title: Effects of epidermal growth factor receptor kinase inhibition on radiation response in canine osteosarcoma cells.
abstract: BACKGROUND
  Radiation therapy is a palliative treatment modality for canine osteosarcoma, with transient improvement in analgesia observed in many cases. However there is room for improvement in outcome for these patients. It is possible that the addition of sensitizing agents may increase tumor response to radiation therapy and prolong quality of life. Epidermal growth factor receptor (EGFR) expression has been documented in canine osteosarcoma and higher EGFR levels have been correlated to a worse prognosis. However, effects of EGFR inhibition on radiation responsiveness in canine osteosarcoma have not been previously characterized. This study examined the effects of the small molecule EGFR inhibitor erlotinib on canine osteosarcoma radiation responses, target and downstream protein expression in vitro. Additionally, to assess the potential impact of treatment on tumor angiogenesis, vascular endothelial growth factor (VEGF) levels in conditioned media were measured.
  
  
  RESULTS
  Erlotinib as a single agent reduced clonogenic survival in two canine osteosarcoma cell lines and enhanced the impact of radiation in one out of three cell lines investigated. In cell viability assays, erlotinib enhanced radiation effects and demonstrated single agent effects. Erlotinib did not alter total levels of EGFR, nor inhibit downstream protein kinase B (PKB/Akt) activation. On the contrary, erlotinib treatment increased phosphorylated Akt in these osteosarcoma cell lines. VEGF levels in conditioned media increased after erlotinib treatment as a single agent and in combination with radiation in two out of three cell lines investigated. However, VEGF levels decreased with erlotinib treatment in the third cell line.
  
  
  CONCLUSIONS
  Erlotinib treatment promoted modest enhancement of radiation effects in canine osteosarcoma cells, and possessed activity as a single agent in some cell lines, indicating a potential role for EGFR inhibition in the treatment of a subset of osteosarcoma patients. The relative radioresistance of osteosarcoma cells does not appear to be related to EGFR signalling exclusively. Angiogenic responses to radiation and kinase inhibitors are similarly likely to be multifactorial and require further investigation.
authors.affiliation: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Fernanda B
authors.initials: FB
authors.lastname: Mantovani
authors.affiliation: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Jodi A
authors.initials: JA
authors.lastname: Morrison
authors.affiliation: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. mutsaers@uoguelph.ca.|Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. mutsaers@uoguelph.ca.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Mutsaers
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D002470:Cell Survival; D003131:Combined Modality Therapy / Q000662:veterinary; D004283:Dog Diseases / Q000188:drug therapy* / Q000532:radiotherapy*; D004285:Dogs; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D000069347:Erlotinib Hydrochloride / Q000627:therapeutic use*; D012516:Osteosarcoma / Q000188:drug therapy / Q000532:radiotherapy / Q000662:veterinary*; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use*; D011836:Radiation Tolerance / Q000187:drug effects; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D047428:Protein Kinase Inhibitors; D042461:Vascular Endothelial Growth Factor A; D000069347:Erlotinib Hydrochloride; D066246:ErbB Receptors
keywords: Canine; Dog; Epidermal growth factor receptor (EGFR); Erlotinib; Osteosarcoma; Radiation; Radiosensitization; Vascular endothelial growth factor (VEGF)