Abstract: OBJECTIVE: To investigate effects of the sesquiterpene lactones (SLs) compound on the induced outcomes of cancer stem cells (CSCs) in human nasopharyngeal carcinoma (NPC) cells with different levels of cyclooxygenase-2 (COX-2). METHODS：The background levels of COX-2 mRNA and COX-2 protein were determined by the real time PCR (qRT-PCR) and Western blot in CNElL and CNE2L cell lines. After treated with different doses of parthenolide (PN)，proliferation of cells was determined by MTT assay，the transcription levels of COX-2，ABCG2， BMI1，OCT4 mRNA were determined by qRT-PCR，the relative content of side population (SP) cells was examined by flow cytometry，and the self-renewal and differentiation proliferation of stem-like cells were measured by colony formation assay. RESULTS：The background levels of COX-2 mRNA and protein were significantly higher in CNE1L compared with CNE2L cells (P<0.05). Compared with control group，in PN-treated group the proliferation inhibition rate was increased in dose-dependent (10-100 μmol/L for 24 h) manner (P<0.05). The mRNA level of stemness relative genes，including COX-2，ABCG2，BMI1 mRNA was increased in CNE1L cells，but COX-2 mRNA was decreased in CNE2L cells，while the level of OCT4 mRNA was reduced in both cell lines. The SP inhibition rate (%) was also increased with dose-dependent pattern (2.5-40 μmol/L for 24 h) (P<0.05)，and the colony formation was significantly lower (0.25-1.5 μmol/L for 72 h) (P<0.05). All the results above were statistically different between CNE1L and CNE2L (P<0.05)，with effects in CNE1L cell more remarkable. CONCLUSION：There were significantly different effects of PN on the inhibition of CSCs function in different NPC cells. The varied expression of COX-2 between cell lines may be related to the susceptibility.

Key words: cyclooxygenase-2, nasopharyngeal carcinoma, stem-like side population cells, parthenolide