CXCR6, a newly defined biomarker of tissue-specific stem cell asymmetric self-renewal, identifies more aggressive human melanoma cancer stem cells

The Interplay between Tumour Microenvironment Components in Malignant Melanoma

Malignant melanoma has shown an increasing incidence during the last two decades, exhibiting a large spectrum of locations and clinicopathological characteristics. Although current histopathological, biochemical, immunohistochemical, and molecular methods provide a deep insight into its biological behaviour and outcome, melanoma is still an unpredictable disease, with poor outcome. This review of the literature is aimed at updating the knowledge regarding melanoma’s clinicopathological and molecular hallmarks, including its heterogeneity and plasticity, involving cancer stem cells population. A special focus is given on the interplay between different cellular components and their secretion products in melanoma, considering its contribution to tumour progression, invasion, metastasis, recurrences, and resistance to classical therapy. Furthermore, the influences of the specific tumour microenvironment or “inflammasome”, its association with adipose tissue products, including the release of “extracellular vesicles”, and distinct microbiota are currently studied, considering their influences on diagnosis and prognosis. An insight into melanoma’s particular features may reveal new molecular pathways which may be exploited in order to develop innovative therapeutic approaches or tailored therapy.

Overall survival in metastatic melanoma correlates with pembrolizumab exposure and T cell exhaustion markers

Trial data support an absence of an exposure-survival relationship for pembrolizumab. As these relationships remain unexamined in a real-world setting, we determined them in metastatic melanoma prospectively in an observational study. Translational objectives included identifying biomarkers of progressive disease (PD). Checkpoint blockade naïve patients receiving 2 mg/kg Q3W pembrolizumab had pharmacokinetic and clinical outcome data collected. Trough, a valid surrogate for drug exposure, was assessed using ELISA. T-cell exhaustion and chemokine markers were determined using flow cytometry. Geometric means of exposures and biomarkers were tested against objective response groups using one-way ANOVA. The cohort was split by the median into high versus low pembrolizumab exposure groups. Kaplan-Meier progression-free survival (PFS) and overall survival (OS) curves were estimated for high versus low exposure, compared using the log rank test. The high pembrolizumab exposure group (n = 14) experienced substantially longer median OS (not reached vs. 48 months, p = .014), than the low exposure group (n = 14). A similar positive exposure PFS relationship was found (median not reached vs. 48 months, p = .045). The frequency of TIM-3 expression on CD4+ T cells was significantly higher in PD (mean 27.8%) than complete response (CR) (13.38%, p = .01) and partial response (12.4%, p = .05). There was a near doubling of CXCR6 and TIM-3 co-expression on CD4+ T cells in PD (mean 23.3%) versus CR (mean 11.4, p = .003) and partial response (9.8%, p = .0001). We describe positive exposure-PFS and exposure-OS relationships for pembrolizumab in metastatic melanoma. TIM-3, alongside co-expression of CXCR6 and TIM-3 on circulating CD4+ T cells are potential bio markers of treatment failure.

Effect of melanoma stem cells on melanoma metastasis

Cancer stem cells (CSCs) are involved in the metastatic process, the resistance of many types of cancer to therapeutic treatments and consequently the onset of recurrences. The CSC concept therefore significantly extends our understanding of melanoma biology. More recently, melanoma stem cells (MSCs) have been described in melanoma as expressing specific biomarkers. These primitive melanoma cells are not only capable of self-renewal and differentiation plasticity, but may also confer virulence via immune evasion and multidrug resistance, and potentially, via vasculogenic mimicry and transition to migratory and metastasizing derivatives. This review will present the specific biomarkers of MSCs, including CD133, ATP binding cassette subfamily B member 5, CD271, CD20 and aldehyde dehydrogenase, which can regulate the transduction of tumor-related signals. These signal molecules can reversely act on tumor cells and regulate tumor angiogenesis, leading to the occurrence of melanoma metastasis. Targeting these specific biomarkers could inhibit the progression of melanoma and may help the development of novel therapeutic strategies for melanoma.

CXC chemokine ligand 16: a Swiss army knife chemokine in cancer

Today, cancer is one of the leading causes of death worldwide. Lately, cytokine and chemokine imbalances have gained attention amongst different involved pathways in cancer development and attracted much consideration in cancer research. CXCL16, as a member of the CXC subgroup of chemokines, has been attributed to be responsible for immune cell infiltration into the tumour microenvironment. The aberrant expression of CXCL16 has been observed in various cancers. This chemokine has been shown to play a conflicting role in tumour development through inducing pro-inflammatory conditions. The infiltration of various immune and non-immune cells such as lymphocytes, cancer-associated fibroblasts and myeloid-derived suppressor cells by CXCL16 into the tumour microenvironment has complicated the tumour fate. Given this diverse role of CXCL16 in cancer, a better understanding of its function might build-up our knowledge about tumour biology. Hence, this study aimed to review the impact of CXCL16 in cancer and explored its therapeutic application. Consideration of these findings might provide opportunities to achieve novel approaches in cancer treatment and its prognosis.

The Role of CXCL16 in the Pathogenesis of Cancer and Other Diseases

CXCL16 is a chemotactic cytokine belonging to the α-chemokine subfamily. It plays a significant role in the progression of cancer, as well as the course of atherosclerosis, renal fibrosis, and non-alcoholic fatty liver disease (NAFLD). Since there has been no review paper discussing the importance of this chemokine in various diseases, we have collected all available knowledge about CXCL16 in this review. In the first part of the paper, we discuss background information about CXCL16 and its receptor, CXCR6. Next, we focus on the importance of CXCL16 in a variety of diseases, with an emphasis on cancer. We discuss the role of CXCL16 in tumor cell proliferation, migration, invasion, and metastasis. Next, we describe the role of CXCL16 in the tumor microenvironment, including involvement in angiogenesis, and its significance in tumor-associated cells (cancer associated fibroblasts (CAF), microglia, tumor-associated macrophages (TAM), tumor-associated neutrophils (TAN), mesenchymal stem cells (MSC), myeloid suppressor cells (MDSC), and regulatory T cells (T_reg)). Finally, we focus on the antitumor properties of CXCL16, which are mainly caused by natural killer T (NKT) cells. At the end of the article, we summarize the importance of CXCL16 in cancer therapy.

Drug-selected population in melanoma A2058 cells as melanoma stem-like cells retained angiogenic features - the potential roles of heparan-sulfate binding ANGPTL4 protein

Malignant cancer may contain highly heterogeneous populations of cells, including stem-like cells which were resistant to chemotherapy agents, radiation, mechanical stress, and immune surveillance. The characterization of these specific subpopulations might be critical to develop novel strategy to remove malignant tumors. We selected and enriched small population of human melanoma A2058 cells by repetitive selection cycles (selection, restoration, and amplification). These subpopulation of melanoma cells persisted the characteristics of slower cell proliferation, enhanced drug-resistance, elevated percentage of side population as analyzed by Hoechst33342 exclusion, in vitro sphere formation, and in vivo xenograft tumor formation by small amount of tumor cells. The selected populations would be melanoma stem-like cells with high expression of stem cell markers and altered kinase activation. Microarray and bioinformatics analysis highlighted the high expression of angiopoietin-like 4 protein in drug-selected melanoma stem-like cells. Further validation by specific shRNA demonstrated the role of angiopoietin-like 4 protein in drug-selected subpopulation associated with enhanced drug-resistance, sphere formation, reduced kinase activation, in vitro tube-forming ability correlated with heparan-sulfate proteoglycans. Our finding would be applicable to explore the mechanism of melanoma stemness and use angiopoietin-like 4 as potential biomarkers to identify melanoma stem-like cells.

