Elucidation of the c-Jun N-terminal kinase pathway mediated by Estein-Barr virus-encoded latent membrane protein 1.

Epstein-Barr virus (EBV) is associated with several human diseases including infectious mononucleosis and nasopharyngeal carcinoma. EBV-encoded latent membrane protein 1 (LMP1) is oncogenic and indispensable for cellular transformation caused by EBV. Expression of LMP1 in host cells constitutively activates both the c-Jun N-terminal kinase (JNK) and NF-kappaB pathways, which contributes to the oncogenic effect of LMP1. However, the underlying signaling mechanisms are not very well understood. Based mainly on overexpression studies with various dominant-negative constructs, LMP1 was generally thought to functionally mimic members of the tumor necrosis factor (TNF) receptor superfamily in signaling. In contrast to the prevailing paradigm, using embryonic fibroblasts from different knockout mice and the small interfering RNA technique, we find that the LMP1-mediated JNK pathway is distinct from those mediated by either TNF-alpha or interleukin-1. Moreover, we have further elucidated the LMP1-mediated JNK pathway by demonstrating that LMP1 selectively utilizes TNF receptor-associated factor 6, TAK1/TAB1, and c-Jun N-terminal kinase kinases 1 and 2 to activate JNK.

Array-based comparative genomic hybridization analysis identified cyclin D1 as a target oncogene at 11q13.3 in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma is highly prevalent in Southern China and Southeast Asia. To unveil the molecular basis of this endemic disease, high-resolution comparative genomic hybridization arrays were used for systematic investigation of genomic abnormalities in 26 nasopharyngeal carcinoma samples. A comprehensive picture of genetic lesions associated with tumorigenesis of nasopharyngeal carcinoma was generated. Consistent chromosomal gains were frequently found on 1q, 3q, 8q, 11q, 12p, and 12q. High incidences of nonrandom losses were identified on chromosomes 3p, 9p, 11q, 14q, and 16q. In addition to previously characterized regions, we have identified several novel minimal regions of gains, including 3q27.3-28, 8q21-24, 11q13.1-13.3, and 12q13, which may harbor candidate nasopharyngeal carcinoma-associated oncogenes. In this study, gain of 11q13.1-13.3 was the most frequently detected chromosomal aberration and a 5.3-Mb amplicon was delineated at this region. Within this 11q13 amplicon, concordant amplification and overexpression of cyclin D1 (CCND1) oncogene was found in nasopharyngeal carcinoma cell lines, xenografts, and primary tumors. Knockdown of cyclin D1 by small interfering RNA in nasopharyngeal carcinoma cell lines led to significant decrease of cell proliferation. The findings suggest that cyclin D1 is a target oncogene at 11q13 in nasopharyngeal carcinoma and its activation plays a significant role in nasopharyngeal carcinoma tumorigenesis.

Epstein-Barr virus-encoded small RNA induces insulin-like growth factor 1 and supports growth of nasopharyngeal carcinoma-derived cell lines.

To assess the role of insulin-like growth factor 1 (IGF-1) in the growth of nasopharyngeal carcinoma (NPC), three NPC-derived cell lines, C666-1, CNE1 and HONE1, were examined. C666-1 cells maintained NPC phenotype of Epstein-Barr virus (EBV) expression and were positive for IGF-1 secretion, and their growth was strikingly inhibited by treatment with an anti-IGF-1 antibody under low serum condition. On the other hand, CNE1 and HONE1 cells were EBV-negative and did not secrete IGF-1. Although they could not grow under low serum condition, addition of recombinant IGF-1 made them grow. EBV conversion of CNE1 and HONE1 cells reproduced NPC phenotype of EBV expression and accompanied IGF-1 expression. Although they could grow under low serum condition, their growth was strikingly inhibited by treatment with the anti-IGF-1 antibody. These results suggest that EBV infection induces IGF-1 in NPC cell lines, and that the secreted IGF-1 acts as an autocrine growth factor. These findings seem to be operative in vivo, as NPC biopsies consistently express IGF-1. Further studies demonstrated that increased IGF-1 expression reflected transcriptional activation, and EBV-encoded small RNA (EBER) was responsible for IGF-1 induction. EBER is invariably expressed in EBV-associated malignancies, including NPC. The present findings strongly suggest that EBER directly affects the pathogenesis of NPC.

