Telomerase: a target for cancer therapeutics

Telomerase Inhibition by MST-312 Sensitizes Breast Cancer Cells to the Anti-cancer Properties of Plumbagin

Breast cancer is the most common cause of malignancy and the second most common cause of death due to cancer in women. This heterogeneous disease is currently broadly classified as estrogen receptor (ER), progesterone receptor (PR) positive luminal tumors, human epidermal growth factor receptor 2 (HER2) amplified tumors and triple-negative breast cancers (TNBC). Phytochemicals are proven to be promising anti-cancer chemotherapeutics agents with minimal cytotoxic effects on normal cells. Plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone) is a phytochemical derived from the roots of Plumbago zeylanica and it is known to possess anti-cancer properties similar to other compounds of naphthoquinones. In about 90% of cancer cells, the telomerase enzyme activity is revived to add telomeric repeats to evade apoptosis. In this study, a combinatorial approach of combining the anti-cancer compound plumbagin to induce genotoxicity and a potent telomerase inhibitor, MST-312 (synthetic derivative of tea catechins), was used to determine the combinational treatment-induced lethality in breast cancer cells such as MDA-MB-231 (TNBC) and MCF-7 (lumina) cells. MDA-MB-231 cells were responsive to combination treatment in both short-term (48 h) and long-term treatment (14 days) in a synergistic manner, whereas in MCF-7, the combination treatment was more effective in the long-term regimen. Furthermore, the cytotoxic effects of the plumbagin and MST-312 combination treatment were not recoverable after the short-term treatment. In conclusion, a combination treatment of MST-312 and plumbagin is proven to be more effective than a single plumbagin compound treatment in inducing DNA damage and telomere dysfunction leading to greater genome instability, cell cycle arrest and eventually cell death in cancer cells.

Combining old and new concepts in targeting telomerase for cancer therapy: transient, immediate, complete and combinatory attack (TICCA)

Telomerase can overcome replicative senescence by elongation of telomeres but is also a specific element in most cancer cells. It is expressed more vastly than any other tumor marker. Telomerase as a tumor target inducing replicative immortality can be overcome by only one other mechanism: alternative lengthening of telomeres (ALT). This limits the probability to develop resistance to treatments. Moreover, telomerase inhibition offers some degree of specificity with a low risk of toxicity in normal cells. Nevertheless, only one telomerase antagonist reached late preclinical studies. The underlying causes, the pitfalls of telomerase-based therapies, and future chances based on recent technical advancements are summarized in this review. Based on new findings and approaches, we propose a concept how long-term survival in telomerase-based cancer therapies can be significantly improved: the TICCA (Transient Immediate Complete and Combinatory Attack) strategy.

Hyperpolarized δ-[1- 13C]gluconolactone imaging visualizes response to TERT or GABPB1 targeting therapy for glioblastoma

TERT promoter mutations are a hallmark of glioblastoma (GBM). Accordingly, TERT and GABPB1, a subunit of the upstream mutant TERT promoter transcription factor GABP, are being considered as promising therapeutic targets in GBM. We recently reported that the expression of TERT or GABP1 modulates flux via the pentose phosphate pathway (PPP). Here, we investigated whether 13C magnetic resonance spectroscopy (MRS) of hyperpolarized (HP) δ- [1-13C]gluconolactone can serve to image the reduction in PPP flux following TERT or GABPB1 silencing. We investigated two different human GBM cell lines stably expressing shRNAs targeting TERT or GABPB1, as well as doxycycline-inducible shTERT or shGABPB1cells. MRS studies were performed on live cells and in vivo tumors, and dynamic sets of 13C MR spectra were acquired following injection of HP δ-[1-13C]gluconolactone. HP 6-phosphogluconolactone (6PG), the product of δ-[1-13C]gluconolactone via the PPP, was significantly reduced in TERT or GABPB1-silenced cells or tumors compared to controls in all our models. Furthermore, a positive correlation between TERT expression and 6PG levels was observed. Our data indicate that HP δ-[1-13C]gluconolactone, an imaging tool with translational potential, could serve to monitor TERT expression and its silencing with therapies that target either TERT or GABPB1 in mutant TERT promoter GBM patients.

Many Functions of Telomerase Components: Certainties, Doubts, and Inconsistencies

A growing number of studies have evidenced non-telomeric functions of "telomerase". Almost all of them, however, investigated the non-canonical effects of the catalytic subunit TERT, and not the telomerase ribonucleoprotein holoenzyme. These functions mainly comprise signal transduction, gene regulation and the increase of anti-oxidative systems. Although less studied, TERC (the RNA component of telomerase) has also been shown to be involved in gene regulation, as well as other functions. All this has led to the publication of many reviews on the subject, which, however, are often disseminating personal interpretations of experimental studies of other researchers as original proofs. Indeed, while some functions such as gene regulation seem ascertained, especially because mechanistic findings have been provided, other ones remain dubious and/or are contradicted by other direct or indirect evidence (e.g., telomerase activity at double-strand break site, RNA polymerase activity of TERT, translation of TERC, mitochondrion-processed TERC). In a critical study of the primary evidence so far obtained, we show those functions for which there is consensus, those showing contradictory results and those needing confirmation. The resulting picture, together with some usually neglected aspects, seems to indicate a link between TERT and TERC functions and cellular stemness and gives possible directions for future research.

