Artemisinin Action and Resistance in Plasmodium falciparum

Unlocking the potential of Artemisia annua for artemisinin production: current insights and emerging strategies

Malaria is a deadly disease, and the best effective treatments depend on artemisinin, a sesquiterpene lactone compound isolated from the plant Artemisia annua. However, artemisinin is produced in very small amount within the plant which is insufficient to meet the global demand. Although researchers have investigated synthetic and semi-synthetic approaches, they still face significant challenges, such as high costs and low efficiency, making A. annua the most viable source. Biotechnological advances in breeding and genetic engineering have developed new A. annua varieties with higher artemisinin content, and some varieties have achieved up to 3.2% of plant dry weight. Furthermore, researchers have identified the key genes and transcription factors that can be modified to boost production further. Environmental factors, such as light and specific plant hormones, play a crucial role in regulating this pathway. Also, tissue culture, hairy root systems, and natural elicitors have shown promising results, but need further refinement. Interestingly, the use of whole plants (such as dried leaf powder) instead of purified artemisinin alone has been found to improve drug absorption in the body, improve its effectiveness, and help combat artemisinin resistance. Beyond treating malaria, A. annua also demonstrates other therapeutic potential in treating other diseases, including cancer and viral infections. These findings highlight that A. annua is not just a source of artemisinin; it is a valuable medicinal plant that deserves continued research focus, primarily through approaches that improve artemisinin production directly in the plant.

Redox Homeostasis within the Drug-Resistant Malarial Parasite Digestive Vacuole

We have developed a cost-effective strategy for the complete synthesis of azetidinyl coumarin fluorophore derivatives that report changes in physiologic levels of glutathione (GSH), which includes a more cost- effective synthesis of the probe precursor hydroxyl derivative and its subsequent derivatization to promote subcellular localization. We functionalize coumarin derivatives with a cyano side chain similar to a previous strategy (Jiang X. et al., Nature Communications 2017, 8; 16087) and validate the 7-azetidinyl conformation as an explanation for enhanced GSH-dependent coumarin fluorescence. We couple the azetidinyl probe to different mass dextrans using either no linker or a 6C linker and also synthesize a morpholino derivative. We titrate the fluorescence of the different functionalized probes vs [GSH] in vitro. We load one dextran-conjugated probe within the digestive vacuole (DV) of live intraerythrocytic P. falciparum malarial parasites and also measure cytosolic localization of the morpholino probe. Using significantly improved single-cell photometry (SCP) methods, we show that the morpholino probe faithfully reports [GSH] from the live parasite cytosol, while the 70 kDa dextran-conjugated probe reports DV redox homeostasis for control chloroquine-sensitive (CQS) and artemisinin-sensitive (ARTS) transfectant parasites vs their genetically matched chloroquine-resistant (CQR)/artemisinin-sensitive (CQR/ARTS) and CQR artemisinin-resistant (CQR/ARTR) strains, respectively. We quantify rapid changes in DV redox homeostasis for these parasites ± drug pulses under live-cell perfusion conditions. The results are important for understanding the pharmacology of antimalarial drugs and the molecular mechanisms underlying CQR and ARTR phenomena.

Study on a TCM evaluation method based on an MIP-modified MOF sensor with highly selective electrocatalytic activity-an Artemisia annua L. perspective

Quantitative analysis of artemisinin (ART) in Artemisia annua decoction samples is crucial for the quality assessment of Artemisia annua samples; however, no comprehensive solution currently exists for its rapid and sensitive quantification. This gap necessitates a novel method that accommodates the complex composition of traditional Chinese medicine samples. In this study, we developed an electrochemical sensor suitable for determining the ART content level in Artemisia annua. By introducing MIP-MOF composites, the sensor was endowed with selectivity based on spatial and electronic structures specific to particular molecules. This sensor, which mimics the in vivo pharmacological activation process of ART, could swiftly and selectively measure ART concentrations, thereby providing a reflection of the efficacy of the samples. The sensors' limit of detection and limit of quantification were determined to be 1.738 × 10-13 M and 4.764 × 10-9 M, respectively. Methodology validation confirmed the great selectivity and accuracy of the sensor. Tests conducted across various Artemisia annua decoction samples, including those from online and offline sources, as well as deteriorated samples, yielded results consistent with the expected ART content levels, demonstrating the sensor's potential for application in Artemisia annua sample quality assessment.

Chemical propulsion of hemozoin crystal motion in malaria parasites

Malaria parasites infect red blood cells where they digest host hemoglobin and release free heme inside a lysosome-like organelle called the food vacuole. To detoxify excess heme, parasites form hemozoin crystals that rapidly tumble inside this compartment. Hemozoin formation is critical for parasite survival and antimalarial drug activity, but crystal motion and its underlying mechanism are unexplored. We used quantitative image analysis to determine the timescale of motion, which requires the intact vacuole but does not require the parasite itself. Using single-particle tracking and Brownian dynamics simulations with experimentally derived interaction potentials, we found that hemozoin motion exhibits unexpectedly tight confinement but is much faster than thermal diffusion. Hydrogen peroxide, which is generated at high concentrations in the food vacuole, has been shown to stimulate metallic nanoparticle motion via surface-catalyzed peroxide decomposition that generates propulsive kinetic energy. We observed that peroxide stimulated the motion of isolated crystals in solution and that conditions that suppress peroxide formation slowed hemozoin motion inside parasites. These data suggest that surface-exposed metals on hemozoin catalyze peroxide decomposition to drive crystal motion and strengthen oxidative stress protection during blood-stage infection. This work reveals hemozoin motion in malaria parasites as a biological example of a self-propelled nanoparticle.

Artemisinin regulates cell proliferation, apoptosis, and the inflammatory response of human dental pulp stem cells through the p53 signaling pathway under LPS-induced inflammation

OBJECTIVE

The purpose of this study was to investigate the effects and mechanism of artemisinin (ART) on the proliferation, apoptosis, and inflammatory response of human dental pulp stem cells (HDPSCs) under lipopolysaccharide (LPS)-induced inflammation.

METHODS

HDPSCs were isolated, cultured, and identified by flow cytometry and three-directional differentiation induction. A suitable concentration of LPS was selected to mimic the inflammatory condition in vitro. After culturing with ART and LPS for 48 h, cell proliferation was observed by CCK-8 assay; cell apoptosis was observed by flow cytometry, western blot, and Caspase-3 activity; and the inflammatory response was observed by qRT-PCR and ELISA. Transcriptome sequencing, immunofluorescence staining, qRT-PCR, western blot, and RITA were used to explore the underlying mechanism.

RESULTS

HDPSCs were successfully isolated and exhibited the potential for multilineage differentiation. 0.1 μg/mL of LPS was utilized to mimic the inflammatory condition. ART promoted HDPSCs proliferation but repressed apoptosis and the inflammatory response under LPS-induced inflammation. Further, ART exerted its effect through the p53 signaling pathway.

CONCLUSION

ART inhibited the p53 signaling pathway to promote HDPSCs proliferation, but hinder apoptosis and the inflammatory response under LPS-induced inflammation.

CLINICAL SIGNIFICANCE

This study demonstrates that ART facilitates the alleviation of inflammation and preserves the viability of HDPSCs. Therefore, ART may serve as a promising therapeutic drug for the repair and regeneration of dental pulp in the treatment of deep caries and reversible pulpitis.

Phase I study on the pharmacokinetics of intravaginal, self-administered artesunate vaginal pessaries among women in Kenya

OBJECTIVES

The primary objective of this study is to investigate the pharmacokinetics of Artesunate (AS) and its active metabolite, dihydroartemisinin (DHA) following intravaginal use at the dosing and frequency intended for cervical precancer treatment. A secondary objective is to assess safety among study participants.

METHODS

We are conducting a single-arm, phase I trial with a sample size of 12 female volunteers. Participants will self-administer artesunate vaginal pessaries in the study clinic daily for 5 consecutive days. Participants will have their blood drawn prior to receiving the first dose of artesunate on day one of the study and then will receive 8 blood draws on study day five, prior to artesunate administration and at 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours, and 8 hours after pessary administration. Pharmacokinetic parameters of artesunate and DHA will be calculated by way of quantitative analysis of with determination of maximum concentration (Cmax), time to Cmax (Tmax), area under the serum concentration versus time curve (AUC), apparent clearance, and elimination half-life (t1/2).

