Pharmacological intervention strategies for affecting telomerase activity: future prospects to treat cancer and degenerative disease

Endometrial telomerase activity in women with either endometrial cancer or hyperplasia: A systematic review and meta-analysis

AIM

We performed a systematic review and meta-analysis to assess whether endometrial telomerase activity is associated with endometrial cancer or hyperplasia.

METHODS

PubMed, Web of Science, Embase, Scielo, LILAC, and CNKI databases were searched to obtain relevant literature for articles published through June 2022, following PRISMA guidelines and a registered PROSPERO protocol. We included observational studies reporting endometrial telomerase activity in patients with either endometrial cancer or hyperplasia compared with benign endometrial tissue (control women). The Newcastle-Ottawa Scale was used to evaluate the quality of studies. Data were expressed as the odds ratios (OR) and 95 % confidence intervals (CI). Random effects and inverse variance methods were used to meta-analyze associations. The I² test was used to assess heterogeneity.

RESULTS

There were significant associations between endometrial telomerase activity and either endometrial cancer (20 studies, OR = 10.65, 95 % CI 6.39, 17.75, p = 0.00001, I² = 21 %) or endometrial hyperplasia (nine studies, OR = 3.62, 95 % CI 1.61, 8.13, p = 0.002, I² = 36 %) compared to women without endometrial cancer and hyperplasia. There was not a significant difference in telomerase activity in women with endometrial cancer compared to those with endometrial hyperplasia (seven studies, OR = 1.03; 95 % CI 0.31, 3.37, p = 0.96, I² = 49 %). In subgroup analyses, there were no significant differences in telomerase activity in patients with endometrial cancer by type of observational studies and by countries of the studies.

CONCLUSION

Endometrial telomerase activity is higher in women with either endometrial cancer or endometrial hyperplasia compared to control women without those lesions.

Repositioning anticancer drugs as novel COVID-19 antivirals: targeting structural and functional similarities between viral proteins and cancer

The current COVID-19 pandemic contributed by the SARS-CoV-2 has put in place an urgent need for new and promising antiviral therapeutics. The viral RNA-dependent RNA polymerase (RdRp) enzyme plays a vital role in viral replication for all RNA viruses, including SARS-CoV-2, thereby making it a prime and promising candidate for novel antiviral targeting. Interestingly, the human telomerase reverse transcriptase (hTERT), a common catalytic subunit of the telomerase enzyme in many cancers, has also been identified with structural and functional similarities to the viral RdRp. Therefore, it becomes essential to evaluate and consider anticancer drugs that target hTERT towards antiviral RdRp activity, and vice versa. For instance, Floxuridine, an hTERT inhibitor, and VX-222, a hepatitis C virus RdRp inhibitor, are now gaining recognition as a potential antiviral against SARS-CoV-2 and anti-hTERT for cancer, simultaneously. While limited studies on hTERT inhibitors for use as viral RdRp, and anti-RdRp inhibitors as hTERT inhibitors are available, in this review, we aim at bringing to light this close structural and functional relationship between both these enzymes. We punctuate this idea with specific examples on how potential anticancer inhibitors can effectively be brought to use as inhibitors against the SARS-CoV-2 virus, a relatively new pathogen, compared to the very well-studied field of cancer research.

The Connection Between Cell Fate and Telomere

Abolition of telomerase activity results in telomere shortening, a process that eventually destabilizes the ends of chromosomes, leading to genomic instability and cell growth arrest or death. Telomere shortening leads to the attainment of the "Hayflick limit", and the transition of cells to state of senescence. If senescence is bypassed, cells undergo crisis through loss of checkpoints. This process causes massive cell death concomitant with further telomere shortening and spontaneous telomere fusions. In functional telomere of mammalian cells, DNA contains double-stranded tandem repeats of TTAGGG. The Shelterin complex, which is composed of six different proteins, is required for the regulation of telomere length and stability in cells. Telomere protection by telomeric repeat binding protein 2 (TRF2) is dependent on DNA damage response (DDR) inhibition via formation of T-loop structures. Many protein kinases contribute to the DDR activated cell cycle checkpoint pathways, and prevent DNA replication until damaged DNA is repaired. Thereby, the connection between cell fate and telomere length-associated telomerase activity is regulated by multiple protein kinase activities. Contrarily, inactivation of DNA damage checkpoint protein kinases in senescent cells can restore cell-cycle progression into S phase. Therefore, telomere-initiated senescence is a DNA damage checkpoint response that is activated with a direct contribution from dysfunctional telomeres. In this review, in addition to the above mentioned, the choice of main repair pathways, which comprise non-homologous end joining and homologous recombination in telomere uncapping telomere dysfunctions, are discussed.

