Radioresistance is one of the main determinants of treatment outcome in head and neck squamous cell carcinoma (HNSCC). We aimed to isolate cancer stem cells (CSC) from HNSCC to investigate the causative effect of CSC in the radioresistance and role Nanog in the maintenance of CSC and radioresistnace.
We used three head and neck cancer cell lines; SCC15, SCC25 and QLL1. All cells were cultured in the serum free media on ultra-low attachment culture flask to induce sphere-forming cells. CSC characteristics of sphere-forming cells were verified by western blot for CD-44, Oct-4, Nanog, Sox-2 and CD-133. We compared radioresistance between CSC and differentiated cancer cells. After inhibition of Nanog in CSC, we observed the change of characteristics and radioresistance of CSC.
Sphere-forming cells were identified in all three cancer cell lines and it took 3-5 days after serum depravation. All sphere-forming cells from three different cancer cell lines expressed stem cell marker, however they showed some different extent of expressions. CSCs showed more radioresistance than the differentiated cells after irradiation by MTT assay and colony forming assay. Knock out of Nanog in the CSCs showed reduced radioresistance as well as decreased size of sphere, low expression of CSC markers, less invasion and migration of CSCs comparing to Nanog expressing CSC.
CSCs seem to be the cause of radioresistant property in the HNSCC. Nanog may have a key role in maintaining radioresistance as well as CSC property and it may be used in target therapy in the radioresistant head and neck cancer.