A combination of the telomerase inhibitor, BIBR1532, and paclitaxel synergistically inhibit cell proliferation in breast cancer cell lines

Natural killer cells in combination with the inhibition of telomerase induced apoptosis in Acute Myeloid Leukemia cells

Background

Recent trends in developing new treatments for cancers, highlight the use of immune cells particularly Natural Killer (NK) cells, as promising therapeutic strategies. While NK cells exhibit significant anti-tumor effects, their effectiveness is often limited. This study investigated the impact of BIBR1532, a human telomerase reverse transcriptase (hTERT) inhibitor, on improving the cytotoxicity of NK cells against Acute Myeloid Leukemia (AML) cells.

Methods

Primary AML cells and Kg-1a cell lines were cultured and treated with the half-maximal inhibitory concentration (IC50) of BIBR1532 for 48 h. The treated cells were then co-cultured with NK cells, after which cytotoxicity, cell proliferation, and apoptosis were assessed using Annexin V/7-AAD and Ki-67 expression analysis. Finally, apoptosis-related genes and proteins, hTERT gene and caspase 3/7 activity were studied.

Results

The Telomerase Inhibition (TI) in primary AML and Kg-1a cells with IC50 values of 38.75 μM and 57.64 μM, respectively, sensitized the AML cells and enhanced the anti-proliferative effects of NK cells. The combination of BIBR1532 and NK cells led to increased apoptosis, as indicated by the upregulation of the Bax and Bad genes, an increased Bax/Bcl-2 ratio, caspase 3/7 activity, Bax protein and a downregulation of mRNA expression levels of Bcl-2, Bcl-xl and decreased Bcl-2 protein.

Conclusion

The findings of this study demonstrate that the concurrent application of BIBR1532 and NK cells promotes apoptosis and reduces proliferation by targeting apoptosis-related genes and proteins such as Bax and Bcl-2.

Telomerase inhibition in breast cancer and breast cancer stem cells: a brief review

Breast cancer is a major health problem, accounting for one third of all cancers in women. There is no definitive treatment for breast cancer and its incidence is increasing worldwide every year. Furthermore, breast cancer stem cells cause resistance to radiation and chemotherapy. Telomerase is an enzyme that protects telomeres and is activated in 90% of cancer cells, and telomerase activation is a hallmark of cancer. In this review, we examine telomerase activation in breast cancer and breast cancer stem cells and the therapeutic effects of telomerase inhibition in these cells. In this review, we aim to highlight the importance and impact of telomerase inhibition in the treatment of breast cancer and the lack of studies specifically in breast cancer stem cells.

Enhanced induction of apoptosis in chronic myeloid leukemia cells through synergistic effect of telomerase inhibitor MST-312 and imatinib

BACKGROUND

Chronic Myeloid Leukemia (CML), accounting for 15-20% of adult leukemia cases, is marked by the Philadelphia chromosome, resulting from the t(9;22)(q34;q11) translocation. This leads to uncontrolled cell proliferation and survival. Imatinib therapy lowers BCR-ABL levels, influencing telomere-associated proteins and increasing telomerase accessibility, indirectly boosting its activity. This study investigates the effects of MST-312 and imatinib, both individually and combined, on a CML cell line.

METHODS

The K562 cells were subjected to different doses of MST-312 and imatinib, including four combination concentrations. Cell viability and metabolic activity were measured using trypan blue and MTT assays at 24-, 36-, and 48-h post-treatment. Flow cytometry (AnnexinV/PI) assessed cell apoptosis after 36 h of treatment with MST-312 and imatinib, both individually and in combination. The expression levels of Bax, Bcl-2, hTERT, P21, P53, and c-Myc were determined via qRT-PCR.

RESULTS

Both MST-312 and imatinib independently reduced cell viability in a dose- and time-dependent manner. Their combination further decreased cell viability compared to monotherapy. Treatment of K562 cells with MST-312 and imatinib for 36 h increased Bax expression and the Bax/Bcl-2 ratio while decreasing Bcl-2 expression. Combined treatment significantly reduced hTERT ansd P21 gene expression compared to imatinib alone.

CONCLUSIONS

The combination of MST-312 and imatinib shows potential as a CML therapy. However, further research and clinical trials are necessary to validate these findings and determine their clinical relevance.

Investigation of cytotoxic effect and action mechanism of a synthetic peptide derivative of rabbit cathelicidin against MDA-MB-231 breast cancer cell line

Antimicrobial peptides (AMPs) have sparked significant interest as potential anti-cancer agents, thereby becoming a focal point in pursuing novel cancer-fighting strategies. These peptides possess distinctive properties, underscoring the importance of developing more potent and selectively targeted versions with diverse mechanisms of action against human cancer cells. Such advancements would offer notable advantages compared to existing cancer therapies. This research aimed to examine the toxicity and selectivity of the nrCap18 peptide in both cancer and normal cell lines. Furthermore, the rate of cellular death was assessed using apoptosis and acridine orange/ethidium bromide (AO/EB) double staining at three distinct incubation times. Additionally, the impact of this peptide on the cancer cell cycle and migration was evaluated, and ultimately, the expression of cyclin-dependent kinase 4/6 (CDK4/6) genes was investigated. The results obtained from the study demonstrated significant toxicity and selectivity in cancer cells compared to normal cells. Moreover, a strong progressive increase in cell death was observed over time. Furthermore, the peptide exhibited the ability to halt the progression of cancer cells in the G1 phase of the cell cycle and impede their migration by suppressing the expression of CDK4/6 genes.

