Artemisinin and the antimalarial endoperoxides: from herbal remedy to targeted chemotherapy

Hybrid Molecules as Efficient Drugs against Multidrug-Resistant Malaria Parasites

This review is focused on hybrid molecules defined as chemical entities with two or more structural domains, as antimalarial drug-candidates, over the past 25 years. Due to their different pharmacophores, such hybrids can interact with a single biological target by different and complementary mechanisms; they can also act simultaneously on several targets having complementary biological functions (dual mode of action), and can theoretically reduce the selection of parasite drug-resistance. This review is not an exhaustive report of all hybrid drugs tested on malaria parasites but a selection of hybrids with pharmacologically relevant antiplasmodial properties and original chemical structures. The choice of pharmacophore synthons and junction arms is obviously decisive. Among the large varieties of hybrid drugs published, emoquine-1 appears at the moment as a promising antimalarial drug candidate, considering 1) its high activities on several multidrug-resistant Plasmodium lab strains and field isolates, 2) its capacity to eliminate the quiescent forms of the artemisinin-resistant parasites, and 3) its curative properties in a malaria mouse model. Such molecules confirm the synergistic effect of hybrid compounds compared to the combination of the pharmacophores leading to novel chemical structures that meet the critical parameters for new antimalarial drugs.

An updated survey on the recent advancement of antimalarial molecules: synthetic methodologies and SAR studies

An ongoing escalation in malaria cases is a critical global health issue and also a leading source of increased mortality rates. Infected mosquitos spread the Plasmodium parasite-based disease,. Recent advancements in antimalarial drug discovery have focused on developing novel molecules with unique mechanisms of action to combat this growing resistance. This review focuses on the latest findings in synthesizing hybrid antimalarial compounds, which combine different pharmacophores to enhance therapeutic efficacy, resulting in compounds that exhibit potent action against both resistant/sensitive strains of chloroquine, quinine, and artemisinin. Notably, the incorporation of diverse scaffolds such as 1,2,4-trioxanes, halogenated quinolines, pyrazoline, and sulfonamides has led to promising candidates that not only demonstrate high potency but also favorable pharmacokinetic profiles for drug development, the exploration of novel targets. This review highlights the progress (2019-2024) made in identifying and synthesizing hybrid antimalarial molecules while addressing existing challenges in the field.

Emerging nanotechnology-driven drug delivery solutions for malaria: Addressing drug resistance and improving therapeutic success

Malaria remains the fifth deadliest parasitic infection worldwide, despite significant advancements in technology. A major challenge in combating this disease lies in the growing resistance of malaria parasites to antimalarial drugs and insect vectors to insecticides. The emerging inefficacy of artemisinin-based combination therapies (ACTs) further exacerbates the issue. Additionally, the absence of a highly effective malaria vaccine continues to be a significant obstacle. The complex biology of the malaria parasite and the multifaceted nature of the disease contribute to these challenges. Recent advancements in nanotechnology offer promising solutions in malaria treatment, providing benefits such as improved drug stability, sustained release, and targeted delivery to specific cells. Encapsulation technology, in particular, addresses critical limitations like poor solubility, low bioavailability, and frequent dosing requirements. Thus, this review explores innovative strategies to combat malaria, focusing on nanotechnology-based antimalarial formulations and their evaluation in vitro and in vivo. Moreover, the study highlights the SAR of potent antimalarial compounds, molecular markers linked with drug resistance, ACTs, advocates for eco-friendly approaches, nanotechnology-driven vaccines, and new antimalarial agents with their specific targets.

Emerging trends and new developments in global research on artemisinin and its derivatives

Background

The World Health Organization recommends the use of artemisinin (ART) and its derivatives for malaria treatment. Furthermore, these compounds exhibit encouraging pharmacological effects for the treatment of several diseases. Nevertheless, ongoing antimalarial treatment efforts have been significantly hindered by the emergence of drug resistance. A systematic evaluation and analysis of relevant studies may yield insights to help resolve this dilemma and reveal options for future research.

Purpose

The objective of this study was to provide researchers with a comprehensive synopsis of the advancements made in the study of ART and its significant derivatives, as well as to visually present the data and provide insightful observations that can inform subsequent investigations in this domain.

Methods

We searched the Web of Science Core Collection for relevant studies published by December 31, 2023. The research hotspots and frontiers pertinent to this field in terms of countries, institutions, authors, journals, references, and keywords were ascertained through scientometric analysis via CiteSpace software.

Results

This study included an extensive assemblage of 12,985 data points, and the findings suggest that ART and its derivatives have garnered considerable interest among scientists. Prolonged international collaboration has fostered progress in this research field. "Antimalarials," "synthesis," "drug resistance," and "Plasmodium vivax" are areas of intense research. Potential areas for future investigations may include "proliferation," "oxidative stress," "pathways," and "mechanisms."

Conclusion

This study offers a comprehensive compendium of the developments and trends in the relevant research field over the past fifty years. Since pharmaceutical drug synthesis can influence both drug efficacy and cost-effectiveness, ongoing efforts to improve drug synthesis are warranted. Although the advent of novel therapeutic approaches has partially mitigated drug resistance, further investigations into the underlying mechanisms are needed. While better treatments for malaria have been developed, the therapeutic potential of ART and its derivatives for numerous additional important diseases is also possible, and future research in this area can lead to dramatic improvements in health.

Novel frontiers through nitrogen substitution at 6th, 10th and 11th position of artemisinin: Synthetic approaches and antimalarial activity

Malaria pertains to an array of catastrophic illnesses spurred on by the Plasmodium spp. Artemisinin (ART) is currently prescribed in conjunction with another medication as part of therapeutic regimens for acute malaria. These currently prescribed pharmaceuticals have been around for a while, even after lack of required thermos-metabolic stabilities, alongside fresh proclaims about surfacing resistance and neurotoxicity linked with sequential administration of such combination therapies. Over the years, ARTs seem to have gained popularity through the accelerated reduction in parasitaemia, thus dictating use of differentially stable ART derivatives, in combination or alone, to control the proliferation of malaria. The endoperoxide bridge in the ART pharmacophore plays a non-negotiable role in its action against multiple stages in the parasitic life cycle. However, shorter half-lives and limited bioavailability tend to open doors for another class of endoperoxides. Nitrogen substitution at 6th, 10th and 11th positions of ART draws attention as the best replacements through their disparate stabilities and inability to demonstrate in vivo hydrolytic decomposition into DHA. Discussions pertaining such azaartemisinins and aminoartemisinins reported over the past 30 years have been strongly focused upon, on account of their synthetic methodologies and antimalarial efficacies, in order to assign future candidature to the meritorious moiety.

Phosphorylation in the Plasmodium falciparum Proteome: A Meta-Analysis of Publicly Available Data Sets

Malaria is a deadly disease caused by Apicomplexan parasites of the Plasmodium genus. Several species of the Plasmodium genus are known to be infectious to humans, of which P. falciparum is the most virulent. Post-translational modifications (PTMs) of proteins coordinate cell signaling and hence regulate many biological processes in P. falciparum homeostasis and host infection, of which the most highly studied is phosphorylation. Phosphosites on proteins can be identified by tandem mass spectrometry (MS) performed on enriched samples (phosphoproteomics), followed by downstream computational analyses. We have performed a large-scale meta-analysis of 11 publicly available phosphoproteomics data sets to build a comprehensive atlas of phosphosites in the P. falciparum proteome, using robust pipelines aimed at strict control of false identifications. We identified a total of 26,609 phosphorylated sites on P. falciparum proteins, split across three categories of data reliability (gold/silver/bronze). We identified significant sequence motifs, likely indicative of different groups of kinases responsible for different groups of phosphosites. Conservation analysis identified clusters of phosphoproteins that are highly conserved and others that are evolving faster within the Plasmodium genus, and implicated in different pathways. We were also able to identify over 180,000 phosphosites within Plasmodium species beyond falciparum, based on orthologue mapping. We also explored the structural context of phosphosites, identifying a strong enrichment for phosphosites on fast-evolving (low conservation) intrinsically disordered regions (IDRs) of proteins. In other species, IDRs have been shown to have an important role in modulating protein-protein interactions, particularly in signaling, and thus warranting further study for their roles in host-pathogen interactions. All data have been made available via UniProtKB, PRIDE, and PeptideAtlas, with visualization interfaces for exploring phosphosites in the context of other data on Plasmodium proteins.

