Cancer stem cells: problems for therapy?

Biological characteristics of a cell subpopulation in tongue squamous cell carcinoma

OBJECTIVES

To isolate the CD133+CD44+ cells from human tongue squamous cell carcinoma (TSCC) Tca8113 cell line and investigate biological characteristics of them.

MATERIALS AND METHODS

Immunomagnetic microbeads were applied to sort the CD133+CD44+ cells. Flow cytometry was used to detect isolation purity. The proliferation, clone-formation efficiencies, invasion and migration, gene expressions, and tumor-formation abilities were analyzed among CD133+CD44+, CD133-CD44-, and total population of cells.

RESULTS

The average purities of CD133+ and CD44+ cells reached 97.3% and 98.7%, respectively. The proliferation of CD133+CD44+ cells was significantly higher than the other two groups. The clone-forming efficiency of three groups was 70%, 8%, and 14%, respectively. The average invaded and migrated cell numbers of CD133+CD44+ and total population cells were 132 and 36.2, 311.6, and 156.2, respectively. The expressions of Bcl-2 and Sox2 in CD133+CD44+ cells were significantly higher than those in total population cells. A total of 10(4) CD133+CD44+ cells could form secondary tumors in nude mice, while the total population group needed 10(6) cells.

CONCLUSIONS

The CD133+CD44+ subpopulation cells possess stem-like characteristics. They appear to be the potential targets for future biology therapy of human TSCC.

Investigational Notch and Hedgehog inhibitors--therapies for cardiovascular disease

INTRODUCTION

During the past decade, a variety of Notch and Hedgehog pathway inhibitors have been developed for the treatment of several cancers. An emerging paradigm suggests that these same gene regulatory networks are often recapitulated in the context of cardiovascular disease and may now offer an attractive target for therapeutic intervention.

AREAS COVERED

This article briefly reviews the profile of Notch and Hedgehog inhibitors that have reached the preclinic and clinic for cancer treatment and discusses the clinical issues surrounding targeted use of these inhibitors in the treatment of vascular disorders.

EXPERT OPINION

Preclinical and clinical data using pan-Notch inhibitors (γ-secretase inhibitors) and selective antibodies to preferentially target notch receptors and ligands have proven successful but concerns remain over normal organ homeostasis and significant pathology in multiple organs. By contrast, the Hedgehog-based drug pipeline is rich with more than a dozen Smoothened (SMO) inhibitors at various stages of development. Overall, refined strategies will be necessary to harness these pathways safely as a powerful tool to disrupt angiogenesis and vascular proliferative phenomena without causing prohibitive side effects already seen with cancer models and patients.

Induction of metastatic cancer stem cells from the NK/LAK-resistant floating, but not adherent, subset of the UP-LN1 carcinoma cell line by IFN-γ

As an advanced status of cancer stem cells (CSCs), metastatic CSCs (mCSCs) have been proposed to be the essential seeds that initiate tumor metastasis. However, the biology of mCSCs is poorly understood. In this study, we used a lymph node (LN) metastatic CEA-producing carcinoma cell line, UP-LN1, characterized by the persistent appearance of adherent (A) and floating (F) cells in culture, to determine the distribution of CSCs and mechanisms for the induction of mCSCs. F and A cells displayed distinct phenotypes, CD44(high)/CD24(low) and CD44(low)/CD24(high), respectively. The CSC-rich nature of F cells was typified by stronger expression of multiple drug resistance genes and a 7.8-fold higher frequency of tumor-initiating cells in NOD/SCID mice when compared with A cells. F cells showed a greater depression in HLA class I expression and an extreme resistance to NK/LAK-mediated cytolysis. Moreover, the NK/LAK-resistant F cells were highly susceptible to IFN-γ-mediated induction of surface CXCR4, with concomitant downregulation of cytoplasmic CXCL12 expression, whereas these two parameters remained essentially unchanged in NK/LAK-sensitive A cells. Following the induction of surface CXCR4, enhanced migratory/invasive potential of F cells was demonstrated by in vitro assays. Confocal immunofluorescence microscopy showed the two distinct phenotypes of F and A cells could be correspondingly identified in monodispersed and compact tumor cell areas within the patient's LN tumor lesion. In response to IFN-γ or activated NK/LAK cells, the CXCR4(+) mCSCs could be only induced from the CSCs, which were harbored in the highly tumorigenic CD44(high)/CD24(low) F subset. Our results revealed the complexity and heterogeneity of the CSC of this cell line/tumor and the differential immunomodulatory roles of F and A cells. A better understanding of the interactions among different classes of CSCs and their niches may assist us in eradicating the CSCs/mCSCs through targeted immunotherapy, chemotherapy, or both.

