Antimalarial action of artesunate involves DNA damage mediated by reactive oxygen species

Artesunate induces HO-1-mediated cell cycle arrest and senescence to protect against ocular fibrosis

Recent research found artesunate could inhibit ocular fibrosis; however, the underlying mechanisms are not fully known. Since the ocular fibroblast is the main effector cell in fibrosis, we hypothesized that artesunate may exert its protective effects by inhibiting the fibroblasts proliferation. TGF-β1-induced ocular fibroblasts and glaucoma filtration surgery (GFS)-treated rabbits were used as ocular fibrotic models. Firstly, we analyzed fibrosis levels by assessing the expression of fibrotic marker proteins, and used Ki67 immunofluorescence, EdU staining, flow cytometry to determine cell cycle status, and SA-β-gal staining to assess cellular senescence levels. Then to predict target genes and pathways of artesunate, we analyzed the differentially expressed genes and enriched pathways through RNA-seq. Western blot and immunohistochemistry were used to detect the pathway-related proteins. Additionally, we validated the dependence of artesunate's effects on HO-1 expression through HO-1 siRNA. Moreover, DCFDA and MitoSOX fluorescence staining were used to examine ROS level. We found artesunate significantly inhibits the expression of fibrosis-related proteins, induces cell cycle arrest and cellular senescence. Knocking down HO-1 in fibroblasts with siRNA reverses these regulatory effects of artesunate. Mechanistic studies show that artesunate significantly inhibits the activation of the Cyclin D1/CDK4-pRB pathway, induces an increase in cellular and mitochondrial ROS levels and activates the Nrf2/HO-1 pathway. In conclusion, the present study identifies that artesunate induces HO-1 expression through ROS to activate the antioxidant Nrf2/HO-1 pathway, subsequently inhibits the cell cycle regulation pathway Cyclin D1/CDK4-pRB in an HO-1-dependent way, induces cell cycle arrest and senescence, and thereby resists periorbital fibrosis.

Exosome-drug conjugates delivery: a promising strategy for ameliorating the pharmacokinetic profile of artesunate

Artesunate (ATS) is considered the most widely employed artemisnin derivative in the treatment of Plasmodium falciparum malaria. However, poor solubility and low bioavailability of ATS limit its further clinical application. Herein, we developed a new strategy based on the exosome (exo) - drug conjugation (EDC) using the milk-derived exosomes for ATS delivery. The Exo-ATS conjugates (EACs) which formed via a facile bio-conjugation of ATS to the exosomal surface, have been demonstrated to be able to not only boost the solubility and bioavailability of ATS but also enable a sustained-release of ATS from exosomes. Maximal improvement of 71.4-fold in the solubility of ATS was attained by EACs. The corresponding entrapment efficiency and drug loading capacities were found to be 90.3% and 73.9% for EACs, respectively. Further, in vivo pharmacokinetics study manifested that maximum 2.6-fold improved bioavailability of ATS was achieved by oral delivery of EACs. Moreover, EACs displayed a distinct sustained-release profile of maximum 36.2-fold prolonged half-life of ATS via intravenous delivery. We reported that for the first time the administration of EACs could be a potential drug delivery strategy aimed at ameliorating the pharmacokinetic profile of ATS based on our encouraging results and hoped that our work opened up a new avenue for the development of EDC delivery system.

Therapeutic potential of hydantoin and thiohydantoin compounds against Schistosoma mansoni: An integrated in vitro, DNA, ultrastructural, and ADMET in silico approach

The study aimed to conduct in vitro biological assessments of hydantoin and thiohydantoin compounds against mature Schistosoma mansoni worms, evaluate their cytotoxic effects and predict their pharmacokinetic parameters using computational methods. The compounds showed low in vitro cytotoxicity and were not considered hemolytic. Antiparasitic activity against adult S. mansoni worms was tested with all compounds at concentrations ranging from 200 to 6.25 μM. Compounds SC01, SC02, and SC03 exhibited low activity. Compounds SC04, SC05, SC06 and SC07 caused 100 % mortality within 24 h of incubation at a concentration of 100 and 200 μM. Thiohydantoin SC04 exhibited the highest activity, resulting in 100 % mortality after 24 h of incubation at a concentration of 50 μM and IC50 of 28 µM. In the ultrastructural analysis (SEM), the compound SC04 (200 µM) induced integumentary changes, formation of integumentary blisters, and destruction of tubercles and spicules. Therefore, the SC04 compound shows promise as an antiparasitic against S. mansoni.

MYST regulates DNA repair and forms a NuA4-like complex in the malaria parasite Plasmodium falciparum

Histone lysine acetyltransferase MYST-associated NuA4 complex is conserved from yeast to humans and plays key roles in cell cycle regulation, gene transcription, and DNA replication/repair. Here, we identified a Plasmodium falciparum MYST-associated complex, PfNuA4, which contains 11 of the 13 conserved NuA4 subunits. Reciprocal pulldowns using PfEAF2, a shared component between the NuA4 and SWR1 complexes, not only confirmed the PfNuA4 complex but also identified the PfSWR1 complex, a histone remodeling complex, although their identities are low compared to the homologs in yeast or humans. Notably, both H2A.Z/H2B.Z were associated with the PfSWR1 complex, indicating that this complex is involved in the deposition of H2A.Z/H2B.Z, the variant histone pair that is enriched in the activated promoters. Overexpression of PfMYST resulted in earlier expression of genes involved in cell cycle regulation, DNA replication, and merozoite invasion, and upregulation of the genes related to antigenic variation and DNA repair. Consistently, PfMYST overexpression led to high basal phosphorylated PfH2A (γ-PfH2A), the mark of DNA double-strand breaks, and conferred protection against genotoxic agent methyl methanesulfonate (MMS), X-rays, and artemisinin, the first-line antimalarial drug. In contrast, the knockdown of PfMYST caused a delayed parasite recovery upon MMS treatment. MMS induced the gradual disappearance of PfMYST in the cytoplasm and concomitant accumulation of PfMYST in the nucleus, suggesting cytoplasm-nucleus shuttling of PfMYST. Meanwhile, PfMYST colocalized with the γ-PfH2A, indicating PfMYST was recruited to the DNA damage sites. Collectively, PfMYST plays critical roles in cell cycle regulation, gene transcription, and DNA replication/DNA repair in this low-branching parasitic protist.IMPORTANCEUnderstanding gene regulation and DNA repair in malaria parasites is critical for identifying targets for antimalarials. This study found PfNuA4, a PfMYST-associated, histone modifier complex, and PfSWR1, a chromatin remodeling complex in malaria parasite Plasmodium falciparum. These complexes are divergent due to the low identities compared to their homologs from yeast and humans. Furthermore, overexpression of PfMYST resulted in substantial transcriptomic changes, indicating that PfMYST is involved in regulating the cell cycle, antigenic variation, and DNA replication/repair. Consistently, PfMYST was found to protect against DNA damage caused by the genotoxic agent methyl methanesulfonate, X-rays, and artemisinin, the first-line antimalarial drug. Additionally, DNA damage led to the relocation of cytoplasmic PfMYST to the nucleus and colocalization of PfMYST with γ-PfH2A, the mark of DNA damage. In summary, this study demonstrated that the PfMYST complex has critical functions in regulating cell cycle, antigenic variation, and DNA replication/DNA repair in P. falciparum.

Plasmodium falciparum Alba6 exhibits DNase activity and participates in stress response

Alba domain proteins, owing to their functional plasticity, play a significant role in organisms. Here, we report an intrinsic DNase activity of PfAlba6 from Plasmodium falciparum, an etiological agent responsible for human malignant malaria. We identified that tyrosine28 plays a critical role in the Mg2+ driven 5'-3' DNase activity of PfAlba6. PfAlba6 cleaves both dsDNA as well as ssDNA. We also characterized PfAlba6-DNA interaction and observed concentration-dependent oligomerization in the presence of DNA, which is evident from size exclusion chromatography and single molecule AFM-imaging. PfAlba6 mRNA expression level is up-regulated several folds following heat stress and treatment with artemisinin, indicating a possible role in stress response. PfAlba6 has no human orthologs and is expressed in all intra-erythrocytic stages; thus, this protein can potentially be a new anti-malarial drug target.

