Identification of side population cells in human hepatocellular carcinoma cell lines with stepwise metastatic potentials

Cancer stem cells and side population cells in breast cancer and metastasis

In breast cancer it is never the primary tumour that is fatal; instead it is the development of metastatic disease which is the major cause of cancer related mortality. There is accumulating evidence that suggests that Cancer Stem Cells (CSC) may play a role in breast cancer development and progression. Breast cancer stem cell populations, including side population cells (SP), have been shown to be primitive stem cell-like populations, being long-lived, self-renewing and highly proliferative. SP cells are identified using dual wavelength flow cytometry combined with Hoechst 33342 dye efflux, this ability is due to expression of one or more members of the ABC transporter family. They have increased resistance to chemotherapeutic agents and apoptotic stimuli and have increased migratory potential above that of the bulk tumour cells making them strong candidates for the metastatic spread of breast cancer. Treatment of nearly all cancers usually involves one first-line agent known to be a substrate of an ABC transporter thereby increasing the risk of developing drug resistant tumours. At present there is no marker available to identify SP cells using immunohistochemistry on breast cancer patient samples. If SP cells do play a role in breast cancer progression/Metastatic Breast Cancer (MBC), combining chemotherapy with ABC inhibitors may be able to destroy both the cells making up the bulk tumour and the cancer stem cell population thus preventing the risk of drug resistant disease, recurrence or metastasis.

Intratumoral neutrophils: a poor prognostic factor for hepatocellular carcinoma following resection

BACKGROUND & AIMS

Neutrophil infiltration has been linked to clinical outcome of various cancer types. However, its role in hepatocellular carcinoma (HCC) is unclear. In this study, we investigated prognostic values for intratumoral and peritumoral neutrophils in HCC patients undergoing curative resection.

METHODS

The expression of CD66b, CD8, TGF-beta, and CD34 was assessed by immunohistochemistry in tissue microarrays containing paired intratumoral and peritumoral tissues from 197 patients receiving curative resection for HCC. Prognostic values for these and other clinicopathologic factors were evaluated.

RESULTS

Intratumoral CD66b(+) neutrophils significantly correlated with CD8(+) T cells (r=0.240, p=0.004), TGF-beta expression (p=0.012), BCLC stage (p=0.016), and early recurrence (p=0.041). Increased intratumoral neutrophils were significantly associated with decreased RFS/OS (p=0.001 and p<0.001, respectively) in univariate analysis and were identified as an independent prognostic factor (HR=1.845, 95% CI=1.169-2.911, p=0.008 for RFS; HR=2.578, 95% CI=1.618-4.106, p<0.001 for OS) in multivariate analysis. Intratumoral neutrophil-to-CD8(+) T cell ratio (iNTR) better predicted the outcome in terms of minimum p values. Intratumoral neutrophils were also demonstrated to be statistically predictive for RFS/OS in the normal AFP subgroup, small HCC subgroup, and validation cohort. However, peritumoral neutrophils were not associated with the outcome of HCC.

CONCLUSIONS

The presence of intratumoral neutrophils was a poor prognostic factor for HCC after resection. Intratumoral neutrophil-to-CD8(+) T cell ratio was a better predictor of outcome.

Characterization of side population cells from laryngeal cancer cell lines

BACKGROUND

Analysis of the hematopoietic system has shown that bone marrow stem cells contain a subpopulation that effluxes the DNA binding dye, Hoechst 33342, out of the cell membrane. These cells are called side population (SP) cells and have been shown to have stem cell characteristics. SP cells have already been found in solid tumors, although there are no published reports examining the role of SP cells in human laryngeal cancer.

METHODS

SP cells were identified in the laryngeal cancer cell lines, AMC-HN-8 (head and neck cancer cell line 8, from the Asan Medical Center) and Hep-2 (human epithelial type 2) cell lines, by flow cytometry. Hep-2 SP cells were isolated and analyzed in proliferation assays, differentiation studies, radiotherapy resistance studies, and tumorigenesis ability.

RESULTS

The AMC-HN-8 and Hep-2 cell lines contained 11.8 ± 1.7% and 17.1 ± 2.0% SP cells, respectively. SP cell proportion was reduced by verapamil. Hep-2 SP cells exhibited higher self-regeneration, proliferation, radiotherapy resistance, and tumorigenicity.