Telomere length: how the length makes a difference

Telomerase is perceived as an immortality enzyme that might provide longevity to cells and whole organisms. Importantly, it is generally inactive in most somatic cells of healthy, adult men. Consequently, its substrates, i.e. telomeres, get shorter in most human cells with time. Noteworthy, cell life limitation due to telomere attrition during cell divisions, may not be as bad as it looks since longer cell life means longer exposition to harmful factors. Consequently, telomere length (attrition rate) becomes a factor that is responsible for inducing the signaling that leads to the elimination of cells that lived long enough to acquire severe damage. It seems that telomere length that depends on many different factors (including telomerase activity but also genetic factors, a hormonal profile that reflects sex, etc.) might become a useful marker of aging and exposition to stress. Thus in the current paper, we review the factors that affect telomere length in human cells focusing on sex that all together with different environmental and hormonal regulations as well as parental aspect affect telomere attrition rate. We also raise some limitations in the assessment of telomere length that hinders a trustworthy meta-analysis that might lead to acknowledgment of the real value of this parameter.

Administration of a Nucleoside Analog Promotes Cancer Cell Death in a Telomerase-Dependent Manner

Telomerase, the end-replication enzyme, is reactivated in malignant cancers to drive cellular immortality. While this distinction makes telomerase an attractive target for anti-cancer therapies, most approaches for inhibiting its activity have been clinically ineffective. As opposed to inhibiting telomerase, we use its activity to selectively promote cytotoxicity in cancer cells. We show that several nucleotide analogs, including 5-fluoro-2'-deoxyuridine (5-FdU) triphosphate, are effectively incorporated by telomerase into a telomere DNA product. Administration of 5-FdU results in an increased number of telomere-induced foci, impedes binding of telomere proteins, activates the ATR-related DNA-damage response, and promotes cell death in a telomerase-dependent manner. Collectively, our data indicate that telomerase activity can be exploited as a putative anti-cancer strategy.

Discovery of potent telomerase activators: Unfolding new therapeutic and anti-aging perspectives

Telomere length, a marker of cellular aging, decreases with age and it has been associated with aging‑related diseases. Environmental factors, including diet and lifestyle factors, affect the rate of telomere shortening which can be reversed by telomerase. Telomerase activation by natural molecules has been suggested to be an anti‑aging modulator that can play a role in the treatment of aging‑related diseases. This study aimed to investigate the effect of natural compounds on telomerase activity in human peripheral blood mononuclear cells (PBMCs). The tested compounds included Centella asiatica extract formulation (08AGTLF), Astragalus extract formulation (Nutrient 4), TA‑65 (containing Astragalus membranaceus extract), oleanolic acid (OA), maslinic acid (MA), and 3 multi‑nutrient formulas (Nutrients 1, 2 and 3) at various concentrations. The mean absorbance values of telomerase activity measured following treatment with some of the above‑mentioned formulations were statistically significantly higher compared to those of the untreated cells. In particular, in order of importance with respect to telomerase activation from highest to lowest, 08AGTLF, OA, Nutrient 4, TA‑65, MA, Nutrient 3 and Nutrient 2, triggered statistically significant increase in telomerase activity compared to the untreated cells. 08AGTLF reached the highest levels of telomerase activity reported to date, at least to our knowledge, increasing telomerase activity by 8.8 folds compared to untreated cells, while Nutrient 4 and OA were also potent activators (4.3‑fold and 5.9‑fold increase, respectively). On the whole, this study indicates that the synergistic effect of nutrients and natural compounds can activate telomerase and produce more potent formulations. Human clinical studies using these formulations are required to evaluate their mode of action. This would reveal the health benefits of telomerase activation through natural molecules and would shed new light onto the treatment of aging‑related diseases.

