Cancer stem cells and metastasis. Semin Cancer Biol. 2012;22:187-193. [PMID: 22774232 DOI: 10.1016/j.semcancer.2012.03.002]

USP44+ Cancer Stem Cell Subclones Contribute to Breast Cancer Aggressiveness by Promoting Vasculogenic Mimicry

Vasculogenic mimicry (VM), a newly defined pattern of tumor blood supply, describes the functional plasticity of aggressive cancer cells that form vascular networks. In our previous study, breast cancer stem cells (CSC) were shown to potentially participate in VM formation. In this study, breast CSCs presented centrosome amplification (CA) phenotype and ubiquitin-specific protease 44 (USP44) upregulation. USP44 expression contributed to the establishment of bipolar spindles in breast CSCs with supernumerary centrosomes by localizing at pole-associated centrosomes. The bipolar spindle patterns of breast CSCs with CA, including planar-like and apico-basal-like, functioned differently during the VM process of CSCs. Moreover, the ability of transendothelial migration in VM-forming cells was increased. In vivo experiment results showed that CSC xenografts presented linearly patterned programmed cell necrosis, which provided a spatial foundation for VM formation as well as angiogenesis. Breast CSCs further showed increased levels of IL6 and IL8. However, USP44 silencing induced spindle multipolarity, abated VM, reduced transendothelial migration, and consequently decreased IL6 and IL8 levels in breast CSCs. Finally, USP44(+) CSC subclones (ALDH1(+)/USP44(+)/IL6(+)/IL8(+)) were identified in breast cancer specimens through consecutive sections scanning. The subclones were related not only to CA, but also to VM. Statistical analysis suggested that USP44(+) CSC subclones could be used as an independent prognostic biomarker of poor clinical outcomes in patients with breast cancer. Collectively, the identification of USP44(+) CSC subclones may contribute to the prediction of VM formation and aggressive behavior. This study provides novel insights into the therapy for advanced breast cancer.

Surface-enhanced laser desorption ionization time-of-flight mass spectrometry used to screen serum diagnostic markers of colon cancer recurrence in situ following surgery

The aim of the present study was to identify specific serum biomarkers in patients with colon cancer recurrence in situ following surgery. The study was conducted at the Renmin Hospital of Wuhan University (Wuhan, China) between January 2012 and January 2014. Surface-enhanced laser desorption ionization time-of-flight mass spectrometry was used to compare and analyze the serum protein profiles of patients with (n=50) and patients without (n=50) recurrence in situ. Biomarker Wizard software was used to analyze and obtain the protein spectrum. In total, nine protein peaks demonstrated statistically significant differences between the recurrence and non-recurrence group (P<0.05), which included two protein peaks (7,731.3 Da and 8,266.5 Da). The two protein peaks were highly expressed in patients with colon cancer recurrence in situ following surgery, but lowly expressed in patients without recurrence. Therefore, the two protein peaks may represent potential biomarkers for the prediction of colon cancer recurrence in situ following surgical treatment.

The Hedgehog signalling pathway mediates drug response of MCF-7 mammosphere cells in breast cancer patients

BCSCs (breast cancer stem cells) have been shown to be resistant to chemotherapy. However, the mechanisms underlying BCSC-mediated chemoresistance remain poorly understood. The Hh (Hedgehog) pathway is important in the stemness maintenance of CSCs. Nonetheless, it is unknown whether the Hh pathway is involved in BCSC-mediated chemoresistance. In the present study, we cultured breast cancer MCF-7 cells in suspension in serum-free medium to obtain BCSC-enriched MCF-7 MS (MCF-7 mammosphere) cells. We showed that MCF-7 MS cells are sensitive to salinomycin, but not paclitaxel, distinct from parent MCF-7 cells. The expression of the critical components of Hh pathway, i.e., PTCH (Patched), SMO (Smoothened), Gli1 and Gli2, was significantly up-regulated in MCF-7 MS cells; salinomycin, but not paclitaxel, treatment caused a remarkable decrease in expression of those genes in MCF-7 MS cells, but not in MCF-7 cells. Salinomycin, but not paclitaxel, increased apoptosis, decreased the migration capacity of MCF-7 MS cells, accompanied by a decreased expression of c-Myc, Bcl-2 and Snail, the target genes of the Hh pathway. The salinomycin-induced cytotoxic effect could be blocked by Shh (Sonic Hedgehog)-mediated Hh signalling activation. Inhibition of the Hh pathway by cyclopamine could sensitize MCF-7 MS cells to paclitaxel. In addition, salinomycin, but not paclitaxel, significantly reduced the tumour growth, accompanied by decreased expression of PTCH, SMO, Gli1 and Gli2 in xenograft tumours. Furthermore, the expression of SMO and Gli1 was positively correlated with the expression of CD44+ / CD24-, and the expression of SMO and Gli1 in CD44+ / CD24- tissues was associated with a significantly shorter OS (overall survival) and DFS (disease-free survival) in breast cancer patients receiving chemotherapy.

Evaporative edge lithography of a liposomal drug microarray for cell migration assays

Lipid multilayer microarrays are a promising approach to miniaturize laboratory procedures by taking advantage of the microscopic compartmentalization capabilities of lipids. Here, we demonstrate a new method to pattern lipid multilayers on surfaces based on solvent evaporation along the edge where a stencil contacts a surface called evaporative edge lithography (EEL). As an example of an application of this process, we use EEL to make microarrays suitable for a cell-based migration assay. Currently existing cell migration assays require a separate compartment for each drug which is dissolved at a single concentration in solution. An advantage of the lipid multilayer microarray assay is that multiple compounds can be tested on the same surface. We demonstrate this by testing the effect of two different lipophilic drugs, Taxol and Brefeldin A, on collective cell migration into an unpopulated area. This particular assay should be scalable to test of 2000 different lipophilic compounds or dosages on a standard microtiter plate area, or if adapted for individual cell migration, it would allow for high-throughput screening of more than 50,000 compounds per plate.

Sensitization of chemo-resistant human chronic myeloid leukemia stem-like cells to Hsp90 inhibitor by SIRT1 inhibition

Development of effective therapeutic strategies to eliminate cancer stem-like cells (CSCs), which play a major role in drug resistance and disease recurrence, is critical to improve cancer treatment outcomes. The current investigation was undertaken to examine the effectiveness of the combination treatment of Hsp90 inhibitor and SIRT1 inhibitor in inhibiting the growth of chemo-resistant stem-like cells isolated from human chronic myeloid leukemia K562 cells. Inhibition of SIRT1 by use of SIRT1 siRNA or SIRT1 inhibitors (amurensin G and EX527) effectively potentiated sensitivity of Hsp90 inhibitors (17-AAG and AUY922) in CD44(high) K562 stem-like cells expressing high levels of CSC-related molecules including Oct4, CD34, β-catenin, c-Myc, mutant p53 (mut p53), BCRP and P-glycoprotein (P-gp) as well as CD44. SIRT1 depletion caused significant down-regulation of heat shock factor 1 (HSF1)/heat shock proteins (Hsps) as well as these CSC-related molecules, which led to the sensitization of CD44(high) K562 cells to Hsp90 inhibitor by SIRT1 inhibitor. Moreover, 17-AAG-mediated activation of HSF1/Hsps and P-gp-mediated efflux, major causes of Hsp90 inhibitor resistance, was suppressed by SIRT1 inhibitor in K562-CD44(high) cells. Our data suggest that combined treatment with Hsp90 inhibitor and SIRT1 inhibitor could be an effective therapeutic approach to target CSCs that are resistant to current therapies.

