Bone marrow niches in the regulation of bone metastasis

The bone marrow has been widely recognised to host a unique microenvironment that facilitates tumour colonisation. Bone metastasis frequently occurs in the late stages of malignant diseases such as breast, prostate and lung cancers. The biology of bone metastasis is determined by tumour-cell-intrinsic traits as well as their interaction with the microenvironment. The bone marrow is a dynamic organ in which various stages of haematopoiesis, osteogenesis, osteolysis and different kinds of immune response are precisely regulated. These different cellular components constitute specialised tissue microenvironments—niches—that play critical roles in controlling tumour cell colonisation, including initial seeding, dormancy and outgrowth. In this review, we will dissect the dynamic nature of the interactions between tumour cells and bone niches. By targeting certain steps of tumour progression and crosstalk with the bone niches, the development of potential therapeutic approaches for the clinical treatment of bone metastasis might be feasible.Subject terms: Bone metastases, Metastasis     

Angiogenesis and ovarian cancer

Ovarian carcinoma is the most important cause of gynaecological cancer-related mortality in Western societies. The age at diagnosis, extent of disease (as expressed by FIGO state), success of primary surgery and the histopathological features of the tumour are important prognostic markers. The majority of patients with ovarian cancer present with advanced disease (FIGO stage III/IV) and in this group of patients the median survival is only three years. New treatment approaches are therefore required to improve outcome in this disease. Angiogenesis, the development of a neovascular blood supply, is a critical step in the propagation of malignant tumour growth and metastasis and represents a promising target. This review will focus on angiogenesis, VEGF biology and the potential value of angiogenic factors with prognostic value in ovarian cancer.     

The seed and soil hypothesis: vascularisation and brain metastases

The development of a relevant mouse model for the establishment and growth of brain metastases is essential for study of the biology and therapy of brain metastasis. Injection of human tumour cells into the internal carotid artery of syngeneic or nude mice produces experimental metastases in specific regions of the brain; these are not due to patterns of initial cell arrest, motility, or invasiveness, but rather to the ability of metastatic tumour cells to grow. Whether the progressive growth of brain metastases depends on neovascularisation is not clear. Immunohistochemical and morphometric analyses show that the density of blood vessels within experimental metastases in the brains of nude mice, or within brain metastases derived from human lung cancer, is lower than in the adjacent, tumour-free brain parenchyma. However, blood vessels associated with brain metastases are dilated and contain many dividing endothelial cells. Immunohistochemical analysis also reveals that tumour cells located less than 100 microm from a blood vessel are viable, whereas more distant tumour cells undergo apoptosis. The blood-brain barrier is intact in and around experimental brain metastases smaller than 0.25 mm in diameter, but is leaky in larger metastases. Nevertheless, the lesions are resistant to chemotherapeutic drugs. The way in which the brain microenvironment influences the biological behaviour of tumour cells is a subject of intense investigation.     

CXCL12／CXCR4生物轴与消化系统恶性肿瘤

消化系统恶性肿瘤发病率及死亡率均远远高于其它系统恶性肿瘤，对消化系统恶性肿瘤的预防和治疗研究亟待进一步深入。细胞移位是相当多病理生理过程的基本步骤，包括恶性肿瘤细胞的生长及转移。越来越多地研究认为肿瘤细胞通过化学趋化因子及其相应受体介导的化学趋化机制调节其生长和转移，趋化因子在恶性肿瘤中具有多方面作用，归纳为：①诱导白细胞向肿瘤组织浸润，调节免疫功能，尤其是肿瘤相关的巨噬细胞、T细胞和树突状细胞；②引导肿瘤细胞迁移到特定部位；③调节血管生成；④直接活化肿瘤细胞，调控其恶性肿瘤相关的功能表现。近年研究发现，趋化因子CXCL12及其受体CXCR4构成的生物轴在包括乳腺癌在内的多种实体瘤的生长、转移中发挥重要作用。CXCL12／CXCR4生物轴与消化系统恶性肿瘤之间关系密切，CXCL12的刺激促进CXCR4的表达及消化系统恶性肿瘤的转移；CXCR4持续高表达预示肿瘤的复发及预后不良；在CXCL12作用下，肿瘤细胞黏附／迁移和增殖能力亦显著增强，这些效应被CXCR4的抗体所拮抗。未来研究寄希望通过拮抗影响肿瘤转移的CXCL12与CXCR4等趋化因子及其受体的作用来阻断消化系统恶性肿瘤转移，将可能会成为一种新的治疗消化系统恶性肿瘤的有效途径。     

