Metastasis is the hallmark of cancer that is responsible for the greatest number of cancer-related deaths. Yet, it remains poorly understood. The continuous evolution of cancer biology research and the emergence of new paradigms in the study of metastasis have revealed some of the molecular underpinnings of this dissemination process. The invading tumor cell, on its way to the target site, interacts with other proteins and cells. Recognition of these interactions improved the understanding of some of the biological principles of the metastatic cell that govern its mobility and plasticity. Communication with the tumor microenvironment allows invading cancer cells to overcome stromal challenges, settle, and colonize. These characteristics of cancer cells are driven by genetic and epigenetic modifications within the tumor cell itself and its microenvironment. Establishing the biological mechanisms of the metastatic process is crucial in finding open therapeutic windows for successful interventions. In this review, the authors explore the recent advancements in the field of metastasis and highlight the latest insights that contribute to shaping this hallmark of cancer.

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Molecular principles of metastasis: a hallmark of cancer revisited

Our knowledge of proteoglycan biology has significantly expanded over the past decade with the discovery of a host of new members of this multifunctional family leading to their present classification into three major categories: (1) small leucine-rich proteoglycans, 2) modular proteoglycans, and 3) cell-surface proteoglycans. In addition to being structural proteins, proteoglycans play a major role in signal transduction with regulatory functions in various cellular processes. Being mostly extracellular, they are upstream of many signaling cascades and are capable of affecting intracellular phosphorylation events and modulating distinct pathways, including those driven by bone morphogenetic protein/transforming growth factor superfamily members, receptor tyrosine kinases, the insulin-like growth factor-I receptor, and Toll-like receptors. Mechanistic insights into the molecular and cellular functions of proteoglycans have revealed both the sophistication of these regulatory proteins and the challenges that remain in uncovering the entirety of their biological functions. This review aims to summarize the multiple functions of proteoglycans with special emphasis on their intricate composition and the newly described signaling events in which these molecules play a key role.

Proteoglycans: from structural compounds to signaling molecules

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer related death. It is lethal in nearly all patients, due to an almost complete chemoresistance. Most if not all drugs that pass preclinical tests successfully, fail miserably in the patient. This raises the question whether traditional 2D cell culture is the correct tool for drug screening. The objective of this study is to develop a simple, high-throughput 3D model of human PDAC cell lines, and to explore mechanisms underlying the transition from 2D to 3D that might be responsible for chemoresistance. Several established human PDAC and a KPC mouse cell lines were tested, whereby Panc-1 was studied in more detail. 3D spheroid formation was facilitated with methylcellulose. Spheroids were studied morphologically, electron microscopically and by qRT-PCR for selected matrix genes, related factors and miRNA. Metabolic studies were performed, and a panel of novel drugs was tested against gemcitabine. Comparing 3D to 2D cell culture, matrix proteins were significantly increased as were lumican, SNED1, DARP32, and miR-146a. Cell metabolism in 3D was shifted towards glycolysis. All drugs tested were less effective in 3D, except for allicin, MT100 and AX, which demonstrated effect. We developed a high-throughput 3D cell culture drug screening system for pancreatic cancer, which displays a strongly increased chemoresistance. Features associated to the 3D cell model are increased expression of matrix proteins and miRNA as well as stromal markers such as PPP1R1B and SNED1. This is supporting the concept of cell adhesion mediated drug resistance.

/pdf/3d-pancreatic-carcinoma-spheroids-induce-a-matrix-rich-28uny55obq.pdf

3D pancreatic carcinoma spheroids induce a matrix-rich, chemoresistant phenotype offering a better model for drug testing

The extracellular matrix (ECM) constitutes a highly dynamic three-dimensional structural network comprised of macromolecules, such as proteoglycans/glycosaminoglycans (PGs/GAGs), collagens, laminins, fibronectin, elastin, other glycoproteins and proteinases In recent years, the field of PGs has expanded rapidly Due to their high structural complexity and heterogeneity, PGs mediate several homeostatic and pathological processes PGs consist of a protein core and one or more covalently attached GAG chains, which provide the protein cores with the ability to interact with several proteins The GAG building blocks of PGs significantly influence the chemical and functional properties of PGs The primary goal of this comprehensive review is to summarize major achievements and paradigm-shifting discoveries made on the PG/GAG chemistry-biology axis, focusing on structural variability, structure-function relationships, metabolic, molecular, and epigenetic mechanisms underlying their synthesis Recent insights related to exosome biogenesis, degradation, and cell signaling, their status as diagnostic tools and potential pharmacological targets in diseases as well as current applications in nanotechnology and biotechnology are addressed Moreover, issues related to docking studies, molecular modeling, GAG/PG interaction networks, and their integration are discussed

Proteoglycan Chemical Diversity Drives Multifunctional Cell Regulation and Therapeutics.

Pancreatic ductal adenocarcinoma (PDAC) has an extraordinarily dense fibrotic stroma that impedes tumor perfusion and delivery of anticancer drugs Since the extracellular matrix (ECM) comprises the bulk of the stroma, it is primarily responsible for the increased interstitial tissue pressure and stiff mechanical properties of the stroma Besides its mechanical influence, the ECM provides important biochemical and physical cues that promote survival, proliferation, and metastasis By serving as a nutritional source, the ECM also enables PDAC cells to survive under the nutrient-poor conditions While therapeutic strategies using stroma-depleting drugs have yielded disappointing results, an increasing body of research indicates the ECM may offer a variety of potential therapeutic targets As preclinical studies of ECM-targeted drugs have shown promising effects, a number of clinical trials are currently investigating agents with the potential to advance the future treatment of PDAC Thus, the present review seeks to give an overview of the complex relationship between the ECM and PDAC

https://www.mdpi.com/2072-6694/10/9/316/pdf

The Extracellular Matrix and Pancreatic Cancer: A Complex Relationship.

Lumican belongs to the family of small leucine-rich repeat proteoglycans. Recent studies have shown that lumican participates in the maintenance of tissue homeostasis and modulates cellular functions including cell proliferation, migration, and differentiation. The expression of lumican has been correlated to the growth and metastasis of various malignancies; however, its exact role in tumorogenesis remains elusive. This review focuses upon the role of lumican in cell biology, providing insights into molecular mechanisms that lumican likely utilizes to control processes relevant to tumorogenesis.

https://iubmb.onlinelibrary.wiley.com/doi/pdf/10.1002/iub.131

Paulos Katonis

Papers

Lumican, a small leucine-rich proteoglycan.