Telomere Biology and Thoracic Aortic Aneurysm

Ascending aortic aneurysms are mostly asymptomatic and present a great risk of aortic dissection or perforation. Consequently, ascending aortic aneurysms are a source of lethality with increased age. Biological aging results in progressive attrition of telomeres, which are the repetitive DNA sequences at the end of chromosomes. These telomeres play an important role in protection of genomic DNA from end-to-end fusions. Telomere maintenance and telomere attrition-associated senescence of endothelial and smooth muscle cells have been indicated to be part of the pathogenesis of degenerative vascular diseases. This systematic review provides an overview of telomeres, telomere-associated proteins and telomerase to the formation and progression of aneurysms of the thoracic ascending aorta. A better understanding of telomere regulation in the vascular pathology might provide new therapeutic approaches. Measurements of telomere length and telomerase activity could be potential prognostic biomarkers for increased risk of death in elderly patients suffering from an aortic aneurysm.

Therapeutic Targeting of Telomerase

Telomere length and cell function can be preserved by the human reverse transcriptase telomerase (hTERT), which synthesizes the new telomeric DNA from a RNA template, but is normally restricted to cells needing a high proliferative capacity, such as stem cells. Consequently, telomerase-based therapies to elongate short telomeres are developed, some of which have successfully reached the stage I in clinical trials. Telomerase is also permissive for tumorigenesis and 90% of all malignant tumors use telomerase to obtain immortality. Thus, reversal of telomerase upregulation in tumor cells is a potential strategy to treat cancer. Natural and small-molecule telomerase inhibitors, immunotherapeutic approaches, oligonucleotide inhibitors, and telomerase-directed gene therapy are useful treatment strategies. Telomerase is more widely expressed than any other tumor marker. The low expression in normal tissues, together with the longer telomeres in normal stem cells versus cancer cells, provides some degree of specificity with low risk of toxicity. However, long term telomerase inhibition may elicit negative effects in highly-proliferative cells which need telomerase for survival, and it may interfere with telomere-independent physiological functions. Moreover, only a few hTERT molecules are required to overcome senescence in cancer cells, and telomerase inhibition requires proliferating cells over a sufficient number of population doublings to induce tumor suppressive senescence. These limitations may explain the moderate success rates in many clinical studies. Despite extensive studies, only one vaccine and one telomerase antagonist are routinely used in clinical work. For complete eradication of all subpopulations of cancer cells a simultaneous targeting of several mechanisms will likely be needed. Possible technical improvements have been proposed including the development of more specific inhibitors, methods to increase the efficacy of vaccination methods, and personalized approaches. Telomerase activation and cell rejuvenation is successfully used in regenerative medicine for tissue engineering and reconstructive surgery. However, there are also a number of pitfalls in the treatment with telomerase activating procedures for the whole organism and for longer periods of time. Extended cell lifespan may accumulate rare genetic and epigenetic aberrations that can contribute to malignant transformation. Therefore, novel vector systems have been developed for a 'mild' integration of telomerase into the host genome and loss of the vector in rapidly-proliferating cells. It is currently unclear if this technique can also be used in human beings to treat chronic diseases, such as atherosclerosis.

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.

Oligonucleotide inhibitors of telomerase: prospects for anticancer therapy and diagnostics

The activity of telomerase allows eukaryotic cells to have unlimited division potential. On its functioning, telomerase synthesizes short DNA repeats at the 3'-end of DNA within chromosomes that ensures genome stability during cell division. Telomerase is active in the majority of cancer cell types and is virtually absent in somatic cells with rare exceptions. This difference allows us to consider inhibition of telomerase activity as a possible approach to antitumor therapy. Telomerase is a nucleoprotein composed of two main components: the reverse transcriptase (hTERT), which is a catalytic subunit, and telomerase RNA (hTR), which encodes a template for synthesis of repeats. The biogenesis and features of telomerase seem very promising for its inhibition due to complementary interactions. In this review, we analyze putative pathways of oligonucleotide influence on telomerase and consider the known native and modified oligonucleotide inhibitors of telomerase, as well as possible mechanisms of their action. We also discuss the application of telomerase-targeted oligonucleotide conjugates for in vivo imaging of tumor cells.