Tumor cell adhesive mechanisms and their relationship to metastasis

Despite recent advances in the diagnosis and therapy of many forms of cancer, metastasis remains the major cause of death in cancer patients. As tumors progress they become increasingly heterogeneous, giving rise to aggressive subpopulations of tumor cells that subsequently invade local tissues, the lymphatics, and the circulatory system. This invasive behavior can ultimately lead to the widespread dissemination and metastasis of the primary tumor. In hematogenous metastasis, emboli consisting of tumor cells, host cells, platelets, and fibrin are transported to distant sites where they arrest in the microvasculature prior to extravasation. It is well accepted that tumor cell adhesion plays a fundamental role in many of the stages of the metastatic process. Tumor cell interactions with extracellular matrix components of tissue, tissue boundaries (basement membranes), or cell adhesion-promoting components of plasma; influence tumor cell motility, invasiveness, and many other important aspects of the metastatic tumor cell phenotype. Tumor cell adhesion also has a rate-limiting influence at various stages within the metastatic process, such as tumor cell arrest and extravasation. In addition, the ability of the immune system to recognize and successfully eradicated tumors is also highly dependent on the adhesion of activated lymphocytes to target tumor cells. Despite the rapid accumulation of information on the molecular basis of cell adhesion, our understanding of the relationship between tumor cell adhesion and hematogenous metastasis per se is fragmented and incomplete. Nevertheless, clear progress has been made, both in understanding the molecular basis of tumor cell adhesion and its relationship to the biology of tumor metastasis. New and exciting directions have been identified that are likely to yield direct benefits in developing new therapeutic or diagnostic approaches for malignant neoplasms. Our purpose is to briefly review the molecular basis of tumor cell adhesion from the standpoint of many of the receptors involved as well as their putative ligands. The relationship between specific tumor cell adhesion events and the formation of metastatic lesions is also addressed.     

Angiogenèse: retour au fondamental

In the evolution of a cancer, tumorigenesis is the stage at which the initial molecular and cellular process develops a tissue dimension and, in particular, takes on a clinical aspect. This stage is made possible by the establishment and development of interactions between transformed epithelial cells and their stromal tissue matrix. The cells which are recruited from the stroma and activated are fibroblast precursors, macrophages, haematopoietic stem cells and inflammatory cells. Through these cells the stroma becomes an active partner in tumour development. As a result of these interactions neoangiogenesis is a key factor for tumour progression, invasion and metastasis. The tumoral cell proliferation is limited by normoxy, fast growing induce hypoxic cell status, and the hypoxic tumoral cell secrete chimioattractant and activating molecules, such as adrenomedullin. Fibroblast precursors, macrophages, inflammatory cells and hypoxic cancerous cells cooperate in the activation of a cascadé of proteases and growth factors, which interact with endothelial cells and pericytes. This destabilises capillary vessels and initiates angiogenesis. The new vessels are constantly refashioned and partially compensate for the tumoral hypoxia caused by rapid tumour growth. However, they constitute an important route for the metastatic spread of tumour. All of these interactions are only a distortion of the physiological processes seen during tissue repair. This latter is limited in its time frame and definitively terminated by healing, whereas the interactions between malignant cells and the micro-environment do not have a mechanism to block them.     

Asn-linked oligosaccharide processing and malignant potential

There is now considerable evidence that malignant transformation is accompanied by many changes in the oligosaccharide structures of glycoproteins and glycolipids. More recently, studies using tumour cell glycosylation mutants and inhibitors of Asn-linked oligosaccharide processing have suggested that the transformation-associated increase in GlcNAc beta 1-6Man alpha 1-6 Man beta- branching of complex-type oligosaccharides may enhance tumour cell metastasis. The synthesis of beta 1-6 branched oligosaccharides and related structures as well as their possible function in cell-cell interactions and tumour cell metastasis are discussed.     

