Biology subjects

Gilson, P. R.

Publications and source records attributed to Gilson, P. R..

14 recordsLinked to original sources

bioRxiv2026

Plasmodium berghei is resistant to aryl amino acetamides that inhibit P. falciparum growth by targeting the phospholipid transfer protein PfSTART1.

In a previous screen for compounds that inhibit Plasmodium falciparum merozoite invasion of red blood cells, we identified the Medicines for Malaria Venture compound MMV006833. This compound inhibits PfSTART1, a protein implicated in the expansion of the nascent parasitophorous vacuole membrane following invasion, to accommodate the developing ring-stage parasite. Live-cell lattice light-sheet microscopy of invading merozoites revealed that mNeonGreen-tagged PfSTART1 is released from structures within the merozoite into the nascent parasitophorous vacuole approximately 109 seconds after invasion. Expansion microscopy of PfSTART1-HA merozoites further showed that these punctate PfSTART1-containing structures do not colocalise with known secretory organelles (rhoptries, micronemes and dense granules). Although analogues of MMV006833 are highly potent against P. falciparum, they were previously found to be ineffective against P. berghei parasites in the mouse malaria model. Here, we demonstrate that PbSTART1 is highly resistant to MMV006833 and its analogues when expressed in P. falciparum, indicating that structural differences between the orthologous proteins reduce inhibitor potency. The crystal structure of PfSTART1 in complex with WEHI-991 revealed the molecular basis for inhibition and provided a structural explanation for the reduced potency of this family of compounds against P. berghei. To sensitise P. berghei parasites to MMV006833 analogues, the parasites were engineered to express PfSTART1; however, these chimeric parasites remained insensitive to the compounds. This suggests that factors beyond target engagement, such as compound half-life or bioavailability, contribute to the lack of efficacy observed in the mouse malaria model.

microbiology↗

bioRxiv2026

MMV687794 blocks Plasmodium falciparum invasion of red blood cells by targeting a Surface-associated Lipid-Interacting Rhoptry Protein, PfSLIRP

Invasion of red blood cells (RBCs) by the human malaria parasite, Plasmodium falciparum, drives disease. During invasion, the parasite pushes its way into the RBC while wrapping the RBC membrane around itself to establish the parasitophorous vacuole, a stable niche within the RBC where the parasite grows. To better understand invasion, we investigated the mechanism of action of an invasion-inhibitory compound, MMV687794 (MMV794). Lattice light-sheet microscopy revealed that MMV794 blocks parasite entry by preventing parasitophorous vacuole formation. In vitro drug resistance selection of parasites with MMV794 found mutations to the /{beta} hydrolase, PF3D7_0403800, and engineering one of these mutations (C36W) into parasites by CRISPR/Cas9 recapitulated the resistance phenotype. Expansion microscopy demonstrated that this protein is expressed in schizonts, localising to the surface of rhoptries, which are specialised apical secretory organelles that function during invasion. Lipidomics and proteomics analyses of C36W parasites uncovered widespread changes to lipid composition/homeostasis and altered abundance of proteins involved in invasion, indicating a role for PF3D7_0403800 in invasion-associated lipid metabolism. Finally, we used solvent-induced proteome profiling and reactivity assays to confirm drug-target engagement. Together, our findings identify a novel Surface-associated Lipid-Interacting Rhoptry Protein (PfSLIRP) that coordinates lipid metabolism at the rhoptries to enable RBC invasion.

microbiology↗

bioRxiv2025

Deconvolution of the on-target activity of plasmepsin V peptidomimetics in P. falciparum parasites

