(-)-Epigallocatechin-3-gallate inhibits nasopharyngeal cancer stem cell self-renewal and migration and reverses the epithelial-mesenchymal transition via NF-κB p65 inactivation.

The cancer stem cell (CSC) theory states that many types of cancer, including nasopharyngeal cancer (NPC), are initiated from and maintained by CSCs, which may be responsible for tumor relapse and resistance to therapy. It is imperative that nasopharyngeal cancer stem cells (NPCSCs) be specifically targeted to eradicate NPC and prevent recurrence. Epigallocatechin-3-gallate (EGCG) inhibits cancer progression by attenuating NF-κB p65 activity, which is upregulated in CSCs and plays an important role in epithelial-mesenchymal transition (EMT). The purpose of this study is to confirm the self-renewal and migration inhibitory effects of EGCG toward NPCSCs and to clarify its mechanism of activity. We enriched and characterized NPCSCs by collecting spheroid-derived cells grown in serum-free medium (SFM) and examined the effects of EGCG on the characteristics of NPCSCs and studied the underlying mechanisms using soft agar colony assays, transwell migration assays, reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analysis, immunofluorescence staining, and xenograft studies. NPC spheroids enriched from NPC cell lines acquired CSC traits and underwent EMT. EGCG inhibited the NPCSCs' self-renewal and migration and reversed EMT, and combined treatment with EGCG and cisplatin reduced the growth of CSC tumor xenografts. Moreover, EGCG inhibited NF-κB p65 activity by modulating the cellular localization of p65 and decreasing the transcriptional regulation of NF-κB p65 on Twist1 expression. NF-κB p65 is a novel therapeutic target in NPCSCs, and the inhibition of activated NF-κB p65 in CSCs by EGCG may offer an effective treatment for NPC.

2-Methoxyestradiol inhibits the proliferation and migration and reduces the radioresistance of nasopharyngeal carcinoma CNE-2 stem cells via NF-κB/HIF-1 signaling pathway inactivation and EMT reversal.

Accumulating evidence indicates that cancer stem cells (CSCs) are a source of resistance to radiation therapy (RT); however, the mechanism of this resistance remains unclear. 2-Methoxyestradiol (2-ME2) is a metabolic product of estrogen in the body. Recent studies have found that 2-ME2 regulates the activation of transcription factors, including nuclear factor (NF)-κB/hypoxia-inducible factor-1 (HIF-1), thus contributing to tumor cell apoptosis and chemosensitivity. Therefore, 2-ME2 is being studied as a potential anticancer drug. The purpose of this study was to determine the effect and mechanism by which 2-ME2 inhibits nasopharyngeal carcinoma CNE-2 stem-like cell (NPCSC) proliferation and migration and reduces NPCSC radioresistance. This study has important significance for reducing the radioresistance of these cells to improve the cure rate of NPC. First, the NPCSCs were collected in a serum-free culture system and then identified by relevant experiments. The NPCSCs were treated with 2-ME2 (0-8 µM) combined with X-ray exposure and Cell Counting Kit-8 (CCK-8), Transwell assay, colony formation assay, western blot analysis, RT-PCR, flow cytometry and RNA interference technology were used to explore the effect and mechanism of 2-ME2 on NPCSCs. The results showed that the microspheres collected in the serum­free culture system possessed CSC traits and radioresistance. 2-ME2 obviously inhibited NPCSC growth and migration and reduced NPCSC radioresistance. 2-ME2 decreased NF-κB p65 and HIF-1α protein expression, downregulated NF-κB p65 nuclear localization, and reversed epithelial-mesenchymal transition (EMT). NF-κB p65 knockdown reduced HIF-1α expression, reversed EMT, and enhanced the suppressive effect of 2-ME2 on NPCSCs. Collectively, these data indicate that 2-ME2 inhibits NPCSC proliferation and migration and reduces the radioresistance of NPCSCs via NF-κB/HIF-1 signaling pathway inactivation and EMT reversal.