Reticulated hyaluronan hydrogels: a model for examining cancer cell invasion in 3D

HYDRHA: Hydrogels of hyaluronic acid. New biomedical approaches in cancer, neurodegenerative diseases, and tissue engineering

In the last decade, hyaluronic acid (HA) has attracted an ever-growing interest in the biomedical engineering field as a biocompatible, biodegradable, and chemically versatile molecule. In fact, HA is a major component of the extracellular matrix (ECM) and is essential for the maintenance of cellular homeostasis and crosstalk. Innovative experimental strategies in vitro and in vivo using three-dimensional (3D) HA systems have been increasingly reported in studies of diseases, replacement of tissue and organ damage, repairing wounds, and encapsulating stem cells for tissue regeneration. The present work aims to give an overview and comparison of recent work carried out on HA systems showing advantages, limitations, and their complementarity, for a comprehensive characterization of their use. A special attention is paid to the use of HA in three important areas: cancer, diseases of the central nervous system (CNS), and tissue regeneration, discussing the most innovative experimental strategies. Finally, perspectives within and beyond these research fields are discussed.

Hyaluronic acid-based hydrogels to study cancer cell behaviors

Hyaluronic acid (HA) is a natural polysaccharide and a key component of the extracellular matrix (ECM) in many tissues. Therefore, HA-based biomaterials are extensively utilized to create three dimensional ECM mimics to study cell behaviors in vitro. Specifically, derivatives of HA have been commonly used to fabricate hydrogels with controllable properties. In this review, we discuss the various chemistries employed to fabricate HA-based hydrogels as a tunable matrix to mimic the cancer microenvironment and subsequently study cancer cell behaviors in vitro. These include Michael-addition reactions, photo-crosslinking, carbodiimide chemistry, and Diels-Alder chemistry. The utility of these HA-based hydrogels to examine cancer cell behaviors such as proliferation, migration, and invasion in vitro in various types of cancer are highlighted. Overall, such hydrogels provide a biomimetic material-based platform to probe cell-matrix interactions in cancer cells in vitro and study the mechanisms associated with cancer progression.

Hydrogels to engineer tumor microenvironments in vitro

Illustration of engineered hydrogel to recapitulate aspects of the tumor microenvironment.

Three-Dimensional Culture System of Cancer Cells Combined with Biomaterials for Drug Screening

Simple Summary

For the research and development of drug discovery, it is of prime importance to construct the three-dimensional (3D) tissue models in vitro. To this end, the enhancement design of cell function and activity by making use of biomaterials is essential. In this review, 3D culture systems of cancer cells combined with several biomaterials for anticancer drug screening are introduced.

Abstract

Anticancer drug screening is one of the most important research and development processes to develop new drugs for cancer treatment. However, there is a problem resulting in gaps between the in vitro drug screening and preclinical or clinical study. This is mainly because the condition of cancer cell culture is quite different from that in vivo. As a trial to mimic the in vivo cancer environment, there has been some research on a three-dimensional (3D) culture system by making use of biomaterials. The 3D culture technologies enable us to give cancer cells an in vitro environment close to the in vivo condition. Cancer cells modified to replicate the in vivo cancer environment will promote the biological research or drug discovery of cancers. This review introduces the in vitro research of 3D cell culture systems with biomaterials in addition to a brief summary of the cancer environment.

Physical Cues in the Microenvironment Regulate Stemness-Dependent Homing of Breast Cancer Cells

Tissue-specific microenvironmental factors contribute to the targeting preferences of metastatic cancers. However, the physical attributes of the premetastatic microenvironment are not yet fully characterized. In this research, we develop a transwell-based alginate hydrogel (TAH) model to study how permeability, stiffness, and roughness of a hanging alginate hydrogel regulate breast cancer cell homing. In this model, a layer of physically characterized alginate hydrogel is formed at the bottom of a transwell insert, which is placed into a matching culture well with an adherent monolayer of breast cancer cells. We found that breast cancer cells dissociate from the monolayer and home to the TAH for continual growth. The process is facilitated by the presence of rich serum in the upper chamber, the increased stiffness of the gel, as well as its surface roughness. This model is able to support the homing ability of MCF-7 and MDA-MB-231 cells drifting across the vertical distance in the culture medium. Cells homing to the TAH display stemness phenotype morphologically and biochemically. Taken together, these findings suggest that permeability, stiffness, and roughness are important physical factors to regulate breast cancer homing to a premetastatic microenvironment.

Breast cancer cells grown on hyaluronic acid-based scaffolds as 3D in vitro model for electroporation

Nowadays, electroporation (EP) represents a promising method for the intracellular delivery of anticancer drugs. To setting up the process, the EP efficiency is usually evaluated by using cell suspension and adherent cell cultures that are not representative of the in vivo conditions. Indeed, cells are surrounded by extracellular matrix (ECM) whose composition and physical characteristics are different for each tissue. So, various three-dimensional (3D) in vitro models, such as spheroids and hydrogel-based cultures, have been proposed to mimic the tumour microenvironment. Herein, a 3D breast cancer in vitro model has been proposed. HCC1954 cells were seeded on crosslinked and lyophilized matrices composed of hyaluronic acid (HA) and ionic complementary self-assembling peptides (SAPs) already known to provide a fibrous structure mimicking collagen network. Herein, SAPs were functionalized with laminin derived IKVAV adhesion motif. Cultures were characterized by spheroids surrounded by ECM produced by cancer cells as demonstrated by collagen1a1 and laminin B1 transcripts. EP was carried out on both 2D and 3D cultures: a sequence of 8 voltage pulses at 5 kHz with different amplitude was applied using a plate electrode. Cell sensitivity to EP seemed to be modulated by the presence of ECM and the different cell organization. Indeed, cells cultured on HA-IKVAV were more sensitive than those treated in 2D and HA cultures, in terms of both cell membrane permeabilization and viability. Collectively, our results suggest that HA-IKVAV cultures may represent an interesting model for EP studies. Further studies will be needed to elucidate the influence of ECM composition on EP efficiency.