Plasmepsin V (PMV), an essential aspartyl protease, plays a critical role during the asexual blood stage of infection of Plasmodium by enabling the export of parasite proteins into the host red blood cell. This export is vital for parasite survival and pathogenesis, making PMV an attractive target for antimalarial drug development. Peptidomimetic inhibitors designed to mimic the natural substrate of PMV have demonstrated potent parasite-killing activity by blocking protein export. While these compounds have been instrumental in validating PMV as a bona fide antimalarial target, inconsistencies between their biochemical potency and cellular activity have raised questions regarding their precise mechanism of action. In this study, we employed chemoproteomic approaches, including solvent induced protein precipitation (SIP) and intact-cell thermal PISA profiling, to demonstrate PMV target engagement by the peptidomimetics. To further support these findings, we generated parasite lines exhibiting reduced sensitivity to peptidomimetics. Through whole-genome sequencing of these parasite lines, a single nucleotide variant (SNV) within the pmv gene was revealed. This mutation was later validated using reverse genetics, confirming its role in mediating resistance. Together, these data provide strong evidence that the peptidomimetics exert their antimalarial activity by directly targeting PMV. These findings further support the potential of PMV as a validated and promising target for future antimalarial drug development.

cell biology↗

bioRxiv2025

Aryl N-acetamide compounds exert antimalarial activity by acting as agonists of rhomboid protease PfROM8 and cation channel PfCSC1.

With resistance to current frontline antimalarials spreading globally, new drug candidates need to be discovered to populate the antimalarial drug development pipeline. We previously screened the Medicines for Malaria Venture Pathogen Box for compounds that prevent Plasmodium falciparum parasites from exiting and invading human erythrocytes, steps essential for the proliferation of parasites in the blood, which causes disease. Compound MMV020512 (M-512) was identified in this screen and live cell imaging here established that it does not specifically inhibit invasion but likely inhibits intraerythrocytic parasite growth. M-512 resistance selection in parasites led to the identification of mutations in the membrane protease PfROM8 and the cation ion channel PfCSC1. PfROM8 was validated as a target of M-512 when a L562R putative resistance mutation was engineered into wildtype parasites reproducing the resistance phenotype. Knockdown of wildtype PfROM8, the L562R mutant and CSC1 reduced parasite growth, indicating the proteins are functionally important. Counterintuitively, the PfROM8 and PfCSC1 knockdown parasites became more resistant to M-512 suggesting that the compound is an agonist of both proteins which may form a functional complex and that dysregulation of this complex is deleterious to parasite growth.

microbiology↗

bioRxiv2023

Aryl amino acetamides prevent the development of Plasmodium falciparum rings via inhibition of the lipid transfer protein PfSTART1

With resistance to most antimalarials increasing, it is imperative that new antimalarial drugs are developed to replace or complement front-line artemisinin therapies. We previously identified an aryl acetamide compound, MMV006833 (M-833), that inhibited ring development of newly invaded merozoites. Here, we selected parasites resistant to M-833 and identified independent mutations arising in the START lipid transfer protein (PF3D7_0104200, PfSTART1). Introduction of the identified PfSTART1 mutations into wildtype parasites reproduced resistance to both M-833 and highly potent analogues, confirming PfSTART1 mutations were sufficient to confer resistance. The analogues bound to recombinant PfSTART1 with nanomolar affinity. We also demonstrated selective PfSTART1 engagement by the analogues using organic solvent-based Proteome Integral Solubility Alteration (Solvent PISA) assay for the first time in Plasmodium. Imaging of newly invaded merozoites showed the inhibitors prevented the conversion into larger amoeboid ring-stage parasites potentially through the inhibition of phospholipid transfer from the parasite to the encasing parasitophorous vacuole membrane (PVM) and/or within the parasite. We show that these PfSTART1 inhibitors also block transmission. With multiple stages of the parasites lifecycle being targeted by PfSTART1 inhibitors, this protein therefore represents a novel drug target with a new mechanism of action.

cell biology↗

bioRxiv2023

A pyridyl-furan series developed from Open Global Health Library blocks red blood cell invasion and protein trafficking in Plasmodium falciparum through potential inhibition of the parasites PI4KIIIb enzyme.

