Telomeric DNA induces apoptosis and senescence of human breast carcinoma cells

Low-power red laser and blue LED modulate telomere maintenance and length in human breast cancer cells

Cancer cells have the ability to undergo an unlimited number of cell divisions, which gives them immortality. Thus, the cancer cell can extend the length of its telomeres, allowing these cells to divide unlimitedly and avoid entering the state of senescence or cellular apoptosis. One of the main effects of photobiomodulation (PBM) is the increase in the production of adenosine triphosphate (ATP) and free radicals, mainly reactive oxygen species (ROS). Existent data indicates that high levels of ROS can cause shortening and dysfunctional telomeres. Therefore, a better understanding of the effects induced by PBM on cancer cell telomere maintenance is needed. This work aimed to evaluate the effects of low-power red laser (658 nm) and blue LED (470 nm) on the TRF1 and TRF2 mRNA levels and telomere length in human breast cancer cells. MCF-7 and MDA-MB-231 cells were irradiated with a low-power red laser (69 J cm-2, 0.77 W/cm-2) and blue LED (482 J cm-2, 5.35 W/cm-2), alone or in combination, and the relative mRNA levels of the genes and telomere length were assessed by quantitative reverse transcription polymerase chain reaction. The results suggested that exposure to certain red laser and blue LED fluences decreased the TRF1 and TRF2 mRNA levels in both human breast cancer cells. Telomere length was increased in MCF-7 cells after exposure to red laser and blue LED. However, telomere length in MDA-MB-231 was shortened after exposure to red laser and blue LED at fluences evaluated. Our research suggests that photobiomodulation induced by red laser and low-power blue LED could alter telomere maintenance and length.

Targeting telomerase utilizing zeolitic imidazole frameworks as non-viral gene delivery agents across different cancer cell types

Telomerase, a ribonucleoprotein coded by the hTERT gene, plays an important role in cellular immortalization and carcinogenesis. hTERT is a suitable target for cancer therapeutics as its activity is highly upregulated in most of cancer cells but absent in normal somatic cells. Here, by employing the two Metal-Organic Frameworks (MOFs), viz. ZIF-C and ZIF-8, based biomineralization we encapsulate Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9 plasmid system that targets hTERT gene (CrhTERT) in cancer cells. When comparing the two biocomposites, ZIF-C shows the better loading capacity and cell viability. The loaded plasmid in ZIF-C is highly protected against enzymatic degradation. CrhTERT@ZIF-C is efficiently endocytosed by cancer cells and the subcellular release of CrhTERT leads to telomerase knockdown. The resultant inhibition of hTERT expression decreases cellular proliferation and causing cancer cell death. Furthermore, hTERT knockdown shows a significant reduction in tumour metastasis and alters protein expression. Collectively we show the high potential of ZIF-C-based biocomposites as a promising general tool for gene therapy of different types of cancers.

The Role of Telomerase in Breast Cancer's Response to Therapy

Currently, breast cancer appears to be the most widespread cancer in the world and the most common cause of cancer deaths. This specific type of cancer affects women in both developed and developing countries. Prevention and early diagnosis are very important factors for good prognosis. A characteristic feature of cancer cells is the ability of unlimited cell division, which makes them immortal. Telomeres, which are shortened with each cell division in normal cells, are rebuilt in cancer cells by the enzyme telomerase, which is expressed in more than 85% of cancers (up to 100% of adenocarcinomas, including breast cancer). Telomerase may have different functions that are related to telomeres or unrelated. It has been shown that high activity of the enzyme in cancer cells is associated with poor cell sensitivity to therapies. Therefore, telomerase has become a potential target for cancer therapies. The low efficacy of therapies has resulted in the search for new combined and more effective therapeutic methods, including the involvement of telomerase inhibitors and telomerase-targeted immunotherapy.

Shelterin complex gene: Prognosis and therapeutic vulnerability in cancer

Telomere encompasses a (TTAGGG)n tandem repeats, and its dysfunction has emerged as the epicenter of driving carcinogenesis by promoting genetic instability. Indeed, they play an essential role in stabilizing chromosomes and therefore protecting them from end-to-end fusion and DNA degradation. Telomere length homeostasis is regulated by several key players including shelterin complex genes, telomerase, and various other regulators. Targeting these regulatory players can be a good approach to combat cancer as telomere length is increasingly correlated with cancer initiation and progression. In this review, we have aimed to describe the telomere length regulator's role in prognostic significance and important drug targets in breast cancer. Moreover, we also assessed alteration in telomeric function by various telomere length regulators and compares this to the regulatory mechanisms that can be associated with clinical biomarkers in cancer. Using publicly available software we summarized mutational and CpG island prediction analysis of the TERT gene breast cancer patient database. Studies have reported that the TERT gene has prognostic significance in breast cancer progression however mechanistic approaches are not defined yet. Interestingly, we reported using the UCSC Xena web-based tool, we confirmed a positive correlation of shelterin complex genes TERF1 and TERF2 in recurrent free survival, indicating the critical role of these genes in breast cancer prognosis. Moreover, the epigenetic landscape of DNA damage repair genes in different breast cancer subtypes also being analyzed using the UCSC Xena database. Together, these datasets provide a comprehensive resource for shelterin complex gene profiles and define epigenetic landscapes of DNA damage repair genes which reveals the key role of shelterin complex genes in breast cancer with the potential to identify novel and actionable targets for treatment.

SPT6 recruits SND1 to co-activate human telomerase reverse transcriptase to promote colon cancer progression

Human telomerase reverse transcriptase (hTERT) plays an extremely important role in cancer initiation and development, including colorectal cancer (CRC). However, the precise upstream regulatory mechanisms of hTERT in different cancer types remain poorly understood. Here, we uncovered the candidate transcriptional factor of hTERT in CRC and explored its role and the corresponding molecular mechanisms in regulating hTERT expression and CRC survival with an aim of developing mechanism-based combinational targeting therapy. The possible binding proteins at the hTERT promoter were uncovered using pull-down/mass spectrometry analysis. The regulation of SPT6 on hTERT expression and CRC survival was evaluated in human CRC cell lines and mouse models. Mechanistic studies focusing on the synergy between SPT6 and staphylococcal nuclease and Tudor domain containing 1 (SND1) in controlling hTERT expression and CRC progression were conducted also in the above two levels. The expression correlation and clinical significance of SPT6, SND1, and hTERT were investigated in tumor tissues from murine models and patients with CRC in situ. SPT6 was identified as a possible transcriptional factor to bind to the hTERT promoter. SPT6 knockdown decreased the activity of hTERT promoter, downregulated the protein expression level of hTERT, suppressed proliferation, invasion, and stem-like properties, promoted apoptosis induction, and enhanced chemotherapeutic drug sensitivity in vitro. SPT6 silencing also led to the delay of tumor growth and metastasis in mice carrying xenografts of human-derived colon cancer cells. Mechanistically, SND1 interacted with SPT6 to co-control hTERT expression and CRC cell proliferation, stemness, and growth in vitro and in vivo. SPT6, SND1, and hTERT were highly expressed simultaneously in CRC tissues, both from the murine model and patients with CRC in situ, and pairwise expression among these three factors showed a significant positive correlation. In brief, our research demonstrated that SPT6 synergized with SND1 to promote CRC development by targeting hTERT and put forward that inhibiting the SPT6-SND1-hTERT axis may create a therapeutic vulnerability in CRC.