The Efficiency of Gene Electrotransfer in Breast-Cancer Cell Lines Cultured on a Novel Collagen-Free 3D Scaffold

Gene Electro-Transfer (GET) is a powerful method of DNA delivery with great potential for medical applications. Although GET has been extensively studied in vitro and in vivo, the optimal parameters remain controversial. 2D cell cultures have been widely used to investigate GET protocols, but have intrinsic limitations, whereas 3D cultures may represent a more reliable model thanks to the capacity of reproducing the tumor architecture. Here we applied two GET protocols, using a plate or linear electrode, on 3D-cultured HCC1954 and MDA-MB231 breast cancer cell lines grown on a novel collagen-free 3D scaffold and compared results with conventional 2D cultures. To evaluate the electrotransfer efficiency, we used the plasmid pEGFP-C3 encoding the enhanced green fluorescent protein (EGFP) reporter gene. The novel 3D scaffold promoted extracellular matrix deposition, which particularly influences cell behavior in both in vitro cell cultures and in vivo tumor tissue. While the transfection efficiency was similar in the 2D-cultures, we observed significant differences in the 3D-model. The transfection efficiency in the 3D vs 2D model was 44% versus 15% (p < 0.01) and 24% versus 17% (p < 0.01) in HCC1954 and MDA-MB231 cell cultures, respectively. These findings suggest that the novel 3D scaffold allows reproducing, at least partially, the peculiar morphology of the original tumor tissues, thus allowing us to detect meaningful differences between the two cell lines. Following GET with plate electrodes, cell viability was higher in 3D-cultured HCC1954 (66%) and MDA-MB231 (96%) cell lines compared to their 2D counterpart (53% and 63%, respectively, p < 0.001). Based on these results, we propose the novel 3D scaffold as a reliable support for the preparation of cell cultures in GET studies. It may increase the reliability of in vitro assays and allow the optimization of GET parameters of in vivo protocols.

Prostate Cancer Phenotype Influences Bone Mineralization at Metastasis: A Study Using an In Vitro Prostate Cancer Metastasis Testbed

In this study, two types of prostate cancer cell lines, highly metastatic PC-3 and low metastatic MDA PCa 2b (PCa) were cultured on bone mimetic scaffolds to recapitulate metastasis to bone. A unique in vitro 3D tumor model that uses a sequential culture (SC) of human mesenchymal stem cells followed by seeding with cancer cells after bone formation was initiated to study the phenotype-specific interaction between prostate cancer cells and bone microenvironment. The PCa cells were observed to be less prolific and less metastatic, and to form multicellular tumoroids in the bone microenvironment, whereas PC-3 cells were more prolific and were highly metastatic, and did not form multicellular tumoroids in the bone microenvironment. The metastatic process exhibited by these two prostate cancer cell lines showed a significant and different effect on bone mineralization and extracellular matrix formation. Excessive bone formation in the presence of PC-3 and significant osteolysis in the presence of PCa were observed, which was also indicated by osteocalcin and MMP-9 expression as measured by ELISA and qRT-PCR. The field emission scanning electron microscopy images revealed that the structure of mineralized collagen in the presence of PC-3 is different than the one observed in healthy bone. All experimental results indicated that both osteolytic and osteoblastic bone lesions can be recapitulated in our tumor testbed model and that different cancer phenotypes have a very different influence on bone at metastasis. The 3D in vitro model presented in this study provides an improved, reproducible, and controllable system that is a useful tool to elucidate osteotropism of prostate cancer cells. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Peptide gels of fully-defined composition and mechanics for probing cell-cell and cell-matrix interactions in vitro

Current materials used for in vitro 3D cell culture are often limited by their poor similarity to human tissue, batch-to-batch variability and complexity of composition and manufacture. Here, we present a "blank slate" culture environment based on a self-assembling peptide gel free from matrix motifs. The gel can be customised by incorporating matrix components selected to match the target tissue, with independent control of mechanical properties. Therefore the matrix components are restricted to those specifically added, or those synthesised by encapsulated cells. The flexible 3D culture platform provides full control over biochemical and physical properties, allowing the impact of biochemical composition and tissue mechanics to be separately evaluated in vitro. Here, we demonstrate that the peptide gels support the growth of a range of cells including human induced pluripotent stem cells and human cancer cell lines. Furthermore, we present proof-of-concept that the peptide gels can be used to build disease-relevant models. Controlling the peptide gelator concentration allows peptide gel stiffness to be matched to normal breast (<1 kPa) or breast tumour tissue (>1 kPa), with higher stiffness favouring the viability of breast cancer cells over normal breast cells. In parallel, the peptide gels may be modified with matrix components relevant to human breast, such as collagen I and hyaluronan. The choice and concentration of these additions affect the size, shape and organisation of breast epithelial cell structures formed in co-culture with fibroblasts. This system therefore provides a means of unravelling the individual influences of matrix, mechanical properties and cell-cell interactions in cancer and other diseases.

