title: Autophagy inhibitor chloroquine enhanced the cell death inducing effect of the flavonoid luteolin in metastatic squamous cell carcinoma cells.
abstract: BACKGROUND
  Flavonoids are widely proposed as very interesting compounds with possible chemopreventive and therapeutic capacities.
  
  
  RESULTS
  In this study, we showed that in vitro treatment with the flavonoid Luteolin induced caspase-dependent cell death in a model of human cutaneous squamous cell carcinoma (SCC) derived cells, representing a matched pair of primary tumor and its metastasis. Notably, no cytotoxic effects were observed in normal human keratinocytes when treated with similar doses of Luteolin. Luteolin-induced apoptosis was accompanied by inhibition of AKT signaling, and sensitivity decreased with tumor progression, as the primary MET1 SCC cells were considerably more sensitive to Luteolin than the isogenic metastatic MET4 cells. Extensive intracellular vacuolization was observed in Luteolin-treated MET4 cells, which were characterized as acidic lysosomal vacuoles, suggesting the involvement of autophagy. Transmission electron microscopy, mRFP-GFP-LC3 assay and p62 protein degradation, confirmed that Luteolin stimulated the autophagic process in the metastatic MET4 cells. Blocking autophagy using chloroquine magnified Luteolin-induced apoptosis in the metastatic SCC cells.
  
  
  CONCLUSIONS
  Together, these results suggest that Luteolin has the capacity to induce selectively apoptotic cell death both in primary cutaneous SCC cells and in metastatic SCC cells in combination with chloroquine, an inhibitor of autophagosomal degradation. Hence, Luteolin might be a promising agent for the treatment of cutaneous SCC.
authors.affiliation: Dermatology, University Hospitals Leuven, & Department of Oncology, KU Leuven, Leuven, Belgium.
authors.forename: Lien
authors.initials: L
authors.lastname: Verschooten
authors.forename: Kathleen
authors.initials: K
authors.lastname: Barrette
authors.forename: Sofie
authors.initials: S
authors.lastname: Van Kelst
authors.forename: Noemí
authors.initials: N
authors.lastname: Rubio Romero
authors.forename: Charlotte
authors.initials: C
authors.lastname: Proby
authors.forename: Rita
authors.initials: R
authors.lastname: De Vos
authors.forename: Patrizia
authors.initials: P
authors.lastname: Agostinis
authors.forename: Marjan
authors.initials: M
authors.lastname: Garmyn
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects*; D002738:Chloroquine / Q000494:pharmacology*; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism; D047311:Luteolin / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D002738:Chloroquine; D051057:Proto-Oncogene Proteins c-akt; D047311:Luteolin