Pharmacokinetics and Pharmacodynamics of a Nanostructured Lipid Carrier Co-Encapsulating Artemether and miRNA for Mitigating Cerebral Malaria

Cerebral malaria (CM), a severe neurological pathology caused by Plasmodium falciparum infection, poses a significant global health threat and has a high mortality rate. Conventional therapeutics cannot cross the blood-brain barrier (BBB) efficiently. Therefore, finding effective treatments remains challenging. The novelty of the treatment proposed in this study lies in the feasibility of intranasal (IN) delivery of the nanostructured lipid carrier system (NLC) combining microRNA (miRNA) and artemether (ARM) to enhance bioavailability and brain targeting. The rational use of NLCs and RNA-targeted therapeutics could revolutionize the treatment strategies for CM management. This study can potentially address the challenges in treating CM, allowing drugs to pass through the BBB. The NLC formulation was developed by a hot-melt homogenization process utilizing 3% (w/w) precirol and 1.5% (w/v) labrasol, resulting in particles with a size of 94.39 nm. This indicates an effective delivery to the brain via IN administration. The results further suggest the effective intracellular delivery of encapsulated miRNAs in the NLCs. Investigations with an experimental cerebral malaria mouse model showed a reduction in parasitaemia, preservation of BBB integrity, and reduced cerebral haemorrhages with the ARM+ miRNA-NLC treatment. Additionally, molecular discoveries revealed that nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) and Interleukin-6 (IL-6) levels were reduced in the treated groups in comparison to the CM group. These results support the use of nanocarriers for IN administration, offering a viable method for mitigating CM through the increased bioavailability of therapeutics. Our findings have far-reaching implications for future research and personalized therapy.

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.

Plasmodium falciparum GCN5 plays a key role in regulating artemisinin resistance-related stress responses

Plasmodium falciparum causes the most severe malaria and is exposed to various environmental and physiological stresses in the human host. Given that GCN5 plays a critical role in regulating stress responses in model organisms, we aimed to elucidate PfGCN5's function in stress responses in P. falciparum. The protein level of PfGCN5 was substantially induced under three stress conditions [heat shock, low glucose starvation, and dihydroartemisinin, the active metabolite of artemisinin (ART)]. With a TetR-DOZI conditional knockdown (KD) system, we successfully down-regulated PfGCN5 to ~50% and found that KD parasites became more sensitive to all three stress conditions. Transcriptomic analysis via RNA-seq identified ~1,000 up- and down-regulated genes in the wild-type (WT) and KD parasites under these stress conditions. Importantly, DHA induced transcriptional alteration of many genes involved in many aspects of stress responses, which were heavily shared among the altered genes under heat shock and low glucose conditions, including ART-resistance-related genes such as K13 and coronin. Based on the expression pattern between WT and KD parasites under three stress conditions, ~300-400 genes were identified to be involved in PfGCN5-dependent, general, and stress-condition-specific responses with high levels of overlaps among three stress conditions. Notably, using ring-stage survival assay, we found that KD or inhibition of PfGCN5 could sensitize the ART-resistant parasites to the DHA treatment. All these indicate that PfGCN5 is pivotal in regulating general and ART-resistance-related stress responses in malaria parasites, implicating PfGCN5 as a potential target for malaria intervention.

Transition Metal Complexes as Antimalarial Agents: A Review

In antimalarial drug development research, overcoming drug resistance has been a major challenge for researchers. Nowadays, several drugs like chloroquine, mefloquine, sulfadoxine, and artemisinin are used to treat malaria. But increment in drug resistance has pushed researchers to find novel drugs to tackle drug resistance problems. The idea of using transition metal complexes with pharmacophores as ligands/ligand pendants to show enhanced antimalarial activity with a novel mechanism of action has gained significant attention recently. The advantages of metal complexes include tunable chemical/physical properties, redox activity, avoiding resistance factors, etc. Several recent reports have successfully demonstrated that the metal complexation of known organic antimalarial drugs can overcome drug resistance by showing enhanced activities than the parent drugs. This review has discussed the fruitful research works done in the past few years falling into this criterion. Based on transition metal series (3d, 4d, or 5d), the antimalarial metal complexes have been divided into three broad categories (3d, 4d, or 5d metal-based), and their activities have been compared with the similar control complexes as well as the parent drugs. Furthermore, we have also commented on the potential issues and their possible solution for translating these metal-based antimalarial complexes into the clinic.

Novel Therapeutics for Malaria

Malaria is a potentially fatal disease caused by protozoan parasites of the genus Plasmodium. It is responsible for significant morbidity and mortality in endemic countries of the tropical and subtropical world, particularly in Africa, Southeast Asia, and South America. It is estimated that 247 million malaria cases and 619,000 deaths occurred in 2021 alone. The World Health Organization's (WHO) global initiative aims to reduce the burden of disease but has been massively challenged by the emergence of parasitic strains resistant to traditional and emerging antimalarial therapy. Therefore, development of new antimalarial drugs with novel mechanisms of action that overcome resistance in a safe and efficacious manner is urgently needed. Based on the evolving understanding of the physiology of Plasmodium, identification of potential targets for drug intervention has been made in recent years, resulting in more than 10 unique potential anti-malaria drugs added to the pipeline for clinical development. This review article will focus on current therapies as well as novel targets and therapeutics against malaria.

Chemogenomic Profiling of a Plasmodium falciparum Transposon Mutant Library Reveals Shared Effects of Dihydroartemisinin and Bortezomib on Lipid Metabolism and Exported Proteins

The antimalarial activity of the frontline drug artemisinin involves generation of reactive oxygen species (ROS) leading to oxidative damage of parasite proteins. To achieve homeostasis and maintain protein quality control in the overwhelmed parasite, the ubiquitin-proteasome system kicks in. Even though molecular markers for artemisinin resistance like pfkelch13 have been identified, the intricate network of mechanisms driving resistance remains to be elucidated. Here, we report a forward genetic screening strategy that enables a broader identification of genetic factors responsible for altering sensitivity to dihydroartemisinin (DHA) and a proteasome inhibitor, bortezomib (BTZ). Using a library of isogenic piggyBac mutants in P. falciparum, we defined phenotype-genotype associations influencing drug responses and highlighted shared mechanisms between the two processes, which mainly included proteasome-mediated degradation and the lipid metabolism genes. Additional transcriptomic analysis of a DHA/BTZ-sensitive piggyBac mutant showed it is possible to find differences between the two response mechanisms on the specific components for regulation of the exportome. Our results provide further insight into the molecular mechanisms of antimalarial drug resistance. IMPORTANCE Malaria control is seriously threatened by the emergence and spread of Plasmodium falciparum resistance to the leading antimalarial, artemisinin. The potent killing activity of artemisinin results from oxidative damage unleashed by free heme activation released by hemoglobin digestion. Although the ubiquitin-proteasome system is considered critical for parasite survival of this toxicity, the diverse genetic changes linked to artemisinin resistance are complex and, so far, have not included the ubiquitin-proteasome system. In this study, we use a systematic forward genetic approach by screening a library of P. falciparum random piggyBac mutants to decipher the genetic factors driving malaria parasite responses to the oxidative stress caused by antimalarial drugs. This study compares phenotype-genotype associations influencing dihydroartemisinin responses with the proteasome inhibitor bortezomib to delineate the role of ubiquitin-proteasome system. Our study highlights shared and unique pathways from the complex array of molecular processes critical for P. falciparum survival resulting from the oxidative damage of artemisinin.

Molecular insights into artemisinin resistance in Plasmodium falciparum: An updated review

Malaria still poses a major burden on human health around the world, especially in endemic areas. Plasmodium resistance to several antimalarial drugs has been one of the major hindrances in control of malaria. Thus, the World Health Organization recommended artemisinin-based combination therapy (ACT) as a front-line treatment for malaria. The emergence of parasites resistant to artemisinin, along with resistant to ACT partner drugs, has led to ACT treatment failure. The artemisinin resistance is mostly related to the mutations in the propeller domain of the kelch13 (k13) gene that encodes protein Kelch13 (K13). The K13 protein has an important role in parasite reaction to oxidative stress. The most widely spread mutation in K13, with the highest degree of resistance, is a C580Y mutation. Other mutations, which are already identified as markers of artemisinin resistance, are R539T, I543T, and Y493H. The objective of this review is to provide current molecular insights into artemisinin resistance in Plasmodium falciparum. The trending use of artemisinin beyond its antimalarial effect is described. Immediate challenges and future research directions are discussed. Better understanding of the molecular mechanisms underlying artemisinin resistance will accelerate implementation of scientific findings to solve problems with malarial infection.

