Telomere and telomerase as targets for cancer therapy. Appl Biochem Biotechnol. 2010;160:1460-1472. [PMID: 19412578 DOI: 10.1007/s12010-009-8633-9]

Targeted therapies of curcumin focus on its therapeutic benefits in cancers and human health: Molecular signaling pathway-based approaches and future perspectives

The curry powder spices turmeric (Curcuma longa L.), which contains curcumin (diferuloylmethane), an orange-yellow chemical. Polyphenols are the most commonly used sources of curcumin. It combats oxidative stress and inflammation in diseases, such as hyperlipidemia, metabolic syndrome, arthritis, and depression. Most of these benefits are due to their anti-inflammatory and antioxidant properties. Curcumin consumption leads to decreased bioavailability, resulting in limited absorption, quick metabolism, and quick excretion, which hinders health improvement. Numerous factors can increase its bioavailability. Piperine enhances bioavailability when combined with curcumin in a complex. When combined with other enhancing agents, curcumin has a wide spectrum of health benefits. This review evaluates the therapeutic potential of curcumin with a specific emphasis on its approach based on molecular signaling pathways. This study investigated its influence on the progression of cancer, inflammation, and many health-related mechanisms, such as cell proliferation, apoptosis, and metastasis. Curcumin has a significant potential for the prevention and treatment of various diseases. Curcumin modulates several biochemical pathways and targets involved in cancer growth. Despite its limited tissue accumulation and bioavailability when administered orally, curcumin has proven useful. This review provides an in-depth analysis of curcumin's therapeutic applications, its molecular signaling pathway-based approach, and its potential for precision medicine in cancer and human health.

POT1 involved in telomeric DNA damage repair and genomic stability of cervical cancer cells in response to radiation

Though telomeres play a crucial role in maintaining genomic stability in cancer cells and have emerged as attractive therapeutic targets in anticancer therapy, the relationship between telomere dysfunction and genomic instability induced by irradiation is still unclear. In this study, we identified that protection of telomeres 1 (POT1), a single-stranded DNA (ssDNA)-binding protein, was upregulated in γ-irradiated HeLa cells and in cancer patients who exhibit radiation tolerance. Knockdown of POT1 delayed the repair of radiation-induced telomeric DNA damage which was associated with enhanced H3K9 trimethylation and enhanced the radiosensitivity of HeLa cells. The depletion of POT1 also resulted in significant genomic instability, by showing a significant increase in end-to-end chromosomal fusions, and the formation of anaphase bridges and micronuclei. Furthermore, knockdown of POT1 disturbed telomerase recruitment to telomere, and POT1 could interact with phosphorylated ATM (p-ATM) and POT1 depletion decreased the levels of p-ATM induced by irradiation, suggesting that POT1 could regulate the telomerase recruitment to telomeres to repair irradiation-induced telomeric DNA damage of HeLa cells through interactions with p-ATM. The enhancement of radiosensitivity in cancer cells can be achieved through the combination of POT1 and telomerase inhibitors, presenting a potential approach for radiotherapy in cancer treatment.

In-Tumor Biosynthetic Construction of Upconversion Nanomachines for Precise Near-Infrared Phototherapy

Targeted construction of therapeutic nanoplatforms in tumor cells with specific activation remains appealing but challenging. Here, we design a cancer-motivated upconversion nanomachine (UCNM) based on porous upconversion nanoparticles (p-UCNPs) for precise phototherapy. The nanosystem is equipped with a telomerase substrate (TS) primer and simultaneously encapsulates 5-aminolevulinic acid (5-ALA) and d-arginine (d-Arg). After coating with hyaluronic acid (HA), it can readily get into tumor cells, where 5-ALA induces efficient accumulation of protoporphyrin IX (PpIX) via the inherent biosynthetic pathway, and the overexpressed telomerase prolonged the TS to form G-quadruplexes (G4) for binding the resulting PpIX as a nanomachine. This nanomachine can respond to near-infrared (NIR) light and promote the active singlet oxygen (¹O₂) production due to the efficiency of Förster resonance energy transfer (FRET) between p-UCNPs and PpIX. Intriguingly, such oxidative stress can oxidize d-Arg into nitric oxide (NO), which relieves the tumor hypoxia and in turn improves the phototherapy effect. This in situ assembly approach significantly enhances targeting in cancer therapy and might be of considerable clinical value.

Shikonin N-benzyl matrinic acid ester derivatives as novel telomerase inhibitors with potent activity against lung cancer cell lines

In this study, a series of novel shikonin N-benzyl matrinic acid ester derivatives (PMMB-299-PMMB-310) were synthesized and tested for their ability to inhibit the proliferation of cancer cells. Compared with shikonin and matrine, some of the ester derivatives were found to exhibit better anti-proliferative activity against seven different cancer cell lines, with less cytotoxicity toward non-cancerous cells. The strongest anti-proliferative activity was exhibited by PMMB-302, which had an IC₅₀ value of 2.71 μM against A549 cells. The compound caused cell cycle arrest in the G2/M phase and induced apoptosis. Effects on the expression of apoptosis-related molecules such as Bcl2, Bcl-XL, caspase-3, caspase-9 and FADD suggested that PMMB-302 has tumor suppressive roles in lung cancer cells. In addition, PMMB-302 inhibited expression of telomerase core proteins, dyskerin and NHP2, and telomerase reverse transcriptase RNA. Moreover, molecular docking of PMMB-302 was subsequently conducted to determine the probable binding mode with telomerase. Taken together, the results indicate that PMMB-302 acts as a tumor suppressor in lung cancer cells by negatively regulating telomerase expression.

