The prevention of parasite transmission from the human host to the mosquito has been recognized as a vital tool for malaria eradication campaigns. However, transmission-blocking antimalarial drug ...and/or vaccine discovery and development is currently hampered by the expense and difficulty of producing mature Plasmodium falciparum gametocytes in vitro-the parasite stage responsible for mosquito infection. Current protocols for P. falciparum gametocyte culture usually require complex parasite synchronization and addition of stimulating and/or inhibitory factors, and they may not have demonstrated the essential property of mosquito infectivity. This protocol details all the steps required for reliable P. falciparum gametocyte production and highlights common factors that influence culture success. The protocol can be completed in 15 d, and particular emphasis is placed upon operating a gametocyte culture facility on a continuous cycle. In addition, we show how functionally viable gametocytes can be used to evaluate transmission-blocking drugs both in a field setting and at high throughput (HTP) for drug discovery.
Spread of parasite resistance to artemisinin threatens current frontline antimalarial therapies, highlighting the need for new drugs with alternative modes of action. Since only 0.2-1% of asexual ...parasites differentiate into sexual, transmission-competent forms, targeting this natural bottleneck provides a tangible route to interrupt disease transmission and mitigate resistance selection. Here we present a high-throughput screen of gametogenesis against a ~70,000 compound diversity library, identifying seventeen drug-like molecules that target transmission. Hit molecules possess varied activity profiles including male-specific, dual acting male-female and dual-asexual-sexual, with one promising N-((4-hydroxychroman-4-yl)methyl)-sulphonamide scaffold found to have sub-micromolar activity in vitro and in vivo efficacy. Development of leads with modes of action focussed on the sexual stages of malaria parasite development provide a previously unexplored base from which future therapeutics can be developed, capable of preventing parasite transmission through the population.
Despite recent successes at controlling malaria, progress has stalled with an estimated 219 million cases and 435,000 deaths in 2017 alone. Combined with emerging resistance to front line ...antimalarial therapies in Southeast Asia, there is an urgent need for new treatment options and novel approaches to halt the spread of malaria.
, the parasite responsible for malaria propagates through mosquito transmission. This imposes an acute bottleneck on the parasite population and transmission-blocking interventions exploiting this vulnerability are recognized as vital for malaria elimination.
13,533 small molecules with known activity against
asexual parasites were screened for additional transmission-blocking activity in an
ookinete development assay. Active molecules were then counterscreened in dose response against HepG2 cells to determine their activity/cytotoxicity window and selected non-toxic representative molecules were fully profiled in a range of transmission and mosquito infection assays. Furthermore, the entire dataset was compared to other published screens of the same molecules against
gametocytes and female gametogenesis.
437 molecules inhibited
ookinete formation with an IC
< 10 μM. of which 273 showed >10-fold parasite selectivity compared to activity against HepG2 cells. Active molecules grouped into 49 chemical clusters of three or more molecules, with 25 doublets and 94 singletons. Six molecules representing six major chemical scaffolds confirmed their transmission-blocking activity against
male and female gametocytes and inhibited
oocyst formation in the standard membrane feeding assay at 1 μM. When screening data in the
development ookinete assay was compared to published screens of the same library in assays against
gametocytes and female gametogenesis, it was established that each assay identified distinct, but partially overlapping subsets of transmission-blocking molecules. However, selected molecules unique to each assay show transmission-blocking activity in mosquito transmission assays.
The
ookinete development assay is an excellent high throughput assay for efficiently identifying antimalarial molecules targeting early mosquito stage parasite development. Currently no high throughput transmission-blocking assay is capable of identifying all transmission-blocking molecules.
Plasmodium falciparum stage V gametocytes are responsible for parasite transmission, and drugs targeting this stage are needed to support malaria elimination. We here screen the Tres Cantos ...Antimalarial Set (TCAMS) using the previously developed P. falciparum female gametocyte activation assay (Pf FGAA), which assesses stage V female gametocyte viability and functionality using Pfs25 expression. We identify over 400 compounds with activities <2 μM, chemically classified into 57 clusters and 33 singletons. Up to 68% of the hits are chemotypes described for the first time as late-stage gametocyte-targeting molecules. In addition, the biological profile of 90 compounds representing the chemical diversity is assessed. We confirm in vitro transmission-blocking activity of four of the six selected molecules belonging to three distinct scaffold clusters. Overall, this TCAMS gametocyte screen provides 276 promising antimalarial molecules with dual asexual/sexual activity, representing starting points for target identification and candidate selection.
The Pint of Science festival is the biggest annual international science festival. In May 2017, we coordinated the first Pint of Science festival in Thailand and reported our initial reflections. ...Building on this work, we set out to evaluate more systematically events conducted in 2018.
In 2018, we conducted Pint of Science events at four different locations in Bangkok. Overall, there were 18 talks held over six event-days in 2018. We administered 180 self-reported questionnaires as well as conducted 11 semi-structured interviews and a focus group discussion with audience members and speakers.
