Matrix metalloproteinases and tumor metastasis

Functions of individual matrix metalloproteinases (MMPs) differentially expressed by tumor cells and stromal cells, are finely regulated by their spatial as well as temporal interactions with distinct cellular and extracellular components of the tumor microenvironment and also distant pre-metastatic sites. Certain aspects of MMP involvement in tumor metastasis such as tumor-induced angiogenesis, tumor invasion, and establishment of metastatic foci at the secondary site, have received extensive attention that resulted in an overwhelming amount of experimental and observational data in favor of critical roles of MMPs in these processes. In particular, dependency of tumor angiogenesis on the activity of MMPs, especially that of MMP-9, renders this step possibly the most effective target of synthetic MMP inhibitors. MMP functioning in other stages of metastasis, including the escape of individual tumor cells from the primary tumor, their intravasation, survival in circulation, and extravasation at the secondary site, have not yet received enough consideration, resulting in insufficient or controversial data. The major pieces of evidence that are most compelling and clearly determine the role and involvement of MMPs in the metastatic cascade are provided by molecular genetic studies employing knock-out or transgenic animals and tumor cell lines, modified to overexpress or downregulate a specific MMP. Findings from all of these studies implicate different functional mechanisms for both tumor and stromal MMPs during distinct steps of the metastatic cascade and indicate that MMPs can exhibit pro-metastatic as well as anti-metastatic roles depending on their nature and the experimental setting. This dual function of individual MMPs in metastasis has become a major focus of this review.     

Matrix metalloproteinases and metastasis

Metastatic disease is responsible for the majority of cancer-related deaths, either directly due to tumor involvement of critical organs or indirectly due to complications of therapy to control tumor growth and spread. An understanding of the mechanisms of tumor cell invasion and metastasis may be important for devising therapies aimed at preventing tumor cell spread. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endoproteinases whose enzymatic activity is directed against components of the extracellular matrix (ECM). In humans, 16 members of this family have been identified by cloning and sequencing. These proteinases are linked by a core of common domain structures and by their relationship to a family of proteinase inhibitors called the tissue inhibitors of metalloproteinases (TIMPs). Four members of the TIMP family have been cloned and sequenced in humans and they inhibit MMPs by forming tight-binding, noncovalent associations with the active site of the MMPs. MMPs facilitate tumor cell invasion and metastasis by at least three distinct mechanisms. First, proteinase action removes physical barriers to invasion through degradation of ECM macromolecules such as collagens, laminins, and proteoglycans. This has been demonstrated in vitro through the use of chemoinvasion assays and in vivo by the presence of active MMPs at the invasive front of tumors. Second, MMPs have the ability to modulate cell adhesion. For cells to move through the ECM, they must be able to form new cell-matrix and cell-cell attachments and break existing ones. Using a cell transfection system that altered the ratio of MMP-2 to TIMP-2 we have demonstrated significant variation in the adhesive phenotype of tumor cells. Finally, MMPs may act on ECM components or other proteins to uncover hidden biologic activities. For example, the angiogenesis inhibitor angiostatin may be produced from plasminogen by MMP action and laminin-5 is specifically degraded by MMP-2 to produce a soluble chemotactic fragment. Thus MMPs play multiple key roles in facilitating the metastasis of tumor cells. Therapies designed to interfere with specific MMP actions may be useful in the control of metastatic disease.     

Critical appraisal of the use of matrix metalloproteinase inhibitors in cancer treatment.