Computational Analysis of Plasmodium falciparum DNA Damage Inducible Protein 1 (PfDdi1): Insights into Binding of Artemisinin and its Derivatives and Implications for Antimalarial Drug Design

Human malaria remains a global health challenge, with Plasmodium falciparum responsible for the most severe cases. Despite global efforts, eradicating malaria has proven difficult, mainly because of the rise in drug resistance, particularly against artemisinin and its derivatives. One possible cause of this resistance is the activation of the unfolded protein response (UPR), which helps maintain cellular balance under stress. In P. falciparum, the UPR operates through the ubiquitin-proteasome system (UPS), which involves proteins such as Dsk2, Rad23, and Ddi1. Among these, Plasmodium falciparum DNA-damage-inducible protein 1 (PfDdi1) plays a crucial role in DNA repair and is present throughout the parasite life cycle, making it an attractive drug target. However, there is limited research on PfDdi1 as a therapeutic target. Recent in vitro studies have indicated that artemisinin (ART) and dihydroartemisinin (DHA) inhibit PfDdi1 activity. Building on this, we investigated whether ART and its derivatives could serve as inhibitors of PfDdi1 using computational modeling. Our study included clinically relevant ART derivatives such as artemether (ARM), arteether (AET), artemiside (AMD), and artesunate (ATS). All these compounds showed strong binding to PfDdi1, with free binding energies ranging from -20.75 kcal/mol for AET to -34.24 kcal/mol for ATS. ARM increased PfDdi1's structural rigidity and hydrophobic stability, whereas AMD improved its kinetic stability, resulting in the least residue motion. Unlike AET and AMD, the other ligands destabilize the PfDdi1 structure. Importantly, three key binding regions-Loop 1 (GLN 266 - ILE 269), Loop 2 (ILE 323 - TYR 326), and Loop 3 (ALA 292 - GLY 294)-were identified as potential targets for new antimalarial drugs against PfDdi1. This study highlights the potential of ART derivatives as PfDdi1 inhibitors, paving the way for further experimental validation.

Cambodian Plasmodium vivax parasites with reduced hemoglobin digestion display delayed clearance upon artesunate treatment

Artemisinin-based combination therapies are the frontline drugs for the treatment of malaria infections but, for Plasmodium falciparum, the efficacy of artemisinin is threatened by the spread of resistance . P. vivax is the second most common cause of human malaria but we have little information on its susceptibility to artemisinin due to the lack of in vitro cultures. Here, we analyze 161 P. vivax infections from Cambodian patients treated with 2 mg/kg/day of artesunate for seven days. All infections were successfully cleared by day 3. However, one third of the infections displayed a slow clearance after treatment, with nine infections (5.7%) with a parasite clearance time greater than 5 hours, meeting the WHO definition of artemisinin resistance. We observed no significant association between slow clearance and either patient- or infection characteristics (including stage composition). We used RNA-seq to characterize the gene expression of parasites from 15 fast- and 16 slow-clearing infections at baseline and 1, 2 and 4 hours after treatment. While fast-clearing parasites showed significant changes in gene expression immediately upon treatment, slow-clearing parasites displayed a significantly delayed gene expression response, with a downregulation of many genes associated with hemoglobin endocytosis and digestion. Overall, our results indicate that some Cambodian P. vivax parasites clear slowly after artesunate treatment, possibly due to a downregulation of hemoglobin metabolism that may reduce the efficiency of the artesunate.

Research in context

Evidence before this study: The WHO treatment guidelines recommend artemisinin-combination therapy (ACT) for treatment of blood-stage infections caused by Plasmodium vivax in all areas (with chloroquine recommended only in areas where P. vivax are still chloroquine-sensitive). In P. falciparum , partial resistance to artemisinin derivatives is defined in vivo as either detected parasitemia on day 3 post treatment or as a half-life of the parasite clearance slope of ≥ 5 hours. We searched Pubmed for studies containing the terms "vivax" AND "clearance" AND ("artesunate" OR "dihydroartemisinin" OR "artemether" OR "artemisinin") published between 1990 and February 2025, with no language restrictions. Our search retrieved 102 studies for which title and abstracts were screened to identify 21 studies reporting outcomes of P. vivax treatment with an artemisinin derivative. While all these studies concluded that artemisinin derivatives provided rapid clearance of P. vivax parasites, two studies reported a low frequency of day 3 positivity following artesunate-amodiaquine treatment (2.6% in Brazil) or dihydroartemisinin-piperaquine (0.6% in Indonesia). No study reported clearance slope half-life ≥ 5 hours. Added value of this study: This study used a cohort of Cambodian patients infected by P. vivax to rigorously examine the efficacy of artesunate monotherapy at clearing blood stage infections. Our study showed significant variations in clearance rates among infections, with 5.7% of the infections with a clearance slope half-life ≥ 5 hours, meeting the criteria for artemisinin partial resistance used for P. falciparum . Variations in clearance rate upon artesunate treatment were not associated with patient or infection characteristics. Gene expression analyses revealed that the slow-clearing parasites down-regulated upon treatment many genes involved in hemoglobin endocytosis and digestion, possibly resulting in a lesser activation of artesunate. Implications of all the available evidence: Our results confirm that 2 mg/kg of artesunate per day for seven days is effective at clearing P. vivax blood stage infections. However, a subset of the P. vivax parasites displayed a slow clearance following artesunate treatment meeting artemisinin partial resistance definition in P. falciparum . Gene expression analyses suggest that metabolic variations may underlie slow clearance. Increased monitoring of treatment efficacy and drug resistance in P. vivax is therefore recommended.

In vitro and in silico evaluation of synthetic compounds derived from bi-triazoles against asexual and sexual forms of Plasmodium falciparum

BACKGROUND

Despite advances in malaria chemotherapy, the disease continues to claim thousands of lives annually. Addressing this issue requires the discovery of new compounds to counteract resistance threatening the current therapeutic arsenal. In this context, bi-triazoles are substances with diverse biological activities, showing promise as lead compound to fight malaria. Triazoles are heterocyclic structures composed of five members, including three nitrogen atoms and two double bonds. Bi-triazoles, the focus of this study, are derivatives of triazoles consisting of two triazole rings (nitrogen heterocyclic) with isolated nuclei lacking a spacer and two substituents at each end. The goal of the present study was to assess the in vitro and in silico, antimalarial activity of bi-triazole compounds 14c, 14d, 13c, and 13d against asexual and sexual forms of Plasmodium falciparum.

METHODS

For in silico predictions, the software OSIRIS, Molinspiration, and ADMETlab were employed. To determine the 50% inhibitory concentration (IC50) on the asexual forms, the W2 clone was used, while the strain NF54 was used to assess inhibition of sexual forms. Cytotoxicity was evaluated using the HepG2 cell line, and haemolysis tests were conducted. Additionally, the selectivity index (SI) of each compound was calculated.

RESULTS

In silico analyses of physicochemical properties revealed that all compounds have favorable potential for drug development. Pharmacokinetics predictions also provided important, novel insights into this chemical class. Antimalarial activity tests showed that compounds 14d and 13d exhibited promising activity, with IC50 values of 3.1 and 4.4 µM, respectively. Antimalarial activity of compounds 14d and 13d may be related to the presence of methyl acetate in substituent R2 conjugated to the bi-triazole. None of the compounds demonstrated cytotoxic or haemolytic activity, with SI values above 51 for the three most active compounds, highlighting their selectivity. For the sexual forms, compounds 14c and 14d were classified as having a high potential to block malaria transmission.

CONCLUSION

Overall, the in vitro and in silico results showed that bi-triazole compounds may guide new biological investigation for malaria, enabling the identification and development of more active and selective antimalarial agents.

Monitoring molecular markers associated with antimalarial drug resistance in south-east Senegal from 2021 to 2023

BACKGROUND

Since 2006, artemisinin-based combination therapies (ACTs) have been introduced in Senegal in response to chloroquine resistance (CQ-R) and have shown high efficacy against Plasmodium falciparum. However, the detection of the PfKelch13R515K mutation in Kaolack, which confers artemisinin resistance in vitro, highlights the urgency of strengthening antimalarial drug surveillance to achieve malaria elimination by 2030.

OBJECTIVE

To assess the proportion of P. falciparum parasites carrying molecular signatures associated with antimalarial resistance (PfKelch13, Pfmdr1, Pfcrt, dhfr and dhps) in isolates collected at Kédougou using multiplex amplicon deep sequencing.

METHODS

Venous blood samples were collected from patients diagnosed with P. falciparum infection over a 3-year period (2021, 2022 and 2023). Parasite DNA was extracted, and multiplex amplicon sequencing was used to investigate gene polymorphisms.

RESULTS

Analysis of PfKelch13 did not reveal any non-synonymous mutations. Pfcrt mutations were present in 45% of the samples, mainly K76T (44%) and I356T (36%). The dominant Pfmdr-1 allele was Y184F (62%). The sextuple mutant 51I/59R/108N + 436A/437G/613S dhfr/dhps was observed in 10% of the samples.