Inhibition of STAT3, FAK and Src mediated signaling reduces cancer stem cell load, tumorigenic potential and metastasis in breast cancer

Cancer stem cells (CSCs) are responsible for aggressive tumor growth, metastasis and therapy resistance. In this study, we evaluated the effects of Shikonin (Shk) on breast cancer and found its anti-CSC potential. Shk treatment decreased the expression of various epithelial to mesenchymal transition (EMT) and CSC associated markers. Kinase profiling array and western blot analysis indicated that Shk inhibits STAT3, FAK and Src activation. Inhibition of these signaling proteins using standard inhibitors revealed that STAT3 inhibition affected CSCs properties more significantly than FAK or Src inhibition. We observed a significant decrease in cell migration upon FAK and Src inhibition and decrease in invasion upon inhibition of STAT3, FAK and Src. Combined inhibition of STAT3 with Src or FAK reduced the mammosphere formation, migration and invasion more significantly than the individual inhibitions. These observations indicated that the anti-breast cancer properties of Shk are due to its potential to inhibit multiple signaling proteins. Shk also reduced the activation and expression of STAT3, FAK and Src in vivo and reduced tumorigenicity, growth and metastasis of 4T1 cells. Collectively, this study underscores the translational relevance of using a single inhibitor (Shk) for compromising multiple tumor-associated signaling pathways to check cancer metastasis and stem cell load.

Quantifying the Landscape for Development and Cancer from a Core Cancer Stem Cell Circuit

Cancer presents a serious threat to human health. The understanding of the cell fate determination during development and tumor-genesis remains challenging in current cancer biology. It was suggested that cancer stem cell (CSC) may arise from normal stem cells or be transformed from normal differentiated cells. This gives hints on the connection between cancer and development. However, the molecular mechanisms of these cell-type transitions and the CSC formation remain elusive. We quantified landscape, dominant paths, and switching rates between cell types from a core gene regulatory network for cancer and development. Stem cell, CSC, cancer, and normal cell types emerge as basins of attraction on associated landscape. The dominant paths quantify the transition processes among CSC, stem cell, normal cell, and cancer cell attractors. Transition actions of the dominant paths are shown to be closely related to switching rates between cell types, but not always to the barriers in between, because of the presence of the curl flux. During the process of P53 gene activation, landscape topography changes gradually from a CSC attractor to a normal cell attractor. This confirms the roles of P53 of preventing the formation of CSC through suppressing self-renewal and inducing differentiation. By global sensitivity analysis according to landscape topography and action, we identified key regulations determining cell-type switchings and suggested testable predictions. From landscape view, the emergence of the CSCs and the associated switching to other cell types are the results of underlying interactions among cancer and developmental marker genes. This indicates that the cancer and development are intimately connected. This landscape and flux theoretical framework provides a quantitative way to understand the underlying mechanisms of CSC formation and interplay between cancer and development.

Expression of Multidrug Resistance Transporter ABCB5 in a Murine Model of Human Conjunctival Melanoma

Conjunctival melanoma (CM) is a rare ocular malignancy with a high tendency to reoccur locally and with a high risk of metastatic disease. Metastases are often unresponsive to conventional treatment. Recently, an animal model was set up using human CM cells. Orthotopic xenografts from human CM were created by subconjunctival injection of three different CM cell lines into NOD.Cg-Prkdc^scid IL2rg^tm1Wjl /SzJ (NSG) mice. Subconjunctival injection of cultured CM cells led to excellent subconjunctival growth, but no metastases were found. When single-cell suspensions were obtained from the subconjunctival xenografts and passaged in vivo, all mice developed metastases. As recent findings indicate that cancer stem cells are linked to tumor recurrences, we used this new murine model to determine the expression of the stem cell marker ABCB5 during tumor progression. Expression of the ABCB5 protein was determined in three cell lines and during different stages of tumor development as observed in our model. All three cell lines contained a subpopulation of cells positive for ABCB5. During tumor development, expression of ABCB5 increased during phases of tumor expansion. Furthermore, expression of ABCB5 was increased in metastases. Using this model for CM, we were able to initiate metastatic spread and determine the expression of the stem cell marker ABCB5 during different stages of tumor development, identifying ABCB5 as a potential novel therapeutic target. This study illustrates the potential of our newly established murine model.

Targeting cancer stem cells in solid tumors by vitamin D

Cancer stem cells (CSCs) are a small subset of cells that may be responsible for initiation, progression, and recurrence of tumors. Recent studies have demonstrated that CSCs are highly tumorigenic and resistant to conventional chemotherapies, making them a promising target for the development of preventive/therapeutic agents. A single or combination of various markers, such as CD44, EpCAM, CD49f, CD133, CXCR4, ALDH-1, and CD24, were utilized to isolate CSCs from various types of human cancers. Notch, Hedgehog, Wnt, and TGF-β signalingregulate self-renewal and differentiation of normal stem cells andare aberrantly activated in CSCs. In addition, many studies have demonstrated that these stem cell-associated signaling pathways are required for the maintenance of CSCs in different malignancies, including breast, colorectal, prostate, and pancreatic cancers. Accumulating evidence has shown inhibitory effects of vitamin D and its analogs on the cancer stem cell signaling pathways, suggesting vitamin D as a potential preventive/therapeutic agent against CSCs. In this review, we summarize recent findings about the roles of Notch, Hedgehog, Wnt, and TGF-β signaling in CSCs as well as the effects of vitamin D on these stem cell signaling pathways. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Role of periostin and its antagonist PNDA-3 in gastric cancer metastasis

The extracellular matrix component periostin is a secreted protein that functions as both a cell attachment protein and an autocrine or paracrine factor that signals through the cell adhesion molecule integrins α_vβ₃ and α_vβ₅. Periostin participates in normal physiological activities such as cardiac development, but is also involved in pathophysiological processes in vascular diseases, wound repair, bone formation, and tumor development. It is of increasing interest in tumor biology because it is frequently overexpressed in a variety of epithelial carcinomas and is functionally involved in multiple steps of metastasis progression. These include the maintenance of stemness, niche formation, EMT, the survival of tumor cells, and angiogenesis, all of which are indispensable for gastric cancer metastasis. Periostin has been reported to activate the PI-3K/AKT, Wnt, and FAK-mediated signaling pathways to promote metastasis. Therefore, periostin represents a potentially promising candidate for the inhibition of metastasis. In this review article, we summarize recent advances in knowledge concerning periostin, its antagonist PNDA-3, and their influence on such key processes in cancer metastasis as maintenance of stemness, niche formation, epithelial-to-mesenchymal transition, tumor cell survival, and angiogenesis. In particular, we focus our attention on the role of periostin in gastric cancer metastasis, speculate as to the usefulness of periostin as a therapeutic and diagnostic target for gastric cancer metastasis, and consider potential avenues for future research.