Experimental studies performed prior to 1990 led to the widely held belief that matrix metalloproteinases (MMPs) produced by cancer cells are of critical importance in tumor invasion and metastasis. Based on this evidence, the pharmaceutical industry produced several well tolerated, orally active MMP inhibitors (MMPIs) which demonstrated efficacy in mouse cancer models. Phase III clinical trials initiated in 1997-98 using marimastat, prinomastat (AG3340), and BAY 12-9566 alone or in combination with standard chemotherapy in patients with advanced cancers (lung, prostate, pancreas, brain, GI tract) have recently been reported; no clinical efficacy was demonstrated. Bayer and Agouron have discontinued their ongoing Phase III drug trials of MMPIs in advanced cancer. In retrospect, the failure of MMPIs to alter disease progression in metastatic cancer might have been anticipated since MMPs appear to be important in early aspects of cancer progression (local invasion and micrometastasis) and may no longer be required once metastases have been established. Our understanding of MMP pathophysiology in cancer has expanded considerably in the past 10 years. Current views indicate that: (1) most MMPs in tumors are made by stromal cells, not carcinoma cells; (2) cancer cells induce stromal cells to synthesize MMPs using extracellular matrix metalloproteinase inducer (EMMPRIN) and cytokine stimulatory mechanisms; and (3) MMPs promote cell migration and the release of growth factors sequestered in the extracellular matrix. MMPs have a dual function in tumor angiogenesis: MMP-2 and MT1-MMP are required in breaking down basement membrane barriers in the early stage of angiogenesis, while other MMPs are involved in the generation of an angiogenic inhibitor, angiostatin. In spite of considerable recent progress in identifying multiple roles of MMPs in disease, our understanding of MMP function in cancer is far from complete (see Table 1). Based on accumulated data, it is recommended that future MMPI trials focus on: (1) patients with early stage cancer; (2) the use of MMPIs along with chemotherapy; (3) the measurement of MMPs in tumor tissue and blood as a means of identifying patients who are more likely to respond to MMPI therapy; and (4) identification of biomarkers that reflect activation or inhibition of MMPs in vivo.     

Macrophage migration inhibitory factor promotes the invasion and metastasis of oral squamous cell carcinoma through matrix metalloprotein‐2/9

Macrophage migration inhibitory factor (MIF) has been shown to closely associate with the malignant progression of a variety of human carcinomas. However, the role and its underlying molecular mechanisms of MIF in the invasion and metastasis of oral squamous cell carcinoma (OSCC) still remains unclear. Here, we found that MIF silencing reduced the cell proliferation, migration, and invasion, as well as matrix metalloprotein‐2 (MMP‐2) and MMP‐9 in OSCC cells. Overexpression of MMP‐2 or MMP‐9 restored the migration and invasion of MIF‐knockdown cells, indicating that MMP‐2 and MMP‐9 are downstream targets of MIF. In the xenograft model, MIF silencing inhibited tumor growth and in lymph metastasis model, MIF silencing reduced tumor metastasis. More importantly, immunohistochemistry staining in a tissue microarray (TMA) demonstrated that MIF expression was positively correlated with clinic stage, recurrence, metastasis, and poor prognosis of patients with OSCC as well as with the levels of MMP‐2 or MMP‐9 in TMA. Therefore, our findings suggest that MIF may promote the invasion and metastasis of OSCC through the activation of MMP‐2 and MMP‐9 and prompt further investigation into the therapeutic value of MIF for OSCC treatment.     

Expression of matrix metalloproteinases 1, 2, 9 and their tissue inhibitors in stage II non-small cell lung cancer: implications for MMP inhibition therapy

Non-small cell lung cancer (NSCLC) is the leading cause of cancer death worldwide, with a very poor survival rate. Therefore there is intense scrutiny to provide a better understanding of the molecular and cellular processes involved in this aggressive disease. The matrix metalloproteinases (MMPs) are a large family of extracellular matrix degrading enzymes believed to play a crucial role in tumor invasion and metastasis. MMP inhibitors are now under development as an adjuvant approach to surgical control of NSCLC. However, there is little data available on MMPs or their tissue inhibitors (TIMPs) in NSCLC. Expression of MMP1, MMP2, MMP9, TIMP1 and TIMP2 was assessed in 44 stage II NSCLC. All proteins were found to be expressed at high levels and significant co-expression was observed. These results suggest that a broad spectrum MMP inhibitor is worthy of evaluation as a therapeutic method of reducing tumor invasion and metastasis in stage II NSCLC.     