The Roles of mitochondrial dysfunction and Reactive Oxygen Species in Aging and Senescence

The aging process deteriorates organs' function at different levels, causing its progressive decline to resist stress, damage, and disease. In addition to alterations in metabolic control and gene expression, the rate of aging has been connected with the generation of high amounts of Reactive Oxygen Species (ROS). The essential perspective in free radical biology is that reactive oxygen species (ROS) and free radicals are toxic, mostly cause direct biological damage to targets, and are thus a major cause of oxidative stress. Different enzymatic and non-enzymatic compounds in the cells have roles in neutralizing this toxicity. Oxidative damage in aging is mostly high in particular molecular targets, such as mitochondrial DNA and aconitase, and oxidative stress in mitochondria can cause tissue aging across intrinsic apoptosis. Mitochondria's function and morphology are impaired through aging, following a decrease in the membrane potential by an increase in peroxide generation and size of the organelles. Telomeres may be the significant trigger of replicative senescence. Oxidative stress accelerates telomere loss, whereas antioxidants slow it down. Oxidative stress is a crucial modulator of telomere shortening, and that telomere-driven replicative senescence is mainly a stress response. The age-linked mitochondrial DNA mutation and protein dysfunction aggregate in some organs like the brain and skeletal muscle, thus contributing considerably to these post-mitotic tissues' aging. The aging process is mostly due to accumulated damage done by harmful species in some macromolecules such proteins, DNA, and lipids. The degradation of non-functional, oxidized proteins is a crucial part of the antioxidant defenses of cells, in which the clearance of these proteins occurs through autophagy in the cells, which is known as mitophagy for mitochondria.

Antitumor Drugs and Their Targets

Through novel methodologies, including both basic and clinical research, progress has been made in the therapy of solid cancer. Recent innovations in anticancer therapies, including immune checkpoint inhibitor biologics, therapeutic vaccines, small drugs, and CAR-T cell injections, mark a new epoch in cancer research, already known for faster (epi-)genomics, transcriptomics, and proteomics. As the long-sought after personalization of cancer therapies comes to fruition, the need to evaluate all current therapeutic possibilities and select the best for each patient is of paramount importance. This is a novel task for medical care that deserves prominence in therapeutic considerations in the future. This is because cancer is a complex genetic disease. In its deadly form, metastatic cancer, it includes altered genes (and their regulators) that encode ten hallmarks of cancer-independent growth, dodging apoptosis, immortalization, multidrug resistance, neovascularization, invasiveness, genome instability, inflammation, deregulation of metabolism, and avoidance of destruction by the immune system. These factors have been known targets for many anticancer drugs and treatments, and their modulation is a therapeutic goal, with the hope of rendering solid cancer a chronic rather than deadly disease. In this article, the current therapeutic arsenal against cancers is reviewed with a focus on immunotherapies.

Fundamental insights into the interaction between telomerase/TERT and intracellular signaling pathways

Telomerase activity is critical for cancer cells to provide unrestricted proliferation and cellular immortality through maintaining telomeres. Telomerase enzymatic activity is regulatable at the level of DNA, mRNA, post translational modifications, cellular transport and enzyme assembly. More recent studies confirm the interaction of the telomerase with various intracellular signaling pathways including PI3K/AKT/mTOR, NF-κB and Wnt/β-catenin which mainly participating in inflammation, epithelial to mesenchymal transition (EMT) and tumor cell invasion and metastasis. Furthermore, hTERT protein has been detected in non-nuclear sites such as the mitochondria and cytoplasm in cells. Mitochondrial TERT indicates various non-telomere-related functions such as decreasing reactive oxygen species (ROS) generation, boosting the respiration rate, protecting mtDNA by direct binding, interacting with mitochondrial tRNAs and increasing mitochondrial membrane potential which can lead to higher chemoresistance rate in cancer cells during therapies. Understanding the molecular mechanisms of the TERT function and depended interactions in tumor cells can suggest novel therapeutic approaches. Hence, in this review we will explain the telomerase activity regulation in translational and post translational levels besides the established correlations with various cell signaling pathways with possible pathways for therapeutic targeting.