Moving from the laboratory bench to patients' bedside: considerations for effective therapy with stem cells

Although stem cell therapy is not a new field, the field was limited to transplantation of hematopoietic stem cells. Such transplantation has provided invaluable information for the emerging field with new stem cells. Mesenchymal stem cells (MSCs) are an attractive source for therapy; reduced ethical concern, ease in expansion, as off-the-shelf stem cells. MSCs exert immune suppressive properties, providing them with the potential for immune suppressive therapy such as autoimmunity, asthma, allergic rhinitis and graft versus host disease. In addition, MSCs, as well as other stem cells, can be applied for bone and cartilage repair, cardiovascular disease, and neural repair/protection. The data thus far with MSCs are mixed. This review discusses the immune-enhancing properties of MSCs to explain the possible confounds of inflammatory microenvironment in the MSCs therapy. Although this review focuses on MSCs, the information can be extrapolated to other stem cells. The review summarizes the biology of MSCs, including multilineage differentiation potential, transdifferentiation capability, and immunological effects. We emphasize the key concepts that may predict the use of these cells in medicine, namely, the application of these cells from the bench to the bedside. Prospects on immunotherapy, neuroregeneration, and cardiovascular repair are used as examples of tissue repair.

Inducing stem cell differentiation using low intensity laser irradiation: a possible novel therapeutic intervention

Developments in adult stem cell (ASC) potentiation have contributed to excitement in the field of stem cell-based therapy. The use of ASCs not only increases therapeutic treatment possibilities but successful use of multipotent cells for gene therapy has been demonstrated in animal models [1]. Concurrent ability of stem cells (SCs) to either contribute to disease development, as identified in cancer stem cells (CSCs), or to replace diseased tissue by induced differentiation using selected growth factors, has highlighted the intricate molecular and cellular mechanisms. Adipose derived stem cells (ADSCs) are capable of self-renewal and respond well to induced differentiation [2]. Auto-immunity and transplant rejection may become minor limitations when selective induction of immunological nonresponsiveness to specific antigens or tissues become possible using autologous cell sources [3]. CSCs initiate tumorogenesis, can generate differentiated daughter cells or undergo self-renewal while thought to instigate tumour regeneration post-treatment. Therapy targeting CSCs has failed to provide feasible alternatives to conventional cancer treatment. Low intensity laser irradiation (LILI), induce a biostimulatory response in several tissue types in addition to a dose-response effect to the detriment of cellular degeneration. Potential of LILI to induce CSC differentiation and subsequent cytotoxic therapy to prevent tumour regeneration is explored in this mini-review.