BID- and BAX-mediated mitochondrial pathway dominates A-1331852-induced apoptosis in senescent A549 cells

Recovered senescent tumor cells harbor higher migration and invasion potential, owing to which they play a crucial role in tumor recurrence and drug resistance. The aim of this study was to explore the ability of BH3 mimetics in clearing senescent A549 cells and elucidate their underlying killing mechanism. Doxorubicin-induced cell senescence was determined using augmented senescence-associated beta-galactosidase (SA-β-Gal) staining and increased P16 expression. CCK-8 and crystal violet staining demonstrated that A-1331852, BH3 mimetic, could kill senescent tumor cells without affecting the proliferating cells. A-1331852 induced caspase-dependent senescent cell death accompanied by nuclear concentration, decreased mitochondrial membrane potential, and cleavage of poly (ADP-ribose) polymerase. Most importantly, A-1331852 upregulated the expression of BID and BAX indicating their role in mediating A-1331852-induced apoptosis in senescent A549 cells. The results of fluorescence resonance energy transfer showed that A-1331852 loosened or even released the binding between BCL-xL and tBID, releasing tBID. In addition, A-1331852 also dissociated the binding between BCL-xL and BAX, eventually leading to BAX oligomerization in the mitochondria, and resulting in apoptosis via the mitochondrial pathway. In conclusion, our data demonstrate for the first time that A-1331852 promotes apoptosis of senescent A549 cells by influencing the interaction between BCL-xL and tBID and that between BCL-xL and BAX.

Hormonal regulation of telomerase activity and hTERT expression in steroid-regulated tissues and cancer

Naturally, in somatic cells chromosome ends (telomeres) shorten during each cell division. This process ensures to limit proliferation of somatic cells to avoid malignant proliferation; however, it leads to proliferative senescence. Telomerase contains the reverse transcriptase TERT, which together with the TERC component, is responsible for protection of genome integrity by preventing shortening of telomeres through adding repetitive sequences. In addition, telomerase has non-telomeric function and supports growth factor independent growth. Unlike somatic cells, telomerase is detectable in stem cells, germ line cells, and cancer cells to support self-renewal and expansion. Elevated telomerase activity is reported in almost all of human cancers. Increased expression of hTERT gene or its reactivation is required for limitless cellular proliferation in immortal malignant cells. In hormonally regulated tissues as well as in prostate, breast and endometrial cancers, telomerase activity and hTERT expression are under control of steroid sex hormones and growth factors. Also, a number of hormones and growth factors are known to play a role in the carcinogenesis via regulation of hTERT levels or telomerase activity. Understanding the role of hormones in interaction with telomerase may help finding therapeutical targets for anticancer strategies. In this review, we outline the roles and functions of several steroid hormones and growth factors in telomerase regulation, particularly in hormone regulated cancers such as prostate, breast and endometrial cancer.

Plasmonic Nanomaterials for Colorimetric Biosensing: A Review

In the last few decades, plasmonic colorimetric biosensors raised increasing interest in bioanalytics thanks to their cost-effectiveness, responsiveness, and simplicity as compared to conventional laboratory techniques. Potential high-throughput screening and easy-to-use assay procedures make them also suitable for realizing point of care devices. Nevertheless, several challenges such as fabrication complexity, laborious biofunctionalization, and poor sensitivity compromise their technological transfer from research laboratories to industry and, hence, still hamper their adoption on large-scale. However, newly-developing plasmonic colorimetric biosensors boast impressive sensing performance in terms of sensitivity, dynamic range, limit of detection, reliability, and specificity thereby continuously encouraging further researches. In this review, recently reported plasmonic colorimetric biosensors are discussed with a focus on the following categories: (i) on-platform-based (localized surface plasmon resonance, coupled plasmon resonance and surface lattice resonance); (ii) colloid aggregation-based (label-based and label free); (iii) colloid non-aggregation-based (nanozyme, etching-based and growth-based).

Test Strip Platform Spin-Off for Telomerase Activity Detection: Development of an Electrochemical Biosensor

Telomerase overexpression has been associated directly with cancer, and the enzyme itself is recognized within the scientific community as a cancer biomarker. BIDEA's biosensing strip (BBS) is an innovative technology capable of detecting the presence of telomerase activity (TA) using electrochemical impedance spectroscopy (EIS). This BBS is an interdigital gold (GID) electrode array similar in size and handling to a portable glucose sensor. For the detection of the biomarker, BBS was modified by the immobilization of a telomere-like single strand DNA (ssDNA) on its surface. The sensor was exposed to telomerase-positive extract from commercially available cancer cells, and the EIS spectra were measured. Telomerase recognizes the sequence of this immobilized ssDNA probe on the BBS, and the reverse transcription process that occurs in cancer cells is replicated, resulting in the ssDNA probe elongation. This surface process caused by the presence of TA generates changes in the capacitive process on the electrode array microchip surface, which is followed by EIS as the sensing tool and correlated with the presence of cancer cells. The telomerases' total cell extraction protocol results demonstrate significant changes in the charge-transfer resistance (R ct) change rate after exposure to telomerase-positive extract with a detection limit of 2.94 × 104 cells/mL. Finally, a preliminary study with a small set of "blind" uterine biopsy samples suggests the feasibility of using the changes in the R ct magnitude change rate (Δ(ΔR ct/R cti)/Δt) to distinguish positive from negative endometrial adenocarcinoma samples by the presence or absence of TA.

The Genetic Makeup of Myeloproliferative Neoplasms: Role of Germline Variants in Defining Disease Risk, Phenotypic Diversity and Outcome

Myeloproliferative neoplasms are hematologic malignancies typified by a substantial heritable component. Germline variants may affect the risk of developing a MPN, as documented by GWAS studies on large patient cohorts. In addition, once the MPN occurred, inherited host genetic factors can be responsible for tuning the disease phenotypic presentation, outcome, and response to therapy. This review covered the polymorphisms that have been variably associated to MPNs, discussing them in the functional perspective of the biological pathways involved. Finally, we reviewed host genetic determinants of clonal hematopoiesis, a pre-malignant state that may anticipate overt hematologic neoplasms including MPNs.