Role of p53 transcription factor in determining the efficacy of telomerase inhibitors in cancer treatment

AIM

Telomerase expression is unique to cancer cells, making it a promising target for therapy. However, a major drawback of telomerase inhibition is that it affects cancer cell proliferation only when telomeres shorten, creating a lag phase post-continuous drug treatment. Acute cytotoxicity of telomerase inhibitors is dependent on their ability to induce DNA damage. p53 senses DNA damage and is the primary effector required for sensitizing cells towards apoptosis.

MAIN METHODS

Isogenic p53+/+ and p53-/- ovarian cancer cell lines were generated using the CRISPR/Cas9 system and the anti-cancer effect of telomerase inhibitors MST-312 and BIBR1532 were determined. Flow cytometry, real-time PCR, and western blot were performed to study cell cycle, apoptosis, and gene expression.

KEY FINDINGS

We report that MST-312 exhibits p53-dependent cytotoxicity, while BIBR1532 exhibits p53-independent cytotoxicity. Colony-forming ability also confirms the p53-dependent effect of MST-312. Re-expression of p53 in p53-/- cells could rescue MST-312 sensitivity. In p53+/+ cells, MST-312 causes S phase arrest and activation of p53-dependent target genes like anti-apoptosis markers (Fas and Puma) and cell cycle markers (p21 and cyclinB). In p53-/- cells, MST-312 causes S/G2/M arrest. BIBR1532 induces S/G2/M phase cell cycle arrest irrespective of p53 status. This correlates with the expression of the DNA damage marker (γ-H2AX). Long-term continuous treatment with MST-312 or BIBR1532 results in p53-independent telomere shortening.

SIGNIFICANCE

In summary, we demonstrate that acute anti-cancer effects of MST-312 are dependent on p53 expression. Hence, it is important to consider the p53 expression status in cancer cells when selecting and administering telomerase inhibitors.

Telomerase and mitochondria inhibition promote apoptosis and TET2 and ANMT3a expression in triple negative breast cancer cell lines

Introduction

High metastasis, resistance to common treatments, and high mortality rate, has made triple-negative breast cancer (TNBC) to be the most invasive type of breast cancer. High telomerase activity and mitochondrial biogenesis are involved in breast cancer tumorigenesis. The catalytic subunit of telomerase, telomerase reverse transcriptase (hTERT), plays a role in telomere lengthening and extra-biological functions such as gene expression, mitochondria function, and apoptosis. In this study, it has been aimed to evaluate intrinsic-, extrinsic-apoptosis and DNMT3a and TET2 expression following the inhibition of telomerase and mitochondria respiration in TNBC cell lines.

Methods

TNBC cells were treated with IC50 levels of BIBR1532, tigecycline, and also their combination. Then, telomere length, and DNMT3a, TET2, and hTERT expression were evaluated. Finally, apoptosis rate, apoptosis-related proteins, and genes were analyzed.

Results

The present results showed that IC50 level of telomerase and inhibition of mitochondria respiration induced apoptosis but did not leave any significant effect on telomere length. The results also indicated that telomerase inhibition induced extrinsic-apoptosis in MDA-MB-231 and caused intrinsic- apoptosis in MDA-MB-468 cells. Furthermore, it was found that the expression of p53 decreased and was ineffective in cell apoptosis. The expressions of DNMT3a and TET2 increased in cells. In addition, combination treatment was better than BIBR1532 and tigecycline alone.

Conclusion

The inhibition of telomerase and mitochondria respiration caused intrinsic- and extrinsic- apoptosis and increased DNMT3a and TET2 expression and it could be utilized in breast cancer treatment.

Retrospective Analysis of the Clinical Characteristics of Patients with Breast Cancer Treated with Telomerase Peptide Immunotherapy Combined with Cytotoxic Chemotherapy

Purpose

Telomerase activation, a critical step in cancer progression, occurs in approximately 95% of breast cancer cases. Telomerase is an attractive therapeutic target for breast cancer owing to its unique expression pattern. GV1001, a telomerase-derived peptide, is loaded onto human leukocyte antigen (HLA) class II antigen-presenting cells and binds to CD4+ T cell activating immune responses. This study aimed to evaluate the effectiveness and safety of co-administration of GV1001 and cytotoxic chemotherapy in patients with heavily-treated metastatic breast cancer.

Patients and methods

We analyzed 63 patients with breast cancer who received both GV1001 and cytotoxic chemotherapy. The GV 1001 administration methods involves 0.56 mg intradermal injection three times during the first week, one time at weeks 2, 3, 4, and 6, and then once every 28 days. The primary endpoint of this study was quality of life according to EORTC QLO-C30 and EQ-5D, while the secondary endpoint was the antitumor response according to RECIST 1.1, progression-free survival, overall survival, and toxicity profile.