Oligonucleotides and microRNAs Targeting Telomerase Subunits in Cancer Therapy

Telomerase provides cancer cells with replicative immortality, and its overexpression serves as a near-universal marker of cancer. Anti-cancer therapeutics targeting telomerase have garnered interest as possible alternatives to chemotherapy and radiotherapy. Oligonucleotide-based therapies that inhibit telomerase through direct or indirect modulation of its subunits, human telomerase reverse transcriptase (hTERT) and human telomerase RNA gene (hTERC), are a unique and diverse subclass of telomerase inhibitors which hold clinical promise. MicroRNAs that play a role in the upregulation or downregulation of hTERT and respective progression or attenuation of cancer development have been effectively targeted to reduce telomerase activity in various cancer types. Tumor suppressor miRNAs, such as miRNA-512-5p, miRNA-138, and miRNA-128, and oncogenic miRNAs, such as miRNA-19b, miRNA-346, and miRNA-21, have displayed preclinical promise as potential hTERT-based therapeutic targets. Antisense oligonucleotides like GRN163L and T-oligos have also been shown to uniquely target the telomerase subunits and have become popular in the design of novel cancer therapies. Finally, studies suggest that G-quadruplex stabilizers, such as Telomestatin, preserve telomeric oligonucleotide architecture, thus inhibiting hTERC binding to the telomere. This review aims to provide an adept understanding of the conceptual foundation and current state of therapeutics utilizing oligonucleotides to target the telomerase subunits, including the advantages and drawbacks of each of these approaches.

Telomerase inhibition regulates EMT mechanism in breast cancer stem cells

BACKROUND

CSCs having the common features of high telomerase activity and high migration and invasion capabilities play a vital role as the initiators of metastasis. Small molecule BIBR1532 has been shown to target cancer cells by inhibiting telomerase. Recent studies have suggested that telomerase activity is associated with epithelial mesenchymal transition (EMT). EMT program, which causes epithelial cells to acquire a mesenchymal morphology, is known to play a significant role in cancer metastasis.

METHODS

The hypothesis of our study was that suppression of telomerase in breast cancer and cancer stem cells would interrupt EMT mechanism. Cytotoxicity of BIBR1532 was evaluated using WST-1 assay in all cell lines and the effects of BIBR1532 on apoptosis were investigated with Annexin V. Migration rate of the cells was examined by wound healing assay and sphere forming capacities were observed by hanging drop test. Finally, the expression of 84 EMT-related genes was analyzed by real-time qPCR.

RESULTS

The IC₅₀ values for the MDA-MB-231 and breast epithelial stem cells of BIBR1532 were analyzed as 18.04 and 38.71 µl at 72 h, respectively. Interestingly, apoptosis was only induced in stem cells. In hanging drop test, sphere areas were reduced in stem cells treated with BIBR1532. In wound healing assay, BIBR1532 decreased the migration rate of stem cells. Together with this, expression of EMT-related genes were regulated in stem cells towards a epithelial phenotype.

CONCLUSION

Our obtained results indicated that telomerase inhibition affects the EMT mechanism. The targeted elimination of breast cancer stem cells by a telomerase inhibitor in cancer treatment may limit the mobility and stemness of cancer cells interrupting the EMT mechanism, thus may prevent metastasis.

BIBR1532, a Selective Telomerase Inhibitor, Enhances Radiosensitivity of Non-Small Cell Lung Cancer Through Increasing Telomere Dysfunction and ATM/CHK1 Inhibition

PURPOSE

Telomerase is reactivated in non-small cell lung cancer (NSCLC), and it increases cell resistance to irradiation through protecting damaged telomeres and enhancing DNA damage repair. We investigated the radiosensitizing effect of BIBR1532, a highly selective telomerase inhibitor, and its corresponding mechanism in NSCLC.

METHODS AND MATERIALS

Cell proliferation, telomerase activity, and telomere dysfunction-induced foci were measured with CCK-8 assay, real-time fluorescent quantitative polymerase chain reaction, and immunofluorescence. The effect of BIBR1532 on the response of NSCLC cells to radiation was analyzed using clonogenic survival and xenograft tumor assays. Cell death and cell senescence induced by BIBR1532 or ionizing radiation (IR), or both, were detected with western blotting, flow cytometry, and senescence-association β-galactosidase staining assay.

RESULTS

We observed dose-dependent direct cytotoxicity of BIBR1532 at relatively high concentrations in NSCLC cells. Low concentrations of BIBR1532 did not appear toxic to NSCLC cells; however, they substantially increased the therapeutic efficacy of IR in vitro by enhancing IR-induced apoptosis, senescence, and mitotic catastrophe. Moreover, in a mouse xenograft model, BIBR1532 treatment synergized with IR at nontoxic dose levels promoted the antitumor efficacy of IR without toxicity to hematologic and internal organs. Mechanistically, lower concentrations of BIBR1532 effectively inhibited telomerase activity and increased IR-induced telomere dysfunction, resulting in disruption of chromosomal stability and inhibition of the ATM/CHK1 (ataxia-telangiectasia-mutated/Checkpoint kinase 1) pathway, which impaired DNA damage repair.

CONCLUSIONS

Our findings demonstrate that disturbances in telomerase function by nontoxic dose levels of BIBR1532 effectively enhance the radiosensitivity of NSCLC cells. This finding provides a rationale for the clinical assessment of BIBR1532 as a radiosensitizer.

Therapeutic strategies for targeting telomerase in cancer

Telomere and telomerase play important roles in abnormal cell proliferation, metastasis, stem cell maintenance, and immortalization in various cancers. Therefore, designing of drugs targeting telomerase and telomere is of great significance. Over the past two decades, considerable knowledge regarding telomere and telomerase has been accumulated, which provides theoretical support for the design of therapeutic strategies such as telomere elongation. Therefore, the development of telomere-based therapies such as nucleoside analogs, non-nucleoside small molecules, antisense technology, ribozymes, and dominant negative human telomerase reverse transcriptase are being prioritized for eradicating a majority of tumors. While the benefits of telomere-based therapies are obvious, there is a need to address the limitations of various therapeutic strategies to improve the possibility of clinical applications. In this study, current knowledge of telomere and telomerase is discussed, and therapeutic strategies based on recent research are reviewed.

