Functional Roles of JNK and p38 MAPK Signaling in Nasopharyngeal Carcinoma

c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members integrate signals that affect proliferation, differentiation, survival, and migration in a cell context- and cell type-specific way. JNK and p38 MAPK activities are found upregulated in nasopharyngeal carcinoma (NPC). Studies have shown that activation of JNK and p38 MAPK signaling can promote NPC oncogenesis by mechanisms within the cancer cells and interactions with the tumor microenvironment. They regulate multiple transcription activities and contribute to tumor-promoting processes, ranging from cell proliferation to apoptosis, inflammation, metastasis, and angiogenesis. Current literature suggests that JNK and p38 MAPK activation may exert pro-tumorigenic functions in NPC, though the underlying mechanisms are not well documented and have yet to be fully explored. Here, we aim to provide a narrative review of JNK and p38 MAPK pathways in human cancers with a primary focus on NPC. We also discuss the potential therapeutic agents that could be used to target JNK and p38 MAPK signaling in NPC, along with perspectives for future works. We aim to inspire future studies further delineating JNK and p38 MAPK signaling in NPC oncogenesis which might offer important insights for better strategies in diagnosis, prognosis, and treatment decision-making in NPC patients.

Acylglycerol kinase promotes paclitaxel resistance in nasopharyngeal carcinoma cells by regulating FOXM1 via the JAK2/STAT3 pathway

OBJECTIVE

Drug resistance is an important factor that impedes the treatment of nasopharyngeal cancer (NPC). Acylglycerol kinase (AGK) has been found to be overexpressed in NPC and correlates with poor prognosis. Our objective was to demonstrate the effect of AGK on paclitaxel resistance in NPC and determine the underlying mechanisms.

METHODS

MTT assay was employed to determine the IC50 of paclitaxel in NPC cells after different treatments. Flow cytometry assays were employed to evaluate cell apoptosis. RT-qPCR and Western blot assays were used to detect alterations in mRNA and protein expression, respectively. Luciferase assays and chromatin immunoprecipitation (ChIP) assays were used to determine the relationship between and the regulatory effect of STAT3 on the promoter of FOXM1.

RESULTS

AGK was elevated in paclitaxel-resistant NPC cells, and knockdown of AGK suppressed the resistance of CNE1-TR and CNE2-TR cells to paclitaxel. Moreover, upregulation of FOXM1 rescued the effects of AGK knockdown. Furthermore, the JAK2/STAT3 signalling pathway was overactivated in CNE1-TR and CNE2-TR cells, and knockdown of AGK suppressed JAK2/STAT3 signalling. STAT3 was verified to bind to and activate the promoter region of FOXM1. An in vivo tumour xenograft assay also verified that AGK knockdown inhibited tumour growth and mitigated paclitaxel resistance by regulating the JAK2/STAT3/FOXM1 axis.

CONCLUSION

AGK levels were increased in paclitaxel-resistant NPC cells. AGK activates JAK2/STAT3 signalling, thus promoting FOXM1 transcription and eventually enhancing the drug resistance of NPC cells.

Parallel genome-wide RNAi screens identify lymphocyte-specific protein tyrosine kinase (LCK) as a targetable vulnerability of cell proliferation and chemoresistance in nasopharyngeal carcinoma

Despite recent in advances in the management of nasopharyngeal carcinoma (NPC), development of targeted therapy remains challenging particularly in patients with recurrent or metastatic disease. To search for clinically relevant targets for the treatment of NPC, we carried out parallel genome-wide functional screens to identified essential genes that are required for NPC cells proliferation and cisplatin resistance. We identified lymphocyte-specific protein tyrosine kinase (LCK) as a key vulnerability of both proliferation and cisplatin resistance. Depletion of endogenous LCK or treatment of cells with LCK inhibitor induced tumor-specific cell death and synergized cisplatin sensitivity in EBV-positive C666-1 and EBV-negative SUNE1 cells. Further analyses demonstrated that LCK is regulating the proliferation and cisplatin resistance through activation of signal transducer and activator of transcription 5 (STAT5). Taken together, our study provides a molecular basis for targeting LCK and STAT5 signaling as potential druggable targets for the management of NPC.

Targeting fatty acid synthase sensitizes human nasopharyngeal carcinoma cells to radiation via downregulating frizzled class receptor 10

Objective: Our aim was to test the hypothesis that fatty acid synthase (FASN) expression contributes to radioresistance of nasopharyngeal carcinoma (NPC) cells and that inhibiting FASN enhances radiosensitivity. Methods: Targeting FASN using epigallocatechin gallate (EGCG) or RNA interference in NPC cell lines that overexpress endogenous FASN was performed to determine their effects on cellular response to radiation in vitro using MTT and colony formation assays, and in vivo using xenograft animal models. Western blot, immunohistochemistry, real-time PCR arrays, and real-time RT-PCR were used to determine the relationship between FASN and frizzled class receptor 10 (FZD10) expression. FZD10 knockdown and overexpression were used to determine its role in mediating FASN function in cellular response to radiation. Immunohistochemical staining was used to determine FASN and FZD10 expressions in human NPC tissues, followed by analysis of their association with the overall survival of patients. Results: FASN knockdown or inhibition significantly enhanced radiosensitivity of NPC cells, both in vitro and in vivo. There was a positive association between FASN and FZD10 expression in NPC cell lines grown as monolayers or xenografts, as well as human tissues. FASN knockdown reduced FZD10 expression, and rescue of FZD10 expression abolished FASN knockdown-induced enhancement of radiosensitivity. FASN and FZD10 were both negatively associated with overall survival of NPC patients. Conclusions: FASN contributes to radioresistance, possibly via FZD10 in NPC cells. Both FZD10 and FASN expressions were associated with poor outcomes of NPC patients. EGCG may sensitize radioresistance by inhibiting FASN and may possibly be developed as a radiosensitizer for better treatment of NPCs.

Clinicopathological and prognostic significance of GPx2 protein expression in nasopharyngeal carcinoma

OBJECTIVE

This study was designed to evaluate the relation between GPx2 (glutathione peroxidase 2) expressions and clinicopathological features as well as prognosis of patients with nasopharyngeal carcinoma (NPC).

METHODS

A total of 89 cases of NPC were investigated to examine the immunohistochemical expression of GPx2. Fourteen pairs of NPC and the control samples were analyzed respectively by qRT-PCR and Western blot. The correlations of GPx2 expressions with the clinicopathologic features and the prognosis of NPC patients were also analyzed.

RESULTS

The expression of GPx2 in NPC tissues was elevated immunohistochemically when compared with normal nasopharyngeal tissues (P< 0.05). The mRNA expression of GPx2 in carcinoma tissues was highly elevated compared with the control tissues (P< 0.05). GPx2 protein in carcinoma tissues was also over expressed than in control tissues (P< 0.05). Also GPx2 expression was significantly higher in the late clinical stage (P= 0.02). While there was no significant association between GPx2 expression and patient age, sex, T-stage, N-stage and the metastasis.

CONCLUSIONS

GPx2 may play an important role in the development of nasopharyngeal carcinoma. Furthermore, GPx2 may serve as a prognostic biomarker for NPC patient.

EBV-encoded miRNAs target ATM-mediated response in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a highly invasive epithelial malignancy that is prevalent in southern China and Southeast Asia. It is consistently associated with latent Epstein-Barr virus (EBV) infection. In NPC, miR-BARTs, the EBV-encoded miRNAs derived from BamH1-A rightward transcripts, are abundantly expressed and contribute to cancer development by targeting various cellular and viral genes. In this study, we establish a comprehensive transcriptional profile of EBV-encoded miRNAs in a panel of NPC patient-derived xenografts and an EBV-positive NPC cell line by small RNA sequencing. Among the 40 miR-BARTs, predominant expression of 22 miRNAs was consistently detected in these tumors. Among the abundantly expressed EBV-miRNAs, BART5-5p, BART7-3p, BART9-3p, and BART14-3p could negatively regulate the expression of a key DNA double-strand break (DSB) repair gene, ataxia telangiectasia mutated (ATM), by binding to multiple sites on its 3'-UTR. Notably, the expression of these four miR-BARTs represented more than 10% of all EBV-encoded miRNAs in tumor cells, while downregulation of ATM expression was commonly detected in all of our tested sequenced samples. In addition, downregulation of ATM was also observed in primary NPC tissues in both qRT-PCR (16 NP and 45 NPC cases) and immunohistochemical staining (35 NP and 46 NPC cases) analysis. Modulation of ATM expression by BART5-5p, BART7-3p, BART9-3p, and BART14-3p was demonstrated in the transient transfection assays. These findings suggest that EBV uses miRNA machinery as a key mechanism to control the ATM signaling pathway in NPC cells. By suppressing these endogenous miR-BARTs in EBV-positive NPC cells, we further demonstrated the novel function of miR-BARTs in inhibiting Zta-induced lytic reactivation. These findings imply that the four viral miRNAs work co-operatively to modulate ATM activity in response to DNA damage and to maintain viral latency, contributing to the tumorigenesis of NPC. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Low expression of nm23-H1 associates with poor survival of nasopharyngeal carcinoma patients: A prisma-compliant meta-analysis

BACKGROUND

Developing a new reliable prognostic marker to predict the prognosis and supply better and more suitable therapy for patients with nasopharyngeal carcinoma (NPC) is urgent. Therefore, we performed this systematic review of the literature with meta-analysis to clarify and explore the associate expression of nm23-H1 with prognosis of NPC patients.