Results

In 34 patients with HR+ breast cancer evaluable for tumor response, the disease control rate (DCR) and overall response rate (ORR) were 58.8% and 26.4%, respectively. The DCR and ORR were 66.6% and 28.5% in 21 patients with HER-2+ and 50% and 25% in patients with triple-negative breast cancer (TNBC), respectively. The median progression free survival was 10.4, 8.7, and 5.6 months in HR+, HER-2+, TNBC, respectively. The overall survival was 19.7, 13.2, and 9.4 months for patients with HR+, HER-2+, and TNBC, respectively. Most patients had an improved quality of life with statistically significant differences in some variables. The patients in this study experienced no additional toxicities other than the cytotoxic chemotherapy-associated side effects.

Conclusion

GV1001 is a relatively safe anticancer vaccine for patients with heavily-treated breast cancer and can to improve the quality of life.

Regulation of telomerase towards tumor therapy

Cancer is an aging-related disease, while aging plays an important role in the development process of tumor, thus the two are inextricably associated. Telomere attrition is one of the recognized hallmark events of senescence. Hence, targeting telomerase which could extends telomere sequences to treat tumors is widely favored. Cancer cells rely on high activity of telomerase to maintain a strong proliferative potential. By inhibiting the expression or protein function of telomerase, the growth of cancer cells can be significantly suppressed. In addition, the human immune system itself has a defense system against malignant tumors. However, excessive cell division results in dramatic shortening on telomeres and decline in the function of immune organs that facilitates cancer cell evasion. It has been shown that increasing telomerase activity or telomere length of these immune cells can attenuate senescence, improve cellular viability, and enhance the immunosuppressive microenvironment of tumor. In this paper, we review the telomerase-targeting progress using different anti-tumor strategies from the perspectives of cancer cells and immune cells, respectively, as well as tracking the preclinical and clinical studies of some representative drugs for the prevention or treatment of tumors.

Research progress of small-molecule drugs in targeting telomerase in human cancer and aging

Telomeres are unique structures located at the ends of linear chromosomes, responsible for stabilizing chromosomal structures. They are synthesized by telomerase, a reverse transcriptase ribonucleoprotein complex. Telomerase activity is generally absent in human somatic cells, except in stem cells and germ cells. Every time a cell divides, the telomere sequence is shortened, eventually leading to replicative senescence and cell apoptosis when the telomeres reach a critical limit. However, most human cancer cells exhibit increased telomerase activity, allowing them to divide continuously. The importance of telomerase in cancer and aging has made developing drugs targeting telomerase a focus of research. Such drugs can inhibit cancer cell growth and delay aging by enhancing telomerase activity in telomere-related syndromes or diseases. This review provides an overview of telomeres, telomerase, and their regulation in cancer and aging, and highlights small-molecule drugs targeting telomerase in these fields.

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

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

Zeolitic Imidazolate Framework-8 (ZIF-8) as a Drug Delivery Vehicle for the Transport and Release of Telomerase Inhibitor BIBR 1532

Telomerase is constitutively overexpressed in the majority of human cancers and telomerase inhibition provides a promising broad-spectrum anticancer therapeutic strategy. BIBR 1532 is a well-known synthetic telomerase inhibitor that blocks the enzymatic activity of hTERT, the catalytic subunit of telomerase. However, water insolubility of BIBR 1532 leads to low cellular uptake and inadequate delivery and thus, limits its anti-tumor effects. Zeolitic imidazolate framework-8 (ZIF-8) is considered as an attractive drug delivery vehicle for improved transport, release and anti-tumor effects of BIBR 1532. Herein, ZIF-8 and BIBR 1532@ZIF-8 were synthesized, respectively, and the physicochemical characterizations confirmed the successful encapsulation of BIBR 1532 in ZIF-8 coupled with an improved stability of BIBR 1532. ZIF-8 could alter the permeability of lysosomal membrane probably by the imidazole ring-dependent protonation. Moreover, ZIF-8 encapsulation facilitated the cellular uptake and release of BIBR 1532 with more accumulation in the nucleus. BIBR 1532 encapsulation with ZIF-8 triggered a more obvious growth inhibition of cancer cells as compared with free BIBR 1532. A more potent inhibition on hTERT mRNA expression, aggravated G0/G1 arrest accompanied with an increased cellular senescence were detected in BIBR 1532@ZIF-8-treated cancer cells. Our work has provided preliminary information on improving the transport, release and efficacy of water-insoluble small molecule drugs by using ZIF-8 as a delivery vehicle.

Deciphering the Functions of Telomerase Reverse Transcriptase in Head and Neck Cancer

Head and neck cancers (HNCs) are among the ten leading malignancies worldwide. Despite significant progress in all therapeutic modalities, predictive biomarkers, and targeted therapies for HNCs are limited and the survival rate is unsatisfactory. The importance of telomere maintenance via telomerase reactivation in carcinogenesis has been demonstrated in recent decades. Several mechanisms could activate telomerase reverse transcriptase (TERT), the most common of which is promoter alternation. Two major hotspot TERT promoter mutations (C228T and C250T) have been reported in different malignancies such as melanoma, genitourinary cancers, CNS tumors, hepatocellular carcinoma, thyroid cancers, sarcomas, and HNCs. The frequencies of TERT promoter mutations vary widely across tumors and is quite high in HNCs (11.9-64.7%). These mutations have been reported to be more enriched in oral cavity SCCs and HPV-negative tumors. The association between TERT promoter mutations and poor survival has also been demonstrated. Till now, several therapeutic strategies targeting telomerase have been developed although only a few drugs have been used in clinical trials. Here, we briefly review and summarize our current understanding and evidence of TERT promoter mutations in HNC patients.

