Inhibition of telomerase in the endothelial cells disrupts tumor angiogenesis in glioblastoma xenografts

Advancements in Telomerase-Targeted Therapies for Glioblastoma: A Systematic Review

Glioblastoma (GBM) is a primary CNS tumor that is highly lethal in adults and has limited treatment options. Despite advancements in understanding the GBM biology, the standard treatment for GBM has remained unchanged for more than a decade. Only 6.8% of patients survive beyond five years. Telomerase, particularly the hTERT promoter mutations present in up to 80% of GBM cases, represents a promising therapeutic target due to its role in sustaining telomere length and cancer cell proliferation. This review examines the biology of telomerase in GBM and explores potential telomerase-targeted therapies. We conducted a systematic review following the PRISMA-P guidelines in the MEDLINE/PubMed and Scopus databases, from January 1995 to April 2024. We searched for suitable articles by utilizing the terms "GBM", "high-grade gliomas", "hTERT" and "telomerase". We incorporated studies addressing telomerase-targeted therapies into GBM studies, excluding non-English articles, reviews, and meta-analyses. We evaluated a total of 777 records and 46 full texts, including 36 studies in the final review. Several compounds aimed at inhibiting hTERT transcription demonstrated promising preclinical outcomes; however, they were unsuccessful in clinical trials owing to intricate regulatory pathways and inadequate pharmacokinetics. Direct hTERT inhibitors encountered numerous obstacles, including a prolonged latency for telomere shortening and the activation of the alternative lengthening of telomeres (ALT). The G-quadruplex DNA stabilizers appeared to be potential indirect inhibitors, but further clinical studies are required. Imetelstat, the only telomerase inhibitor that has undergone clinical trials, has demonstrated efficacy in various cancers, but its efficacy in GBM has been limited. Telomerase-targeted therapies in GBM is challenging due to complex hTERT regulation and inadequate inhibitor pharmacokinetics. Our study demonstrates that, despite promising preclinical results, no Telomerase inhibitors have been approved for GBM, and clinical trials have been largely unsuccessful. Future strategies may include Telomerase-based vaccines and multi-target inhibitors, which may provide more effective treatments when combined with a better understanding of telomere dynamics and tumor biology. These treatments have the potential to be integrated with existing ones and to improve the outcomes for patients with GBM.

Premature senescence and cardiovascular disease following cancer treatments: mechanistic insights

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality, especially among the aging population. The "response-to-injury" model proposed by Dr. Russell Ross in 1999 emphasizes inflammation as a critical factor in atherosclerosis development, with atherosclerotic plaques forming due to endothelial cell (EC) injury, followed by myeloid cell adhesion and invasion into the blood vessel walls. Recent evidence indicates that cancer and its treatments can lead to long-term complications, including CVD. Cellular senescence, a hallmark of aging, is implicated in CVD pathogenesis, particularly in cancer survivors. However, the precise mechanisms linking premature senescence to CVD in cancer survivors remain poorly understood. This article aims to provide mechanistic insights into this association and propose future directions to better comprehend this complex interplay.

Possible molecular mechanisms underlying the development of atherosclerosis in cancer survivors

Cancer survivors undergone treatment face an increased risk of developing atherosclerotic cardiovascular disease (CVD), yet the underlying mechanisms remain elusive. Recent studies have revealed that chemotherapy can drive senescent cancer cells to acquire a proliferative phenotype known as senescence-associated stemness (SAS). These SAS cells exhibit enhanced growth and resistance to cancer treatment, thereby contributing to disease progression. Endothelial cell (EC) senescence has been implicated in atherosclerosis and cancer, including among cancer survivors. Treatment modalities for cancer can induce EC senescence, leading to the development of SAS phenotype and subsequent atherosclerosis in cancer survivors. Consequently, targeting senescent ECs displaying the SAS phenotype hold promise as a therapeutic approach for managing atherosclerotic CVD in this population. This review aims to provide a mechanistic understanding of SAS induction in ECs and its contribution to atherosclerosis among cancer survivors. We delve into the mechanisms underlying EC senescence in response to disturbed flow and ionizing radiation, which play pivotal role in atherosclerosis and cancer. Key pathways, including p90RSK/TERF2IP, TGFβR1/SMAD, and BH4 signaling are explored as potential targets for cancer treatment. By comprehending the similarities and distinctions between different types of senescence and the associated pathways, we can pave the way for targeted interventions aim at enhancing the cardiovascular health of this vulnerable population. The insights gained from this review may facilitate the development of novel therapeutic strategies for managing atherosclerotic CVD in cancer survivors.