SUV39H2/KMT1B Inhibits the cardiomyocyte senescence phenotype by down-regulating BTG2/PC3

Suppressor of variegation 3-9 homolog 2 (SUV39H2/KMT1B), a member of the SUV39 subfamily of lysine methyltransferases (KMTs), functions as an oncogene in various types of cancers. Here, we demonstrate a novel function of SUV39H2 that drives the cardiomyocyte aging process through BTG2. In our study, cardiomyocyte aging was induced by H2O2 and aging cells exhibited increases in SUV39H2. Knockdown of SUV39H2 accelerated cardiomyocyte senescence, while overexpression of SUV39H2 inhibited the cardiomyocyte senescence phenotype. These effects of SUV39H2 on cardiomyocytes were independent of DNA damage and mitochondrial dysfunction. Interestingly, RNA sequencing and bioinformatics analyses identified a strong correlation between SUV39H2 and BTG2. In addition to this, BTG2 protein levels were significantly increased in SUV39H2-deficient cardiomyocytes, and BTG2 knockdown virtually rescued the cardiomyocyte senescence phenotype induced by SUV39H2 knockdown. Taken together, these results indicate that SUV39H2 protects cardiomyocytes from H2O2 exposure-induced oxidative stress, DNA damage, and mitochondrial dysfunction by regulating the p53-BTG2 pathway. Our findings provide evidence that the activation of SUV39H2 has therapeutic or preventive potential against cardiac aging.

Nuclear compartmentalization of TERT mRNA and TUG1 lncRNA is driven by intron retention

The spatial partitioning of the transcriptome in the cell is an important form of gene-expression regulation. Here, we address how intron retention influences the spatio-temporal dynamics of transcripts from two clinically relevant genes: TERT (Telomerase Reverse Transcriptase) pre-mRNA and TUG1 (Taurine-Upregulated Gene 1) lncRNA. Single molecule RNA FISH reveals that nuclear TERT transcripts uniformly and robustly retain specific introns. Our data suggest that the splicing of TERT retained introns occurs during mitosis. In contrast, TUG1 has a bimodal distribution of fully spliced cytoplasmic and intron-retained nuclear transcripts. We further test the functionality of intron-retention events using RNA-targeting thiomorpholino antisense oligonucleotides to block intron excision. We show that intron retention is the driving force for the nuclear compartmentalization of these RNAs. For both RNAs, altering this splicing-driven subcellular distribution has significant effects on cell viability. Together, these findings show that stable retention of specific introns can orchestrate spatial compartmentalization of these RNAs within the cell. This process reveals that modulating RNA localization via targeted intron retention can be utilized for RNA-based therapies.

Recent advances in co-delivery nanosystems for synergistic action in cancer treatment

Nanocarrier delivery systems have been widely studied to carry unique or dual chemical drugs. The major challenge of chemotherapies is to overcome the multidrug-resistance (MDR) of cells to antineoplastic medicines. In this context, nano-scale technology has allowed researchers to develop biocompatible nano-delivery systems to overcome the limitation of chemical agents. The development of nano-vehicles may also be directed to co-deliver different agents such as drugs and genetic materials. The delivery of nucleic acids targeting specific cells is based on gene therapy principles to replace the defective gene, correct genome errors or knock-down a particular gene. Co-delivery systems are attractive strategies due to the possibility of achieving synergistic therapeutic effects, which are more effective in overcoming the MDR of cancer cells. These combined therapies can provide better outcomes than separate delivery approaches carrying either siRNA, miRNA, pDNA, or drugs. This article reviews the main design features that need to be associated with nano-vehicles to co-deliver drugs, genes, and gene-drug combinations with efficacy. The advantages and disadvantages of co-administration approaches are also overviewed and compared with individual nanocarrier systems. Herein, future trends and perspectives in designing novel nano-scale platforms to co-deliver therapeutic agents are also discussed.

Effects of Reverse Transcriptase Inhibitors on Proliferation, Apoptosis, and Migration in Breast Carcinoma Cells

High telomerase activity in human breast cancer is associated with aggressive tumors resulting in decreased survival. Recent studies have shown that telomerase inhibitors may display anticancer properties in some human cancer cell lines. In the present study, we examined the effects of 4 reverse transcriptase inhibitors (RTIs), used for the treatment of HIV; Abacavir (AC), Lamivudine (LV), Stavudine (SV), and Tenofovir (TF) on proliferation, apoptosis, and migration in the normal human mammary epithelial cell line, hTERT-HME1, and the human breast cancer cell line, MCF-7. Cells were treated with AC, LV, SV, or TF alone or in combination with paclitaxel (PAC), a known drug used to treat breast cancer. Conduct of the thiazolyl blue tetrazolium bromide assay demonstrated that AC, SV, and TF had stronger cytotoxic effects on MCF-7 cells than in hTERT-HME1 cells. The combined treatment of RTIs and PAC caused high rates of cell death in MCF-7 and low rates of cell death in HTERT-HME1 by apoptosis. The percentages of apoptotic cells in the treatment of AC and SV in combination with PAC for 48 and 72 hours were higher than PAC. Significantly increased apoptosis and decreased migration levels were found in MCF-7 cells treated with AC and co-treatment of AC+PAC or SV+PAC than HME1 cells. These treatments can also prevent migration capacity more than PAC. Therefore, a combination strategy based on telomerase inhibitors such as AC or SV and anticancer drugs may be more effective in the treatment of certain breast cancers.

