In silico, in vitro and in vivo evaluation of natural Bignoniaceous naphthoquinones in comparison with atovaquone targeting the selection of potential antimalarial candidates

Selective activity of Tabebuia avellanedae against Giardia duodenalis infecting organoid-derived human gastrointestinal epithelia

Giardia duodenalis is a widespread intestinal protozoan that affects mammals, including humans. Symptoms can range from being subclinical to causing severe abdominal pain and diarrhoea. Giardiasis often requires repeated treatment with synthetic drugs like metronidazole. In recent years, treatment failures in clinical cases involving nitroimidazoles have been increasingly reported. Consequently, identifying therapeutic alternatives is necessary. Medicinal plants have traditionally been used as antiparasitic compounds, but systematic evaluation under controlled experimental conditions is often lacking. Here, we evaluated the in vitro efficacy of Tabebuia avellanedae dry and hydroalcoholic extracts, as well as one of its active compounds, β-lapachone, as potential treatment against G. duodenalis infection. We observed effective antigiardial activity for all tested compounds, with β-lapachone exhibiting lower IC50 values than metronidazole. Cytotoxic effects often limit therapeutic concentration windows of opportunity, and choosing an informative model to assess them is not straightforward. In the present case, only T. avellanedae hydroalcoholic extract showed no cytotoxicity on tumoral human intestinal Caco-2 cell line, and only a trend of inhibition when tested on canine epithelial kidney MDCK cells. To introduce a more physiological test system, we used in vitro G. duodenalis infection experiments in a trans-well set-up using organoid derived monolayers (ODM) to assess at the same time drug efficacy against the parasite and safety on primary human intestinal epithelia, a likely surrogate for in vivo conditions. Our studies using this model point towards the potential therapeutic opportunity for non-systemic applications of T. avellanedae extracts and a relevant ingredient of these, β-lapachone. The data suggest that ODM co-cultures with G. duodenalis are suitable for testing antigiardial compounds, providing a more informative in vitro model before progressing to in vivo tests.

Sulfonamide based pyrimidine derivatives combating Plasmodium parasite by inhibiting falcipains-2 and falcipains-3 as antimalarial agents

In this report, we present the design and synthesis of a novel series of pyrimidine-tethered spirochromane-based sulfonamide derivatives aimed at combating drug resistance in malaria. The antimalarial effectiveness of these compounds was assessed in vitro. Structural validation of the synthesized compounds was conducted using mass spectrometry and NMR spectroscopy. Strong antimalarial activity against CQ-sensitive (3D7) and CQ-resistant (W2) strains of Plasmodium falciparum was demonstrated by the majority of the compounds. Notably, compounds SZ14 and SZ9 demonstrated particularly potent effects, with compound SZ14 showing IC50 values of 2.84 μM and SZ9 3.22 μM, indicating single-digit micromolar activity. The compounds exhibiting strong antimalarial activity were assessed through enzymatic tests against the cysteine protease enzymes of P. falciparum, falcipain-2 and falcipain-3. The results indicated that SZ14 and SZ9 inhibited PfFP-2 (IC50 values: 4.1 and 5.4 μM, respectively), and PfFP-3 (IC50 values: 4.9 and 6.3 μM, respectively). To confirm the compounds' specificity towards the parasite, we investigated their cytotoxicity against Vero cell lines, revealing strong selectivity indices and no significant cytotoxic effects. Additionally, in vitro hemolysis testing showed these compounds to be non-toxic to normal human blood cells. Moreover, predicted in silico ADME parameters and physiochemical characteristics demonstrated the drug-likeness of the synthetic compounds. These collective findings suggest that sulfonamide derivatives based on pyrimidine-tethered oxospirochromane could serve as templates for the future development of potential antimalarial drugs.