Telomere shortening in breast cancer cells (MCF7) under treatment with low doses of the benzylisoquinoline alkaloid chelidonine

Telomeres, the specialized dynamic structures at chromosome ends, regularly shrink with every replication. Thus, they function as an internal molecular clock counting down the number of cell divisions. However, most cancer cells escape this limitation by activating telomerase, which can maintain telomere length. Previous studies showed that the benzylisoquinoline alkaloid chelidonine stimulates multiple modes of cell death and strongly down-regulates telomerase. It is still unknown if down-regulation of telomerase by chelidonine boosts substantial telomere shortening. The breast cancer cell line MCF7 was sequentially treated with very low concentrations of chelidonine over several cell passages. Telomere length and telomerase activity were measured by a monochrome multiplex quantitative PCR and a q-TRAP assay, respectively. Changes in population size and doubling time correlated well with telomerase inhibition and telomere shortening. MCF7 cell growth was arrested completely after three sequential treatments with 0.1 μM chelidonine, each ending after 48 h, while telomere length was reduced to almost 10% of the untreated control. However, treatment with 0.01 μM chelidonine did not have any apparent consequence. In addition to dose and time dependent telomerase inhibition, chelidonine changed the splicing pattern of hTERT towards non-enzyme coding isoforms of the transcript. In conclusion, telomere length and telomere stability are strongly affected by chelidonine in addition to microtubule formation.

Novel Naphthalimide Derivatives as Selective G-Quadruplex DNA Binders

A new derivate of 4-bromo-1,8-naphthalic anhydride and its quaternized analogue have been prepared and characterized. The interactions of both derivatives with human telomere quadruplex-DNA and ds-DNA have been comparatively studied by UV-visible (UV-Vis), fluorescent intercalator displacement assays, competition dialysis, circular dichroism (CD), agarose gel electrophoresis, and polyacrylamide gel electrophoresis. The results show that both derivatives can stabilize G-quadruplexes DNA, and they show different binding affinities for G-quadruplexes-DNA and ds-DNA. All spectroscopic studies have shown that the derivatives have a modest selectivity for G-quadruplex versus ds-DNA.

Quantum Dots-siRNA Nanoplexes for Gene Silencing in Central Nervous System Tumor Cells

RNA interfering (RNAi) using short interfering RNA (siRNA) is becoming a promising approach for cancer gene therapy. However, owing to the lack of safe and efficient carriers, the application of RNAi for clinical use is still very limited. In this study, we have developed cadmium sulphoselenide/Zinc sulfide quantum dots (CdSSe/ZnS QDs)-based nanocarriers for in vitro gene delivery. These CdSSe/ZnS QDs are functionalized with polyethyleneimine (PEI) to form stable nanoplex (QD-PEI) and subsequently they are used for siRNA loading which specially targets human telomerase reverse transcriptase (TERT). High gene transfection efficiency (>80%) was achieved on two glioblastoma cell lines, U87 and U251. The gene expression level (49.99 ± 10.23% for U87, 43.28 ± 9.66% for U251) and protein expression level (51.58 ± 7.88% for U87, 50.69 ± 7.59% for U251) of TERT is observed to decrease substantially after transfecting the tumor cells for 48 h. More importantly, the silencing of TERT gene expression significantly suppressed the proliferation of glioblastoma cells. No obvious cytotoxicity from these QD-PEI nanoplexes were observed over at 10 times of the transfected doses. Based on these results, we envision that QDs engineered here can be used as a safe and efficient gene nanocarrier for siRNA delivery and a promising tool for future cancer gene therapy applications.

Nucleolus-derived mediators in oncogenic stress response and activation of p53-dependent pathways

Rapid growth and division of cells, including tumor ones, is correlated with intensive protein biosynthesis. The output of nucleoli, organelles where translational machineries are formed, depends on a rate of particular stages of ribosome production and on accessibility of elements crucial for their effective functioning, including substrates, enzymes as well as energy resources. Different factors that induce cellular stress also often lead to nucleolar dysfunction which results in ribosome biogenesis impairment. Such nucleolar disorders, called nucleolar or ribosomal stress, usually affect cellular functioning which in fact is a result of p53-dependent pathway activation, elicited as a response to stress. These pathways direct cells to new destinations such as cell cycle arrest, damage repair, differentiation, autophagy, programmed cell death or aging. In the case of impaired nucleolar functioning, nucleolar and ribosomal proteins mediate activation of the p53 pathways. They are also triggered as a response to oncogenic factor overexpression to protect tissues and organs against extensive proliferation of abnormal cells. Intentional impairment of any step of ribosome biosynthesis which would direct the cells to these destinations could be a strategy used in anticancer therapy. This review presents current knowledge on a nucleolus, mainly in relation to cancer biology, which is an important and extremely sensitive element of the mechanism participating in cellular stress reaction mediating activation of the p53 pathways in order to counteract stress effects, especially cancer development.