Targeting the NCOA3-SP1-TERT axis for tumor growth in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a high mortality rate and lacks an effective therapeutic target. Elevated expression of human telomerase reverse transcriptase (TERT) is an important hallmark in cancers, but the mechanism by which TERT is activated differentially in cancers is poorly understood. Here, we have identified nuclear receptor coactivator-3 (NCOA3) as a new modulator of TERT expression and tumor growth in HCC. NACO3 specifically binds to the TERT promoter at the -234 to -144 region and transcriptionally activates TERT expression. NCOA3 promotes HCC cell growth and tumor progression in vitro and in vivo through upregulating the TERT signaling. Knockdown of NACO3 suppresses HCC cell viability and colony formation, whereas TERT overexpression rescues this suppression. NCOA3 interacts with and recruits SP1 binding on the TERT promoter. Knockdown of NCOA3 also inhibits the expression of the Wnt signaling-related genes but has no effect on the Notch signaling-targeting genes. Moreover, NCOA3 is positively correlated with TERT expression in HCC tumor tissues, and high expression of both NCOA3 and TERT predicts a poor prognosis in HCC patients. Our findings indicate that targeting the NCOA3-SP1-TERT signaling axis may benefit HCC patients.

Role of telomerase in the tumour microenvironment

Telomeres are specialized genomic structures that protect chromosomal ends to maintain genomic stability. Telomeric length is primarily regulated by the telomerase complex, essentially consisting of an RNA template (TERC), an enzymatic subunit (telomerase reverse transcriptase, TERT). In humans, telomerase activity is repressed during embryonic differentiation and is absent in most somatic cells. However, it is upregulated or reactivated in 80%-90% of the primary tumours in humans. The human TERT (hTERT) plays a pivotal role in cellular immortality and tumourigenesis. However, the molecular mechanisms of telomerase functioning in cancer have not been fully understood beyond the telomere maintenance. Several research groups, including ours, have demonstrated that hTERT possesses vital functions independent of its telomere maintenance, including angiogenesis, inflammation, cancer cell stemness, and epithelial-mesenchymal transformation (EMT). All these telomere-independent activities of hTERT may contribute to the regulation of the dynamics and homeostasis of the tumour microenvironment (TME), thereby promoting tumour growth and development. Cancer progression and metastasis largely depend upon the interactions between cancer cells and their microenvironment. In this review, the involvement of TERT in the tumour microenvironment and the underlying implications in cancer therapeutics have been summarized.

The non-canonical functions of telomerase: to turn off or not to turn off

Telomerase is perceived as an immortality enzyme that enables passing the Hayflick limit. Its main function is telomere restoration but only in a limited group of cells, including cancer cells. Since it is found in a vast majority of cancer cells, it became a natural target for cancer therapy. However, it has much more functions than just altering the metabolism of telomeres-it also reveals numerous so-called non-canonical functions. Thus, a question arises whether it is always beneficial to turn it off when planning a cancer strategy and considering potential side effects? The purpose of this review is to discuss some of the recent discoveries about telomere-independent functions of telomerase in the context of cancer therapy and potential side effects.

Cellular prion protein and γ-synuclein overexpression in LS 174T colorectal cancer cell drives endothelial proliferation-to-differentiation switch

Background

Tumor-induced angiogenesis is an imperative event in pledging new vasculature for tumor metastasis. Since overexpression of neuronal proteins gamma-synuclein (γ-Syn) and cellular prion protein (PrP^C) is always detected in advanced stages of cancer diseases which involve metastasis, this study aimed to investigate whether γ-Syn or PrP^C overexpression in colorectal adenocarcinoma, LS 174T cells affects angiogenesis of endothelial cells, EA.hy 926 (EA).