MicroRNA-222 Regulates Melanoma Plasticity

Melanoma is one of the most aggressive and highly resistant tumors. Cell plasticity in melanoma is one of the main culprits behind its metastatic capabilities. The detailed molecular mechanisms controlling melanoma plasticity are still not completely understood. Here we combine mathematical models of phenotypic switching with experiments on IgR39 human melanoma cells to identify possible key targets to impair phenotypic switching. Our mathematical model shows that a cancer stem cell subpopulation within the tumor prevents phenotypic switching of the other cancer cells. Experiments reveal that hsa-mir-222 is a key factor enabling this process. Our results shed new light on melanoma plasticity, providing a potential target and guidance for therapeutic studies.

Cancer stem cells, epigenetics, tumor microenvironment and future therapeutics in cutaneous malignant melanoma: a review

This review provides an overview of the current understanding of the ontogeny and biology of melanoma stem cells in cutaneous malignant melanoma. This article also summarizes and evaluates the current knowledge of the underlying epigenetic mechanisms, the regulation of melanoma progress by the tumor microenvironment as well as the therapeutic implications and applications of these novel insights, in the setting of personalized medicine. Unraveling the complex ecosystem of cutaneous malignant melanoma and the interplay between its components, aims to provide novel insights into the establishment of efficient therapeutic strategies.

A novel immune-related genes prognosis biomarker for melanoma: associated with tumor microenvironment

BACKGROUND

Melanoma is a cancer of the skin with potential to spread to other organs and is responsible for most deaths due to skin cancer. It is imperative to identify immune biomarkers for early melanoma diagnosis and treatment.

RESULTS

63 immune-related genes of the total 1039 unique IRGs retrieved were associated with overall survival of melanoma. A multi-IRGs classifier constructed using eight IRGs showed a powerful predictive ability. The classifier had better predictive power compared with the current clinical data. GSEA analysis showed multiple signaling differences between high and low risk score group. Furthermore, biomarker was associated with multiple immune cells and immune infiltration in tumor microenvironment.

CONCLUSIONS

The immune-related genes prognosis biomarker is an effective potential prognostic classifier in the immunotherapies and surveillance of melanoma.

METHODS

Melanoma samples of genes were retrieved from TCGA and GEO databases while the immune-related genes (IRGs) were retrieved from the ImmPort database. WGCNA, Cox regression analysis and LASSO analysis were used to classify melanoma prognosis. ESTIMATE and CIBERSORT algorithms were used to explore the relationship between risk score and tumor immune microenvironment. GSEA analysis was performed to explore the biological signaling pathway.

Targeting cancer stem cells by melatonin: Effective therapy for cancer treatment

Melatonin is a physiological hormone produced by the pineal gland. In recent decades, enormous investigations showed that melatonin can prompt apoptosis in cancer cells and inhibit tumor metastasis and angiogenesis in variety of malignancies such as ovarian, melanoma, colon, and breast cancer; therefore, its possible therapeutic usage in cancer treatment was confirmed. CSCs, which has received much attention from researchers in past decades, are major challenges in the treatment of cancer. Because CSCs are resistant to chemotherapeutic drugs and cause recurrence of cancer and also have the ability to be regenerated; they can cause serious problems in the treatment of various cancers. For these reasons, the researchers are trying to find a solution to destroy these cells within the tumor mass. In recent years, the effect of melatonin on CSCs has been investigated in some cancers. Given the importance of CSCs in the process of cancer treatment, this article reviewed the studies conducted on the effect of melatonin on CSCs as a solution to the problems caused by CSCs in the treatment of various cancers.

Effect of gastric cancer stem cell on gastric cancer invasion, migration and angiogenesis

Purpose: Using the gastric cancer cell line SGC7901 and gastric cancer stem cell (CSC-G), we conducted this study to investigate the role of cancer stem cells in invasion, metastasis and tumor angiogenesis. Methods: Stem cell markers (OCT4, SOX2, C-Myc and Klf4) expression was detected by RT-PCR and Western blotting. The proliferation, migration, invasion abilities, L-OHP and 5-FU resistance, angiogenesis were assessed using in vitro spherical clone formation assays, plate cloning experiments, transwell migration, transwell invasion, drug resistance, scratch-wound migration, ring formation assay, and their tumorigenic and ability were assessed using a tumor formation experiment in mice. Results: Compared with the SGC7901, the expression of Oct4, Sox2, Klf4 and CD44 mRNA was significantly higher in CSC-G, the mRNA relative expression of E-cadherin in CSC-G was lower than SGC7901, while the expression of c-Myc did not significantly change. The proliferation, drug resistance, migration, and invasion abilities were significantly higher in CSC-G, and the tumorigenic ability in mice was also significantly higher. Conclusion: The proliferation, drug resistance, migration, invasion, and tumorigenic abilities of CSC-G significantly were higher than SGC7901. CSC-G plays important roles in proliferation, migration, invasion, and tumorigenicity.

Effect of overexpression of Oct4 and Sox2 genes on the biological and oncological characteristics of gastric cancer cells

Objective: Using the gastric cancer cell line SGC7901, we constructed a cell line that overexpressed octamer-binding protein 4 (Oct4) and SRY-box 2 (Sox2) to explore the stem cell oncological and biological characteristics of these cells and to elucidate the mechanisms of Oct4 and Sox2 in cancer.

Methods: A lentiviral vector containing the Sox2 gene was constructed and transfected into a gastric cancer cell line overexpressing Oct4 (SGC7901-Oct4) to obtain a stably transfected cell line (SGC7901-Oct4-Sox2). Oct4 and Sox2 expression was detected by RT-PCR and Western blotting. The proliferation, drug resistance, migration, and invasion abilities of the cells were assessed using in vitro (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium), drug resistance, scratch-wound migration, transwell migration, transwell invasion, and spherical clone formation assays, and their tumorigenic ability was assessed using a tumor formation experiment in mice.

Results: Compared with the control group, the expression of Oct4, Sox2, CD44, and E-cadherin was significantly higher in the group that overexpressed Oct4 and Sox2, while the expression of c-Myc and Klf4 did not significantly change. The proliferation, drug resistance, migration, and invasion abilities were significantly enhanced in the overexpression group, and the tumorigenic ability in mice was also significantly enhanced, with significantly increased tumor size and weight.