Dual-degradable and injectable hyaluronic acid hydrogel mimicking extracellular matrix for 3D culture of breast cancer MCF-7 cells

In tumor biology, it is widely recognized that 3D rather than 2D cell culture can recapitulate key features of solid tumors, including cell-extracellular matrix (ECM) interactions. In this study, to mimick the ECM of breast cancer, hyaluronic acid (HA) hydrogels were synthesized from two polyvalent HA derivatives through a hydrazone and photo dual crosslinking process. HA hydrogels could be formed within 120 s. The hydrogels had similar topography and mechanical properties to breast tumor and displayed glutathione and hyaluronidase dual-responsive degradation behavior. Biological studies demonstrated that HA hydrogel could support the proliferation and clustering of breast cancer MCF-7 cells. The expression levels of VEGF, IL-8 and bFGF in hydrogel-cultured cells were significantly greater than those in 2D culture. Moreover, cells from hydrogel culture exhibited greater migration/invasion abilities and tumorigenicity than 2D-cultured cells. Therefore, the HA hydrogels are a promising ECM-mimicking matrix for in vitro construction of breast cancer.

Integration of Ca2+ signaling regulates the breast tumor cell response to simvastatin and doxorubicin

Recent studies have suggested that the lipid-lowering agent simvastatin holds great promise as a cancer therapeutic; it inhibits the growth of multiple tumors, including triple-negative breast cancer. Doxorubicin- and simvastatin-induced cytotoxicity has been associated with the modulation of Ca2+ signaling, but the underlying mechanisms remain incompletely understood. Here we identify how Ca2+ signaling regulates the breast tumor cell response to doxorubicin and simvastatin. These two drugs inhibit cell survival while increasing apoptosis in two human breast cancer cell lines and five primary breast tumor specimens through the modulation of Ca2+ signaling. Signal transduction and functional studies revealed that both simvastatin and doxorubicin trigger persistent cytosolic Ca2+ release, thereby stimulating the proapoptotic BIM pathway and mitochondrial Ca2+ overload, which are responsible for metabolic dysfunction and apoptosis induction. Simvastatin and doxorubicin suppress the prosurvival ERK1/2 pathway in a Ca2+-independent and Ca2+-dependent manner, respectively. In addition, reduction of the Ca2+ signal by chelation or pharmacological inhibition significantly prevents drug-mediated anticancer signaling. Unexpectedly, a scratch-wound assay indicated that these two drugs induce rapid cell migration, while inhibiting cell invasion and colony formation in a Ca2+-dependent manner. Further, the in vivo data for MDA-MB-231 xenografts demonstrate that upon chelation of Ca2+, the ability of both drugs to reduce the tumor burden was significantly reduced via caspase-3 deactivation. Our results establish a calcium-based mechanism as crucial for executing the cell death process triggered by simvastatin and doxorubicin, and suggest that combining simvastatin with doxorubicin may be an effective regimen for the treatment of breast cancer.

An Experimenter's Guide to Glioblastoma Invasion Pathways

Glioblastoma is a highly aggressive brain tumor that is characterized by its unparalleled invasiveness. Invasive glioblastoma cells not only escape surgery and focal therapies but also are more resistant to current radio- and chemo-therapeutic approaches. Thus, any curative therapy for this deadly disease likely should include treatment strategies that interfere with glioblastoma invasiveness. Understanding glioblastoma invasion mechanisms is therefore critical. We discuss the strengths and weaknesses of various glioblastoma invasion models and conclude that robust experimental evidence has been obtained for a pro-invasive role of Ephrin receptors, Rho GTPases, and casein kinase 2 (CK2). Extensive interplay occurs between these proteins, suggesting the existence of a glioblastoma invasion signaling network that comprises several targets for therapy.

The Combined Influence of Hydrogel Stiffness and Matrix-Bound Hyaluronic Acid Content on Glioblastoma Invasion

Glioblastoma (GBM) is the most common and lethal form of brain cancer. Its high mortality is associated with its aggressive invasion throughout the brain. The heterogeneity of stiffness and hyaluronic acid (HA) content within the brain makes it difficult to study invasion in vivo. A dextran-bead assay is employed to quantify GBM invasion within HA-functionalized gelatin hydrogels. Using a library of stiffness-matched hydrogels with variable levels of matrix-bound HA, it is reported that U251 GBM invasion is enhanced in softer hydrogels but reduced in the presence of matrix-bound HA. Inhibiting HA-CD44 interactions reduces invasion, even in hydrogels lacking matrix-bound HA. Analysis of HA biosynthesis suggests that GBM cells compensate for a lack of matrix-bound HA by producing soluble HA to stimulate invasion. Together, a robust method is showed to quantify GBM invasion over long culture times to reveal the coordinated effect of matrix stiffness, immobilized HA, and compensatory HA production on GBM invasion.

Polymeric Biomaterials for In Vitro Cancer Tissue Engineering and Drug Testing Applications

Biomimetic polymers and materials have been widely used in tissue engineering for regeneration and replication of diverse types of both normal and diseased tissues. Cancer, being a prevalent disease throughout the world, has initiated substantial interest in the creation of tissue-engineered models for anticancer drug testing. The development of these in vitro three-dimensional (3D) culture models using novel biomaterials has facilitated the investigation of tumorigenic and associated biological phenomena with a higher degree of complexity and physiological context than that provided by established two-dimensional culture models. In this review, an overview of a wide range of natural, synthetic, and hybrid biomaterials used for 3D cancer cell culture and investigation of cancer cell behavior is presented. The role of these materials in modulating cell-matrix interactions and replicating specific tumorigenic characteristics is evaluated. In addition, recent advances in biomaterial design, synthesis, and fabrication are also assessed. Finally, the advantages of incorporating polymeric biomaterials in 3D cancer models for obtaining efficacy data in anticancer drug testing applications are highlighted.