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.

Aloe emodin inhibits telomerase activity in breast cancer cells: transcriptional and enzymological mechanism

BACKGROUND

Telomerase plays an essential role in cancer cell proliferation. In this study, we investigated inhibition mechanism of aloe emodin (AE) on three different types of breast cancer cell lines, MDA-MB-453, MDA-MB-231 and MCF-7.

METHODS

The cells were treated with different concentrations of AE. Relative length of telomere and human telomerase reverse-transcriptase (hTERT) mRNA level was analyzed by quantitative PCR (qPCR). Protein level was assayed by Western blot. Sodium bisulfite methylation sequencing was performed to assess the methylation status of gene promoter. Enzymology kinetics was applied to reveal the interaction between AE and telomerase. Ultraviolet-visible titration and fluorescence resonance energy transfer (FRET) melting experiment were carried out to study the interaction between AE and telomeric DNA.

RESULTS

Continuous AE exposure of these cells for 48 h results in shortening of telomeres and inhibition of telomerase. The transcription of hTERT was repressed by activation of E2F1 and inactivation of c-myc proteins. Significant demethylation of CpG islands in hTERT gene promoter was observed in MDA-MB-453 and MCF-7 cells. AE competed with dNTP for occupation of the enzyme active site. AE was a telomeric G-quadruplex structure stabilizer as indicated by titration test and FRET experiments.

CONCLUSIONS

AE was a competitive inhibitor of telomerase and a G-quadruplex structure stabilizer. AE decreased the transcription of hTERT gene in the three breast cancer cell lines via up-regulation E2F1 and down-regulation c-myc expressions. The suppressed transcription was also related to the demethylation of the gene promoter.

Structural Features of Nucleoprotein CST/Shelterin Complex Involved in the Telomere Maintenance and Its Association with Disease Mutations

Telomere comprises the ends of eukaryotic linear chromosomes and is composed of G-rich (TTAGGG) tandem repeats which play an important role in maintaining genome stability, premature aging and onsets of many diseases. Majority of the telomere are replicated by conventional DNA replication, and only the last bit of the lagging strand is synthesized by telomerase (a reverse transcriptase). In addition to replication, telomere maintenance is principally carried out by two key complexes known as shelterin (TRF1, TRF2, TIN2, RAP1, POT1, and TPP1) and CST (CDC13/CTC1, STN1, and TEN1). Shelterin protects the telomere from DNA damage response (DDR) and regulates telomere length by telomerase; while, CST govern the extension of telomere by telomerase and C strand fill-in synthesis. We have investigated both structural and biochemical features of shelterin and CST complexes to get a clear understanding of their importance in the telomere maintenance. Further, we have analyzed ~115 clinically important mutations in both of the complexes. Association of such mutations with specific cellular fault unveils the importance of shelterin and CST complexes in the maintenance of genome stability. A possibility of targeting shelterin and CST by small molecule inhibitors is further investigated towards the therapeutic management of associated diseases. Overall, this review provides a possible direction to understand the mechanisms of telomere borne diseases, and their therapeutic intervention.

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.

Ultrastructural analysis of the Krebs-2 ascites cancer cells treated with extracellular double-stranded DNA preparation

Electron-microscopic analysis of the ultrastructure of the Krebs-2 carcinoma ascites cells in the first 90 min immediately after their exposure to fragmented double-stranded DNA has been performed. Morphological attributes of the treated cancer cells indicate the induction in these cells of destructive processes of presumably apoptotic type. The predominance of dystrophic-destructive changes in cells after the addition of DNA is supposed to be a consequence of the disturbance in metabolic processes caused by the experimental action.

Oligonucleotides Targeting Telomeres and Telomerase in Cancer

Telomeres and telomerase have become attractive targets for the development of anticancer therapeutics due to their involvement in cancer cell immortality. Currently, several therapeutics have been developed that directly target telomerase and telomeres, such as telomerase inhibitors and G-quadruplex stabilizing ligands. Telomere-specific oligonucleotides that reduce telomerase activity and disrupt telomere architecture are also in development as novel anticancer therapeutics. Specifically, GRN163L and T-oligos have demonstrated promising anticancer activity in multiple cancers types via induction of potent DNA damage responses. Currently, several miRNAs have been implicated in the regulation of telomerase activity and may prove to be valuable targets in the development of novel therapies by reducing expression of telomerase subunits. Targeting miRNAs that are known to increase expression of telomerase subunits may be another strategy to reduce carcinogenesis. This review aims to provide a comprehensive understanding of current oligonucleotide-based anticancer therapies that target telomeres and telomerase. These studies may help design novel therapeutic approaches to overcome the challenges of oligonucleotide therapy in a clinical setting.

Mechanism of Action of G-Quadruplex-Forming Oligonucleotide Homologous to the Telomere Overhang in Melanoma

T-oligo, a guanine-rich oligonucleotide homologous to the 3'-telomeric overhang of telomeres, elicits potent DNA-damage responses in melanoma cells; however, its mechanism of action is largely unknown. Guanine-rich oligonucleotides can form G-quadruplexes (G4), which are stabilized by the hydrogen bonding of guanine residues. In this study, we confirmed the G4-forming capabilities of T-oligo using nondenaturing PAGE, nuclear magnetic resonance, and immunofluorescence. Using an anti-G-quadruplex antibody, we showed that T-oligo can form G4 in the nuclei of melanoma cells. Furthermore, using DNase I in a nuclease degradation assay, G4-T-oligo was found to be more stable than single-stranded T-oligo. G4-T-oligo had decreased antiproliferative effects compared with single-stranded T-oligo. However, G4-T-oligo has similar cellular uptake as single-stranded T-oligo, as shown by FACS analysis. Inhibition of JNK, which causes DNA damage-induced apoptosis, partially reversed the antiproliferative activity of T-oligo. T-oligo also inhibited mRNA expression of human telomerase reverse transcriptase, a catalytic subunit of telomerase that was reversed by JNK inhibition. Furthermore, two shelterin complex proteins TRF2/POT1 were found to be up-regulated and bound by T-oligo, suggesting that T-oligo may mediate dissociation of these proteins from the telomere overhang. These studies show that T-oligo can form a G-quadruplex and that the antitumor effects of T-oligo may be mediated through POT1/TRF2 and via human telomerase reverse transcriptase inhibition through JNK activation.

Epithelial cell senescence: an adaptive response to pre-carcinogenic stresses?