Notch is an essential upstream regulator of NF-κB and is relevant for survival of Hodgkin and Reed-Sternberg cells

A major pathogenetic mechanism in classical Hodgkin lymphoma (cHL) is constitutive activation of canonical nuclear factor-κB (NF-κB) p50/p65 signaling, controlling lymphoma cell proliferation and survival. Recently, we demonstrated that aberrant Notch1 activity is a negative regulator of the B cell program in B cell-derived Hodgkin and Reed-Sternberg (HRS) cells. Despite abundant evidence for a complex context-dependent cross talk between Notch and NF-κB signaling in hematopoietic cells, it is unknown whether these pathways interact in HRS cells. Here, we show that Notch-signaling inhibition in HRS cells by the γ-secretase inhibitor (GSI) XII results in decreased alternative p52/RelB NF-κB signaling, interfering with processing of the NF-κB2 gene product p100 into its active form p52. As a result, expression of Notch and NF-κB target genes is reduced, and survival of HRS cells is impaired. Stimulation of alternative NF-κB signaling in the Hodgkin cell line L540cy by activation of the CD30 receptor rescued GSI-mediated loss of cell viability and apoptosis induction. Our data reveal that Notch is an essential upstream regulator of alternative NF-κB signaling and indicate cross talk between both the pathways in HRS cells. Therefore, we suggest that targeting the Notch pathway is a promising therapeutic option in cHL.

Cross-regulation between protein L-isoaspartyl O-methyltransferase and ERK in epithelial mesenchymal transition of MDA-MB-231 cells

AIM

Protein L-isoaspartyl O-methyltransferase (PIMT) regulates cell adhesion in various cancer cell lines through activation of integrin αv and the PI3K pathway. The epithelial mesenchymal transition (EMT) enables epithelial cells to acquire the characteristics of mesenchymal cells, and to allow them to migrate for metastasis. Here, we examined the relationship between PIMT and EMT with attached or detached MDA-MB 231 cells.

METHODS

Human breast cancer cell line MDA-MB-231 cells were maintained in a suspension on poly-HEMA in the presence or absence of PIMT siRNA or ERK inhibitor PD98059. The mRNAs and proteins were analyzed using RT-PCR and immunoblotting, respectively.

RESULTS

During cellular incubation under detached conditions, PIMT, integrin αv and EMT proteins, such as Snail, Slug and matrix metalloproteinase 2 (MMP-2), were significantly increased in correlation with the phosphorylation of ERK1/2. The ERK inhibitor PD98059 (25 μmol/L) strongly suppressed the expression of the proteins and PIMT. Interestingly, PIMT siRNA blocked the phosphorylation of ERK and the expression of the EMT proteins. Additionally, PIMT and ERK phosphorylation were both co-activated by treatment with TGF-β (10 ng/mL) and TNF-α (10 ng/mL).

CONCLUSION

A tight cross-regulation exists between ERK and PIMT in regards to their activation and expression during the EMT.

Phenotypic plasticity and epithelial-mesenchymal transitions in cancer and normal stem cells?

Cancer stem cells (CSCs) are similar to normal stem cells in their ability to self-renew and to generate large populations of more differentiated descendants. In contrast to the hierarchical organization that is presumed to be the prevalent mode of normal tissue homeostasis, phenotypic plasticity allows cancer cells to dynamically enter into and exit from stem-cell states. The epithelial-mesenchymal transition (EMT) has been closely associated with the acquisition of both invasive and stem-cell properties in cancer cells. Thereby, EMT programs emerge as important regulators of phenotypic plasticity in cancer cells including their entrance into stem-cell states. Much is still to be learned about the regulation of EMTs through epigenetic mechanisms in cancer cells and the contributions that EMT programs make to normal tissue homeostasis.

LGR5 is a negative regulator of tumourigenicity, antagonizes Wnt signalling and regulates cell adhesion in colorectal cancer cell lines

Background

LGR5 (Leucine-rich repeat-containing G-protein coupled receptor 5) is the most established marker for intestinal stem cells. Mouse models show that LGR5+ cells are the cells of origin of intestinal cancer, and LGR5 expression is elevated in human colorectal cancers, however very little is known about LGR5 function or its contribution to the stem cell phenotype and to colorectal cancer.