Hit Identification of a Novel Dual Binder for h-telo/c-myc G-Quadruplex by a Combination of Pharmacophore Structure-Based Virtual Screening and Docking Refinement

It is well known that G-quadruplexes are targets of great interest for their roles in crucial biological processes, such as aging and cancer. Hence, a promising strategy for anticancer drug therapy is the stabilization of these structures by small molecules. We report a high-throughput in silico screening of commercial libraries from several different vendors by means of a combined structure-based pharmacophore model approach followed by docking simulations. The compounds selected by the virtual screening procedure were then tested for their ability to interact with human telomeric G-quadruplex folding by circular dichroism, fluorescence spectroscopy, and fluorescence intercalator displacement. Our approach resulted in the identification of a 13-[(dimethylamino)methyl]-12-hydroxy-8H-benzo[c]indolo[3,2,1-ij][1,5]naphthyridin-8-one derivative as a novel promising stabilizer of G-quadruplex structures within the human telomeric and the c-myc promoter sequences.

Ret finger protein-like 3 promotes tumor cell growth by activating telomerase reverse transcriptase expression in human lung cancer cells

In this study, we identified ret finger protein-like 3 (RFPL3) as a hTERT promoter binding protein in lung cancer cells. The high hTERT promoter-binding activity of RFPL3 was detected in lung cancer cells compared to normal cells. Chromatin immunoprecipitation confirmed RFPL3 as a tumor-specific hTERT promoter binding protein. Overexpression of RFPL3 activated hTERT promoter and up-regulated hTERT expression and telomerase activity. Inhibition of RFPL3 expression by siRNA suppressed hTERT promoter activation and telomerase activity. Inhibition of RFPL3 by siRNA or shRNA also significantly inhibited tumor cell growth in vitro and in a xenograft mouse model in vivo. Immunohistochemical analysis of 181 human lung adenocarcinomas specimens showed a significant correlation between RFPL3 and hTERT expression. The overexpression of RFPL3 was also associated significantly with lymph node metastasis. Univariate and multivariate Cox model analyses of NSCLC clinical specimens revealed a strong correlation between RFPL3 expression and overall survival. These results demonstrate that RFPL3 is an important cellular factor which promotes lung cancer growth by activating hTERT expression and may be a potential novel therapeutic target for lung cancer.

Telomerase activity: An attractive target for cancer therapeutics

Telomeres are non-coding tandem repeats of 1000-2000 TTAGGG nucleotide DNA sequences on the 3’ termini of human chromosomes where they serve as protective “caps” from degradation and loss of genes. The “cap” at the end of chromosome required to protect its integrity is a 150-200 nucleotide-long single stranded G-rich 3’ overhang that forms two higher order structures, a T-loop with Sheltering complex, or a G-quadruplex complex. Telomerase is a human ribonucleoprotein reverse transcriptase that continually added single stranded TTAGGG DNA sequences onto the single strand 3’ of telomere in the 5’ to 3’ direction. Telomerase activity is detected in male germ line cells, proliferative cells of renewal tissues, some adult pluripotent stem cells, embryonic cells, but in most somatic cells is not detected. Re-expression or up-regulation of telomerase in tumours cells is considered as a critical step in cell tumorigenesis and telomerase is widely considered as a tumour marker and a target for anticancer drugs. Different approaches have been used in anticancer therapeutics targeting telomerase. Telomerase inhibitors can block directly Human TElomerase Reverse Transcriptase (hTERT) or Human TElomerase RNA telomerase subunits activity, or G-quadruplex and Sheltering complex components, shortening telomeres and inhibiting cell proliferation. Telomerase can become an immune target and GV1001, Vx-001, I540 are the most widespread vaccines used with encouraging results. Another method is to use hTERT promoter to drive suicide gene expression or to control a lytic virus replication. Recently telomerase activity was used to activate pro-drugs such as Acycloguanosyl 5’-thymidyltriphosphate, a synthetic ACV-derived molecule when it is activated by telomerase it does not require any virus or host active immune response to induce suicide gene therapy. Advantage of all these therapies is that target only neoplastic cells without any effects in normal cells, avoiding toxicity and adverse effects of the current chemotherapy. However, as not all the approaches are equally efficient, further studies will be necessary.

Targeting unimolecular G-quadruplex nucleic acids: a new paradigm for the drug discovery?

INTRODUCTION

G-quadruplexes (G4s) are targets of great interest because of their roles in crucial biological processes, such as aging and cancer. G4s are based on the formation of G-quartets, stabilised by Hoogsteen-type hydrogen bonds and by interaction with cations between the tetrads. These biologically relevant conformations were first discovered in eukaryotic chromosomal telomeric DNA, but have also been found in the proximal location of promoters in a number of human genes. Therefore, the extensive analysis of an intriguing target could move towards the rational drug design of new selective anticancer agents.

AREAS COVERED

The authors review G4 structural characterisation, with detailed insight related to the polymorphism issue. The authors describe the topologically distinct G4 structural forms and the factors involved in their interconversion mechanisms, such as the sequence of the oligonucleotides, the strand stoichiometry and orientation, the syn-anti conformation of the guanine glycosidic bonds and the G4 loop types and the environmental factors. Furthermore, the authors report several studies related to folding and unfolding kinetic profiles in order to understand the conformational view of monomolecular G4 formations.