With resistance increasing to current antimalarial medicines, there is an urgent need to discover new drug targets and to develop new medicines against these targets. We therefore screened the Open Global Health Library of Merck KGaA, Darmstadt, Germany of 250 compounds against the asexual blood stage of the deadliest malarial parasite Plasmodium falciparum, from which eight inhibitors with low micromolar potency were found. Due to its combined potencies against parasite growth and inhibition of red blood cell invasion, the pyridyl-furan compound OGHL250, was prioritised for further optimisation. The potency of the series lead compound (WEHI-518) was improved 250-fold to low nanomolar levels against parasite blood-stage growth. Parasites selected for resistance to a related compound MMV396797, were also resistant to WEHI-518 as well as KDU731, an inhibitor of the phosphatidylinositol kinase PfPI4KIIIB, suggesting this kinase is the target of the pyridyl-furan series. Inhibition of PfPI4KIIIB blocks multiple stages of the parasites life cycle and other potent inhibitors are currently under preclinical development. MMV396797-resistant parasites possess an E1316D mutation in PfPKI4IIIB which clusters with known resistance mutations of other inhibitors of the kinase. Building upon earlier studies which showed that PfPI4KIIIB inhibitors block the development of the invasive merozoite parasite stage, we show that members of the pyridyl-furan series also block invasion and/or the conversion of merozoites into ring-stage intracellular parasites through inhibition of protein secretion and export into red blood cells.

microbiology↗

bioRxiv2023

The delayed bloodstream clearance of Plasmodium falciparum parasites after M5717 treatment is attributable to the inability to modify their red blood cell hosts.

M5717 is a promising antimalarial drug under development thatacts against multiple stages of the life cycle of Plasmodium parasites by inhibiting the translation elongation factor 2 (PfeEF2), thereby preventing protein synthesis. The parasite clearance profile after drug treatment in preclinical studies in mice, and clinical trials in humans showed a notable delayed clearance phenotype whereby parasite infected red blood cells (iRBCs) persisted in the bloodstream for a significant period before eventual clearance. In a normal P. falciparum infection iRBCs sequester in the deep circulation by cytoadherence, allowing them to avoid surveillance and clearance in the spleen. In this work we show that M5717 treatment renders iRBCs invisible to normal splenic clearance mechanisms. We found that M5717 blocks parasite modification of their host red blood cells (RBCs) by preventing synthesis of new exported proteins, rather than by directly blocking the export of these proteins into the RBC compartment. Using in vitro models, we demonstrated that M5717 treated ring/trophozoite stage iRBCs became less rigid, and cytoadhered less well compared to untreated iRBCs. This indicates that in vivo persistence of M5717 treated iRBCs in the blood stream is likely due to reduced cytoadherence and splenic clearance.

microbiology↗

bioRxiv2023

The Dual Action of Human Antibodies Specific to Plasmodium falciparum PfRH5 and PfCyRPA: Blocking Invasion and Inactivating Extracellular Merozoites

The Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) is the current leading blood-stage malaria vaccine candidate. PfRH5 functions as part of the pentameric PCRCR complex containing PTRAMP, CSS, PfCyRPA and PfRIPR, all of which are essential for infection of human red blood cells (RBCs). To trigger RBC invasion, PfRH5 engages with RBC protein basigin in a step termed the RH5-basigin binding stage. Although we know increasingly more about how antibodies specific for PfRH5 can block invasion, much less is known about how antibodies recognizing other members of the PCRCR complex can inhibit invasion. To address this, we performed live cell imaging using monoclonal antibodies (mAbs) which bind PfRH5 and PfCyRPA. We measured the degree and timing of the invasion inhibition, the stage at which it occurred, as well as subsequent events. We show that parasite invasion is blocked by individual mAbs, and the degree of inhibition is enhanced when combining a mAb specific for PfRH5 with one binding PfCyRPA. In addition to directly establishing the invasion-blocking capacity of the mAbs, we identified a secondary action of certain mAbs on extracellular parasites that had not yet invaded where the mAbs appeared to inactivate the parasites by triggering a developmental pathway normally only seen after successful invasion. These findings suggest that epitopes within the PfCyRPA-PfRH5 sub-complex that elicit these dual responses may be more effective immunogens than neighboring epitopes by both blocking parasites from invading and rapidly inactivating extracellular parasites. These two protective mechanisms, prevention of invasion and inactivation of uninvaded parasites, resulting from antibody to a single epitope indicate a possible route to the development of more effective vaccines. Author SummaryMalaria is a sometimes-fatal disease caused by protozoan parasites of which Plasmodium falciparum is the most deadly species that causes hundreds of millions of infections and half a million deaths per year. A partially effective vaccine is available to block parasite forms transmitted by mosquitoes but not the subsequent blood stage which causes symptomatic disease. To fight blood stage parasites, proteins have been identified such as PfRH5, that aid parasite entry into human red blood cells (RBCs) and vaccines made from these proteins can trigger the production of antibodies that bind the parasite proteins thereby blocking RBC invasion. PfRH5 forms a complex with another parasite protein called PfCyRPA and together antibodies to PfCyRPA and PfRH5 are highly effective in reducing parasite growth. Here we investigated how antibodies to PfCyRPA and PfRH5 actually block invasion using video microscopy of live parasites. As anticipated, we found the antibodies not only stopped most parasites from invading but of those parasites that did invade, they took longer to do so, suggesting the antibodies were physically inhibiting the invasion process. One unanticipated effect of both PfRH5 antibodies and one of three PfCyRPA antibodies tested, was that they triggered the uninvaded parasites to change into cellular forms normally only seen inside RBCs. These intracellular forms are no longer competent to invade and so the PfRH5/CyRPA antibodies have the potential of both neutralize parasites by physically preventing RBC entry and by changing the parasites into invasion incompetent forms.