Principal Findings

We have modulated the expression of LGR5 by RNAi (inhibitory RNAs) or overexpression in colorectal cancer cell lines. Paradoxically, ablation of LGR5 induces increased invasion and anchorage-independent growth, and enhances tumourigenicity in xenografts experiments. Conversely, overexpression of LGR5 augments cell adhesion, reduces clonogenicity and attenuates tumourigenicity. Expression profiling revealed enhanced wnt signalling and upregulation of EMT genes upon knockdown of LGR5, with opposite changes in LGR5 overexpressing cells. These findings suggest that LGR5 is important in restricting stem cells to their niche, and that loss of LGR5 concomitant with activated wnt signalling may contribute to the invasive phenotype of colorectal carcinomas.

The ins and outs of the epithelial to mesenchymal transition in health and disease

The epithelial to mesenchymal transition (EMT) converts epithelial cells into migratory and invasive cells and is a fundamental event in morphogenesis. Although its relevance in the progression of cancer and organ fibrosis had been debated until recently, the EMT is now established as an important step in the metastatic cascade of epithelial tumors. The similarities between pathological and developmental EMTs validate the embryo as the best model to understand the molecular and cellular mechanisms involved in this process, identifying those that are hijacked during the progression of cancer and organ degeneration. Our ever-increasing understanding of how transcription factors regulate the EMT has revealed complex regulatory loops coupled to posttranscriptional and epigenetic regulatory programs. The EMT is now integrated into the systemic activities of whole organisms, establishing links with cell survival, stemness, inflammation, and immunity. In addition, the EMT now constitutes a promising target for the treatment of cancer and organ-degenerative diseases.

Alpha-fetoprotein-producing pancreatic cancer cells possess cancer stem cell characteristics

We aimed to demonstrate the existence of cancer stem cells in human pancreatic cancer, and to clarify that they are alpha-fetoprotein (AFP) producing cells. Six cell lines derived from human pancreatic cancers were examined, and AsPC-1 and PANC-1 were noted to express AFP. Single cell culture assays and xenotransplantation revealed that the AFP-producing cells had the capacity for self-renewal and differentiation, and that these cells were tumorigenic. Furthermore, they were resistant to anti-cancer agents. The ABCA12 transporter was expressed in the AFP-producing cells at a level more than twice as high as that in the non-AFP-producing cells. The AFP-producing cells were shown to be putative pancreatic cancer stem cells. Furthermore, the expression of ABCA12 appears to be associated with drug resistance.

Novel therapeutic strategies for targeting liver cancer stem cells

The cancer stem cell (CSC) hypothesis was first proposed over 40 years ago. Advances in CSC isolation were first achieved in hematological malignancies, with the first CSC demonstrated in acute myeloid leukemia. However, using similar strategies and technologies, and taking advantage of available surface markers, CSCs have been more recently demonstrated in a growing range of epithelial and other solid organ malignancies, suggesting that the majority of malignancies are dependent on such a compartment.

Primary liver cancer consists predominantly of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). It is believed that hepatic progenitor cells (HPCs) could be the origin of some HCCs and ICCs. Furthermore, stem cell activators such as Wnt/β-catenin, TGF-β, Notch and Hedgehog signaling pathways also expedite tumorigenesis, and these pathways could serve as molecular targets to assist in designing cancer prevention strategies. Recent studies indicate that additional factors such as EpCAM, Lin28 or miR-181 may also contribute to HCC progression by targeting HCC CSCs. Various therapeutic drugs that directly modulate CSCs have been examined in vivo and in vitro. However, CSCs clearly have a complex pathogenesis, with a considerable crosstalk and redundancy in signaling pathways, and hence targeting single molecules or pathways may have a limited benefit for treatment. Many of the key signaling molecules are shared by both CSCs and normal stem cells, which add further challenges for designing molecularly targeted strategies specific to CSCs but sparing normal stem cells to avoid side effects. In addition to the direct control of CSCs, many other factors that are needed for the maintenance of CSCs, such as angiogenesis, vasculogenesis, invasion and migration, hypoxia, immune evasion, multiple drug resistance, and radioresistance, should be taken into consideration when designing therapeutic strategies for HCC.

