Assessment of the transmission blocking activity of antimalarial compounds by membrane feeding assays using natural Plasmodium falciparum gametocyte isolates from West-Africa

N.B. Henry et al., PLOS One, 2023


Antimalarial drugs that can block the transmission of Plasmodium gametocytes to mosquito vectors would be highly beneficial for malaria elimination efforts. Identifying transmission-blocking drugs currently relies on evaluation of their activity against gametocyte-producing laboratory parasite strains and would benefit from a testing pipeline with genetically diverse field isolates. The aims of this study were to develop a pipeline to test drugs against Pfalciparum gametocyte field isolates and to evaluate the transmission-blocking activity of a set of novel compounds. Two assays were designed so they could identify both the overall transmission-blocking activity of a number of marketed and experimental drugs (more…)

A versatile Plasmodium falciparum reporter line expressing NanoLuc enables highly sensitive multi-stage drug assays

Y. Miyazaki et al., Communications biology (6), 2023


Transgenic luciferase-expressing Plasmodium falciparum parasites have been widely used for the evaluation of anti-malarial compounds. Here, to screen for anti-malarial drugs effective against multiple stages of the parasite, we generate a P. falciparum reporter parasite that constitutively expresses NanoLuciferase (NanoLuc) throughout its whole life cycle. The NanoLuc-expressing P. falciparum reporter parasite shows a quantitative NanoLuc signal in the asexual blood, gametocyte, mosquito, and liver stages. We also establish assay systems to evaluate the anti-malarial activity of compounds at the asexual blood, gametocyte, and liver stages, (more…)

Metabolic activity organizes olfactory representations

W. Qian et al., eLife 12, 2023


Hearing and vision sensory systems are tuned to the natural statistics of acoustic and electromagnetic energy on earth and are evolved to be sensitive in ethologically relevant ranges. But what are the natural statistics of odors, and how do olfactory systems exploit them? Dissecting an accurate machine learning model (Lee et al., 2022) for human odor perception, we find a computable representation for odor at the molecular level that can predict the odor-evoked receptor, neural, and behavioral responses of nearly all terrestrial organisms studied in olfactory neuroscience. Using this olfactory representation (principal odor map [POM]), (more…)

Assessment of the drugability of initial malaria infection through miniaturized sporozoite assays and high-throughput screening

M. Miglianico et al., Communications Biology 6(1), 2023


The sporozoite stages of malaria parasites are the primary cause of infection of the vertebrate host and are targeted by (experimental) vaccines. Yet, little is known about their susceptibility to chemical intervention. Phenotypic high-throughput screens have not been feasible due to a lack of in vitro systems. Here we tested 78 marketed and experimental antimalarial compounds in miniaturized assays addressing sporozoite viability, gliding motility, hepatocyte traversal, and intrahepatocytic schizogony. None potently interfered with sporozoite viability or motility but ten compounds acted at the level of schizogony with IC50s < 100 nM. To identify compounds directly targeting sporozoites, (more…)

Potent transmission-blocking monoclonal antibodies from naturally exposed individuals target a conserved epitope on Plasmodium falciparum Pfs230

D. Ivanoschko et al., Immunity (56), 2023


Pfs230 is essential for Plasmodium falciparum transmission to mosquitoes and is the protein targeted by the most advanced malaria-transmission-blocking vaccine candidate. Prior understanding of functional epitopes on Pfs230 is based on two monoclonal antibodies (mAbs) with moderate transmission-reducing activity (TRA), elicited from subunit immunization. Here, we screened the B cell repertoire of two naturally exposed individuals possessing serum TRA and identified five potent mAbs from sixteen Pfs230 domain-1-specific mAbs. Structures of three potent and three low-activity antibodies bound to Pfs230 domain 1 revealed four distinct epitopes. (more…)

Highly potent, naturally acquired human monoclonal antibodies against Pfs48/45 block Plasmodium falciparum transmission to mosquitoes