CONCLUSIONS

SP cells purified from the Hep-2 cell line harbor cancer stem cell-like properties, and they are heterogeneous, indicating that SP cells are not identical to stem cells.

In vitro and in vivo evidence for the importance of breast cancer resistance protein transporters (BCRP/MXR/ABCP/ABCG2)

The breast cancer resistance protein (BCRP/ABCG2) is a member of the G-subfamiliy of the ATP-binding cassette (ABC)-transporter superfamily. This half-transporter is assumed to function as an important mechanism limiting cellular accumulation of various compounds. In context of its tissue distribution with localization in the sinusoidal membrane of hepatocytes, and in the apical membrane of enterocytes ABCG2 is assumed to function as an important mechanism facilitating hepatobiliary excretion and limiting oral bioavailability, respectively. Indeed functional assessment performing mouse studies with genetic deletion or chemical inhibition of the transporter, or performing pharmacogenetic studies in humans support this assumption. Furthermore the efflux function of ABCG2 has been linked to sanctuary blood tissue barriers as described for placenta and the central nervous system. However, in lactating mammary glands ABCG2 increases the transfer of substrates into milk thereby increasing the exposure to potential noxes of a breastfed newborn. With regard to its broad substrate spectrum including various anticancer drugs and environmental carcinogens the function of ABCG2 has been associated with multidrug resistance and tumor development/progression. In terms of cancer biology current research is focusing on the expression and function of ABCG2 in immature stem cells. Recent findings support the notion that the physiological function of ABCG2 is involved in the elimination of uric acid resulting in higher risk for developing gout in male patients harboring genetic variants. Taken together ABCG2 is implicated in various pathophysiological and pharmacological processes.

Granulin-epithelin precursor and ATP-dependent binding cassette (ABC)B5 regulate liver cancer cell chemoresistance

BACKGROUND & AIMS

Chemotherapy is used to treat unresectable liver cancer with marginal efficacy; this might result from hepatic cancer cells with stem cell and chemoresistant features. Gene expression profiling studies have shown that hepatic cancer cells express granulin-epithelin precursor (GEP); we investigated its role in hepatic cancer stem cell functions and chemoresistance.

METHODS

The effects of GEP and drug transporter signaling on chemoresistance were investigated in hepatic cancer stem cells. We analyzed the expression patterns of 142 clinical samples from liver tumors, adjacent nontumorous liver tissue, and liver tissue from patients who did not have cancer.

RESULTS

GEP regulated the expression of the adenosine triphosphate-dependent binding cassette (ABC)B5 drug transporter in liver cancer cells. Chemoresistant cells that expressed GEP had increased levels of ABCB5; suppression of ABCB5 sensitized the cells to doxorubicin uptake and apoptosis. Most cells that expressed GEP and ABCB5 also expressed the hepatic cancer stem cell markers CD133 and EpCAM; blocking ABCB5 reduced their expression. Expression levels of GEP and ABCB5 were correlated in human liver tumor samples. ABCB5 levels were increased in liver cancer cells compared with nontumor liver tissue from patients with cirrhosis or hepatitis, or normal liver tissue. ABCB5 expression was associated with the recurrence of hepatocellular carcinoma after partial hepatectomy.

CONCLUSIONS

Expression of GEP and ABCB5 in liver cancer stem cells is associated with chemoresistance and reduced survival times of patients with hepatocellular carcinoma. Reagents designed to target these proteins might be developed as therapeutics and given in combination with chemotherapy to patients with liver cancer.

Lupeol targets liver tumor-initiating cells through phosphatase and tensin homolog modulation

Liver tumor-initiating cells (T-ICs) are capable of self-renewal and tumor initiation and are more chemoresistant to chemotherapeutic drugs. The current therapeutic strategies for targeting stem cell self-renewal pathways therefore represent rational approaches for cancer prevention and treatment. In the present study, we found that Lup-20(29)-en-3β-ol (lupeol), a triterpene found in fruits and vegetables, inhibited the self-renewal ability of liver T-ICs present in both hepatocellular carcinoma (HCC) cell lines and clinical HCC samples, as reflected by hepatosphere formation. Furthermore, lupeol inhibited in vivo tumorigenicity in nude mice and down-regulated CD133 expression, which was previously shown to be a T-IC marker for HCC. In addition, lupeol sensitized HCC cells to chemotherapeutic agents through the phosphatase and tensin homolog (PTEN)-Akt-ABCG2 pathway. PTEN plays a crucial role in the self-renewal and chemoresistance of liver T-ICs; down-regulation of PTEN by a lentiviral-based approach reversed the effect of lupeol on liver T-ICs. Using an in vivo chemoresistant HCC tumor model, lupeol dramatically decreased the tumor volumes of MHCC-LM3 HCC cell line-derived xenografts, and the effect was equivalent to that of combined cisplatin and doxorubicin treatment. Lupeol exerted a synergistic effect without any adverse effects on body weight when combined with chemotherapeutic drugs.