Senescence is a cell state occurring in vitro and in vivo after successive replication cycles and/or upon exposition to various stressors. It is characterized by a strong cell cycle arrest associated with several molecular, metabolic and morphologic changes. The accumulation of senescent cells in tissues and organs with time plays a role in organismal aging and in several age-associated disorders and pathologies. Moreover, several therapeutic interventions are able to prematurely induce senescence. It is, therefore, tremendously important to characterize in-depth, the mechanisms by which senescence is induced, as well as the precise properties of senescent cells. For historical reasons, senescence is often studied with fibroblast models. Other cell types, however, much more relevant regarding the structure and function of vital organs and/or regarding pathologies, are regrettably often neglected. In this article, we will clarify what is known on senescence of epithelial cells and highlight what distinguishes it from, and what makes it like, replicative senescence of fibroblasts taken as a standard.

Telomerase and drug resistance in cancer

It is well known that a decreased expression or inhibited activity of telomerase in cancer cells is accompanied by an increased sensitivity to some drugs (e.g., doxorubicin, cisplatin, or 5-fluorouracil). However, the mechanism of the resistance resulting from telomerase alteration remains elusive. There are theories claiming that it might be associated with telomere shortening, genome instability, hTERT translocation, mitochondria functioning modulation, or even alterations in ABC family gene expression. However, association of those mechanisms, i.e., drug resistance and telomerase alterations, is not fully understood yet. We review the current theories on the aspect of the role of telomerase in cancer cells resistance to therapy. We believe that revealing/unravelling this correlation might significantly contribute to an increased efficiency of cancer cells elimination, especially the most difficult ones, i.e., drug resistant.

Targeting telomerase and telomeres to enhance ionizing radiation effects in in vitro and in vivo cancer models

One of the hallmarks of cancer consists in the ability of tumor cells to divide indefinitely, and to maintain stable telomere lengths throughout the activation of specific telomere maintenance mechanisms (TMM). Therefore in the last fifteen years, researchers proposed to target telomerase or telomeric structure in order to block limitless replicative potential of cancer cells providing a fascinating strategy for a broad-spectrum cancer therapy. In the present review, we report in vitro and in vivo evidence regarding the use of chemical agents targeting both telomerase or telomere structure and showing promising antitumor effects when used in combination with ionizing radiation (IR). RNA interference, antisense oligonucleotides (e.g., GRN163L), non-nucleoside inhibitors (e.g., BIBR1532) and nucleoside analogs (e.g., AZT) represent some of the most potent strategies to inhibit telomerase activity used in combination with IR. Furthermore, radiosensitizing effects were demonstrated also for agents acting directly on the telomeric structure such as G4-ligands (e.g., RHPS4 and Telomestatin) or telomeric-oligos (T-oligos). To date, some of these compounds are under clinical evaluation (e.g., GRN163L and KML001). Advantages of Telomere/Telomerase Targeting Compounds (T/TTCs) coupled with radiotherapy may be relevant in the treatment of radioresistant tumors and in the development of new optimized treatment plans with reduced dose adsorbed by patients and consequent attenuation of short- end long-term side effects. Pros and cons of possible future applications in cancer therapy based on the combination of T/TCCs and radiation treatment are discussed.

Treating Cancer by Targeting Telomeres and Telomerase

Telomerase is expressed in more than 85% of cancer cells. Tumor cells with metastatic potential may have a high telomerase activity, allowing cells to escape from the inhibition of cell proliferation due to shortened telomeres. Human telomerase primarily consists of two main components: hTERT, a catalytic subunit, and hTR, an RNA template whose sequence is complimentary to the telomeric 5′-dTTAGGG-3′ repeat. In humans, telomerase activity is typically restricted to renewing tissues, such as germ cells and stem cells, and is generally absent in normal cells. While hTR is constitutively expressed in most tissue types, hTERT expression levels are low enough that telomere length cannot be maintained, which sets a proliferative lifespan on normal cells. However, in the majority of cancers, telomerase maintains stable telomere length, thereby conferring cell immortality. Levels of hTERT mRNA are directly related to telomerase activity, thereby making it a more suitable therapeutic target than hTR. Recent data suggests that stabilization of telomeric G-quadruplexes may act to indirectly inhibit telomerase action by blocking hTR binding. Telomeric DNA has the propensity to spontaneously form intramolecular G-quadruplexes, four-stranded DNA secondary structures that are stabilized by the stacking of guanine residues in a planar arrangement. The functional roles of telomeric G-quadruplexes are not completely understood, but recent evidence suggests that they can stall the replication fork during DNA synthesis and inhibit telomere replication by preventing telomerase and related proteins from binding to the telomere. Long-term treatment with G-quadruplex stabilizers induces a gradual reduction in the length of the G-rich 3’ end of the telomere without a reduction of the total telomere length, suggesting that telomerase activity is inhibited. However, inhibition of telomerase, either directly or indirectly, has shown only moderate success in cancer patients. Another promising approach of targeting the telomere is the use of guanine-rich oligonucleotides (GROs) homologous to the 3’ telomere overhang sequence (T-oligos). T-oligos, particularly a specific 11-base oligonucleotide (5’-dGTTAGGGTTAG-3’) called T11, have been shown to induce DNA damage responses (DDRs) such as senescence, apoptosis, and cell cycle arrest in numerous cancer cell types with minimal or no cytostatic effects in normal, non-transformed cells. As a result, T-oligos and other GROs are being investigated as prospective anticancer therapeutics. Interestingly, the DDRs induced by T-oligos in cancer cells are similar to the effects seen after progressive telomere degradation in normal cells. The loss of telomeres is an important tumor suppressor mechanism that is commonly absent in transformed malignant cells, and hence, T-oligos have garnered significant interest as a novel strategy to combat cancer. However, little is known about their mechanism of action. In this review, we discuss the current understanding of how T-oligos exert their antiproliferative effects in cancer cells and their role in inhibition of telomerase. We also discuss the current understanding of telomerase in cancer and various therapeutic targets related to the telomeres and telomerase.

Positive and negative effects of cellular senescence during female reproductive aging and pregnancy

Cellular senescence is a phenomenon occurring when cells are no longer able to divide even after treatment with growth stimuli. Because senescent cells are typically associated with aging and age-related diseases, cellular senescence is hypothesized to contribute to the age-related decline in reproductive function. However, some data suggest that senescent cells may also be important for normal physiological functions during pregnancy. Herein, we review the positive and negative effects of cellular senescence on female reproductive aging and pregnancy. We discuss how senescent cells accelerate female reproductive aging by promoting the decline in the number of ovarian follicles and increasing complications during pregnancy. We also describe how cellular senescence plays an important role in placental and fetal development as a beneficial process, ensuring proper homeostasis during pregnancy.