Combination bcl-2 antisense and radiation therapy for nasopharyngeal cancer.

PURPOSE: A wide variety of tumors depend on the dysregulation of Bcl-2 family proteins for survival. The resulting apoptotic block can often provide a mechanism for resistance to anticancer treatments, such as chemotherapy and radiation. This current study evaluates the efficacy of combining systemically delivered Bcl-2 phosphorothioate antisense (Bcl-2 ASO) and radiation for nasopharyngeal cancer therapy. RESULTS: Antisense uptake was unaffected by 0, 3, or 6 Gy radiation. Radiation decreased the fraction of viable C666-1 cells to 60%, with a further decrease to 40% in combination with Bcl-2 ASO. Despite a modest in vitro effect, Bcl-2 ASO alone caused the regression of established xenograft tumors in mice, extending survival by 15 days in a C666-1 and by 6 days in a C15 model. The survival times for mice treated with both Bcl-2 ASO and radiation increased by 52 days in C666-1 and by 20 days in C15 tumors. This combination resulted in a more-than-additive effect in C666-1 tumors. Less impressive gains observed in C15 tumors might be attributable to higher expression of antiapoptotic Bcl-2 family proteins and limited drug distribution in the tumor. Retreatment of C666-1 tumors with the Bcl-2 ASO-radiation combination, however, was effective, resulting in mice surviving for >80 days relative to untreated controls. CONCLUSIONS: Our results show that the Bcl-2 ASO and radiation combination is a highly potent therapy for nasopharyngeal cancer. Further examination of combination therapy with radiation and other Bcl-2 family-targeted anticancer agents in both preclinical and clinical settings is definitely warranted.

Plasma Epstein-Barr virus DNA and residual disease after radiotherapy for undifferentiated nasopharyngeal carcinoma.

BACKGROUND: Epstein-Barr virus (EBV) DNA can be detected and quantified in the plasma of patients with EBV-related tumors, such as nasopharyngeal carcinoma (NPC). Although NPC at early stages can be cured by radical radiotherapy, there is a high recurrence rate in patients with advanced NPC. The pretreatment level of circulating EBV DNA is a prognostic factor for NPC, but the prognostic value of post-treatment EBV DNA has not been studied. We designed a prospective study in Hong Kong, China, to investigate the value of plasma EBV DNA as a prognostic factor for NPC. METHODS: One hundred seventy NPC patients, without metastatic disease at presentation, were treated with a uniform radiotherapy protocol. Circulating EBV DNA was measured by real-time quantitative polymerase chain reaction before treatment and 6-8 weeks after radiotherapy was completed. Risk ratios (RRs) were determined with a Cox regression model, and associations of various factors with progression-free and overall survival and recurrence rates were determined with a stepwise Cox proportional hazards model. All statistical tests were two-sided. RESULTS: Ninety-nine percent of patients achieved complete clinical remission. Levels of post-treatment EBV DNA dominated the effect of levels of pretreatment EBV DNA for progression-free survival. The RR for NPC recurrence was 11.9 (95% confidence interval [CI] = 5.53 to 25.43) for patients with higher post-treatment EBV DNA and 2.5 (95% CI = 1.14 to 5.70) for patients with higher pretreatment EBV DNA. Higher levels of post-treatment EBV DNA were statistically significantly associated with overall survival (P<.001; RR for NPC recurrence = 8.6, 95% CI = 3.69 to 19.97). The positive and negative predictive values for NPC recurrence for a higher level of post-treatment EBV DNA were 87% (95% CI = 58% to 98%) and 83% (95% CI = 76% to 89%), respectively. CONCLUSION: Levels of post-treatment plasma EBV DNA in patients with NPC appear to strongly predict progression-free and overall survival and to accurately reflect the post-treatment residual tumor load.

Tumor-targeted gene therapy for nasopharyngeal carcinoma.

