Effects of chemopreventive and antitelomerase agents on the spontaneous immortalization of breast epithelial cells

Regulation of telomerase activity by apparently opposing elements

Telomeres, the ends of chromosomes, undergo frequent remodeling events that are important in cell development, proliferation and differentiation, and neoplastic immortalization. It is not known how the cellular environment influences telomere remodeling, stability, and lengthening or shortening. Telomerase is a ribonucleoprotein complex that maintains and lengthens telomeres in the majority of cancers. Recent studies indicate that a number of factors, including hormones, cytokines, ligands of nuclear receptor, vitamins and herbal extracts have significantly influence telomerase activity and, in some instances, the remodeling of telomeres. This review summarizes the advances in understanding of the positive and negative regulation by extracellular factors of telomerase activity in cancer, stem cells and other systems in mammals.

Low telomerase activity: possible role in the progression of human medullary thyroid carcinoma

Maintenance of telomere length has been reported to be an absolute requirement for unlimited growth of human tumour cells and in about 85% of cases, this is achieved by reactivation of telomerase, the enzyme that elongates telomeres. Only in rare cases, like in human medullary thyroid carcinomas (MTC), telomerase activity (TA) is low or undetectable; however, this does not limit tumours to become clinically significant. Here, we report that very low TA (below 5% of HEK293) observed in MTC cell strains derived from different patients, although not sufficient for immortalising the cells, is necessary for prolonging their replicative life span. Telomere erosion led to induction of a crisis period after long-term in vitro cultivation, which was reached earlier when treating the cells with MST-312, a telomerase inhibitor at non-toxic concentrations. Crisis was bypassed either by ectopic hTERT introduction or by infrequent spontaneous immortalisation, the latter of which was always associated with telomerase reactivation and changes of the cellular phenotype. While confirming the high importance of telomerase for tumour development, these data draw attention to the relevance of low TA: although insufficient for telomere stabilisation, it allows MTC cells to reach more population doublings, increasing both cell numbers as well as the risk of accumulating mutations and thus might support the development of clinically significant MTC.

hTERT knockdown in human embryonic kidney cells using double-stranded RNA

The method of RNA interference (RNAi) is an easy means of knocking down a gene without having to generate knockout mutants, which may prove to be difficult and time consuming. RNAi is a naturally occurring process that involves targeting the mRNA of a gene by introducing RNAs that are complementary to the target mRNA. The foreign RNAs activate an endogenous enzyme, DICER, which degrades the target mRNA. There are many ways of eliciting the RNAi response in a cell. In this chapter, we describe the use of double-stranded RNA (dsRNA) to knockdown human telomerase reverse transcriptase (hTERT), the gene that codes for the catalytic subunit of the human telomerase enzyme. dsRNA can be used to generate the RNAi response in cells of embryonic origin, such as human embryonic kidney (HEK) cells. The RNAi effect is transient because the dsRNA eventually gets degraded in the cells, and it is useful to study the short-term effects of a gene knockdown.

Antioxidant agents transiently inhibit aneuploidy progression in Li-Fraumeni cell strains

Cultured human fibroblasts from patients with the Li-Fraumeni syndrome (LFS) containing heterozygous germline p53 mutations develop genomic instability, loss of the wild-type p53 allele, and immortalize at a low frequency. Since genomic instability and phenotypic change are observed in presenescent cells without specific exposure to mutagens, we hypothesized that reactive oxygen species (ROS) produced during normal cell metabolism coupled with deficient p53 dependent DNA damage repair pathways make a significant contribution to immortalization related parameters. To test this hypothesis, three LFS cell strains (MDAH087, MDAH041, and MDAH172) were exposed to five compounds with demonstrated antioxidant properties for > or =85% of their proliferative lifetimes. Agent effectiveness was evaluated every five passages during subculturing by analyzing aberrant chromosome number, anchorage independent growth (AIG), and p16 expression. Cytogenetic analysis revealed that of the five antioxidants tested, only oltipraz was significantly effective in transiently delaying a shift to hyperdiploidy in all three cell strains. However, treated populations were not different from untreated controls when measured in the last 10% of their lifetimes. Additionally, no differences were observed in AIG and p16 expression in antioxidant treated or untreated control populations. Epidemiological studies, in vitro and in vivo experimentation and some clinical trials have suggested that antioxidants may inhibit the progression of cancer and other mutation related diseases. This data, however, does not support the hypothesis that the antioxidants tested have chemopreventive potential in cancers that develop genomic instability due to loss of p53.