Telomere and Telomerase Therapeutics in Cancer

Telomerase is a reverse transcriptase capable of utilizing an integrated RNA component as a template to add protective tandem telomeric single strand DNA repeats, TTAGGG, to the ends of chromosomes. Telomere dysfunction and telomerase reactivation are observed in approximately 90% of human cancers; hence, telomerase activation plays a unique role as a nearly universal step on the path to malignancy. In the past two decades, multiple telomerase targeting therapeutic strategies have been pursued, including direct telomerase inhibition, telomerase interference, hTERT or hTERC promoter driven therapy, telomere-based approaches, and telomerase vaccines. Many of these strategies have entered clinical development, and some have now advanced to phase III clinical trials. In the coming years, one or more of these new telomerase-targeting drugs may be expected to enter the pharmacopeia of standard care. Here, we briefly review the molecular functions of telomerase in cancer and provide an update about the preclinical and clinical development of telomerase targeting therapeutics.

Apoptosis or senescence? Which exit route do epithelial cells and fibroblasts preferentially follow?

Senescence and apoptosis constitute types of cellular responses that normally ensure homeostasis, when endogenous or exogenous signals occur. Their deregulation is often observed in various pathologies, such as age and non-age related diseases including cancer. Although epithelial cells and fibroblasts are capable to exert both functions, under a plethora of insults, the fact that they exhibit notable intrinsic differences in cell/tissue homeostasis properties, might be a crucial determinant of the mode of response to a certain stress signal. Sparse evidence in the literature reveals that in the same tissue/organ context and under the same conditions, the cell type seems to drive the differential counteraction between epithelia and fibroblasts. Based on the above notion we propose that, upon stress insults, human fibroblasts seem to predominantly respond via senescence, while epithelial cells prefer to exert apoptosis. We suggest that considering the tissue as a whole (epithelium and stroma) would benefit research into new therapeutic strategies for chronic diseases and cancer.

Telomere Fragment Induced Amnion Cell Senescence: A Contributor to Parturition?

Oxidative stress (OS)-induced senescence of the amniochorion has been associated with parturition at term. We investigated whether telomere fragments shed into the amniotic fluid (AF) correlated with labor status and tested if exogenous telomere fragments (T-oligos) could induce human and murine amnion cell senescence. In a cross-sectional clinical study, AF telomere fragment concentrations quantitated by a validated real-time PCR assay were higher in women in labor at term compared to those not in labor. In vitro treatment of primary human amnion epithelial cells with 40 μM T-oligos ([TTAGGG]₂) that mimic telomere fragments, activated p38MAPK, produced senescence-associated (SA) β-gal staining and increased interleukin (IL)-6 and IL-8 production compared to cells treated with complementary DNA sequences (Cont-oligos, [AATCCC]₂). T-oligos injected into the uteri of pregnant CD1 mice on day 14 of gestation, led to increased p38MAPK, SA-β-gal (SA β-gal) staining in murine amniotic sacs and higher AF IL-8 levels on day 18, compared to saline treated controls. In summary, term labor AF samples had higher telomere fragments than term not in labor AF. In vitro and in situ telomere fragments increased human and murine amnion p38MAPK, senescence and inflammatory cytokines. We propose that telomere fragments released from senescent fetal cells are indicative of fetal cell aging. Based on our data, these telomere fragments cause oxidative stress associated damages to the term amniotic sac and force them to release other DAMPS, which, in turn, provide a sterile immune response that may be one of the many inflammatory signals required to initiate parturition at term.

Cytotoxicity of guanine-based degradation products contributes to the antiproliferative activity of guanine-rich oligonucleotides

Guanine-rich oligonucleotides with lower nuclease resistance exhibited higher antiproliferative activity; guanine-based compounds showed highly concentration-dependent cytotoxicity.

Guanine-rich oligonucleotides (GROs) have attracted considerable attention as anticancer agents, because they exhibit cancer-selective antiproliferative activity and can form G-quadruplex structures with higher nuclease resistance and cellular uptake. Recently, a GRO, AS1411 has reached phase II clinical trials for acute myeloid leukemia and renal cell carcinoma. The antiproliferative activity of GROs has been associated with various protein targets; however the real mechanisms of action remain unclear. In this study, we showed evidence that antiproliferative activity of GROs (including AS1411) is mainly contributed by the cytotoxicity of their guanine-based degradation products, such as monophosphate deoxyguanosine (dGMP), deoxyguanosine (dG) and guanine. The GROs with lower nuclease resistance exhibited higher antiproliferative activity. Among nucleotides, nucleosides and nucleobases, only guanine-based compounds showed highly concentration-dependent cytotoxicity. Our results suggest that it is necessary to reconsider the cancer-selective antiproliferative activity of GROs. Since guanine-based compounds are endogenous substances in living organisms, systematic studies of the cytotoxicity of these compounds will provide new information for the understanding of certain diseases and offer useful information for drug design.

Star-shaped tetraspermine enhances cellular uptake and cytotoxicity of T-oligo in prostate cancer cells

PURPOSE

An oligonucleotide termed 'T-oligo' having sequence homology with telomere overhang has shown cytotoxicity in multiple cancers. We have demonstrated that T-oligo can induce apoptosis in androgen independent prostate cancer cell line DU-145. In this report, we evaluate the use of star-shaped tetraspermine (SSTS) for delivery of T-oligo.

METHODS

SSTS was synthesized from spermine and its intrinsic cytotoxicity towards DU-145 cells was compared with spermine and branched polyethyleneimine (bPEI). Atomistic molecular dynamic (MD) simulations were conducted to understand binding and complexation of spermine and SSTS with T-oligo. Complexation was also determined using gel electrophoresis and SYBR gold assay. Complexes were characterized for size, cellular uptake and antiproliferative effect.

RESULTS

SSTS exhibited significantly lower toxicity than spermine and bPEI. Its affinity towards T-oligo was significantly higher than spermine as determined by experimental studies and confirmed by MD simulations and it formed stable complexes (TONPs) with T-oligo. TONPs facilitated cellular uptake and nuclear accumulation of T-oligo and their cytotoxic potential was observed at concentration several folds lower than that required for T-oligo alone.

CONCLUSION

SSTS significantly enhanced therapeutic benefits associated with the use of T-oligo and can be developed as a delivery vehicle for its in-vivo therapeutic applications.

T-oligo as an anticancer agent in colorectal cancer

In the United States, there will be an estimated 96,830 new cases of colorectal cancer (CRC) and 50,310 deaths in 2014. CRC is often detected at late stages of the disease, at which point there is no effective chemotherapy. Thus, there is an urgent need for effective novel therapies that have minimal effects on normal cells. T-oligo, an oligonucleotide homologous to the 3'-telomere overhang, induces potent DNA damage responses in multiple malignant cell types, however, its efficacy in CRC has not been studied. This is the first investigation demonstrating T-oligo-induced anticancer effects in two CRC cell lines, HT-29 and LoVo, which are highly resistant to conventional chemotherapies. In this investigation, we show that T-oligo may mediate its DNA damage responses through the p53/p73 pathway, thereby inhibiting cellular proliferation and inducing apoptosis or senescence. Additionally, upregulation of downstream DNA damage response proteins, including E2F1, p53 or p73, was observed. In LoVo cells, T-oligo induced senescence, decreased clonogenicity, and increased expression of senescence associated proteins p21, p27, and p53. In addition, downregulation of POT1 and TRF2, two components of the shelterin protein complex which protects telomeric ends, was observed. Moreover, we studied the antiproliferative effects of T-oligo in combination with an EGFR tyrosine kinase inhibitor, Gefitinib, which resulted in an additive inhibitory effect on cellular proliferation. Collectively, these data provide evidence that T-oligo alone, or in combination with other molecularly targeted therapies, has potential as an anti-cancer agent in CRC.