CONCLUSION

The absence of PfKelch13 mutants suggests that ACT efficacy remains uncompromised, although clinical outcome studies are required to confirm this. Analysis of Pfcrt and Pfmdr-1 shows that CQ-R alleles, probably from previous CQ use, are slowly decreasing. Likewise, the detection of the dhfr/dhps sextuple mutant highlights the need to monitor sulfadoxine-pyrimethamine resistance and the emergence of 581G. There is therefore a need for continued antimalarial resistance surveillance in Senegal.

Towards next-generation treatment options to combat Plasmodium falciparum malaria

Malaria, which is caused by infection of red blood cells with Plasmodium parasites, can be fatal in non-immune individuals if left untreated. The recent approval of the pre-erythrocytic vaccines RTS, S/AS01 and R21/Matrix-M has ushered in hope of substantial reductions in mortality rates, especially when combined with other existing interventions. However, the efficacy of these vaccines is partial, and chemotherapy remains central to malaria treatment and control. For many antimalarial drugs, clinical efficacy has been compromised by the emergence of drug-resistant Plasmodium falciparum strains. Therefore, there is an urgent need for new antimalarial medicines to complement the existing first-line artemisinin-based combination therapies. In this Review, we discuss various opportunities to expand the present malaria treatment space, appraise the current antimalarial drug development pipeline and highlight examples of promising targets. We also discuss other approaches to circumvent antimalarial resistance and how potency against drug-resistant parasites could be retained.

Phase I study on the pharmacokinetics of intravaginal, self-administered artesunate vaginal pessaries among women in Kenya

Cervical cancer remains a significant global health issue, especially in low- and middle-income countries (LMICs), where access to prevention and treatment is limited and women are at a higher risk of cervical cancer. Artesunate, a widely available drug used to treat malaria, has shown promise in treating human papillomavirus (HPV)-associated anogenital lesions including high-grade cervical precancer, in a recent Phase I studies in the United States. Data on the pharmacokinetics of artesunate following intravaginal use, and its implications on malaria resistance, are lacking.

Objectives

The primary objective of this study is to investigate the pharmacokinetics of Artesunate (AS) and its active metabolite, dihydroartemisinin (DHA) following intravaginal use at the dosing and frequency intended for cervical precancer treatment. A secondary objective is to assess safety among study participants.

Methods

We are conducting a single-arm, phase I trial with a sample size of 12 female volunteers. Participants will self-administer artesunate vaginal pessaries in the study clinic daily for 5 consecutive days. Participants will have their blood drawn prior to receiving the first dose of artesunate on day one of the study and then will receive 8 blood draws on study day five, prior to artesunate administration and at 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours, and 8 hours after pessary administration. Pharmacokinetic parameters of artesunate and DHA will be calculated by way of quantitative analysis of with determination of maximum concentration (Cmax), time to Cmax (Tmax), area under the serum concentration versus time curve (AUC), apparent clearance, and elimination half-life (t1/2).

Population genomics and transcriptomics of Plasmodium falciparum in Cambodia and Vietnam uncover key components of the artemisinin resistance genetic background

The emergence of Plasmodium falciparum parasites resistant to artemisinins compromises the efficacy of Artemisinin Combination Therapies (ACTs), the global first-line malaria treatment. Artemisinin resistance is a complex genetic trait in which nonsynonymous SNPs in PfK13 cooperate with other genetic variations. Here, we present population genomic/transcriptomic analyses of P. falciparum collected from patients with uncomplicated malaria in Cambodia and Vietnam between 2018 and 2020. Besides the PfK13 SNPs, several polymorphisms, including nonsynonymous SNPs (N1131I and N821K) in PfRad5 and an intronic SNP in PfWD11 (WD40 repeat-containing protein on chromosome 11), appear to be associated with artemisinin resistance, possibly as new markers. There is also a defined set of genes whose steady-state levels of mRNA and/or splice variants or antisense transcripts correlate with artemisinin resistance at the base level. In vivo transcriptional responses to artemisinins indicate the resistant parasite's capacity to decelerate its intraerythrocytic developmental cycle (IDC), which can contribute to the resistant phenotype. During this response, PfRAD5 and PfWD11 upregulate their respective alternatively/aberrantly spliced isoforms, suggesting their contribution to the protective response to artemisinins. PfRAD5 and PfWD11 appear under selective pressure in the Greater Mekong Sub-region over the last decade, suggesting their role in the genetic background of the artemisinin resistance.

Screening the Global Health Priority Box against Plasmodium berghei liver stage parasites using an inexpensive luciferase detection protocol

BACKGROUND

Malaria, a disease caused by parasites of the genus Plasmodium, continues to impact many regions globally. The rise in resistance to artemisinin-based anti-malarial drugs highlights the need for new treatments. Ideally, new anti-malarials will kill the asymptomatic liver stages as well as the symptomatic blood stages. While blood stage screening assays are routine and efficient, liver stage screening assays are more complex and costly. To decrease the cost of liver stage screening, a previously reported luciferase detection protocol requiring only common laboratory reagents was adapted for testing against luciferase-expressing Plasmodium berghei liver stage parasites.

METHODS

After optimizing cell lysis conditions, the concentration of reagents, and the density of host hepatocytes (HepG2), the protocol was validated with 28 legacy anti-malarials to show this simple protocol produces a stable signal useful for obtaining quality small molecule potency data similar to that obtained from a high content imaging endpoint. The protocol was then used to screen the Global Health Priority Box (GHPB) and confirm the potency of hits in dose-response assays. Selectivity was determined using a galactose-based, 72 h HepG2 assay to avoid missing mitochondrial-toxic compounds due to the Crabtree effect. Receiver-operator characteristic plots were used to retroactively characterize the screens' predictive value.

RESULTS

Optimal luciferase signal was achieved using a lower HepG2 seed density (5 × 103 cells/well of a 384-well microtitre plate) compared to many previously reported luciferase-based screens. While producing lower signal compared to a commercial alternative, this luciferase detection method was found much more stable, with a > 3 h half-life, and robust enough for producing dose-response plots with as few as 500 sporozoites/well. A screen of the GHPB resulted in 9 hits with selective activity against P. berghei liver schizonts, including MMV674132 which exhibited 30.2 nM potency. Retrospective analyses show excellent predictive value for both anti-malarial activity and cytotoxicity.

CONCLUSIONS

This method is suitable for high-throughput screening at a cost nearly 20-fold less than using commercial luciferase detection kits, thereby enabling larger liver stage anti-malarial screens and hit optimization make-test cycles. Further optimization of the hits detected using this protocol is ongoing.

Antimalarial Mechanisms and Resistance Status of Artemisinin and Its Derivatives

Artemisinin is an endoperoxide sesquiterpene lactone isolated from Artemisia annua and is often used to treat malaria. Artemisinin's peroxide bridge is the key structure behind its antimalarial action. Scientists have created dihydroartemisinin, artemether, artesunate, and other derivatives preserving artemisinin's peroxide bridge to increase its clinical utility value. Artemisinin compounds exhibit excellent efficacy, quick action, and minimal toxicity in malaria treatment and have greatly contributed to malaria control. With the wide and unreasonable application of artemisinin-based medicines, malaria parasites have developed artemisinin resistance, making malaria prevention and control increasingly challenging. Artemisinin-resistant Plasmodium strains have been found in many countries and regions. The mechanisms of antimalarials and artemisinin resistance are not well understood, making malaria prevention and control a serious challenge. Understanding the antimalarial and resistance mechanisms of artemisinin drugs helps develop novel antimalarials and guides the rational application of antimalarials to avoid the spread of resistance, which is conducive to malaria control and elimination efforts. This review will discuss the antimalarial mechanisms and resistance status of artemisinin and its derivatives, which will provide a reference for avoiding drug resistance and the research and development of new antimalarial drugs.

Single cell transcriptional changes across the blood stages of artemisinin resistant K13580Y Plasmodium falciparum upon dihydroartemisinin exposure

Artemisinins have been a cornerstone of malaria control, but resistance in Plasmodium falciparum, due to mutations in the Kelch13 (K13) protein, threaten these advances. Artemisinin exposure results in a dynamic transcriptional response across multiple pathways, but most work has focused on ring stages and ex vivo transcriptional analysis. We applied single cell RNAseq to two unsynchronized coisogenic parasite lines (K13C580 and K13580Y) over 6 hrs after a pulse exposure to dihydroartemisinin (DHA). Transcription was altered across all stages, with the greatest occurring at the trophozoite and ring stage in both lines. This response involved the arrest of metabolic processes, support for a dormancy phenomenon upon treatment, and the enhancement of protein trafficking and the unfolded protein response. While similar, the response was consistent across stages in K13580Y, with enhanced parasite survival to drug induced stress. Increased surface protein expression was seen in K13580Y parasites at baseline and upon drug exposure, highlighted by the increased expression of PfEMP1 and GARP, a potential therapeutic target. Antibody targeting GARP maintained anti-parasitic efficacy in K13580Y parasites. This work provides single cell insight of gene transcription across all life cycle stages revealing transcriptional changes that could initiate a dormancy state and mediate survival upon treatment.

