Brain tumour stem cells: implications for cancer therapy and regenerative medicine

The cancer relapse and mortality rate suggest that current therapies do not eradicate all malignant cells. Currently, it is accepted that tumorigenesis and organogenesis are similar in many respects, as for example, homeostasis is governed by a distinct sub-population of stem cells in both situations. There is increasing evidence that many types of cancer contain their own stem cells: cancer stem cells (CSC), which are characterized by their self-renewing capacity and differentiation ability. The investigation of solid tumour stem cells has gained momentum particularly in the area of brain tumours. Gliomas are the most common type of primary brain tumours. Nearly two-thirds of gliomas are highly malignant lesions with fast progression and unfortunate prognosis. Despite recent advances, two-year survival for glioblastoma (GBM) with optimal therapy is less than 30%. Even among patients with low-grade gliomas that confer a relatively good prognosis, treatment is almost never curative. Recent studies have demonstrated the existence of a small fraction of glioma cells endowed with features of primitive neural progenitor cells and a tumour-initiating function. In general, this fraction is characterized for forming neurospheres, being endowed with drug resistance properties and often, we can isolate some of them using sorting methods with specific antibodies. The molecular characterization of these stem populations will be critical to developing an effective therapy for these tumours with very dismal prognosis. To achieve this aim, the development of a mouse model which recapitulates the nature of these tumours is essential. This review will focus on glioma stem cell knowledge and discuss future implications in brain cancer therapy and regenerative medicine.     

Telomerase-directed molecular therapeutics

The management of malignant disease remains one of the most challenging areas of modern medicine. The lifetime risk of developing cancer in the western world is estimated to be as high as 1 in 3. Traditionally, surgery, chemotherapy and radiotherapy have been the primary choice of treatment for patients with malignant tumours. Despite advances in the use and development of conventional cytotoxic agents, the cure rate remains disappointing in most patients with advanced disease of the common solid tumours. Consequently, the development of novel anti-cancer therapies is a high priority in cancer medicine. In recent years, a new generation of cancer therapies has emerged, based on a growing understanding of the molecular events that contribute to malignant transformation. A major difference between normal and cancer cells is the ability of cancer cells to multiply in an unrestricted and ungoverned fashion. In this context, there is considerable interest in elucidating the mechanisms that allow this unrestricted proliferation and that ultimately result in immortal cancer cells. It is now clear that the enzyme telomerase confers immortality on cells in most types of cancer. With the cancer cell reliant on telomerase for its survival, telomerase represents an extremely attractive mechanism-based target for the development of new cancer therapeutics.     

Molecular and genomic characterisation of a panel of human anal cancer cell lines

Anal cancer is a rare disease that has doubled in incidence over the last four decades. Current treatment and survival of patients with this disease has not changed substantially over this period of time, due, in part, to a paucity of preclinical models to assess new therapeutic options. To address this hiatus, we set-out to establish, validate and characterise a panel of human anal squamous cell carcinoma (ASCC) cell lines by employing an explant technique using fresh human ASCC tumour tissue. The panel of five human ASCC cell lines were validated to confirm their origin, squamous features and tumourigenicity, followed by molecular and genomic (whole-exome sequencing) characterisation. This panel recapitulates the genetic and molecular characteristics previously described in ASCC including phosphoinositide-3-kinase (PI3K) mutations in three of the human papillomavirus (HPV) positive lines and TP53 mutations in the HPV negative line. The cell lines demonstrate the ability to form tumouroids and retain their tumourigenic potential upon xenotransplantation, with varied inducible expression of major histocompatibility complex class I (MHC class I) and Programmed cell death ligand 1 (PD-L1). We observed differential responses to standard chemotherapy, radiotherapy and a PI3K specific molecular targeted agent in vitro, which correlated with the clinical response of the patient tumours from which they were derived. We anticipate this novel panel of human ASCC cell lines will form a valuable resource for future studies into the biology and therapeutics of this rare disease.Subject terms: Targeted therapies, Anal cancer, Immune evasion, Cancer models     

An adult tissue-specific stem cell molecular phenotype is activated in epithelial cancer stem cells and correlated to patient outcome

Recent studies have shown that embryonic stem cell-like molecular phenotypes are commonly activated in human epithelial primary tumors and are linked to adverse patient prognosis. However it remains unclear whether these correlations to outcome are linked to the differentiation status of the human primary tumours1 or represent molecular reminiscences of epithelial cancer stem cells. In addition, while it has been demonstrated that leukemic cancer stem cells re-acquire an embryonic stem cell-like phenotype, the molecular basis of stem cell function in epithelial cancer stem cells has not been investigated. Here we show that a normal adult tissue-specific stem cell molecular phenotype is commonly activated in epithelial cancer stem cells and for the first time provide evidence that enrichment in cancer stem cells-specific molecular signatures are correlated to highly aggressive tumor phenotypes in human epithelial cancers.     

