Targeting telomerase for cancer therapeutics

Innovating Cancer Treatment Through Cell Cycle, Telomerase, Angiogenesis, and Metastasis

Cancer remains a formidable challenge in the field of medicine, necessitating innovative therapeutic strategies to combat its relentless progression. The cell cycle, a tightly regulated process governing cell growth and division, plays a pivotal role in cancer development. Dysregulation of the cell cycle allows cancer cells to proliferate uncontrollably. Therapeutic interventions designed to disrupt the cell cycle offer promise in restraining tumor growth and progression. Telomerase, an enzyme responsible for maintaining telomere length, is often overactive in cancer cells, conferring them with immortality. Targeting telomerase presents an opportunity to limit the replicative potential of cancer cells and hinder tumor growth. Angiogenesis, the formation of new blood vessels, is essential for tumor growth and metastasis. Strategies aimed at inhibiting angiogenesis seek to deprive tumors of their vital blood supply, thereby impeding their progression. Metastasis, the spread of cancer cells from the primary tumor to distant sites, is a major challenge in cancer therapy. Research efforts are focused on understanding the underlying mechanisms of metastasis and developing interventions to disrupt this deadly process. This review provides a glimpse into the multifaceted approach to cancer therapy, addressing critical aspects of cancer biology-cell cycle regulation, telomerase activity, angiogenesis, and metastasis. Through ongoing research and innovative strategies, the field of oncology continues to advance, offering new hope for improved treatment outcomes and enhanced quality of life for cancer patients.

From Crypts to Cancer: A Holistic Perspective on Colorectal Carcinogenesis and Therapeutic Strategies

Colorectal cancer (CRC) represents a significant global health burden, with high incidence and mortality rates worldwide. Recent progress in research highlights the distinct clinical and molecular characteristics of colon versus rectal cancers, underscoring tumor location's importance in treatment approaches. This article provides a comprehensive review of our current understanding of CRC epidemiology, risk factors, molecular pathogenesis, and management strategies. We also present the intricate cellular architecture of colonic crypts and their roles in intestinal homeostasis. Colorectal carcinogenesis multistep processes are also described, covering the conventional adenoma-carcinoma sequence, alternative serrated pathways, and the influential Vogelstein model, which proposes sequential APC, KRAS, and TP53 alterations as drivers. The consensus molecular CRC subtypes (CMS1-CMS4) are examined, shedding light on disease heterogeneity and personalized therapy implications.

Telomerase reverse transcriptase induces targetable alterations in glutathione and nucleotide biosynthesis in glioblastomas

Telomerase reverse transcriptase (TERT) is essential for glioblastoma (GBM) proliferation. Delineating metabolic vulnerabilities induced by TERT can lead to novel GBM therapies. We previously showed that TERT upregulates glutathione (GSH) pool size in GBMs. Here, we show that TERT acts via the FOXO1 transcription factor to upregulate expression of the catalytic subunit of glutamate-cysteine ligase (GCLC), the rate-limiting enzyme of de novo GSH synthesis. Inhibiting GCLC using siRNA or buthionine sulfoximine (BSO) reduces synthesis of 13 C-GSH from [U- 13 C]-glutamine and inhibits clonogenicity. However, GCLC inhibition does not induce cell death, an effect that is associated with elevated [U- 13 C]-glutamine metabolism to glutamate and pyrimidine nucleotide biosynthesis. Mechanistically, GCLC inhibition activates MYC and leads to compensatory upregulation of two key glutamine-utilizing enzymes i.e., glutaminase (GLS), which generates glutamate from glutamine, and CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotatase), the enzyme that converts glutamine to the pyrimidine nucleotide precursor dihydroorotate. We then examined the therapeutic potential of inhibiting GLS and CAD in combination with GCLC. 6-diazo-5-oxy-L-norleucin (DON) is a potent inhibitor of glutamine-utilizing enzymes including GLS and CAD. The combination of BSO and DON suppresses GSH and pyrimidine nucleotide biosynthesis and is synergistically lethal in GBM cells. Importantly, in vivo stable isotope tracing indicates that combined treatment with JHU-083 (a brain-penetrant prodrug of DON) and BSO abrogates synthesis of GSH and pyrimidine nucleotides from [U- 13 C]-glutamine and induces tumor shrinkage in mice bearing intracranial GBM xenografts. Collectively, our studies exploit a mechanistic understanding of TERT biology to identify synthetically lethal metabolic vulnerabilities in GBMs.

SIGNIFICANCE

Using in vivo stable isotope tracing, metabolomics, and loss-of-function studies, we demonstrate that TERT expression is associated with metabolic alterations that can be synergistically targeted for therapy in glioblastomas.

Current understanding and future prospects on Berberine for anticancer therapy

Berberine (BBR) is a potential plant metabolite and has remarkable anticancer properties. Many kinds of research are being focused on the cytotoxic activity of berberine in in vitro and in vivo studies. A variety of molecular targets which lead to the anticancer effect of berberine ranges from p-53 activation, Cyclin B expression for arresting cell cycles; protein kinase B (AKT), MAP kinase and IKB kinase for antiproliferative activity; effect on beclin-1 involved in autophagy; reduced expression of MMP-9 and MMP-2 for the inhibition of invasion and metastasis etc. Berberine also interferes with transcription factor-1 (AP-1) activity responsible for the expression of oncogenes and neoplastic transformation of the cell. It also leads to the inhibition of various enzymes which are directly or indirectly involved in carcinogenesis like N acetyl transferase, Cyclo-oxygenase-2, Telomerase and Topoisomerase. In addition to these actions, Berberine plays a role in, the regulation of reactive oxygen species and inflammatory cytokines in preventing cancer formation. Berberine anticancer properties are demonstrated due to the interaction of berberine with micro-RNA. The summarized information presented in this review article may help and lead the researchers, scientists/industry persons to use berberine as a promising candidate against cancer.

Telomere Targeting Chimera Enables Targeted Destruction of Telomeric Repeat-Binding Factor Proteins

Telomeres are naturally shortened after each round of cell division in noncancerous normal cells, while the activation of telomerase activity to extend telomere in the cancer cell is essential for cell transformation. Therefore, telomeres are regarded as a potential anticancer target. In this study, we report the development of a nucleotide-based proteolysis-targeting chimera (PROTAC) designed to degrade TRF1/2 (telomeric repeat-binding factor 1/2), which are the key components of the shelterin complex (telosome) that regulates the telomere length by directly interacting with telomere DNA repeats. The prototype telomere-targeting chimeras (TeloTACs) efficiently degrade TRF1/2 in a VHL- and proteosome-dependent manner, resulting in the shortening of telomeres and suppressed cancer cell proliferation. Compared to the traditional receptor-based off-target therapy, TeloTACs have potential application in a broad spectrum of cancer cell lines due to their ability to selectively kill cancer cells that overexpress TRF1/2. In summary, TeloTACs provide a nucleotide-based degradation approach for shortening the telomere and inhibiting tumor cell growth, representing a promising avenue for cancer treatment.

