During development, all the tissues of multicellular organisms grow and differentiate and, the ECM plays a fundamental role regulating, at the macroscopic level, the expansion of the tissues through mechanical forces and, at the microscopic level, intervening in the processes of cell proliferation, survival, migration and others (1) The ECM is a highly complex structure present in every tissue. It is made up of a variable combination of proteins, proteoglycans and other molecules that influence a wide range of processes including cell adhesion and growth (2–4). The ECM is constantly subject to processes of remodeling, repair and renewal thanks to enzymes that cause its degradation and induce structural changes. Cell-ECM interactions regulate tissue homeostasis influencing processes such as proliferation, migration and differentiation (5). Also, the ECM mediates interaction between cells by both chemical and electrical ways (6). ECM is secreted mainly by fibroblasts, but in several specialized tissues such as cartilage or bone, it is produced by chondroblasts and osteoblasts, respectively. The physiological ECM is highly heterogeneous among organs. For example, fibroblasts are capable of synthesizing and secreting collagen I or III, elastic fibers, reticular fibers, and proteoglycans, whereas chondroblasts synthesize and secrete a cartilaginous ECM consisting of elastic fibers, collagen II, and glycosaminoglycans. Furthermore, several studies have shown that also other cells (pericytes, vascular smooth muscle cells) are able to produce ECM such as collagen IV, laminin, fibronectin (6). Given the diversity of origins of these ECM-secreting cells, their synergy contributes to the heterogeneity and complexity of the physiological ECM, which is continuously remodeled in order to adapt and maintain tissue homeostasis.

Two types of ECM have been described, the interstitial ECM and the basement membrane. The interstitial ECM represents the matrix between cells (7). This latter is composed of many structural proteins, such as collagen I and III, proteoglycans, such as versican, aggrecan, brevican, and decorins, and fibronectin that provide tissue support. Furthermore, it is also made up of other proteins such as nidogen-entactin, produced by epithelial cells, endothelial cells and myofibroblasts (6, 7). The collagen IV structural network maintains cell stability and is tightly cross-linked. On the other hand, the basement membrane is a layer of specialized ECM, positioned at the interface between parenchymal and connective tissues. The basement membrane is responsible for the isolation of the epithelium from the underlying stroma, and for the regulation of cellular organization and differentiation through interactions with the cell surface receptors. and consists of laminins, collagens (predominantly collagen IV), proteoglycans, calcium binding proteins such as fibulin, and various other structural or adhesive proteins. In particular, laminin networks, are non-covalent and are biologically more active than the collagen IV network (8). The two networks are connected to each other by nidogen which, together with other components, dynamically stabilizes the structure (9). The bone marrow, for example, is ─ not surprisingly ─ denser as it largely contains collagen IV, laminin and heparan sulfate proteoglycans (HSPG). Hemidesmosomes and integrins are cell-membrane receptors expressed in the bone marrow and bind to ECM proteins. Matrix proteins also connect to receptors such as sulfated glycolipids, dystroglycan, Lutheran glycoprotein (10). Furthermore, fine communication between cells is required to correctly assemble the basement membrane (9).

The entire ensemble of genes encoding components of the ECM and its associated proteins is called matrisome; the first are regarded as the ‘core matrisome’ (10, 11). The mammalian matrisome contains approximately 1,100 genes that can be gathered into different groups according to their final localization. In particular, we can recognize the core-matrisome molecules (~300 genes) and the matrix-associated molecules (~800 genes). Matrisomal proteins encoded by these genes are thought to be approximately 4% of the entire human proteome (10, 11). The core matrisome consists of ECM proteoglycans, glycoproteins, and collagens; whereas ECM-associated proteins include proteins that are structurally similar to ECM proteins and ECM remodeling enzymes (11).

