Telomerase and breast cancer

Impact of khat (Catha edulis) and oral contraceptive use on telomerase levels and tumor suppressor genes p53 and p21 in normal subjects and breast cancer patients

This study aimed to evaluate the effects of oral contraceptive (OC) use, khat chewing, and their combined effect on telomerase level and tumor suppressor genes, p53 and p21 in breast cancer (BC) patients and normal volunteers. 140 Yemeni women aged 25-40 years old enrolled, 60 newly diagnosed pretreated BC patients, and 80 control subjects. Venous blood (5 ml) was collected and the results showed BC patients to have significantly raised levels of telomerase, p53, and p21 compared to the control group. The use of OCs significantly raised telomerase in control group with no effect in BC patients; whereas p53 and p21 were significantly increased in BC patients. On the other hand, khat chewing significantly increased p53 in controls and BC patients, whereas p21 was significantly raised in BC patients. The combined use of OCs and khat chewing significantly increased telomerase and p53 in control group, and significantly increased p53 and p21 in BC patients. Telomerase was shown to be a risk factor (OR 4.4) for BC, and the use of OCs was a high-risk factor for increasing telomerase (OR 27.8) in normal subjects. In contrast, khat chewing was shown to be protective (OR 0.142), and the combined use of OCs and khat chewing decreased the risk factor of telomerase from OR 27.8 to 2.1.

Recent advancement of autophagy in polyploid giant cancer cells and its interconnection with senescence and stemness for therapeutic opportunities

Recurrent chemotherapy-induced senescence and resistance are attributed to the polyploidization of cancer cells that involve genomic instability and poor prognosis due to their unique form of cellular plasticity. Autophagy, a pre-dominant cell survival mechanism, is crucial during carcinogenesis and chemotherapeutic stress, favouring polyploidization. The selective autophagic degradation of essential proteins associated with cell cycle progression checkpoints deregulate mitosis fidelity and genomic integrity, imparting polyploidization of cancer cells. In connection with cytokinesis failure and endoreduplication, autophagy promotes the formation, maintenance, and generation of the progeny of polyploid giant cancer cells. The polyploid cancer cells embark on autophagy-guarded elevation in the expression of stem cell markers, along with triggered epithelial and mesenchymal transition and senescence. The senescent polyploid escapers represent a high autophagic index than the polyploid progeny, suggesting regaining autophagy induction and subsequent autophagic degradation, which is essential for escaping from senescence/polyploidy, leading to a higher proliferative phenotypic progeny. This review documents the various causes of polyploidy and its consequences in cancer with relevance to autophagy modulation and its targeting for therapeutic intervention as a novel therapeutic strategy for personalized and precision medicine.

High-Fidelity Sensitive Tracing Circulating Tumor Cell Telomerase Activity

Dynamic tracing of intracellular telomerase activity plays a crucial role in cancer cell recognition and correspondingly in earlier cancer diagnosis and personalized precision therapy. However, due to the complexity of the required reaction system and insufficient loading of reaction components into cells, achieving a high-fidelity determination of telomerase activity is still a challenge. Herein, an Aptamer-Liposome mediated Telomerase activated poly-Molecular beacon Arborescent Nanoassembly(ALTMAN) approach was described for direct high-fidelity visualization of telomerase activity. Briefly, intracellular telomerase activates molecular beacons, causing their hairpin structures to unfold and produce fluorescent signals. Furthermore, multiple molecular beacons can self-assemble, forming arborescent nanostructures and leading to exponential amplification of fluorescent signals. Integrating the enzyme-free isothermal signal amplification successfully increased the sensitivity and reduced interference by leveraging the skillful design of the molecular beacon and the extension of the telomerase-activated TTAGGG repeat sequence. The proposed approach enabled ultrasensitive visualization of activated telomerase exclusively with a prominent detection limit of 2 cells·μL-1 and realized real-time imaging of telomerase activity in living cancer cells including blood samples from breast cancer patients and urine samples from bladder cancer patients. This approach opens an avenue for establishing a telomerase activity determination and in situ monitoring technique that can facilitate both telomerase fundamental biological studies and cancer diagnostics.

Regulation and clinical potential of telomerase reverse transcriptase (TERT/hTERT) in breast cancer

Telomerase reverse transcriptase (TERT/hTERT) serves as the pivotal catalytic subunit of telomerase, a crucial enzyme responsible for telomere maintenance and human genome stability. The high activation of hTERT, observed in over 90% of tumors, plays a significant role in tumor initiation and progression. An in-depth exploration of hTERT activation mechanisms in cancer holds promise for advancing our understanding of the disease and developing more effective treatment strategies. In breast cancer, the expression of hTERT is regulated by epigenetic, transcriptional, post-translational modification mechanisms and DNA variation. Besides its canonical function in telomere maintenance, hTERT exerts non-canonical roles that contribute to disease progression through telomerase-independent mechanisms. This comprehensive review summarizes the regulatory mechanisms governing hTERT in breast cancer and elucidates the functional implications of its activation. Given the overexpression of hTERT in most breast cancer cells, the detection of hTERT and its associated molecules are potential for enhancing early screening and prognostic evaluation of breast cancer. Although still in its early stages, therapeutic approaches targeting hTERT and its regulatory molecules show promise as viable strategies for breast cancer treatment. These methods are also discussed in this paper. Video Abstract.