Biological and clinical perspectives of TERT promoter mutation detection on bladder cancer diagnosis and management

The telomerase reverse transcriptase (TERT) promoter mutations are associated with increased TERT mRNA and TERT protein levels, telomerase activity, and shorter but stable telomere length. TERT promoter mutation is the most common mutation that occurs in approximately 60-80% of patients with bladder cancer. The TERT promoter mutations occur in a wide spectrum of urothelial lesions, including benign urothelial proliferation and tumor-like conditions, benign urothelial tumors, premalignant and putative precursor lesions, urothelial carcinoma and its variants, and nonurothelial malignancies. The prevalence and incidence of TERT promoter mutations in a total of 7259 cases from the urinary tract were systematically reviewed. Different platforms of TERT promoter mutation detection were presented. In this review, we also discussed the significance and clinical implications of TERT promoter mutation detection in urothelial tumorigenesis, surveillance and early detection, diagnosis, differential diagnosis, prognosis, prediction of treatment responses, and clinical outcome. Identification of TERT promoter mutations from urine or plasma cell-free DNA (liquid biopsy) will facilitate bladder cancer screening program and optimal clinical management. A better understanding of TERT promoter mutation and its pathway would open new therapeutic avenues for patients with bladder cancer.

P19 a Parthenin Analog Induces Cell Lineage Dependent Apoptotic and Immunomodulatory Signaling in Acute Lymphoid Leukemia Cells

Leukemia is a type of cancer that affects the blood and bone marrow. Acute lymphoid leukaemia, also known as ALL, is regarded as one of the deadliest forms of cancer. Due to the rapid increase in various cancer cases and the development of resistance in cancer cells, it is necessary to identify novel lead molecules with more potent anticancer properties. There is a growing interest in using herbal products/analogs as multi-component agents (as anticancer agents and immunomodulators) for cancer treatment. In the present investigation, an attempt has been made to explore the anticancer and immunomodulatory activity of P19, an analog of parthenin in ALL. P19 was reported to exhibit anticancer efficacy by triggering apoptotic signaling events in human leukaemia HL-60 cells by significant NO production. In contrast to this finding, ROS and NO were not required for P19-mediated apoptosis in Raji cells. The mechanism of action of P19 was observed to be cancer cell lineage dependent. P19 demonstrated very effective anticancer properties against ALL (IC50 3µM). Molecular investigations revealed that P19 induced mitochondrion mediated apoptosis by Bax localization to mitochondria and enhanced cytosolic calcium in the cytoplasm. Further activation of the caspase 3, caspase 8 and PARP cleavage suggested the involvement of the caspase-mediated apoptosis. Anti-proliferative activity revealed the telomerase inhibition and cell cycle arrest in G0/G1 phase after P19 treatment. Immunomodulatory effects of the P19 revealed the enhanced INFɣ and NO production in Jurkat and THP cells. Owing to its antiproliferative and immunomodulatory potential against leukemia cells P19 can further be explored as effective therapeutics against leukemia.

Teloxantron inhibits the processivity of telomerase with preferential DNA damage on telomeres

Telomerase reactivation is one of the hallmarks of cancer, which plays an important role in cellular immortalization and the development and progression of the tumor. Chemical telomerase inhibitors have been shown to trigger replicative senescence and apoptotic cell death both in vitro and in vivo. Due to its upregulation in various cancers, telomerase is considered a potential target in cancer therapy. In this study, we identified potent, small-molecule telomerase inhibitors using a telomerase repeat amplification protocol assay. The results of the assay are the first evidence of telomerase inhibition by anthraquinone derivatives that do not exhibit G-quadruplex-stabilizing properties. The stability of telomerase in the presence of its inhibitor was evaluated under nearly physiological conditions using a cellular thermal shift assay. Our data showed that the compound induced aggregation of the catalytic subunit (hTERT) of human telomerase, and molecular studies confirmed the binding of the hit compound with the active site of the enzyme. The ability of new derivatives to activate DNA double-strand breaks (DSBs) was determined by high-resolution microscopy and flow cytometry in tumor cell lines differing in telomere elongation mechanism. The compounds triggered DSBs in TERT-positive A549 and H460 lung cancer cell lines, but not in TERT-negative NHBE normal human bronchial epithelial and ALT-positive U2OS osteosarcoma cell lines, which indicates that the induction of DSBs was dependent on telomerase inhibition. The observed DNA damage activated DNA damage response pathways involving ATM/Chk2 and ATR/Chk1 cascades. Additionally, the compounds induced apoptotic cell death through extrinsic and intrinsic pathways in lung cancer cells. Taken together, our study demonstrated that anthraquinone derivatives can be further developed into novel telomerase-related anticancer agents.

Τelomerase inhibitors and activators in aging and cancer: A systematic review

The main aim of the present systematic review was to summarize the most frequently used telomerase regulators with an impact on aging and cancer that are referred to in in vitro and in vivo studies. For this purpose, a systematic review of the available literature on telomerase regulators referred to in articles from PubMed and Scopus libraries published from 2002 to 2021 and in accordance with PRISMA 2020 criteria, was conducted. Articles were included if they met the following criteria: They referred to telomerase modulators in aging and in cancer and were in vitro and/or in vivo studies, while studies that did not provide sufficient data or studies not written in English were excluded. In the present systematic review, 54 publications were included, of which 29 were full‑text published studies, 11 were full‑text reviews, 10 structure‑based design studies and 4 abstracts are reported in this review. Telomerase regulators were then categorized as synthetic direct telomerase inhibitors, synthetic indirect telomerase inhibitors, synthetic telomerase activators, natural direct telomerase activators, natural telomerase inhibitors and natural indirect telomerase activators, according to their origin and their activity. On the whole, as demonstrated herein, telomerase regulators appear to be promising treatment agents in various age‑related diseases. However, further in vivo and in vitro studies need to be performed in order to clarify the potentiality of telomerase as a therapeutic target.

