Telomerase activity of cultured human pancreatic carcinoma cell lines correlates with their potential for migration and invasion

Understanding, diagnosing, and treating pancreatic cancer from the perspective of telomeres and telomerase

Telomerase is associated with cellular aging, and its presence limits cellular lifespan. Telomerase by preventing telomere shortening can extend the number of cell divisions for cancer cells. In adult pancreatic cells, telomeres gradually shorten, while in precancerous lesions of cancer, telomeres in cells are usually significantly shortened. At this time, telomerase is still in an inactive state, and it is not until before and after the onset of cancer that telomerase is reactivated, causing cancer cells to proliferate. Methylation of the telomerase reverse transcriptase (TERT) promoter and regulation of telomerase by lactate dehydrogenase B (LDHB) is the mechanism of telomerase reactivation in pancreatic cancer. Understanding the role of telomeres and telomerase in pancreatic cancer will help to diagnose and initiate targeted therapy as early as possible. This article reviews the role of telomeres and telomerase as biomarkers in the development of pancreatic cancer and the progress of research on telomeres and telomerase as targets for therapeutic intervention.

Telomeric DNA breaks in human induced pluripotent stem cells trigger ATR-mediated arrest and telomerase-independent telomere damage repair

Although mechanisms of telomere protection are well-defined in differentiated cells, how stem cells sense and respond to telomere dysfunction, in particular telomeric double-strand breaks (DSBs), is poorly characterized. Here, we report the DNA damage signaling, cell cycle, and transcriptome changes in human induced pluripotent stem cells (iPSCs) in response to telomere-internal DSBs. We engineer human iPSCs with an inducible TRF1-FokI fusion protein to acutely induce DSBs at telomeres. Using this model, we demonstrate that TRF1-FokI DSBs activate an ATR-dependent DNA damage response, which leads to p53-independent cell cycle arrest in G2. Using CRISPR-Cas9 to cripple the catalytic domain of telomerase reverse transcriptase, we show that telomerase is largely dispensable for survival and lengthening of TRF1-FokI-cleaved telomeres, which instead are effectively repaired by robust homologous recombination (HR). In contrast to HR-based telomere maintenance in mouse embryonic stem cells, where HR causes ZSCAN4-dependent extension of telomeres beyond their initial lengths, HR-based repair of telomeric breaks is sufficient to maintain iPSC telomeres at a normal length, which is compatible with sustained survival of the cells over several days of TRF1-FokI induction. Our findings suggest a previously unappreciated role for HR in telomere maintenance in telomerase-positive iPSCs and reveal distinct iPSC-specific responses to targeted telomeric DNA damage.

A subset of gut leukocytes has telomerase-dependent "hyper-long" telomeres and require telomerase for function in zebrafish

BACKGROUND

Telomerase, the enzyme capable of elongating telomeres, is usually restricted in human somatic cells, which contributes to progressive telomere shortening with cell-division and ageing. T and B-cells cells are somatic cells that can break this rule and can modulate telomerase expression in a homeostatic manner. Whereas it seems intuitive that an immune cell type that depends on regular proliferation outbursts for function may have evolved to modulate telomerase expression it is less obvious why others may also do so, as has been suggested for macrophages and neutrophils in some chronic inflammation disease settings. The gut has been highlighted as a key modulator of systemic ageing and is a key tissue where inflammation must be carefully controlled to prevent dysfunction. How telomerase may play a role in innate immune subtypes in the context of natural ageing in the gut, however, remains to be determined.

RESULTS

Using the zebrafish model, we show that subsets of gut immune cells have telomerase-dependent"hyper-long" telomeres, which we identified as being predominantly macrophages and dendritics (mpeg1.1+ and cd45+mhcII+). Notably, mpeg1.1+ macrophages have much longer telomeres in the gut than in their haematopoietic tissue of origin, suggesting that there is modulation of telomerase in these cells, in the gut. Moreover, we show that a subset of gut mpeg1.1+ cells express telomerase (tert) in young WT zebrafish, but that the relative proportion of these cells decreases with ageing. Importantly, this is accompanied by telomere shortening and DNA damage responses with ageing and a telomerase-dependent decrease in expression of autophagy and immune activation markers. Finally, these telomerase-dependent molecular alterations are accompanied by impaired phagocytosis of E. coli and increased gut permeability in vivo.

CONCLUSIONS

Our data show that limiting levels of telomerase lead to alterations in gut immunity, impacting on the ability to clear pathogens in vivo. These are accompanied by increased gut permeability, which, together, are likely contributors to local and systemic tissue degeneration and increased susceptibility to infection with ageing.

Adaptation to chronic acidic extracellular pH elicits a sustained increase in lung cancer cell invasion and metastasis

Acidic extracellular pH (pH_e) is an important microenvironment for cancer cells. This study assessed whether adaptation to acidic pH_e enhances the metastatic phenotype of tumor cells. The low metastatic variant of Lewis lung carcinoma (LLCm1) cells were subjected to stepwise acidification, establishing acidic pH_e-adapted (LLCm1A) cells growing exponentially at pH 6.2. These LLCm1A cells showed increased production of matrix metalloproteinases (MMPs), including MMP-2, -3, -9, and -13, and pulmonary metastasis following injection into mouse tail veins. Although LLCm1A cells exhibited a fibroblastic shape, keratin-5 expression was increased and α-smooth muscle actin expression was reduced. Despite serial passage of these cells at pH 7.4, high invasive activity through Matrigel^® was sustained for at least 28 generations. Thus, adaptation to acidic pH_e resulted in a more invasive phenotype, which was sustained during passage at pH 7.4, suggesting that an acidic microenvironment at the primary tumor site is important in the acquisition of a metastatic phenotype.

Telomerase reverse transcriptase promotes cancer cell proliferation by augmenting tRNA expression

Transcriptional reactivation of telomerase reverse transcriptase (TERT) reconstitutes telomerase activity in the majority of human cancers. Here, we found that ectopic TERT expression increases cell proliferation, while acute reductions in TERT levels lead to a dramatic loss of proliferation without any change in telomere length, suggesting that the effects of TERT could be telomere independent. We observed that TERT determines the growth rate of cancer cells by directly regulating global protein synthesis independently of its catalytic activity. Genome-wide TERT binding across 5 cancer cell lines and 2 embryonic stem cell lines revealed that endogenous TERT, driven by mutant promoters or oncogenes, directly associates with the RNA polymerase III (pol III) subunit RPC32 and enhances its recruitment to chromatin, resulting in increased RNA pol III occupancy and tRNA expression in cancers. TERT-deficient mice displayed marked delays in polyomavirus middle T oncogene-induced (PyMT-induced) mammary tumorigenesis, increased survival, and reductions in tRNA levels. Ectopic expression of either RPC32 or TERT restored tRNA levels and proliferation defects in TERT-depleted cells. Finally, we determined that levels of TERT and tRNA correlated in breast and liver cancer samples. Together, these data suggest the existence of a unifying mechanism by which TERT enhances translation in cells to regulate cancer cell proliferation.