Membrane and membrane-associated proteins involved in the aggressive phenotype displayed by highly invasive cancer cells

Invasion, the penetration of tumour cells into adjacent tissues, is a fundamental characteristic of malignant carcinomas and a first step in the metastatic process. The molecular mechanisms involved in tumour cell invasion are complex, but over the last couple of decades the knowledge base has grown quite considerably and many proteins with important roles in invasion have been identified and characterised. Benign tumours typically are encapsulated, which inhibits their ability to behave in a malignant manner, meaning these tumours do not grow in a location-limited less aggressive manner, do not invade surrounding tissues and do not metastasise. The ability of malignant tumours to invade and metastasise is the major cause of death for cancer patients. A greater insight into the molecular basis of cancer invasion and metastasis will lead to the development of novel therapies and specific panels of biomarkers for use in the treatment and diagnosis/monitoring in many types of metastatic cancer.     

Cell Fate Decisions in Malignant Hematopoiesis: Leukemia Phenotype Is Determined by Distinct Functional Domains of the MN1 Oncogene

Extensive molecular profiling of leukemias and preleukemic diseases has revealed that distinct clinical entities, like acute myeloid (AML) and T-lymphoblastic leukemia (T-ALL), share similar pathogenetic mutations. It is not well understood how the cell of origin, accompanying mutations, extracellular signals or structural differences in a mutated gene determine the phenotypic identity of leukemias. We dissected the functional aspects of different protein regions of the MN1 oncogene and their effect on the leukemic phenotype, building on the ability of MN1 to induce leukemia without accompanying mutations. We found that the most C-terminal region of MN1 was required to block myeloid differentiation at an early stage, and deletion of an extended C-terminal region resulted in loss of myeloid identity and cell differentiation along the T-cell lineage in vivo. Megakaryocytic/erythroid lineage differentiation was blocked by the N-terminal region. In addition, the N-terminus was required for proliferation and leukemogenesis in vitro and in vivo through upregulation of HoxA9, HoxA10 and Meis2. Our results provide evidence that a single oncogene can modulate cellular identity of leukemic cells based on its active gene regions. It is therefore likely that different mutations in the same oncogene may impact cell fate decisions and phenotypic appearance of malignant diseases.     

Defining a molecularly normal colon.

As techniques evolve that allow molecular characterization of disease processes such as cancer, definition of "normal" at a molecular level becomes increasingly important. Increasingly large numbers of mutations are found at the genomic level, but whether all of those mutations contribute to the malignant state of a carcinoma cell is not clear. Without knowledge of what constitutes normality on the proteomic level in an organ or cell, we cannot determine what genomic changes are physiologically important. Traditionally, colon cancer is identified and classified by histological criteria. Margins of the colon are defined as "grossly uninvolved" when the histology is indistinguishable from that of normal (free from disease) colon. By using molecular pathology techniques and working backward from colon adenocarcinoma to hypoplastic polyps to presumably normal mucosa, we defined some of those protein differences. Our results may provide a molecular basis for identifying tumor formation and progression in situ.(J Histochem Cytochem 49:667-668, 2001)     

Digenic/multilocus aetiology of multiple self-healing squamous epithelioma (Ferguson-Smith disease): TGFBR1 and a second linked locus

Multiple self-healing squamous epithelioma (MSSE) is a rare familial skin cancer in which multiple tumours resembling crateriform squamous carcinomas are locally invasive but regress spontaneously after several months, leaving deep disfiguring facial scars and shallower scars on the limbs. First identified in a number of Scottish families, the condition has since been reported more widely. We review here the investigations leading to the discovery of loss of function mutations in TGFBR1 that are responsible for the disease. Loss of heterozygosity in tumours reveals that TGFBR1 acts as a tumour suppressor gene. TGFBR1 was initially excluded as the MSSE gene because it lies outside an extensive chromosome 9 haplotype shared by Scottish families. MSSE can now be regarded as a digenic/multilocus disease in view of the evidence of a second linked locus necessary for pathogenesis located within the Scottish haplotype.This article is part of a Directed Issue entitled: Rare Cancers.     

