A residue in the S2 subsite controls substrate selectivity of matrix metalloproteinase-2 and matrix metalloproteinase-9

Fluorescent Peptomer Substrates for Differential Degradation by Metalloproteases

Proteases, especially MMPs, are attractive biomarkers given their central role in both physiological and pathological processes. Distinguishing MMP activity with degradable substrates, however, is a difficult task due to overlapping substrate specificity profiles. Here, we developed a system of peptomers (peptide-peptoid hybrids) to probe the impact of non-natural residues on MMP specificity for an MMP peptide consensus sequence. Peptoids are non-natural, N-substituted glycines with a large side-chain diversity. Given the presence of a hallmark proline residue in the P3 position of MMP consensus sequences, we hypothesized that peptoids may offer N-substituted alternatives to generate differential interactions with MMPs. To investigate this hypothesis, peptomer substrates were exposed to five different MMPs, as well as bacterial collagenase, and monitored by fluorescence resonance energy transfer and liquid chromatography-mass spectrometry to determine the rate of cleavage and the composition of degraded fragments, respectively. We found that peptoid residues are well tolerated in the P3 and P3' substrate sites and that the identity of the peptoid in these sites displays a moderate influence on the rate of cleavage. However, peptoid residues were even better tolerated in the P1 substrate site where activity was more strongly correlated with side-chain identity than side-chain position. All MMPs explored demonstrated similar trends in specificity for the peptomers but exhibited different degrees of variability in proteolytic rate. These kinetic profiles served as "fingerprints" for the proteases and yielded separation by multivariate data analysis. To further demonstrate the practical application of this tunability in degradation kinetics, peptomer substrates were tethered into hydrogels and released over distinct timescales. Overall, this work represents a significant step toward the design of probes that maximize differential MMP behavior and presents design rules to tune degradation kinetics with peptoid substitutions, which has promising implications for diagnostic and prognostic applications using array-based sensors.

Identification of a Common Pharmacophore for Binding to MMP2 and RGD Integrin: Towards a Multitarget Approach to Inhibit Cancer Angiogenesis and Metastasis

During tumor angiogenesis different growth factors, cytokines and other molecules interact closely with each other to facilitate tumor cell invasion and metastatic diffusion. The most intensively studied as molecular targets in anti-angiogenic therapies are vascular endothelial growth factor (VEGF) and related receptors, integrin receptors and matrix metalloproteinases (MMPs). Considering the poor efficacy of cancer angiogenesis monotherapies, we reasoned combining the inhibition of αvβ3 and MMP2 as a multitarget approach to deliver a synergistic blockade of tumor cell migration, invasion and metastasis. Accordingly, we identified a common pharmacophore in the binding cavity of MMP2 and αvβ3, demonstrating such approach with the design, synthesis and bioassays of tyrosine-derived peptidomimetics carrying the necessary functional groups to bind to key pharmacophoric elements of MMP2 and αvβ3 RGD integrin.

Quantitative profiling of protease specificity

Proteases are an important class of enzymes, whose activity is central to many physiologic and pathologic processes. Detailed knowledge of protease specificity is key to understanding their function. Although many methods have been developed to profile specificities of proteases, few have the diversity and quantitative grasp necessary to fully define specificity of a protease, both in terms of substrate numbers and their catalytic efficiencies. We have developed a concept of “selectome”; the set of substrate amino acid sequences that uniquely represent the specificity of a protease. We applied it to two closely related members of the Matrixin family–MMP-2 and MMP-9 by using substrate phage display coupled with Next Generation Sequencing and information theory-based data analysis. We have also derived a quantitative measure of substrate specificity, which accounts for both the number of substrates and their relative catalytic efficiencies. Using these advances greatly facilitates elucidation of substrate selectivity between closely related members of a protease family. The study also provides insight into the degree to which the catalytic cleft defines substrate recognition, thus providing basis for overcoming two of the major challenges in the field of proteolysis: 1) development of highly selective activity probes for studying proteases with overlapping specificities, and 2) distinguishing targeted proteolysis from bystander proteolytic events.

Proteases and proteolysis are intimately involved in virtually all biological processes from embryonic development to programmed cell death and cellular protein recycling. As the only irreversible posttranslational modification, proteolysis represents a committed step in regulation of biological networks and pathways. Imbalance of proteolytic activity has catastrophic implications and is the basis of many genetic disorders as well as a multitude of pathological states of varying etiologies. To understand protease function, one must gain insight into the repertoires of substrates targeted by these enzymes. As many proteases recognize a wide variety of sequences in proteins, it is a challenge to establish if a particular cleavage represents a targeted or a bystander proteolytic event. In addition, since many proteases have overlapping specificities, especially among closely related members of the same gene families, it is a challenge to develop highly selective tools for studying or inhibition of these enzymes. In this work, we used two closely related proteases (MMP-2 and 9) as a model system for development of an information theory-based approach to quantification of substrate specificity and demonstrated its potential for distinguishing between the target and bystander proteolytic events as well as for uncovering selectivity between closely related proteases.

Fluorescent polymer dots and graphene oxide based nanocomplexes for "off-on" detection of metalloproteinase-9

Numerous studies have demonstrated that cancer-related matrix metalloproteinase-9 (MMP-9) is an ideal biomarker for cancer diagnosis. However, most MMP-9 detection methods are expensive and time-consuming, and more convenient and specific MMP-9 detection methods are needed both clinically and in research. In the present study, peptide-linked polymer dots were assembled onto a graphene oxide surface to construct a graphene oxide-peptide-polymer dot (GO-Pep-Pdot) nanocomplex for sensitive, rapid, and accurate detection of MMP-9. In the absence of MMP-9, the nanocomplex was in an "off" state, whereas in the presence of MMP-9, the nanocomplex was turned "on", resulting in the emission of a fluorescence signal that is linearly correlated with the MMP-9 concentration. The limit of detection of the nanocomplex was 3.75 ng mL^-1, lower than most methods. This method was successfully verified by detecting MMP-9 in clinical serum samples of prostate cancer. The results suggest that this protease nanocomplex is generic and can be adopted to respond to other proteases by selecting specific peptides with suitable cleavage sites in clinics.