A. Fabra-Garcia et al., Immunity (56), 2023


Malaria transmission-blocking vaccines (TBVs) aim to induce antibodies that interrupt malaria parasite development in the mosquito, thereby blocking onward transmission, and provide a much-needed tool for malaria control and elimination. The parasite surface protein Pfs48/45 is a leading TBV candidate. Here, we isolated and characterized a panel of 81 human Pfs48/45-specific monoclonal antibodies (mAbs) from donors naturally exposed to Plasmodium parasites. Genetically diverse mAbs against each of the three domains (D1-D3) of Pfs48/45 were identified. The most potent mAbs targeted D1 and D3 and achieved >80% transmission-reducing activity (more…)

Creation and preclinical evaluation of genetically attenuated malaria parasites arresting growth late in the liver

B. Franke-Fayard et al., npj Vaccines 7, 2022


Whole-sporozoite (WSp) malaria vaccines induce protective immune responses in animal malaria models and in humans. A recent clinical trial with a WSp vaccine comprising genetically attenuated parasites (GAP) which arrest growth early in the liver (PfSPZ-GA1), showed that GAPs can be safely administered to humans and immunogenicity is comparable to radiation-attenuated PfSPZ Vaccine. GAPs that arrest late in the liver stage (LA-GAP) have potential for increased potency as shown in rodent malaria models. Here we describe the generation of four putative P. falciparum LA-GAPs, generated by CRISPR/Cas9-mediated gene deletion. (more…)

Replenishing the malaria drug discovery pipeline: Screening and hit evaluation of the MMV Hit Generation Library 1 (HGL1) against asexual blood stage Plasmodium falciparum, using a nano luciferase reporter read-out

K. Dechering et al., SLAS Discovery (22), 2022


A central challenge of antimalarial therapy is the emergence of resistance to the components of artemisinin-based combination therapies (ACTs) and the urgent need for new drugs acting through novel mechanism of action. Over the last decade, compounds identified in phenotypic high throughput screens (HTS) have provided the starting point for six candidate drugs currently in the Medicines for Malaria Venture (MMV) clinical development portfolio. However, the published screening data which provided much of the new chemical matter for malaria drug discovery projects have been extensively mined. Here we present a new screening and selection cascade for generation of hit compounds active against the blood stage of Plasmodium falciparum.

Preclinical characterization and target validation of the antimalarial pantothenamide MMV693183

L.E. de Vries et al., Nature Communications 13(1), 2022


Drug resistance and a dire lack of transmission-blocking antimalarials hamper malaria elimination. Here, we present the pantothenamide MMV693183 as a first-in-class acetyl-CoA synthetase (AcAS) inhibitor to enter preclinical development. Our studies demonstrate attractive drug-like properties and in vivo efficacy in a humanized mouse model of Plasmodium falciparum infection. The compound shows single digit nanomolar in vitro activity against P. falciparum and P. vivax clinical isolates, and potently blocks P. falciparum transmission to Anopheles mosquitoes. Genetic and biochemical studies identify AcAS as the target of the MMV693183-derived antimetabolite, CoA-MMV693183.

The Nitrobenzoxadiazole Derivative NBDHEX Behaves as Plasmodium falciparum Gametocyte Selective Inhibitor with Malaria Parasite Transmission Blocking Activity

G. Siciliano et al., Pharmaceuticals 15(2), 2022


This work describes the activity of 6-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio)hexan-1-ol (NBDHEX) and of its newly identified carboxylic acid metabolite on the human malaria parasite Plasmodium falciparum. NBDHEX has been previously identified as a potent cytotoxic agent against murine and human cancer cells as well as towards the protozoan parasite Giardia duodenalis. We show here that NBDHEX is active in vitro against all blood stages of P. falciparum, with the rare feature of killing the parasite stages transmissible to mosquitoes, the gametocytes, with a 4-fold higher potency than that on the pathogenic asexual stages. This activity importantly translates into blocking parasite transmission through the Anopheles vector in mosquito experimental infections.