Inhibitory effects of β-cyclodextrin-helenalin complexes on H-TERT gene expression in the T47D breast cancer cell line - results of real time quantitative PCR

BACKGROUND

Nowadays, the encapsulation of cytotoxic chemotherapeutic agents is attracting interest as a method for drug delivery. We hypothesized that the efficiency of helenalin might be maximized by encapsulation in β-cyclodextrin nanoparticles. Helenalin, with a hydrophobic structure obtained from flowers of Arnica chamissonis and Arnica Montana, has anti-cancer and anti-inflammatory activity but low water solubility and bioavailability. β-Cyclodextrin (β-CD) is a cyclic oligosaccharide comprising seven D-glucopyranoside units, linked through 1,4-glycosidic bonds.

MATERIALS AND METHODS

To test our hypothesis, we prepared β-cyclodextrin- helenalin complexes to determine their inhibitory effects on telomerase gene expression by real-time polymerase chain reaction (q-PCR) and cytotoxic effects by colorimetric cell viability (MTT) assay.

RESULTS

MTT assay showed that not only β-cyclodextrin has no cytotoxic effect on its own but also it demonstrated that β-cyclodextrin- helenalin complexes inhibited the growth of the T47D breast cancer cell line in a time and dose-dependent manner. Our q-PCR results showed that the expression of telomerase gene was effectively reduced as the concentration of β-cyclodextrin-helenalin complexes increased.

CONCLUSIONS

β-Cyclodextrin-helenalin complexes exerted cytotoxic effects on T47D cells through down-regulation of telomerase expression and by enhancing Helenalin uptake by cells. Therefore, β-cyclodextrin could be superior carrier for this kind of hydrophobic agent.

Telomeric overhang length determines structural dynamics and accessibility to telomerase and ALT-associated proteins

The G-rich single-stranded DNA at the 3' end of human telomeres can self-fold into G-quaduplex (GQ). However, telomere lengthening by telomerase or the recombination-based alternative lengthening of telomere (ALT) mechanism requires protein loading on the overhang. Using single-molecule fluorescence spectroscopy, we discovered that lengthening the telomeric overhang also increased the rate of dynamic exchanges between structural conformations. Overhangs with five to seven TTAGGG repeats, compared with four repeats, showed much greater dynamics and accessibility to telomerase binding and activity and loading of the ALT-associated proteins RAD51, WRN, and BLM. Although the eight repeats are highly dynamic, they can fold into two GQs, which limited protein accessibility. In contrast, the telomere-specific protein POT1 is unique in that it binds independently of repeat number. Our results suggest that the telomeric overhang length and dynamics may contribute to the regulation of telomere extension via telomerase action and the ALT mechanism.

Telomeres and atherosclerosis

Abstract

In humans and other multicellular organisms that have an extended lifespan, the leading causes of death are atherosclerotic cardiovascular disease and cancer. Experimental and clinical evidence indicates that these age-related disorders are linked through dysregulation of telomere homeostasis. Telomeres are DNA protein structures located at the terminal end of chromosomes and shorten with each cycle of cell replication, thereby reflecting the biological age of an organism. Critically shortened telomeres provoke cellular senescence and apoptosis, impairing the function and viability of a cell. The endothelial cells within atherosclerotic plaques have been shown to display features of cellular senescence. Studies have consistently demonstrated an association between shortened telomere length and coronary artery disease (CAD).

Several of the CAD risk factors and particularly type 2 diabetes are linked to telomere shortening and cellular senescence. Our interest in telomere biology was prompted by the high incidence of premature CAD and diabetes in a subset of our population, and the hypothesis that these conditions are premature-ageing syndromes. The assessment of telomere length may serve as a better predictor of cardiovascular risk and mortality than currently available risk markers, and anti-senescence therapy targeting the telomere complex is emerging as a new strategy in the treatment of atherosclerosis. We review the evidence linking telomere biology to atherosclerosis and discuss methods to preserve telomere length.