A novel genome-wide in vivo screen for metastatic suppressors in human colon cancer identifies the positive WNT-TCF pathway modulators TMED3 and SOX12

The progression of tumors to the metastatic state involves the loss of metastatic suppressor functions. Finding these, however, is difficult as in vitro assays do not fully predict metastatic behavior, and the majority of studies have used cloned cell lines, which do not reflect primary tumor heterogeneity. Here, we have designed a novel genome-wide screen to identify metastatic suppressors using primary human tumor cells in mice, which allows saturation screens. Using this unbiased approach, we have tested the hypothesis that endogenous colon cancer metastatic suppressors affect WNT-TCF signaling. Our screen has identified two novel metastatic suppressors: TMED3 and SOX12, the knockdown of which increases metastatic growth after direct seeding. Moreover, both modify the type of self-renewing spheroids, but only knockdown of TMED3 also induces spheroid cell spreading and lung metastases from a subcutaneous xenograft. Importantly, whereas TMED3 and SOX12 belong to different families involved in protein secretion and transcriptional regulation, both promote endogenous WNT-TCF activity. Treatments for advanced or metastatic colon cancer may thus not benefit from WNT blockers, and these may promote a worse outcome.

Elimination of ALDH+ breast tumor initiating cells by docosahexanoic acid and/or gamma tocotrienol through SHP-1 inhibition of Stat3 signaling

Study investigated the ability of docosahexaenoic acid (DHA) alone and in combination with gamma-tocotrienol (γT3) to eliminate aldehyde dehydrogenase positive (ALDH+) cells and to inhibit mammosphere formation, biomarker and functional assay for tumor initiating cells (TICs), respectively, in human triple negative breast cancer cells (TNBCs), and investigated possible mechanisms of action. DHA upregulated Src homology region 2 domain-containing protein tyrosine phosphatase-1 (SHP-1) protein levels and suppressed levels of phosphorylated signal transducer and activator of transcription-3 (pStat3) and its downstream mediators c-Myc, and cyclin D1. siRNA to SHP-1 enhanced the percentage of ALDH+ cells and Stat-3 signaling, as well as inhibited, in part, the ability of DHA to reduce the percentage of ALDH+ cells and Stat-3 signaling. γT3 alone and in combination with DHA reduced ALDH+ TNBCs, up-regulated SHP-1 protein levels, and suppressed Stat-3 signaling. Taken together, data demonstrate the anti-TIC potential of achievable concentrations of DHA alone as well as in combination with γT3.

Upregulation of circulating cancer stem cell marker, DCLK1 but not Lgr5, in chemoradiotherapy-treated colorectal cancer patients

Cancer stem cell (CSC) markers have attracted considerable attention in tumor diagnostic, prognostic, and therapeutic implications. Detection of cancer stem cells in circulating blood using cancer stem cell markers has received remarkable attention recently. In this study, we aimed to investigate the messenger RNA (mRNA) expression level of Lgr5 and DCLK1 as most proposed colorectal CSC markers in blood circulation also determine the subsequent association to patients' clinical and pathological findings. Peripheral blood mononuclear cells (PBMCs) of 58 patients with colorectal cancer at stage I-IV with 33 out of 58 patients undergoing preoperative chemoradiotherapy (CRT), as well as 58 healthy controls have been isolated and the extracted RNAs were analyzed using real-time PCR. The mRNA expression pattern of CSC markers of patients and controls was compared using ΔΔCt method. The expression level of Lgr5 was significantly higher in colorectal cancer (CRC) patients comparing to healthy group (4.8-fold change, p < 0.001). Also there was a significant increase in expression level of Lgr5 in patients at stages III and IV comparing to stages I and II (p = 0.031) and higher grades (p = 0.039) of CRC. The expression of DCLK1 was also elevated in patients significantly (2.7-fold change, p < 0.001) and the related expression was increased by increasing disease stage (p = 0.025). Combination of DCLK1 and Lgr5 markers was analyzed by logistic regression and proved to be a slightly better marker compared to each marker alone. Interestingly the DCLK1 expression level was significantly higher in patients undergoing preoperative CRT (p = 0.041); however, no association to neoadjuvant CRT was observed for Lgr5. Considering the over-expression of DCLK1 and Lgr5 in circulating blood of CRC patients comparing to controls, our results might emphasize on the presence of CSCs in blood of these patients which might be attributed to their clinical and pathological characteristics and may lead to apply in future clinical implications. Moreover, the higher expression level of DCLK1 in patients undergoing CRT can propose it as a more relevant candidate among CSC markers comparing to Lgr5 for CRC patients.

Cancer stem cells, lymphangiogenesis, and lymphatic metastasis

Although current opinion indicates that tumor-induced lymphangiogenesis plays a key role in promoting the initial spread of malignant tumors, the mechanism that underlies lymphatic spread is not clear. The recent discovery of cancer stem cells (CSCs) in human tumors has challenged our current understanding of tumor recurrence, drug resistance, and metastasis, and opens up new research directions on how cancer cells are capable of switching from dormancy to malignancy. CSCs can be directly and indirectly involved in tumor-induced lymphangiogenesis and ultimately promote lymphatic metastasis. However, the details and the possible relationship between CSCs, lymphangiogenesis, and lymphatic metastasis remain ambiguous, and the origin of tumor lymphatic endothelial cells is controversial. Elucidation of these factors may provide useful information for future research and cancer treatment. In this article, we summarize current knowledge of CSCs, tumor-induced lymphangiogenesis, and lymphatic metastasis and attempt to find an association between key molecular and cellular mechanisms. We provide an overview of CSCs and lymphatic vasculature as potential therapeutic targets. CSC- and lymphatic vasculature-targeted therapy may bring new hope for cancer treatment.

Cancer cells remodel themselves and vasculature to overcome the endothelial barrier

Metastasis refers to the spread of cancer cells from a primary tumor to distant organs mostly via the bloodstream. During the metastatic process, cancer cells invade blood vessels to enter circulation, and later exit the vasculature at a distant site. Endothelial cells that line blood vessels normally serve as a barrier to the movement of cells into or out of the blood. It is thus critical to understand how metastatic cancer cells overcome the endothelial barrier. Epithelial cancer cells acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT), which enables them to move toward vasculature. Cancer cells also express a variety of adhesion molecules that allow them to attach to vascular endothelium. Finally, cancer cells secrete or induce growth factors and cytokines to actively prompt vascular hyperpermeability that compromises endothelial barrier function and facilitates transmigration of cancer cells through the vascular wall. Elucidation of the mechanisms underlying metastatic dissemination may help develop new anti-metastasis therapeutics.

Cancer stem cells are enriched in Fanconi anemia head and neck squamous cell carcinomas

Fanconi anemia (FA) patients have an increased risk of head and neck squamous cell carcinoma (HNSCC) at a higher rate with no apparent risk factors. HNSCC of FA patients is an aggressive tumor characterized by multifocal origin, early metastases and frequent recurrences. Given that cancer stem cells (CSC) drive tumorigenesis, tumor recurrence and metastasis, in this study, we characterized the CSC population in FA and sporadic HNSCC. The Aldefluor assay was used to characterize and isolate CSC with high aldehyde dehydrogenase (ALDH) activity (ALDHpos) in cell lines derived from FA and sporadic HNSCC. Isolated ALDHpos and ALDHneg cells were examined for the expression of stemness genes using reverse transcription-polymerase chain reaction (RT-PCR) array. Tumor cell-derived FA and sporadic HNSCC were examined for their ability to form tumorspheres in vitro. Stem-like cell population in FA and sporadic HNSCC in human and mouse xenograft tumors were evaluated using ALDH isoform 1 (ALDH1) immunohistochemistry. FA‑HNSCC cell lines harbor a greater proportion of ALDHpos cells (15-31%) compared to sporadic HNSCC (10%). Expression of Nanog, Oct-3/4 and Stella, molecular markers of undifferentiated embryonic stem (ES) cells were detected in the ALDHpos FA‑HNSCC cells and not in the ALDHneg cells. FA‑HNSCC cell lines revealed enhanced in vitro tumorsphere formation compared to sporadic HNSCC cells. A higher percentage of ALDH1pos tumor cells are noted in the human and mouse xenograft tumors of FA‑HNSCC compared to sporadic HNSCC tumors. FA‑HNSCC are highly enriched for CSC and may serve as a model to develop CSC-targeted therapies for HNSCC.