Linking Pregnancy and Long-Term Health: The Impact of Cardiovascular Risk on Telomere Shortening in Pregnant Women

Background and Objectives: Telomeres are repetitive DNA sequences located at the end of chromosomes that play a crucial role in maintaining chromosomal stability. Shortening of telomeres has been associated with an increased risk of cardiovascular disease. The aim of this study was to investigate whether the length of telomeres in pregnant women with cardiovascular risk is shorter compared to those without cardiovascular risk. Materials and Methods: A total of 68 participants were enrolled, including 30 pregnant women with cardiovascular risk and 38 without cardiovascular risk, who were followed-up during their pregnancy between 2020 and 2022 at the Obstetrical and Gynecology Department of the "Pius Brînzeu" Emergency County Clinical Hospital in Timişoara, Romania. All included women underwent delivery via cesarean section at the same medical institution. The telomere length was measured in each participant using quantitative Polymerase chain reaction (PCR). Results: The results showed that the telomere length was negatively correlated with cardiovascular risk in pregnant women, with significantly shorter telomeres observed in the cardiovascular risk group (mean telomere length = 0.3537) compared to the group without cardiovascular risk (mean telomere length = 0.5728) (p = 0.0458). Conclusions: These findings suggest that cardiovascular risk during pregnancy may be associated with accelerated telomere shortening, which could have implications for the long-term health of both the mother and the child. Further research is needed to investigate the potential mechanisms underlying this association and to identify interventions that may mitigate the negative effects of cardiovascular risk on the telomere length during pregnancy.

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.

Invasion and Metastasis as a Central Hallmark of Breast Cancer

Hanahan and Weinberg introduced the "hallmarks of cancer" and typified essential biological abilities acquired by human cancer. Since then, a growing understanding of hallmark principles associated with breast cancer has assisted knowledge-based therapeutics development; however, despite the rapidly increasing number of targeted therapeutics, enduring disease-free responses for most forms of breast cancer is rare. Invasion and metastasis are the most defining feature of breast cancer malignancy and the leading cause of patient mortality. Hence, we propose a modified hallmarks model adapted to breast cancer, in which invasion and metastasis are shifted to the center of attention, thereby emphasizing it as a potentially superior therapeutic target. Although the scientific community highly appreciates the importance of the invasion and metastasis hallmark, as can be demonstrated by the growing number of publications on breast cancer metastasis, very few clinical trials concentrate on testing anti-metastasis inhibitors and even fewer trials focus on inhibitors for breast cancer metastasis. Here, we discuss the obstacles of applying research on invasion and metastasis therapeutics into the clinic and present current developments that could provide a potential solution to this dilemma.

Effects of Reverse Transcriptase Inhibitors on Proliferation, Apoptosis, and Migration in Breast Carcinoma Cells

High telomerase activity in human breast cancer is associated with aggressive tumors resulting in decreased survival. Recent studies have shown that telomerase inhibitors may display anticancer properties in some human cancer cell lines. In the present study, we examined the effects of 4 reverse transcriptase inhibitors (RTIs), used for the treatment of HIV; Abacavir (AC), Lamivudine (LV), Stavudine (SV), and Tenofovir (TF) on proliferation, apoptosis, and migration in the normal human mammary epithelial cell line, hTERT-HME1, and the human breast cancer cell line, MCF-7. Cells were treated with AC, LV, SV, or TF alone or in combination with paclitaxel (PAC), a known drug used to treat breast cancer. Conduct of the thiazolyl blue tetrazolium bromide assay demonstrated that AC, SV, and TF had stronger cytotoxic effects on MCF-7 cells than in hTERT-HME1 cells. The combined treatment of RTIs and PAC caused high rates of cell death in MCF-7 and low rates of cell death in HTERT-HME1 by apoptosis. The percentages of apoptotic cells in the treatment of AC and SV in combination with PAC for 48 and 72 hours were higher than PAC. Significantly increased apoptosis and decreased migration levels were found in MCF-7 cells treated with AC and co-treatment of AC+PAC or SV+PAC than HME1 cells. These treatments can also prevent migration capacity more than PAC. Therefore, a combination strategy based on telomerase inhibitors such as AC or SV and anticancer drugs may be more effective in the treatment of certain breast cancers.

Evaluation of chemotherapeutic and cancer-protective properties of sphingosine and C2-ceramide in a human breast stem cell derived carcinogenesis model

The overall goal of the present study was to evaluate the chemotherapeutic and cancer-protective properties of D-erythro-sphingosine (sphingosine) and C₂-ceramide using a human breast epithelial cell (HBEC) culture system, which represents multiple-stages of breast carcinogenesis. The HBEC model includes Type I HBECs (normal stem), Type II HBECs (normal differentiated) and transformed cells (immortal/non-tumorigenic cells and tumorigenic cells, which are transformed from the same parental normal stem cells). The results of the present study indicate that sphingosine preferentially inhibits proliferation and causes death of normal stem cells (Type I), tumorigenic cells, and MCF7 breast cancer cells, but not normal differentiated cells (Type II). In contrast to the selective anti-proliferative effects of sphingosine, C₂-ceramide inhibits proliferation of normal differentiated cells as well as normal stem cells, tumorigenic cells, and MCF7 cancer cells with similar potency. Both sphingosine and C₂-ceramide induce apoptosis in tumorigenic cells. Among the sphingosine stereoisomers (D-erythro, D-threo, L-erythro, and L-threo) and sphinganine that were tested, L-erythro-sphingosine most potently inhibits proliferation of tumorigenic cells. The inhibition of breast tumorigenic/cancer cell proliferation by sphingosine was accompanied by inhibition of telomerase activity. Sphingosine at non-cytotoxic concentrations, but not C₂-ceramide, induces differentiation of normal stem cells (Type I), thereby reducing the number of stem cells that are more susceptible to neoplastic transformation. To the best of our knowledge, the present study demonstrates one of the first results that sphingosine can be a potential chemotherapeutic and cancer-protective agent, whereas C₂-ceramide is not an ideal chemotherapeutic and cancer-protective agent due to its anti-proliferative effects on Type II HBECs and its inability to induce the differentiation of Type I to Type II HBECs.

