A novel fungal metabolite inhibits Plasmodium falciparum transmission and infection

Abstract

Background Malaria transmission depends on infected mosquitoes and can be controlled by transmission-blocking drugs. The recently discovered FREP1-mediated malaria transmission pathway is an excellent target to screen drugs for limiting transmission. Methods To identify candidate small molecules, we used an ELISA-based approach to analyze extracts from a fungal library for inhibition of the FREP1–parasite interaction. We isolated and determined one active compound by chromatography and crystallography, respectively. We measured the effects of the bioactive compound on malaria transmission to mosquitoes through standard membrane-feeding assays (SMFA) and on parasite proliferation in blood by culturing. Results We discovered the ethyl acetate extract of the fungus Purpureocillium lilacinum that inhibited Plasmodium falciparum transmission to mosquitoes. Pre-exposure to the extract rendered Anopheles gambiae resistant to Plasmodium infection. Furthermore, we isolated one novel active compound from the extract and identified it as 3-amino-7,9-dihydroxy-1-methyl-6H-benzo[c]chromen-6-one, or “pulixin.” Pulixin prevented FREP1 from binding to P. falciparum-infected cell lysate. Pulixin blocked the transmission of the parasite to mosquitoes with an EC50 (the concentration that gave half-maximal response) of 11 µM based on SMFA. Notably, pulixin also inhibited the proliferation of asexual-stage P. falciparum with an EC50 of 47 nM. The compound did not show cytotoxic effects at a concentration of 116 µM or lower. Conclusion By targeting the FREP1–Plasmodium interaction, we discovered that Purpureocillium lilacinum extract blocked malaria transmission. We isolated and identified the bioactive agent pulixin as a new compound capable of stopping malaria transmission to mosquitoes and inhibiting parasite proliferation in blood culture.

Studies of the Parasite-Midgut Interaction Reveal Plasmodium Proteins Important for Malaria Transmission to Mosquitoes

“…Besides targeted by transmission-blocking vaccines, these interactive proteins can also be targeted by small molecules to block malaria transmission. The fungal secondary metabolite P -orlandin from Aspergillus niger ( Niu et al., 2015 ), asperaculane B from Aspergillus aculeatus ( Niu et al., 2020b ), and pulixin ( Niu et al., 2021 ) that prevent FREP1 in mosquito midgut from binding to sexual stage Plasmodium falciparum inhibit malaria transmission to mosquitoes. A synthetic polysulfonated polymer limits malaria transmission by inhibiting the interaction between midgut chondroitin sulfate glycosaminoglycans and ookinetes ( Mathias et al., 2013 ).…”

Plasmodium parasitophorous vacuole membrane protein Pfs16 promotes malaria transmission by silencing mosquito immunity

“…Besides regular vaccines to prevent parasites from infecting humans, many studies over the last decade also focused on vaccine development to block malaria transmission, for example, transmission-blocking vaccines, and discovered some key targets such as Pfs25, Pfs47, and α-tubulin-1 from the parasite ( 12 , 33 , 34 , 35 ) and AnAPN1 and FREP1 from the mosquito ( 32 , 35 , 36 , 37 , 38 , 39 ). Blocking malaria transmission by small molecules is also under investigation, and several fungal secondary metabolites have been identified ( 40 , 41 , 42 ).…”

Contemporary exploitation of natural products for arthropod-borne pathogen transmission-blocking interventions

“…Consequently, such disruption, as at low dose of 3 µg/ml, effectively reduced P. falciparum infection load in mosquitoes by 56.7% oocyst numbers and 35% infection prevalence. In continuation with this work by Jun Li’s group, other fungal compounds, Asperaculane B ( 10 ) and [3-amino-7,9-dihydroxy-1-methyl-6 H -benzo[c]chromen-6-one (Pulixin, ( 11 )], with Plasmodium transmission-blocking activities have been identified [ 63 , 64 ]. Compound 10 derived from Aspergillus aculeatus inhibits Plasmodium transmission at IC 50 7.89 µM, while 11 isolated from Purpureocillium lilacinum exerts its activity in mosquitoes at EC 50 11 µM, without notable host cytotoxicity.…”