The effect of hypoxic microenvironment on matrix metalloproteinase expression in xenografts of human oral squamous cell carcinoma

Hypoxia is a common environmental stress factor and is associated with physiological and pathological conditions related to cancer invasion and metastasis. The process of cancer cell invasion involves degradation of the extracellular matrix. Here, we examine the effect of hypoxic microenvironment on matrix metalloproteinase expression in human oral squamous cell carcinoma under in vitro and in vivo conditions. At first, the expression levels of HIF-1alpha and matrix metalloproteinase (MMP) proteins in human oral squamous cell carcinoma cell lines, SAS and HSC-2 cultured under hypoxic or normoxic condition, were assessed by Western blotting. Enzyme activity and mRNA of MMP under hypoxic or normoxic condition were also investigated. Then the SAS and HSC-2 cells were transplanted subcutaneously into immunodeficient mice and the correlation between hypoxia and protein expression for MMPs, HIF-1alpha and Ki-67 were assessed. Hypoxic region was detected by in situ hypoxic probe, pimonidazole. MMP proteins and mRNA in both SAS and HSC-2 cells were increased under hypoxic condition. In xenograft, MMP-2 was expressed in tumor tissue, especially in hypoxic region. In contrast, MMP-9 expression was recognized in tumor tissue, especially neighboring stromal tissues containing blood vessels. Our study suggests that the hypoxic microenvironment in human oral squamous cell carcinoma plays important roles in expression for HIF-1alpha and MMPs, and proliferative activity of tumor cells.     

Pleiotropic Roles of Metalloproteinases in Hematological Malignancies: an Update

Controlled remodeling of the extracellular matrix (ECM) is essential for cell growth, invasion and metastasis. Matrix metalloproteinases (MMPs) are a family of secreted, zincdependent endopeptidases capable of degradation of ECM components. The expression and activity of MMPs in a variety of human cancers have been intensively studied. They play important roles at different steps of malignant tumor formation and have central significance in embryogenesis, tissue remodeling, inflammation, angiogenesis and metastasis. However, increasing evidence demonstrates that MMPs are involved earlier in tumorigenesis. Recent studies also suggest that MMPs play complex roles in tumor progression. MMPs and membrane type (MT)MMPs are potentially significant therapeutic targets in many cancers, so that designing of specific MMP inhibitors would be helpful for clinical trials. Here, we review the pleiotropic roles of the MMP system in hematological malignancies invitro and invivo models.     

Organ heterogeneity of host-derived matrix metalloproteinase expression and its involvement in multiple-organ metastasis by lung cancer cell lines

Cancer metastasis is tightly regulated by the interaction of tumor cells and host organ microenvironments. Matrix metalloproteinases (MMPs), produced by both tumor cells and host stromal cells, play a central role in tumor invasion and angiogenesis. We determined whether metastatic potential of lung cancer to multiple organs is dependent solely on the expression of MMPs by tumor cells, using two metastasis models of human lung cancer cell lines expressing various levels of MMPs and a MMP inhibitor (ONO-4817). In the lung metastasis model, tumor cells (PC14, PC14PE6, H226, A549) inoculated i.v. into nude or SCID mice metastasized only in the lung. In the multiple-organ metastasis model, tumor cells (RERF-LC-AI, SBC-3/DOX, H69/VP, which express low levels of MMPs) inoculated i.v. into natural killer cell-depleted SCID mice metastasized into the liver, kidneys, and systemic lymph nodes. Film in situ zymography analysis revealed that the nontumor parenchyma of the lung had no gelatinolytic activity, whereas gelatinolytic activity of the liver and kidney was high and low, respectively. In the lung metastasis model, gelatinolytic activity of lung nodules directly correlated with the in vitro expression of MMP-2 and MMP-9 by tumor cells. Inhibition of MMP activity by ONO-4817 suppressed lung metastasis by the cell lines that expressed MMPs, but not those that did not express MMP, via the inhibition of MMP activity of lung tumors. In the multiple-organ metastasis model, liver parenchyma, but not liver nodules, showed gelatinolytic activity. The MMP inhibition reduced metastasis to the liver, but not to the kidney or lymph nodes, via inhibition of MMP activity of liver parenchyma. These findings suggest that MMP expression varies among the host organ microenvironments and that stromal MMPs may promote metastasis of lung cancer. Therefore, antimetastatic effects based on MMP inhibition may be dependent on MMPs derived not only from tumor cells but also from organ-specific microenvironments.     