microbiology↗

bioRxiv2022

PTEX helps efficiently traffic haemoglobinases to the food vacuole in Plasmodium falciparum.

A key element of Plasmodium biology and pathogenesis is the trafficking of ~10% of the parasite proteome into the host red blood cell (RBC) it infects. To cross the parasite-encasing parasitophorous vacuole membrane, exported proteins utilise a channel-containing protein complex termed the Plasmodium translocon of exported proteins (PTEX). PTEX is obligatory for parasite survival, both in vitro and in vivo, suggesting that at least some exported proteins have essential metabolic functions. However, to date only one essential PTEX-dependent process, the new permeability pathway, has been described. To identify other essential PTEX-dependant proteins/processes, we conditionally knocked down the expression of one of its core components, PTEX150, and examined which metabolic pathways were affected. Surprisingly, the food vacuole mediated process of haemoglobin (Hb) digestion was substantially perturbed by PTEX150 knockdown. Using a range of transgenic parasite lines and approaches, we show that two major Hb proteases; falcipain 2a and plasmepsin II, interact with PTEX core components, implicating the translocons involvement in the trafficking of Hb proteases. We propose a model where these proteases are translocated into the PV via PTEX in order to reach the cytostome, located at the parasite periphery, prior to food vacuole entry. This work offers a another mechanistic explanation for why PTEX function is essential for growth of the parasite within its host RBC. Author summaryPlasmodium falciparum is the causative agent of the most severe form of malaria in humans, where the symptoms of the disease are derived from the continuous asexual replication of the parasite within the human red blood cells (RBCs) it infects. To survive within this niche, the parasite exports hundreds of parasite effector proteins across the vacuole it resides within and into the RBC. About a quarter of the exported proteins appear to be essential during the blood stage but the functions of these proteins largely remain uncharacterised. Protein export is facilitated by an essential protein complex termed the Plasmodium translocon of exported proteins (PTEX). Conditional depletion of PTEXs core components results in rapid parasite death presumably because essential proteins do not reach their functional destination in the RBC and their associated metabolic functions cannot be performed. To uncover what these essential metabolic functions are we knocked down PTEX150, a core component of PTEX. Metabolic analysis of the knockdown parasites indicated that haemoglobin (Hb) digestion was inhibited resulting in a reduction of Hb derived peptides, which serve as an amino acid source for the parasite. We determined that knocking down HSP101, another PTEX core component, also disrupted the Hb digestion pathway. Furthermore, we provide evidence that reduction of Hb digestion might be due to the failure to efficiently deliver early acting Hb digesting proteases to the cytostome, a specialised location where vesicles of Hb are taken into the parasite. PTEX may therefore play a role in delivering Hb proteases to the cytostome.