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

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

hTERT Downregulation Attenuates Resistance to DOX, Impairs FAK-Mediated Adhesion, and Leads to Autophagy Induction in Breast Cancer Cells

Telomerase is known to contribute to telomere maintenance and to provide cancer cell immortality. However, numerous reports are showing that the function of the enzyme goes far beyond chromosome ends. The study aimed to explore how telomerase downregulation in MCF7 and MDA-MB-231 breast cancer cells affects their ability to survive. Consequently, sensitivity to drug resistance, proliferation, and adhesion were assessed. The lentiviral-mediated human telomerase reverse transcriptase (hTERT) downregulation efficiency was performed at gene expression and protein level using qPCR and Western blot, respectively. Telomerase activity was evaluated using the Telomeric Repeat Amplification Protocol (TRAP) assay. The study revealed that hTERT downregulation led to an increased sensitivity of breast cancer cells to doxorubicin which was demonstrated in MTT and clonogenic assays. During a long-term doubling time assessment, a decreased population doubling level was observed. Interestingly, it did not dramatically affect cell cycle distribution. hTERT downregulation was accompanied by an alteration in β1-integrin- and by focal adhesion kinase (FAK)-driven pathways together with the reduction of target proteins phosphorylation, i.e., paxillin and c-Src. Additionally, autophagy activation was observed in MDA-MB-231 cells manifested by alternations in Atg5, Beclin 1, LC3II/I ratio, and p62. These results provide new evidence supporting the possible therapeutic potential of telomerase downregulation leading to induction of autophagy and cancer cells elimination.

The Small Molecule BIBR1532 Exerts Potential Anti-cancer Activities in Preclinical Models of Feline Oral Squamous Cell Carcinoma Through Inhibition of Telomerase Activity and Down-Regulation of TERT

Expression of telomerase reverse transcriptase (TERT) and telomerase activity (TA) is a main feature of cancer, contributing to cell immortalization by causing telomeres dysfunction. BIBR1532 is a potent telomerase inhibitor that showed potential anti-tumor activities in several types of cancer, by triggering replicative senescence and apoptosis. In a previous work, we detected, for the first time, TERT expression and TA in preclinical models of feline oral squamous cell carcinoma (FOSCC); therefore, we aimed at extending our investigation by testing the effects of treatment with BIBR1532, in order to explore the role of telomerase in this tumor and foreshadow the possibility of it being considered as a future therapeutic target. In the present study, treatment of FOSCC cell lines SCCF1, SCCF2, and SCCF3 with BIBR1532 resulted in successful inhibition of TA, with subsequent cell growth stoppage and decrease in cell viability. Molecular data showed that up-regulation of cell cycle inhibitor p21, unbalancing of Bax/Bcl-2 ratio, and down-regulation of survival gene Survivin were mostly involved in the observed cellular events. Moreover, BIBR1532 diminished the expression of TERT and its transcriptional activator cMyc, resulting in the down-regulation of epidermal growth factor receptor (EGFR), phospho-ERK/ERK ratio, and matrix metalloproteinases (MMPs)-1/-2 and−9, likely as a consequence of an impairment of TERT extra-telomeric functions. Taken together, our data suggest that BIBR1532 exerts multiple anti-cancer activities in FOSCC by inhibiting telomerase pathway and interfering with signaling routes involved in cell proliferation, cell survival, and invasion, paving the way for future translational studies aimed at evaluating its possible employment in the treatment of this severe tumor of cats.

Targeting telomerase for its advent in cancer therapeutics

Telomerase has emerged as an important primary target in anticancer therapy. It is a distinctive reverse transcriptase enzyme, which extends the length of telomere at the 3' chromosomal end, and uses telomerase reverse transcriptase (TERT) and telomerase RNA template-containing domains. Telomerase has a vital role and is a contributing factor in human health, mainly affecting cell aging and cell proliferation. Due to its unique feature, it ensures unrestricted cell proliferation in malignancy and plays a major role in cancer disease. The development of telomerase inhibitors with increased specificity and better pharmacokinetics is being considered to design and develop newer potent anticancer agents. Use of natural and synthetic compounds for the inhibition of telomerase activity can lead to an opening of new vistas in cancer treatment. This review details about the telomerase biochemistry, use of natural and synthetic compounds; vaccines and oncolytic virus in therapy that suppress the telomerase activity. We have discussed structure-activity relationships of various natural and synthetic telomerase inhibitors to help medicinal chemists and chemical biology researchers with a ready reference and updated status of their clinical trials. Suppression of human TERT (hTERT) activity through inhibition of hTERT promoter is an important approach for telomerase inhibition.

Arsenic trioxide and BIBR1532 synergistically inhibit breast cancer cell proliferation through attenuation of NF-κB signaling pathway

AIMS

Despite the remarkable anti-proliferative effects of Arsenic trioxide (ATO) in breast cancer cells, the requirement of high, toxic concentrations to induce apoptosis may cause serious side effects in patients. In the present study, we aimed to use BIBR1532, an hTERT inhibitor, in combination with ATO to sensitize MCF7 and MDA-231 cells to lower concentrations of ATO.