Integrated analysis of promoter methylation and expression of telomere related genes in breast cancer

Telomeres at the ends of eukaryotic chromosomes play a critical role in tumorgenesis. Using microfluidic PCR and next-generation bisulfite sequencing technology, we investigated the promoter methylation of 29 telomere related genes in paired tumor and normal tissues from 184 breast cancer patients. The expression of significantly differentially methylated genes was quantified using qPCR method.We observed that the average methylation level of the 29 telomere related genes was significant higher in tumor than that in normal tissues (P = 4.30E-21). A total of 4 genes (RAD50, RTEL, TERC and TRF1) showed significant hyper-methylation in breast tumor tissues. RAD51D showed significant methylation difference among the four breast cancer subtypes. The methylation of TERC showed significant association with ER status of breast cancer. The expression profiles of the 4 hyper-methylated genes showed significantly reduced expression in tumor tissues. The integration analysis of methylation and expression of these 4 genes showed a good performance in breast cancer prediction (AUC = 0.947).Our results revealed the methylation pattern of telomere related genes in breast cancer and suggested a novel 4-gene panel might be a valuable biomarker for breast cancer diagnosis.

Highly Aggressive Metastatic Melanoma Cells Unable to Maintain Telomere Length

Unlimited replicative potential is one of the hallmarks of cancer cells. In melanoma, hTERT (telomerase reverse transcriptase) is frequently overexpressed because of activating mutations in its promoter, suggesting that telomerase is necessary for melanoma development. We observed, however, that a subset of melanoma metastases and derived cell lines had no telomere maintenance mechanism. Early passages of the latter displayed long telomeres that progressively shortened and fused before cell death. We propose that, during melanoma formation, oncogenic mutations occur in precursor melanocytes with long telomeres, providing cells with sufficient replicative potential, thereby bypassing the need to re-activate telomerase. Our data further support the emerging idea that long telomeres promote melanoma formation. These observations are important when considering anticancer therapies targeting telomerase.

Telomerase Activity in Breast Cancer in Western India (Gujarat)

The purpose of this study was to examine the association of telomerase activity with clinical and histopathological prognostic variables in primary breast cancer (n=64). Telomerase activity in breast cancer was also compared with that in benign (n=10) and non-malignant tissues (n=8; post-lumpectomy tissues histopathologically defined as containing no residual tumor). The parameter was assessed using the Telomerase PCR ELISA kit. Values above OD 0.120 were considered positive. Estrogen and progesterone receptors (ER and PgR) were assayed by the dextran-coated charcoal method and levels >10 fmol/mg cytosol protein were taken as positive. Telomerase activity was detected in 20% and 50% of the patients with benign lesions and primary breast cancer, respectively, and in 50% of post-lumpectomy breast tissues histopathologically defined as containing no residual tumor. Telomerase activity was present in all stages of breast carcinoma and showed a significant inverse correlation with lymph node status (p=0.006), lymphatic invasion (p=0.035) and necrosis (p=0.033). Moreover, when stage II patients were grouped according to nodal involvement, a trend towards significance was observed (p=0.055). No correlation was observed with ER and PgR. The results of our study suggest that telomerase activity might be associated with the presence of cancer cells. Furthermore, telomerase activation may occur early in breast cancer and may be periodically downregulated during subsequent tumor progression.

TERT promoter hotspot mutations in breast cancer

BACKGROUND

Telomerase reverse transcriptase (TERT) promoter mutations have been discovered in solid and hematological malignancies, where they reflect TERT activation and cell-cycle progression. In melanoma, glioma, and thyroid cancers, TERT promoter mutations are associated with a poor prognosis. However, no studies have evaluated the prevalence and prognostic significance of TERT promoter mutations in breast cancer.

METHODS

We analyzed TERT promoter hotspot mutations (C228T and C250T) using direct sequencing of DNA from 319 tumor tissues. We also collected clinical data from cases that were positive for TERT promoter mutations.

RESULTS

We detected TERT promoter mutations in three (0.9%) of the 319 cases. Two patients had hormone receptor-positive and human epidermal growth factor receptor 2-negative cancer, while the third patient had triple-negative cancer. All three patients had initially been diagnosed with operable breast cancer and undergone surgical treatment. The relapse-free survivals of these patients were 83, 226, and 270 months, respectively. The mutations were C250T in the triple-negative cancer case and C228T in the remaining two cases.

CONCLUSION

Given the rarity of TERT promoter mutations, further studies are needed to confirm their prognostic significance in breast cancer cases.

Enterolactone Reduces Telomerase Activity and The Level of Its Catalytic Subunit in Breast Cancer Cells

OBJECTIVE

There is a positive correlation between higher serum phytoestrogen concentrations and lower risk of breast cancer. The activation of telomerase is crucial for the growth of cancer cells; therefore, the aim of this study was to examine the effects of enterolactone (ENL) and enterodiol (END) on this enzyme.

MATERIALS AND METHODS

In this experimental study, we performed the viability assay to determine the effects of different concentrations of ENL and END on cell viability, and the effective concentrations of these two compounds on cell growth. We used western blot analysis to evaluate human telomerase reverse transcriptase catalytic subunit (hTERT) expression and polymerase chain reaction (PCR)-ELISA based on the telomeric repeat amplification protocol (TRAP) assay for telomerase activity.

RESULTS

Both ENL and END, at 100 μM concentrations, significantly (P<0.05) reduced cell viability. However, only the 100 μM concentration of ENL significantly (P<0.05) decreased hTERT protein levels and telomerase activity. Lower concentrations of ENL did not have any significant effects on telomerase activity and hTERT protein levels.