The unique feature of human nasopharyngeal carcinoma (NPC) is its almost universal association with the EBV, which is expressed in a latent form exclusively in cancer cells, and not in the surrounding tissues. We have exploited this differential by constructing a novel replication-deficient adenovirus vector (ad5.oriP) in which transgene expression is under the transcriptional regulation of the family of repeats domain of the origin of replication (oriP) of EBV. When EBNA1, one of the latent gene products of EBV, binds to the family of repeats sequence, this activates transcription of downstream genes. Vector constructs were made using the beta-galactosidase and luciferase reporter genes (ad5oriP.betagal and ad5oriP.luc) or the p53 tumor suppressor gene (ad5oriP.p53). 5-Bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining demonstrated extensive expression only in EBV-positive NPC cells, specifically in response to the presence of EBNA1. The relative difference in expression between EBV-positive and -negative cell lines is approximately 1000-fold. This selective expression was corroborated in EBV-positive and -negative tumor models, along with an absence of transgene expression in the host liver. Significant cytotoxicity was achieved using the adv.oriP.p53 therapeutic gene only in EBV-positive NPC cells, which was enhanced with the addition of ionizing radiation. Cytotoxicity was mediated primarily by induction of apoptosis. These results demonstrate that the oriP sequence can achieve high levels of gene expression targeted specifically to EBV-positive NPC cells in the context of the adv vector. This has now provided the tumor-specific expression system from which additional interventions can be evaluated in future treatment strategies for patients with nasopharyngeal cancers.

Epigenetic silencing of cellular retinol-binding proteins in nasopharyngeal carcinoma.

Aberrant retinoid signaling in human cancers is extending from the nucleus to the cytoplasm. Recently, we have demonstrated frequent epigenetic inactivation of a retinoic acid receptor (RAR), RARbeta2, in nasopharyngeal carcinoma (NPC). To further explore targets contributing to aberrant retinoid signaling in NPC, the expression of cellular retinol-binding proteins (CRBPs), cellular retinoic acid-binding proteins (CRABPs), RARs, and retinoid X receptors (RXRs) was examined. Apart from RARbeta2, transcriptional silencing of two CRBPs, CRBPI and CRBPIV, was observed in NPC cell lines and xenografts. Hypermethylation of CRBPI and CRBPIV CpG islands was found to be closely correlated with the loss of expression. Treatment with the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine, resulted in reexpression of CRBP1 and CRBPIV gene expression in NPC cell lines. Both CRBPI and CRBPIV hypermethylations were also observed in 43/48 (87.8%) and 26/48 (54.2%) primary NPC tumors, respectively. Here, we reported for the first time that CRBPIV was transcriptionally inactivated by promoter hypermethylation in human cancer. Simultaneous methylation of CRBPI, CRBPIV, and RARbeta2 was commonly found in NPC primary tumors. Our findings implied that epigenetic disruption of the CRBPs, CRBPI and CRBPIV, is important in NPC tumorigenesis and may contribute to the loss of retinoic acid responsiveness in cancer.

Characterization of chromosome 3q and 12q amplicons in nasopharyngeal carcinoma cell lines.

Nasopharyngeal carcinoma (NPC) is a distinct geographical disease with high incidence in Southeast Asia. Previous CGH studies have located multiple regions of chromosomal gains and losses in NPC. To elucidate the regions of gain and amplification, a high-resolution array comparative genomic hybridization (array CGH) was applied to characterize the common amplicons in NPC cell lines and xenografts. Consistent with our previous CGH findings, frequent gains at chromosomes 1q, 3q, 7, 8, 9q, 12q and 20q were detected. High incidence of gains were identified on chromosome 3q and 12q. The findings were further confirmed by FISH analysis. Using 16 BAC clones on 3q26-28 and 6 BAC clones on 12q13, the smallest regions of gain at 3q and 12q were defined on five NPC cell lines. Chromosome 3q26.33 (RP11-510K16) and 12q13.2-q13.3 (RP11-183H16) showed the highest amplification frequency in FISH analysis with 100 and 66.7%, respectively. PIK3CA, a candidate oncogene located at 3q26.32 adjacent to this 3q amplicon was investigated by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Overexpression of this gene was found in 4 NPC cell lines and 3 xenografts. The findings implied that PIK3CA may be a putative oncogene involved in the tumorigenesis of NPC.

Promoter hypermethylation of multiple genes in nasopharyngeal carcinoma.