Mechanism of DNA damage responses induced by exposure to an oligonucleotide homologous to the telomere overhang in melanoma

T-oligo, an 11-base oligonucleotide homologous to the 3'-telomeric overhang, is a novel, potent therapeutic modality in melanoma and multiple other tumor types. T-oligo is proposed to function in a manner similar to experimental disruption of the telomere overhang and induces DNA damage responses including apoptosis, differentiation and senescence. However, important components involved in T-oligo induced responses are not defined, particularly the role of p53, TRF1 and TRF2 in mediating the T-oligo induced responses. In MU, PM-WK, and MM-MC melanoma cells, exposure to T-oligo upregulates p53 expression and phosphorylation, resulting in cellular differentiation and activation of a caspase-mediated apoptotic cascade. However, siRNA-mediated knockdown of p53 completely blocks T-oligo induced differentiation and significantly decreases apoptosis, suggesting that p53 is an important mediator of T-oligo induced responses. In addition, we characterized the roles of telomere binding proteins, TRF1, TRF2, and tankyrase-1, in T-oligo induced damage responses. We demonstrate that tankyrase-1 activity is required for initiation of T-oligo induced damage responses including p53 phosphorylation and reduction of cellular proliferation. These results highlight TRF1, TRF2, tankyrase-1 and p53 as important elements in T-oligo mediated responses and suggest new avenues for research into T-oligo's mechanism of action.

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.

Novel delivery system for T-oligo using a nanocomplex formed with an alpha helical peptide for melanoma therapy

Oligonucleotides homologous to 3′-telomere overhang (T-oligos) trigger inherent telomere-based DNA damage responses mediated by p53 and/or ATM and induce senescence or apoptosis in various cancerous cells. However, T-oligo has limited stability in vivo due to serum and intracellular nucleases. To develop T-oligo as an innovative, effective therapeutic drug and to understand its mechanism of action, we investigated the antitumor effects of T-oligo or T-oligo complexed with a novel cationic alpha helical peptide, PVBLG-8 (PVBLG), in a p53 null melanoma cell line both in vitro and in vivo. The uptake of T-oligo by MM-AN cells was confirmed by immunofluorescence, and fluorescence-activated cell sorting analysis indicated that the T-oligo-PVBLG nanocomplex increased uptake by 15-fold. In vitro results showed a 3-fold increase in MM-AN cell growth inhibition by the T-oligo-PVBLG nanocomplex compared with T-oligo alone. Treatment of preformed tumors in immunodeficient mice with the T-oligo-PVBLG nanocomplex resulted in a 3-fold reduction in tumor volume compared with T-oligo alone. This reduction in tumor volume was associated with decreased vascular endothelial growth factor expression and induction of thrombospondin-1 expression and apoptosis. Moreover, T-oligo treatment downregulated procaspase-3 and procaspase-7 and increased catalytic activity of caspase-3 by 4-fold in MM-AN cells. Furthermore, T-oligo induced a 10-fold increase of senescence and upregulated the melanoma tumor-associated antigens MART-1, tyrosinase, and thrombospondin-1 in MM-AN cells, which are currently being targeted for melanoma immunotherapy. Interestingly, siRNA-mediated knockdown of p73 (4–10-fold) abolished this upregulation of tumor-associated antigens. In summary, we suggest a key role of p73 in mediating the anticancer effects of T-oligo and introduce a novel nanoparticle, the T-oligo-PVBLG nanocomplex, as an effective anticancer therapeutic.

Beyond Telomerase: Telomere Instability as a Novel Target for Cancer Therapy

Telomeres are areas of heterochromatin composed of TTAGGG repeats located at the ends of linear chromosomes. They play a critical role in keeping genome stable and preventing premature aging diseases and the development of cancer. Characterizing mechanisms of telomere maintenance and understanding how their deregulation contributes to human diseases are therefore important for developing novel therapies. A key mechanism driving telomere maintenance and replicative immortality in cancer cells is telomere elongation by telomerase, and many emerging potential telomere-based therapies have focused on targeting telomerase components. By contrast, recent studies on telomere maintenance mechanism suggest that disrupting telomere stability by interfering with alternative mechanisms of telomere synthesis or protection may also yield new strategies for the treatment of cancer. This review will focus on emerging regulators of telomere synthesis or maintenance, such as G4 telomeric DNA, the CST complex, the t-loop, and shelterins, and discuss their potential as targets for anti-cancer chemotherapeutic intervention in the future.

Non-small cell lung cancer is susceptible to induction of DNA damage responses and inhibition of angiogenesis by telomere overhang oligonucleotides

Exposure of the telomere overhang acts as a DNA damage signal, and exogenous administration of an 11-base oligonucleotide homologous to the 3'-telomere overhang sequence (T-oligo) mimics the effects of overhang exposure by inducing senescence and cell death in non-small cell lung cancer (NSCLC) cells, but not in normal bronchial epithelial cells. T-oligo-induced decrease in cellular proliferation in NSCLC is likely directed through both p53 and its homolog, p73, with subsequent induction of senescence and expression of senescence-associated proteins, p21, p33(ING), and p27(Kip1) both in vivo and in vitro. Additionally, T-oligo decreases tumor size and inhibits angiogenesis through decreased VEGF signaling and increased TSP-1 expression.

Clinical implications of antitelomeric drugs with respect to the nontelomeric functions of telomerase in cancer

Telomerase is responsible for maintaining the length of telomeres at the ends of chromosomes. Although most somatic cells do not exhibit telomerase activity, it is reactivated in approximately 85% of cancers. This simple and attractive phenomenon steers the development of anticancer drugs targeting telomeres and telomerase. Recent studies have been revealing extratelomeric roles of telomerase in normal tissues, affecting processes that are critical for survival and aging of organisms. In this review, we will discuss the current therapeutic strategies targeting telomeres and telomerase and evaluate their potential advantages and risks with respect to nontelomeric functions.