Dehydroepiandrosterone inhibits the progression phase of mammary carcinogenesis by inducing cellular senescence via a p16-dependent but p53-independent mechanism

INTRODUCTION

Dehydroepiandrosterone (DHEA), an adrenal 17-ketosteroid, is a precursor of testosterone and 17beta-estradiol. Studies have shown that DHEA inhibits carcinogenesis in mammary gland and prostate as well as other organs, a process that is not hormone dependent. Little is known about the molecular mechanisms of DHEA-mediated inhibition of the neoplastic process. Here we examine whether DHEA and its analog DHEA 8354 can suppress the progression of hyperplastic and premalignant (carcinoma in situ) lesions in mammary gland toward malignant tumors and the cellular mechanisms involved.

METHODS

Rats were treated with N-nitroso-N-methylurea and allowed to develop mammary hyperplastic and premalignant lesions with a maximum frequency 6 weeks after carcinogen administration. The animals were then given DHEA or DHEA 8354 in the diet at 125 or 1,000 mg/kg diet for 6 weeks. The effect of these agents on induction of apoptosis, senescence, cell proliferation, tumor burden and various effectors of cellular signaling were determined.

RESULTS

Both agents induced a dose-dependent decrease in tumor multiplicity and in tumor burden. In addition they induced a senescent phenotype in tumor cells, inhibited cell proliferation and increased the number of apoptotic cells. The DHEA-induced cellular effects were associated with increased expression of p16 and p21, but not p53 expression, implicating a p53-independent mechanism in their action.

CONCLUSION

We provide evidence that DHEA and DHEA 8354 can suppress mammary carcinogenesis by altering various cellular functions, inducing cellular senescence, in tumor cells with the potential involvement of p16 and p21 in mediating these effects.

Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Telomerase in breast cancer: a critical evaluation

Human chromosomes have highly specialized structures at their ends termed telomeres, repetitive, non-coding DNA sequences (5'-TTAGGG-3'), ranging in size from 5 to 20 kb in human cells. These highly specialized structures prevent chromosome ends from being recognized as double-strand DNA breaks, and they also provide protection from destabilizing agents. The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences lost during replication by using an intrinsic RNA component as a template for polymerization. Telomerase has two core functional components required for its activity: the catalytic subunit of human telomerase reverse transcriptase (hTERT) and a telomerase RNA template (hTR). Telomerase is activated in the majority of immortal cell lines in culture and in most malignant tumors. This review outlines our current understanding of telomerase in breast cancer development and critically evaluates potential utilities in diagnosis, prognosis, and therapy.

Telomeric recombination in mismatch repair deficient human colon cancer cells after telomerase inhibition

The majority of human malignancies use telomerase to maintain telomere homeostasis. Antitelomerase therapy is therefore a promising approach for a cancer-specific therapy. The alternative lengthening of telomeres pathway (ALT) is a recombination-based, telomerase-independent mechanism of telomere length control. It is widely believed that ALT could be engaged when cancer cells escape from telomerase inhibition. However, no reports exist that would support this concept of therapy resistance. We inhibited telomerase in a human cancer cell line with a mismatch repair defect and observed a telomerase-independent, ALT-like telomere elongation. This is the first report of inducing a telomerase-independent telomere elongation in human cancer cells when telomerase is inhibited, thus describing a novel mechanism of resistance to antitelomerase therapy.