CONCLUSION

Our results suggest that lupeol may be an effective dietary phytochemical that targets liver T-ICs.

Isolation and characterization of tumorigenic extrahepatic cholangiocarcinoma cells with stem cell-like properties

Recent studies suggest that the ability to form and grow tumors specifically resides in a small cell population called cancer stem cells (CSCs). These studies were conducted mainly on various human cancers; however, isolation and characterization of stem cells from cholangiocarcinoma have not been attempted. The molecular markers CD24, CD44, CD34, and epithelial cell adhesion molecule (EpCAM) are widely used, individually or in combination, to characterize some types of CSCs. In this study, we used these markers to identify a subpopulation of cells in extrahepatic cholangiocarcinoma (ECC) with cancer stem/progenitor cell-like properties. We found that CD24(+) CD44(+) EpCAM(high) cells (0.39-2.27%) were present in human ECC tissues. The expression of a CD24(+) CD44(+) EpCAM(high) subpopulation was consistent with primary cancers and could be duplicated during serial in vivo passaging in NOD/SCID mice. CD24(+) CD44(+) EpCAM(high) cells isolated from 3 cholangiocarcinoma xenografts showed high tumorigenic potential compared with CD24(-) CD44(-) EpCAM(low/-) cells. These tumorigenic ECC cells exhibited the stem cell properties of self-renewal and ability to produce heterogeneous progeny. We report the identification of a CSC population in ECC characterized by CD24, CD44 and EpCAM phenotypes. Our findings could provide new insight into the tumorigenesis of cholangiocarcinoma and offer a potential target for anti-cancer therapy.

MicroRNAs involved in neoplastic transformation of liver cancer stem cells

Background

The existence of cancer stem cells in hepatocellular carcinoma (HCC) has been verified by characterizing side population (SP) cells based on efflux of Hoechst 33342 dye from stem cells. Recent advances in microRNA (miRNA) biology have revealed that miRNAs play an important role in embryonic development and tumorigenesis. However, it is still unclear which miRNAs participate in the neoplastic transformation of liver cancer stem cells (LCSCs) during hepatocarcinogenesis.

Methods

To identify the unique set of miRNAs differentially regulated in LCSCs, we applied SP sorting to primary cultures of F344 rat HCC cancer cells treated with diethylnitrosamine (DEN) and normal syngenic fetal liver cells, and the stem-like characteristics of SP cells were verified through detecting expression of CD90.1, AFP and CK-7. Global miRNA expression profiles of two groups of SP cells were screened through microarray platform.

Results

A total of 68 miRNAs, including miR-10b, miR-21, miR-470*, miR-34c-3p, and let-7i*, were identified as overexpressed in SP of HCC cells compared to fetal liver cells. Ten miRNAs were underexpressed, including miR-200a* and miR-148b*. These miRNAs were validated using stem-loop real-time reverse transcriptase polymerase chain reaction (RT-PCR).

Conclusions

Our results suggest that LCSCs may have a distinct miRNA expression fingerprint during hepatocarcinogenesis. Dissecting these relationships will provide a new understanding of the function of miRNA in the process of neoplastic transformation of LCSCs.

New advances on critical implications of tumor- and metastasis-initiating cells in cancer progression, treatment resistance and disease recurrence