EXPERT OPINION

G4 unimolecular nucleic acids can be considered as valid targets for the rational drug development of novel anticancer agents. Structural biology represents an essential link between the biology and medicinal chemistry knowledge in this field. In silico methods have already been demonstrated to be useful, especially if well integrated with biophysical tests. If this proves successful, the G4-targeting paradigm could also be extended to drug discovery beyond neoplastic pathologies.

In vitro anti-telomerase activity of novel lycopene-loaded nanospheres in the human leukemia cell line K562

Background:

Lycopene, a plant carotenoid, has potent effects against the various types of cancer cells. To date, the effect of lycopene in the free and encapsulated forms on the telomerase activity in human leukemia cell line K562 have not been investigated. The aim of the present study was to prepare a novel lycopene-loaded nanosphere and compare its anti-telomearse activity in K562 cell line with those of free lycopene.

Materials and Methods:

The lycopene-loaded nanospheres were prepared by nanoprecipitation method. The lycopene entrapment efficacy was measured by high-performance liquid chromatography (HPLC) method. The anti-proliferation effect of the lycopene in the free and encapsulated forms in the different times (0-72 h) and the different doses (0-100 μg/ml) on K562 cell line was studied using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The changes of telomerase activity, following treatment with the lycopene in the free and encapsulated forms, were detected using the telomeric repeat amplification protocol-enzyme-linked immunosorbent assay.

Results:

The entrapment efficacy of lycopene was 78.5% ± 2. Treatment of the K562 cell line with lycopene, in particular in encapsulated form, resulted in a significant inhibition of the cell growth and increasing of percentage of apoptotic cells. It has also been observed that the telomerase activity in the lycopene-loaded nanospheres-treated cells was significantly inhibited in a dose and time-dependent manner.

Conclusion:

Our data suggest a novel mechanism in the anti-cancer activity of the lycopene, in particular in encapsulated form, and could be provided a basis for the future development of anti-telomerase therapies.

CPSF4 activates telomerase reverse transcriptase and predicts poor prognosis in human lung adenocarcinomas

The elevated expression and activation of human telomerase reverse transcriptase (hTERT) is associated with the unlimited proliferation of cancer cells. However, the excise mechanism of hTERT regulation during carcinogenesis is not well understood. In this study, we discovered cleavage and polyadenylation specific factor 4 (CPSF4) as a novel tumor-specific hTERT promoter-regulating protein in lung cancer cells and identified the roles of CPSF4 in regulating lung hTERT and lung cancer growth. The ectopic overexpression of CPSF4 upregulated the hTERT promoter-driven report gene expression and activated the endogenous hTERT mRNA and protein expression and the telomerase activity in lung cancer cells and normal lung cells. In contrast, the knockdown of CPSF4 by siRNA had the opposite effects. CPSF4 knockdown also significantly inhibited tumor cell growth in lung cancer cells in vitro and in a xenograft mouse model in vivo, and this inhibitory effect was partially mediated by decreasing the expression of hTERT. High expression of both CPSF4 and hTERT proteins were detected in lung adenocarcinoma cells by comparison with the normal lung cells. Tissue microarray immunohistochemical analysis of lung adenocarcinomas also revealed a strong positive correlation between the expression of CPSF4 and hTERT proteins. Moreover, Kaplan-Meier analysis showed that patients with high levels of CPSF4 and hTERT expression had a significantly shorter overall survival than those with low CPSF4 and hTERT expression levels. Collectively, these results demonstrate that CPSF4 plays a critical role in the regulation of hTERT expression and lung tumorigenesis and may be a new prognosis factor in lung adenocarcinomas.

hnRNP C1/C2 and Pur-beta proteins mediate induction of senescence by oligonucleotides homologous to the telomere overhang

Background

Experimental disruption of the telomere overhang induces a potent DNA damage response and is the target of newly emerging cancer therapeutics. Introduction of T-oligo, an eleven-base oligonucleotide homologous to the 3′-telomeric overhang, mimics telomere disruption and induces DNA damage responses through activation of p53, p73, p95/Nbs1, E2F1, pRb, and other DNA damage response proteins. ATM (ataxia telangiectasia mutated) was once thought to be the primary driver of T-oligo-induced DNA damage responses; however, recent experiments have highlighted other key proteins that may also play a significant role.

Methods

To identify proteins associated with T-oligo, MM-AN cells were treated with biotinylated T-oligo or complementary oligonucleotide, cell lysates were run on SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis), and the protein bands observed after treatment of cells with T-oligo or complementary oligonucleotide were analyzed using mass spectrometry. To study the effect of T-oligo on expression of hnRNP C1/C2 (heterogeneous nuclear ribonucleoprotein C1 and C2) and purine-rich element binding proteins (Pur proteins), cells were treated with T-oligo, and immunoblotting experiments were performed. To determine their role in senescence, cells were treated with shRNA (short hairpin ribonucleic acid) against these proteins, and senescence was studied using the senescence associated beta-galactosidase assay.

