Safety, infectivity and immunogenicity of a genetically attenuated blood-stage malaria vaccine.

Background: There is a clear need for novel approaches to malaria vaccine development. We aimed to develop a genetically attenuated blood-stage vaccine and test its safety, infectivity, and immunogenicity in healthy volunteers. Our approach was to target the gene encoding the knob-associated histidine-rich protein (KAHRP), which is responsible for the assembly of knob structures at the infected erythrocyte surface.

Development and evaluation of a new Plasmodium falciparum 3D7 blood stage malaria cell bank for use in malaria volunteer infection studies.

Background: New anti-malarial therapeutics are required to counter the threat of increasing drug resistance. Malaria volunteer infection studies (VIS), particularly the induced blood stage malaria (IBSM) model, play a key role in accelerating anti-malarial drug development. Supply of the reference 3D7-V2 Plasmodium falciparum malaria cell bank (MCB) is limited.

Anti- Drug Discovery: Current Status and Gut Feelings.

parasites are ubiquitous protozoans of global importance that impact a wide range of animals including humans. They are the most common enteric pathogen of cats and dogs in developed countries and infect ∼1 billion people worldwide. While infections can be asymptomatic, they often result in severe and chronic diseases.

Identification of Antimalarial Inhibitors Using Late-Stage Gametocytes in a Phenotypic Live/Dead Assay.

Malaria remains a major cause of morbidity and mortality worldwide with ~3.3 billion people at risk of contracting malaria and an estimated 450,000 deaths each year. While tools to reduce the infection prevalence to low levels are currently under development, additional efforts will be required to interrupt transmission.

A bioreactor system for the manufacture of a genetically modified Plasmodium falciparum blood stage malaria cell bank for use in a clinical trial.

Background: Although the use of induced blood stage malaria infection has proven to be a valuable tool for testing the efficacy of vaccines and drugs against Plasmodium falciparum, a limiting factor has been the availability of Good Manufacturing Practice (GMP)-compliant defined P. falciparum strains for in vivo use. The aim of this study was to develop a cost-effective method for the large-scale production of P.

The development of sexual stage malaria gametocytes in a Wave Bioreactor.

Background: Blocking malaria gametocyte development in RBCs or their fertilization in the mosquito gut can prevent infection of the mosquito vector and passage of disease to the human host. A 'transmission blocking' strategy is a component of future malaria control. However, the lack of robust culture systems for producing large amounts of Plasmodium falciparum gametocytes has limited our understanding of sexual-stage malaria biology and made vaccine or chemotherapeutic discoveries more difficult.

Infectivity of Plasmodium falciparum in Malaria-Naive Individuals Is Related to Knob Expression and Cytoadherence of the Parasite.

Plasmodium falciparum is the most virulent human malaria parasite because of its ability to cytoadhere in the microvasculature. Nonhuman primate studies demonstrated relationships among knob expression, cytoadherence, and infectivity. This has not been examined in humans.

A Plasmodium falciparum S33 proline aminopeptidase is associated with changes in erythrocyte deformability.

Infection with the apicomplexan parasite Plasmodium falciparum is a major cause of morbidity and mortality worldwide. One of the striking features of this parasite is its ability to remodel and decrease the deformability of host red blood cells, a process that contributes to disease. To further understand the virulence of Pf we investigated the biochemistry and function of a putative Pf S33 proline aminopeptidase (PfPAP).

Linking Murine and Human Plasmodium falciparum Challenge Models in a Translational Path for Antimalarial Drug Development.

Effective progression of candidate antimalarials is dependent on optimal dosing in clinical studies, which is determined by a sound understanding of pharmacokinetics and pharmacodynamics (PK/PD). Recently, two important translational models for antimalarials have been developed: the NOD/SCID/IL2Rγ(-/-) (NSG) model, whereby mice are engrafted with noninfected and Plasmodium falciparum-infected human erythrocytes, and the induced blood-stage malaria (IBSM) model in human volunteers. The antimalarial mefloquine was used to directly measure the PK/PD in both models, which were compared to previously published trial data for malaria patients.

A repeat sequence domain of the ring-exported protein-1 of Plasmodium falciparum controls export machinery architecture and virulence protein trafficking.

The malaria parasite Plasmodium falciparum dramatically remodels its host red blood cell to enhance its own survival, using a secretory membrane system that it establishes outside its own cell. Cisternal organelles, called Maurer's clefts, act as a staging point for the forward trafficking of virulence proteins to the red blood cell (RBC) membrane. The Ring-EXported Protein-1 (REX1) is a Maurer's cleft resident protein.

Development of cultured Plasmodium falciparum blood-stage malaria cell banks for early phase in vivo clinical trial assessment of anti-malaria drugs and vaccines.

Background: The ability to undertake controlled human malaria infection (CHMI) studies for preliminary evaluation of malaria vaccine candidates and anti-malaria drug efficacy has been limited by the need for access to sporozoite infected mosquitoes, aseptic, purified, cryopreserved sporozoites or blood-stage malaria parasites derived ex vivo from malaria infected individuals. Three different strategies are described for the manufacture of clinical grade cultured malaria cell banks suitable for use in CHMI studies.

Methods: Good Manufacturing Practices (GMP)-grade Plasmodium falciparum NF54, clinically isolated 3D7, and research-grade P.