Methods

EA cells were treated with conditioned media (CM) of LS 174T-γ-Syn or LS 174T-PrP, and their proliferation, invasion, migration, adhesion and ability to form angiogenic tubes were assessed using a range of biological assays. To investigate plausible background mechanisms in conferring the properties of EA cells above, nitrite oxide (NO) levels were measured and the expression of angiogenesis-related factors was assessed using a human angiogenesis antibody array.

Results

EA proliferation was significantly inhibited by LS 174T-PrP CM whereas its telomerase activity was reduced by CM of LS 174T-γ-Syn or LS 174T-PrP, as compared to EA incubated with LS 174T CM. Besides, LS 174T-γ-Syn CM or LS 174T-PrP CM inhibited EA invasion and migration in Boyden chamber assay. Furthermore, LS 174T-γ-Syn CM significantly inhibited EA migration in scratch wound assay. Gelatin zymography revealed reduced secretion of MMP-2 and MMP-9 by EA treated with LS 174T-γ-Syn CM or LS 174T-PrP CM. In addition, cell adhesion assay showed lesser LS 174T-γ-Syn or LS 174T-PrP cells adhered onto EA, as compared to LS 174T. In tube formation assay, LS 174T-γ-Syn CM or LS 174T-PrP CM induced EA tube formation. Increased NO secretion by EA treated with LS 174T-γ-Syn CM or LS 174T-PrP CM was also detected. Lastly, decreased expression of pro-angiogenic factors like CXCL16, IGFBP-2 and amphiregulin in LS 174T-γ-Syn CM or LS 174T-PrP CM was detected using the angiogenesis antibody array.

Discussion

These results suggest that overexpression of γ-Syn or PrP^C could possibly be involved in colorectal cancer-induced angiogenesis by inducing an endothelial proliferation-differentiation switch. NO could be the main factor in governing this switch, and modulation on the secretion patterns of angiogenesis-related proteins could be the strategy of colorectal cancer cells overexpressing γ-Syn or PrP^C in ensuring this transition.

Evaluation of Energy Balance on Human Telomerase Reverse Transcriptase (hTERT) Alternative Splicing by Semi-quantitative RT-PCR in Human Umbilical Vein Endothelial Cells

Background:

Decreased high-energy phosphate level is involved in endothelial cell injury and dysfunction. Reduced telomerase activity in endothelial cells in parallel with reduced energy levels might be due to altered direction of alternative splicing machine as a complication of depleted energy during the process of atherosclerosis.

Materials and Methods:

Isolated human umbilical vein endothelial cells (HUVECs) were treated for 24 hours by oligomycine (OM) and 2-deoxy glucose (2-DG). After 24 hours, the effect of energy depletion on telomerase splicing pattern was evaluated using RT-PCR. Indeed, in both treated and untargeted cells, nitric oxide (NO) and von Willebrand factor (vWF) were measured.

Results:

ATP was depleted in treated cells by 43.9% compared with control group. We observed a slight decrease in NO levels (P = 0.09) and vWF (P = 0.395) in the setting of 49.36% ATP depletion. In both groups, no telomerase gene expression was seen. Telomerase and housekeeping gene expression were found in positive control group (colon cancer tissue) and sample tissue.

Conclusions:

The absence of telomerase gene expression in HUVECs might be due to the mortality of these cells or the low level of telomerase gene expression in these cells under normal circumstances.

hTERT promotes tumor angiogenesis by activating VEGF via interactions with the Sp1 transcription factor

Angiogenesis is recognized as an important hallmark of cancer. Although telomerase is thought to be involved in tumor angiogenesis, the evidence and underlying mechanism remain elusive. Here, we demonstrate that human telomerase reverse transcriptase (hTERT) activates vascular epithelial growth factor (VEGF) gene expression through interactions with the VEGF promoter and the transcription factor Sp1. hTERT binds to Sp1 in vitro and in vivo and stimulates angiogenesis in a manner dependent on Sp1. Deletion of the mTert gene in the first generation of Tert null mice compromised tumor growth, with reduced VEGF expression. In addition, we show that hTERT expression levels are positively correlated with those of VEGF in human gastric tumor samples. Together, our results demonstrate that hTERT facilitates tumor angiogenesis by up-regulating VEGF expression through direct interactions with the VEGF gene and the Sp1 transcription factor. These results provide novel insights into hTERT function in tumor progression in addition to its role in telomere maintenance.