Characterizing the pharmacological interaction of the antimalarial combination artefenomel-piperaquine in healthy volunteers with induced blood-stage Plasmodium falciparum to predict efficacy in patients with malaria

BACKGROUND

The combination antimalarial artefenomel-piperaquine failed to achieve target efficacy in a phase 2b study in Africa and Vietnam. We retrospectively evaluated whether characterizing the pharmacological interaction of this antimalarial combination in a volunteer infection study (VIS) would have enabled prediction of the phase 2b study results.

METHODS

Twenty-four healthy adults enrolled over three consecutive cohorts were inoculated with Plasmodium falciparum-infected erythrocytes on day 0. Participants were randomized within each cohort to one of seven dose combination groups and administered a single oral dose of artefenomel-piperaquine on day 8. Participants received definitive antimalarial treatment with artemether-lumefantrine upon parasite regrowth or on day 42 ± 2. The general pharmacodynamic interaction (GPDI) model implemented in the Bliss Independence additivity criterion was developed to characterize the pharmacological interaction between artefenomel and piperaquine. Simulations based on the model were performed to predict the outcomes of the phase 2b combination study.

RESULTS

For a dose of 800 mg artefenomel administered with 640 mg, 960 mg, or 1440 mg piperaquine, the simulated adequate parasitological response at day 28 (APR28), incorporating actual patient pharmacokinetic (PK) data from the phase 2b trial, was 69.4%, 63.9%, and 74.8%, respectively. These results closely matched the observed APR28 in the phase 2b trial of 67.0%, 65.5%, and 75.4%, respectively.

CONCLUSIONS

These results indicate that VIS offer an efficient means for informing antimalarial combination trials conducted in the field, potentially expediting clinical development.

TRIAL REGISTRATION

This study was registered on ClinicalTrials.gov on 11 May 2018 with registration number NCT03542149.

Syntheses of deuterium-labeled dihydroartemisinic acid (DHAA) isotopologues and mechanistic studies focused on elucidating the conversion of DHAA to artemisinin

Dihydroartemisinic acid (DHAA), a sesquiterpenoid natural product from Artemisia annua, converts to artemisinin, an anti-malarial natural product that contains an endoperoxide bridge. The endoperoxide moiety is responsible for the biological activity of artemisinin. Therefore, understanding the biosynthesis of this functional group could lead to the optimization of the process to produce this medicine. DHAA converts to artemisinin through the incorporation of two molecules of oxygen in a four-step process. The reaction is a spontaneous cascade process that involves (i) the initial incorporation of a molecule of oxygen through the reaction of an allylic C-H bond of DHAA, (ii) followed by the cleavage of a C-C bond, (iii) the incorporation of a second molecule of oxygen, and (iv) polycyclization to yield artemisinin. This manuscript is focused on describing the chemical syntheses of regioselectively polydeuterated DHAA isotopologues at C3 and C15, in addition to research efforts related to clarifying how the endoperoxide-forming process of artemisinin occurs.

Evaluation of the binding interactions between Plasmodium falciparum Kelch-13 mutant recombinant proteins with artemisinin

Malaria, an ancient mosquito-borne illness caused by Plasmodium parasites, is mostly treated with Artemisinin Combination Therapy (ACT). However, Single Nucleotide Polymorphisms (SNPs) mutations in the P. falciparum Kelch 13 (PfK13) protein have been associated with artemisinin resistance (ART-R). Therefore, this study aims to generate PfK13 recombinant proteins incorporating of two specific SNPs mutations, PfK13-V494I and PfK13-N537I, and subsequently analyze their binding interactions with artemisinin (ART). The recombinant proteins of PfK13 mutations and the Wild Type (WT) variant were expressed utilizing a standard protein expression protocol with modifications and subsequently purified via IMAC and confirmed with SDS-PAGE analysis and Orbitrap tandem mass spectrometry. The binding interactions between PfK13-V494I and PfK13-N537I propeller domain proteins ART were assessed through Isothermal Titration Calorimetry (ITC) and subsequently validated using fluorescence spectrometry. The protein concentrations obtained were 0.3 mg/ml for PfK13-WT, 0.18 mg/ml for PfK13-V494I, and 0.28 mg/ml for PfK13-N537I. Results obtained for binding interaction revealed an increased fluorescence intensity in the mutants PfK13-N537I (83 a.u.) and PfK13-V494I (143 a.u.) compared to PfK13-WT (33 a.u.), indicating increased exposure of surface proteins because of the looser binding between PfK13 protein mutants with ART. This shows that the PfK13 mutations may induce alterations in the binding interaction with ART, potentially leading to reduced effectiveness of ART and ultimately contributing to ART-R. However, this study only elucidated one facet of the contributing factors that could serve as potential indicators for ART-R and further investigation should be pursued in the future to comprehensively explore this complex mechanism of ART-R.

Novel ether derivatives of 11-azaartemisinins with high order antimalarial activity against multidrug-resistant Plasmodium yoelii in Swiss mice

This study investigates cutting-edge synthetic chemistry approaches for designing and producing innovative antimalarial drugs with improved efficacy and fewer adverse effects. Novel amino (-NH2) and hydroxy (-OH) functionalized 11-azaartemisinins 9, 12, and 14 were synthesized along with their derivatives 11a, 13a-e, and 15a-b through ART and were tested for their AMA (antimalarial activity) against Plasmodium yoelii via intramuscular (i.m.) and oral routes in Swiss mice. Ether derivative 13c was the most active compound by i.m. route, it has shown 100 % protection at the dose of 12 mg/kg × 4 days and showed 100 % clearance of parasitaemia on day 4 at dose of 6 mg/kg. Amine 11a, ether derivatives 13d, 13e and ether 15a also showed promising antimalarial activity. β-Arteether gave 100 % protection at the dose of 48 mg/kg × 4 days and 20 % protection at 24 mg/kg × 4 days dose by oral route, while it showed 100 % protection at 6 mg/kg × 4 days and no protection at 3 mg/kg × 4 days by i.m. route.

Whole genome sequencing identifies novel mutations in malaria parasites resistant to artesunate (ATN) and to ATN + mefloquine combination

Introduction

The global evolution of resistance to Artemisinin-based Combination Therapies (ACTs) by malaria parasites, will severely undermine our ability to control this devastating disease.

Methods

Here, we have used whole genome sequencing to characterize the genetic variation in the experimentally evolved Plasmodium chabaudi parasite clone AS-ATNMF1, which is resistant to artesunate + mefloquine.

Results and discussion

Five novel single nucleotide polymorphisms (SNPs) were identified, one of which was a previously undescribed E738K mutation in a 26S proteasome subunit that was selected for under artesunate pressure (in AS-ATN) and retained in AS-ATNMF1. The wild type and mutated three-dimensional (3D) structure models and molecular dynamics simulations of the P. falciparum 26S proteasome subunit Rpn2 suggested that the E738K mutation could change the toroidal proteasome/cyclosome domain organization and change the recognition of ubiquitinated proteins. The mutation in the 26S proteasome subunit may therefore contribute to altering oxidation-dependent ubiquitination of the MDR-1 and/or K13 proteins and/or other targets, resulting in changes in protein turnover. In light of the alarming increase in resistance to artemisin derivatives and ACT partner drugs in natural parasite populations, our results shed new light on the biology of resistance and provide information on novel molecular markers of resistance that may be tested (and potentially validated) in the field.