Of the 180 questionnaires handed out, 125 attendees completed the questionnaire. The majority of attendees came because they were interested in science (68.0%), to learn something new (46.4%) and to enjoy themselves (44.8%). Our qualitative results confirm the quantitative findings. In addition, speakers viewed that they benefited by improving their communication skills and having the opportunity to network with scientists and non-scientists. Speakers also mentioned that such events were a good means to engage with the public, can improve the visibility of their work and potentially attract more funding. To improve the Pint of Science activities, audience members suggested to include a more diverse range of topics, more collaborations with other local research institutions and to hold the event at larger venues.
We conclude that Pint of Science was well received in Bangkok with recommendations to improve minor issues related to practicalities and logistics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The malaria parasite replicates within an intraerythrocytic parasitophorous vacuole (PV). The PV and host cell membranes eventually rupture, releasing merozoites in a process called egress. Certain ...inhibitors of serine and cysteine proteases block egress, indicating a crucial role for proteases. The Plasmodium falciparum genome encodes nine serine-repeat antigens (SERAs), each of which contains a central domain homologous to the papain-like (clan CA, family C1) protease family. SERA5 and SERA6 are indispensable in blood-stage parasites, but the function of neither is known. Here we show that SERA6 localizes to the PV where it is precisely cleaved just prior to egress by an essential serine protease called PfSUB1. Mutations that replace the predicted catalytic Cys of SERA6, or that block SERA6 processing by PfSUB1, could not be stably introduced into the parasite genomic sera6 locus, indicating that SERA6 is an essential enzyme and that processing is important for its function. We demonstrate that cleavage of SERA6 by PfSUB1 converts it to an active cysteine protease. Our observations reveal a proteolytic activation step in the malarial PV that may be required for release of the parasite from its host erythrocyte.
Background: Malaria parasite egress from host erythrocytes requires cysteine protease activity, but the identity of key parasite proteases is unknown.
Results: SERA6 is an essential parasite cysteine protease that resides in the parasitophorous vacuole and is activated by SUB1, a parasite serine protease.
Conclusion: SERA6 may play a role in egress.
Significance: SERA6 is a potential new antimalarial drug target.
Higher academic institutions in the UK need to drive improvements in equity, diversity, and inclusion (EDI) through sustainable practical interventions. A broad view of inclusivity is based on an ...intersectional approach that considers race, geographical location, caring responsibilities, disability, neurodiversity, religion, and LGBTQIA+ identities. We describe the establishment of a diverse stakeholder group to develop practical grass-roots recommendations through which improvements can be advanced. We have developed a manifesto for change, comprising six domains through which academic institutions can drive progress through setting short, medium, and long-term priorities. Interventions will yield rewards in recruitment and retention of a diverse talent pool, leading to enhanced impact and output.
As part of the global effort toward malaria eradication, phenotypic whole-cell screening revealed the 2-aminopyridine class of small molecules as a good starting point to develop new antimalarial ...drugs. Stemming from this series, we found that the derivative, MMV390048, lacked cross-resistance with current drugs used to treat malaria. This compound was efficacious against all
life cycle stages, apart from late hypnozoites in the liver. Efficacy was shown in the humanized
mouse model, and modest reductions in mouse-to-mouse transmission were achieved in the
mouse model. Experiments in monkeys revealed the ability of MMV390048 to be used for full chemoprotection. Although MMV390048 was not able to eliminate liver hypnozoites, it delayed relapse in a
monkey model. Both genomic and chemoproteomic studies identified a kinase of the
parasite, phosphatidylinositol 4-kinase, as the molecular target of MMV390048. The ability of MMV390048 to block all life cycle stages of the malaria parasite suggests that this compound should be further developed and may contribute to malaria control and eradication as part of a single-dose combination treatment.
Resistance to artemisinin-based combination therapy (ACT) in the
parasite is threatening to reverse recent gains in reducing global deaths from malaria. While resistance manifests as delayed parasite ...clearance in patients, the phenotype can only spread geographically via the sexual stages and mosquito transmission. In addition to their asexual killing properties, artemisinin and its derivatives sterilize sexual male gametocytes. Whether resistant parasites overcome this sterilizing effect has not, however, been fully tested. Here, we analyzed
clinical isolates from the Greater Mekong Subregion, each demonstrating delayed clinical clearance and known resistance-associated polymorphisms in the
(PfK13
) gene. As well as demonstrating reduced asexual sensitivity to drug, certain PfK13
isolates demonstrated a marked reduction in sensitivity to artemisinin in an
male gamete formation assay. Importantly, this same reduction in sensitivity was observed when the most resistant isolate was tested directly in mosquito feeds. These results indicate that, under artemisinin drug pressure, while sensitive parasites are blocked, resistant parasites continue transmission. This selective advantage for resistance transmission could favor acquisition of additional host-specificity or polymorphisms affecting partner drug sensitivity in mixed infections. Favored resistance transmission under ACT coverage could have profound implications for the spread of multidrug-resistant malaria beyond Southeast Asia.
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