Telomerase, telomerase inhibition, and cancer

Telomeres, located at the ends of eukaryotic chromosomes, are synthesized by the enzyme telomerase and are responsible for maintaining chromosome length. The absence of telomerase in most somatic cells has been associated with telomere shortening and aging of these cells. In contrast, high levels of telomerase activity are observed in over 90% of human cancer cells. The absence of telomerase in normal and aging cells is considered a natural defense against development of cancer. However, we do not know 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 believed to be controlled primarily at the level of transcription. Elucidation of the control of telomerase in aging and in cancer as an age-related disease has considerable potential in leading to novel approaches in anti-aging medicine.

Hallmarks of senescence in carcinogenesis and cancer therapy

Cellular senescence is a signal transduction program leading to irreversible cell cycle arrest. This growth arrest can be triggered by many different mechanisms including recognition by cellular sensors of DNA double-strand breaks leading to the activation of cell cycle checkpoint responses and recruitment of DNA repair foci. Senescence is initiated by the shortening of telomeres (replicative senescence) or by other endogenous and exogenous acute and chronic stress signals (STASIS: stress or aberrant signaling-induced senescence). The process of carcinogenesis involves a series of changes that allow tumor cells to bypass the senescence program. Nevertheless, tumor cells retain the capacity to undergo senescence. Treatment of tumor cells with many conventional anticancer therapies activates DNA damage signaling pathways, which induce apoptosis in some cells and senescence in others. Overexpression of tumor suppressors or inhibition of oncogenes can also induce rapid senescence in tumor cells. Senescent cells, while not dividing, remain metabolically active and produce many secreted factors, some of which stimulate and others inhibit the growth of tumors. The emerging knowledge about the pathways that lead to senescence and determine the pattern of gene expression in senescent cells may lead to more effective treatments for cancer.

Increased gap junctional intercellular communication is directly related to the anti-tumor effect of all-trans-retinoic acid plus tamoxifen in a human mammary cancer cell line

Additive effects against tumor cells might be achieved by combining anti-neoplastic agents directed against one or more altered mechanisms in cancer. We investigated the participation of gap junctional intercellular communication (GJIC), which is commonly dysfunctional in tumor cells as a possible mediating mechanism of the effect of all-trans-retinoic acid (RA) and tamoxifen (Tx) in MCF-7 human breast cancer cell lines. The combination of RA + Tx stimulated GJIC in approximately 53 +/- 3% of MCF-7 cells as early as after 6 h of treatment remaining communicated through 144 h of culture. The GJIC enhancement occurred along with immunolocalization of Cx26 and 43 at the membrane of contacting cells and correlated with higher protein levels. Cx40 immunoreactive plaques were detected at cell-to-cell contacts during 48 h of RA + Tx treatment that did not involve higher protein expression, to the contrary, a downregulation occurred after 72 h of treatment. Cell proliferation inhibition upon RA + Tx exposure was observed with optimal effects at 96-120 h of culture with an accumulation of cells primarily in G2/M and G0/G1 cell cycle boundaries. An enhancement of the pre-existing E-cadherin levels was observed after drug exposure along with a downregulation of Bcl-2 and C-myc protein levels and a reduction of telomerase activity, suggesting partial tumor phenotype reversion. Blockage of the RA + Tx-induced GJIC with 18-beta-glycyrrhetinic acid (beta-Gly) prevented in 34% the inhibition of MCF-7 proliferation and the E-cadherin increment in 30% at 96 h of culture. GJIC blockage did not alter the downregulation of Bcl-2, c-Myc, or telomerase activity induced by RA + Tx. Our results showed the participation of GJIC as a mediator mechanism of the combined action of RA and Tx in MCF-7 cells. The chemopreventive modulation of GJIC might represent an approachable alternative for the improvement of cancer therapy.

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.