Cost-Effective Trap qPCR Approach to Evaluate Telomerase Activity: an Important Tool for Aging, Cancer, and Chronic Disease Research

OBJECTIVES

Telomeres are a terminal "DNA cap" that prevent chromosomal fusion and degradation. However, aging is inherent to life, and so is the loss of terminal sequences. Telomerase is a specialized reverse transcriptase encoded by self-splicing introns that counteract chromosome erosion. Telomerase activity is observed during early embryonic development, but after the blastocyst stage, the expression of telomerase reduces. The consequences of either insufficient or unrestrained telomerase activity underscore the importance of ongoing studies aimed at elucidating the regulation of telomerase activity in humans. In the present study, we aimed to standardize a simplified telomerase repeat-amplification protocol (TRAP) assay to detect telomerase activity in unstimulated and PHA-stimulated mononuclear cells.

METHODS AND RESULTS

Our optimized qPCR-based can efficiently evaluate telomerase activity. Quantification of protein and DNA between unstimulated and PHA-stimulated peripheral blood mononuclear cells revealed cellular activation and cell-cycle entry. The assay also showed that relative telomerase activity is significantly different between these two conditions, supporting the applicability of the assay. Furthermore, our findings corroborated that telomerase activity decreases with age.

CONCLUSIONS

Telomeres and telomerase are implicated in aging and development of chronic diseases and cancer; however, difficulty in accessing commercial kits to investigate these aspects is a critical constraint in health surveillance studies. Our optimized assay was successfully used to differentiate telomerase activity between unstimulated and stimulated cells, clearly showing the reactivation of telomerase upon cell activation. This assay is affordable, reproducible, and can be executed in resource-limited settings.

TERT-Regulation and Roles in Cancer Formation

Telomerase reverse transcriptase (TERT) is a catalytic subunit of telomerase. Telomerase complex plays a key role in cancer formation by telomere dependent or independent mechanisms. Telomere maintenance mechanisms include complex TERT changes such as gene amplifications, TERT structural variants, TERT promoter germline and somatic mutations, TERT epigenetic changes, and alternative lengthening of telomere. All of them are cancer specific at tissue histotype and at single cell level. TERT expression is regulated in tumors via multiple genetic and epigenetic alterations which affect telomerase activity. Telomerase activity via TERT expression has an impact on telomere length and can be a useful marker in diagnosis and prognosis of various cancers and a new therapy approach. In this review we want to highlight the main roles of TERT in different mechanisms of cancer development and regulation.

Drug repurposing towards targeting cancer stem cells in pediatric brain tumors

In the pediatric population, brain tumors represent the most commonly diagnosed solid neoplasms and the leading cause of cancer-related deaths globally. They include low-grade gliomas (LGGs), medulloblastomas (MBs), and other embryonal, ependymal, and neuroectodermal tumors. The mainstay of treatment for most brain tumors includes surgical intervention, radiation therapy, and chemotherapy. However, resistance to conventional therapy is widespread, which contributes to the high mortality rates reported and lack of improvement in patient survival despite advancement in therapeutic research. This has been attributed to the presence of a subpopulation of cells, known as cancer stem cells (CSCs), which reside within the tumor bulk and maintain self-renewal and recurrence potential of the tumor. An emerging promising approach that enables identifying novel therapeutic strategies to target CSCs and overcome therapy resistance is drug repurposing or repositioning. This is based on using previously approved drugs with known pharmacokinetic and pharmacodynamic characteristics for indications other than their traditional ones, like cancer. In this review, we provide a synopsis of the drug repurposing methodologies that have been used in pediatric brain tumors, and we argue how this selective compilation of approaches, with a focus on CSC targeting, could elevate drug repurposing to the next level.

Arsenic trioxide as a novel anti-glioma drug: a review

Arsenic trioxide has shown a strong anti-tumor effect with little toxicity when used in the treatment of acute promyelocytic leukemia (APL). An effect on glioma has also been shown. Its mechanisms include regulation of apoptosis and autophagy; promotion of the intracellular production of reactive oxygen species, causing oxidative damage; and inhibition of tumor stem cells. However, glioma cells and tissues from other sources show different responses to arsenic trioxide. Researchers are working to enhance its efficacy in anti-glioma treatments and reducing any adverse reactions. Here, we review recent research on the efficacy and mechanisms of action of arsenic trioxide in the treatment of gliomas to provide guidance for future studies.

Facile synthesis of fluorescent tungsten oxide quantum dots for telomerase detection based on the inner filter effect

The traditional detection of telomerase activity is mainly based on the polymerase chain reaction (PCR), which has the disadvantages of being time-consuming and susceptible to interferences; thus, here, we propose a facile method for the fabrication of fluorescent tungsten oxide quantum dots (WO_x QDs) and employ them for telomerase activity sensing. It is found that the fluorescence of WO_x QDs can be significantly quenched by hemin based on the inner filter effect (IFE). However, in the presence of telomerase, the primer-DNA can be extended to generate repeating units of TTAGGG to form G-quadruplex and thus, hemin can be encapsulated to reduce its absorbance, resulting in decreased IFE and efficient fluorescence recovery of WO_x QDs. Based on the fluorescence changes of IFE between hemin and WO_x QDs, the telomerase activity within the range of 50-30 000 HeLa cells can be detected and the lowest detection amount can reach 17 cells. The method exhibits good versatility that can also be applied to telomerase detection in A549 and L929 cells. In addition, because of the good biocompatibility of the sensor, it can be used for the real-time monitoring of telomerase activity in living cells, thus showing great potential in tumor diagnosis and inhibitor drug screening.

Synthesis of Combretastatin A-4 and 3'-Aminocombretastatin A-4 derivatives with Aminoacid Containing Pendants and Study of Their Interaction with Tubulin and as Downregulators of the VEGF, hTERT and c-Myc Gene Expression

Natural product combretastatin A-4 (CA-4) and its nitrogenated analogue 3′-aminocombretastatin A-4 (AmCA-4) have shown promising antitumor activities. In this study, a range of CA-4 and AmCA-4 derivatives containing amino acid pendants have been synthesized in order to compare their biological actions with those of their parent compounds. Thus, inhibition of cell proliferation on tumor cell lines HT-29, MCF-7 and A-549, as well as on the nontumor cell line HEK-273; in vitro tubulin polymerization; mitotic cell arrest; action on the microtubule cell network and inhibition of VEGF, hTERT, and c-Myc genes have been evaluated. Some AmCA-4 derivatives bearing L-amino acids exhibited inhibition of cell proliferation at low nanomolar levels exceeding the values shown by AmCA-4. Furthermore, while CA-4 and AmCA-4 derivatives do not show significant effects on the in vitro tubulin polymerization and cell cycle arrest, some selected CA-4 and AmCA-4 derivatives are able to cause total depolymerization of the microtubule network on A-549 cells. The best results were obtained in the inhibition of gene expression, particularly on the VEGF gene, in which some AmCA-4 derivatives greatly exceeded the inhibition values achieved by the parent compound.