MAIN METHODS

Breast cancer cell lines MCF7 and MDA-231 were cultured and treated with different doses of ATO and BIBR1532 for 48 h and its effects on cell survival and proliferation were analyzed by MTT, crystal violet staining, colony formation assay, cell cycle, AnnexinV/PI and Real-time PCR tests.

KEY FINDINGS

ATO and BIBR1532 synergistically inhibited proliferation and colony-forming ability of breast cancer cells. Besides, BIBR1532 augmented ATO-induced cytotoxic effects via triggering G1 cell cycle arrest and induction of apoptosis coupled with the down-regulation of NF-κB target genes that were involved in cell cycle progression (e.g. CCND1 and CDK6) and prevention of apoptosis such as Bcl-2, Bcl-xl, c-IAP2, and Survivin Respectively. Moreover, ATO-BIBR1532 significantly reduced the mRNA expression level of RELA, NFKB1, and several validated target genes of the NF-κB signaling pathway including NFKBIA, VEGFC, c-Myc, and hTERT.

SIGNIFICANCE

The combination of ATO and BIBR1532 synergistically induced its anti-proliferative effect in breast cancer cells by targeting the two key cancer-related pathways, hTERT and NF-κB, and disrupting their feed-forward loop at the same time which result in the reduction of NF-κB transcriptional activity and subsequent down-regulation of its target genes.

Telomerase: Key regulator of inflammation and cancer

The telomerase holoenzyme, which has a highly conserved role in maintaining telomere length, has long been regarded as a high-profile target in cancer therapy due to the high dependency of the majority of cancer cells on constitutive and elevated telomerase activity for sustained proliferation and immortality. In this review, we present the salient findings in the telomerase field with special focus on the association of telomerase with inflammation and cancer. The elucidation of extra-telomeric roles of telomerase in inflammation, reactive oxygen species (ROS) generation, and cancer development further complicated the design of anti-telomerase therapy. Of note, the discovery of the unique mechanism that underlies reactivation of the dormant telomerase reverse transcriptase TERT promoter in somatic cells not only enhanced our understanding of the critical role of TERT in carcinogenesis but also opens up new intervention ideas that enable the differential targeting of cancer cells only. Despite significant effort invested in developing telomerase-targeted therapeutics, devising efficacious cancer-specific telomerase/TERT inhibitors remains an uphill task. The latest discoveries of the telomere-independent functionalities of telomerase in inflammation and cancer can help illuminate the path of developing specific anti-telomerase/TERT therapeutics against cancer cells.

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.

Biological behavior exploration of a paclitaxel-eluting poly-l-lactide-coated Mg–Zn–Y–Nd alloy intestinal stent in vivo

As a new type of intestinal stent, the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stent has shown good degradability, although its biocompatibility in vitro and in vivo has not been investigated in detail. In this study, its in vivo biocompatibility was evaluated by animal study. New Zealand white rabbits were implanted with degradable intestinal Mg–Zn–Y–Nd alloy stents that were exposed to different treatments. Stent degradation behavior was observed both macroscopically and using a scanning electron microscope (SEM). Energy dispersion spectrum (EDS) and histological observations were performed to investigate stent biological safety. Macroscopic analysis showed that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents could not be located 12 days after implantation. SEM observations showed that corrosion degree of the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents implanted in rabbits was significantly lower than that in the PLLA/Mg–Zn–Y–Nd stent group. Both histopathological testing and serological analysis of in vivo biocompatibility demonstrated that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stents could significantly inhibit intestinal tissue proliferation compared to the PLLA/Mg–Zn–Y–Nd alloy stents, thus providing the basis for designing excellent biodegradable drug stents.

Mg–Zn–Y–Nd alloy stents coated with MAO/PLLA/paclitaxel coating were implanted into the New Zealand rabbits intestine to investigate the biocompatibility and degradation behavior.

Telomerase Inhibitor TMPyP4 Alters Adhesion and Migration of Breast-Cancer Cells MCF7 and MDA-MB-231

Human telomeres were one of the first discovered and characterized sequences forming quadruplex structures. Association of these structures with oncogenic and tumor suppressor proteins suggests their important role in cancer development and therapy efficacy. Since cationic porphyrin TMPyP4 is known as G-quadruplex stabilizer and telomerase inhibitor, the aim of the study was to analyze the anticancer properties of this compound in two different human breast-cancer MCF7 and MDA-MB-231 cell lines. The cytotoxicity of TMPyP4 alone or in combination with doxorubicin was measured by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromid) and clonogenic assays, and the cell-cycle alterations were analyzed by flow cytometry. Telomerase expression and activity were evaluated using qPCR and telomeric repeat amplification protocol (TRAP) assays, respectively. The contribution of G-quadruplex inhibitor to protein pathways engaged in cell survival, DNA repair, adhesion, and migration was performed using immunodetection. Scratch assay and functional assessment of migration and cell adhesion were also performed. Consequently, it was revealed that in the short term, TMPyP4 neither revealed cytotoxic effect nor sensitized MCF7 and MDA-MB-231 to doxorubicin, but altered breast-cancer cell adhesion and migration. It suggests that TMPyP4 might substantially contribute to a significant decrease in cancer cell dissemination and, consequently, cancer cell survival reduction. Importantly, this effect might not be associated with telomeres or telomerase.