Azidothymidine "Clicked" into 1,2,3-Triazoles: First Report on Carbonic Anhydrase-Telomerase Dual-Hybrid Inhibitors

Cancer cells rely on the enzyme telomerase (EC 2.7.7.49) to promote cellular immortality. Telomerase inhibitors (i.e., azidothymidine) can represent promising antitumor agents, although showing high toxicity when administered alone. Better outcomes were observed within a multipharmacological approach instead. In this context, we exploited the validated antitumor targets carbonic anhydrases (CAs; EC 4.2.1.1) IX and XII to attain the first proof of concept on CA–telomerase dual-hybrid inhibitors. Compounds 1b, 7b, 8b, and 11b showed good in vitro inhibition potency against the CAs IX and XII, with K_I values in the low nanomolar range, and strong antitelomerase activity in PC-3 and HT-29 cells (IC₅₀ values ranging from 5.2 to 9.1 μM). High-resolution X-ray crystallography on selected derivatives in the adduct with hCA II as a model study allowed to determine their binding modes and thus to set the structural determinants necessary for further development of compounds selectively targeting the tumoral cells.

In silico design of telomerase inhibitors

Telomerase is a reverse transcriptase enzyme involved in DNA synthesis at the end of linear chromosomes. Unlike in most other cells, telomerase is reactivated most cancerous cells and, therefore, has become a promising new anticancer target. Despite extensive research, direct telomerase inhibitors have yet not been introduced to the clinics because of the complexity of this enzyme. Structures of this protein from simple organisms and human homology models are currently available and have been used in structure-based drug design efforts to find potential inhibitors. Different is silico strategies have been applied and different chemical groups have been explored. Here, we provide an overview of recent discoveries.

Quantitative Detection and Imaging of Multiple Biological Molecules in Living Cells for Cell Screening

Because of insufficient information, a single biomarker is not sufficient for early diagnosis of cancer, whereas sensitive and selective detection of multiple biomolecules can significantly reduce analysis time, sample size, and accurately perform cell screening in early cancer. Therefore, the development of a noninvasive strategy that can simultaneously quantify multiple biomarkers (i.e., nucleic acids, proteins, and small molecules) in a single cell is particularly important. Herein, a universal sensing system (functional DNA@mesoporous silica nanoparticles (MSN)-Black Hole Quencher-rhodamine 6G (RhB), FDSBR), which is based on the combination of functionalized DNA and smart responsive nanomaterial, was successfully constructed. After incubation with the cells, different types of targets trigger the strand displacement reaction to release the fluorophore-labeled nucleic acids as the output signals to reflect the intracellular level of the telomerase and adenosine triphosphate (ATP), respectively. Simultaneously, intracellular miR-21 can be clearly indicated by the restored fluorescence of RhB when the caged double-stranded DNA was substituted into single-stranded DNA to open the pore. The concentrations of intracellular telomerase, miR-21, and ATP were identified successfully in three cell lines at the single-cell level. The results show that the contents of three biomolecules have significant differences in the three model cell lines and provide a promising route for developing innovative early disease diagnosis and cell screening assay.

Telomere maintenance mechanisms in cancer: telomerase, ALT or lack thereof

Cancer cells acquire replicative immortality by activating a telomere maintenance mechanism (TMM), either the telomerase or the Alternative Lengthening of Telomeres (ALT) mechanism. ALT is frequently activated in tumors derived from mesenchymal cells, which are more frequent in childhood cancers. Recent studies showed that, occasionally, cancer cells can arise without any TMM activation. Here, we discuss the challenge in assessing which TMM is activated in tumors. We also evaluate the prevalence of ALT mechanism in pediatric cancers and review the associated survival prognosis in different tumor types. Finally, we discuss about possible anti-TMM therapies for new emerging cancer treatments.

TOE1 acts as a 3' exonuclease for telomerase RNA and regulates telomere maintenance

In human cells, telomeres are elongated by the telomerase complex that contains the reverse transcriptase hTERT and RNA template TERC/hTR. Poly(A)-specific ribonuclease (PARN) is known to trim hTR precursors by removing poly(A) tails. However, the precise mechanism of hTR 3′ maturation remains largely unknown. Target of Egr1 (TOE1) is an Asp-Glu-Asp-Asp (DEDD) domain containing deadenylase that is mutated in the human disease Pontocerebella Hypoplasia Type 7 (PCH7) and implicated in snRNA and hTR processing. We have previously found TOE1 to localize specifically in Cajal bodies, where telomerase RNP complex assembly takes place. In this study, we showed that TOE1 could interact with hTR and the telomerase complex. TOE1-deficient cells accumulated hTR precursors, including oligoadenylated and 3′-extended forms, which was accompanied by impaired telomerase activity and shortened telomeres. Telomerase activity in TOE1-deficient cells could be rescued by wild-type TOE1 but not the catalytically inactive mutant. Our results suggest that hTR 3′ end processing likely involves multiple exonucleases that work in parallel and/or sequentially, where TOE1 may function non-redundantly as a 3′-to-5′ exonuclease in conjunction with PARN. Our study highlights a mechanistic link between TOE1 mutation, improper hTR processing and telomere dysfunction in diseases such as PCH7.

Multidisciplinary oncolytic virotherapy for gastrointestinal cancer

Replication-selective tumor-specific viruses represent a novel approach for treating neoplastic diseases. These vectors are designed to induce virus-mediated lysis of tumor cells after selective intracellular virus propagation. For targeting cancer cells, the use of tissue- or cell-specific promoters that are expressed in diverse tumor types but silent in normal cells is required. Human telomerase is highly active in more than 85% of primary cancers, regardless of tissue origin, and its activity is closely correlated with human telomerase reverse transcriptase (hTERT) expression. We constructed an attenuated adenovirus 5 vector (telomelysin, OBP-301) in which the hTERT promoter element drives expression of E1 genes. As only tumor cells that express the telomerase can activate this promoter, the hTERT proximal promoter allows for preferential expression of viral genes in tumor cells, leading to selective viral replication and oncolytic cell death. Upon US Food and Drug Administration approval, a phase 1 dose-escalation study of intratumoral injection of telomelysin for various solid tumors has been completed to confirm the safety, tolerability, and feasibility of the agent. Moreover, we found that adenoviral E1B 55-kDa protein in telomelysin inhibits the radiation-induced DNA repair machinery. Thus, tumor cells infected with telomelysin could be rendered sensitive to ionizing radiation. Recently, we assessed the safety and efficacy of intratumoral injection of telomelysin with radiotherapy in esophageal cancer patients not suited for standard treatments. This review highlights some very promising clinical advances in cancer therapeutic technologies using telomerase-specific oncolytic virotherapy.