Conclusion: The proliferation, drug resistance, migration, invasion, and tumorigenic abilities of SGC7901 cells overexpressing Oct4 and Sox2 were significantly improved. Oct4 and Sox2 play important roles in the proliferation, migration, invasion, and tumorigenicity of gastric cancer cells, and the two genes may be synergistic to a certain degree.

Higher CXCL16 exodomain is associated with aggressive ovarian cancer and promotes the disease by CXCR6 activation and MMP modulation

Ovarian cancer (OvCa) is the leading cause of death from gynecological malignancies. Five-year survival rate of OvCa ranges from 30–92%, depending on the spread of disease at diagnosis. Role of chemokines is well appreciated in cancer, including OvCa. However, their precise role is understudied. Here, we show clinical and biological significance of CXCR6-CXCL16 and ADAM10 in OvCa. Expression of CXCR6 and N-terminal CXCL16 was significantly higher in serous carcinoma tissues compared to endometrioid. OvCa cells (SKOV-3 and OVCAR-3) also showed higher expression of CXCR6 than normal ovarian epithelial cells (IOSE-7576) while CXCL16 was higher in SKOV-3 than IOSE-7576. Furthermore, N-terminal CXCL16 was higher in conditioned media of OvCa cells than IOSE-7576. Compared to OVCAR-3, SKOV-3 cells, which had higher CXCL16, expressed significantly higher transcripts of ADAM10, a protease that cleaves CXCL16. OVCAR-3 cells showed higher CXCR6 specific migration whereas SKOV-3 cells showed more invasion. Difference in invasive potential of these cells was due to modulation of different MMPs after CXCL16 stimulation. Higher CXCR6 expression in serous papillary carcinoma tissues suggests its association with aggressive OvCa. Increased migration-invasion towards CXCL16 implies its role in metastatic spread. Therefore, CXCR6-CXCL16 axis could be used to differentiate between aggressive versus non-aggressive disease and as a target for better prognosis.

Melanoma: Genetic Abnormalities, Tumor Progression, Clonal Evolution and Tumor Initiating Cells

Melanoma is an aggressive neoplasia issued from the malignant transformation of melanocytes, the pigment-generating cells of the skin. It is responsible for about 75% of deaths due to skin cancers. Melanoma is a phenotypically and molecularly heterogeneous disease: cutaneous, uveal, acral, and mucosal melanomas have different clinical courses, are associated with different mutational profiles, and possess distinct risk factors. The discovery of the molecular abnormalities underlying melanomas has led to the promising improvement of therapy, and further progress is expected in the near future. The study of melanoma precursor lesions has led to the suggestion that the pathway of tumor evolution implies the progression from benign naevi, to dysplastic naevi, to melanoma in situ and then to invasive and metastatic melanoma. The gene alterations characterizing melanomas tend to accumulate in these precursor lesions in a sequential order. Studies carried out in recent years have, in part, elucidated the great tumorigenic potential of melanoma tumor cells. These findings have led to speculation that the cancer stem cell model cannot be applied to melanoma because, in this malignancy, tumor cells possess an intrinsic plasticity, conferring the capacity to initiate and maintain the neoplastic process to phenotypically different tumor cells.

High expression of CXC chemokine receptor 6 associates with poor prognosis in patients with clear cell renal cell carcinoma

PURPOSE

Accumulating evidence indicates that CXC chemokine receptor 6 (CXCR6) has a crucial role in cancer development and progression, however, its role in clear cell renal cell carcinoma (ccRCC) remains obscure. The aim of this study is to investigate the prognostic value of CXCR6 expression in patients with ccRCC following surgery.

MATERIALS AND METHODS

This study retrospectively included 239 patients with ccRCC who underwent nephrectomy and had paraffin tissue available at a single center. CXCR6 expression in tumor tissue was evaluated by immunohistochemistry and its associations with overall survival (OS) and recurrence-free survival (RFS) were investigated.

RESULTS

A total of 47.3% tumors were considered as high expression of CXCR6, which was significantly associated with the male sex (P = 0.003) and high Fuhrman grade (P<0.001). A high expression of CXCR6 indicated a reduced OS (P<0.001) and RFS (P = 0.007). Multivariate analysis demonstrated that CXCR6 expression was an independent prognostic factor of OS (hazard ratio = 2.604; 95% CI: 1.338-5.068; P = 0.005) and RFS (hazard ratio = 1.957; 95% CI: 1.065-3.595; P = 0.031). Subgroup analysis found that CXCR6 expression could differentiate survival risks among patients with high-risk disease. Moreover, a nomogram integrating CXCR6 expression and traditional clinical and pathologic features was established and predicted postsurgical recurrence-risk well at 3- and 5-year.

CONCLUSIONS

The expression of CXCR6 in tumor tissue may serve as a potential prognostic biomarker to refine clinical prognosis prediction combined with traditional clinical and pathological analysis for patients with ccRCC after surgery.

Complexity in cancer stem cells and tumor evolution: Toward precision medicine

In this review, we discuss recent advances on the plasticity of cancer stem cells and highlight their relevance to understand the metastatic process and to guide therapeutic interventions. Recent results suggest that the strict hierarchical structure of cancer cell populations advocated by the cancer stem cell model must be reconsidered since the depletion of cancer stem cells leads the other tumor cells to switch back into the cancer stem cell phenotype. This plasticity has important implications for metastasis since migrating cells do not need to be cancer stem cells in order to seed a metastasis. We also discuss the important role of the immune system and the microenvironment in modulating phenotypic switching and suggest possible avenues to exploit our understanding of this process to develop an effective strategy for precision medicine.

Therapeutic implications of cellular and molecular biology of cancer stem cells in melanoma

Melanoma is a form of cancer that initiates in melanocytes. Melanoma has multiple phenotypically distinct subpopulation of cells, some of them have embryonic like plasticity which are involved in self-renewal, tumor initiation, metastasis and progression and provide reservoir of therapeutically resistant cells. Cancer stem cells (CSCs) can be identified and characterized based on various unique cell surface and intracellular markers. CSCs exhibit different molecular pattern with respect to non-CSCs. They maintain their stemness and chemoresistant features through specific signaling cascades. CSCs are weak in immunogenicity and act as immunosupressor in the host system. Melanoma treatment becomes difficult and survival is greatly reduced when the patient develop metastasis. Standard conventional oncology treatments such as chemotherapy, radiotherapy and surgical resection are only responsible for shrinking the bulk of the tumor mass and tumor tends to relapse. Thus, targeting CSCs and their microenvironment niche addresses the alternative of traditional cancer therapy. Combined use of CSCs targeted and traditional therapies may kill the bulk tumor and CSCs and offer a promising therapeutic strategy for the management of melanoma.