Accumulating lines of experimental evidence have revealed that the malignant transformation of multipotent tissue-resident adult stem/progenitor cells into cancer stem/progenitor cells endowed with a high self-renewal capacity and aberrant multilineage differentiation potential may be at origin of the most types of human aggressive and recurrent cancers. Based on new cancer stem/progenitor cell concepts of carcinogenesis, it is suggested that a small subpopulation of highly tumorigenic and migrating cancer stem/progenitor cells, also designated as cancer- and metastasis-initiating cells, can provide critical roles for primary tumor growth, metastases at distant tissues and organs, treatment resistance and disease relapse. Particularly, cancer initiation and progression to locally invasive and metastatic stages is often associated with a persistent activation of distinct developmental signaling pathways in these immature cells during epithelial-mesenchymal transition program. The signaling cascades that are often deregulated in cancer stem/progenitor cells include hedgehog, epidermal growth factor receptor (EGFR), Wnt/beta-catenin, NOTCH, polycomb gene product BMI-1 and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4). Importantly, the results from recent investigations have also indicated that different cancer subtypes may harbor distinct subsets and/or number of cancer-initiating cells during cancer progression as well as before or after therapy initiation and disease recurrence. Therefore, the identification of the molecular transforming events that frequently occur in cancer- and metastasis-initiating cells versus their differentiated progenies is of immense interest to develop new targeting approach for improving current therapies against aggressive, metastatic, recurrent and lethal cancers.

Epigenetic regulation of cancer stem cells in liver cancer: current concepts and clinical implications

The two dominant models of carcinogenesis postulate stochastic (clonal evolution) or hierarchic organization of tumor (cancer stem cell model). According to the latter, at the germinal center of tumor evolution is a cancer stem cell (CSC) which, similar to normal adult stem cells, possesses the capacity of self-renewal and a differentiation potential. Over the past few years, compelling evidence has emerged in support of the hierarchic cancer model for many solid tumors including hepatocellular cancers. The CSCs are posited to be responsible not only for tumor initiation but also for the generation of distant metastasis and relapse after therapy. These characteristics are particularly relevant for a multi-resistant tumor entity like human hepatocellular carcinoma and may herald a paradigm shift in the management of this deadly disease. Identification and detailed characterization of liver CSCs is therefore imperative for improving prevention approaches, enhancing early detection, and extending the limited treatment options. Despite the current progress in understanding the contribution of CSCs to the generation of heterogeneity of tumors, the molecular complexity and exact regulation of CSCs is poorly understood. This review focuses on the genetic and epigenetic mechanisms that regulate and define the unique CSC properties with an emphasis on key regulatory pathways of liver CSCs and their clinical significance.

hsa-miR-520h downregulates ABCG2 in pancreatic cancer cells to inhibit migration, invasion, and side populations

Background:

Expression of ABCG2 is normally absent or low in the pancreas, but high in human pancreatic cancer cells. The mechanism by which ABCG2 is altered in human cancers remains unknown.

Methods:

We investigated ABCG2 expression in four pancreatic cancer cell lines, and used three microRNA (miRNA) target prediction programmes, and information from the existing literature to predict and identify hsa-miR-520h as an miRNA that targets ABCG2. The function of this miRNA was investigated by transient transfection of the pancreatic cancer cell line PANC-1 with oligonucleotides that mimic hsa-miR-520h.

Results:

Results showed that both mRNA and protein levels of ABCG2 were reduced, indicating that it was a target of hsa-miR-520h. Introduction of hsa-miR-520h mimics into PANC-1 cells also resulted in inhibition of cell migration and invasion, and reduction of side population cells. Cell proliferation, cell cycle progression and apoptosis were not affected.

Conclusions:

We propose that the effects of hsa-miR-520h may be, at least in part, caused by its regulation of ABCG2. Thus, our findings provide a new insight into the function of miRNA in the regulation of ABCG2 expression in pancreatic cancer. Gene therapy using miRNA mimics may therefore be useful as a pancreatic cancer therapy.

CD151 modulates expression of matrix metalloproteinase 9 and promotes neoangiogenesis and progression of hepatocellular carcinoma

Tetraspanin CD151 is involved in several pathological activities associated with tumor progression, including neoangiogenesis. However, the role and molecular mechanism of CD151 in the neoangiogenesis of hepatocellular carcinoma (HCC) remain enigmatic. We found that the level of expression of matrix metalloproteinase 9 (MMP9) was positively associated with CD151 expression in HCC cells. We developed a zone-by-zone blockade and demonstrated that overexpression of CD151 in HCC cells facilitated MMP9 expression through a phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/glycogen synthase kinase 3beta (GSK-3beta)/Snail signaling pathway. In contrast, down-regulation of CD151 expression impaired the ability of HCC cells to form microvessels in vitro and reduced their in vivo metastatic potential. In a clinical setting, a significant correlation of the expression of CD151 with MMP9 expression and with microvessel density (MVD) was revealed by Pearson correlation analysis of HCC patients. The postoperative 3-, 5-, and 7-year overall survival rates of HCC patients with CD151(high)/MMP9(high)/MVD(high) were significantly lower than those of the CD151(low)/MMP9(low)/MVD(low) group or groups in which only one or two of CD151, MMP9, and MVD were highly expressed. Cumulative recurrence rates were also highest in HCC patients with CD151(high)/MMP9(high)/MVD(high) in comparison with the other groups. Multivariate Cox proportional hazards analysis showed that the concomitant overexpression of CD151, MMP9, and MVD was an independent marker for predicting poor prognosis of HCC.