Cyst Fluid Telomerase Activity Predicts the Histologic Grade of Cystic Neoplasms of the Pancreas

PURPOSE

Pancreatic cysts frequently pose clinical dilemmas. On one hand, cysts with high-grade dysplasia offer opportunities for cure, on the other hand, those with low-grade dysplasia are easily over treated. Cyst fluid markers have the potential to improve the evaluation of these cysts. Because telomerase activity is commonly activated in malignant cells, we evaluated the diagnostic performance of cyst fluid telomerase activity measurements for predicting histologic grade.

EXPERIMENTAL DESIGN

Telomerase activity was measured using telomerase repeat amplification with digital-droplet PCR in surgically aspirated cyst fluid samples from 219 patients who underwent pancreatic resection for a cystic lesion (184 discovery, 35 validation) and 36 patients who underwent endoscopic ultrasound fine-needle aspiration. Methodologic and clinical factors associated with telomerase activity were examined.

RESULTS

Telomerase activity was reduced in samples that had undergone prior thawing. Among 119 samples not previously thawed, surgical cyst fluids from cystic neoplasms with high-grade dysplasia ± associated invasive cancer had higher telomerase activity [median (interquartile range), 1,158 (295.9-13,033)] copies/μL of cyst fluid than those without [19.74 (2.58-233.6) copies/μL; P < 0.001)]. Elevated cyst fluid telomerase activity had a diagnostic accuracy for invasive cancer/high-grade dysplasia of 88.1% (discovery), 88.6% (validation), and 88.2% (merged). Among cysts classified preoperatively as having "worrisome features," cyst fluid telomerase activity had high diagnostic performance (sensitivity 73.7%, specificity 90.6%, accuracy, 86.1%). In multivariate analysis, telomerase activity independently predicted the presence of invasive cancer/high-grade dysplasia.

CONCLUSIONS

Cyst fluid telomerase activity can be a useful predictor of the neoplastic grade of pancreatic cysts. Clin Cancer Res; 22(20); 5141-51. ©2016 AACRSee related commentary by Allen et al., p. 4966.

Telomerase activity in pancreatic juice differentiates pancreatic cancer from chronic pancreatitis: A meta-analysis

BACKGROUND/OBJECTIVE

To evaluate the usefulness of genetic markers in pancreatic juice (PJ), and the combination of these markers with telomerase activity in the differential diagnosis of pancreatic ductal adenocarcinoma (PDAC) from chronic pancreatitis.

METHODS

We conducted a meta-analysis for the diagnostic utility of the four major altered genes in PDAC (KRAS, CDKN2A/p16, TP53, and SMAD4/DPC4), telomerase activity, and a combination assay using PJ samples. A literature search was conducted in MEDLINE, Cochrane Library, and Web of Science. Data were pooled and presented as diagnostic sensitivity and specificity with 95% confidence intervals (CIs).

RESULTS

Thirty-nine studies fulfilled the inclusion criteria. Pooled estimates of KRAS analysis were as follows: sensitivity was 0.67 (95% CI, 0.63-0.71) and specificity, 0.82 (95% CI, 0.79-0.85). For telomerase activity analysis, sensitivity was 0.82 (95% CI, 0.76-0.87) and specificity, 0.96 (95% CI, 0.90-0.99). The other three tumor suppressors demonstrated low sensitivity. The data did not suggest any publication bias. A combined analysis of KRAS and telomerase activity showed a higher diagnostic sensitivity (0.94; 95% CI, 0.83-0.99) than KRAS alone. A combined analysis of telomerase activity and cytology revealed more reliable diagnostic accuracy than telomerase activity alone, with high sensitivity (0.88; 95% CI, 0.74-0.96) and specificity (1.00; 95% CI, 0.91-1.00).

CONCLUSIONS

The most reliable marker in PJ samples for diagnosis of PDAC was telomerase activity. Telomerase activity can play a central role in diagnostic analysis using PJ samples, and can increase diagnostic accuracy when combined with KRAS mutations or cytological examination.

Telomerase inhibition decreases alpha-fetoprotein expression and secretion by hepatocellular carcinoma cell lines: in vitro and in vivo study

Alpha-fetoprotein (AFP) is a diagnostic marker for hepatocellular carcinoma (HCC). A direct relationship between poor prognosis and the concentration of serum AFP has been observed. Telomerase, an enzyme that stabilizes the telomere length, is expressed by 90% of HCC. The aim of this study was to investigate the effect of telomerase inhibition on AFP secretion and the involvement of the PI3K/Akt/mTOR signaling pathway. Proliferation and viability tests were performed using tetrazolium salt. Apoptosis was determined through the Annexin V assay using flow cytometry. The concentrations of AFP were measured using ELISA kits. The AFP mRNA expression was evaluated using RT-PCR, and cell migration was evaluated using a Boyden chamber assay. The in vivo effect of costunolide on AFP production was tested in NSG mice. Telomerase inhibition by costunolide and BIBR 1532 at 5 and 10 μM decreased AFP mRNA expression and protein secretion by HepG2/C3A cells. The same pattern was obtained with cells treated with hTERT siRNA. This treatment exhibited no apoptotic effect. The AFP mRNA expression and protein secretion by PLC/PRF/5 was decreased after treatment with BIBR1532 at 10 μM. In contrast, no effect was obtained for PLC/PRF/5 cells treated with costunolide at 5 or 10 μM. Inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP concentration. In contrast, the MAPK/ERK pathway appeared to not be involved in HepG2/C3A cells, whereas ERK inhibition decreased the AFP concentration in PLC/PRF/5 cells. Modulation of the AFP concentration was also obtained after the inhibition or activation of PKC. Costunolide (30 mg/kg) significantly decreased the AFP serum concentration of NSG mice bearing HepG2/C3A cells. Both the inhibition of telomerase and the inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP production of HepG2/C3A and PLC/PRF/5 cells, suggesting a relationship between telomerase and AFP expression through the PI3K/Akt/mTOR pathway.