Comparison of inhibitory effect of curcumin nanoparticles and free curcumin in human telomerase reverse transcriptase gene expression in breast cancer

PURPOSE

Telomerase is expressed in most cancers, including breast cancer. Curcumin, a polyphenolic compound that obtained from the herb of Curcuma longa, has many anticancer effects. But, its effect is low due to poor water solubility. In order to improve its solubility and drug delivery, we have utilized a β-cyclodextrin-curcumin inclusion complex.

METHODS

To evaluate cytotoxic effects of cyclodextrin-curcumin and free curcumin, MTT assay was done. Cells were treated with equal concentration of cyclodextrin-curcumin and free curcumin. Telomerase gene expression level in two groups was compared by Real-time PCR.

RESULTS

MTT assay demonstrated that β-cyclodextrin-curcumin enhanced curcumin delivery in T47D breast cancer cells. The level of telomerase gene expression in cells treated with cyclodextrin-curcumin was lower than that of cells treated with free curcumin (P=0.001).

CONCLUSION

RESULTS are suggesting that cyclodextrin-curcumin complex can be more effective than free curcumin in inhibition of telomerase expression.

A small molecule inhibitor of Pot1 binding to telomeric DNA

Chromosome ends are complex structures, consisting of repetitive DNA sequence terminating in an ssDNA overhang with many associated proteins. Because alteration of the regulation of these ends is a hallmark of cancer, telomeres and telomere maintenance have been prime drug targets. The universally conserved ssDNA overhang is sequence-specifically bound and regulated by Pot1 (protection of telomeres 1), and perturbation of Pot1 function has deleterious effects for proliferating cells. The specificity of the Pot1/ssDNA interaction and the key involvement of this protein in telomere maintenance have suggested directed inhibition of Pot1/ssDNA binding as an efficient means of disrupting telomere function. To explore this idea, we developed a high-throughput time-resolved fluorescence resonance energy transfer (TR-FRET) screen for inhibitors of Pot1/ssDNA interaction. We conducted this screen with the DNA-binding subdomain of Schizosaccharomyces pombe Pot1 (Pot1pN), which confers the vast majority of Pot1 sequence-specificity and is highly similar to the first domain of human Pot1 (hPOT1). Screening a library of ∼20 000 compounds yielded a single inhibitor, which we found interacted tightly with sub-micromolar affinity. Furthermore, this compound, subsequently identified as the bis-azo dye Congo red (CR), was able to competitively inhibit hPOT1 binding to telomeric DNA. Isothermal titration calorimetry and NMR chemical shift analysis suggest that CR interacts specifically with the ssDNA-binding cleft of Pot1, and that alteration of this surface disrupts CR binding. The identification of a specific inhibitor of ssDNA interaction establishes a new pathway for targeted telomere disruption.

Telomere structure and telomerase in health and disease (review)

Telomerase is the enzyme responsible for maintenance of the length of telomeres by addition of guanine-rich repetitive sequences. Telomerase activity is exhibited in gametes and stem and tumor cells. In human somatic cells, proliferation potential is strictly limited and senescence follows approximately 50–70 cell divisions. In most tumor cells, on the contrary, replication potential is unlimited. The key role in this process of the system of the telomere length maintenance with involvement of telomerase is still poorly studied. Undoubtedly, DNA polymerase is not capable of completely copying DNA at the very ends of chromosomes; therefore, approximately 50 nucleotides are lost during each cell cycle, which results in gradual telomere length shortening. Critically short telomeres cause senescence, following crisis and cell death. However, in tumor cells the system of telomere length maintenance is activated. Much work has been done regarding the complex telomere/telomerase as a unique target, highly specific in cancer cells. Telomeres have additional proteins that regulate the binding of telomerase. Telomerase, also associates with a number of proteins forming the sheltering complex having a central role in telomerase activity. This review focuses on the structure and function of the telomere/telomerase complex and its altered behavior leading to disease, mainly cancer. Although telomerase therapeutics are not approved yet for clinical use, we can assume that based on the promising in vitro and in vivo results and successful clinical trials, it can be predicted that telomerase therapeutics will be utilized soon in the combat against malignancies and degenerative diseases. The active search for modulators is justified, because the telomere/telomerase system is an extremely promising target offering possibilities to decrease or increase the viability of the cell for therapeutic purposes.