CONCLUSION

Overexpression of CD151 up-regulated the expression of MMP9 through the PI3K/Akt/GSK-3beta/Snail pathway. CD151-dependent neoangiogenesis appeared to promote the progression of HCC, and this suggests that CD151 may be useful as a high-priority therapeutic target for antiangiogenesis in HCC.

Novel therapies against aggressive and recurrent epithelial cancers by molecular targeting tumor- and metastasis-initiating cells and their progenies

A growing body of experimental evidence has revealed that the highly tumorigenic cancer stem/progenitor cells endowed with stem cell-like properties might be responsible for initiation and progression of numerous aggressive epithelial cancers into locally invasive, metastatic and incurable disease states. The malignant transformation of tissue-resident adult stem/progenitor cells or their progenies into tumorigenic and migrating cancer stem/progenitor cells and their resistance to current cancer therapies have been associated with their high expression levels of specific oncogenic products and drug resistance-associated molecules. In this regard, we describe the tumorigenic cascades that are frequently activated in cancer stem/progenitor cells versus their differentiated progenies during the early and late stages of the epithelial cancer progression. The emphasis is on the growth factor signaling pathways involved in the malignant behavior of prostate and pancreatic cancer stem/progenitor cells and their progenies. Of clinical interest, the potential molecular therapeutic targets to eradicate the tumor- and metastasis-initiating cells and their progenies and develop new effective combination therapies against locally advanced and metastatic epithelial cancers are also described.

Side population cells and liver cancer stem cells

Liver cancer is a life-threatening disease whose etiology and pathogenesis remain unclear now. No effective therapeutic targets for the disease have been found. Recent studies suggest that a small population of cells having the potential of self-renewal and differentiation in tumors may be the source of tumor metastasis and recurrence. Liver cancer stem cells may also exist. The side population (SP) cells, a small population of tumor cells, have many properties of stem cells and are easy to isolate. Identification and isolation of SP cells in liver cancer may help us find liver cancer stem cells, elucidate the mechanisms behind the metastasis and recurrence of liver cancer, and provide an efficient target for therapy of liver cancer.

Hepatic cancer stem cells and drug resistance: Relevance in targeted therapies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of most common malignancies in the world. Systemic treatments for HCC, particularly for advanced stages, are limited by the drug resistance phenomenon which ultimately leads to therapy failure. Recent studies have indicated an association between drug resistance and the existence of the cancer stem cells (CSCs) as tumor initiating cells. The CSCs are resistant to conventional chemotherapies and might be related to the mechanisms of the ATP Binding Cassette (ABC) transporters and alterations in the CSCs signaling pathways. Therefore, to contribute to the development of new HCC treatments, further information on the characterization of CSCs, the modulation of the ABC transporters expression and function and the signaling pathway involved in the self renewal, initiation and maintenance of the cancer are required. The combination of transporters modulators/inhibitors with molecular targeted therapies may be a potent strategy to block the tumoral progression. This review summarizes the association of CSCs, drug resistance, ABC transporters activities and changes in signaling pathways as a guide for future molecular therapy for HCC.

New promising drug targets in cancer- and metastasis-initiating cells

The unique properties of cancer- and metastasis-initiating cells endowed with a high self-renewal and aberrant differentiation potential (including their elevated expression levels of anti-apoptotic factors, multidrug transporters, and DNA repair and detoxifying enzymes) might be associated with their resistance to current clinical cancer therapies and disease recurrence. The eradication of cancer- and metastasis-initiating cells by molecular targeting of distinct deregulated signaling elements that might contribute to their sustained growth, survival, and treatment resistance, therefore, is of immense therapeutic interest. These novel targeted approaches should improve the efficacy of current therapeutic treatments against highly aggressive, metastatic, recurrent, and lethal cancers.