Recent advances in the synthesis and antimalarial activity of 1,2,4-trioxanes

The increasing resistance of various malarial parasite strains to drugs has made the production of a new, rapid-acting, and efficient antimalarial drug more necessary, as the demand for such drugs is growing rapidly. As a major global health concern, various methods have been implemented to address the problem of drug resistance, including the hybrid drug concept, combination therapy, the development of analogues of existing medicines, and the use of drug resistance reversal agents. Artemisinin and its derivatives are currently used against multidrug- resistant P. falciparum species. However, due to its natural origin, its use has been limited by its scarcity in natural resources. As a result, finding a substitute becomes more crucial, and the peroxide group in artemisinin, responsible for the drugs biological action in the form of 1,2,4-trioxane, may hold the key to resolving this issue. The literature suggests that 1,2,4-trioxanes have the potential to become an alternative to current malaria drugs, as highlighted in this review. This is why 1,2,4-trioxanes and their derivatives have been synthesized on a large scale worldwide, as they have shown promising antimalarial activity in vivo and in vitro against Plasmodium species. Consequently, the search for a more convenient, environment friendly, sustainable, efficient, and effective synthetic pathway for the synthesis of 1,2,4-trioxanes continues. The aim of this work is to provide a comprehensive analysis of the synthesis and mechanism of action of 1,2,4-trioxanes. This systematic review highlights the most recent summaries of derivatives of 1,2,4-trioxane compounds and dimers with potential antimalarial activity from January 1988 to 2023.

A TetR family regulator of an RND efflux system that directs artemisinin resistance in Vibrio cholerae

Artemisinin (ARS) displayed bactericidal activity against Vibrio cholerae. To assess the mechanistic details of its antibacterial action, we have isolated V. cholerae mutants with enhanced ARS resistance and identified a gene (VCA0767) whose loss-of-function resulted in the ARS resistance phenotypes. This gene (atrR) encodes a TetR family transcriptional regulator, and its deletion mutant displayed the reduction in ARS-induced ROS formation and DNA damage. Transcriptomic analysis revealed that the genes encoding a resistance-nodulation-cell division (RND) efflux pump operon (vexRAB) and the outer membrane component (tolC) were highly upregulated in the artR mutant, suggesting that AtrR might act as a negative regulator of this operon and tolC. Gene deletion of vexR, vexB, or tolC abrogated the ARS resistance of the atrR mutant, and more importantly, the ectopic expression of VexAB-TolC was sufficient for the ARS resistance, indicating that the increased expression of the VexAB-TolC efflux system is necessary and sufficient for the ARS resistance of the atrR mutant. The cytoplasmic accumulation of ARS was compromised in the vexBtolC mutant, suggesting that the VexAB-TolC might be the primary efflux system exporting ARS to reduce its toxicity inside of the bacterial cells. The atrR mutant displayed resistance to erythromycin as well in a VexR-dependent manner. This result suggests that AtrR may act as a global regulator responsible for preventing intracellular accumulation of toxic chemicals by enhancing the RND efflux system.IMPORTANCEDrug efflux protein complexes or efflux pumps are considered as the major determinants of multiple antimicrobial resistance by exporting a wide range of structurally diverse antibiotics in bacterial pathogens. Despite the clinical significance of the increased expression of the efflux pumps, their substrate specificity and regulation mechanisms are poorly understood. Here, we demonstrated that VexAB-TolC, a resistance-nodulation-cell division (RND) efflux pump of V. cholerae, is responsible for the resistance to artemisinin (ARS), an antimalarial drug with bactericidal activity. Furthermore, we newly identified AtrR, a TetR family repressor, as a global regulator for VexRAB and the common outer membrane channel, TolC, where VexR functions as the pathway-specific regulator of the vexAB operon. Our findings will help improve our insight into a broad range of substrate specificity of the VexAB-TolC system and highlight the complex regulatory networks of the multiple RND efflux systems during V. cholerae pathogenesis.

Voltammetric methods for electrochemical characterization and quantification of artemether-based antimalarials

Every year substandard and falsified (SF) artemisinin derivative-based antimalarials are responsible for the loss of 450 000 deaths and billions of GBP. The lack of infrastructure and funds to support pharmaceutical quality control in many low-and-middle-income countries contributes to this problem. This work assesses fitness for purpose of voltammetric methods for identification and quantification of artemether in the presence of excipients. Electrochemical characterization of artemether using cyclic voltammetry shows that the reduction of artemether is chemically irreversible within the potential range of -0.4 V to -1.4 V. A chronocoulometric quantification algorithm for artemether is created and tested with pure artemether, as well as filtered and unfiltered Riamet® tablets. Filtration of Riamet® tablets provides no additional benefit for the quantification of artemether in Riamet®. In addition, artemether's response to pH indicates possible protonation and coupled homogeneous chemistry. Finally, sodium sulfite is an effective means of removing dissolved oxygen and improving artemether signal resolution in air-equilibrated PBS. This concludes that electrochemical analysis is a promising method for artemether identification and quantification.

An overview on the antimalarial activity of 1,2,4-trioxanes, 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes

The demand for novel, fast-acting, and effective antimalarial medications is increasing exponentially. Multidrug resistant forms of malarial parasites, which are rapidly spreading, pose a serious threat to global health. Drug resistance has been addressed using a variety of strategies, such as targeted therapies, the hybrid drug idea, the development of advanced analogues of pre-existing drugs, and the hybrid model of resistant strains control mechanisms. Additionally, the demand for discovering new potent drugs grows due to the prolonged life cycle of conventional therapy brought on by the emergence of resistant strains and ongoing changes in existing therapies. The 1,2,4-trioxane ring system in artemisinin (ART) is the most significant endoperoxide structural scaffold and is thought to be the key pharmacophoric moiety required for the pharmacodynamic potential of endoperoxide-based antimalarials. Several derivatives of artemisinin have also been found as potential treatments for multidrug-resistant strain in this area. Many 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes derivatives have been synthesised as a result, and many of these have shown promise antimalarial activity both in vivo and in vitro against Plasmodium parasites. As a consequence, efforts to develop a functionally straight-forward, less expensive, and vastly more effective synthetic pathway to trioxanes continue. This study aims to give a thorough examination of the biological properties and mode of action of endoperoxide compounds derived from 1,2,4-trioxane-based functional scaffolds. The present system of 1,2,4-trioxane, 1,2,4-trioxolane, and 1,2,4,5-tetraoxane compounds and dimers with potentially antimalarial activity will be highlighted in this systematic review (January 1963-December 2022).

Targeting HSP70 chaperones by rhein sensitizes liver cancer to artemisinin derivatives

BACKGROUND

Liver cancer is one of common types of cancer with poor prognosis and limited therapies. Heat shock proteins (HSP) are molecular chaperones that have important roles in tumorigenesis, and emerging as therapeutic targets. Artemisinin and rhein are natural agents from Artemisia annua L. and Rheum undulatum L., respectively. Both rhein and artemisinin have anticancer effects; however, the molecular targets of rhein remain to be identified. It is also unclear whether rhein can synergize with artemisinin derivatives to inhibit liver cancer.

PURPOSE

We aim to identify the targets of rhein in the treatment of hepatocarcinoma and determine the effects of combining rhein and artemisinin derivatives on liver cancer cells.

METHODS

The targets of rhein were detected by mass spectrometry and validated by rhein-proteins interaction assays. The effects of rhein on the chaperone activity of HSP72/HSC70/GRP78 were determined by luciferase refolding assays. Cell viability and apoptosis were determined by CCK8 and flow cytometry assays. For in vivo study, xenograft tumor models were established and treated with rhein and artesunate. Tumor growth was monitored regularly.