Chemopreventive agents induce a senescence-like phenotype in rat mammary tumours

Terminal replicative senescence (TRS) is a physiological process associated with terminal differentiation, shortening of the telomere, and lack of proliferative activity. Immortalised and tumour cells have lost their differentiation potential and the ability to develop a senescence phenotype. Recently, others and we [11] have observed that some antitumour agents and radiation induce a senescence-like phenotype (SLP) in human immortalized and tumour cell lines. The main purpose of this study was to identify senescence-like cells (SLC) in mammary tumours of rats and assess whether chemopreventive agents that have been used for the prevention and/or treatment of breast cancer can induce a SLP in tumour cells. Sprague-Dawley rats with N-methyl-N-nitrosourea (MNU)-induced mammary tumours were randomised and treated with tamoxifen, vorozole, 4-(hydroxyphenyl)retinamide (4-HPR), or 9-cis-retinoic acid (9cRA). The SLC in mammary tumours were identified and characterised by: (a) SA-beta-Gal staining method, which has been considered specific for human cells in TRS (b) staining for lipofuscin, which, although not specific, accumulates in the cytoplasm of cells in senescence; (c) lack of 5-Bromodeoxyuridine (BrdU) labelling after continuous (7 days) infusion of BrdU via osmotic pumps; (d) 90 degrees side light scatter (9OLS) as evaluated by flow cytometry; and (e) decreased telomerase activity. We found that in control tumours, SA-beta-Gal-positive cells were rare (below 1.0%) among the tumour cells, stroma fibroblast, myoepithelial and endothelial cells. SA-beta-Gal-positive cells increased significantly in the tumours treated with chemopreventive agents and this was associated with a lack of proliferative activity, increased cell granularity, lipofuscin accumulation, and decreased telomerase activity. Thus, in this study we provide for the first time evidence that cells in replicative senescence are present in mammary tumours of rats and that chemopreventive agents can suppress tumor growth by a novel cellular mechanism, inducing a SLP in the tumor cells.

Telomerase: a target for cancer therapeutics

The continuous growth of advanced malignancies almost universally correlates with the reactivation of telomerase. While there is still a great deal of basic and applied research to be done, telomerase remains a very attractive novel target for cancer therapeutics. In this review, we will discuss the challenges and the pros and cons of the most promising antitelomerase approaches currently being investigated.

A G-quadruplex-interactive potent small-molecule inhibitor of telomerase exhibiting in vitro and in vivo antitumor activity

The telomerase complex is responsible for telomere maintenance and represents a promising cancer therapeutic target. We describe herein the antitelomerase and antitumor properties of a small-molecule compound designed by computer modeling to interact with and stabilize human G-quadruplex DNA, a structure that may form with telomeric DNA, thereby inhibiting access to telomerase. The 3,6,9-trisubstituted acridine 9-[4-(N,N-dimethylamino)phenylamino]-3,6-bis(3-pyrrolodinopropionamido) acridine (BRACO19) represents one of the most potent cell-free inhibitors of human telomerase yet described (50% inhibitory concentration of 115 +/- 18 nM). Moreover, in contrast to G-quadruplex interactive agents described previously, BRACO19 did not cause nonspecific acute cytotoxicity at similar concentrations to those required to completely inhibit telomerase activity. There exists a 90-fold differential (mean 50% inhibitory concentration for acute cell kill across seven human tumor cell lines of 10.6 +/- 0.7 microM). The exposure of 21NT human breast cancer cells, which possess relatively short telomeres, to nonacute cytotoxic concentrations of BRACO19 (2 microM) resulted in a marked reduction in cell growth after only 15 days. This was concomitant with a reduction in intracellular telomerase activity and onset of senescence as indicated by an increase in the number of beta-galactosidase positive-staining cells. Intraperitoneal administration of nontoxic doses of BRACO19 (2 mg/kg) to mice bearing advanced stage A431 human vulval carcinoma subcutaneous xenografts and previously treated with paclitaxel induced a significant increase in antitumor effect compared with that observed with paclitaxel alone. BRACO19 thus represents the first of a "second generation" of G-quadruplex-mediated telomerase/telomere-interactive compounds. It possesses nanomolar potency against telomerase but low nonspecific cytotoxicity, growth inhibitory effects, and induction of senescence in a human breast cancer cell line and, moreover, significant antitumor activity in vivo when administered post paclitaxel to mice bearing a human tumor xenograft carcinoma.