Pluripotency-associated genes in human nasopharyngeal carcinoma CNE-2 cells are reactivated by a unique epigenetic sub-microenvironment

BACKGROUND

There is increasing evidence that cancers contain their own stem-like cells, and particular attention has been paid to one subset of cancer-stem cells termed side population (SP). Stem cells under normal physical conditions are tightly controlled by their microenvironment, however, the regulatory role of the microenvironment surrounding cancer stem cells is not well characterized yet. In this study we found that the phenotype of SP can be "generated" by macrophage-like cells under conditioned culture. Furthermore the gene regulation pathway involved in cellular reprogramming process was investigated.

METHODS

The selection and identification of SP in 50 CNE-2 single cell clones were performed by flow cytometry. The transwell assay and immunofluorescence staining were used to measure migration and cancer stem cell characters of non-SP single clone cells cultured with conditioned medium respectively. The subtraction suppression hybridization (SSH) technique and northern blotting analysis was applied to explore the pluripotency-associated genes under a unique epigenetic sub-microenvironment.

RESULTS

Among 50 clones, only one did not possess SP subpopulation while others did. The non-SP cells induced by macrophage-like cells showed more aggressive characters, which increased cell migration compared with the control cells and showed some fraction of SP phenotype. These cells expressed distinguished level of pluripotency-associated genes such as ADP-ribosylation factor-like 6 interacting protein (ARMER), poly (rC) binding protein 1 (PCBP1) and pyruvate dehydrogenase E1-beta subunit (PDHB) when subjected to the environment.

CONCLUSION

To our knowledge, this is the first study to demonstrate that non-SP single-clone cells can be induced to generate a SP phenotype when they are cultured with conditioned medium of macrophage-like cells, which is associated with the reactivation of pluripotency-associated genes.

ABCG2: a potential marker of stem cells and novel target in stem cell and cancer therapy

ABCG2 is a member of the ATP binding cassette (ABC) transporters, which can pump a wide variety of endogenous and exogenous compounds out of cells. Widely expressed in stem cells, ABCG2 is also found to confer the side population phenotype and is recognized as a universal marker of stem cells. Although the precise physiological role of ABCG2 in stem cells is still unclear, existing data strongly suggest that ABCG2 plays an important role in promoting stem cell proliferation and the maintenance of the stem cell phenotype. In addition, ABCG2 is also found to be expressed in a number of cancer cells and appears to be a marker of cancer stem cells. Moreover, ABCG2 expression in tumors may contribute to their formation and progression. Thus, ABCG2 has potential applications in stem cell and tumor therapy.

Stem cells in hepatocarcinogenesis: evidence from genomic data

Increasing evidence suggests that many, perhaps all solid tumors contain a subset of cells that possess functional properties similar to the normal tissue stem cells, including self-renewal, unlimited proliferative capacity, and pluripotency. The hierarchical cancer model that places a cancer stem cell (CSC) population at the apex of tumor formation is based on this notion. The cancer stem cell hypothesis posits that CSCs are responsible not only for tumor initiation, but also generation of metastasis and local recurrence after therapy. Current definitions of the CSC are based only on functional properties regardless of potential cellular origin. Histopathology investigations of chronic liver diseases and experimental studies support the existence of CSCs in liver cancer. In particular, recent advances in microarray technologies utilizing integrative comparative genomic analysis of human hepatocellular carcinoma specimens, cancer cell lines, and transgenic models establish the molecular similarities between CSC and normal tissue stem cells and highlight the importance of CSC for the prognosis of liver cancer patients. The results have also uncovered the key "stemness" and oncogenic pathways frequently disrupted during hepatocarcinogenesis providing the basis for identifying novel therapeutic targets against CSC.

Advances in research on liver cancer stem cells

Cancer stem cells have been identified in various human tumors. However, it remains controversial as to whether or not liver cancer stem cells (LCSCs) exist until now. There are two hypotheses to explain the origin of liver cancer stem cells: the dedifferentiation of mature hepatocytes and the maturation arrest of liver stem cells. Now, the latter is generally acknowledged to be the better one. To obtain direct evidence for the existence of LCSCs, many researchers focus their studies on the surface markers on LCSCs to identify ideal markers for isolation of LCSCs. Besides, the relationship between side population (SP) cells and LCSCs also attracts much attention. Therefore, the study of LCSCs is probably of great significance for the diagnosis and treatment of liver cancer.