Label-Free Telomerase Detection in Single Cell Using a Five-Base Telomerase Product-Triggered Exponential Rolling Circle Amplification Strategy

Telomerase is a universal biomarker of malignant tumors. Sensitive and reliable analysis for telomerase activity is of vital importance for both early diagnosis and therapy of malignant tumors. Herein, a novel fluorescent strategy was proposed for sensitive and label-free detection of telomerase activity. One highlight of this strategy is that an exponential signal amplification can be triggered by a very short telomerase extension product (TEP). Without adding dATP, the designed telomerase primer can be easily controlled to extend five bases (GGGTT) to give short TEP with definite length. The resulting short TEP can then be constructed as a circular rolling circle amplification (RCA) template and thus initiate a nicking enzyme-mediated exponential RCA, producing G-rich amplification products that can be sensitively probed via specific binding between the fluorescent dye Thioflavin T (ThT) and the nucleic acid G-quadruplexes. Elevated telomerase translocation efficiency, combined with exponential signal amplification and specific probing of RCA products by ThT, endow the sensing platform with extraordinarily high detection sensitivity. The requirement for short TEP increases the possibility to analyze telomerase with low activity. The proposed sensing platform can achieve sensitive telomerase activity detection in individual cells, even with the interference of accumulated normal cells. It was also demonstrated to show excellent capability in screening for the inhibitors of telomerase. Therefore, the proposed sensing platform has great potential for not only clinical diagnosis but also anticancer drug development.

Luteolin inhibits cell cycle progression and induces apoptosis of breast cancer cells through downregulation of human telomerase reverse transcriptase

Luteolin is a flavonoid, which has been extensively investigated due to its antitumor effects; however, the underlying mechanisms of its action remain largely unknown. The present study aimed to investigate the role of luteolin in breast cancer (BC), and explored how luteolin suppresses the growth and induces the apoptosis of BC cells. The MTS assay was used to determine the anticancer activity of luteolin. Colony formation and Transwell assays were performed to evaluate the effects of luteolin on cell growth and invasion. Cell cycle progression and apoptosis were analyzed by flow cytometry. In addition, western blotting was performed to analyze cellular apoptosis and signaling pathways elicited by luteolin. The present study revealed that the proliferation of the BC cell line MDA-MB-231 was effectively suppressed by luteolin in a dose-dependent manner. Additionally, luteolin was revealed to increase apoptotic rates in BC cells. Dose-dependent cell cycle arrest in S phase was observed following treatment with luteolin in MDA-MB-231 cells. Mechanistically, luteolin reduced telomerase levels in a dose-dependent manner. Additionally, luteolin inhibited phosphorylation of the nuclear factor-κB inhibitor α and its target gene c-Myc, to suppress human telomerase reverse transcriptase (hTERT) expression, which encodes the catalytic subunit of telomerase. Collectively, the results of the present study indicated that luteolin may inhibit BC cell growth by targeting hTERT, suggesting that the mechanism of hTERT regulation by luteolin may justify further study regarding its potential as a therapeutic target for BC treatment.

Investigation of the effect of telomerase inhibitor BIBR1532 on breast cancer and breast cancer stem cells

It is emphasized that cancer stem cells (CSCs) forming the subpopulation of tumour cells are responsible for tumour growth, metastasis, and cancer drug resistance. Inadequate response to conventional therapy in breast cancer leads researchers to find new treatment methods and literature surveys that support CSC studies. A selective anticancer agent BIBR1532 inhibits the telomerase enzyme. Many of the chemotherapeutic drugs used in clinical trials have harmful effects, but the advantage of telomerase-based inhibitors is that they are less toxic to healthy tissues. The phosphoinositide 3-kinase (PI3K)/serine/threonine kinase (Akt)/mammalian target of rapamycin (mTOR) pathway is common in breast cancer, and the interaction between the mTOR pathway and human telomerase reverse transcriptase (hTERT) is essential for the survival of cancer cells. In our study, we treated MCF-7, breast cancer stem cell (BCSC) and normal breast epithelial cell MCF10A with the BIBR1532 inhibitor. The IC ₅₀ doses for the 48th hour of BIBR1532 treatment were detected as 34.59 μM in MCF-7, 29.91 μM in BCSCs, and 29.07 μM in MCF10A. It has been observed that this agent induces apoptosis in the BCSC and MCF-7 cell lines. According to the results of cell cycle analysis, G ₂ /M phase accumulation was observed in BCSC and MCF-7 cell lines. It has also been shown that BIBR1532 suppresses telomerase activity in BCSC and MCF-7. The effect of BIBR1532 on the mTOR signalling pathway has been investigated for the first time in this study. It is thought that the telomerase inhibitor may bring a new approach to the treatment and it may be useful in the treatment of CSCs.