LncRNA: a link between RNA and cancer

Unraveling the gene expression networks governing cancer initiation and development is essential while remains largely uncompleted. With the innovations in RNA-seq technologies and computational biology, long noncoding RNAs (lncRNAs) are being identified and characterized at a rapid pace. Recent findings reveal that lncRNAs are implicated in serial steps of cancer development. These lncRNAs interact with DNA, RNA, protein molecules and/or their combinations, acting as an essential regulator in chromatin organization, and transcriptional and post-transcriptional regulation. Their misexpression confers the cancer cell capacities for tumor initiation, growth, and metastasis. The review here will emphasize their aberrant expression and function in cancer, and the roles in cancer diagnosis and therapy will be also discussed.

Identification of drug-resistant subpopulations in canine hemangiosarcoma

Canine hemangiosarcoma is a rapidly progressive disease that is poorly responsive to conventional chemotherapy. Despite numerous attempts to advance treatment options and improve outcomes, drug resistance remains a hurdle to successful therapy. To address this problem, we used recently characterized progenitor cell populations derived from canine hemangiosarcoma cell lines and grown as non-adherent spheres to identify potential drug resistance mechanisms as well as drug-resistant cell populations. Cells from sphere-forming cultures displayed enhanced resistance to chemotherapy drugs, expansion of dye-excluding side populations and altered ATP-binding cassette (ABC) transporter expression. Invasion studies demonstrated variability between cell lines as well as between sphere and monolayer cell populations. Collectively, our results suggest that sphere cell populations contain distinct subpopulations of drug-resistant cells that utilize multiple mechanisms to evade cytotoxic drugs. Our approach represents a new tool for the study of drug resistance in hemangiosarcoma, which could alter approaches for treating this disease.

Downregulation of Ras association domain family member 6 (RASSF6) underlies the treatment resistance of highly metastatic nasopharyngeal carcinoma cells

Radiation and cisplatin-based chemotherapy are major treatments for nasopharyngeal carcinoma (NPC). However, a major impediment for further improving the cure rate is the development of treatment resistance with an undetermined molecular mechanism in metastatic NPC cells. Our established, highly metastatic NPC cells have been reported to be more resistant to cisplatin chemotherapy. In the present study, we found that Ras association domain family member 6 (RASSF6) was downregulated in highly metastatic cells but upregulated in low metastatic cells in comparison to their parental cell line. Ectopic-expression of RASSF6 enhanced the sensitivity of highly metastatic NPC cells to cisplatin or radiation by enhancing apoptosis. RASSF6 depletion conversely reduced treatment sensitivity by decreasing the apoptosis rate. Over-expression of RASSF6 in highly metastatic NPC cells could enhance the phosphorylation of JNK when exposed to cisplatin or radiation treatment, while knocking down RASSF6 in low metastatic NPC cells could reduce the level of phospho-JNK when exposed to the same treatments. The activation of JNK signaling by RASSF6 and its subsequent sensitivity to apoptosis in NPC cells could be inhibited by applying the JNK inhibitor SP600125. In conclusion, the downregulation of RASSF6 in highly metastatic NPC cells contributed to their treatment resistance, and over-expression of RASSF6 conferred treatment sensitivity to highly metastatic NPC cells by activating JNK signaling. RASSF6 could be a valuable molecular marker for identifying sensitive metastatic NPC tumors during cisplatin treatment or radiotherapy.

Functional characteristics of cancer stem cells and their role in drug resistance of prostate cancer

Cancer stem cells (CSCs) have the ability to self-renew and differentiate to give rise to heterogeneous phenotype of the tumor cells. It is believed that these cells are involved in metastasis, recurrence and therapy resistance in various cancers. CSCs have been identified in prostate cancer (PCa), one of the most diagnosed malignancies in men over the world, for which chemotherapy resistance is a major problem in the treatment of castration-resistant advanced stages. Molecular signatures, gene expression and functional features have been reported for PCa CSCs. Most data come from cell lines which may not represent the actual tumor. In the present work, a CSCs enriched population obtained from PCa explants was functionally characterized and analyzed for drug resistance. Tumorsphere cultures positive for ABCG2 transporter, CD133, CD44, cytokeratins 5 and 18 (CK5 and CK18) and negatives for androgen receptor (AR) and prostate-specific antigen (PSA) showed higher clonogenic capacity, holoclone-forming ability, colony-forming capacity in soft agar and lower proliferative and apoptotic rate than control adherent cell cultures. Furthermore, exposing tumorsphere cultures to ABCG2 substrate drugs resulted in a high survival rate compared with control PCa cells. This high drug resistance was decreased using a selective inhibitor of ABCG2. According to these results, tumorspheres from PCa explants showed a functional stem phenotype and a marked drug resistance, probably mediated by high expression of the ABCG2 transporter, which might be considered as a suitable therapeutic target for CSCs.

Oncogenic mutations in intestinal adenomas regulate Bim-mediated apoptosis induced by TGF-β

In the majority of microsatellite-stable colorectal cancers (CRCs), an initiating mutation occurs in the adenomatous polyposis coli (APC) or β-catenin gene, activating the β-catenin/TCF pathway. The progression of resulting adenomas is associated with oncogenic activation of KRas and inactivation of the p53 and TGF-β/Smad functions. Most established CRC cell lines contain mutations in the TGF-β/Smad pathway, but little is known about the function of TGF-β in the early phases of intestinal tumorigenesis. We used mouse and human ex vivo 3D intestinal organoid cultures and in vivo mouse models to study the effect of TGF-β on the Lgr5(+) intestinal stem cells and their progeny in intestinal adenomas. We found that the TGF-β-induced apoptosis in Apc-mutant organoids, including the Lgr5(+) stem cells, was mediated by up-regulation of the BH3-only proapoptotic protein Bcl-2-like protein 11 (Bim). BH3-mimetic compounds recapitulated the effect of Bim not only in the adenomas but also in human CRC organoids that had lost responsiveness to TGF-β-induced apoptosis. However, wild-type intestinal crypts were markedly less sensitive to TGF-β than Apc-mutant adenomas, whereas the KRas oncogene increased resistance to TGF-β via the activation of the Erk1/2 kinase pathway, leading to Bim down-regulation. Our studies identify Bim as a critical mediator of TGF-β-induced apoptosis in intestinal adenomas and show that the common progression mutations modify Bim levels and sensitivity to TGF-β during intestinal adenoma development.

Synthetic modification of salinomycin: selective O-acylation and biological evaluation

Salinomycin has found renewed interest as an agent for prevention of cancer recurrence through selectively targeting cancer stem cells. Strategies for generation of improved salinomycin analogs by individual modification of its hydroxyl groups are presented. An evaluation of the dose-response effects of the resulting library on breast cancer cell lines shows that acylation of the C20 hydroxyl can be used to improve IC50 values down to one fifth that of salinomycin.

