Effect of antisense human telomerase RNA transfection on the growth of human gastric cancer cell lines

Telomerase and Anticancer Treatment

Current chemotherapy uses compounds of organometallic nature that act with different mechanisms of action. Many pharmacological studies are directed toward the creation of compounds with more specific and selective activity toward tumor targets, including telomerase. The design and synthesis of such compounds with specific antitelomerase activity must consider the mechanism of action of the enzyme and its structure. The discovery of a close correlation between telomerase activation, cell immortalization and oncogenesis has suggested that telomerase inhibitors could be potent therapeutic agents, capable of selectively killing cancer cells. Inhibition of telomerase is expected to lead toward shortening of telomeres to a critical length, such that replicative senescence and cell death due to irreparable chromosomal damage can result. It has been observed that cancer cells generally have shorter telomeres than the normal replicative cell population, probably because the malignant cells have undergone more divisions. Therefore, the inhibition telomeres of cancer cells after a few cycles of cell division, without the normal cells suffering harmful consequences during therapy. Telomerase is certainly an interesting target on which to continue to study molecules that inhibit its function to obtain a specificity of therapeutic intervention and a reduction of the nonspecific cytotoxicity of chemotherapy.

Inhibition of human telomerase reverse transcriptase in vivo and in vitro for retroviral vector-based antisense oligonucleotide therapy in ovarian cancer

Human telomerase is absent in most normal tissues, but is abnormally activated in all major cancer cells. Telomerase enables tumor cells to maintain telomere length, allowing indefinite replicative capacity. Albeit not sufficient in itself to induce neoplasia, telomerase is believed to be necessary for cancer cells to grow without limit. Studies using an antisense oligonucleotide (ASODN) to the RNA component of telomerase or human telomerase reverse transcriptase (hTERT) demonstrate that telomerase in human tumor lines can be blocked in vivo. Inhibition of hTERT led to telomere shortening and cancer cell death, validating telomerase as a target for anticancer genetic therapy. Varieties of approaches for hTERT inhibition have been investigated. The aim of this study was to analyze the biological activity of ASODN to the hTERT mediated by retrovirus vector, which was used as therapy for ovarian tumor. We constructed and characterized a recombinant retrovirus vector with full-length hTERT antisense complementary DNA. The vector was introduced into ES-2 by lipofectamine-mediated gene transfection. The cellular proliferation and telomerase activity of the transformant cells were retarded. The hTERT gene expression and the telomerase activity of the transformant cells were both decreased. The transformant cells show partial reversion of the malignant phenotype. PT67 cells were also transfected with the recombinant vector and virus-producer cells were generated. The retrovirus-containing supernatant effectively inhibited the growth of human ovarian tumor xenografts in mouse models (subcutaneous tumor model), and enhanced the mouse survival time.

Antisense oligodeoxynucleotide against human telomerase reverse transcriptase inhibits the proliferation of Eca-109 esophageal carcinoma cells

Previous studies have demonstrated that the growth of tumor cells may be inhibited by antisense oligonucleotides (ASODNs) targeted against human telomerase (hTR) or human telomerase reverse transcriptase (hTERT), resulting in antitumor activity in a wide variety of tumors. However, few studies have investigated the effect of hTERT gene-targeted ASODNs on telomerase activity and cell proliferation in human esophageal cancer. In the present study, an MTT assay was used to determine the growth inhibition rate of Eca-109 cells treated with a hTERT-targeted phosphorothioate-ASODN (PS-ASODN). An inverted microscope was used to observe the morphologic changes of the cells following treatment with 5 μM PS-ASODN for 10 days. Telomerase activity was detected using the silver staining semi-quantitative telomeric repeat amplification protocol (TRAP) assay. Following treatment with the PS-ASODN (1–5 μmol/l), the proliferation of the Eca-109 cells was inhibited. The differences in inhibition rate between the PS-ASODN and blank control groups were statistically significant (P<0.05) when the concentration of the PS-ASODN was ≥2 μmol/l, whereas no statistically significant difference was identified between the non-specific-ASODN and blank control groups. The inhibition rate increased gradually as the concentration of the PS-ASODN increased and with time, suggesting that the PS-ASODN inhibited the growth of Eca-109 cells in a concentration-dependent, time-dependent and sequence-specific manner. The growth rate of the cells incubated with the PS-ASODN was reduced compared with that of the control cells. Cells treated with the PS-ASODN became round, suspended and reduced in size. The PS-ASODN was also found to inhibit telomerase activity. The ability of the PS-ASODN to inhibit the telomerase activity and cell proliferation of the Eca-109 cell line suggests that ASODNs have the potential to be novel therapeutic agents for the treatment of esophageal cancer.

