Toll-like receptor-7/8 agonist kill Leishmania amazonensis by acting as pro-oxidant and pro-inflammatory agent

J Pharm Pharmacol. 2021 Aug 12;73(9):1180-1190. doi: 10.1093/jpp/rgab063.


Objectives: Evaluation of the anti-Leishmanial activity of imidazoquinoline-based TLR7/8 agonists.

Methods: TLR7/8-active imidazoquinolines (2 and 3) were synthesized and assessed for activity against Leishmania amazonensis-intracellular amastigotes using mouse peritoneal macrophages. The production of reactive oxygen species (ROS), nitric oxide (NO) and cytokines was determined in infected and non-infected macrophages.

Key findings: The imidazoquinolines, 2 and 3, were primarily agonists of TLR7 with compound 3 also showing modest TLR8 activity. Docking studies showed them to occupy the same binding pocket on TLR7 and 8 as the known agonists, imiquimod and resiquimod. Compounds 2 and 3 inhibited the growth of L. amazonensis-intracellular amastigotes with the most potent compound (3, IC50 = 5.93 µM) having an IC50 value close to miltefosine (IC50 = 4.05 µM), a known anti-Leishmanial drug. Compound 3 induced macrophages to produce ROS, NO and inflammatory cytokines that likely explain the anti-Leishmanial effects.

Conclusions: This study shows that activating TLR7 using compounds 2 or 3 induces anti-Leishmanial activity associated with induction of free radicals and inflammatory cytokines able to kill the parasites. While 2 and 3 had a very narrow cytotoxicity window for macrophages, this identifies the possibility to further develop this chemical scaffold to less cytotoxic TLR7/8 agonist for potential use as anti-Leishmanial drug.

Keywords: Leishmania; TLR7; TLR8; Toll-like receptor; immunomodulation; immunotherapy.

MeSH terms

  • Animals
  • Antiprotozoal Agents / chemical synthesis
  • Antiprotozoal Agents / pharmacology*
  • Cytokines / metabolism
  • Female
  • Humans
  • Imidazoles
  • Imiquimod
  • Inflammation / metabolism
  • Leishmania / drug effects*
  • Leishmaniasis / parasitology
  • Macrophages, Peritoneal / drug effects*
  • Macrophages, Peritoneal / parasitology
  • Mice, Inbred BALB C
  • Nitric Oxide / metabolism
  • Reactive Oxygen Species / metabolism
  • Toll-Like Receptor 7 / agonists*
  • Toll-Like Receptor 8 / agonists*


  • Antiprotozoal Agents
  • Cytokines
  • Imidazoles
  • Reactive Oxygen Species
  • TLR7 protein, human
  • TLR8 protein, human
  • Toll-Like Receptor 7
  • Toll-Like Receptor 8
  • Nitric Oxide
  • Imiquimod
  • resiquimod