Ginger Extract Promotes Telomere Shortening and Cellular Senescence in A549 Lung Cancer Cells

Replicative senescence, which is caused by telomere shortening from the end replication problem, is considered one of the tumor-suppressor mechanisms in eukaryotes. However, most cancers escape this replicative senescence by reactivating telomerase, an enzyme that extends the 3'-ends of the telomeres. Previously, we reported the telomerase inhibitory effect of a crude Zingiber officinale extract (ZOE), which suppressed hTERT expression, leading to a reduction in hTERT protein and telomerase activity in A549 lung cancer cells. In the present study, we found that ZOE-induced telomere shortening and cellular senescence during the period of 60 days when these A549 cells were treated with subcytotoxic doses of ZOE. Using assay-guided fractionation and gas chromatography/mass spectrometry analysis, we found that the major compounds in the active subfractions were paradols and shogaols of various chain lengths. The results from studies of pure 6-paradol and 6-shogaol confirmed that these two compounds could suppress hTERT expression as well as telomerase activity in A549 cells. These results suggest that these paradols and shogaols are likely the active compounds in ZOE that suppress hTERT expression and telomerase activity in these cells. Furthermore, ZOE was found to be nontoxic and had an anticlastogenic effect against diethylnitrosamine-induced liver micronucleus formation in rats. These findings suggest that ginger extract can potentially be useful in dietary cancer prevention.

New N,C-Diaryl-1,2,4-triazol-3-ones: Synthesis and Evaluation as Anticancer Agents

BACKGROUND

A set of 2,5-diaryl-1,2,4-triazol-3-ones was synthesized in two steps and evaluated as regards their activity in some relevant biological targets related to cancer.

OBJECTIVE

This study is focused on the synthesis and the biological evaluation of 2,5-diaryl-1,2,4- triazol-3-ones. In this sense, the effect of the synthetic triazolones on the proliferation of HT-29 and A549 cancer cells and on HEK non-cancer cells has been measured. In addition, the effects of triazolones on the expression of hTERT, c-Myc and PD-L1 genes and on the production of c-Myc and PD-L1 proteins have also been evaluated.

METHOD

A set of 2,5-diaryl-1,2,4-triazol-3-ones was synthesized in two steps. Firstly, N- (aminocarbonyl)-3-methoxybenzamide was prepared by coupling 3-methoxybenzoic acid and cyanamide followed by aqueous HCl hydrolysis. Then, the 2,5-diaryl-1,2,4-triazol-3-ones were obtained upon reaction of N-(aminocarbonyl)-3-methoxybenzamide with arylhydrazines in decaline at 170ºC. The ability of the triazolones to inhibit cell proliferation was measured against two human carcinoma cell lines (colorectal HT-29 and lung A549), and one non-tumor cell line (HEK- 293) by MTT assay. The downregulation of the synthetic triazolones on the expression of the hTERT, c-Myc and PD-L1 genes was measured by an RT-qPCR analysis. Their ability to regulate the expression of the c-Myc and PD-L1 proteins, as well as their direct interaction with c-Myc protein, was determined by the ELISA method. Finally, the direct interaction of triazolones with PD-L1 protein was assessed by the thermal shift assay.

RESULTS

Ten 2,5-diaryl-1,2,4-triazol-3-ones were synthesized and characterized by spectroscopic methods. A thorough study by 1H, 13C, 15N and 19F NMR spectroscopy showed that all the synthetic compounds exist as 4H-triazolones and not as hydroxytriazoles or 1H-triazolones. Some triazolones showed relatively high activities together with very poor toxicity in non-tumor cell line HEK-293. 2-(2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (4) was particularly active in downregulating c-Myc and PD-L1 gene expression although 2-(4- chloro-2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (8) is the one that combines the best downregulatory activities in the three genes studied. Considering protein expression, the most active compounds are 2-(4-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro- 3H-1,2,4-triazol-3-one (5) and 2-(2,4,6-trifluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H- 1,2,4-triazol-3-one (10) (c-Myc expression) and 2-(2,3,5,6-tetrafluorophenyl)-5-(3-methoxyphenyl)- 2,4-dihydro-3H-1,2,4-triazol-3-one (11) and (8) (PD-L1 expression).

CONCLUSION

Some of the triazolones studied have shown relevant activities in the inhibition of the hTERT, c-Myc and PD-L1 genes, and in the inhibition of c-Myc and PD-L1 protein secretion, the 2-(4-chloro-2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (8) was found to be a particularly promising lead compound.

Interleukin 8 is a biomarker of telomerase inhibition in cancer cells

Background

Telomerase activity is required for both initiation and maintenance of tumorigenesis and over 90% cancers overexpress telomerase. Therefore, telomerase targeting has emerged as a potential strategy for cancer treatment. In agreement with this, several telomerase inhibitors are being tested for cancer treatment and have shown some promise. However, because of the variability in response between the cancer patients, it is important to identify biomarkers that allow for distinguishing cancers that are responsive to telomerase inhibition from the cancers that are not. Therefore, in this study we performed experiments to identify a biomarker that can be used to predict telomerase inhibition induced tumor growth inhibition.

Methods

In our study, we have performed transcriptome-wide gene expression analysis on multiple ovarian and colon cancer cell lines that were treated with telomerase inhibitor imetelstat and were responsive to telomerase inhibition-induced tumor growth attenuation.

Results

We demonstrate that telomerase inhibition by telomerase inhibitor imetelstat results in decreased expression of interleukin 8 (IL8) in all telomerase responsive cancer cell lines. This phenomenon is of general occurrence because we find that multiple ovarian and colon cell lines show decrease in IL8 mRNA and protein levels after telomerase inhibition. Additionally, we find loss of IL8 phenocopy Telomerase inhibition mediated growth inhibitory effect in cancer cells.

Conclusion

Taken together, our results show that IL8 is a biomarker that predict telomerase inhibition mediated growth attenuation of cancer cells and its loss phenocopy telomerase inhibition. Therefore, IL8 expression can be utilized as a biomarker for telomerase targeted cancer therapies to potentially predict therapeutic response.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4633-x) contains supplementary material, which is available to authorized users.