NDV targets the invasion pathway in malaria parasite through cell surface sialic acid interaction

Merozoites utilize sialic acids on the red blood cell (RBC) cell surface to rapidly adhere to and invade the RBCs. Newcastle disease virus (NDV) displays a strong affinity toward membrane-bound sialic acids. Incubation of NDV with the malaria parasites dose-dependently reduces its cellular viability. The antiplasmodial activity of NDV is specific, as incubation with Japanese encephalitis virus, duck enteritis virus, infectious bronchitis virus, and influenza virus did not affect the parasite propagation. Interestingly, NDV is reducing more than 80% invasion when RBCs are pretreated with the virus. Removal of the RBC surface proteins or the NDV coat proteins results in disruption of the virus binding to RBC. It suggests the involvement of specific protein: ligand interaction in virus binding. We established that the virus engages with the parasitized RBCs (PRBCs) through its hemagglutinin neuraminidase (HN) protein by recognizing sialic acid-containing glycoproteins on the cell surface. Blocking of the HN protein with free sialic acid or anti-HN antibodies abolished the virus binding as well as its ability to reduce parasite growth. Interestingly, the purified HN from the virus alone could inhibit the parasite's growth in a dose-dependent manner. NDV binds strongly to knobless murine parasite strain Plasmodium yoelii and restricted the parasite growth in mice. Furthermore, the virus was found to preferentially target the PRBCs compared to normal erythrocytes. Immunolocalization studies reveal that NDV is localized on the plasma membrane as well as weakly inside the PRBC. NDV causes neither any infection nor aggregation of the human RBCs. Our findings suggest that NDV is a potential candidate for developing targeted drug delivery platforms for the Plasmodium-infected RBCs.

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 molecular inhibitor design for Plasmodium falciparum Lactate dehydrogenase enzyme using machine learning generated library of diverse compounds

Generative machine learning models offer a novel strategy for chemogenomics and de novo drug design, allowing researchers to streamline their exploration of the chemical space and concentrate on specific regions of interest. In cases with limited inhibitor data available for the target of interest, de novo drug design plays a crucial role. In this study, we utilized a package called 'mollib,' trained on ChEMBL data containing approximately 365,000 bioactive molecules. By leveraging transfer learning techniques with this package, we generated a series of compounds, starting from five initial compounds, which are potential Plasmodium falciparum (Pf) Lactate dehydrogenase inhibitors. The resulting compounds exhibit structural diversity and hold promise as potential novel Pf Lactate dehydrogenase inhibitors.

An overview of artemisinin-resistant malaria and associated Pfk13 gene mutations in Central Africa

Malaria caused by Plasmodium falciparum is one of the deadliest and most common tropical infectious diseases. However, the emergence of artemisinin drug resistance associated with the parasite's Pfk13 gene, threatens the public health of individual countries as well as current efforts to reduce malaria burdens globally. It is of concern that artemisinin-resistant parasites may be selected or have already emerged in Africa. This narrative review aims to evaluate the published evidence concerning validated, candidate, and novel Pfk13 polymorphisms in ten Central African countries. Results show that four validated non-synonymous polymorphisms (M476I, R539T, P553L, and P574L), directly associated with a delayed therapy response, have been reported in the region. Also, two Pfk13 polymorphisms associated to artemisinin resistance but not validated (C469F and P527H) have been reported. Furthermore, several non-validated mutations have been observed in Central Africa, and one allele A578S, is commonly found in different countries, although additional molecular and biochemical studies are needed to investigate whether those mutations alter artemisinin effects. This information is discussed in the context of biochemical and genetic aspects of Pfk13, and related to the regional malaria epidemiology of Central African countries.

Post-Translational Modifications of Proteins of Malaria Parasites during the Life Cycle

Post-translational modifications (PTMs) are essential for regulating protein functions, influencing various fundamental processes in eukaryotes. These include, but are not limited to, cell signaling, protein trafficking, the epigenetic control of gene expression, and control of the cell cycle, as well as cell proliferation, differentiation, and interactions between cells. In this review, we discuss protein PTMs that play a key role in the malaria parasite biology and its pathogenesis. Phosphorylation, acetylation, methylation, lipidation and lipoxidation, glycosylation, ubiquitination and sumoylation, nitrosylation and glutathionylation, all of which occur in malarial parasites, are reviewed. We provide information regarding the biological significance of these modifications along all phases of the complex life cycle of Plasmodium spp. Importantly, not only the parasite, but also the host and vector protein PTMs are often crucial for parasite growth and development. In addition to metabolic regulations, protein PTMs can result in epitopes that are able to elicit both innate and adaptive immune responses of the host or vector. We discuss some existing and prospective results from antimalarial drug discovery trials that target various PTM-related processes in the parasite or host.

Omega-3 and omega-6 polyunsaturated fatty acids and their potential therapeutic role in protozoan infections

Protozoa exert a serious global threat of growing concern to human, and animal, and there is a need for the advancement of novel therapeutic strategies to effectively treat or mitigate the impact of associated diseases. Omega polyunsaturated fatty acids (ω-PUFAs), including Omega-3 (ω-3) and omega-6 (ω-6), are constituents derived from various natural sources, have gained significant attention for their therapeutic role in parasitic infections and a variety of essential structural and regulatory functions in animals and humans. Both ω-3 and ω-6 decrease the growth and survival rate of parasites through metabolized anti-inflammatory mediators, such as lipoxins, resolvins, and protectins, and have both in vivo and in vitro protective effects against various protozoan infections. The ω-PUFAs have been shown to modulate the host immune response by a commonly known mechanism such as (inhibition of arachidonic acid (AA) metabolic process, production of anti-inflammatory mediators, modification of intracellular lipids, and activation of the nuclear receptor), and promotion of a shift towards a more effective immune defense against parasitic invaders by regulation the inflammation like prostaglandins, leukotrienes, thromboxane, are involved in controlling the inflammatory reaction. The immune modulation may involve reducing inflammation, enhancing phagocytosis, and suppressing parasitic virulence factors. The unique properties of ω-PUFAs could prevent protozoan infections, representing an important area of study. This review explores the clinical impact of ω-PUFAs against some protozoan infections, elucidating possible mechanisms of action and supportive therapy for preventing various parasitic infections in humans and animals, such as toxoplasmosis, malaria, coccidiosis, and chagas disease. ω-PUFAs show promise as a therapeutic approach for parasitic infections due to their direct anti-parasitic effects and their ability to modulate the host immune response. Additionally, we discuss current treatment options and suggest perspectives for future studies. This could potentially provide an alternative or supplementary treatment option for these complex global health problems.

Photoaffinity probe-based antimalarial target identification of artemisinin in the intraerythrocytic developmental cycle of Plasmodium falciparum

Malaria continues to pose a serious global health threat, and artemisinin remains the core drug for global malaria control. However, the situation of malaria resistance has become increasingly severe due to the emergence and spread of artemisinin resistance. In recent years, significant progress has been made in understanding the mechanism of action (MoA) of artemisinin. Prior research on the MoA of artemisinin mainly focused on covalently bound targets that are alkylated by artemisinin-free radicals. However, less attention has been given to the reversible noncovalent binding targets, and there is a paucity of information regarding artemisinin targets at different life cycle stages of the parasite. In this study, we identified the protein targets of artemisinin at different stages of the parasite's intraerythrocytic developmental cycle using a photoaffinity probe. Our findings demonstrate that artemisinin interacts with parasite proteins in vivo through both covalent and noncovalent modes. Extensive mechanistic studies were then conducted by integrating target validation, phenotypic studies, and untargeted metabolomics. The results suggest that protein synthesis, glycolysis, and oxidative homeostasis are critically involved in the antimalarial activities of artemisinin. In summary, this study provides fresh insights into the mechanisms underlying artemisinin's antimalarial effects and its protein targets.

In silico screening of selective ATP mimicking inhibitors targeting the Plasmodium falciparum Grp94

Plasmodium falciparum parasites export more than 400 proteins to remodel the host cell environment and increase its chances of surviving and reproducing. The endoplasmic reticulum (ER) plays a central role in protein export by facilitating protein sorting and folding. The ER resident member of the Hsp90 family, glucose-regulated protein 94 (Grp94), is a molecular chaperone that facilitates the proper folding of client proteins in the ER lumen. In P. falciparum, Grp94 (PfGrp94) is essential for parasite survival, rendering it a promising anti-malarial drug target. Despite this, its druggability has not been fully explored. Consequently, this study sought to identify small molecule inhibitors targeting the PfGrp94. Potential small molecule inhibitors of PfGrp94 were designed and screened using in silico studies. Molecular docking studies indicate that two novel compounds, Compound S and Compound Z selectively bind to PfGrp94 over its human homologues. Comparatively, Compound Z had a higher affinity for PfGrp94 than Compound S. Further interrogation of the inhibitor binding using molecular dynamics (MD) analysis confirmed that Compound Z formed stable binding poses within the ATP-binding pocket of the PfGrp94 N-terminal domain (NTD) during the 250 ns simulation run. PfGrp94 interacted with Compound Z through hydrogen bonding and hydrophobic interactions with residues Asp 148, Asn 106, Gly 152, Ile 151 and Lys 113. Based on the findings of this study, Compound Z could serve as a competitive and selective inhibitor of PfGrp94 and may be useful as a starting point for the development of a potential drug for malaria.