Design, synthesis of 4,5-diazafluorene derivatives and their anticancer activity via targeting telomeric DNA G-quadruplex

In our work, 19 novel 4,5-diazafluorene derivatives (11a-d, 12a-d, 13a-d, 14a-c, 15c, 16a-c) bearing a 1,3-disubstituted pyrazol/thioxothiazolidinone or thioxothiazolidinone-oxadiazole moieties were designed, synthesized, preliminarily explored for their antitumor activities and in vitro mechanism. All compounds showed different values of antiproliferative activity against A549, AGS, HepG2 and MCF-7 cell lines through CCK-8. Especially, the compound 14c exhibited the strongest activity and best selectivity against A549 cells with an IC₅₀ 1.13 μM and an SI value of 7.01 relative to MRC-5 cells, which was better than cisplatin (SI = 1.80) as a positive control. Experimental results at extracellular level demonstrated that compounds 14a-c could strongly interact with the G-quadruplex(es) formed in a 26 nt telomeric G-rich DNA, in particular, the 14c exhibits quite strong binding affinity with an association equilibrium constant (K_A) of 7.04(±0.16) × 10⁷ M^-1 and more than 1000-fold specificity to G4-DNA over ds-DNA and Mut-DNA at the compound/G4-DNA ratio of 1:1. Further trap assay ascertained that compounds 14a-c owned strong inhibitory ability of telomerase activity in A549 cells, suggesting that these compounds have great possibility to target telomeric G-quadruplexes and consequently indirectly inhibit the telomerase activity. In addition, it is worthy of note that the remarkable inhibitory effects of 14a-c on the mobility of tested cancer cells were observed by wound healing assays. Furthermore, molecular docking and UV-Vis spectral results unclose the rationale for the interaction of compounds with such G-quadruplex(es). These results indicate that the growth and metastasis inhibition of cancer cells mediated by these 4,5-diazafluorene derivatives possibly result from their interaction with telomeric G-quadruplexes, suggesting that 4,5-diazafluorene derivatives, especially 14c, possess potential as anticancer drugs.

Ethenesulfonyl fluoride derivatives as telomerase inhibitors: structure-based design, SAR, and anticancer evaluation in vitro

Based on our previous docking model, in order to carry out more rational drug design, totally 82 vinyl sulfonyl fluorides, including some 2-(hetero)arylethenesulfonyl fluorides and 1,3-dienylsulfonyl fluorides derivatives as potential human telomerase inhibitors were designed and synthesised. The in vitro anticancer activity assay showed that compound 57 (1E,3E)-4-(4-((E)-2-(fluorosulfonyl)vinyl)phenyl)buta-1,3-diene-1-sulfonyl fluoride exhibited high activity against A375 and MDA-MB-231 cell lines with IC₅₀ 1.58 and 3.22 µM, but it manifested obvious un-toxic effect against GES-1 and L-02 with IC₅₀ with IC₅₀ values less than 2.00 mM. By the modified TRAP assay, some compounds including 57 exhibited potent inhibitory activities against telomerase with IC₅₀ values of 0.71–0.97 µM.

Group I Intron-Based Therapeutics Through Trans-Splicing Reaction

In 1982, the Cech group discovered that an intron structure in an rRNA precursor of Tetrahymena thermophila is sufficient to complete splicing without assistance from proteins. This was the first moment that scientists recognized RNAs can have catalytic activities derived from their own unique three-dimensional structures and thus play more various roles in biological processes than thought before. Several additional catalytic RNAs, called ribozymes, were subsequently identified in nature followed by intense studies to reveal their mechanisms of action and to engineer them for use in fields such as molecular cell biology, therapeutics, imaging, etc. Naturally occurring RNA-targeting ribozymes can be broadly classified into two categories by their abilities: Self-cleavage and self-splicing. Since ribozymes use base-pairing to recognize cleavage sites, identification of the catalytic center of naturally occurring ribozymes enables to engineer from "self" to "trans" acting ones which has accelerated to design and use ribozyme as valuable tools in gene therapy fields. Especially, group I intron-based trans-splicing ribozyme has unique property to use as a gene therapeutic agent. It can destroy and simultaneously repair (and/or reprogram) target RNAs to yield the desired therapeutic RNAs, maintaining endogenous spatial and temporal gene regulation of target RNAs. There have been progressive improvements in trans-splicing ribozymes and successful applications of these elements in gene therapy and molecular imaging approaches for various pathogenic conditions. In this chapter, current status of trans-splicing ribozyme therapeutics, focusing on Tetrahymena group I intron-based ribozymes, and their future prospects will be discussed.

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.

Efficient expression of recombinant human telomerase inhibitor 1 (hPinX1) in Pichia pastoris

PinX1 encoded by a remarkable tumor suppressor gene and located in human chromosome 8p23 is known as telomerase inhibitor. In recent years, this protein has been of interest as clinically tumor suppressor. Pichia pastoris expression system is preferred to produce heterologous proteins and is suitable for industrial and research purposes. In the present study, human PinX1 gene (hPinX1) was cloned in E. coli One Shot TOP10 cells and overexpressed in P. pastoris strain X-33 intracellularly, using a strong AOX (alcohol oxidase) promoter. The recombinant cells were grown in shaking flask. Induction time, methanol concentration and initial pH were optimized for obtaining high levels of hPinX1 protein production. Recombinant protein production was confirmed by Western blot analysis and the relative expression levels of rhPinX1 were quantified. According to Western blot analysis, molecular mass of produced hPinX1 was determined as 47.5 kDa. At the end of optimization studies, the best fermentation conditions were determined as induction time 48 h, methanol concentration 3% and initial culture pH 5.0. This process would be an applicable way for obtaining recombinant hPinX1 using P. pastoris expression system. This is the first report on recombinant production of hPinX1 in P. pastoris.

