Masitinib mesylate does not enhance sensitivity to radiation in three feline injection-site sarcoma cell lines under normal growth conditions

Masitinib, a selective tyrosine kinase inhibitor, was investigated as a radiosensitizer in three primary feline injection-site sarcoma (ISS) cell lines. Sensitivity to masitinib was previously assessed via cell growth inhibition assays with mean IC₅₀ values of 5.5–8.6 μM. Clonogenic assays were performed to determine the effect of masitinib and radiation on cell survival. Single dose radiation (0–12 Gy) experiments were carried out under normal growth conditions in control ISS cells and in cells incubated with 1 or 6 μM masitinib for 72 h prior to irradiation. Radiation administered either alone or in combination with masitinib induced a dose-dependent reduction in clonogenic survival. Survival from the combined masitinib and radiation treatment was not significantly different from that of radiation alone. Results suggest that masitinib does not directly enhance ISS cell radiosensitivity under normal in vitro conditions, although this does not preclude the utility of further investigations to assess sensitization properties under altered conditions.