Barcoded Asaia bacteria enable mosquito in vivo screens and identify novel systemic insecticides and inhibitors of malaria transmission

A. Sturm et al., PLOS Biology 19(12) 2021


This work addresses the need for new chemical matter in product development for control of pest insects and vector-borne diseases. We present a barcoding strategy that enables phe- notypic screens of blood-feeding insects against small molecules in microtiter plate-based arrays and apply this to discovery of novel systemic insecticides and compounds that block malaria parasite development in the mosquito vector. Encoding of the blood meals was achieved through recombinant DNA-tagged Asaia bacteria that successfully colonised Aedes and Anopheles mosquitoes.

Prioritization of Molecular Targets for Antimalarial Drug Discovery

B. Forte et al., ACS Infect Dis. 2021 Sep 15


There is a shift in antimalarial drug discovery from phenotypic screening toward target-based approaches, as more potential drug targets are being validated in Plasmodium species. Given the high attrition rate and high cost of drug discovery, it is important to select the targets most likely to deliver progressible drug candidates. In this paper, we describe the criteria that we consider important for selecting targets for antimalarial drug discovery. We describe the analysis of a number of drug targets in the Malaria Drug Accelerator (MalDA) pipeline, which has allowed us to prioritize targets that are ready to enter the drug discovery process. (more…)

Discovery and Structure-Activity Relationships of Quinazolinone-2-carboxamide Derivatives as Novel Orally Efficacious Antimalarials

Laleu B., et al., J Med Chem. 2021 Aug 26


A phenotypic high-throughput screen allowed discovery of quinazolinone-2-carboxamide derivatives as a novel antimalarial scaffold. Structure-activity relationship studies led to identification of a potent inhibitor 19f, 95-fold more potent than the original hit compound, active against laboratory-resistant strains of malaria. Profiling of 19f suggested a fast in vitro killing profile. In vivo activity in a murine model of human malaria in a dose-dependent manner constitutes a concomitant benefit. (more…)

MalDA, Accelerating Malaria Drug Discovery

Yang et al., Trends Parasitol. 2021 Jul 7


The Malaria Drug Accelerator (MalDA) is a consortium of 15 leading scientific laboratories. The aim of MalDA is to improve and accelerate the early antimalarial drug discovery process by identifying new, essential, druggable targets. In addition, it seeks to produce early lead inhibitors that may be advanced into drug candidates suitable for preclinical development and subsequent clinical testing in humans.

Repositioning and Characterization of 1-(Pyridin-4-yl)pyrrolidin-2-one Derivatives as Plasmodium Cytoplasmic Prolyl-tRNA Synthetase Inhibitors

Okaniwa et al., ACS Infect Dis. 2021 jun 11


Prolyl-tRNA synthetase (PRS) is a clinically validated antimalarial target. Screening of a set of PRS ATP-site binders, initially designed for human indications, led to identification of 1-(pyridin-4-yl)pyrrolidin-2-one derivatives representing a novel antimalarial scaffold. Evidence designates cytoplasmic PRS as the drug target. The frontrunner 1 and its active enantiomer 1-S exhibited low-double-digit nanomolar activity against resistant Plasmodium falciparum (Pf) laboratory strains and development of liver schizonts. No cross-resistance with strains resistant to other known antimalarials was noted. In addition, a similar level of growth inhibition was observed against clinical field isolates of Pf and P. vivax. (more…)

Generation of a Genetically Modified Chimeric Plasmodium falciparum Parasite Expressing Plasmodium vivax Circumsporozoite Protein for Malaria Vaccine Development

Miyazaki et al., Front Cell Infect Micorbiol. 2020 Dec 17


Chimeric rodent malaria parasites with the endogenous circumsporozoite protein (csp) gene replaced with csp from the human parasites Plasmodium falciparum (Pf) and P. vivax (Pv) are used in preclinical evaluation of CSP vaccines. Chimeric rodent parasites expressing PfCSP have also been assessed as whole sporozoite (WSP) vaccines. Comparable chimeric P. falciparum parasites expressing CSP of P. vivax could be used both for clinical evaluation of vaccines targeting PvCSP in controlled human P. falciparum infections and in WSP vaccines targeting P. vivax and P. falciparum. (more…)

The Plasmodium falciparum circumsporozoite protein produced in Lactococcus lactis is pure and stable.