Peptide Cross-Linked Poly(2-oxazoline) as a Sensor Material for the Detection of Proteases with a Quartz Crystal Microbalance

Inflammatory conditions are frequently accompanied by increased levels of active proteases, and there is rising interest in methods for their detection to monitor inflammation in a point of care setting. In this work, new sensor materials for disposable single-step protease biosensors based on poly(2-oxazoline) hydrogels cross-linked with a protease-specific cleavable peptide are described. The performance of the sensor material was assessed targeting the detection of matrix metalloproteinase-9 (MMP-9), a protease that has been shown to be an indicator of inflammation in multiple sclerosis and other inflammatory conditions. Films of the hydrogel were formed on gold-coated quartz crystals using thiol-ene click chemistry, and the cross-link density was optimized. The degradation rate of the hydrogel was monitored using a quartz crystal microbalance (QCM) and showed a strong dependence on the MMP-9 concentration. A concentration range of 0-160 nM of MMP-9 was investigated, and a lower limit of detection of 10 nM MMP-9 was determined.

Discretionary Transduction of MMP-Sensitized Tousled in Head and Neck Cancer

Oral radiotoxicity is often a limiting factor in cancer treatment. Previously, we demonstrated that transfer of cell-permeable, TAT-fusion Tousled-like kinase 1B (TLK1B) protein in salivary glands effectively mitigates radiation-induced salivary dysfunction. However, similar to most radioprotectors, TLK1B can carry the risk of limiting cancer treatment efficacy. The central goal of the study was, therefore, to reengineer TLK1B as a selective radioprotector of normal cells. Degradation of the extracellular matrix by proteases such as matrix metalloproteinases (MMPs) is a hallmark of aggressive tumors. Increased expression of membrane type 1-MMP (MT1-MMP; also called MMP14) is observed in a variety of cancers including head and neck squamous cell carcinoma (HNSCC). To limit TLK1B transduction to normal cells, we rendered the protein susceptible to MT1-MMP cleavage on the premise that high expression of MT1-MMP on the cell surface of HNSCC will suppress TLK1B internalization. Two optimal MT1-MMP-sensitive sequences (MS) were identified that when incorporated in TAT-TLK1B excluded its cellular entry in HNSCC, SCC40, but not immortalized salivary acinar cells, NS-SV-AC. Importantly, administration of MS-harboring TAT-TLK1B did not affect the sensitivity of tumors to radiation in a nude mouse xenograft tumor model. We conclude that a MMP-sensitive TLK1B can be an attractive therapeutic to allay salivary radiotoxicity without compromising cancer treatment efficacy.

SheddomeDB: the ectodomain shedding database for membrane-bound shed markers

BACKGROUND

A number of membrane-anchored proteins are known to be released from cell surface via ectodomain shedding. The cleavage and release of membrane proteins has been shown to modulate various cellular processes and disease pathologies. Numerous studies revealed that cell membrane molecules of diverse functional groups are subjected to proteolytic cleavage, and the released soluble form of proteins may modulate various signaling processes. Therefore, in addition to the secreted protein markers that undergo secretion through the secretory pathway, the shed membrane proteins may comprise an additional resource of noninvasive and accessible biomarkers. In this context, identifying the membrane-bound proteins that will be shed has become important in the discovery of clinically noninvasive biomarkers. Nevertheless, a data repository for biological and clinical researchers to review the shedding information, which is experimentally validated, for membrane-bound protein shed markers is still lacking.

RESULTS

In this study, the database SheddomeDB was developed to integrate publicly available data of the shed membrane proteins. A comprehensive literature survey was performed to collect the membrane proteins that were verified to be cleaved or released in the supernatant by immunological-based validation experiments. From 436 studies on shedding, 401 validated shed membrane proteins were included, among which 199 shed membrane proteins have not been annotated or validated yet by existing cleavage databases. SheddomeDB attempted to provide a comprehensive shedding report, including the regulation of shedding machinery and the related function or diseases involved in the shedding events. In addition, our published tool ShedP was embedded into SheddomeDB to support researchers for predicting the shedding event on unknown or unrecorded membrane proteins.

CONCLUSIONS

To the best of our knowledge, SheddomeDB is the first database for the identification of experimentally validated shed membrane proteins and currently may provide the most number of membrane proteins for reviewing the shedding information. The database included membrane-bound shed markers associated with numerous cellular processes and diseases, and some of these markers are potential novel markers because they are not annotated or validated yet in other databases. SheddomeDB may provide a useful resource for discovering membrane-bound shed markers. The interactive web of SheddomeDB is publicly available at http://bal.ym.edu.tw/SheddomeDB/ .

Emerging challenges in the design of selective substrates, inhibitors and activity-based probes for indistinguishable proteases

Proteases are enzymes that hydrolyze the peptide bond of peptide substrates and proteins. Despite significant progress in recent years, one of the greatest challenges in the design and testing of substrates, inhibitors and activity‐based probes for proteolytic enzymes is achieving specificity toward only one enzyme. This specificity is particularly important if the enzyme is present with other enzymes with a similar catalytic mechanism and substrate specificity but completely different functionality. The cross‐reactivity of substrates, inhibitors and activity‐based probes with other enzymes can significantly impair or even prevent investigations of a target protease. In this review, we describe important concepts and the latest challenges, focusing mainly on peptide‐based substrate specificity techniques used to distinguish individual enzymes within major protease families.

Secreted Matrix Metalloproteinase-9 of Proliferating Smooth Muscle Cells as a Trigger for Drug Release from Stent Surface Polymers in Coronary Arteries

Cardiovascular diseases are the leading causes of death in industrialized countries. Atherosclerotic coronary arteries are commonly treated with percutaneous transluminal coronary intervention followed by stent deployment. This treatment has significantly improved the clinical outcome. However, triggered vascular smooth muscle cell (SMC) proliferation leads to in-stent restenosis in bare metal stents. In addition, stent thrombosis is a severe side effect of drug eluting stents due to inhibition of endothelialization. The aim of this study was to develop and test a stent surface polymer, where cytotoxic drugs are covalently conjugated to the surface and released by proteases selectively secreted by proliferating smooth muscle cells. Resting and proliferating human coronary artery smooth muscle cells (HCASMC) and endothelial cells (HCAEC) were screened to identify an enzyme exclusively released by proliferating HCASMC. Expression analyses and enzyme activity assays verified selective and exclusive activity of the matrix metalloproteinase-9 (MMP-9) in proliferating HCASMC. The principle of drug release exclusively triggered by proliferating HCASMC was tested using the biodegradable stent surface polymer poly-l-lactic acid (PLLA) and the MMP-9 cleavable peptide linkers named SRL and AVR. The specific peptide cleavage by MMP-9 was verified by attachment of the model compound fluorescein. Fluorescein release was observed in the presence of MMP-9 secreting HCASMC but not of proliferating HCAEC. Our findings suggest that cytotoxic drug conjugated polymers can be designed to selectively release the attached compound triggered by MMP-9 secreting smooth muscle cells. This novel concept may be beneficial for stent endothelialization thereby reducing the risk of restenosis and thrombosis.