CONCLUSION

High concentration of ENL decreased the viability of MCF-7 breast cancer cells and inhibited the expression and activity of telomerase in these cells. Although END could reduce breast cancer cell viability, it did not have any effect on telomerase expression and activity.

Telomeres in cancer: tumour suppression and genome instability

The shortening of human telomeres has two opposing effects during cancer development. On the one hand, telomere shortening can exert a tumour-suppressive effect through the proliferation arrest induced by activating the kinases ATM and ATR at unprotected chromosome ends. On the other hand, loss of telomere protection can lead to telomere crisis, which is a state of extensive genome instability that can promote cancer progression. Recent data, reviewed here, provide new evidence for the telomere tumour suppressor pathway and has revealed that telomere crisis can induce numerous cancer-relevant changes, including chromothripsis, kataegis and tetraploidization.

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.

Expression distribution of cancer stem cells, epithelial to mesenchymal transition, and telomerase activity in breast cancer and their association with clinicopathologic characteristics

A total of 167 surgically resected primary invasive breast carcinomas and 63 metastatic lymph node lesions were analyzed for immunohistochemical (IHC) localization of the CD44⁺CD24^−low breast cancer stem cell (CSC) markers, epithelial to mesenchymal transition (EMT) markers, and telomerase activity by double-staining IHC technique, in formalin-fixed, paraffin-embedded tissue, the results were validated by double-staining immunofluorescent and flow cytometry techniques. The results showed that CSCs with CD44⁺CD24^−low phenotype were significantly increased in node-positive tumors, high-grade tumors, and ductal carcinoma in situ (DCIS). There was a high incidence of telomerase expression in metastatic lymph node lesion. There were considerably high number of tumor cells with EMT expression in metastatic lymph node lesion, and triple-negative tumor. The occurrence of EMT phenomena was usually accompanied by the co-existence of CSCs of CD44⁺CD24^−low phenotype. There was no association between the existence of CSCs and detection of telomerase activity in tumor cells. Increased numbers of both CSCs of CD44⁺CD24^−low phenotype and cells underwent EMT in DCIS lesion might be an initial step in the stromal invasion and propagation of breast cancer, and occurrence of EMT in the breast tumor associated with high prevalence of CSCs, promoting tumor invasiveness and metastasis.

Inhibitory effects of β-cyclodextrin-helenalin complexes on H-TERT gene expression in the T47D breast cancer cell line - results of real time quantitative PCR

BACKGROUND

Nowadays, the encapsulation of cytotoxic chemotherapeutic agents is attracting interest as a method for drug delivery. We hypothesized that the efficiency of helenalin might be maximized by encapsulation in β-cyclodextrin nanoparticles. Helenalin, with a hydrophobic structure obtained from flowers of Arnica chamissonis and Arnica Montana, has anti-cancer and anti-inflammatory activity but low water solubility and bioavailability. β-Cyclodextrin (β-CD) is a cyclic oligosaccharide comprising seven D-glucopyranoside units, linked through 1,4-glycosidic bonds.

MATERIALS AND METHODS

To test our hypothesis, we prepared β-cyclodextrin- helenalin complexes to determine their inhibitory effects on telomerase gene expression by real-time polymerase chain reaction (q-PCR) and cytotoxic effects by colorimetric cell viability (MTT) assay.

RESULTS

MTT assay showed that not only β-cyclodextrin has no cytotoxic effect on its own but also it demonstrated that β-cyclodextrin- helenalin complexes inhibited the growth of the T47D breast cancer cell line in a time and dose-dependent manner. Our q-PCR results showed that the expression of telomerase gene was effectively reduced as the concentration of β-cyclodextrin-helenalin complexes increased.

CONCLUSIONS

β-Cyclodextrin-helenalin complexes exerted cytotoxic effects on T47D cells through down-regulation of telomerase expression and by enhancing Helenalin uptake by cells. Therefore, β-cyclodextrin could be superior carrier for this kind of hydrophobic agent.

PAMAM dendrimers augment inhibitory effects of curcumin on cancer cell proliferation: possible inhibition of telomerase

BACKGROUND

Despite numerous useful anticancer properties of curcumin, its utility is limited due to its hydrophobic structure. In this study, we investigated the comparative antiproliferative effect of PAMAM encapsulating curcumin with naked curcumin on the T47D breast cancer cell line.

MATERIALS AND METHODS

Cytotoxic effects of PAMAM dendrimers encapsulating curcumin and curcumin alone were investigated by MTT assay. After treating cells with different concentrations of both curcumin alone and curcumin encapsulated for 24h, telomerase activity was determined by TRAP assay.

RESULTS

While PAMAM dendrimers encapsulating curcumin had no cytotoxicity on cancer cells, they decreased the IC50 for proliferation and also increased the inhibitory effect on telomerase activity.

CONCLUSIONS

Considering the non-toxicity in addition to effectiveness for enhancing curcumin anticancer properties, dendrimers could be considered good therapeutic vehicles for this hydrophobic agent.

Breast cancer biomarkers and molecular medicine: part II

In this second part of the two-part review of breast cancer biomarkers and molecular medicine, the first section will consider additional breast cancer prognostic factors, including oncogenes, tumor suppressor genes, cell adhesion molecules, invasion-associated proteins and proteases, hormone receptor proteins, drug resistance proteins, apoptosis regulators, transcription factors, telomerase, DNA repair and methylation and transcriptional profiling using high-density genomic microarrays. The second section will consider the prediction of therapy response using the techniques of pharmacogenetics and pharmacogenomics.