CXCL16/CXCR6 chemokine signaling mediates breast cancer progression by pERK1/2-dependent mechanisms

Our previous studies demonstrate that CXCL6/CXCR6 chemokine axis induces prostate cancer progression by the AKT/mTOR signaling pathway; however, its role and mechanisms underlying invasiveness and metastasis of breast cancer are yet to be elucidated. In this investigation, CXCR6 protein expression was examined using high-density tissue microarrays and immunohistochemistry. Expression of CXCR6 shows a higher epithelial staining in breast cancer nest site and metastatic lymph node than the normal breast tissue, suggesting that CXCR6 may be involved in breast cancer (BC) development. In vitro and in vivo experiments indicate that overexpression of CXCR6 in BC cells has a marked effect on increasing cell migration, invasion and metastasis. In contrast, reduction of CXCR6 expression by shRNAs in these cells greatly reduce its invasion and metastasis ability. Mechanistic analyses show that CXCL16/CXCR6 chemokine axis is capable of modulating activation of RhoA through activating ERK1/2 signaling pathway, which then inhibits the activity of cofilin, thereby enhancing the stability of F-actin, responsible for invasiveness and metastasis of BC.

Taken together, our data shows for the first time that the CXCR6 / ERK1/2/ RhoA / cofilin /F-actin pathway plays a central role in the development of BC. Targeting the signaling pathway may prove beneficial to prevent metastasis and provide a more effective therapeutic strategy for BC.

Human skin-derived fibroblasts used as a 'Trojan horse' for drug delivery

BACKGROUND

Drug toxicity currently represents the main challenge of tumour chemotherapy. Our group recently developed a new method for drug delivery inspired by the 'Trojan Horse' concept. Human mesenchymal stem cells (hMSCs) have been shown to play the role of new 'horses' in delivering anti-tumour agents, without involving any genetic manipulation. As human stromal dermal fibroblasts (hSDFs) represent an interesting alternative to hMSCs, being easy to isolate, they could be an ideal candidate for this kind of procedure.

AIM

To investigate whether hSDFs can take up and deliver paclitaxel (PTX) in sufficient concentrations to inhibit a very aggressive melanoma tumour (IgR39) in vitro.

METHODS

hSDFs were primed with high doses of PTX, and then the effect of drug delivery on IgR39 melanoma proliferation in vitro was evaluated using several assays (antiproliferation, transwell cocultures, rosette assays and colony growth assays). Furthermore, the cell cycle and PTX uptake/release mechanism of hSDFs were studied both under both normal and hypoxic conditions.

RESULTS

hSDFs incorporated PTX and then released it with unaffected pharmacological activity, inhibiting human IgR39 melanoma growth in vitro. The hypoxic conditions did not induce changes in cell cycle pattern and the uptake-release mechanism with PTX was not affected.

CONCLUSIONS

hSDFs can be used as a Trojan horse, as the released drug was functionally active. These results indicated that these cells could be used for clinical treatment as the drug was released into the cellular environment and the primed cells underwent apoptosis.

Expression of stem cell markers nanog and PSCA in gastric cancer and its significance

The present study aimed to determine the expression of stem cell markers Nanog compared with PSCA in gastric cancer tissues and adjacent normal tissues, and to investigate the association between tumor stem cells and initiation, progression, metastasis, and prognosis of gastric cancer. One hundred chemotherapy- and radiotherapy-naive patients with pathologically confirmed gastric cancer were enrolled from the General Surgery Department and Surgical Oncology Department of the Affiliated Hospital of Inner Mongolia Medical University (Hohhot, P.R. China), between October 2011 and June 2013. Surgically resected specimens of cancer tissues and adjacent normal tissues (>5 cm from the boundary of cancerous component) were collected. The mRNA expression levels of Nanog and PSCA in those tissues was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The correlation between the expression of stem cell markers Nanog and PSCA in gastric cancer tissues and clinicopathological factors was analyzed. The qPCR results demonstrated that the relative expression of Nanog was increased in gastric cancer tissues compared with in the adjacent tissues (P<0.05); and relative expression of PSCA was reduced in gastric cancer tissues compared with adjacent tissues (P<0.05). The expression of Nanog and PSCA in gastric cancer tissues was associated with tumor differentiation. The expression of Nanog was increased in poorly-differentiated and undifferentiated tumors compared with moderately- and well-differentiated tumors (P<0.05). The expression of PSCA was reduced in poorly differentiated and undifferentiated tumors compared with moderately- and well-differentiated tumors (P<0.05). However, the expression of Nanog and PSCA was not associated with age, gender, tumor size, TNM stage, depth of invasion, or lymph node metastasis. Therefore, Nanog and PSCA may have potential as molecular markers to reflect the differentiation status of gastric cancer.

Common stemness regulators of embryonic and cancer stem cells

Pluripotency of embryonic stem cells (ESCs) and induced pluripotent stem cells is regulated by a well characterized gene transcription circuitry. The circuitry is assembled by ESC specific transcription factors, signal transducing molecules and epigenetic regulators. Growing understanding of stem-like cells, albeit of more complex phenotypes, present in tumors (cancer stem cells), provides a common conceptual and research framework for basic and applied stem cell biology. In this review, we highlight current results on biomarkers, gene signatures, signaling pathways and epigenetic regulators that are common in embryonic and cancer stem cells. We discuss their role in determining the cell phenotype and finally, their potential use to design next generation biological and pharmaceutical approaches for regenerative medicine and cancer therapies.

Overshoot during phenotypic switching of cancer cell populations

The dynamics of tumor cell populations is hotly debated: do populations derive hierarchically from a subpopulation of cancer stem cells (CSCs), or are stochastic transitions that mutate differentiated cancer cells to CSCs important? Here we argue that regulation must also be important. We sort human melanoma cells using three distinct cancer stem cell (CSC) markers - CXCR6, CD271 and ABCG2 - and observe that the fraction of non-CSC-marked cells first overshoots to a higher level and then returns to the level of unsorted cells. This clearly indicates that the CSC population is homeostatically regulated. Combining experimental measurements with theoretical modeling and numerical simulations, we show that the population dynamics of cancer cells is associated with a complex miRNA network regulating the Wnt and PI3K pathways. Hence phenotypic switching is not stochastic, but is tightly regulated by the balance between positive and negative cells in the population. Reducing the fraction of CSCs below a threshold triggers massive phenotypic switching, suggesting that a therapeutic strategy based on CSC eradication is unlikely to succeed.

MEK inhibitor diminishes nasopharyngeal carcinoma (NPC) cell growth and NPC-induced osteoclastogenesis via modulating CCL2 and CXCL16 expressions

Nasopharyngeal carcinoma (NPC) is a common malignancy in southern China and Southeast Asia. NPC frequently metastasizes to the bone in advanced patients resulting in high mortality. The molecular mechanisms for NPC development and cancer-induced bone lesions are unclear. In this study, we firstly determined chemokine receptor CCR2 and CXCR6 expressions in clinical specimens and CNE2, SUNE1, CNE1, and HK1 cell lines. Then, we measured chemokine CCL2 and CXCL16 production in these NPC cell lines by ELISA. Expression levels of these chemokines and their receptors were observed to positively correlate with tumor aggressiveness. Furthermore, U0126 (MEK inhibitor) was used to treat these NPC cell lines. CCL2 and CXCL16 expression levels and cell proliferation were significantly inhibited by U0126 in a dose- and time-dependent manner. Finally, we collected conditioned medium (CM) from NPC cell cultures in the presence of U0126 treatment. When mouse bone marrow non-adherent cells were treated with the CM, the numbers of multinucleated osteoclast formation were dramatically diminished. These results indicate that MEK inhibitor diminishes NPC cell proliferation and NPC-induced osteoclastogenesis via modulating CCL2 and CXCL16 expressions. This study provides novel therapeutic targets such as CCL2/CCR2 and CXCL16/CXCR6 for advanced NPC patients.