New therapeutic strategies based on interference with telomeric DNA synthesis of tumor cells to suppress the growth of tumors

An unusual enzyme called telomerase acts on parts of chromosomes known as telomeres. The enzyme has recently been found in many human tumors and is viewed as a new target for tumor therapy. In this research, we chose the analogue of guanine "2',3'-dideoxyguanosine" (ddG) as the telomerase inhibitor and prepared the ddG-loaded cationic nanoliposomes (ddG-Clip) to specifically target the tumor tissue and preferentially occupy the telomerase nucleotide binding site. The mean diameter of ddG-Clip is 101.54 ± 2.60 nm and they are cationically charged with a zeta potential of 34.0 ± 9.43 mV; also, the encapsulation efficiency of ddG-Clip is 53.44% ± 2.29%. In vitro cytotoxicity results show that cationic nanoliposomes by themselves are almost non-toxic, but with the increase in ddG concentration, ddG-Clip has the ability to kill S180 tumor cells. The anti-tumor activity study suggests that ddG-Clip could not only suppress the tumor growth, but also inhibit tumor liver metastasis well. In conclusion, reverse transcriptase inhibitor-loaded cationic nanoliposomes could interfere with the synthesis of telomeric DNA and block abnormal proliferation of tumor cells, therefore achieving tumor apoptosis.

The Emerging Roles for Telomerase in the Central Nervous System

Telomerase, a specialized ribonucleoprotein enzyme complex, maintains telomere length at the 3′ end of chromosomes, and functions importantly in stem cells, cancer and aging. Telomerase exists in neural stem cells (NSCs) and neural progenitor cells (NPCs), at a high level in the developing and adult brains of humans and rodents. Increasing studies have demonstrated that telomerase in NSCs/NPCs plays important roles in cell proliferation, neuronal differentiation, neuronal survival and neuritogenesis. In addition, recent works have shown that telomerase reverse transcriptase (TERT) can protect newborn neurons from apoptosis and excitotoxicity. However, to date, the link between telomerase and diseases in the central nervous system (CNS) is not well reviewed. Here, we analyze the evidence and summarize the important roles of telomerase in the CNS. Understanding the roles of telomerase in the nervous system is not only important to gain further insight into the process of the neural cell life cycle but would also provide novel therapeutic applications in CNS diseases such as neurodegenerative condition, mood disorders, aging and other ailments.

Determination of the activity of telomerase in cancer cells by using BSA-protected gold nanoclusters as a fluorescent probe

Gold nanoclusters (AuNCs) protected with a bovine serum albumin (BSA) coating are known to emit red fluorescence (peaking at 650 nm) on photoexcitation with ultraviolet light (365 nm). On addition of Cu(II) ions, fluorescence is quenched because Cu(II) complexes certain amino acid units in the BSA chain. Fluorescence is, however, restored if pyrophosphate (PPi) is added because it will chelate Cu(II) and remove it from the BSA coating on the AuNCs. Because PPi is involved in the function of telomerase, the BSA@AuNCs loaded with Cu(II) can act as a fluorescent probe for determination of the activity of telomerase. A fluorescent assay was worked out for telomerase that is highly sensitive and has a wide linear range (10 nU to 10 fM per mL). The fluorescent probe was applied to the determination of telomerase activity in cervix carcinoma cells via imaging. It is shown that tumor cells can be well distinguished from normal cells by monitoring the differences in intracellular telomerase activity. Graphical abstract Gold nanoclusters (AuNCs) protected by bovine serum albumin (BSA) and displaying red photoluminescence were prepared as fluorescent probe for the determination of telomerase activity and used for imaging of cervix carcinoma (HeLa) cells.

Arsenic trioxide inhibits glioma cell growth through induction of telomerase displacement and telomere dysfunction

Glioblastomas are resistant to many kinds of treatment, including chemotherapy, radiation and other adjuvant therapies. As₂O₃ reportedly induces ROS generation in cells, suggesting it may be able to induce telomerase suppression and telomere dysfunction in glioblastoma cells. We show here that As₂O₃ induces ROS generation as well as telomerase phosphorylation in U87, U251, SHG4 and C6 glioma cells. It also induces translocation of telomerase from the nucleus to the cytoplasm, thereby decreasing total telomerase activity. These effects of As₂O₃ trigger an extensive DNA damage response at the telomere, which includes up-regulation of ATM, ATR, 53BP1, γ-H₂AX and Mer11, in parallel with telomere fusion and 3′-overhang degradation. This ultimately results in induction of p53- and p21-mediated cell apoptosis, G2/M cell cycle arrest and cellular senescence. These results provide new insight into the antitumor effects of As₂O₃ and can perhaps contribute to solving the problem of glioblastoma treatment resistance.

New perspectives on telomerase RNA structure and function

Telomerase is an ancient ribonucleoprotein (RNP) that protects the ends of linear chromosomes from the loss of critical coding sequences through repetitive addition of short DNA sequences. These repeats comprise the telomere, which together with many accessory proteins, protect chromosomal ends from degradation and unwanted DNA repair. Telomerase is a unique reverse transcriptase (RT) that carries its own RNA to use as a template for repeat addition. Over decades of research, it has become clear that there are many diverse, crucial functions played by telomerase RNA beyond simply acting as a template. In this review, we highlight recent findings in three model systems: ciliates, yeast and vertebrates, that have shifted the way the field views the structural and mechanistic role(s) of RNA within the functional telomerase RNP complex. Viewed in this light, we hope to demonstrate that while telomerase RNA is just one example of the myriad functional RNA in the cell, insights into its structure and mechanism have wide-ranging impacts. WIREs RNA 2018, 9:e1456. doi: 10.1002/wrna.1456 This article is categorized under: RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution.

Anticancer effects of methanol extract of Myrmecodia platytyrea Becc. leaves against human hepatocellular carcinoma cells via inhibition of ERK and STAT3 signaling pathways

Myrmecodia platytyrea Becc., a member of the Rubiaceae family, is found throughout Southeast Asia and has been traditionally used to treat cancer. However, there is limited pharmacological information on this plant. We investigated the anticancer effects of the methanol extract of Myrmecodia platytyrea Becc. leaves (MMPL) and determined the molecular mechanisms underlying the effects of MMPL on metastasis in human hepatocellular carcinoma (HCC) cells. MMPL dose-dependently inhibited cell migration and invasion in SK‑Hep1 and Huh7 cells. In addition, MMPL strongly suppressed the enzymatic activity of matrix metalloproteinases (MMP‑2 and MMP‑9). Diminished telomerase activity by MMPL resulted in the suppression of both telomerase activity and telomerase-associated gene expression. The levels of urokinase-type plasminogen activator receptor (uPAR) expression as well as the phosphorylation levels of signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase (ERK) were also attenuated by MMPL. The above results collectively suggest that MMPL has anticancer effects in HCC and that MMPL can serve as an effective therapeutic agent for treating human liver cancer.