Singh, S.K. et al., J Biol Chem. 2020 Jan 10


The Plasmodium falciparum circumsporozoite protein (PfCSP) is a sporozoite surface protein whose role in sporozoite motility and cell invasion has made it the leading candidate for a pre-erythrocytic malaria vaccine. However, production of high yields of soluble recombinant PfCSP, including its extensive NANP and NVDP repeats, has proven problematic. Here, we report on the development and characterization of a secreted, soluble, and stable full-length PfCSP (containing 4 NVDP and 38 NANP repeats) produced in the Lactococcus lactis expression system. The recombinant full-length PfCSP, denoted PfCSP4/38, was produced initially with a histidine tag and purified by a simple two-step procedure. (more…)

Antimalarial pantothenamide metabolites target acetyl–coenzyme A biosynthesis in Plasmodium falciparum

Schalkwijk et al., Sci. Transl. Med 2019 Sept 19


Malaria eradication is critically dependent on new therapeutics that target resistant Plasmodium parasites and block transmission of the disease. Here, we report that pantothenamide bioisosteres were active against blood-stage Plasmodium falciparum parasites and also blocked transmission of sexual stages to the mosquito vector. These compounds were resistant to degradation by serum pantetheinases, showed favorable pharmacokinetic properties, and cleared parasites in a humanized mouse model of P. falciparum infection. (more…)

Repurposing isoxazoline veterinary drugs for control of vector-borne human diseases

Miglianico M. et al., PNAS 2018 July 02


Isoxazolines are oral insecticidal drugs currently licensed for ectoparasite control in companion animals. Here we propose their use in humans for the reduction of vector-borne disease incidence. Fluralaner and afoxolaner rapidly killed Anopheles, Aedes, and Culex mosquitoes and Phlebotomus sand flies after feeding on a drug-supplemented blood meal, with IC50 values ranging from 33 to 575 nM, and were fully active against strains with preexist- ing resistance to common insecticides.

Antimalarial agents against both sexual and asexual parasites stages: structure-activity relationships and biological studies of the Malaria Box compound 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine (MMV019918) and analogues.

Vallone et al., Eur J Med Chem. 2018 Mar 10


Therapies addressing multiple stages of Plasmodium falciparum life cycle are highly desirable for implementing malaria elimination strategies. MMV019918 (1, 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine) was selected from the MMV Malaria Box for its dual activity against both asexual stages and gametocytes. In-depth structure-activity relationship studies and cytotoxicity evaluation led to the selection of 25 for further biological investigation. The potential transmission blocking activity of 25 versus P. falciparum was confirmed through the standard membrane-feeding assay. (more…)

Modelling mosquito infection at natural parasite densities identifies drugs targeting EF2, PI4K or ATP4 as key candidates for interrupting malaria transmission

Dechering KJ. et al., Sci. Rep. 2017 Dec 15


Eradication of malaria requires a novel type of drug that blocks transmission from the human to the mosquito host, but selection of such a drug is hampered by a lack of translational models. Experimental mosquito infections yield infection intensities that are substantially higher than observed in natural infections and, as a consequence, underestimate the drug effect on the proportion of mosquitoes that become infected. (more…)

A potent series targeting the malarial cGMP-dependent protein kinase clears infection and blocks transmission

Baker DA. et al., Nat Commun. 2017 Sep. 5


To combat drug resistance, new chemical entities are urgently required for use in next generation anti-malarial combinations. We report here the results of a medicinal chemistry programme focused on an imidazopyridine series targeting the Plasmodium falciparumcyclic GMP-dependent protein kinase (PfPKG). (more…)

Antimalarial efficacy of MMV390048, an inhibitor of Plasmodium phosphatidylinositol 4-kinase.