METHODS

Literature research in Cochrane Library, PubMed, and EMBASE was performed up to July 2016. Eligible case-control studies of associate expression of nm23-H1 with prognosis of NPC patients were included.

RESULTS

Nine studies met our inclusion criteria and were finally included for the analysis, involving 861 participants. Our meta-analysis revealed that the low expression of nm23-H1 in NPC was: RR = 2.13, 95% CI 1.15-3.95 and R = 2.56, 95% CI 2.03-3.22; and poorer overall survival (OS) rate was 3-year OS rate: RR: 0.55; 95% CI: 0.45-0.67 and 5-year OS rate: RR: 0.60; 95% CI: 0.52-0.69. Furthermore, the statistical significance was constant irrespective of different NPC subtypes.

CONCLUSION

The low expression of nm23-H1 is associated with poorer prognosis in patients with NPC, suggesting that it is a prognostic factor and potential biomarker for survival in NPC.

Prognostic significance of pretreated serum lactate dehydrogenase level in nasopharyngeal carcinoma among Chinese population: A meta-analysis

BACKGROUND

A large number of studies have investigated the prognostic value of pretreated lactate dehydrogenase (LDH) level in nasopharyngeal carcinoma (NPC) patients while the role of it was inconsistent and inconclusive. Hence, the aim of the current study was to conduct a meta-analysis of all published studies to quantify the prognostic impact of pretreated serum LDH in NPC for Chinese population.

OBJECTIVES

The aim of the current study was to conduct a meta-analysis of all published studies to quantify the prognostic impact of pretreated serum lactate dehydrogenase (LDH) in nasopharyngeal carcinoma (NPC) for Chinese population.

METHODS

The PubMed, Medline, Embase, and Web of Science databases were searched for studies that assessed survival outcome and LDH in NPC. Overall survival (OS) was the primary survival outcome. Distant metastasis-free survival (DMFS) and disease-free survival (DFS) were secondary outcomes. The pooled hazard ratios (HRs), associated with 95% confidence intervals (95% CIs), were combined to calculate overall effects. The Cochran Q and I statistics were used to assess heterogeneity. When apparent heterogeneity was observed, sensitivity and meta-regression analyses were performed to explore its origin.

RESULTS

Sixteen studies, which included 14,803 patients, were enrolled in the current meta-analysis to yield statistics. Overall, the pooled HR for OS in 11 eligible studies with high LDH level was 1.79 (95% CI = 1.47-2.12), and the pooled HR for DMFS in 9 eligible studies with high LDH level was 1.85 (95% CI = 1.48-2.22). Meanwhile, the pooled HR for DFS in 5 eligible studies with high LDH level was 1.63 (95% CI = 1.34-1.91). Egger test and funnel plots revealed that the publication bias in the current meta-analysis was insignificant.

CONCLUSIONS

The present meta-analysis demonstrated that high pretreated LDH level is significantly associated with poorer OS, DMFS, and DFS, suggesting that pretreated LDH could sever as a prognostic factor in NPC among Chinese population.

Contribution of Matrix Metallopeptidase-1 Genotypes, Smoking, Alcohol Drinking and Areca Chewing to Nasopharyngeal Carcinoma Susceptibility

BACKGROUND/AIM

The up-regulation of matrix metalloproteinase-1 (MMP-1) has been demonstrated to be correlated with lymph node metastasis of nasopharyngeal carcinoma (NPC); however, the genotypic role of MMP-1 is not well understand. The present study aimed to assess the contribution of MMP-1 promoter -1607 genotypes, combined with environmental carcinogens, on the predisposition to NPC tumorigenesis.

MATERIALS AND METHODS

The MMP-1 promoter -1607 genotypes were examined for 352 age- and gender-matched controls and 176 NPC patients by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methodology.

RESULTS

We found that the MMP-1 promoter -1607 heterozygous 1G/2G and homozygous 1G/1G genotypes, were more and more prone to be associated with NPC risk (odds ratio (OR)=0.64 and 0.63, 95% confidence interval (CI)=0.43-1.03 and 0.36-0.96, p=0.0659 and 0.0932, respectively). In the dominant models, there was a significant association between the genotype of MMP-1 promoter -1607 and NPC risk (OR=0.64, 95% CI=0.43-0.91, p=0.0359). In addition, individuals carrying the 1G allele at MMP-1 promoter -1607 were less susceptible to NPC (OR=0.73; 95%CI=0.59 to 0.96, p=0.0418) after adjustment for age, gender, cigarette, alcohol and areca consumption.

CONCLUSION

The 1G/1G genotype of MMP-1 promoter -1607 may independently have a protective effect on NPC risk, without interaction with behavioral factors, including cigarette, alcohol and areca consumption.

Upregulation of KLHDC4 Predicts a Poor Prognosis in Human Nasopharyngeal Carcinoma

Kelch proteins are implicated in the pathogenesis of many human diseases, including cancer. Nasopharyngeal carcinoma (NPC) is a rare malignancy in most countries, but prevalent in southern China and certain areas of Southeast Asia. In this study, we identified Kelch Domain Containing 4 (KLHDC4), an orphan member of the kelch repeat superfamily, as a prognosis marker for NPC. We examined the expression of KLHDC4 in 168 NPC cases by immunohistochemical staining and found a substantially higher level of KLHDC4 in NPC biopsies compared to adjacent normal nasopharyngeal mucosa. KLHDC4 expression was significantly related to the T classification (P <0.05), N classification (P <0.05) and total staging (P <0.01) in NPC, and patients with higher KLHDC4 expression had poorer overall (P <0.01) and metastasis-free survival (P <0.05) rates. Knockout (KO) of KLHDC4 via CRISPR/Cas9-mediated gene editing in NPC cell line dramatically inhibited cell proliferation, colony formation in soft agar and tumor formation in nude mice. In addition, cell migration and invasion were also impaired by KLHDC4 depletion as revealed by wound healing and Transwell assay. Mechanically, loss of KLHDC4 markedly induced spontaneous apoptosis in NPC cells, as evidenced by increased levels of cleaved caspase-3 and cleaved PARP. Consistently, KLHDC4 knockout cell-derived xenografts also showed elevated cleaved caspase-3 and PARP but reduced Ki-67 staining. In conclusion, our results suggest that KLHDC4 promotes NPC oncogenesis by suppressing cellular apoptosis. Thus, KLHDC4 may serve as a prognosis biomarker and a potential therapeutic target for NPC.

Prognostic value of matrix metalloproteinase 9 in nasopharyngeal carcinoma: a meta-analysis

INTRODUCTION

Recent studies have shown that matrix metalloproteinase 9 (MMP9) plays a vital role in tumor metastasis and is overexpressed in many human cancers. However, the prognostic value of MMP9 overexpression in nasopharyngeal carcinoma (NPC) is conflicting and heterogeneous. We therefore conducted a meta-analysis to investigate the association between MMP9 expression and the prognostic value in NPC.

EVIDENCE ACQUISITION

Relevant literature that evaluating the relationship between MMP-9 expression and the outcome of NPC patients were searched in PubMed, Embase, Cochrane, Ovid Medline and Chinese wanfang databases updated to May 2015. The primary study outcome was overall survival (OS). Secondary endpoint was disease-free survival (DFS). The combined hazard ratios (HRs) with their 95% confidence intervals (CIs) were assessed using STATA 12.0 software.

EVIDENCE SYNTHESIS

A total of 6 studies were included with the defined including and excluding criteria and subjected to meta-analysis. The pooled result showed that MMP9 overexpression was significantly associated with poor prognosis in terms of OS (HR: 1.65, 95% CI: 1.38-1.95, P<0.0001) and poor DFS (HR: 1.61, 95% CI: 1.28-2.02, P<0.0001) in NPC patients. Subgroup analysis suggested that high expression of MMP9 was associated with poor OS in NPC patients with different sample types. No evidence for publication bias was observed in our meta-analysis.

CONCLUSIONS

The current limited evidence suggests that increased MMP9 expression is associated with poor OS, and DFS in NPC. Therefore, we conclude that overexpression of MMP9 in both NPC tissue and blood sample might serve as an indicator of prognosis in NPC patients.

IL-6/NOS2 inflammatory signals regulate MMP-9 and MMP-2 activity and disease outcome in nasopharyngeal carcinoma patients

The role of nitric oxide (NO)(·) in the development of the metastatic properties of nasopharyngeal carcinoma (NPC) is not fully understood. Previous studies proposed that interleukin-6 (IL-6) would act as regulator of matrix metalloprotease activation in NPC. Recently, we showed that (NO)(·) was a critical mediator of tumor growth in patients. The aim of this study was to determine the implication of IL-6 in the progression of NPC pathology via metalloprotease (MMP) activation and their possible correlation with (NO)(·) production. We observed a significant increase in IL-6 and nitrite (NO2 (-)) synthesis in patients (n = 17) as well as a strong expression of IL-6 and nitric oxide synthase 2 (NOS2) in the analyzed tumors (n = 8). In patients' plasma, a negative correlation associated IL-6 with circulating nitrites (r = -0.33). A negative correlation associated the H-scores of these signals in the tumors (r = -0.47). In patients' plasma, nitrite synthesis was positively associated with MMP-9 activation (r = 0.45), pro-MMP-2 expression (r = 0.37), and negatively correlated with MMP-2 activation (r = -0.51). High nitrite levels was associated with better recurrence-free survival (RFS) (p = 0.02). Overall, our results suggest that the IL-6/NOS2 inflammatory signals are involved in the regulation of MMP-9- and MMP-2-dependent metastatic activity and that high circulating nitrite levels in NPC patients may constitute a prognostic predictor for survival.

