Strong off-target antibody reactivity to malarial antigens induced by RTS,S/AS01E vaccination is associated with increased protection

The RTS,S/AS01E vaccine targets the circumsporozoite protein (CSP) of the Plasmodium falciparum parasite. Using protein microarrays, levels of IgG to 1,000 P. falciparum antigens were measured in 2,138 infants (age 6-12 weeks) and children (age 5-17 months) from 6 African sites of the phase 3 trial, sampled before and at four longitudinal visits after vaccination. One month post-vaccination, IgG responses to 17% of all probed antigens showed differences between RTS,S/AS01E and comparator vaccination groups, whereas no prevaccination differences were found. A small subset of antigens presented IgG levels reaching 4- to 8 fold increases in the RTS,S/AS01E group, comparable in magnitude to anti-CSP IgG levels (~11-fold increase). They were strongly cross-correlated and correlated with anti CSP levels, waning similarly over time and re-increasing with the booster dose. Such an intriguing phenomenon may be due to cross-reactivity of anti-CSP antibodies with these antigens. RTS,S/AS01E vaccinees with strong off target IgG responses had an estimated lower clinical malaria incidence after adjusting for age group, site and post-vaccination anti-CSP levels. RTS,S/AS01E-induced IgG may bind strongly not only to CSP, but to unrelated malaria antigens, and this seems to either confer, or at least be a marker of, increased protection from clinical malaria.

The antimalarial MMV688533 provides potential for single-dose cures with a high barrier to Plasmodium falciparum parasite resistance

The emergence and spread of Plasmodium falciparum resistance to first-line antimalarials creates an imperative to identify and develop potent preclinical candidates with distinct modes of action. Here, we report the identification of MMV688533, an acylguanidine that was developed following a whole-cell screen with compounds known to hit high-value targets in human cells. MMV688533 displays fast parasite clearance in vitro and is not cross-resistant with known antimalarials. In a P. falciparum NSG mouse model, MMV688533 displays a long-lasting pharmacokinetic profile and excellent safety. Selection studies reveal a low propensity for resistance, with modest loss of potency mediated by point mutations in PfACG1 and PfEHD. These proteins are implicated in intracellular trafficking, lipid utilization, and endocytosis, suggesting interference with these pathways as a potential mode of action. This preclinical candidate may offer the potential for a single low-dose cure for malaria.

4-Aminoquinoline-ferrocene Hybrids as Potential Antimalarials

Background: Malaria is a deadly disease. It is mostly treated using 4- aminoquinoline derivatives such as chloroquine etc. because it is well-tolerated, displays low toxicity, and after administration, it is rapidly absorbed. The combination of 4-aminoquinoline with other classes of antimalarial drugs has been reported to be an effective approach for the treatment of malaria. Furthermore, some patents reported hybrids 4-aminoquinolines containing ferrocene moiety with potent antimalarial activity. Objective: The objective of the current study is to prepare 4-aminoquinoline-ferrocene hybrids via esterification and amidation reactions. The compounds were characterized via FTIR, LC-MS and NMR spectroscopy. In vitro screening against chloroquine-sensitive P. falciparum parasite (NF54) at concentrations (1 μM and 5 μM) and an inhibitory concentration (full dose-response) was studied. Methods: The compounds were prepared via known reactions and monitored by Thin Layer Chromatography. The compounds were purified by column chromatography and characterized using FTIR, NMR and MS. In vitro antiplasmodial evaluation was performed against asexual parasite and chloroquine was used as a reference drug. Results: The percentage inhibition effects of the hybrid compounds were in a range of 97.9-102% at 5 μM and 36-96% at 1 μM. Furthermore, the IC50 values of the compounds were in the range of 0.7-1.6 μM when compared to the parent drug, 4-ferrocenylketobutanoic acid. Conclusion: The hybrid compounds displayed significant antimalarial activity when compared to the parent drug. However, they were not as effective as chloroquine on the drug-sensitive parasite. The findings revealed that 4-aminoquinolines and ferrocene are potential scaffolds for developing potent antimalarials.

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

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. We generated chimeric P. falciparum parasites expressing both PfCSP and PvCSP. These Pf-PvCSP parasites produced sporozoite comparable to wild type P. falciparum parasites and expressed PfCSP and PvCSP on the sporozoite surface. Pf-PvCSP sporozoites infected human hepatocytes and induced antibodies to the repeats of both PfCSP and PvCSP after immunization of mice. These results support the use of Pf-PvCSP sporozoites in studies optimizing vaccines targeting PvCSP.

Invitro Antimalarial and Antibacterial Activities of Methanol Stem Bark Extract of Frankincense Tree (Boswellia dalzielii) and Leaves Extract of Kenaf (Hibiscus cannabinus)

Aim: This research investigated the anti-malarial and antibacterial activities of stem bark methanol extract of Frankincense tree and Kenaf leaves extract on Plasmodium falciparum parasite and against five clinically significant bacteria. Study Design: Laboratory-experimental design was used for this study. Place and Duration of Study: This study was carried out between September 2019 and November 2019 at Biochemistry and Microbiology laboratories, Sokoto State University, Sokoto, Nigeria. Methodology: The in vitro antimalarial activity test was conducted by determining the parasitemia for each sample concentration by manual counting on thin Giemsa smears after a 24-hour incubation with the extracts in order to determine the IC50 values. The antibacterial study was done using a modified agar well diffusion technique. Results: The testing revealed that methanol stem bark extract of Frankincense tree and Kenaf leaves exhibited good and potent (very good) antimalarial activities against P. falciparum respectively with IC50 values of 1.25 μg/mL and 0.16 μg/mL respectively. They also show good inhibitory activities against E.coli but slight inhibitory activities against the other pathogens tested. Conclusion: The current study indicates that extracts of these plants exhibit anti-malarial and antibacterial activities and may serve as useful sources of drugs for treatment of malaria caused by P. falciparum parasite as well as bacterial infections caused by the tested bacteria.