Inhibition of the epidermal growth factor receptor suppresses telomerase activity in HSC-1 human cutaneous squamous cell carcinoma cells

Combining old and new concepts in targeting telomerase for cancer therapy: transient, immediate, complete and combinatory attack (TICCA)

Telomerase can overcome replicative senescence by elongation of telomeres but is also a specific element in most cancer cells. It is expressed more vastly than any other tumor marker. Telomerase as a tumor target inducing replicative immortality can be overcome by only one other mechanism: alternative lengthening of telomeres (ALT). This limits the probability to develop resistance to treatments. Moreover, telomerase inhibition offers some degree of specificity with a low risk of toxicity in normal cells. Nevertheless, only one telomerase antagonist reached late preclinical studies. The underlying causes, the pitfalls of telomerase-based therapies, and future chances based on recent technical advancements are summarized in this review. Based on new findings and approaches, we propose a concept how long-term survival in telomerase-based cancer therapies can be significantly improved: the TICCA (Transient Immediate Complete and Combinatory Attack) strategy.

Hormonal regulation of telomerase activity and hTERT expression in steroid-regulated tissues and cancer

Naturally, in somatic cells chromosome ends (telomeres) shorten during each cell division. This process ensures to limit proliferation of somatic cells to avoid malignant proliferation; however, it leads to proliferative senescence. Telomerase contains the reverse transcriptase TERT, which together with the TERC component, is responsible for protection of genome integrity by preventing shortening of telomeres through adding repetitive sequences. In addition, telomerase has non-telomeric function and supports growth factor independent growth. Unlike somatic cells, telomerase is detectable in stem cells, germ line cells, and cancer cells to support self-renewal and expansion. Elevated telomerase activity is reported in almost all of human cancers. Increased expression of hTERT gene or its reactivation is required for limitless cellular proliferation in immortal malignant cells. In hormonally regulated tissues as well as in prostate, breast and endometrial cancers, telomerase activity and hTERT expression are under control of steroid sex hormones and growth factors. Also, a number of hormones and growth factors are known to play a role in the carcinogenesis via regulation of hTERT levels or telomerase activity. Understanding the role of hormones in interaction with telomerase may help finding therapeutical targets for anticancer strategies. In this review, we outline the roles and functions of several steroid hormones and growth factors in telomerase regulation, particularly in hormone regulated cancers such as prostate, breast and endometrial cancer.

Regular, Intense Exercise Training as a Healthy Aging Lifestyle Strategy: Preventing DNA Damage, Telomere Shortening and Adverse DNA Methylation Changes Over a Lifetime

Exercise training is one of the few therapeutic interventions that improves health span by delaying the onset of age-related diseases and preventing early death. The length of telomeres, the 5'-TTAGGG n -3' tandem repeats at the ends of mammalian chromosomes, is one of the main indicators of biological age. Telomeres undergo shortening with each cellular division. This subsequently leads to alterations in the expression of several genes that encode vital proteins with critical functions in many tissues throughout the body, and ultimately impacts cardiovascular, immune and muscle physiology. The sub-telomeric DNA is comprised of heavily methylated, heterochromatin. Methylation and histone acetylation are two of the most well-studied examples of the epigenetic modifications that occur on histone proteins. DNA methylation is the type of epigenetic modification that alters gene expression without modifying gene sequence. Although diet, genetic predisposition and a healthy lifestyle seem to alter DNA methylation and telomere length (TL), recent evidence suggests that training status or physical fitness are some of the major factors that control DNA structural modifications. In fact, TL is positively associated with cardiorespiratory fitness, physical activity level (sedentary, active, moderately trained, or elite) and training intensity, but is shorter in over-trained athletes. Similarly, somatic cells are vulnerable to exercise-induced epigenetic modification, including DNA methylation. Exercise-training load, however, depends on intensity and volume (duration and frequency). Training load-dependent responses in genomic profiles could underpin the discordant physiological and physical responses to exercise. In the current review, we will discuss the role of various forms of exercise training in the regulation of DNA damage, TL and DNA methylation status in humans, to provide an update on the influence exercise training has on biological aging.

Colorectal cancer residual disease at maximal response to EGFR blockade displays a druggable Paneth cell-like phenotype

Blockade of epidermal growth factor receptor (EGFR) causes tumor regression in some patients with metastatic colorectal cancer (mCRC). However, residual disease reservoirs typically remain even after maximal response to therapy, leading to relapse. Using patient-derived xenografts (PDXs), we observed that mCRC cells surviving EGFR inhibition exhibited gene expression patterns similar to those of a quiescent subpopulation of normal intestinal secretory precursors with Paneth cell characteristics. Compared with untreated tumors, these pseudodifferentiated tumor remnants had reduced expression of genes encoding EGFR-activating ligands, enhanced activity of human epidermal growth factor receptor 2 (HER2) and HER3, and persistent signaling along the phosphatidylinositol 3-kinase (PI3K) pathway. Clinically, properties of residual disease cells from the PDX models were detected in lingering tumors of responsive patients and in tumors of individuals who had experienced early recurrence. Mechanistically, residual tumor reprogramming after EGFR neutralization was mediated by inactivation of Yes-associated protein (YAP), a master regulator of intestinal epithelium recovery from injury. In preclinical trials, Pan-HER antibodies minimized residual disease, blunted PI3K signaling, and induced long-term tumor control after treatment discontinuation. We found that tolerance to EGFR inhibition is characterized by inactivation of an intrinsic lineage program that drives both regenerative signaling during intestinal repair and EGFR-dependent tumorigenesis. Thus, our results shed light on CRC lineage plasticity as an adaptive escape mechanism from EGFR-targeted therapy and suggest opportunities to preemptively target residual disease.