Resting leukocyte telomerase activity is elevated in major depression and predicts treatment response

Telomeres are DNA-protein complexes that cap linear DNA strands, protecting DNA from damage. When telomeres critically shorten, cells become susceptible to senescence and apoptosis. Telomerase, a cellular ribonucleoprotein enzyme, rebuilds the length of telomeres and promotes cellular viability. Leukocyte telomeres are reportedly shortened in major depression, but telomerase activity in depression has not been previously reported. Further, there are no published reports of the effects of antidepressants on telomerase activity or on the relationship between telomerase activity and antidepressant response. Peripheral blood mononuclear cell (PBMC) telomerase activity was assessed in 20 medication-free depressed individuals and 18 controls. In total, 16 of the depressed individuals were then treated with sertraline in an open-label manner for 8 weeks, and PBMC telomerase activity was reassessed in 15 of these individuals after treatment. Pre- and post-treatment symptom severity was rated with the Hamilton Depression Rating Scale. All analyses were corrected for age and sex. Pre-treatment telomerase activity was significantly elevated in the depressed individuals compared with the controls (P=0.007) and was directly correlated with depression ratings (P<0.05) across all subjects. In the depressed group, individuals with relatively lower pre-treatment telomerase activity and with relatively greater increase in telomerase activity during treatment, showed superior antidepressant responses (P<0.05 and P<0.005, respectively). This is the first report characterizing telomerase activity in depressed individuals. PBMC telomerase activity might reflect a novel aspect of depressive pathophysiology and might represent a novel biomarker of antidepressant responsiveness.

Telomerase: structure, functions, and activity regulation

Telomerase is the enzyme responsible for maintenance of the length of telomeres by addition of guanine-rich repetitive sequences. Telomerase activity is exhibited in gametes and stem and tumor cells. In human somatic cells proliferation potential is strictly limited and senescence follows approximately 50-70 cell divisions. In most tumor cells, on the contrary, replication potential is unlimited. The key role in this process of the system of the telomere length maintenance with involvement of telomerase is still poorly studied. No doubt, DNA polymerase is not capable to completely copy DNA at the very ends of chromosomes; therefore, approximately 50 nucleotides are lost during each cell cycle, which results in gradual telomere length shortening. Critically short telomeres cause senescence, following crisis, and cell death. However, in tumor cells the system of telomere length maintenance is activated. Besides catalytic telomere elongation, independent telomerase functions can be also involved in cell cycle regulation. Inhibition of the telomerase catalytic function and resulting cessation of telomere length maintenance will help in restriction of tumor cell replication potential. On the other hand, formation of temporarily active enzyme via its intracellular activation or due to stimulation of expression of telomerase components will result in telomerase activation and telomere elongation that can be used for correction of degenerative changes. Data on telomerase structure and function are summarized in this review, and they are compared for evolutionarily remote organisms. Problems of telomerase activity measurement and modulation by enzyme inhibitors or activators are considered as well.

HIV-Tat-mediated delivery of an LPTS functional fragment inhibits telomerase activity and tumorigenicity of hepatoma cells

BACKGROUND & AIMS

Human liver-related putative tumor suppressor (LPTS) is a gene that encodes a telomerase inhibitory protein that is similar to human Pin2/TRF1-interacting protein. The LPTS protein binds directly to the telomerase catalytic subunit (human telomerase reverse transcriptase) and suppresses telomerase activity. Telomere maintenance and telomerase activity are required for long-term proliferation of cancer cells, so LPTS might be used in anticancer strategies.