Enhanced cytotoxicity from deoxyguanosine-enriched T-oligo in prostate cancer cells

Prostate cancer represents approximately 10 percent of all cancer cases in men and accounts for more than a quarter of all cancer types. Advances in understanding the molecular mechanisms of prostate cancer progression, however, have not translated well to the clinic. Patients with metastatic and hormone-refractory disease have only palliative options for treatment, as chemotherapy seldom produces durable or complete responses, highlighting the need for novel therapeutic approaches. T-oligo, a single-stranded deoxyribonucleic acid with partial sequence homology to human telomeric DNA, has elicited cytostatic and/or cytotoxic effects in multiple cancer cell types. In contrast, normal primary cells of varying tissue types are resistant to cytotoxic actions of T-oligo, underscoring its potential utility as a novel targeted cancer therapeutic. Mechanistically, T-oligo is hypothesized to interfere with normal telomeric structure and form G-quadruplex structures, thereby inducing genomic stress in addition to aberrant upregulation of DNA damageresponse pathways. Here, we present data demonstrating the enhanced effectiveness of a deoxyguanosine-enriched sequence of T-oligo, termed (GGTT)4, which elicits robust cytotoxic effects in prostate cancer cells at lower concentrations than the most recent T-oligo sequence (5'-pGGT TAG GTG TAG GTT T 3') described to date and used for comparison in this study, while exerting no cytotoxic actions on nontransformed human prostate epithelial cells. Additionally, we provide evidence supporting the T-oligo induced activation of cJun N-terminal kinase (JNK) signaling in prostate cancer cells consistent with G-quadruplex formation, thereby significantly advancing the understanding of the T-oligo mechanism of action.

Telomere-homologous G-rich oligonucleotides sensitize human ovarian cancer cells to TRAIL-induced growth inhibition and apoptosis

G-rich T-oligos (GT-oligos; oligonucleotides with homology to telomeres) elicit a DNA damage response in cells and induce cytotoxic effects in certain tumor cell lines. We have previously shown that GT-oligo inhibits growth, arrests cell cycle, and induces apoptosis in ovarian, pancreatic, and prostate cancer cells. However, not all ovarian cancer cell lines are susceptible to GT-oligo exposure. GT-oligo was found to induce transcript expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR-4 and DR-5, which are generally silenced in ovarian cancer cells, rendering them insensitive to TRAIL. Exposure of TRAIL- and GT-oligo-resistant cell lines to GT-oligo rendered them sensitive to the cytotoxic effects of TRAIL, producing more than additive inhibition of growth. An intracellular inhibitor of the extrinsic apoptotic pathway, FLICE-like Inhibitory Protein-Short (FLIPs), was down-regulated and Jun kinase (JNK) was activated by exposure to GT-oligo. JNK inhibition partially reversed the growth inhibition caused by the combination of GT-oligo and TRAIL indicating partial involvement of the Jun kinase pathway in the resulting cytotoxic effect. Both capase-8 and caspases 3/7 were activated by exposure to GT-oligo plus TRAIL, consistent with activation of the extrinsic apoptotic pathway. These results demonstrate a novel way of sensitizing resistant ovarian cancer cells to TRAIL-mediated cytotoxicity.

Suppressive oligodeoxynucleotides synergistically enhance antiproliferative effects of anticancer drugs in A549 human lung cancer cells

Immunosuppressive oligodeoxynucleotides (Sup ODNs) containing repetitive TTAGGG motifs reduce inflammation and, thus, may have an impact on inflammation-related tumor growth. In this study, we found a significant antiproliferative effect of Sup ODNs on the A549 non-small cell lung cancer (NSCLC) cell line compared to those treated with control ODNs (p<0.05). Sup-ODN-mediated G1 phase cell cycle arrest was achieved via inhibition of Akt and extra-cellular signal-regulated kinase 1/2 phosphorylation and the p15^INK4b and p27^KIP1/retinoblastoma protein pathway. In addition, Sup ODNs induced apoptosis and enhanced apoptosis when combined with vinorelbine. In a setting similar to clinical use of multidrug chemotherapy for advanced NSCLC, these effects were investigated by using Sup ODNs in combination with conventional anticancer drugs. Sup ODNs had a significant synergistic effect with 5-fluorouracil, vinorelbine, gemcitabine, paclitaxel and irinotecan, with a mean combination index of 0.43–0.78 (<1.0 indicates synergism) in the A549 NSCLC cell line. In conclusion, our results showed that Sup ODNs have an anticancer effect and increase the sensitivity of NSCLC cells to conventional anticancer drugs by modifying Akt and the extra-cellular signal-regulated kinase 1/2 pathway. Thus, Sup ODNs may serve as a novel therapeutic strategy for NSCLC patients.

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.

Mechanism of T-oligo-induced cell cycle arrest in Mia-PaCa pancreatic cancer cells

DNA oligonucleotides with sequence homology to human telomeric DNA (T-oligo) induce cell cycle arrest, followed by apoptosis, senescence, or autophagy in a human cancer cell type-specific manner. T-oligo has potential as a new therapeutic strategy in oncology because of its ability to target certain types of tumor cells while sparing normal ones. In the present study, we demonstrate the T-oligo-induced S-phase cell cycle arrest in four pancreatic cancer cell lines. To further contribute to the mechanistic understanding of T-oligo, we also identify cyclin dependent kinase 2 (cdk2) as a functional mediator in the T-oligo-induced cell cycle arrest of pancreatic cancer cells. Ectopic expression of a constitutively active cdk2 mutant abrogates T-oligo-induced cell cycle arrest in these tumor cells while knockdown of cdk2 expression alone recapitulates the T-oligo effect. Finally, we demonstrate the dispensability of T-oligo-induced ATM/ATR-mediated DNA damage response-signaling pathways, which have long been considered functional in the T-oligo signaling mechanism.

Photodynamic therapy of Pheophorbide a inhibits the proliferation of human breast tumour via both caspase-dependent and -independent apoptotic pathways in in vitro and in vivo models

Breast cancer is conventionally treated by surgery and radiotherapy, with adjuvant chemotherapy and hormonotherapy as supplementary treatments. However, such treatments are associated with adverse side effects and drug resistance. In this study, Pheophorbide a (Pa), a photosensitizer isolated from Scutelleria barbata, was analysed for its antiproliferative effect on human breast tumour cells. The IC (inhibitory concentration)(50) of the combined treatment of Pa and photodynamic therapy (Pa-PDT) on human breast tumour MCF-7 cells was 0.5 µm. Mechanistic studies in MCF-7 cells demonstrated that Pa was localized in the mitochondria, and reactive oxygen species were found to be released after Pa-PDT. Apoptosis was the major mechanism responsible for the tumour cell death, and mitochondrial membrane depolarization and cytochrome c release highlighted the role of mitochondria in the apoptotic mechanism. Up-regulation of tumour suppressor protein p53, cleavage of caspase-9 and poly (ADP-ribose) polymerase suggested that the caspase-dependent pathway was induced, while the release of apoptosis-inducing factors demonstrated that the apoptosis was also mediated by the caspase-independent mechanism. In vivo study using the mouse xenograft model showed a significant inhibition of MCF-7 tumour growth by Pa-PDT. Together, the results of this study provide a basis for understanding and developing Pa-PDT as a cure for breast cancer.