[Expression of phosphofructokinase 1 protein and it's enzyme activity on nasopharyngeal carcinoma]

OBJECTIVE

The aim of this study is to investigate the expression of phosphofructokinase 1 and it's enzyme activity in nasopharyngeal carcinoma biopsy samples.

METHOD

Sixty-one biopsy samples were detected, including 41 tissues from patients with nasopharyngeal carcinoma as experimental group and 20 tissues from patients with chronic nasopharyngitis as control group. Phosphofructokinase 1 protein was detected by Western blot and it's enzyme activity was detected.

RESULT

It was observed that the expression levels of phosphofructokinase 1 protein and it's enzyme activities in the experimental group were higher than that in the control group (P < 0.01). In the experimental group, the expression levels of phosphofructokinase 1 protein and it's enzyme activities in patients with lymph node metastasis were higher than that in patients without lymph node metastasis (P < 0.01).

CONCLUSION

Phosphofructokinase 1 may be a marker in occurrence and metastasis of nasopharyngeal carcinoma.

Aberrant expression of CDK5 infers poor outcomes for nasopharyngeal carcinoma patients

PURPOSE

Aberrant expression of CDK5 involved in epithelial-to-mesenchymal transition had been reported in various types of cancers, but its functions in nasopharyngeal carcinoma have not been fully clarified yet. The principal purpose of this research was to investigate the clinicopathological significance of CDK5 and its potential effect on NPC carcinogenesis.

METHODS

Pre-treated formalin-fixed paraffin-embedded biopsy samples of 393 patients between January 2011 and December 2013 were collected for tissue microarrays (TMAs). Immunohistochemistry was performed on sequential TMA sections stained with antibodies against CDK5, EGFR and P53.

RESULTS

The expression of CDK5 in NPC tissues was significantly higher than that in normal nasopharyngeal tissues. Among squamous carcinomas, the expression of CDK5 in undifferentiated tissues was noticeably increased compared with that in differentiated tissues. NPC patients in advanced T category showed a perceptibly higher level of CDK5 than those in early T category. The relative level of CDK5 in NPC sufferers with lymph node metastasis was obviously higher than that of patients without. Compared with patients in early TNM stages, the relative expression level of CDK5 of those in advanced TNM stages was notably up-regulated. Moreover, the CDK5 expression was positively correlated with EGFR and P53 expression. Nevertheless, no significant association was observed between CDK5 and gender, age or histological type.

CONCLUSION

Overexpression of CDK5 might be considered as a warning signal for NPC. Consequently, CDK5 could serve as a potential target for diagnosis and gene therapy for NPC patients.

Telomerase activity impacts on Epstein-Barr virus infection of AGS cells

The Epstein-Barr virus (EBV) is transmitted from host-to-host via saliva and is associated with epithelial malignancies including nasopharyngeal carcinoma (NPC) and some forms of gastric carcinoma (GC). Nevertheless, EBV does not transform epithelial cells in vitro where it is rapidly lost from infected primary epithelial cells or epithelial tumor cells. Long-term infection by EBV, however, can be established in hTERT-immortalized nasopharyngeal epithelial cells. Here, we hypothesized that increased telomerase activity in epithelial cells enhances their susceptibility to infection by EBV. Using HONE-1, AGS and HEK293 cells we generated epithelial model cell lines with increased or suppressed telomerase activity by stable ectopic expression of hTERT or of a catalytically inactive, dominant negative hTERT mutant. Infection experiments with recombinant prototypic EBV (rB95.8), recombinant NPC EBV (rM81) with increased epithelial cell tropism compared to B95.8, or recombinant B95.8 EBV with BZLF1-knockout that is not able to undergo lytic replication, revealed that infection frequencies positively correlate with telomerase activity in AGS cells but also partly depend on the cellular background. AGS cells with increased telomerase activity showed increased expression mainly of latent EBV genes, suggesting that increased telomerase activity directly acts on the EBV infection of epithelial cells by facilitating latent EBV gene expression early upon virus inoculation. Thus, our results indicate that infection of epithelial cells by EBV is a very selective process involving, among others, telomerase activity and cellular background to allow for optimized host-to-host transmission via saliva.

Serum alkaline phosphatase predicts survival outcomes in patients with skeletal metastatic nasopharyngeal carcinoma

OBJECTIVE

Bone metastasis is frequently associated with nasopharyngeal carcinoma. The diagnosis and follow-up of bone metastatic patients usually relies on skeletal X-ray and bone scintigraphy, which are time-consuming and costly. This study aimed to evaluate whether serum alkaline phosphatase offers clinical value in predicting the clinical response and survival outcome for skeletal metastatic nasopharyngeal carcinoma.

METHODS

Serum alkaline phosphatase was measured at baseline and then before each cycle of treatment in 416 nasopharyngeal carcinoma patients with bone metastasis. The correlations between the pre-treatment and post-treatment alkaline phosphatase levels and the treatment efficacy were analyzed using the chi-square test. Survival was analyzed using the Kaplan-Meier method and then compared using the log-rank test.

RESULTS

Patients with elevated pre-treatment alkaline phosphatase (>110 IU/L) had significantly worse progression-free survival (P<0.001) and overall survival (P<0.001) than those with a normal level of this marker (≤110 IU/L). Patients with elevated post-treatment alkaline phosphatase had worse progression-free survival (P<0.001) and overall survival (P<0.001) compared with those with a normal level. Patients with normal pre-treatment and post-treatment alkaline phosphatase showed the most favorable prognosis. The Cox multivariate analysis revealed that only the pre-treatment and post-treatment alkaline phosphatase levels were independent prognostic factors for progression-free survival (HR ϝ 1.656, P<0.001; HR ϝ 2.226, P<0.001) and for overall survival (HR ϝ 1.794, P<0.001; HR ϝ 2.657, P<0.001).

CONCLUSIONS

Serum alkaline phosphatase appears to be a significant independent prognostic index in patients with skeletal metastatic nasopharyngeal carcinoma, which could reflect the short-term treatment response of palliative chemotherapy and the long-term survival outcomes.

[Sodium butyrate down-regulates IFN-γ-induced indoleamine 2, 3 dioxygenase and promotes its acetylation and ubiquitination in CNE2 nasopharyngeal carcinoma cells]

OBJECTIVE

To investigate molecular mechanisms of posttranslational regulation of sodium butyrate (NaB) on indoleamine 2, 3-dioxygenase (IDO) expression induced by interferon γ (IFN-γ) in CNE2 nasopharyngeal carcinoma cells.

METHODS

Western blotting and co-immunoprecipitation assay were used to detect the expression, acetylation and ubiquitination of IDO in CNE2 nasopharyngeal carcinoma cells.

RESULTS

Western blotting demonstrated that while the cells were treated with IFN-γ and NaB compared with IFN-γ treatment only, the expression of IDO protein increased significantly; furthermore, in the co-immunoprecipitation assay, while the cells were treated with IFN-γ and NaB compared with the ones treated with IFN-γ only, acetylation and ubiquitination of IDO increased significantly. Western blotting showed that the cells treated with NaB and IFN-γ presented with lower IDO protein expression than the ones treated with NaB, IFN-γ and bortezomib simultaneously.

CONCLUSION

NaB could down-regulate the expression of IDO induced by IFN-γ in a dose-dependent manner, and the combined treatment of IFN-γ and NaB could promote the acetylation and ubiquitination of IDO in CNE2 nasopharyngeal carcinoma cells.

EGCG inhibits proliferation, invasiveness and tumor growth by up-regulation of adhesion molecules, suppression of gelatinases activity, and induction of apoptosis in nasopharyngeal carcinoma cells

(-)-Epigallocatechin-3-gallate (EGCG), a major green tea polyphenol, has been shown to inhibit the proliferation of a variety of tumor cells. Epidemiological studies have shown that drinking green tea can reduce the incidence of nasopharyngeal carcinoma (NPC), yet the underlying mechanism is not well understood. In this study, the inhibitory effect of EGCG was tested on a set of Epstein Barr virus-negative and -positive NPC cell lines. Treatment with EGCG inhibited the proliferation of NPC cells but did not affect the growth of a non-malignant nasopharyngeal cell line, NP460hTert. Moreover, EGCG treated cells had reduced migration and invasive properties. The expression of the cell adhesion molecules E-cadherin and β-catenin was found to be up-regulated by EGCG treatment, while the down-regulation of matrix metalloproteinases (MMP)-2 and MMP-9 were found to be mediated by suppression of extracellular signal-regulated kinase (ERK) phosphorylation and AP-1 and Sp1 transactivation. Spheroid formation by NPC cells in suspension was significantly inhibited by EGCG. Oral administration of EGCG was capable of suppressing tumor growth in xenografted mice bearing NPC tumors. Treatment with EGCG was found to elevate the expression of p53 and p21, and eventually led to apoptosis of NPC cells via caspase 3 activation. The nuclear translocation of NF-κB and β-catenin was also suppressed by EGCG treatment. These results indicate that EGCG can inhibit the proliferation and invasiveness, and induce apoptosis, of NPC cells, making it a promising agent for chemoprevention or adjuvant therapy of NPC.