Contributory role of microRNAs in anti-cancer effects of small molecule inhibitor of telomerase (BIBR1532) on acute promyelocytic leukemia cell line

Telomerase-mediated immortalization and proliferation of tumor cells is a promising anti-cancer treatment strategy and development of potent telomerase inhibitors is believed to open new window of treatments in human malignancies. In the present study, we found that BIBR1532, a small molecule inhibitor of human telomerase, exerted cytotoxic effects on a panel of human cancer cells spanning from solid tumors to hematologic malignancies; however, as compared with solid tumors, leukemic cells were more sensitive to this inhibitor. This was independent of molecular status of p53 in the leukemic cells. The results of a miRNA PCR array revealed that BIBR1532-induced cytotoxic effects in NB4, the most sensitive cell line, was coupled with alteration in a substantial number of cancer-related miRNAs. Interestingly, most of these miRNAs were found to act as tumor suppressors with validated targets in cell cycle or nuclear factor (NF)-κB-mediated apoptosis. In accordance with a bioinformatics analysis, our experimental studies showed that BIBR1532-induced apoptosis is mediated, at least partly, by inhibition of NF-κB. Moreover, we found that the alteration in the expression of miRNAs was coupled with the alteration in the cell cycle progression. To sum up with, a straightforward interpretation of our results is that telomerase inhibition using BIBR1532 not only induced CDKN1A-mediated G1 arrest in NB4, but also resulted in a caspase-3-dependent apoptotic cell death mostly through suppression of NF-κB axis.

Quartz crystal microbalance for telomerase sensing based on gold nanoparticle induced signal amplification

A mass-sensitive quartz crystal microbalance biosensor was constructed for telomerase sensing based on gold nanoparticle induced signal amplification.

Down regulation of human telomerase reverse transcriptase (hTERT) expression by BIBR1532 in human glioblastoma LN18 cells

Increased telomerase activity can be blocked by targeting the hTERT activity at both RNA and catalytic subunits. Various inhibitors had been used to regulate hTERT activity in glioblastoma cell lines and showed promising results. The present study hypothesized that the telomerase specific inhibitor BIBR1532 can effectively down-regulate the telomerase activity in LN18 glioblastoma cell line. LN18 glioblastoma cell line was treated with various concentrations of BIBR1532 at different time intervals. MTT assay was performed to determine cell viability after BIBR1532 treatment. hTERT mRNA and protein expression were determined by qRT-PCR and western blotting, respectively. Flow cytometry and TRAP assay was performed to detect the rate of apoptosis and telomerase activity in treated and control samples. One-way ANOVA was performed to compare the mean values of variables in control and BIBR1532 treated groups. LN18 cells showed a significant dose dependent cytotoxic effect after treatment with BIBR1532. hTERT mRNA expression in cells treated with 25, 100 and 200 μM BIBR1532 treated groups was decreased ~ 21, ~ 61.2, and ~ 77%, respectively (p < 0.05). We also observed that, BIBR1532 treatment reduced the expression of hTERT protein in LN18 cells in a dose dependent manner. The Flow cytometry data showed that, the drug induced significant increase in the total percentage of apoptotic cells with 200 μM concentration of BIBR1532 at all time points. BIBR1532 exhibited potent inhibition of telomerase activity in a dose-dependent manner in LN18 cells. BIBR1532 could induce apoptosis in LN18 cells through the downregulation of telomerase activity at transcriptional and translational level. We conclude that BIBR1532 may be a therapeutic agent to suppress telomerase activity, however, further efforts are necessary in order to explore this therapeutic strategy.

Telomerase reverse transcriptase mediates EMT through NF-κB signaling in tongue squamous cell carcinoma

Locoregional lymph nodes metastasis in oral tongue squamous cell carcinoma represents one of important and common prognostic factors for poor clinical outcome. The human Telomerase Reverse Transcriptase (hTERT) is one of key players in cancer metastasis and stemness, but its exact function in tongue squamous cell carcinoma remains unknown. Here, we aim to understand the role of hTERT by utilizing the CRISPR/Cas9 gene editing system to deplete hTERT in the SCC-15 cell line. Functional comparison of SCC-15 control and knockout cells (hTERT^−/−) showed that loss of hTERT suppressed cell proliferation and migration/invasion. Furthermore, hTERT depletion significantly decreased tumorigenesis, including alterations in cellular morphology that areindicative for epithelial-mesenchymal transition (EMT). Mechanistically we demonstrated that the hTERT knockout attenuates NF-κB signaling via a negative feedback regulation in tumorprogression. From these results we propose a novel molecular mechanism of hTERT to promote SCC-15 invasion and metastasis via NF-κB activation. We conclude that targeting hTERT may represent a new therapeutic strategy to improve therapy and survival of tongue squamous cell carcinoma patients.

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.

Synergistic Anticancer Effects of Silibinin and Chrysin in T47D Breast Cancer Cells

Objective:

Breast cancer is one of the most significant causes of female cancer death worldwide. Although several chemotherapeutics have been developed to treat this type of cancer, issues remain such as low survival rates and high reoccurrence after chemotherapy and radiotherapy. To explore a chemopreventive approach to enhancing breast cancer treatment efficacy, the antiproliferative effects of a combination of chrysin and silibinin, two herbal substances, in T47D breast cancer cells were assessed.

Materials and Methods:

Cytotoxicity of the agents singly and in combination was evaluated by MTT assay. Also, qRT-PCR was used to measure the expression levels of hTERT and cyclin D1 genes after 48 h treatment.