Hyaluronan in cancer - from the naked mole rat to nanoparticle therapy

Hyaluronan, a glycosaminoglycan, abundant in the tumour microenvironment, is a key player in many processes associated with cancer. Recently the cancer resistance of the naked mole rat has been attributed to the presence of an ultra-high molecular weight form of this molecule. The physical properties of this multifunctional biopolymer have been extensively studied in the context of synovial joints. However, relatively little has been reported with regard to the soft matter properties of hyaluronan in relation to cancer. In this review we examine the role of hyaluronan in cancer, paying particular attention to its mechanical interactions with malignant cells and its soft matter properties. In addition we discuss the use of hyaluronan based gels to study cancer invasion as well as nanoparticle based strategies for disease treatment.

Remodeling Components of the Tumor Microenvironment to Enhance Cancer Therapy

Solid tumor pathophysiology is characterized by an abnormal microenvironment that guides tumor progression and poses barriers to the efficacy of cancer therapies. Most common among tumor types are abnormalities in the structure of the tumor vasculature and stroma. Remodeling the tumor microenvironment with the aim to normalize any aberrant properties has the potential to improve therapy. In this review, we discuss structural abnormalities of the tumor microenvironment and summarize the therapeutic strategies that have been developed to normalize tumors as well as their potential to enhance therapy. Finally, we present different in vitro models that have been developed to analyze and better understand the effects of the tumor microenvironment on cancer cell behavior.

Life is three dimensional-as in vitro cancer cultures should be

For many decades, fundamental cancer research has relied on two-dimensional in vitro cell culture models. However, these provide a poor representation of the complex three-dimensional (3D) architecture of living tissues. The more recent 3D culture systems, which range from ridged scaffolds to semiliquid gels, resemble their natural counterparts more closely. The arrangement of the cells in 3D systems allows better cell-cell interaction and facilitates extracellular matrix secretion, with concomitant effects on gene and protein expression and cellular behavior. Many studies have reported differences between 3D and 2D systems as regards responses to therapeutic agents and pivotal cellular processes such as cell differentiation, morphology, and signaling pathways, demonstrating the importance of 3D culturing for various cancer cell lines.

Engineered microenvironments provide new insights into ovarian and prostate cancer progression and drug responses

Tissue engineering technologies, which have originally been designed to reconstitute damaged tissue structure and function, can mimic not only tissue regeneration processes but also cancer development and progression. Bioengineered approaches allow cell biologists to develop sophisticated experimentally and physiologically relevant cancer models to recapitulate the complexity of the disease seen in patients. Tissue engineering tools enable three-dimensionality based on the design of biomaterials and scaffolds that re-create the geometry, chemistry, function and signalling milieu of the native tumour microenvironment. Three-dimensional (3D) microenvironments, including cell-derived matrices, biomaterial-based cell culture models and integrated co-cultures with engineered stromal components, are powerful tools to study dynamic processes like proteolytic functions associated with cancer progression, metastasis and resistance to therapeutics. In this review, we discuss how biomimetic strategies can reproduce a humanised niche for human cancer cells, such as peritoneal or bone-like microenvironments, addressing specific aspects of ovarian and prostate cancer progression and therapy response.

Bioengineering 3D environments for cancer models

Tumor development is a dynamic process where cancer cells differentiate, proliferate and migrate interacting among each other and with the surrounding matrix in a three-dimensional (3D) context. Interestingly, the process follows patterns similar to those involved in early tissue formation by accessing specific genetic programs to grow and disseminate. Thus, the complex biological mechanisms driving tumor progression cannot easily be recreated in the laboratory. Yet, essential tumor stages, including epithelial-mesenchymal transition (EMT), tumor-induced angiogenesis and metastasis, urgently need more realistic models in order to unravel the underlying molecular and cellular mechanisms that govern them. The latest implementation of successful 3D models is having a positive impact on the fight against cancer by obtaining more predictive systems for pre-clinical research, therapeutic drug screening, and early cancer diagnosis. In this review we explore the latest advances and challenges in tumor tissue engineering, by accessing knowledge and tools from cancer biology, material science and bioengineering.

Three-dimensional in vitro tumor models for cancer research and drug evaluation

Cancer occurs when cells acquire genomic instability and inflammation, produce abnormal levels of epigenetic factors/proteins and tumor suppressors, reprogram the energy metabolism and evade immune destruction, leading to the disruption of cell cycle/normal growth. An early event in carcinogenesis is loss of polarity and detachment from the natural basement membrane, allowing cells to form distinct three-dimensional (3D) structures that interact with each other and with the surrounding microenvironment. Although valuable information has been accumulated from traditional in vitro studies in which cells are grown on flat and hard plastic surfaces (2D culture), this culture condition does not reflect the essential features of tumor tissues. Further, fundamental understanding of cancer metastasis cannot be obtained readily from 2D studies because they lack the complex and dynamic cell-cell communications and cell-matrix interactions that occur during cancer metastasis. These shortcomings, along with lack of spatial depth and cell connectivity, limit the applicability of 2D cultures to accurate testing of pharmacologically active compounds, free or sequestered in nanoparticles. To recapitulate features of native tumor microenvironments, various biomimetic 3D tumor models have been developed to incorporate cancer and stromal cells, relevant matrix components, and biochemical and biophysical cues, into one spatially and temporally integrated system. In this article, we review recent advances in creating 3D tumor models employing tissue engineering principles. We then evaluate the utilities of these novel models for the testing of anticancer drugs and their delivery systems. We highlight the profound differences in responses from 3D in vitro tumors and conventional monolayer cultures. Overall, strategic integration of biological principles and engineering approaches will both improve understanding of tumor progression and invasion and support discovery of more personalized first line treatments for cancer patients.