Telomere and telomerase in the initial stage of immortalization of esophageal epithelial cell

AIM: To search for the biomarker of cellular immortalization, the telomere length, telomerase activity and its subunits in cultured epithelial cells of human fetal esophagus in the process of immortalization.

METHODS: The transgenic cell line of human fetal esophageal epithelium (SHEE) was established with E₆E₇ genes of human papillomavirus (HPV) type 18 in our laboratory. Morphological phenotype of cultured SHEE cells from the 6th to 30th passages, was examined by phase contrast microscopy, the telomere length was assayed by Southern blot method, and the activity of telomerase was analyzed by telomeric repeat amplification protocol (TRAP). Expressions of subunits of telomerase, hTR and hTERT, were assessed by RT-PCR. DNA content in cell cycle was detected by flow cytometry. The cell apoptosis was examined by electron microscopy (EM) and TUNEL label.

RESULTS: SHEE cells from the 6th to 10th passages showed cellular proliferation with a good differentiation. From the 12th to the 16th passages, many senescent and apoptotic cells appeared, and the telomere length sharply shortened from 23 kb to 17 kb without expression of hTERT and telomerase activity. At the 20th passage, SHEE cells overcame the senescence and apoptosis and restored their proliferative activity with expression of telomerase and hTERT at low levels, but the telomere length shortened continuously to the lowest of 3 kb. After the 30th passage cells proliferation was restored by increment of cells at S and G₂M phase in the cell cycle and telomerase activity expressed at high levels and with maintenance of telomere length.

CONCLUSION: At the early stage of SHEE cells, telomeres are shortened without expression of telomerase and hTERT causing cellular senescence and cell death. From the 20th to the 30th passages, the activation of telomerase and maintenance of telomere length show a progressive process for immortalization of esophageal epithelial cells. The expression of telomerase may constitute a biomarker for detection of immortalization of cells.

Glucuronidation: an important mechanism for detoxification of benzo[a]pyrene metabolites in aerodigestive tract tissues

UDP-glucuronosyltransferases (UGTs) have been implicated as important detoxifying enzymes for several major tobacco carcinogens. Because the aerodigestive tract is a primary target for exposure to tobacco smoke carcinogens, the major goal of the present study was to determine whether aerodigestive tract tissues exhibit glucuronidating activity against metabolites of benzo[a]pyrene (BaP) and to explore the pattern of expression of UGT genes in a series of aerodigestive tract tissue specimens. Glucuronidation of the phenolic BaP metabolites 3-, 7-, and 9-hydroxy-BaP was observed in all upper aerodigestive tract tissue microsome specimens tested, as determined by high-pressure liquid chromatography analysis. Glucuronidating activity toward the procarcinogenic BaP metabolite trans-BaP-7,8-dihydrodiol(+/-) was also detected in aerodigestive tract tissues. By semiquantitative duplex reverse transcription-polymerase chain reaction analysis, UGT1A7 and UGT1A10 were shown to be well expressed in all aerodigestive tract tissues examined, including tongue, tonsil, floor of mouth, larynx, and esophagus. UGT1A8 and UGT1A6 were expressed primarily in larynx; no expression was observed for UGTs 1A1, 1A3, 1A4, 1A5, 1A9. Of the family 2B UGTs, only UGT2B4 and UGT2B17 exhibited significant levels of expression in aerodigestive tract tissues. Of the aerodigestive tract-expressing UGTs, only UGTs 1A7, 1A8, and 1A10 exhibited glucuronidating activity against 7-hydroxy-BaP, with UGT1A10 exhibiting the highest affinity as determined by kinetic analysis (K(m) = 49 microM). No UGT expression or glucuronidating activity was observed for any of the lung specimens analyzed in this study. These results suggest that several family 1 UGTs may potentially play an important role in BaP detoxification in the aerodigestive tract.

