Tumor metastasis and cell adhesion molecules

The adhesive interaction between tumor cells, host cells or extracellular matrix (ECM) plays a crucial role in metastatic formation. We used synthetic polypeptide containing a repetitive core sequence, Arg-Gly-Asp (RGD), of cell-adhesive molecules; poly (RGD), to antagonize the adhesive interaction between ECM and integrin receptors on tumor cell surface during the metastatic cascade. Poly (RGD) significantly inhibited the experimental lung and liver metastasis as compared with RGD peptide when it was coinjected i.v. with different types of tumors. In a spontaneous lung metastasis model using B16-BL6 melanoma, multiple i.v. administrations of poly (RGD), before or after surgical excision of the primary tumor, resulted in significant reduction of the lung colonization. The mechanism responsible for the inhibition is partly associated with the ability to interfere with cell functions such as adhesiveness, motility, and invasiveness in the metastatic process. Poly (RGD) showed no cytotoxicity against host and tumor cells. Thus, the regulation of adhesive interaction of tumor cells with ECM or host cells by anti-adhesive polypeptides may provide a promising approach for the prevention of tumor metastasis.     

Endothelial cell membrane vesicles in the study of organ preference of metastasis

Many malignancies exhibit distinct patterns of metastasis that appear to be mediated by receptor/ligand-like interactions between tumor cells and organ-specific vascular endothelium. In order to study endothelial cell surface molecules involved in the binding of metastatic cells, we developed a perfusion method to isolate outside-out membrane vesicles from the lumenal surface of rat lung microvascular endothelium. Lungs were perfused in situ for 4 h at 37 degrees C with a solution of 100 mM formaldehyde, 2 mM dithiothreitol in phosphate-buffered saline to induce endothelial cell vesiculation. Radioiodinated rat lung endothelial cell membrane vesicles bound lung-metastatic tumor cells (B16F10, R323OAC-MET) in significantly higher numbers than their low or nonmetastatic counterparts (B16F0, R323OAC-LR). In contrast, leg endothelial membrane vesicle showed no binding preference for either cell line. Neuraminidase treatment of vesicles abolished specificity of adhesion of lung-derived vesicles to lung metastatic tumor cells. These results demonstrate that in situ perfusion is an appropriate technique to obtain pure endothelial cell membrane vesicles containing functionally active adhesion molecules. The preferential binding of lung-derived endothelial cell membrane vesicles by lung metastatic tumor cells is evidence of the importance of endothelial cell adhesion molecules in the formation of metastases.     

Tumor progression and metastasis

It is now widely accepted that cancer is attributed to the accumulation of genetic alterations in cells. Thus, to understand the molecular mechanisms of cancer metastasis, it is indispensable to identify the genes whose alterations accumulate during cancer progression as well as the genes whose expression is responsible for the acquisition of metastatic potential in cancer cells. Molecular analyses of cancer cells in various stages of progression have revealed that alterations in tumor suppressor genes and oncogenes accumulate during tumor progression and correlate with the clinical aggressiveness of cancer. Comparative analyses of gene expression profiles between metastatic and non-metastatic cells have revealed that various genes are differentially expressed in association with the metastatic potential of cancer cells. A number of genes have been also identified as having functions in inducing or suppressing metastasis in experimental models. However, the association between causative genetic alterations and resulting phenotypic alterations with respect to the metastatic potential of cancer cells is not fully understood. Therefore, elucidation of genotype-phenotype correlation will be required to further understand a complex process of metastasis. Here, I review the progress on molecular studies of tumor progression and metastasis of the past 20 years and discuss the future direction in this field of science.     

Tumor metastasis and the lymphatic vasculature

Tumor‐associated lymphatic vessels act as a conduit by which disseminating tumor cells access regional lymph nodes and form metastases there. Lymph node metastasis is of major prognostic significance for many types of cancer, although lymph node metastases are themselves rarely life‐threatening. These observations focus our attention on understanding how tumor cells interact with the lymphatic vasculature, and why this interaction is so significant for prognosis. Tumors interact with the lymphatic vasculature in a number of ways, including vessel co‐option, chemotactic migration and invasion into lymphatic vessels and induction of lymphangiogenesis. Tumor‐induced lymphangiogenesis both locally and in regional lymph nodes has been correlatively and functionally associated with metastasis formation and poor prognosis. The investigation of the molecular regulation of lymphangiogenesis has identified ways of interfering with prolymphangiogenic signaling. Blockade of tumor‐induced lymphangiogenesis in preclinical models inhibits metastasis formation in lymph nodes and often also in other organs, suggesting that blocking the lymphatic route of dissemination might suppress metastasis formation not only in lymph nodes but also in other organs. However, randomized clinical trials that have investigated the efficacy of therapeutic removal of lymph nodes have concluded that lymph node metastases act only as indicators that primary tumors have developed metastatic potential, and do not govern the further spread of metastatic cells. To reconcile these apparently paradoxical observations we suggest a model in which tumor‐induced lymphangiogenesis and lymph node metastasis formation act as indicators that tumors are producing factors that can act systemically to promote metastasis formation in distant organs. © 2009 UICC     

