Identifying apicoplast-targeting antimalarials using high-throughput compatible approaches.

Area of Science:

• Parasitology
• Drug Discovery
• Molecular Biology

Background:

• Plasmodium falciparum malaria parasites are developing resistance to existing therapies, including artemisinins.
• Novel antimalarial drugs with new mechanisms of action are urgently needed to combat drug resistance.

Purpose of the Study:

• To develop and implement a high-throughput screening (HTS) assay to identify novel antimalarial compounds targeting the Plasmodium falciparum apicoplast.
• To discover new antimalarials effective against drug-resistant malaria strains.

Main Methods:

• Developed a "delayed death" HTS assay targeting the apicoplast, exploiting a phenotype where drug-treated parasite progeny die.
• Utilized a primary assay with a luciferase reporter gene and a secondary flow cytometry assay with nucleic acid and mitochondrial dyes.
• Screened the U.S. National Institutes of Health Clinical Collection.

Main Results:

• Identified known and novel antimalarial compounds, including the macrolide kitasamycin.
• Kitasamycin demonstrated potent in vitro activity (IC50 ~50 nM) against the apicoplast, comparable to azithromycin.
• Confirmed kitasamycin's apicoplast targeting and observed in vivo efficacy in a murine malaria model.

Conclusions:

• The developed HTS assays are effective for identifying novel antimalarial chemotypes targeting the apicoplast.
• Kitasamycin represents a promising candidate for further development, potentially for combination therapies against multidrug-resistant malaria.