Blockade of the CXCR6 signaling inhibits growth and invasion of hepatocellular carcinoma cells through inhibition of the VEGF expression

Chemokines have been shown to play a critical role in tumor development and progression. However, little is known about the function and molecular mechanisms of CXCR6 in multiple malignancies. In the present study, we aimed to investigate the role of CXCR6 in human hepatocellular carcinoma (HCC). The expression of CXCR6 was examined by immunohistochemical assay using a tissue microarray procedure. A loss-of-function experiment was performed to explore the effects of lentivirus-mediated CXCR6 shRNA (shCXCR6) on cell proliferation and invasive potential by MTT and Transwell assays in HCC cell line (SMMC-7721). It was found that the expression of CXCR6 protein was significantly increased in HCC tissues compared with that in adjacent non-cancerous tissues (ANCT) (63.04&#x0025; vs 36.96&#x0025;, P=0.019), and correlated with the lymph-vascular space invasion in HCC patients (P=0.038). Knockdown of CXCR6 repressed cell proliferation and invasion of HCC cells followed by the down-regulation of vascular endothelial growth factor (VEGF). Taken together, our findings show that high expression of CXCR6 is positively associated with distant invasion of HCC patients, and blockade of CXCR6 signaling suppresses the growth and invasion of HCC cells through inhibition of the VEGF expression, suggesting that CXCR6 may represent a promising therapeutic target for the treatment of HCC.

CD133⁺ melanoma subpopulation acquired resistance to caffeic acid phenethyl ester-induced apoptosis is attributed to the elevated expression of ABCB5: significance for melanoma treatment

According to the cancer stem-like cell (CSC) hypothesis, neoplastic clones are maintained by a small fraction of cells with stem cell properties. Also, melanoma resistance to chemo- and radiotherapy is thought to be attributed to melanoma stem-like cells (MSCs). Caffeic acid phenethyl ester (CAPE) is a bioactive molecule, whose antitumor activity is approved in different tumor types. CAPE induced both apoptosis and E2F1 expression in CD133(-), but not in CD133(+) melanoma subpopulations. The resistance of CD133(+) melanoma subpopulation is attributed to the enhanced drug efflux mediated by ATP-binding cassette sub-family B member 5 (ABCB5), since the knockdown of ABCB5 was found to sensitize CD133(+) cells to CAPE. CAPE-induced apoptosis is mediated by E2F1 as evidenced by the abrogation of apoptosis induced in response to the knockdown of E2F1. The functional analysis of E2F1 in CD133(+) melanoma subpopulation demonstrated the ability of E2F1 gene transfer to trigger apoptosis of CD133(+) cells and to enhance the activation of apoptosis signal-regulating kinase (ASK1), c-Jun N-terminal kinase and p38, and the DNA-binding activities of the transcription factors AP-1 and p53. Also, the induction of E2F1 expression was found to enhance the expression of the pro-apoptotic proteins Bax, Noxa and Puma, and to suppress the anti-apoptotic protein Mcl-1. Using specific pharmacological inhibitors we could demonstrate that E2F1 overcomes the chemo-resistance of MSCs/CD133(+) cells by a mechanism mediated by both mitochondrial dysregulation and ER-stress-dependent pathways. In conclusion, our data addresses the mechanisms of CAPE/E2F1-induced apoptosis of chemo-resistant CD133(+) melanoma subpopulation.

The role of chemoattractant receptors in shaping the tumor microenvironment

Chemoattractant receptors are a family of seven transmembrane G protein coupled receptors (GPCRs) initially found to mediate the chemotaxis and activation of immune cells. During the past decades, the functions of these GPCRs have been discovered to not only regulate leukocyte trafficking and promote immune responses, but also play important roles in homeostasis, development, angiogenesis, and tumor progression. Accumulating evidence indicates that chemoattractant GPCRs and their ligands promote the progression of malignant tumors based on their capacity to orchestrate the infiltration of the tumor microenvironment by immune cells, endothelial cells, fibroblasts, and mesenchymal cells. This facilitates the interaction of tumor cells with host cells, tumor cells with tumor cells, and host cells with host cells to provide a basis for the expansion of established tumors and development of distant metastasis. In addition, many malignant tumors of the nonhematopoietic origin express multiple chemoattractant GPCRs that increase the invasiveness and metastasis of tumor cells. Therefore, GPCRs and their ligands constitute targets for the development of novel antitumor therapeutics.

Mechanical properties of growing melanocytic nevi and the progression to melanoma

Melanocytic nevi are benign proliferations that sometimes turn into malignant melanoma in a way that is still unclear from the biochemical and genetic point of view. Diagnostic and prognostic tools are then mostly based on dermoscopic examination and morphological analysis of histological tissues. To investigate the role of mechanics and geometry in the morpholgical dynamics of melanocytic nevi, we study a computation model for cell proliferation in a layered non-linear elastic tissue. Numerical simulations suggest that the morphology of the nevus is correlated to the initial location of the proliferating cell starting the growth process and to the mechanical properties of the tissue. Our results also support that melanocytes are subject to compressive stresses that fluctuate widely in the nevus and depend on the growth stage. Numerical simulations of cells in the epidermis releasing matrix metalloproteinases display an accelerated invasion of the dermis by destroying the basal membrane. Moreover, we suggest experimentally that osmotic stress and collagen inhibit growth in primary melanoma cells while the effect is much weaker in metastatic cells. Knowing that morphological features of nevi might also reflect geometry and mechanics rather than malignancy could be relevant for diagnostic purposes.

Established and Emerging Biomarkers in Cutaneous Malignant Melanoma

In an era of personalized medicine, disease specific biomarkers play an increasing role in the stratification of high-risk patient groups. Cutaneous malignant melanoma is the most deadly form of skin cancer with an ever-increasing global incidence, especially in patients under 35-years of age. Despite the excellent prognosis for patients diagnosed with early stage disease, metastatic disease still carries significant overall mortality. Biomarkers aim not only to identify high-risk patients, but also to provide potential therapeutic targets for differing patient subgroups. Furthermore, accessibility to tissue samples from a range of disease stages in malignant melanoma, unlike most other solid tissue tumours, provides the unique opportunity to explore the biology of tumour progression that may be relevant in the biology of cancer as a whole. Over the past decade, there have been major advances in targeted therapies, providing new avenues and hope to patients with this devastating disease. This review will focus on most up to date histological, serological and molecular biomarkers in malignant melanoma.