Telomere fusions in early human breast carcinoma

Several lines of evidence suggest that defects in telomere maintenance play a significant role in the initiation of genomic instability during carcinogenesis. Although the general concept of defective telomere maintenance initiating genomic instability has been acknowledged, there remains a critical gap in the direct evidence of telomere dysfunction in human solid tumors. To address this topic, we devised a multiplex PCR-based assay, termed TAR (telomere-associated repeat) fusion PCR, to detect and analyze chromosome end-to-end associations (telomere fusions) within human breast tumor tissue. Using TAR fusion PCR, we found that human breast lesions, but not normal breast tissues from healthy volunteers, contained telomere fusions. Telomere fusions were detected at similar frequencies during early ductal carcinoma in situ and in the later invasive ductal carcinoma stage. Our results provide direct evidence that telomere fusions are present in human breast tumor tissue and suggest that telomere dysfunction may be an important component of the genomic instability observed in this cancer. Development of this robust method that allows identification of these genetic aberrations (telomere fusions) is anticipated to be a valuable tool for dissecting mechanisms of telomere dysfunction.

Pharmaceutical regulation of telomerase and its clinical potential

Telomeres serve the dual function of protecting chromosomes from genomic instability as well as protecting the ends of chromosomes from DNA damage machinery. The enzyme responsible for telomere maintenance is telomerase, an enzyme capable of reverse transcription. Telomerase activity is typically limited to specific cell types. However, telomerase activation in somatic cells serves as a key step toward cell immortalization and cancer. Targeting telomerase serves as a potential cancer treatment with significant therapeutic benefits. Beyond targeting cancers by inhibiting telomerase, manipulating the regulation of telomerase may also provide therapeutic benefit to other ailments, such as those related to aging. This review will introduce human telomeres and telomerase and discuss pharmacological regulation of telomerase, including telomerase inhibitors and activators, and their use in human diseases.

The causes and consequences of polyploidy in normal development and cancer

Although nearly all mammalian species are diploid, whole-genome duplications occur in select mammalian tissues as part of normal development. Such programmed polyploidization involves changes in the regulatory pathways that normally maintain the diploid state of the mammalian genome. Unscheduled whole-genome duplications, which lead primarily to tetraploid cells, also take place in a substantial fraction of human tumors and have been proposed to constitute an important step in the development of cancer aneuploidy. The origins of these polyploidization events and their consequences for tumor progression are explored in this review.

Antiproliferative effects of cucurbitacin B in breast cancer cells: down-regulation of the c-Myc/hTERT/telomerase pathway and obstruction of the cell cycle

Naturally occurring cucurbitacins have been shown to have anticancer, antimicrobial and anti-inflammatory activities. In this study, we determined the effects of cucurbitacin B extracted from the Thai herb Trichosanthes cucumerina L. on telomerase regulation in three human breast cancer cell lines (T47D, SKBR-3, and MCF-7) and a mammary epithelium cell line (HBL-100). Cell viability after treatment with cucurbitacin B, which is an active ingredient of this herb, was assessed. Telomeric Repeat Amplification Protocol (TRAP) assays and RT-PCR (qualitative and realtime) were performed to investigate activity of telomerase as well as expression of human telomerase reverse transcriptase (hTERT) and c-Myc. The c-Myc protein level was also determined in SKBR-3 and HBL-100 cells. Our results show that the cucurbitacin B inhibits growth and telomerase activity in the three breast cancer cell lines and exerts an obvious inhibitory effect in the estrogen receptor (ER)-negative breast cancer SKBR-3 cells. The expression of hTERT and c-Myc were also inhibited by cucurbitacin B, In addition, a clear reduction of c-Myc protein was observed after treatment in SKBR-3 cells even with a concentration of cucurbitacin B that was ten-times lower compared to the concentration used for HBL-100. Our findings imply that cucurbitacin B exerts an anticancer effect by inhibiting telomerase via down regulating both the hTERT and c-Myc expression in breast cancer cells.

From bench to bedside: the growing use of translational research in cancer medicine

Cancer is responsible for one in eight deaths worldwide, with more than twelve million new cases diagnosed yearly. A large percentage of patients die after developing cancer despite aggressive treatment, indicating a need for new approaches to cancer therapy. The push for development of novel diagnostic and therapeutic agents has allowed translational cancer research to flourish. Genomic and proteomic technologies have generated an enormous amount of information critical to expanding our understanding of cancer biology. New research on the differences between normal and malignant cell biology has paved the way for the development of drugs targeted to specific biological molecules, potentially increasing antitumor efficacy while minimizing the toxicity to the patient that is seen with conventional therapeutics. Current targets in include regulators of cell cycle, angiogenesis, apoptosis, DNA repair, and growth factors and their receptors. Collaboration among researchers, clinicians, and pharmaceutical companies is vital to conducting clinical trials to translate laboratory findings into clinically applicable therapeutics. In this review, we discuss current therapeutic approaches and present an introduction to a wide range of topics undergoing investigation in an effort to highlight the importance of translational research in the development of clinically relevant therapeutic strategies.

Novel benzothiazolyl urea and thiourea derivatives with potential cytotoxic and antimicrobial activities

A novel series of benzothiazole urea and thiourea derivatives was synthesized and evaluated for its in vitro cytotoxicity against MCF-7 breast cancer cells. The N1-(benzothiazol-2-yl)-N3-morpholinourea 3 displayed the highest cytotoxic activity in this series. A docked pose of 3 was obtained bound to G-quadruplex of human telomere DNA active site using the Molecular Operating Environment (MOE) module. Moreover, the synthesized compounds were screened for their antimicrobial activity against Mycobacterium tuberculosis H37Rv, E. coli, S. aureus and C. albicans. Again, 3 showed the best activity against M. tuberculosis H37Rv while other compounds were equipotent with ampicillin against S. aureus and E. coli.

