Small-molecule histone methyltransferase inhibitors display rapid antimalarial activity against all blood stage forms in Plasmodium falciparum

Epigenetic regulation as a therapeutic target in the malaria parasite Plasmodium falciparum

Over the past thirty years, epigenetic regulation of gene expression has gained increasing interest as it was shown to be implicated in illnesses ranging from cancers to parasitic diseases. In the malaria parasite, epigenetics was shown to be involved in several key steps of the complex life cycle of Plasmodium, among which asexual development and sexual commitment, but also in major biological processes like immune evasion, response to environmental changes or DNA repair. Because epigenetics plays such paramount roles in the Plasmodium parasite, enzymes involved in these regulating pathways represent a reservoir of potential therapeutic targets. This review focuses on epigenetic regulatory processes and their effectors in the malaria parasite, as well as the inhibitors of epigenetic pathways and their potential as new anti-malarial drugs. Such types of drugs could be formidable tools that may contribute to malaria eradication in a context of widespread resistance to conventional anti-malarials.

Anti-babesial activity of a series of 6,7-dimethoxyquinazoline-2,4-diamines (DMQDAs)

Diminazene aceturate (DA), imidocarb dipropionate (ID), atovaquone (ATO), azithromycin (AZI), clindamycin, and quinine have been used to treat animal and human babesiosis for many years, despite their negative effects and rising indications of resistance. Thus, finding anti-babesial compounds that can either treat the infection or lower the dose of drugs given has been a primary objective. Quinazolines are one of the most important nitrogen heterocycles, with a wide range of pharmacological activities including analgesic, anti-inflammatory, sedative-hypnotic, anti-histaminic, anti-cancer, and anti-protozoan properties. The present study investigated the anti-babesial activities of twenty 6,7-dimethoxyquinazoline-2,4-diamines on Babesia spp. One candidate, 6,7-dimethoxy-N4-ethylisopropyl-N2-ethyl(pyridin-4-yl)quinazoline-2,4-diamine (SHG02), showed potent inhibition on Babesia gibsoni in vitro, as well as on B. microti and B. rodhaini in mice. Our findings indicate that the candidate compound SHG02 is promising for further development of anti-babesial drugs and provides a new structure to be explored for developing anti-Babesia therapeutics.

Epidrugs as Promising Tools to Eliminate Plasmodium falciparum Artemisinin-Resistant and Quiescent Parasites

The use of artemisinin and its derivatives has helped reduce the burden of malaria caused by Plasmodium falciparum. However, artemisinin-resistant parasites are able, in the presence of artemisinins, to stop their cell cycles. This quiescent state can alter the activity of artemisinin partner drugs leading to a secondary drug resistance and thus threatens malaria eradication strategies. Drugs targeting epigenetic mechanisms (namely epidrugs) are emerging as potential antimalarial drugs. Here, we set out to evaluate a selection of various epidrugs for their activity against quiescent parasites, to explore the possibility of using these compounds to counter artemisinin resistance. The 32 chosen epidrugs were first screened for their antiplasmodial activity and selectivity. We then demonstrated, thanks to the specific Quiescent-stage Survival Assay, that four epidrugs targeting both histone methylation or deacetylation as well as DNA methylation decrease the ability of artemisinin-resistant parasites to recover after artemisinin exposure. In the quest for novel antiplasmodial drugs with new modes of action, these results reinforce the therapeutic potential of epidrugs as antiplasmodial drugs especially in the context of artemisinin resistance.

G9a and Sirtuin6 epigenetically modulate host cholesterol accumulation to facilitate mycobacterial survival

Cholesterol derived from the host milieu forms a critical factor for mycobacterial pathogenesis. However, the molecular circuitry co-opted by Mycobacterium tuberculosis (Mtb) to accumulate cholesterol in host cells remains obscure. Here, we report that the coordinated action of WNT-responsive histone modifiers G9a (H3K9 methyltransferase) and SIRT6 (H3K9 deacetylase) orchestrate cholesterol build-up in in vitro and in vivo mouse models of Mtb infection. Mechanistically, G9a, along with SREBP2, drives the expression of cholesterol biosynthesis and uptake genes; while SIRT6 along with G9a represses the genes involved in cholesterol efflux. The accumulated cholesterol in Mtb infected macrophages promotes the expression of antioxidant genes leading to reduced oxidative stress, thereby supporting Mtb survival. In corroboration, loss-of-function of G9a in vitro and pharmacological inhibition in vivo; or utilization of BMDMs derived from Sirt6-/- mice or in vivo infection in haplo-insufficient Sirt6-/+ mice; hampered host cholesterol accumulation and restricted Mtb burden. These findings shed light on the novel roles of G9a and SIRT6 during Mtb infection and highlight the previously unknown contribution of host cholesterol in potentiating anti-oxidative responses for aiding Mtb survival.

MAPK-ERK-CREB signaling pathway upregulates Nav1.6 in oxaliplatin-induced neuropathic pain in the rat

The voltage-gated sodium channel subtype Nav1.6 is involved in the electrophysiological changes of primary sensory neurons that occur in oxaliplatin-induced neuropathic pain, but its regulatory mechanism remains unclear. In this study, Western blot, RT-qPCR, immunofluorescence staining, chromatin immunoprecipitation were used to prove the mechanism of MAPK-ERK-CREB signaling pathway participating in oxaliplatin-induced neuropathic pain by regulating Nav1.6. The results showed that p-Raf1 and p-ERK, key molecules in MAPK/ERK pathway, and Nav1.6 were significantly increased in DRGs of oxaliplatin-induced neuropathic pain rats. Inhibition of p-Raf1 and p-ERK respectively not only reduced the expression of Nav1.6 protein in DRGs of OXA rats, but also caused a decrease in Nav1.6 mRNA, which led us to further explore the transcription factor CREB regulated by MAPK/ERK pathway. Results showed that CREB was co-distributed with Nav1.6. Inhibition of CREB resulted in decreased mRNA and protein expression of Nav1.6, and alleviated oxaliplatin-induced neuropathic pain. A chromatin immunoprecipitation experiment proved that OXA caused p-CREB to directly bind to the promoter region of Scn8A, which is the encoding gene for Nav1.6, and promote the transcription of Scn8A. In summary, in this study, we found that oxaliplatin can activate the MAPK/ERK pathway, which promotes the expression and activation of CREB and leads to an increase in Scn8A transcription, and then leads to an increase in Nav1.6 protein expression to enhance neuronal excitability and cause pain. This study provides an experimental basis for the molecular mechanism of sodium channel regulation in oxaliplatin-induced neuropathic pain.

