from the 4-aminoquinoline ring in conjugation to hydrazones (HQ) and imines (IQ). Physicochemical and pharmacokinetic properties were found to be favorable when analyzed in silico and cytotoxicity and antiplasmodial activity were assayed in vitro and in vivo showing low cytotoxicity and selectiveness to the parasites. Candidates IQ5 and IQ6 showed important values of parasite growth inhibition in vivo on the 5th day after infection (IQ5 15 mg/kg = 72.64% and IQ6 15 mg/kg = 71.15% and 25 mg/kg = 93.7%). IQ6 also showed interaction with ferriprotoporphyrin IX similarly to CQ. The process of applying condensation reactions to yield imines is promising and capable of producing molecules with antiplasmodial activity.

Dehydrobufotenin extracted from the Amazonian toad Rhinella marina (Anura: Bufonidae) as a prototype molecule for the development of antiplasmodial drugs

Background:

The resistance against antimalarial drugs represents a global challenge in the fight and control of malaria. The Brazilian biodiversity can be an important tool for research and development of new medicinal products. In this context, toxinology is a multidisciplinary approach on the development of new drugs, including the isolation, purification, and evaluation of the pharmacological activities of natural toxins. The present study aimed to evaluate the cytotoxicity, as well as the antimalarial activity in silico and in vitro of four compounds isolated from Rhinella marina venom as potential oral drug prototypes.

Methods:

Four compounds were challenged against 35 target proteins from P. falciparum and screened to evaluate their physicochemical properties using docking assay in Brazilian Malaria Molecular Targets (BraMMT) software and in silico assay in OCTOPUS® software. The in vitro antimalarial activity of the compounds against the 3D7 Plasmodium falciparum clones were assessed using the SYBR Green I based assay (IC₅₀). For the cytotoxic tests, the LD₅₀ was determined in human pulmonary fibroblast cell line using the [3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay.

Results:

All compounds presented a ligand-receptor interaction with ten Plasmodium falciparum-related protein targets, as well as antimalarial activity against chloroquine resistant strain (IC₅₀ = 3.44 μM to 19.11 μM). Three of them (dehydrobufotenine, marinobufagin, and bufalin) showed adequate conditions for oral drug prototypes, with satisfactory prediction of absorption, permeability, and absence of toxicity. In the cell viability assay, only dehydrobufotenin was selective for the parasite.

Conclusions:

Dehydrobufotenin revealed to be a potential oral drug prototype presenting adequate antimalarial activity and absence of cytotoxicity, therefore should be subjected to further studies.

Synthesis of Novel 1,2,3-Triazole Derivatives of Isocoumarins and 3,4-Dihydroisocoumarin with Potential Antiplasmodial Activity In Vitro

BACKGROUND

Malaria greatly affects the world health, having caused more than 228 million cases only in 2018. The emergence of drug resistance is one of the main problems in its treatment, demonstrating the need for the development of new antimalarial drugs.

OBJECTIVE

Synthesis and in vitro antiplasmodial evaluation of triazole compounds derived from isocoumarins and a 3,4-dihydroisocoumarin.

METHODS

The compounds were synthesized in 4 to 6-step reactions with the formation of the triazole ring via the Copper(I)-catalyzed 1,3-dipolar cycloaddition between isocoumarin or 3,4- dihydroisocoumarin azides and terminal alkynes. This key reaction provided compounds with an unprecedented connection of isocoumarin or 3,4-dihydroisocoumarin and the 1,2,3-triazole ring. The products were tested for their antiplasmodial activity against a Plasmodium falciparum chloroquine resistant and sensitive strains (W2 and 3D7, respectively).

RESULTS

Thirty-one substances were efficiently obtained by the proposed routes with an overall yield of 25-53%. The active substances in the antiplasmodial test displayed IC50 values ranging from 0.68-2.89 μM and 0.85-2.07 μM against W2 and 3D7 strains, respectively.

CONCLUSION

This study demonstrated the great potential of isocoumarin or 3,4-dihydroisocoumarin derivatives because practically all the tested substances were active against Plasmodium falciparum.