Identification of Orthosteric and Allosteric Pharmacological Chaperones for Mucopolysaccharidosis Type IIIB

Mucopolysaccharidosis type IIIB (MPS IIIB) is an autosomal inherited disease caused by mutations in gene encoding the lysosomal enzyme N-acetyl-alpha-glucosaminidase (NAGLU). These mutations result in reduced NAGLU activity, preventing it from catalyzing the hydrolysis of the glycosaminoglycan heparan sulfate (HS). There are currently no approved treatments for MPS IIIB. A novel approach in the treatment of lysosomal storage diseases is the use of pharmacological chaperones (PC). In this study, we used a drug repurposing approach to identify and characterize novel potential PCs for NAGLU enzyme. We modeled the interaction of natural and artificial substrates within the active cavity of NAGLU (orthosteric site) and predicted potential allosteric sites. We performed a virtual screening for both the orthosteric and the predicted allosteric site against a curated database of human tested molecules. Considering the binding affinity and predicted blood-brain barrier permeability and gastrointestinal absorption, we selected atovaquone and piperaquine as orthosteric and allosteric PCs. The PCs were evaluated by their capacity to bind NAGLU and the ability to restore the enzymatic activity in human MPS IIIB fibroblasts These results represent novel PCs described for MPS IIIB and demonstrate the potential to develop novel therapeutic alternatives for this and other protein deficiency diseases.

Brazilian plants with antimalarial activity: A review of the period from 2011 to 2022

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria continues to be a serious global public health problem in subtropical and tropical countries of the world. The main drugs used in the treatment of human malaria, quinine and artemisinin, are isolates of medicinal plants, making the use of plants a widespread practice in countries where malaria is endemic. Over the years, due to the increased resistance of the parasite to chloroquine and artemisinin in certain regions, new strategies for combating malaria have been employed, including research with medicinal plants.

AIM

This review focuses on the scientific production regarding medicinal plants from Brazil whose antimalarial activity was evaluated during the period from 2011 to 2022. 2.

METHODOLOGY

For this review, four electronic databases were selected for research: Pubmed, ScienceDirect, Scielo and Periódicos CAPES. Searches were made for full texts published in the form of scientific articles written in Portuguese or English and in a digital format. In addition, prospects for new treatments as well as future research that encourages the search for natural products and antimalarial derivatives are also presented.

RESULTS

A total of 61 publications were encountered, which cited 36 botanical families and 92 species using different Plasmodium strains in in vitro and in vivo assays. The botanical families with the most expressive number of species found were Rubiaceae, Apocynaceae, Fabaceae and Asteraceae (14, 14, 9 and 6 species, respectively), and the most frequently cited species were of the genera Psychotria L. (8) and Aspidosperma Mart. (12), which belong to the families Rubiaceae and Apocynaceae. Altogether, 75 compounds were identified or isolated from 28 different species, 31 of which are alkaloids. In addition, the extracts of the analyzed species, including the isolated compounds, showed a significant reduction of parasitemia in P. falciparum and P. berghei, especially in the clones W2 CQ-R (in vitro) and ANKA (in vivo), respectively. The Brazilian regions with the highest number of species analyzed were those of the north, especially the states of Pará and Amazonas, and the southeast, especially the state of Minas Gerais.

CONCLUSION

Although many plant species with antimalarial potential have been identified in Brazil, studies of new antimalarial molecules are slow and have not evolved to the production of a phytotherapeutic medicine. Given this, investigations of plants of traditional use and biotechnological approaches are necessary for the discovery of natural antimalarial products that contribute to the treatment of the disease in the country and in other endemic regions.