Plasmodium falciparum GCN5 plays a key role in regulating artemisinin resistance-related stress responses

Plasmodium falciparum causes the most severe malaria and is exposed to various environmental and physiological stresses in the human host. Given that GCN5 plays a critical role in regulating stress responses in model organisms, we aimed to elucidate PfGCN5's function in stress responses in P. falciparum . The protein level of PfGCN5 was substantially induced under three stress conditions (heat shock, low glucose starvation, and dihydroartemisinin, the active metabolite of artemisinin (ART)). With a TetR-DOZI conditional knockdown (KD) system, we successfully down-regulated PfGCN5 to ∼50% and found that KD parasites became more sensitive to all three stress conditions. Transcriptomic analysis via RNA-seq identified ∼1,000 up-and down-regulated genes in the wildtype (WT) and KD parasites under these stress conditions. Importantly, DHA induced transcriptional alteration of many genes involved in many aspects of stress responses, which were heavily shared among the altered genes under heat shock and low glucose conditions, including ART-resistance-related genes such as K13 and coronin . Based on the expression pattern between WT and KD parasites under three stress conditions, ∼300-400 genes were identified to be involved in PfGCN5-dependent, general and stress-condition-specific responses with high levels of overlaps among three stress conditions. Notably, using ring-stage survival assay (RSA), we found that KD or inhibition of PfGCN5 could sensitize the ART-resistant parasites to the DHA treatment. All these indicate that PfGCN5 is pivotal in regulating general and ART-resistance-related stress responses in malaria parasites, implicating PfGCN5 as a potential target for malaria intervention.

IMPORTANCE

Malaria leads to about half a million deaths annually and these casualties were majorly caused by the infection of Plasmodium falciparum . This parasite strives to survive by defending against a variety of stress conditions, such as malaria cyclical fever (heat shock), starvation due to low blood sugar (glucose) levels (hypoglycemia), and drug treatment. Previous studies have revealed that P. falciparum has developed unique stress responses to different stresses including ART treatment, and ART-resistant parasites harbor elevated stress responses. In this study, we provide critical evidence on the role of PfGCN5, a histone modifier, and a chromatin coactivator, in regulating general and stress-specific responses in malaria parasites, indicating that PfGCN5 can be used as a potential target for anti-malaria intervention.

Artemisinin derivatives induce oxidative stress leading to DNA damage and caspase-mediated apoptosis in Theileria annulata-transformed cells

BACKGROUND

Bovine theileriosis caused by the eukaryotic parasite Theileria annulata is an economically important tick-borne disease. If it is not treated promptly, this lymphoproliferative disease has a significant fatality rate. Buparvaquone (BPQ) is the only chemotherapy-based treatment available right now. However, with the emergence of BPQ resistance on the rise and no backup therapy available, it is critical to identify imperative drugs and new targets against Theileria parasites.

METHODS

Artemisinin and its derivatives artesunate (ARS), artemether (ARM), or dihydroartemisinin (DHART) are the primary defence line against malaria parasites. This study has analysed artemisinin and its derivatives for their anti-Theilerial activity and mechanism of action.

RESULTS

ARS and DHART showed potent activity against the Theileria-infected cells. BPQ in combination with ARS or DHART showed a synergistic effect. The compounds act specifically on the parasitised cells and have minimal cytotoxicity against the uninfected host cells. Treatment with ARS or DHART induces ROS-mediated oxidative DNA damage leading to cell death. Further blocking intracellular ROS by its scavengers antagonised the anti-parasitic activity of the compounds. Increased ROS production induces oxidative stress and DNA damage causing p53 activation followed by caspase-dependent apoptosis in the Theileria-infected cells.

CONCLUSIONS

Our findings give unique insights into the previously unknown molecular pathways underpinning the anti-Theilerial action of artemisinin derivatives, which may aid in formulating new therapies against this deadly parasite. Video abstract.

A Metabolomic and Transcriptomic Study Revealed the Mechanisms of Lumefantrine Inhibition of Toxoplasma gondii

Toxoplasma gondii is an obligate protozoon that can infect all warm-blooded animals including humans. T. gondii afflicts one-third of the human population and is a detriment to the health of livestock and wildlife. Thus far, traditional drugs such as pyrimethamine and sulfadiazine used to treat T. gondii infection are inadequate as therapeutics due to relapse, long treatment period, and low efficacy in parasite clearance. Novel, efficacious drugs have not been available. Lumefantrine, as an antimalarial, is effective in killing T. gondii but has no known mechanism of action. We combined metabolomics with transcriptomics to investigate how lumefantrine inhibits T. gondii growth. We identified significant alternations in transcripts and metabolites and their associated functional pathways that are attributed to lumefantrine treatment. RH tachyzoites were used to infect Vero cells for three hours and subsequently treated with 900 ng/mL lumefantrine. Twenty-four hours post-drug treatment, we observed significant changes in transcripts associated with five DNA replication and repair pathways. Metabolomic data acquired through liquid chromatography-tandem mass spectrometry (LC-MS) showed that lumefantrine mainly affected sugar and amino acid metabolism, especially galactose and arginine. To investigate whether lumefantrine damages T. gondii DNA, we conducted a terminal transferase assay (TUNEL). TUNEL results showed that lumefantrine significantly induced apoptosis in a dose-dependent manner. Taken together, lumefantrine effectively inhibited T. gondii growth by damaging DNA, interfering with DNA replication and repair, and altering energy and amino acid metabolisms.

Antiplasmodial Properties of Aqueous and Ethanolic Extracts of Ten Herbal Traditional Recipes Used in Thailand against Plasmodium falciparum

This study evaluated the in vitro and in vivo antiplasmodial efficacy and toxicity of aqueous and ethanolic extracts from traditional recipes used in Thailand. The aqueous and ethanolic extracts of ten traditional recipes were tested for in vitro antiplasmodial activity (parasite lactate dehydrogenase assay), cytotoxicity (MTT assay), and hemolysis). Oxidant levels were measured using cell-permeable probe 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate fluorescent dye-based assays. The best candidate was chosen for testing in mouse models using 4-day suppressive and acute toxicity assays. An in vitro study showed that ethanolic extracts and three aqueous extracts exhibited antiplasmodial activity, with an IC₅₀ in the range of 2.8-15.5 µg/mL. All extracts showed high CC₅₀ values, except for ethanolic extracts from Benjakul, Benjalotiga, and Trikatuk in HepG2 and Benjalotiga and aqueous extract from Chan-tang-ha in a Vero cell. Based on the results of the in vitro antiplasmodial activity, an aqueous extract of Triphala was chosen for testing in mouse models. The aqueous extract of Triphala exhibited good antiplasmodial activity, was safe at an oral dose of 2 g/kg, and is a potential candidate as a new source for the development of antimalarial drugs.

Transcriptome-module phenotype association study implicates extracellular vesicles biogenesis in Plasmodium falciparum artemisinin resistance

Plasmodium falciparum malaria is still an important disease in sub-Saharan Africa (sSA). Great strides have been made in its control spear-headed by artemisinin (ART)-based combination therapies (ACTs). However, concerns about the imminent spread of ART-resistant (ARTr) malaria parasites to sSA threaten gains already made. Attempts to mitigate this risk have highlighted the need to discover novel P. falciparum drug targets. Therefore, studies to deepen our understanding of the biology of P. falciparum are needed. The role of extracellular vesicles (EVs) in the biology of malaria parasites is not fully understood. Recently, the ART resistance-associated transcriptional profile has been reported to involve several biological processes connected to vesicular trafficking, proteotoxic stress, erythrocyte remodelling, and mitochondrial metabolism. We explored a role for EVs in developing the P. falciparum ARTr phenotype using bulk RNA sequencing of unsynchronized parasite cultures under untreated, 0.1% dimethyl sulfoxide and 700nM dihydroartemisinin treated conditions for six hours. As pathway and gene ontology analysis is limited in its curated knowledge repertoire on EVs biogenesis in P. falciparum, we used a modular (gene set) analysis approach to explore whether an EVs biogenesis module is associated with the ARTr phenotype in P. falciparum. We first generated well-defined EVs modules of interest and used statistical tools to determine differences in their expression among the parasite and treatment conditions. Then we used gene set enrichment analysis to determine the strength of the association between each EVs module of interest and the ARTr phenotype. This transcriptome-module phenotype association study (TMPAS) represents a well-powered approach to making meaningful discoveries out of bulk gene expression data. We identified four EVs module of interest and report that one module representing gene sets with correlated expression to PF3D7_1441800 – involved with EVs biogenesis in P. falciparum - is associated with the ARTr phenotype (R539T_DHA_treated versus R539T_untreated: normalized enrichment score (NES) = 1.1830174, FDR q-value < 0.25; C580R_DHA_treated versus C580R_untreated: NES = 1.2457103, FDR q-value < 0.25). PF3D7_1441800 has been reported to reduce EVs production when knocked out in P. falciparum. Altogether, our findings suggest a role for EVs in developing ART resistance and warrant further studies interrogating this association.