Inducible nitric oxide inhibitor enhances the anti-tumor effect of cisplatin on CNE-2 cells by inducing cell apoptosis

OBJECTIVE

Inducible nitric oxide (NO) synthase (iNOS) inhibitor S-methylisothiourea (SMT) has been reported to have anti-tumor effects on several types of cancers.  We aimed to investigate whether SMT can inhibit nasopharyngeal carcinoma cells CNE-2 proliferation through raise chemotherapy effect of diaminodichloroplatinum (DDP).

MATERIALS AND METHODS

CNE-2 cells were treated with SMT, DDP and both of them respectively. MTT and colony-forming assay was performed to detect the proliferation effect of the treatment. Hoechst 33258 staining and apoptosis analysis were performed to investigate the apoptosis effect of chemotherapy. Additionally, the NO level was detected to estimate the activity of iNOS.

RESULTS

CNE-2 cells expressed high level of iNOS. SMT can inhibit CNE-2 cells growth in a dose-dependent manner and have the effect on reducing dosage of DDP as well as enhancing the anti-tumor efficacy by promote cell apoptosis.

CONCLUSIONS

Our findings suggested that SMT play a synergism role in the inhibition process of DDP on nasopharyngeal carcinoma, and SMT could be a promising therapeutic factor for cancer prevention.

Epigenetic inactivation of inositol polyphosphate 4-phosphatase B (INPP4B), a regulator of PI3K/AKT signaling pathway in EBV-associated nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a common viral-associated neoplasm in which multiple signaling cascades are interfered with by Epstein-Bar virus (EBV) latent proteins and various genetic alterations. Aside from the previously reported PIK3CA amplification, we examined the role of INPP4B, a negative regulator of the PI3K/AKT signaling pathway in the development of NPC. By RT-PCR and Western blotting, we revealed that the expression of INPP4B was down-regulated in all five established EBV-positive tumor lines. While INPP4B was consistently expressed in normal nasopharyngeal epithelial cells, downregulation of INPP4B was found in 32/65 (49.2%) of primary tumors by immunohistochemistry. Furthermore, our study also demonstrated the hypermethylation of the 5'CpG island of INPP4B in the tumors in which INPP4B transcription was downregulated. Notably, the re-expression of INPP4B was detected in the NPC cells treated with the demethylation agent (5-aza-2'deoxycytidine). Our study showed that promoter hypermethylation was the major mechanism for transcriptional silencing of INPP4B in NPC. Furthermore, restoration of INPP4B expression significantly suppressed PI3K/AKT downstream signals in the NPC C666-1 cells. In vivo growth inhibition was clearly demonstrated in the tumor cells stably expressing INPP4B. The findings indicate that epigenetic inactivation of INPP4B is one of the key mechanisms in activating PI3K/AKT signaling cascade and playing a role in the tumorigenesis of NPC.

Matrine-induced apoptosis of human nasopharyngeal carcinoma cells via in vitro vascular endothelial growth factor-A/extracellular signal-regulated kinase1/2 pathway inactivation

Matrine, a main active extract from Sophora flavescens Ait, has been demonstrated to exert anticancer effects on various cancer cell lines, such as malignant melanoma, breast cancer, and lung cancer. However, it is currently unclear whether matrine could also elicit an inhibitory effect on growth of nasopharyngeal carcinoma (NPC), let alone the possible molecular mechanisms. Therefore, in a previous study, we investigated matrine-induced proliferation inhibition and apoptosis in NPC cells. It was shown that proliferation of human NPC cells (CNE1 and CNE2) was significantly diminished by matrine in a dose- and time-dependent manner, and apoptosis was induced in both 2 NPC cells, particularly in CNE2 cells. Moreover, the increased apoptosis rate in matrine-treated CNE2 cells confirmed the proapoptotic activity of matrine. We further found that matrine treatment dose- and time-dependently reduced the levels of vascular endothelial growth factor-A (VEGF-A), and inactivated extracellular signal-regulated kinase1/2 (ERK1/2), followed by increased expression of downstream target caspase-3. Overall, we conclude that matrine could induce apoptosis of human NPC cells via VEGF-A/ERK1/2 pathway, which supports the potential use of matrine in clinically treating NPC.

Identification of CD24 as a cancer stem cell marker in human nasopharyngeal carcinoma

Cancer stem cells (CSCs) represent a unique sub-population of tumor cells with the ability to initiate tumor growth and sustain self-renewal. Although CSC biomarkers have been described for various tumors, only a few markers have been identified for nasopharyngeal carcinoma (NPC). In this study, we show that CD24⁺ cells isolated from human NPC cell lines express stem cell genes (Sox2, Oct4, Nanog, Bmi-1, and Rex-1), and show activation of the Wnt/β-catenin signaling pathway. CD24⁺ cells possess typical CSC characteristics that include enhanced cell proliferation, increased colony and sphere formation, maintenance of cell differentiation potential in prolonged culture, and enhanced resistance to chemotherapeutic drugs. Notably, CD24⁺ cells produce tumors following inoculation of as few as 500 cells in immunodeficient NOD/SCID mice. CD24⁺ cells further show increased invasion ability in vitro, which correlates with enhanced expression of matrix metalloproteinase 2 and 9. In summary, our results suggest that CD24 represents a novel CSC biomarker in NPC.

Monoacylglycerol lipase promotes metastases in nasopharyngeal carcinoma

Monoacylglycerol lipase (MAGL) is a serine hydrolase that hydrolyzes monoacylglycerides into free fatty acids and glycerol. It has recently been found to be involved in cancer progression through the free fatty acid or endocannabinoid network after studies on its function in the endocannabinoid system. Here, we determined a role for MAGL in nasopharyngeal carcinoma (NPC), which is known for its high metastatic potential. Among the different NPC cells we tested, MAGL was highly expressed in high metastatic NPC cells, whereas low metastatic potential NPC cells exhibited lower expression of MAGL. Overexpression of MAGL in low metastatic NPC cells enhanced their motile behavior and metastatic capacity in vivo. Conversely, knockdown of MAGL reduced the motility of highly metastatic cells, reducing their metastatic capacity in vivo. Growth rate was not influenced by MAGL in either high or low metastatic cells. MAGL expression was associated with the epithelial-mesenchymal transition (EMT) proteins, such as E-cadherin, vimentin and Snail. It was also related to the sidepopulation (SP) of NPC cells. Our findings establish that MAGL promotes metastases in NPC through EMT, and it may serve as a target for the prevention of NPC metastases.

Oncogenic roles of carbonic anhydrase IX in human nasopharyngeal carcinoma

Carbonic anhydrase IX (CA IX), a hypoxia-inducible protein in tumors, has been shown to be valuable for the prognosis of nasopharyngeal carcinoma (NPC). However, the function and mechanism of CA IX has been not explored in NPC. Here, we found that CA IX was detected at higher levels in NPC cells and tissues than their corresponding partners. Furthermore, the cell growth, migration and invasion in vitro were altered with shRNA or overexpression of CA IX in NPC cells. More importantly, the metastatic ability of NPC cells stably expressing CA IX was significantly enhanced using the hepatic metastasis model of nude mice in vivo. Finally, the mTOR pathway was indicated to be involved in such effects of CA IX on NPC. This is the first evidence that CA IX may promote the NPC metastasis to potentially be a therapeutic target for NPC, and that the inhibitory molecules of CA IX and/or the mTOR pathway alone or combination with both may be worth to have a clinical trial for the patients with NPC.

[The inhibited effect of matrine on human nasopharyngeal carcinoma CNE2 cells and the expression of apoptosis related gene Caspase in vitro]

OBJECTIVE

To evaluate the inhibited effect of matrine on human nasopharyngeal carcinoma CNE2 cells and the expression of apoptosis-related gene Caspase-3 mRNA, Caspase-3, Caspase-8, Caspase-9 protein. And to explore the inhibiting effect of matrine on the apoptosis of human nasopharyngeal carcinoma CNE2 cells.

METHOD

In vitro experiments, MTT assay was used to detect the effect of matrine on CNE2 cell proliferation with different concentration. The expression levels of Caspase-3 were detected by real-time PCR. Western Blot was used to gauge the levels of Caspase-3, Caspase-8 and Caspase-9 protein.

RESULT

MTT results showed significant inhibitory action of matrine on CNE2 cells proliferation in does-dependent manner, which could up-regulate the expression of Caspase-3 mRNA and Caspase-3, Caspase-8, Caspase-9 protein in a dose-dependent manner.

CONCLUSION

Matrine could inhibit CNE2 cells proliferation in a does-dependent,that was closely related to the up-regulation of Caspase-3 mRNA and Caspase-3, Caspase-8 and Caspase-9 protein expression, and to the cascade reaction of Caspase.

N,N'-dinitrosopiperazine-mediated AGR2 is involved in metastasis of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) has a high metastatic character in the clinic, but its mechanism is not clear. As a carcinogen with organ specificity for the nasopharyngeal epithelium, N,N'-Dinitrosopiperazine (DNP) is involved in NPC metastasis. Herein, our data revealed that anterior gradient 2 (AGR2) was overexpressed in human NPC tissues, particularly in cervical lymph node metastatic NPC (LMNPC). High AGR2 expression was associated with NPC metastasis. Importantly, DNP induced AGR2 expression, and increased cell motility and invasion in the NPC cell line 6-10B. However, DNP-mediated cell motility and invasion was dramatically decreased when transfected with siRNA-AGR2. Further, AGR2 directly regulated cathepsin (CTS) B and D by binding them in vitro. These results indicate that DNP induces AGR2 expression, regulates CTSB and CTSD, increases cell motility and invasion, and promotes NPC tumor metastasis. Therefore, DNP-mediated AGR2 expression may be an important factor in prolific NPC metastasis.

