Radiotherapy is a standard treatment in incompletely excised canine mast cell tumors. VEGF plays an important role as proangiogenic and autocrine growth factor in a number of malignancies. Radiation is known to upregulate VEGF and VEGF receptors (VEGFR) expression in several neoplasms resulting in radioresistance and relapse. The aim of the present study was to evaluate radiosensitivity and influence of irradiation on VEGF and VEGFR expression in the canine mastocytoma cell line C2. C2 cells were irradiated with single doses of 2, 4, 6 and 8 Gy, respectively. MTT-assays and 3H-thymidine proliferation assays were used for radiosensitvity studies. VEGFR expression was evaluated by flow cytometry and apoptotic rate was determined by Annexin assay. Human and canine VEGF ELISA kits were evaluated in crossover assay studies and the canine kit was thereafter used to measure VEGF in cell lysates and cell-free supernatants. The canine VEGF ELISA kit was superior in detecting canine VEGF in comparison to the human assay. C2 cells secreted VEGF constitutively. However, radiation did not induce the significant increase in VEGF secretion regardless of radiation dose.
Furthermore, radiation did not stimulate VEGFR upregulation. Cell survival rates decreased in a dose-dependent manner. Apoptotic death rate showed a dose-dependent increase that reached its maximum 24-48 hrs post irradiation. Results indicate that in C2 cell line apoptosis plays the central role in radiation-induced cell killing. Further, it is suggested that C2 cells do not use upregulation of VEGF and its receptors to protect themselves against radiation damage.