Identification of novel antiplasmodial compound by hierarquical virtual screening and in vitro assays

Malaria is an infectious disease caused by protozoa of the genus Plasmodium spp. with approximately 219 million cases in 2017. P. falciparum is main responsible for the most severe form of the disease, cerebral malaria. Despite of public health impacts, chemotherapy against malaria is still limited due to the emergence of drug resistance cases used in monotherapy and combination therapies. Thus, the development of new antimalarial drugs becomes emergency. One way of achieve this goal is to explore essential and/or unique therapeutic targets of the parasite, or at least sufficiently different to ensure selective inhibition. Enoil-ACP reductase (ENR) is a NADH-dependent enzyme responsible for the limiting step of the type II fatty acid biosynthetic pathway (FAS II). Thus, pharmacophore and docking based virtual screening were applied to prioritize molecules for in vitro assays against P. falciparum W2 strain. The application of successive filters at OOCC database (n = 618) resulted in the identification of one molecule (13) (EC₅₀ = 0.098 ± 0.021 μM) with similar biological activity to artemether. The molecule 13 is a typical drug repurposing case due to previous other approved therapeutic uses on Chinese medicine as a non-specific cholinergic antagonist, thus it could be accelerated the drug development process. Additionally, molecular dynamics studies were used to confirm stability of the molecular interactions identified by molecular docking. Thus, representative structures of P. falciparum ENR can be used in a study to propose new derivatives for evaluation of biological activity in vitro and in vivo. Communicated by Ramaswamy H. Sarma.

Halogenation as a Strategy to Improve Antiplasmodial Activity: A Report of New 3-Alkylpyridine Marine Alkaloid Analogs

Introduction: Due to the emergence of resistance to antimalarial drugs as well as the lack of vaccination for malaria, there is an urgent demand for the development of new antimalarial alternatives. Recently, our research group developed a new set of 3-alkylpyridine marine alkaloid analogs, of which a compound known as compound 5 was found to be inactive against Plasmodium falciparum.Methods: Herein, we report a successful halogenation strategy to improve the antiplasmodial activity of compound 5 through the replacement of a hydroxyl group by chlorine (compound 6) and fluorine (compound 7) atoms. Results: Compounds 6 and 7 showed improved antiplasmodial activities (IC50 = 7.2 and 8.3 µM, respectively) 20 times higher than that of their precursor, compound 5 (IC50 = 210.7 µM). Ultraviolet-visible titration experiments demonstrated that halogenation of compound 5 did not alter its ability to bind its target, hematin. Conclusion: Halogenation can enhance the antiplasmodial activity of a compound without altering its mechanism of action.

Improvement of antimalarial activity of a 3-alkylpiridine alkaloid analog by replacing the pyridine ring to a thiazole-containing heterocycle: Mode of action, mutagenicity profile, and Caco-2 cell-based permeability

The development of new antimalarial drugs is urgent to overcome the spread of resistance to the current treatment. Herein we synthesized the compound 3, a hit-to‑lead optimization of a thiazole based on the most promising 3-alkylpyridine marine alkaloid analog. Compound 3 was tested against Plasmodium falciparum and has shown to be more potent than its precursor (IC₅₀ values of 1.55 and 14.7 μM, respectively), with higher selectivity index (74.7) for noncancerous human cell line. This compound was not mutagenic and showed genotoxicity only at concentrations four-fold higher than its IC₅₀. Compound 3 was tested in vivo against Plasmodium berghei NK65 strain and inhibited the development of parasite at 50 mg/kg. In silico and UV-vis approaches determined that compound 3 acts impairing hemozoin crystallization and confocal microscopy experiments corroborate these findings as the compound was capable of diminishing food vacuole acidity. The assay of uptake using human intestinal Caco-2 cell line showed that compound 3 is absorbed similarly to chloroquine, a standard antimalarial agent. Therefore, we present here compound 3 as a potent new lead antimalarial compound.