External stimuli are mediated by the ECM and are transduced via adhesion molecules, integrins and other mechanotransducers (12), which connect, integrating into the focal adhesion complexes, the cellular cytoskeleton and the ECM for a mutual communication of forces between the cells and the microenvironment (13). Conformational changes in focal adhesion molecules, due to mechanotransduction mediated and regulated by various receptors, lead to cytoskeletal tension and downstream intracellular signaling, which in turn regulates migration, adhesion, proliferation and remodeling of the ECM (13).

In fibrosis, cancer, and many other non-tumoral pathological conditions, the composition of the ECM becomes dysregulated and ECM structure becomes rigid and more abundant (10), leading to a consequent imbalance of tissue homeostasis (14). Here, we provide an overview of the main changes occurring to the ECM which favor cancer progression and are increasingly recognized as potential targets for antitumor strategies.

The tumor matrix is subjected to a high remodeling that leads to the rapid degradation of the normal, physiological matrix and its replacement with a ‘tumor’ matrix which can reinforce the aggressive cancer characteristics and induce the formation of bioactive fragments (known as matricryptins or matrikines) with pro-tumor features (15). Also, the matrix degradation can release growth factors/mitogens from the ECM reservoir and remove physical barriers (such as basement membranes), facilitating tumor proliferation, invasion and spreading (16). Here we focus on several aspects that characterize ECM remodeling during tumor progression.

As early as 1986, Dvorak defined tumors as “wounds that do not heal”. This definition stems from the observation that tumor growth leads to a continuous lesion of the surrounding stromal tissue which also triggers a chronic inflammation in order to try to repair the lesion and restore tissue homeostasis (62). This reaction causes a continuous state of inflammation with the recruitment and concerted activity of inflammatory molecules, fibroblasts, and immune cells. As matter of fact, when a tumor lesion occurs, immune cells, such as leukocytes, macrophages and/or bone marrow-derived myeloid precursors, are recruited to the damaged site. These infiltrating immune cells, together with stromal cells, release high levels of transforming growth factor β (TGF β) into the TME, exerting pleiotropic effects on both tumor and normal cells adjacent to the lesion through autocrine and paracrine ways (63).

The neoplastic transformation of cells and tumor progression are not solely reliant on the accumulation of mutations in oncogenes or tumor suppressor genes, but also on the alteration of cellular communication and interaction with the surrounding environment (97, 98). Quiescent cell clones with mutations in oncogenes or tumor suppressors, which are found in healthy tissues, are incapable of initiating tumor growth (99, 100). While constitutive activation of oncogenic pathways is insufficient to reprogram and promote neoplastic transformation of breast and pancreatic cells in a soft microenvironment that resembles that of healthy tissue, a rigid microenvironment seem to favor tumor formation (101). Therefore, oncogenic reprogramming of normal cells is dependent on both cell-autonomous events, such as oncogenic activation, and non-cell-autonomous events, such as increased stiffness of the environment. Oncogenic signaling enhances cellular mechanotransduction in response to physical inputs received from the environment. Subsequently, even a relatively modest increase in substrate rigidity of the microenvironment, in which oncogene-expressing cells are embedded, is sufficient to ignite oncogenic mechano-signaling and empower oncogene-mediated cell reprogramming (101). Only cells expressing oncogenes respond to sub-threshold mechanical stimuli for healthy cells by increasing contractile actomyosin bundles, heightened by elevated phospho-myosin light chain (pMLC), enhancing the formation and maturation of focal adhesions (FA), and YAP/TAZ activation, as evidenced by their nuclear accumulation (102).

Imbalances in ECM deposition and degradation lead to the accumulation of matrix proteins in the TME (7). Covalent interfiber bonds enable the ECM to withstand external loads, leading to a highly elastic behavior. The cycles of proteolytic degradation, new synthesis, and crosslinking enable permanent remodeling of elastic matrices, resulting in permanent alignment of collagen fibers perpendicular to the tumor margin, which is linked to worse cancer outcomes (103). An increased elastic modulus enhances the ECM’s resistance to the force generated by tumor and CAFs via ROCK-dependent actomyosin contractility, contributing to increased cell and ECM stiffness (104). These contractile forces lead to increased hydrostatic pressure and tensile stress on F-actin fibers, which are transferred to the ECM through integrin interaction.

