title: How do the alkaloids emetine and homoharringtonine kill trypanosomes? An insight into their molecular modes of action.
abstract: BACKGROUND
  Although Trypanosoma brucei causes deadly sleeping sickness, the number of the registered medications is rather limited. Some plant alkaloids are potent trypanocidal agents.
  
  
  OBJECTIVE
  In this study, we wanted to elucidate the molecular modes of trypanocidal activity of the alkaloids emetine and homoharringtonine against Trypanosoma brucei brucei.
  
  
  METHODS
  We investigated the activity of both alkaloids regarding growth recovery from alkaloid-induced stress. We measured the inhibition of protein biosynthesis using the Click-iT®AHA Alexa Fluor®488 Protein Synthesis HCS Assay kit. Reduction of mitochondrial membrane potential and cell cycle arrest were measured by means of flow cytometry. Additionally, we determined spectrophotometrically the inhibition of the trypanosome specific enzyme trypanothione reductase activity and DNA intercalation.
  
  
  RESULTS
  Both alkaloids prevented that parasites could resume normal growth after pretreatment with the alkaloids. They inhibited protein biosynthesis in a time- and concentration-dependent manner. In contrast to homoharringtonine, emetine is also a DNA intercalator. Homoharringtonine decreased the mitochondrial membrane potential. Both alkaloids caused cell cycle arrest. Both alkaloids failed to affect trypanothione reductase, a crucial component of the redox system of trypanosomes.
  
  
  CONCLUSIONS
  We assume that both alkaloids are primarily inhibitors of protein biosynthesis in trypanosomes, with DNA intercalation as an additional mechanism for emetine. This is the first study that elucidates the molecular mode of trypanocidal action of emetine and homoharringtonine.
authors.affiliation: Heidelberg University, Institute of Pharmacy and Molecular Biotechnology, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany. Electronic address: krstin@uni-heidelberg.de.
authors.forename: Sonja
authors.initials: S
authors.lastname: Krstin
authors.affiliation: Heidelberg University, Institute of Pharmacy and Molecular Biotechnology, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany.
authors.forename: Tamer
authors.initials: T
authors.lastname: Mohamed
authors.affiliation: Heidelberg University, Institute of Pharmacy and Molecular Biotechnology, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany.
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Wang
authors.affiliation: Heidelberg University, Institute of Pharmacy and Molecular Biotechnology, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany. Electronic address: wink@uni-hd.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Wink
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D020533:Angiogenesis Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D016054:DNA, Protozoan / Q000378:metabolism; D004640:Emetine / Q000494:pharmacology*; D006248:Harringtonines / Q000494:pharmacology*; D000077863:Homoharringtonine; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D008517:Phytotherapy; D010936:Plant Extracts / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects*; D015800:Protozoan Proteins / Q000378:metabolism; D014344:Trypanocidal Agents / Q000494:pharmacology*; D014346:Trypanosoma brucei brucei / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D014353:Trypanosomiasis, African / Q000188:drug therapy / Q000469:parasitology*
chemical_list: D000470:Alkaloids; D020533:Angiogenesis Inhibitors; D016054:DNA, Protozoan; D006248:Harringtonines; D010936:Plant Extracts; D015800:Protozoan Proteins; D014344:Trypanocidal Agents; D000077863:Homoharringtonine; D009247:NADH, NADPH Oxidoreductases; C049608:trypanothione reductase; D004640:Emetine
keywords: Cell cycle; Emetine; Homoharringtonine; Mitochondrial membrane potential; Protein biosynthesis; Trypanosome