New insights into the substrate specificity of macrophage elastase MMP-12

Macrophage elastase, or MMP-12, is mainly produced by alveolar macrophages and is believed to play a major role in the development of chronic obstructive pulmonary disease (COPD). The catalytic domain of MMP-12 is unique among MMPs in that it is very highly active on numerous substrates including elastin. However, measuring MMP-12 activity in biological fluids has been hampered by the lack of highly selective substrates. We therefore synthesized four series of fluorogenic peptide substrates based on the sequences of MMP-12 cleavage sites in its known substrates. Human MMP-12 efficiently cleaved peptide substrates containing a Pro at P3 in the sequence Pro-X-X↓Leu but lacked selectivity towards these substrates compared to other MMPs, including MMP-2, MMP-7, MMP-9 and MMP-13. On the contrary, the substrate Abz-RNALAVERTAS-EDDnp derived from the CXCR5 chemokine was the most selective substrate for MMP-12 ever reported. All substrates were cleaved more efficiently by full-length MMP-12 than by its catalytic domain alone, indicating that the C-terminal hemopexin domain influences substrate binding and/or catalysis. Docking experiments revealed unexpected interactions between the peptide substrate Abz-RNALAVERTAS-EDDn and MMP-12 residues. Most of our substrates were poorly cleaved by murine MMP-12 suggesting that human and murine MMP-12 have different substrate specificities despite their structural similarity.

2-Photon Characterization of Optical Proteolytic Beacons for Imaging Changes in Matrix-Metalloprotease Activity in a Mouse Model of Aneurysm

Abdominal aortic aneurysm is a multifactorial disease that is a leading cause of death in developed countries. Matrix-metalloproteases (MMPs) are part of the disease process, however, assessing their role in disease initiation and progression has been difficult and animal models have become essential. Combining Förster resonance energy transfer (FRET) proteolytic beacons activated in the presence of MMPs with 2-photon microscopy allows for a novel method of evaluating MMP activity within the extracellular matrix (ECM). Single and 2-photon spectra for proteolytic beacons were determined in vitro. Ex vivo experiments using the apolipoprotein E knockout angiotensin II-infused mouse model of aneurysm imaged ECM architecture simultaneously with the MMP-activated FRET beacons. 2-photon spectra of the two-color proteolytic beacons showed peaks for the individual fluorophores that enable imaging of MMP activity through proteolytic cleavage. Ex vivo imaging of the beacons within the ECM revealed both microstructure and MMP activity. 2-photon imaging of the beacons in aneurysmal tissue showed an increase in proteolytic cleavage within the ECM (p<0.001), thus indicating an increase in MMP activity. Our data suggest that FRET-based proteolytic beacons show promise in assessing MMP activity within the ECM and will therefore allow future studies to identify the heterogeneous distribution of simultaneous ECM remodeling and protease activity in aneurysmal disease.

Matrix metalloproteinases as therapeutic targets for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a restrictive lung disease that is associated with high morbidity and mortality. Current medical therapies are not fully effective at limiting mortality in patients with IPF, and new therapies are urgently needed. Matrix metalloproteinases (MMPs) are proteinases that, together, can degrade all components of the extracellular matrix and numerous nonmatrix proteins. MMPs and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the pathogenesis of IPF based upon the results of clinical studies reporting elevated levels of MMPs (including MMP-1, MMP-7, MMP-8, and MMP-9) in IPF blood and/or lung samples. Surprisingly, studies of gene-targeted mice in murine models of pulmonary fibrosis (PF) have demonstrated that most MMPs promote (rather than inhibit) the development of PF and have identified diverse mechanisms involved. These mechanisms include MMPs: (1) promoting epithelial-to-mesenchymal transition (MMP-3 and MMP-7); (2) increasing lung levels or activity of profibrotic mediators or reducing lung levels of antifibrotic mediators (MMP-3, MMP-7, and MMP-8); (3) promoting abnormal epithelial cell migration and other aberrant repair processes (MMP-3 and MMP-9); (4) inducing the switching of lung macrophage phenotypes from M1 to M2 types (MMP-10 and MMP-28); and (5) promoting fibrocyte migration (MMP-8). Two MMPs, MMP-13 and MMP-19, have antifibrotic activities in murine models of PF, and two MMPs, MMP-1 and MMP-10, have the potential to limit fibrotic responses to injury. Herein, we review what is known about the contributions of MMPs and TIMPs to the pathogenesis of IPF and discuss their potential as therapeutic targets for IPF.

Active site specificity profiling of the matrix metalloproteinase family: Proteomic identification of 4300 cleavage sites by nine MMPs explored with structural and synthetic peptide cleavage analyses

Secreted and membrane tethered matrix metalloproteinases (MMPs) are key homeostatic proteases regulating the extracellular signaling and structural matrix environment of cells and tissues. For drug targeting of proteases, selectivity for individual molecules is highly desired and can be met by high yield active site specificity profiling. Using the high throughput Proteomic Identification of protease Cleavage Sites (PICS) method to simultaneously profile both the prime and non-prime sides of the cleavage sites of nine human MMPs, we identified more than 4300 cleavages from P6 to P6' in biologically diverse human peptide libraries. MMP specificity and kinetic efficiency were mainly guided by aliphatic and aromatic residues in P1' (with a ~32-93% preference for leucine depending on the MMP), and basic and small residues in P2' and P3', respectively. A wide differential preference for the hallmark P3 proline was found between MMPs ranging from 15 to 46%, yet when combined in the same peptide with the universally preferred P1' leucine, an unexpected negative cooperativity emerged. This was not observed in previous studies, probably due to the paucity of approaches that profile both the prime and non-prime sides together, and the masking of subsite cooperativity effects by global heat maps and iceLogos. These caveats make it critical to check for these biologically highly important effects by fixing all 20 amino acids one-by-one in the respective subsites and thorough assessing of the inferred specificity logo changes. Indeed an analysis of bona fide MEROPS physiological substrate cleavage data revealed that of the 37 natural substrates with either a P3-Pro or a P1'-Leu only 5 shared both features, confirming the PICS data. Upon probing with several new quenched-fluorescent peptides, rationally designed on our specificity data, the negative cooperativity was explained by reduced non-prime side flexibility constraining accommodation of the rigidifying P3 proline with leucine locked in S1'. Similar negative cooperativity between P3 proline and the novel preference for asparagine in P1 cements our conclusion that non-prime side flexibility greatly impacts MMP binding affinity and cleavage efficiency. Thus, unexpected sequence cooperativity consequences were revealed by PICS that uniquely encompasses both the non-prime and prime sides flanking the proteomic-pinpointed scissile bond.