Here we provide a brief review of molecular signaling in liver CSCs and present insights into new therapeutic strategies for targeting liver CSCs.

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

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

Colon Cancer Stem Cells: Bench-to-Bedside-New Therapeutical Approaches in Clinical Oncology for Disease Breakdown

It is widely accepted by the scientific community that cancer, including colon cancer, is a “stem cell disease”. Until a few years ago, common opinion was that all neoplastic cells within a tumor contained tumorigenic growth capacity, but recent evidences hint to the possibility that such a feature is confined to a small subset of cancer-initiating cells, also called cancer stem cells (CSCs). Thus, malignant tumors are organized in a hierarchical fashion in which CSCs give rise to more differentiated tumor cells. CSCs possess high levels of ATP-binding cassette (ABC) transporters and anti-apoptotic molecules, active DNA-repair, slow replication capacities and they produce growth factors that confer refractoriness to antineoplastic treatments. The inefficacy of conventional therapies towards the stem cell population might explain cancer chemoresistance and the high frequency of relapse shown by the majority of tumors. Nowadays, in fact all the therapies available are not sufficient to cure patients with advanced forms of colon cancer since they target differentiated cancer cells which constitute most of the tumor mass and spare CSCs. Since CSCs are the entities responsible for the development of the tumor and represent the only cell population able to sustain tumor growth and progression, these cells represent the elective target for innovative therapies.

Cancer biology and genomics: translating discoveries, transforming pathology

Advances in our understanding of cancer biology and discoveries emerging from cancer genomics are being translated into real clinical benefits for patients with cancer. The 2011 Journal of Pathology Annual Review Issue provides a snapshot of recent rapid progress on multiple fronts in the war on cancer or, more precisely, the wars on cancers. Indeed, perhaps the most notable recent shift is reflected by the sharp increase in understanding the biology of multiple specific cancers and using these new insights to inform rationally targeted therapies, with often striking successes. These recent developments, as reviewed in this issue, show how the long-term investments in basic cancer research are finally beginning to bear fruit.

Analyses of the secondary particle radiation and the DNA damage it causes to human keratinocytes

High-energy protons, and high mass and energy ions, along with the secondary particles they produce, are the main contributors to the radiation hazard during space explorations. Skin, particularly the epidermis, consisting mainly of keratinocytes with potential for proliferation and malignant transformation, absorbs the majority of the radiation dose. Therefore, we used normal human keratinocytes to investigate and quantify the DNA damage caused by secondary radiation. Its manifestation depends on the presence of retinol in the serum-free media, and is regulated by phosphatidylinositol 3-kinases. We simulated the generation of secondary radiation after the impact of protons and iron ions on an aluminum shield. We also measured the intensity and the type of the resulting secondary particles at two sample locations; our findings agreed well with our predictions. We showed that secondary particles inflict DNA damage to different extents, depending on the type of primary radiation. Low-energy protons produce fewer secondary particles and cause less DNA damage than do high-energy protons. However, both generate fewer secondary particles and inflict less DNA damage than do high mass and energy ions. The majority of cells repaired the initial damage, as denoted by the presence of 53BPI foci, within the first 24 hours after exposure, but some cells maintained the 53BP1 foci longer.

Chronic inflammation and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) invariably develops within a setting of chronic inflammation caused by either hepatotropic viruses, toxins, metabolic liver disease or autoimmunity. Mechanisms that link these two processes are not completely understood, but transcription factors of the NF-κB family and signal transducer and activator of transcription 3 (STAT3), cytokines such as IL-6 and IL-1α and ligands of the epidermal growth factor receptor (EGFR) family are clearly pivotal players. HCC may have its origins in either hepatocytes or hepatic progenitor cells (HPCs), and HCCs, like other solid tumours appear to be sustained by a minority population of cancer stem cells.