miR-135b suppresses tumorigenesis in glioblastoma stem-like cells impairing proliferation, migration and self-renewal

Glioblastoma multiforme (GBM) is the most common and fatal malignant adult primary brain tumor. Currently, the overall prognosis for GBM patients remains poor despite advances in neurosurgery and adjuvant treatments. MicroRNAs (miRNAs) contribute to the pathogenesis of various types of tumor, including GBM. In this study we analyzed the expression of a panel of miRNAs, which are known to be differentially expressed by the brain and GBM tumor, in a collection of patient-derived GBM stem-like cells (GSCs). Notably, the average expression level of miR-135b, was the most downregulated compared to its normal counterpart, suggesting a potential role as anti-oncogene.

Restoration of miR-135b in GSCs significantly decreased proliferation, migration and clonogenic abilities. More importantly, miR-135b restoration was able to significantly reduce brain infiltration in mouse models of GBM obtained by intracerebral injection of GSC lines. We identified ADAM12 and confirmed SMAD5 and GSK3β as miR-135b targets and potential mediators of its effects. The whole transcriptome analysis ascertained that the expression of miR-135b downmodulated additional genes driving key pathways in GBM survival and infiltration capabilities.

Our results identify a critical role of miR-135b in the regulation of GBM development, suggesting that miR-135b might act as a tumor-suppressor factor and thus providing a potential candidate for the treatment of GBM patients.

Genomic instability in human cancer: Molecular insights and opportunities for therapeutic attack and prevention through diet and nutrition

Genomic instability can initiate cancer, augment progression, and influence the overall prognosis of the affected patient. Genomic instability arises from many different pathways, such as telomere damage, centrosome amplification, epigenetic modifications, and DNA damage from endogenous and exogenous sources, and can be perpetuating, or limiting, through the induction of mutations or aneuploidy, both enabling and catastrophic. Many cancer treatments induce DNA damage to impair cell division on a global scale but it is accepted that personalized treatments, those that are tailored to the particular patient and type of cancer, must also be developed. In this review, we detail the mechanisms from which genomic instability arises and can lead to cancer, as well as treatments and measures that prevent genomic instability or take advantage of the cellular defects caused by genomic instability. In particular, we identify and discuss five priority targets against genomic instability: (1) prevention of DNA damage; (2) enhancement of DNA repair; (3) targeting deficient DNA repair; (4) impairing centrosome clustering; and, (5) inhibition of telomerase activity. Moreover, we highlight vitamin D and B, selenium, carotenoids, PARP inhibitors, resveratrol, and isothiocyanates as priority approaches against genomic instability. The prioritized target sites and approaches were cross validated to identify potential synergistic effects on a number of important areas of cancer biology.

A BMP7 Variant Inhibits Tumor Angiogenesis In Vitro and In Vivo through Direct Modulation of Endothelial Cell Biology

Bone morphogenetic proteins (BMPs), members of the TGF-β superfamily, have numerous biological activities including control of growth, differentiation, and vascular development. Using an in vitro co-culture endothelial cord formation assay, we investigated the role of a BMP7 variant (BMP7v) in VEGF, bFGF, and tumor-driven angiogenesis. BMP7v treatment led to disruption of neo-endothelial cord formation and regression of existing VEGF and bFGF cords in vitro. Using a series of tumor cell models capable of driving angiogenesis in vitro, BMP7v treatment completely blocked cord formation. Pre-treatment of endothelial cells with BMP7v significantly reduced their cord forming ability, indicating a direct effect on endothelial cell function. BMP7v activated the canonical SMAD signaling pathway in endothelial cells but targeted gene knockdown using shRNA directed against SMAD4 suggests this pathway is not required to mediate the anti-angiogenic effect. In contrast to SMAD activation, BMP7v selectively decreased ERK and AKT activation, significantly decreased endothelial cell migration and down-regulated expression of critical RTKs involved in VEGF and FGF angiogenic signaling, VEGFR2 and FGFR1 respectively. Importantly, in an in vivo angiogenic plug assay that serves as a measurement of angiogenesis, BMP7v significantly decreased hemoglobin content indicating inhibition of neoangiogenesis. In addition, BMP7v significantly decreased angiogenesis in glioblastoma stem-like cell (GSLC) Matrigel plugs and significantly impaired in vivo growth of a GSLC xenograft with a concomitant reduction in microvessel density. These data support BMP7v as a potent anti-angiogenic molecule that is effective in the context of tumor angiogenesis.