Cancer stem cell characteristics, ALDH1 expression in the invasive front of nasopharyngeal carcinoma

The invasive tumor front underlies the biological aggressiveness and epithelial-mesenchymal transition (EMT) in various human malignances. However, the molecular and biological characteristics of invasive tumor front in NPC have rarely been described. Additionally, the features of cancer stem cells (CSCs) in the invasive front of tumors and its correlation with EMT also remain elusive. Our study was to investigate the expression of CSCs marker aldehyde dehydrogenase 1 (ALDH1) in the invasive front of nasopharyngeal carcinoma (NPC) and its clinical significance. Immunohistochemistry was mainly used to detect ALDH1 expression in the invasive front of NPC. The relationship between ALDH1 expression and EMT-associated markers was also examined. ALDH1 expression in the invasive front correlated strongly with lymphatic invasion (p<0.001), T classification (p=0.001), M classification (p<0.001), clinical stage (p<0.001), and local recurrence (p=0.008). ALDH1 overexpression in the invasive front contributed to worse survival of NPC, particularly in patients with early stage (T1-T2 or N0-N1) (p<0.001 and p=0.002, respectively), though it was not an independent prognostic factor (p=0.196). Furthermore, in the invasive front of NPC, ALDH1 expression correlated significantly with EMT-related biomarkers E-cadherin (p=0.026), Vimentin (p<0.001), Periostin (p<0.001), and Snail (p<0.001), but not with β-catenin (p=0.143). Our findings demonstrate first that ALDH1 expression in the invasive front links closely with EMT characteristics and tumor aggressiveness, which might provide a useful prognostic marker for NPC patients.

Sodium butyrate inhibits interferon-gamma induced indoleamine 2,3-dioxygenase expression via STAT1 in nasopharyngeal carcinoma cells

AIMS

Indoleamine 2,3-dioxygenase (IDO) inhibits T-cell proliferation by catalyzing the conversion of l-tryptophan to l-kynurenine. IDO-induced immune tolerance weakens the clinical outcomes of immunotherapies. Sodium butyrate (NaB), one of the histone deacetylase inhibitors (HDACIs), has potential anti-tumor effects. Our previous studies revealed that NaB could inhibit IFN-γ induced IDO expression in nasopharyngeal carcinoma cells, CNE2. In the present study, we aim to investigate to the mechanism of NaB interfering with the interferon-gamma (IFN-γ)-mediated IDO expression signaling transduction.

MAIN METHODS

IDO expression and STAT1 phosphorylation in CNE2 cells were analyzed by western blotting and STAT1 acetylation was evaluated by immunoprecipitation. STAT1 nuclear translocation and NF-κB activity were detected by transient transfection and reporter gene assay.

KEY FINDINGS

We found that NaB inhibited IFN-γ-induced IDO expression in CNE2 cells via decreasing phosphorylation and nuclear translocation of STAT1, but not via down-regulation of IFN-γ-receptor (IFNGR). Immunoprecipitation assays revealed that NaB increased STAT1 acetylation. Furthermore, NaB elevated the activity of NF-κB in CNE2 cells, and blocking the NF-κB activity had no effect on the IFN-γ-induced IDO expression.

SIGNIFICANCE

These results suggest that NaB inhibited IFN-γ-induced IDO expression via STAT1 increased acetylation, decreased phosphorylation, and reduced nuclear translocation. These provided new evidence for the anti-tumor action of NaB and potential drug targets to reduce the IDO-induced immune tolerance.

Aldehyde dehydrogenase 1, a functional marker for identifying cancer stem cells in human nasopharyngeal carcinoma

Aldehyde dehydrogenase 1 (ALDH1) activity has now been employed successfully as a cancer stem cells (CSCs) marker in various tumors. We wanted to investigate whether ALDH1 can be used as a putative CSCs marker and a powerful prognostic factor in nasopharyngeal carcinoma (NPC). Here, we isolated ALDH1-positive cells from human NPC cell lines (5-8F and CNE2) and found that ALDH1-positive cancer cells grew faster and had higher clone formation efficiency (0.435±0.15; 0.431±0.025 vs. 0.131±0.007; 0.121±0.126), differentiation capability and had higher migration (233.00±5.29; 228.60±9.34 vs. 123.20±7.70 vs. 97.20±6.61) than those of ALDH1-negative cancer cells in vitro. In addition, ALDH1- positive cancer cells formed significantly more tumor spheres. Our in vivo experiments showed that only 5×10(3) ALDH1-positive NPC cells were required to induce tumors. Notably, ALDH1-positive cells are enriched in the side-population (SP) cells, and stem cells-like genes OCT4, BMI1, KLF4 and SOX2 are preferentially expressed in ALDH1-positive cells. Immunohistochemical results showed that the expression of ALDH1 correlated significantly with T classification (P=0.011), N classification (P=0.005), M classification (P=0.002) and clinical stage (P=0.001). Interestingly, ALDH1 expression in the tumor correlated significantly with epithelial-mesenchymal transition (EMT) markers including vimentin expression and loss of E-cadherin (P=0.003 and 0.008, respectively). Furthermore, multivariate analyses showed that ALDH1 expression was an independent prognostic indicator (P=0.032). Taken together, for the first time, we demonstrate that ALDH1 could be a novel stem cells marker and a valuable predictor of poor survival NPC.

Correlation between expression of extracellular matrix metalloproteinase inducer and matrix metalloproteinase-2 and cervical lymph node metastasis of nasopharyngeal carcinoma

OBJECTIVES

We evaluated the expression of extracellular matrix metalloproteinase inducer (EMMPRIN) and matrix metalloproteinase-2 (MMP-2) in nasopharyngeal carcinoma (NPC) and studied their relationship with cervical lymph node metastasis.

METHODS

Immunohistochemical staining was used to detect the expression of EMMPRIN and MMP-2 in specimens from patients with chronic nasopharyngitis (CN), nonmetastastic NPC (NM-NPC), and lymph node-metastatic NPC (LNM-NPC).

RESULTS

The rates of positive EMMPRIN expression in CN, NM-NPC, and LNM-NPC were 13.3%, 30.0%, and 66.7%, respectively. Significant differences were found between the rates in CN and LNM-NPC (p <0.01) and between the rates in NM-NPC and LNM-NPC (p = 0.01). In the LNM-NPC group, NPC cells had a higher rate of expression of EMMPRIN in tumor metastases than in the primary tumor (81.8% versus 66.7%; p = 0.01). The rates of positive MMP-2 expression in CN, NM-NPC, and LNM-NPC were 13.3%, 35.0%, and 60.6%, respectively. A significant difference was found between the rates in CN and LNM-NPC (p < 0.01). In the LNM-NPC group, NPC cells had a higher rate of MMP-2 expression in tumor metastases than in the primary tumor (72.7% versus 60.6%; p <0.01). The expressions of MMP-2 and EMMPRIN were highly correlated (rs = 0.466; p <0.01).

CONCLUSIONS

Nasopharyngeal carcinoma cells may attain enhanced metastastic capability through the expression of MMP-2 induced by EMMPRIN.

αV integrin induces multicellular radioresistance in human nasopharyngeal carcinoma via activating SAPK/JNK pathway

BACKGROUND

Tumor cells acquire the capacity of resistance to chemotherapy or radiotherapy via cell-matrix and cell-cell crosstalk. Integrins are the most important cell adhesion molecules, in which αV integrin mainly mediating the tight contact between tumor cells.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate the role of αV integrin in multi-cellular radioresistance (MCR) of human nasopharyngeal carcinoma (NPC), we performed immunohistochemistry and Western blotting to find that the expression of αV integrin in the tumor tissue of radioresistant patients is much higher than that in radiosensitive patients. In vitro, we cultured human NPC cell line CNE-2 cells as multi-cellular spheroids (MCSs) or as monolayer cells (MCs), and found that the expression of αV integrin in MCSs is significantly higher than that in MCs. MTT, flow cytometry and clonogenic survival assays showed that MCSs are less sensitive to X-ray irradiation than MCs while blocking of αV integrin in MCSs dramatically reversed their radioresistance. Furthermore, as detected by Western blotting, MCSs displayed sustained activation of the stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK) pathway in presence of irradiation. Blocking of αV integrin in MCSs decreased the expression of phosphorylated JNK. Additionally, blocking of SAPK/JNK signaling pathway synergistically induced apoptosis of MCSs exposed to irradiation by increasing the expression of cleaved caspase-3. In vivo, we found that irradiation combined with αV integrin blocking treatment significantly enhanced the radiosensitivity of NPC xenografts.

CONCLUSIONS

Our results indicate a novel role of αV integrin in multi-cellular radioresistance of NPCs.