RESULTS

Mass spectrometry analysis of rhein-binding proteins in HepG2 cells revealed that HSP72, HSC70 and GRP78 were more profoundly pulled down by rhein-crosslinked sepharose 4B beads compared to the control beads. Further experiments demonstrated that rhein directly interacted with HSP72/HSC70/GRP78 proteins, and inhibit their activity of refolding denatured luciferase. Meanwhile, rhein induced proteasomal degradation of HIF1α and β-catenin. Artesunate or dihydroartemisinin in combination with knockdown of both HSP72 and HSC70 significantly inhibited cell viability. The HSP70/HSC70/GRP78 inhibitors VER-155,008 and rhein phenocopied HSP72/HSC70 knockdown, synergizing with artesunate or dihydroartemisinin to inhibit hepatocarcinoma cell viability. Combinatorial treatment with rhein and artemisinin derivatives significantly induced hepatocarcinoma cell apoptosis, and inhibited tumor growth in vivo.

CONCLUSIONS

The current study demonstrates that rhein is a novel HSP72/HSC70/GRP78 inhibitor that suppresses the chaperone activity of HSP70s. Dual inhibition of HSP72 and HSC70 can enhance the sensitivity of hepatocarcinoma cells to artemisinin derivatives. Combined treatment with artemisinin derivative and rhein significantly inhibits hepatocarcinoma. Artemisinin derivatives in combination with dual inhibition of HSP72 and HSC70 represents a new approach to improve cancer therapy.

Evaluation of 4-Aminoquinoline Hydrazone Analogues as Potential Leads for Drug-Resistant Malaria

The emergence of resistance to first-line antimalarial drugs calls for the development of new therapies for drug-resistant malaria. The efficacy of quinoline-based antimalarial drugs has prompted the development of novel quinolines. A panel of 4-aminoquinoline hydrazone analogues were tested on the multidrug-resistant K1 strain of Plasmodium falciparum: IC50 values after a 48 h cycle ranged from 0.60 to 49 µM, while the 72 h cycle ranged from 0.026 to 0.219 μM. Time-course assays were carried out to define the activity of the lead compounds, which inhibited over 50% growth in 24 h and 90% growth in 72 h. Cytotoxicity assays with HepG2 cells showed IC50 values of 0.87-11.1 μM, whereas in MDBK cells, IC50 values ranged from 1.66 to 11.7 μM. High selectivity indices were observed for the lead compounds screened at 72 h on P. falciparum. Analyses of stage specificity revealed that the ring stages of the parasite life cycle were most affected. Based on antimalarial efficacy and in vitro safety profiles, lead compound 4-(2-benzylidenehydrazinyl)-6-methoxy-2-methylquinoline 2 was progressed to drug combination studies for the detection of synergism, with a combinatory index of 0.599 at IC90 for the combination with artemether, indicating a synergistic antimalarial activity. Compound 2 was screened on different strains of P. falciparum (3D7, Dd2), which maintained similar activity to K1, suggesting no cross-resistance between multidrug resistance and sensitive parasite strains. In vivo analysis with 2 showed the suppression of parasitaemia with P. yoelii NL (non-lethal)-treated mice (20 mg/kg and 5 mg/kg).

Environmental differences between Japan and Indonesia provide endophyte diversity associated with Artemisia plant and variety of artemisinin derivatives in microbial conversion

We compared the endophytic compositions of Artemisia plant from different environments (Japan and Indonesia) to demonstrate that the endophytic filamentous fungi in both species differed based on their environments. To prove that the species were identical, both Artemisia plants were identified by comparing the scanning electron micrographs of their pollens, as well as the nucleotide sequences (ribosomal internal transcribed spacer and mitochondrial maturase K) of the two gene regions. After isolating the endophytic filamentous fungi from each plant, we observed that those from Japan and Indonesia comprised 14 and 6 genera, respectively. We assumed that the genera, Arthrinium and Colletotrichum, which exist in both Artemisia species, were species-specific filamentous fungi, while the other genera were environment-dependent. In the microbial-conversion reaction with artemisinin as a substrate using Colletotrichum sp., the peroxy bridge of artemisinin, which is an active site for achieving antimalarial effect, was converted into an ether bond. However, the reaction using the environment-dependent endophyte did not eliminate the peroxy bridge. These endophytic reactions indicated the different roles of endophytes within Artemisia plants.

Molecular Interactions Identified by Two-Dimensional Analysis-Detailed Insight into the Molecular Interactions of the Antimalarial Artesunate with the Target Structure β-Hematin by Means of 2D Raman Correlation Spectroscopy

A thorough understanding of the interaction of endoperoxide antimalarial agents with their biological target structures is of utmost importance for the tailored design of future efficient antimalarials. Detailed insights into molecular interactions between artesunate and β-hematin were derived with a combination of resonance Raman spectroscopy, two-dimensional correlation analysis, and density functional theory calculations. Resonance Raman spectroscopy with three distinct laser wavelengths enabled the specific excitation of different chromophore parts of β-hematin. The resonance Raman spectra of the artesunate-β-hematin complexes were thoroughly analyzed with the help of high-resolution and highly sensitive two-dimensional correlation spectroscopy. Spectral changes in the peak properties were found with increasing artesunate concentration. Changes in the low-frequency, morphology-sensitive Raman bands indicated a loss in crystallinity of the drug-target complexes. Differences in the high-wavenumber region were assigned to increased distortions of the planarity of the structure of the target molecule due to the appearance of various coexisting alkylation species. Evidence for the appearance of high-valent ferryl-oxo species could be observed with the help of differences in the peak properties of oxidation-state sensitive Raman modes. To support those findings, the relaxed ground-state structures of ten possible covalent mono- and di-meso(Cm)-alkylated hematin-dihydroartemisinyl complexes were calculated using density functional theory. A very good agreement with the experimental peak properties was achieved, and the out-of-plane displacements along the lowest-frequency normal coordinates were investigated by normal coordinate structural decomposition analysis. The strongest changes in all data were observed in vibrations with a high participation of Cm-parts of β-hematin.

Drug resistance profiling of asymptomatic and low-density Plasmodium falciparum malaria infections on Ngodhe island, Kenya, using custom dual-indexing next-generation sequencing

Malaria control initiatives require rapid and reliable methods for the detection and monitoring of molecular markers associated with antimalarial drug resistance in Plasmodium falciparum parasites. Ngodhe island, Kenya, presents a unique malaria profile, with lower P. falciparum incidence rates than the surrounding region, and a high proportion of sub-microscopic and low-density infections. Here, using custom dual-indexing and Illumina next generation sequencing, we generate resistance profiles on seventy asymptomatic and low-density P. falciparum infections from a mass drug administration program implemented on Ngodhe island between 2015 and 2016. Our assay encompasses established molecular markers on the Pfcrt, Pfmdr1, Pfdhps, Pfdhfr, and Pfk13 genes. Resistance markers for sulfadoxine-pyrimethamine were identified at high frequencies, including a quintuple mutant haplotype (Pfdhfr/Pfdhps: N51I, C59R, S108N/A437G, K540E) identified in 62.2% of isolates. The Pfdhps K540E biomarker, used to inform decision making for intermittent preventative treatment in pregnancy, was identified in 79.2% of isolates. Several variants on Pfmdr1, associated with reduced susceptibility to quinolones and lumefantrine, were also identified (Y184F 47.1%; D1246Y 16.0%; N86 98%). Overall, we have presented a low-cost and extendable approach that can provide timely genetic profiles to inform clinical and surveillance activities, especially in settings with abundant low-density infections, seeking malaria elimination.