Histone modification analysis reveals common regulators of gene expression in liver and blood stage merozoites of Plasmodium parasites

Gene expression in malaria parasites is subject to various layers of regulation, including histone post-translational modifications (PTMs). Gene regulatory mechanisms have been extensively studied during the main developmental stages of Plasmodium parasites inside erythrocytes, from the ring stage following invasion to the schizont stage leading up to egress. However, gene regulation in merozoites that mediate the transition from one host cell to the next is an understudied area of parasite biology. Here, we sought to characterize gene expression and the corresponding histone PTM landscape during this stage of the parasite lifecycle through RNA-seq and ChIP-seq on P. falciparum blood stage schizonts, merozoites, and rings, as well as P. berghei liver stage merozoites. In both hepatic and erythrocytic merozoites, we identified a subset of genes with a unique histone PTM profile characterized by a region of H3K4me3 depletion in their promoter. These genes were upregulated in hepatic and erythrocytic merozoites and rings, had roles in protein export, translation, and host cell remodeling, and shared a DNA motif. These results indicate that similar regulatory mechanisms may underlie merozoite formation in the liver and blood stages. We also observed that H3K4me2 was deposited in gene bodies of gene families encoding variant surface antigens in erythrocytic merozoites, which may facilitate switching of gene expression between different members of these families. Finally, H3K18me and H2K27me were uncoupled from gene expression and were enriched around the centromeres in erythrocytic schizonts and merozoites, suggesting potential roles in the maintenance of chromosomal organization during schizogony. Together, our results demonstrate that extensive changes in gene expression and histone landscape occur during the schizont-to-ring transition to facilitate productive erythrocyte infection. The dynamic remodeling of the transcriptional program in hepatic and erythrocytic merozoites makes this stage attractive as a target for novel anti-malarial drugs that may have activity against both the liver and blood stages.

Isoliensinine from Cissampelos pariera rhizomes exhibits potential gametocytocidal and anti-malarial activities against Plasmodium falciparum clinical isolates

BACKGROUND

The unmet demand for effective malaria transmission-blocking agents targeting the transmissible stages of Plasmodium necessitates intensive discovery efforts. In this study, a bioactive bisbenzylisoquinoline (BBIQ), isoliensinine, from Cissampelos pariera (Menispermaceae) rhizomes was identified and characterized for its anti-malarial activity.

METHODS

Malaria SYBR Green I fluorescence assay was performed to evaluate the in vitro antimalarial activity against D6, Dd2, and F32-ART5 clones, and immediate ex vivo (IEV) susceptibility for 10 freshly collected P. falciparum isolates. To determine the speed- and stage-of-action of isoliensinine, an IC₅₀ speed assay and morphological analyses were performed using synchronized Dd2 asexuals. Gametocytocidal activity against two culture-adapted gametocyte-producing clinical isolates was determined using microscopy readouts, with possible molecular targets and their binding affinities deduced in silico.

RESULTS

Isoliensinine displayed a potent in vitro gametocytocidal activity at mean IC₅₀^gam values ranging between 0.41 and 0.69 µM for Plasmodium falciparum clinical isolates. The BBIQ compound also inhibited asexual replication at mean IC₅₀^Asexual of 2.17 µM, 2.22 µM, and 2.39 µM for D6, Dd2 and F32-ART5 respectively, targeting the late-trophozoite to schizont transition. Further characterization demonstrated a considerable immediate ex vivo potency against human clinical isolates at a geometric mean IC₅₀^IEV = 1.433 µM (95% CI 0.917-2.242). In silico analyses postulated a probable anti-malarial mechanism of action by high binding affinities for four mitotic division protein kinases; Pfnek1, Pfmap2, Pfclk1, and Pfclk4. Additionally, isoliensinine was predicted to possess an optimal pharmacokinetics profile and drug-likeness properties.

CONCLUSION

These findings highlight considerable grounds for further exploration of isoliensinine as an amenable scaffold for malaria transmission-blocking chemistry and target validation.

Babesia duncani multi-omics identifies virulence factors and drug targets

Babesiosis is a malaria-like disease in humans and animals that is caused by Babesia species, which are tick-transmitted apicomplexan pathogens. Babesia duncani causes severe to lethal infection in humans, but despite the risk that this parasite poses as an emerging pathogen, little is known about its biology, metabolic requirements or pathogenesis. Unlike other apicomplexan parasites that infect red blood cells, B. duncani can be continuously cultured in vitro in human erythrocytes and can infect mice resulting in fulminant babesiosis and death. We report comprehensive, detailed molecular, genomic, transcriptomic and epigenetic analyses to gain insights into the biology of B. duncani. We completed the assembly, 3D structure and annotation of its nuclear genome, and analysed its transcriptomic and epigenetics profiles during its asexual life cycle stages in human erythrocytes. We used RNA-seq data to produce an atlas of parasite metabolism during its intraerythrocytic life cycle. Characterization of the B. duncani genome, epigenome and transcriptome identified classes of candidate virulence factors, antigens for diagnosis of active infection and several attractive drug targets. Furthermore, metabolic reconstitutions from genome annotation and in vitro efficacy studies identified antifolates, pyrimethamine and WR-99210 as potent inhibitors of B. duncani to establish a pipeline of small molecules that could be developed as effective therapies for the treatment of human babesiosis.

Lysine Methyltransferase EhPKMT2 Is Involved in the In Vitro Virulence of Entamoeba histolytica

Lysine methylation, a posttranslational modification catalyzed by protein lysine methyltransferases (PKMTs), is involved in epigenetics and several signaling pathways, including cell growth, cell migration and stress response, which in turn may participate in virulence of protozoa parasites. Entamoeba histolytica, the etiologic agent of human amebiasis, has four PKMTs (EhPKMT1 to EhPKMT4), but their role in parasite biology is unknown. Here, to obtain insight into the role of EhPKMT2, we analyzed its expression level and localization in trophozoites subjected to heat shock and during phagocytosis, two events that are related to amoeba virulence. Moreover, the effect of EhPKMT2 knockdown on those activities and on cell growth, migration and cytopathic effect was investigated. The results indicate that this enzyme participates in all these cellular events, suggesting that it could be a potential target for development of novel therapeutic strategies against amebiasis.

New Transmission-Selective Antimalarial Agents through Hit-to-Lead Optimization of 2-([1,1'-Biphenyl]-4-carboxamido)benzoic Acid Derivatives

Malaria elimination requires multipronged approaches, including the application of antimalarial drugs able to block human-to-mosquito transmission of malaria parasites. The transmissible gametocytes of Plasmodium falciparum seem to be highly sensitive towards epidrugs, particularly those targeting demethylation of histone post-translational marks. Here, we report exploration of compounds from a chemical library generated during hit-to-lead optimization of inhibitors of the human histone lysine demethylase, KDM4B. Derivatives of 2-([1,1'-biphenyl]-4-carboxamido) benzoic acid, around either the amide or a sulfonamide linker backbone (2-(arylcarboxamido)benzoic acid, 2-carboxamide (arylsulfonamido)benzoic acid and N-(2-(1H-tetrazol-5-yl)phenyl)-arylcarboxamide), showed potent activity towards late-stage gametocytes (stage IV/V) of P. falciparum, with the most potent compound reaching single digit nanomolar activity. Structure-activity relationship trends were evident and frontrunner compounds also displayed microsomal stability and favourable solubility profiles. Simplified synthetic routes support further derivatization of these compounds for further development of these series as malaria transmission-blocking agents.