PURPOSE: The methylation profile of nasopharyngeal carcinoma (NPC) has been investigated by a candidate gene approach. EXPERIMENTAL DESIGN: Four NPC cell lines, 4 NPC xenografts, 33 NPC primary tumors, and 6 samples of normal nasopharyngeal epithelium were subjected to methylation-specific PCR for analysis of promoter methylation of eight cancer-related genes. These eight genes were RASSF1A, RARbeta2, DAP-kinase, p16, p15, p14, MGMT, and GSTP1. The correlation between methylation status of these genes and clinical features such as stage, local-regional recurrence, distant metastasis, and survival has been analyzed. RESULTS: The incidence of promoter methylation in NPC samples was 84% for RASSF1A, 80% for RARbeta2, 76% for DAP-kinase, 46% for p16, 17% for p15, 20% for p14, 20% for MGMT, and 3% for GSTP1. No methylation of these genes was detected in the six normal nasopharyngeal epithelium samples. All NPC tumor samples in this study displayed aberrant methylation in at least one of these eight genes. No significant correlation between methylation status of these genes and clinical parameters of the patients was found. CONCLUSIONS: A high frequency of aberrant methylation of the 5' CpG island of the RASSF1A, RARbeta2, DAP-kinase, and p16 genes in the present study was noted. Our findings suggest that methylation of the genes in the critical pathways is common in NPC.

Quantitative Epstein-Barr virus DNA analysis and detection of gene promoter hypermethylation in nasopharyngeal (NP) brushing samples from patients with NP carcinoma.

PURPOSE: Nasopharyngeal carcinoma (NPC) is highly prevalent in southern China and characterized by a strong association with EBV. We aimed to detect EBV DNA and cancer-related gene promoter hypermethylation in nasopharyngeal (NP) brushing samples and provide a novel noninvasive approach for NPC detection. EXPERIMENTAL DESIGN: Twenty-eight NPC cases and 26 noncancerous subjects were prospectively recruited. NP brushing samples were subjected to quantitative real-time PCR analysis of EBV DNA and methylation-specific PCR analysis of the DAP-kinase, RASSF1A, and p16 genes. RESULTS: EBV DNA quantity in NP brushing samples from NPC patients (median, 8.94 copies/actin) was significantly higher than that of controls (median, 0 copies/actin; P < 0.0001). Twenty-seven of 28 NPC patients had detectable EBV DNA in NP brushes, whereas 25 of 26 controls had undetectable or very low levels of EBV DNA. Elevated EBV DNA level in brushing samples as a tumor marker had a sensitivity of 96.4% and a specificity of 96.2% for NPC detection. Moreover, T(1) disease had a significantly lower EBV DNA level as compared with locally more advanced disease (P = 0.037). In brushing samples of NPC patients, the frequencies of DAP-kinase, RASSF1A, and p16 promoter hypermethylation were 50.0%, 39.3%, and 46.4%, respectively. Seventy-eight percent of cases showed methylation of at least one gene. No aberrant hypermethylation was detected in control samples. CONCLUSIONS: Our study demonstrated the feasibility of detecting multiple molecular tumor markers in NP brushing samples with a high sensitivity and specificity for NPC detection. It offers a powerful yet noninvasive approach for the diagnosis of NPC in high-risk populations.

Disparity of sensitivities in detection of radiation-naïve and postirradiation recurrent nasopharyngeal carcinoma of the undifferentiated type by quantitative analysis of circulating Epstein-Barr virus DNA1,2.

PURPOSE: The purpose of this research was to compare the sensitivities of plasma EBV DNA in detection of postirradiation locally recurrent nasopharyngeal carcinoma (NPC), postirradiation distant metastatic NPC, and radiation-naïve NPC. EXPERIMENTAL DESIGN: Twenty-four patients with postirradiation local recurrence of NPC were assessed for plasma EBV DNA levels by a real-time quantitative PCR system. The results were compared with those of a cohort of 140 patients with newly diagnosed NPC and with those of 25 patients with distant metastatic relapse. EBV-encoded RNA positivity was also assessed in locally recurrent tumors and newly diagnosed tumors with undetectable plasma EBV DNA levels. RESULTS: Postirradiation locally recurrent tumors were associated with a significantly lower rate of detectable plasma EBV DNA compared with radiation-naïve tumors of comparable stage [stage I-II tumors: 5 of 12 (42%) versus 47 of 51 (92%), P = 0.0002; stage III-IV tumors: 10 of 12 (83%) versus 88 of 89 (99%), P = 0.01; Fisher's exact test], and compared with distant metastatic recurrences [15 of 24 (63%) versus 24 of 25 (96%), P < 0.02; Fisher's exact test]. The median EBV DNA level in patients with detectable EBV DNA was also significantly lower in locally recurrent tumors than in radiation-naïve tumors. All of the tissue samples of tumors associated with undetectable EBV DNA levels, where available, were EBV-encoded RNA positive. CONCLUSIONS: The sensitivity of EBV DNA in the detection of tumors regrowing from an irradiated site is much lower than that from a radiation-naïve site. Although plasma EBV DNA is very effective in detecting distant metastatic relapse of NPC, it cannot be relied on as the sole surveillance tool for detection of local relapse.