Inhibition of telomerase activity by HDV ribozyme in cancers

Background

Telomerase plays an important role in cell proliferation and carcinogenesis and is believed to be a good target for anti-cancer drugs. Elimination of template function of telomerase RNA may repress the telomerase activity.

Methods

A pseudo-knotted HDV ribozyme (g.RZ57) directed against the RNA component of human telomerase (hTR) was designed and synthesized. An in vitro transcription plasmid and a eukaryotic expression plasmid of ribozyme were constructed. The eukaryotic expression plasmid was induced into heptocellular carcinoma 7402 cells, colon cancer HCT116 cells and L02 hepatocytes respectively. Then we determine the cleavage activity of ribozyme against human telomerase RNA component (hTR) both in vitro and in vivo, and detect telomerase activity continuously.

Results

HDV ribozyme showed a specific cleavage activity against the telomerase RNA in vitro. The maximum cleavage ratio reached about 70.4%. Transfection of HDV ribozyme into 7402 cells and colon cancer cells HCT116 led to growth arrest and the spontaneous apoptosis of cells, and the telomerase activity dropped to 10% of that before.

Conclussion

HDV ribozyme (g.RZ57) is an effective strategy for gene therapy.

Rapid blockade of telomerase activity and tumor cell growth by the DPL lipofection of ribbon antisense to hTR

Ribbon antisense (RiAS) to the hTR RNA, a component of the telomerase complex, was employed to inhibit telomerase activity and cancer cell growth. The antisense molecule, hTR-RiAS, combined with enhanced cellular uptake was shown to effectively inhibit telomerase activity and cause rapid cell death in various cancer cell lines. When cancer cells were treated with hTR-RiAS, the level of hTR RNA was reduced by more than 90% accompanied with reduction in telomerase activity. When checked for cancer cell viability, cancer cell lines treated with hTR-RiAS using DNA+Peptide+Lipid complex showed 70-80% growth inhibition in 3 days. The reduced cell viability was due to apoptosis as the percentage of cells exhibiting the sub-G0 arrest and DNA fragmentation increased after antisense treatment. Further, when subcutaneous tumors of a colon cancer cell line (SW480) were treated intratumorally with hTR-RiAS, tumor growth was markedly suppressed with almost total ablation of hTR RNA in the tumor tissue. Cells in the tumor tissue were also found to undergo apoptosis after hTR-RiAS treatment. These results suggest that hTR-RiAS is an effective anticancer reagent, with a potential for broad efficacy to diverse malignant tumors.

Inhibitory effect of human telomerase antisense oligodeoxyribonucleotides on the growth of gastric cancer cell lines in variant tumor pathological subtype

AIM: To investigate the inhibitory effect of specialized human telomerase antisense oligodeoxyribonucleotides on the growth of well (MKN-28), moderately (SGC-7901) and poorly (MKN-45) differentiated gastric cancer cell lines under specific conditions and its inhibition mechanism, and to observe the correlation between the growth inhibition ratio and the tumor pathologic subtype of gastric cancer cells.

METHODS: Telomerase activity in three gastric cancer cell lines of variant tumor pathologic subtype was determined by modified TRAP assay before and after the specialized human telomerase antisense oligodeoxyribonucleotides were dealt with under specific conditions. Effect of antisense oligomer under specific conditions of the growth and viability of gastric cancer cell lines was explored by using trypan blue dye exclusion assay, and cell apoptosis was detected by cell morphology observation, flow cytometry and TUNEL assay.