Epigenetic and Epitranscriptomic Gene Regulation in Plasmodium falciparum and How We Can Use It against Malaria

Malaria, caused by Plasmodium parasites, is still one of the biggest global health challenges. P. falciparum is the deadliest species to humans. In this review, we discuss how this parasite develops and adapts to the complex and heterogenous environments of its two hosts thanks to varied chromatin-associated and epigenetic mechanisms. First, one small family of transcription factors, the ApiAP2 proteins, functions as master regulators of spatio-temporal patterns of gene expression through the parasite life cycle. In addition, chromatin plasticity determines variable parasite cell phenotypes that link to parasite growth, virulence and transmission, enabling parasite adaptation within host conditions. In recent years, epitranscriptomics is emerging as a new regulatory layer of gene expression. We present evidence of the variety of tRNA and mRNA modifications that are being characterized in Plasmodium spp., and the dynamic changes in their abundance during parasite development and cell fate. We end up outlining that new biological systems, like the mosquito model, to decipher the unknowns about epigenetic mechanisms in vivo; and novel methodologies, to study the function of RNA modifications; are needed to discover the Achilles heel of the parasite. With this new knowledge, future strategies manipulating the epigenetics and epitranscriptomic machinery of the parasite have the potential of providing new weapons against malaria.

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.

Drug Repurposing of Quisinostat to Discover Novel Plasmodium falciparum HDAC1 Inhibitors with Enhanced Triple-Stage Antimalarial Activity and Improved Safety

Our previous work found that the clinical histone deacetylase (HDAC) inhibitor quisinostat exhibited a significant antimalarial effect but with severe toxicity. In this work, 35 novel derivatives were designed and synthesized based on quisinostat as the lead compound, and their in vitro antimalarial activities and cytotoxicities were systematically evaluated. Among them, JX35 showed potent inhibition against both wild-type and multidrug-resistant parasite strains and displayed a significant in vivo killing effect against all life cycles of parasites, including the blood stage, liver stage, and gametocyte stage, indicating its potential for the simultaneous treatment, chemoprevention, and blockage of malaria transmission. Compared with quisinostat, JX35 exhibited stronger antimalarial efficacy, more adequate safety, and good pharmacokinetic properties. Additionally, mechanistic studies via molecular docking studies, induced PfHDAC1/2 knockdown assays, and PfHDAC1 enzyme inhibition assays jointly indicated that the antimalarial target of JX35 was PfHDAC1. In summary, we discovered the promising candidate PfHDAC1 inhibitor JX35, which showed stronger triple-stage antimalarial effects and lower toxicity than quisinostat.

Malaria Parasite Stress Tolerance Is Regulated by DNMT2-Mediated tRNA Cytosine Methylation

Malaria parasites need to cope with changing environmental conditions that require strong countermeasures to ensure pathogen survival in the human and mosquito hosts. The molecular mechanisms that protect Plasmodium falciparum homeostasis during the complex life cycle remain unknown. Here, we identify cytosine methylation of tRNA^{Asp (GTC)} as being critical to maintain stable protein synthesis. Using conditional knockout (KO) of a member of the DNA methyltransferase family, called Pf-DNMT2, RNA bisulfite sequencing demonstrated the selective cytosine methylation of this enzyme of tRNA^{Asp (GTC)} at position C38. Although no growth defect on parasite proliferation was observed, Pf-DNMT2KO parasites showed a selective downregulation of proteins with a GAC codon bias. This resulted in a significant shift in parasite metabolism, priming KO parasites for being more sensitive to various types of stress. Importantly, nutritional stress made tRNA^{Asp (GTC)} sensitive to cleavage by an unknown nuclease and increased gametocyte production (>6-fold). Our study uncovers an epitranscriptomic mechanism that safeguards protein translation and homeostasis of sexual commitment in malaria parasites. IMPORTANCE P. falciparum is the most virulent malaria parasite species, accounting for the majority of the disease mortality and morbidity. Understanding how this pathogen is able to adapt to different cellular and environmental stressors during its complex life cycle is crucial in order to develop new strategies to tackle the disease. In this study, we identified the writer of a specific tRNA cytosine methylation site as a new layer of epitranscriptomic regulation in malaria parasites that regulates the translation of a subset of parasite proteins (>400) involved in different metabolic pathways. Our findings give insight into a novel molecular mechanism that regulates P. falciparum response to drug treatment and sexual commitment.

Histone deacetylase inhibitor AR-42 and achiral analogues kill malaria parasites in vitro and in mice

Malaria is caused by infection with Plasmodium parasites and results in significant health and economic impacts. Malaria eradication is hampered by parasite resistance to current drugs and the lack of a widely effective vaccine. Compounds that target epigenetic regulatory proteins, such as histone deacetylases (HDACs), may lead to new therapeutic agents with a different mechanism of action, thereby avoiding resistance mechanisms to current antimalarial drugs. The anticancer HDAC inhibitor AR-42, as its racemate (rac-AR-42), and 36 analogues were investigated for in vitro activity against P. falciparum. Rac-AR-42 and selected compounds were assessed for cytotoxicity against human cells, histone hyperacetylation, human HDAC1 inhibition and oral activity in a murine malaria model. Rac-AR-42 was tested for ex vivo asexual and in vitro exoerythrocytic stage activity against P. berghei murine malaria parasites. Rac-AR-42 and 13 achiral analogues were potent inhibitors of asexual intraerythrocytic stage P. falciparum 3D7 growth in vitro (IC₅₀ 5–50 nM), with four of these compounds having >50-fold selectivity for P. falciparum versus human cells (selectivity index 56–118). Rac-AR-42 induced in situ hyperacetylation of P. falciparum histone H4, consistent with PfHDAC(s) inhibition. Furthermore, rac-AR-42 potently inhibited P. berghei infected erythrocyte growth ex vivo (IC₅₀ 40 nM) and P. berghei exoerythrocytic forms in hepatocytes (IC₅₀ 1 nM). Oral administration of rac-AR-42 and two achiral analogues inhibited P. berghei growth in mice, with rac-AR-42 (50 mg/kg/day single dose for four days) curing all infections. These findings demonstrate curative properties for HDAC inhibitors in the oral treatment of experimental mouse malaria.

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HDAC inhibitors rac-AR-42 and 13 analogues inhibit P. falciparum growth in vitro.

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Rac-AR-42 inhibits P. berghei exoerythrocytic forms in hepatocytes (IC₅₀ 1 nM).

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Rac-AR-42 causes in situ hyperacetylation of P. falciparum histone H4.

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Rac-AR-42 cures P. berghei infected mice with oral dosing.

Raf1 interacts with OIP5 to participate in oxaliplatin-induced neuropathic pain

AIMS

Oxaliplatin is an effective anti-cancer platinum-based chemotherapy drug which can cause severe chronic neuropathy, but the molecular mechanism underlying this adverse effect is still unclear. Opa interacting protein 5 (OIP5) is a member of the cancer/testis antigen (CTA) family and is involved in a variety of cancers. Studies have shown that Raf1, which is a serine/threonine-protein kinase, can directly combine with OIP5 to promote its expression. Whether Raf1 and OIP5 can participate in oxaliplatin-induced neuropathic pain has not been reported.

