Recently pharmacological studies have revealed that

Recently, pharmacological studies have revealed that natural compounds achieve increasing attention due to its high therapeutic effectiveness and low adverse effect, compared with the chemically synthesized compounds. Emodin is a kind of natural anthraquinone derivative enriched in traditional Chinese medicine (Rheum palmatum) for decades. Emodin has extensive pharmacological actions such as anticancer, antiinflammatory, antioxidant, hepatoprotective, neuroprotective, anti-tumor activities, and antimicrobial activities [31]. Several studies reported that emodin is a tyrosine kinase inhibitor that restricts the activities of the p56lck, HER-2/neu, and ras-oncogenes, all of which are involved in cell proliferation, transformation, and differentiation signaling pathways [32]. Emodin also induced apotosis in the breast cancer by reducing the level of Bcl-2 and increased levels of cleaved caspase-3, PARP, p53 and Bax [14]. Additionally, emodin inhibits human cancer cell invasiveness by specifically antagonizing the adenosine 5′-triphosphate (ATP)-gated Ca2+-permeable channel P2×7 receptor (P2×7R) [33]. These pharmacological properties are fully indicated that emodin could be an effective therapeutic option for the prophylaxis and treatment of various diseases. Therefore, this prompted us to investigate the effects of emodin on nasopharyngeal carcinoma and the signaling pathways involved in nasopharyngeal carcinoma. In this work, MTT and FCM assay were carried out after indicated treatment of emodin in CNE-2Z betaxolol together with the normal nasopharyngeal epithelial NP69-SV40T cells to evaluate whether emodin could specifically inhibit the caicinoma cells against normal cells. We found that higher concentration (up to 100μM) of emodin failed to induce a similar cytotoxicity in NP69-SV40T cells as emodin did in CNE-2Z cells with the half inhibitory concentration (IC50) of 33.7μM. Thus, it suggested emodin specifically inhibited CNE-2Z cell growth. Furthermore, we observed that emodin inhibited cell growth of CNE-2Z cells through the S phase arrest and induction of apoptosis. Emodin also induced the changes of cell ultrastructure. Relatively, emodin had little cytotoxicity on the normal cells and only high concerntration (50μM) of emodin could slightly inhibit cell growth of NP69-SV40T cells. Moreover, we observed the AVD process after exposed to emodin. The cell volume decreased obviously in CNE-2Z cells, whereas even if application of 50μM emodin in NP69-SV40T cells for 120min, no apparent AVD was observed. After exposed to emodin in the AVD process, the cell volume of CNE-2Z cells decreased obviously and this effects can be inhibited by chloride blocker. Chloride blocker also inhibited emodin-activated chloride currents and reversed the emodin induced cell apotosis and roughness in CNE-2Z cells. Emodin which has broader anticancer spectrum and less toxicity in other normal cells, has also been presented previously, such as human gingival fibroblasts [34], hemopoietic progenitor cells [35] and primary astrocytes and fibroblasts [36]. The high selective cytotoxicity to tumor cells further shows that emodin could be a potent chemotherapeutic drug. Our former studies have shown that the ClC-3 chloride channel to be expressed at much higher level in CNE-2Z cells compared with the NP69-SV40T cells [7]. And the proliferation of cancerous cells was more dependent on the activities of ClC-3 chloride channels [37]. These findings are in line with other studies of glioblastoma [38] and taken together support an important role for the ClC-3 chloride channel in the development of cancer. This has led to the hypothesis that selective activation of the ClC-3 chloride channel may represent a new strategy for cancer therapeutics [39]. The above results indicate there was certain relationship between the high selectivity effects of emodin in normal and cancer cells and the expression and function of ClC-3 chloride channel. The results showed that 1) Emodin could activate moderate outward-rectified and voltage-dependent Cl− currents which could be inhibited by NPPB and tamoxifen in CNE-2Z cells but not in NP69-SV40T cells. 2) Silence of the ClC-3 chloride channel inhibits the emodin-activated Cl− currents. Thus, these results suggest that ClC-3 may be the main chloride channel protein mediating the apoptosis of CNE-2Z cells induced by emodin. However, further studies are needed to identify the molecular components of chloride channels that contribute to the cancerous cell apoptosis and differentiation induced by emodin.