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed “senescence,” can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells’ heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Combined PDK1 and CHK1 inhibition is required to kill glioblastoma stem-like cells in vitro and in vivo

Glioblastoma (GBM) is the most common and deadly adult brain tumor. Despite aggressive surgery, radiation, and chemotherapy, the life expectancy of patients diagnosed with GBM is ∼14 months. The extremely aggressive nature of GBM results from glioblastoma stem-like cells (GSCs) that sustain GBM growth, survive intensive chemotherapy, and give rise to tumor recurrence. There is accumulating evidence revealing that GSC resilience is because of concomitant activation of multiple survival pathways. In order to decode the signal transduction networks responsible for the malignant properties of GSCs, we analyzed a collection of GSC lines using a dual, but complementary, experimental approach, that is, reverse-phase protein microarrays (RPPMs) and kinase inhibitor library screening. We treated GSCs in vitro with clinically relevant concentrations of temozolomide (TMZ) and performed RPPM to detect changes in phosphorylation patterns that could be associated with resistance. In addition, we screened GSCs in vitro with a library of protein and lipid kinase inhibitors to identify specific targets involved in GSC survival and proliferation. We show that GSCs are relatively insensitive to TMZ treatment in terms of pathway activation and, although displaying heterogeneous individual phospho-proteomic profiles, most GSCs are resistant to specific inhibition of the major signaling pathways involved in cell survival and proliferation. However, simultaneous multipathway inhibition by the staurosporin derivative UCN-01 results in remarkable inhibition of GSC growth in vitro. The activity of UCN-01 on GSCs was confirmed in two in vivo models of GBM growth. Finally, we used RPPM to study the molecular and functional effects of UCN-01 and demonstrated that the sensitivity to UCN-01 correlates with activation of survival signals mediated by PDK1 and the DNA damage response initiated by CHK1. Taken together, our results suggest that a combined inhibition of PDK1 and CHK1 represents a potentially effective therapeutic approach to reduce the growth of human GBM.

Kisspeptin-10 induces endothelial cellular senescence and impaired endothelial cell growth

The KPs (kisspeptins) are a family of multifunctional peptides with established roles in cancer metastasis, puberty and vasoconstriction. The effects of KPs on endothelial cells have yet to be determined. The aim of the present study was to investigate the effects of KP-10 on endothelial cell growth and the mechanisms underlying those effects. The administration of recombinant KP-10 into the hindlimbs of rats with ischaemia significantly impaired blood flow recovery, as shown by laser Doppler, and capillary growth, as shown using histology, compared with the controls. HUVECs (human umbilical vein endothelial cells) express the KP receptor and were treated with KP-10 in culture studies. KP-10 inhibited endothelial cell tube formation and proliferation in a significant and dose-dependent manner. The HUVECs treated with KP exhibited the senescent phenotype, as determined using a senescence-associated β-galactosidase assay, cell morphology analysis, and decreased Sirt1 (sirtuin 1) expression and increased p53 expression shown by Western blot analysis. Intriguingly, a pharmacological Rho kinase inhibitor, Y-27632, was found to increase the proliferation of HUVECs and to reduce the number of senescent phenotype cells affected by KP-10. In conclusion, KP-10 suppressed endothelial cells growth both in vivo and in vitro in the present study. The adverse effect of KP on endothelial cells was attributable, at least in part, to the induction of cellular senescence.

Telomerase: central regulator of all of the hallmarks of cancer

The hallmarks of cancer described by Hanahan and Weinberg are properties that cancer cells must possess for successful transformation. It is believed that each of these hallmarks is independently driven. Although elongation of telomeres is thought to be the prime function of reactivated telomerase reverse transcriptase, this activity does not account for all its effects, such as increasing cell proliferation, resistance to apoptosis, and invasion. Recent studies suggest that the telomerase subunit telomerase reverse transcriptase (TERT) has novel molecular functions including transcriptional regulation and metabolic reprogramming. We summarize these functions and discuss how they could directly regulate the various hallmarks of cancer. Finally, we suggest that therapeutics targeting noncanonical telomerase functions may work better than those that target its role in telomere extension.

