Novel endochin-like quinolones exhibit potent in vitro activity against Plasmodium knowlesi but do not synergize with proguanil

Donelly A. Van Schalkwyk, Michael K. Riscoe, Sovitj Pou, Rolf W. Winter, Aaron Nilsen, Maëlle Duffey, Robert W. Moon, Colin J. Sutherland

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Quinolones, such as the antimalarial atovaquone, are inhibitors of the malarial mitochondrial cytochrome bc1 complex, a target critical to the survival of both liver-and blood-stage parasites, making these drugs useful as both prophylaxis and treatment. Recently, several derivatives of endochin have been optimized to produce novel quinolones that are active in vitro and in animal models. While these quinolones exhibit potent ex vivo activity against Plasmodium falciparum and Plasmodium vivax, their activity against the zoonotic agent Plasmodium knowlesi is unknown. We screened several of these novel endochin-like quinolones (ELQs) for their activity against P. knowlesi in vitro and compared this with their activity against P. falciparum tested under identical conditions. We demonstrated that ELQs are potent against P. knowlesi (50% effective concentration, <117 nM) and equally effective against P. falciparum. We then screened selected quinolones and partner drugs using a longer exposure (2.5 life cycles) and found that proguanil is 10-fold less potent against P. knowlesi than P. falciparum, while the quinolones demonstrate similar potency. Finally, we used isobologram analysis to compare combinations of the ELQs with either proguanil or atovaquone. We show that all quinolone combinations with proguanil are synergistic against P. falciparum. However, against P. knowlesi, no evidence of synergy between proguanil and the quinolones was found. Importantly, the combination of the novel quinolone ELQ-300 with atovaquone was synergistic against both species. Our data identify potentially important species differences in proguanil susceptibility and in the interaction of proguanil with quinolones and support the ongoing development of novel quinolones as potent antimalarials that target multiple species.

Original languageEnglish (US)
Article numbere02549-19
JournalAntimicrobial agents and chemotherapy
Issue number5
StatePublished - May 2020


  • Antimalarial chemotherapy
  • Drug susceptibility
  • In vitro
  • Isobolograms
  • Plasmodium falciparum
  • Plasmodium knowlesi

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)
  • Infectious Diseases


Dive into the research topics of 'Novel endochin-like quinolones exhibit potent in vitro activity against Plasmodium knowlesi but do not synergize with proguanil'. Together they form a unique fingerprint.

Cite this