Matrix metalloproteinases as emerging targets for cancer therapy

The matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that play a key role in connective tissue-remodeling proceses. The expression and activity of these proteolytic enzymes is highly regulated by growth factors, cytokines, and hormones, as well as by interactions with specific tissue inhibitors of metalloproteinases (TIMPs). These enzymes are frequently overexpressed in many tumors, and in some cases it has been demonstrated a correlation of high MMP levels with local recurrence and increased invasive and metastatic potential of different malignant tumors. Functional studies have provided evidence that MMPs play an important role in the proteolytic destruction of extracellular matrix and basement membranes, thereby facilitating tumor invasion and metastasis. However, recent studies have indicated that MMPs may be also important in other steps of tumor evolution including neoplastic cell proliferation and angiogenesis stimulation at primary and metastatic sites. Based on the functional relevance of MMPs in tumor progression and metastasis, a number of inhibitors have been developed to try to block the activity of these enzymes. Clinical studies currently in progress will contribute to clarify whether these protease inhibitors may be part of future therapeutic strategies to control the metastatic capacity of neoplastic cells.     

Matrix metalloproteinase inhibitors

Matrix metalloproteinases (MMPs) are a family of zincdependent proteinases that are associated with the tumorigenic process. MMPs degrade the extracellular matrix, promoting tumor invasion and metastasis. They also regulate host defense mechanisms and normal cell function; blocking all MMPs may not lead to a positive therapeutic outcome. Most clinical trials of MMP inhibitors (MMPIs) have yielded disappointing results, perhaps due to inappropriate study design or tumor staging, or to lack of selectivity. Positive results have been seen in gastric cancer with marimastat and in Kaposi’s sarcoma with metastat. This review summarizes the current status of MMPIs.     

基质金属蛋白酶和金属蛋白酶的组织抑制物在人胰腺癌的基因表达

观察胰腺组织及其癌变标本中基质金属蛋白酶（ＭａｔｒｉｘＭｅｔａｌｌｏｐｒｏｔｅｉｎａｓｅｓ,ＭＭＰｓ）和金属蛋白酶的组织抑制物（ＴｉｓｓｕｅＩｎｂｉｉｔｏｒｓｏｆＭｅｔａｌｌｏｐｏｔｅｉｍａｓｅｓ,ＴＩＭＰｓ）基因表达的变化关系,以探讨ＭＭＰｓ在肿瘤侵袭和转移过程中的作用。方法：用原位杂交（ｉｎｓｉｔｕｈｙｂｒｉｄｉｚａｔｉｏｎ,ＩＳＨ）方法,采用ＣＤＮＡ探针（ＭＭＰ２,ＭＭＰ９,ＴＩＭＰ１）对两     

Raf kinase inhibitor protein suppresses nuclear factor-κB-dependent cancer cell invasion through negative regulation of matrix metalloproteinase expression

Accumulating evidence suggests that Raf kinase inhibitor protein (RKIP), which negatively regulates multiple signaling cascades including the Raf and nuclear factor-κB (NF-κB) pathways, functions as a metastasis suppressor. However, the basis for this activity is not clear. We investigated this question in a panel of breast cancer, colon cancer and melanoma cell lines. We found that RKIP negatively regulated the invasion of the different cancer cells through three-dimensional extracellular matrix barriers by controlling the expression of matrix metalloproteinases (MMPs), particularly, MMP-1 and MMP-2. Silencing of RKIP expression resulted in a highly invasive phenotype and dramatically increased levels of MMP-1 and MMP-2 expression, while overexpression of RKIP decreased cancer cell invasion in vitro and metastasis in vivo of murine tumor allografts. Knockdown of MMP-1 or MMP-2 in RKIP-knockdown cells reverted their invasiveness to normal. In contrast, when examining migration of the different cancer cells in a two-dimensional, barrier-less environment, we found that RKIP had either a positive regulatory activity or no activity, but in no case a negative one (as would be expected if RKIP suppressed metastasis at the level of cell migration itself). Therefore, RKIP’s function as a metastasis suppressor appears to arise from its ability to negatively regulate expression of specific MMPs, and thus invasion through barriers, and not from a direct effect on the raw capacity of cells to move. The NF-κB pathway, but not the Raf pathway, appeared to positively control the invasion of breast cancer cells. A regulatory loop involving an opposing relationship between RKIP and the NF-κB pathway may control the level of MMP expression and cell invasion.     

