Endochin-like quinolones are highly efficacious against acute and latent experimental toxoplasmosis

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 39; pp. 15936 - 15941
• Main Authors: Doggett, J. Stone, Nilsen, Aaron, Forquer, Isaac, Wegmann, Keith W, Jones-Brando, Lorraine, Yolken, Robert H, Bordón, Claudia, Charman, Susan A, Katneni, Kasiram, Schultz, Tracey, Burrows, Jeremy N, Hinrichs, David J, Meunier, Brigitte, Carruthers, Vern B, Riscoe, Michael K
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25-09-2012; National Acad Sciences
• Subjects: AIDS; amino acid substitution; Amino acids; Animals; Antimalarials; Antiprotozoal Agents - pharmacology; Biological Sciences; central nervous system; Chemical compounds; Cysts; cytochrome c; Cytochromes; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; drugs; Electron Transport Complex III - antagonists & inhibitors; Enzyme Inhibitors - pharmacology; Female; Humans; Infections; Inhibitory concentration 50; mechanism of action; Mice; nervous system diseases; oral administration; Parasitic diseases; Parasitic protozoa; pathogens; Proteins; Protozoan Proteins - antagonists & inhibitors; Quinolines - pharmacology; Quinolones; Rats; Rodents; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - antagonists & inhibitors; Toxoplasma - enzymology; Toxoplasma - growth & development; Toxoplasma gondii; Toxoplasmosis; Toxoplasmosis - drug therapy; Toxoplasmosis - enzymology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1208069109

Toxoplasma gondii is a widely distributed protozoan pathogen that causes devastating ocular and central nervous system disease. We show that the endochin-like quinolone (ELQ) class of compounds contains extremely potent inhibitors of T. gondii growth in vitro and is effective against acute and latent toxoplasmosis in mice. We screened 50 ELQs against T. gondii and selected two lead compounds, ELQ-271 and ELQ-316, for evaluation. ELQ-271 and ELQ-316, have in vitro IC ₅₀ values of 0.1 nM and 0.007 nM, respectively. ELQ-271 and ELQ-316 have ED ₅₀ values of 0.14 mg/kg and 0.08 mg/kg when administered orally to mice with acute toxoplasmosis. Moreover, ELQ-271 and ELQ-316 are highly active against the cyst form of T. gondii in mice at low doses, reducing cyst burden by 76–88% after 16 d of treatment. To investigate the ELQ mechanism of action against T. gondii , we demonstrate that endochin and ELQ-271 inhibit cytochrome c reduction by the T. gondii cytochrome bc ₁ complex at 8 nM and 31 nM, respectively. We also show that ELQ-271 inhibits the Saccharomyces cerevisiae cytochrome bc ₁ complex, and an M221Q amino acid substitution in the Q ᵢ site of the protein leads to >100-fold resistance. We conclude that ELQ-271 and ELQ-316 are orally bioavailable drugs that are effective against acute and latent toxoplasmosis, likely acting as inhibitors of the Q ᵢ site of the T. gondii cytochrome bc ₁ complex.