Coexpression of hypoxia-inducible factors 1alpha and 2alpha, carbonic anhydrase IX, and vascular endothelial growth factor in nasopharyngeal carcinoma and relationship to survival.

PURPOSE: Tumor hypoxia is known to be associated with resistance to chemotherapy, radiotherapy, and poorer survival. Recently, it is shown that hypoxia induces the expression of hypoxia-inducible factor-1alpha and 2alpha (HIF-1alpha and HIF-2alpha), which then up-regulates the expression of downstream genes such as carbonic anhydrase IX (CA IX) and vascular endothelial growth factor (VEGF). EXPERIMENTAL DESIGN: We examined the expression of HIF-1alpha, HIF-2alpha, CA IX, and VEGF by immunohistochemistry in nasopharyngeal carcinoma (NPC) biopsies from 90 consecutive patients recruited between 1994 and 1997 in a randomized controlled trial of chemoradiation in locally advanced NPC and investigated their relationship with survival. RESULTS: HIF-1alpha was expressed in 52 of 90 (58%), HIF-2alpha in 6 of 89 (7%), CA IX in 51 of 90 (57%), and VEGF in 54 of 90 (60%) of tumors. Tumor HIF-1alpha expression correlated significantly with that of CA IX (P = 0.008) and VEGF (P = 0.003). High tumor HIF-1alpha expression was associated with a trend for poor overall survival (P = 0.06). Tumors with a positive hypoxic profile (defined as high expression of both HIF-1alpha and CA9) were associated with worse progression-free survival (P = 0.04). Tumors with both hypoxic and angiogenic profile (defined as high VEGF expression) were associated with a worse progression-free survival (P = 0.0095). CONCLUSION: Overexpression of HIF-1alpha, CA IX, and VEGF is common in NPC, which is probably related to hypoxia up-regulated expression involving a HIF-dependent pathway, and is associated with poor prognosis. Targeting the hypoxia pathway may be useful in the treatment of NPC.

Antitumor effect and enhancement of cytotoxic drug activity by cetuximab in nasopharyngeal carcinoma cells.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is the most common head and neck cancer in southern China and South East Asia. Epidermal growth factor receptor (EGFR) has been proposed as a new target for anticancer therapy. EGFR was over-expressed in 85% of NPC tissues and was associated with poor prognosis. MATERIALS AND METHODS: EGFR protein expression in four NPC cell lines, CNE-2, HONE-1, HK1 and C666-1, was examined by Western immunoblotting. The antitumor effect of cetuximab was studied in the cell lines, either alone or in combination with cisplatin or paclitaxel. RESULTS: EGFR protein expression was highest in the HK1 cell line, moderate in CNE-2 and HONE-1, and lowest in C666-1. Single agent cetuximab demonstrated significant antitumor effect in the HK1 and HONE-1 cell lines, but minimal activity in CNE-2 and C666-1 cells. When cetuximab was combined with cisplatin or paclitaxel in the HK1 and HONE-1 cell lines, an additive enhancement of cytotoxic drug activity was demonstrated. CONCLUSION: Cetuximab demonstrated single agent activity selectively in NPC cell lines with moderate to high EGFR protein expression. Cetuximab could also additively enhance the antitumor effects of cisplatin or paclitaxel in these NPC cell lines. These results support the rationale of combining cetuximab with current standard chemotherapy to further improve the therapeutic ratio in the treatment of NPC. Future studies should aim at defining the predictive markers for response to cetuximab in order to select the responsive tumor for the correctly targeted agents.