New tools for the quantitative assessment of prodrug delivery and neurotoxicity

Systemic off-target toxicities, including neurotoxicity, are prevalent side effects in cancer patients treated with a number of otherwise highly efficacious anticancer drugs. In the current study, we have: (1) developed a new analytical metric for the in vivo preclinical assessment of systemic toxicities/neurotoxicity of new drugs and delivery systems; and (2) evaluated, in mice, the in vivo efficacy and toxicity of a versatile and modular NanoDendron (ND) drug delivery and imaging platform that we recently developed. Our paclitaxel-carrying ND prodrug, ND(PXL), is activated following proteolytic cleavage by MMP9, resulting in localized cytotoxic chemotherapy. Using click chemistry, we combined ND(PXL) with a traceable beacon, ND(PB), yielding ND(PXL)-ND(PB) that functions as a theranostic compound. In vivo fluorescence FRET imaging of this theranostic platform was used to confirm localized delivery to tumors and to assess the efficiency of drug delivery to tumors, achieving 25-30% activation in the tumors of an immunocompetent mouse model of breast cancer. In this model, ND-drug exhibited anti-tumor efficacy comparable to nab-paclitaxel, a clinical formulation. In addition, we combined neurobehavioral metrics of nociception and sensorimotor performance of individual mice to develop a novel composite toxicity score that reveals and quantifies peripheral neurotoxicity, a debilitating long-term systemic toxicity of paclitaxel therapy. Importantly, mice treated with nab-paclitaxel developed changes in behavioral metrics with significantly higher toxicity scores indicative of peripheral neuropathy, while mice treated with ND(PXL) showed no significant changes in behavioral responses or toxicity score. Our ND formulation was designed to be readily adaptable to incorporate different drugs, imaging modalities and/or targeting motifs. This formulation has significant potential for preclinical and clinical tools across multiple disease states. The studies presented here report a novel toxicity score for assessing peripheral neuropathy and demonstrate that our targeted, theranostic NDs are safe and effective, providing localized tumor delivery of a chemotherapeutic and with reduced common neurotoxic side-effects.

Disposable MMP-9 sensor based on the degradation of peptide cross-linked hydrogel films using electrochemical impedance spectroscopy

Matrix metalloproteinase-9 (MMP-9) plays an important role in both physiological and pathological processes. This enzyme is a peripheral biomarker of neuroinflammation in multiple sclerosis (MS), a chronic autoimmune disease of the central nervous system. Presently, expensive magnetic resonance imaging (MRI) studies are used to monitor subclinical disease activity in MS. An alternative to costly MRI scans could be the detection of MMP-9, using a low-cost, disposable sensor system for MMP-9 suitable for home-monitoring of inflammation. This would allow an early prediction of the failure of anti-inflammatory therapies and more timely clinical intervention to limit neuronal damage and prevent disability. Herein we present the development of a disposable sensor for fast and straightforward detection of MMP-9. Biosensors were produced by coating electrodes with oxidized dextran and subsequent cross-linking with peptides containing specific cleavage sites for MMP-9. Exposure of the films to the enzyme resulted in the degradation of the films, which was monitored using impedance measurements. Sensor response was rapid, a significant impedance change was usually observed within 5 min after the addition of MMP-9. Sensors showed a negligible response to matrix metalloproteinase-2 (MMP-2), a protease which may interfere with MMP-9 detection. The peptide sequence with the highest sensitivity and selectivity Leu-Gly-Arg-Met-Gly-Leu-Pro-Gly-Lys was selected to construct calibration curves. MMP-9 was successfully detected in a clinically relevant range from 50 to 400 ng/ml. Two different processes of hydrogel degradation were observed on electrode surfaces with different roughness, and both appeared suitable to monitor MMP-9 activity. The sensor materials are generic and can be easily adopted to respond to other proteases by selecting peptide cross-linkers with suitable cleavage sites.

Matrix metalloproteinase-14 both sheds cell surface neuronal glial antigen 2 (NG2) proteoglycan on macrophages and governs the response to peripheral nerve injury

Neuronal glial antigen 2 (NG2) is an integral membrane chondroitin sulfate proteoglycan expressed by vascular pericytes, macrophages (NG2-Mφ), and progenitor glia of the nervous system. Herein, we revealed that NG2 shedding and axonal growth, either independently or jointly, depended on the pericellular remodeling events executed by membrane-type 1 matrix metalloproteinase (MT1-MMP/MMP-14). Using purified NG2 ectodomain constructs, individual MMPs, and primary NG2-Mφ cultures, we demonstrated for the first time that MMP-14 performed as an efficient and unconventional NG2 sheddase and that NG2-Mφ infiltrated into the damaged peripheral nervous system. We then characterized the spatiotemporal relationships among MMP-14, MMP-2, and tissue inhibitor of metalloproteinases-2 in sciatic nerve. Tissue inhibitor of metalloproteinases-2-free MMP-14 was observed in the primary Schwann cell cultures using the inhibitory hydroxamate warhead-based MP-3653 fluorescent reporter. In teased nerve fibers, MMP-14 translocated postinjury toward the nodes of Ranvier and its substrates, laminin and NG2. Inhibition of MMP-14 activity using the selective, function-blocking DX2400 human monoclonal antibody increased the levels of regeneration-associated factors, including laminin, growth-associated protein 43, and cAMP-dependent transcription factor 3, thereby promoting sensory axon regeneration after nerve crush. Concomitantly, DX2400 therapy attenuated mechanical hypersensitivity associated with nerve crush in rats. Together, our findings describe a new model in which MMP-14 proteolysis regulates the extracellular milieu and presents a novel therapeutic target in the damaged peripheral nervous system and neuropathic pain.

