Reaksudsan, K. | bioRxiv Science

bioRxiv2026

Targeting PTRAMP-CSS potently inhibits P. falciparum across blood, liver and mosquito stages

Malaria, caused by Plasmodium falciparum spans liver, blood, and mosquito stages, limiting the effectiveness of single-stage vaccines. The PTRAMP-CSS heterodimer, a core component of the essential PCRCR invasion complex, is expressed on merozoites, mature gametocytes, and salivary gland sporozoites, enabling single-antigen targeting across multiple lifecycle stages. Nanobodies against PTRAMP-CSS block merozoite invasion of erythrocytes, reduce mosquito infection in membrane-feeding assays, and inhibit sporozoite invasion of primary human hepatocytes. High-resolution crystal structures of inhibitory and non-inhibitory nanobody-antigen complexes identify conserved inhibitory epitopes and guide the design of bispecific nanobody Fc constructs with enhanced potency. In semi-immune Kenyan CHMI samples, higher baseline IgG to PTRAMP-CSS and Ripr is associated with improved parasite control. By demonstrating conserved vulnerability across all three major lifecycle stages, PTRAMP-CSS offers a realistic path to single-antigen, multistage vaccines and biologics that aim to prevent disease and block transmission.

microbiology↗

bioRxiv2023

Aryl amino acetamides prevent the development of Plasmodium falciparum rings via inhibition of the lipid transfer protein PfSTART1

With resistance to most antimalarials increasing, it is imperative that new antimalarial drugs are developed to replace or complement front-line artemisinin therapies. We previously identified an aryl acetamide compound, MMV006833 (M-833), that inhibited ring development of newly invaded merozoites. Here, we selected parasites resistant to M-833 and identified independent mutations arising in the START lipid transfer protein (PF3D7_0104200, PfSTART1). Introduction of the identified PfSTART1 mutations into wildtype parasites reproduced resistance to both M-833 and highly potent analogues, confirming PfSTART1 mutations were sufficient to confer resistance. The analogues bound to recombinant PfSTART1 with nanomolar affinity. We also demonstrated selective PfSTART1 engagement by the analogues using organic solvent-based Proteome Integral Solubility Alteration (Solvent PISA) assay for the first time in Plasmodium. Imaging of newly invaded merozoites showed the inhibitors prevented the conversion into larger amoeboid ring-stage parasites potentially through the inhibition of phospholipid transfer from the parasite to the encasing parasitophorous vacuole membrane (PVM) and/or within the parasite. We show that these PfSTART1 inhibitors also block transmission. With multiple stages of the parasites lifecycle being targeted by PfSTART1 inhibitors, this protein therefore represents a novel drug target with a new mechanism of action.

cell biology↗