Telomere length regulation through epidermal growth factor receptor signaling in cancer

Length of the telomere (TL), a structure at the tip of chromosome that protects and ensures stability, is determined by multi-protein complexes such as telosome/shelterin and telomerase. Earlier studies from our laboratory show that longer TL has potential to be positive predictive biomarker of clinical outcome to anti-epidermal growth factor receptor (EGFR) monoclonal antibody therapy in patients with KRAS WT metastatic colorectal cancer. Although there is extensive literature suggesting the role of shelterin and telomerase, not much literature exists that describes the role of EGFR and KRAS pathway in regulating TL. This detailed review focuses on an insight into various components, including proteins, enzymes and transcription factors, interlinking between EGFR pathways and telomerase that regulate TL.

Therapeutic Targeting of Telomerase

Telomere length and cell function can be preserved by the human reverse transcriptase telomerase (hTERT), which synthesizes the new telomeric DNA from a RNA template, but is normally restricted to cells needing a high proliferative capacity, such as stem cells. Consequently, telomerase-based therapies to elongate short telomeres are developed, some of which have successfully reached the stage I in clinical trials. Telomerase is also permissive for tumorigenesis and 90% of all malignant tumors use telomerase to obtain immortality. Thus, reversal of telomerase upregulation in tumor cells is a potential strategy to treat cancer. Natural and small-molecule telomerase inhibitors, immunotherapeutic approaches, oligonucleotide inhibitors, and telomerase-directed gene therapy are useful treatment strategies. Telomerase is more widely expressed than any other tumor marker. The low expression in normal tissues, together with the longer telomeres in normal stem cells versus cancer cells, provides some degree of specificity with low risk of toxicity. However, long term telomerase inhibition may elicit negative effects in highly-proliferative cells which need telomerase for survival, and it may interfere with telomere-independent physiological functions. Moreover, only a few hTERT molecules are required to overcome senescence in cancer cells, and telomerase inhibition requires proliferating cells over a sufficient number of population doublings to induce tumor suppressive senescence. These limitations may explain the moderate success rates in many clinical studies. Despite extensive studies, only one vaccine and one telomerase antagonist are routinely used in clinical work. For complete eradication of all subpopulations of cancer cells a simultaneous targeting of several mechanisms will likely be needed. Possible technical improvements have been proposed including the development of more specific inhibitors, methods to increase the efficacy of vaccination methods, and personalized approaches. Telomerase activation and cell rejuvenation is successfully used in regenerative medicine for tissue engineering and reconstructive surgery. However, there are also a number of pitfalls in the treatment with telomerase activating procedures for the whole organism and for longer periods of time. Extended cell lifespan may accumulate rare genetic and epigenetic aberrations that can contribute to malignant transformation. Therefore, novel vector systems have been developed for a 'mild' integration of telomerase into the host genome and loss of the vector in rapidly-proliferating cells. It is currently unclear if this technique can also be used in human beings to treat chronic diseases, such as atherosclerosis.

Genetic Polymorphism, Telomere Biology and Non-Small Lung Cancer Risk

Recent genome-wide association studies (GWAS) have identified a number of chromosomal regions associated with the risk of lung cancer. Of these regions, single-nucleotide polymorphisms (SNPs), especially rs2736100 located in the telomerase reverse transcriptase (TERT) gene show unique and significant association with non-small cell lung cancer (NSCLC) in a few subpopulations including women, nonsmokers, East Asians and those with adenocarcinoma. Recent studies have also linked rs2736100 with a longer telomere length and lung cancer risk. In this review, we seek to summarize the relationship between these factors and to further link the underlying telomere biology to lung cancer etiology. We conclude that genetic alleles combined with environmental (e.g., less-smoking) and physiological factors (gender and age) that confer longer telomere length are strong risk factors for NSCLC. This linkage may be particularly relevant in lung adenocarcinoma driven by epidermal growth factor receptor (EGFR) mutations, as these mutations have also been strongly linked to female gender, less-smoking history, adenocarcinoma histology and East Asian ethnicity. By establishing this connection, a strong argument is made for further investigating of the involvement of these entities during the tumorigenesis of NSCLC.

Modulating the structure of EGFR with UV light: new possibilities in cancer therapy

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. EGFR is activated upon binding to e.g. epidermal growth factor (EGF), leading to cell survival, proliferation and migration. EGFR overactivation is associated with tumor progression. We have previously shown that low dose UVB illumination of cancer cells overexpressing EGFR prior to adding EGF halted the EGFR signaling pathway. We here show that UVB illumination of the extracellular domain of EGFR (sEGFR) induces protein conformational changes, disulphide bridge breakage and formation of tryptophan and tyrosine photoproducts such as dityrosine, N-formylkynurenine and kynurenine. Fluorescence spectroscopy, circular dichroism and thermal studies confirm the occurrence of conformational changes. An immunoassay has confirmed that UVB light induces structural changes in the EGF binding site. A monoclonal antibody which competes with EGF for binding sEGFR was used. We report clear evidence that UVB light induces structural changes in EGFR that impairs the correct binding of an EGFR specific antibody that competes with EGF for binding EGFR, confirming that the 3D structure of the EGFR binding domain suffered conformational changes upon UV illumination. The irradiance used is in the same order of magnitude as the integrated intensity in the solar UVB range. The new photonic technology disables a key receptor and is most likely applicable to the treatment of various types of cancer, alone or in combination with other therapies.