Results:

Cell viability assays revealed that chrysin or silibinin alone inhibited proliferation in a dose and time-dependent manner, and combining the drugs synergistically induced growth inhibition in the breast cancer cell line. The precise nature of this interaction was further analyzed by the median-effect method, where the combination indices (CI) were <1 for combination treatments, indicating synergism regarding T47D cell proliferation. qPCR results showed that the drug combination also synergistically down-regulated the mRNA levels of hTERT and cyclin D1 at all used concentrations compared with the drugs used alone after 48 h treatment (P ≤ 0.05).

Conclusion:

The data provide evidence that synergistic antiproliferative effects of Chrysin and Silibinin are linked to the down-regulation of cyclin D1 and hTERT genes, and suggest that their combination may have therapeutic value in treatment of breast cancer.

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.

Inhibition of telomerase using BIBR1532 enhances doxorubicin-induced apoptosis in pre-B acute lymphoblastic leukemia cells

OBJECTIVES

Interest into targeting telomerase in cancer has increased by the recent disclosure that elevated telomerase activity is associated with disease recurrence and poor outcome in cancers. In addition, cellular acquisition of unlimited replicative potential, which is closely related to the maintenance of telomeres mostly via the reactivation of telomerase, has been shown to confer loss of sensitivity to a wide range of anti-neoplastic agents.

METHODS

To evaluate whether telomerase inhibition using non-nucleosidic inhibitor of telomerase BIBR1532 could enhance cytotoxic effect of doxorubicin in acute lymphoblastic leukemia, Nalm-6 pre-B ALL cells were subjected to combination treatment and subsequent cell viability, growth kinetics, caspase-3 activity, and transcriptional alteration of p73, p21, FOXO3a, c-Myc, hTERT, and other apoptosis-related target genes were investigated.

RESULTS

Combination of BIBR1532 with doxorubicin produced a synergistic anticancer effect probably through induction of p73. Transcription factor p73 not only suppressed the proliferative capacity of the cells through induction of p21-mediated G1 arrest, but also down-regulated the mRNA level of hTERT and c-Myc. Our results also report that BIBR1532 induced a caspase-dependent apoptosis, at least partially, through heightened ROS levels, and noteworthy enhanced the pro-oxidant property of doxorubicin. In harmony, transcriptional repression of survivin could be a probable underlying mechanism for the induction of apoptosis through shifting the ratio of death promoters to death repressors via alteration of Bax and Bcl2 expression.

CONCLUSIONS

Overall, it seems that combination of BIBR1532 and doxorubicin could be a novel therapeutic strategy for acute lymphoblastic leukemia that may be clinically accessible in the near future.

Tumor-selective peptide-carrier delivery of Paclitaxel increases in vivo activity of the drug

Taxanes are highly effective chemotherapeutic drugs against proliferating cancer and an established option in the standard treatment of ovarian and breast cancer. However, treatment with paclitaxel is associated with severe side effects, including sensory axonal neuropathy, and its poor solubility in water complicates its formulation. In this paper we report the in vitro and in vivo activity of a new form of paclitaxel, modified for conjugation with a tumor-selective tetrabranched peptide carrier (NT4). NT4 selectively targets tumor cells by binding to membrane sulfated glycosaminoglycans (GAG) and to endocytic receptors, like LRP1 and LRP6, which are established tumor markers. Biological activity of NT4-paclitaxel was tested in vitro on MDA-MB 231 and SKOV-3 cell lines, representing breast and ovarian cancer, respectively, and in vivo in an orthotopic mouse model of human breast cancer. Using in vivo bioluminescence imaging, we found that conjugation of paclitaxel with the NT4 peptide led to increased therapeutic activity of the drug in vivo. NT4-paclitaxel induced tumor regression, whereas treatment with unconjugated paclitaxel only produced a reduction in tumor growth. Moreover, unlike paclitaxel, NT4-paclitaxel is very hydrophilic, which may improve its pharmacokinetic profile and allow the use of less toxic dilution buffers, further decreasing its general chemotherapic toxicity.

Knockdown of hTERT and Treatment with BIBR1532 Inhibit Cell Proliferation and Invasion in Endometrial Cancer Cells

Telomerase activity and expression of the catalytic protein hTERT are associated with cell proliferation and advanced stage in endometrial cancer. Our objective was to evaluate the effect of inhibition of hTERT by siRNA and BIBR1532 on cell growth, apoptosis and invasion in endometrial cancer cells. Knockdown of hTERT or treatment of the cells with BIBR1532 decreased telomerase activity, inhibited cell proliferation, induced apoptosis, and reduced cell invasion in Ishikawa and ECC-1 cells. Either hTERT siRNA or BIBR1532 in combination with paclitaxel promoted a synergistic inhibitory effect on cell growth through induction of Annexin V expression and a remarkable reduction in cell invasion through reduction of protein expression of MMP9, MMP2, and MMP3. Increased telomerase activity and hTERT protein expression by transfections enhanced the protein expression of MMPs and increased the cell invasion ability. BIBR1532 significantly antagonized cell invasion induced by increased hTERT expression. These findings suggest that telomerase and hTERT facilitate cell invasion via MMP family in human endometrial cancer cells.