Dihydroartemisinin Disrupts Zinc Homeostasis in Plasmodium falciparum To Potentiate Its Antimalarial Action via Pyknosis

Artemisinins have been used as first-line drugs worldwide to treat malaria caused by Plasmodium falciparum; however, its underlying mechanism is still unclear. This study aimed to identify the factors inducing growth inhibition via pyknosis, a state of intraerythrocytic developmental arrest, when exposing the parasite to dihydroartemisinin (DHA). Changes in the expression of genome-wide transcripts were assessed in the parasites treated with antimalarials, revealing the specific downregulation of zinc-associated proteins by DHA. The quantification of zinc levels in DHA-treated parasite indicated abnormal zinc depletion. Notably, the zinc-depleted condition in the parasite produced by a zinc chelator induced the generation of a pyknotic form and the suppression of its proliferation. The evaluation of the antimalarial activity of DHA or a glutathione-synthesis inhibitor in the zinc-depleted state showed that the disruption of zinc and glutathione homeostasis synergistically potentiated the growth inhibition of P. falciparum through pyknosis. These findings could help further understand the antimalarial actions of artemisinins for advancing malaria therapy.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

T follicular helper cells in autoimmune diseases

T follicular helper (Tfh) cells with the phenotype of mainly expressing surface molecules C-X-C motif chemokine receptor type 5 (CXCR5), inducible co-stimulator (ICOS), secreting cytokine interleukin-21 (IL-21) and requiring the transcription factor B cell lymphoma 6 (BCL-6) have been recently defined as a new subset of CD4⁺ T cells. They exist in germinal centers (GCs) of lymphoid organs and in peripheral blood. With the ability to promote B cell development, GC formation and antibody production, Tfh cells play critical roles in the pathogenesis of many autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), primary Sjögren's syndrome (pSS), etc. The aberrant proliferation and function of Tfh cells will cause the pathological process like autoantibody production and tissue injury. In this paper, we review the recent advances in Tfh cell biology and their roles in autoimmune diseases, with a mention of their use as therapeutic targets, which will shed more light on the pathogenesis and treatment of certain autoimmune diseases.

LC-MS/TOF Characterization and Stability Study of Artesunate in Different Solvent Systems

Artemisinin (ART) is a sesquiterpene lactone and a popular malaria drug used in many parts of the world. Artesunate (ARTS) is a semi-synthetic derivative of ART with improved pharmacokinetic properties. However, the half-life of ARTS is less than an hour in vivo. The analysis of this drug in vitro in different solvent systems using LC-MS/TOF showed a solvent-driven breakdown. ARTS breakdown formed several derivatives, including dihydroartemisinin (DHA), artemether (ARTM) and DHA-dimer among others, at different rates in different solvent composition systems. The change in temperature from room temperature to physiological temperature (37 °C) was found to enhance the rate of the ARTS breakdown. In methanol, ARTS mainly formed ARTM with a chromatographic peak decrease of about 3.13%, while methanol and water (90:10) v/v mainly gave rise to DHA and ARTM with about an 80% chromatographic peak decrease. On the other hand, ARTS in methanol and ammonium acetate (85:15) v/v formed DHA, ARTM, DHA-dimer and other reaction peaks with about a 97% peak decrease and the formation of an orange solution pointing to a molecular re-arrangement reaction. These results have an important bearing on research on the analysis of artemisinin drugs conducted on these common solvents.

Mechanistic Evaluation of the Stability of Arylvinyl-1,2,4-trioxanes under Acidic Conditions for Their Oral Administration as an Antimalarial Drug

A mechanistic approach to understand the course of metabolism for synthetic 1,2,4-trioxanes, potent antimalarial compounds, to evaluate their bioavailability for antimalarial action has been studied in the present work. It is an important parameter to study the course of metabolism of a drug candidate molecule when administered via oral route during its journey from oral intake to its target site. From the pharmacokinetics point of view, it determines the bioavailability of an active drug or a prodrug at the target point. In this work, synthetic arylvinyl-1,2,4-trioxanes 1a-u have been evaluated under various acidic conditions to mimic the milieu of the stomach (pH between 1.5 and 3.5) through which they have to pass when administered orally. The effect of acid on trioxanes led to their degradation into corresponding ketones and glyoxal. Under such acidic conditions glyoxal polymerized to form a nonisolable condensate product. The study indicates that the actual bioavailability of the drug is far less than the administered dose.

Resistance to Gemcitabine in Pancreatic Ductal Adenocarcinoma: A Physiopathologic and Pharmacologic Review

Pancreatic ductal adenocarcinoma (PDAC) is a very aggressive tumor with a poor prognosis and inadequate response to treatment. Many factors contribute to this therapeutic failure: lack of symptoms until the tumor reaches an advanced stage, leading to late diagnosis; early lymphatic and hematic spread; advanced age of patients; important development of a pro-tumoral and hyperfibrotic stroma; high genetic and metabolic heterogeneity; poor vascular supply; a highly acidic matrix; extreme hypoxia; and early development of resistance to the available therapeutic options. In most cases, the disease is silent for a long time, andwhen it does become symptomatic, it is too late for ablative surgery; this is one of the major reasons explaining the short survival associated with the disease. Even when surgery is possible, relapsesare frequent, andthe causes of this devastating picture are the low efficacy ofand early resistance to all known chemotherapeutic treatments. Thus, it is imperative to analyze the roots of this resistance in order to improve the benefits of therapy. PDAC chemoresistance is the final product of different, but to some extent, interconnected factors. Surgery, being the most adequate treatment for pancreatic cancer and the only one that in a few selected cases can achieve longer survival, is only possible in less than 20% of patients. Thus, the treatment burden relies on chemotherapy in mostcases. While the FOLFIRINOX scheme has a slightly longer overall survival, it also produces many more adverse eventsso that gemcitabine is still considered the first choice for treatment, especially in combination with other compounds/agents. This review discusses the multiple causes of gemcitabine resistance in PDAC.

Autoxidation of a C2-Olefinated Dihydroartemisinic Acid Analogue to Form an Aromatic Ring: Application to Serrulatene Biosynthesis

Dihydroartemisinic acid (DHAA) is a plant natural product that undergoes a spontaneous endoperoxide-forming cascade reaction to yield artemisinin in the presence of air. The endoperoxide functional group gives artemisinin its biological activity that kills Plasmodium falciparum, the parasite that causes malaria. To enhance our understanding of the mechanism of this cascade reaction, 2,3-didehydrodihydroartemisinic acid (2,3-didehydro-DHAA), a DHAA derivative with a double bond at the C2-position, was synthesized. When 2,3-didehydro-DHAA was exposed to air over time, instead of forming an endoperoxide, this compound predominantly underwent aromatization. This olefinated DHAA analogue reveals the requirement of a monoalkene functional group to initiate the endoperoxide-forming cascade reaction to yield artemisinin from DHAA. In addition, this aromatization process was exploited to illustrate the autoxidation process of a different plant natural product, dihydroserrulatene, to form the aromatic ring in serrulatene. This spontaneous aromatization process has applications in other natural products such as leubethanol and erogorgiaene. Due to their similarity in structure to antimicrobial natural products, the synthesized compounds in this study were tested for biological activity. A group of the tested compounds had minimum inhibitory concentration (MIC) values ranging from 12.5 to 25 μg/mL against the bacterial pathogen Staphylococcus aureus and the fungal pathogen Cryptococcus neoformans.

Predicting new potential antimalarial compounds by using Zagreb topological indices

Molecular topology allows describing molecular structures following a two-dimensional approach by taking into account how the atoms are arranged internally through a connection matrix between the atoms that are part of a structure. Various molecular indices (unique for each molecule) can be determined, such as Zagreb, Balaban, and topological indices. These indices have been correlated with physical chemistry properties such as molecular weight, boiling point, and electron density. Furthermore, their relationship with a specific biological activity has been found in other reports. Therefore, its knowledge and interpretation could be critical in the rational design of new compounds, saving time and money in their development process. In this research, the molecular graph of antimalarials already in the pharmaceutical market, such as chloroquine, primaquine, quinine, and artemisinin, was calculated and used to compute the Zagreb indices; a relationship between these indices and the antimalarial activities was found. According to the results reported in this work, the smaller the Zagreb indices, the higher the antimalarial activity. This relationship works very well for other compounds series. Therefore, it seems to be a fundamental structural requirement for this activity. Three triazole-modified structures are proposed as possible potential antimalarials based on this hypothesis. Finally, this work shows that the Zagreb indices could be a cornerstone in designing and synthesizing new antimalarial compounds, albeit they must be proved experimentally.

