Abstract
Summary Statement
Combination of sorafenib with irradiation achieved synergistic effect with dose reduction in both 143B and HOS cell lines. This demonstrated the potential application of sorafenib in the treatment of osteosarcoma metastasis and radiation resistance.
Introduction
More than 20% of patients with osteosarcoma die of the disease within 5 years due to tumour relapse and metastasis. Identifying new treatment that works singly or in combination with conventional therapies is urgently required. We previously found that the Ras/Raf/MAPK pathway was associated with lung metastasis in a 143B inoculated osteosarcoma orthotopic mouse model1. Sorafenib, a multi-kinase inhibitor, has shown potent anticancer effect including in osteosarcoma2 through the inhibition of Raf-1 and other targets3. The aims of this study were to investigate effect of sorafenib on osteosarcoma cell lines with or without activated Ras/Raf/MAPK signalling and to decide whether sorafenib could enhance irradiation on these cells.
Materials and Methods
Osteosarcoma cell lines 143B (HOS with Ras gene transfection), HOS and U2OS were used. Clonogenic assay was applied for assessing tumour growth and colony formation with or without treatment. Sorefenib was provided by Bayer gratis. Irradiation was performed using the Therapax DXT300 Orthovoltage Radiation System (Pantak, Connecticut, USA). Three doses of sorafenib (1, 2, 4 ug/ml) and three doses of radiation (50, 100, 200 cGy) were used with vehicle controls. In the combination therapy sorafenib was given at pre-, concurrent and post-irradiation. Each treatment was duplicated with the experiment being repeated once.
Results
Sorafenib monotherapy achieved 50% inhibition (EC50) effects in all three tested cell lines with 7.05 ug/ml for 143B, 1.59 for HOS and 2.41 for U2OS. The 143B cell line was seriously resistant to irradiation with EC50 of 167 Gy, whilst other cell lines were relatively sensitive (HOS, 1.5 Gy and U2OS, 1.0 Gy). Combination of sorafenib with irradiation achieved synergistic effect with dose reduction in both 143B and HOS cell lines, but no obvious effect in U2OS cells.
Discussion
Sorafenib demonstrated inhibitory effects on cell growth and colony formation even in a Ras/Raf/MAPK signalling activated osteosarcoma cell line, suggesting its potential application in the treatment of some metastatic osteosarcoma. Activated Ras/Raf/MAPK signalling is one of the mechanisms of radiation resistance and the synergistic effect of soratenib with irradiation combination therapy in this cell population indicated it's potential application in the treatment of irradiation resistant osteosarcoma. The dose reduction achieved by this combination could benefit patients with less specific side effects.