Direct effect of bevacizumab on glioblastoma cell lines in vitro

Bevacizumab is a humanized monoclonal antibody directed against the pro-angiogenic factor vascular and endothelial growth factor-A (VEGF-A) used in the treatment of glioblastomas. Although most patients respond initially to this treatment, studies have shown that glioblastomas eventually recur. Several non-mutually exclusive theories based on the anti-angiogenic effect of bevacizumab have been proposed to explain these mechanisms of resistance. In this report, we studied whether bevacizumab can act directly on malignant glioblastoma cells. We observe changes in the expression profiles of components of the VEGF/VEGF-R pathway and in the response to a VEGF-A stimulus following bevacizumab treatment. In addition, we show that bevacizumab itself acts on glioblastoma cells by activating the Akt and Erks survival signaling pathways. Bevacizumab also enhances proliferation and invasiveness of glioblastoma cells in hyaluronic acid hydrogel. We propose that the paradoxical effect of bevacizumab on glioblastoma cells could be due to changes in the VEGF-A-dependent autocrine loop as well as in the intracellular survival pathways, leading to the enhancement of tumor aggressiveness. Investigation of how bevacizumab interacts with glioblastoma cells and the resulting downstream signaling pathways will help targeting populations of resistant glioblastoma cells.

Gelatine methacrylamide-based hydrogels: an alternative three-dimensional cancer cell culture system

Modern cancer research requires physiological, three-dimensional (3-D) cell culture platforms, wherein the physical and chemical characteristics of the extracellular matrix (ECM) can be modified. In this study, gelatine methacrylamide (GelMA)-based hydrogels were characterized and established as in vitro and in vivo spheroid-based models for ovarian cancer, reflecting the advanced disease stage of patients, with accumulation of multicellular spheroids in the tumour fluid (ascites). Polymer concentration (2.5-7% w/v) strongly influenced hydrogel stiffness (0.5±0.2kPa to 9.0±1.8kPa) but had little effect on solute diffusion. The diffusion coefficient of 70kDa fluorescein isothiocyanate (FITC)-labelled dextran in 7% GelMA-based hydrogels was only 2.3 times slower compared to water. Hydrogels of medium concentration (5% w/v GelMA) and stiffness (3.4kPa) allowed spheroid formation and high proliferation and metabolic rates. The inhibition of matrix metalloproteinases and consequently ECM degradability reduced spheroid formation and proliferation rates. The incorporation of the ECM components laminin-411 and hyaluronic acid further stimulated spheroid growth within GelMA-based hydrogels. The feasibility of pre-cultured GelMA-based hydrogels as spheroid carriers within an ovarian cancer animal model was proven and led to tumour development and metastasis. These tumours were sensitive to treatment with the anti-cancer drug paclitaxel, but not the integrin antagonist ATN-161. While paclitaxel and its combination with ATN-161 resulted in a treatment response of 33-37.8%, ATN-161 alone had no effect on tumour growth and peritoneal spread. The semi-synthetic biomaterial GelMA combines relevant natural cues with tunable properties, providing an alternative, bioengineered 3-D cancer cell culture in in vitro and in vivo model systems.

Toward 3D biomimetic models to understand the behavior of glioblastoma multiforme cells

Glioblastoma multiforme (GBM) tumors are one of the most deadly forms of human cancer and despite improved treatments, median survival time for the majority of patients is a dismal 12-15 months. A hallmark of these aggressive tumors is their unique ability to diffusively infiltrate normal brain tissue. To understand this behavior and successfully target the mechanisms underlying tumor progression, it is crucial to develop robust experimental ex vivo disease models. This review discusses current two-dimensional (2D) experimental models, as well as animal-based models used to examine GBM cell migration, including their advantages and disadvantages. Recent attempts to develop three-dimensional (3D) tissue engineering-inspired models and their utility in unraveling the role of microenvironment on tumor cell behaviors are also highlighted. Further, the use of 3D models to bridge the gap between 2D and animal models is explored. Finally, the broad utility of such models in the context of brain cancer research is examined.

A novel tissue engineered three-dimensional in vitro colorectal cancer model

The interactions of cancer cells within a solid mass with the surrounding reactive stroma are critical for growth and progression. The surrounding vasculature is recruited into the periphery of the growing tumour to supply cancer cells with nutrients and O₂. This study focuses on developing a novel three-dimensional (3-D) in vitro biomimetic colorectal cancer model using colorectal cancer cells and connective tissue cells. The 3-D model comprises a dense artificial cancer mass, created by partial plastic compression of collagen type I containing HT29 colorectal cancer cells, nested in a non-dense collagen type I gel populated by fibroblasts and/or endothelial cells. HT29 cells within the dense mass proliferate slower than when cultured in a two-dimensional system. These cells form tumour spheroids which invade the surrounding matrix, away from the hypoxic conditions in the core of the construct, measured using real time O₂ probes. This model is also characterized by the release of vascular endothelial growth factor (VEGF) by HT29 cells, mainly at the invading edge of the artificial cancer mass. This characterization is fundamental in establishing a reproducible, complex model that could be used to advance our understanding of cancer pathology and will facilitate therapeutic drug testing.