Lysine acetylation in sexual stage malaria parasites is a target for antimalarial small molecules.

Therapies to prevent transmission of malaria parasites to the mosquito vector are a vital part of the global malaria elimination agenda. Primaquine is currently the only drug with such activity; however, its use is limited by side effects. The development of transmission-blocking strategies requires an understanding of sexual stage malaria parasite (gametocyte) biology and the identification of new drug leads.

Identification of Potent and Selective Inhibitors of the Plasmodium falciparum M18 Aspartyl Aminopeptidase (PfM18AAP) of Human Malaria via High-Throughput Screening.

The target of this study, the PfM18 aspartyl aminopeptidase (PfM18AAP), is the only AAP present in the genome of the malaria parasite Plasmodium falciparum. PfM18AAP is a metallo-exopeptidase that exclusively cleaves N-terminal acidic amino acids glutamate and aspartate. It is expressed in parasite cytoplasm and may function in concert with other aminopeptidases in protein degradation, of, for example, hemoglobin.

Plasmodium gametocyte inhibition identified from a natural-product-based fragment library.

Fragment-based screening is commonly used to identify compounds with relatively weak but efficient localized binding to protein surfaces. We used mass spectrometry to study fragment-sized three-dimensional natural products. We identified seven securinine-related compounds binding to Plasmodium falciparum 2'-deoxyuridine 5'-triphosphate nucleotidohydrolase (PfdUTPase).

Plasmodium falciparum gametocytes: with a view to a kill.

Drugs that kill or inhibit the sexual stages of Plasmodium in order to prevent transmission are important components of malaria control programmes. Reducing gametocyte carriage is central to the control of Plasmodium falciparum transmission as infection can result in extended periods of gametocytaemia. Unfortunately the number of drugs with activity against gametocytes is limited.

Experimentally induced blood-stage Plasmodium vivax infection in healthy volunteers.

Background: Major impediments to development of vaccines and drugs for Plasmodium vivax malaria are the inability to culture this species and the extreme difficulty in undertaking clinical research by experimental infection.

Methods: A parasite bank was collected from a 49-year-old woman with P. vivax infection, characterized, and used in an experimental infection study.

Enhanced gametocyte formation in erythrocyte progenitor cells: a site-specific adaptation by Plasmodium falciparum.

Gametocytogenesis by Plasmodium falciparum is essential for transmission of the parasite from human to mosquito, yet developing gametocytes lack expression of surface proteins required for cytoadherence. Therefore, elimination from the circulation should occur unless they are sequestered in regions of low blood flow such as the extracellular spaces of the bone marrow. Our data indicate that gametocytogenesis is enhanced in the presence of erythroid progenitors found within the bone marrow.

Temporal evaluation of commitment to sexual development in Plasmodium falciparum.

Background: The production of gametocytes is essential for transmission of malaria parasites from the mammalian host to the mosquito vector. However the process by which the asexual blood-stage parasite undergoes commitment to sexual development is not well understood. This process is known to be sensitive to environmental stimuli and it has been suggested that a G protein dependent system may mediate the switch, but there is little evidence that the Plasmodium falciparum genome encodes heterotrimeric G proteins.

X-ray crystal structure and specificity of the Plasmodium falciparum malaria aminopeptidase PfM18AAP.

The malarial aminopeptidases have emerged as promising new drug targets for the development of novel antimalarial drugs. The M18AAP of Plasmodium falciparum malaria is a metallo-aminopeptidase that we show demonstrates a highly restricted specificity for peptides with an N-terminal Glu or Asp residue. Thus, the enzyme may function alongside other aminopeptidases in effecting the complete degradation or turnover of proteins, such as host hemoglobin, which provides a free amino acid pool for the growing parasite.

The aminopeptidase inhibitor CHR-2863 is an orally bioavailable inhibitor of murine malaria.

Malaria remains a significant risk in many areas of the world, with resistance to the current antimalarial pharmacopeia an ever-increasing problem. The M1 alanine aminopeptidase (PfM1AAP) and M17 leucine aminopeptidase (PfM17LAP) are believed to play a role in the terminal stages of digestion of host hemoglobin and thereby generate a pool of free amino acids that are essential for parasite growth and development. Here, we show that an orally bioavailable aminopeptidase inhibitor, CHR-2863, is efficacious against murine malaria.

Fingerprinting the substrate specificity of M1 and M17 aminopeptidases of human malaria, Plasmodium falciparum.

Background: Plasmodium falciparum, the causative agent of human malaria, expresses two aminopeptidases, PfM1AAP and PfM17LAP, critical to generating a free amino acid pool used by the intraerythrocytic stage of the parasite for proteins synthesis, growth and development. These exopeptidases are potential targets for the development of a new class of anti-malaria drugs.

Methodology/principal Findings: To define the substrate specificity of recombinant forms of these two malaria aminopeptidases we used a new library consisting of 61 fluorogenic substrates derived both from natural and unnatural amino acids.

Anti-malarial drugs: how effective are they against Plasmodium falciparum gametocytes?

Background: Recent renewed emphasis on the eradication of malaria has highlighted the need for more tools with which to achieve this ambitious goal. One high priority area is the need to determine the gametocytocidal activity of both currently used anti-malarial drugs and those in the development pipeline. However, testing the activity of compounds against Plasmodium falciparum gametocytes is technically challenging both in vivo and in vitro.