Telomerase inhibition, oligonucleotides, and clinical trials

Telomerase is expressed in most types of tumors but not in most somatic cells. This observation has led to two hypotheses; (i) telomerase activity is necessary for the proliferation of cancer cells; and (ii) telomerase inhibitors are a powerful strategy for cancer chemotherapy. Testing the latter hypothesis requires the development of potent and selective inhibitors of telomerase and their testing in clinical trials. Assaying the efficacy of telomerase inhibitors will not be simple because telomere erosion will be slow and antiproliferative effects will probably require weeks to become apparent. This review will describe the properties of 2'-O-alkyl oligonucleotide inhibitors of telomerase. Oligonucleotides that block expression of other cancer targets have favorable pharmacokinetic properties and are already in clinical trials. This experience is likely to facilitate clinical trials of anti-telomerase oligomers.

Telomerase in cancer and aging

The telomere-telomerase hypothesis is the science of cellular aging (senescence) and cancer. The ends of chromosomes, telomeres, count the number of divisions a cell can undergo before entering permanent growth arrest. As divisions are being counted, events occur on the cellular and molecular level, which may either delay or hasten this arrest. As humans age, a particular concern is the accumulation of events that lead to the progression of cancer. Telomerase is a mechanism that most normal cells do not possess, but almost all cancer cells acquire, to overcome their mortality and extend their lifespan. This review aims to provide a comprehensive understanding of the role of telomerase in cancer development, progression, diagnosis, and in the future, treatment. The ultimate goal of telomerase research is to use our understanding to develop anti-telomerase therapies, an almost universal tumor target.

The role of chemotherapy in early non-small-cell lung cancer management

Great advances have been made in chemotherapy in advanced and metastatic non-small-cell lung cancer (NSCLC), and a major milestone was reached with the administration of neoadjuvant chemotherapy in stage IIIA N2 disease. The systemic nature of lung cancer has been confirmed by many genetic analyses documenting micrometastases in negative lymph nodes and bone marrow, and mRNA gene overexpression as a surrogate of cancer cells has been identified in peripheral blood. Furthermore, serum or plasma cell-free tumor DNA has been observed even in tumors with a diameter of less than 2 cm. Pharmacogenetic screening can lead to tailored chemotherapy even in patients with early disease through the use of a genetic tool kit that will allow us to optimize the use of chemotherapy by using serial measurements of serum DNA that can help to detect residual disease and re-assess the chemosensitivity of sub-clinical micrometastatic disease. The ongoing (neo)adjuvant taxol/carboplatin hope (NATCH) trial is testing the value of three cycles of chemotherapy given pre- or post-operatively compared with surgery alone and will analyze genetic abnormalities in serum DNA at three different points during patient follow-up. Our major concern in this review is to analyze the pros and cons of chemotherapy in NSCLC. Although this review is not a formal meta-analysis, we have discussed the most relevant published studies in this field. We conclude that not only is there no evidence of detrimental effects of chemotherapy, in fact, there are many indications that chemotherapy induces response in up to 80% of patients and downgrades N2 disease in up to 50% of patients. This translates into significantly better survival when accompanied by complete resection. Since at least 50% of patients with stage IB disease develop distant metastases, it seems logical to explore the role of chemotherapy in early disease.

Effects of N-(4-hydroxyphenyl)retinamide on hTERT expression in the bronchial epithelium of cigarette smokers

BACKGROUND

Telomerase activation plays a critical role in tumorigenesis. To determine the role of telomerase in early lung carcinogenesis and as a potential biomarker in chemoprevention trials, we analyzed the expression of the human telomerase reverse transcriptase catalytic subunit (hTERT) in bronchial biopsy specimens from cigarette smokers who were enrolled in a randomized, double-blinded, placebo-controlled chemoprevention trial of N-(4-hydroxyphenyl)retinamide (4-HPR).