Telomerase- and angiogenesis-related gene responses to irradiation in human umbilical vein endothelial cells

In this study, we investigated the effects of ionizing radiation (IR) on human umbilical vein endothelial cells (HUVECs) in the context of senescence. HUVECs at passage number (PN)1, PN2 and PN3 were exposed to irradiation (2 Gy). The growth rate of the HUVECS was measured by proliferation assay and senescence-associated β-galactosidase assay was used to measure the number of senescent cells. Telomerase activity and the expression of telomerase- and angiogenesis-related genes were measured by telomerase assay and real-time PCR, respectively. The number of senescent cells was significantly increased in the irradiated HUVECs at all PNs. Compared to the controls, telomerase activity, the expression of human telomerase reverse transcriptase (hTERT) and c-Myc in the irradiated HUVECs were downregulated during serial passage. The downregulation of vascular endothelial growth factor (VEGF) was observed in the irradiated HUVECs as the PN increased. The data presented in this study may aid in the understanding of the mechanisms behind IR‑induced EC senescence and telomerase- and angiogenesis‑related gene response.

Prognostic significance of telomerase-associated parameters in glioblastoma: effect of patient age

BACKGROUND

Glioblastoma multiforme (GBM) is a heterogeneous, highly aggressive primary brain tumor with strongly variable patient survival. Because reliable prognostic biomarkers are lacking, we investigated the relation between telomerase-associated parameters and the disease course.

METHODS

Telomerase-associated parameters were determined in 100 GBM tissues and associated with clinical characteristics and overall survival. Expressions of telomere length, telomerase activity (TA), and human telomerase reverse transcriptase (hTERT) were analyzed by quantitative PCR, telomeric repeat amplification protocol assay, and reverse transcriptase-PCR, respectively. Mutation status of isocitrate dehydrogenase (IDH)1 was determined by direct sequencing, and O(6)-methylguanine DNA methyltransferase (MGMT) promoter methylation by methylation-specific PCR.

RESULTS

Of 100 GBM tissues, 61 were positive for both hTERT mRNA and TA, with a highly significant correlation between both parameters (linear regression, P < .0001). Telomere length determination revealed a significant difference between the hTERT/TA-positive and -negative subgroups, with markedly longer telomeres in the hTERT/TA-negative cohort (unpaired Student's t-test, P = .0001). Accordingly, significantly shorter telomeres were detected in GBM tissues derived from older patients (>60 y at diagnosis, P < .0001). While no association of telomere parameters with MGMT promoter status was found, all tumors with IDH1 mutation (6/100) were negative for both hTERT expression and TA and harbored significantly longer telomeres. Patients with tumors lacking hTERT expression/TA showed a significant survival benefit (Kaplan-Meier test, both P < .01), which, however, was based exclusively on the younger patient subgroup (≤60 y, both P < .005; >60 y, both ns).

CONCLUSIONS

Telomerase activation is not an independent prognostic parameter in GBM but predicts aggressive tumor behavior solely in a younger patient cohort.

Lonafarnib (SCH66336) improves the activity of temozolomide and radiation for orthotopic malignant gliomas

Malignant gliomas are highly lethal tumors resistant to current therapies. The standard treatment modality for these tumors, surgical resection followed by radiation therapy and concurrent temozolomide, has demonstrated activity, but development of resistance and disease progression is common. Although oncogenic Ras mutations are uncommon in gliomas, Ras has been found to be constitutively activated through the action of upstream signaling pathways, suggesting that farnesyltransferase inhibitors may show activity against these tumors. We now report the in vitro and orthotopic in vivo results of combination therapy using radiation, temozolomide and lonafarnib (SCH66336), an oral farnesyl transferase inhibitor, in a murine model of glioblastoma. We examined the viability, proliferation, farnesylation of H-Ras, and activation of downstream signaling of combination-treated U87 cells in vitro. Lonafarnib alone or in combination with radiation and temozolomide had limited tumor cell cytotoxicity in vitro although it did demonstrate significant inhibition in tumor cell proliferation. In vivo, lonafarnib alone had a modest ability to inhibit orthotopic U87 tumors, radiation and temozolomide demonstrated better inhibition, while significant anti-tumor activity was found with concurrent lonafarnib, radiation, and temozolomide, with the majority of animals demonstrating a decrease in tumor volume. The use of tumor neurospheres derived from freshly resected adult human glioblastoma tissue was relatively resistant to both temozolomide and radiation therapy. Lonafarnib had a significant inhibitory activity against these neurospheres and could potentate the activity of temozolomide and radiation. These data support the continued research of high grade glioma treatment combinations of farnesyl transferase inhibitors, temozolomide, and radiation therapy.