Isolation of melanoma cell subpopulations using negative selection

Melanomas are phenotypically and functionally heterogeneous tumors comprising of distinct subpopulations that drive disease progression and are responsible for resistance to therapy. Identification and characterization of such subpopulations are highly important to develop novel targeted therapies. However, this can be a challenging task as there is a lack of clearly defined markers to distinguish the melanoma subpopulations from a general tumor cell population. Also, there is a lack of optimal isolation methods and functional assays that can fully recapitulate their phenotype. Here we describe a method for isolating tumor cells from fresh human tumor tissue specimens using an antibody coupled magnetic bead sorting technique that is well established in our laboratory. Thus, melanoma cells are enriched by negative cell sorting and elimination of non-tumor cell population such as erythrocytes, leukocytes, and endothelial cells. Enriched unmodified tumor cells can be further used for phenotypic and functional characterization of melanoma subpopulations.

Antibody-drug conjugates: targeting melanoma with cisplatin encapsulated in protein-cage nanoparticles based on human ferritin

A novel antibody-drug conjugate (ADC) was synthesized incorporating ferritin-based nanoparticles. An average of three molecules of monoclonal antibody (mAb) Ep1 to the human melanoma-specific antigen CSPG4 were conjugated to a single ferritin cage encapsulating about 50 cisplatin molecules (HFt-Pt-Ep1). The HFt-Pt-Ep1 nanoparticle had an estimated molecular size of about 900 kD and 33 nm, and flow cytometry demonstrated specific binding to a CSPG4(+) melanoma cell line, but not to a CSPG4(-) breast carcinoma cell line. As compared to the cisplatin-containing ferritin nanoparticle alone (HFt-Pt), which inhibited thymidine incorporation more efficiently in breast carcinoma than melanoma cells, the mAb-derivatized HFt-Pt-Ep1 nanoparticle had a 25-fold preference for the latter. A similar preference for melanoma was observed upon systemic intravenous administration of HFt-Pt-Ep1 to nude mice xenotransplanted with pre-established, palpable melanoma and breast carcinoma tumors. Thus, we have been able to determine precise combinations and stoichiometric relationships between mAbs and nanoparticle protein cages, whereby the latter lose their tropism for ubiquitously distributed cellular receptors, and acquire instead remarkably lineage-selective binding. HFt-Pt-Ep1 is therefore an interesting model to improve the therapeutic index of antiblastic therapy in a tumor such as melanoma, which at its advanced stages is totally refractory to mono- and combination-chemotherapy.

CXCL16 and CXCR6 in Ewing sarcoma family tumor

Chemokines are a family of peptide mediators that play an essential role in cellular migration and intracellular communication in tumor cells as well as immune cells. We hypothesized that the CXCL16-CXCR6 ligand-receptor system plays an important role in Ewing sarcoma (ES) family tumor (ESFT) progression. Using real-time quantitative reverse transcription-polymerase chain reaction, we investigated the mRNA expression of CXCL16, CXCR6, and ADAM 10 in various cell lines. We also investigated the expression of CXCL16, CXCR6, ADAM 10, and ADAM 17 in tissue samples from 61 ESFT patients using immunohistochemistry. The mRNA expression levels of CXCL16 and CXCR6 in the ES cell line were higher than those in the other cell lines. Immunohistochemical staining revealed that CXCL16 and CXCR6 were highly expressed in tumor cells of ESFT and showed a positive correlation between them. The expression of CXCL16 and CXCR6 was associated with the occurrence of lung metastasis. Univariate analysis revealed that CXCL16 or CXCR6 expression was associated with worse prognosis of ESFT patients. In addition, CXCL16 and CXCR6 expression was associated with shorter overall survival irrespective of other prognostic factors. Our results suggest that the CXCL16/CXCR6 axis appears to be important in the progression of ESFT, resulting in more aggressive clinical behavior. Furthermore, there may be a decrease in the overall survival in ESFT patients who have tumors that stain strongly for CXCL16 and CXCR6.

CXC chemokine ligand 16, inversely correlated with CD99 expression in Hodgkin Reed-Sternberg cells, is widely expressed in diverse types of lymphomas

The present study examined a correlation between CXC chemokine ligand 16 (CXCL16) and cell differentiation antigen 99 (CD99) expression and investigated the role of CXCL16 in human lymphoma cell lines and clinical samples. Cytokine antibody arrays were used to measure the differentially expressed cytokines in tumor tissues. The expression of CXCL16 and CD99 was analyzed by quantitative PCR (qPCR) and western blotting, while the pathways involved were assessed by western blotting and enzyme-linked immunosorbent assay (ELISA). The expression of CXCL16 was investigated in 9 lymphoma cell lines (L428, RPMI-8226, KM3, Jurkat, OCI-Ly1, OCI-Ly8, OCI-Ly10, Karpass299 and Raji) as well as in clinical lymphoma samples using qPCR, western blotting and immunochemistry. Soluble CXCL16 (sCXCL16) levels were measured by ELISA and proliferation was analyzed by CCK‑8 proliferation assays. CXCL16 was one of the upregulated chemokines when lymphoma cells where transferred from in vitro to in vivo conditions. The increased expression and secretion of CXCL16 paralleled with a decrease of mCD99L2 and was accompanied by NF-κB pathway activation and vice versa. CXCL16 was expressed in all 9 lymphoma cell lines with the highest levels in the Hodgkin lymphoma (HL) cell line L428, the plasma cell-derived cell lines RPMI‑8226 and KM3 and the T leukemia-derived cell line Jurkat. Higher levels of sCXCL16 were secreted by L428 cells, the diffuse large B-cell lymphoma (DLBCL)-derived cell lines (OCI-Ly1, OCI-Ly8 and OCI-Ly10) and Jurkat cells. CXCL16 was widely expressed in clinical samples of lymphoma patients with higher levels in HL compared to non-Hodgkin lymphoma. Human recombinant CXCL16 had no significant effect on L428 cell proliferation, but was able to stimulate CD4+ T lymphocytes to proliferate. CXCL16, inversely correlated with CD99 expression in Hodgkin Reed-Sternberg (H/RS) cells, is widely expressed in diverse types of lymphomas.

CXCR6: the role of environment in tumor progression. Challenges for therapy

The role of chemokines in tumor progression is an essential event that leads to homing and metastasis of tumor cells in a receptor-dependent, organ specific manner. In recent years, the involvement of CXCR6 and its ligand CXCL16 in tumor progression is becoming more evident. Here I review the recent literature on CXCR6/CXCL16. Since CXCR6 was shown recently to be involved in stem cell self renewal and the same cytokine is expressed by a subpopulation of melanoma cells, I discuss new evidences on cancer stem cell theory and the involvement of CXCR6. In particular, in the effort to develop more specific strategies to stop the tumor growth, the present review proposes and discusses the possibility to modulate tumor self renewal affecting asymmetric/symmetric cell division targeting specific factors such as CXCR6.