Artemisinin displays bactericidal activity via copper-mediated DNA damage

Artemisinin (ARS) and its semi-synthetic derivatives are effective drugs to treat malaria and possess multiple therapeutic activities based on their endoperoxide bridge. Here, we showed that ARS displayed antibacterial efficacy in Drosophila systemic infections caused by bacterial pathogens but killed only Vibrio cholerae (VC) in vitro, involving reactive oxygen species (ROS) generation and/or DNA damage. This selective antibacterial activity of ARS was attributed to the higher intracellular copper levels in VC, in that the antibacterial activity was observed in vitro upon addition of cuprous ions even against other bacteria and was compromised by the copper-specific chelators neocuproine (NC) and triethylenetetramine (TETA) in vitro and in vivo. We suggest that copper can enhance or reinforce the therapeutic activities of ARS to be repurposed as an antibacterial drug for the treatment of bacterial infections.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

Novel hydrazone derivatives of N-amino-11-azaartemisinin with high order of antimalarial activity against multidrug-resistant Plasmodium yoelii nigeriensis in Swiss mice via intramuscular route

Novel hydrazone derivatives 10a-m were prepared from N-Amino-11-azaartemisinin (9) and screened for their antimalarial activity by oral and intramuscular (i.m.) routes against multidrug-resistant Plasmodium yoelii in Swiss mice model. Several of the hydrazone derivatives showed higher order of antimalarial activity. Compounds 10b, 10g, 10m provided 100% protection to the infected mice at the dose of 24 mg/kg × 4 days via oral route. Fluorenone based hydrazone 10m the most active compound of the series, provided 100% protection at the dose of 6 mg/kg × 4 days via intramuscular route and also provided 100% protection at the dose of 12 mg/kg × 4 days via oral route. While artemisinin gave 100% protection at 48 mg/kg × 4 days and only 60% protection at 24 mg/kg × 4 days via intramuscular (i.m.) route. Compound 10m found to be four-fold more active than artemisinin via intramuscular route.

Flipping the Switch: Innovations in Inducible Probes for Protein Profiling

Over the past two decades, activity-based probes have enabled a range of discoveries, including the characterization of new enzymes and drug targets. However, their suitability in some labeling experiments can be limited by nonspecific reactivity, poor membrane permeability, or high toxicity. One method for overcoming these issues is through the development of “inducible” activity-based probes. These probes are added to samples in an unreactive state and require in situ transformation to their active form before labeling can occur. In this Review, we discuss a variety of approaches to inducible activity-based probe design, different means of probe activation, and the advancements that have resulted from these applications. Additionally, we highlight recent developments which may provide opportunities for future inducible activity-based probe innovations.

Drug-induced hypersensitivity to artemisinin-based therapies for malaria

In the early 2000s, artemisinin-based combination therapy (ACT) was introduced as first-line treatment for uncomplicated Plasmodium falciparum malaria in virtually all endemic countries. However, despite the well-known excellent tolerability of ACTs, hypersensitivity to artemisinin derivatives remains a repeatedly documented adverse drug reaction of still unknown frequency. The clinical features of an artemisinin-induced hypersensitivity reaction range from mild to life-threatening severity, and a significant number of cases may pass unnoticed. In this review, we discuss the medical importance of hypersensitivity to artemisinin derivatives and we review data on the presumed frequency and its potential underlying mechanisms. Furthermore, we advocate to make alternative non-artemisinin-based drugs available for patients who do not tolerate artemisinin derivatives and to continue investing in the development of novel non-artemisinin-based combination regimens.

Artemisinin DNA Base Interaction Studies in Presence of Fe(II): LC/TOF MS Separation of Reaction Products

Artemisinin (ART) is a sesquiterpene lactone and a popular malaria drug with potential anticancer properties. In this work, LC/TOF/MS, was used to investigate the reaction of ART with DNA bases. ART-deoxyadenosine and ART-deoxycytidine interactions, were studied in the presence of iron II ions. ART-deoxyadenosine and ART-deoxycytidine reaction mixtures gave chromatographic signatures that remained fairly unchanged at room temperature but grew after incubation at 37 °C. The change in temperature from room temperature to 37 °C was the main driver of adduct formation in these reactions. ART was found to react with Fe(II) ions as observed from several new chromatographic peaks. ART-deoxyadenosine as well as ART-deoxycytidine in the presence of Fe(II) ions resulted in formation of new chromatographic signatures of adducts consisting of DNA bases and ART. It was clear that addition of iron (II) to DNA base-ART mixtures gave rise to new reaction products mediated by a different reaction mechanism. Studies of ART reactions with DNA in vitro is key in elucidating elusive mechanism of this drug.

The multifaceted NF-kB: are there still prospects of its inhibition for clinical intervention in pediatric central nervous system tumors?

Despite advances in the understanding of the molecular mechanisms underlying the basic biology and pathogenesis of pediatric central nervous system (CNS) malignancies, patients still have an extremely unfavorable prognosis. Over the years, a plethora of natural and synthetic compounds has emerged for the pharmacologic intervention of the NF-kB pathway, one of the most frequently dysregulated signaling cascades in human cancer with key roles in cell growth, survival, and therapy resistance. Here, we provide a review about the state-of-the-art concerning the dysregulation of this hub transcription factor in the most prevalent pediatric CNS tumors: glioma, medulloblastoma, and ependymoma. Moreover, we compile the available literature on the anti-proliferative effects of varied NF-kB inhibitors acting alone or in combination with other therapies in vitro, in vivo, and clinical trials. As the wealth of basic research data continues to accumulate, recognizing NF-kB as a therapeutic target may provide important insights to treat these diseases, hopefully contributing to increase cure rates and lower side effects related to therapy.

Anti-malarial drug: the emerging role of artemisinin and its derivatives in liver disease treatment

Artemisinin and its derivatives belong to a family of drugs approved for the treatment of malaria with known clinical safety and efficacy. In addition to its anti-malarial effect, artemisinin displays anti-viral, anti-inflammatory, and anti-cancer effects in vivo and in vitro. Recently, much attention has been paid to the therapeutic role of artemisinin in liver diseases. Several studies suggest that artemisinin and its derivatives can protect the liver through different mechanisms, such as those pertaining to inflammation, proliferation, invasion, metastasis, and induction of apoptosis and autophagy. In this review, we provide a comprehensive discussion of the underlying molecular mechanisms and signaling pathways of artemisinin and its derivatives in treating liver diseases. Further pharmacological research will aid in determining whether artemisinin and its derivatives may serve as promising medicines for the treatment of liver diseases in the future.

Artemisinin inspired synthetic endoperoxide drug candidates: Design, synthesis, and mechanism of action studies

Artemisinin combination therapies (ACTs) have been used as the first-line treatments against Plasmodium falciparum malaria for decades. Recent advances in chemical proteomics have shed light on the complex mechanism of action of semi-synthetic artemisinin (ARTs), particularly their promiscuous alkylation of parasite proteins via previous heme-mediated bioactivation of the endoperoxide bond. Alarmingly, the rise of resistance to ART in South East Asia and the synthetic limitations of the ART scaffold have pushed the course for the necessity of fully synthetic endoperoxide-based antimalarials. Several classes of synthetic endoperoxide antimalarials have been described in literature utilizing various endoperoxide warheads including 1,2-dioxanes, 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes. Two of these classes, the 1,2,4-trioxolanes (arterolane and artefenomel) and the 1,2,4,5-tetraoxanes (N205 and E209) based antimalarials, have been explored extensively and are still in active development. In contrast, the most recent publication pertaining to the development of the 1,2-dioxane, Arteflene, and 1,2,4-trioxanes fenozan-50F, DU1301, and PA1103/SAR116242 was published in 2008. This review summarizes the synthesis, biological and clinical evaluation, and mechanistic studies of the most developed synthetic endoperoxide antimalarials, providing an update on those classes still in active development.