MAIN METHODS

In this study, the oxaliplatin-induced neuropathic pain model was prepared by intraperitoneal injection of oxaliplatin. OIP5 and Raf1 were knocked down by intrathecal injection of siRNA against Raf1 and OIP5 (siRaf1, siOIP5). Von Frey fiber and acetone were used to detect pain behavior, and western blot was used to detect the protein expression changes of OIP5 and Raf1 in the dorsal root ganglion (DRG).

KEY FINDINGS

The expression levels of p-Raf1 and OIP5 were increased in DRGs of oxaliplatin-induced neuropathic pain rats. Intrathecal administration of siOIP5 to inhibit the expression of OIP5 not only effectively alleviated oxaliplatin-induced mechanical allodynia and cold hyperalgesia, but also decreased the protein expression of Raf1. Intrathecal administration of siRaf1 inhibited the expression of OIP5 and attenuated oxaliplatin-induced neuropathic pain.

SIGNIFICANCE

This study confirmed that Raf1 interacts with OIP5 to participate in oxaliplatin-induced neuropathic pain. The restricted expression of OIP5 in normal tissues may make it an ideal drug target for the treatment of oxaliplatin-induced neuropathic pain.

Procainamide-SAHA Fused Inhibitors of hHDAC6 Tackle Multidrug-Resistant Malaria Parasites

Epigenetic post-translational modifications are essential for human malaria parasite survival and progression through its life cycle. Here, we present new functionalized suberoylanilide hydroxamic acid (SAHA) derivatives that chemically combine the pan-histone deacetylase inhibitor SAHA with the DNA methyltransferase inhibitor procainamide. A three- or four-step chemical synthesis was designed starting from cheap raw materials. Compared to the single drugs, the combined molecules showed a superior activity in Plasmodium and a potent inhibition against human HDAC6, exerting no cytotoxicity in human cell lines. These new compounds are fully active in multidrug-resistant Plasmodium falciparum Cambodian isolates. They target transmission of the parasite by inducing irreversible morphological changes in gametocytes and inhibiting exflagellation. The compounds are slow-acting and have an additive antimalarial effect in combination with fast-acting epidrugs and dihydroartemisinin. The lead compound decreases parasitemia in mice in a severe malaria model. Taken together, this novel fused molecule offers an affordable alternative to current failing antimalarial therapy.

Designing the Next Generation of Vaccines: Relevance for Future Pandemics

The development of vaccines is one of the greatest medical interventions in the history of global infectious diseases and has contributed to the annual saving of at least 2 to 3 million lives worldwide. However, many diseases are not preventable through currently available vaccines, and the potential of modulating the immune response during vaccination has not been fully exploited. The first golden age of vaccines was based on the germ theory and the use of live, attenuated, inactivated pathogens or toxins. New strategies and formulations (e.g., adjuvants) with an immunomodulatory capacity to enhance the protective qualities and duration of vaccines have been incompletely exploited. These strategies can prevent disease and improve protection against infectious diseases, modulate the course of some noncommunicable diseases, and increase the immune responses of patients at a high risk of infection, such as the elderly or immunocompromised patients. In this minireview, we focus on how metabolic and epigenetic modulators can amplify and enhance the function of immunity in a given vaccine. We propose the term “amplifier” for such additives, and we pose that future vaccines will have three components: antigen, adjuvant, and amplifier.

Targeting EHMT2/ G9a for cancer therapy: Progress and perspective

Euchromatic histone lysine methyltransferase-2, also known as G9a, is a ubiquitously expressed SET domain-containing histone lysine methyltransferase linked with both facultative and constitutive heterochromatin formation and transcriptional repression. It is an essential developmental gene and reported to play role in embryonic development, establishment of proviral silencing in ES cells, tumor cell growth, metastasis, T-cell immune response, cocaine induced neural plasticity and cognition and adaptive behavior. It is mainly responsible for carrying out mono, di and tri methylation of histone H3K9 in euchromatin. G9a levels are elevated in many cancers and its selective inhibition is known to reduce the cell growth and induce autophagy, apoptosis and senescence. We carried out a thorough search of online literature databases including Pubmed, Scopus, Journal websites, Clinical trials etc to gather the maximum possible information related to the G9a. The main messages from the cited papers are presented in a systematic manner. Chemical structures were drawn by Chemdraw software. In this review, we shed light on current understanding of structure and biological activity of G9a, the molecular events directing its targeting to genomic regions and its post-translational modification. Finally, we discuss the current strategies to target G9a in different cancers and evaluate the available compounds and agents used to inhibit G9a functions. The review provides the present status and future directions of research in targeting G9a and provides the basis to persuade the development of novel strategies to target G9a -related effects in cancer cells.

Protein Modification Characteristics of the Malaria Parasite Plasmodium falciparum and the Infected Erythrocytes

Malaria elimination is still pending on the development of novel tools that rely on a deep understanding of parasite biology. Proteins of all living cells undergo myriad posttranslational modifications (PTMs) that are critical to multifarious life processes. An extensive proteome-wide dissection revealed a fine PTM map of most proteins in both Plasmodium falciparum, the causative agent of severe malaria, and the infected red blood cells. More than two-thirds of proteins of the parasite and its host cell underwent extensive and dynamic modification throughout the erythrocytic developmental stage. PTMs critically modulate the virulence factors involved in the host-parasite interaction and pathogenesis. Furthermore, P. falciparum stabilized the supporting proteins of erythrocyte origin by selective demodification. Collectively, our multiple omic analyses, apart from having furthered a deep understanding of the systems biology of P. falciparum and malaria pathogenesis, provide a valuable resource for mining new antimalarial targets.

Down-Regulation of NOX4 Expression in Dorsal Horn of Spinal Cord Could Alleviate Cancer-Induced Bone Pain in Rats by Reducing Oxidative Stress Response

Introduction

Cancer-induced bone pain (CIBP) is very common in patients with advanced cancer. Recent studies have shown that reactive oxygen species (ROS) can sense and regulate pain response process through spinal cord mechanism, and play a role in CIBP. NADPH oxidase (NOX) is a group of protease complexes that produce ROS. In the current study, we investigated the expression of NOX4 in the spinal dorsal horn of rats with CIBP and its related role and molecular mechanism.

Materials and Methods

A rat CIBP model was established by injecting Walker-256 cells into the tibia medullary cavity, and the expression of NOX4 in spinal dorsal horn was down-regulated by injecting lentivirus into spinal cord. RT-PCR, Western blot and immunofluorescence staining were used to detect the expression of NOX4 in CIBP rats, cell localization and its effect on CIBP rats, and the effect of down-regulating the expression of NOX4 on the expression of H₂O₂, nitric oxide synthase nNO, antioxidant enzyme SOD, and the activity of neuro-receptor in spinal dorsal horn of rats.