RESULTS: Telomerase activity was detected in well, moderately and poorly differentiated gastric cancer cell lines (the quantification expression of telomerase activity was 43.7TPG, 56.5TPG, 76.7TPG, respectively).Telomerase activity was controlled to 30.2TPG, 36.3TPG and 35.2TPG for MKN-28, SGC-7901 and MKN-45 cell lines respectively after treatment with human telomerase antisense oligomers at the concentration of 5 μmol/L, and was entirely inhibited at 10 μmol/L, against the template region of telomerase RNA component, whereas no inhibition effect was detected in missense oligomers (P<0.05). After treatment with antisense oligomers at different concentrations under specific conditions for 96 h, significant growth inhibition effects were found in MKN-45 and SGC-7901 gastric cancer cell lines (the inhibition ratio was 40.89% and 71.28%), but not in MKN-28 cell lines (15.86%). The ratio of inactive SGC-7901 cells increased according to the prolongation of treatment from 48 to 96 h. Missense oligomers could not lead to the same effect (P<0.05). Apoptosis of SGC-7901 and MKN-45 cells was detected not only by morphology and TUNEL assay but also by flow cytometry. The apoptotic rate reached 33.56% for SGC-7901 cells and 44.75% for MKN-45 cells.

CONCLUSION: The viability and proliferation of gastric cancer cells can be inhibited by antisense telomerase oligomers. The growth inhibition of gastric cancer cells is correlated with concentration, time and sequence specialty of antisense oligomers. The inhibition mechanism of antisense human telomerase oligomers depends not only on the sequence specialty but also on the biological characteristics of gastric cancer cell lines.

Combination of telomerase antisense oligonucleotides simultaneously targeting hTR and hTERT produces synergism of inhibition of telomerase activity and growth in human colon cancer cell line

AIM: To investigate synergism of inhibition of telomerase activity and proliferation of human colon cancer cells by combination of telomerase antisense oligonucleotides (ASODNs) simultaneously targeting human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) in vitro.

METHODS: ASODN of hTR and ASODN of hTERT were transfected into human colon cancer SW480 cells by liposomal transfection reagents. Telomerase activity of SW480 cells was examined using telomeric repeat amplification protocol (TRAP)-enzyme-linked immunosorbent assay (PCR-ELISA). Proliferation activity of SW480 cells was tested by methyl thiazolyl tetrazolium assay. Apoptosis and cell cycle were analyzed by flow cytometry.

RESULTS: The telomerase activity and cell survival rate in SW480 cells transfected with 0.2 µmol/L of ASODN of hTR or ASODN of hTERT for 24-72 h were significantly decreased in a time-dependent manner compared with those after treatment with sense oligonucleotides and untreated (telomerase activity: 24 h, 73%, 74% vs 99%, 98%; 48 h, 61%, 55% vs 98%, 99%; 72 h, 41%, 37% vs 99%, 97%; P<0.01; cell survival rate: 24 h, 88%, 86% vs 94%, 98%; 48 h, 49%, 47% vs 94%, 97%; 72 h, 44%, 42% vs 92%, 96%; P<0.01). Moreover, the telomerase activity and the cell survival rate in SW480 cells treated by the combination of telomerase anti-hTR and anti-hTERT were more significantly suppressed than single anti-hTR or anti-hTERT (telomerase activity: 24 h, 59% vs 73%, 74%; 48 h, 43% vs 61%, 55%; 72 h, 18% vs 41%, 37%; P<0.01; cell survival rate: 24 h, 64% vs 88%, 86%; 48 h, 37% vs 49%, 47%; 72 h, 25% vs 44%, 42%; P<0.01). Meanwhile, the apoptosis rates in the combination group were markedly increased compared with those in the single group (24 h, 18.0% vs 7.2%, 7.4%; 48 h, 23.0% vs 13.0%, 14.0%; 72 h, 28.6% vs 13.2%, 13.75; P<0.01). Cells in combination group were arrested at G₀/G₁ phase.

CONCLUSION: Telomerase anti-hRT and anti-hTERT suppress telomerase activity, and inhibit growth of human colon cancer cells probably via induction of apoptosis and retardation of cell cycle. Additionally, combined use of telomerase ASODNs targeting both hTR and hTERT yields synergistic action selective for human colon cancer.

Histone H3 acetylation is associated with reduced p21(WAF1/CIP1) expression by gastric carcinoma