Bioengineering embryonic stem cell microenvironments for the study of breast cancer

Breast cancer is the most prevalent disease amongst women worldwide and metastasis is the main cause of death due to breast cancer. Metastatic breast cancer cells and embryonic stem (ES) cells display similar characteristics. However, unlike metastatic breast cancer cells, ES cells are nonmalignant. Furthermore, embryonic microenvironments have the potential to convert metastatic breast cancer cells into a less invasive phenotype. The creation of in vitro embryonic microenvironments will enable better understanding of ES cell-breast cancer cell interactions, help elucidate tumorigenesis, and lead to the restriction of breast cancer metastasis. In this article, we will present the characteristics of breast cancer cells and ES cells as well as their microenvironments, importance of embryonic microenvironments in inhibiting tumorigenesis, convergence of tumorigenic and embryonic signaling pathways, and state of the art in bioengineering embryonic microenvironments for breast cancer research. Additionally, the potential application of bioengineered embryonic microenvironments for the prevention and treatment of invasive breast cancer will be discussed.

T-oligos inhibit growth and induce apoptosis in human ovarian cancer cells

Ovarian cancer remains a leading cause of death among women worldwide, and current treatment regimens for advanced disease are inadequate. Oligonucleotides with sequence homology to telomeres (called T-oligos) have been shown to mimic DNA damage responses in cells and induce cytotoxic effects in certain tumor cell lines. We studied the effects of 2 distinct 16 mer T-oligos in 4 human ovarian epithelial carcinoma cell lines. A T-oligo with perfect homology to the telomere overhang region demonstrated some cytotoxic activity in half of the cell lines. A G-rich T-oligo derivative showed more potency and broader cytotoxic activity in these lines than the parental T-oligo. Activation of apoptotic pathways in ovarian cancer cells by exposure to the T-oligo was demonstrated by multiple independent assays. T-oligo was shown to have additive, or more than additive, activity in combination with 2 different histone deacetylase drugs currently in clinical testing. T-oligos may therefore provide a new and tumor-targeted approach to ovarian cancers.

Radiosensitization of mammary carcinoma cells by telomere homolog oligonucleotide pretreatment

Introduction

Ionizing radiation (IR) is a widely used approach to cancer therapy, ranking second only to surgery in rate of utilization. Responses of cancer patients to radiotherapy depend in part on the intrinsic radiosensitivity of the tumor cells. Thus, promoting tumor cell sensitivity to IR could significantly enhance the treatment outcome and quality of life for patients.

Methods

Mammary tumor cells were treated by a 16-base phosphodiester-linked oligonucleotide homologous to the telomere G-rich sequence TTAGGG (T-oligo: GGTTAGGTGTAGGTTT) or a control-oligo (the partial complement, TAACCCTAACCCTAAC) followed by IR. The inhibition of tumor cell growth in vitro was assessed by cell counting and clonogenic cell survival assay. The tumorigenesis of tumor cells after various treatments was measured by tumor growth in mice. The mechanism underlying the radiosensitization by T-oligo was explored by immunofluorescent determination of phosphorylated histone H2AX (γH2AX) foci, β-galactosidase staining, comet and Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assays. The efficacy of the combined treatment was assessed in a spontaneous murine mammary tumor model.

Results

Pretreatment of tumor cells with T-oligo for 24 hours in vitro enhanced both senescence and apoptosis of irradiated tumor cells and reduced clonogenic potential. Radiosensitization by T-oligo was associated with increased formation and/or delayed resolution of γH2AX DNA damage foci and fragmented DNA. T-oligo also caused radiosensitization in two in vivo mammary tumor models. Indeed, combined T-oligo and IR-treatment in vivo led to a substantial reduction in tumor growth. Of further significance, treatment with T-oligo and IR led to synergistic inhibition of the growth of spontaneous mammary carcinomas. Despite these profound antitumor properties, T-oligo and IR caused no detectable side effects under our experimental conditions.

Conclusions

Pretreatment with T-oligo sensitizes mammary tumor cells to radiation in both in vitro and in vivo settings with minimal or no normal tissue side effects.

Inhibition of melanoma angiogenesis by telomere homolog oligonucleotides

Telomere homolog oligonucleotides (T-oligos) activate an innate telomere-based program that leads to multiple anticancer effects. T-oligos act at telomeres to initiate signaling through the Werner protein and ATM kinase. We wanted to determine if T-oligos have antiangiogenic effects. We found that T-oligo-treated human melanoma (MM-AN) cells had decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor 2, angiopoeitin-1 and -2 and decreased VEGF secretion. T-oligos activated the transcription factor E2F1 and inhibited the activity of the angiogenic transcription factor, HIF-1α. T-oligos inhibited EC tubulogenesis and total tumor microvascular density matrix invasion by MM-AN cells and ECs in vitro. In melanoma SCID xenografts, two systemic T-oligo injections decreased by 60% (P < .004) total tumor microvascular density and the functional vessels density by 80% (P < .002). These findings suggest that restriction of tumor angiogenesis is among the host's innate telomere-based anticancer responses and provide further evidence that T-oligos may offer a powerful new approach for melanoma treatment.

T-oligo induces apoptosis in advanced prostate cancer cells

Prostate cancer is the most frequently diagnosed malignancy in men. As cancer progresses from an androgen-sensitive stage to hormone-refractory stage, it turns resistant to androgen ablation therapy. At this stage, effective newer therapies that induce apoptosis are needed for treatment of prostate cancer. DNA oligonucleotides homologous to the telomere 3' overhang (T-oligo) induce apoptosis in several human cancer cells. In the present study, we studied the effect of T-oligo on prostate cancer cells. Our studies showed that androgen-independent DU-145 cells are sensitive to T-oligo in terms of inhibition of proliferation. Moreover, T-oligo induced DU-145 cells to undergo apoptosis. Therefore, our results are encouraging for further investigation in the potential application of T-oligo as a novel therapeutic approach for prostate cancer, especially the androgen-independent.

Telomeric DNA induces p53-dependent reactive oxygen species and protects against oxidative damage

BACKGROUND

Reactive oxygen species (ROS) are generated by cellular metabolism as well as by exogenous agents. While ROS can promote cellular senescence, they can also act as signaling molecules for processes that do not lead to senescence. Telomere homolog oligonucleotides (T-oligos) induce adaptive DNA damage responses including increased DNA repair capacity and these effects are mediated, at least in part, through p53.

OBJECTIVE

Studies were undertaken to determine whether such p53-mediated protective responses include enhanced antioxidant defenses.

METHODS

Normal human fibroblasts as well as R2F fibroblasts expressing wild type or dominant negative p53 were treated with an 11-base T-oligo, a complementary control oligo or diluents alone and then examined by western blot analysis, immunofluorescence microscopy and various biochemical assays.

RESULTS

We now report that T-oligo increases the level of the antioxidant enzymes superoxide dismutase 1 and 2 and protects cells from oxidative damage; and that telomere-based gammaH2AX (DNA damage) foci that form in response to T-oligos contain phosphorylated ATM and Chk2, proteins known to activate p53 and to mediate cell cycle arrest in response to oxidative stress. Further, T-oligo increases cellular ROS levels via a p53-dependent pathway, and these increases are abrogated by the NAD(P)H oxidase inhibitor diphenyliodonium chloride.