CD166/ALCAM expression is characteristic of tumorigenicity and invasive and migratory activities of pancreatic cancer cells

BACKGROUND

CD166, also known as activated leukocyte cell adhesion molecule (ALCAM), is expressed by various cells in several tissues including cancer. However, the role of CD166 in malignant tumors is controversial, especially in pancreatic cancer. This study aimed to clarify the role and significance of CD166 expression in pancreatic cancer.

METHODS

We performed immunohistochemistry and flow cytometry to analyze the expression of CD166 in surgical pancreatic tissues and pancreatic cancer cell lines. The differences between isolated CD166+ and CD166- pancreatic cancer cells were analyzed by invasion and migration assays, and in mouse xenograft models. We also performed quantitative RT-PCR and microarray analyses to evaluate the expression levels of CD166 and related genes in cultured cells.

RESULTS

Immunohistochemistry revealed high expression of CD166 in pancreatic cancer tissues (12.2%; 12/98) compared with that in normal pancreas controls (0%; 0/17) (p = 0.0435). Flow cytometry indicated that CD166 was expressed in 33.8-70.2% of cells in surgical pancreatic tissues and 0-99.5% of pancreatic cancer cell lines. Invasion and migration assays demonstrated that CD166- pancreatic cancer cells showed stronger invasive and migratory activities than those of CD166+ cancer cells (p<0.05). On the other hand, CD166+ Panc-1 cells showed a significantly stronger colony formation activity than that of CD166- Panc-1 cells (p<0.05). In vivo analysis revealed that CD166+ cells elicited significantly greater tumor growth than that of CD166- cells (p<0.05) in both subcutaneous and orthotopic mouse tumor models. mRNA expression of the epithelial-mesenchymal transition activator Zeb1 was over-expressed in CD166- cells (p<0.001). Microarray analysis showed that TSPAN8 and BST2 were over-expressed in CD166+ cells, while BMP7 and Col6A1 were over-expressed in CD166- cells.

CONCLUSIONS

CD166+ pancreatic cancer cells are strongly tumorigenic, while CD166- pancreatic cancer cells exhibit comparatively stronger invasive and migratory activities. These findings suggest that CD166 expression is related to different functions in pancreatic cancer cells.

Peritoneal myofibroblasts at metastatic foci promote dissemination of pancreatic cancer

Myofibroblasts in the stroma of pancreatic cancers promote tumor proliferation, invasion and metastasis by increasing extracellular matrix and secretion of several growth factors. In contrast, the role of myofibroblasts at peritoneally disseminated sites of pancreatic cancer has not yet been determined. This study was designed to assess the role of myofibroblasts at peritoneally disseminated sites of pancreatic cancer. Three primary cultures of human peritoneal myofibroblasts (hPMFs) were established from disseminated sites of pancreatic cancer and their interactions with the SUIT-2 and CAPAN-1 human pancreatic cancer cell lines were analyzed in vitro. Using a model in BALB/c nu/nu mice, we compared the dissemination ability of intraperitoneally implanted pancreatic cancer cells, with and without hPMFs, and examined the presence of green fluorescent protein (GFP)-labeled hPMFs at peritoneally disseminated sites in mice. hPMFs significantly promoted the migration and invasion of pancreatic cancer cells (P<0.05), while the cancer cells significantly promoted the migration and invasion of hPMFs (P<0.05). In vivo, the number of peritoneally disseminated nodules, more than 3 mm in size, was significantly greater in mice implanted with cancer cells plus hPMFs compared to mice implanted with cancer cells alone, with GFP-labeled hPMFs surviving in the peritoneal cavity of the former. hPMFs promote the peritoneal dissemination of pancreatic cancer. The cancer-stromal cell interaction in the peritoneal cavity may be a new therapeutic target to prevent the dissemination of pancreatic cancer.

Overexpression of human telomerase reverse transcriptase promotes the motility and invasiveness of HepG2 cells in vitro

Recent studies have indicated that telomerase activity promotes cancer invasion and metastasis, but the underlying mechanism remains unclear. Several studies have shown that expression of exogenous human telomerase reverse transcriptase (hTERT) can promote motility and invasiveness among telomerase-negative tumor cells, and inhibition of endogenous telomerase activity can reduce invasiveness in tumor cells. However, whether overexpression of hTERT can further enhance the motility and invasiveness of telomerase‑positive tumor cells has yet to be determined. In the present study, we showed that stable overexpression of hTERT can increase telomerase activity and telomere length, which significantly promotes the invasive and metastatic potential of telomerase‑positive HepG2 cells but does not affect cell proliferation. Further analysis suggested that enhanced invasiveness and metastasis may act through corresponding upregulation of mRNA and protein expression of matrix metalloproteinase 9 (MMP9) and Ras homolog gene family member C (RhoC). Our study indicated that exogenous expression of hTERT may promote invasiveness and metastasis through upregulation of MMP9 and RhoC.

Sequential hTERT knockdown and apigenin treatment inhibited invasion and proliferation and induced apoptosis in human malignant neuroblastoma SK-N-DZ and SK-N-BE2 cells

Human telomerase reverse transcriptase (hTERT) plays a key role in conferring immortality to human malignant neuroblastomas. We first determined differential expression of hTERT in four human malignant neuroblastoma SH-SY5Y, SK-N-DZ, SK-N-BE2, and IMR-32 cell lines. We then used SK-N-DZ and SK-N-BE2 cell lines, which showed the highest expression of hTERT, to investigate the therapeutic effects of sequential hTERT knockdown and apigenin (APG) treatment. We performed cell invasion assay and studied alterations in expression of matrix metalloproteinases and cell cycle regulatory molecules after this combination therapy. We also investigated induction of apoptosis by using in situ Wright staining, Annexin V staining, and Western blotting. Sequential hTERT knockdown and APG treatment significantly downregulated expression of hTERT so as to cause over 90 % inhibition of cell invasion and 70 % induction of apoptosis in both SK-N-DZ and SK-N-BE2 cell lines. Western blotting demonstrated downregulation of the molecules involved in cell invasion and proliferation, but upregulation of the cell cycle inhibitor and apoptosis-inducing molecules. In conclusion, our current results clearly showed that sequential hTERT knockdown and APG treatment could be a promising therapeutic strategy for effective inhibition of invasion and proliferation and induction of apoptosis in hTERT overexpressing malignant neuroblastoma cells.

What is recent in pancreatic cancer immunotherapy?