Crosstalk between TGF-β signaling and miRNAs in breast cancer metastasis

Transforming growth factor-β (TGF-β) signaling pathway is a key regulator of various cancer biologies, including cancer cell migration, invasion, angiogenesis, proliferation, as well as apoptosis, and it is one of indispensable signaling pathways during cancer metastasis. TGF-β signaling pathway can regulate and be regulated by a series of molecular and signaling pathways where microRNAs (miRNAs) seem to play important roles. miRNAs are small non-coding RNAs that can regulate expressions of their target genes. Emerging evidence suggest that miRNAs participate in various biological and pathologic processes such as cancer cells apoptosis, proliferation, invasion, migration, and metastasis by influencing multiple signaling pathways. In this article, we focus on the interaction between miRNAs and TGF-β in breast cancer (BC) metastasis through modulating invasion-metastasis-related factors, including epithelial-to-mesenchymal transition (EMT), cancer stem cells (CSCs), matrix metalloproteinase (MMP), tissue inhibitors of MMPs (TIMPs), cell adhesion molecules (CAMs), and tumor microenvironment (TME). Through a clear understanding of the complicated links between TGF-β pathway and miRNAs, it may provide a novel and safer therapeutic target to prevent BC metastasis.     

Matrix metalloproteinases target protease-activated receptors on the tumor cell surface

Matrix metalloproteinases, or MMPs, have been implicated in tumor invasion and metastasis by virtue of their ability to degrade the extracellular matrix (ECM) barrier. However, MMPs are also capable of cleaving non-ECM molecules. The protease-activated receptors (PARs) are the latest MMP targets. The thrombin receptor PAR1 has now been shown to be cleaved and activated on the tumor cell surface by stromal-derived MMP1. The resulting PAR1 activates intracellular G proteins to turn on the migratory and invasive program in tumor cells. This MMP-PAR axis may represent a novel signaling pathway communicating between tumor and stromal cells during tumor progression.     

Increased plasma MMP9 in integrin alpha1-null mice enhances lung metastasis of colon carcinoma cells

Inhibitors of matrix metalloproteinases (MMPs) were developed as anticancer agents based on the observation that MMPs facilitate local tumor spread and metastasis by promoting matrix degradation and cell migration. Unfortunately, these inhibitors were unsuccessful in the clinical treatment of several cancers, including lung cancer. A possible reason contributing to their failure is that MMP activity is critical for the generation of inhibitors of tumor angiogenesis, including angiostatin. Thus, MMPs might play opposing roles in tumor vascularization and invasion. To determine which effect of elevated MMP levels dominates in the progression of metastatic cancer, experimental lung metastasis assays were performed in integrin alpha1-null mice, a genetic model for increased plasma levels of MMP9 and MMP9-generated angiostatin (Pozzi et al., Proc. Natl. Acad. Sci. USA 2000;97:2202-7). We show that while the number of lung colonies in integrin alpha1-null mice was significantly increased compared to their wild-type counterparts, tumor volume was markedly reduced. In vivo treatment with the MMP inhibitor doxycycline resulted in a significant decrease in the number of lung colonies in both genotypes, but the tumors that formed were bigger and more vascularized. Increased tumor vascularization paralleled decreased plasma levels of MMP9 and consequent decreased angiostatin synthesis. These results demonstrate that while inhibition of MMPs prevents and/or reduces tumor invasion and lung metastasis, it has the paradoxical effect of increasing the size and vascularization of metastatic tumors due to decreased generation of inhibitors of endothelial cell proliferation. The continued growth of these large well-vascularized tumors may explain the poor efficacy of MMP inhibitors in lung cancer clinical trials.     

Modifying the soil to affect the seed: role of stromal-derived matrix metalloproteinases in cancer progression

In the 1980's, as the importance of matrix metalloproteinases (MMPs) in cancer progression was discovered, it was recognized that in most tumors these proteases were abundantly and sometimes exclusively expressed not by tumor cells, but by normal host-derived cells like fibroblasts, vascular endothelial cells, myofibroblasts, pericytes or inflammatory cells that contribute to the tumor microenvironment. Later experiments in mice deficient in specific MMPs revealed that host-derived MMPs play a critical role not only in tumor cell invasion, but also in carcinogenesis, angiogenesis, vasculogenesis and metastasis. Tumor cells secrete many factors, cytokines and chemokines that directly or indirectly increase the expression of these MMPs in the tumor microenvironment where they exert extracellular matrix (ECM) degrading and sheddase activities. The knowledge of the complex role that stromal-derived MMPs play in the interaction between tumor cells and stromal cells should allow us to consider specific windows in cancer treatment when MMP inhibition could have a valuable therapeutic effect.     