Artesunate Inhibits the Cell Growth in Colorectal Cancer by Promoting ROS-Dependent Cell Senescence and Autophagy

Although artesunate has been reported to be a promising candidate for colorectal cancer (CRC) treatment, the underlying mechanisms and molecular targets of artesunate are yet to be explored. Here, we report that artesunate acts as a senescence and autophagy inducer to exert its inhibitory effect on CRC in a reactive oxygen species (ROS)-dependent manner. In SW480 and HCT116 cells, artesunate treatment led to mitochondrial dysfunction, drastically promoted mitochondrial ROS generation, and consequently inhibited cell proliferation by causing cell cycle arrest at G0/G1 phase as well as subsequent p16- and p21-mediated cell senescence. Senescent cells underwent endoplasmic reticulum stress (ERS), and the unfolded protein response (UPR) was activated via IRE1α signaling, with upregulated BIP, IRE1α, phosphorylated IRE1α (p-IRE1α), CHOP, and DR5. Further experiments revealed that autophagy was induced by artesunate treatment due to oxidative stress and ER stress. In contrast, N-Acetylcysteine (NAC, an ROS scavenger) and 3-Methyladenine (3-MA, an autophagy inhibitor) restored cell viability and attenuated autophagy in artesunate-treated cells. Furthermore, cellular free Ca²⁺ levels were increased and could be repressed by NAC, 3-MA, and GSK2350168 (an IRE1α inhibitor). In vivo, artesunate administration reduced the growth of CT26 cell-derived tumors in BALB/c mice. Ki67 and cyclin D1 expression was downregulated in tumor tissue, while p16, p21, p-IRE1α, and LC3B expression was upregulated. Taken together, artesunate induces senescence and autophagy to inhibit cell proliferation in colorectal cancer by promoting excessive ROS generation.

Advances in the pharmacological treatment of hepatic alveolar echinococcosis: From laboratory to clinic

Hepatic alveolar echinococcosis (HAE) is a zoonotic parasitic disease caused by the larvae of Echinococcus multilocularis. Because of its characteristics of diffuse infiltration and growth similar to tumors, the disability rate and mortality rate are high among patients. Although surgery (including hepatectomy, liver transplantation, and autologous liver transplantation) is the first choice for the treatment of hepatic alveolar echinococcosis in clinic, drug treatment still plays an important and irreplaceable role in patients with end-stage echinococcosis, including patients with multiple organ metastasis, patients with inferior vena cava invasion, or patients with surgical contraindications, etc. However, Albendazole is the only recommended clinical drug which could exhibit a parasitostatic rather than a parasitocidal effect. Novel drugs are needed but few investment was made in the field because the rarity of the cases. Drug repurposing might be a solution. In this review, FDA-approved drugs that have a potential curative effect on hepatic alveolar echinococcosis in animal models are summarized. Further, nano drug delivery systems boosting the therapeutic effect on hepatic alveolar echinococcosis are also reviewed. Taken together, these might contribute to the development of novel strategy for advanced hepatic alveolar echinococcosis.

Copper (I)-Chloroquine Complexes: Interactions with DNA and Ferriprotoporphyrin, Inhibition of β-Hematin Formation and Relation to Antimalarial Activity

A new Cu(I)-chloroquine (CQ) complex [Cu(CQ)(PPh₃)₂]NO₃ (1) was synthesized and characterized, and its mechanism of action studied concomitant with the previously reported complex [Cu(CQ)₂]Cl (2). These copper (I) coordination compounds can be considered as potential antimalarial agents because they show better inhibition of the CQ-resistant strain in in vitro studies than CQ alone. In comparison with other metal-CQ complexes, only the gold complex was similar to (1), i.e., more active than CQ against both CQ-susceptible (3D7) and CQ-resistant strains (W2). These two copper (I)-compounds also demonstrated higher antiplasmodial activity against W2 than other copper complexes reported to date. This suggests that the incorporation of the copper metal center enhanced the biological activity of CQ. To better understand their significant growth inhibition of the Plasmodium falciparum parasite, the interaction with two essential molecular targets for the survival and proliferation of the malarial parasite were studied. These were the ferriprotoporphyrin group and the DNA, both important targets for current antimalarial drugs at the asexual erythrocytic stages. Both compounds (1,2) exhibited significant interactions with these targets. In particular, interactions with the DNA were dominated by the intercalator properties of the CQ ligand but may have also been affected by the presence of copper. Overall, these compounds were better parasitic inhibitors than chloroquine diphosphate (CQDP) alone or other previously reported metal-CQ complexes such as platinum, ruthenium and gold.

Title: A Comprehensive Review on Classifying Fast-acting and Slow-acting Antimalarial Agents Based on Time of Action and Target Organelle of Plasmodium sp

The clinical resistance towards malarial parasites has rendered many antimalarials ineffective, likely due to a lack of understanding of time of action and stage specificity of all life stages. Therefore, to tackle this problem a more incisive comprehensive analysis of the fast and slow-acting profile of antimalarial agents relating to parasite time-kill kinetics and the target organelle on the progression of blood-stage parasites was carried out. It is evident from numerous findings that drugs targeting food vacuole, nuclear components, and endoplasmic reticulum mainly exhibit a fast-killing phenotype within 24h affecting first-cycle activity. Whereas drugs targeting mitochondria, apicoplast, microtubules, parasite invasion and egress exhibit a largely slow-killing phenotype within 96-120h, affecting second-cycle activity with few exemptions as moderately fast-killing. It is essential to understand the susceptibility of drugs on rings, trophozoites, schizonts, merozoites, and the appearance of organelle at each stage of 48h intraerythrocytic parasite cycle. Therefore, these parameters may facilitate the paradigm for understanding the timing of antimalarials action in deciphering its precise mechanism linked with time. Thus, classifying drugs based on the time of killing may promote designing new combination regimens against varied strains of P. falciparum and evaluating potential clinical resistance.

Identification of Co-Existing Mutations and Gene Expression Trends Associated With K13-Mediated Artemisinin Resistance in Plasmodium falciparum

Plasmodium falciparum infects millions and kills thousands of people annually the world over. With the emergence of artemisinin and/or multidrug resistant strains of the pathogen, it has become even more challenging to control and eliminate the disease. Multiomics studies of the parasite have started to provide a glimpse into the confounding genetics and mechanisms of artemisinin resistance and identified mutations in Kelch13 (K13) as a molecular marker of resistance. Over the years, thousands of genomes and transcriptomes of artemisinin-resistant/sensitive isolates have been documented, supplementing the search for new genes/pathways to target artemisinin-resistant isolates. This meta-analysis seeks to recap the genetic landscape and the transcriptional deregulation that demarcate artemisinin resistance in the field. To explore the genetic territory of artemisinin resistance, we use genomic single-nucleotide polymorphism (SNP) datasets from 2,517 isolates from 15 countries from the MalariaGEN Network (The Pf3K project, pilot data release 4, 2015) to dissect the prevalence, geographical distribution, and co-existing patterns of genetic markers associated with/enabling artemisinin resistance. We have identified several mutations which co-exist with the established markers of artemisinin resistance. Interestingly, K13-resistant parasites harbor α-ß hydrolase and putative HECT domain-containing protein genes with the maximum number of SNPs. We have also explored the multiple, publicly available transcriptomic datasets to identify genes from key biological pathways whose consistent deregulation may be contributing to the biology of resistant parasites. Surprisingly, glycolytic and pentose phosphate pathways were consistently downregulated in artemisinin-resistant parasites. Thus, this meta-analysis highlights the genetic and transcriptomic features of resistant parasites to propel further exploratory studies in the community to tackle artemisinin resistance.

Different Drugs, Same End: Ultrastructural Hallmarks of Autophagy in Pathogenic Protozoa

Protozoan parasites interact with a wide variety of organisms ranging from bacteria to humans, representing one of the most common causes of parasitic diseases and an important public health problem affecting hundreds of millions of people worldwide. The current treatment for these parasitic diseases remains unsatisfactory and, in some cases, very limited. Treatment limitations together with the increased resistance of the pathogens represent a challenge for the improvement of the patient’s quality of life. The continuous search for alternative preclinical drugs is mandatory, but the mechanisms of action of several of these compounds have not been described. Electron microscopy is a powerful tool for the identification of drug targets in almost all cellular models. Interestingly, ultrastructural analysis showed that several classes of antiparasitic compounds induced similar autophagic phenotypes in trypanosomatids, trichomonadids, and apicomplexan parasites as well as in Giardia intestinalis and Entamoeba spp. with the presence of an increased number of autophagosomes as well as remarkable endoplasmic reticulum profiles surrounding different organelles. Autophagy is a physiological process of eukaryotes that maintains homeostasis by the self-digestion of nonfunctional organelles and/or macromolecules, limiting redundant and damaged cellular components. Here, we focus on protozoan autophagy to subvert drug effects, discussing its importance for successful chemotherapy.