Biodegradable Black Phosphorus Nanosheets Mediate Specific Delivery of hTERT siRNA for Synergistic Cancer Therapy

Human telomerase reverse transcriptase (hTERT) has been found to be closely related to tumor transformation, growth, and metastasis. Thus, the delivery of hTERT small interfering RNA (siRNA) is an important approach for cancer gene therapy. However, the single anticancer effect of gene silencing is often limited by poor specificity or low efficiency in siRNA delivery and release. In this work, we present small and thin black phosphorus (BP) nanosheets as a biodegradable delivery system for hTERT siRNA. The BP nanosheets prepared with poly(ethylene glycol) (PEG) and polyethylenimine (PEI) modification (PPBP), exhibited high siRNA loading capacity and robust cell uptake. The PPBP nanosheets also exhibited potent photodynamic therapy/photothermal therapy (PDT/PTT) activities when exposed to different wavelengths of laser irradiation. More importantly, PPBP nanosheets underwent a gradual degradation when presented in a mixture of low pH and reactive oxygen species (ROS)-rich environment. The degradation of PPBP was strengthened especially after local and minimal invasive PDT treatment, because of excessive ROS production. Further delivery and release of siRNA to the cytoplasm for gene silencing was achieved by PEI-aided escape from the acidic lysosome. Thus, PPBP-siRNA efficiently inhibited tumor growth and metastasis by specific delivery of hTERT siRNA and a synergistic combination of targeted gene therapy, PTT and PDT.

WITHDRAWN: Structural and biophysical insight into dual site binding of the protoberberine alkaloid palmatine to parallel G-quadruplex DNA using NMR, fluorescence and circular dichroism spectroscopy

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.biochi.2018.02.002. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Therapeutic applications of group I intron-based trans-splicing ribozymes

Since the breakthrough discovery of catalytic RNAs (ribozymes) in the early 1980s, valuable ribozyme-based gene therapies have been developed for incurable diseases ranging from genetic disorders to viral infections and cancers. Ribozymes can be engineered and used to downregulate or repair pathogenic genes via RNA cleavage mediated by trans-cleaving ribozymes or repair and reprograming mediated by trans-splicing ribozymes, respectively. Uniquely, trans-splicing ribozymes can edit target RNAs via simultaneous destruction and repair (and/or reprograming) to yield the desired therapeutic RNAs, thus selectively inducing therapeutic gene activity in cells expressing the target RNAs. In contrast to traditional gene therapy approaches, such as simple addition of therapeutic transgenes or inhibition of disease-causing genes, the selective repair and/or reprograming abilities of trans-splicing ribozymes in target RNA-expressing cells facilitates the maintenance of endogenous spatial and temporal gene regulation and reduction of disease-associated transcript expression. In molecular imaging technologies, trans-splicing ribozymes can be used to reprogram specific RNAs in living cells and organisms by the 3'-tagging of reporter RNAs. The past two decades have seen progressive improvements in trans-splicing ribozymes and the successful application of these elements in gene therapy and molecular imaging approaches for various pathogenic conditions, such as genetic, infectious, and malignant disease. This review provides an overview of the current status of trans-splicing ribozyme therapeutics, focusing on Tetrahymena group I intron-based ribozymes, and their future prospects. This article is categorized under: RNA in Disease and Development > RNA in Disease.

A simple “mix-and-detection” method for the sensitive detection of telomerase from cancer cells under absolutely isothermal conditions

We develop a simple “mix-and-detection” method for the sensitive detection of telomerase from cancer cells under absolutely isothermal conditions.

MYC drives overexpression of telomerase RNA (hTR/TERC) in prostate cancer

Telomerase consists of at least two essential elements, an RNA component hTR or TERC that contains the template for telomere DNA addition and a catalytic reverse transcriptase (TERT). While expression of TERT has been considered the key rate-limiting component for telomerase activity, increasing evidence suggests an important role for the regulation of TERC in telomere maintenance and perhaps other functions in human cancer. By using three orthogonal methods including RNAseq, RT-qPCR, and an analytically validated chromogenic RNA in situ hybridization assay, we report consistent overexpression of TERC in prostate cancer. This overexpression occurs at the precursor stage (e.g. high-grade prostatic intraepithelial neoplasia or PIN) and persists throughout all stages of disease progression. Levels of TERC correlate with levels of MYC (a known driver of prostate cancer) in clinical samples and we also show the following: forced reductions of MYC result in decreased TERC levels in eight cancer cell lines (prostate, lung, breast, and colorectal); forced overexpression of MYC in PCa cell lines, and in the mouse prostate, results in increased TERC levels; human TERC promoter activity is decreased after MYC silencing; and MYC occupies the TERC locus as assessed by chromatin immunoprecipitation (ChIP). Finally, we show that knockdown of TERC by siRNA results in reduced proliferation of prostate cancer cell lines. These studies indicate that TERC is consistently overexpressed in all stages of prostatic adenocarcinoma and that its expression is regulated by MYC. These findings nominate TERC as a novel prostate cancer biomarker and therapeutic target. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A PCR-free colorimetric strategy for visualized assay of telomerase activity

A simple yet powerful polymerase chain reaction (PCR)-free strategy for visualized assay of human telomerase activity was reported in this work. Gold nanoparticles (AuNPs) based colorimetric strategy was applied with well-designed enzyme-aided cyclic amplification. Briefly, the detection relies on the elongated primers of telomerase substrate (TS) induced by telomerase, which open the hairpin DNA and hybridize with linker DNA, the trigger of AuNPs aggregation. Nicking endonuclease was added in the sensing system, which cleaved linker DNA after hybridization and released complimentary strand for cyclic hybridization with linker DNA, resulted in high sensitivity for the detection of telomerase. Down to 25 HeLa cells with high expression of telomerase could be recognized. The proposed strategy provides a good platform for the determination of telomerase activity, differentiation of cancer cell lines from normal cell line and screening of telomerase-targeted anticancer drugs.