Pancreatic cancer (PC) represents an unresolved therapeutic challenge, due to the poor prognosis and the reduced response to currently available treatments. Pancreatic cancer is the most lethal type of digestive cancers, with a median survival of 4-6 months. Only a small proportion of PC patients is curative by surgical resection, whilst standard chemotherapy for patients in advanced disease generates only modest effects with considerable toxic damages. Thus, new therapeutic approaches, specially specific treatments such as immunotherapy, are needed. In this paper we analyze recent preclinical and clinical efforts towards immunotherapy of pancreatic cancer, including passive and active immunotherapy approaches, designed to target pancreatic-cancer-associated antigens and to elicit an antitumor response in vivo.

Inhibition of p600 expression suppresses both invasiveness and anoikis resistance of gastric cancer

BACKGROUND

Advanced gastric cancers often metastasize to distant organs and the peritoneum, leading to a poor prognosis. Both invasiveness and resistance to anchorage-independent cell death (anoikis) are important factors in the process of metastasis. p600 (600-kDa protein), recently identified from a cervical cancer cell line, plays a role in both anoikis resistance and cell migration. In this study, we examined whether p600 is involved in the progression of gastric cancer.

METHODS

We used both normal gastric mucosal cells and cancer cells laser-microdissected from 42 gastric cancers and their normal counterparts, and compared their p600 mRNA expression levels with quantitative reverse transcriptase-polymerase chain reaction. We inhibited p600 expression in two gastric cancer cell lines with siRNA and examined its effect on the invasiveness and anoikis resistance both in vitro and in vivo.

RESULTS

Expression of p600 mRNA was significantly higher in gastric cancer cells than in normal mucosal cells (P = 0.027). The invasion assay revealed that invasiveness was significantly reduced by inhibition of p600 (P < 0.01). In vitro experiments revealed that cell viability and colony-formation capacity under anchorage-independent conditions were significantly reduced by inhibition of p600 (P < 0.05). In vivo experiments also showed that the establishment of intraperitoneal disseminated tumors was significantly suppressed by transient inhibition of p600 (P < 0.001).

CONCLUSIONS

Our results strongly suggest that p600 is involved in gastric cancer progression, and has a potential to be a new molecular target for gastric cancer therapy.

MicroRNA, hsa-miR-200c, is an independent prognostic factor in pancreatic cancer and its upregulation inhibits pancreatic cancer invasion but increases cell proliferation

Background

Recently, the microRNA-200 family was reported to affect cancer biology by regulating epithelial to mesenchymal transition (EMT). Especially, the expression of miR-200c has been shown to be associated with upregulating the expression of E-cadherin, a gene known to be involved in pancreatic cancer behavior. However, the significance of miR-200c in pancreatic cancer is unknown.

Methods

In the present study, we investigated the relationship between E-cadherin and miR-200c expression in a panel of 14 pancreatic cancer cell lines and in macro-dissected formalin-fixed paraffin-embedded (FFPE) tissue samples obtained from 99 patients who underwent pancreatectomy for pancreatic cancer. We also investigated the effects of miR-200c on the proliferation and invasion of pancreatic cancer cells.

Results

We found that patients with high levels of miR-200c expression had significantly better survival rates than those with low levels of miR-200c expression. We also found a remarkably strong correlation between the levels of miR-200c and E-cadherin expression.

Conclusions

These data indicate that miR-200c may play a role in the pancreatic cancer biology and may be a novel marker for the prognosis of pancreatic cancer.

Knockdown of hTERT and concurrent treatment with interferon-gamma inhibited proliferation and invasion of human glioblastoma cell lines

Human telomerase reverse transcriptase (hTERT) is the catalytic component of telomerase that facilitates tumor cell invasion and proliferation. Telomerase and hTERT are remarkably upregulated in majority of cancers including glioblastoma. Interferon-gamma (IFN-gamma) modulates several cellular activities including cell cycle and multiplication through transcriptional regulation. The present investigation was designed to unravel the molecular mechanisms of the inhibition of cell proliferation, migration, and invasion of human glioblastoma SNB-19 and LN-18 cell lines after knockdown of hTERT using a plasmid vector based siRNA and concurrent treatment with IFN-gamma. We observed more than 80% inhibition of cell proliferation, migration, and invasion of both cell lines after the treatment with combination of hTERT siRNA and IFN-gamma. Our studies also showed accumulation of apoptotic cells in subG1 phase and an increase in cell population in G0/G1 with a reduction in G2/M phase indicating cell cycle arrest in G0/G1 phase for apoptosis. Semiquantitative and real-time RT-PCR analyses demonstrated significant downregulation of c-Myc and upregulation of p21 Waf1 and p27 Kip1. Western blotting confirmed the downregulation of the molecules involved in cell proliferation, migration, and invasion and also showed upregulation of cell cycle inhibitors. In conclusion, our study demonstrated that knockdown of hTERT and concurrent treatment with IFN-gamma effectively inhibited cell proliferation, migration, and invasion in glioblastoma cells through downregulation of the molecules involved in these processes and cell cycle inhibition. Therefore, the combination of hTERT siRNA and IFN-gamma offers a potential therapeutic strategy for controlling growth of human glioblastoma cells.

hTERT-promoter-dependent oncolytic adenovirus enhances the transduction and therapeutic efficacy of replication-defective adenovirus vectors in pancreatic cancer cells

Adenovirus-mediated gene therapy shows promise for cancer therapy, but transgene expression of replication-defective adenovirus may be low and transient in clinical settings. Recent reports have shown that the use of a conditionally replication-competent adenovirus (CRAd) enhanced the gene transduction of a replication-defective adenovirus vector. The control of tumor-stromal interactions has also been determined to be important in cancer therapy. In this study, we investigated the effect of the human telomerase reverse transcriptase (hTERT)-CRAd, Ad5/3hTERTE1, which possesses the tumor-specific hTERT promoter with the chimeric fiber 5/3, on the transgene expression and therapeutic efficacy of a replication-defective adenovirus vector expressing NK4 under the control of the CMV promoter, Ad-NK4. In addition, we established a new strategy to target both cancer cells and cancer-stromal interactions. Human pancreatic cancer cells were infected with Ad-NK4 and either Ad5/3hTERTE1 (CRAd-combination group) or Ad5/3hTERTLuc (control-combination group). In the CRAd-combination group, Ad-NK4-delivered transgene expression was increased, leading to an enhanced inhibitory effect on the invasion of cancer cells. In in vivo experiments, NK4 expression within tumors and its inhibitory effect on tumor growth, angiogenesis, and metastasis were enhanced in the CRAd-combination group. These results suggest that hTERT-CRAd enhances the transgene expression and therapeutic efficacies of Ad-NK4, possibly through the in-trans replication of Ad-NK4 induced by adenovirus E1 derived from co-infected hTERT-CRAd. This approach may be a promising combination therapy against advanced pancreatic cancer.