Oral squamous papilloma: a view under clinical, fluorescence and histopathological aspects

Oral squamous papilloma is a benign tumor whose pathogenesis has been associated with human papillomavirus infection. Thus, it is noteworthy that human papillomavirus infection is one of the risk factors associated with the development of cervical, anogenital, pharynx, larynx and oral cavity carcinomas. Oral squamous papilloma can affect any region of the oral cavity, and transmission of human papillomavirus can occur by direct contact, sexual intercourse or from mother to child during delivery. The diagnosis is clinical and histopathological, with surgical removal representing the treatment of choice. Recently, widefield optical fluorescence has been used as a complementary examination to the conventional clinical examination in the screening of oral pathological lesions and for the delimitation of surgical margins. We report a case of oral squamous papilloma with its clinical, histopathological features and, in addition, from the perspective of wide field optical fluorescence.

Hairy Tongue: Differential Diagnosis by Use of Widefield Optical Fluorescence

Hairy tongue is a benign pathology, characterized clinically by hyperkeratinized plaques on the dorsal surface of the tongue, hairlike, whose coloration ranges from unpigment, whitish, yellowish, green, brown to black. Diagnosis is clinical, and, in cases of whitish plaques, it may be difficult to differentiate between oral hairy leukoplakia, potentially malignant leukoplakia or squamous cell carcinoma. Thus, widefield optical fluorescence complementary examination may allow a better visualization of the local hairlike pattern of hyperkeratinization, typical of the hairy tongue, facilitating the diagnosis. In this work, a 57-year-old man was referred to the Dental Specialties Department of the Divinópolis Health Department (MG, Brazil) by a general dental practitioner, aiming a differential diagnosis of possible malignant lesion on the dorsal tongue surface. The complementary examination by wide-field optical fluorescence was performed. For this, it was employed a device with high-power light-emitting diode emitting light centered at a wavelength of (400±10) nm and maximum irradiance of (0.040±0.008) W/cm2 was used for fluorescence visualization. Fluorescence images showed projections of hairlike appearance in tongue dorsal surface with no aspects of malignancy. Hairlike appearance is the principal feature of hairy tongue. In this way, the final diagnosis was established. In conclusion, in this case, the use of widefield optical fluorescence in oral diagnostic routine provided a differential diagnosis, with no need of an incisional biopsy.

Mucosal vitiligo in angles of the mouth: clinical and fluorescence aspects

Vitiligo is the most common depigmenting, chronic acquired disease of the skin and mucosa. However, vitiligo of an unclassified type and mucosal subtype affecting only one area of the mucosa is considered quite uncommon. The diagnosis of vitiligo, regardless of its type, is clinical. Nonetheless, a device that allows the visualization of the tissue fluorescence may be useful for confirming the diagnosis. We present the use of wide-field optical fluorescence device for complementary examination and diagnosis of unusual cases of mucosal vitiligo located only in angles of the mouth.

Brazilian malaria molecular targets (BraMMT): selected receptors for virtual high-throughput screening experiments

BACKGROUND

Owing to increased spending on pharmaceuticals since 2010, discussions about rising costs for the development of new medical technologies have been focused on the pharmaceutical industry. Computational techniques have been developed to reduce costs associated with new drug development. Among these techniques, virtual high-throughput screening (vHTS) can contribute to the drug discovery process by providing tools to search for new drugs with the ability to bind a specific molecular target.

OBJECTIVES

In this context, Brazilian malaria molecular targets (BraMMT) was generated to execute vHTS experiments on selected molecular targets of Plasmodium falciparum.

METHODS

In this study, 35 molecular targets of P. falciparum were built and evaluated against known antimalarial compounds.

FINDINGS

As a result, it could predict the correct molecular target of market drugs, such as artemisinin. In addition, our findings suggested a new pharmacological mechanism for quinine, which includes inhibition of falcipain-II and a potential new antimalarial candidate, clioquinol.