Reinvestigation of diphenylmethylpiperazine analogues of pyrazine as new class of Plasmodial cysteine protease inhibitors for the treatment of malaria

Malaria eradication is still a global challenge due to the lack of a broadly effective vaccine and the emergence of drug resistance to most of the currently available drugs as part of the mainline artemisinin-based combination therapy. A variety of experimental approaches are quite successful in identifying and synthesizing new promising pharmacophore hybrids with distinct mechanisms of action. Based on our recent findings, the current study demonstrates the reinvestigation of a series of diphenylmethylpiperazine and pyrazine-derived molecular hybrids. Pyrazine-derived molecular hybrids were screened to investigate the antiplasmodial activity on drug-susceptible Pf3D7 and drug-resistant PfW2 strains. The selected compounds were shown to be potent dual inhibitors of cysteine protease PfFP2 and PfFP3. Time-course parasitic development study demonstrated that compounds were able to arrest the growth of the parasite at the early trophozoite stage. The compounds did not show hemolysis of red blood cells and showed selectivity to the parasite compared with the mammalian Vero and A5489 cell lines. The study underlined HR5 and HR15 as a new class of Plasmodial falcipain inhibitors with an IC50 of 6.2 μM and 5.9 μM for PfFP2 and 6.8 μM and 6.4 μM for PfFP3, respectively. Both compounds have antimalarial efficacy with IC50 values of 3.05 μM and 2.80 μM for the Pf3D7 strain, and 4.35 μM and 3.39 μM for the PfW2 strain, respectively. Further structural optimization may turn them into potential Plasmodial falcipain inhibitors for malaria therapeutics.

Plumbagin: A Promising In Vivo Antiparasitic Candidate against Schistosoma mansoni and In Silico Pharmacokinetic Properties (ADMET)

Schistosomiasis, a potentially fatal chronic disease whose etiological agents are blood trematode worms of the genus Schistosoma spp., is one of the most prevalent and debilitating neglected diseases. The treatment of schistosomiasis depends exclusively on praziquantel (PZQ), a drug that has been used since the 1970s and that already has reports of reduced therapeutic efficacy, related with the development of Schistosoma-resistant or -tolerant strains. Therefore, the search for new therapeutic alternatives is an urgent need. Plumbagin (PLUM), a naphthoquinone isolated from the roots of plants of the genus Plumbago, has aroused interest in research due to its antiparasitic properties against protozoa and helminths. Here, we evaluated the in vivo schistosomicidal potential of PLUM against Schistosoma mansoni and the in silico pharmacokinetic parameters. ADMET parameters and oral bioavailability were evaluated using the PkCSM and SwissADME platforms, respectively. The study was carried out with five groups of infected mice and divided as follows: an untreated control group, a control group treated with PZQ, and three groups treated orally with 8, 16, or 32 mg/kg of PLUM. After treatment, the Kato-Katz technique was performed to evaluate a quantity of eggs in the feces (EPG). The animals were euthanized for worm recovery, intestine samples were collected to evaluate the oviposition pattern, the load of eggs was determined on the hepatic and intestinal tissues and for the histopathological and histomorphometric evaluation of tissue and hepatic granulomas. PLUM reduced EPG by 65.27, 70.52, and 82.49%, reduced the total worm load by 46.7, 55.25, and 72.4%, and the female worm load by 44.01, 52.76, and 71.16%, for doses of 8, 16, and 32 mg/kg, respectively. PLUM also significantly reduced the number of immature eggs and increased the number of dead eggs in the oogram. A reduction of 36.11, 46.46, and 64.14% in eggs in the hepatic tissue, and 57.22, 65.18, and 80.5% in the intestinal tissue were also observed at doses of 8, 16, and 32 mg/kg, respectively. At all doses, PLUM demonstrated an effect on the histopathological and histomorphometric parameters of the hepatic granuloma, with a reduction of 41.11, 48.47, and 70.55% in the numerical density of the granulomas and 49.56, 57.63, and 71.21% in the volume, respectively. PLUM presented itself as a promising in vivo antiparasitic candidate against S. mansoni, acting not only on parasitological parameters but also on hepatic granuloma. Furthermore, in silico, PLUM showed good predictive pharmacokinetic profiles by ADMET.