Epstein-Barr virus latent membrane protein 2A promotes invasion of nasopharyngeal carcinoma cells through ERK/Fra-1-mediated induction of matrix metalloproteinase 9

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is highly metastatic, and this malignant feature may be promoted by an EBV oncoprotein, latent membrane protein 2A (LMP2A). Acting as a signal regulator, LMP2A can enhance invasiveness and motility of epithelial cells. Downstream from the LMP2A-triggered signaling events, it is largely unknown what key effector proteins are induced and essentially promote cell invasion. In the present study, we found that in NPC cells, LMP2A upregulated matrix metalloproteinase 9 (MMP9), a metastasis-associated protease. LMP2A increased MMP9 expression at both the mRNA and protein levels. It also activated the MMP9 promoter, in which two AP-1 elements were required for the promoter activation. Among AP-1 transcription factors, Fra-1 was induced by LMP2A and is essential for LMP2A-triggered MMP9 expression. Induction of Fra-1 was dependent on the LMP2A-activated ERK1/2 pathway, and induction of the ERK1/2-Fra-1-MMP9 axis required PY motifs in the amino-terminal domain of LMP2A. Notably, LMP2A-promoted invasion of NPC cells was blocked when MMP9 expression, Fra-1 induction, or ERK1/2 activation was inhibited. In addition, we found an association of LMP2A with MMP9 expression in NPC tumor biopsy specimens, where Fra-1 was a major mediation factor. This study reveals an underlying mechanism of LMP2A-induced cell invasion, from signal transduction to upregulation of a critical protease. Considering that MMP9 can also be upregulated by another EBV oncoprotein, LMP1, this protease may be a pivotal effector at which the EBV-induced, invasion-promoting mechanisms converge, serving as an attractive therapeutic target for NPC treatment.

Activation of AKT is associated with metastasis of nasopharyngeal carcinoma

Although radiotherapy results of nasopharyngeal carcinoma (NPC) at an early stage are better than other tumors, there is still a portion of patients with NPC who die before 5 years after the treatment; the underlying mechanism remains to be further understood. This study aims to investigate the mechanism by which NPC cells escape from irradiation. Patients with NPC at stage I was included in this study. All the patients were treated with irradiation. NPC biopsies were obtained from each patient before and 1 week after the start of radiotherapy. Expression of AKT in NPC tissue was assessed by Western blotting. NPC cell line, SUNE-1 cells, was treated with irradiation. The levels of AKT in SUNE-1 cells were also assessed. The frequency of apoptotic SUNE-1 cells was evaluated by flow cytometry. The levels of AKT were markedly increased in NPC tissue after treatment with irradiation, which was significantly correlated with NPC metastasis and mortality. After irradiation, NPC cell line, SUNE-1 cells, expressed higher levels of AKT than control cells. The knockdown of AKT in SUNE-1 cells markedly increased apoptotic cell rate. Radiotherapy can increase the levels of AKT in NPC cells that are associated with NPC metastasis and increase in mortality.

Increased expression of MMP9 is correlated with poor prognosis of nasopharyngeal carcinoma

INTRODUCTION

The aim of the present study was to analyze the expression of matrix metalloproteinase 9 (MMP9) in nasopharyngeal carcinoma (NPC) and its correlation with clinicopathologic features, including the survival of patients with NPC.

METHODS

Using real-time PCR, we detected the mRNA expression of MMP9 in normal nasopharyngeal tissues and nasopharyngeal carcinoma (NPC) tissues. Using immunohistochemistry analysis, we analyzed MMP9 protein expression in clinicopathologically characterized 164 NPC cases (116 male and 48 female) with age ranging from 17 to 80 years (median = 48.4 years) and 32 normal nasopharyngeal tissues. Cases with greater than or equal to 6 and less than 6 of the score value of cytoplasmic MMP9 immunostaining were regarded as high expression and low expression, respectively. The relationship between the expression levels of MMP9 and clinical features was analyzed.

RESULTS

The expression level of MMP9 mRNA was markedly greater in NPC tissues than that in the nasopharyngeal tissues. Immunohistochemical analysis revealed that the protein expression of MMP9 detected in NPC tissues was higher than that in the nasopharyngeal tissues (P = 0.004). In addition, high levels of MMP9 protein were positively correlated with the status of lymph node metastasis (N classification) (P = 0.002) and clinical stage (P < 0.001) of NPC patients. Patients with higher MMP9 expression had a significantly shorter overall survival time than did patients with low MMP9 expression. Multivariate analysis suggested that the level of MMP9 expression was an independent prognostic indicator (P = 0.008) for the survival of patients with NPC.

CONCLUSION

High level of MMP9 expression is a potential unfavorable prognostic factor for patients with NPC.

Significance of Plk1 regulation by miR-100 in human nasopharyngeal cancer

Polo-like kinase 1 (Plk1) is a critical regulator of many stages of mitosis; increasing evidence indicates that Plk1 overexpression correlates with poor clinical outcome, yet its mechanism of regulation remains unknown. Hence, a detailed evaluation was undertaken of Plk1 expression in human nasopharyngeal cancer (NPC), the cellular effects of targeting Plk1 using siRNA in combination with ionizing radiation (RT) and potential upstream microRNAs (miRs) that might regulate Plk1 expression. Using immunohistochemistry, Plk1 was observed to be overexpressed in 28 of 40 (70%) primary NPC biopsies, which in turn was associated with a higher likelihood of recurrence (p = 0.018). SiPlk1 significantly inhibited Plk1 mRNA and protein expression, and decreased Cdc25c levels in NPC cell lines. This depletion resulted in cytotoxicity of C666-1 cells, enhanced by the addition of RT, mediated by G2/M arrest, increased DNA double-strand breaks, apoptosis, and caspase activation. Immunofluorescence demonstrated that the G2/M arrest was associated with aberrant spindle formation, leading to mitotic arrest. In vivo, transfection of C666-1 cells and systemic delivery of siPlk1 decreased tumour growth. MicroRNA-100 (miR-100) was predicted to target Plk1 mRNA, which was indeed underexpressed in C666-1 cells, inversely correlating with Plk1 expression. Using luciferase constructs containing the 3'-UTR of Plk1 sequence, we document that miR-100 can directly target Plk1. Hence, our data demonstrate for the first time that underexpressed miR-100 leads to Plk1 overexpression, which in turn contributes to NPC progression. Targeting Plk1 will cause mitotic catastrophe, with significant cytotoxicity both in vitro and in vivo, underscoring the important therapeutic opportunity of Plk1 in NPC.

[Tumor-targeted human telomerase reverse transcriptase promoter/tk gene therapy against human nasopharyngeal carcinoma cells in vitro]

OBJECTIVE

To investigate the targeted killing effect of human telomerase reverse transcriptase promoter (hTERTp)/tk gene on human nasopharyngeal carcinoma (NPC) cells.

METHODS

The recombinant plasmid hTERTp/tk/pGL3 was transfected into human NPC HNE1 cells and the expressions of TK and telomerase were investigated. The targeted killing effect induced by hTERTp/tk on HNE1 cells was assessed using RT-PCR and MTT assay.

RESULTS

TK gene expression was detected in HNE1 cells transfected by hTERTp/tk/pGL3, and the cells showed reduced telomerase and hTERT expression as compared with the control cells. hTERTp/tk/pGL3 resulted in target killing of HNE1 cells but not of the normal control cells. The tumor cell-killing effect of hTERTp/tk/pGL3 was slightly milder than that of the positive control CMV/tk/pGL3 that produced nonselective cell killing.

CONCLUSION

hTERTp/tk, a tumor-specific expression system, allows targeted tumor cell killing and reduces the activity of telomerase in NPC cells in vitro.

Epstein-Barr virus latent membrane protein 1 induces the chemotherapeutic target, thymidine phosphorylase, via NF-kappaB and p38 MAPK pathways

High thymidine phosphorylase (TP) expression is significantly correlated with poor prognosis in patients with nasopharyngeal carcinoma (NPC). NPC is an Epstein-Barr Virus (EBV)-associated cancer in which the EBV-encoded oncogene product, latent membrane protein 1 (LMP1), is expressed in approximately 60% of tumor tissues. However, no previous study has examined whether LMP1 is involved in up-regulating TP expression in NPC tissues. We herein show that LMP1 expression is correlated with TP expression in tumor cells, as examined by quantitative RT-PCR and immunohistochemical staining. We further show that the CTAR1 and CTAR2 domains of LMP1 mediate TP induction, as demonstrated by quantitative RT-PCR and Western blot analyses using LMP1 deletion and site-specific mutants. Mechanistically, LMP1-mediated TP induction is abolished by inhibitors of NF-kappaB and p38 MAPK, dominant-negative IkappaB and p38, and siRNA-mediated knockdown of p38 MAPK. Clinically, there were significant correlations among the expression levels of TP, activated p65, and phospho-p38 MAPK in NPC biopsy samples. Functionally, LMP1-mediated induction of TP expression enhanced the sensitivity of NPC cells to the chemotherapeutic prodrug, 5'-DFUR. Our results provide new insights into the roles of LMP1-mediated NF-kappaB and p38 MAPK signaling pathways in TP induction, potentially suggesting new therapeutic strategies for the treatment of NPC.

[Correlation of O6-methylguanine-DNA methyltransferase to radiation sensitivity of nasopharyngeal carcinoma]

OBJECTIVE

To assess the correlation of O6-methylguanine-DNA methyltransferase (MGMT) to radiation sensitivity of nasopharyngeal carcinoma (NPC).

METHODS

Eighty randomly selected NPC patients were divided into high (+/++, n=62) and low (-/+/+, n=18) MGMT groups according to the results of MGMT detection using immunohistochemistry. All the patients received irradiation with external beam radiotherapy, and the radiation sensitivity of NPC was analyzed after the irradiation.

RESULTS

The rates of high and low radiation sensitivity were 83.3% and 16.7% in low MGMT group, respectively, showing significant differences from those of the high MGMT group (45.2% and 54.8%, respectively, chi(2)=4.393, P=0.036).