microbiology↗

bioRxiv2022

The sulfonylpiperazine MMV020291 prevents red blood cell invasion by the malaria parasite Plasmodium falciparum through interference with actin-1/profilin dynamics

With emerging resistance to frontline treatments, it is vital that new antimalarial drugs are identified to target Plasmodium falciparum. We have recently described a compound, MMV020291, as a specific inhibitor of red blood cell invasion, and have generated analogues with improved potency. Here, we identify actin and profilin as putative targets of the MMV020291 series through resistance selection and whole genome sequencing of three MMV020291 resistant populations. This revealed three non-synonymous single nucleotide polymorphisms in two genes; two in profilin (N154Y, K124N) and a third one in actin-1 (M356L). Using CRISPR-Cas9, we engineered these mutations into wildtype parasites which rendered them resistant to MMV020291. We demonstrate that MMV020291 reduces actin polymerisation that is required by the merozoite stage parasites to invade red blood cells. Additionally, the series inhibits the actin-1 dependent process of apicoplast segregation, leading to a delayed death phenotype. In vitro co-sedimentation experiments using recombinant P. falciparum actin-1 and profilin proteins indicate that potent MMV020291 analogues amplify the actin-monomer sequestering effect of profilin, thereby reducing the formation of filamentous actin. Altogether, this study identifies the first compound series targeting the actin-1/profilin interaction in P. falciparum and paves the way for future antimalarial development against the highly dynamic process of actin polymerisation.

molecular biology↗

bioRxiv2022

The Medicines for Malaria Venture Malaria Box contains inhibitors of protein secretion in Plasmodium falciparum blood stage parasites

Plasmodium falciparum parasites which cause malaria, traffic hundreds of proteins into the red blood cells (RBCs) they infect. These exported proteins remodel their RBCs enabling host immune evasion through processes such as cytoadherence that greatly assist parasite survival. As resistance to all current anti-malarial compounds is rising new compounds need to be identified and those that could inhibit parasite protein secretion and export would both rapidly reduce parasite virulence and ultimately lead to parasite death. To identify compounds that inhibit protein export we used transgenic parasites expressing an exported nanoluciferase reporter to screen the Medicines for Malaria Venture Malaria box of 400 anti-malarial compounds with mostly unknown targets. The most potent inhibitor identified in this screen was MMV396797 whose application led to export inhibition of both the reporter and endogenous exported proteins. MMV396797 mediated blockage of protein export and slowed the rigidification and cytoadherence of infected RBCs - modifications which are both mediated by parasite-derived exported proteins. Overall, we have identified a new protein export inhibitor in P. falciparum whose target though unknown, could be developed into a future anti-malarial that rapidly inhibits parasite virulence before eliminating parasites from the host. SynopsisPlasmodium falciparum exports proteins into its host cell to perform a myriad of functions required for survival. We adapted an assay to screen for small molecules that inhibit protein secretion and export. Screening the 400-compound Medicines for Malaria Venture (MMV) Malaria Box uncovered several potential export inhibitors. The most promising of these compounds, MMV396797, blocked protein export at the parasite and reduced host rigidification and cytoadherence, two functions which are mediated by exported proteins.

biochemistry↗

bioRxiv2019

Screening the Medicines for Malaria Venture Pathogen Box for invasion and egress inhibitors of the blood stage of Plasmodium falciparum reveals several inhibitory compounds