Highly pigmented human melanoma variant which metastasizes widely in nude mice, including to skin and brain

The properties of a highly malignant human melanoma variant cell line which metastasizes in nude mice in a tissue-specific pattern are described. The variant, called 70-W, was isolated from the MeWo malignant melanoma by exposure of the latter to stepwise increasing concentrations of the toxic lectin, wheat germ agglutinin. After nine cycles of treatment a population of wheat germ agglutinin-resistant cells was obtained that manifested a 4-fold resistance to wheat germ agglutinin, a property which was found to be stable in culture for over 6 months in the absence of the lectin. Intravenous inoculation of 70-W cells into 4-6-week-old nude mice revealed remarkable differences in metastatic (organ colonization) behavior. Whereas the parent MeWo cells gave rise only to lung metastases, most of which were amelanotic, injection of the 70-W cells resulted in multiple skin (s.c.) and brain and, to a lesser extent, bone marrow, ovarian, mesenteric (gut-associated), muscle, and abdominal metastases all of which were highly melanotic. This is the first report of brain metastases of a human tumor in nude mice. They were found to be bilateral and confined to the deeper layers of the cerebral cortex. The unique malignant behavior of 70-W cells in nude mice should facilitate studies of host and tumor cell factors involved in human melanoma metastasis, melanogenesis, and development of new treatment strategies for disseminated human malignant melanoma.     

Biologie de la métastase

Metastatic dissemination represents the true cause of the malignant character of cancers. Its targeting is much more difficult than that of cell proliferation, because metastasis, like angiogenesis, involves a number of complex interactions between tumour and stroma; the contribution of adhesion and motility pathways is added to that of proliferation and survival pathways. Long distance extension, discontinuous in respect to the primitive tumour, is a major feature of cancer and the main cause of patients' death. Cancer cells use two main dissemination pathways: the lymphatic pathway, leading to the invasion of the lymph nodes draining the organs where the tumour evolves; and the blood pathway, leading to the invasion of distant organs such as liver, brain, bone or lung. Metastasis is inscribed within the properties of the primitive tumour, as shown by the comparative molecular analysis of the primitive tumour and its own metastases: their similarity is always more important than what could be expected from the general activation of “metastasis genes” or the inhibition of “metastasis suppressor genes”. Among the signalling pathways involved in metastasis, one can mention the integrin pathway, the transforming growth factor beta (TGFβ) pathway, the chemokine pathway, the dependence receptor pathway and many others. These pathways allow the possibility of therapeutic targeting, thanks to therapeutic antibodies or small molecules inhibiting the kinases involved in these signalling pathways, but not a single properly anti-metastatic drug has yet been proposed: the complexity and the diversity of the processes allowing metastasis emergence, as well as the fact that the activation mechanisms are more often epigenetic than genetic and are generally physiological processes misled by the malignant cell, render especially difficult the therapeutic approach of metastasis.     

TTF-1 in der Differenzialdiagnose zwischen Lungenkarzinom und Lungenmetastase

The differential diagnosis between primary lung cancer, metastasis of another primary carcinoma to the lung, and detection of distant metastases of lung cancer is important because of different therapeutic consequences. Immunohistological detection of TTF-1 in tumour cells provides important additional information. Apart from thyroid and lung tissue, TTF-1 expression has been found in malignant tumours of other provenance. Therefore, TTF-1 positivity in tumour cells needs to be interpreted with caution and restrictions. Nonetheless, it can help in discriminating lung cancer from metastasis to the lung or in revealing distant metastasis of primary lung cancer.     

Genetic evidence for progressive selection and overgrowth of primary tumors by metastatic cell subpopulations

We have exploited random insertions of transfected DNA as unique clonotypic markers to follow cell lineages during primary and metastatic tumor growth of a mouse mammary adenocarcinoma, SP1. Southern analysis was undertaken of primary solid tumors and metastases obtained after injection of a pooled population of individual SP1 transfectants, or reconstituted mixtures of genetically marked metastatic and unmarked nonmetastatic cells. Here we provide evidence for the reproducible selection and eventual overgrowth of primary tumors by genotypically distinct metastatic clones, thereby illustrating that late-state, advanced primary tumors can evolve to become biologically similar, or even identical, to distant metastases. The selective growth advantage of metastatic cells within primary tumors was shown to occur despite the fact that tumors generated by both metastatic and nonmetastatic SP1 cell populations grew at comparable growth rates when injected and analyzed separately. The extent of the local growth advantage manifested by individual metastatic clones varied considerably, from 5- to 50-fold. Clonal overgrowth was also observed whether the tumor cells were injected ectopically, or orthotopically (i.e., into the mammary fat). This type of experimental approach should provide new insights into the dynamics of tumor progression and metastasis, the lineage relationship of primary tumors to metastases, the influence of clonal interactions on tumor behavior, and the physiological changes which are causative of malignant disease.     