METHODS

The carboxy-terminal (functional) fragment of LPTS was fused to the transactivator of transcription of human immunodeficiency virus (Tat)-an 11-amino acid peptide that translocates across the cell membrane; the TAT-fused C-terminal of LPTS (TAT-LPTS-LC) was purified and transduced into cells. Telomerase activity was identified by using the telomeric repeat amplification protocol. The effects of the TAT-LPTS-LC protein on cell proliferation and death were evaluated by colorimetric tetrazolium salt and flow cytometry analyses. Tumor growth was analyzed in nude mice.

RESULTS

The purified TAT-LPTS-LC protein was efficiently delivered into the cells, where it suppressed telomerase activity and shortened telomere length. TAT-LPTS-LC inhibited proliferation of telomerase-positive hepatocellular carcinoma BEL-7404 and hepatoblastoma HepG2cells and induced their death; however, it had no effect on telomerase-negative liver cell line L02 and osteosarcoma cell line Saos-2. In mice, tumor formations by BEL-7404 cells were suppressed by TAT-LPTS-LC treatments.

CONCLUSIONS

Transduction of hepatoma cells with a fusion protein that contains the C-terminal, functional fragment of LPTS and human immunodeficiency virus Tat (TAT-LPTS-LC) causes telomere shortening, limits proliferation, and inhibits growth of tumors from these cells in mice. TAT-LPTS-LC inhibits telomerase activity and might be developed as an anticancer agent.

Formation of aminyl radicals on electron attachment to AZT: abstraction from the sugar phosphate backbone versus one-electron oxidation of guanine

Employing electron spin resonance (ESR) spectroscopy, we have characterized the radicals formed in 3'-azido-3'-deoxythymidine (3'-AZT) and in its 5'-analog 5'-azido-5'-deoxythymidine (5'-AZT) after electron attachment in gamma-irradiated aqueous (H(2)O or D(2)O) glassy (7.5 M LiCl) systems. ESR spectral studies and theoretical calculations show that the predominant site of electron capture in 3'-AZT and in 5'-AZT is at the azide group and not at the thymine moiety. The azide group in AZT is therefore more electron affinic than the most electron affinic DNA base, thymine. Electron attachment to 3'-AZT and 5'-AZT results in an unstable azide anion radical intermediate (RN(3)*(-)) that is too short-lived to be observed in our work even at 77 K. At 77 K, we observe the neutral aminyl radical (RNH*) after loss of N(2) from RN(3)*(-) followed by protonation of nitrene anion radical (RN*(-)) to give RNH*. The expected RN*(-) intermediate is not observed as protonation from water is complete at 77 K even under highly basic conditions. Formation of RND* in D(2)O solutions confirms water as the source of the NH proton in the RNH*. Our assignments to these radicals are aided by DFT calculations for hyperfine coupling constants that closely match the experimental values. On annealing to higher temperatures (ca. 160-170 K), RNH* undergoes bimolecular hydrogen abstraction reactions from the thymine methyl group and the sugar moiety resulting in the formation of the thymine allyl radical (UCH(2)*) and two sugar radicals, C3'* and C5'*. RNH* also results in one-electron oxidation of the guanine base in 3'-AZG. This work provides a potential mechanism for the reported radiosensitization effects of AZT.

Mechanism of interaction of small transcription inhibitors with DNA in the context of chromatin and telomere

Small molecules from natural and synthetic sources have long been employed as human drugs. The transcription inhibitory potential of one class of these molecules has paved their use as anticancer drugs. The principal mode of action of these molecules is via reversible interaction with genomic DNA, double and multiple stranded. In this article we have revisited the mechanism of the interaction in the context of chromatin and telomere. The established modes of association of these molecules with double helical DNA provide a preliminary mechanism of their transcription inhibitory potential, but the scenario assumes a different dimension when the genomic DNA is associated with proteins in the transcription apparatus of both prokaryotic and eukaryotic organisms. We have discussed this altered scenario as a prelude to understand the chemical biology of their action in the cell. For the telomeric quadruplex DNA, we have reviewed the mechanism of their association with the quadruplex and resultant cellular consequence.