EGFR tyrosine kinase inhibitor pelitinib regulates radiation-induced p65-dependent telomerase activation in squamous cell carcinoma

Our earlier studies indicated that ionizing radiation (IR) induces NF-κB-dependent clonal expansion of therapy resistant tumor cells. Herein, we investigated whether mitigation of NF-κB-dependent telomerase activation by EGFR tyrosine kinase inhibitor can enhance IR-induced celling killing. SCC-4 and SCC-9 cells exposed to IR with or without Pelitinib were examined for NF-κB and hTERT transcription using luciferase reporter assays. NF-κB-dependent hTERT transcription was confirmed by either muting NF-κB or by using hTERT constructs lacking NF-κB binding sites. hTERT, mRNA, telomerase activity and cell survival of tumor cells were analyzed using QPCR, TRAP and clonogenic assay, respectively. Pelitinib inhibited IR-induced NF-κB, telomerase activity and hTERT transactivation. Ionizing radiation-induced telomerase activity is regulated at the transcriptional level by triggering TERT promoter activation. Functional NF-κB mediates telomerase activity by binding to the κB binding region in the promoter region of TERT. Elimination of the NF-κB recognition site on telomerase or muting NF-κB compromises IR-induced telomerase promoter activation. We found that Pelitinib inhibited IR-induced TERT transcription, transactivation and telomerase activation in IR-exposed and NF-κB-overexpressed cells. Furthermore, Pelitinib potentiates IR-induced cell killing. Our results strongly suggest that IR-induced NF-κB-mediated cell survival is supported by telomerase activation. We propose that if this pathway can be inhibited with Pelitinib treatment, one could further enhance therapeutic outcome in squamous cell carcinoma.

Inhibition of the epidermal growth factor receptor by erlotinib prevents immortalization of human cervical cells by Human Papillomavirus type 16

The Human Papillomavirus type-16 (HPV-16) E6 and E7 oncogenes are selectively retained and expressed in cervical carcinomas, and expression of E6 and E7 is sufficient to immortalize human cervical epithelial cells. Expression of the epidermal growth factor receptor (EGFR) is often increased in cervical dysplasia and carcinoma, and HPV oncoproteins stimulate cell growth via the EGFR pathway. We found that erlotinib, a specific inhibitor of EGFR tyrosine kinase activity, prevented immortalization of cultured human cervical epithelial cells by the complete HPV-16 genome or the E6/E7 oncogenes. Erlotinib stimulated apoptosis in cells that expressed HPV-16 E6/E7 proteins and induced senescence in a subpopulation of cells that did not undergo apoptosis. Since immortalization by HPV E6/E7 is an important early event in cervical carcinogenesis, the EGFR is a potential target for chemoprevention or therapy in women who have a high risk for cervical cancer.

Combinational RNAi gene therapy of hepatocellular carcinoma by targeting human EGFR and TERT

Both human telomerase reverse transcriptase (hTERT) and epidermal growth factor receptor (hEGFR) are ideal targets for RNA interference (RNAi)-based gene therapy of hepatocellular carcinoma. Two shRNA expression plasmids pU6-shTERT and pU6-shEGFR targeting hTERT and hEGFR, respectively, were separately formulated as pegylated immuno-lipopolyplexes, a novel non-viral gene delivery system. In vitro studies showed that when pU6-shTERT and pU6-shEGFR were combined and applied to SMMC-7721 cells, there was a significant additive effect on cytotoxicity as well as cell apoptosis, compared to pU6-shTERT or pU6-shEGFR alone, with a cell viability of 50.9±7.4%, 79.2±3.6% and 77.1±3.6%, respectively, and with a cell apoptotic rate of 44.8±0.9%, 25.1±0.4% and 29.5±0.8%, respectively. In vivo study in SMMC-7721 xenograft tumor model demonstrated that intravenous administration of PILP-formulated pU6-shTERT and pU6-shEGFR caused an additive effect on tumor growth inhibition, compared to pU6-shTERT or pU6-shEGFR alone, with a tumor growth inhibition rate of 74.0%, 36.3% and 46.1%, respectively, which is consistent with the downregulated EGFR and TERT mRNA expression. The results suggest that combinational RNAi gene therapy of hepatocellular carcinoma by targeting human EGFR and TERT with pegylated immuno-lipopolyplexes is a new and good strategy.