Regulation of glioma cell phenotype in 3D matrices by hyaluronic acid

Human glioblastoma multiforme (hGBM) is the most common, aggressive, and deadly form of brain cancer. A major obstacle to understanding the impact of extracellular cues on glioblastoma invasion is the absence of model matrix systems able to replicate compositional and structural elements of the glioma mass as well as the surrounding brain tissue. Contact with a primary extracellular matrix component in the brain, hyaluronan, is believed to play a pivotal role in glioma cell invasion and malignancy. In this study we report use of gelatin and poly(ethylene glycol) (PEG) based hydrogel platforms to evaluate the effect of extracellular (composition, mechanics, HA incorporation) and intracellular (epidermal growth factor receptor overexpression) factors on the malignant transformation of U87MG glioma cells. Three-dimensional culture platforms elicit significantly different responses of U87MG glioma cells versus standard 2D culture. Critically, grafting brain-mimetic hyaluronic acid (HA) into the hydrogel network was found to induce significant, dose-dependent alterations of markers of glioma malignancy versus non-grafted 3D gelatin or PEG hydrogels. Clustering of glioma cells was observed exclusively in HA containing gels and expression profiles of malignancy-associated genes were found to vary biphasically with incorporated HA content. We also found HA-induced expression of MMP-2 is blocked by +EGFR signaling, suggesting a connection between CD44 and EGFR in glioma malignancy. Together, this work describes an adaptable platform for manipulating the local extracellular microenvironment surrounding glioma cells and highlights the importance of developing such systems for investigating the etiology and early growth of glioblastoma multiforme tumors.

Two-dimensional vs. three-dimensional in vitro tumor migration and invasion assays

Motility and invasion are key hallmarks that distinguish benign from malignant tumors, enabling cells to cross tissue boundaries, disseminate in blood and lymph and establish metastases at distant sites. Similar properties are also utilized by activated endothelial cells during tumor-induced angiogenesis. It is now appreciated that these processes might provide a rich source of novel molecular targets with the potential for inhibitors to restrain both metastasis and neoangiogenesis. Such therapeutic strategies require assays that can rapidly and quantitatively measure cell movement and the ability to traverse physiological barriers. The need for high-throughput, however, must be balanced by assay designs that accommodate, as far as possible, the complexity of the in vivo tumor microenvironment. This chapter aims to give an overview of some commonly used migration and invasion assays to aid in the selection of a balanced portfolio of techniques for the rapid and accurate evaluation of novel therapeutic agents.

Survival of cord blood haematopoietic stem cells in a hyaluronan hydrogel for ex vivo biomimicry

Haematopoietic stem cells (HSCs) and haematopoietic progenitor cells (HPCs) grow in a specified niche in close association with the microenvironment, the so-called 'haematopoietic niche'. Scaffolds have been introduced to overcome the liquid culture limitations, mimicking the presence of the extracellular matrix (ECM). In the present study the hyaluronic acid scaffold, already developed in the laboratory, has been used for the first time to maintain long-term cultures of CD34⁺ haematopoietic cells obtained from human cord blood. One parameter investigated was the impact on ex vivo survival of CD34⁺ cord blood cells (CBCs) on the hyaluronic acid surface, immobilized with peptides containing the RGD motif. This peptide was conjugated by coating the hyaluronan hydrogel and cultured in serum-free liquid phase complemented with stem cell factor (SCF), a commonly indispensable cytokine for haematopoiesis. Our work demonstrated that these hyaluronan hydrogels were superior to traditional liquid cultures by maintaining and expanding the HPCs without the need for additional cytokines, and a colonization of 280-fold increment in the hydrogel compared with liquid culture after 28 days of ex vivo expansion.

Elucidating the mechanobiology of malignant brain tumors using a brain matrix-mimetic hyaluronic acid hydrogel platform

Glioblastoma multiforme (GBM) is a malignant brain tumor characterized by diffuse infiltration of single cells into the brain parenchyma, which is a process that relies in part on aberrant biochemical and biophysical interactions between tumor cells and the brain extracellular matrix (ECM). A major obstacle to understanding ECM regulation of GBM invasion is the absence of model matrix systems that recapitulate the distinct composition and physical structure of brain ECM while allowing independent control of adhesive ligand density, mechanics, and microstructure. To address this need, we synthesized brain-mimetic ECMs based on hyaluronic acid (HA) with a range of stiffnesses that encompasses normal and tumorigenic brain tissue and functionalized these materials with short Arg-Gly-Asp (RGD) peptides to facilitate cell adhesion. Scanning electron micrographs of the hydrogels revealed a dense, sheet-like microstructure with apparent nanoscale porosity similar to brain extracellular space. On flat hydrogel substrates, glioma cell spreading area and actin stress fiber assembly increased strongly with increasing density of RGD peptide. Increasing HA stiffness under constant RGD density produced similar trends and increased the speed of random motility. In a three-dimensional (3D) spheroid paradigm, glioma cells invaded HA hydrogels with morphological patterns distinct from those observed on flat surfaces or in 3D collagen-based ECMs but highly reminiscent of those seen in brain slices. This material system represents a brain-mimetic model ECM with tunable ligand density and stiffness amenable to investigations of the mechanobiological regulation of brain tumor progression.

3D tumour models: novel in vitro approaches to cancer studies

3D in vitro models have been used in cancer research as a compromise between 2-dimensional cultures of isolated cancer cells and the manufactured complexity of xenografts of human cancers in immunocompromised animal hosts. 3D models can be tailored to be biomimetic and accurately recapitulate the native in vivo scenario in which they are found. These 3D in vitro models provide an important alternative to both complex in vivo whole organism approaches, and 2D culture with its spatial limitations. Approaches to create more biomimetic 3D models of cancer include, but are not limited to, (i) providing the appropriate matrix components in a 3D configuration found in vivo, (ii) co-culturing cancer cells, endothelial cells and other associated cells in a spatially relevant manner, (iii) monitoring and controlling hypoxia- to mimic levels found in native tumours and (iv) monitoring the release of angiogenic factors by cancer cells in response to hypoxia. This article aims to overview current 3D in vitro models of cancer and review strategies employed by researchers to tackle these aspects with special reference to recent promising developments, as well as the current limitations of 2D cultures and in vivo models. 3D in vitro models provide an important alternative to both complex in vivo whole organism approaches, and 2D culture with its spatial limitations. Here we review current strategies in the field of modelling cancer, with special reference to advances in complex 3D in vitro models.