Adhesion molecules in lymphoma metastasis

Summary Recently, many surface proteins of lymphoid cells that mediate adhesion to other cells and extracellular matrix have been identified. Several of these cellular adhesion molecules (CAM) are also expressed by metastatic lymphoma cells and may mediate adhesion to tissue components during the metastatic process. Correlations observed between expression of certain CAM, like MEL-14 and CD44, and particular patterns of spread, support this notion, but conclusive evidence is scarce.We have used T-cell hybridomas to study the mechanisms of wide-spread lymphoid metastasis. The results obtained with this model are reviewed here. The advantages are that a large number of genetically similar cell lines can be generated, which can be grouped in large panels of highly invasive and non-invasive cells. Invasiveness of these cells in hepatocyte and fibroblast monolayers correlates with exprimental metastasis.Lymphoid CAM that are potentially involved in metastasis are reviewed. Several of these CAM are not, or not consistently, expressed by the invasive T-cell hybridomas, indicating that they are not indispensable. Notably, some of the CAM involved in the onset of an immune response or in migration into inflamed tissues, like ICAM-1 and VLA-4, and the homing receptors MEL-14 and LPAM-1 do not seem to be involved. CAM that are consistently expressed by the T-cell hybrids include LFA-1, the beta-1 integrin subunit CD29, CD31 (PECAM-1) and CD44 (Hermes homing receptor).We have generated considerable evidence that LFA-1 is required for efficient metastasis of T-cell hybrids, based on the behavior of LFA-1-deficient mutants and revertants. High levels of LFA-1 are required. The relevant counterstructure is probably ICAM-2 rather than ICAM-1. Preliminary results suggest that also a beta-1 integrin, possibly VLA-5, plays a role. Finally, we summarize evidence indicating that CD31 and CD44 are primary candidates for involvement in metastatic spread of T-cell hybridomas.     

Adhesion molecules and cancer metastasis

In accordance with the recent development of molecular biology and genetic technology for the study of adhesion molecule of cell-cell and cell-extracellular matrix interaction, correlation of these interactions with cancer metastasis have been progressing rapidly. For several years, active peptides derived from extracellular matrix (RGD) in fibronectin, YIGSR in laminin) have been used to inhibit tumor cell adhesion receptors, and block malignant cell adhesion and metastatic properties. Recently we have investigated the correlation between expression of cell-cell adhesion molecule (Ecadherin: E-CD) and metastasis in human esophageal, gastric and breast cancers by immunohistochemical staining using anti-human E-CD antibody (HE-CD-1). E-CD expression of these tumors was reduced in more than half cases when compared to normal epithelium. Moreover, E-CD expression of metastatic tumor in the primary sites was reduced significantly more than that of non-metastatic tumor. These results indicate that a firmly formed cluster of tumor cells might detach from the tumor nests with unstable adhesiveness, transit in the circulation and form metastatic foci in the secondary sites.     

肿瘤微环境与肿瘤转移

肿瘤转移与肿瘤微环境中成纤维细胞、转化生长因子、肿瘤相关巨噬细胞、趋化因子及其受体、凝血酶等多种因素密切相关。成纤维细胞通过促进肿瘤血管生成、促进癌细胞与细胞外基质黏附、促进细胞外基质降解等环节参与肿瘤的转移。TGF-β是由巨噬细胞、间质细胞和肿瘤细胞产生,它能对抗血管内皮的紧密连接和黏附连接,使毛细血管壁完整性受到破坏,从而导致毛细血管通透性增加,使肿瘤细胞从血管中游出进入器官组织中形成种植转移。肿瘤相关性巨噬细胞可合成和分泌EGF等细胞因子,引导肿瘤细胞穿越血管壁,促进肿瘤的转移。趋化因子及其受体对肿瘤细胞的迁移起着决定性的作用。凝血酶能通过影响微环境中其他细胞的行为而为肿瘤转移提供一个相容的环境。明晰肿瘤转移与肿瘤微环境的关系,进而明确在肿瘤发生、发展、转移过程中发挥重要作用的关键分子,寻找其相对应的靶点,对于肿瘤的诊断及治疗具有重要的作用。     

Tumor metastasis and growth factors

Massive investigations are being carried out on growth factors. Growth factors are an important determinant for the formation of successive tumor metastasis at target organs. We review the findings, including our data, of growth factors in relation to tumor metastasis.     