The in vivo anti-leukemia activity of N-(1-Pyrenlyl) maleimide in a bioluminescent mouse model

In a search for anticancer drugs by screening for inhibitors of telomerase, we have identified several small-molecule inhibitors that selectively inhibit telomerase in a cell-free system. Among these inhibitors, N-(1-pyrenyl) maleimide (NPM) induced apoptosis and displayed the greatest differential cytotoxicity against acute T cell leukemia-derived Jurkat cells cultured in vitro. In this work, the in vivo anti-leukemia activity of NPM was investigated using a bioluminescent mouse model. The luciferase-expressing Jurkat cells (Jurkat-Luc) were mixed with matrigel and injected subcutaneously into the nude mice. Drug treatment was commenced on day 7 after tumor implantation. The growth of xenografted tumors was significantly inhibited in the mice treated with NPM, which is comparable to the inhibitory effect of a classical anti-leukemia drug, cyclophosphamide. Combined treatment with NPM and cyclophosphamide further enhanced the growth inhibition of xenografted Jurkat-Luc cells. Immunohistochemistry staining with cleaved caspase 3 (cl-caspase 3) indicated a very heavy staining of cl-caspase 3 only in the tumor implants excised from the NPM-treated mice. We conclude that NPM induced apoptosis and inhibited the growth of xenografted Jurkat-Luc cells in nude mice, demonstrating that NPM displays anti-leukemia activity in vivo.

Emerging roles of hnRNPA1 in modulating malignant transformation

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA-binding proteins associated with complex and diverse biological processes such as processing of heterogeneous nuclear RNAs (hnRNAs) into mature mRNAs, RNA splicing, transactivation of gene expression, and modulation of protein translation. hnRNPA1 is the most abundant and ubiquitously expressed member of this protein family and has been shown to be involved in multiple molecular events driving malignant transformation. In addition to selective mRNA splicing events promoting expression of specific protein variants, hnRNPA1 regulates the gene expression and translation of several key players associated with tumorigenesis and cancer progression. Here, we will summarize our current knowledge of the involvement of hnRNPA1 in cancer, including its roles in regulating cell proliferation, invasiveness, metabolism, adaptation to stress and immortalization. WIREs RNA 2017, 8:e1431. doi: 10.1002/wrna.1431 For further resources related to this article, please visit the WIREs website.

Telomere Biology-Insights into an Intriguing Phenomenon

Bacteria and viruses possess circular DNA, whereas eukaryotes with typically very large DNA molecules have had to evolve into linear chromosomes to circumvent the problem of supercoiling circular DNA of that size. Consequently, such organisms possess telomeres to cap chromosome ends. Telomeres are essentially tandem repeats of any DNA sequence that are present at the ends of chromosomes. Their biology has been an enigmatic one, involving various molecules interacting dynamically in an evolutionarily well-trimmed fashion. Telomeres range from canonical hexameric repeats in most eukaryotes to unimaginably random retrotransposons, which attach to chromosome ends and reverse-transcribe to DNA in some plants and insects. Telomeres invariably associate with specialised protein complexes that envelop it, also regulating access of the ends to legitimate enzymes involved in telomere metabolism. They also transcribe into repetitive RNA which also seems to be playing significant roles in telomere maintenance. Telomeres thus form the intersection of DNA, protein, and RNA molecules acting in concert to maintain chromosome integrity. Telomere biology is emerging to appear ever more complex than previously envisaged, with the continual discovery of more molecules and interplays at the telomeres. This review also includes a section dedicated to the history of telomere biology, and intends to target the scientific audience new to the field by rendering an understanding of the phenomenon of chromosome end protection at large, with more emphasis on the biology of human telomeres. The review provides an update on the field and mentions the questions that need to be addressed.

Targeting human telomerase RNA component using antisense oligonucleotide induces rapid cell death and increases ATO-induced apoptosis in APL cells

The impressive advances carried out in designing pharmacological strategies with the aim of telomerase inhibition in cancers emerged a consensus that telomerase-targeted therapies could be exciting prospect in repertoire of future cancer strategies. The results of the present study indicated that targeting telomerase using an oligonucleotide-based molecule against human telomerase RNA template (hTR ASODN) reduced the survival rate of NB4 cells and induced a caspase-3-dependent apoptosis. Our finding was even noticeable in the synergistic experiments, where we found an enhanced reduction in the viability of the cells after short-term treatment with ATO in combination with the inhibitor. The resulting data delineated that short-term treatment of the cells with hTR ASODN either as single agent or in combination with ATO resulted in apoptotic cell death through activation of DNA damage response via up-regulation of p73 and ATM coupled with down-regulation of c-Myc. Moreover, we found that induction of p21 and subsequent disturbance of the death promoter to death repressor genes may contribute to the enhanced growth suppressive effect of the drugs combination. Overall, our findings support the idea that telomerase activity may have pivotal role in attenuating ATO effectiveness and combination of ATO with telomerase inhibitor seems to be a novel promising strategy, which may increase APL cure rates.

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.

Means to the ends: The role of telomeres and telomere processing machinery in metastasis

Despite significant clinical advancements, cancer remains a leading cause of mortality throughout the world due largely to the process of metastasis and the dissemination of cancer cells from their primary tumor of origin to distant secondary sites. The clinical burden imposed by metastasis is further compounded by a paucity of information regarding the factors that mediate metastatic progression. Linear chromosomes are capped by structures known as telomeres, which dictate cellular lifespan in humans by shortening progressively during successive cell divisions. Although telomere shortening occurs in nearly all somatic cells, telomeres may be elongated via two seemingly disjoint pathways: (i) telomerase-mediated extension, and (ii) homologous recombination-based alternative lengthening of telomeres (ALT). Both telomerase and ALT are activated in various human cancers, with more recent evidence implicating both pathways as potential mediators of metastasis. Here we review the known roles of telomere homeostasis in metastasis and posit a mechanism whereby metastatic activity is determined by a dynamic fluctuation between ALT and telomerase, as opposed to the mere activation of a generic telomere elongation program. Additionally, the pleiotropic nature of the telomere processing machinery makes it an attractive therapeutic target for metastasis, and as such, we also explore the therapeutic implications of our proposed mechanism.

