Clinical significance of immunohistochemically detected extracellular matrix proteins and their spatial distribution in primary cancer

Tumor Stroma Content Regulates Penetration and Efficacy of Tumor-targeting Bacteria

Bacteria-based cancer therapy (BBCT) strains grow selectively in primary tumors and metastases, colonize solid tumors independent of genetics, and kill cells resistant to standard molecular therapy. Clinical trials of BBCT in solid tumors have not reported any survival advantage yet, partly due to the limited bacterial colonization. Collagen, abundant in primary and metastatic solid tumors, has a well-known role in hindering intratumoral penetration of therapeutics. Nevertheless, the effect of collagen content on the intratumoral penetration and antitumor efficacy of BBCT is rarely unexplored. We hypothesized that the presence of collagen limits the penetration and, thereby, the antitumor effects of tumor-selective Salmonella. Typhimurium VNP20009 cheY+. We tested our hypothesis in low and high collagen content tumor spheroid models of triple-negative murine breast cancer. We found that high collagen content significantly hinders bacteria transport in tumors, reducing bacteria penetration and distribution by ~7-fold. The higher penetration of bacteria in low collagen-content tumors led to an overwhelming antitumor effect (~73% increase in cell death), whereas only a 28% increase in cell death was seen in the high collagen-content tumors. Our mathematical modeling of intratumoral bacterial colonization delineates the role of growth and diffusivity, suggesting an order of magnitude lower diffusivity in the high collagen-content tumors dominates the observed outcomes. Finally, our single-cell resolution analysis reveals a strong spatial correlation between bacterial spatial localization and collagen content, further corroborating that collagen acts as a barrier to bacterial penetration despite S. Typhimurium VNP20009 cheY+ motility. Understanding the effect of collagen on BBCT performance could lead to engineering more efficacious BBCT strains capable of overcoming this barrier to colonization of primary tumors and metastases.

Characterisation of collagen type I matrices for pathophysiologically relevant spatial cancer cell cultures

Specific cues provided to cells by the extracellular matrix (ECM) are determined by its composition. Except of collagens other naturally occurring ECM components should be considered in designing 3D models of diseases. We used spectrophotometric and rheological measurements and confocal imaging to characterise collagen matrices of human origin that can be modified by clinically relevant ECM components. pH of the neutralising solution, but not incubation of solidified collagen matrices in serum-free culture medium with pH 5.0-9.0 affected distribution of collagen fibres. Admixture of fibronectin or tenascin-C influenced assembly kinetics and resulted in slight increase in the Young's moduli of the matrices, indicating their incorporation into the collagen matrices. Co-localization of fibronectin with collagen fibres was confirmed by fluorescence imaging. Various cell types relevant for tumour tissue were able to proliferate within the matrices suggesting that they can be used to study role of ECM components in cancer in spatial models.

Role of Immunotherapy in the Treatment of Triple-Negative Breast Cancer: A Literature Review

Numerous malignancies, including metastatic triple-negative breast cancer (TNBC), which has long been associated with a poor prognosis, have been transformed by the widespread use of immunotherapy. Immune checkpoint inhibitors (ICIs) that target and block programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1) have demonstrated encouraging outcomes in the treatment of patients with metastatic TNBC. The PD-1 inhibitor pembrolizumab is the first-line treatment of metastatic PD-L1+ TNBC in combination with chemotherapy, and the PD-L1 inhibitor atezolizumab has also shown clinical activity. The median progression-free survival for pembrolizumab or atezolizumab combined with chemotherapy increased by 4.1 months and 2.5 months, respectively, with the addition of immunotherapy. Despite this progress, there is still more to be desired. The addition of immunotherapy to chemotherapy improved the pathological complete response (PCR) rate compared to chemotherapy with placebo in landmark phase III trials in the early-stage neoadjuvant context, whereas others reported no meaningful improvement in PCR. There are various ongoing trials that show that more research and studies are needed for components in the TNBC microenvironment and to further explore its importance in the treatment of TNBC.