α-dystroglycan is a potential target of matrix metalloproteinase MMP-2

Dystroglycan (DG) is a member of the glycoprotein complex associated to dystrophin and composed by two subunits, the β-DG, a transmembrane protein, and the α-DG, an extensively glycosylated extracellular protein. The β-DG ectodomain degradation by the matrix metallo-proteinases (i.e., MMP-2 and MMP-9) in both, pathological and physiological conditions, has been characterized in detail in previous publications. Since the amounts of α-DG and β-DG at the cell surface decrease when gelatinases are up-regulated, we investigated the degradation of α-DG subunit by MMP-2. Present data show, for the first time, that the proteolysis of α-DG indeed occurs on a native glycosylated molecule enriched from rabbit skeletal muscle. In order to characterize the α-DG portion, which is more prone to cleavage by MMP-2, we performed different degradations on tailored recombinant domains of α-DG spanning the whole subunit. The overall bulk of results casts light on a relevant susceptibility of the α-DG to MMP-2 degradation with particular reference to its C-terminal domain, thus opening a new scenario on the role of gelatinases (in particular of MMP-2) in the degradation of this glycoprotein complex, taking place in the course of pathological processes.

Basis for substrate recognition and distinction by matrix metalloproteinases

Genomic sequencing and structural genomics produced a vast amount of sequence and structural data, creating an opportunity for structure-function analysis in silico [Radivojac P, et al. (2013) Nat Methods 10(3):221-227]. Unfortunately, only a few large experimental datasets exist to serve as benchmarks for function-related predictions. Furthermore, currently there are no reliable means to predict the extent of functional similarity among proteins. Here, we quantify structure-function relationships among three phylogenetic branches of the matrix metalloproteinase (MMP) family by comparing their cleavage efficiencies toward an extended set of phage peptide substrates that were selected from ∼ 64 million peptide sequences (i.e., a large unbiased representation of substrate space). The observed second-order rate constants [k(obs)] across the substrate space provide a distance measure of functional similarity among the MMPs. These functional distances directly correlate with MMP phylogenetic distance. There is also a remarkable and near-perfect correlation between the MMP substrate preference and sequence identity of 50-57 discontinuous residues surrounding the catalytic groove. We conclude that these residues represent the specificity-determining positions (SDPs) that allowed for the expansion of MMP proteolytic function during evolution. A transmutation of only a few selected SDPs proximal to the bound substrate peptide, and contributing the most to selectivity among the MMPs, is sufficient to enact a global change in the substrate preference of one MMP to that of another, indicating the potential for the rational and focused redesign of cleavage specificity in MMPs.

Synthesis and in vitro efficacy of MMP9-activated NanoDendrons

Chemotherapeutics such as doxorubicin (DOX) and paclitaxel (PXL) have dose-limiting systemic toxicities, including cardiotoxicity and peripheral neuropathy. Delivery strategies to minimize these undesirable effects are needed and could improve efficacy, while reducing patient morbidity. Here, DOX and PXL were conjugated to a nanodendron (ND) through an MMP9-cleavable peptide linker, producing two new therapies, ND2(DOX) and ND2(PXL), designed to improve delivery specificity to the tumor microenvironment and reduce systemic toxicity. Comparative cytotoxicity assays were performed between intact ND-drug conjugates and the MMP9 released drug in cell lines with and without MMP9 expression. While ND2(DOX) was found to lose cytotoxicity due to the modification of DOX for conjugation to the ND; ND2(PXL) was determined to have the desired properties for a prodrug delivery system. ND2(PXL) was found to be cytotoxic in MMP9-expressing mouse mammary carcinoma (R221A-luc) (53%) and human breast carcinoma (MDA-MB-231) (66%) at a concentration of 50 nM (in PXL) after 48 h. Treating ND2(PXL) with MMP9 prior to the cytotoxicity assay resulted in a faster response; however, both cleaved and intact versions of the drug reached the same efficacy as the unmodified drug by 96 h in the R221A-luc and MDA-MB-231 cell lines. Further studies in modified Lewis lung carcinoma cells that either do (LLC(MMP9)) or do not (LLC(RSV)) express MMP9 demonstrate the selectivity of ND2(PXL) for MMP9. LLC(MMP9) cells were only 20% viable after 48 h of treatment, while LLC(RSV) were not affected. Inclusion of an MMP inhibitor, GM6001, when treating the LLC(MMP9) cells with ND2(PXL) eliminated the response of the MMP9 expressing cells (LLC(MMP9)). The data presented here suggests that these NDs, specifically ND2(PXL), are nontoxic until activated by MMP9, a protease common in the microenvironment of tumors, indicating that incorporation of chemotherapeutic or cytostatic agents onto the ND platform have potential for tumor-targeted efficacy with reduced in vivo systemic toxicities.

Non-destructive and selective imaging of the functionally active, pro-invasive membrane type-1 matrix metalloproteinase (MT1-MMP) enzyme in cancer cells

Proteolytic activity of cell surface-associated MT1-matrix metalloproteinase (MMP) (MMP-14) is directly related to cell migration, invasion, and metastasis. MT1-MMP is regulated as a proteinase by activation and conversion of the latent proenzyme into the active enzyme, and also via inhibition by tissue inhibitors of MMPs (TIMPs) and self-proteolysis. MT1-MMP is also regulated as a membrane protein through its internalization and recycling. Routine immunohistochemistry, flow cytometry, reverse transcription-PCR, and immunoblotting methodologies do not allow quantitative imaging and assessment of the cell-surface levels of the active, TIMP-free MT1-MMP enzyme. Here, we developed a fluorescent reporter prototype that targets the cellular active MT1-MMP enzyme alone. The reporter (MP-3653) represents a liposome tagged with a fluorochrome and functionalized with a PEG chain spacer linked to an inhibitory hydroxamate warhead. Our studies using the MP-3653 reporter and its inactive derivative demonstrated that MP-3653 can be efficiently used not only to visualize the trafficking of MT1-MMP through the cell compartment, but also to quantify the femtomolar range amounts of the cell surface-associated active MT1-MMP enzyme in multiple cancer cell types, including breast carcinoma, fibrosarcoma, and melanoma. Thus, the levels of the naturally expressed, fully functional, active cellular MT1-MMP enzyme are roughly equal to 1 × 10(5) molecules/cell, whereas these levels are in a 1 × 10(6) range in the cells with the enforced MT1-MMP expression. We suggest that the reporter we developed will contribute to the laboratory studies of MT1-MMP and then, ultimately, to the design of novel, more efficient prognostic approaches and personalized cancer therapies.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Matrix metalloproteinase proteolysis of the mycobacterial HSP65 protein as a potential source of immunogenic peptides in human tuberculosis