Development of new targeted therapies for breast cancer

Clinical application of truly targeted therapy relies on identification of a specific molecular feature (the target) that is biologically relevant, reproducibly measurable and definably correlated with clinical benefit. Ideally the target should be crucial to the tumor's malignant phenotype. The target must be easily measurable in readily obtained clinical samples. Interruption, interference or inhibition of the target should yield a clinical response in a significant proportion of patients whose tumors express the target but in few patients whose tumors do not express the target. As such, targeted therapy offers the twin hopes of maximizing efficacy while minimizing toxicity. A critical review of the hallmarks of malignancy provides a framework for considering potential targets and novel therapeutic interventions. The hallmarks of malignancy include uncontrolled proliferation, insensitivity to negative growth regulation, evasion of apoptosis, lack of senescence, invasion and metastasis, angiogenesis, and genomic elasticity. Existing therapies predominantly target proliferation either with cytotoxic agents, ionizing radiation or inhibition of estrogen receptor and HER2 growth factor signaling pathways. Further improvements in therapy must attack the other hallmarks of malignancy and will undoubtedly be accompanied by better means of individual patient selection for such therapies. Indeed, each of these hallmarks presents a therapeutic opportunity. To believe otherwise would be to assume that a feature is both biologically crucial yet therapeutically unimportant, an unlikely paradox.

Telomere length, telomeric proteins and genomic instability during the multistep carcinogenic process

Telomeres form specialized structures at the ends of eukaryotic chromosomes, preventing them from being wrongly recognized as DNA damage. The human telomere DNA sequence is a tandem repetition of the sequence TTAGGG. In normal cells, the DNA replication machinery is unable to completely duplicate the telomeric DNA; thus, telomeres are shortened after every cell division. Having reached a critical length, telomeres may be recognized as double strand break DNA lesions, and cells eventually enter senescence. Carcinogenesis is a multistep process involving multiple mutations and chromosomal aberrations. One of the most prevalent aberrations in pre-cancerous lesions is telomere shortening and telomerase activation. We discuss the role and homeostasis of telomeres in normal cells and their implication in the early steps of carcinogenesis. We also discuss various techniques used, and their limitations, in the study of telomeres and genome instability and their role in carcinogenesis and related genomic modifications.

Telomere-related genome instability in cancer

Genome instability is a hallmark of most human cancers. Although a mutator phenotype is not required for tumorigenesis, it can foster mutations that promote tumor progression. Indeed, several inherited cancer-prone syndromes are due to mutations in DNA repair pathways. However, sporadic tumors are usually proficient in DNA repair, making it unlikely that unrepaired lesions are a major source of genome instability in sporadic cancers. A decade ago, I argued in another CSHL Press publication that a "collapse in telomere function can explain a significant portion of the genetic instability in tumors" (de Lange 1995). Since that time, the structure of mammalian telomeres has been analyzed, the consequences of telomere dysfunction have been determined, a mouse model for cancer-relevant aspects of telomere biology has been developed, and the nature and magnitude of cancer genome rearrangements have been revealed. In light of these developments, this is an opportune time to revisit the conjecture that telomere dysfunction contributes to genome instability in human cancer.

Histone deacetylase 8 safeguards the human ever-shorter telomeres 1B (hEST1B) protein from ubiquitin-mediated degradation

Histone deacetylases (HDACs) are enzymes that regulate the functions of histones as well as nonhistones by catalyzing the removal of acetyl groups from lysine residues. HDACs regulate many biological processes, including the cell division cycle and tumorigenesis. Although recent studies have implicated HDAC8 in tumor cell proliferation, the molecular mechanisms linking HDAC8 to cell growth remain unknown. Here, we report that the human ortholog of the yeast ever-shorter telomeres 1B (EST1B) binds HDAC8. This interaction is regulated by protein kinase A-mediated HDAC8 phosphorylation and protects human EST1B (hEST1B) from ubiquitin-mediated degradation. Phosphorylated HDAC8 preferentially recruits Hsp70 to a complex that inhibits the CHIP (C-terminal heat shock protein interacting protein) E3 ligase-mediated degradation of hEST1B. Importantly, HDAC8 regulation of hEST1B protein stability modulates total telomerase enzymatic activity. Our findings reveal a novel mechanism by which HDAC8 contributes to tumorigenesis by regulating telomerase activity.

Telomerase activity in fine needle aspiration biopsy samples: Application to diagnosis of human thyroid carcinoma

BACKGROUND

The diagnosis of thyroid follicular carcinoma by fine needle aspiration biopsy is a well known problem in thyroid pathology.

METHODS

We evaluated telomerase activity (TA) in 85 fine needle aspiration biopsy (FNAB) samples from patients with thyroid nodules. Surgery samples from patients with tumor or follicular adenomas were also analyzed.

RESULTS

Twenty of the FNAB samples corresponded to carcinomas and were positive to telomerase assay (TA >10 Units). Among them, 4 follicular carcinomas and 1 papillary carcinoma were labeled as indeterminate by FNAB cytological examination. Four percent false positive cases and no false negative cases for TA in FNABs were reported. FNAB samples from follicular adenomas were diagnosed as indeterminate by cytological examination, but they showed no detectable TA. Tumor tissues from patients with follicular or papillary thyroid carcinomas presented TA >10 Units, whereas follicular adenoma tissues (benign nodules) showed no TA.

