Joo-Shik Shin

The role of telomeres and telomerase in the pathology of human cancer and aging.

&NA; Cellular senescence, the state of permanent growth arrest, is the inevitable fate of replicating normal somatic cells. Postulated to underlie this finite replicative span is the physiology of telomeres, which constitute the ends of chromosomes. The repetitive sequences of these DNA‐protein complexes progressively shorten with each mitosis. When the critical length is bridged, telomeres trigger DNA repair and cell cycle checkpoint mechanisms that result in chromosomal fusions, cell cycle arrest, senescence and/or apoptosis. Should senescence be bypassed at such time, continued cell divisions in the face of dysfunctional telomeres and activated DNA repair machinery can result in the genomic instability favourable for oncogenesis. The longevity and malignant progression of the thus transformed cell requires coincident telomerase expression or other means to negate the constitutional telomeric loss. Practically then, telomeres and telomerase may represent plausible prognostic and screening cancer markers. Furthermore, if the argument is extended, with assumptions that telomeric attrition is indeed the basis of cellular senescence and that accumulation of the latter equates to aging at the organismal level, then telomeres may well explain the increased incidence of cancer with human aging.

Surface antigen profiling of colorectal cancer using antibody microarrays with fluorescence multiplexing

A procedure is described for the disaggregation of colorectal cancers (CRC) and normal intestinal mucosal tissues to produce suspensions of viable single cells, which are then captured on customized antibody microarrays recognising 122 different surface antigens (DotScan CRC microarray). Cell binding patterns recorded by optical scanning of microarrays provide a surface profile of antigens on the cells. Sub-populations of cells bound on the microarray can be profiled by fluorescence multiplexing using monoclonal antibodies tagged with Quantum Dots or other fluorescent dyes. Surface profiles are presented for 6 CRC cell lines (T84, LIM1215, SW480, HT29, CaCo and SW620) and surgical samples from 40 CRC patients. Statistical analysis revealed significant differences between profiles for CRC samples and mucosal controls. Hierarchical clustering of CRC data identified several disease clusters that showed some correlation with clinico-pathological stage as determined by conventional histopathological analysis. Fluorescence multiplexing using Phycoerythrin- or Alexa Fluor 647-conjugated antibodies was more effective than multiplexing with antibodies labelled with Quantum Dots. This relatively simple method yields a large amount of information for each patient sample and, with further application, should provide disease signatures and enable the identification of patients with good or poor prognosis.

Radiotherapy Response in Microsatellite Instability Related Rectal Cancer

Preoperative radiotherapy may improve the resectability and subsequent local control of rectal cancers. However, the extent of radiation induced regression in these tumours varies widely between individuals. To date no reliable predictive marker of radiation sensitivity in rectal cancer has been identified. At the cellular level, radiation injury initiates a complex molecular network of DNA damage response (DDR) pathways that leads to cell cycle arrest, attempts at re-constituting the damaged DNA and should this fail, then apoptosis. This review presents the details which suggest the roles of DNA mismatch repair proteins, the lack of which define a distinct subset of colorectal cancers with microsatellite instability (MSI), in the DDR pathways. Hence routine assessment of the MSI status in rectal cancers may potentially serve as a predictor of radiotherapy response, thereby improving patient stratification in the administration of this otherwise toxic treatment.

The significance of the senescence pathway in breast cancer progression

Invasive breast cancer develops through prolonged accumulation of multiple genetic changes. The progression to a malignant phenotype requires overriding of growth inhibition. It is evident that some breast cancers have an inherited basis, and both hereditary and sporadic cancers appear to involve molecular mechanisms that are linked to the cell cycle. Frequently, changes in the molecular pathways with gene deletions, point mutations and/or overexpression of growth factors can be seen in these cancers. Recent evidence also implicates the senescence pathway in breast carcinogenesis. It has a barrier effect towards excessive cellular growth, acting as the regulator of tumour initiation and progression. Later in carcinogenesis, acquisition of the senescence associated secretory phenotype may instead promote tumour progression by stimulating growth and transformation in adjacent cells. This two-edge role of senescence in cancer directs more investigations into the effects of the senescence pathway in the development of malignancy. This review presents the current evidence on the roles of senescence molecular pathways in breast cancer and its progression.

Telomerase expression as a predictive marker of radiotherapy response in rectal cancer: in vitro and in vivo study

Aims: To investigate telomerase as a predictive marker of radiotherapy response in rectal cancer. Methods: Expression of the telomerase catalytic subunit hTERT was quantified with reverse transcription PCR in the radioresistant colorectal cancer cell line SW620 following exposure to 5Gy of radiation. Additionally, 52 rectal cancer cases were pre-operatively treated with either the short (n = 19) or long (n = 33) course radiotherapy (SCR, LCR, respectively) regimes, before and after which their hTERT expressions were semi-quantified with immunohistochemistry (IHC). This was correlated with the histological tumour regression in the resected bowel, dichotomised into good and poor responses. Results: SW620 cells expressed gradually increasing levels of hTERT after radiation. hTERT IHC positivity of ⩽75% tumour cells in pre-radiotherapied cancer was the optimal negative cut-off level [sensitivity 63.2%, specificity 45.8%, area under curve (AUC) 0.5362] in predicting good tumour response. As significantly more LCR cases showed good tumour response (p<0.0001), the SCR cases were excluded and AUC re-analysed, which still remained low (0.5357). Conclusions: While our in vitro results suggest that hTERT up-regulation may contribute to radiation resistance of colorectal cancer cells, our in vivo results demonstrated poor ability of hTERT IHC in predicting histological tumour regression in rectal cancer.