Protein kinase Ciota is required for pancreatic cancer cell transformed growth and tumorigenesis

Pancreatic cancer is the fourth leading cause of cancer deaths in the United States, with an overall 5-year survival rate of <5%. Pancreatic ductal adenocarcinoma (PDAC), the most common form of pancreatic cancer, is highly resistant to conventional chemotherapies, underscoring the critical need for new molecular targets for pancreatic cancer chemotherapy. The KRAS proto-oncogene is mutated in >90% of PDAC. Protein kinase Ciota (PKCiota) is required for the oncogenic Ras-mediated transformed growth of lung cancer and intestinal epithelial cells. However, little is known about the role of PKCiota in pancreatic cancer. In this study, we evaluated the expression of PKCiota in human pancreatic cancer and the requirement for PKCiota for the transformed growth and tumorigenicity of PDAC cells. We find that PKCiota is significantly overexpressed in human pancreatic cancer, and high PKCiota expression correlates with poor patient survival. Inhibition of PKCiota expression blocks PDAC cell transformed growth in vitro and tumorigenicity in vivo. Inhibition of PKCiota expression in pancreatic tumors also significantly reduces tumor angiogenesis and metastasis. Analysis of downstream PKCiota effectors implicates the Rac1-MEK/ERK1/2 signaling axis in PKCiota-mediated transformed growth and cellular invasion. Taken together, our data show a required role for PKCiota in the transformed growth of pancreatic cancer cells and reveal a novel role for PKCiota in pancreatic cancer cell metastasis and angiogenesis in vivo. Our results strongly indicate that PKCiota will be an effective target for pancreatic cancer therapy.

Combination with low-dose gemcitabine and hTERT-promoter-dependent conditionally replicative adenovirus enhances cytotoxicity through their crosstalk mechanisms in pancreatic cancer

To overcome the limited clinical efficacy of conditionally replicative adenoviruses (CRAds), we investigated the effects of combination therapy with gemcitabine (GEM) and the hTERT-promoter-dependent CRAd (hTERT-CRAd), Ad5/3hTERTE1. This combination therapy exhibited enhanced cytotoxic effects on pancreatic cancer both in vitro and in vivo. Furthermore, we revealed that this enhancement effect was due to the multiple bidirectional interactions between hTERT-CRAd and GEM. The GEM-sensitizing effect of E1 expression derived from hTERT-CRAd, and the enhancement effect by GEM on hTERT promoter activity which led to the increase of adenovirus E1 and viral infectivity. This combination therapy may be a promising therapeutic approach for pancreatic cancer.

Inhibition of osteopontin suppresses in vitro and in vivo angiogenesis in endometrial cancer

OBJECTIVE

Osteopontin (OPN) has been found to play an important role in tumor angiogenesis in recent years. Our previous studies have shown that OPN is overexpressed in tumor-associated human endometrial endothelial cells (HEECs) isolated from tissue samples of patients with endometrial cancer. In the present study, we aimed to further determine the role of OPN in endometrial cancer-associated angiogenesis.

METHODS

We knock down OPN expression in HEECs and human endometrial cancer Ishikawa (ISK) cells using the small interference RNA method, and then evaluate the effects of OPN on endometrial cancer-associated angiogenesis by in vivo mouse studies and in vitro assays.

RESULTS

Our results revealed that proliferative activity of HEECs and ISK cells in vitro was not affected by transfection with the siOPN-RNA (P>0.05). Inhibition of OPN expression in HEECs reduced the cell migration, with the percentage of repaired area of 36.32+/-2.88 vs. 8.54+/-1.13 (P=0.007). HEEC/siOPN and ISK/siOPN demonstrated 67.4% and 51.2% decreased invasiveness compared with controls, respectively (P<0.05). The number of branched points per well was obviously lower in HEEC/siOPN than that in HEEC/Control (32.46+/-17.10 vs. 53.15+/-15.44, P=0.021). Furthermore, ISK cells transfected with OPN siRNA formed smaller tumor in mice and led to a lower microvessel density, i.e., angiogenesis, in transplanted tumors of mice than scrambled siRNA controls (12.88+/-7.14 vs. 28.42+/-9.69 vessels per HPF, P=0.019).

CONCLUSION

These data confirm the positive role of OPN in endometrial cancer-associated angiogenesis and might be of great benefit for finding rational approach in endometrial cancer therapy.

Chemotherapeutic agents potentiate adenoviral gene therapy for pancreatic cancer

Adenovirus-mediated gene therapy combined with chemotherapeutic agents is expected to represent a new approach for treating pancreatic cancer. However, there have been no reports of definitive effects of chemotherapeutic agents on adenovirus-mediated gene therapies. In the present study, we investigated the effects of chemotherapeutic agents on the transduction efficiency of an adenovirus-based gene therapy. Adenovirus (Ad-NK4) expressing NK4, which acts as a hepatocyte growth factor antagonist, was used as a representative gene therapy. Pancreatic cancer cells infected with Ad-NK4 were treated with chemotherapeutic agents (5-fluorouracil [5FU], cisplatin or etoposide), and the NK4 levels in their culture media were measured. To examine the effects of chemotherapeutic agents in vivo, Ad-NK4 was administered to subcutaneous tumors in mice after treatment with the agents, and the tumor NK4 levels were measured. The NK4 levels in culture media from cells treated with 5FU, cisplatin and etoposide were 5.2-fold (P = 0.026), 6-fold (P < 0.001) and 4.3-fold (P < 0.001) higher than those of untreated cells, respectively. The chemotherapeutic agents also increased Ad-NK4 uptake. The NK4 levels in tumors treated with 5FU, cisplatin and etoposide were 5.4-fold (P = 0.006), 11.8-fold (P < 0.001) and 4.9-fold (P = 0.017) higher than those in untreated tumors, respectively. The present findings suggest that chemotherapeutic agents significantly improve the efficiency of adenovirus-mediated gene transfer in pancreatic cancer. Furthermore, they will contribute to decreases in the adenovirus doses required for gene transfer, thereby controlling the side-effects of adenovirus infection in normal tissues.