CONCLUSION

Our results showed a good correlation between TA in FNAB samples and tumor/nodule thyroid tissue. This suggested that use of TA as a biological marker of malignancy might be a useful tool in the diagnosis of follicular thyroid carcinomas or follicular thyroid adenomas using FNAB samples.

Tankyrase, a positive regulator of telomere elongation, is over expressed in human breast cancer

Tankyrase promotes telomere elongation by interaction with the telomeric protein binding factor TRF1, a negative regulator of telomere extension. We measured tankyrase mRNA by real-time RT-PCR in 66 breast cancers and in paired normal tissues. Results were compared with hTERT mRNA expression. The levels of tankyrase in breast cancers were significantly higher in comparison to normal tissues (P<0.0001) and significantly related to the status of progesterone receptors. No relationship was found between tankyrase and hTERT mRNA expression in breast cancers. According to our results, tankyrase expression appeared up regulated in breast cancers.

In situ analyses of genome instability in breast cancer

Transition through telomere crisis is thought to be a crucial event in the development of most breast carcinomas. Our goal in this study was to determine where this occurs in the context of histologically defined breast cancer progression. To this end, we assessed genome instability (using fluorescence in situ hybridization) and other features associated with telomere crisis in normal ductal epithelium, usual ductal hyperplasia, ductal carcinoma in situ and invasive cancer. We modeled this process in vitro by measuring these same features in human mammary epithelial cell cultures during ZNF217-mediated transition through telomere crisis and immortalization. Taken together, the data suggest that transition through telomere crisis and immortalization in breast cancer occurs during progression from usual ductal hyperplasia to ductal carcinoma in situ.

Cell-type-specific responses to chemotherapeutics in breast cancer

Recent microarray studies have identified distinct subtypes of breast tumors that arise from different cell types and that show statistically significant differences in patient outcome. To gain insight into these differences, we identified in vitro and in vivo changes in gene expression induced by chemotherapeutics. We treated two cell lines derived from basal epithelium (immortalized human mammary epithelial cells) and two lines derived from luminal epithelium (MCF-7 and ZR-75-1) with chemotherapeutics used in the treatment of breast cancer and assayed for changes in gene expression using DNA microarrays. Treatment doses for doxorubicin and 5-fluorouracil were selected to cause comparable cytotoxicity across all four cell lines. The dominant expression response in each of the cell lines was a general stress response; however, distinct expression patterns were observed. Both cell types induced DNA damage-response genes such as p21(waf1), but the response in the luminal cells showed higher fold changes and included more p53-regulated genes. Luminal cell lines repressed a large number of cell cycle-regulated genes and other genes involved in cellular proliferation, whereas the basal cell lines did not. Instead, the basal cell lines repressed genes that were involved in differentiation. These in vitro responses were compared with expression responses in breast tumors sampled before and after treatment with doxorubicin or 5-fluorouracil/mitomycin C. The in vivo data corroborated the cell-type-specific responses to chemotherapeutics observed in vitro, including the induction of p21(waf1). Similarities between in vivo and in vitro responses help to identify important response mechanisms to chemotherapeutics.

Telomeres and telomerase: a dual role in hepatocarcinogenesis

Telomere shortening limits the proliferative capacity of primary human cells and restrains the regenerative capacity of organ systems during chronic diseases and aging. Telomere shortening apparently has a dual role in tumor development and progression. On the one hand, it induces chromosomal instability and the initiation of cancer; on the other hand, tumor progression requires stabilization of telomeres. The predominant mechanism of telomere stabilization in tumor cells is the activation of the telomere-synthesizing enzyme telomerase. The potential use of telomerase activators for the treatment of regenerative disorders will ultimately depend on their effects on tumorigenesis. This review focuses on the role of telomere shortening and telomerase in carcinogenesis with a special focus on hepatocellular carcinoma.

Telomeres, telomerase, and tumorigenesis--a review

Human telomeres function as a protective structure capping both ends of the chromosome. They are composed of long, repetitive sequences of TTAGGG, associated with a variety of telomere-binding proteins. Telomeres protect the chromosomes from end-to-end fusion, recombination, and degradation, all events that can lead to cell death. At cell replication, telomeres cannot be completely replicated. They are gradually shortened, and when the telomeres reach a critical threshold, cell replication is arrested in what is called "replicative senescence." Thus, telomeres act as an intrinsic "counting" mechanism of the cell's aging process. Telomerase is an enzymatic ribonucleoprotein complex that acts as a reverse transcriptase in the elongation of telomeres. Telomerase activity is almost absent in somatic cells, but it is detected in embryonic stem cells and in the vast majority of tumor cells. Tumor cells, in fact, may contain short and stable telomeres that confer immortality to the cancer cells, which are thus able to replicate indefinitely. The deregulation of telomeres thus plays an important role in the relationship between premature aging syndrome and cancer. This review describes the recent advances in the molecular characterization of telomeres, the regulation of telomerase

Tumor-derived p53 mutants induce oncogenesis by transactivating growth-promoting genes

We have studied the mechanism of mutant p53-mediated oncogenesis using several tumor-derived mutants. Using a colony formation assay, we found that the majority of the mutants increased the number of colonies formed compared to the vector. Expression of tumor-derived p53 mutants increases the rate of cell growth, suggesting that the p53 mutants have 'gain of function' properties. We have studied the gene expression profile of cells expressing tumor-derived p53-D281G to identify genes transactivated by mutant p53. We report the transactivation of two genes, asparagine synthetase and human telomerase reverse transcriptase. Quantitative real-time PCR confirms this upregulation. Transient transfection promoter assays verify that tumor-derived p53 mutants transactivate these promoters significantly. An electrophoretic mobility shift assay shows that tumor-derived p53-mutants cannot bind to the wild-type p53 consensus sequence. The results presented here provide some evidence of a possible mechanism for mutant p53-mediated transactivation.