Deregulated cell growth contributes to tumor stiffening, which leads to increased cell density and ECM elastic modulus (105). The basal membrane (BM), which acts as a physical barrier, restricts tumor growth within a limited space (106). The tension exerted by the expanding tumor affects tissue shape and can stimulate the proliferation of neighboring healthy cells. Additionally, tumor pressure can be increased by interstitial fluid pressure due to absorption of water into extracellular proteins from hyper permeable tumor vessels and a disrupted lymphatic system (107). The pressure exerted by the interstitial fluid, BM, and healthy tissue, tumor proliferation and elastic ECM slow down the cellular motion, causing cells to acquire a spherical shape and transition from an active fluid-like state (known as unjamming) to a passive solid-like state (known as jamming) (108, 109).

The considerable compressive stress to which the tumor interior reaches results in cell cycle arrest, whereas tensile stress at the tumor periphery can lead to heterogeneous proliferation rates across the tumor (110). In this context tumor cells trapped in solid like state require to transit from jammed to unjammed fluid like phase in order to become malignant and proliferate, migrate and disseminate. Ductal carcinoma in situ (DCIS) typically grow at high cell density within the confinement of the mammary duct lumina and are indolent, quasi benign lesions as they enter a solid (jammed) and kinetically arrested state (111, 112). However, external stress can force some cancer cells to undergo a solid-to-liquid, or jammed-unjammed, phase transition. This change in cellular behavior is induced by the modulation of genes such as RAB5, E-cadherin, and p120 catenin, which promote this phase transition by regulating cell-cell adhesion, substrate adhesion, cell activity (such as traction generation or contractile stress), cell stiffness, cell polarity, cytoskeletal deformability, proliferation, and tumor cell shape (113, 114). In the unjammed state, cells acquire an elongated morphology, which promotes tissue fluidity. This particular cell shape allows for increased mobility by increasing the number of degrees of freedom, reducing geometric constraints, and necessitating the coordination of multiple neighboring cells to restrict its movement (115).

Although the factors that drive unjamming in different contexts are not yet clear, including the role of inducing signals, transcriptional regulators, and downstream effectors (111, 116–118), it can occur independently EMT. While epithelial cells can undergo to unjammed transition in the absence of EMT and move collectively without losing their barrier function, it remains uncertain whether EMT can occur without unjamming (119).

In dense tumors, cancer cells display various dynamic behaviors, where unjammed cells become trapped within a globally jammed layer (120). This encasement of fluid cells by jammed cells results in increased tension network and tissue rigidity (120). Cells and epithelial sheets can adapt to acute stress by activating a nuclear mechanoprotective response that protects them from extensive genomic damage. This response involves increased nuclear rigidity and size, heightened chromatin compaction, and the reorganization of peri-nuclear cytoskeletal actin to form actin rings (114, 121–123). The cell’s mechanical constraints, resulting from the surrounding microenvironment, are transmitted to the nuclear envelope via the cytoskeleton network or compressive stress. This can cause nuclear envelope rupture, allowing an exchange of transcription factor and nuclear contents between the cytoplasm and nucleus. The extrusion of DNA from the nucleus generates shear stress, which leads to an increase in γH2AX foci, a sign of DNA damage and double-strand breaks. These breaks can result in significant genomic alterations and activation of cGAS-mediated inflammatory (92, 114, 121, 124–126). Pleomorphisms, or the variance in nuclear shapes and sizes, are crucial clinical markers for tumor aggressiveness and correlate with the tumor cell unjamming transition (127).