Frequent deregulations in the hedgehog signaling network and cross-talks with the epidermal growth factor receptor pathway involved in cancer progression and targeted therapies

The hedgehog (Hh)/glioma-associated oncogene (GLI) signaling network is among the most important and fascinating signal transduction systems that provide critical functions in the regulation of many developmental and physiological processes. The coordinated spatiotemporal interplay of the Hh ligands and other growth factors is necessary for the stringent control of the behavior of diverse types of tissue-resident stem/progenitor cells and their progenies. The activation of the Hh cascade might promote the tissue regeneration and repair after severe injury in numerous organs, insulin production in pancreatic beta-cells, and neovascularization. Consequently, the stimulation of the Hh pathway constitutes a potential therapeutic strategy to treat diverse human disorders, including severe tissue injuries; diabetes mellitus; and brain, skin, and cardiovascular disorders. In counterbalance, a deregulation of the Hh signaling network might lead to major tissular disorders and the development of a wide variety of aggressive and metastatic cancers. The target gene products induced through the persistent Hh activation can contribute to the self-renewal, survival, migration, and metastasis of cancer stem/progenitor cells and their progenies. Moreover, the pivotal role mediated through the Hh/GLI cascade during cancer progression also implicates the cooperation with other oncogenic products, such as mutated K-RAS and complex cross-talk with different growth factor pathways, including tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR), Wnt/beta-catenin, and transforming growth factor-beta (TGF-beta)/TGF-beta receptors. Therefore, the molecular targeting of distinct deregulated gene products, including Hh and EGFR signaling components and other signaling elements that are frequently deregulated in highly tumorigenic cancer-initiating cells and their progenies, might constitute a potential therapeutic strategy to eradicate the total cancer cell mass. Of clinical interest is that these multitargeted approaches offer great promise as adjuvant treatments for improving the current antihormonal therapies, radiotherapies, and/or chemotherapies against locally advanced and metastatic cancers, thereby preventing disease relapse and the death of patients with cancer.

n-Butylidenephthalide induced apoptosis in the A549 human lung adenocarcinoma cell line by coupled down-regulation of AP-2alpha and telomerase activity

AIM

To investigate the role of hTERT gene expression and AP-2alpha in n-butylidenephthalide (n-BP)-induced apoptosis in A549 lung cancer cells.

METHODS

Viability of A549 cells was measured by MTT assay. Protein expression was determined by Western blot. Telomerase activity was measured using the modified telomere repeat amplification protocol (TRAP) assay. Xenograft mice were used as a model system to study the cytotoxic effect of n-BP in vivo. The morphology of tumor was examined by immunohistochemical staining.

RESULTS

The growth of A549 lung cancer cells treated with n-BP was significantly inhibited. Telomerase activity and hTERT mRNA expression were determined by telomeric repeat amplification protocol and reverse transcription-polymerase chain reaction, respectively. n-BP inhibited telomerase activity and hTERT mRNA expression in A549 cells while overexpression of hTERT could abolish BP-induced growth inhibition in the A549 cells. We also showed that hTERT promoter activity in the presence of n-BP was mediated via AP-2alpha. We saw an inhibition of tumor growth when nude mice carrying A549 subcutaneous xenograft tumors were treated with n-BP. Immunohistochemistry of this tumor tissue also showed a decrease in the expression of hTERT.

CONCLUSION

The antiproliferative effects of n-BP on A549 cells in vitro and in vivo suggest a novel clinical application of this compound in the treatment of lung cancers.

Lysyl oxidase (LOX) mRNA expression and genes of the differentiated osteoblastic phenotype are upregulated in human osteosarcoma cells by suramin

It is well known that suramin influences proliferation and differentiation of tumour cells. To study whether and how suramin effects osteosarcoma (OS) cells, proliferation, differentiation, LOX mRNA expression and telomerase activity (TA) was analysed in the human MG-63 and U-2 OS, and the rat UMR-106 OS cell lines. Data show that suramin inhibited proliferation in the human cell lines and upregulated alkaline phosphatase activity. TA was attenuated in the human cells while in UMR-106 it was not changed. In UMR-106 suramin had no influence on osteocalcin and LOX expression, in the human cells however, both genes were upregulated.

Telomerase activity in pig granulosa cells proliferating and differentiating in vitro

The aim of the work was to analyze the telomerase activity (TA) in two different populations of pig granulosa cells (GC) proliferating and differentiating in vitro: (a) in relatively undifferentiated granulosa cells isolated from small (1-2 mm) antral follicles and (b) in functionally advanced, differentiated cells obtained from large (5-7 mm) antral follicles. The proliferative potential in vitro of small follicle granulosa cells (SF-GC) was higher than that of large follicle granulosa cells (LF-GC). EGF stimulated significantly (p<0.01) proliferation in SF-GC as well as LF-GC. FSH did not have a stimulating effect on proliferation in both of the GC populations. Steroidogenesis was induced in both SF- and LF-GC in vitro. Significantly higher (p<0.01) levels of estradiol were measured in LF-GC cultures. In SF-GC, no significantly different effects of EGF and FSH on estradiol production were found. The production of progesterone in vitro was higher in LF-GC than in SF-GC and its production was specifically promoted by FSH in contrast to estradiol the synthesis of which in vitro was less dependent on culture conditions. Using the TRAP assay telomerase activity was detected in freshly isolated and in vitro cultured pig SF- and LF-GC. In EGF, but not FSH stimulated SF-GC, significantly enhanced (p<0.05) TA in comparison with the control was observed at an interval of 24 h of culture. After the 48 h in vitro, levels of TA in both EGF and FSH treated cells were comparable with control. In LF-GC, both EGF and FSH stimulated significantly (p<0.05) TA after the 24h of in vitro culture. At an interval of 48 h, no significant differences in the level of TA were observed between control, EGF and FSH stimulated LF-GC. Comparing the levels of TA in SF- and LF-GC, significantly higher levels of TA were found in control (p<0.05) and EGF (p<0.01) treated SF-GC after 24 h in vitro. On the other hand, absolutely, but not significantly, higher levels of TA were found in LF-GC versus SF-GC in all culture conditions after 48 h in vitro.