Histopathological regression grading versus staging of rectal cancer following radiotherapy

Aims: To compare histological grading of rectal cancer radiotherapy response with pathological staging as a prognostic indicator. Methods: Histological tumour regression was five tier graded in 102 rectal cancer patients treated with preoperative radiotherapy [short course (n = 34), long course (n = 68)]. Differences between these grades and between the two radiotherapy regimes were assessed. These variables, pTMN staging and others were correlated with relapse free survival at 3 years. Results: 22 patients suffered disease recurrence and four died during a mean post-operative follow-up of 40.3 months. There were 52 good responders (tumour regression grades 1–3) and 50 poor responders (tumour regression grades 4–5). Regression was greater following the long course regime (p < 0.0001). Otherwise, there were no significant differences between the response groups and between the two regimes, including the number of lymph nodes found in the resected bowel. Only the pN status correlated with relapse free survival on multivariate analysis (p = 0.0004; HR = 4.26, 95%CI = 1.66–10.93 for pN2 versus pN0). Conclusions: The number of lymph nodes found for staging was not influenced by either the extent of primary tumour regression or the type of radiotherapy. pN status, but not tumour regression grade, is a reliable predictor of survival.

The senescence pathway in prostatic carcinogenesis

&NA; Prostate cancer is a disease of the old and with increasing life expectancy, its incidence will continue to increase in the future. Control of prostate cancer has involved androgen ablation as a routine form of therapy. However, after an initial response, therapy‐resistant clones can appear and result in cancer progression and metastasis with high mortality. The precise mechanisms for the development of androgen resistance are yet uncertain. It appears to be multi‐factorial and relates not only to newly acquired genomic capabilities of the cancer cells but also to their interaction with their microenvironment. Overcoming cellular senescence is essential for oncogenesis. Although it seems to be a protective response for normal cells to avoid malignant transformation, senescence can on the other hand promote tumour progression. Interaction of senescent cancer cells with their microenvironment may be the key link to survival or regression of neoplastic cells. Hence, there is speculation that senescence may be a useful new target for therapy in the future. We review the role of senescence in prostate cancer and the effect of tumour microenvironment on androgen resistance.

Breast cancer precursors : diagnostic issues and current understanding on their pathogenesis

Summary The development of breast malignancy has been recognised to progress through a number of morphological precursor lesions. More recently, specific molecular alterations have been recognised in these precursor lesions. These changes appear to determine a specific malignant phenotype, which in turn, may realign the current opinion on the classification of breast cancer along molecular characteristics. This review will highlight the morphological features of these precursor lesions and their relationship to the complex molecular processes involved in their development.

MRE11 and ATM Expression Levels Predict Rectal Cancer Survival and Their Association with Radiotherapy Response.

Background Aberrant expression of DNA repair proteins is associated with poor survival in cancer patients. We investigated the combined expression of MRE11 and ATM as a predictive marker of response to radiotherapy in rectal cancer. Methods MRE11 and ATM expression were examined in tumor samples from 262 rectal cancer patients who underwent surgery for rectal cancer, including a sub-cohort of 54 patients who were treated with neoadjuvant radiotherapy. The relationship between expression of the two-protein panel and tumor regression grade (TRG) was assessed by Mann–Whitney U test and receiver operating characteristics area under curve (ROC-AUC) analysis. The association between expression of the two-protein panel and clinicopathologic variables and survival was examined by Kaplan-Meier methods and Cox regression analysis. Results A high score for two-protein combined expression in the tumor center (TC) was significantly associated with worse disease-free survival (DFS) (P = 0.035) and overall survival (OS) (P = 0.003) in the whole cohort, and with DFS (P = 0.028) and OS (P = 0.024) in the neoadjuvant subgroup (n = 54). In multivariate analysis, the two-protein combination panel (HR = 2.178, 95% CI 1.115–4.256, P = 0.023) and perineural invasion (HR = 2.183, 95% CI 1.222–3.899, P = 0.008) were significantly associated with DFS. Using ROC-AUC analysis of good versus poor histological tumor response among patients treated preoperatively with radiotherapy, the average ROC-AUC was 0.745 for the combined panel, 0.618 for ATM alone, and 0.711 for MRE11 alone. Conclusions The MRE11/ATM two-protein panel developed in this study may have clinical value as a predictive marker of tumor response to neoadjuvant radiotherapy, and a prognostic marker for disease-free and overall survival.

Molecular interactions of polo-like kinase 1 in human cancers

Polo-like kinase 1 (PLK1) is an essential protein in communicating cell-cycle progression and DNA damage. Overexpression of PLK1 has been validated as a marker for poor prognosis in many cancers. PLK1 knockdown decreases the survival of cancer cells. PLK1 is therefore an attractive target for anticancer treatments. Several inhibitors have been developed, and some have been clinically tested to show additive effects with conventional therapies. Upstream regulation of PLK1 involves multiple interactions of proteins such as FoxM1, E2F and p21. Other cancer-related proteins such as pRB and p53 also indirectly influence PLK1 expression. With the high mutation rates of these genes seen in cancers, they may be associated with PLK1 deregulation. This raises the question of whether PLK1 overexpression is a cause or a consequence of oncogenesis. In addition, hypomethylation of the CpG island of the PLK1 promoter region contributes to its upregulation. PLK1 expression can be affected by many factors; thus, it is possible that PLK1 deregulation in each individual patient tumours could be due to different underlying mechanisms.