CONCLUSION

The content of MGMT correlates to the radiation sensitivity of NPC and may serve as valuable indicators for predicting the radiation sensitivity of NPC.

Anaplastic lymphoma kinase-positive diffuse large B-cell lymphoma presenting as an isolated nasopharyngeal mass: a case report and review of literature

Anaplastic lymphoma kinase (ALK)-positive diffuse large B-cell lymphoma is a rare and distinct variant of diffuse large B-cell lymphoma with characteristic morphologic, immunophenotypic, and cytogenetic features. We report a case of ALK-positive diffuse large B-cell lymphoma in a 44-year-old male with progressively worsening unilateral nasal congestion and obstruction secondary to a nasopharyngeal mass. Radiologically, the mass was showed to extend to orophanrynx from nasopharynx. Histologically, the tumor cells exhibited plasmablastic morphology with expression of Bob-1, CD4, CD10, CD45, CD56, CD138, EMA, MUM1, Oct-2, and kappa immunoglobulin light chain, but negative for CD20, CD30, CD79a, PAX-5, and lambda. More importantly, the neoplastic cells showed positive immunoreactivity for ALK with exclusive cytoplasmic granular staining pattern. This case represented the second reported ALK-positive diffuse large B-cell lymphoma in the nasopharyngeal region.

Overexpression of phospho-Akt correlates with phosphorylation of EGF receptor, FKHR and BAD in nasopharyngeal carcinoma

The Akt pathway is one of the most common molecular alterations in various human malignancies. However, its involvement in nasopharyngeal carcinoma (NPC) tumorigenesis has not been well established. In this study, the status of Akt activation and expression of its upstream and downstream molecules was investigated in 64 NPC and 38 non-malignant nasopharyngeal tissues by immunohistochemistry. The hotspot mutations of PIK3CA, encoding the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K), were also determined in 25 of these NPC tissues. No hotspot mutations were found in any of the samples tested. Akt was activated in 27 (42.2%) and 23 (35.9%) NPCs, as indicated by p-Akt (Thr308) and p-Akt (Ser473) immunoreactivity, respectively. PTEN loss did not correlate statistically with activated Akt. However, a positive correlation was observed between activated Akt and phospho-epidermal growth factor receptor (p-EGFR), suggesting that the EGFR signaling might be one of the upstream regulators of the Akt pathway. The phosphorylation of forkhead (FKHR) and Bcl-2 associated death domain (BAD), but not mammalian target of rapamycin and glycogen synthase kinase-3beta, was significantly correlated with Akt activation. This implies that Akt promotes cell proliferation (as estimated by Ki-67) and survival, at least, through the inactivation of FKHR and BAD in NPC. Our data revealed that the EGFR/PI3K/Akt signaling pathway is important in NPC pathogenesis and that PIK3CA hotspot mutations are rare in NPC.

Phosphorylation and nuclear translocation of STAT3 regulated by the Epstein-Barr virus latent membrane protein 1 in nasopharyngeal carcinoma

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) oncoprotein has been shown to mediate activation of the signal transducer and activator of transcription 3 (STAT3). In the present study, we delineated the mechanism by which LMP1 stimulates STAT3 in a human nasopharyngeal carcinoma (NPC) cell line. LMP1 stimulated STAT3 Tyr 705-dependent nuclear accumulation, as well as the phosphorylation of STAT3 at both Tyr 705 and Ser 727. Treatment of cells with interleukin-6 neutralizing antibody inhibited the phosphorylation of STAT3 Tyr 705 and Ser 727. The differential phosphorylation of STAT3 was found to be a result of activation of Janus kinase 3 (JAK3) and extracellular signal-regulated kinase (ERK). The biological significance of JAK3-mediated activation of STAT3 Tyr 705 phosphorylation was further assessed by treating the cells with an inhibitor (WHI-P131) of JAK3. Inhibition of ERK activity by an inhibitor (PD98059) of MAPK/extracellular signal-regulated kinase kinase (MEK1) decreased the LMP1-induced activation of STAT3 Ser 727. Furthermore, immunohistochemical analysis showed an increased nuclear STAT3 Tyr 705 staining in LMP1-positive cells and STAT3 Tyr 705 phosphorylation related to NPC stages III and IV. Demonstration of the involvement of different kinases in LMP1-induced STAT3 activation supports the involvement of the JAK/STAT and mitogen-activated protein kinase (MAPK)/ERK signaling pathways in the regulation of STAT3 activation by LMP1.

Induction of cell cycle arrest and apoptosis in human nasopharyngeal carcinoma cells by ZD6474, an inhibitor of VEGFR tyrosine kinase with additional activity against EGFR tyrosine kinase

ZD6474 is a vascular endothelial growth factor receptor (VEGFR) and epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor. The present study was undertaken to investigate the direct antiproliferative effect of ZD6474 on human nasopharyngeal carcinoma (NPC) in vitro and the antitumor activity on NPC xenografts in vivo. Results indicated that ZD6474 treatment inhibited EGFR phosphorylation and led to a dose- and time-dependent decrease in NPC cell (CNE-1, CNE-2 and C666-1) proliferation. Further investigation demonstrated G0/G1 cell cycle arrest in all 3 cell lines, which was associated with an upregulation of p21 and/or p27, and downregulation of CDK4, CDK6 and CDK2. ZD6474 treatment also induced apoptosis in CNE-1 and CNE-2 cells. The apoptosis mechanisms involved reduction of Bcl-2 and/or Bcl-XL, induction of Bak and/or Bax, and activation of caspases-3, -9 and/or -8. The in vivo antitumor activity was evaluated in CNE-2 and C666-1 xenografted nude mice. Administration of ZD6474 (25-100 mg/kg/day, once-daily, p.o.) produced a dose-dependent inhibition of tumor growth and prolonged survival in both models. This study suggests that ZD6474 exerts direct antiproliferative effects on NPC cell lines in vitro by inducing G0/G1 arrest and apoptosis, and potent antitumor effects on NPC xenografts in vivo. It indicates that ZD6474 may offer a new and effective treatment for human NPC.

Serum lactate dehydrogenase level is a prognostic factor in patients with locoregionally advanced nasopharyngeal carcinoma treated with chemoradiotherapy

We investigated the treatment results and probable prognostic factors in patients with locoregionally advanced nasopharyngeal carcinoma (NPC) treated with neoadjuvant chemotherapy (NCT) plus conventional radiotherapy (RT) or concomitant chemoradiotherapy (CCRT) at our hospital. We retrospectively evaluated 61 patients (48 males, 13 females) with locoregionally advanced NPC treated either with 2 cycles of NCT plus RT (Group A, 37 patients) or with three cycles of NCT plus CCRT (Group B, 24 patients) between September 1995 and October 2002. According to the AJCC 1997 classification system, 19 patients had Stage III disease and 42 had Stage IV. NCT consisted of cisplatin and 5-fluorouracil. Total RT doses were ranged between 59.4-71.6 Gy (median: 66.2 Gy). Concomitant cisplatin (75 mg/m(2)) was given on first days of Weeks 1, 4, 7 of CCRT. Patient sex, histopathologic subtype, T status, ECOG performance status, stage, serum lactate dehydrogenase (LDH) level, and cranial nerve involvement at diagnosis were comparable in the 2 groups. There were statistically significant differences between median follow-up times and N status for the 2 groups. Fifty-five (90.2 percent) patients completed all planned NCT. Univariate analysis revealed the pretreatment LDH level as the only statistically significant prognostic factor for disease-free survival (DFS) and overall survival (OS). Four-year DFS rates were 55.9 percent and 21.3 percent for patients with normal and high serum LDH levels, respectively (P = 0.04). Four-year OS rates were 68.7 percent and 28.5 percent for patients with normal and high serum LDH levels, respectively (P = 0.01). Multivariate analysis also revealed that high serum LDH level was the only independent risk factor that predicted OS. The relative risk was 2.43 (95%CI: 1.08-5.45) for patients with high serum LDH levels (P = 0.03). No independent risk factors associated with DFS were found for other prognosticators. Our study demonstrated that high serum LDH level is the only independent unfavorable risk factor for OS in patients with locoregionally advanced NPC who were treated with NCT plus RT or CCRT.

DNA-dependent protein kinase activity and radiosensitivity of nasopharyngeal carcinoma cell lines CNE1/CNE2

The present study investigated the relationship between DNA-dependent protein kinase (DNA-PK) and radiosensitivity of nasopharyngeal carcinoma (NPC) cell lines. The dose-survival relationship for NPC cell lines, CNE1 and CNE2, was analyzed using clonogenic formation assay, the activity of DNA-PK of the two cell lines was measured using the Signa TECT DNA-PK assay kit, and the localization and expression of Kus (a heterodimer) and DNA-PKcs protein in CNE1 and CNE2 before irradiation and 15 min, 1 h, 6 h, 12 h, 24 h after 4 Gy irradiation were analyzed by immunofluorescence, laser scanning confocal microscope (LSCM) and Western blot. The results showed that the surviving fraction of CNE1 was higher than that of CNE2 at each dose. The DNA-PK activity of CNE1 was also significantly higher than that of CNE2 before and after irradiation (P<0.05), while the expression of total Ku70/Ku80 in CNE1 and CNE2 had no significant difference. Increasing translocation of Ku70 and Ku80 from the cytoplasm to the nuclei in the two cell lines was observed with increase of irradiation time as detected by Western blot, and the immunofluorescence of the DNA-PK complex subunits showed greater nuclear translocation in CNE1 than CNE2 after irradiation. The results suggest that the relatively higher radio-resistance of CNE1 correlates with the higher activity of DNA-PK as compared to that of more radiosensitive CNE2 (or lower radio-resistance) before and after irradiation. Thus, DNA-PK activity may be a useful predictor of radiosensitivity of NPC.