Results

In rats with CIBP, the expression of NOX4 was significantly increased, and immunofluorescence showed that NOX4 was mainly expressed in microglia in the dorsal horn of spinal cord. Down-regulating the expression of NOX4 in rats can reduce the level of H₂O₂ and nNO in dorsal horn tissue, and increase the expression of SOD to reduce the oxidative stress response. At the same time, down-regulating NOX4 can reduce the sensitivity of spinal cord and relieve the pain of bone cancer by inhibiting the expression of NMDAR and GABAA-γ2 in dorsal horn tissue.

Conclusion

NOX4 is a promising therapeutic target in CIBP, and down-regulation of NOX4 expression can alleviate CIBP in rats by reducing oxidative stress and weakening spinal cord sensitization.

A Histone Methyltransferase Inhibitor Can Reverse Epigenetically Acquired Drug Resistance in the Malaria Parasite Plasmodium falciparum

Malaria parasites invade and replicate within red blood cells (RBCs), extensively modifying their structure and gaining access to the extracellular environment by placing the plasmodial surface anion channel (PSAC) into the RBC membrane. Expression of members of the cytoadherence linked antigen gene 3 (clag3) family is required for PSAC activity, a process that is regulated epigenetically. PSAC is a well-established route of uptake for large, hydrophilic antimalarial compounds, and parasites can acquire resistance by silencing clag3 gene expression, thereby reducing drug uptake. We found that exposure to sub-IC₅₀ concentrations of the histone methyltransferase inhibitor chaetocin caused substantial changes in both clag3 gene expression and RBC permeability, and reversed acquired resistance to the antimalarial compound blasticidin S that is transported through PSACs. Chaetocin treatment also altered progression of parasites through their replicative cycle, presumably by changing their ability to modify chromatin appropriately to enable DNA replication. These results indicate that targeting histone modifiers could represent a novel tool for reversing epigenetically acquired drug resistance in P. falciparum.

Disruption of the Plasmodium falciparum Life Cycle through Transcriptional Reprogramming by Inhibitors of Jumonji Demethylases

Little is known about the role of the three Jumonji C (JmjC) enzymes in Plasmodium falciparum (Pf). Here, we show that JIB-04 and other established inhibitors of mammalian JmjC histone demethylases kill asexual blood stage parasites and are even more potent at blocking gametocyte development and gamete formation. In late stage parasites, JIB-04 increased levels of trimethylated lysine residues on histones, suggesting the inhibition of P. falciparum Jumonji demethylase activity. These epigenetic defects coincide with deregulation of invasion, cell motor, and sexual development gene programs, including gene targets coregulated by the PfAP2-I transcription factor and chromatin-binding factor, PfBDP1. Mechanistically, we demonstrate that PfJmj3 converts 2-oxoglutarate to succinate in an iron-dependent manner consistent with mammalian Jumonji enzymes, and this catalytic activity is inhibited by JIB-04 and other Jumonji inhibitors. Our pharmacological studies of Jumonji activity in the malaria parasite provide evidence that inhibition of these enzymatic activities is detrimental to the parasite.

Discovery of a new predominant cytosine DNA modification that is linked to gene expression in malaria parasites

DNA cytosine modifications are key epigenetic regulators of cellular processes in mammalian cells, with their misregulation leading to varied disease states. In the human malaria parasite Plasmodium falciparum, a unicellular eukaryotic pathogen, little is known about the predominant cytosine modifications, cytosine methylation (5mC) and hydroxymethylation (5hmC). Here, we report the first identification of a hydroxymethylcytosine-like (5hmC-like) modification in P. falciparum asexual blood stages using a suite of biochemical methods. In contrast to mammalian cells, we report 5hmC-like levels in the P. falciparum genome of 0.2–0.4%, which are significantly higher than the methylated cytosine (mC) levels of 0.01–0.05%. Immunoprecipitation of hydroxymethylated DNA followed by next generation sequencing (hmeDIP-seq) revealed that 5hmC-like modifications are enriched in gene bodies with minimal dynamic changes during asexual development. Moreover, levels of the 5hmC-like base in gene bodies positively correlated to transcript levels, with more than 2000 genes stably marked with this modification throughout asexual development. Our work highlights the existence of a new predominant cytosine DNA modification pathway in P. falciparum and opens up exciting avenues for gene regulation research and the development of antimalarials.

Design, synthesis, and antiprotozoal evaluation of new 2,4-bis[(substituted-aminomethyl)phenyl]quinoline, 1,3-bis[(substituted-aminomethyl)phenyl]isoquinoline and 2,4-bis[(substituted-aminomethyl)phenyl]quinazoline derivatives

A series of new 2,4-bis[(substituted-aminomethyl)phenyl]quinoline, 1,3-bis[(substituted-aminomethyl)phenyl]isoquinoline, and 2,4-bis[(substituted-aminomethyl)phenyl]quinazoline derivatives was designed, synthesised, and evaluated in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani, and Trypanosoma brucei brucei). Biological results showed antiprotozoal activity with IC₅₀ values in the µM range. In addition, the in vitro cytotoxicity of these original molecules was assessed with human HepG2 cells. The quinoline 1c was identified as the most potent antimalarial candidate with a ratio of cytotoxic to antiparasitic activities of 97 against the P. falciparum CQ-sensitive strain 3D7. The quinazoline 3h was also identified as the most potent trypanosomal candidate with a selectivity index (SI) of 43 on T. brucei brucei strain. Moreover, as the telomeres of the parasites P. falciparum and Trypanosoma are possible targets of this kind of nitrogen heterocyclic compounds, we have also investigated stabilisation of the Plasmodium and Trypanosoma telomeric G-quadruplexes by our best compounds through FRET melting assays.

Activity-based protein profiling: Recent advances in medicinal chemistry

Activity-based protein profiling (ABPP) has become an emerging chemical proteomic approach to illustrate the interaction mechanisms between compounds and proteins. This approach has combined organic synthesis, biochemistry, cell biology, biophysics and bioinformatics to accelerate the process of drug discovery in target identification and validation, as well as in the stage of lead discovery and optimization. This review will summarize new developments and applications of ABPP in medicinal chemistry. Here, we mainly described the design principles of activity-base probes (ABPs) and general workflows of ABPP approach. Moreover, we discussed various basic and advanced ABPP strategies and their applications in medicinal chemistry, including competitive and comparative ABPP, two-step ABPP, fluorescence polarization ABPP (FluoPol-ABPP) and ABPs for visualization. In conclusion, this review will give a general overview of the applications of ABPP as a powerful and efficient technique in medicinal chemistry.