Protective effect of telomerase-based 16-mer peptide vaccine (GV1001) on inferior epigastric island skin flap survivability in ischaemia-reperfusion injury rat model

BACKGROUND

Ischaemia-reperfusion injury (IRI) results in oxidative damage and a profound inflammatory reaction, leading to cell death. GV 1001 is a telomerase-based 16-mer peptide vaccine developed against cancer. However, it has also been reported to possess antioxidant and anti-inflammatory properties. The aim of this study was to determine if GV 1001 can reduce the negative effects caused by IRI in a rat skin flap model owing to its anti-oxidant and anti-inflammatory properties.

MATERIALS AND METHODS

In order to evaluate the effect of GV 1001, 5 × 5 cm² inferior epigastric artery based island skin flaps were dissected in 39 8-week-old Sprague-Dawley rats weighing 220-270 g. The rats were divided into three groups: (I) non-ischaemic group; (II) IRI with saline; and (III) IRI with 10 mg GV 1001 treatment. Drugs were administered intra-muscularly directly before and after ischaemia. Flap survival area, neutrophil infiltration, cytokine levels (interleukin [IL]-1, IL-6, and tumour necrosis factor-α), malondialdehyde (MDA) level, and superoxide dismutase (SOD) activity were measured. Flap survivability was analysed at 7 days after surgery.

RESULTS

Flap survival area was significantly larger in group III than in group II. Cytokine release level was also significantly lower in group III. Neutrophil infiltration grade, MDA level, and SOD activity slightly decreased in Group III; however, the changes were not statistically significant.

CONCLUSION

These results imply that GV 1001 exerts a protective effect against IRI through antioxidant effects, reducing reactive oxygen species, and suppressing the inflammatory cascade.

Telomerase inhibitors: a patent review (2010-2015)

INTRODUCTION

Telomerase is a ribonucleoprotein that catalyses the addition of telomeric repeat sequences (having the sequence 5'-TTAGGG-3' in humans) to the ends of chromosomes. Telomerase activity is detected in most types of human tumours, but it is almost undetectable in normal somatic cells. Therefore, telomerase is a promising therapeutic target. To date, the known inhibitors of telomerase include nucleoside analogues, oligonucleotides and G-quadruplex stabilizers. This review highlights recent advances in our understanding of telomerase inhibitors, the relationships between telomerase inhibitors, cancer, and fields such as inflammation.

AREAS COVERED

This review summarizes new patents published on telomerase inhibitors from 2010 to 2015.

EXPERT OPINION

The review provides a brief account of the background, development, and on-going issues involving telomerase inhibitors. In particular, this review emphasizes imetelstat (GRN163L) and some typical G-quadruplex stabilizers that participate in telomerase inhibition. Overall, the research scope of antineoplastic is becoming broader and telomerase inhibitors have been shown to be a promising therapeutic target. Therefore, novel antineoplastic agents with greater activity and higher specificity must be developed.

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.

Structural Basis of Telomerase Inhibition by the Highly Specific BIBR1532

BIBR1532 is a highly specific telomerase inhibitor, although the molecular basis for inhibition is unknown. Here we present the crystal structure of BIBR1532 bound to Tribolium castaneum catalytic subunit of telomerase (tcTERT). BIBR1532 binds to a conserved hydrophobic pocket (FVYL motif) on the outer surface of the thumb domain. The FVYL motif is near TRBD residues that bind the activation domain (CR4/5) of hTER. RNA binding assays show that the human TERT (hTERT) thumb domain binds the P6.1 stem loop of CR4/5 in vitro. hTERT mutations of the FVYL pocket alter wild-type CR4/5 binding and cause telomere attrition in cells. Furthermore, the hTERT FVYL mutations V1025F, N1028H, and V1090M are implicated in dyskeratosis congenita and aplastic anemia, further supporting the biological and clinical relevance of this novel motif. We propose that CR4/5 contacts with the telomerase thumb domain contribute to telomerase ribonucleoprotein assembly and promote enzymatic activity.

miR-512-5p suppresses tumor growth by targeting hTERT in telomerase positive head and neck squamous cell carcinoma in vitro and in vivo

Telomerase activation has very important implications for head and neck squamous cell carcinoma (HNSCC), but the regulatory mechanisms of telomerase in HNSCC remain unclear. In our present study, we found that miR-512-5P was markedly downregulated in telomerase-positive HNSCC cell lines. Both in vitro and in vivo assays revealed that miR-512-5P mimic attenuated HNSCC cell proliferation, and tumor growth in nude mice, which exerts its tumor suppressor function through elevated apoptosis, inhibition of the telomerase activity, decrease of telomere-binding proteins and shortening of telomere length by human telomerase reverse transcriptase (hTERT) downregulation. Furthermore, the dual-luciferase reporter gene assay results demonstrated that hTERT was a direct target of miR-512-5P. We conclude that the frequently miR-512-5P overexpression can regulate hTERT and function as a tumor suppressor in HNSCC. Therefore, miR-512-5P may serve as a potential therapeutic agent for miR-based HNSCC therapy.

An improved model for the hTERT promoter quadruplex

Mutations occur at four specific sites in the hTERT promoter in >75% of glioblastomas and melanomas, but the mechanism by which the mutations affect gene expression remains unexplained. We report biophysical computational studies that show that the hTERT promoter sequence forms a novel G-quadruplex structure consisting of three contiguous, stacked parallel quadruplexes. The reported hTERT mutations map to the central quadruplex within this structure, and lead to an alteration of its hydrodynamic properties and stability.

Antisense oligonucleotides targeting human telomerase mRNA increases the radiosensitivity of nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is associated with a high incidence rate in South China and is predominantly treated with radiotherapy; however, the survival rate remains low. The therapeutic effects of radiation and chemotherapy may be enhanced when combined with anti‑sense oligonucleotides targeting human telomerase RNA (hTR ASODN). However, the influence of hTR ASODN on the anti‑tumor effects of radiation in NPC remain unknown. The present study investigated the effects of hTR ASODN on the proliferation and radiosensitivity of NPC cells, and further explored the underlying mechanisms. hTR ASODN significantly inhibited the proliferation and decreased the telomere length of CNE‑2 human NPC cells. Furthermore, combined treatment of hTR ASODN with radiation significantly enhanced anti‑tumor efficacy. The apoptotic rate and cleavage of caspase 9 were increased in the cells treated with the combined therapy, as compared with the cells treated with hTR ASODN or radiotherapy alone. In conclusion, these results suggest that hTR ASODN may inhibit the proliferation of NPC cells and enhance the anti‑tumor effects of radiation by inducing cell apoptosis. Therefore hTR ASODN may be a potential adjuvant agent for the treatment of NPC combined with radiation therapy, and these findings are of translational importance.