Stem Cell Markers in Gliomas

Gliomas are the most common tumours of the central nervous system (CNS) and a frequent cause of mental impairment and death. Treatment of malignant gliomas is often palliative because of their infiltrating nature and high recurrence. Genetic events that lead to brain tumours are mostly unknown. A growing body of evidence suggests that gliomas may rise from cancer stem cells (CSC) sharing with neural stem cells (NSC) the capacity of cell renewal and multipotency. Accordingly, a population of cells called “side population” (SP), which has been isolated from gliomas on the basis of their ability to extrude fluorescent dyes, behaves as stem cells and is resistant to chemotherapeutic treatments. This review will focus on the expression of the stem cell markers nestin and CD133 in glioma cancer stem cells. In addition, the possible role of Platelet Derived Growth Factor receptor type α (PDGFR-α) and Notch signalling in normal development and tumourigenesis of gliomas are also discussed. Future work elucidating the mechanisms that control normal development will help to identify new cancer stem cell-related genes. The identification of important markers and the elucidation of signalling pathways involved in survival, proliferation and differentiation of CSCs appear to be fundamental for developing an effective therapy of brain tumours. Special issue article in honor of Dr. Anna Maria Giuffrida-Stella.     

Signalling networks that cause cancer

Cancer is caused by the stepwise accumulation of mutations that affect growth control, differentiation and survival. The view that mutations affect discrete signalling pathways, each contributing to a specific aspect of the full malignant phenotype, has proved to be too simplistic. We now know that oncogenes and tumour suppressors depend on one another for their selective advantage, and that they affect multiple pathways that intersect and overlap. The interactive nature of each genetic change has important implications for cancer therapy and for the stepwise model of carcinogenesis.     

Signalling networks that cause cancer

Cancer is caused by the stepwise accumulation of mutations that affect growth control, differentiation and survival. The view that mutations affect discrete signalling pathways, each contributing to a specific aspect of the full malignant phenotype, has proved to be too simplistic. We now know that oncogenes and tumour suppressors depend on one another for their selective advantage, and that they affect multiple pathways that intersect and overlap. The interactive nature of each genetic change has important implications for cancer therapy and for the stepwise model of carcinogenesis.     

Signalling networks that cause cancer

Cancer is caused by the stepwise accumulation of mutations that affect growth control, differentiation and survival. The view that mutations affect discrete signalling pathways, each contributing to a specific aspect of the full malignant phenotype, has proved to be too simplistic. We now know that oncogenes and tumour suppressors depend on one another for their selective advantage, and that they affect multiple pathways that intersect and overlap. The interactive nature of each genetic change has important implications for cancer therapy and for the stepwise model of carcinogenesis.     

Biology of human papillomavirus (HPV) infections and their role in squamous cell carcinogenesis

Current data implicating the role of human papillomavirus (HPV) infections in squamous cell carcinogenesis may be summarised as follows: animal models have shown that PVs can induce malignant transformation; HPV involvement in both benign and malignant human squamous cell tumours has been demonstrated by morphological, immunohistochemical and DNA hybridisation techniques; HPV infections in the genital tract are venereally transmitted and are associated with the same risk factors as cervical carcinoma; the natural history of cervical HPV lesions is similar to that of CIN, namely, they have the potential to develop into carcinoma in situ; malignant transformation of PV-induced lesions seems to depend on virus type and the physical state of its DNA, e.g., whether or not it is integrated in the host cell DNA; malignant transformation most probably requires synergistic actions between the PVs and chemical or physical carcinogens, or other infectious agents; genetic disposition (at least in animals) significantly contributes to malignant transformation; immunological defence mechanisms of the host are probably capable of modifying the course of PV infections (efficacy in man remains to be elucidated). Many details of the molecular mechanisms, however, still remain to be clarified. Although BPV1 is capable of transforming fibroblasts, the way that papillomaviruses transform epithelial cells is unclear. Which gene is capable of inducing the limited cell proliferation in benign lesions? No model systems exist to provide the answer nor to elucidate the progression to malignant cells and then to invasive cancer. Improved tissue culture systems for in vitro differentiation of keratinocytes should help in elucidating the biology of papillomaviruses and their interaction with cell division and differentiation.     