CONCLUSION

These results suggest the existence of innate telomere-based protective responses that act to reduce oxidative damage to cells. T-oligo treatment induces the same responses and offers a new model for studying intracellular ROS signaling and the relationships between DNA damage, ROS, oxidative stress, and cellular defense mechanisms.

Telomere-mediated effects on melanogenesis and skin aging

UV-induced melanogenesis (tanning) and "premature aging" or photoaging result in large part from DNA damage. This article reviews data tying both phenomena to telomere-based DNA damage signaling and develops a conceptual framework in which both responses may be understood as cancer-avoidance protective mechanisms.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 25-31; doi:10.1038/jidsymp.2009.9.

Discovery and development of the G-rich oligonucleotide AS1411 as a novel treatment for cancer

Certain guanine-rich (G-rich) DNA and RNA molecules can associate intermolecularly or intramolecularly to form four stranded or "quadruplex" structures, which have unusual biophysical and biological properties. Several synthetic G-rich quadruplex-forming oligodeoxynucleotides have recently been investigated as therapeutic agents for various human diseases. We refer to these biologically active G-rich oligonucleotides as aptamers because their activities arise from binding to protein targets via shape-specific recognition (analogous to antibody-antigen binding). As therapeutic agents, the G-rich aptamers may have some advantages over monoclonal antibodies and other oligonucleotide-based approaches. For example, quadruplex oligonucleotides are non-immunogenic, heat stable and they have increased resistance to serum nucleases and enhanced cellular uptake compared to unstructured sequences. In this review, we describe the characteristics and activities of G-rich oligonucleotides. We also give a personal perspective on the discovery and development of AS1411, an antiproliferative G-rich phosphodiester oligonucleotide that is currently being tested as an anticancer agent in Phase II clinical trials. This molecule functions as an aptamer to nucleolin, a multifunctional protein that is highly expressed by cancer cells, both intracellularly and on the cell surface. Thus, the serendipitous discovery of the G-rich oligonucleotides also led to the identification of nucleolin as a new molecular target for cancer therapy.

Telomere homolog oligonucleotides induce apoptosis in malignant but not in normal lymphoid cells: mechanism and therapeutic potential

Human B- or T-cell lymphoma lines and primary murine lymphomas were treated with DNA oligonucleotides homologous to the telomere (TTAGGG repeat; "T-oligo"), either alone or in combination with standard, widely-used anticancer chemotherapeutic agents. T-oligo induces cell cycle arrest and apoptosis in cultured human or murine B or T-lymphoma cell lines and primary tumor cells, but exerts no detectable toxicity on normal human or murine primary lymphocytes. Exposure to T-oligo is hypothesized to mimic exposure of the 3' telomere repeat sequence, activating the ataxia telangiectasia mutated kinase, which phosphorylates downstream effectors such as p53, but effects are not dependent solely on functional p53. T-oligo causes early S-phase arrest and cooperates well with G(2)- or M-phase-specific anticancer agents; when combined at 1/10th of the conventional dose, vincristine and T-oligo produce greater-than-additive killing of human or murine lymphoma cells (78% of cells undergoing apoptosis after 6 hr vs. 5% of control cells). In mice, 1/10th of the conventional dose of a standard combination of cyclophosphamide, adriamycin, vincristine and prednisone is twice as effective when used in combination with low dose T-oligo. Thus, T-oligo sensitizes tumors to traditional anticancer agents and represents a potentially important new addition to the therapeutic arsenal for aggressive lymphomas.

Telomerase inhibitors and 'T-oligo' as cancer therapeutics: contrasting molecular mechanisms of cytotoxicity

Telomeres, the specialized structures that comprise the ends of chromosomes, form a closed structure, or t-loop, that is important in preventing genomic instability. Forced modulation of this structure, via overexpression of a dominant-negative form of telomere repeat binding factor 2, a protein critical for maintaining t-loop structure, for example, can result in the activation of DNA-damage responses, and ultimately cellular senescence or apoptosis. This response is also seen in normal somatic cells, where telomeres steadily decrease in length as cellular proliferation occurs owing to inefficient replication of terminal telomeric DNA. When telomere length becomes critically short, t-loop structure is compromised, and the cell undergoes senescence. Telomerase, the enzyme responsible for telomere length maintenance, is overexpressed in a majority of cancers. Its lack of expression in most normal somatic cells makes it an attractive target in designing cancer therapeutics. Compounds currently under development that seek to inhibit hTERT, the reverse transcriptase component of telomerase, include nucleoside analogs and the small molecule BIBR1532. Compounds inhibiting the RNA component of telomerase, hTERC, include peptide nucleic acids, 2-5A antisense oligonucleotides, and N3'-P5' thio-phosphoramidates. Recently, an oligonucleotide sharing sequence homology with terminal telomeric DNA, termed 'T-oligo', has shown cytotoxic effects in multiple cancers in culture and animal models. Independent of telomerase function, T-oligo is thought to mimic the DNA-damage response a cell normally experiences when the telomere t-loop structure becomes dysfunctional. In this review, the molecular mechanisms attributed to telomerase inhibitors and T-oligo, as well as their potential as cancer therapeutics, are discussed.

Topical thymidine dinucleotide treatment reduces development of ultraviolet-induced basal cell carcinoma in Ptch-1+/- mice

Treatment with thymidine dinucleotide (pTT) has well documented DNA-protective effects and reduces development of squamous cell carcinoma in UV-irradiated mice. The preventive effect of pTT on basal cell carcinoma (BCC) was evaluated in UV-irradiated Ptch-1(+/-) mice, a model of the human disease Gorlin syndrome. Topical pTT treatment significantly reduced the number and size (P < 0.001) of BCCs in murine skin after 7 months of chronic irradiation. Skin biopsies collected 24 hours after the final UV exposure showed that pTT reduced the number of nuclei positive for cyclobutane pyrimidine dimers by 40% (P < 0.0002) and for 8-hydroxy-2'-deoxyguanosine by 61% (P < 0.01 compared with vehicle control). Immunostaining with an antibody specific for mutated p53 revealed 63% fewer positive patches in BCCs of pTT-treated mice compared with controls (P < 0.01), and the number of Ki-67-positive cells was decreased by 56% (P < 0.01) in pTT-treated tumor-free epidermis and by 76% (P < 0.001) in BCC tumor nests (P < 0.001). Terminal dUTP nick-end labeling staining revealed a 213% increase (P < 0.04) in the number of apoptotic cells in BCCs of pTT-treated mice. Cox-2 immunostaining was decreased by 80% in tumor-free epidermis of pTT-treated mice compared with controls (P < 0.01). We conclude that topical pTT treatment during a prolonged period of intermittent UV exposure decreases the number and size of UV-induced BCCs through several anti-cancer mechanisms.