Paquet T. et al., Sci Transl Med. 2017 Apr 26


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. (more…)

Diversity-oriented synthesis yields novel multistage antimalarial inhibitors.

Kato N, et. al., Nature. 2016 Oct 20


Antimalarial drugs have thus far been chiefly derived from two sources-natural products and synthetic drug-like compounds. Here we investigate whether antimalarial agents with novel mechanisms of action could be discovered using a diverse collection of synthetic compounds that have three-dimensional features reminiscent of natural products and are underrepresented in typical screening collections. (more…)

Characterization of Novel Antimalarial Compound ACT-451840: Preclinical Assessment of Activity and Dose-Efficacy Modeling.

Le Bihan A et al., PLoS Med. 2016 Oct 4


BACKGROUND: Artemisinin resistance observed in Southeast Asia threatens the continued use of artemisinin-based combination therapy in endemic countries. Additionally, the diversity of chemical mode of action in the global portfolio of marketed antimalarials is extremely limited. (more…)

An inter-laboratory comparison of standard membrane-feeding assays for evaluation of malaria transmission-blocking vaccines.

Miura K. et al.,Malar J. 2016 Sep 9


BACKGROUND: An effective malaria transmission-blocking vaccine may play an important role in malaria elimination efforts, and a robust biological assay is essential for its development. The standard membrane-feeding assay (SMFA) for Plasmodium falciparum infection of mosquitoes is considered a "gold standard" assay to measure transmission-blocking activity of test antibodies, and has been utilized widely in both non-clinical and clinical studies. (more…)

Analysis of the dose-dependent stage-specific in vitro efficacy of a multi-stage malaria vaccine candidate cocktail.

Boes A. et al., Malar J. 2016 May 17


BACKGROUND: The high incidence and mortality rate of malaria remains a serious burden for many developing countries, and a vaccine that induces durable and highly effective immune responses is, therefore, desirable. (more…)

A semi-automated luminescence based standard membrane feeding assay identifies novel small molecules that inhibit transmission of malaria parasites by mosquitoes.

Vos MW. et al., Sci Rep. 2015 Dec 21


Current first-line treatments for uncomplicated falciparum malaria rapidly clear the asexual stages of the parasite, but do not fully prevent parasite transmission by mosquitoes. The standard membrane feeding assay (SMFA) is the biological gold standard assessment of transmission reducing activity (TRA), but its throughput is limited by the need to determine mosquito infection status by dissection and microscopy. (more…)

A simple and predictive phenotypic High Content Imaging assay for Plasmodium falciparum mature gametocytes to identify malaria transmission blocking compounds.

Lucantoni L. et al., Sci Rep. 2015 Nov 10


Plasmodium falciparum gametocytes, specifically the mature stages, are the only malaria parasite stage in humans transmissible to the mosquito vector. Anti-malarial drugs capable of killing these forms are considered essential for the eradication of malaria and tools allowing the screening of large compound libraries with high predictive power are needed to identify new candidates. (more…)

Salinomycin and other ionophores as a new class of antimalarial drugs with transmission-blocking activity.

D'Alessandro S. et al., Antimicrob Agents Chemother. 2015 Sep


The drug target profile proposed by the Medicines for Malaria Venture for a malaria elimination/eradication policy focuses on molecules active on both asexual and sexual stages of Plasmodium, thus with both curative and transmission-blocking activities. (more…)

A long-duration dihydroorotate dehydrogenase inhibitor (DSM265) for prevention and treatment of malaria.