Pyk2/ERK 1/2 mediate Sp1- and c-Myc-dependent induction of telomerase activity by epidermal growth factor

Epidermal growth factor (EGF) promotes growth of normal ovarian surface as well as malignant ovarian epithelial cells. Further, EGF receptors are present on both normal and malignant ovarian surface epithelial cells and they are often constitutively activated in many cancers. Since telomerase confers cellular immortalization and survival through increased cellular proliferation, we sought to investigate the potential role of EGF to regulate telomerase activity in normal and ovarian cancer cells. While exogenous EGF failed to activate telomerase in normal ovarian surface epithelial cells, in cancer cells we herein report that: exogenous EGF activates telomerase activity and human telomerase reverse transcriptase gene (hTERT) transcription; EGF-induced telomerase activity is ERK 1/2-dependent; EGF targets Sp1 and c-Myc binding sites within the core region of the hTERT promoter; and proline-rich tyrosine kinase 2 (Pyk2) is a key mediator of EGF-mediated telomerase activity. Together, these data show that dysregulation of EGF signaling may promote cancer cell survival through up-regulation of telomerase activity.

LRIG inhibitors of growth factor signalling - double-edged swords in human cancer?

The leucine-rich repeats and immunoglobulin-like domains (LRIG) proteins are newly discovered negative regulators of growth factor signalling and proposed tumour suppressors. They antagonise signalling by interacting with growth factor receptors and by enhancing their ubiquitylation and degradation. Data on the expression of LRIG in human cancer have recently begun to accumulate; however, not all data appear consistent with the notion that the LRIG proteins always function as tumour suppressors. In the present review, we argue that the LRIG proteins could be double-edged swords, promoting or suppressing human cancer depending on cellular context.

Identification of potentially useful combinations of epidermal growth factor receptor tyrosine kinase antagonists with conventional cytotoxic agents using median effect analysis

Targeted therapy for breast carcinoma has achieved a major advance with the use of trastuzumab in Her2/neu-positive tumors. The epidermal growth factor receptor superfamily thus becomes an attractive target for therapeutic agents. As the epidermal growth factor receptor tyrosine kinase family has a conformational binding site, which allows small molecules to interfere with its function, we have explored the effects of a dual kinase (epidermal growth factor receptor-1 and epidermal growth factor receptor-2) inhibitor (GW282974X) with a variety of cytotoxic agents looking for synergistic effects in vitro. Using a median effect model in four breast cancer cell lines in vitro, cytotoxic agents commonly used in treatment of human malignant disease were combined with trastuzumab or one of two epidermal growth factor receptor tyrosine kinase inhibitors in a 72-h culture and then analyzed for cytotoxic effect by 3-[26]-2,5-diphenyl-tetrazolium bromide assay. Combination index values within one standard deviation of unity were considered additive, less than unity as synergistic and more than unity as antagonistic. Synergistic results were confirmed by curve shift analysis and by an enzyme-linked immunosorbent assay measuring apoptosis by cytoplasmic histone-associated DNA fragments. Quantitative real-time polymerase chain reaction analysis was used to measure the expression of three of the critical enzymes in 5'-deoxy-5-fluorouridine metabolism and activity: thymidine phosphorylase, dihydropyrimidine dehydrogenase and thymidine synthase. 5'-Deoxy-5-fluorouridine with GW282974X demonstrated global synergy, both in high and low expressing epidermal growth factor receptor breast cancer cell lines. These results were confirmed by apoptosis assay and cell counts. RNA quantification following treatment with the dual kinase inhibitor suggested reduction in thymidine synthase levels to be a potential mechanism of synergy. The triplet of trastuzumab, GW282974X and 5'-deoxy-5-fluorouridine, and the triplet of GW282974X, epirubicin and 5'-deoxy-5-fluorouridine were highly synergistic in low expression cells (MCF7/wt) and high expression cells (MCF7/adr). These experiments suggest further studies of the dual kinase inhibitor with selected cytotoxics such as 5'-deoxy-5-fluorouridine are warranted.

Effects of cotransfection of antisense-EGFR and wild-type PTEN cDNA on human glioblastoma cells

The main molecular genetic changes identified in glioblastomas are overexpression/amplification of the epidermal growth factor receptor (EGFR) gene and mutation/ deletion of the tumor suppressor PTEN gene. These two genetic changes both play important roles in glial tumorigenesis and progression. In this study, we demonstrated that wild-type PTEN transfection inhibited the growth and transforming ability of U87MG cells by 69.3% and 73.5%, respectively. On the other hand, antisense-EGFR transfection inhibited the growth and transforming phenotype of these cells by 50.3% and 46.8%, respectively. However, cotransfection of U87MG cells with wild-type PTEN and antisense EGFR constructs could inhibit the cellular growth by 91.7%. The transforming phenotype of these cells was completely inhibited. In addition, these cotransfected cells showed a differentiated form and expressed much lower telomerase activity than cells transfected with wild-type PTEN or antisense-EGFR alone. In summary, these results suggest that cotransfection is a better approach to suppress glioma cell growth than wild-type PTEN transfer or antisense-EGFR transfection alone. This approach may prove useful as an adjunct therapy in the treatment of glioblastomas.