Non-genomic estrogen/estrogen receptor α promotes cellular malignancy of immature ovarian teratoma in vitro

Malignant immature ovarian teratomas (IOTs) most often occur in women of reproductive age. It is unclear, however, what roles estrogenic signaling plays in the development of IOT. In this study, we examined whether estrogen receptors (ERα and β) promote the cellular malignancy of IOT. Estradiol (E2), PPT (propylpyrazole), and DPN (diarylpropionitrile) (ERα- and β-specific agonists, respectively), as well as ERα- or ERβ-specific short hairpin (sh)RNA were applied to PA-1 cells, a well-characterized IOT cell line. Cellular tumorigenic characteristics, for example, cell migration/invasion, expression of the cancer stem/progenitor cell marker CD133, and evidence for epithelial-mesenchymal transition (EMT) were examined. In PA-1 cells that expressed ERα and ERβ, we found that ERα promoted cell migration and invasion. We also found that E2/ERα signaling altered cell behavior through non-classical transactivation function. Our data show non-genomic E2/ERα activations of focal adhesion kinase-Ras homolog gene family member A (FAK-RhoA) and ERK governed cell mobility capacity. Moreover, E2/ERα signaling induces EMT and overexpression of CD133 through upregulation micro-RNA 21 (miR21; IOT stem/progenitor promoter), and ERK phosphorylations. Furthermore, E2/ERα signaling triggers a positive feedback regulatory loop within miR21 and ERK. At last, expression levels of ERα, CD133, and EMT markers in IOT tissue samples were examined by immunohistochemistry. We found that cytosolic ERα was co-expressed with CD133 and mesenchymal cell markers but not epithelial cell markers. In conclusion, estrogenic signals exert malignant transformation capacity of cancer cells, exclusively through non-genomic regulation in female germ cell tumors.

Circulating tumour cells: the evolving concept and the inadequacy of their enrichment by EpCAM-based methodology for basic and clinical cancer research

Increasing evidence suggests that circulating tumour cells (CTCs) are responsible for metastatic relapse and this has fuelled interest in their detection and quantification. Although numerous methods have been developed for the enrichment and detection of CTCs, none has yet reached the 'gold' standard. Since epithelial cell adhesion molecule (EpCAM)-based enrichment of CTCs offers several advantages, it is one of the most commonly used and has been adapted for high-throughput technology. However, emerging evidence suggests that CTCs are highly heterogeneous: they consist of epithelial tumour cells, epithelial-to-mesenchymal transition (EMT) cells, hybrid (epithelial/EMT(+)) tumour cells, irreversible EMT(+) tumour cells, and circulating tumour stem cells (CTSCs). The EpCAM-based approach does not detect CTCs expressing low levels of EpCAM and non-epithelial phenotypes such as CTSCs and those that have undergone EMT and no longer express EpCAM. Thus, the approach may lead to underestimation of the significance of CTCs, in general, and CTSCs and EMT(+) tumour cells, in particular, in cancer dissemination. Here, we provide a critical review of research literature on the evolving concept of CTCs and the inadequacy of their enrichment by EpCAM-based technology for basic and clinical cancer research. The review also outlines future perspectives in the field.

The culture of cancer cell lines as tumorspheres does not systematically result in cancer stem cell enrichment

Cancer stem cells (CSC) have raised great excitement during the last decade and are promising targets for an efficient treatment of tumors without relapses and metastases. Among the various methods that enable to enrich cancer cell lines in CSC, tumorspheres culture has been predominantly used. In this report, we attempted to generate tumorspheres from several murine and human cancer cell lines: B16-F10, HT-29, MCF-7 and MDA-MB-231 cells. Tumorspheres were obtained with variable efficiencies from all cell lines except from MDA-MB-231 cells. Then, we studied several CSC characteristics in both tumorspheres and adherent cultures of the B16-F10, HT-29 and MCF-7 cells. Unexpectedly, tumorspheres-forming cells were less clonogenic and, in the case of B16-F10, less proliferative than attached cells. In addition, we did not observe any enrichment in the population expressing CSC surface markers in tumorspheres from B16-F10 (CD133, CD44 and CD24 markers) or MCF-7 (CD44 and CD24 markers) cells. On the contrary, tumorspheres culture of HT-29 cells appeared to enrich in cells expressing colon CSC markers, i.e. CD133 and CD44 proteins. For the B16-F10 cell line, when 1 000 cells were injected in syngenic C57BL/6 mice, tumorspheres-forming cells displayed a significantly lower tumorigenic potential than adherent cells. Finally, tumorspheres culture of B16-F10 cells induced a down-regulation of vimentin which could explain, at least partially, the lower tumorigenicity of tumorspheres-forming cells. All these results, along with the literature, indicate that tumorspheres culture of cancer cell lines can induce an enrichment in CSC but in a cell line-dependent manner. In conclusion, extensive characterization of CSC properties in tumorspheres derived from any cancer cell line or cancer tissue must be performed in order to ensure that the generated tumorspheres are actually enriched in CSC.

The low chamber pancreatic cancer cells had stem-like characteristics in modified transwell system: is it a novel method to identify and enrich cancer stem-like cells?

Cancer stem cells (CSCs) or cancer-initiating cells (CICs) play an important role in tumor initiation, progression, metastasis, chemoresistance, and recurrence. It is important to construct an effective method to identify and isolate CSCs for biotherapy of cancer. During the past years, many researchers had paid more attention to it; however, this method was still on seeking. Therefore, compared to the former methods that were used to isolate the cancer stem cell, in the present study, we tried to use modified transwell system to isolate and enrich CSCs from human pancreatic cancer cell lines (Panc-1). Our results clearly showed that the lower chamber cells in modified transwell system were easily forming spheres; furthermore, these spheres expressed high levels of stem cell markers (CD133/CD44/CD24/Oct-4/ESA) and exhibited chemoresistance, underwent epithelial-to-mesenchymal transition (EMT), and possessed the properties of self-renewal in vitro and tumorigenicity in vivo. Therefore, we speculated that modified transwell assay system, as a rapid and effective method, can be used to isolate and enrich CSCs.

An overview of the role of cancer stem cells in spine tumors with a special focus on chordoma

Primary malignant tumors of the spine are relatively rare, less than 5% of all spinal column tumors. However, these lesions are often among the most difficult to treat and encompass challenging pathologies such as chordoma and a variety of invasive sarcomas. The mechanisms of tumor recurrence after surgical intervention, as well as resistance to radiation and chemotherapy, remain a pervasive and costly problem. Recent evidence has emerged supporting the hypothesis that solid tumors contain a sub-population of cancer cells that possess characteristics normally associated with stem cells. Particularly, the potential for long-term proliferation appears to be restricted to subpopulations of cancer stem cells (CSCs) functionally defined by their capacity to self-renew and give rise to differentiated cells that phenotypically recapitulate the original tumor, thereby causing relapse and patient death. These cancer stem cells present a unique opportunity to better understand the biology of solid tumors in general, as well as targets for future therapeutics. The general objective of the current study is to discuss the fundamental concepts for understanding the role of CSCs with respect to chemoresistance, radioresistance, special cell surface markers, cancer recurrence and metastasis in tumors of the osseous spine. This discussion is followed by a specific review of what is known about the role of CSCs in chordoma, the most common primary malignant osseous tumor of the spine.