Histone acetylation appears to play an important role in transcriptional regulation. Inactivation of chromatin by histone deacetylation is involved in the transcriptional repression of several tumour suppressor genes, including p21(WAF1/CIP1). However, the in vivo status of histone acetylation in human cancers, including gastric carcinoma, is not well understood. This study shows that histone H3 in the p21(WAF1/CIP1) promoter region is hypoacetylated and that this hypoacetylation is associated with reduced p21(WAF1/CIP1) expression in gastric carcinoma specimens. Chromatin immunoprecipitation assays revealed that histone H3 was hypoacetylated in the p21(WAF1/CIP1) promoter and coding regions in 10 (34.5%) and 10 (34.5%) of 29 gastric carcinoma specimens, respectively. Hypoacetylation of histone H4 in the p21(WAF1/CIP1) promoter and coding regions was observed in 6 (20.7%) and 16 (55.2%) of 29 gastric carcinoma specimens, respectively. p21(WAF1/CIP1) mRNA levels were associated with histone H3 acetylation status in the p21(WAF1/CIP1) promoter region (p = 0.047) but not p53 mutation status (p = 0.460). In gastric carcinoma cell lines, expression of p21(WAF1/CIP1) protein was induced by trichostatin A, a histone deacetylase inhibitor. This induction was associated with hyperacetylation of histone H3 in the p21(WAF1/CIP1) promoter region. Hyperacetylation of histone H4 in the p21(WAF1/CIP1) promoter region did not appear to be associated with increased expression. Induction of p21(WAF1/CIP1) protein expression was associated with hyperacetylation of histones H3 and H4 in the p21(WAF1/CIP1) coding region. Expression of a dominant-negative mutant of p53 reduced expression of p21(WAF1/CIP1) protein. Histone H4 acetylation in both the promoter and coding regions of the p21(WAF1/CIP1) gene in cells expressing dominant-negative p53 was less than half of that in cells expressing wild-type p53, whereas histone H3 acetylation in both the promoter and coding regions was slightly reduced (by approximately 20%) in cells expressing the dominant-negative p53. These findings provide evidence that alteration of histone acetylation occurs in human cancer tissue specimens such as those from gastric carcinoma.

Effective inhibition of cancer cell growth by a novel tripartite transfection complex containing ribbon antisense molecules to hTR

PURPOSE

In the present study, ribbon antisense to the hTR RNA, a component of the telomerase complex, was employed to inhibit telomerase activity and cancer cell growth.

MATERIALS AND METHODS

Ribbon antisense molecules to the human hTR gene (hTR-RiAS) were constructed and complexed with a short modified peptide and cationic liposomes to improve the cellular uptake of the antisense molecules. The DPL complexes containing hTR-RiAS were transfected into target cancer cells. Various assays were performed to confirm the effects of the hTR-RiAS on the gene expression and cell proliferation.

RESULTS

When cancer cells were treated with hTR-RiAS, the cellular level of hTR mRNA was reduced by more than 95%, as shown by RT-PCR. Further, the telomerase acti vity was also affected by the antisense treatment. In contrast, both mismatched and scrambled oligonucleotides failed to reduce the levels of hTR mRNA and telomerase activity. When checked for cancer cell viability, hTR-RiAS inhibited cell growth by more than 70%, in a very rapid manner. The reduced cell viability was found to be due to apoptosis of cancer cells.

CONCLUSION

These results show that hTR-RiAS is a powerful anticancer reagent, with the potential for broad efficacy to diverse malignant tumors.

Antisense hTERT inhibits thyroid cancer cell growth

Activation of telomerase represents an early step in carcinogenesis. Increased telomerase expression in malignant thyroid tumors suggests that inactivation of telomerase may represent a potential chemotherapeutic target. The purpose of this study was to inhibit the protein component of telomerase, hTERT, in a human thyroid cancer cell line in vitro and in vivo using an antisense strategy. A 235-bp fragment of hTERT cDNA was subcloned, and sense and antisense hTERT expression vectors were constructed. These vectors were transfected into a human thyroid carcinoma cell line (FRO). Tumorigenic potential was determined by cellular growth assay, rate of apoptosis, anchorage-independent growth, and tumor growth in a nude mouse model. Significant down-regulation of hTERT expression was seen in the antisense transfected cells, compared with control and those transfected with the sense vector. A decrease in telomerase activity by TRAP assay was observed in the antisense hTERT cells but not in cells transfected with the sense hTERT construct. Inhibition of cell growth was observed after approximately 20 population doublings in the antisense-hTERT clones and was associated with an increase in the rate of apoptosis and a change in cellular morphology. Moreover, anchorage-independent growth was reduced in vitro, and tumor growth rate was diminished in vivo in the antisense hTERT clones. Inhibition of telomerase activity with antisense hTERT in human thyroid cancer cells is achievable and may represent a novel target to inhibit tumor growth.