Increased tumor stiffness can promote the assembly of focal adhesions, which in turn leads to EMT. Focal adhesions are known to recruit various protein kinases and adaptor molecules, such as p130Cas and paxillin, and function as signaling hubs by activating Src-family kinases, FAK, RHO-family GTPases, and ERK, while also inhibiting the tumor suppressor PTEN (128, 129). As a result, rigid substrates promote the activation of transcription regulators YAP1 and TAZ, which in turn promotes the expression of pro-proliferative and pro-migratory genes (130). Additionally, stiff substrates reduce the association of TWIST1 with G3BP2, promoting the activation of EMT (131). Adhesion to stiff surfaces affects the balance of F-actin and G-actin levels. Reduced G-actin levels release MKL1 transcriptional regulators, leading to increased expression of genes promoting proliferation and migration (132). The expression of ECM proteins, such as CTGF and CYR61, as well as pro-contractile cytoskeleton components induced by YAP1 and SRF activation, forms a positive feedback loop that reinforces matrix stiffness (130, 133).

EMT results in loss of cell-cell adhesion, enhanced mobility, and reduced tissue integrity, affecting cancer cell stiffness (134). When tumor cells move through tissue, their nuclei undergo significant deformation and communicate with the actomyosin cortex via stretch-sensitive proteins in the nuclear envelope (124, 135). In vitro, nuclei passing through narrow constrictions can result in nuclear envelope rupture, DNA translocation, and the activation of inflammatory responses (92, 136). Although these ruptures are usually repaired quickly, they can still cause double-strand breaks in DNA, which can contribute to mutagenesis and genetic instability in invasive cells (137). DNA damage and nuclear envelope rupture markers are frequently observed in the invasive margins of both mouse and human mammary tumors (138). Moreover, compression of the nucleus can result in epigenetic consequences, including the formation of heterochromatin in cancer cell lines, which is associated with increased invasiveness.

EMT and unjamming state transition lead to a reduction in cell-cell adhesion and an increase in motility, which ultimately impairs tissue integrity. This phenomenon facilitates tumor growth and cancer cell invasion, resulting in decreased cancer cell stiffness (139).

The tumor development process is a multifaceted phenomenon influenced by genetic elements and the chemical-physical properties of the microenvironment. This interaction triggers mechanosensing pathways, which cause the remodeling of the physical and phenotypic properties of tumor cells. As a result, tumor growth repression mechanisms are bypassed, enabling the invasion of tumor cells from dense tissues into more relaxed distant tissues.