Tissue inhibitor of matrix metalloproteinase-2 in nasopharyngeal carcinoma

By regulating matrix metalloproteinase (MMP) activity and controlling the breakdown of extracellular matrix components, tissue inhibitors of metalloproteinases (TIMPs) play an important role in the process of tumor invasion and metastasis. The present study was designed to clarify the role of TIMP-2 in nasopharyngeal carcinoma (NPC) patients and to evaluate its importance relative to clinicopathologic parameters. It was carried out in 30 patients with NPC and 20 controls. Tissue biopsies were studied and graded pathologically, and Western blot analysis was performed to assess TIMP-2 protein expression. Clinically, in accordance with TNM classification (T: tumor size, N: lymph node involvement, M: distant metastasis), 8 cases were diagnosed as stage II, 12 as stage III, and 10 cases as stage IV; however, pathologic typing with use of the World Health Organization (WHO) classification revealed the presence of 9 specimens of squamous cell carcinoma (WHO type 1), 6 cases of nonkeratinizing carcinoma (WHO type 2), and 15 cases of undifferentiated carcinoma (WHO type 3). The difference in percentage of TIMP-2 positivity between NPC patients (76.6%) and normal controls (30%) was statistically highly significant (P < .01). In addition, there was a significant positive correlation between TIMP-2 protein positivity and either the clinical staging or the histopathologic typing (P < .01) using Chi-square test (x(2)), suggesting that TIMP-2 can be used as a marker of the severity of NPC.Accordingly, we can assume that TIMP-2 may play a role in regional lymph node and/or distant metastasis and in progression of squamous cell carcinoma. Further studies are needed to investigate the role of TIMP-2 as a marker for tumor progression and to evaluate its potential value in the follow-up of patients.

Long-circulating liposome-encapsulated ganciclovir enhances the efficacy of HSV-TK suicide gene therapy

To enhance the efficacy of ganciclovir/herpes simplex virus thymidine kinase (GCV/HSV-TK) suicide gene therapy for nasopharyngeal cancer KB, we developed long-circulating liposome-encapsulated GCV, and evaluated cytotoxicity in vitro and in vivo. PEGylated liposome-encapsulated GCV (PEG-GCV-lipo) was prepared by the freeze-thawing method. In vitro experiments demonstrated that GCV from liposomes was gradually released over a period of 3 days. The in vitro cytotoxicity of PEG-GCV-lipo was similar to that of GCV solution in human cervical carcinoma HeLa cells expressing HSV-TK. Pharmacokinetics studies in mice showed that, compared with GCV solution, intravenous and intraperitoneal injection of PEG-GCV-lipo (10 mg/kg) led to long circulation in plasma; the area under the curve was 36-fold or 32-fold higher than that of GCV solution, respectively. In GCV/HSV-TK suicide gene therapy, the HSV-TK gene complexed with nanoparticle vector was directly injected into KB xenografts, and PEG-GCV-lipo or GCV solution was injected intravenously in mice once a day (25 mg/kg/day every 2nd day, 4 times). PEG-GCV-lipo was significantly 3-fold more effective than GCV solution in inhibiting tumor growth and produced durable complete tumor remissions on day 11 after injection. These findings demonstrate that long-circulating liposome-encapsulated GCV is a new approach to drug carriers to enhance the efficacy of suicide gene therapy.

Effect of RNA interference targeting human telomerase reverse transcriptase on telomerase and its related protein expression in nasopharyngeal carcinoma cells

OBJECTIVE

Analysis of the correlation between telomerase and the expression of its related proteins may provide insight into the molecular mechanism of nasopharyngeal carcinogenesis. We investigated the effect of short hair pin ribonucleic acid (RNA) specific for human telomerase reverse transcriptase messenger RNA on the expression of the proteins c-myc (the transcription factor c-myc is a shortlived nuclear phospho-protein involved in cell proliferation and differentiation, belongs to the myc family), proliferating cell nuclear antigen and Caspase-3 in nasopharyngeal carcinoma cells.

METHODS

Short hairpin RNA expression vectors targeting the messenger RNA of human telomerase reverse transcriptase were constructed. Cells were treated with the short hairpin RNA expression vectors targeting human telomerase reverse transcriptase or vectors that included mismatched short hairpin RNA, and telomerase activity was measured by telomeric repeat amplification enzyme-linked immunosorbent assay. Cell viability was examined using the 3-(4,5-dimethyl thizol-2-yl) 2,5-diphenyl tetrazolium bromide assay. The expression of the three proteins (c-myc, proliferating cell nuclear antigen and Caspase-3) was determined by Western blotting.

RESULTS

Short hairpin RNA specific for human telomerase reverse transcriptase messenger RNA significantly inhibited telomerase activity. In addition, the expression of and proliferating cell nuclear antigen were both inhibited, while the expression of Caspase-3 was up-regulated.

CONCLUSIONS

Our results suggest that short hairpin RNA directed against human telomerase reverse transcriptase inhibits cell viability by regulating telomerase activity and its related proteins expression in nasopharyngeal carcinoma cells. Therefore, RNA interference technology may be a promising strategy for the treatment of nasopharyngeal cancer.

Expression of CYP2E1 in human nasopharynx and its metabolic effect in vitro

It was evident that nitrosamines can act directly on target tissue and result in carcinogenesis. As has been shown, the carcinogenic activity of nitrosamines relied on its bioactivation by Cytochrome P450 2E1 (CYP2E1). In this study, we investigated the expression of CYP2E1 in Nasopharyngeal carcinoma (NPC) cells, embryonic nasopharyngeal epithelial tissue (ENET) specimens, and NPC biopsies by RT-PCR analysis. CYP2E1 was expressed in all NPC cell lines (6/6, including 7429) and ENET (6/6), and 80% of NPC biopsie (8/10). The fact that Human nasopharynx expresses CYP2E1 suggests that CYP2E1 may play an important role in the course of NPC by indirect carcinogens nitrosamines. To further evaluate the function of CYP2E1, the CYP2E1 was stably expressed in the cell line NIH 3T3/rtTA under a tetracycline-controlled transactivator. The expression of CYP2E1 was tightly regulated in a dose-dependent manner by Doxycycline (Dox) When the catalytic activity of CYP2E1 was assayed, the result showed that the generation of 6-hydroxychlorzoxazone (6-OH-CZ) from chlorzoxazone (CZ) was dose- and time-dependent on Dox addition to the medium. In the presence of 1 microg/ml Dox, the CZ 6-hydroxylase activity of the cell line was found to be 0.986 +/- 0.034 nmol/10(6) cells/h. The metabolic activation of Tet/3T3/2E1-6 cells was also assayed by N,N'-dinitrosopiperazine (DNP) cytotoxicity, and the viability of Tet/3T3/2E1-6 cells treated with Dox was lower than that of untreated cells with a significant difference between them in 80 and 160 microg/ml DNP (P ( 0.05, t test. This cell line will be useful not only to assess the metabolic characteristics of CYP2E1, but also will be useful to investigate the role of CYP2E1 in metabolic activation of carcinogenic nitrosamines in vitro.

Effect of methylation-associated silencing of the death-associated protein kinase gene on nasopharyngeal carcinoma

Death-associated protein kinase (DAPK) is a Ca/calmodulin-regulated serine/threonine kinase and a positive mediator of apoptosis. Loss of expression of the DAPK gene by aberrant promoter methylation may play an important role in cancer development and progression. The aim of this study was to investigate the frequency of gene promoter methylation of DAPK in nasopharyngeal carcinoma (NPC) and the effect of 5-Aza-2'-deoxycytidine (5-Aza-CdR), a demethylating agent, on CNE cells, a human nasopharyngeal carcinoma cell line, and on xenografts of CNE cells. Methylation-specific PCR and RT-PCR were used to determine the promoter methylation status and mRNA expression of the DAPK gene in NPC. Furthermore, CNE cells were treated in vitro and in vivo with 5-Aza-CdR to explore the effect of demethylating agents on DAPK mRNA expression and tumor growth. Hypermethylation of the DAPK gene promoter was found in 35 (76.1%) of 46 NPC samples. There was no significant difference in the promoter hypermethylation rate among samples from patients with different TNM stages. No promoter hypermethylation of the DAPK gene was found in all six chronic inflammatory nasopharyngeal tissue specimens. DAPK mRNA expression was not detected in NPC tumor specimens with promoter hypermethylation. However, DAPK mRNA expression was observed in unmethylated NPC tumors and in the chronic inflammatory nasopharyngeal tissue specimens. Promoter hypermethylation of the DAPK gene was found and no DAPK mRNA expression was detected in CNE cells. DAPK mRNA expression in CNE cells and xenografts could be restored by treatment with 5-Aza-CdR. The CNE cell xenografts of nude mice treated with 5-Aza-CdR were obviously smaller in tumor volume than those of nude mice treated with PBS. These results demonstrate that loss of DAPK expression could be associated with promoter region methylation in NPC. 5-Aza-CdR may slow the growth of CNE cells in vitro and in vivo by reactivating the DAPK gene silenced by de novo methylation.