Epigenetic inhibitors target multiple stages of Plasmodium falciparum parasites

The epigenome of the malaria parasite, Plasmodium falciparum, is associated with regulation of various essential processes in the parasite including control of proliferation during asexual development as well as control of sexual differentiation. The unusual nature of the epigenome has prompted investigations into the potential to target epigenetic modulators with novel chemotypes. Here, we explored the diversity within a library of 95 compounds, active against various epigenetic modifiers in cancerous cells, for activity against multiple stages of P. falciparum development. We show that P. falciparum is differentially susceptible to epigenetic perturbation during both asexual and sexual development, with early stage gametocytes particularly sensitive to epi-drugs targeting both histone and non-histone epigenetic modifiers. Moreover, 5 compounds targeting histone acetylation and methylation show potent multistage activity against asexual parasites, early and late stage gametocytes, with transmission-blocking potential. Overall, these results warrant further examination of the potential antimalarial properties of these hit compounds.

Subtelomeric Transcription and its Regulation

The subtelomeres, highly heterogeneous repeated sequences neighboring telomeres, are transcribed into coding and noncoding RNAs in a variety of organisms. Telomereproximal subtelomeric regions produce non-coding transcripts i.e., ARRET, αARRET, subTERRA, and TERRA, which function in telomere maintenance. The role and molecular mechanisms of the majority of subtelomeric transcripts remain unknown. This review depicts the current knowledge and puts into perspective the results obtained in different models from yeasts to humans.

The chromatin bound proteome of the human malaria parasite

Proteins interacting with DNA are fundamental for mediating processes such as gene expression, DNA replication and maintenance of genome integrity. Accumulating evidence suggests that the chromatin of apicomplexan parasites, such as Plasmodium falciparum, is highly organized, and this structure provides an epigenetic mechanism for transcriptional regulation. To investigate how parasite chromatin structure is being regulated, we undertook comparative genomics analysis using 12 distinct eukaryotic genomes. We identified conserved and parasite-specific chromatin-associated domains (CADs) and proteins (CAPs). We then used the chromatin enrichment for proteomics (ChEP) approach to experimentally capture CAPs in P. falciparum. A topological scoring analysis of the proteomics dataset revealed stage-specific enrichments of CADs and CAPs. Finally, we characterized, two candidate CAPs: a conserved homologue of the structural maintenance of chromosome 3 protein and a homologue of the crowded-like nuclei protein, a plant-like protein functionally analogous to animal nuclear lamina proteins. Collectively, our results provide a comprehensive overview of CAPs in apicomplexans, and contribute to our understanding of the complex molecular components regulating chromatin structure and genome architecture in these deadly parasites.

DNA Methylation Bisubstrate Inhibitors Are Fast-Acting Drugs Active against Artemisinin-Resistant Plasmodium falciparum Parasites

Malaria is the deadliest parasitic disease affecting over 200 million people worldwide. The increasing number of treatment failures due to multi-drug-resistant parasites in South-East Asia hinders the efforts for elimination. It is thus urgent to develop new antimalarials to contain these resistant parasites. Based on a previous report showing the presence of DNA methylation in Plasmodium, we generated new types of DNA methylation inhibitors against malaria parasites. The quinoline-quinazoline-based inhibitors kill parasites, including artemisinin-resistant field isolates adapted to culture, in the low nanomolar range. The compounds target all stages of the asexual cycle, including early rings, during a 6 h treatment period; they reduce DNA methylation in the parasite and show in vivo activity at 10 mg/kg. These potent inhibitors are a new starting point to develop fast-acting antimalarials that could be used in combination with artemisinins.

Modifications of histones in parasites as drug targets

Post-translational modifications of histones and histone modifying enzymes play important roles in gene regulations and other physiological processes in parasites. Inhibitors of such modifying enzymes could be useful as novel therapeutics against parasitic diseases or as chemical probes for investigation of epigenetics. Development of parasitic histone modulators has got rapid expansion in the last few years. A number of highly potent and selective compounds have been reported, together with extensive preclinical studies of their biological activity. Some of these compounds have been widely used in humans targeting cancer and are found non-toxic. This review summarizes the antiparasitic activities of histone and histone modifying enzymes inhibitors evaluated in last few years. As the current chemotherapy against parasites is still not satisfactory, therefore, such compounds represents good starting points for the discovery of effective antiparasitic drugs.

Plasmodium falciparum GCN5 acetyltransferase follows a novel proteolytic processing pathway that is essential for its function

The pathogenesis of human malarial parasite Plasmodium falciparum is interlinked with its timely control of gene expression during its complex life cycle. In this organism, gene expression is partially controlled through epigenetic mechanisms, the regulation of which is, hence, of paramount importance to the parasite. The P. falciparum (Pf)-GCN5 histone acetyltransferase (HAT), an essential enzyme, acetylates histone 3 and regulates global gene expression in the parasite. Here, we show the existence of a novel proteolytic processing for PfGCN5 that is crucial for its activity in vivo We find that a cysteine protease-like enzyme is required for the processing of PfGCN5 protein. Immunofluorescence and immuno-electron microscopy analysis suggest that the processing event occurs in the vicinity of the digestive vacuole of the parasite following its trafficking through the classical ER-Golgi secretory pathway, before it subsequently reaches the nucleus. Furthermore, blocking of PfGCN5 processing leads to the concomitant reduction of its occupancy at the gene promoters and a reduced H3K9 acetylation level at these promoters, highlighting the important correlation between the processing event and PfGCN5 activity. Altogether, our study reveals a unique processing event for a nuclear protein PfGCN5 with unforeseen role of a food vacuolar cysteine protease. This leads to a possibility of the development of new antimalarials against these targets.This article has an associated First Person interview with the first author of the paper.

Noise-induced loss of sensory hair cells is mediated by ROS/AMPKα pathway

The formation of reactive oxygen species (ROS) is a well-documented process in noise-induced hearing loss (NIHL). We have also previously shown that activation of 5' adenosine monophosphate (AMP)-activated protein kinase (AMPKα) at its catalytic residue T172 is one of the key reactions triggering noise-induced outer hair cell (OHC) death. In this study, we are addressing the link between ROS formation and activation of AMPKα in OHCs after noise exposure. In-vivo treatment of CBA/J mice with the antioxidant N-acetyl cysteine (NAC) reduced noise-induced ROS formation (as assessed by the relative levels of 4-hydroxynonenal and 3-nitrotyrosine) and activation of AMPKα in OHCs. Forskolin, an activator of adenylyl cyclase (AC) and an antioxidant, significantly increased cyclic adenosine monophosphate (cAMP) and decreased ROS formation and noise-induced activation of AMPKα. Consequently, treatment with forskolin attenuated noise-induced losses of OHCs and NIHL. In HEI-OC1 cells, H₂O₂-induced activation of AMPKα and cell death were inhibited by the application of forskolin. The sum of our data indicates that noise activates AMPKα in OHCs through formation of ROS and that noise-exposure-induced OHC death is mediated by a ROS/AMPKα-dependent pathway. Forskolin may serve as a potential compound for prevention of NIHL.

