Although artemisinin combination therapies have succeeded in reducing the global burden of malaria, multidrug resistance of the deadliest malaria parasite, Plasmodium falciparum, is emerging worldwide. Innovative antimalarial drugs that kill all life-cycle stages of malaria parasites are urgently needed. Here, we report the discovery of the compound JX21108 with broad antiplasmodial activity against multiple life-cycle stages of malaria parasites. JX21108 was developed from chemical optimization of quisinostat, a histone deacetylase inhibitor. We identified P. falciparum histone deacetylase 1 (PfHDAC1), an epigenetic regulator essential for parasite growth and invasion, as a molecular target of JX21108. PfHDAC1 knockdown leads to the downregulation of essential parasite genes, which is highly consistent with the transcriptomic changes induced by JX21108 treatment. Collectively, our data support that PfHDAC1 is a potential drug target for overcoming multidrug resistance and that JX21108 treats malaria and blocks parasite transmission simultaneously.

The protective immunity induced by the whole-killed parasite vaccine against malarial blood-stage infection is dependent on the CD4+ T cell response. However, the mechanism underlying this robust CD4+ T cell response elicited by the whole-killed parasite vaccine is still largely unknown. In this study, we observe that immunization with Plasmodium yoelii–parasitized RBC lysate activates complement C5 and generates C5a. However, the protective efficacy against P. yoelii 17XL challenge is considerably reduced, and the malaria-specific CD4+ T cell activation and memory T cell differentiation are largely suppressed in the C5aR-deficient (C5aR−/−) mice. An adoptive transfer assay demonstrates that the reduced protection of C5aR−/− mice is closely associated with the severely impaired CD4+ T cell response. This is further confirmed by the fact that administration of C5aR antagonist significantly reduces the protective efficacy of the immunized B cell–deficient mice. Further study indicates that the defective CD4+ T cell response in C5aR−/− mice is unlikely involved in the expansion of CD4+CD25+Foxp3+ T cells, but strongly linked to a defect in dendritic cell (DC) maturation and the ability to allostimulate CD4+ T cells. These results demonstrate that C5aR signaling is essential for the optimal induction of the malaria-specific CD4+ T cell response by the whole-killed parasite vaccine through modulation of DCs function, which provides us with new clues to design an effective blood-stage subunit vaccine and helps us to understand the mechanism by which the T cell response is regulated by the complement system.

TLR2 specifically recognizes a wide range of ligands by homodimerizing or heterodimerizing with TLR1 or TLR6. However, the molecular basis of the specific signalling transduction induced by TLR2 homodimerization or heterodimerization with TLR1 or TLR6 is largely unknown. In this study, we found three amino acid residues, two (663L and 688N) outside and one (681P) inside the BB loop, which were conserved in all of the TLRs, except for the TLR3 toll/IL-1R(TIR) domain. The responsiveness of human TLR2/2, TLR2/1 or TLR2/6 was completely lost when 663L and 688N were replaced with the corresponding amino acid residues in the TLR3 TIR domain, respectively. However, the response of TLR2 (P681A) to the high concentration of TLR2/TLR6 agonist was almost intact, but the activity of TLR2 (P681A) was greatly reduced when stimulated with the TLR2/1 agonist or the TLR2/2 agonist. Although the surface expression of TLR2 (L663E) was sharply reduced, both the intracellular distribution and the surface expression of all of the other TLR2 mutants were unchanged. The ability of all three TLR2 mutants to recruit MyD88, was consistent with their responsivenesses. Computer modelling indicated that the surface negative charge of all of the TLR2 mutants' BB loops was reduced. Thus, our data demonstrated that the 663L and 688N residues outside of the BB loop were essential for the responsiveness of TLR2/2, TLR2/1 and TLR2/6, but the 681P residue inside of the BB loop exhibited divergent roles in TLR2/2, TLR2/1 and TLR2/6 signalling transduction, thereby providing clues regarding the specific signalling transduction of TLR2/2, TLR2/1 and TLR2/6.

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Previously, we identified the clinical anticancer drug candidate quisinostat as a novel and potent antimalarial lead compound. To further enhance the antimalarial effect and improve safety, 31 novel spirocyclic hydroxamic acid derivatives were synthesized based on the structure of quisinostat, and their antimalarial activities and cytotoxicity were evaluated. Among them, compound 11 displayed broad potency in vitro against several multiresistant malarial parasites, especially two artemisinin-resistant clinical isolates. Moreover, 11 could eliminate both liver and erythrocytic parasites in vivo, kill all morphological erythrocytic parasites with specific potency against schizonts, and show acceptable metabolic stability and pharmacokinetic properties. Western blot analysis, PfHDAC gene knockdown, and enzymatic inhibition experiments collectively confirmed that PfHDAC1 was the target of 11. In summary, 11 is a structurally novel PfHDAC1 inhibitor with the potential to prevent and cure malaria, overcome multidrug resistance, and provide a prospective prototype for antimalarial drug research.