Induction of a p95/Nbs1-mediated S phase checkpoint by telomere 3' overhang specific DNA

Telomere shortening induces a nonproliferative senescent phenotype, believed to reduce cancer risk, and telomeres are involved in a poorly understood manner in responses to DNA damage. Although telomere disruption induces p53 and triggers apoptosis or cell cycle arrest, the features of the disrupted telomere that trigger this response and the precise mechanism involved are poorly understood. Using human cells, we show that DNA oligonucleotides homologous to the telomere 3' overhang sequence specifically induce and activate p53 and activate an S phase checkpoint by modifying the Nijmegen breakage syndrome protein, known to mediate the S phase checkpoint after DNA damage. These responses are mediated, at least in part, by the ATM kinase and are not attributable to disruption of cellular telomeres. Based on these and earlier data, we propose that these oligonucleotides mimic a physiological signal, exposure of the telomere 3' overhang due to opening of the normal telomere loop structure, and hence evoke these protective antiproliferative responses in the absence of DNA damage or telomere disruption.

Telomeres, telomerase, and telomerase inhibition: clinical implications for cancer

Telomeres are located at the ends of eukaryotic chromosomes. The enzyme telomerase synthesized them, and they are responsible for maintaining the lengths of chromosomes. Absence of telomerase is associated with telomere shortening and aging of somatic cells, but high telomerase activity is observed in over 90% of human cancer cells. Although the disappearance of telomerase with aging is considered a natural defense against development of cancer, it is not known what triggers the reappearance of telomerase in cancer cells. Telomerase activity is directly correlated with the expression of its active catalytic component, the human telomerase reverse transcriptase (hTERT), which is controlled primarily at the level of transcription. An earlier paper discussed the relationship of telomerase with aging. In this article, the contemporary literature is reviewed to explore the associations between telomerase, telomerase inhibition, and cancer. Because most cancers occur in old age, with the aging of the population, the number of people suffering from cancer is expected to increase in the coming decades. It is not known what roles telomerase and hTERT play in the complex relationship between aging and cancer. Data from experimental studies suggest that telomerase assay could potentially play a role in the diagnosis and prognosis of cancers. There is also evidence that telomerase inhibitors might be used as anticancer agents. As the knowledge of the relationships between telomerase and cancer and between telomerase and aging advances, it is hoped that more about the interacting relationships between telomerase, aging, and cancer will be learned.

Effect of antisense human telomerase RNA on malignant phenotypes of gastric carcinoma

AIM

The study was designed to explore the effects of antisense human telomerase RNA (ahTR) on the malignant phenotype of gastric carcinoma cell line SGC-7901, and its potential role in gene therapy for tumors.

METHODS

An ahTR eukaryotic expression vector, including the sequence of template region of telomere repeats, was constructed by recombinant technology of molecules and then transfected into gastric carcinoma cell line SGC-7901 by liposome DOTAP. Subsequently, the expression of hTR RNA and ahTR RNA by reverse transcription-polymerase chain reaction, telomerase activity by telomeric repeat amplification protocol-ELISA (TRAP-ELISA), telomere length by Southern blotting, cell morphology under light microscope, cellular proliferation capacity by 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide assay, cell-cycle distribution by flow cytometry, efficiency of clone formation in soft agar, and tumorigenecity in nude mice were examined and evaluated in ahTR-transfected cells, control plasmid pCI-neo transfected cells and their parental cells.

RESULTS

An ahTR eukaryotic expression vector was constructed and successfully transfected into SGC-7901 cells. The telomerase activity in ahTR-transfected SGC-7901 cells decreased from 100% to approximately 25%, and telomere length in the cells shortened to 3.35 from 4.08 Kb at 60 population doublings. Compared with the parental cells and pCI-neo transfected cells, ahTR-transfected cells displayed some morphological changes, such as decreased atypia, and recovery of contact inhibition and density inhibition under light microscope. Furthermore, ahTR-transfected cells displayed decreased invasive capacity in Borden's chamber invasive model, increased G0/G1 phase rate and apoptotic rate. Surprisingly, ahTR-transfected SGC-7901 cells lost their capacity for clone formation in soft agar and tumorigencity in nude mice.

CONCLUSION

Antisense-hTR transfection can inhibit the growth of SGC-7901 cells and partially reverse the malignant phenotypes. This study provides an exciting approach for cancer therapy by inhibiting telomerase activity using an antisense gene.