Liver-intestine cadherin predicts microvascular invasion and poor prognosis of hepatitis B virus-positive hepatocellular carcinoma

BACKGROUND

Liver-intestine cadherin (LI-cadherin; CDH-17) is a new member of the cadherin superfamily with distinct structural and functional features. The study was designed to investigate the role of LI-cadherin in tumor invasion and prognosis of human hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC).

METHODS

LI-cadherin expression in HBV-positive hepatocellular carcinoma cell lines with low- and high-invasive potentials was evaluated by Western-blot, immunofluorescence, and real-time polymerase chain reaction (PCR) analyses. The role of LI-cadherin in tumor invasion was also evaluated in vitro by a small-interfering ribonucleic acid (siRNA)-mediated approach. The prognostic significance of LI-cadherin was validated in a cohort of HBV-positive HCC patients by immunohistochemistry and Western-blot.

RESULTS

Significant high levels of LI-cadherin mRNA and protein were found in the high-invasive HCCLM3 as compared with those in low-invasive PLC/PRF/5 and Hep3B cell line. Cell migration, adhesion to extracellular matrix, and matrigel invasion were significantly reduced after LI-cadherin knockdown in HCCLM3 cells. Immunohistochemical analysis of 255 HBV-positive HCC cases showed that overexpression of LI-cadherin was well correlated with microvascular invasion, which was confirmed by Western-blot in 32 tumor tissues, and its overexpression was strongly associated with shorter overall survival as well as higher incidence of tumor recurrence.

CONCLUSIONS

LI-cadherin is predictive of microvascular invasion and poor prognosis of HBV-positive HCC, and would be a potential useful intervention target for HCC.

Liver cancer stem cells: implications for a new therapeutic target

Hepatocellular carcinoma (HCC) is an aggressive tumour with a poor prognosis. Current therapeutic strategies against this disease target mostly rapidly growing differentiated tumour cells. However, the result is often dismal due to the chemoresistant nature of this tumour type. Recent research efforts on stem cells and cancer biology have shed light on new directions for the eradication of cancer stem cells (CSCs) in HCC. The liver is a distinctive organ with the ability of tissue renewal in response to injury. Based on the hypothesis that cancer development is derived from the hierarchy of the stem cell system, we will briefly discuss the origin of liver stem cells and its relation to HCC development. We will also summarize the current CSC markers in HCC and discuss their relevance to the treatment of this deadly disease.

Side population of a murine mantle cell lymphoma model contains tumour-initiating cells responsible for lymphoma maintenance and dissemination

‘Cancer stem cells’ or ‘tumour initiating cells’ in B-cell non-Hodgkin lymphomas have not been demonstrated, although some studies focused on other cancer types suggest that such populations exist and represent tumour cells resistant to therapy and involved in relapse. These cells may also represent a putative neoplastic ‘cell of origin’ in lymphomas, but there is little substantive data to support this suggestion. Using cell lines derived from a recently established murine IL-14α× c-Myc double transgenic/mantle cell lymphoma-blastoid variant model, heretofore referred to as DTG cell lines, we identified a subset of cells within the side population (SP) with features of ‘tumour-initiating cells’. These features include higher expression of ABCG2 and BCL-2, longer telomere length, greater self-renewal ability and higher in vitro clonogenic and in vivo tumorigenic capacities compared with non-SP. In addition, in vitro viability studies demonstrated that the non-SP lymphoma subpopulation has a limited lifespan in comparison with the SP fraction. Syngenic transplant studies showed that non-SP derived tumours, in comparison to the SP-derived tumours, exhibit greater necrosis/apoptosis and less systemic dissemination capability. In conclusion, our data support the interpretation that the DTG SP fraction contains a cell population highly capable of tumour maintenance and systemic dissemination and lends support to the concept that ‘tumour-initiating cells’ occur in lymphomas.