Tumor cell motility and metastasis

Cellular locomotion plays a critical role in such normal processes as embryonic development, tissue segregation, as well as the infiltration of fibroblasts and vascular cells during wound repair and the inflammatory responses of the adult immune system. During tumor invasion and metastasis the processes of cell migration achieve dire significance. Disruption of normal homeostatic mechanisms to benefit the survival of the individual tumor cell is a common theme discovered during the characterization of factors once thought to be tumor-specific. One such molecule, tumor cell autocrine motility factor, was so described and has only recently been identified as a normal protein involved in intracellular glycolysis as well as implicated as an extracellular effector of normal cell functions including survival of certain populations of neurons. This molecule represents a member of the newly emerging family of intracellular enzymes whose disparate functions as extracellular mediators of cellular responses defines a new class of ecto/exoenzymes which play a role in normal cellular processes and are inappropriately utilized by tumor cells to elicit new survival strategies.     

Tumor cell progression and differentiation in metastasis

The development and evolution of tumors is regulated by both genetic and epigenetic events. It is thought that these processes tend to drive neoplastic development in opposing directions so that tumor progression, predominantly as a consequence of mutational events, leads to increasing tumor aggression. Conversely the induction of differentiation, largely through epigenetic mechanisms, tends to cause tumors to evolve to a more benign phenotype. However, these generalizations are a simplistic view of a complex dynamic event where both processes can be overlaid within a single neoplasm. Using malignant melanoma as a model system the alterations in gene expression and their effects upon metastatic dissemination, that accompany some of these changes, both natural and induced, are described.     

肝癌血管生成的研究

肝癌是比较典型的多血管肿瘤,其生长和转移依赖肿瘤血管生成。栓塞已有的血管(肝动脉栓塞化疗),和阻断血管生成(索拉菲尼)的治疗已是临床标准的肝癌治疗方法。最近的证据显示侵袭性较强的肝癌可在癌周诱导特殊的环境     

The role of the organ microenvironment in brain metastasis

More than 40% of patients with lung cancer and breast cancer develop brain metastasis. With improved local control and therapy of metastasis to visceral organs, the morbidity and mortality due to late diagnosed brain metastasis are projected to rise. The median survival for untreated patients is 1-2 months, which may be extended to 6 months with surgery, radiotherapy, and chemotherapy. The development of a relevant mouse model for the establishment and growth of brain metastasis has advanced our understanding of the biology and therapy of this most feared consequence of cancer. Injection of murine or human tumor cells into the internal carotid artery of mice produces experimental metastases in specific regions of the brain that are not due to patterns of initial cell arrest, motility, or invasiveness, but rather to the ability of metastatic tumor cells to exploit homeostatic mechanisms and proliferate. Immunohistochemical and morphometric analyses demonstrate that the density of blood vessels within experimental metastases in brains of mice or in clinical specimen of human lung cancer brain metastases is lower than that in the adjacent tumor-free brain parenchyma. However, brain metastasis-associated blood vessels are dilated and contain numerous dividing endothelial cells. Immunohistochemical analysis also reveals that tumor cells located less than 100 μm from a blood vessel are viable, whereas more distant tumor cells undergo apoptosis. Tumor cells within brain metastasis produce VEGF which induces permeability in adjacent vessels. The BBB in metastases that are larger than 0.25 mm in diameter is leaky. Metastases in the brain are resistant to chemotherapeutic drugs. The venerable "seed and soil" hypothesis suggests that the outcome of metastasis depends on the interaction between unique tumor cells and the specific organ microenvironment. The demonstration that activated astrocytes whose physiological role is to protect neurons from toxic substances can be exploited by tumor cells for protection from chemotherapeutic drugs suggests new approaches to the treatment of this fatal disease.     