Pathogenesis and treatment of nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC), an endemic tumor in southern China, has three unique etiologic factors, including genetic susceptibility, chemical carcinogens, and association with Epstein-Barr virus (EBV) infection. Recent identification of critical genetic changes in this cancer has allowed the description of a multistep model for the pathogenesis of NPC. NPC is highly radiosensitive and chemosensitive. Attempts have been made to improve treatment results by integrating radiotherapy with some form of chemotherapy. Here, we review the current evidence available on the various chemotherapy-radiotherapy sequencing approaches and seek to define the optimal integration of radiotherapy and chemotherapy. Despite consistently high response rates to platinum-based neoadjuvant chemotherapy, none of six randomized studies of neoadjuvant and/or adjuvant chemotherapy showed any improvement in overall survival, although two did demonstrate significant improvement in local control rates and progression-free survival. However, three randomized studies of concurrent cisplatin-radiotherapy one with, and two without, adjuvant chemotherapy demonstrated significant improvement in progression-free survival and two of these have demonstrated improvement in overall survival. Preliminary data on the use of neoadjuvant chemotherapy followed by concurrent chemoradiation have been highly encouraging. Concurrent cisplatin-radiation with or without adjuvant chemotherapy should be considered as standard practice for locoregionally advanced NPC. The addition of neoadjuvant chemotherapy warrants further investigation and appears to be the most likely approach to further improve treatment results.

Involvement of both endoplasmic reticulum and mitochondria in photokilling of nasopharyngeal carcinoma cells by the photosensitizer Zn-BC-AM.

Photodynamic therapy (PDT) is recently developed as an effective treatment for malignant disease. In PDT, the photosensitizer eradicates tumour by induction of apoptosis. In this study, we investigated the mechanistic actions of a recently developed second generation photosensitizer, Zn-BC-AM, on nasopharyngeal carcinoma (NPC) cells. Zn-BC-AM was found to localize in the mitochondria, endoplasmic reticulum (ER), and golgi body. Photoactivation of Zn-BC-AM loaded NPC cells resulted in a rapid collapse of mitochondrial membrane potential (Deltapsim) (15 min), followed by the release of cytochrome c (1 h), and activation of caspases-9 and -3 (4 h). Expression of ER chaperones Bip/Grp78 and Grp94, and ER resident lectin-like chaperone calnexin (CNX) was also enhanced in PDT-stressed NPC cells. Caspase-12, an important caspase involved in ER stress-induced apoptosis, was also activated. Inhibition of Ca2+ uptake into mitochondria by ruthenium red (RR) or loading the cells with EGTA-AM, an agent that buffers intracellular Ca2+ released from ER, resulted in a significant reduction of Zn-BC-AM PDT-induced cell death. These observations suggest that both ER and mitochondria are the subcellular targets of Zn-BC-AM. Effective activation of ER- and mitochondria-mediated apoptotic pathways is responsible for Zn-BC-AM PDT-induced NPC cell death.

Apoptosis and TRAF-1 cleavage in Epstein-Barr virus-positive nasopharyngeal carcinoma cells treated with doxorubicin combined with a farnesyl-transferase inhibitor.

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinomas (NPC) are much more sensitive to chemotherapy than other head and neck carcinomas. Spectacular regressions are frequently observed after induction chemotherapy. However, these favorable responses are difficult to predict and often of short duration. So far there have been only few experiments to investigate the mechanisms which underline the cytotoxic effects of anti-neoplastic drugs against NPC cells. In addition, these studies were performed almost entirely on EBV-negative cell lines therefore not truly representative of NPC cells. For the first time, we have used two EBV-positive NPC tumor lines derived from a North African (C15) and a Chinese (C666-1) patient as in vitro targets for a panel of anti-neoplastic agents. Doxorubicin, taxol and in a lesser extent cis-platinum efficiently inhibited NPC cell proliferation at clinically relevant concentrations, but all three agents failed to induce apoptosis. However, massive apoptosis of C15 cells was achieved when doxorubicin (1 microM) was combined with a farnesyl-transferase inhibitor, BIM 2001 (5 microM). Moreover, this apoptotic process was associated with a caspase-dependent early cleavage of the TNF-receptor associated factor 1 (TRAF-1) molecule, a signaling adaptor which is specifically expressed in latently EBV-infected cells. TRAF-1 cleavage might become a useful indicator of chemo-induced apoptosis in EBV-associated NPCs.

Genome wide detection of oncogene amplifications in nasopharyngeal carcinoma by array based comparative genomic hybridization.