Target fishing reveals PfPYK-1 and PfRab6 as potential targets of an antiplasmodial 4-anilino-2-trichloromethylquinazoline hit compound

We present investigations about the mechanism of action of a previously reported 4-anilino-2-trichloromethylquinazoline antiplasmodial hit-compound (Hit A), which did not share a common mechanism of action with established commercial antimalarials and presented a stage-specific effect on the erythrocytic cycle of P. falciparum at 8 < t < 16 h. The target of Hit A was searched by immobilising the molecule on a solid support via a linker and performing affinity chromatography on a plasmodial lysate. Several anchoring positions of the linker (6,7 and 3') and PEG-type linkers were assessed, to obtain a linked-hit molecule displaying in vitro antiplasmodial activity similar to that of unmodified Hit A. This allowed us to identify the PfPYK-1 kinase and the PfRab6 GTP-ase as potential targets of Hit A.

Enhanced Antimalarial Activity of Extracts of Artemisia annua L. Achieved with Aqueous Solutions of Salicylate Salts and Ionic Liquids

Artemisinin, a drug used to treat malaria, can be chemically synthesized or extracted from Artemisia annua L. However, the extraction method for artemisinin from biomass needs to be more sustainable while maintaining or enhancing its bioactivity. This work investigates the use of aqueous solutions of salts and ionic liquids with hydrotropic properties as alternative solvents for artemisinin extraction from Artemisia annua L. Among the investigated solvents, aqueous solutions of cholinium salicylate and sodium salicylate were found to be the most promising. To optimize the extraction process, a response surface method was further applied, in which the extraction time, hydrotrope concentration, and temperature were optimized. The optimized conditions resulted in extraction yields of up to 6.50 and 6.44 mg·g-1, obtained with aqueous solutions of sodium salicylate and cholinium salicylate, respectively. The extracts obtained were tested for their antimalarial activity, showing a higher efficacy against the Plasmodium falciparum strain compared with pure (synthetic) artemisinin or extracts obtained with conventional organic solvents. Characterization of the extracts revealed the presence of artemisinin together with other compounds, such as artemitin, chrysosplenol D, arteannuin B, and arteannuin J. These compounds act synergistically with artemisinin and enhance the antimalarial activity of the obtained extracts. Given the growing concern about artemisinin resistance, the results here obtained pave the way for the development of sustainable and biobased antimalarial drugs.

Plasmodium falciparum topoisomerases: Emerging targets for anti-malarial therapy

Different metabolic pathways like DNA replication, transcription, and recombination generate topological constrains in the genome. These topological constraints are resolved by essential molecular machines known as topoisomerases. To bring changes in DNA topology, the topoisomerases create a single or double-stranded nick in the template DNA, hold the nicked ends to let the tangled DNA pass through, and finally re-ligate the breaks. The DNA nicking and re-ligation activities as well as ATPase activities (when present) in topoisomerases are subjected to inhibition by several anticancer and antibacterial drugs, thus establishing these enzymes as successful targets in anticancer and antibacterial therapies. The anti-topoisomerase drugs interfere with the functioning of these enzymes and result in the accumulation of DNA tangles or lethal genomic breaks, thereby promoting host cell (or organism) death. The potential of topoisomerases in the human malarial parasite, Plasmodium falciparum in antimalarial drug development has received little attention so far. Interestingly, the parasite genome encodes orthologs of topoisomerases found in eukaryotes, prokaryotes, and archaea, thus, providing an enormous opportunity for investigating these enzymes for antimalarial therapeutics. This review focuses on the features of Plasmodium falciparum topoisomerases (PfTopos) with respect to their closer counterparts in other organisms. We will discuss overall advances and basic challenges with topoisomerase research in Plasmodium falciparum and our attempts to understand the interaction of PfTopos with classical and new-generation topoisomerase inhibitors using in silico molecular docking approach. The recent episodes of parasite resistance against artemisinin, the only effective antimalarial drug at present, further highlight the significance of investigating new drug targets including topoisomerases in antimalarial therapeutics.

The problem of antimalarial resistance and its implications for drug discovery

INTRODUCTION

Malaria remains a devastating infectious disease with hundreds of thousands of casualties each year. Antimalarial drug resistance has been a threat to malaria control and elimination for many decades and is still of concern today. Despite the continued effectiveness of current first-line treatments, namely artemisinin-based combination therapies, the emergence of drug-resistant parasites in Southeast Asia and even more alarmingly the occurrence of resistance mutations in Africa is of great concern and requires immediate attention.

AREAS COVERED

A comprehensive overview of the mechanisms underlying the acquisition of drug resistance in Plasmodium falciparum is given. Understanding these processes provides valuable insights that can be harnessed for the development and selection of novel antimalarials with reduced resistance potential. Additionally, strategies to mitigate resistance to antimalarial compounds on the short term by using approved drugs are discussed.

EXPERT OPINION

While employing strategies that utilize already approved drugs may offer a prompt and cost-effective approach to counter antimalarial drug resistance, it is crucial to recognize that only continuous efforts into the development of novel antimalarial drugs can ensure the successful treatment of malaria in the future. Incorporating resistance propensity assessment during this developmental process will increase the likelihood of effective and enduring malaria treatments.

Plasmodium falciparum ring-stage plasticity and drug resistance

Malaria is a life-threatening tropical disease caused by parasites of the genus Plasmodium, of which Plasmodium falciparum is the most lethal. Malaria parasites have a complex life cycle, with stages occurring in both the Anopheles mosquito vector and human host. Ring stages are the youngest form of the parasite in the intraerythrocytic developmental cycle and are associated with evasion of spleen clearance, temporary growth arrest (TGA), and drug resistance. This formidable ability to survive and develop into mature, sexual, or growth-arrested forms demonstrates the inherent population heterogeneity. Here we highlight the role of the ring stage as a crossroads in parasite development and as a reservoir of surviving cells in the human host via TGA survival mechanisms.

Drug Discovery Efforts to Identify Novel Treatments for Neglected Tropical Diseases - Cysteine Protease Inhibitors

BACKGROUND

Neglected tropical diseases are a severe burden for mankind, affecting an increasing number of people around the globe. Many of those diseases are caused by protozoan parasites in which cysteine proteases play a key role in the parasite's pathogenesis.

OBJECTIVE

In this review article, we summarize the drug discovery efforts of the research community from 2017 - 2022 with a special focus on the optimization of small molecule cysteine protease inhibitors in terms of selectivity profiles or drug-like properties as well as in vivo studies. The cysteine proteases evaluated by this methodology include Cathepsin B1 from Schistosoma mansoni, papain, cruzain, falcipain, and rhodesain.

METHODS

Exhaustive literature searches were performed using the keywords "Cysteine Proteases" and "Neglected Tropical Diseases" including the years 2017 - 2022. Overall, approximately 3'000 scientific papers were retrieved, which were filtered using specific keywords enabling the focus on drug discovery efforts.

RESULTS AND CONCLUSION

Potent and selective cysteine protease inhibitors to treat neglected tropical diseases were identified, which progressed to pharmacokinetic and in vivo efficacy studies. As far as the authors are aware of, none of those inhibitors reached the stage of active clinical development. Either the inhibitor's potency or pharmacokinetic properties or safety profile or a combination thereof prevented further development of the compounds. More efforts with particular emphasis on optimizing pharmacokinetic and safety properties are needed, potentially by collaborations of academic and industrial research groups with complementary expertise. Furthermore, new warheads reacting with the catalytic cysteine should be exploited to advance the research field in order to make a meaningful impact on society.