Hypothesizing that targeting mechanotransduction players could have an anti-tumor effect by influencing the cross talk between stromal cells and the matrix, and given the importance and key role of cellular mechanotransduction in tumor progression, several molecular targets and related drugs have been identified and many of them show anticancer properties in preclinical studies. In particular, TME, mechanical forces and stiffness of the ECM activate cell-membrane receptors (i.e. DDR1) and ion channels (i.e. PIEZO1; TRPV4)-induced intracellular signaling pathways involved in the cancer hallmarks such as inflammation, angiogenesis, and migration and spreading (140) ( Figure 1 ). The research on potential mechanotherapy focused on collagen as the main actor in the formation of the stiff matrix. On this issue, several intracellular signaling pathways involved in the synthesis, folding and secretion of collagen were targeted, such as Hsp47 and TGFβ. Small molecules (141) and SiRNA containing nanoparticles targeting these two molecules inhibited hepatic, pancreatic and lung fibrosis (142, 143). Hyaluronic acid has been considered a prognostic biomarker associated with poor prognosis in patients with various types of cancer, such as pancreatic, breast, and ovarian cancer (144–146). Changes in hyaluronic acid metabolism, content and deposition in inflammation and cancer are generally related to the modulation of hyaluronic acid synthesizing (HAS) and degrading (HYALS) enzymes (90). Inhibition of HAS2 activity can be accomplished by drugs such as 4-methylumbelliferone (4-MU) (147, 148). In particular, 4-MU is a chemo-preventive and therapeutic agent used to treat prostate cancer (149). Additionally, treatment of estrogen ER+ breast cancer cells with 4-MU, was shown to reduce cell migration, adhesion and invasion (150). Moreover, the use of HA-degrading hyaluronidase (HYAL) in breast cancer therapy has been approved by the FDA, demonstrating that hyaluronic acid plays a crucial function in cancer progression (151). Other potential mechanotherapeutic targets are represented by the LOX family members (152) and the Hippo Pathway, that regulates the YAP-TAZ nuclear transcription, correlates with EMT, malignancy therapy resistance and metastasis (153). In particular, LOX and the other members of its LOXL family deaminate lysine and hydroxylysine residues by promoting collagen and elastin crosslinking and consequently extracellular matrix stiffening. Therefore, inhibition of LOX and LOXL with specific molecules such as beta-aminopropionitrile (BAPN), which irreversibly binds to the catalytic domain, or with antibodies directed to the catalytic domain of LOXL2, such as simtuzumab, or by inactivation of bone morphogenetic protein 1 (BMP1), which activates LOX by cleavage, or the use of copper chelators, such as tetrathiomolybdate, which is essential for the activity of the catalytic domain of LOX, has been shown in preclinical studies to improve the anti-tumor response of therapies in several tumor types. The efficacy of such compounds, such as simtuzumab, antibody AB0023, Tetrathiomolybdate, in combination with different therapies, has been tested in several phase I-III clinical trials in cancer patients (154–160) ( Table 1 ). Another strategy to prevent extracellular matrix stiffness involves the use of antifibrotics that repress collagen synthesis and maturation by inhibiting SMAD3 with halofuginone or TGFβ with pirfenidon or losartan in cancer-associated fibroblasts, the major producers of collagen. Several clinical trials are still underway to determine whether the administration of such inhibitors of collagen synthesis can improve the prognosis of patients undergoing various cancer therapies (161–166) ( Table 1 ). Collagen degradation can be induced by the incorporation of proline analogs, such as thiaproline, which destabilize the triple helix structure of collagen. This approach has been found to be effective in preclinical mesothelioma models. In the tumor microenvironment, CAFs are the major producers of collagen; therefore, depletion of these cells using CAR-Ts specific for surface proteins, such as fibroblast activated protein (FAP), mainly expressed by CAFs, is another promising strategy for reshaping the tumor microenvironment and making it more accessible to drugs and immune cells. Clinical trials are currently evaluating the efficacy of CAR-T directed against FAP in lung tumors (167–170) ( Table 1 ). Alignment of collagen fibers directed by discoidin domain receptor 1 (DDR1) makes the microenvironment less accessible to immune system cells and consequently generates a pro-tumoral environment, thus preventing immune recognition and response ( Figure 1 ). Antibodies directed against DDR, such as PRTH-101, have shown good efficacy in inhibiting the growth of breast tumors by increasing immunoinfiltration in preclinical models and are under evaluation in clinical trials conducted in patients with colon or breast cancer (171, 172) ( Table 1 ). Another therapeutic strategy under investigation involves the use of adenoviruses expressing genes such as relaxin, decorin, and MMP-8, which can inhibit collagen synthesis, assembly, and degradation, respectively, or the use of bacteria expressing collagenase (collagen I-degrading Salmonella). In preclinical models, the administration of these therapies has shown positive and encouraging outcomes in slowing the growth of pancreatic and renal cancers (173–176). Mechanical and biochemical remodeling of the matrix and changes in tissue stiffness activate, among others, the mechanosensors PIEZO1 and TRPV4 (180). Piezoelectric channels are non-selective, Ca2+-permeable channels that constitute pores activated in response to mechanical stimuli applied to the cell membrane, converting various mechanical forces into biochemical signals (181–183). Deregulation and aberrant expression of PIEZO1and PIEZO2 have been linked to increased tumor proliferation and metastasis and to the mechanotransduction of matrix stiffness (184, 185). Several studies were conducted in order to find selective and promising PIEZO inhibitors, but results on tumor growth and metastasis are still unsatisfactory (186). The high expression of TRPV4 is characteristic of epithelial tissues and of the tumor counterpart, these receptors responding to heat, osmotic changes and mechanical stretching, inducing the influx of Ca2+, TRPV4 also regulates cell volume by interacting with F-actin (187–190). TRPV4 also promotes the process of EMT caused by matrix rigidity, upstream of metastatic dissemination, enhancing activation of the Akt kinase and the translocation of YAP/TAZ into the nucleus (191). Small molecules and monoclonal antibodies aimed at TRPV4 inhibition are in early phase clinical trials (192, 193).