Promoter trapping method: transcription factor purification using human telomerase reverse transcriptase promoter

Background

Transcription factors bind to response elements on the promoter regions of genes to regulate transcriptional activity. One of the major problems with identifying transcription factors is their low abundance relative to other proteins in the cell. Developing a purification technique specific for transcription factors is crucial to the understanding of gene regulation. Promoter trapping is a method developed that uses the promoter regions as bait to trap proteins of interest and then purified using column chromatography. Here we utilize this technique to study the telomerase promoter, which has increased transcriptional activity in cancer cells. Gaining insight on how to control the enzyme at the promoter level may give new routes towards cancer treatments.

Results

Our findings show that the telomerase promoter (−170 - +91) and Promoter Trapping isolate a transcriptionally active and reproducible complex, when analyzed by liquid chromatography tandem mass spectrometry. We were also able to identify transcription factors, including AP-2 and SP1 known to bind this promoter, as well as show that these two proteins can bind to each other’s response element.

Conclusion

Here we focus on verifying the ability and versatility of Promoter Trapping coupled with additional well-characterized methods to identify already known factors responsible for telomerase transcriptional regulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-014-0053-2) contains supplementary material, which is available to authorized users.

Telomerase activated thymidine analogue pro-drug is a new molecule targeting hepatocellular carcinoma

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. Although hepatectomy and transplantation have significantly improved survival, there is no effective chemotherapeutic treatment for HCC and its prognosis remains poor. Sustained activation of telomerase is essential for the growth and progression of HCC, suggesting that telomerase is a rational target for HCC therapy. Therefore, we developed a thymidine analogue pro-drug, acycloguanosyl-5'-thymidyltriphosphate (ACV-TP-T), which is specifically activated by telomerase in HCC cells and investigated its anti-tumour efficacy.

METHODS

First, we verified in vitro whether ACV-TP-T was a telomerase substrate. Second, we evaluated proliferation and apoptosis in murine (Hepa1-6) and human (Hep3B, HuH7, HepG2) hepatic cancer cells treated with ACV-TP-T. Next, we tested the in vivo treatment efficacy in HBV transgenic mice that spontaneously develop hepatic tumours, and in a syngeneic orthotopic murine model where HCC cells were implanted directly in the liver.

RESULTS

In vitro characterization provided direct evidence that the pro-drug was actively metabolized in liver cancer cells by telomerase to release the active form of acyclovir. Alterations in cell cycle and apoptosis were observed following in vitro treatment with ACV-TP-T. In the transgenic and orthotopic mouse models, treatment with ACV-TP-T reduced tumour growth, increased apoptosis, and reduced the proliferation of tumour cells.

CONCLUSIONS

ACV-TP-T is activated by telomerase in HCC cells and releases active acyclovir that reduces proliferation and induces apoptosis in human and murine liver cancer cells. This pro-drug holds a great promise for the treatment of HCC.

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.

Novel trisubstituted acridines as human telomeric quadruplex binding ligands

A novel series of trisubstituted acridines were synthesized with the aim of mimicking the effects of BRACO19. These compounds were synthesized by modifying the molecular structure of BRACO19 at positions 3 and 6 with heteroacyclic moieties. All of the derivatives presented in the study exhibited stabilizing effects on the human telomeric DNA quadruplex. UV-vis spectroscopy, circular dichroism, linear dichroism and viscosimetry were used in order to study the nature of the DNA binding in more detail. The results show that all of the novel derivatives were able to fold the single-stranded DNA sequences into antiparallel G-quadruplex structures, with derivative 15 exhibiting the highest stabilizing capability. Cell cycle analysis revealed that a primary trend of the "braco"-like derivatives was to arrest the cells in the S- and G2M-phases of the cell cycle within the first 72h, with derivative 13 and BRACO19 proving particularly effective in suppressing cell proliferation. All studies derivatives were less toxic to human fibroblast cell line in comparison with HT 29 cancer cell line.

Identification and functional characterization of nuclear mortalin in human carcinogenesis

The Hsp70 family protein mortalin is an essential chaperone that is frequently enriched in cancer cells and exists in various subcellular sites, including the mitochondrion, plasma membrane, endoplasmic reticulum, and cytosol. Although the molecular mechanisms underlying its multiple subcellular localizations are not yet clear, their functional significance has been revealed by several studies. In this study, we examined the nuclear fractions of human cells and found that the malignantly transformed cells have more mortalin than the normal cells. We then generated a mortalin mutant that lacked a mitochondrial targeting signal peptide. It was largely localized in the nucleus, and, hence, is called nuclear mortalin (mot-N). Functional characterization of mot-N revealed that it efficiently protects cancer cells against endogenous and exogenous oxidative stress. Furthermore, compared with the full-length mortalin overexpressing cancer cells, mot-N derivatives showed increased malignant properties, including higher proliferation rate, colony forming efficacy, motility, and tumor forming capacity both in in vitro and in vivo assays. We demonstrate that mot-N promotes carcinogenesis and cancer cell metastasis by inactivation of tumor suppressor protein p53 functions and by interaction and functional activation of telomerase and heterogeneous ribonucleoprotein K (hnRNP-K) proteins.

Knockdown of hTERT by siRNA inhibits cervical cancer cell growth in vitro and in vivo

Human telomerase reverse transcriptase (hTERT) is the catalytic component of telomerase that facilitates tumor cell invasion and proliferation. It has been reported that telomerase and hTERT are significantly upregulated in majority of cancers including cervical cancer, thus, downregulation of hTERT is a promising target in malignant tumor treatment. We established a short interfering RNA (siRNA) targeting hTERT, and transfected it into HeLa cells (a cervical cancer cell line) to investi-gate the effect of cell proliferation, apoptosis, migration and invasion in cervical cancer cells. The results showed that siRNA targeting hTERT could effectively knock down hTERT expression, remarkably suppress telomerase activity, cell proliferation, migration and invasion, and induced cell apoptosis of cervical cancers cells in vitro. In addition, we evaluated whether siRNA targeting hTERT affects tumor growth in nude mice, and found that it dramatically inhibited tumorigenesis and growth of mice injected with siRNA targeting hTERT. Furthermore, we also found that knockdown of hTERT was able to significantly suppress constitutive phosphorylation of Akt, PI3K, which might imply that reduction of hTERT inhibited tumor growth via the PI3K/Akt signaling pathway to some extent. These results suggest that the suppression of hTERT expression by siRNA inhibits cervical cancer cell growth in vitro and in vivo, and may provide a novel target for anticancer gene therapy.