MAIN CONCLUSIONS

The BraMMT is available to perform vHTS experiments using OCTOPUS or Raccoon software to improve the search for new antimalarial compounds. It can be retrieved from www.drugdiscovery.com.br or download of Supplementary data.

Target-Guided Synthesis and Antiplasmodial Evaluation of a New Fluorinated 3-Alkylpyridine Marine Alkaloid Analog

The need to develop new alternatives for antimalarial treatment is urgent. Herein, we report the synthesis and antimalarial evaluation of a small library of synthetic 3-alkylpyridine marine alkaloid (3-APA) analogs. First, the compounds were evaluated in vitro against Plasmodium falciparum. The most active compound 5c was selected for optimization of its antimalarial properties. An in silico approach was used based on pure ab initio electronic structure prediction, and the results indicated that a substitution of the hydroxyl group by a fluorine atom could favor a more stable complex with heme at a molecular ratio of 2:1 (heme/3-APA halogenated). A new fluorinated 3-APA analog was synthesized (compound 7), and its antimalarial activity was re-evaluated. Compound 7 exhibited optimized antimalarial properties (P. falciparum IC₅₀ = 2.5 μM), low genotoxicity, capacity to form a more stable heme/3-APA complex at a molecular ratio of 2:1, and conformity to RO5. The new compound, therefore, has great potential as a new lead antimalarial agent.

Firearm Projectile in the Maxillary Tuberosity Located by Adjunctive Examination of Wide-Field Optical Fluorescence

OBJECTIVE

Demonstrate the use of wide-field optical fluorescence as an adjunctive examination in a clinical routine to oral diagnosis.

BACKGROUND DATA

Use of wide-field optical fluorescence in the oral cavity has been restricted to topics related to the detection and diagnosis of oral cancer.

MATERIALS AND METHODS

In a regular medical appointment, a 58-year-old female patient, without any complaint or oral symptom, underwent the complementary examination by wide-field optical fluorescence. A device with high-power light-emitting diode emitting light centered at a wavelength of (400 ± 10) nm and maximum irradiance of (0.040 ± 0.008) W/cm² was used for fluorescence visualization.

RESULTS

We report the location of a firearm projectile, intraosseous, in the maxillary tuberosity using wide-field optical fluorescence.

CONCLUSIONS

It is evidenced that wide-field optical fluorescence, within a clinical routine, can provide relevant images and data, with an immediate result, without the use of ionizing radiation, enabling an efficient oral diagnosis.

Oral cancer from the perspective of wide-field optical fluorescence: Diagnosis, tumor evolution and post-treatment follow up

In this communication, we present that wide-field optical fluorescence might be useful for: the screening of oral lesions that are imperceptible to the naked eye, determination of biopsy area, better definition of treatment, and previous and post-treatment follow-up.

Digoxin reduces the mutagenic effects of Mitomycin C in human and rodent cell lines

Digoxin is a drug widely used to treat heart failure and studies have demonstrated its potential as anticancer agent. In addition, digoxin presents the potential to interact with a series of other compounds used in medicine. The aim of the present study was to evaluate in vitro the cytotoxicity, genotoxicity and mutagenicity of digoxin and its potential to interact with the mutagen Mitomycin C (MMC). The cytotoxicity of digoxin was assessed by employing the MTT method and the comet assay was performed to assess the genotoxicity of this medicine in CHO-K1 and HeLa cell lines. Besides, the cytokinesis-block micronucleus assay was performed to assess the mutagenicity and the antimutagenicity of this drug. The Ames assay was also performed with TA98 and TA100 strains of S. typhimurium. Results showed that digoxin was cytotoxic, genotoxic and mutagenic for HeLa and CHO-K1 cell lines at concentrations many times higher than those observed in human therapeutic conditions. Nevertheless, an antimutagenic effect against the mutagen MMC was observed on both cell lines in concentrations near those used therapeutically in humans. This chemoprotective effect observed is an interesting finding that should be better explored regarding its impact in anticancer chemotherapy.