Brain Tumor Stem Cells

Primary malignant brain cancer, one of the most deadly diseases, has a high rate of recurrence after treatment. Studies in the past several years have led to the hypothesis that the root of the recurrence may be brain tumor stem cells (BTSCs), stem-like subpopulation of cells that are responsible for propagating the tumor. Current treatments combining surgery and chemoradiotherapy could not eliminate BTSCs because these cells are highly infiltrative and possess several properties that can reduce the damages caused by radiation or anti-cancer drugs. BTSCs are similar to NSCs in molecular marker expression and multi-lineage differentiation potential. Genetic analyses of Drosophila CNS neoplasia, mouse glioma models, and human glioma tissues have revealed a link between increased NSC self-renewal and brain tumorigenesis. Furthermore, data from various rodent models of malignant brain tumors have provided compelling evidence that multipotent NSCs and lineage-restricted neural progenitor cells (NPCs) could be the cell origin of brain tumors. Thus, the first event of brain tumorigenesis might be the occurrence of oncogenic mutations in the stem cell self-renewal pathway in an NSC or NPC. These mutations convert the NSC or NPC to a BTSC, which then initiates and sustains the growth of the tumor. The self-renewal of BTSCs is controlled by several evolutionarily conserved signaling pathways and requires an intact vascular niche. Targeting these pathways and the vascular niche could be a principle in novel brain tumor therapies aimed to eliminate BTSCs.     

Cancer as an overhealing wound: an old hypothesis revisited

What is the relationship between the wound-healing process and the development of cancer? Malignant tumours often develop at sites of chronic injury, and tissue injury has an important role in the pathogenesis of malignant disease, with chronic inflammation being the most important risk factor. The development and functional characterization of genetically modified mice that lack or overexpress genes that are involved in repair, combined with gene-expression analysis in wounds and tumours, have highlighted remarkable similarities between wound repair and cancer. However, a few crucial differences were also observed, which could account for the altered metabolism, impaired differentiation capacity and invasive growth of malignant tumours.     

Somatic variation and cancer: therapies lost in the mix

Cancer arises as a consequence of mutations in genomes of cancer cells, which over time allow them to proliferate and spread to distant sites. Large-scale sequencing of cancer genomes is revealing an increasing number of potential driver mutations that may allow specific targeting of cancer genes, proteins, and pathways. Comprehensive views of cancer genomes are also revealing enormous heterogeneity of mutation profiles, even among tumours derived from the same organs and having similar pathological characteristics. There are now many examples where mutation profiles observed in tumours have been shown to correlate with clinical features of disease, drug response, and patient outcomes. When ignored, molecular heterogeneity can lead to failures in drug development, as drugs that may have efficacy in subgroups of patients with specific molecular phenotypes may show marginal response when tested in large groups of unselected patients. This article explores issues relevant to the clinical translation of sequence-based mutation profiles in the clinical development of targeted therapies and in the future management of cancer patients.     

Lymphangiogenesis and its role in cancer

In many tumour types, lymphatic vasculature serves as a major route for tumour metastasis. The dissemination of malignant cells to the regional lymph nodes is an early step in the progression of many solid tumours and is an important determinant of prognosis. Lymphangiogenesis (formation of new lymphatic vessels) is thought to be crucial for cancer cells to metastasise to the regional lymph nodes. However research in this important process has been neglected largely due to the lack of molecular markers specific to the lymphatic endothelium. Recently, several specific markers have been identified including LYVE-1, podoplanin and prox-1. Although the biology of lymphangiogeneis, particularly its regulation, is still far from clear, it is now well established that tumours are lymphangiogenic i.e. they could induce the generation of their own lymphatics and metastasise to the regional lymph nodes. It is thought that the interruption of the main signalling pathways involved in this process could help to prevent lymphatic spread of many tumours. Furthermore, understanding the molecular mechanisms in lymphangiogenesis might help to develop new therapeutic strategies against cancer lymphatic spread. Here, we reviewed the literature in regards to the biology of lymphangiogenesis, its molecular regulation, lymphatic markers and the significance in human solid tumours.     