We have applied the method of genomic microarray to investigate amplification of oncogenes throughout the genome of nasopharyngeal carcinoma (NPC). Array based comparative genomic hybridization (array CGH) allows simultaneous examination of 58 oncogenes commonly amplified in various human cancers. In the present study, we have examined 15 NPC samples including five cell lines, two xenografts and eight primary tumours with array CGH to reveal the particular oncogenes associated with this cancer. This is the first genome wide survey of multiple oncogene amplifications involved in the development of NPC. Non-random gene amplifications were identified for the first time in NPC on MYCL1 in 1p34.3 and on TERC and PIK3CA at 3q26.3. Other high level amplified oncogenes included NRAS, RAF1, MYB, EGFR, FGF4, EMS1, and D17S167. Highest frequencies of gain of novel oncogenes were detected on MYCL1 (66.7%), TERC (46.7%), ESR (46.7%), PIK3CA (40%), LAMC2 (33.3%), and CSE1L (33.3%).

Molecular cytogenetic characterization of nasopharyngeal carcinoma cell lines and xenografts by comparative genomic hybridization and spectral karyotyping.

Nasopharyngeal carcinoma (NPC) cell lines and xenografts represent valuable models for functional and therapeutic studies on this common malignancy in Southeast Asia. The karyotypic information in most NPC cell lines and xenografts, however, remains largely unclear to date. We have characterized the chromosomal aberrations in six commonly used human NPC cell lines and xenografts using the molecular cytogenetic technique of comparative genomic hybridization (CGH). Genomic imbalances identified in cell lines were further correlated with structural abnormalities indicated from spectral karyotyping (SKY) analysis. CGH revealed consistent overrepresentations of 8q (six out of six cases) with a smallest overlapping region identified on 8q21.1 approximately q22. Other common gains included 7p (4/6 cases), 7q (4/6 cases), 12q (4/6), and 20q (4/6 cases), where minimal overlapping regions were suggested on 7p15 approximately p14, 7q11.2 approximately q21, and 12q22 approximately q24.1. Common losses were detected on 3p12 approximately p21 (4/6 cases) and 11q14 approximately qter (4/6 cases). Although SKY analysis on cell lines revealed predominantly unbalanced rearrangements, reciprocal translocations that involved chromosome 2 [i.e., t(1;2), t(2;3), and t(2;4)] were suggested. Furthermore, SKY examination illustrated additional breakpoints on a number of apparently balanced chromosomes. These breakpoints included 3p21, 3q26, 5q31, 6p21.1 approximately p25, 7p14 approximately p22, and 8q22. Our finding of regional gains and losses and breakpoints represents information that may contribute to NPC studies in vitro.

Aberrant methylation of RASSF4/AD037 in nasopharyngeal carcinoma.

Ras-association domain family of proteins (RASSF) is characterized by the Ras-association (RA) domain at the C-terminal. Frequent inactivation of RASSF1A gene in human cancers suggests that other members of the family may also play an important role in tumorigenesis. By in silico gene searches, the number of RASSF family members is increasing. Two new members of RASSF family, RASSF4/AD037 and NORE1, were recently identified. While the status of RASSF4/AD037 is poorly understood, methylation of NORE1A was reported to be common in human cancers. In this study, we aimed to investigate the expression and methylation status of RASSF4/AD037 and NORE1 in nasopharyngeal carcinoma (NPC) in which RASSF1A is frequently inactivated by promoter hypermethylation. Our results showed that expression of RASSF4/AD037 was lost in 12.5% (1/8) of NPC cell lines/xenografts. Bisulfite sequencing analysis revealed dense methylation in the promoter region of RASSF4/AD037 in the cell line. Restoration of RASSF4/AD037 mRNA was observed by treatment with a demethylating agent. Moreover, methylation of primary NPC was found in 5% (1/20) of the samples examined. For NORE1A, partial methylation was detected in 37.5% (3/8) of NPC cell lines/xenografts while expression of NORE1A was found in all NPC cell lines/xenografts. No aberrant methylation of NORE1A was observed in 20 primary tumors. In summary, epigenetic inactivation of RASSF4/AD037 and NORE1A is rare in NPC, suggesting that these two RASSF family members may not be critical targets for gene inactivation during the tumorigenesis of NPC.