Expression profile and regulation of telomerase reverse transcriptase on oxygen-induced retinal neovascularization

PURPOSE

Telomerase is critical for the control of replicative capacity, which plays a major role in proliferative retinal neovascularization. In this study, we investigated the expression profiles of telomerase reverse transcriptase (Tert) in a mouse model of oxygen-induced retinal neovascularization and explored the possibility of inhibiting a retinal Tert expression with small interfering RNAs (SiRNA) as a novel potential approach to suppress proliferative retinopathy.

METHODS

The mouse oxygen-induced retinal neovascularization model was used to examine expression profiles in different developmental phases and to assess the anti-angiogenic activity of Tert-SiRNA. Recombinant SiRNA plasmids were injected intravitreously into mice with or without pathological retinal neovascularization. Fluorescein angiography, vessel counting, and the expression levels of Tert mRNA and protein were used to evaluate the anti-angiogenic effects.

RESULTS

Retinal Tert expression, as assessed by both mRNA and protein levels, was significantly up-regulated during the proliferative phase of oxygen-induced retinal neovascularization. Intravitreous injection of Tert-SiRNA effectively suppressed the expression of Tert mRNA and proteins and inhibited retinal neovascularization, as confirmed by retinal flat angiography and vessel counting.

CONCLUSIONS

The expression of Tert was up-regulated during the development of oxygen-induced retinal neovascularization. Inhibiting Tert expression with SiRNA is effective in suppressing retinal neovascularization, suggesting that telomerase may be a potential therapeutic target for treating proliferative retinopathy.

Cellular aging reflected by leukocyte telomere length predicts advanced atherosclerosis and cardiovascular disease risk

OBJECTIVE

To determine the association between leukocyte telomere length (TL) and atherosclerosis and its clinical sequelae stroke and myocardial infarction.

METHODS AND RESULTS

Within the scope of the prospective population-based Bruneck Study, leukocyte TL was measured by quantitative polymerase chain reaction in 800 women and men aged 45 to 84 years (in 1995). The manifestation of cardiovascular disease (CVD) (1995-2005) and the progression of atherosclerosis (1995-2000) were carefully assessed. The TL was shorter in men than in women (age-adjusted mean [95% CI], 1.41 [1.33 to 1.49] versus 1.55 [1.47 to 1.62]; P=0.02) and inversely correlated to age (r=-0.22, P<0.001) and family history of CVD (P=0.03). Participants with CVD events during follow-up (n=88) had significantly shorter telomeres (age- and sex-adjusted mean [95% CI], 1.25 [1.08 to 1.42] versus 1.51 [1.45 to 1.57]; P<0.001). In multivariable Cox models, baseline TL emerged as a significant and independent risk predictor for the composite CVD end point and its individual components (myocardial infarction and stroke); however, this was not the case for de novo stable angina and intermittent claudication. Subjects in the top and bottom TL tertile group differed in their CVD risk by a factor of 2.72 (95% CI, 1.41 to 5.28), which is the risk ratio attributable to a 13.9-year difference in chronological age. Remarkably, in our atherosclerosis progression model, TL was strongly associated with advanced, but not early, atherogenesis. All findings were consistent in women and men.

CONCLUSIONS

Our findings indicate a differential role of telomere shortening in the various stages of atherosclerosis, with preferential involvement in advanced vessel pathology and acute vascular syndromes.

Combination of hTERT knockdown and IFN-gamma treatment inhibited angiogenesis and tumor progression in glioblastoma

PURPOSE

The limitless invasive and proliferative capacities of tumor cells are associated with telomerase and expression of its catalytic component, human telomerase reverse transcriptase (hTERT). IFN-gamma modulates several cellular activities, including signaling pathways and cell cycle, through transcriptional regulation.