Elastin-derived peptides: matrikines critical for glioblastoma cell aggressiveness in a 3-D system

In the most common primary brain tumors, malignant glioma cells invade the extracellular matrix (ECM) and proliferate rapidly in the cerebral tissue, which is mainly composed of hyaluronan (HA) along with the elastin present in the basement membrane of blood vessels. To determine the role of ECM components in the invasive capacity of glioma cell lines, we developed a 3-D cell-culture system, based on a hydrogel in which HA can be coreticulated with kappa-elastin (HA-kappaE). Using this system, the invasiveness of cells from four glioma cell lines was dramatically increased by the presence of kappaE and a related, specific peptide (VGVAPG)(3). In addition, MMP-2 secretion increased and MMP-12 synthesis occurred. Extracellular injections of kappaE or (VGVAPG)(3) provoked a pronounced and dose-dependent increase in [Ca(2+)](i). kappaE significantly enhanced the expression of the genes encoding elastin-receptor and tropoelastin. We propose the existence of a positive feedback loop in which degradation of elastin generates fragments that stimulate synthesis of tropoelastin followed by further degradation as well as migration and proliferation of the very cells responsible for degradation. All steps in this ECM-based loop could be blocked by the addition of either of the EBP antagonists, lactose, and V-14 peptide, suggesting that the loop itself should be considered as a new therapeutic target.

The effect of hyaluronic Acid on the invasiveness of malignant glioma cells : comparison of invasion potential at hyaluronic Acid hydrogel and matrigel

OBJECTIVE

Hyaluronidase (HAse), a degrading enzyme of hyaluronic acid (HA), is highly expressed in patients with malignant glioma. The purpose of this study was to verify whether HAse is related to the invasion of glioma cells. We also investigated if glioma cells with higher mobility in 2-dimensioal (2-D) method have also higher mobility at 3-dimensional (3-D) environment.

METHODS

Malignant glioma cell lines (U87MG, U251MG, U343MG-A, and U373MG) were used, and their HAse expressions were evaluated by HA zymography. The migration ability was evaluated by simple scratch technique. The invasiveness of each cell lines was evaluated by Matrigel invasion assay and HA hydrogel invasion assay. In HA hydrogel invasion assay, colonies larger than 150 microm were regarded as positive ones and counted. Statistical analysis of migration ability and invasion properties of each cell lines was performed using t-test.

RESULTS

In scratch test to examine migration ability of each cell lines, U87MG cells were most motile than others, and U343MG-A least motile. The HAse was expressed in U251MG and U343MG-A cell lines. However, U87MG and U373MG cell lines did not express HAse activity. In Matrigel invasion assay, the cell lines expressing HAse (U251MG and U343MG-A) were more invasive in the presence of HA than HAse deficient cell lines (U87MG and U373MG). In HA hydrogel invasion assay, the HAse-expressing cell lines formed colonies more invasively than HAse-deficient ones.

CONCLUSION

Malignant Glioma cells expressing HAse were more invasive than HAse-deficient ones in 3-dimensional environment. Therefore, it might be suggested that invasion of malignant gliomas is suppressed by inhibition of HAse expression or HA secretion. Additionally, the ability of 2-D migration and 3-D invasion might not be always coincident to each other in malignant glioma cells.

Collagens, stromal cell-derived factor-1alpha and basic fibroblast growth factor increase cancer cell invasiveness in a hyaluronan hydrogel

OBJECTIVE

Beyond to control of cell migration, differentiation and proliferation, the extracellular matrix (ECM) also contributes to invasiveness of human cancers. As the roles of hyaluronan (HA) and collagens in this process are still controversial, we have investigated their involvement in cancer pathogenesis.

MATERIALS AND METHODS

With this aim in view, we developed a three-dimensional matrix, as reticulate HA hydrogel alone or coated with different collagens, in which cells could invade and grow.

RESULTS

We show that cancer cells, which were non-invasive in a single HA hydrogel, acquired this capacity in the concomitant presence of type I or III collagens. Both types of ECM compound, HA and collagens, possess the capacity to stimulate production of metalloprotease-2, recognized otherwise as a factor for poor cancer prognosis. HA-provoked cellular invasiveness resulted from CD44-mediated increase in cytosolic [Ca2+] and its subsequent hydrolysis due to ADAM (a disintegrin and metalloprotease) proteolytic activity. Interestingly, this mechanism seemed to be absent in non-invasive cancer cell lines.

CONCLUSION

Furthermore, using basic fibroblast growth factor and stromal cell-derived factor-1alpha, we also show that this three-dimensional reticulate matrix may be considered as a valuable model to study chemokinetic and chemotactic potentials of factors present in tumour stroma.