The G9a Histone Methyltransferase Inhibitor BIX-01294 Modulates Gene Expression during Plasmodium falciparum Gametocyte Development and Transmission

Transmission of the malaria parasite Plasmodium falciparum from the human to the mosquito is initiated by specialized sexual cells, the gametocytes. In the human, gametocytes are formed in response to stress signals and following uptake by a blood-feeding Anopheles mosquito initiate sexual reproduction. Gametocytes need to fine-tune their gene expression in order to develop inside the mosquito to continue life-cycle progression. Previously, we showed that post-translational histone acetylation controls gene expression during gametocyte development and transmission. However, the role of histone methylation remains poorly understood. We here use the histone G9a methyltransferase inhibitor BIX-01294 to investigate the role of histone methylation in regulating gene expression in gametocytes. In vitro assays demonstrated that BIX-01294 inhibits intraerythrocytic replication with a half maximal inhibitory concentration (IC₅₀) of 13.0 nM. Furthermore, BIX-01294 significantly impairs gametocyte maturation and reduces the formation of gametes and zygotes. Comparative transcriptomics between BIX-01294-treated and untreated immature, mature and activated gametocytes demonstrated greater than 1.5-fold deregulation of approximately 359 genes. The majority of these genes are transcriptionally downregulated in the activated gametocytes and could be assigned to transcription, translation, and signaling, indicating a contribution of histone methylations in mediating gametogenesis. Our combined data show that inhibitors of histone methylation may serve as a multi-stage antimalarial.

Disrupting the Code: Epigenetic Dysregulation of Lymphocyte Function during Infectious Disease and Lymphoma Development

Lymphocyte differentiation and identity are controlled by signals in the microenvironment that ultimately mediate gene expression in the nucleus. Although much focus has centered on the strategic and often unique roles transcription factors play within lymphocyte subsets, it is increasingly clear that another level of molecular regulation is crucial for regulating gene expression programs. In particular, epigenetic regulation is critical for appropriately regulated temporal and cell-type-specific gene expression during immune responses. As such, mutations in epigenetic modifiers are linked with lymphomagenesis. Furthermore, certain infections can remodel the epigenome in host cells, either through the microenvironment or by directly co-opting host epigenetic mechanisms, leading to inappropriate gene expression and/or ineffective cellular behavior. This review will focus on how histone modifications and DNA methylation, and the enzymes that regulate the epigenome, underpin lymphocyte differentiation and function in health and disease.

Transcriptome and histone epigenome of Plasmodium vivax salivary-gland sporozoites point to tight regulatory control and mechanisms for liver-stage differentiation in relapsing malaria

Plasmodium vivax is the key obstacle to malaria elimination in Asia and Latin America, largely attributed to its ability to form resilient hypnozoites (sleeper cells) in the host liver that escape treatment and cause relapsing infections. The decision to form hypnozoites is made early in the liver infection and may already be set in sporozoites prior to invasion. To better understand these early stages of infection, we undertook a comprehensive transcriptomic and histone epigenetic characterization of P. vivax sporozoites. Through comparisons with recently published proteomic data for the P. vivax sporozoite, our study found that although highly transcribed, transcripts associated with functions needed for early infection of the vertebrate host are not detectable as proteins and may be regulated through translational repression. We identified differential transcription between the sporozoite and published transcriptomes of asexual blood stages and mixed versus hypnozoite-enriched liver stages. These comparisons point to multiple layers of transcriptional, post-transcriptional and post-translational control that appear active in sporozoites and to a lesser extent hypnozoites, but are largely absent in replicating liver schizonts or mixed blood stages. We also characterised histone epigenetic modifications in the P. vivax sporozoite and explored their role in regulating transcription. Collectively, these data support the hypothesis that the sporozoite is a tightly programmed stage to infect the human host and identify mechanisms for hypnozoite formation that may be further explored in liver stage models.

The antimalarial screening landscape-looking beyond the asexual blood stage

In recent years, the research agenda to tackle global morbidity and mortality from malaria disease has shifted towards innovation, in the hope that efforts at the frontiers of scientific research may re-invigorate gains made towards eradication. Discovery of new antimalarial drugs with novel chemotypes or modes of action lie at the heart of these efforts. There is a particular interest in drug candidates that target stages of the malaria parasite lifecycle beyond the symptomatic asexual blood stages. This is especially important given the spectre of emerging drug resistance to all current frontline antimalarials. One approach gaining increased interest is the potential of designing novel drugs that target parasite passage from infected individual to feeding mosquito and back again. Action of such therapeutics is geared much more at the population level rather than just concerned with the infected individual. The search for novel drugs active against these stages has been helped by improvements to in vitro culture of transmission and pre-erythrocytic parasite lifecycle stages, robotic automation and high content imaging, methodologies that permit the high-throughput screening (HTS) of compound libraries for drug discovery. Here, we review recent advances in the antimalarial screening landscape, focussed on transmission blocking as a key aim for drug-treatment campaigns of the future.

Epigenetic Players of Chromatin Structure Regulation in Plasmodium falciparum

The protozoan parasite Plasmodium has evolved to survive in different hosts and environments. The diverse strategies of adaptation to different niches involve differential gene expression mechanisms mediated by chromatin plasticity that are poorly characterized in Plasmodium. The parasite employs a wide variety of regulatory mechanisms to complete their life cycle and survive inside hosts. Among them, epigenetic-mediated mechanisms have been implicated for controlling chromatin organization, gene regulation, morphological differentiation, and antigenic variation. The differential gene expression in parasite is largely dependent on the nature of the chromatin structure. The histone core methylation marks and methyl mark readers contribute to chromatin dynamics. Here, we review the recent developments on various epigenetic marks and its enzymes in the Plasmodium falciparum, how these marks play a key role in the regulation of transcriptional activity of variable genes and coordinate the differential gene expression. We also discuss the possible roles of these epigenetic marks in chromatin structure regulation and plasticity at various stages of its development.

Clipped histone H3 is integrated into nucleosomes of DNA replication genes in the human malaria parasite Plasmodium falciparum

Post-translational modifications of histone H3 N-terminal tails are key epigenetic regulators of virulence gene expression and sexual commitment in the human malaria parasite Plasmodium falciparum Here, we identify proteolytic clipping of the N-terminal tail of nucleosome-associated histone H3 at amino acid position 21 as a new chromatin modification. A cathepsin C-like proteolytic clipping activity is observed in nuclear parasite extracts. Notably, an ectopically expressed version of clipped histone H3, PfH3p-HA, is targeted to the nucleus and integrates into mononucleosomes. Furthermore, chromatin immunoprecipitation and next-generation sequencing analysis identified PfH3p-HA as being highly enriched in the upstream region of six genes that play a key role in DNA replication and repair: In these genes, PfH3p-HA demarcates a specific 1.5 kb chromatin island adjacent to the open reading frame. Our results indicate that, in P. falciparum, the process of histone clipping may precede chromatin integration hinting at preferential targeting of pre-assembled PfH3p-containing nucleosomes to specific genomic regions. The discovery of a protease-directed mode of chromatin organization in P. falciparum opens up new avenues to develop new anti-malarials.