The expression of hTERT mRNA and cellular immunity in gastric cancer and precancerosis

AIM: To observe the expression of Human telomerase reverse transcriptase (hTERT) in gastric carcinomas and precancerosis lesions, to evaluate the immune state of such patients, and to then study the clinical significance of hTERT and immune state for the diagnosis, treatment and prognosis of gastric cancer.

METHODS: In situ hybridization was used to detect the expression of hTERT mRNA in 116 endoscopic of gastric mucosa. Analyzed tissue samples were as follows: 30 cases of chronic superficial gastritis (CSG), 44 of precancerosis lesions (including 27 of chronic atrophic gastritis, 8 of adenomatous polyp and 9 of gastric ulcer) and 42 of gastric cancer (GC). In addition, the T lymphocyte subsets (CD3⁺, CD4⁺, CD8⁺, CD4⁺/CD8⁺) and natural killer cells (NK) in peripheral blood were determined by flow cytometric analysis (FCM) in 30 cases of CSG, 27 of precancerosis (chronic atrophic gastritis, CAG), and 42 of GC. The data were compared with those of normal control (NC).

RESULTS: The detected positive rate of hTERT varied as follows: 86% (36/42) in GC, 36% (16/44) in precancerosis lesions and 0% (0/30) in CSG. The expression of hTERT mRNA was not associated with patient gender, tumor location, macroscopic type, lymph node metastasis, or degree of differentiation. It was found that the CD3⁺, CD4⁺ of the CSG group were lower than that of NC (P < 0.05). Meanwhile, the T lymphocyte subsets (CD3⁺, CD4⁺, CD4⁺/CD8⁺ ratio) and NK cells of CAG were remarkably lower than that of NC and CSG groups (P < 0.05-0.01). Values of T cells and NK cells of the GC group were significantly abnormal when compared with the CAG group (P < 0.05-0.01). Furthermore, with tumor progression, the function of T cells was weakened gradually.

CONCLUSION: The expression of telomerase may be a crucial step in gastric carcinogenesis and increased hTERT mRNA may serve as a novel marker for diagnosis of GC. The immune state of patients with GC and precancerosis was somewhat depressed, which indicates the importance of cellular immunological assays in cancer patients.

2-5A antisense therapy directed against human telomerase RNA inhibits telomerase activity and induces apoptosis without telomere impairment in cervical cancer cells

Human telomerase RNA (hTR), an important component of telomerase, is a possible target of telomerase-based cancer gene therapy. The present study was undertaken to assess the efficacy of antisense hTR therapy using newly developed 2-5A (5'-phosphorylated 2'-5'-linked oligoadenylate)-linked oligonucleotides against cervical cancer cells. ME180 and SiHa cells were treated with 2-5A-linked antisense hTR designed to complement the region of hTR between residues 76 and 94. The hTR expression, telomerase activity, cell viability, and apoptosis were then examined. The 2-5A anti-hTR effectively degraded hTR and inhibited telomerase activity. The 2-5A mutant anti-hTR and the anti-hTR without 2-5A were not capable of inhibiting telomerase activity. Inhibition of telomerase by 2-5A anti-hTR rapidly decreased cell viability only in telomerase-positive cells within 3-6 days after the treatment, when telomere length has not yet been shortened. This inhibition was associated with apoptosis, possibly through activation of caspase family members. These findings suggest that 2-5A-linked antisense-hTR therapy has a potent telomerase-inhibitory effect associated with a cytocidal effect from caspase-induced apoptosis, and may therefore be a potential tool in telomerase-based gene therapy against cervical cancers.

Tiptoeing to chromosome tips: facts, promises and perils of today's human telomere biology

The past decade has witnessed an explosion of knowledge concerning the structure and function of chromosome terminal structures-telomeres. Today's telomere research has advanced from a pure descriptive approach of DNA and protein components to an elementary understanding of telomere metabolism, and now to promising applications in medicine. These applications include 'passive' ones, among which the use of analysis of telomeres and telomerase (a cellular reverse transcriptase that synthesizes telomeres) for cancer diagnostics is the best known. The 'active' applications involve targeted downregulation or upregulation of telomere synthesis, either to mortalize immortal cancer cells, or to rejuvenate mortal somatic cells and tissues for cellular transplantations, respectively. This article reviews the basic data on structure and function of human telomeres and telomerase, as well as both passive and active applications of human telomere biology.