Results

Using mass spectrometry, RNA-binding hnRNP C1/C2 and DNA-binding Pur proteins were found to associate with T-oligo. hnRNP C1/C2 exhibited increased expression (3.6–12.0-fold) in non-small-cell lung cancer (NSCLC) and in melanoma cells (4.5–5.2-fold), and Pur proteins exhibited increased expression of 2.2-fold in NSCLC and 2.0-fold in melanoma cells after T-oligo treatment. Experimental knockdown of hnRNP C1/C2 and Pur-beta completely abrogated T-oligo induced senescence in both MU melanoma and H358 NSCLC cells. Additionally, knockdown of Pur-beta prevented T-oligo-induced phosphorylation of p53, hypophosphorylation of pRb, and upregulation of E2F1, p21, and p53.

Conclusion

These novel findings highlight proteins essential to T-oligo’s anticancer effects that may be of interest in telomere biology and cancer therapeutics.

Silencing tankyrase and telomerase promotes A549 human lung adenocarcinoma cell apoptosis and inhibits proliferation

Telomeres are the end structures of chromosomes in mammalian cells; they play a pivotal role in maintaining the stability of the chromosome and become shorter with each cell division. However, several types of tumor cells express telomerase in very high levels to overcome this crisis and achieve the ability to proliferate endlessly. The telomerase inhibitors can partly inhibit tumor cell proliferation and promote apoptosis, but their roles are only limited. Tankyrase is a poly(ADP-ribose) polymerase which has synergistic effect on telomerase, and is expressed in lung cancer cells in high levels. In the present study, antisense oligonucleotides of telomerase (ashTERT) and tankyrase (asTANKS) were used as specific inhibitors to silence the expression of target genes in A549 human lung adenocarcinoma cells by transfection. The results showed that ashTERT and asTANKS suppressed the expression of telomerase and tankyrase significantly; both inhibited the activity of telomerase and the combination group achieved better effect, but only ashTERT shortened the length of telomeres, asTANKS did not. Further studies showed that ashTERT and asTANKS-promoted A549 apoptosis was not mediated by downregulation of the expression of the anti-apoptotic gene BCL-2 or upregulation of the expression of the pro-apoptotic gene BAX, but by adjusting the two isoforms proportion of myeloid cell leukemia-1 (MCL-1) which can interact with tankyrase directly. MCL-1short (MCL-1S), a pro-apoptotic gene, increased more than MCL-1Long (MCL-1L) which is an anti-apoptotic gene, leading to A549 cell apoptosis and a similar result was obtained in nude mice in vivo. The present study suggests that combination of the inhibitors of telomerase and tankyrase can be used as a strategy for the treatment of lung cancer in humans.

The antiretroviral agent saquinavir enhances hTERT expression and telomerase activity in human T leukaemia cells in vitro

BACKGROUND

Saquinavir, a protease inhibitor utilized in HIV infection, shows antitumor activity in various experimental models. In previous studies performed in our laboratory the drug was found to induce a substantial increase of telomerase activity in normal peripheral blood mononuclear cells. Aim of the present investigation was to test whether saquinavir was able to increase telomerase activity and the expression of the catalytic subunit of telomerase, hTERT, in human malignant hematopoietic cells.

METHODS

Human Jurkat CD4+ T cell leukaemia cell line was used throughout the present study. The antiproliferative effect of saquinavir was tested by the MTT assay. Telomerase activity was determined according to the telomeric repeat amplification protocol. The expression of hTERT mRNA was semi-quantitative evaluated by RT-PCR amplification and quantitative Real Time PCR. The binding of the transcription factor c-Myc to its specific E-Box DNA binding-site of hTERT promoter was analyzed by Electophoretic Mobility Shift Assay (EMSA). The amount of c-Myc in cytoplasm and nucleus of leukemia cells was determined by Western Blot analysis, and c-Myc down-regulation was obtained by siRNA transfection.

RESULTS

Saquinavir produced a substantial increase of telomerase activity in Jurkat cells in vitro without increasing but rather reducing target cell proliferation rate. Telomerase up-regulation appeared to be the result of enhanced expression of hTERT. Saquinavir-mediated up-regulation of hTERT gene was the result of the increased binding of proteins to the E-Box sequence of the promoter. Moreover, saquinavir amplified the expression of c-Myc especially in the nuclear cell fraction. The direct influence of saquinavir on this transcription factor was also demonstrated by the antagonistic effect of the drug on siRNA induced c-Myc suppression. Since c-Myc is the main responsible for hTERT transcription, these findings suggest that the main mechanism underlying saquinavir-induced telomerase activation is mediated by c-Myc up-regulation.

CONCLUSIONS

Saquinavir augments hTERT expression while inhibiting leukemic cell growth. Experimental evidences show that this effect is mediated by saquinavir-influenced increase of c-Myc levels. This could have relevance in terms of enhanced hTERT-dependent tumor cell immunogenicity and suggests new paharmacological approaches interfering with c-Myc dependent pathways.

