The role of cancer stem cell in acquiring radioresistance of head and neck cancer

Abstract

Purpose: Radioresistance is one of the main determinants of the treatment outcome in head and neck cancer. The aim of this study was to establish radioresistant head and neck cancer cell lines and separate cancer stem cells from them to investigate the role of cancer stem cells in radioresistant head and neck cancer.

Methods: To induce radioresistant cell lines, irradiation was delivered to SCC15, SCC25, and QLL1 cells with an accumulated dosage of 60 Gy over 30 cycles of irradiation. Radioresistance of irradiated cancer cells were verified by MTT assay. Radioresistant cells were cultured in serum-free media in ultra-low？attachment culture flasks to induce sphere-forming cells. Cancer stem cell characteristics of sphere-forming cells were verified by western blot for CD-44, Oct-4, Nanog, Sox-2, and CD-133.

Results: The MTT assay of cell viability showed more radioresistance in the irradiated cancer cell lines than in the non-irradiated cancer cell lines. Sphere-forming cells were identified in all three cancer cell lines 3 to 5 days after serum deprivation. All sphere-forming cells from the three different cancer cell lines expressed stem cell markers; however, they showed different levels of expression. Sphere-forming cells showed more radioresistance than monolayer cells after irradiation by colony forming assay. Inhibition of Src in sphere-forming cells showed reduced radioresistance, low expression of cancer stem cell markers, and less invasion and migration in radioresistant head and neck cancer.

Conclusion: Cancer stem cells seem to be the cause of the radioresistant properties of radioresistant head and neck cancer. Src may also play a key role in maintaining radioresistance, and it may be used in target therapy for radioresistant head and neck cancer.