Mycobacterium tuberculosis is the causative agent of human tuberculosis (TB). Mycobacterial secretory protein ESAT-6 induces matrix metalloproteinase (MMP)-9 in epithelial cells neighboring infected macrophages. MMP-9 then enhances recruitment of uninfected macrophages, which contribute to nascent granuloma maturation and bacterial growth. Disruption of MMP-9 function attenuates granuloma formation and bacterial growth. The abundant mycobacterial 65 kDa heat shock protein (HSP65) chaperone is the major target for the immune response and a critical component in M. tuberculosis adhesion to macrophages. We hypothesized that HSP65 is susceptible to MMP-9 proteolysis and that the resulting HSP65 immunogenic peptides affect host adaptive immunity. To identify MMPs that cleave HSP65, we used MMP-2 and MMP-9 gelatinases, the simple hemopexin domain MMP-8, membrane-associated MMP-14, MMP-15, MMP-16 and MMP-24, and glycosylphosphatidylinositol-linked MMP-17 and MMP-25. We determined both the relative cleavage efficiency of MMPs against the HSP65 substrate and the peptide sequence of the cleavage sites. Cleavage of the unstructured PAGHG474L C-terminal region initiates the degradation of HSP65 by MMPs. This initial cleavage destroys the substrate-binding capacity of the HSP65 chaperone. Multiple additional cleavages of the unfolded HSP65 then follow. MMP-2, MMP-8, MMP-14, MMP-15 and MMP-16, in addition to MMP-9, generate the known highly immunogenic N-terminal peptide of HSP65. Based on our biochemical data, we now suspect that MMP proteolysis of HSP65 in vivo, including MMP-9 proteolysis, also results in the abundant generation of the N-terminal immunogenic peptide and that this peptide, in addition to intact HSP65, contributes to the complex immunomodulatory interplay in the course of TB infection.

Near-infrared optical proteolytic beacons for in vivo imaging of matrix metalloproteinase activity

The exuberant expression of proteinases by tumor cells has long been associated with the breakdown of the extracellular matrix, tumor invasion, and metastasis to distant organs. There are both epidemiological and experimental data that support a causative role for proteinases of the matrix metalloproteinase (MMP) family in tumor progression. Optical imaging techniques provide an extraordinary opportunity for non-invasive "molecular imaging" of tumor-associated proteolytic activity. The application of optical proteolytic beacons for the detection of specific proteinase activities associated with tumors has several potential purposes: (1) Detection of small, early-stage tumors with increased sensitivity due to the catalytic nature of the proteolytic activity, (2) diagnosis and prognosis to distinguish tumors that require particularly aggressive therapy or those that will not benefit from therapy, (3) identification of tumors appropriate for specific anti-proteinase therapeutics and optimization of drug and its dose based on determination of target modulation, and (4) as an indicator of the efficacy of proteolytically activated pro-drugs. This chapter describes the synthesis, characterization, and application of reagents that use visible and near-infrared fluorescence resonance energy transfer (FRET) fluorophore pairs to detect and measure MMP proteolytic activity in tumors in murine models of cancer.

Biochemical characterization of the cellular glycosylphosphatidylinositol-linked membrane type-6 matrix metalloproteinase

Ubiquitously expressed membrane type-1 matrix metalloproteinase (MT1-MMP), an archetype member of the MMP family, binds tissue inhibitor of metalloproteinases-2 (TIMP-2), activates matrix metalloproteinase-2 (MMP-2), and stimulates cell migration in various cell types. In contrast with MT1-MMP, the structurally similar MT6-MMP associates with the lipid raft compartment of the plasma membrane using a GPI anchor. As a result, MT6-MMP is functionally distinct from MT1-MMP. MT6-MMP is insufficiently characterized as yet. In addition, a number of its biochemical features are both conflicting and controversial. To reassess the biochemical features of MT6-MMP, we have expressed the MT6-MMP construct tagged with a FLAG tag in breast carcinoma MCF-7 and fibrosarcoma HT1080 cells. We then used phosphatidylinositol-specific phospholipase C to release MT6-MMP from the cell surface and characterized the solubilized MT6-MMP fractions. We now are confident that cellular MT6-MMP partially exists in its complex with TIMP-2. Both TIMP-1 and TIMP-2 are capable of inhibiting the proteolytic activity of MT6-MMP. MT6-MMP does not stimulate cell migration. MT6-MMP, however, generates a significant level of gelatinolysis of the fluorescein isothiocyanate-labeled gelatin and exhibits an intrinsic, albeit low, ability to activate MMP-2. As a result, it is exceedingly difficult to record the activation of MMP-2 by cellular MT6-MMP. Because of its lipid raft localization, cellular MT6-MMP is inefficiently internalized. MT6-MMP is predominantly localized in the cell-to-cell junctions. Because MT6-MMP has been suggested to play a role in disease, including cancer and autoimmune multiple sclerosis, the identity of its physiologically relevant cleavage targets remains to be determined.

Kinetic and binding effects in peptide substrate selectivity of matrix metalloproteinase-2: Molecular dynamics and QM/MM calculations

Herein, we examine computationally the binding and hydrolysis reaction of the MMP-2 enzyme with two peptide substrates selected by the enzyme from a phage peptide library. Molecular dynamics simulations of the Michaelis complexes (25 ns) allow us to characterize the main enzyme/substrate contacts. Subsequently MM-PBSA calculations using independent trajectories for the complexes and the free substrates provide relative binding energies in good agreement with the experimental K(M) results. Computational alanine scanning analyses of the enzyme/substrate interaction energies confirm the relevance of the P(3), P(2), and P(1)' side chains for ligand binding. Finally, the hydrolysis of both peptides taking place at the MMP-2 active site is explored by means of hybrid quantum mechanical/molecular mechanics calculations. The computed reaction mechanisms result in rate-determining energy barriers being in consonance with the experimental k(cat) values. Overall, the computational protocol seems to capture the subtle differences in binding and catalysis experimentally observed for the two peptide substrates. Some implications of our results for the future design of novel and more specific MMP-2 inhibitors are also discussed.