Interpretation of interlocking key issues of cancer stem cells in malignant solid tumors

OBJECTIVE

In this review, several interlinking issues related to cancer stem cells (CSCs) in malignant solid tumors are sequentially discussed.

METHODS

A literature search was performed using PubMed, Web of Science and the Cochrane library, combining the words CSCs, solid tumor, isolation, identification, origination, therapy, target and epithelial-mesenchymal transition.

RESULTS

Because a primary problem is the isolation of CSCs, we first analyzed the advantages and disadvantages of recently used methods, which were mostly based on the physical or immunochemical characteristics of CSCs. Once CSCs are isolated, they should be identified by their stem cell properties. Here, we suggest how to establish a standard identification strategy. We also focused on the origination hypotheses of CSCs. The supporting molecular mechanisms for each theory were thoroughly analyzed and integrated. Especially, epithelial- mesenchymal transition is an increasingly recognized mechanism to generate CSCs that are endowed with a more invasive and metastatic phenotype. Finally, we discuss putative strategies of eliminating CSCs as effective cancer therapies.

CONCLUSION

After several interlocking issues of CSCs are thoroughly clarified, these CSCs in solid malignant tumors may specifically be targeted, which raises a new hope for eliminating these tumors.

The emerging role of CXC chemokines and their receptors in cancer

Chemokines and their receptors have a multifaceted role in tumor biology and are implicated in nearly all aspects of cancer growth, survival and dissemination. Modulation of the interaction between chemokines and their cell surface receptor is, therefore, a promising area for the development of new cancer medicines. In this review, we look at the compelling evidence that is emerging to support targeting CXC chemokines, also known as family α chemokines, as novel therapeutic strategies in the treatment of cancer.

Melanoma molecular classes and prognosis in the postgenomic era

Gene expression profiling is a powerful method to classify human tumours on the basis of biological aggressiveness, response to therapy, and outcome for the patient, but its application in melanoma lags behind that of other cancers. From more than 100 articles available on the topic, we selected 14 focusing on patients' outcome. We review and briefly discuss salient findings, and list ten reasons why melanoma molecular classes are not yet used in clinical diagnosis and prognosis. The available evidence suggests that we are on the verge of creating a framework for the use of melanoma molecular classes in prognosis, but so far there is little consensus to put together informative diagnostic and prognostic gene sets.

CXCR6 upregulation contributes to a proinflammatory tumor microenvironment that drives metastasis and poor patient outcomes in hepatocellular carcinoma

CXC chemokines and their cognate receptors have been implicated widely in cancer pathogenesis. In this study, we report a critical causal relationship between CXCR6 expression and tumorigenesis in the setting of human hepatocellular carcinoma (HCC). Among the CXC chemokine receptors, only CXCR6 was detected in all the hepatoma cell lines studied. Moreover, in HCC tissue, CXCR6 expression was significantly higher than in noncancerous liver tissues. Reduction of CXCR6 or its ligand CXCL16 in cancer cells reduced cell invasion in vitro and tumor growth, angiogenesis, and metastases in vivo. Importantly, loss of CXCR6 led to reduced Gr-1+ neutrophil infiltration and decreased neoangiogenesis in hepatoma xenografts via inhibition of proinflammatory cytokine production. Clinically, high expression of CXCR6 was an independent predictor of increased recurrence and poor survival in HCCs. Human HCC samples expressing high levels of CXCR6 also contained an increased number of CD66b+ neutrophils and microvessels, and the combination of CXCR6 and neutrophils was a superior predictor of recurrence and survival than either marker used alone. Together, our findings suggest that elevated expression of CXCR6 promotes HCC invasiveness and a protumor inflammatory environment and is associated with poor patient outcome. These results support the concept that inhibition of the CXCR6-CXCL16 pathway may improve prognosis after HCC treatment.

MicroRNA and cutaneous melanoma: from discovery to prognosis and therapy

Melanoma incidence and associated mortality continue to increase worldwide. The lack of treatments with durable responses for stage IV melanoma may be due, at least in part, to an incomplete understanding of the molecular mechanisms that regulate tumor initiation and/or progression to metastasis. Recent evidence supports miRNA dysregulation in melanoma impacting several well-known pathways such as the PI3K/AKT or RAS/MAPK pathways, but also underexplored cellular processes like protein glycosylation and immune modulation. There is also increasing evidence that miRNA can improve patient prognostic classification over the classical staging system and provide new therapeutic opportunities. The integration of this recently acquired knowledge with known molecular alterations in protein coding genes characteristic of these tumors (i.e., BRAF and NRAS mutations, CDKN2A inactivation) is critical for a complete understanding of melanoma pathogenesis. Here, we compile the evidence of the functional roles of miRNAs in melanomagenesis and progression, and of their clinical utility as biomarkers, prognostic tools and potential therapeutic targets. Characterization of miRNA alterations in melanoma may provide new angles for therapeutic intervention, help to decipher mechanisms of drug resistance, and improve patient classification for disease surveillance and clinical benefit.

Do cancer cells undergo phenotypic switching? The case for imperfect cancer stem cell markers

The identification of cancer stem cells in vivo and in vitro relies on specific surface markers that should allow to sort cancer cells in phenotypically distinct subpopulations. Experiments report that sorted cancer cell populations after some time tend to express again all the original markers, leading to the hypothesis of phenotypic switching, according to which cancer cells can transform stochastically into cancer stem cells. Here we explore an alternative explanation based on the hypothesis that markers are not perfect and are thus unable to identify all cancer stem cells. Our analysis is based on a mathematical model for cancer cell proliferation that takes into account phenotypic switching, imperfect markers and error in the sorting process. Our conclusion is that the observation of reversible expression of surface markers after sorting does not provide sufficient evidence in support of phenotypic switching.

Head and neck cancer stem cells

Most cancers contain a small sub-population of cells that are endowed with self-renewal, multipotency, and a unique potential for tumor initiation. These properties are considered hallmarks of cancer stem cells. Here, we provide an overview of the field of cancer stem cells with a focus on head and neck cancers. Cancer stem cells are located in the invasive fronts of head and neck squamous cell carcinomas (HNSCC) close to blood vessels (perivascular niche). Endothelial cell-initiated signaling events are critical for the survival and self-renewal of these stem cells. Markers such as aldehyde dehydrogenase (ALDH), CD133, and CD44 have been successfully used to identify highly tumorigenic cancer stem cells in HNSCC. This review briefly describes the orosphere assay, a method for in vitro culture of undifferentiated head and neck cancer stem cells under low attachment conditions. Notably, recent evidence suggests that cancer stem cells are exquisitely resistant to conventional therapy and are the "drivers" of local recurrence and metastatic spread. The emerging understanding of the role of cancer stem cells in the pathobiology of head and neck squamous cell carcinomas might have a profound impact on the treatment paradigms for this malignancy.