Stromal Characteristics and Impact on New Therapies for Metastatic Triple-Negative Breast Cancer

The heterogenous nature of triple-negative breast cancer (TNBC) is an underlying factor in therapy resistance, metastasis, and overall poor patient outcome. The lack of hormone and growth factor receptors lends to the use of chemotherapy as the first-line treatment for TNBC. However, the failure of chemotherapy demonstrates the need to develop novel immunotherapies, antibody-drug conjugates (ADCs), and other tumor- and stromal-targeted therapeutics for TNBC patients. The potential for stromal-targeted therapy is driven by studies indicating that the interactions between tumor cells and the stromal extracellular matrix (ECM) activate mechanisms of therapy resistance. Here, we will review recent outcomes from clinical trials targeting metastatic TNBC with immunotherapies aimed at programed death ligand-receptor interactions, and ADCs specifically linked to trophoblast cell surface antigen 2 (Trop-2). We will discuss how biophysical and biochemical cues from the ECM regulate the pathophysiology of tumor and stromal cells toward a pro-tumor immune environment, therapy resistance, and poor TNBC patient outcome. Moreover, we will highlight how ECM-mediated resistance is motivating the development of new stromal-targeted therapeutics with potential to improve therapy for this disease.

The Functional Role of Extracellular Matrix Proteins in Cancer

The extracellular matrix (ECM) is highly dynamic as it is constantly deposited, remodeled and degraded to maintain tissue homeostasis. ECM is a major structural component of the tumor microenvironment, and cancer development and progression require its extensive reorganization. Cancerized ECM is biochemically different in its composition and is stiffer compared to normal ECM. The abnormal ECM affects cancer progression by directly promoting cell proliferation, survival, migration and differentiation. The restructured extracellular matrix and its degradation fragments (matrikines) also modulate the signaling cascades mediated by the interaction with cell-surface receptors, deregulate the stromal cell behavior and lead to emergence of an oncogenic microenvironment. Here, we summarize the current state of understanding how the composition and structure of ECM changes during cancer progression. We also describe the functional role of key proteins, especially tenascin C and fibronectin, and signaling molecules involved in the formation of the tumor microenvironment, as well as the signaling pathways that they activate in cancer cells.

Phenotypical modifications of immune cells are enhanced by extracellular matrix

Immune cells not only constitute tumour microenvironment but they may even affect disease prognosis as a result of dual functional roles that they may play in tumour tissues. Two frequently used established immune cell lines (lymphocytic Jurkat and monocytic THP-1) were used to test whether microenvironmental factors, especially molecular components of extracellular matrix, can shape the phenotype of immune cells. Proliferation, morphological and phenotypical analyses were applied to compare behaviour of the immune cells, typically cultured as suspensions in culture medium, with their behaviour in collagen type I-based and Matrigel-based 3D cultures. Density of both immune cell types in routine suspension cultures affected their subsequent proliferation in extracellular matrices. THP-1 cells appeared to be more sensitive to their surrounding microenvironment as judged from extracellular matrix type-dependent changes in their cell doubling times and from slight increase in their diameters in both extracellular matrix-containing cell cultures. Moreover, even chemically uninduced monocytic THP-1 cells were present in a minor fraction as CD68 positive cell population in collagen type I matrix indicating their partial differentiation to macrophages. Observed modifications of immune cells by microenvironmental factors may have profound implications for their roles in healthy and pathological tissues.

The extracellular matrix in tumor progression and metastasis

The extracellular matrix (ECM) constitutes the scaffold of tissues and organs. It is a complex network of extracellular proteins, proteoglycans and glycoproteins, which form supramolecular aggregates, such as fibrils and sheet-like networks. In addition to its biochemical composition, including the covalent intermolecular cross-linkages, the ECM is also characterized by its biophysical parameters, such as topography, molecular density, stiffness/rigidity and tension. Taking these biochemical and biophysical parameters into consideration, the ECM is very versatile and undergoes constant remodeling. This review focusses on this remodeling of the ECM under the influence of a primary solid tumor mass. Within this tumor stroma, not only the cancer cells but also the resident fibroblasts, which differentiate into cancer-associated fibroblasts (CAFs), modify the ECM. Growth factors and chemokines, which are tethered to and released from the ECM, as well as metabolic changes of the cells within the tumor bulk, add to the tumor-supporting tumor microenvironment. Metastasizing cancer cells from a primary tumor mass infiltrate into the ECM, which variably may facilitate cancer cell migration or act as barrier, which has to be proteolytically breached by the infiltrating tumor cell. The biochemical and biophysical properties therefore determine the rates and routes of metastatic dissemination. Moreover, primed by soluble factors of the primary tumor, the ECM of distant organs may be remodeled in a way to facilitate the engraftment of metastasizing cancer cells. Such premetastatic niches are responsible for the organotropic preference of certain cancer entities to colonize at certain sites in distant organs and to establish a metastasis. Translational application of our knowledge about the cancer-primed ECM is sparse with respect to therapeutic approaches, whereas tumor-induced ECM alterations such as increased tissue stiffness and desmoplasia, as well as breaching the basement membrane are hallmark of malignancy and diagnostically and histologically harnessed.