To identify potential inhibitors of egress and invasion in the asexual blood stage of Plasmodium falciparum, we screened the Medicines for Malaria Venture (MMV) Pathogen Box. This compound library comprises of 400 drugs against neglected tropical diseases, including 125 with antimalarial activity. For this screen, we utilised transgenic parasites expressing a bioluminescent reporter, Nanoluciferase (Nluc), to measure inhibition of parasite egress and invasion in the presence of the Pathogen Box compounds. At a concentration of 2 {micro}M, we found 15 compounds that inhibited parasite egress by >40% and 24 invasion-specific compounds that inhibited invasion by >90%. We further characterised 11 of these inhibitors through cell-based assays and live cell microscopy and found two compounds that inhibited merozoite maturation in schizonts, one compound that inhibited merozoite egress, one compound that directly inhibited parasite invasion and one compound that slowed down invasion and arrested ring formation. The remaining compounds were general growth inhibitors that acted during the egress and invasion phase of the cell cycle. We found the sulfonylpiperazine, MMV020291, to be the most invasion-specific inhibitor, blocking successful merozoite internalisation within human RBCs and having no substantial effect on other stages of the cell cycle. This has greater implications for the possible development of an invasion-specific inhibitor as an antimalarial in a combination based therapy, in addition to being a useful tool for studying the biology of the invading parasite.\n\nImportancePlasmodium falciparum causes the most severe form of malaria and with emerging resistance to frontline treatments, there is the need to identify new drug targets in the parasite. One of the most critical processes during the asexual blood stage in the parasites lifecycle is the egress from old red blood cells (RBCs) and subsequent invasion of new RBCs. Many unique parasite ligands, receptors and enzymes are employed during egress and invasion that are essential for parasite proliferation and survival, therefore making these processes druggable targets. Identifying novel compounds that inhibit these essential processes would further their development into possible antimalarials that would be highly effective at killing asexual RBC stage parasites when used in combination with drugs that target the intraerythrocytic growth phase. These compounds potentially may also be used as novel tools to study the complex biology of parasites to gain further insight into the mechanisms behind egress and invasion.

cell biology↗

bioRxiv2019

Malaria vaccine candidates displayed on novel virus-like particles are immunogenic and induce transmission-blocking activity

The development of effective malaria vaccines remains a global health priority. Currently, the most advanced vaccine, known as RTS,S, has only shown modest efficacy in clinical trials. Thus, the development of more efficacious vaccines by improving the formulation of RTS,S for increased efficacy or to interrupt malaria transmission are urgently needed. The RTS,S vaccine is based on the presentation of a fragment of the sporozoite antigen on the surface of virus-like particles (VLPs) based on human hepatitis B virus (HBV). In this study, we have developed and evaluated a novel VLP platform based on duck HBV (known as Metavax) for malaria vaccine development. This platform can incorporate large and complex proteins into VLPs and is produced in a Hansenula cell line compatible with cGMP vaccine production. Here, we have established the expression of leading P. falciparum malaria vaccine candidates as VLPs. This includes Pfs230 and Pfs25, which are candidate transmission-blocking vaccine antigens. We demonstrated that the VLPs effectively induce antibodies to malaria vaccine candidates with minimal induction of antibodies to the duck-HBV scaffold antigen. Antibodies to Pfs230 also recognised native protein on the surface of gametocytes, and antibodies to both Pfs230 and Pfs25 demonstrated transmission-reducing activity in standard membrane feeding assays. These results establish the potential utility of this VLP platform for malaria vaccines, which may be suitable for the development of multi-component vaccines that achieve high vaccine efficacy and transmission-blocking immunity.

immunology↗

bioRxiv2018

Knockdown of the translocon protein EXP2, reduces growth and protein export in malaria parasites.

Malaria parasites remodel their host erythrocytes to gain nutrients and avoid the immune system. Host erythrocytes are modified by hundreds of effectors proteins exported from the parasites into the host cell. Protein export is mediated by the PTEX translocon comprising five core components of which EXP2 is considered to form the putative pore that spans the vacuole membrane enveloping the parasite within its erythrocyte. To explore the function and importance of EXP2 for parasite survival in the asexual blood stage of Plasmodium falciparum we inducibly knocked down the expression of EXP2. Reduction in EXP2 expression strongly reduced parasite growth proportional to the degree of protein knockdown and tended to stall development about half way through the asexual cell cycle. Once the knockdown inducer was removed and EXP2 expression restored, parasite growth recovered dependent upon the length and degree of knockdown. To establish EXP2 function and hence the basis for growth reduction, the trafficking of an exported protein was monitored following EXP2 knockdown. This resulted in severe attenuation of protein export and is consistent with EXP2, and PTEX in general, being the conduit for export of proteins into the host compartment.

microbiology↗