Targeting the Wnt pathway in zebrafish as a screening method to identify novel therapeutic compounds

Activating mutations in the Wnt signaling pathway account for the initiation of greater than 90% of all colorectal cancers and this pathway has been implicated in numerous other diseases. Therefore, identifying small molecule inhibitors of this pathway is of critical importance towards identifying clinically relevant drugs. Numerous screens have been employed to identify therapeutic reagents, but none have made it to advanced clinical trials, suggesting that traditional screening methods are ineffective at identifying clinically relevant targets. Here, we describe a novel in vivo screen to identify small molecule inhibitors of the Wnt pathway. Specifically, treatment of zebrafish embryos with LiCl inhibits GSK3 kinase function, resulting in hyperactivation of the signaling pathway and an eyeless phenotype at 1 day post fertilization. Using the small molecule XAV939, a known inhibitor of Wnt signaling, we rescued the LiCl induced eyeless phenotype, confirming efficacy of the screen. We next tested our assay with 400 known small molecule kinase inhibitors, none of which should inhibit Wnt signaling below the level of GSK3 based on their known targets. Accordingly, none of these small molecules rescued the eyeless phenotype, which demonstrates the stringency of the assay. However, several of these small molecule kinase inhibitors did generate a non-Wnt phenotype in accordance with the kinase they targeted. Therefore, combining the efficacy, sensitivity, and stringency of this preliminary screen, this model will provide an alternative to the traditional in vitro screen, generating potentially clinical relevant drugs in a rapid and cost-effective way.

Melanoma stem cells and metastasis: mimicking hematopoietic cell trafficking?

Malignant melanoma is a highly metastatic cancer that bears responsibility for the majority of skin cancer-related deaths. Amidst the research efforts to better understand melanoma progression, there has been increasing evidence that hints at a role for a subpopulation of virulent cancer cells, termed malignant melanoma stem or initiating cells (MMICs), in metastasis formation. MMICs are characterized by their preferential ability to initiate and propagate tumor growth and their selective capacity for self-renewal and differentiation into less tumorigenic melanoma cells. The frequency of MMICs has been shown to correlate with poor clinical prognosis in melanoma. In addition, MMICs are enriched among circulating tumor cells in the peripheral blood of cancer patients, suggesting that MMICs may be a critical factor in the metastatic cascade. Although these links exist between MMICs and metastatic disease, the mechanisms by which MMICs may advance metastatic progression are only beginning to be elucidated. Recent studies have shown that MMICs express molecules critical for hematopoietic cell maintenance and trafficking, providing a possible explanation for how circulating MMICs could drive melanoma dissemination. We therefore propose that MMICs might fuel melanoma metastasis by exploiting homing mechanisms commonly utilized by hematopoietic cells. Here we review the biological properties of MMICs and the existing literature on their metastatic potential. We will discuss possible mechanisms by which MMICs might initiate metastases in the context of established knowledge of cancer stem cells in other cancers and of hematopoietic homing molecules, with a particular focus on selectins, integrins, chemokines and chemokine receptors known to be expressed by melanoma cells. Biological understanding of how these molecules might be utilized by MMICs to propel the metastatic cascade could critically impact the development of more effective therapies for advanced disease.

Metastatic mechanisms in follicular cell-derived thyroid cancer

Thyroid cancer incidence is rising annually largely related to enhanced detection and early stage well-differentiated primary tumors. The prognosis for patients with early stage thyroid cancer is outstanding with most patients being cured with surgery. In selected cases, I-131 is administered to treat known or suspected residual or metastatic disease. Even patients with loco-regional metastases typically have an outstanding long-term prognosis, albeit with monitoring and occasional intervention for residual or recurrent disease. By contrast, individuals with distant metastases from thyroid cancer, particularly older patients with larger metastatic burdens and those with poorly differentiated tumors, have a poor prognosis. Patients with metastatic anaplastic thyroid cancer have a particularly poor prognosis. Published clinical trials indicate that transient disease control and partial remissions can be achieved with kinase inhibitor therapy directed toward angiogenic targets and that in some cases I-131 uptake can be enhanced. However, the direct targets of activity in metastatic lesions are incompletely defined and clear evidence that these treatments increase the duration or quality of life of patients is lacking, underscoring the need for improved knowledge regarding the metastatic process to inform the development of new therapies. In this review, we will focus on current data and hypotheses regarding key regulators of metastatic dormancy, metastatic progression, and the role of putative cancer stem cells.

Crossing the endothelial barrier during metastasis

During metastasis, cancer cells disseminate to other parts of the body by entering the bloodstream in a process that is called intravasation. They then extravasate at metastatic sites by attaching to endothelial cells that line blood vessels and crossing the vessel walls of tissues or organs. This Review describes how cancer cells cross the endothelial barrier during extravasation and how different receptors, signalling pathways and circulating cells such as leukocytes and platelets contribute to this process. Identification of the mechanisms that underlie cancer cell extravasation could lead to the development of new therapies to reduce metastasis.

Grp78 as a therapeutic target for refractory head-neck cancer with CD24(-)CD44(+) stemness phenotype

Cancer stem cells are refractory to conventional therapy, which result to cancer metastasis and chemo-radioresistance. Grp78 is known to have important roles in cytoprotection and tumorigenesis in several cancers. We therefore examined whether Grp78 can serve as a therapeutic target for refractory stemness phenotype of head and neck cancer (HNC). Six HNC cell lines were used. Fluorescence-activated cell sorting (FACS) analysis was used to sort CD24(-)CD44(+) and Grp78(+) cells. The small interfering RNA (siRNA) knockdown and cDNA transfection were applied to examine the effects of Grp78 on cellular function. Western blot and confocol microscopy were used to determine the effects of downstream protein expressions. Xenografted mouse tumors and immunohistochemistry were used to validate the results. We found that Grp78 regulated the conversion of CD24(-)CD44(+) cells, a characteristic of HNC stem cells. The CD24(-)CD44(+)Grp78(+) cells showed superior chemo-radioresistance and invasion ability compared with CD24(-)CD44(+), Grp78(+) or the parental cells. Silencing Grp78 increased chemo-radiosensitivity, inhibited cell invasion, reverse epithelial-mesenchymal transition, suppressed cancer stemness, withdrew CD24(-)CD44(+) cell conversion and induced differentiated phenotype. Study in xenografted mice further showed that CD24(-)CD44(+)Grp78(+) cells exhibited highest tumorigenesis, compared with CD24(-)CD44(+) CD24(+)CD44(+) or the parental cells. Grp78 knockdown dramatically restrained tumor growth along with the inhibition of stem cell regulatory proteins Oct-4 and Slug. Grp78 may serve as a molecular target that can be further developed for eradication of refractory HNC with stemness phenotype.

Critical research gaps and translational priorities for the successful prevention and treatment of breast cancer

INTRODUCTION

Breast cancer remains a significant scientific, clinical and societal challenge. This gap analysis has reviewed and critically assessed enduring issues and new challenges emerging from recent research, and proposes strategies for translating solutions into practice.