Autophagy Underlies the Proteostasis Mechanisms of Artemisinin Resistance in P. falciparum Malaria

Emerging resistance to artemisinin (ART) has become a challenge for reducing worldwide malaria mortality and morbidity. The C580Y mutation in Plasmodium falciparum Kelch13 has been identified as the major determinant for ART resistance in the background of other mutations, which include the T38I mutation in autophagy-related protein PfATG18. Increased endoplasmic reticulum phosphatidylinositol-3-phosphate (ER-PI3P) vesiculation, unfolded protein response (UPR), and oxidative stress are the proteostasis mechanisms proposed to cause ART resistance. While UPR and PI3P are known to stimulate autophagy in higher organisms to clear misfolded proteins, participation of the parasite autophagy machinery in these mechanisms of ART resistance has not yet been experimentally demonstrated. Our study establishes that ART-induced ER stress leads to increased expression of P. falciparum autophagy proteins through induction of the UPR. Furthermore, the ART-resistant K13^C580Y isolate shows higher basal expression levels of autophagy proteins than those of its isogenic counterpart, and this magnifies under starvation conditions. The copresence of PfK13 with PfATG18 and PI3P on parasite hemoglobin-trafficking vesicles demonstrate interactions between the autophagy and hemoglobin endocytosis pathways proposed to be involved in ART resistance. Analysis of PfK13 mutations in 2,517 field isolates, revealing an impressive >85% coassociation between PfK13 C580Y and PfATG18 T38I, together with our experimental studies with an ART-resistant P. falciparum strain establishes that parasite autophagy underpins various mechanisms of ART resistance and is a starting point to further explore this pathway for developing antimalarials.

Ferroptosis plays an essential role in the antimalarial mechanism of low-dose dihydroartemisinin

The activation of artemisinin and its derivatives (ARTs) to generate ROS and other free radicals is mainly heme- or ferrous iron-dependent. ARTs induce ferroptosis in tumor cells, although the involvement of ferroptosis in malaria remains unclear. We found that three typical inducers of ferroptosis (erastin, RSL3 and sorafenib) could effectively mimic DHA inhibition on the growth of blood-stage parasites, which exhibited synergistic or nearly additive interactions in vitro with DHA, while the combination of DHA with ferroptosis inhibitors (deferoxamine, liproxstatin-1) had an obvious antagonistic effect. DHA, similar to ferroptosis inducers, can simultaneously induce the accumulation of ferroptosis-associated cellular labile iron and lipid peroxide. However, deferoxamine and liproxstatin-1 reduced the increase in ferrous iron and lipid peroxide caused by DHA. These results suggested that ferroptosis might be an effective way to induce cell death in parasites and could be a primary mechanism by which DHA kills parasites, with almost 50% contribution at low concentrations. These results provide a new strategy for antimalarial drug screening and clinical medication guidance.

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

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

Artesunate Inhibits the Growth Behavior of Docetaxel-Resistant Prostate Cancer Cells

Novel therapeutic strategies are urgently needed for advanced metastatic prostate cancer (PCa). Phytochemicals used in Traditional Chinese Medicine seem to exhibit tumor suppressive properties. Therefore, the therapeutic potential of artesunate (ART) on the progressive growth of therapy-sensitive (parental) and docetaxel (DX)-resistant PCa cells was investigated. Parental and DX-resistant PCa cell lines DU145, PC3, and LNCaP were incubated with artesunate (ART) [1-100 µM]. ART-untreated and 'non-cancerous' cells served as controls. Cell growth, proliferation, cell cycle progression, cell death and the expression of involved proteins were evaluated. ART, dose- and time-dependently, significantly restricted cell growth and proliferation of parental and DX-resistant PCa cells, but not of 'normal, non-cancerous' cells. ART-induced growth and proliferation inhibition was accompanied by G0/G1 phase arrest and down-regulation of cell cycle activating proteins in all DX-resistant PCa cells and parental LNCaP. In the parental and DX-resistant PC3 and LNCaP cell lines, ART also promoted apoptotic cell death. Ferroptosis was exclusively induced by ART in parental and DX-resistant DU145 cells by increasing reactive oxygen species (ROS). The anti-cancer activity displayed by ART took effect in all three PCa cell lines, but through different mechanisms of action. Thus, in advanced PCa, ART may hold promise as a complementary treatment together with conventional therapy.

Resistance to artemisinin in falciparum malaria parasites: A redox-mediated phenomenon

Malaria remains a major public health disease due to its high yearly mortality and morbidity. Resistance to the gold standard drug, artemisinin, is worrisome and needs better understanding in order to be overcome. In this work, we sought to study whether redox processes are involved in artemisinin resistance. As artemisinin is known to act among others via production of reactive species, we first compared the production of reactive oxygen species and concomitant protein oxidation in artemisinin-sensitive and artemisinin-resistant parasites when treated with artemisinin. The results undoubtedly demonstrated, using different original methods, that the level of ROS, including superoxide production, and oxidized protein were lower in the resistant strain. Interestingly, the major in-between strain difference was reported at the earlier ring stages, which are the forms able to enter in a quiescence state according to the ART resistance phenomenon. Moreover, we demonstrated a better homeostasis regulation in relation with higher expression of antioxidants in the artemisinin-resistant parasites than their sensitive counterparts after artemisinin exposure, notably, superoxide dismutase and the glutathione (GSH) system. These findings enrich the body of knowledges about the multifaceted mechanism of artemisinin resistance and will help in the design and development of newer antimalarials strategies active against resistant parasites.

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.

Curcumin modulates multiple cell death, matrix metalloproteinase activation and cardiac protein release in susceptible and resistant Plasmodium berghei-infected mice

Pro-inflammatory signaling, cell death, and metalloproteinases activation are events in Plasmodium infection. However, it is not known if treatment with mefloquine (MF), and curcumin (CM) supplementation, will modulate these conditions. Malaria was induced in two different studies using susceptible (NK 65, study 1) and resistant (ANKA, study 2) strains of mouse malaria parasites (Plasmodium berghei) in thirty male Swiss mice (n = 5) in each study. Following confirmation of parasitemia, mice received 10 mL/kg distilled water (infected control), MF (10 mg/kg), MF and CM (25 mg/kg), MF and CM (50 mg/kg), CM (25 mg/kg) and CM (50 mg/kg). Five mice (not infected) were used as control. After treatment, the animals were sacrificed, serum obtained and liver mitochondria were isolated. Serum Tumour Necrosis Factor alpha (TNF-α), C-reactive protein (CRP), Interleukins-1 beta (IL-1β) and Interleukins-6 (IL-6) as well as caspases-3, 9 (C3 and C9), p53, serum troponin I (TI) and creatine kinase (CK), were assayed using ELISA techniques. Mitochondrial membrane permeability transition (mPT) pore opening, mitochondrial F₀F₁ ATPase activity, and lipid peroxidation (mLPO) were determined spectrophotometrically. Matrix metalloproteinases 2 (MMP-2) and 9 (MMP-9) expressions were determined using electrophoresis. CM supplementation (25 mg/kg) significantly decreased serum p53, TNF-α, CRP and IL-6 compared with MF. In the resistant model, CM prevented mPT pore opening, significantly decreased F₀F₁ ATPase activity and mLPO. MF activated caspase-3 while supplementation with CM significantly decreased this effect. Furthermore, MMP-2 and MMP-9 were selectively expressed in the susceptible model. Malarial treatment with mefloquine elicits different cell death responses while supplementation with curcumin decreased TI level and CK activities.

Reactive Oxygen Species as the Brainbox in Malaria Treatment

Several measures are in place to combat the worldwide spread of malaria, especially in regions of high endemicity. In part, most common antimalarials, such as quinolines and artemisinin and its derivatives, deploy an ROS-mediated approach to kill malaria parasites. Although some antimalarials may share similar targets and mechanisms of action, varying levels of reactive oxygen species (ROS) generation may account for their varying pharmacological activities. Regardless of the numerous approaches employed currently and in development to treat malaria, concerningly, there has been increasing development of resistance by Plasmodium falciparum, which can be connected to the ability of the parasites to manage the oxidative stress from ROS produced under steady or treatment states. ROS generation has remained the mainstay in enforcing the antiparasitic activity of most conventional antimalarials. However, a combination of conventional drugs with ROS-generating ability and newer drugs that exploit vital metabolic pathways, such antioxidant machinery, could be the way forward in effective malaria control.