Phillips MA et al., Sci Transl Med. 2015 Jul 15


Malaria is one of the most significant causes of childhood mortality, but disease control efforts are threatened by resistance of the Plasmodium parasite to current therapies. Continued progress in combating malaria requires development of new, easy to administer drug combinations with broad-ranging activity against all manifestations of the disease. (more…)

Analysis of a Multi-component Multi-stage Malaria Vaccine Candidate–Tackling the Cocktail Challenge.

Boes A, et al., PLoS One. 2015 Jul 6


Combining key antigens from the different stages of the P. falciparum life cycle in the context of a multi-stage-specific cocktail offers a promising approach towards the development of a malaria vaccine ideally capable of preventing initial infection, the clinical manifestation as well as the transmission of the disease. (more…)

A novel multiple-stage antimalarial agent that inhibits protein synthesis.

Baragaña B et al., Nature. 2015 Jun 18


There is an urgent need for new drugs to treat malaria, with broad therapeutic potential and novel modes of action, to widen the scope of treatment and to overcome emerging drug resistance. Here we describe the discovery of DDD107498, a compound with a potent and novel spectrum of antimalarial activity against multiple life-cycle stages of the Plasmodium parasite, with good pharmacokinetic properties and an acceptable safety profile. (more…)

A combination of new screening assays for prioritization of transmission-blocking antimalarials reveals distinct dynamics of marketed and experimental drugs.

Bolscher JM. et al., J Antimicrob Chemother. 2015 May


OBJECTIVES: The development of drugs to reduce malaria transmission is an important part of malaria eradication plans. We set out to develop and validate a combination of new screening assays for prioritization of transmission-blocking molecules. (more…)

Novel pantothenate derivatives for anti-malarial chemotherapy.

Pett HE, Jansen PA, Hermkens PH, Botman PN, Beuckens-Schortinghuis CA, Blaauw RH, Graumans W, van de Vegte-Bolmer M, Koolen KM, Rutjes FP, Dechering KJ, Sauerwein RW, Schalkwijk J. Malar J. 2015 Apr 18


BACKGROUND: A number of synthetic pantothenate derivatives, such as pantothenamides, are known to inhibit the growth of the human malaria parasite Plasmodium falciparum, by interfering with the parasite Coenzyme A (CoA) biosynthetic pathway. (more…)

A scalable assessment of Plasmodium falciparum transmission in the standard membrane-feeding assay, using transgenic parasites expressing green fluorescent protein-luciferase.

Stone WJ. et al., J Infect Dis. 2014 Nov 1


BACKGROUND: The development of drugs and vaccines to reduce malaria transmission is an important part of eradication plans. The transmission-reducing activity (TRA) of these agents is currently determined in the standard membrane-feeding assay (SMFA), based on subjective microscopy-based readouts and with limitations in upscaling and throughput. (more…)

Targeting Plasmodium PI(4)K to eliminate malaria.

McNamara CW et al., Nature. 2013 Dec 12


Achieving the goal of malaria elimination will depend on targeting Plasmodium pathways essential across all life stages. Here we identify a lipid kinase, phosphatidylinositol-4-OH kinase (PI(4)K), as the target of imidazopyrazines, a new antimalarial compound class that inhibits the intracellular development of multiple Plasmodium species at each stage of infection in the vertebrate host. (more…)

A Plasmodium falciparum screening assay for anti-gametocyte drugs based on parasite lactate dehydrogenase detection.

D'Alessandro S. et al., J Antimicrob Chemother. 2013 Sep


OBJECTIVES: Plasmodium gametocytes, responsible for malaria parasite transmission from humans to mosquitoes, represent a crucial target for new antimalarial drugs to achieve malaria elimination/eradication. We developed a novel colorimetric screening method for anti-gametocyte compounds based on the parasite lactate dehydrogenase (pLDH) assay, already standardized for asexual stages, to measure gametocyte viability and drug susceptibility. (more…)