Inhibition of EHMT1/2 rescues synaptic and cognitive functions for Alzheimer's disease

Epigenetic dysregulation, which leads to the alteration of gene expression in the brain, is suggested as one of the key pathophysiological bases of ageing and neurodegeneration. Here we found that, in the late-stage familial Alzheimer's disease (FAD) mouse model, repressive histone H3 dimethylation at lysine 9 (H3K9me2) and euchromatic histone methyltransferases EHMT1 and EHMT2 were significantly elevated in the prefrontal cortex, a key cognitive region affected in Alzheimer's disease. Elevated levels of H3K9me2 were also detected in the prefrontal cortex region of post-mortem tissues from human patients with Alzheimer's disease. Concomitantly, H3K9me2 at glutamate receptors was increased in prefrontal cortex of aged FAD mice, which was linked to the diminished transcription, expression and function of AMPA and NMDA receptors. Treatment of FAD mice with specific EHMT1/2 inhibitors reversed histone hyper-methylation and led to the recovery of glutamate receptor expression and excitatory synaptic function in prefrontal cortex and hippocampus. Chromatin immunoprecipitation-sequencing (ChIP-seq) data indicated that FAD mice exhibited genome-wide increase of H3K9me2 enrichment at genes involved in neuronal signalling (including glutamate receptors), which was reversed by EHMT1/2 inhibition. Moreover, the impaired recognition memory, working memory, and spatial memory in aged FAD mice were rescued by the treatment with EHMT1/2 inhibitors. These results suggest that disrupted epigenetic regulation of glutamate receptor transcription underlies the synaptic and cognitive deficits in Alzheimer's disease, and targeting histone methylation enzymes may represent a novel therapeutic strategy for this prevalent neurodegenerative disorder.

Evaluation of 4-Amino 2-Anilinoquinazolines against Plasmodium and Other Apicomplexan Parasites In Vitro and in a P. falciparum Humanized NOD-scid IL2Rγnull Mouse Model of Malaria

A series of 4-amino 2-anilinoquinazolines optimized for activity against the most lethal malaria parasite of humans, Plasmodium falciparum, was evaluated for activity against other human Plasmodium parasites and related apicomplexans that infect humans and animals. Four of the most promising compounds from the 4-amino 2-anilinoquinazoline series were equally as effective against the asexual blood stages of the zoonotic P. knowlesi, suggesting that they could also be effective against the closely related P. vivax, another important human pathogen. The 2-anilinoquinazoline compounds were also potent against an array of P. falciparum parasites resistant to clinically available antimalarial compounds, although slightly less so than against the drug-sensitive 3D7 parasite line. The apicomplexan parasites Toxoplasma gondii, Babesia bovis, and Cryptosporidium parvum were less sensitive to the 2-anilinoquinazoline series with a 50% effective concentration generally in the low micromolar range, suggesting that the yet to be discovered target of these compounds is absent or highly divergent in non-Plasmodium parasites. The 2-anilinoquinazoline compounds act as rapidly as chloroquine in vitro and when tested in rodents displayed a half-life that contributed to the compound's capacity to clear P. falciparum blood stages in a humanized mouse model. At a dose of 50 mg/kg of body weight, adverse effects to the humanized mice were noted, and evaluation against a panel of experimental high-risk off targets indicated some potential off-target activity. Further optimization of the 2-anilinoquinazoline antimalarial class will concentrate on improving in vivo efficacy and addressing adverse risk.

Fast-Acting Small Molecules Targeting Malarial Aspartyl Proteases, Plasmepsins, Inhibit Malaria Infection at Multiple Life Stages

The eradication of malaria remains challenging due to the complex life cycle of Plasmodium and the rapid emergence of drug-resistant forms of Plasmodium falciparum and Plasmodium vivax. New, effective, and inexpensive antimalarials against multiple life stages of the parasite are urgently needed to combat the spread of malaria. Here, we synthesized a set of novel hydroxyethylamines and investigated their activities in vitro and in vivo. All of the compounds tested had an inhibitory effect on the blood stage of P. falciparum at submicromolar concentrations, with the best showing 50% inhibitory concentrations (IC₅₀) of around 500 nM against drug-resistant P. falciparum parasites. These compounds showed inhibitory actions against plasmepsins, a family of malarial aspartyl proteases, and exhibited a marked killing effect on blood stage Plasmodium. In chloroquine-resistant Plasmodium berghei and P. berghei ANKA infected mouse models, treating mice with both compounds led to a significant decrease in blood parasite load. Importantly, two of the compounds displayed an inhibitory effect on the gametocyte stages (III-V) of P. falciparum in culture and the liver-stage infection of P. berghei both in in vitro and in vivo. Altogether, our findings suggest that fast-acting hydroxyethylamine-phthalimide analogs targeting multiple life stages of the parasite could be a valuable chemical lead for the development of novel antimalarial drugs.

Inhibition of Histone Methyltransferase G9a Attenuates Noise-Induced Cochlear Synaptopathy and Hearing Loss

Posttranslational modification of histones alters their interaction with DNA and nuclear proteins, influencing gene expression and cell fate. In this study, we investigated the effect of G9a (KMT1C, EHMT2), a major histone lysine methyltransferase encoded by the human EHMT2 gene and responsible for histone H3 lysine 9 dimethylation (H3K9me2) on noise-induced permanent hearing loss (NIHL) in adult CBA/J mice. The conditions of noise exposure used in this study led to losses of cochlear synapses and outer hair cells (OHCs) and permanent auditory threshold shifts. Inhibition of G9a with its specific inhibitor BIX 01294 or with siRNA significantly attenuated these pathological features. Treatment with BIX 01294 also prevented the noise-induced decrease of KCNQ4 immunolabeling in OHCs. Additionally, G9a was increased in cochlear cells, including both outer and inner sensory hair cells, some spiral ganglion neurons (SGNs), and marginal cells, 1 h after the completion of the noise exposure. Also subsequent to noise exposure, immunoreactivity for H3K9me2 appeared in some nuclei of OHCs following a high-to-low frequency gradient with more labeled OHCs in the 45-kHz than the 32-kHz region, as well as in the marginal cells and in some SGNs of the basal turn. These findings suggest that epigenetic modifications of H3K9me2 are involved in NIHL and that pharmacological targeting of G9a may offer a strategy for protection against cochlear synaptopathy and NIHL.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Transcriptomic analysis reveals reduced transcriptional activity in the malaria parasite Plasmodium cynomolgi during progression into dormancy

Relapses of Plasmodium dormant liver hypnozoites compromise malaria eradication efforts. New radical cure drugs are urgently needed, yet the vast gap in knowledge of hypnozoite biology impedes drug discovery. We previously unraveled the transcriptome of 6 to 7 day-old P. cynomolgi liver stages, highlighting pathways associated with hypnozoite dormancy (Voorberg-van der Wel et al., 2017). We now extend these findings by transcriptome profiling of 9 to 10 day-old liver stage parasites, thus revealing for the first time the maturation of the dormant stage over time. Although progression of dormancy leads to a 10-fold decrease in transcription and expression of only 840 genes, including genes associated with housekeeping functions, we show that pathways involved in quiescence, energy metabolism and maintenance of genome integrity remain the prevalent pathways active in mature hypnozoites.