Telomerase and telomeres: from basic biology to cancer treatment

The limited capacity to divide is one of the major differences between normal somatic cells and cancerous cells. This 'finite life span' of somatic cells is closely linked to loss of telomeric DNA at telomeres, the 'chromosome caps' consisting of repeated (7TAGGG) sequences., In more than 85% of advanced cancers, this telomeric attrition is compensated by telomerase, 'the immortality enzyme', implying that telomerase inhibition may restore mortality in tumor cells. This review discusses the progress in research on the structure and function of telomeres and the telomerase holoenzyme. In addition, new developments in telomere/telomerase targeting compounds such as antisense oligonucleotides and G-quadruplex stabilizing substances, but also new telomerase expression-related strategies such as telomerase promoter-driven suicide gene therapy and telomerase immunotherapy will be presented. It will be discussed how these data can be implemented in telomerase-directed therapies.

Inhibition of human colon cancer cell growth by antisense oligodeoxynucleotides targeted at basic fibroblast growth factor

BACKGROUND

Basic fibroblast growth factor has been shown to be mitogenic in colon cancer cell lines. In human malignant melanoma cells, antisense oligodeoxynucleotides targeted against basic fibroblast growth factor messenger RNA significantly inhibit cell growth. However, the efficacy of such an antisense oligodeoxynucleotide strategy has not been evaluated for colon cancer cells.

AIM

To investigate whether basic fibroblast growth factor can stimulate the growth of HT-29 human colon cancer cells and whether antisense oligodeoxynucleotides can inhibit growth of these cells at baseline.

METHODS

Western blotting analyses were used to confirm the presence of basic fibroblast growth factor protein in this cell line. Cell growth was assessed after 2, 4 and 6 days of treatment by cell counting using the trypan blue exclusion method. Phosphorothioate-modified oligodeoxynucleotides (10 microM) were used, complementary to codon 60 of the basic fibroblast growth factor messenger RNA. Cationic liposomes (DOTAP) were used to enhance the cellular uptake of the oligodeoxynucleotides.

RESULTS

Western blotting demonstrated the presence of basic fibroblast growth factor protein in this cell line. Basic fibroblast growth factor (1-40 ng/mL) dose-dependently stimulated cell growth and peak values were obtained at a dose of 20 ng/mL. By contrast, antisense oligodeoxynucleotide treatment significantly inhibited cell growth compared with the sense oligodeoxynucleotide-treated cells (P=0.007). This inhibition was reversed by the addition of basic fibroblast growth factor, 20 ng/mL.

CONCLUSION

Treatment targeted against basic fibroblast growth factor messenger RNA inhibits growth of HT-29 human colon cancer cells. This finding may provide a rationale for the therapeutic use of antisense oligodeoxynucleotides targeted at basic fibroblast growth factor for the treatment of colon cancer.

Genetic and epigenetic changes in stomach cancer

Genetic and epigenetic alterations of multiple cancer-related genes and molecules are implicated in the development and progression of human gastric carcinomas. Reactivation of telomerase, inactivation of p53 tumor suppressor gene, overexpression of cyclin E, and reduced expression of p27 KIP1 by disorganized degradation in proteasome are common events of both well-differentiated and poorly differentiated gastric adenocarcinomas. Inactivation of hMLH1 mismatch repair gene by CpG hypermethylation resulting in microsatellite instability, amplification of c-erbB2 oncogene, inactivation of APC tumor suppressor gene, and K-ras mutations are preferentially associated with well-differentiated gastric cancer. Conversely, reduction or loss of E-cadherin and catenins by both mutation and CpG hypermethylation and K-sam and c-met oncogene amplification are necessary for the development and progression of poorly differentiated or scirrhous gastric carcinomas. Interaction between cancer cells expressing c-met and hepatocyte growth factor from stromal cells is implicated in morphogenesis of gastric cancer.