Naphthyl bearing 1,3,4-thiadiazoleacetamides targeting the parasitic folate pathway as anti-infectious agents: in silico, synthesis, and biological approach

Malaria is still a complex and lethal parasitic infectious disease, despite the availability of effective antimalarial drugs. Resistance of malaria parasites to current treatments necessitates new antimalarials targeting P. falciparum proteins. The present study reported the design and synthesis of a series of a 2-(4-substituted piperazin-1-yl)-N-(5-((naphthalen-2-yloxy)methyl)-1,3,4-thiadiazol-2-yl)acetamide hybrids for the inhibition of Plasmodium falciparum dihydrofolate reductase (PfDHFR) using computational biology tools followed by chemical synthesis, structural characterization, and functional analysis. The synthesized compounds were evaluated for their in vitro antimalarial activity against CQ-sensitive PfNF54 and CQ-resistant PfW2 strain. Compounds T5 and T6 are the most active compounds having anti-plasmodial activity against PfNF54 with IC50 values of 0.94 and 3.46 μM respectively. Compound T8 is the most active against the PfW2 strain having an IC50 of 3.91 μM. Further, these active hybrids (T5, T6, and T8) were also evaluated for enzyme inhibition assay against PfDHFR. All the tested compounds were non-toxic against the Hek293 cell line with good selectivity indices. Hemolysis assay also showed non-toxicity of these compounds on normal uninfected human RBCs. In silico molecular docking studies were carried out in the binding pocket of both the wild-type and quadruple mutant Pf-DHFR-TS to gain further insights into probable modes of action of active compounds. ADME prediction and physiochemical properties support their drug-likeness. Additionally, they were screened for antileishmanial activity against L. donovani promastigotes to explore broader applications. Thus, this study provides molecular frameworks for developing potent antimalarials and antileishmanial agents.

The many paths to artemisinin resistance in Plasmodium falciparum

Emerging resistance against artemisinin (ART) poses a major challenge in controlling malaria. Parasites with mutations in PfKelch13, the major marker for ART resistance, are known to reduce hemoglobin endocytosis, induce unfolded protein response (UPR), elevate phosphatidylinositol-3-phosphate (PI3P) levels, and stimulate autophagy. Nonetheless, PfKelch13-independent resistance is also reported, indicating extensive complementation by reconfiguration in the parasite metabolome and transcriptome. These findings implicate that there may not be a single 'universal identifier' of ART resistance. This review sheds light on the molecular, transcriptional, and metabolic pathways associated with ART resistance, while also highlighting the interplay between cellular heterogeneity, environmental stress, and ART sensitivity.

Designing hybrid CRISPR-Cas12 and LAMP detection systems for treatment-resistant Plasmodium falciparum with in silico method

Genes associated with drug resistance of first line drugs for Plasmodium falciparum have been identified and characterized of which three genes most commonly associated with drug resistance are P. falciparum chloroquine resistance transporter gene (PfCRT), P. falciparum multidrug drug resistance gene 1 (PfMDR1), and P. falciparum Kelch protein K13 gene (PfKelch13). Polymorphism in these genes could be used as molecular markers for identifying drug resistant strains. Nucleic acid amplification test (NAAT) along with DNA sequencing is a powerful diagnostic tool that could identify these polymorphisms. However, current NAAT and DNA sequencing technologies require specific instruments which might limit its application in rural areas. More recently, a combination of isothermal amplification and CRISPR detection system showed promising results in detecting mutations at a nucleic acid level. Moreover, the Loop-mediated isothermal amplification (LAMP)-CRISPR systems offer robust and straightforward detection, enabling it to be deployed in rural and remote areas. The aim of this study was to develop a novel diagnostic method, based on LAMP of targeted genes, that would enable the identification of drug-resistant P. falciparum strains. The methods were centered on sequence analysis of P. falciparum genome, LAMP primers design, and CRISPR target prediction. Our designed primers are satisfactory for identifying polymorphism associated with drug resistant in PfCRT, PfMDR1, and PfKelch13. Overall, the developed system is promising to be used as a detection method for P. falciparum treatment-resistant strains. However, optimization and further validation the developed CRISPR-LAMP assay are needed to ensure its accuracy, reliability, and feasibility.

Artemisinin resistance in P. falciparum: probing the interacting partners of Kelch13 protein in parasite

OBJECTIVES

Artemisinin (ART) resistance in Plasmodium is threatening the artemisinin combination therapies-the first line of defence against malaria. ART resistance has been established to be mediated by the Plasmodium Kelch13 (PfK13) protein. For the crucial role of PfK13 in multiple pathways of the Plasmodium life cycle and ART resistance, it is imperative that we investigate its interacting partners.

METHODS

We recombinantly expressed PfK13-p (Bric a brac/Poxvirus and zinc finger and propeller domains), generating anti-PfK13-p antibodies to perform co-immunoprecipitation assays and probed PfK13 interacting partners. Surface plasmon resonance and pull-down assays were performed to establish physical interactions of representative proteins with PfK13-p.

RESULTS

The co-immunoprecipitation assays identified 17 proteins with distinct functions in the parasite life cycle- protein folding, cellular metabolism, and protein binding and invasion. In addition to the overlap with previously identified proteins, our study identified 10 unique proteins. Fructose-biphosphate aldolase and heat shock protein 70 demonstrated strong biophysical interaction with PfK13-p, with KD values of 6.6 µM and 7.6 µM, respectively. Additionally, Plasmodium merozoite surface protein 1 formed a complex with PfK13-p, which is evident from the pull-down assay.

CONCLUSION

This study adds to our knowledge of the PfK13 protein in mediating ART resistance by identifying new PfK13 interacting partners. Three representative proteins-fructose-biphosphate aldolase, heat shock protein 70, and merozoite surface protein 1-demonstrated clear evidence of biophysical interactions with PfK13-p. However, elucidation of the functional relevance of these physical interactions are crucial in context of PfK13 role in ART resistance.

Distribution of Plasmodium falciparum K13 gene polymorphisms across transmission settings in Ghana

Malaria is a significant global health concern, with a majority of cases in Sub-Saharan African nations. Numerous antimalarial drugs have been developed to counter the rampant prevalence of Plasmodium falciparum malaria. Artemisinin-based Combination Therapy (ACT) has served as the primary treatment of uncomplicated malaria in Ghana since 2005. However, a growing concern has emerged due to the escalating reports of ACT resistance, particularly in Southeast Asia, and its encroachment into Africa. Specifically, mutations in the Kelch propeller domain on chromosome 13 (Pfk13) have been linked to ACT resistance. Yet, our understanding of mutation prevalence in Africa remains largely uncharted. In this study, we compared Pfk13 sequences obtained from 172 P. falciparum samples across three ecological and transmission zones in Ghana. We identified 27 non-synonymous mutations among these sequences, of which two of the mutations, C580Y (found in two samples from the central region) and Y493H (found in one sample from the north), had previously been validated for their association with artemisinin resistance, a phenomenon widespread in Southeast Asia. The Pfk13 gene diversity was most pronounced in the northern savannah than the central forest and south coastal regions, where transmission rates are lower. The observed mutations were not significantly associated with geographical regions, suggesting a frequent spread of mutations across the country. The ongoing global surveillance of artemisinin resistance remains pivotal, and our findings provides insights into the potential spread of resistant parasites in West Africa. Furthermore, the identification of novel codon mutations in this study raises their potential association to ACT resistance, warranting further investigation through in vitro assays to ascertain their functional significance.

Tackling the emerging Artemisinin-resistant malaria parasite by modulation of defensive oxido-reductive mechanism via nitrofurantoin repurposing

Oxidative stress-mediated cell death has remained the prime parasiticidal mechanism of front line antimalarial, artemisinin (ART). The emergence of resistant Plasmodium parasites characterized by oxidative stress management due to impaired activation of ART and enhanced reactive oxygen species (ROS) detoxification has decreased its clinical efficacy. This gap can be filled by development of alternative chemotherapeutic agents to combat resistance defense mechanism. Interestingly, repositioning of clinically approved drugs presents an emerging approach for expediting antimalarial drug development and circumventing resistance. Herein, we evaluated the antimalarial potential of nitrofurantoin (NTF), a clinically used antibacterial drug, against intra-erythrocytic stages of ART-sensitive (Pf3D7) and resistant (PfKelch13R539T) strains of P. falciparum, alone and in combination with ART. NTF exhibited growth inhibitory effect at submicro-molar concentration by arresting parasite growth at trophozoite stage. It also inhibited the survival of resistant parasites as revealed by ring survival assay. Concomitantly, in vitro combination assay revealed synergistic association of NTF with ART. NTF was found to enhance the reactive oxygen and nitrogen species, and induced mitochondrial membrane depolarization in parasite. Furthermore, we found that exposure of parasites to NTF disrupted redox balance by impeding Glutathione Reductase activity, which manifests in enhanced oxidative stress, inducing parasite death. In vivo administration of NTF, alone and in combination with ART, in P. berghei ANKA-infected mice blocked parasite multiplication and enhanced mean survival time. Overall, our results indicate NTF as a promising repurposable drug with therapeutic potential against ART-sensitive as well as resistant parasites.