NADPH Oxidase: a Possible Therapeutic Target for Cognitive Impairment in Experimental Cerebral Malaria

Long-term cognitive impairment associated with seizure-induced hippocampal damage is the key feature of cerebral malaria (CM) pathogenesis. One-fourth of child survivors of CM suffer from long-lasting neurological deficits and behavioral anomalies. However, mechanisms on hippocampal dysfunction are unclear. In this study, we elucidated whether gp91^phox isoform of nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) (a potent marker of oxidative stress) mediates hippocampal neuronal abnormalities and cognitive dysfunction in experimental CM (ECM). Mice symptomatic to CM were rescue treated with artemether monotherapy (ARM) and in combination with apocynin (ARM + APO) adjunctive based on scores of Rapid Murine Come behavior Scale (RMCBS). After a 30-day survivability period, we performed Barnes maze, T-maze, and novel object recognition cognitive tests to evaluate working and reference memory in all the experimental groups except CM. Sensorimotor tests were conducted in all the cohorts to assess motor coordination. We performed Golgi-Cox staining to illustrate cornu ammonis-1 (CA1) pyramidal neuronal morphology and study overall hippocampal neuronal density changes. Further, expression of NOX2, NeuN (neuronal marker) in hippocampal CA1 and dentate gyrus was determined using double immunofluorescence experiments in all the experimental groups. Mice administered with ARM monotherapy and APO adjunctive treatment exhibited similar survivability. The latter showed better locomotor and cognitive functions, reduced ROS levels, and hippocampal NOX2 immunoreactivity in ECM. Our results show a substantial increase in hippocampal NeuN immunoreactivity and dendritic arborization in ARM + APO cohorts compared to ARM-treated brain samples. Overall, our study suggests that overexpression of NOX2 could result in loss of hippocampal neuronal density and dendritic spines of CA1 neurons affecting the spatial working and reference memory during ECM. Notably, ARM + APO adjunctive therapy reversed the altered neuronal morphology and oxidative damage in hippocampal neurons restoring long-term cognitive functions after CM.

Artemisinin Binds and Inhibits the Activity of Plasmodium falciparum Ddi1, a Retroviral Aspartyl Protease

Reduced sensitivity of the human malaria parasite, Plasmodium falciparum, to Artemisinin and its derivatives (ARTs) threatens the global efforts towards eliminating malaria. ARTs have been shown to cause ubiquitous cellular and genetic insults, which results in the activation of the unfolded protein response (UPR) pathways. The UPR restores protein homeostasis, which otherwise would be toxic to cellular survival. Here, we interrogated the role of DNA-damage inducible protein 1 (PfDdi1), a unique proteasome-interacting retropepsin in mediating the actions of the ARTs. We demonstrate that PfDdi1 is an active A₂ family protease that hydrolyzes ubiquitinated proteasome substrates. Treatment of P. falciparum parasites with ARTs leads to the accumulation of ubiquitinated proteins in the parasites and blocks the destruction of ubiquitinated proteins by inhibiting the PfDdi1 protease activity. Besides, whereas the PfDdi1 is predominantly localized in the cytoplasm, exposure of the parasites to ARTs leads to DNA fragmentation and increased recruitment of the PfDdi1 into the nucleus. Furthermore, we show that Ddi1 knock-out Saccharomycescerevisiae cells are more susceptible to ARTs and the PfDdI1 protein robustly restores the corresponding functions in the knock-out cells. Together, these results show that ARTs act in multiple ways; by inducing DNA and protein damage and might be impairing the damage recovery by inhibiting the activity of PfDdi1, an essential ubiquitin-proteasome retropepsin.

An SR protein is essential for activating DNA repair in malaria parasites

Plasmodium falciparum, the parasite responsible for the deadliest form of human malaria, replicates within the erythrocytes of its host, where it encounters numerous pressures that cause extensive DNA damage, which must be repaired efficiently to ensure parasite survival. Malaria parasites, which have lost the non-homologous end joining (NHEJ) pathway for repairing DNA double-strand breaks, have evolved unique mechanisms that enable them to robustly maintain genome integrity under such harsh conditions. However, the nature of these adaptations is unknown. We show that a highly conserved RNA splicing factor, P. falciparum (Pf)SR1, plays an unexpected and crucial role in DNA repair in malaria parasites. Using an inducible and reversible system to manipulate PfSR1 expression, we demonstrate that this protein is recruited to foci of DNA damage. Although loss of PfSR1 does not impair parasite viability, the protein is essential for their recovery from DNA-damaging agents or exposure to artemisinin, the first-line antimalarial drug, demonstrating its necessity for DNA repair. These findings provide key insights into the evolution of DNA repair pathways in malaria parasites as well as the ability of the parasite to recover from antimalarial treatment.

Summary: There is an unexpected role for the alternative splicing factor PfSR1 in activating the DNA damage response in the human malaria parasite Plasmodium falciparum.

INFLUENCE OF ARTESUNATE COMBINATIVE THERAPY CO-ADMINISTRATION WITH RUTIN ON INFLAMMATORY CYTOKINES AND IMMUNOGLOBULINS IN PLASMODIUM BERGHEI-INFECTED MICE

Some antimalarial drugs are immune-modulators that impact multiple pathways of innate immunity in malarial treatment. However, information on the immunomodulatory effects of artequine and rutin in the treatment of malaria remains elusive. Twenty-five Swiss mice (18 ± 2 g) were used for this study. Twenty were infected with Plasmodium berghei (NK65). Parasitemia was confirmed, and the animals were grouped (n = 5) as follows: Group A was not infected but treated orally with vehicle. Groups B to E were infected and treated (B) orally with vehicle (10 ml/kg), (C) with 10 mg/kg artequine, (D) with 10 mg/kg of artequine supplemented with 100 mg rutin/kg, and (D) with 10 mg/kg of artequine supplemented with 200 mg rutin/kg, for 7 days. Blood was collected for hematological, inflammatory cytokines, and immunoglobulins G and M assays. Post mitochondrial supernatant fraction was used for antioxidant assays. Rutin co-administration (200 mg/kg) significantly (P < 0.001) increased platelet and neutrophil counts (P < 0.01) but significantly (P < 0.01) decreased white blood cell count and lymphocyte relative to parasitized control. Also, it significantly (P < 0.05) decreased lipid peroxidation, xanthine oxidase, and superoxide dismutase activities but significantly (P < 0.05) increased reduced glutathione and glutathione S-transferase activity. Rutin co-administration also caused a significant (P < 0.001) increase in tumor necrosis factor-alpha, interleukin-6, and immunoglobulin M levels, while interleukin-1β and immunoglobulin G decreased significantly (P < 0.001) compared with parasitized control. These results showed that rutin co-administration with artequine improved host antioxidant status and modulated the immune and inflammatory responses.

Plasmodium falciparum resistance to ACTs: Emergence, mechanisms, and outlook

Emergence and spread of resistance in Plasmodium falciparum to the frontline treatment artemisinin-based combination therapies (ACTs) in the epicenter of multidrug resistance of Southeast Asia threaten global malaria control and elimination. Artemisinin (ART) resistance (or tolerance) is defined clinically as delayed parasite clearance after treatment with an ART drug. The resistance phenotype is restricted to the early ring stage and can be measured in vitro using a ring-stage survival assay. ART resistance is associated with mutations in the propeller domain of the Kelch family protein K13. As a pro-drug, ART is activated primarily by heme, which is mainly derived from hemoglobin digestion in the food vacuole. Activated ARTs can react promiscuously with a wide range of cellular targets, disrupting cellular protein homeostasis. Consistent with this mode of action for ARTs, the molecular mechanisms of K13-mediated ART resistance involve reduced hemoglobin uptake/digestion and increased cellular stress response. Mutations in other genes such as AP-2μ (adaptor protein-2 μ subunit), UBP-1 (ubiquitin-binding protein-1), and Falcipain 2a that interfere with hemoglobin uptake and digestion also increase resistance to ARTs. ART resistance has facilitated the development of resistance to the partner drugs, resulting in rapidly declining ACT efficacies. The molecular markers for resistance to the partner drugs are mostly associated with point mutations in the two food vacuole membrane transporters PfCRT and PfMDR1, and amplification of pfmdr1 and the two aspartic protease genes plasmepsin 2 and 3. It has been observed that mutations in these genes can have opposing effects on sensitivities to different partner drugs, which serve as the principle for designing triple ACTs and drug rotation. Although clinical ACT resistance is restricted to Southeast Asia, surveillance for drug resistance using in vivo clinical efficacy, in vitro assays, and molecular approaches is required to prevent or slow down the spread of resistant parasites.