In vitro and in vivo antimalarial potential of oleoresin obtained from Copaifera reticulata Ducke (Fabaceae) in the Brazilian Amazon rainforest

BACKGROUND

In view of the wide variety of the flora of the Amazon region, many plants have been studied in the search for new antimalarial agents. Copaifera reticulata is a tree distributed throughout the Amazon region which contains an oleoresin rich in sesquiterpenes and diterpenes with β-caryophyllene as the major compound. The oleoresin has demonstrated antiparasitic activity against Leishmania amazonensis. Because of this previously reported activity, this oleoresin would be expected to also have antimalarial activity.

PURPOSE

In this study we evaluated the in vitro and in vivo antimalarial potential of C. reticulata oleoresin.

METHODS

In vitro assays were done using P. falciparum W2 and 3D7 strains and the human fibroblast cell line 26VA Wi-4. For in vivo analysis, BALB/c mice were infected with approximately 10⁶ erythrocytes parasitized by P. berghei and their parasitemia levels were observed over 7 days of treatment with C. reticulata; hematological and biochemical parameters were analyzed at the end of experiment.

RESULTS

The oleoresin of C. reticulata containing the sesquiterpenes β-caryophyllene (41.7%) and β-bisabolene (18.6%) was active against the P. falciparum W2 and 3D7 strains (IC₅₀ = 1.66 and 2.54 µg/ml, respectively) and showed low cytotoxicity against the 26VA Wi-4 cell line (IC₅₀ > 100 µg/ml). The C. reticulata oleoresin reduced the parasitemia levels of infected animals and doses of 200 and 100 mg/kg/day reached a rate of parasitemia elimination resembling that obtained with artemisinin 100 mg/kg/day. In addition, treatment with oleoresin improved the hypoglycemic, hematologic, hepatic and renal parameters of the infected animals.

CONCLUSION

The oleoresin of C. reticulata has antimalarial properties and future investigations are necessary to elucidate its mechanism of action.

Successful application of virtual screening and molecular dynamics simulations against antimalarial molecular targets

The main challenge in the control of malaria has been the emergence of drug-resistant parasites. The presence of drug-resistant Plasmodium sp. has raised the need for new antimalarial drugs. Molecular modelling techniques have been used as tools to develop new drugs. In this study, we employed virtual screening of a pyrazol derivative (Tx001) against four malaria targets: plasmepsin-IV, plasmepsin-II, falcipain-II, and PfATP6. The receiver operating characteristic curves and area under the curve (AUC) were established for each molecular target. The AUC values obtained for plasmepsin-IV, plasmepsin-II, and falcipain-II were 0.64, 0.92, and 0.94, respectively. All docking simulations were carried out using AutoDock Vina software. The ligand Tx001 exhibited a better interaction with PfATP6 than with the reference compound (-12.2 versus -6.8 Kcal/mol). The Tx001-PfATP6 complex was submitted to molecular dynamics simulations in vacuum implemented on an NAMD program. The ligand Tx001 docked at the same binding site as thapsigargin, which is a natural inhibitor of PfATP6. Compound TX001 was evaluated in vitro with a P. falciparum strain (W2) and a human cell line (WI-26VA4). Tx001 was discovered to be active against P. falciparum (IC50 = 8.2 µM) and inactive against WI-26VA4 (IC50 > 200 µM). Further ligand optimisation cycles generated new prospects for docking and biological assays.

Docking, QM/MM, and molecular dynamics simulations of the hexose transporter from Plasmodium falciparum (PfHT)