Development of diphenylmethylpiperazine hybrids of chloroquinoline and triazolopyrimidine using Petasis reaction as new cysteine proteases inhibitors for malaria therapeutics

Malaria is a widespread infectious disease, causing nearly 247 million cases in 2021. The absence of a broadly effective vaccine and rapidly decreasing effectiveness of most of the currently used antimalarials are the major challenges to malaria eradication efforts. To design and develop novel antimalarials, we synthesized a series of 4,7-dichloroquinoline and methyltriazolopyrimidine analogues using a multi-component Petasis reaction. The synthesized molecules (11-31) were screened for in-vitro antimalarial activity against drug-sensitive and drug-resistant strains of Plasmodium falciparum with an IC₅₀ value of 0.53 μM. The selected compounds were screened to evaluate in-vitro and in-silico enzyme inhibition efficacy against two cysteine proteases, PfFP2 and PfFP3. The compounds 15 and 17 inhibited PfFP2 with an IC₅₀ = 3.5 and 4.8 μM, respectively and PfFP3 with an IC₅₀ = 4.9 and 4.7 μM, respectively. Compounds 15 and 17 were found equipotent against the Pf3D7 strain with an IC₅₀ value of 0.74 μM, whereas both were displayed IC₅₀ values of 1.05 μM and 1.24 μM for the PfW2 strain, respectively. Investigation of effect of compounds on parasite development demonstrated that compounds were able to arrest the growth of the parasites at trophozoite stage. The selected compounds were screened for in-vitro cytotoxicity against mammalian lines and human red-blood-cell (RBC), which demonstrated no significant cytotoxicity associated with the molecules. In addition, in silico ADME prediction and physiochemical properties supported the drug-likeness of the synthesized molecules. Thus, the results highlighted the diphenylmethylpiperazine group cast on 4,7-dichloroquinoline and methyltriazolopyrimidine using Petasis reaction may serve as models for the development of new antimalarial agents.

Epoxy-α-lapachone (2,2-Dimethyl-3,4-dihydro-spiro[2H-naphtho[2,3-b]pyran-10,2'-oxirane]-5(10H)-one): a promising molecule to control infections caused by protozoan parasites

Natural products and their derivatives have been sources of search and research for new drugs for the treatment of neglected diseases. Naphthoquinones, a special group of quinones, are products of natural metabolites with a wide spectrum of biological activities and represent a group of interesting molecules for new therapeutic propositions. Among these compounds, lapachol stands out as a molecule from the heartwood of Tabebuia sp. whose structural changes resulted in compounds considered promising, such as epoxy-α-lapachone (ELAP). The biological activity of ELAP has been demonstrated, so far, for parasitic protozoa such as Leishmania spp., Trypanosoma cruzi and Plasmodium spp., species causing diseases needing new drug development and adequate health policy. This work gathers in vitro and in vivo studies on these parasites, as well as the toxicity profile, and the probable mechanisms of action elucidated until then. The potential of ELAP-based technology alternatives for a further drug is discussed here.

Antiplasmodial and cytotoxic effects of the methanol extract, canthinone alkaloids, squalene- and protolimonoid-type triterpenes from Homalolepis suffruticosa roots

ETHNOPHARMACOLOGICAL RELEVANCE

Different species of the Simaroubaceae family are used in traditional medicine to treat malaria. Among these is Homalolepis suffruticosa (syn. Simaba suffruticosa and Quassia suffruticosa), which is native to Central Brazil and popularly known as calunga. However, there is a lack of investigation concerning its antimalarial effects.

AIM OF THE STUDY

To investigate the antiplasmodial and cytotoxic effects of the isolated metabolites and methanol extract from H. suffruticosa roots as well as to conduct the dereplication of this extract aiming to characterize its metabolic profile by UPLC-DAD-ESI-MS/MS.

MATERIALS AND METHODS

Methanol extract of the H. suffruticosa roots and six isolated compounds were evaluated against chloroquine-resistant Plasmodium falciparum W2 strain by the PfLDH method and cytotoxicity in HepG2 cells by the MTT assay. Dereplication of the extract was performed by UPLC-DAD-ESI-MS/MS.