Extracellular matrix affects different aspects of cell behaviour potentially involved in response to aminolevulinic acid-based photoinactivation

Two-dimensional cell cultures do not seem to be reliable models for anticancer drug discovery and validation. Numerous in vitro tumour models of different complexity have been evaluated with the aim to enhance anticancer drug development, but whether all these models could be considered as physiologically relevant is a question. Even type of the extracellular matrix may markedly influence experimental results and supposedly also clinical treatment outcome. By using three human oesophageal cell lines and three-dimensional cultures based on collagen type I, abundant component of stromal tissue, and Matrigel, a surrogate of basement membrane, we tested the impact of extracellular matrix on different aspects of cell behaviour. We applied live cell fluorescence confocal microscopy in combination with image analysis and supplemented it with immunohistochemical analysis of differentiation markers in fixed samples. We found that cell morphogenesis, differentiation, extracellular vesicle formation, protoporphyrin IX production from aminolevulinic acid and response to subsequent photodynamic intervention induced by red light may be affected by the type of extracellular matrix and these modifications occur in a cell-type dependent manner. Our results demonstrate that the choice of the correct extracellular matrix for in vitro tumour models is crucial for gathering clinically relevant information from in vitro experimental studies.

Potassium hydroxide treatment of UV-curable polysiloxane-type polymer for reproducible enhancement of cell adhesion and survival

Polysiloxanes have shown exquisite properties for fabrication of microstructures for various biomedical and biotechnological applications. Nevertheless, their biocompatibility in terms of cell adhesion and survival ability is controversial. A simple polysiloxane modifying procedure that reproducibly enhances cell adhesion was proposed. Sonication of the hybrid organic-inorganic polymer of polysiloxane type, Ormocomp, in potassium hydroxide (KOH)/ethanol solution enhanced adhesion and subsequent survival of a panel of four cell lines. Characterization of surface properties of untreated and KOH-treated Ormocomp coatings has revealed considerable negative charge of Ormocomp substrates based on measurements of zeta potentials. KOH treatment did not modify surface morphology as visualized by scanning electron microscopy, but it resulted in alteration in both chemical composition according to SIMS analysis and hydrophilicity evaluated by static water contact angles. The results suggest that the failure of the adherent cells to survive on Ormocomp coatings is related to cell adhesion. The negative surface charge of Ormocomp substrates may be one of the influencing factors; however, the modification of surface chemistry mediated by KOH and the resulting increase in hydrophilicity accompanied by modification of protein adsorption are more likely responsible for enhanced cell adhesion and survival on Ormocomp coatings. KOH treatment thus may serve as a simple, cost-effective procedure modifying polysiloxane-type polymers that leads to reproducible enhancement of cell adhesion.

Extracellular Matrix Containing in vitro Three-dimensional Tumor Models in Photodynamic Therapy-related Research

Three-dimensional (3D) tumor models have been intensively evaluated for their use in cancer research, and there is a strong rationale behind using 3D cell cultures in photodynamic therapy (PDT)-related experimentation. In this contribution, it is explained why 3D cell cultures containing extracellular matrix (ECM) are preferred for this purpose. Results of experimental studies utilizing ECM-containing 3D cellular models in PDT research are summarized. Finally, the design of in vitro 3D models that would provide clinically relevant information is discussed.