METHODS

More than 100 internationally recognised specialist breast cancer scientists, clinicians and healthcare professionals collaborated to address nine thematic areas: genetics, epigenetics and epidemiology; molecular pathology and cell biology; hormonal influences and endocrine therapy; imaging, detection and screening; current/novel therapies and biomarkers; drug resistance; metastasis, angiogenesis, circulating tumour cells, cancer 'stem' cells; risk and prevention; living with and managing breast cancer and its treatment. The groups developed summary papers through an iterative process which, following further appraisal from experts and patients, were melded into this summary account.

RESULTS

The 10 major gaps identified were: (1) understanding the functions and contextual interactions of genetic and epigenetic changes in normal breast development and during malignant transformation; (2) how to implement sustainable lifestyle changes (diet, exercise and weight) and chemopreventive strategies; (3) the need for tailored screening approaches including clinically actionable tests; (4) enhancing knowledge of molecular drivers behind breast cancer subtypes, progression and metastasis; (5) understanding the molecular mechanisms of tumour heterogeneity, dormancy, de novo or acquired resistance and how to target key nodes in these dynamic processes; (6) developing validated markers for chemosensitivity and radiosensitivity; (7) understanding the optimal duration, sequencing and rational combinations of treatment for improved personalised therapy; (8) validating multimodality imaging biomarkers for minimally invasive diagnosis and monitoring of responses in primary and metastatic disease; (9) developing interventions and support to improve the survivorship experience; (10) a continuing need for clinical material for translational research derived from normal breast, blood, primary, relapsed, metastatic and drug-resistant cancers with expert bioinformatics support to maximise its utility. The proposed infrastructural enablers include enhanced resources to support clinically relevant in vitro and in vivo tumour models; improved access to appropriate, fully annotated clinical samples; extended biomarker discovery, validation and standardisation; and facilitated cross-discipline working.

CONCLUSIONS

With resources to conduct further high-quality targeted research focusing on the gaps identified, increased knowledge translating into improved clinical care should be achievable within five years.

High expression level of TMPRSS4 predicts adverse outcomes of colorectal cancer patients

Transmembrane protease/serine 4 (TMPRSS4), a member of the type II transmembrane serine protease family, is highly expressed in some human cancers and involved in the EMT regulation of cancer cells. The prognostic value of TMPRSS4 in colorectal cancer (CRC) has not been discussed. This study aims to evaluate the association between TMPRSS4 expressions and survival in CRC patients. Immunohistochemistry revealed high expression of TMPRSS4 in 69/122 CRC samples, compared with 14/47 in normal tissues (P < 0.01). Correlation analysis showed high expression of TMPRSS4 was significantly associated with advanced TNM stage (P = 0.011), pT (P = 0.019), pN (P = 0.035), and pM status (P = 0.004). Higher TMPRSS4 predicted shorter overall survival (OS) and disease-free survival (DFS) in CRC patients (P < 0.01, both). Moreover, both TMPRSS4 expression and TNM stage were independent predictive factors of OS and DFS in Cox regression analysis. The findings in our study demonstrated the potential value of TMPRSS4 expression level as a prognostic biomarker for CRC patients.

Role of the ROS/AMPK signaling pathway in tetramethylpyrazine-induced apoptosis in gastric cancer cells

Tetramethylpyrazine (TMPZ) is one of the active compounds extracted from the traditional Chinese medicinal herb Chuanxiong and several studies have shown it to possess anticancer properties. However, its effectiveness in gastric cancer and its cellular mechanisms are relatively unknown. The present study aimed to investigate the effect of TMPZ on SGC7901 cells, and it was demonstrated that a high dose of TMPZ inhibited cell viability and induced apoptosis by stimulating AMP-activated protein kinase (AMPK) through the generation of reactive oxygen species (ROS). Furthermore, TMPZ-induced apoptosis resulted in the sequential events beginning with the translocation of Bax, the collapse of mitochondrial membrane potential (ΔΨm), the release of cytochrome c and the activation of caspase-9 and -3. Each of these events was inhibited by compound C, a pharmacological inhibitor of AMPK. To the best of our knowledge, these results demonstrate for the first time that the induction of apoptosis by TMPZ in gastric cancer cells is associated with the activation of the ROS/AMPK pathway. AMPK activation induces apoptosis through the mitochondrial apoptotic pathway. In addition, these results raise the possibility that TMPZ may have a future therapeutic role in gastric cancer.

Cisplatin induces differentiation of breast cancer cells

Breast tumors are heterogeneous including cells with stem cell properties and more differentiated cells. This heterogeneity is reflected into the molecular breast cancer subtypes. Breast cancer stem cells are resistant to chemotherapy, thus recent efforts are focusing on identifying treatments that shift them toward a more differentiated phenotype, making them more susceptible to chemotherapy. We examined whether the drug cisplatin induces differentiation in breast cancer cell lines that represent different breast cancer subtypes. We used three cell lines representing triple-negative breast cancers, BT-549 and MDA-MB-231 (claudin-low), and MDA-MB-468 (basal-like), along with estrogen and progesterone receptor positive MCF-7 cells (luminal). Cisplatin was applied at 2.5, 5, 10, and 20 μM, and cell viability and proliferation were measured using MTS and BrdU assays, respectively. The effect of cisplatin on the cellular hierarchy was examined by flow cytometry, immunofluorescence and qRT-PCR. Cisplatin treatment of 10 and 20 μM reduced cell viability by 36–51% and proliferation capacity by 36–67%. Treatment with cisplatin resulted in 12–67% down-regulation of stem cell markers (CD49f, SSEA4) and 10–130% up-regulation of differentiation markers (CK18, SMA, β-tubulin). At the mRNA level, CD49f was down-regulated whilst β-tubulin was up-regulated in the claudin-low cell lines. SSEA4 protein expression decreased upon cisplatin treatment, but SSEA4 mRNA expression increased indicating a differential regulation of cisplatin at the post-transcriptional level. It is concluded that cisplatin reduces breast cancer cell survival and induces differentiation of stem/progenitor cell subpopulations within breast cancer cell lines. These effects indicate the potential of this drug to target specific chemotherapy-resistant cells within a tumor.

Strategies for isolating and enriching cancer stem cells: well begun is half done

Cancer stem cells (CSCs) constitute a subpopulation of cancer cells that have the potential for self-renewal, multipotent differentiation, and tumorigenicity. Studies on CSC biology and CSC-targeted therapies depend on CSC isolation and/or enrichment methodologies. Scientists have conducted extensive research in this field since John Dick's group successfully isolated CSCs based on the expression of the CD34 and CD38 surface markers. Progress in CSC research has been greatly facilitated by the enrichment and isolation of these cells. In this review, we summarize the current strategies used in our and other laboratories for CSC isolation and enrichment, including methods based on stem cell surface markers, intracellular enzyme activity, the concentration of reactive oxygen species, the mitochondrial membrane potential, promoter-driven fluorescent protein expression, autofluorescence, suspension/adherent culture, cell division, the identification of side population cells, resistance to cytotoxic compounds or hypoxia, invasiveness/adhesion, immunoselection, and physical property. Although many challenges remain to be overcome, it is reasonable to believe that more reliable, efficient, and convenient methods will be developed in the near future.