Mad1 suppresses bladder cancer cell proliferation by inhibiting human telomerase reverse transcriptase transcription and telomerase activity

OBJECTIVES

To study the effects and possible mechanisms of mitosis arrest deficiency 1 (Mad1), the heterodimerizer of Max and a transcriptional repressor, on cell proliferation of bladder cancer in vitro and in vivo.

METHODS

Combining methyl thiazolyl tetrazolium (MTT) assay, flow cytometry, luciferase assay, telomeric repeat amplification protocol-enzyme-linked immunosorbent assay, real-time reverse transcriptase polymerase chain reaction, experimental animal models, and other assays, we detected the alterations of cell proliferation, cell cycle, promoter activity and expression of human telomerase reverse transcriptase (hTERT), and telomerase activity in different treated bladder cells and xenograft tissues.

RESULTS

Mad1 inhibited cell proliferation, increased G0/G1 accumulation in cell cycle distribution, decreased the transcription and expression of hTERT, and reduced telomerase activity compared with controls in T24 and EJ cells. Mad1 also arrested tumor growth and downregulated hTERT expression and telomerase activity in bladder cancer xenograft BALB/c nude mice.

CONCLUSIONS

Mad1 inhibited the proliferation of human bladder cancer cells by inhibiting hTERT transcription and telomerase activity. Mad1 could be a potentially useful candidate for inhibition of bladder cancer growth.

Concise review: recent advances on the significance of stem cells in tissue regeneration and cancer therapies

In this study, we report on recent advances on the functions of embryonic, fetal, and adult stem cell progenitors for tissue regeneration and cancer therapies. We describe new procedures for derivation and maturation of these stem cells into the tissue-specific cell progenitors. The localization of the adult stem cells and their niches, as well as their implication in the tissue repair after injuries and during cancer progression, are also described. The emphasis is on the interactions among certain developmental signaling factors, such as hormones, epidermal growth factor, hedgehog, Wnt/beta-catenin, and Notch. These factors and their pathways are involved in the stringent regulation of the self-renewal and/or differentiation of adult stem cells. Novel strategies for the treatment of both diverse degenerating disorders, by cell replacement, and some metastatic cancer types, by molecular targeting multiple tumorigenic signaling elements in cancer progenitor cells, are also illustrated.

Transforming growth factor beta suppresses human telomerase reverse transcriptase (hTERT) by Smad3 interactions with c-Myc and the hTERT gene

Telomerase underpins stem cell renewal and proliferation and is required for most neoplasia. Recent studies suggest that hormones and growth factors play physiological roles in regulating telomerase activity. In this report we show a rapid repression of the telomerase reverse transcriptase (TERT) gene by transforming growth factor beta (TGF-beta) in normal and neoplastic cells by a mechanism depending on the intracellular signaling protein Smad3. In human breast cancer cells TGF-beta induces rapid entry of Smad3 into the nucleus where it binds to the TERT gene promoter and represses TERT gene transcription. Silencing Smad3 gene expression or genetically deleting the Smad3 gene disrupts TGF-beta repression of TERT gene expression. Expression of the Smad3 antagonist, Smad7, also interrupts TGF-beta-mediated Smad3-induced repression of the TERT gene. Mutational analysis identified the Smad3 site on the TERT gene promoter, mediating TERT repression. In response to TGF-beta, Smad3 binds to c-Myc; knocking down c-Myc, Smad3 does not bind to the TERT gene, suggesting that c-Myc recruits Smad3 to the TERT promoter. Thus, TGF-beta negatively regulates telomerase activity via Smad3 interactions with c-Myc and the TERT gene promoter. Modifying the interaction between Smad3 and TERT gene may, thus, lead to novel strategies to regulate telomerase.

Transcriptionally mediated inhibition of telomerase of fungal immunomodulatory protein from Ganoderma tsugae in A549 human lung adenocarcinoma cell line

Telomerase expression is the hallmark of tumor cells, and activation of this ribonucleoprotein complex may be a rate-limiting or critical step in cellular immortalization and oncogenesis. Fungal immunomodulatory protein, FIP-gts, has been isolated from Ganoderma tsugae. In the present study, we expressed and purified the recombinant fungal immunomodulatory protein reFIP-gts in E. coli. We found that reFIP-gts significantly and selectively inhibits the growth of A549 cancer cells while not affecting the growth of normal MRC-5 fibroblasts. The reFIP-gts suppression of telomerase activity is concentration-dependent, due to the downregulation of the telomerase catalytic subunit (hTERT). It also happens at the mRNA level. These results were confirmed by transient transfections of A549 cells with pGL3-Basic plasmid constructs containing the functional hTERT promoter and its E-box-deleted sequences cloned upstream of a luciferase reporter gene. With electrophoretic mobility shift assays and Western blotting, we demonstrated that in response to reFIP-gts, binding of c-myc transcriptional factor to the E-box sequence on the hTERT promoter is inhibited. These results show that reFIP-gts suppresses telomerase activity and inhibits transcriptional regulation of hTERT via a c-myc-responsive element-dependent mechanism. Our findings provide new insight into both the anticancer function of reFIP-gts and the regulation of hTERT/telomerase expression, which may be valuable in the development of a promising chemopreventive agent.