Malaria is the most prevalent parasitic disease in the world. Currently, an effective vaccine for malaria does not exist, and chemotherapy must be used to treat the disease. Because of increasing resistance to current antimalarial drugs, new treatments must be developed. Among the many potential molecular targets, the hexose transporter of Plasmodium falciparum (PfHT) is particularly promising because it plays a vital role in glucose transport for the parasite. Thus, this study aims to determine the three-dimensional structure of PfHT and to describe the intermolecular interactions between active glycoside derivatives and PfHT. Such information should aid in the development of new antimalarial drugs. The receptor PfHT was constructed from primary sequences deposited in the SWISS MODEL database. Next, molecular docking simulations between O-(undec-10-en)-l-D-glucose and the constructed active site models were performed using Autodock Vina. The glycoside derivative-PfHT complexes were then refined using the hybrid QM/MM (PM3/ff03) method within the AMBER package. The models were then evaluated using Ramachandran plots, which indicated that 93.2% of the residues in the refined PfHT models (P5) were present in favorable regions. Furthermore, graphical plots using ANOLEA showed that the potential energies of interaction for atoms unbonded to P5 were negative. Finally, the O-(undec-10-en)-l-D-glucose-PfHT complex was evaluated using 20-ns Molecular Dynamics simulations with an ff03 force field. Docking and QM/MM studies revealed the amino acids essential for molecular recognition of and activity on glycosides. Inhibition of glucose transporters may prevent the development and metabolism of P. falciparum, so a description of the receptor's structure is a critical step towards rational drug design.

Intracellular calcium is a target of modulation of apoptosis in MCF-7 cells in the presence of IgA adsorbed to polyethylene glycol

PURPOSE

Clinical and epidemiological studies have indicated that breastfeeding has a protective effect on breast cancer risk. Protein-based drugs, including antibodies, are being developed to attain better forms of cancer therapy. Secretory IgA (SIgA) is the antibody class in human breast milk, and its activity can be linked to the protective effect of breastfeeding. The aim of this study was to investigate the effect of polyethylene glycol (PEG) microspheres with adsorbed SIgA on MCF-7 human breast cancer cells.

METHODS

The PEG microspheres were characterized by flow cytometry and fluorescence microscopy. The MCF-7 cells were obtained from American Type Culture Collection. MCF-7 cells were pre-incubated for 24 hours with or without SIgA (100 ng/mL), PEG microspheres or SIgA adsorbed in PEG microspheres (100 ng/mL). Viability, intracellular calcium release, and apoptosis in MCF-7 cells were determined by flow cytometry.

RESULTS

Fluorescence microscopy and flow cytometry analyses revealed that SIgA was able to adsorb to the PEG microspheres. The MCF-7 cells that were incubated with PEG microspheres with adsorbed SIgA showed decreased viability. MCF-7 cells that were incubated with SIgA or PEG microspheres with adsorbed SIgA had increased intracellular Ca(2+) levels. In the presence of SIgA, an increase in the percentage of apoptotic cells was observed. The highest apoptosis index was observed when the cells were treated with PEG microspheres with adsorbed SIgA.

CONCLUSION

These data suggest that colostral SIgA adsorbed to PEG microspheres has antitumor effects on human MCF-7 breast cancer cells and that the presence of large amounts of this protein in secreted breast milk may provide protection against breast tumors in women who breastfed.

The Effect of Melatonin Adsorbed to Polyethylene Glycol Microspheres on the Survival of MCF-7 Cells

Although melatonin exhibits oncostatic properties such as antiproliferative effects, the oral bioavailability of this hormone is less than 20%. Modified drug release systems have been used to improve the pharmacological efficiency of drugs. These systems can change the pharmacokinetics and biodistribution of the associated drugs. Thus, this study investigated the effect of melatonin adsorbed to polyethylene glycol (PEG) microspheres on MCF-7 human breast cancer cells. The MCF-7 cells were obtained from the American Type Culture Collection. MCF-7 cells were preincubated for 24 h with or without melatonin (100 ng/ml), PEG microspheres or melatonin adsorbed to PEG microspheres (100 ng/ml). Viability, intracellular calcium release and apoptosis in MCF-7 cells were determined by flow cytometry. MCF-7 cells incubated with melatonin adsorbed to PEG microspheres showed a lower viability rate (40.0 ± 8.3 with melatonin adsorbed to PEG microspheres compared to 54.1 ± 7.3 with melatonin; 81.8 ± 12.5 with PEG microsphere and 92.7 ± 4.1 with medium), increased spontaneous intracellular Ca2+ release (27.0 ± 8.6 with melatonin adsorbed to PEG microspheres compared to 21.5 ± 13.4 with melatonin; 10.1 ± 5.4 with PEG microsphere and 9.1 ± 5.6 with medium) and increased apoptosis index (51.2 ± 2.7 with melatonin adsorbed to PEG microspheres compared to 36.0 ± 2.1 with melatonin; 4.9 ± 0.5 with PEG microsphere and 3.1 ± 0.6 with medium). The results indicate that melatonin adsorbed to PEG microspheres exerts antitumor effects on human MCF-7 breast cancer cells. However, clinical tests must be performed to confirm the use of melatonin adsorbed to PEG microspheres as an alternative therapy against cancer.