EXPERIMENTAL DESIGN

Using a recombinant plasmid with hTERT siRNA cDNA, we downregulated hTERT during IFN-gamma treatment in human glioblastoma SNB-19 and LN-18 cell lines and examined whether such a combination could inhibit angiogenesis and tumor growth in nude mice. In vitro angiogenesis assay was done using coculture of tumor cells with human microvascular endothelial cells. In vivo angiogenesis assay was done using diffusion chambers under the dorsal skin of nude mice. In vivo imaging of intracerebral tumorigenesis and longitudinal solid tumor development studies were conducted in nude mice.

RESULTS

In vitro and in vivo angiogenesis assays showed inhibition of capillary-like network formation of microvascular endothelial cells and neovascularization under dorsal skin of nude mice, respectively. We observed inhibition of intracerebral tumorigenesis and s.c. solid tumor formation in nude mice after treatment with combination of hTERT siRNA and IFN-gamma. Western blotting of solid tumor samples showed significant downregulation of the molecules that regulate cell invasion, angiogenesis, and tumor progression.

CONCLUSIONS

Our study showed that the combination of hTERT siRNA and IFN-gamma effectively inhibited angiogenesis and tumor progression through the downregulation of molecules involved in these processes. Therefore, the combination of hTERT siRNA and IFN-gamma is a promising therapeutic strategy for controlling the growth of human glioblastoma.

Enhanced adhesion of early endothelial progenitor cells to radiation-induced senescence-like vascular endothelial cells in vitro

The effects of ionizing radiation (IR) on tumor neovascularization are still unclear. We previously reported that vascular endothelial cells (ECs) expressing the IR-induced senescence-like (IRSL) phenotype exhibit a significant decrease in angiogenic activity in vitro. In this study, we examined the effects of the IRSL phenotype on adhesion to early endothelial progenitor cells (early EPCs). Adhesion of human peripheral blood-derived early EPCs to human umbilical vein endothelial cells (HUVECs) expressing the IRSL phenotype was evaluated by an adhesion assay under static conditions. It was revealed that the IRSL HUVECs supported significantly more adhesion of early EPCs than normal HUVECs. Expressions of ICAM-1, VCAM-1 and E-selectin were up-regulated in IRSL HUVECs. Pre-treatment of IRSL HUVECs with adhesion-blocking monoclonal antibodies against E-selectin and VCAM-1 significantly reduced early EPC adhesion to IRSL HUVECs, suggesting a potential role for the E-selectin and VCAM-1 in the adhesion between IRSL ECs and early EPCs. Therefore, the IRSL phenotype expressed in ECs may enhance neovascularization via increased homing of early EPCs. Our findings are first to implicate the complex effects of this phenotype on tumor neovascularization following irradiation.

Targeting critical steps of cancer metastasis and recurrence using telomerase template antagonists

Metastasis, tumor relapse, and drug resistance remain major obstacles in the treatment of cancer. Therefore, more research on the mechanisms of these processes in disease is warranted for improved treatment options. Recent evidence suggests that the capability to sustain tumor growth and metastasis resides in a subpopulation of cells, termed cancer stem cells or tumor-initiating cells. Continuous proliferation and self-renewal are characteristics of stem/progenitor cells. Telomerase and the maintenance of telomeres are key players in the ability of stem and cancer cells to bypass senescence and be immortal. Therefore, telomerase inhibitors have the therapeutic potential for reducing tumor relapse by targeting cancer stem cells and other processes involved in metastasis. Herein we review the role of telomerase in the immortal phenotype of cancer and cancer stem cells, targeting telomerase in cancer, and discuss other opportunities for telomerase inhibitors to target critical steps in cancer metastasis and recurrence.

Vascular endothelial senescence: from mechanisms to pathophysiology

Most mitotically competent mammalian cell types can react to stress by undergoing a phenotypically distinctive and permanent form of growth arrest called "cellular senescence." This response has been extensively characterized in cell culture and more recently it has been found to occur also in vivo in a number of tissues. In this review I will present the case for the occurrence of senescence in the vascular endothelium. I will also discuss the mechanisms and factors that modulate endothelial cell replicative capacity and the onset of senescence. Finally, I will examine the senescent phenotype and its possible consequences for the development and progression of vascular diseases.