Overexpression of human telomerase RNA in Helicobacter pylori-infected human gastric mucosa

Telomerase, an enzyme associated with cellular immortality and malignancy, plays an important role in cellular immortalization and tumorigenesis. Furthermore, overexpression of the RNA component of the telomerase, called human telomerase RNA (hTR), has been demonstrated in various human cancers as an early event. The pattern of hTR expression following Helicobacter pylori (H. pylori) infection in human gastric mucosa was investigated by a radioactive in situ hybridization (ISH) assay. Paraffin-embedded sections of 50 biopsy specimens taken from the gastric antrum of individual patients infected to different extents with H. pylori, as well as normal gastric mucosa, were studied. In normal gastric mucosa, only weak hTR expression was noted and the expression was limited to basal cells of the gastric glands. However, the degree of hTR expression gradually increased in parallel with the degree of H. pylori infection. The mean scores of gastric mucosa with mild, moderate and severe degrees of H. pylori infection were 2.3, 2.8, and 3.7 times higher than that of normal gastric mucosa, respectively. The results of this study suggested that up-regulation of hTR expression is a frequent and early event associated with H. pylori infection in the gastric mucosa and may play some role in gastric carcinogenesis. Sufficient synthesis of hTR during this early stage may be a prerequisite for telomerase reactivation to occur in gastric cancer.

Molecular characteristics of eight gastric cancer cell lines established in Japan

Molecular characterization of eight gastric cancer cell lines established in Japan are summarized according to the genetic and epigenetic alterations and growth factor status. TMK-1 poorly differentiated adenocarcinoma cell line harbors mutant p53 tumor suppressor gene and rearrangement of p15MTS2. MKN-1 adenosquamous carcinoma line with mutant p53 reveals silencing of E-cadherin by promoter CpG hypermethylation. MKN-7 well-differentiated adenocarcinoma cell line has amplification of c-erbB2 oncogene and cyclin E gene. MKN-28 well-differentiated adenocarcinoma cell line reveals mutations in p53 and APC tumor suppressor genes and silencing of CD44. The MKN-45 poorly differentiated adenocarcinoma cell line with wild-type p53 is characterized by homozygous deletion of p16CDKN2/MTS1/INK4A and p15MTS2, amplification of c-met oncogene and promoter mutation of E-cadherin. MKN-74 derived from moderately differentiated tubular adenocarcinoma has wild-type p53. KATO-III signet ring cell carcinoma line has genomic deletion of p53, amplification of K-sam and c-met oncogene and mutation of E-cadherin. HSC-39 signet ring cell carcinoma cell line harboring p53 missense mutation has homozygous deletion of p16CDKN2/MTS1/INK4A and p15MTS2, amplifications of c-myc, c-met, K-sam and CD44 gene and mutation in beta-catenin gene.

The 5'-end of hTERT mRNA is a good target for hammerhead ribozyme to suppress telomerase activity

Because the expression level of hTERT, a catalytic subunit of human telomerase, is a rate-limiting determinant of telomerase activity, hTERT mRNA would be an excellent target of hammerhead ribozymes for the regulation of telomerase activity. We studied the efficiency of several hammerhead ribozymes targeting hTERT mRNA by transient and stable transfection procedures. To screen the potency of the ribozymes, transient ribozyme transfection and telomerase determination were performed. The ribozyme targeting 13 nucleotides downstream from the 5'-end of hTERT mRNA (13-ribozyme) exhibited the strongest telomerase-inhibitory activity, and the ribozyme to target 59 nucleotides upstream from the poly(A) tail showed clear activity. A stable transfection study confirmed that the 13-ribozyme suppressed telomerase. These observations suggest that the 13-ribozyme can regulate telomerase activity and may possess potential for cancer therapy.

Recent advances in the development of telomerase inhibitors for the treatment of cancer

Telomerase is an holoenzyme responsible for the maintenance of telomeres, the protein-nucleic acid structures which exist at the ends of eukaryotic chromosomes that serve to protect chromosomal stability and integrity. Telomerase activity is essential for the sustained proliferation of most immortal cells, including cancer cells. Since the discovery that telomerase activity is expressed in 85 - 90% of all human tumours and tumour-derived cell lines but not in most normal somatic cells, telomerase has become the focus of much attention as a novel and potentially highly-specific target for the development of new anticancer chemotherapeutics. Herein we review recent advances in the development of telomerase inhibitors for the treatment of cancer. To date, these have included antisense strategies, reverse transcriptase inhibitors and compounds capable of interacting with high-order telomeric DNA tetraplex ('G-quadruplex') structures to prevent enzyme access to the necessary linear telomere substrate. In addition, a number of telomerase-inhibitory therapies have been shown to synergistically enhance the effects of clinically-established anticancer drugs. Critical appraisal of each individual approach is provided, together with highlighted areas of likely future development. We also review recent developments in telomere and telomerase biology, of which a more detailed understanding would be essential in order to further develop the present classes of telomerase inhibitors into viable, clinically applicable therapies.