Micromolar Dihydroartemisinin Concentrations Elicit Lipoperoxidation in Plasmodium falciparum-Infected Erythrocytes

Malaria is still the most important parasitic infectious disease. Numerous substances are known to have antimalarial activity; among them, artemisinin is the most widely used one, and artemisinin-based combination therapy (ACT) is recommended for the treatment of Plasmodium falciparum (P.f.) malaria. Antitumor, immunomodulatory, and other therapeutic applications of artemisinin are under extensive study. Several different mechanisms of action were proposed for dihydroartemisinin (DHA), the active metabolite of artemisinin, such as eliciting oxidative stress in target cells. The goal of this study is to monitor the generation of reactive oxygen species (ROS) and lipid peroxidation product 4-hydroxynonenal (4-HNE) by DHA in P.f.-infected human erythrocytes. Checking ROS and 4-HNE-protein adducts kinetics along the maturation of the parasite, we detected the highest level of 4-HNE in ring forms of P.f. due to DHA treatment. Low micromolar concentrations of DHA quickly induced levels of 4-HNE-adducts which are supposed to be damaging. Mass spectrometry identified the P.f. protein cysteine proteinase falcipain-1 as being heavily modified by 4-HNE, and plausibly, 4-HNE conjugation with vital P.f. proteins might contribute to DHA-elicited parasite death. In conclusion, significant 4-HNE accumulation was detectable after DHA treatment, though, at concentrations well above pharmacologically effective ranges in malaria treatment, but at concentrations described for antitumor activity. Thus, lipid peroxidation with consequent 4-HNE conjugation of functionally relevant proteins might be considered as a uniform mechanism for how DHA potentiates antimalarials' action in ACT and controls the progression of tumors.

Is structural hybridization invoking new dimensions for antimalarial drug discovery research?

Despite effective prevention methods, malaria is a devastating, persistent infection caused by protozoal parasites that result in nearly half a million fatalities annually. Any progress made thus far in the eradication of the disease is jeopardized by the expansion of malaria parasites that have evolved to become resistant to a wide range of drugs, including first-line therapy. To surmount this significant obstacle, it is necessary to develop newly synthesized drugs with multiple modes of action that may have a novel target in various stages of Plasmodium parasite development and this is made possible by the hybridization concept. Hybridization is the combination of at least two diverse pharmacophore units with some linkers bringing about a single molecule with a diverse mode of action. It intensifies a drug's physiological and chemical characteristics, such as absorption, cellular target contact, metabolism, excretion, distribution, and toxicity. This review article outlines the currently published most potent hybrid drugs against the Plasmodium species.

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.

Antimalarial Drug Resistance: A Brief History of Its Spread in Indonesia

Malaria remains to be a national and global challenge and priority, as stated in the strategic plan of the Indonesian Ministry of Health and Sustainable Development Goals. In Indonesia, it is targeted that malaria elimination can be achieved by 2030. Unfortunately, the development and spread of antimalarial resistance inflicts a significant risk to the national malaria control programs which can lead to increased malaria morbidity and mortality. In Indonesia, resistance to widely used antimalarial drugs has been reported in two human species, Plasmodium falciparum and Plasmodium vivax. With the exception of artemisinin, resistance has surfaced towards all classes of antimalarial drugs. Initially, chloroquine, sulfadoxine-pyrimethamine, and primaquine were the most widely used antimalarial drugs. Regrettably, improper use has supported the robust spread of their resistance. Chloroquine resistance was first reported in 1974, while sulfadoxine-pyrimethamine emerged in 1979. Twenty years later, most provinces had declared treatment failures of both drugs. Molecular epidemiology suggested that variations in pfmdr1 and pfcrt genes were associated with chloroquine resistance, while dhfr and dhps genes were correlated with sulfadoxine-pyrimethamine resistance. Additionally, G453W, V454C and E455K of pfk13 genes appeared to be early warning sign to artemisinin resistance. Here, we reported mechanisms of antimalarial drugs and their development of resistance. This insight could provide awareness toward designing future treatment guidelines and control programs in Indonesia.

Recent advances on patents of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) inhibitors as antimalarial agents

INTRODUCTION

Pyrimidine nucleotides are essential for the parasite's growth and replication. Parasites have only a de novo pathway for the biosynthesis of pyrimidine nucleotides. Dihydroorotate dehydrogenase (DHODH) enzyme is involved in the rate-limiting step of the pyrimidine biosynthesis pathway. DHODH is a biochemical target for the discovery of new antimalarial agents.

AREA COVERED

This review discussed the development of patented PfDHODH inhibitors published between 2007 and 2023 along with their chemical structures and activities.

EXPERT OPINION

PfDHODH enzyme is involved in the rate-limiting fourth step of the pyrimidine biosynthesis pathway. Thus, inhibition of PfDHODH using species-selective inhibitors has drawn much attention for treating malaria because they inhibit parasite growth without affecting normal human functions. Looking at the current scenario of antimalarial drug resistance with most of the available antimalarial drugs, there is a huge need for targeted newer agents. Newer agents with unique mechanisms of action may be devoid of drug toxicity, adverse effects, and the ability of parasites to quickly gain resistance, and PfDHODH inhibitors can be those newer agents. Many PfDHODH inhibitors were patented in the past, and the dependency of Plasmodium on de novo pyrimidine provided a new approach for the development of novel antimalarial agents.

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.

The Potential of Artemisinins as Novel Treatment for Thyroid Eye Disease by Inhibiting Adipogenesis in Orbital Fibroblasts

Purpose

Thyroid eye disease (TED) causes cosmetic defect and even threatens eyesight due to tissue remodeling in which orbital fibroblast (OF) plays a central role mainly by differentiating into adipocytes. Repurposing old drugs to novel applications is of particular interest. Here, we aimed to evaluate the effects of the antimalarials artemisinin (ARS) and the derivatives on the OFs isolated from patients with TED and their counterparts.

Methods

OFs isolated from patients with TED or their counterparts were cultured and passaged in proliferation medium (PM) and stimulated by differentiation medium (DM) for adipogenesis. OFs were treated with or without ARS, dihydroartemisinin (DHA), and artesunate (ART) at different concentrations, before being examined in vitro. CCK-8 were used to assess cellular viability. Cell proliferation was determined by EdU incorporation and flow cytometry. Lipid accumulation within the cells was evaluated by Oil Red O staining. Hyaluronan production was determined by ELISA. RNAseq, qPCR, and Western blot analysis were performed to illustrate the underlying mechanisms.

Results

ARSs dose-dependently interfered with lipid accumulation of TED-OFs, rather than non-TED-OFs. Meanwhile, the expression of key adipogenic markers, such as PLIN1, PPARG, FABP4, and CEBPA, was suppressed. During adipogenesis as being cultivated in DM, instead of PM, ARSs also inhibited cell cycle, hyaluronan production and the expression of hyaluronan synthase 2 (HAS2) in a concentration-dependent manner. Mechanically, the favorable effects were potentially mediated by the repression of IGF1R-PI3K-AKT signaling by dampening IGF1R expression.

Conclusions

Collectedly, our data evidenced that the conventional antimalarials ARSs were potentially therapeutic for TED.

Genomic analysis of Indian isolates of Plasmodium falciparum: Implications for drug resistance and virulence factors

The emergence of drug resistance to frontline treatments such as Artemisinin-based combination therapy (ACT) is a major obstacle to the control and eradication of malaria. This problem is compounded by the inherent genetic variability of the parasites, as many established markers of resistance do not accurately predict the drug-resistant status. There have been reports of declining effectiveness of ACT in the West Bengal and Northeast regions of India, which have traditionally been areas of drug resistance emergence in the country. Monitoring the genetic makeup of a population can help to identify the potential for drug resistance markers associated with it and evaluate the effectiveness of interventions aimed at reducing the spread of malaria. In this study, we performed whole genome sequencing of 53 isolates of Plasmodium falciparum from West Bengal and compared their genetic makeup to isolates from Southeast Asia (SEA) and Africa. We found that the Indian isolates had a distinct genetic makeup compared to those from SEA and Africa, and were more similar to African isolates, with a high prevalence of mutations associated with antigenic variation genes. The Indian isolates also showed a high prevalence of markers of chloroquine resistance (mutations in Pfcrt) and multidrug resistance (mutations in Pfmdr1), but no known mutations associated with artemisinin resistance in the PfKelch13 gene. Interestingly, we observed a novel L152V mutation in PfKelch13 gene and other novel mutations in genes involved in ubiquitination and vesicular transport that have been reported to support artemisinin resistance in the early stages of ACT resistance in the absence of PfKelch13 polymorphisms. Thus, our study highlights the importance of region-specific genomic surveillance for artemisinin resistance and the need for continued monitoring of resistance to artemisinin and its partner drugs.