A microRNA miR-34a-regulated bimodal switch targets Notch in colon cancer stem cells

microRNAs regulate developmental cell-fate decisions, tissue homeostasis, and oncogenesis in distinct ways relative to proteins. Here, we show that the tumor suppressor microRNA miR-34a is a cell-fate determinant in early-stage dividing colon cancer stem cells (CCSCs). In pair-cell assays, miR-34a distributes at high levels in differentiating progeny, whereas low levels of miR-34a demarcate self-renewing CCSCs. Moreover, miR-34a loss of function and gain of function alter the balance between self-renewal versus differentiation both in vitro and in vivo. Mechanistically, miR-34a sequesters Notch1 mRNA to generate a sharp threshold response where a bimodal Notch signal specifies the choice between self-renewal and differentiation. In contrast, the canonical cell-fate determinant Numb regulates Notch levels in a continuously graded manner. Altogether, our findings highlight a unique microRNA-regulated mechanism that converts noisy input into a toggle switch for robust cell-fate decisions in CCSCs.

Exploring the biology of cancer of unknown primary: breakthroughs and drawbacks

BACKGROUND

Cancer of unknown primary (CUP) ranks among the ten most common malignancies worldwide. Cancer of unknown primary presents as disseminated disease, has a dismal prognosis and remains a diagnosis of exclusion. The natural history and biology of the disease is poorly understood, and efforts are focused on identifying the specific 'CUP signature'.

MATERIALS AND METHODS

We collected and analysed all published research in the biology of CUP from 1974 till present (Medline, Embase, ASCO and ESMO Congresses).

RESULTS

Current scientific evidence suggests that aneuploidy and karyotype changes are frequent, while more subtle molecular aberrations, such as epidermal growth factor receptor family proteins, cKit/PDGFR are frequently overexpressed, although without prognostic significance. Loss of function of tumour suppressor genes, active angiogenesis, a hypoxic genetic programme and a mesenchymal transitory phenotype have been reported in CUP and may be indicative of unfavourable prognosis. Molecular pathway analyses have identified various biomolecules impacting on survival (pAKT, pMAPK, c-Met, p21 and pPRS6). Finally, circulating tumour cells have recently been reported as a frequent phenomenon in CUP.

CONCLUSIONS

Overall, advances in understanding CUP biology have been weak and the application of gene expression profiling failed to identify an as yet elusive 'CUP molecular signature'. MicroRNA, epigenetic and proteomic studies are warranted to better characterize the biological profile of CUP and unravel its mystery.

The cancer stem cell hypothesis applied to oral carcinoma

It has been proposed that the development of tumors is based exclusively on the activity of cancer stem cells (CSCs) leading to a new model of carcinogenesis, the CSC hypothesis, in opposition to the conventional model of clonal evolution. The new model may help to explain the high mortality of oral cancer, unchanged over the past decades, the low response to treatment and the tendency of oral squamous cell carcinoma (OSCC) patients to develop multiple tumors. However, a more profound understanding of the molecular pathways involved in maintaining the stem cell (SC) state and of their alterations is required to elucidate the mechanisms underlying the development of tumors and metastatic spread, but research into SC biopathology is hampered by the lack of specific markers for identifying SCs and CSCs in tissues and for establishing topographic relationships with their lineage. We review current knowledge on stem cells in relation to oral cancer, including their possible origins, focusing on the CSC hypothesis of oral tumorigenesis and attempts being made to identify oral stem cells.

Differential expression of ID4 and its association with TP53 mutation, SOX2, SOX4 and OCT-4 expression levels

Inhibitor of DNA Binding 4 (ID4) is a member of the helix-loop-helix ID family of transcription factors, mostly present in the central nervous system during embryonic development, that has been associated with TP53 mutation and activation of SOX2. Along with other transcription factors, ID4 has been implicated in the tumorigenic process of astrocytomas, contributing to cell dedifferentiation, proliferation and chemoresistance. In this study, we aimed to characterize the ID4 expression pattern in human diffusely infiltrative astrocytomas of World Health Organization (WHO) grades II to IV of malignancy (AGII-AGIV); to correlate its expression level to that of SOX2, SOX4, OCT-4 and NANOG, along with TP53 mutational status; and to correlate the results with the clinical end-point of overall survival among glioblastoma patients. Quantitative real time PCR (qRT-PCR) was performed in 130 samples of astrocytomas for relative expression, showing up-regulation of all transcription factors in tumor cases. Positive correlation was found when comparing ID4 relative expression of infiltrative astrocytomas with SOX2 (r = 0.50; p<0.005), SOX4 (r = 0.43; p<0.005) and OCT-4 (r = 0.39; p<0.05). The results from TP53 coding exon analysis allowed comparisons between wild-type and mutated status only in AGII cases, demonstrating significantly higher levels of ID4, SOX2 and SOX4 in mutated cases (p<0.05). This pattern was maintained in secondary GBM and further confirmed by immunohistochemistry, suggesting a role for ID4, SOX2 and SOX4 in early astrocytoma tumorigenesis. Combined hyperexpression of ID4, SOX4 and OCT-4 conferred a much lower (6 months) median survival than did hypoexpression (18 months). Because both ID4 alone and a complex of SOX4 and OCT-4 activate SOX2 transcription, it is possible that multiple activation of SOX2 impair the prognosis of GBM patients. These observational results of associated expression of ID4 with SOX4 and OCT-4 may be used as a predictive factor of prognosis upon further confirmation in a larger GBM series.

Gastric cancer stem cells: a novel therapeutic target

Gastric cancer remains one of the leading causes of global cancer mortality. Multipotent gastric stem cells have been identified in both mouse and human stomachs, and they play an essential role in the self-renewal and homeostasis of gastric mucosa. There are several environmental and genetic factors known to promote gastric cancer. In recent years, numerous in vitro and in vivo studies suggest that gastric cancer may originate from normal stem cells or bone marrow-derived mesenchymal cells, and that gastric tumors contain cancer stem cells. Cancer stem cells are believed to share a common microenvironment with normal niche, which play an important role in gastric cancer and tumor growth. This mini-review presents a brief overview of the recent developments in gastric cancer stem cell research. The knowledge gained by studying cancer stem cells in gastric mucosa will support the development of novel therapeutic strategies for gastric cancer.

Response to stress in early tumor colonization modulates switching of CD133-positive and CD133-negative subpopulations in a human metastatic colon cancer cell line, SW620

According to the cancer stem cell (CSC) model, higher CD133 expression in tumor tissue is associated with metastasis and poor prognosis in colon cancer. As such, the CD133-positive (CD133⁺) subpopulation of cancer cells is believed to play a central role in tumor development and metastatic progression. Although CD133⁺ cells are believed to display more CSC-like behavior and be solely responsible for tumor colonization, recent research indicates that CD133⁻ cells from metastatic colon tumors not only also possess colonization capacity but also promote the growth of larger tumors in a mouse model than CD133⁺ cells, suggesting that an alternative mechanism of metastasis exists. This study investigated this possibility by examining the cell viability, tumorigenicity, and proliferation and growth capacity of the CD133⁺ and CD133⁻ subpopulations of the SW620 cell line, a human metastatic colon cancer cell line, in both an in vitro cell model and an in vivo mouse model. While both SW620 ^CD133− and SW620^CD133+ cells were found to engage in bidirectional cell-type switching in reaction to exposure to environmental stressors, including hypoxia, a cell adhesion-free environment, and extracellular matrix stimulation, both in vitro and in vivo, CD133⁻ cells were found to have a growth advantage during early colonization due to their greater resistance to proliferation inhibition. Based on these findings, a hypothetical model in which colon cancer cells engage in cell-type switching in reaction to exposure to environmental stressors is proposed. Such switching may provide a survival advantage during early colonization, as well as that explain previous conflicting observations.