METHODS

We obtained biopsy specimens from six predetermined sites in the bronchial tree from the 57 participants, before treatment and 6 months after treatment with 4-HPR or placebo. We used in situ hybridization to examine hTERT messenger RNA (mRNA) expression in 266 pretreatment (baseline) and post-treatment site-paired biopsy specimens from 27 patients in the 4-HPR-treated group and from 30 patients in the placebo-treated group. All statistical tests were two-sided.

RESULTS

At baseline, 62.4% (95% confidence interval [CI] = 53.9% to 71%) of the biopsy specimens obtained from the group treated with 4-HPR and 65.2% (95% CI = 57.4% to 73.1%) of the biopsy specimens obtained from the placebo-treated group expressed hTERT mRNA. After 6 months, 45.6% (95% CI = 36.9% to 54.3%) of the biopsy specimens obtained from the 4-HPR-treated group and 68.1% (95% CI = 60.4% to 75.8%) of the biopsy specimens obtained from the placebo-treated group expressed hTERT mRNA. The reduction in hTERT expression observed between the two treatment groups over time was statistically significant (P =.01) when we used the biopsy site as the unit of analysis, but not when we used the individual as the unit of analysis (P =.37).

CONCLUSIONS

Telomerase is frequently reactivated in the lungs of cigarette smokers. The modulation of hTERT expression in 4-HPR-treated smokers suggests that a novel molecular mechanism underlies the potential chemopreventive properties of 4-HPR. hTERT expression is a promising potential biomarker for risk assessment and for the evaluation of the efficacy of chemopreventive agents in lung carcinogenesis.

An old epithelial cell never dies, it just agonesces away

The behavior of mammary epithelial cells during aging is dynamic and is likely to have significant implications in the pathogenesis of human breast cancer. The growth of epithelial cells over time was thought to parallel that of their underlying stroma, sequentially undergoing a defined period of growth, followed by senescence and, ultimately, cell crisis or rarely immortalization. Recent findings, however, suggest that the evolution of mammary epithelium at the proliferative and chromosomal levels is distinct from that of stroma, contributing to the neoplastic susceptibilities of epithelial cells.

Epigenetic downregulation of the retinoic acid receptor-beta2 gene in breast cancer

A growing body of evidence supports the hypothesis that the retinoic acid receptor beta2 (RAR-beta2) gene is a tumor suppressor gene which induces apoptosis and that the chemopreventive and therapeutic effects of retinoids are due to induction of RAR-beta2. During breast cancer progression, RAR-beta2 is reduced or even lost. It is known from studies of other tumor-suppressor genes that methylation of the 5'-region is the cause of loss of expression. Several groups demonstrated that this is also true for the RAR-beta2 in breast cancer by treating breast cancer cell lines with a demethylating agent and examining expression of the RAR-beta2 gene in response to a challenge with retinoic acid. Studies using sodium bisulfite genomic sequencing as well as methylation specific PCR showed that a number of breast cancer cell lines as well as breast cancer tissue showed signs of methylation. The RAR-beta2 gene was unmethylated in non-neoplastic breast tissue as well as in other normal tissues. A combination of retinoic acid with demethylating agents as well as with histone deacetylase inhibitors acts synergistically to inhibit growth. This review presents data that suggest that treatment of cancer patients with demethylating agents followed by retinoic acid may offer a new therapeutic modality. Both the time of commencement of chemoprevention and the choice of substances that are able either to prevent de novo methylation or to reverse methylation-caused gene silencing may be important considerations.

Telomerase and breast cancer

Current therapies for breast cancer include treatments that are toxic and often result in drug resistance. Telomerase, a cellular reverse transcriptase that maintains the ends of chromosomes (telomeres), is activated in the vast majority of breast cancers (over 90% of breast carcinomas) but not in normal adjacent tissues. Telomerase is thus an attractive target for both diagnosis and therapy because of its distinct pattern of expression. We address the use of telomerase in the diagnostics of breast pathology, as well as the use of telomerase inhibitors in the treatment and prevention of breast cancer.