Investigation of mammary epithelial cell-bone marrow stroma interactions using primary human cell culture as a model of metastasis

A model has been established using primary human cell culture to study the cell biology of breast cancer metastasis to bone marrow. Mammary epithelia were obtained in single cell suspension from tumour (macroscopically involved), benign (macroscopically uninvolved) and normal (reduction mammoplasty) breast tissue as well as from locally involved lymph nodes. Stromal layers were generated from long-term cultures of human bone marrow or from mammary fibroblasts derived from normal or malignant tissue. The interaction between epithelia and stroma has been studied in terms of adhesion of the epithelia to the stroma and their subsequent growth in co-culture. Our results show that when assayed up to 9 hr after plating, epithelial cells from malignant tissue (14 primary tumours and 9 metastases in lymph nodes) displayed a significant preference for adhesion to bone marrow stroma compared with mammary fibroblasts. In contrast, epithelial cells from 4 normal and 2 of 4 benign samples showed no significant preferential adherence. Subsequent co-culture of mammary epithelia with each of the 3 stromal layers revealed that under serum-free, in vitro conditions, bone marrow stromal layers did not provide an advantageous environment for colony growth, in contrast to their ability to provide a preferential substratum for adhesion. Int. J. Cancer 73:690–696, 1997. © 1997 Wiley-Liss, Inc.     

Microvessel density and endothelial cell proliferation levels in colorectal liver metastases from patients given neo‐adjuvant cytotoxic chemotherapy and bevacizumab

The treatment of patients with colorectal liver metastasis has improved significantly and first line therapy is often combined chemotherapy and bevacizumab, although it is unknown who responds to this regimen. Colorectal liver metastases grow in different histological growth patterns showing differences in angiogenesis. To identify possible response markers, histological markers of angiogenesis were assessed. Patients who underwent resection of colorectal liver metastasis at Rigshospitalet, Copenhagen, Denmark from 2007 to 2011 were included (n = 254) including untreated and patients treated with chemotherapy or chemotherapy plus bevacizumab. The resected liver metastases were characterised with respect to growth pattern, endothelial and tumour cell proliferation as well as microvessel density and tumour regression. Tumour regression grade of liver metastases differed significantly between untreated/chemotherapy treated patients in comparison to chemotherapy plus bevacizumab treated patients (both p < 0.0001). Microvessel density was decreased in liver metastases from patients treated with bevacizumab in comparison to those from untreated/chemotherapy‐treated patients (p = 0.006/p = 0.002). Tumour cell proliferation assessed by Ki67 expression correlated to a shorter recurrence free survival in the total patient cohort. In conclusion, liver metastases from patients treated with neo‐adjuvant chemotherapy and bevacizumab had significantly lower microvessel densities and tumour regression grades when compared to liver metastases from untreated or chemotherapy treated patients. This may indicate that bevacizumab treatment results in altered vascular biology and tumour viability, with possible tumour reducing effect.     

Genetic disparity between primary tumours,disseminated tumour cells,and manifest metastasis

Recent genetic analyses of paired samples from primary tumours and disseminated tumour cells have uncovered a bewildering genetic disparity. It was therefore proposed that ectopically residing tumour cells disseminate early and develop independently into metastases parallel to the primary tumour. Alternatively, these cells may represent an irrelevant cell population unable to spawn metastases whereas only cells that disseminated late in primary tumour development (which therefore are similar to the primary tumour) will form manifest metastasis. Here, we review comparative analyses of paired samples from primary tumours and disseminated tumour cells or primary tumours and metastases. The data demonstrate a striking disparity, questioning the use of primary tumours as surrogate for the genetics of systemic cancer. In the era of molecular therapies that build upon genetic defects of tumour cells, these data call for a direct diagnostic pathology of systemic cancer.     

Functional role of melanoma inhibitory activity in regulating invasion and metastasis of malignant melanoma cells in vivo

MIA (melanoma inhibitory activity) has been previously isolated from the tissue culture supernatant of melanoma cell lines as an autoregulatory activity, inhibiting thymidine incorporation. However, subsequent analyses of melanocytic tumours in vivo have correlated enhanced MIA expression with progression of melanocytic tumours, conflicting with the idea that MIA acts as a tumour suppressor. To investigate the role of MIA in vivo, we have therefore generated a panel of stably transfected B16 cell clones secreting different amounts of MIA. The capacity of these cell clones to form lung metastases in syngeneic C57Bl6 mice was strictly correlated to the level of MIA secretion, but the clones did not differ with respect to their proliferation in vitro. In summary, we suggest that MIA plays a causal role in promoting the metastasis of malignant melanomas, involving inhibition of tumour cell attachment to extracellular matrix molecules within their local milieu.     