RESULTS

The six isolated compounds disclosed high to moderate antiplasmodial activity (IC₅₀ 0.0548 ± 0.0083 μg/mL to 26.65 ± 2.40 μg/mL) and cytotoxicity was in the range of CC₅₀ 0.62 ± 0.33 μg/mL to 56.43 ± 2.54 μg/mL, while 5-metoxycantin-6-one proved to be the most potent constituent of the six assayed ones. The methanol extract of the roots showed high in vitro antiplasmodial activity (IC₅₀ 1.88 ± 0.56 μg/mL), moderate cytotoxicity (CC₅₀ 41.93 ± 2.30 μg/mL), and good selectivity index (SI = 22.30). Finally, C₂₀ quassinoids and canthin-6-one alkaloids were putatively identified in the H. suffruticosa methanol extract by LC-MS.

CONCLUSIONS

Taken together, the isolated compounds, mainly the 5-metoxycantin-6-one and the methanol extract from H. suffruticosa roots, disclose good antiplasmodial activity, supporting the ethnopharmacological history of the Simaroubaceae species as traditional antimalarial drugs.

In vitro antiplasmodial activity, targeted LC-MS metabolite profiling, and identification of major natural products in the bioactive extracts of Palicourea and Psychotria species from the Amazonia and Atlantic Forest biomes, Brazil

INTRODUCTION

A great variety of bioactive natural products has been reported for different Palicourea and Psychotria species (Rubiaceae). However, few of them as well as few of species of these botanical genera have been evaluated for antiplasmodial activity.

OBJECTIVE

To assess the antiplasmodial activity of 24 extracts from Palicourea and Psychotria genera, along with the targeted LC-MS metabolite profiling, as well as identification of the main metabolites in the bioactive extracts.

METHODS

Twenty four ethanol and acid-base extracts from Palicourea and Psychotria genera collected in the Amazonia and Atlantic Forest, Brazil, were evaluated against chloroquine-resistant Plasmodium falciparum W2 strain by PfLDH. The metabolite profiling and putative identification of metabolites from bioactive extracts were determined by LC-DAD-ESI-MS and LC-HRMS, respectively.

RESULTS

The ethanol extracts disclosed low antiplasmodial activity (% GI < 50%). High antiplasmodial effect was observed for the acid-base extracts from Psychotria apoda and Psychotria colorata with 100% inhibition of parasite growth inhibition. Fragment ions related to pyrrolidinoindoline alkaloids were observed by LC-DAD-ESI-MS mainly in the most bioactive extracts. The results of the in vitro screening associated with the LC-DAD-ESI-MS and LC-HRMSⁿ data allowed to predict, for the first time, the pyrrolidinoindoline alkaloids as possible antiplasmodial representing, then, new potential natural antimalarial hits. In addition, other metabolite classes such as flavanones, lignans and chalcones were also putatively identified in the bioactive extracts of Psychotria apoda, Psychotria capitata, and Psychotria poeppigiana.

CONCLUSION

The present results point to Palicourea and Psychotria species as sources of new antimalarial hits.

Antimalarial application of quinones: A recent update

Atovaquone belongs to a naphthoquinone class of drugs and is used in combination with proguanil (Malarone) for the treatment of acute, uncomplicated malaria caused by Plasmodium falciparum (including chloroquine-resistant P. falciparum/P. vivax). Numerous quinone-derived compounds have attracted considerable attention in the last few decades due to their potential in antimalarial drug discovery. Several semi-synthetic derivatives of natural quinones, synthetic quinones (naphtho-/benzo-quinone, anthraquinones, thiazinoquinones), and quinone-based hybrids were explored for their in vitro and in vivo antimalarial activities. A careful literature survey revealed that this topic has not been compiled as a review article so far. Therefore, we herein summarise the recent discovery (the year 2009-2020) of quinone based antimalarial compounds in chronological order. This compilation would be very useful towards the exploration of novel quinone-derived compounds against malarial parasites with promising efficacy and lesser side effects.