Inflammatory proprotein convertase-matrix metalloproteinase proteolytic pathway in antigen-presenting cells as a step to autoimmune multiple sclerosis

Multiple sclerosis (MS) is a disease of the central nervous system with autoimmune etiology. Susceptibility to MS is linked to viral and bacterial infections. Matrix metalloproteinases (MMPs) play a significant role in the fragmentation of myelin basic protein (MBP) and demyelination. The splice variants of the single MBP gene are expressed in the oligodendrocytes of the central nervous system (classic MBP) and in the immune cells (Golli-MBPs). Our data suggest that persistent inflammation caused by environmental risk factors is a step to MS. We have discovered biochemical evidence suggesting the presence of the inflammatory proteolytic pathway leading to MS. The pathway involves the self-activated furin and PC2 proprotein convertases and membrane type-6 MMP (MT6-MMP/MMP-25) that is activated by furin/PC2. These events are followed by MMP-25 proteolysis of the Golli-MBP isoforms in the immune system cells and stimulation of the specific autoimmune T cell clones. It is likely that the passage of these autoimmune T cell clones through the disrupted blood-brain barrier to the brain and the recognition of neuronal, classic MBP causes inflammation leading to the further up-regulation of the activity of the multiple individual MMPs, the massive cleavage of MBP in the brain, demyelination, and MS. In addition to the cleavage of Golli-MBPs, MMP-25 proteolysis readily inactivates crystallin alphaB that is a suppressor of MS. These data suggest that MMP-25 plays an important role in MS pathology and that MMP-25, especially because of its restricted cell/tissue expression pattern and cell surface/lipid raft localization, is a promising drug target in MS.

To bind zinc or not to bind zinc: an examination of innovative approaches to improved metalloproteinase inhibition

This short review highlights some recent advances in matrix metalloproteinase inhibitor (MMPi) design and development. Three distinct approaches to improved MMP inhibition are discussed: (1) the identification and investigation of novel zinc-binding groups (ZBGs), (2) the study of non-zinc-binding MMPi, and (3) mechanism-based MMPi that form covalent adducts with the protein. Each of these strategies is discussed and their respective advantages and remaining challenges are highlighted. The studies discussed here bode well for the development of ever more selective, potent, and well-tolerated MMPi for treating several important disease pathologies.

Optical proteolytic beacons for in vivo detection of matrix metalloproteinase activity

The exuberant expression of proteinases by tumor cells has long been associated with the breakdown of the extracellular matrix, tumor invasion, and metastasis to distant organs. There are both epidemiological and experimental data that support a causative role for proteinases of the matrix metalloproteinase (MMP) family in tumor progression. Optical imaging techniques provide an extraordinary opportunity for noninvasive "molecular imaging" of tumor-associated proteolytic activity. The application of optical proteolytic beacons for the detection of specific proteinase activities associated with tumors has several potential purposes: (1) Detection of small, early-stage tumors with increased sensitivity due to the catalytic nature of proteolytic activity, (2) diagnosis and prognosis to distinguished tumors that require particularly aggressive therapy or those that will not benefit from therapy, (3) identification of tumors appropriate for specific antiproteinase therapeutics and optimization of drug and dose based on determination of target modulation, and (4) as an indicator of efficacy of proteolytically activated prodrugs. This chapter describes the synthesis, characterization, and application of reagents that use visible and near infrared fluorescence resonance energy transfer (FRET) fluorophore pairs to detect and measure MMP-referable proteolytic activity in tumors in mouse models of cancer.

Molecular dynamics simulations of the active matrix metalloproteinase-2: positioning of the N-terminal fragment and binding of a small peptide substrate

Herein we use different computational methods to study the structure and energetic stability of the catalytic domain of the active MMP-2 enzyme considering two different orientations of its N-terminal coil. The first orientation is largely solvent accessible and corresponds to that observed in the 1CK7 crystal structure of the proenzyme. In the second orientation, the N-terminal coil is packed against the Omega-loop and the alpha3-helix of the MMP-2 enzyme likewise in the so-called "superactivated" form of other MMPs. Binding to the MMP-2 catalytic domain of a short peptide substrate, which mimics the sequence of the alpha1 chain of collagen type I, is also examined considering again the two configurations of the N-terminal coil. All these MMP-2 models are subject to 20 ns molecular dynamics (MD) simulations followed by MM-PBSA (Molecular Mechanics Poisson-Boltzmann Surface Area) calculations. The positioning of the N-terminal coil in the "superactivated" form is found to be energetically favored for the MMP-2 enzyme. Moreover, this configuration of the N-terminal moiety can facilitate the binding of peptide substrates. Globally, the results obtained in this study could be relevant for the structural-based design of specific MMP inhibitors.

Peptide hydrolysis catalyzed by matrix metalloproteinase 2: a computational study

The MMP-2 reaction mechanism is investigated by using different computational methodologies. First, quantum mechanical (QM) calculations are carried out on a cluster model of the active site bound to an Ace-Gly approximately Ile-Nme peptide. Along the QM reaction path, a Zn-bound water molecule attacks the Gly carbonyl group to give a tetrahedral intermediate. The breaking of the C-N bond is completed thanks to the Glu 404 residue that shuttles a proton from the water molecule to Ile-N atom. The gas-phase QM energy barrier is quite low ( approximately 14 kcal/mol), thus suggesting that the essential catalytic machinery is included in the cluster model. A similar reaction path occurs in the MMP-2 catalytic domain bound to an octapeptide substrate according to hybrid QM and molecular mechanical (QM/MM) geometry optimizations. However, the rupture of the Gly( P 1) approximately Ile( P 1') amide bond is destabilized in the static QM/MM calculations, owing to the positioning of the Ile( P 1') side chain inside the MMP-2 S 1' pocket and to the inability of simple energy miminization methodologies to properly relax complex systems. Molecular dynamics simulations show that these steric limitations are overcome easily through structural fluctuations. The energetic effect of structural fluctuations is taken into account by combining QM energies with average MM Poisson-Boltzmann free energies, resulting in a total free energy barrier of 14.8 kcal/mol in good agreement with experimental data. The rate-determining event in the MMP-2 mechanism corresponds to a H-bond rearrangement involving the Glu 404 residue and/or the Glu 404-COOH --> N-Ile( P 1') proton transfer. Overall, the present computational results and previous experimental data complement each other well in order to provide a detailed view of the MMPs catalytic mechanism.