Early growth response protein-1 promoter-mediated synergistic antitumor effect of hTERTC27 gene therapy and 5-Flurorouracil on nasopharyngeal carcinoma

hTERTC27 is a newly constructed polypeptide that can induce telomere dysfunction. To study the synergistic antitumor effects of the hTERTC27 polypeptide driven by the early growth response protein-1 (Egr-1) promoter and chemotherapeutic 5-flurorouracil (5-FU) on nasopharyngeal carcinoma, a series of in vitro and in vivo experiments were performed. The results showed that hTERTC27 expression was significantly increased up to 7.21-folds by the 5-FU-activated Egr-1 promoter in C666-1 cells. Overexpressed hTERTC27 made the cells more sensitive to 5-FU, and additionally, inhibited cell proliferation about 20.41%. Combinational therapy of overexpressed hTERTC27 driven by the 5-FU-activated Egr-1 promoter and 5-FU synergistically inhibited cell proliferation and promoted apoptosis of C666-1 cells for about 4.75-fold and 1.76-fold in comparison with a sole therapy of hTERTC27 or 5-FU in vitro. In vivo experiments showed that overexpressed hTERTC27 driven by 5-FU-activated Egr-1 promoter and 5-FU synergistically reduced tumor volume, tumor weight, and local infiltration, which may be relative to tumor cell apoptosis. These results suggest that combinational therapy of overexpressed hTERTC27, which is driven by the 5-FU-activated Egr-1 promoter, and 5-FU may provide a novel approach to treat nasopharyngeal cancer.

Novel anticancer therapeutics targeting telomerase

Telomeres are protective caps at the ends of human chromosomes. Telomeres shorten with each successive cell division in normal human cells whereas, in tumors, they are continuously elongated by human telomerase reverse transcriptase (hTERT). Telomerase is overexpressed in 80-95% of cancers and is present in very low levels or is almost undetectable in normal cells. Because telomerase plays a pivotal role in cancer cell growth it may serve as an ideal target for anticancer therapeutics. Inhibition of telomerase may lead to a decrease of telomere length resulting in cell senescence and apoptosis in telomerase positive tumors. Several strategies of telomerase inhibition are reviewed, including small molecule inhibitors, antisense oligonucleotides, immunotherapies and gene therapies, targeting the hTERT or the ribonucleoprotein subunit hTER. G-quadruplex stabilizers, tankyrase and HSP90 inhibitors targeting telomere and telomerase assembly, and T-oligo approach are also covered. Based on this review, the most promising current telomerase targeting therapeutics are the antisense oligonucleotide inhibitor GRN163L and immunotherapies that use dendritic cells (GRVAC1), hTERT peptide (GV1001) or cryptic peptides (Vx-001). Most of these agents have entered phase I and II clinical trials in patients with various tumors, and have shown good response rates as evidenced by a reduction in tumor cell growth, increased overall disease survival, disease stabilization in advanced staged tumors and complete/partial responses. Most therapeutics have shown to be more effective when used in combination with standard therapies, resulting in concomitant telomere shortening and tumor mass shrinkage, as well as preventing tumor relapse and resistance to single agent therapy.

Prospects for rejuvenation of aged tissue by telomerase reactivation

Human aging is associated with loss of tissue homeostasis and a greatly elevated risk of debilitating disease, with associated costs in terms of diminished quality of life for the individual and financial burdens on health-care providers. Any advances that hold out the realistic prospect of tackling age-related morbidity are therefore to be welcomed. The recent report by Jeskelioff et al. published in 2010 that telomerase reactivation in adult male mice can not only halt but actually reverse significant tissue pathologies provides a long-awaited proof of principle that it is possible to rejuvenate aged tissues. This review assesses the impact of this new work and considers possible problems and potential benefits of telomerase activation as a therapy to tackle the morbidities associated with human aging.

Telomerase-specific GV1001 peptide vaccination fails to induce objective tumor response in patients with cutaneous T cell lymphoma

BACKGROUND

There is currently no curative therapy for cutaneous T cell lymphoma (CTCL). New therapies are therefore needed. Telomerase, the enzyme that allows for unrestricted cell divisions of cancer cells, is a promising target for cancer therapy. The telomerase-specific peptide vaccination GV1001 has shown promising results in previous studies. Since telomerase is expressed in malignant cells of CTCL, GV1001 vaccination in CTCL is a promising new therapeutic approach.

OBJECTIVE

We sought to investigate the efficacy of GV1001 vaccination in CTCL patients and characterize the induced immune response.

METHODS

Six CTCL patients were vaccinated with the GV-peptide using granulocyte/macrophage colony-stimulating factor as adjuvant. Objective clinical response and the T cell response were assessed.

RESULTS

None of the patients demonstrated objective clinical response to the vaccination whereas one patient showed disease progression. 1/6 patients acquired a GV1001-specifc T cell response with a Th1 cytokine profile and expression of skin-homing receptors. This hTERT-specific T cell response was not associated with beneficial modulation of the tumor-infiltrating leukocytes. Furthermore, removal of regulatory T cells did not enhance responsiveness to GV1001 in vitro in any of the patients analyzed.

CONCLUSIONS

Our results suggest that the GV1001 vaccination is not effective in CTCL patients and disease progression in 1/6 patients raises concerns about its safety. By analyzing skin-homing properties of GV1001-specific T cells and the involvement of regulatory T cells we nevertheless provide insight into vaccine-induced immune responses which may help to improve vaccine strategies in CTCL.