Mitigating the risk of antimalarial resistance via covalent dual-subunit inhibition of the Plasmodium proteasome

The Plasmodium falciparum proteasome constitutes a promising antimalarial target, with multiple chemotypes potently and selectively inhibiting parasite proliferation and synergizing with the first-line artemisinin drugs, including against artemisinin-resistant parasites. We compared resistance profiles of vinyl sulfone, epoxyketone, macrocyclic peptide, and asparagine ethylenediamine inhibitors and report that the vinyl sulfones were potent even against mutant parasites resistant to other proteasome inhibitors and did not readily select for resistance, particularly WLL that displays covalent and irreversible binding to the catalytic β2 and β5 proteasome subunits. We also observed instances of collateral hypersensitivity, whereby resistance to one inhibitor could sensitize parasites to distinct chemotypes. Proteasome selectivity was confirmed using CRISPR/Cas9-edited mutant and conditional knockdown parasites. Molecular modeling of proteasome mutations suggested spatial contraction of the β5 P1 binding pocket, compromising compound binding. Dual targeting of P. falciparum proteasome subunits using covalent inhibitors provides a potential strategy for restoring artemisinin activity and combating the spread of drug-resistant malaria.

Dual-pharmacophore artezomibs hijack the Plasmodium ubiquitin-proteasome system to kill malaria parasites while overcoming drug resistance

Artemisinins (ART) are critical anti-malarials and despite their use in combination therapy, ART-resistant Plasmodium falciparum is spreading globally. To counter ART resistance, we designed artezomibs (ATZs), molecules that link an ART with a proteasome inhibitor (PI) via a non-labile amide bond and hijack parasite's own ubiquitin-proteasome system to create novel anti-malarials in situ. Upon activation of the ART moiety, ATZs covalently attach to and damage multiple parasite proteins, marking them for proteasomal degradation. When damaged proteins enter the proteasome, their attached PIs inhibit protease function, potentiating the parasiticidal action of ART and overcoming ART resistance. Binding of the PI moiety to the proteasome active site is enhanced by distal interactions of the extended attached peptides, providing a mechanism to overcome PI resistance. ATZs have an extra mode of action beyond that of each component, thereby overcoming resistance to both components, while avoiding transient monotherapy seen when individual agents have disparate pharmacokinetic profiles.

Fast-Killing Tyrosine Amide ((S)-SW228703) with Blood- and Liver-Stage Antimalarial Activity Associated with the Cyclic Amine Resistance Locus (PfCARL)

Current malaria treatments are threatened by drug resistance, and new drugs are urgently needed. In a phenotypic screen for new antimalarials, we identified (S)-SW228703 ((S)-SW703), a tyrosine amide with asexual blood and liver stage activity and a fast-killing profile. Resistance to (S)-SW703 is associated with mutations in the Plasmodium falciparum cyclic amine resistance locus (PfCARL) and P. falciparum acetyl CoA transporter (PfACT), similarly to several other compounds that share features such as fast activity and liver-stage activity. Compounds with these resistance mechanisms are thought to act in the ER, though their targets are unknown. The tyramine of (S)-SW703 is shared with some reported PfCARL-associated compounds; however, we observed that strict S-stereochemistry was required for the activity of (S)-SW703, suggesting differences in the mechanism of action or binding mode. (S)-SW703 provides a new chemical series with broad activity for multiple life-cycle stages and a fast-killing mechanism of action, available for lead optimization to generate new treatments for malaria.

Novel Plasmodium falciparum k13 gene polymorphisms from Kisii County, Kenya during an era of artemisinin-based combination therapy deployment

BACKGROUND

Currently, chemotherapy stands out as the major malaria intervention strategy, however, anti-malarial resistance may hamper global elimination programs. Artemisinin-based combination therapy (ACT) stands as the drug of choice for the treatment of Plasmodium falciparum malaria. Plasmodium falciparum kelch13 gene mutations are associated with artemisinin resistance. Thus, this study was aimed at evaluating the circulation of P. falciparum k13 gene polymorphisms from Kisii County, Kenya during an era of ACT deployment.

METHODS

Participants suspected to have malaria were recruited. Plasmodium falciparum was confirmed using the microscopy method. Malaria-positive patients were treated with artemether-lumefantrine (AL). Blood from participants who tested positive for parasites after day 3 was kept on filter papers. DNA was extracted using chelex-suspension method. A nested polymerase chain reaction (PCR) was conducted and the second-round products were sequenced using the Sanger method. Sequenced products were analysed using DNAsp 5.10.01 software and then blasted on the NCBI for k13 propeller gene sequence identity using the Basic Local Alignment Search Tool (BLAST). To assess the selection pressure in P. falciparum parasite population, Tajima' D statistic and Fu & Li's D test in DnaSP software 5.10.01 was used.

RESULTS

Out of 275 enrolled participants, 231 completed the follow-up schedule. 13 (5.6%) had parasites on day 28 hence characterized for recrudescence. Out of the 13 samples suspected of recrudescence, 5 (38%) samples were positively amplified as P. falciparum, with polymorphisms in the k13-propeller gene detected. Polymorphisms detected in this study includes R539T, N458T, R561H, N431S and A671V, respectively. The sequences have been deposited in NCBI with bio-project number PRJNA885380 and accession numbers SAMN31087434, SAMN31087433, SAMN31087432, SAMN31087431 and SAMN31087430 respectively.

CONCLUSIONS

WHO validated polymorphisms in the k13-propeller gene previously reported to be associated with ACT resistance were not detected in the P. falciparum isolates from Kisii County, Kenya. However, some previously reported un-validated k13 resistant single nucleotide polymorphisms were reported in this study but with limited occurrences. The study has also reported new SNPs. More studies need to be carried out in the entire country to understand the association of reported mutations if any, with ACT resistance.

A whole-genome scan for Artemisinin cytotoxicity reveals a novel therapy for human brain tumors

The natural compound Artemisinin is the most widely used antimalarial drug worldwide. Based on its cytotoxicity, it is also used for anticancer therapy. Artemisinin and its derivates are endoperoxides that damage proteins in eukaryotic cells; their definite mechanism of action and host cell targets, however, have remained largely elusive. Using yeast and haploid stem cell screening, we demonstrate that a single cellular pathway, namely porphyrin (heme) biosynthesis, is required for the cytotoxicity of Artemisinins. Genetic or pharmacological modulation of porphyrin production is sufficient to alter its cytotoxicity in eukaryotic cells. Using multiple model systems of human brain tumor development, such as cerebral glioblastoma organoids, and patient-derived tumor spheroids, we sensitize cancer cells to dihydroartemisinin using the clinically approved porphyrin enhancer and surgical fluorescence marker 5-aminolevulinic acid, 5-ALA. A combination treatment of Artemisinins and 5-ALA markedly and specifically killed brain tumor cells in all model systems tested, including orthotopic patient-derived xenografts in vivo. These data uncover the critical molecular pathway for Artemisinin cytotoxicity and a sensitization strategy to treat different brain tumors, including drug-resistant human glioblastomas.

Dihydroartemisinin-ursodeoxycholic acid conjugate is a potential treatment agent for inflammatory bowel disease

BACKGROUND

A novel artemisinin derivative, dihydroartemisinin-ursodeoxycholic acid conjugate (4), was found to exhibit strong immunosuppressive activity. Various methods were used to evaluate the immunosuppressive activity and mechanism of action of the compound to explore its potential applications.

METHODS

T cell proliferation, mixed lymphocyte reaction (MLR), and Th1/Th17 differentiation assays were used to evaluate the immunosuppressive activity of the compound. Differentially expressed genes from RNA sequencing were analysed with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, while enriched signalling pathways were further validated by western blotting (WB). In vivo efficacy was validated with delayed-type hypersensitivity (DTH) mouse models and dextran sodium sulphate (DSS)-induced inflammatory bowel disease (IBD) mouse model.

RESULTS

Compound 4 inhibited concanavalin A -induced mouse splenic T cell proliferation (IC₅₀ = 15 nM) and anti-CD3/CD28-induced human primary T cell proliferation (IC₅₀ = 30 nM) while also reducing the secretion of hIFN-γ. Compound 4 exhibited similar inhibitory activity in MLR assay. Compound 4 dose-dependently inhibited human Th1/Th17 differentiation. The KEGG pathway enrichment analysis indicated that the genes related to T cell activation signalling pathways PI3K-AKT, MAPK, and NF-κB were significantly enriched. WB confirmed that compound 4 inhibited the AKT/MAPK and NF-κB signalling pathways. Compound 4 dose-dependently inhibited ear and foot pad swelling in DTH mouse models. In the DSS-induced IBD mouse model, compound 4 significantly decreased the disease activity index and colon density, and inhibited splenomegaly of the mice.

CONCLUSION

The in vitro and in vivo results indicated that compound 4 has the potential to be developed into an anti-IBD drug.