Constraining specificity in the N-domain of tissue inhibitor of metalloproteinases-1; gelatinase-selective inhibitors

The tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors of the matrix metalloproteinases (MMPs). Since unregulated MMP activities are linked to arthritis, cancer, and atherosclerosis, TIMP variants that are selective inhibitors of disease-related MMPs have potential therapeutic value. The structures of TIMP/MMP complexes reveal that most interactions with the MMP involve the N-terminal pentapeptide of TIMP and the C-D beta-strand connector which occupy the primed and unprimed regions of the active site. The loop between beta-strands A and B forms a secondary interaction site for some MMPs, ranging from multiple contacts in the TIMP-2/membrane type-1 (MT1)-MMP complex to none in the TIMP-1/MMP-1 complex. TIMP-1 and its inhibitory domain, N-TIMP-1, are weak inhibitors of MT1-MMP; inhibition is not improved by grafting the longer AB loop from TIMP-2 into N-TIMP-1, but this change impairs binding to MMP-3 and MMP-7. Mutational studies with N-TIMP-1 suggest that its weak inhibition of MT1-MMP, as compared to other N-TIMPs, arises from multiple (>3) sequence differences in the interaction site. Substitutions for Thr2 of N-TIMP-1 strongly influence MMP selectivity; Arg and Gly, that generally reduce MMP affinity, have less effect on binding to MMP-9. When the Arg mutation is added to the N-TIMP-1(AB2) mutant, it produces a gelatinase-specific inhibitor with Ki values of 2.8 and 0.4 nM for MMP-2 and -9, respectively. Interestingly, the Gly mutant has a Ki of 2.1 nM for MMP-9 and >40 muM for MMP-2, indicating that engineered TIMPs can discriminate between MMPs in the same subfamily.

Crystal Structures of MMP-9 Complexes with Five Inhibitors: Contribution of the Flexible Arg424 Side-chain to Selectivity

Human matrix metalloproteinase 9 (MMP-9), also called gelatinase B, is particularly involved in inflammatory processes, bone remodelling and wound healing, but is also implicated in pathological processes such as rheumatoid arthritis, atherosclerosis, tumour growth, and metastasis. We have prepared the inactive E402Q mutant of the truncated catalytic domain of human MMP-9 and co-crystallized it with active site-directed synthetic inhibitors of different binding types. Here, we present the X-ray structures of five MMP-9 complexes with gelatinase-specific, tight binding inhibitors: a phosphinic acid (AM-409), a pyrimidine-2,4,6-trione (RO-206-0222), two carboxylate (An-1 and MJ-24), and a trifluoromethyl hydroxamic acid inhibitor (MS-560). These compounds bind by making a compromise between optimal coordination of the catalytic zinc, favourable hydrogen bond formation in the active-site cleft, and accommodation of their large hydrophobic P1' groups in the slightly flexible S1' cavity, which exhibits distinct rotational conformations of the Pro421 carbonyl group in each complex. In all these structures, the side-chain of Arg424 located at the bottom of the S1' cavity is not defined in the electron density beyond C(gamma), indicating its mobility. However, we suggest that the mobile Arg424 side-chain partially blocks the S1' cavity, which might explain the weaker binding of most inhibitors with a long P1' side-chain for MMP-9 compared with the closely related MMP-2 (gelatinase A), which exhibits a short threonine side-chain at the equivalent position. These novel structural details should facilitate the design of more selective MMP-9 inhibitors.

Selective gene silencing of either MMP-2 or MMP-9 inhibits invasion of human saphenous vein smooth muscle cells

Activation of matrix metalloproteinases (MMPs) facilitates smooth muscle cell (SMC) invasion, an important event in the development of intimal hyperplasia in saphenous vein (SV) bypass grafts. In this study, we performed selective gene silencing using small inhibitory RNA (siRNA) oligonucleotides to examine the relative contributions of MMP-2 and MMP-9 to the invasiveness of cultured human SV-SMCs. Cultures were established from human SV obtained from patients undergoing coronary artery bypass surgery. Transfection of SV-SMCs with MMP-2 siRNA selectively reduced MMP-2 secretion and inhibited invasion through a Matrigel barrier. Supplementation of medium with recombinant MMP-2 overcame these effects. Similarly, transfection of SV-SMCs with MMP-9 siRNA selectively reduced MMP-9 secretion and subsequent invasion, effects reversed by recombinant MMP-9 supplementation. Neither MMP-2 nor MMP-9 siRNA inhibited SV-SMC migration in the absence of a Matrigel barrier. Our data demonstrate that selective gene-silencing of either MMP-2 or MMP-9 markedly reduces the invasive capacity of cultured human SV-SMCs, indicating that these MMPs play distinct non-overlapping roles in SV-SMC invasion in vitro. Specific manipulation of either MMP-2 or MMP-9 may therefore provide a valuable strategy for prevention of SV graft stenosis in man.

Gelatinase-mediated migration and invasion of cancer cells

The matrix metalloproteinases(MMP)-2 and -9, also known as the gelatinases have been long recognized as major contributors to the proteolytic degradation of extracellular matrix during tumor invasion. In the recent years, a plethora of non-matrix proteins have also been identified as gelatinase substrates thus significantly broadening our understanding of these enzymes as proteolytic executors and regulators in various physiological and pathological states including embryonic growth and development, angiogenesis and tumor progression, inflammation, infective diseases, degenerative diseases of the brain and vascular diseases. Although the effect of broad-spectrum inhibitors of MMPs in the treatment of cancer has been disappointing in clinical trials, novel mechanisms of gelatinase inhibition have been now identified. Inhibition of the association of the gelatinases with cell-surface integrins appears to offer highly specific means to target these enzymes without inhibiting their catalytic activity in multiple cell types including endothelial cells, tumor cells and leukocytes. Here, we review the multiple functions of the gelatinases in cancer, and especially their role in the tumor cell migration and invasion.