Hyaluronan hydrogel: an appropriate three-dimensional model for evaluation of anticancer drug sensitivity

The extracellular polysaccharide hyaluronan (HA) controls cell migration, differentiation and proliferation, and contributes to the invasiveness of human cancers. In order to investigate the sensitivity of cancer cells to antimitotic agents, we developed a cross-linked HA hydrogel, a three-dimensional matrix in which cells can invade and grow. We have studied three cell lines (SA87, NCI-H460 and H460M), from primary tumors and metastases, that migrated into the HA hydrogel and proliferated giving rise to clusters and colonies. Concurrently, we studied the growth of these cell lines in a usual monolayer culture system. In these two models, increasing concentrations of doxorubicin and 5-fluorouracil were evaluated for their ability to inhibit tumor cell growth and colony formation. Taken together, our data suggest that the cancer cells were more resistant in the three-dimensional model than in monolayer cell systems. The antimitotic drugs were efficient after 24h of treatment in the monolayer cultures, whereas they were significantly efficient only after one week of incubation in the HA hydrogels. Herein, we show that this cross-linked matrix provides a three-dimensional model particularly appropriate for investigating mechanisms involved in cancer cell line sensitivity to antimitotic drugs.

Antiangiogenic activity of the endocannabinoid anandamide: correlation to its tumor-suppressor efficacy

Endocannabinoids are now emerging as suppressors of key cell-signaling pathways involved in cancer cell growth, invasion, and metastasis. We have previously observed that the metabolically stable anandamide analog, 2-methyl-2'-F-anandamide (Met-F-AEA) can inhibit the growth of thyroid cancer in vivo. Our hypothesis was that the anti-tumor effect observed could be at least in part ascribed to inhibition of neo-angiogenesis. Therefore, the aim of this study was to assess the anti-angiogenic activity of Met-F-AEA, to investigate the molecular mechanisms underlying this effect and whether Met-F-AEA could antagonize tumor-induced endothelial cell sprouting. We show that Met-F-AEA inhibited bFGF-stimulated endothelial cell proliferation, in a dose-dependent manner, and also induced apoptosis, both effects reliant on cannabinoid CB1 receptor stimulation. Analyzing the signaling pathways implicated in angiogenesis, we observed that the bFGF-induced ERK phosphorylation was antagonized by Met-F-AEA, and we found that p38 MAPK was involved in Met-F-AEA-induced apoptosis. Moreover, Met-F-AEA was able to inhibit bi-dimensional capillary-like tube formation and activity of matrix metalloprotease MMP-2, a major matrix degrading enzyme. Importantly, we demonstrated that Met-F-AEA is also functional in vivo since it inhibited angiogenesis in the chick chorioallantoic neovascularization model. Finally, Met-F-AEA inhibited tumor-induced angiogenesis in a three-dimensional model of endothelial and thyroid tumor cell (KiMol) spheroids co-cultures in different 3-D polymeric matrices that resemble tumor microenvironment and architecture. Thus, our results suggest that anandamide could be involved in the control of cancer growth targeting both tumor cell proliferation and the angiogenic stimulation of the vasculature.

Interactions of hypocrellin B with hyaluronan and photo-induced interactions

In the current work, the molecular recognition and interaction were studied by taking advantages of the environmentally sensitive fluorescence of hypocrellin B (HB) and the structural knowledge of hyaluronan (HYA), a polysaccharide over-expressed in tumor cells or tissues. Interestingly, it was found that, binding to HYA, the absorbance of HB would be greatly strengthened, suggesting HB fitting to a hydrophobic environment in HYA, while the fluorescence seriously quenched at pH 7.0, which was very distinct from the binding of HB to proteins, liposome, other polysaccharide molecules or HYA at pH 2.0. Synchronously, the particle size of HYA would become bigger after interaction with HB, suggesting an aggregation of HYA. Considering the spectral responses of HB and the particle size change of HYA, a specific interaction of HB with HYA was proposed, that is, an HB molecule would link two HYA molecules not only by hydrophobic interaction but also by formations of intermolecular hydrogen bonds at physiological pH values. Furthermore, the estimated binding constant suggests a quite high affinity of HB to HYA. Besides, an oxygen-dependent degradation of HYA and photobleaching of HB were observed via photosensitization of HB.

Unfolding Features of Bovine Testicular Hyaluronidase Studied by Fluorescence Spectroscopy and Fourier Transformed Infrared Spectroscopy

Chemical unfolding of bovine testicular hyaluronidase (HAase) has been studied by fluorescence spectroscopy and Fourier transformed infrared spectroscopy (FTIR). Thermodynamic parameters were determined for unfolding HAase from changes in the intrinsic fluorescence emission intensity and the formations of several possible unfolding intermediates have been identified. This was further confirmed by representation of fluorescence data in terms of 'phase diagram'. The secondary structures of HAase have been assigned and semiquantitatively estimated from the FTIR. The occurrence of conformational change during chemical unfolding as judged by fluorescence and FTIR spectroscopy indicated that the unfolding of HAase may not follow the typical two-state model.

Cell migration/invasion assays and their application in cancer drug discovery

Invasive capacity is the single most important trait that distinguishes benign from malignant lesions. Tumour cells, during intravasation and extravasation of blood and lymphatic channels and when establishing colonies at secondary sites, must move through tissue boundaries that normal adult cells (other than, for example activated leukocytes) do not cross. Similar mechanisms are also utilised by activated endothelial cells during the generation of new blood vessels that enable the sustained growth and dissemination of tumours. It is now increasingly recognised that these processes--cell motility and invasion--might provide a rich source of novel targets for cancer therapy and that appropriate inhibitors may restrain both metastasis and neoangiogenesis. This new paradigm demands screening assays that can rapidly and quantitatively measure cell movement and the ability to traverse physiological barriers. We also need to consider whether simple reductionist in vitro approaches can reliably model the complexity of in vivo tumour invasion/neoangiogenesis. There are both opportunities and challenges ahead in developing a balanced portfolio of assays that will be able to evaluate accurately and finally deliver novel anti-invasive agents with therapeutic potential for clinical use.