Repurposing of Antimicrobial Agents for Cancer Therapy: What Do We Know?

The substantial costs of clinical trials, the lengthy timelines of new drug discovery and development, along the high attrition rates underscore the need for alternative strategies for finding quickly suitable therapeutics agents. Given that most approved drugs possess more than one target tightly linked to other diseases, it encourages promptly testing these drugs in patients. Over the past decades, this has led to considerable attention for drug repurposing, which relies on identifying new uses for approved or investigational drugs outside the scope of the original medical indication. The known safety of approved drugs minimizes the possibility of failure for adverse toxicology, making them attractive de-risked compounds for new applications with potentially lower overall development costs and shorter development timelines. This latter case is an exciting opportunity, specifically in oncology, due to increased resistance towards the current therapies. Indeed, a large body of evidence shows that a wealth of non-cancer drugs has beneficial effects against cancer. Interestingly, 335 drugs are currently being evaluated in different clinical trials for their potential activities against various cancers (Redo database). This review aims to provide an extensive discussion about the anti-cancer activities exerted by antimicrobial agents and presents information about their mechanism(s) of action and stage of development/evaluation.

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.

K13-Mediated Reduced Susceptibility to Artemisinin in Plasmodium falciparum Is Overlaid on a Trait of Enhanced DNA Damage Repair

Southeast Asia has been the hotbed for the development of drug-resistant malaria parasites, including those with resistance to artemisinin combination therapy. While mutations in the kelch propeller domain (K13 mutations) are associated with artemisinin resistance, a range of evidence suggests that other factors are critical for the establishment and subsequent transmission of resistance in the field. Here, we perform a quantitative analysis of DNA damage and repair in the malaria parasite Plasmodium falciparum and find a strong link between enhanced DNA damage repair and artemisinin resistance. This experimental observation is further supported when variations in seven known DNA repair genes are found in resistant parasites, with six of these mutations being associated with K13 mutations. Our data provide important insights on confounding factors that are important for the establishment and spread of artemisinin resistance and may explain why resistance has not yet arisen in Africa.

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High-throughput MalariaCometChip to measure DNA damage level in P. falciparum

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Subpopulation of Cambodian isolates possess enhanced DNA damage repair

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Important link between enhanced DNA damage repair and artemisinin resistance

Superoxide: A major role in the mechanism of action of essential antimalarial drugs

Understanding the mode of action of antimalarials is central to optimizing their use and the discovery of new therapeutics. Currently used antimalarials belong to a limited series of chemical structures and their mechanisms of action are coutinuously debated. Whereas the involvement of reactive species that in turn kill the parasites sensitive to oxidative stress, is accepted for artemisinins, little is known about the generation of such species in the case of quinolines or hydroxynaphtoquinone. Moreover, the nature of the reactive species involved has never been characterized in Plasmodium-infected erythrocytes. The aim of this work was to determine and elucidate the production of the primary radical, superoxide in Plasmodium-infected erythrocytes treated with artemisinin, dihydroartemisinin, chloroquine and atovaquone, as representatives of three major classes of antimalarials. The intracellular generation of superoxide was quantified by liquid chromatography coupled to mass spectrometry (LC-MS). We demonstrated that artemisinins, atovaquone and to a lesser extent chloroquine, generate significant levels of superoxide radicals in Plasmodium falciparum sensitive strains. More so, the production of superoxide was lowered in chloroquine-resistant strain of Plasmodium treated with chloroquine. These results consolidate the knowledge about the mechanism of action of these different antimalarials and should be taken into consideration in the design of future drugs to fight drug-resistant parasites.

Implicating extracellular vesicles in Plasmodium falciparum artemisinin resistance development

Plasmodium falciparum malaria remains a disease of significant public health impact today. With the risk of emerging artemisinin resistance stalling malaria control efforts, the need to deepen our understanding of the parasite's biology is dire. Extracellular vesicles (EVs) are vital to the biology of P. falciparum and play a role in the pathogenesis of malaria. Recent studies have also shown that EVs may play a role in the development of artemisinin resistance in P. falciparum. Here, we highlight evidence on EVs in P. falciparum biology and malaria pathogenesis and argue that there is sufficient ground to propose a role for EVs in the development of P. falciparum artemisinin resistance. We suggest that EVs are actively secreted functional organelles that contribute to cellular homeostasis in P. falciparum-infected red blood cells under artemisinin pressure. Further exploration of this hypothesized EVs-based molecular mechanism of artemisinin resistance will aid the discovery of novel antimalarial therapies.

Predicting the Disposition of the Antimalarial Drug Artesunate and Its Active Metabolite Dihydroartemisinin Using Physiologically Based Pharmacokinetic Modeling

Artemisinin-based combination therapies (ACTs) have proven to be effective in helping to combat the global malaria epidemic. To optimally apply these drugs, information about their tissue-specific disposition is required, and one approach to predict these pharmacokinetic characteristics is physiologically based pharmacokinetic (PBPK) modeling. In this study, a whole-body PBPK model was developed to simulate the time-dependent tissue concentrations of artesunate (AS) and its active metabolite, dihydroartemisinin (DHA). The model was developed for both rats and humans and incorporated drug metabolism of the parent compound and major metabolite. Model calibration was conducted using data from the literature in a Bayesian framework, and model verification was assessed using separate sets of data. Results showed good agreement between model predictions and the validation data, demonstrating the capability of the model in predicting the blood, plasma, and tissue pharmacokinetics of AS and DHA. It is expected that such a tool will be useful in characterizing the disposition of these chemicals and ultimately improve dosing regimens by enabling a quantitative assessment of the tissue-specific drug levels critical in the evaluation of efficacy and toxicity.

The Evaluation of 68Ga-Citrate PET/CT Imaging for Dihydroartemisinin in the Treatment of Rheumatoid Arthritis

PURPOSE

We aimed to use 68Ga-citrate, a labeled product of gallium (iron analog), combined with positron emission tomography/computed tomography (PET/CT) to non-invasively evaluate the potential of the iron-responsive product dihydroartemisinin (DHA) in the treatment of rheumatoid arthritis.

PROCEDURES

From the establishment of chicken II collagen-induced arthritis (CIA) rat model over 40 days, 20 rats with one-to-one corresponding arthritis index (AI) scores were randomly divided into two groups. One group received oral DHA (at a dose of 1.5 ml/(kg day), containing 20 mg DHA per 1 ml) for 15 days; the other group received stroke-physiological saline solution (SSS, 1.5 ml/(kg day) for 15 days. 68Ga-citrate micro-PET/CT imaging was performed on day 0 (D0), day 5 (D5), day 10 (D10), and day 15 (D15) of oral administration. After data reconstruction, the cross-sectional length "d" of the ankle joint of each rat was measured on the transverse CT, and the SUVmax of the ankle joint and muscle background was measured for statistical analysis. After micro-PET/CT collection, the ankle joint tissue was observed by HE staining.

RESULTS

The ankle joint swelling in the DHA group was significantly suppressed, but the SSS group showed no significant suppression. 68Ga-citrate micro-PET/CT imaging results and microscope observation confirmed this finding. Statistical analysis indicated that the time tendency of AI score (Binteraction = 0.495, P < 0.001) and T/NT (Binteraction = 1.345, P < 0.001) were discrepant between DHA and SSS groups. The AI score and T/NT of the DHA group gradually increased with time, while the SSS group score gradually decreased. Furthermore, the Spearman correlation coefficient was used to describe the relationship between "d" and T/NT, which was positively correlated (r = 0.855, P < 0.001).

CONCLUSIONS

This study showed that the anti-inflammatory effect of the iron-responsive product DHA in arthritis can be monitored by an iron-like radioactive tracer (68Ga-citrate).

Phosphorylation of the Canonical Histone H2A Marks Foci of Damaged DNA in Malaria Parasites

Plasmodium falciparum is the deadliest human parasite that causes malaria when it reaches the bloodstream and begins proliferating inside red blood cells, where the parasites are particularly prone to DNA damage. The molecular mechanisms that allow these pathogens to maintain their genome integrity under such conditions are also the driving force for acquiring genome plasticity that enables them to create antigenic variation and become resistant to essentially all available drugs.

