Abstract: Objective To investigate the way that nasopharyngeal carcinoma (NPC) and NPC stem cells develops resistance to cisplatin through anti-reactive oxygen species mechanism. Methods Using CCK-8 cell counting kit, we measured the half inhibitory concentration of cisplatin against NPC cells "CNE-2" and NPC stem cells "CNE-2S", and compared their resistant index. We examined the differences in the reactive oxygen species (ROS) levels, total glutathione (GSH) levels, and total superoxide dismutase (SOD) levels between CNE-2 and CNE-2S at different concentrations of cisplatin administration (0.1,0.5 and 1.0μmol·L-1). Using q-PCR, we determined the mRNA expression level of GSS,GCLC, GCLM, SOD1 and SOD2 after 48 hours administration of cisplatin at 1 μmol·L- 1. Protein expression level of SOD2 was also tested using Western Blot after 48 hours administration of cisplatin at 1 μmol·L- 1. Upon silencing the
SOD2 in NPC cell through siRNA, Trypan blue was used to analyze cell survival after cisplatin was administrated at 1 μmol · L- 1. Results The inhibition concentration of cisplatin against CNE- 2 was higher than that against CNE- 2S（μmol·L-1： 9.8±1.1 vs 2.4±0.6， P＜0.05） . ROS levels in CNE-2 and CNE-2S both rise with cisplatin administration, but ROS levels of CNE-2 before and after cisplatin treatment were both higher than those in CNE-2S (P< 0.05). The total glutathione levels in CNE-2 and CNE-2S were both increased after 1 μmol·L-1 cisplatin treatment but there is no significant difference in levels of glutathione between these two cell lines. After treated with cisplatin, SOD level were increased in both CNE-2S and CNE-2, but it is higher in CNE-2S than that in CNE-2 (P < 0.05). The mRNA levels of GSS, GCLC, GCLM,and SOD1 were not different significantly between in CNE-2 and in CNE-2S with or without cisplatin treatment. However,SOD2 in CNE-2S were higher than that in CNE-2 on both mRNA and protein levels (P < 0.05). Silenced SOD2 disrupted
the resistance of cisplatin in CNE-2S. Conclusion These data suggest that NPC stem cells (CNE-2S) enhance its drug resistance to cisplatin through highly expression of SOD2 which posed anti-ROS capacity.

Key words: nasopharyngeal carcinoma, cancer stem cells, Cisplatin, drug resistance, reactive oxygen, glutathione, superoxide dismutase, RNA interference, nasopharyngeal carcinoma, cancer stem cells, Cisplatin, drug resistance, reactive oxygen, glutathione, superoxide dismutase, RNA interference