Tumor microenvironment B cells increase bladder cancer metastasis via modulation of the IL-8/androgen receptor (AR)/MMPs signals

While B cells in the tumor microenvironment may play important roles in cancer progression, their impacts on the bladder cancer (BCa) metastasis remain unclear. Here we found from human clinical BCa samples that BCa tissues could recruit more B cells than the surrounding normal bladder tissues and the in vitro co-culture assay also demonstrated that B cells could be recruited more easily towards BCa cells compared to normal bladder cells. Chamber invasion and 3D invasion assays showed the recruited B cells could then significantly increase the BCa cell invasion. Mechanism dissection found that recruited B cells could increase IL-8/androgen receptor (AR) signals in BCa cells that could then promote the expression of metastasis genes including MMP1 and MMP13. Blocking the IL-8/AR/MMPs signals either by anti-IL-8 neutralizing antibody, AR-siRNA, or MMPs inhibitors all partially reversed the infiltrating B cells capacity to increase the BCa cell invasion. The in vivo data from orthotopically xenografted BCa mouse model also confirmed that infiltrating B cells could increase BCa cell invasion via increasing AR signals. Together, these results demonstrate the key roles of B cells within the bladder tumor microenvironment that increase the BCa metastasis and may help us to develop the potential therapies via targeting these newly identified IL-8/AR/MMPs signals to better battle the BCa progression.     

Human T-cell lymphotropic virus type I-infected cells extravasate through the endothelial barrier by a local angiogenesis-like mechanism

Extravasation of tumor cells through the endothelial barrier is a critical step in cancer metastasis. Human T-cell lymphotropic virus type I (HTLV-I)-associated adult T-cell leukemia/lymphoma (ATL) is an aggressive disease characterized by visceral invasion. We show that ATL and HTLV-I-associated myelopathy patients exhibit high plasma levels of functional vascular endothelial growth factor and basic fibroblast growth factor. The viral oncoprotein Tax transactivates the promoter of the gap-junction protein connexin-43 and enhances gap-junction-mediated heterocellular communication with endothelial cells. The interaction of HTLV-I-transformed cells with endothelial cells induces the gelatinase activity of matrix metalloproteinase (MMP)-2 and MMP-9 in endothelial cells and down-regulates the tissue inhibitor of MMP. This leads to subendothelial basement membrane degradation followed by endothelial cell retraction, allowing neoplastic lymphocyte extravasation. We propose a model that offers a mechanistic explanation for extravasation of HTLV-I-infected cells: after specific adhesion to endothelia of target organs, tumor cells induce a local and transient angiogenesis-like mechanism through paracrine stimulation and direct cell-cell communication with endothelial cells. This culminates in a breach of the endothelial barrier function, allowing cancer cell invasion. This local and transient angiogenesis-like sequence that may facilitate visceral invasion in ATL represents a potential target for ATL therapy.     

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs): Positive and negative regulators in tumor cell adhesion

Cells adhere to one another and/or to matrices that surround them. Regulation of cell–cell (intercellular) and cell–matrix adhesion is tightly controlled in normal cells, however, defects in cell adhesion are common in the majority of human cancers. Multilateral communication among tumor cells with the extracellular matrix (ECM) and neighbor cells is accomplished through adhesion molecules, ECM components, proteolytic enzymes and their endogenous inhibitors. There is sufficient evidence to suggest that reduced adherence is a tumor cell property engaged during tumor progression. Tumor cells acquire the ability to change shape, detach and easily move through spaces disorganizing the normal tissue architecture. This property is due to changes in expression levels of adhesion molecules and/or due to elevated levels of secreted proteolytic enzymes, including matrix metalloproteinases (MMPs). Among other roles, MMPs degrade the ECM and, therefore, prepare the path for tumor cells to migrate, invade and spread to distant secondary areas, where they form metastasis. Tissue inhibitors of metalloproteinases or TIMPs control MMP activities and, therefore, minimize matrix degradation. Both MMPs and TIMPs are involved in tissue remodeling and decisively regulate tumor cell progression including tumor angiogenesis. In this review, we describe and discuss data that support the important role of MMPs and TIMPs in cancer cell adhesion and tumor progression.