Tumor-stromal interactions reciprocally modulate gene expression patterns during carcinogenesis and metastasis

This study used a unique xenogeneic breast cancer model to study the effects of tumor cells and neighboring host cells upon each other in tumor growth and metastasis. It exploited species differences between the interacting components to determine how the host influenced the tumor and vice versa. It was found that the gene expression profiles of highly and poorly metastatic clones from the same human breast carcinoma changed differentially when the cells were transferred from growth in vitro to the mammary gland. We describe novel sets of genes, validated by human-specific probes, which were induced in the 2 isogenic, but phenotypically different, tumor lineages by the mammary environment. Conversely, the tumor cells also induced changes in gene expression in the neighboring host stromal (i.e., mesenchymal) cell lineages, validated by mouse-specific probes. Reciprocal inductive interactions were also demonstrated in the tumor deposits formed preferentially in the lungs and lymph nodes by the highly metastatic tumor cells. Subtraction of the induced gene changes in the primary site from those in the metastases revealed that the number and magnitude of specific gene inductions in colonized organs were moderate. This finding indicates that the gene expression program causing metastasis has only limited flexibility and fits well with clinical observations that tumor cells form metastases preferentially in select organs, although tumor cells are scattered ubiquitously. This dependency on suitable host niches suggests new molecular therapeutic avenues that target genes in the host-support system that is manipulated by the malignant cells.     

Cell-cell and cell-stromal interactions in breast cancer invasion and metastasis (review)

Tumour cell invasion and metastasis is a highly orchestrated process in which the malignant cells exhibit an altered relationship to the surrounding host stroma. This is reflected in a change in expression pattern of the receptors which mediate cell-cell and cell-stromal interactions. Down regulation of E-cadherin and of many integrin receptors is associated with tumour development. Conversely, up-regulation or de novo expression of certain integrin receptors enhances tumour cell invasion. It is of fundamental importance to elucidate the mechanisms controlling expression of cell adhesion molecules, and the effects of their altered expression. Cell adhesion molecule expression may be altered by changes in cytoskeletal protein interactions, and there is evidence that both integrin and possibly E-cadherin mediated signalling can modulate expression of matrix degrading proteases, which would further influence invasive and metastatic behaviour.     

Lack of relationship between TIMP-1 tumour cell immunoreactivity,treatment efficacy and prognosis in patients with advanced epithelial ovarian cancer

Background  

Tissue inhibitor of metalloproteinase 1 (TIMP-1) is a natural inhibitor of the matrix metalloproteinases (MMPs) which are proteolytic enzymes involved in degradation of extracellular matrix thereby favoring tumour cell invasion and metastasis. TIMP-1 activity in tumour tissue may therefore play an essential role in the progression of a malignant tumour.     

Unraveling the biology of multiple myeloma disease: cancer stem cells, acquired intracellular changes and interactions with the surrounding micro-environment

Cancerogenesis is believed to be a multistep process composed of different alterations that drive the transformation of normal human cells into highly malignant derivatives. These changes include self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, the evasion of programmed cell death, a limitless replicative potential, sustained angiogenesis, and tissue invasion and metastasis. Some evidence suggests that these cancer cells are derived from immature, proliferative precursors that feed the cancer cell compartment. Both, precursors and cancer cells, intensively interact with their surroundings, commonly described as their micro-environment. The processes above are also important in the biology of multiple myeloma, a malignant bone marrow disorder consisting of monoclonal plasma cells accumulation. In the current review we describe the biology of this disease, stressing the origin of myeloma cells, their acquired genetic changes and interactions with their bone marrow microenvironment.     

Metastatic malignant melanoma: regression induced by combined treatment with interferon [HuIFN-alpha(Le)] and cimetidine

With the aim of potentiating the anti-tumour effect of interferon in metastatic malignant melanoma by concomitant inhibition of suppressor T cells, oral cimetidine (histamine-2 receptor antagonist) medication was added to interferon (HuIFN-alpha(Le] therapy in a series of 20 patients. While no objective tumour responses were recorded with interferon treatment alone administered intramuscularly or intratumorally, six patients had objective tumour regressions on subsequent combined therapy. Five out of eight patients with metastases confined to skin and subcutaneous tissue had complete tumour regressions while one patient with skin and lung metastases achieved an extensive partial regression of the skin tumour and a complete roentgenological regression of the lung metastasis. Three additional patients attained a stable disease status for prolonged periods of time. Histopathological examinations confirmed disappearance and/or degeneration of melanoma cells and demonstrated a marked lymphocyte infiltration in tumour sites of the patients with objective tumour regression.