Positive regulation of human telomerase reverse transcriptase gene expression and telomerase activity by DNA methylation in pancreatic cancer

AIM

We sought to determine the role of telomerase and its catalytic subunit hTERT in pancreatic cancer and evaluate the epigenetic regulation of hTERT by promoter methylation.

METHODS

Thirty paired samples of pancreatic ductal adenocarcinomas and adjacent normal tissue and 12 chronic pancreatitis samples were studied. Reverse transcriptase polymerase chain reaction, telomeric repeat amplification protocol assay, and methylation-specific polymerase chain reaction were performed to analyze hTERT expression, telomerase activity, and methylation status of gene promoters, respectively.

RESULT

hTERT and telomerase activity were upregulated in pancreatic cancer compared with paired normal tissues and samples of pancreatitis. hTERT expression correlated with telomerase activity (P \ .05) and in turn correlated positively with hTERT promoter methylation (P \ .001) and p16 promoter methylation. hTERT transcript expression and telomerase activity both conferred a worse outcome by univariate and multivariate analysis (P \ .05).

CONCLUSION

hTERT expression and telomerase activity are predictors of poor outcome in pancreatic cancer. hTERT gene expression is positively regulated by promoter methylation.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

Radiation Enhances Adenoviral Gene Therapy in Pancreatic Cancer via Activation of Cytomegalovirus Promoter and Increased Adenovirus Uptake

Purpose: Adenovirus-mediated gene therapy combined with radiation is expected to be a new approach to treat pancreatic cancer. However, there are no reports of definitive effects of radiation on adenovirus-mediated gene therapies. In the present study, we investigated the effect of radiation on the transduction efficiency of an adenovirus-based gene therapy.

Experimental Design: We used adenovirus expressing NK4 (Ad-NK4), an antagonist for hepatocyte growth factor, as a representative gene therapy. Pancreatic cancer cells preinfected with Ad-NK4 were irradiated, and NK4 levels in culture media of these cells were measured. We investigated cytomegalovirus (CMV) promoter activity and uptake of adenovirus in these cells. To examine the effect of radiation in vivo, Ad-NK4 was given to irradiated subcutaneous tumors in nude mice, and NK4 levels in tumors were measured.

Results: NK4 levels in culture media of irradiated cells were 4.5-fold (P &lt; 0.01) higher than those of nonirradiated cells. Radiation enhanced activation of the CMV promoter and adenovirus uptake (P &lt; 0.01), leading to increased levels of NK4. We found that activation of p38 mitogen-activated protein kinase and up-regulation of dynamin 2 may be involved in the radiation-induced activation of the CMV promoter and adenovirus uptake, respectively. NK4 levels in irradiated tumors were 5.8-fold (P = 0.017) higher than those in nonirradiated tumors.

Conclusions: The present findings suggest that radiation significantly improves the efficiency of adenovirus-mediated gene transfer in pancreatic cancer and probably contributes to decreasing the dose of adenovirus required for gene transfer and controlling side effects of adenovirus infection in nonirradiated normal tissue.

The functional interplay between EGFR overexpression, hTERT activation, and p53 mutation in esophageal epithelial cells with activation of stromal fibroblasts induces tumor development, invasion, and differentiation

Esophageal cancer is a prototypic squamous cell cancer that carries a poor prognosis, primarily due to presentation at advanced stages. We used human esophageal epithelial cells as a platform to recapitulate esophageal squamous cell cancer, thereby providing insights into the molecular pathogenesis of squamous cell cancers in general. This was achieved through the retroviral-mediated transduction into normal, primary human esophageal epithelial cells of epidermal growth factor receptor (EGFR), the catalytic subunit of human telomerase (hTERT), and p53(R175H), genes that are frequently altered in human esophageal squamous cell cancer. These cells demonstrated increased migration and invasion when compared with control cells. When these genetically altered cells were placed within the in vivo-like context of an organotypic three-dimensional (3D) culture system, the cells formed a high-grade dysplastic epithelium with malignant cells invading into the stromal extracellular matrix (ECM). The invasive phenotype was in part modulated by the activation of matrix metalloproteinase-9 (MMP-9). Using pharmacological and genetic approaches to decrease MMP-9, invasion into the underlying ECM could be suppressed partially. In addition, tumor differentiation was influenced by the type of fibroblasts within the stromal ECM. To that end, fetal esophageal fibroblasts fostered a microenvironment conducive to poorly differentiated invading tumor cells, whereas fetal skin fibroblasts supported a well-differentiated tumor as illustrated by keratin "pearl" formation, a hallmark feature of well-differentiated squamous cell cancers. When inducible AKT was introduced into fetal skin esophageal fibroblasts, a more invasive, less-differentiated esophageal cancer phenotype was achieved. Invasion into the stromal ECM was attenuated by genetic knockdown of AKT1 as well as AKT2. Taken together, alterations in key oncogenes and tumor suppressor genes in esophageal epithelial cells, the composition and activation of fibroblasts, and the components of the ECM conspire to regulate the physical and biological properties of the stroma.

Telomerase activity is not a key determinant of sensitivity to standard cytotoxic drugs in human esophageal carcinoma cell lines

The aim of the present study was to investigate if basal telomerase activity levels may predict sensitivity to cytotoxic drugs in a panel of human esophageal carcinoma cell lines. The TRAPeze telomerase detection assay was used to investigate telomerase activity in the cell lines. Cytotoxic drug sensitivity for 20 standard cytotoxic agents was assessed using the fluorometric microculture cytotoxicity assay (FMCA). Telomerase activity was detected in all cell lines with a broad range of activity levels. Drug sensitivity also varied considerably between the cell lines. Except for a P value towards a correlation between mitoxantrone and telomerase activity (P=0.054), no statistically significant correlation was found between telomerase activity levels and sensitivity to investigated drugs, including key drugs such as cisplatin (P=0.9), 5-fluorouracil (P=0.8) and doxorubicin (P=0.54). We therefore conclude that basal telomerase activity level is not a key determinant of sensitivity to standard cytotoxic drugs in esophageal carcinoma cell lines.

Clinical utility of telomerase for the diagnosis of malignant well-differentiated endocrine tumours

OBJECTIVE

The distinction between benign and malignant well-differentiated endocrine tumours is hard to achieve. The aim of the present study was to determine whether detection of telomerase or quantification of human telomerase reverse transcriptase protein subunit (hTERT) differ between benign and malignant endocrine tumours.