Tumor invasion and host extracellular matrix

In this review some of the major mechanistic pathways by which tumor cells are thought to invade host tissues are discussed. Tumor invasion has been conceived to be the result of pathological, close-range interactions between malignant cells and host stroma. The sequence of events that characterize invasion can be summarized as follows: (a) Tumor cell clusters break from the confinement of the primary tumor. Loss of intercellular junctions (desmosomes), alterations in the chemical composition and physical properties of the cell surface coat (loss of fibronectin and heparan sulfate; excessive amounts of hyaluronate), and loosening of cell-substrate interactions (loss of hemidesmosomes, fibronectin, and heparan sulfate), are among the most frequently listed causes of tumor cell shedding. (b) Increased proteolytic activities at the invasion front cause focal alterations in the surrounding extracellular matrix, thereby changing its physical properties. Collagenases and cathepsins, as well as elastase and other neutral proteinases are the enzymes most frequently associated with matrix destruction and invasion. In some tissues this process is effectively regulated by inhibitors of matrix-degrading, proteolytic enzymes. (c) Tumor cells migrate into the altered matrix, possibly moving as aggregates along guidance tracks provided by host structures (blood vessels, lymphatics, nerves) or matrix macromolecules (collagen and fibronectin tracks). Migration seems to be preceded by increased swelling of glycosaminoglycan (i.e., hyaluronate) in the matrix, ahead of the migrating cell population. Various host cell types (mast cells, fibroblasts, endothelial cells, macrophages, etc.) may participate in these events.     

Early tumor growth in metastatic organs influenced by the microenvironment is an important factor which provides organ specificity of colon cancer metastasis

We have previously demonstrated that liver metastases in nude mice and lung metastases in nude rats occurred specifically, when KM12SM human colon carcinoma cells were inoculated orthotopically into the cecal wall of nude mice and rats. To clarify the relationship between the tumor growth potential in the metastatic organs and the metastatic organ preference in these two metastatic models, we have evaluated the in vitro cell growth activities affected by the organ conditioned medium (CM) from the liver and lung, and the in vivo growth activities of the ectopic implanted tumors in the liver and lung. The tumorigenicity of the ectopic implanted tumors was 100% in mouse liver, 33% in rat liver, 50% in mouse lung, and 75% in rat lung. The crude liver CM of the animals showed inhibitory activities for KM12SM cell growth in a dosage-dependent manner, and the crude lung CM stimulated KM12SM cell growth. The liver CM of nude mice inhibited the KM12SM cell growth more strongly compared with the CM of nude rats, and the lung CM of nude rats was more strongly stimulated compared with the CM of nude mice. The liver CM of nude mice had non-heparin binding factors, which stimulated or inhibited KM12SM cell growth, in a molecular weight range of 50 to 100 kDa. By contrast, the liver CM of nude rats showed no growth stimulating activity for KM12SM cells. These results suggest that the metastatic organ specificity of KM12SM cells may depend on the early tumor growth influenced by the microenvironment in metastatic organs.     

肿瘤淋巴管生成与肿瘤的淋巴道转移

淋巴管在肿瘤转移过程中起着至关重要的作用。近年来发现,在多种肿瘤组织内部也存在微淋巴管,只是处于萎缩状态,肿瘤内淋巴管生成显著影响未发生肿瘤转移患者的存活率。肿瘤内淋巴管的存在与否有赖于特异淋巴管内皮标志物,近年来发现并被认可的主要有VEGFR-3、Podoplanin、Prox-1、LYVE-1等。研究证实VEGF-C及VEGF-D通过活化VEGFR-3对肿瘤淋巴管生成进行调控。VEGF-C的表达可促进瘤周淋巴管增生,促进肿瘤的淋巴结转移,多数人认为可作为患者预后不良的独立指标;VEGF-D不但可诱导肿瘤内的淋巴管生成,而且可导致肿瘤细胞向附近淋巴道播散,其表达水平与淋巴转移及低生存率相关。针对VEGFR-3信号转导系统的抗淋巴管生成治疗,有望成为抗淋巴转移的一个有效途径,而其中每一个环节都可能成为控制肿瘤生长、转移以及治疗肿瘤的潜在靶点。     

Growth and metastasis of human melanoma xenografts in the hamster host.

Cells from three human melanoma cell culture lines (UCLASO-M-12, UCLASO-M-7, and WEG-1) were transplanted into the cheek pouches of immunosuppressed hamsters. Tumor nodules were found in the cheek pouches of hamsters receiving any one of these lines, and by 90--100 days after transplantation, nearly all hamsters had grossly visible lung metastases. Metastases were noted only in hamsters receiving continuous immunosuppression during the transplant period.     

黏附分子与鼻咽癌的侵袭和转移

黏附分子是一类由细胞产生的膜表面糖蛋白.多项研究已证实,黏附分子可介导肿瘤细胞与细胞外基质、血管内皮细胞、淋巴细胞或其他肿瘤细胞之间的相互作用,因此在恶性肿瘤的侵袭和转移过程中起着重要作用.近年来,已有大量关于黏附分子表达水平的变化可抑制或促进鼻咽癌转移的研究.