Anti-parasitic drugs modulate the non-selective channels formed by connexins or pannexins

The proteins connexins, innexins, and pannexins are the subunits of non-selective channels present in the cell membrane in vertebrates (connexins and pannexins) and invertebrates (innexins). These channels allow the transfer of ions and molecules across the cell membrane or, and in many cases, between the cytoplasm of neighboring cells. These channels participate in various physiological processes, particularly under pathophysiological conditions, such as bacterial, viral, and parasitic infections. Interestingly, some anti-parasitic drugs also block connexin- or pannexin-formed channels. Their effects on host channels permeable to molecules that favor parasitic infection can further explain the anti-parasitic effects of some of these compounds. In this review, the effects of drugs with known anti-parasitic activity that modulate non-selective channels formed by connexins or pannexins are discussed. Previous studies that have reported the presence of these proteins in worms, ectoparasites, and protozoa that cause parasitic infections have also been reviewed.

Synthesis of novel artesunate-benzothiophene and artemisinin-benzothiophene derivatives

Natural products are used for the treatment of a variety of diseases for many years. Last decades, design and synthesis of novel biologically active hybrid molecules including natural product is gained big importance due to their unique and new biological properties. In the present study, novel artemisinin-benzothiophene derivatives (12 A-F) are synthesised. Initially, benzothiophene derivatives (4 A-4F) are prepared via the Pd-catalyzed coupling reactions and iodocyclisation reactions. Then, Suzuki-Miyaura coupling reactions were used for the formation of intermediates 6 A-6F (between 64% and 91% yields). Finally, the Steglich esterification reaction between intermediate 6 and artesunate formed the artemisinin-benzothiophene hybrids (9 A-9F) in moderate to excellent yields under very mild reaction conditions. When intermediate 6 was reacted with dihydroartemisinin, product 12 A-12F was also obtained with high yields.

Advancement of chimeric hybrid drugs to cure malaria infection: An overview with special emphasis on endoperoxide pharmacophores

Emergence and spread of Plasmodium falciparum resistant to artemisinin-based combination therapy has led to a situation of haste in the scientific and pharmaceutical communities. Sincere efforts are redirected towards finding alternative chemotherapeutic agents that are capable of combating multidrug-resistant parasite strains. Extensive research yielded the concept of "Chimeric Bitherapy (CB)" which involves the linking of two molecules with individual pharmacological activity and exhibit dual mode of action into a single hybrid molecule. Current research in this field seems to endorse hybrid molecules as the next-generation antimalarial drugs and are more effective compared to the multi-component drugs because of the lower occurrence of drug-drug adverse effects. This review is an attempt to congregate complete survey on endoperoxide based hybrid antiplasmodial molecules that will give glimpse on the future directions for successful development and discovery of useful antimalarial hybrid drugs.

Botanical Medicines Cryptolepis sanguinolenta, Artemisia annua, Scutellaria baicalensis, Polygonum cuspidatum, and Alchornea cordifolia Demonstrate Inhibitory Activity Against Babesia duncani

Human babesiosis is a CDC reportable disease in the United States and is recognized as an emerging health risk in multiple parts of the world. The current treatment for human babesiosis is suboptimal due to treatment failures and unwanted side effects. Although Babesia duncani was first described almost 30 years ago, further research is needed to elucidate its pathogenesis and clarify optimal treatment regimens. Here, we screened a panel of herbal medicines and identified Cryptolepis sanguinolenta, Artemisia annua, Scutellaria baicalensis, Alchornea cordifolia, and Polygonum cuspidatum to have good in vitro inhibitory activity against B. duncani in the hamster erythrocyte model. Furthermore, we found their potential bioactive compounds, cryptolepine, artemisinin, artesunate, artemether, and baicalein, to have good activity against B. duncani, with IC₅₀ values of 3.4 μM, 14 μM, 7.4 μM, 7.8 μM, and 12 μM, respectively, which are comparable or lower than that of the currently used drugs quinine (10 μM) and clindamycin (37 μM). B. duncani treated with cryptolepine and quinine at their respective 1×, 2×, 4× and 8× IC₅₀ values, and by artemether at 8× IC₅₀ for three days could not regrow in subculture. Additionally, Cryptolepis sanguinolenta 90% ethanol extract also exhibited no regrowth after 6 days of subculture at doses of 2×, 4×, and 8× IC₅₀ values. Our results indicate that some botanical medicines and their active constituents have potent activity against B. duncani in vitro and may be further explored for more effective treatment of babesiosis.

Polymorphisms in Plasmodium falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) in Nigerian children 10 years post-adoption of artemisinin-based combination treatments

The emergence and spread of Plasmodium falciparum parasites resistant to artemisinin derivatives and their partners in southeastern Asia threatens malaria control and elimination efforts, and heightens the need for an alternative therapy. We have explored the distribution of P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) haplotypes 10 years following adoption of artemisinin-based combination therapies in a bid to investigate the possible re-emergence of Chloroquine-sensitive parasites in Nigeria, and investigated the effect of these P. falciparum haplotypes on treatment outcomes of patients treated with artemisinin-based combination therapies. A total of 271 children aged <5 years with uncomplicated falciparum malaria were included in this study. Polymorphisms on codons 72-76 of the Pfcrt gene and codon 86 and 184 of Pfmdr-1 were determined using the high resolution melting assay. Of 240 (88.6%) samples successfully genotyped with HRM for Pfcrt, wildtype C72M74N75K76 (42.9%) and mutant C72I74E75T76 (53.8%) were observed. Also, wildtype N86Y184 (62.9%) and mutant N86F184 (21.1%), Y86Y184 (6.4%), and Y86F184 (0.4%) haplotypes of Pfmdr-1 were observed. Measures of responsiveness to ACTs were similar in children infected with P. falciparum crt haplotypes (C72I74E75T76 and C72M74N75K76) and major mdr-1 haplotypes (N86Y184, N86F184 and Y86Y184). Despite a 10 year gap since the malaria treatment policy changed to ACTs, over 50% of the P. falciparum parasites investigated in this study harboured the Chloroquine-resistant C72I74E75T76 haplotype, however this did not compromise the efficacy of artemisinin-based combination therapies. Should complete artemisinin resistance emerge from or spread to Nigeria, chloroquine might not be a good alternative therapy.

Artemisinin protects endothelial function and vasodilation from oxidative damage via activation of PI3K/Akt/eNOS pathway

INTRODUCTION

Previous studies showed that artemisinin (ART) may be useful in the protection against the early development of atherosclerosis, but the effects of ART on vasodilation and eNOS remained unclear.

OBJECTIVES AND METHODS

In the current study, we investigated the protective effect of ART on endothelial cell injury induced by oxidative stress and its underlying mechanism via MTT assay, Flow Cytometry Assay, Vasodilation study, Western blotting and vivo assay.

RESULTS

We found that pretreatment of human umbilical vein endothelial cells (HUVECs) with ART significantly suppressed H2O2-induced cell death by decreasing the extent of oxidation and MDA activity, activating SOD, increasing NO production and inhibiting caspase 3/7 activity. Meanwhile, we also found that ART was able to activate PI3K/Akt/eNOS pathway. PI3K inhibitor LY294002 or Akt kinase specific inhibitor Akt inhibitor VIII blocked the protective effect of ART. To explore the effect of ART in the damage of vasodilation induced by H2O2 in mice, we treated the aortic ring from C57BL/6 mice with H2O2 with or without ART, the results demonstrated that ART ameliorated endothelium-dependent vasodilation damage induced by H2O2.

CONCLUSION

Taken together, these data suggest that ART is able to protect endothelial function and vasodilation from oxidative damage, at least in part through activation of PI3K/Akt/eNOS pathway. Our findings indicate that artemisinin maybe as a potential therapeutic agent for patients with atherosclerosis.