PATIENTS AND METHODS

This retrospective study investigated 31 well-differentiated primary endocrine tumours. Based on clinical and histopathological criteria, tumours were categorized with the most recent WHO classification as 'benign' (n = 14), 'uncertain' (n = 5) or 'malignant' (n = 12) with (n = 7) or without (n = 5) metastasis after a mean follow-up of 40.4 +/- 25.8 months (4-122 months). All these tumours were assayed for telomerase activity and hTERT mRNA expression [real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR)].

RESULTS

Telomerase activity was detected in 7 malignant and metastatic tumours, in 1 malignant tumour without metastases, in 1 uncertain tumour and in 1 benign tumour. hTERT mRNA levels were significantly higher in malignant endocrine tumours with or without metastases (P = 0.001) when compared to benign tumours. The negative predictive value of hTERT mRNA quantification for the diagnosis of malignancy was 88.9%, whereas the positive predictive value was 68.7%.

CONCLUSION

The presence of telomerase activity within the primary endocrine tumour might indicate a malignant tumour and might suggest the need for an attentive search for concomitant metastases. Quantification of hTERT mRNA could be used in clinical practice to exclude malignancy in most endocrine tumours.

Concomitant reduction of matrix metalloproteinase-2 secretion and intracellular reactive oxygen species following anti-sense inhibition of telomerase activity in PC-3 prostate carcinoma cells

BACKGROUND

The level of activity of the telomerase has been shown to correlate with the degree of invasiveness in several tumor types. In addition, cellular redox state is believed to regulate the secretion of matrix metalloproteinase-2 (MMP-2).

AIMS

To determine the effect of anti-sense telomerase treatment of prostate cancer cells on MMP-2 activity, and the reactive oxygen and nitrogen species (two effectors of cellular redox state).

METHODS

Anti-sense oligonucleotide against RNA component of human telomerase (hTR) was introduced into the cells using Fugene-6 transfection reagent. The activity of telomerase was assessed using Telomere Repeat Amplification Protocol (TRAP assay). Activity of matrix metalloproteinase-2 (MMP-2) was determined by zymography. Levels of intracellular reactive oxygen species (ROS) and nitric oxide metabolites were measured by dichlorofluorescein diacetate (DCFH-DA) staining and Griess reagent, respectively. The level of apoptosis was determined using TUNEL assay.

RESULTS

TRAP assay showed more than 90% inhibition of telomerase activity after 72 h of transfection. Pro-MMP-2 activity was decreased down to 50% of the control levels. Intracellular reactive oxygen species were also significantly decreased. Neither apoptosis rate nor the level of nitric oxide metabolites was significantly different between anti-sense treated and control cells.

CONCLUSIONS

Concomitant reduction of the pro-MMP-2 secretion and ROS in PC-3 cells following hTR inhibition suggests that over-activity of telomerase in cancer cells might increase the level of matrix metalloproteinase-2 and thus, be directly involved in the invasion process through enhancement of intracellular oxidative stress.

Radiation to stromal fibroblasts increases invasiveness of pancreatic cancer cells through tumor-stromal interactions

Radiotherapy represents a major treatment option for patients with pancreatic cancer, but recent evidence suggests that radiation can promote invasion and metastasis of cancer cells. Interactions between cancer cells and surrounding stromal cells may play an important role in aggressive tumor progression. In the present study, we investigated the invasive phenotype of pancreatic cancer cells in response to coculture with irradiated fibroblasts. Using in vitro invasion assay, we demonstrated that coculture with nonirradiated fibroblasts significantly increased the invasive ability of pancreatic cancer cells and, surprisingly, the increased invasiveness was further accelerated when they were cocultured with irradiated fibroblasts. The hepatocyte growth factor (HGF) secretion from fibroblasts remained unchanged after irradiation, whereas exposure of pancreatic cancer cells to supernatant from irradiated fibroblasts resulted in increased phosphorylation of c-Met (HGF receptor) and mitogen-activated protein kinase activity, possibly or partially via increased expression of c-Met. We also demonstrated that scattering of pancreatic cancer cells was accelerated by the supernatant from irradiated fibroblasts. The enhanced invasiveness of pancreatic cancer cells induced by coculture with irradiated fibroblasts was completely blocked by NK4, a specific antagonist of HGF. These data suggest that invasive potential of certain pancreatic cancer cells is enhanced by soluble mediator(s) released from irradiated fibroblasts possibly through up-regulation of c-Met expression/phosphorylation and mitogen-activated protein kinase activity in pancreatic cancer cells. Our present findings further support the potential use of NK4 during radiotherapy for patients with pancreatic cancer.

Inhibitory effect of all-trans retinoic acid on human hepatocellular carcinoma cell proliferation

AIM: To study the inhibitory effect of all-trans retinoic acid on human hepatocellular carcinoma cell line SMMC-7721 and to explore the mechanism of its effect.

METHODS: SMMC-7721 cells were divided into two groups, one treated with all-trans retinoic acid (ATRA) for 5 days and the other as a control group. Light microscope and electron microscope were used to observe the morphological changes. Telomerase activity was analyzed with silver-stained telomere repeated assay protocal (TRAP). Expression of Caspase-3 was demonstrated with western blot.

RESULTS: ATRA-treated cells showed differentiation features including small and pyknotic nuclei, densely stained chromatin and fewer microvilli. Besides, ATRA could inhibit the activity of telomerase, promote the expression of Caspase-3 and its activation.

CONCLUSION: Telomerase activity and Caspase-3 expression are changed in human hepatocellular carcinoma cell line SMMC-7721 treated with all-trans retinioc acid. The inhibition of telomerase activity and the activation of Caspase-3 may be the key steps through which ATRA inhibits the proliferation of SMMC-7721 cell line.

Relationship between telomerase activity and its subunit expression and inhibitory effect of antisense hTR on pancreatic carcinoma

AIM: To directly investigate the relationship between telomerase activity and its subunit expression and the inhibitory effect of antisense hTR on pancreatic carcinogenesis.

METHODS: We examined the telomerase activity and its subunit expression by cell culture, polymerase chain reaction (PCR), PCR-silver staining, PCR-ELISA, DNA sequencing, MTT and flow cytometry methods.