Telomere length regulation during cloning, embryogenesis and ageing

Telomeres are nucleoprotein complexes at the end of eukaryotic chromosomes with an essential role in chromosome capping. Owing to the end-replication problem of DNA polymerase, telomeres shorten during each cell division. When telomeres become critically short, they loose their capping function, which in turn induces a DNA damage-like response. This mechanism inhibits cell proliferation at the senescence stage and there is evidence that it limits the regenerative capacity of tissues and organs during chronic diseases and ageing. The holoenzyme telomerase synthesises telomeric DNA de novo, but, in humans, it is active only during embryogenesis, in immature germ cells and in a subset of stem/progenitor cells during postnatal life. Telomere length can be maintained or increased by telomerase, a process that appears to be regulated by a variety of telomere-binding proteins that control telomerase recruitment and activity at the telomeres. During embryogenesis, telomerase is strongly activated at the morula/blastocyst transition. At this transition, telomeres are significantly elongated in murine and bovine embryos. Early embryonic telomere elongation is telomerase dependent and leads to a rejuvenation of telomeres in cloned bovine embryos. Understanding of the molecular mechanisms underlying this early embryonic telomere elongation programme is of great interest for medical research in the fields of regeneration, cell therapies and therapeutic cloning.

Microarray analyses in bladder cancer cells: Inhibition of hTERT expression down-regulates EGFR

The human telomerase reverse transcriptase (hTERT) contributes to the immortal phenotype of the majority of cancers. Targeting hTERT by transfection with antisense oligonucleotides (AS-ODNs) induced immediate growth inhibition in human bladder cancer (BCa) cells. The molecular basis of the antiproliferative capacity of hTERT AS-ODNs was investigated by oligonucleotide microarray analyses and was compared to effects caused by siRNA-mediated knock-down of hTERT in EJ28 BCa cells. Two different AS-ODNs -- both down-regulated the expression of hTERT -- changed the expression of different genes mainly involved in stress response (including EGR1, ATF3 and GDF15), but without an association to telomerase function. This indicates that the immediate growth inhibition was caused, at least in part, by off-target effects. In comparison to that the blockade of the expression of hTERT using 2 different siRNAs was accompanied by the down-regulation of the oncogenes FOS-like antigen 1 (FOSL1) and epidermal growth factor receptor (EGFR), known to be overexpressed in BCa. We show here for the first time that repression of the hTERT transcript number decreased the expression of EGFR both at the mRNA and protein levels, suggesting a potential new function of hTERT in the regulation of EGFR-stimulated proliferation. Furthermore, the suppression of hTERT by siRNAs caused an enhancement of the antiproliferative capacity of the chemotherapeutics mitomycin C and cisplatin. The results presented herein may support the hypothesis that hTERT promotes the growth of tumor cells by mechanisms independent from telomere lengthening. The detailed clarification of these processes will shed light on the question, whether telomerase inhibitors might constitute suitable anticancer tools.

Creating oral squamous cancer cells: a cellular model of oral-esophageal carcinogenesis

Immortalization and malignant transformation are important steps in tumor development. The ability to induce these processes from normal human epithelial cells with genetic alterations frequently found in the corresponding human cancer would significantly enhance our understanding of tumor development. Alterations in several key intracellular regulatory pathways (the pRB, p53, and mitogenic signaling pathways and the telomere maintenance system) appear to be sufficient for the neoplastic transformation of normal human cells. Nevertheless, in vitro transformation models to date depend on viral oncogenes, most prominently the simian virus 40 early region, to induce immortalization and malignant transformation of normal human epithelial cells. Here, we demonstrate a transformation model creating oral-esophageal cancer cells by using a limited set of genetic alterations frequently observed in the corresponding human cancer. In a stepwise model, cyclin D1 overexpression and p53 inactivation led to immortalization of oral keratinocytes. Additional ectopic epithelial growth factor receptor overexpression followed by c-myc overexpression as well as consecutive reactivation of telomerase induced by epithelial growth factor receptor sufficed to transform oral epithelial cells, truly recapitulating the development of the corresponding human disease.

Inhibitory effects of costunolide on the telomerase activity in human breast carcinoma cells

Costunolide, a natural sesquiterpene compound, has been known having cytotoxic and chemopreventive effects on various human cancer cells. In the present study, we examined the effects of costunolide on telomerase activity and on the components of telomerase in MCF-7 (wild-type p53) and MDA-MB-231 (mutant p53) cells. We found that costunolide inhibited the growth and telomerase activity of MCF-7 and MDA-MB-231 cells in a concentration- and time-dependent manner. The expression of hTERT mRNA was also inhibited but hTR mRNA was not. In addition, the bindings of transcription factors in hTERT promoters were significantly decreased in both cells by the treatment of costunolide. These results suggest that costunolide inhibited the growth of both MCF-7 and MDA-MB-231 cells and this effect was mediated at least in part by a significant reduction in telomerase activity.