Exploration of artemisinin derivatives and synthetic peroxides in antimalarial drug discovery research

Malaria is a life-threatening infectious disease caused by protozoal parasites belonging to the genus Plasmodium. It caused an estimated 405,000 deaths and 228 million malaria cases globally in 2018 as per the World Malaria Report released by World Health Organization (WHO) in 2019. Artemisinin (ART), a "Nobel medicine" and its derivatives have proven potential application in antimalarial drug discovery programs. In this review, antimalarial activity of the most active artemisinin derivatives modified at C-10/C-11/C-16/C-6 positions and synthetic peroxides (endoperoxides, 1,2,4-trioxolanes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes) are systematically summarized. The developmental trend of ART derivatives, and cyclic peroxides along with their antimalarial activity and how the activity is affected by structural variations on different sites of the compounds are discussed. This compilation would be very useful towards scaffold hopping aimed at avoiding the unnecessary complexity in cyclic peroxides, and ultimately act as a handy resource for the development of potential chemotherapeutics against Plasmodium species.

Design, synthesis and pharmacological evaluation of novel Artemisinin-Thymol

A molecular hybridization of natural products is a new concept in drug discovery and having critical roles to design new molecules with improved biological properties. Hybrid molecules display higher biological activities when compared to the parent drugs. In the present study, two natural products (thymol and artemisinin (ART)) are used for the synthesis of new hybrid thymol-artemisinin. After characterization, the cytotoxic activity of ART-thymol was tested against different cancer cell lines and non-cancerous human cell line. ART-Thymol show the cytotoxic effect with EC₅₀ values 70,96μM for HepG2, 97,31μM for LnCap, 6,03μM for Caco-2, 77,98μM for HeLa and 62,28μM for HEK293 cells, respectively. Moreover, ART-Thymol was checked for drug-likeness, and the kinase inhibitory activity. ART-Thymol is investigated by using molecular docking. The results of qPCR was indicated CDK2 and P38 were inhibited by ART-Thymol. These results improved that thymol-artemisinin may be new candidates as an anticancer agents.

Research Advances on Health Effects of Edible Artemisia Species and Some Sesquiterpene Lactones Constituents

The genus Artemisia, often known collectively as "wormwood", has aroused great interest in the scientific community, pharmaceutical and food industries, generating many studies on the most varied aspects of these plants. In this review, the most recent evidence on health effects of edible Artemisia species and some of its constituents are presented and discussed, based on studies published until 2020, available in the Scopus, Web of Sciences and PubMed databases, related to food applications, nutritional and sesquiterpene lactones composition, and their therapeutic effects supported by in vivo and clinical studies. The analysis of more than 300 selected articles highlights the beneficial effect on health and the high clinical relevance of several Artemisia species besides some sesquiterpene lactones constituents and their derivatives. From an integrated perspective, as it includes therapeutic and nutritional properties, without ignoring some adverse effects described in the literature, this review shows the great potential of Artemisia plants and some of their constituents as dietary supplements, functional foods and as the source of new, more efficient, and safe medicines. Despite all the benefits demonstrated, some gaps need to be filled, mainly related to the use of raw Artemisia extracts, such as its standardization and clinical trials on adverse effects and its health care efficacy.

The Heme-Regulated Inhibitor Pathway Modulates Susceptibility of Poor Prognosis B-Lineage Acute Leukemia to BH3-Mimetics

Antiapoptotic MCL1 is one of the most frequently amplified genes in human cancers and elevated expression confers resistance to many therapeutics including the BH3-mimetic agents ABT-199 and ABT-263. The antimalarial, dihydroartemisinin (DHA) translationally represses MCL-1 and synergizes with BH3-mimetics. To explore how DHA represses MCL-1, a genome-wide CRISPR screen identified that loss of genes in the heme synthesis pathway renders mouse BCR-ABL⁺ B-ALL cells resistant to DHA-induced death. Mechanistically, DHA disrupts the interaction between heme and the eIF2α kinase heme-regulated inhibitor (HRI) triggering the integrated stress response. Genetic ablation of Eif2ak1, which encodes HRI, blocks MCL-1 repression in response to DHA treatment and represses the synergistic killing of DHA and BH3-mimetics compared with wild-type leukemia. Furthermore, BTdCPU, a small-molecule activator of HRI, similarly triggers MCL-1 repression and synergizes with BH3-mimetics in mouse and human leukemia including both Ph⁺ and Ph-like B-ALL. Finally, combinatorial treatment of leukemia bearing mice with both BTdCPU and a BH3-mimetic extended survival and repressed MCL-1 in vivo. These findings reveal for the first time that the HRI-dependent cellular heme-sensing pathway can modulate apoptosis in leukemic cells by repressing MCL-1 and increasing their responsiveness to BH3-mimetics. This signaling pathway could represent a generalizable mechanism for repressing MCL-1 expression in malignant cells and sensitizing them to available therapeutics. IMPLICATIONS: The HRI-dependent cellular heme-sensing pathway can modulate apoptotic sensitivity in leukemic cells by repressing antiapoptotic MCL-1 and increasing their responsiveness to BH3-mimetics.

Total Synthesis of (±)-Phaeocaulisin D

The tropone sesquiterpene phaeocaulisin D, isolated from the rhizomes of Curcuma phaeocaulis, has previously been shown to inhibit nitric oxide production in macrophages. A total synthesis of phaeocaulisin D was accomplished by using an intramolecular cyclization-dearomatization as a key step. The highlights of the synthesis are effective formation of the 5-7 fused tropone system, and selective methylation of a late-stage intermediate.

The Effect of Artemisinin on Inflammation-Associated Lymphangiogenesis in Experimental Acute Colitis

Inflammatory bowel disease (IBD) is characterized by inflammation, angiogenesis, and lymphangiogenesis. Artemisinin (Art), a chemical compound isolated from Artemisia annua L. (sweet wormwood), has several biochemical properties including antibacterial, anticancer, anti-inflammation, and anti-angiogenesis effects. We investigated the effects of Art on inflammation-induced lymphangiogenesis in a dextran sulfate sodium (DSS)-induced mouse acute colitis model. The mice were orally administered Art for 7 days before being evaluated using the disease activity index (DAI) and documenting colonic inflammatory changes, colon edema, microvessel density, lymphatic vessel density (LVD), proinflammatory cytokine levels, and vascular endothelial growth factor (VEGF)-C and VEGF-D/VEGF receptor (VEGFR)-3 mRNA expression levels in colon tissue. Art reduced DSS-induced lymphatic vessel endothelial hyaluronan receptor-1-positive LVD. Art also reduced the symptoms of colitis, improved tissue histology, and relieved inflammatory edema in mice affected by colitis. In addition, Art decreased the infiltration of immunomodulatory cells and inflammatory cytokines, which involved reduction of VEGF-C, -D, and VEGFR-3 expression. Taken together, our findings suggest that Art ameliorates inflammation-driven lymphangiogenesis in an experimental colitis mouse model via the VEGF-C/VEGFR-3 signaling pathway, implicating this pathway as a potential target for the treatment of IBD.

An insight into the recent development of the clinical candidates for the treatment of malaria and their target proteins

Malaria is an endemic disease, prevalent in tropical and subtropical regions which cost half of million deaths annually. The eradication of malaria is one of the global health priority nevertheless, current therapeutic efforts seem to be insufficient due to the emergence of drug resistance towards most of the available drugs, even first-line treatment ACT, unavailability of the vaccine, and lack of drugs with a new mechanism of action. Intensification of antimalarial research in recent years has resulted into the development of single dose multistage therapeutic agents which has advantage of overcoming the antimalarial drug resistance. The present review explored the current progress in the development of new promising antimalarials against prominent target proteins that have the potential to be a clinical candidate. Here, we also reviewed different aspects of drug resistance and highlighted new drug candidates that are currently in a clinical trial or clinical development, along with a few other molecules with excellent antimalarial activity overs ACTs. The summarized scientific value of previous approaches and structural features of antimalarials related to the activity are highlighted that will be helpful for the development of next-generation antimalarials.