Thoughts about cancer stem cells in solid tumors

Cancer chemotherapy efficacy is frequently impaired by either intrinsic or acquired tumor resistance. A fundamental problem in cancer research is identifying the cell type that is capable of sustaining neoplastic growth and its origin from normal tissue cells. In recent years, the cancer stem cell (CSC) theory has changed the classical view of tumor growth and therefore the therapeutic perspective. Overcoming intrinsic and acquired resistance of cancer stem/progenitor cells to current clinical treatments represents a major challenge in treating and curing the most aggressive and metastatic cancers. On the other hand, the identification of CSCs in vivo and in vitro relies on specific surface markers that should allow the sorting cancer cells into phenotypically distinct subpopulations. In the present review, recent papers published on CSCs in solid tumors (breast, prostate, brain and melanoma) are discussed, highlighting critical points such as the choice of markers to sort CSCs and mouse models to demonstrate that CSCs are able to replicate the original tumor. A discussion of the possible role of aldehyde dehydrogenase and CXCR6 biomarkers as signaling molecules in CSCs and normal stem cells is also discussed. The author believes that efforts have to be made to investigate the functional and biological properties of putative CSCs in cancer. Developing diagnostic/prognostic tools to follow cancer development is also a challenge. In this connection it would be useful to develop a multidisciplinary approach combining mathematics, physics and biology which merges experimental approaches and theory. Biological models alone are probably unable to resolve the problem completely.

Human breast and melanoma cancer stem cells biomarkers

Cancer progression in humans is difficult to infer because we do not routinely sample patients at multiple stages of their disease. The identification cancer stem cell (CSC) subpopulations inside tumor opens a new view of cancer development, since it implies that tumors can only be eradicated by targeting CSCs. Several markers have been proposed in the literature to identify CSCs both in breast and melanoma but no consensus has been reached, leading to the hypothesis that the CSC phenotype might be dynamically switched. Herein we provide a critical discussion of the biological markers described in the literature for breast cancer and melanoma. Due to its complexity the field would benefit from an interdisciplinary approach to investigate tumor heterogeneity and its progression. Similar considerations could also be relevant for normal tissue stem cells.

Senescent cells in growing tumors: population dynamics and cancer stem cells

Tumors are defined by their intense proliferation, but sometimes cancer cells turn senescent and stop replicating. In the stochastic cancer model in which all cells are tumorigenic, senescence is seen as the result of random mutations, suggesting that it could represent a barrier to tumor growth. In the hierarchical cancer model a subset of the cells, the cancer stem cells, divide indefinitely while other cells eventually turn senescent. Here we formulate cancer growth in mathematical terms and obtain predictions for the evolution of senescence. We perform experiments in human melanoma cells which are compatible with the hierarchical model and show that senescence is a reversible process controlled by survivin. We conclude that enhancing senescence is unlikely to provide a useful therapeutic strategy to fight cancer, unless the cancer stem cells are specifically targeted.

It is commonly believed that cell senescence – the loss of replicative capacity of cells – acts as a barrier for tumor growth. Here we follow the evolution of senescence markers in melanoma cells and find that while most cancer cells eventually turn senescent, this is at root irrelevant for the long-term growth rate of a tumor. To demonstrate this, we construct a mathematical population dynamics model incorporating cancer stem cells which is able to reproduce quantitatively the experimental data. Our results support the existence of cancer stem cells in melanoma and explain why it is difficult to fight cancer by inducing senescence in cancer cells. Only a fraction of the cells are susceptible to senescence, but those cells are irrelevant for tumor growth. A successful therapeutic strategy should instead target cancer stem cells, which are, however, likely to be strongly resistant to drug induced senescence.

Intratumoral heterogeneity as a therapy resistance mechanism: role of melanoma subpopulations

Malignant melanoma is an aggressive form of skin cancer whose incidence continues to increase worldwide. Increased exposure to sun, ultraviolet radiation, and the use of tanning beds can increase the risk of melanoma. Early detection of melanomas is the key to successful treatment mainly through surgical excision of the primary tumor lesion. But in advanced stage melanomas, once the disease has spread beyond the primary site to distant organs, the tumors are difficult to treat and quickly develop resistance to most available forms of therapy. The advent of molecular and cellular techniques has led to a better characterization of tumor cells revealing the presence of heterogeneous melanoma subpopulations. The discovery of gene mutations and alterations of cell-signaling pathways in melanomas has led to the development of new targeted drugs that show dramatic response rates in patients. Single-agent therapies generally target one subpopulation of tumor cells while leaving others unharmed. The surviving subpopulations will have the ability to repopulate the original tumors that can continue to progress. Thus, a rational approach to target multiple subpopulations of tumor cells with a combination of drugs instead of single-agent therapy will be necessary for long-lasting inhibition of melanoma lesions. In this context, the recent development of immune checkpoint reagents provides an additional armor that can be used in combination with targeted drugs to expand the presence of melanoma reactive T cells in circulation to prevent tumor recurrence.

SACK-expanded hair follicle stem cells display asymmetric nuclear Lgr5 expression with non-random sister chromatid segregation

We investigated the properties of clonally-expanded mouse hair follicle stem cells (HF-SCs) in culture. The expansion method, suppression of asymmetric cell kinetics (SACK), is non-toxic and reversible, allowing evaluation of the cells' asymmetric production of differentiating progeny cells. A tight association was discovered between non-random sister chromatid segregation, a unique property of distributed stem cells (DSCs), like HF-SCs, and a recently described biomarker, Lgr5. We found that nuclear Lgr5 expression was limited to the HF-SC sister of asymmetric self-renewal divisions that retained non-randomly co-segregated chromosomes, which contain the oldest cellular DNA strands, called immortal DNA strands. This pattern-specific Lgr5 association poses a potential highly specific new biomarker for delineation of DSCs. The expanded HF-SCs also maintained the ability to make differentiated hair follicle cells spontaneously, as well as under conditions that induced cell differentiation. In future human cell studies, this capability would improve skin grafts and hair replacement therapies.

The biology of head and neck cancer stem cells

Emerging evidence indicates that a small population of cancer cells is highly tumorigenic, endowed with self-renewal, and has the ability to differentiate into cells that constitute the bulk of tumors. These cells are considered the "drivers" of the tumorigenic process in some tumor types, and have been named cancer stem cells. Epithelial-mesenchymal transition (EMT) appears to be involved in the process leading to the acquisition of stemness by epithelial tumor cells. Through this process, cells acquire an invasive phenotype that may contribute to tumor recurrence and metastasis. Cancer stem cells have been identified in human head and neck squamous cell carcinomas (HNSCC) using markers such as CD133 and CD44 expression, and aldehyde dehydrogenase (ALDH) activity. The head and neck cancer stem cells reside primarily in perivascular niches in the invasive front where endothelial-cell initiated events contribute to their survival and function. In this review, we discuss the state-of-the-knowledge on the pathobiology of cancer stem cells, with a focus on the impact of these cells to head and neck tumor progression.