RESULTS: PCR-silver staining and PCR-ELISA methods had the same specificity and sensitivity as the TRAP method. Telomerase activity was detected in the extract of the 10^th, 20^thand 30^th passages of P3 cells,while it was absent in fibroblasts. Furthermore, after the 30th generation, the proliferation period of fibroblast cells was significantly prolonged. Telomerase activity and hTERTmRNA were detected in two pancreatic carcinoma cell lines, but were found to be negative in human fibroblast cells. Telomerase activity and hTERTmRNA were tested in pancreatic carcinoma specimens of 24 cases. The telomerase activity was positive in 21 of the 24 cases (87.5%), and the hTERTmRNA in 20 cases (83.3%). In adjacent normal tissues positive rates were both 12.5%. There was a significant difference between the two groups. This indicated a significant correlation between the expression level of telomerase activity and histologic differentiation, metastasis and advanced clinical stage of pancreatic carcinoma. Our findings showed that the expressions of hTR and TP1mRNA were not correlated with the activity of telomerase but the expression of hTERTmRNA was. After treatment with PS-ODNs, telomerase activity in P₃ cells weakened and the inhibiting effect became stronger with an increase in PS-ODNs concentration. There was a significant difference between different PS-ODN groups (P < 0.05). Inhibition of telomerase activity occurred most significant with PS-ODN1.The results of the FCM test of pancreatic cancer P₃ cells showed an increase in the apoptotic rate with increasing PS-ODN1 and PS-ODN2 concentrations.

CONCLUSION: The expression of telomerase activity has a significant relationship to carcinogenesis. A strong correlation exists between telomerase activity and hTERTmRNA expression. The up-regulation of hTERTmRNA expression may play a critical role in human carcinogenesis. The expression of telomerase activity and its subunit level in pancreatic carcinoma significantly correlate with the clinical stage of pancreatic carcinoma and hence, may be helpful in its diagnosis and prognosis. The anti-hTR complementary to the template region of hTR is sufficient to inhibit P3 cell telomerase activity and cell proliferation in vitro, and can lead to a profound induction of programmed cell death.

Radiation stimulates HGF receptor/c-Met expression that leads to amplifying cellular response to HGF stimulation via upregulated receptor tyrosine phosphorylation and MAP kinase activity in pancreatic cancer cells

Hepatocyte growth factor (HGF) is a stromal-derived cytokine that plays a crucial role in invasion and metastasis of tumor cells through the interaction with HGF receptor, c-Met, which is frequently overexpressed in pancreatic cancer. The present study was designed to investigate the change in HGF receptor and HGF-mediated signaling after irradiation in pancreatic cancer cells. Six cell lines from human pancreatic cancer were included in the study. Gamma-radiation was used for irradiation treatment. The changes in expression levels of c-Met were evaluated by immunoblot and confirmed morphologically by indirect immunofluorescence staining. Whether the resultant alteration in c-Met would cascade as biologically usable signals upon HGF ligation was traced by receptor tyrosine phosphorylation analysis and mitogen activated protein kinase (MAP kinase or MAPK) activity assay. The various biological responses to HGF (including cell proliferation, cell scattering, migration and invasion) were evaluated as well. We also used a 4-kringle antagonist of HGF, NK4, to block the HGF/c-Met signaling pathway. Both immunoblot and immunofluorescent analysis showed moderate increased expression of c-Met in 3 of 6 pancreatic cancer cell lines after irradiation. The actions seemed to be dose-responsible, which began at 3 hr and reached its peak value at 24 hr following irradiation. The radiation-increased expression of c-Met could transform into magnifying receptor tyrosine phosphorylation reaction and MAP kinase activity once the ligand was added, fairly corresponding with alteration in the receptor. Sequentially, the cellular responses to HGF, including scattering and invasion but not proliferation, were enhanced. Also, in the presence of HGF, the elevated receptor could help to recover the radiation-compromised cell migration. A recombinant HGF antagonist, NK4 could effectively block these aberrant effects activated by irradiation both in molecular and cellular levels, thus suggesting the deep involvement of the c-Met/HGF pathway in the enhanced malignant potential after irradiation. These results suggest that radiation may promote HGF-induced malignant biological behaviors of certain pancreatic cancer cells through the up-regulated HGF/c-Met signal pathway. Selectively targeted blockade of the HGF/c-Met pathway could help to abolish the enforced malignant behavior of tumor cells by irradiation and therefore may improve the efficacy of radiotherapy for pancreatic cancer.

Analysis of telomerase activity and detection of its catalytic subunit, hTERT

The discovery of the enzyme telomerase and its subunits has led to major advances in understanding the mechanisms of cellular proliferation, immortalization, aging, and neoplastic transformation. The expression of telomerase in more than 85% of tumors provides an excellent tool for the diagnosis, prognosis, and treatment of cancer. However, the techniques employed in its detection appear to play a significant role in the interpretation of the results. The telomeric repeat amplification protocol (TRAP assay) has been the standard assay in the detection of telomerase activity and many variations of this technique have been reported. Recent advances in the development of the TRAP assay and the incorporation of techniques that provide a quantitative and qualitative estimate of telomerase activity are assessed in this review. In addition to histological and cytological examination of tissues, distribution patterns of the catalytic subunit of telomerase, hTERT, are frequently used in the prognosis of tumors. The methods involved in the detection of hTERT as a biomarker of cellular transformation are also analyzed.

Telomeres, telomerase, and telomerase inhibition: clinical implications for cancer

Telomeres are located at the ends of eukaryotic chromosomes. The enzyme telomerase synthesized them, and they are responsible for maintaining the lengths of chromosomes. Absence of telomerase is associated with telomere shortening and aging of somatic cells, but high telomerase activity is observed in over 90% of human cancer cells. Although the disappearance of telomerase with aging is considered a natural defense against development of cancer, it is not known what triggers the reappearance of telomerase in cancer cells. Telomerase activity is directly correlated with the expression of its active catalytic component, the human telomerase reverse transcriptase (hTERT), which is controlled primarily at the level of transcription. An earlier paper discussed the relationship of telomerase with aging. In this article, the contemporary literature is reviewed to explore the associations between telomerase, telomerase inhibition, and cancer. Because most cancers occur in old age, with the aging of the population, the number of people suffering from cancer is expected to increase in the coming decades. It is not known what roles telomerase and hTERT play in the complex relationship between aging and cancer. Data from experimental studies suggest that telomerase assay could potentially play a role in the diagnosis and prognosis of cancers. There is also evidence that telomerase inhibitors might be used as anticancer agents. As the knowledge of the relationships between telomerase and cancer and between telomerase and aging advances, it is hoped that more about the interacting relationships between telomerase, aging, and cancer will be learned.