Structure-based drug design studies of the interactions of ent-kaurane diterpenes derived from Wedelia paludosa with the Plasmodium falciparum sarco/endoplasmic reticulum Ca²⁺-ATPase PfATP6

Malaria is responsible for more deaths around the world than any other parasitic disease. Due to the emergence of strains that are resistant to the current chemotherapeutic antimalarial arsenal, the search for new antimalarial drugs remains urgent though hampered by a lack of knowledge regarding the molecular mechanisms of artemisinin resistance. Semisynthetic compounds derived from diterpenes from the medicinal plant Wedelia paludosa were tested in silico against the Plasmodium falciparum Ca²⁺-ATPase, PfATP6. This protein was constructed by comparative modelling using the three-dimensional structure of a homologous protein, 1IWO, as a scaffold. Compound 21 showed the best docking scores, indicating a better interaction with PfATP6 than that of thapsigargin, the natural inhibitor. Inhibition of PfATP6 by diterpene compounds could promote a change in calcium homeostasis, leading to parasite death. These data suggest PfATP6 as a potential target for the antimalarial ent-kaurane diterpenes.

Antiplasmodial activity of aryltetralone lignans from Holostylis reniformis

Extracts from Holostylis reniformis were tested in vivo against Plasmodium berghei and in vitro against a chloroquine-resistant strain of Plasmodium falciparum. The hexane extract of the roots was the most active, causing 67% reduction of parasitemia in vivo. From this extract, six lignans, including a new (7'R,8S,8'S)-3',4'-methylenedioxy-4,5-dimethoxy-2,7'-cyclolignan-7-one, were isolated and tested in vitro against P. falciparum. The three most active lignans showed 50% inhibitor concentrations of < or =0.32 microM. An evaluation of minimum lethal dose (30%) values showed low toxicity for these lignans in a hepatic cell line (Hep G2A16). Therefore, these compounds are potential candidates for the development of antimalarial drugs.

Enhanced activity of mefloquine and artesunic acid against Plasmodium falciparum in vitro and P. berghei in mice by combination with ciprofloxacin

The antimalarial activity of combinations of mefloquine or artesunic acid with ciprofloxacin and other synthetic fluoroquinolone was tested in vitro against Plasmodium falciparum using a strain (BHz26/86) partially resistant to chloroquine and a resistant clone (W2); both are sensitive to mefloquine. Inhibition of parasite growth was measured in relation to controls without drugs, either by counting parasitemia in Giemsa-stained blood smears or by measuring the reduction in [(3)H]-hypoxanthine uptake. Combinations containing artesunic acid or mefloquine with ciprofloxacin had significant in vitro activity, inhibiting by more than 90% of the growth of both strains of P. falciparum at doses significantly lower than those of the antimalarials alone. When tested in mice inoculated with P. berghei chloroquine-sensitive parasites (NK65 strain), ciprofloxacin was inactive, whereas mefloquine and artesunic acid were active (IC(50)=2.5 and 4.2 mg/kg, respectively); combinations containing mefloquine at an equivalent dose of 0.5 mg/kg reduced parasitemia by 59% and artesunic acid activity was also improved by ciprofloxacin. Our data support the idea that ciprofloxacin in combination with antimalarials may be useful in the treatment of chloroquine-resistant human malaria, allowing the use of lower doses of these drugs.