Plasmodium falciparum parasites proliferate within circulating red blood cells and are responsible for the deadliest form of human malaria. These parasites are exposed to numerous intrinsic and external sources that could cause DNA damage; therefore, they have evolved efficient mechanisms to protect their genome integrity and allow them to proliferate under such conditions. In higher eukaryotes, double-strand breaks rapidly lead to phosphorylation of the core histone variant H2A.X, which marks the site of damaged DNA. We show that in P. falciparum that lacks the H2A.X variant, the canonical P. falciparum H2A (PfH2A) is phosphorylated on serine 121 upon exposure to sources of DNA damage. We further demonstrate that phosphorylated PfH2A is recruited to foci of damaged chromatin shortly after exposure to sources of damage, while the nonphosphorylated PfH2A remains spread throughout the nucleoplasm. In addition, we found that PfH2A phosphorylation is dynamic and that over time, as the parasite activates the repair machinery, this phosphorylation is removed. Finally, we demonstrate that these phosphorylation dynamics could be used to establish a novel and direct DNA repair assay in P. falciparum.

IMPORTANCEPlasmodium falciparum is the deadliest human parasite that causes malaria when it reaches the bloodstream and begins proliferating inside red blood cells, where the parasites are particularly prone to DNA damage. The molecular mechanisms that allow these pathogens to maintain their genome integrity under such conditions are also the driving force for acquiring genome plasticity that enables them to create antigenic variation and become resistant to essentially all available drugs. However, mechanisms of DNA damage response and repair have not been extensively studied for these parasites. The paper addresses our recent discovery that P. falciparum that lacks the histone variant H2A.X phosphorylates its canonical core histone PfH2A in response to exposure to DNA damage. The process of DNA repair in Plasmodium was mostly studied indirectly. Our findings enabled us to establish a direct DNA repair assay for P. falciparum similar to assays that are widely used in model organisms.

Antiplasmodial, antinociceptive and antipyretic potential of the stem bark extract of Burkea africana and identification of its antiplasmodial-active fraction

Background and aim

Burkea africana stem bark is used as a remedy for malaria in north-central and southern Nigeria. Based on its traditional use, this study was conducted to investigate the antiplasmodial, antinociceptive and antipyretic potential of an extract of B. africana stem bark.

Experimental procedure

A 70% v/v ethanol extract of stem bark of B. africana was prepared by cold maceration. Fractions (dichloromethane, ethyl acetate, and residual) were also prepared. The extract was screened for hemolytic, cytotoxic and antiplasmodial activity effects. The effect of the extract and fractions against chloroquine-sensitive (3D7) and multi-drug resistant (W2mef) P. falciparum was assessed. Acute toxicity test, acetic acid-induced abdominal writhing in mice, and lipopolysaccharide-induced fever in rats were also employed to screen the extract. Chromatographic fingerprints of the extract and active fraction were obtained.

Results

B. africana extract showed no cytotoxic or significant hemolytic effects and did not cause acute toxicity or mortality. The ethanol extract exhibited moderate antiplasmodial activity while the dichloromethane fraction showed high activity against P. falciparum 3D7 (IC₅₀ = 6.44 μg/ml) and W2mef (IC₅₀ = 6.30 μg/ml) respectively. The extract elicited significant (p < 0.05) attenuation of acetic acid-induced writhing and significantly (p < 0.05) ameliorated lipopolysaccharide-induced pyrexia at 300 mg/kg. The HPLC profile of the dichloromethane fraction showed peaks with retention times that corresponded with those of rutin and caffeic acid.

Conclusion

Burkea africana extract has antiplasmodial, antinociceptive and antipyretic potential and its antiplasmodial constituents are concentrated in its dichloromethane fraction.

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Burkea africana used as antimalarial remedy alleviates peripheral pain and fever.

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The extract and its dichloromethane fraction possess antiplasmodial activity.

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Antiplasmodial activity is concentrated in the dichloromethane fraction.

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Intra-erythrocytic targets may be distinct from those of chloroquine and artesunate.

Elucidation of DNA Repair Function of PfBlm and Potentiation of Artemisinin Action by a Small-Molecule Inhibitor of RecQ Helicase

Malaria continues to be a serious threat to humankind not only because of the morbidity and mortality associated with the disease but also due to the huge economic burden that it imparts. Resistance to all available drugs and the unavailability of an effective vaccine cry for an urgent discovery of newer drug targets.

Artemisinin (ART)-based combination therapies are recommended as first- and second-line treatments for Plasmodium falciparum malaria. Here, we investigated the impact of the RecQ inhibitor ML216 on the repair of ART-mediated damage in the genome of P. falciparum. PfBLM and PfWRN were identified as members of the RecQ helicase family in P. falciparum. However, the role of these RecQ helicases in DNA double-strand break (DSB) repair in this parasite has not been explored. Here, we provide several lines of evidence to establish the involvement of PfBlm in DSB repair in P. falciparum. First, we demonstrate that PfBlm interacts with two well-characterized DSB repair proteins of this parasite, namely, PfRad51 and PfalMre11. Second, we found that PfBLM expression was upregulated in response to DNA-damaging agents. Third, through yeast complementation studies, we demonstrated that PfBLM could complement the DNA damage sensitivity of a Δsgs1 mutant of Saccharomyces cerevisiae, in contrast to the helicase-dead mutant PfblmK83R. Finally, we observe that the overexpression of PfBLM induces resistance to DNA-damaging agents and offers a survival advantage to the parasites. Most importantly, we found that the RecQ inhibitor ML216 inhibits the repair of DSBs and thereby renders parasites more sensitive to ART. Such synergism between ART and ML216 actions was observed for both drug-sensitive and multidrug-resistant strains of P. falciparum. Taken together, these findings establish the implications of PfBlm in the Plasmodium DSB repair pathway and provide insights into the antiparasitic activity of the ART-ML216 combination.

IMPORTANCE Malaria continues to be a serious threat to humankind not only because of the morbidity and mortality associated with the disease but also due to the huge economic burden that it imparts. Resistance to all available drugs and the unavailability of an effective vaccine cry for an urgent discovery of newer drug targets. Here, we uncovered a role of the PfBlm helicase in Plasmodium DNA double-strand break repair and established that the parasitic DNA repair mechanism can be targeted to curb malaria. The small-molecule inhibitor of PfBlm tested in this study acts synergistically with two first-line malaria drugs, artemisinin (ART) and chloroquine, in both drug-sensitive and multidrug-resistant strains of P. falciparum, thus qualifying this chemical as a potential partner in ART-based combination therapy. Additionally, the identification of this new specific inhibitor of the Plasmodium homologous recombination (HR) mechanism will now allow us to investigate the role of HR in Plasmodium biology.

In vitro and in vivo Effects of Artesunate on Echinococcus granulosus Protoscoleces and Metacestodes

Background

In this study, we aim to investigate the efficiency of artesunate (AS) on Echinococcus granulosus protoscoleces and metacestodes.

Methods

For the in vitro assay, the eosin dye exclusion test and transmission electron microscope (TEM) were utilized to evaluate the effects of AS against protoscoleces (PSCs) from Echinococcus granulosus. In addition, mortality, ultrastructure change, reactive oxygen species (ROS) content and DNA damage were measured in order to explore the anti-echinococcosis mechanism of AS. For the in vivo assay, CE-infected mice were divided into model group, albendazole (ABZ) group (200 mg/kg), low AS (AS-L) group (50 mg/kg), moderate AS (AS-M) group (100 mg/kg), and high AS (AS-H) group (200 mg/kg). Upon 6 weeks oral administration, wet weight of cysts and the ultrastructural changes of cystic wall were utilized to evaluate the effects of AS on metacestodes. In addition, the liver biochemical parameters, tumor necrosis factor-α (TNF-α), glutathione/glutathione oxidized (GSH/GSSG) ratio in serum, and H₂O₂, total superoxide dismutase (T-SOD) in cyst fluid were detected.

Results

Both in vivo and in vitro experiments showed that AS showed anti-parasitic effects on CE. The AS could elevate the ROS level in the PSCs, which then resulted in obvious DNA damages. AS could significantly improve the liver biochemical parameters in infected mice compared with the model group (P < 0.05). Compared with the model group, AS-M and AS-H decrease the TNF-α content (P < 0.05); AS-H group significantly decrease in the serum GSH/GSSG ratio (P < 0.05). The content of H₂O₂ in hydatid fluid treated by AS showed significant decrease compared with the model group (P < 0.01), while the T-SOD level showed significant elevation compared with model group (P < 0.01).

Conclusion

In this study, we confirmed that the effects of AS on Echinococcus granulosus protoscoleces and metacestodes may be related to the DNA damages induced by oxidative stress, which provided solid information for the research and development of drugs for cystic echinococcosis.