Discovery of (4-bromophenyl)(3-hydroxy-4-methoxyphenyl)methanone through upregulating hTERT induces cell apoptosis and ERS

Dominant-negative mutants of telomerase hTERT were demonstrated to have selective effects in tumor cells. However, no any effective and highly selective hTERT inhibitor has been developed so far. We focused on developing new hTERT modulators and synthesized a small molecular compound, named (4-bromophenyl)(3-hydroxy-4-methoxyphenyl)methanone. Our in vitro studies found that title compound showed high inhibitory activity against telomerase, had high antiproliferative capacity on SMMC-7721 cells with IC₅₀ value 88 nm, and had no obvious toxic effect on human normal hepatocyte cells with IC₅₀ value 10 μM. Our in vivo studies showed that this compound significantly inhibited tumor growth in xenograft tumor models. The further molecular mechanisms of title compound inhibition SMMC-7721 cell proliferation by modulating hTERT were explored; the results showed that endoplasmic reticulum stress (ERS) through ER over response (EOR) activates the expression of hTERT, and then induces ERS, which is believed to be intricately associated with oxidative stress and mitochondrial dysfunction, resulting in apoptotic cell death, thereby modulating the expression of downstream signaling molecules including CHOP (CAAT/enhancer-binding protein homologous protein)) and mitochondrion pathway of apoptosis, leading to inhibition of cell proliferation.

Azidothymidine inhibits cell growth and telomerase activity and induces DNA damage in human esophageal cancer

Esophageal cancer is one of the most common type of malignancies. Telomerase activity, which is absent or weakly detected in the majority of human somatic cells, is elevated in esophageal cancer. Although azidothymidine (AZT), a reverse transcriptase inhibitor, has been utilized as a treatment for tumors, its role in treating esophageal cancer has not been confirmed. The aim of the present study was to determine the effect of AZT on telomerase activity and the proliferation of the human esophageal cancer cell line TE-11. A telomeric repeat amplification assay was utilized to detect telomerase activity following treatment of TE-11 cells with AZT. The effect of AZT on TE-11 cell cycle distribution was determined by flow cytometry. Cellular DNA damage was evaluated by a comet assay and an MTT assay demonstrated that AZT significantly inhibited the viability of TE-11 cells, in a time-and dose-dependent manner. In addition, TE-11 cells treated with various concentrations of AZT exhibited a significant reduction in telomerase activity and percentage of cells in the G1/G0 phase, and an increase in the percentage of cells in the S phase. High doses of AZT caused DNA damage, and enhanced the expression levels of γ-H2A histone family member X and phosphorylated checkpoint kinase 2 in TE-11 cells. These results demonstrated that AZT effectively inhibits proliferation of the TE-11 human esophageal cancer cell line in vitro. The growth inhibitory effects were associated with a reduction in telomerase activity, S and G2/M phase cell cycle arrest, and enhanced DNA damage, suggesting that AZT may be utilized in the clinic for the treatment of esophageal cancer.

Sensing telomerase: From in vitro detection to in vivo imaging

Telomerase is a ribonucleoprotein reverse transcriptase that is responsible for maintaining the telomere length in cells. Telomerase overexpresses in almost all malignant tumor cells, and it has become a promising biomarker and a potential therapy target for cancers. Consequently, accurate and efficient quantification of the telomerase is highly essential to medical diagnostics and therapeutics. Recently, a series of novel telomerase detection methods with excellent performance have been developed, but a overview of in vivo telomerase detection methods is lacking. In this Minireview, we summarize the emerging strategies for telomerase assays in the last five years, including both in vitro assays and in vivo imaging methods, and discuss their future directions as well.

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.

Circadian Clock Gene Bmal1 Inhibits Tumorigenesis and Increases Paclitaxel Sensitivity in Tongue Squamous Cell Carcinoma

Circadian clock genes regulate cancer development and chemotherapy susceptibility. Accordingly, chronotherapy based on circadian phenotypes might be applied to improve therapeutic efficacy. In this study, we investigated whether the circadian clock gene Bmal1 inhibited tumor development and increased paclitaxel sensitivity in tongue squamous cell carcinoma (TSCC). Bmal1 expression was downregulated and its rhythmic pattern of expression was affected in TSCC samples and cell lines. Ectopic Bmal1 inhibited cell proliferation, migration and invasion in vitro, and tumor growth in mouse xenograft models of TSCC. After exposure to paclitaxel, Bmal1-overexpressing cells displayed a relative increase in apoptosis and were more susceptible to paclitaxel treatment in vivo Mechanistic investigations suggested a regulatory connection between Bmal1, TERT, and the oncogenic transcriptional repressor EZH2 (enhancer of zeste homolog 2), the recruitment of which to the TERT promoter increased paclitaxel-induced apoptosis and cell growth inhibition. Clinically, paclitaxel efficacy correlated positively with Bmal1 expression levels in TSCC. Overall, our results identified Bmal1 as a novel tumor suppressor gene that elevates the sensitivity of cancer cells to paclitaxel, with potential implications as a chronotherapy timing biomarker in TSCC. Cancer Res; 77(2); 532-44. ©2016 AACR.