Jekyll and Hyde: evolving perspectives on the function and potential of the adult liver progenitor (oval) cell

The liver progenitor cell (LPC) has enormous potential for use in cell therapy to treat liver disease. Since liver regenerates readily from pre-existing hepatocytes, a role for LPCs and, indeed, their existence have been questioned. Research during the last decade has established that LPCs are an important alternative source of cells for liver regeneration. Their utility for cell therapy lies in their ability to generate both hepatocytes and cholangiocytes. However, they are observed in liver diseases that often lead to cancer and there is experimental evidence that implicates LPCs as the source of tumours. This article provides a brief history of the studies that established the functional importance of LPCs in liver disease. It focuses on mouse models that have led to the identification of factors that regulate LPC growth and differentiation and discusses LPCs derived from different sources. Recent promising results from both in vitro and vivo studies suggest that LPCs could be useful for cell therapy. In the context of liver disease, LPCs may indeed be the cell of the future and understandably "our favourite cell".     

An overview of the mechanisms of mutagenesis and carcinogenesis

Cancer is a genetic disease due to the accumulation of numerous mutations rendering the tumour cell insensitive to control by the local cellular environment and by the whole organism. Analysis of the frequency of appearance of human cancer as a function of age shows that between four and seven mutations in key genes are usually necessary to produce most human cancers. Interesting debates in the literature are concerned with the idea that normal mutation rates followed by selective advantage of mutated clones are enough to produce the numerous mutations found in human cancers. Alternatively, the mutator phenotype hypothesis is based on the idea that the normal mutation rates are insufficient to account for the multiple mutations found in tumours. It is, however, difficult not only to know this exact mutation frequency in cells but also to know the total number of cell divisions giving rise to a cancer. Therefore, during at least one step in the carcinogenic process, a mutator phenotype in target cells may occur due to mutations controlling the fidelity of DNA replication or DNA repair, the apoptosis pathways or the cell cycle checkpoint regulations. Among the multiple mutations found in human cancers such as gene amplification, chromosome alterations and translocations, point mutations are very important and the molecular mechanisms of their production are well documented. I will describe in detail the various mechanisms that a cell can use to produce point mutations due to lower fidelity in the DNA polymerisation step or to inefficient repair pathways. The presence of multiple mutations in human cancer is interesting not only in terms of understanding the carcinogenesis process in humans but also in eventually promoting strategies to decrease the efficiency of this process and to increase cancer therapy regimen.     

Chromosome 3 anomalies investigated by genome wide SNP analysis of benign, low malignant potential and low grade ovarian serous tumours

Ovarian carcinomas exhibit extensive heterogeneity, and their etiology remains unknown. Histological and genetic evidence has led to the proposal that low grade ovarian serous carcinomas (LGOSC) have a different etiology than high grade carcinomas (HGOSC), arising from serous tumours of low malignant potential (LMP). Common regions of chromosome (chr) 3 loss have been observed in all types of serous ovarian tumours, including benign, suggesting that these regions contain genes important in the development of all ovarian serous carcinomas. A high-density genome-wide genotyping bead array technology, which assayed >600,000 markers, was applied to a panel of serous benign and LMP tumours and a small set of LGOSC, to characterize somatic events associated with the most indolent forms of ovarian disease. The genomic patterns inferred were related to TP53, KRAS and BRAF mutations. An increasing frequency of genomic anomalies was observed with pathology of disease: 3/22 (13.6%) benign cases, 40/53 (75.5%) LMP cases and 10/11 (90.9%) LGOSC cases. Low frequencies of chr3 anomalies occurred in all tumour types. Runs of homozygosity were most commonly observed on chr3, with the 3p12-p11 candidate tumour suppressor region the most frequently homozygous region in the genome. An LMP harboured a homozygous deletion on chr6 which created a GOPC-ROS1 fusion gene, previously reported as oncogenic in other cancer types. Somatic TP53, KRAS and BRAF mutations were not observed in benign tumours. KRAS-mutation positive LMP cases displayed significantly more chromosomal aberrations than BRAF-mutation positive or KRAS and BRAF mutation negative cases. Gain of 12p, which harbours the KRAS gene, was particularly evident. A pathology review reclassified all TP53-mutation positive LGOSC cases, some of which acquired a HGOSC status. Taken together, our results support the view that LGOSC could arise from serous benign and LMP tumours, but does not exclude the possibility that HGOSC may derive from LMP tumours.