Solid tumors are characterized by a rigid matrix and altered ECM components which translates into an increase in interstitial fluid pressure and chemo resistance given by the lack of perfusion of stiff tumor tissues to drugs (194). These evaluations push several studies towards strategies that, by targeting the components of the ECM, develop therapeutic agents that favor the perfusion and release of drugs within tumor cells and stroma, capable of extending the current strategies of precision medicine by expanding the range of targets also to the constituents of the altered matrix. Therefore, while genetic modifications in tumor cells undoubtedly initiate and guide the malignancy of the tumor in an incisive way, favoring neoplastic progression, the tumor stroma and its matrix play, with each other, a fundamental and synergistic role. Indeed, since the tumor progresses within an ECM, the matrisome is in its dynamic evolution and in close cross-talk with the oncosome. We can therefore hypothesize a “Matrix Addiction” process with one or several matrisome drivers, with a prevalent function in some contexts and tumor histotypes, to be combined in synergistic way with the genes driving the “Oncogene Addiction” process (195). This fine and yet not fully explored dynamic balance modulates virtually every tumor hallmark, reciprocally influencing cancer-associated stromal cells, responsible for the most part of the matrix remodeling, creating a feedback loop between ECM, stromal cells and tumor cells, in a continuously evolving mutual dynamic manner. Changes in qualitative and quantitative variations in composition, architecture and cell-ECM interactions have impactful consequences on cellular and tissue functions. These processes are regulated on multiple levels to preserve tissue homeostasis and involve the interaction of different cell types. Alterations in ECM remodeling play a critical role in cancer development and progression. The collagen IV protein is critical for the maintenance of BM structure and function. Laminin is sufficient to maintain the structure of the BM in the early stages, although collagen IV is responsible for maintaining membrane stability and integrity. Therefore, abnormal expression of laminin and collagen is a hallmark of some cancers. The BM was previously thought to be invaded by protease degradation, but with experimental progress, it can be observed that cancer cells also have physical factors that facilitate this invasion. Several immune cells contribute significantly to changes in the ECM and are also functionally affected by these changes. It should also be considered that advanced proteomic analysis provides adequate tools to study the entire tissue matrisome in tumor and non-tumor pathological contexts. An interesting research direction centers on new 3D technologies that shed light on the cellular context of ECM remodeling and cell-ECM interactions at single and subcellular levels. With these new advanced technologies, biomedical research can adequately approach and understand the global interactions of individual cells in their environment, which could lead to the development of more effective ECM-targeted therapies involving more realistic precision therapy because considers not only the mutational alterations and PTM of the oncosome but also those of the matrisome. The ultimate aim of this review is to underline how the complexity of the redundant interactions between the matrisome and the oncosome and their variants PTM, Driver mutations, alternative splicing) translate into the clinical reality of personalized therapy, forcing us to evaluate and target both compartments in synchrony (196–198).

AM: Funding acquisition, Writing – original draft, Writing – review & editing. MTG: Funding acquisition, Writing – original draft, Writing – review & editing. FP: Writing – original draft, Writing – review & editing. SC: Writing – review & editing, Writing – original draft. MG: Supervision, Writing – review & editing. AG: Supervision, Writing – review & editing.