Hormones and growth factors regulate telomerase activity in ageing and cancer

Telomerase is a specialised reverse transcriptase that synthesises and preserves telomeres (the ends of chromosomes), thereby playing a key role in regulating the lifespan of cell proliferation. Telomerase activity is critically involved in cell development, ageing and tumourigenesis. Activation of telomerase to maintain telomeres is required for self renewal and proliferative expansion of a number of cell types, including stem cells, activated lymphocytes and cancerous cells. However, recent studies show that the safeguard mechanisms and the modes of regulation of telomerase are more revealing than thought under various physiological and pathological conditions. Considerable evidence suggests that hormones and growth factors are crucially involved in regulating telomerase activity and gene expression of telomerase reverse transcriptase (TERT). This review briefly summarises our current understanding of how hormones and growth factors regulate the telomerase and telomere network and how deregulation can induce ageing and related diseases such as cancer.

AEE788, a Dual Tyrosine Kinase Receptor Inhibitor, Induces Endothelial Cell Apoptosis in Human Cutaneous Squamous Cell Carcinoma Xenografts in Nude Mice

PURPOSE

We investigated whether concomitant blockade of the epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) signaling pathways by AEE788, a dual inhibitor of EGFR and VEGFR tyrosine kinases, would inhibit the growth of cutaneous squamous cell carcinoma (SCC) cells and human cutaneous cancer xenografts in nude mice.

EXPERIMENTAL DESIGN

We examined the effects of AEE788 on the phosphorylation of EGFR and VEGFR-2 in cutaneous SCC cells expressing EGFR and VEGFR-2 and cutaneous SCC cell growth and apoptosis. We assessed the in vivo antitumor effects of AEE788 in a xenograft model in nude mice. AEE788 (50 mg/kg) was given orally thrice weekly to mice that had been s.c. injected with Colo16 tumor cells. Mechanisms of in vivo AEE788 activity were determined by immunohistochemical analysis.

RESULTS

Treatment of cutaneous SCC cells with AEE788 led to dose-dependent inhibition of EGFR and VEGFR-2 phosphorylation, growth inhibition, and induction of apoptosis. In mice treated with AEE788, tumor growth was inhibited by 54% at 21 days after the start of treatment compared with control mice (P < 0.01). Immunohistochemical analysis revealed that AEE788 inhibited phosphorylation of EGFR and VEGFR and induced apoptosis of tumor cells and tumor-associated endothelial cells.

CONCLUSIONS

In addition to inhibiting cutaneous cancer cell growth by blocking EGFR and VEGFR signaling pathways in vitro, AEE788 inhibited in vivo tumor growth by inducing tumor and endothelial cell apoptosis.

Retinoic acid suppresses telomerase activity in HSC-1 human cutaneous squamous cell carcinoma

BACKGROUND

Activation of telomerase is crucial for the continued growth and progression of cancer cells. In a previous study, we showed that telomerase is frequently activated in skin tumours.

OBJECTIVE

Because retinoic acid (RA) plays an important role in the growth and differentiation of keratinocytes and as RA has some preventive and therapeutic effects on human skin cancers, we examined the effect of RA on the telomerase activity of HSC-1 human cutaneous squamous cell carcinoma cells.

RESULTS

Treatment of HSC-1 cells with all-trans RA (ATRA) significantly suppressed their telomerase activity. The suppression of telomerase activity was obvious at day 4 and was maximal at day 5 after the start of treatment with RA. This suppression was reversible as removal of ATRA allowed the recovery of telomerase activity. The suppression of telomerase activity correlated with the decreased expression of mRNA of human telomerase catalytic subunit (hTERT), the rate-limiting determinant of enzyme activity. The production of c-myc and of Sp1 proteins, transcription factors regulating hTERT expression, was not suppressed in HSC-1 cells by ATRA, but phosphorylation of extracellular signal-regulated kinases (ERK)1/2 and of the serine/threonine kinase Akt was significantly suppressed. Phosphorylation of the epidermal growth factor receptor, which regulates hTERT expression in HSC-1 cells, was not altered by ATRA.

CONCLUSIONS

These data indicate that RA is effective in inhibiting telomerase activity in HSC-1 cells. Suppression of ERK1/2 and Akt activation is presumed to be involved in the RA-induced suppression of hTERT.

New advances on the functions of epidermal growth factor receptor and ceramides in skin cell differentiation, disorders and cancers

Recent advances in understanding of the biological functions of the epidermal growth factor and epidermal growth factor receptor (EGF-EGFR) system and ceramide production for the maintenance of skin integrity and barrier function are reported. In particular, the opposite roles of EGFR and ceramide cascades in epithelial keratinocyte proliferation, migration and terminal differentiation are described. Moreover, the functions of ceramides in the epidermal permeability barrier are reviewed. The alterations in EGFR signaling and ceramide metabolism, which might be involved in the etiopathogenesis of diverse skin disorders and cancers, are described. New progress in understanding of skin organization, which might provide the basis for the design of new transcutaneous drug delivery techniques as well as for the development of new therapies of skin disorders and cancers, are reported.

On the road to immortality: hTERT upregulation in cancer cells

Telomere attrition limits the replicative potential of most somatic cells. In contrast, tumor cells acquire immortality by continuous telomere maintenance which is predominantly due to the transcriptional upregulation of the limiting component of telomerase, hTERT (human telomerase reverse transcriptase). Recent findings have provided mechanistic insight into how oncogenic activation as well as derepression, often due to the inactivation of tumor suppressors, stimulate the hTERT promoter. Knowledge gained from the study of hTERT transcriptional regulation may prove instrumental in the development of cancer therapies directed at the suppression of telomerase activity in tumor cells.