Telomere-associated aging disorders

Telomeres are dynamic nucleoprotein-DNA structures that cap and protect linear chromosome ends. Several monogenic inherited diseases that display features of human premature aging correlate with shortened telomeres, and are referred to collectively as telomeropathies. These disorders have overlapping symptoms and a common underlying mechanism of telomere dysfunction, but also exhibit variable symptoms and age of onset, suggesting they fall along a spectrum of disorders. Primary telomeropathies are caused by defects in the telomere maintenance machinery, whereas secondary telomeropathies have some overlapping symptoms with primary telomeropathies, but are generally caused by mutations in DNA repair proteins that contribute to telomere preservation. Here we review both the primary and secondary telomeropathies, discuss potential mechanisms for tissue specificity and age of onset, and highlight outstanding questions in the field and future directions toward elucidating disease etiology and developing therapeutic strategies.

DNA-fueled molecular machine for label-free and non-enzymatic ultrasensitive detection of telomerase activity

Herein, a non-enzymatic and label-free strategy based on DNA-fueled molecular machine was developed for ultrasensitive detection of telomerase activity in cancer cell extracts even at the single-cell level.

PinX1 serves as a potential prognostic indicator for clear cell renal cell carcinoma and inhibits its invasion and metastasis by suppressing MMP-2 via NF-κB-dependent transcription

PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) is a novel cloned gene which has been identified as a major haploinsufficient tumor suppressor essential for maintaining telomerase activity, the length of telomerase and chromosome stability. This study explored the clinical significance and biological function of PinX1 in human clear cell renal cell carcinoma (ccRCC). The clinical relevance of PinX1 in ccRCC was evaluated using tissue microarray and immunohistochemical staining in two independent human ccRCC cohorts. Our data demonstrated that PinX1 expression was dramatically decreased in ccRCC tissues compared with normal renal tissues and paired adjacent non-tumor tissues. Low PinX1 expression was significantly correlated with depth of invasion, lymph node metastasis and advanced TNM stage in patients, as well as with worse overall and disease-specific survival. Cox regression analysis revealed that PinX1 expression was an independent prognostic factor for ccRCC patients. Moreover, PinX1 inhibited the migration and invasion of ccRCC by suppressing MMP-2 expression and activity via NF-κB-dependent transcription in vitro. In vivo studies confirmed that PinX1 negatively regulated ccRCC metastasis and the expression of MMP-2 and NF-κB-p65. These findings indicate that PinX1 suppresses ccRCC metastasis and may serve as a ccRCC candidate clinical prognostic marker and a potential therapeutic target.

Reconstruction of gene regulatory networks reveals chromatin remodelers and key transcription factors in tumorigenesis

Background

Alterations in genetic and epigenetic landscapes are known to contribute to the development of different types of cancer. However, the mechanistic links between transcription factors and the epigenome which coordinate the deregulation of gene networks during cell transformation are largely unknown.

Methods

We used an isogenic model of stepwise tumorigenic transformation of human primary cells to monitor the progressive deregulation of gene networks upon immortalization and oncogene-induced transformation. We applied a systems biology approach by combining transcriptome and epigenome data for each step during transformation and integrated transcription factor–target gene associations in order to reconstruct the gene regulatory networks that are at the basis of the transformation process.

Results

We identified 142 transcription factors and 24 chromatin remodelers/modifiers (CRMs) which are preferentially associated with specific co-expression pathways that originate from deregulated gene programming during tumorigenesis. These transcription factors are involved in the regulation of divers processes, including cell differentiation, the immune response, and the establishment/modification of the epigenome. Unexpectedly, the analysis of chromatin state dynamics revealed patterns that distinguish groups of genes which are not only co-regulated but also functionally related. Decortication of transcription factor targets enabled us to define potential key regulators of cell transformation which are engaged in RNA metabolism and chromatin remodeling.

Conclusions

We reconstructed gene regulatory networks that reveal the alterations occurring during human cellular tumorigenesis. Using these networks we predicted and validated several transcription factors as key players for the establishment of tumorigenic traits of transformed cells. Our study suggests a direct implication of CRMs in oncogene-induced tumorigenesis and identifies new CRMs involved in this process. This is the first comprehensive view of the gene regulatory network that is altered during the process of stepwise human cellular tumorigenesis in a virtually isogenic system.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0310-3) contains supplementary material, which is available to authorized users.

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.

Dihydropyrazole derivatives as telomerase inhibitors: Structure-based design, synthesis, SAR and anticancer evaluation in vitro and in vivo

It is of our interest to generate and identify novel compounds with regulation telomerase for cancer therapy. In order to carry out more rational design, based on structure-based drug design, several series of N-substituted-dihydropyrazole derivatives, totally 78 compounds as potential human telomerase inhibitors were designed and synthesized. The results demonstrated that some compounds had potent anticancer activity against four tumor cell lines, and showed good selectivity on tumor cells over somatic cells. By the modified TRAP assay, compound 13i exhibited the most potent inhibitory activity against telomerase with an IC50 value of 0.98 μM. In vivo evaluation results indicated that compound 13i could inhibit growth of S180 and HepG2 tumor-bearing mice, and it also significantly enhanced the survival rate of EAC tumor-bearing mice. The further results in vivo confirmed that it could significantly improve pathological changes of N,N-diethylnitrosamine (DEN)-induced rat hepatic tumor. These data support further studies to assess rational design of more efficient telomerase inhibitors in the future.

Homogeneous and ultrasensitive detection of telomerase activity via gold nanorod-based fluorescence resonance energy transfer

A homogeneous and PCR-free fluorescent strategy has been developed for sensitively and specifically studying telomerase activity and inhibition via GNR-based fluorescence resonance energy transfer.