Activated platelets rapidly up-regulate CD40L expression and can effectively mature and activate autologous ex vivo differentiated DC

Background DC are a promising immunotherapeutic for treatment of infectious/malignant disease. For clinical trials, immature DC generated from precursor cells such as monocytes, using serum-free media containing GM-CSF and IL-4, can be matured with specific cytokines/factors. CD40 ligand (CD40L) plays an important role in DC activation/maturation but is not available for clinical applications. These studies evaluated the feasibility of using activated platelets with elevated CD40L surface expression to stimulate autologous DC maturation. Methods Pilot and clinical scale studies were executed using magnetic/centrifugal separation. Monocyte precursors were differentiated to immature DC with GM-CSF and IL-4 and the ability of activated autologous platelets to mature these cells was evaluated on the basis of phenotype and function. Results In small-scale studies, DC cultures stimulated with activated autologous platelets (CD40L-AP), tumor necrosis factor-alpha (TNF-alpha) or soluble CD40L (sCD40L) up-regulated expression of phenotype markers indicative of activation and maturation. CD86 expression was significantly enhanced (P<0.05) by stimulation with either CD40L-AP (75.5+/-14.5%) or sCD40L (80.5%+/-5.3%) compared with immature DC (55.2+/-14.8%), as were CD80 and CD83. Similarly, in large-scale studies using Isolex 300I to enrich for monocytes and platelets for DC generation/maturation on a clinical scale, stimulation with CD40L-AP increased CD86 and CD80 expression as well as the ability to stimulate allogeneic lymphocytes compared with control cultures. Discussion These results demonstrate that thrombin-activated platelets express CD40L and are effective at inducing matured DC with potent immunogenic activity. Furthermore, these studies demonstrate the feasibility of this approach for clinical immunotherapeutic interventions.

Exploiting the hallmarks of cancer: the future conquest of breast cancer

What separates a malignant from a normal cell? This question has occupied scientists for decades. Although a simple answer remains elusive, several hallmarks of malignancy have been identified. These critical features include uncontrolled proliferation, insensitivity to negative growth regulation, evasion of apoptosis, lack of senescence, invasion and metastasis, angiogenesis and genomic elasticity. Existing therapies predominantly target proliferation either with cytotoxic agents, ionising radiation or more targeted attacks on growth factor signalling pathways. Our most successful therapies to date inhibit proliferation via the oestrogen receptor (ER) and HER2 pathways. Further improvements in therapy must attack the other hallmarks of malignancy and will undoubtedly be accompanied by a better means of individual patient selection for such therapies. Indeed, each of these hallmarks presents a therapeutic opportunity. To believe otherwise would be to assume that a feature is both biologically crucial, yet therapeutically unimportant, an unlikely paradox. Here, we suggest the hallmarks of malignancy as a conceptual framework for understanding novel breast cancer therapies.

Assessment of telomere length and factors that contribute to its stability

Short strands of tandem hexameric repeats known as telomeres cap the ends of linear chromosomes. These repeats protect chromosomes from degradation and prevent chromosomal end-joining, a phenomenon that could occur due to the end-replication problem. Telomeres are maintained by the activity of the enzyme telomerase. The total number of telomeric repeats at the terminal end of a chromosome determines the telomere length, which in addition to its importance in chromosomal stabilization is a useful indicator of telomerase activity in normal and malignant tissues. Telomere length stability is one of the important factors that contribute to the proliferative capacity of many cancer cell types; therefore, the detection and estimation of telomere length is extremely important. Until relatively recently, telomere lengths were analyzed primarily using the standard Southern blot technique. However, the complexities of this technique have led to the search for more simple and rapid detection methods. Improvements such as the use of fluorescent probes and the ability to sort cells have greatly enhanced the ease and sensitivity of telomere length measurements. Recent advances, and the limitations of these techniques are evaluated. Drugs that assist in telomere shortening may contribute to tumor regression. Therefore, factors that contribute to telomere stability may influence the efficiency of the drugs that have potential in cancer therapy. These factors in relation to telomere length are also examined in this analysis.

Tiptoeing to chromosome tips: facts, promises and perils of today's human telomere biology

The past decade has witnessed an explosion of knowledge concerning the structure and function of chromosome terminal structures-telomeres. Today's telomere research has advanced from a pure descriptive approach of DNA and protein components to an elementary understanding of telomere metabolism, and now to promising applications in medicine. These applications include 'passive' ones, among which the use of analysis of telomeres and telomerase (a cellular reverse transcriptase that synthesizes telomeres) for cancer diagnostics is the best known. The 'active' applications involve targeted downregulation or upregulation of telomere synthesis, either to mortalize immortal cancer cells, or to rejuvenate mortal somatic cells and tissues for cellular transplantations, respectively. This article reviews the basic data on structure and function of human telomeres and telomerase, as well as both passive and active applications of human telomere biology.

Telomerase in cancer and aging

The telomere-telomerase hypothesis is the science of cellular aging (senescence) and cancer. The ends of chromosomes, telomeres, count the number of divisions a cell can undergo before entering permanent growth arrest. As divisions are being counted, events occur on the cellular and molecular level, which may either delay or hasten this arrest. As humans age, a particular concern is the accumulation of events that lead to the progression of cancer. Telomerase is a mechanism that most normal cells do not possess, but almost all cancer cells acquire, to overcome their mortality and extend their lifespan. This review aims to provide a comprehensive understanding of the role of telomerase in cancer development, progression, diagnosis, and in the future, treatment. The ultimate goal of telomerase research is to use our understanding to develop anti-telomerase therapies, an almost universal tumor target.