Recent insights into the molecular mechanisms involved in aging and the malignant transformation of adult stem/progenitor cells and their therapeutic implications

Recent advancements in tissue-resident adult stem/progenitor cell research have revealed that enhanced telomere attrition, oxidative stress, ultraviolet radiation exposure and oncogenic events leading to severe DNA damages and genomic instability may occur in these immature and regenerative cells during chronological aging. Particularly, the alterations in key signaling components controlling their self-renewal capacity and an up-regulation of tumor suppressor gene products such as p16(INK4A), p19(ARF), ataxia-telangiectasia mutated (ATM) kinase, p53 and/or the forkhead box O (FOXOs) family of transcription factors may result in their dysfunctions, growth arrest and senescence or apoptotic death during the aging process. These molecular events may culminate in a progressive decline in the regenerative functions and the number of tissue-resident adult stem/progenitor cells, and age-related disease development. Conversely, the telomerase re-activation and accumulation of numerous genetic and/or epigenetic alterations in adult stem/progenitor cells with advancing age may result in their immortalization and malignant transformation into highly leukemic or tumorigenic cancer-initiating cells and cancer initiation. Therefore, the cell-replacement and gene therapies and molecular targeting of aged and dysfunctional adult stem/progenitor cells including their malignant counterpart, cancer-initiating cells, hold great promise for treating and even curing diverse devastating human diseases. These diseases include premature aging diseases, hematopoietic, cardiovascular, musculoskeletal, pulmonary, ocular, urogenital, neurodegenerative and skin disorders and aggressive and recurrent cancers.

Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly

The worldwide shortage of donor livers to transplant end stage liver disease patients has prompted the search for alternative cell therapies for intractable liver diseases, such as acute liver failure, cirrhosis and hepatocellular carcinoma (HCC). Under normal circumstances the liver undergoes a low rate of hepatocyte 'wear and tear' renewal, but can mount a brisk regenerative response to the acute loss of two-thirds or more of the parenchymal mass. A body of evidence favours placement of a stem cell niche in the periportal regions, although the identity of such stem cells in rodents and man is far from clear. In animal models of liver disease, adopting strategies to provide a selective advantage for transplanted hepatocytes has proved highly effective in repopulating recipient livers, but the poor success of today's hepatocyte transplants can be attributed to the lack of a clinically applicable procedure to force a similar repopulation of the human liver. The activation of bipotential hepatic progenitor cells (HPCs) is clearly vital for survival in many cases of acute liver failure, and the signals that promote such reactions are being elucidated. Bone marrow cells (BMCs) make, at best, a trivial contribution to hepatocyte replacement after damage, but other BMCs contribute to the hepatic collagen-producing cell population, resulting in fibrotic disease; paradoxically, BMC transplantation may help alleviate established fibrotic disease. HCC may have its origins in either hepatocytes or HPCs, and HCCs, like other solid tumours appear to be sustained by a minority population of cancer stem cells.

Role of overexpression of CD151 and/or c-Met in predicting prognosis of hepatocellular carcinoma

It has been reported that tetraspanin CD151 acts as a promoter of metastasis in several tumors and plays an important role in c-Met/hepatocyte growth factor signaling. However, the role of CD151 alone and coexpression of CD151/c-Met in hepatocellular carcinoma (HCC) remains unclear. We found that expression of CD151 was positively related to metastatic potential of HCC cell lines, and modified cells with CD151(high) showed higher secretion of matrix metalloproteinase 9 and aggressiveness in vitro and higher metastatic ability in vivo. Furthermore, HCC patients with vascular invasion, large tumors, multiple tumors, high tumor-node-metastasis stage, and undifferentiated tumor were prone to have higher CD151 expression. The postoperative 3-, 5-, and 7-year overall survival (OS) of patients in HCCs with CD151(high) were significantly lower than those in the CD151(low) group, and correspondingly cumulative recurrence rates in HCCs with CD151(high) were significantly higher than those in the CD151(low) group. Both CD151 and c-Met were remarkably overexpressed in HCCs, compared with adjacent nontumorous and normal liver tissues. Pearson correlation analysis showed a slight correlation between CD151 and c-Met in HCCs. Importantly, the 5- and 7-year OS rates in CD151(high)/c-Met(high) patients were 50.5% and 37.8%, respectively, significantly lower than those of CD151(low)/c-Met(low) patients (63.9% and 54.6%, respectively). Five- and 7-year cumulative recurrence rates in CD151(high)/c-Met(high) patients were 53.3% and 71.9%, respectively, markedly higher than those of CD151(low)/c-Met(low) patients (39.0% and 52.5%, respectively). Multivariate analysis revealed that CD151 and combination of CD151/c-Met were independent prognostic indicators for OS and cumulative recurrence.

CONCLUSION

CD151 is positively associated with invasiveness of HCC, and CD151 or combination of CD151/c-Met is a novel marker in predicting the prognosis of HCC and a potential therapeutic target.