Proliferation and enrichment of CD133(+) glioblastoma cancer stem cells on 3D chitosan-alginate scaffolds

Fabrication and Characterization of Chitosan-Hyaluronic Acid Scaffolds with Varying Stiffness for Glioblastoma Cell Culture

The invasive and recurrent nature of glioblastoma multiforme (GBM) is linked to a small subpopulation of cancer cells, which are self-renewing, resistant to standard treatment regimens, and induce formation of new tumors. Matrix stiffness is implicated in the regulation of cell proliferation, drug resistance, and reversion to a more invasive phenotype. Therefore, understanding the relationship between matrix stiffness and tumor cell behavior is vital to develop appropriate in vitro tumor models. Here, chitosan-hyaluronic acid (CHA) polyelectrolyte complex scaffolds are fabricated with statistically significant stiffness variances to characterize the effect of scaffold stiffness on morphology, proliferation, drug resistance, and gene expression in human glioblastoma cells (U-87 MG). All scaffolds support GBM proliferation over a 12-day culture period, yet larger spheroids are observed in scaffolds with higher stiffness. Additionally, GBM cells cultured in stiffer CHA scaffolds prove significantly more resistant to the common chemotherapeutic temozolomide. Moreover, the stiffer 8% CHA scaffolds exhibit an increase in expression of drug resistance and invasion related genes compared to 2D culture. CHA scaffolds present a tunable microenvironment for enhanced tumor cell malignancy and may provide a valuable in vitro microenvironment for studying tumor progression and screening anticancer therapies.

Design of spherically structured 3D in vitro tumor models -Advances and prospects

Three-dimensional multicellular tumor models are receiving an ever-growing focus as preclinical drug-screening platforms due to their potential to recapitulate major physiological features of human tumors in vitro. In line with this momentum, the technologies for assembly of 3D microtumors are rapidly evolving towards a comprehensive inclusion of tumor microenvironment elements. Customized spherically structured platforms, including microparticles and microcapsules, provide a robust and scalable technology to imprint unique biomolecular tumor microenvironment hallmarks into 3D in vitro models. Herein, a comprehensive overview of novel advances on the integration of tumor-ECM components and biomechanical cues into 3D in vitro models assembled in spherical shaped platforms is provided. Future improvements regarding spatiotemporal/mechanical adaptability, and degradability, during microtumors in vitro 3D culture are also critically discussed considering the realistic potential of these platforms to mimic the dynamic tumor microenvironment. From a global perspective, the production of 3D multicellular spheroids with tumor ECM components included in spherical models will unlock their potential to be used in high-throughput screening of therapeutic compounds. It is envisioned, in a near future, that a combination of spherically structured 3D microtumor models with other advanced microfluidic technologies will properly recapitulate the flow dynamics of human tumors in vitro.

STATEMENT OF SIGNIFICANCE

The ability to correctly mimic the complexity of the tumor microenvironment in vitro is a key aspect for the development of evermore realistic in vitro models for drug-screening and fundamental cancer biology studies. In this regard, conventional spheroid-based 3D tumor models, combined with spherically structured biomaterials, opens the opportunity to precisely recapitulate complex cell-extracellular matrix interactions and tumor compartmentalization. This review provides an in-depth focus on current developments regarding spherically structured scaffolds engineered into in vitro 3D tumor models, and discusses future advances toward all-encompassing platforms that may provide an improved in vitro/in vivo correlation in a foreseeable future.

Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities

The past decade has witnessed rapid advances in porous polyelectrolytes and there is tremendous interest in their synthesis as well as their applications in environmental, energy, biomedicine, and catalysis technologies. Research on porous polyelectrolytes is motivated by the flexible choice of functional organic groups and processing technologies as well as the synergy of the charge and pores spanning length scales from individual polyelectrolyte backbones to their nano-/micro-superstructures. This Review surveys recent progress in porous polyelectrolytes including membranes, particles, scaffolds, and high surface area powders/resins as well as their derivatives. The focus is the interplay between surface chemistry, Columbic interaction, and pore confinement that defines new chemistry and physics in such materials for applications in energy conversion, molecular separation, water purification, sensing/actuation, catalysis, tissue engineering, and nanomedicine.

Microfluidics in Malignant Glioma Research and Precision Medicine

Glioblastoma multiforme (GBM) is an aggressive form of brain cancer that has no effective treatments and a prognosis of only 12-15 months. Microfluidic technologies deliver microscale control of fluids and cells, and have aided cancer therapy as point-of-care devices for the diagnosis of breast and prostate cancers. However, a few microfluidic devices are developed to study malignant glioma. The ability of these platforms to accurately replicate the complex microenvironmental and extracellular conditions prevailing in the brain and facilitate the measurement of biological phenomena with high resolution and in a high-throughput manner could prove useful for studying glioma progression. These attributes, coupled with their relatively simple fabrication process, make them attractive for use as point-of-care diagnostic devices for detection and treatment of GBM. Here, the current issues that plague GBM research and treatment, as well as the current state of the art in glioma detection and therapy, are reviewed. Finally, opportunities are identified for implementing microfluidic technologies into research and diagnostics to facilitate the rapid detection and better therapeutic targeting of GBM.

Looking into the Future: Toward Advanced 3D Biomaterials for Stem-Cell-Based Regenerative Medicine

Stem-cell-based therapies have the potential to provide novel solutions for the treatment of a variety of diseases, but the main obstacles to such therapies lie in the uncontrolled differentiation and functional engraftment of implanted tissues. The physicochemical microenvironment controls the self-renewal and differentiation of stem cells, and the key step in mimicking the stem cell microenvironment is to construct a more physiologically relevant 3D culture system. Material-based 3D assemblies of stem cells facilitate the cellular interactions that promote morphogenesis and tissue organization in a similar manner to that which occurs during embryogenesis. Both natural and artificial materials can be used to create 3D scaffolds, and synthetic organic and inorganic porous materials are the two main kinds of artificial materials. Nanotechnology provides new opportunities to design novel advanced materials with special physicochemical properties for 3D stem cell culture and transplantation. Herein, the advances and advantages of 3D scaffold materials, especially with respect to stem-cell-based therapies, are first outlined. Second, the stem cell biology in 3D scaffold materials is reviewed. Third, the progress and basic principles of developing 3D scaffold materials for clinical applications in tissue engineering and regenerative medicine are reviewed.

Biomaterials-Based Approaches to Tumor Spheroid and Organoid Modeling

Evolving understanding of structural and biological complexity of tumors has stimulated development of physiologically relevant tumor models for cancer research and drug discovery. A major motivation for developing new tumor models is to recreate the 3D environment of tumors and context-mediated functional regulation of cancer cells. Such models overcome many limitations of standard monolayer cancer cell cultures. Under defined culture conditions, cancer cells self-assemble into 3D constructs known as spheroids. Additionally, cancer cells may recapitulate steps in embryonic development to self-organize into 3D cultures known as organoids. Importantly, spheroids and organoids reproduce morphology and biologic properties of tumors, providing valuable new tools for research, drug discovery, and precision medicine in cancer. This Progress Report discusses uses of both natural and synthetic biomaterials to culture cancer cells as spheroids or organoids, specifically highlighting studies that demonstrate how these models recapitulate key properties of native tumors. The report concludes with the perspectives on the utility of these models and areas of need for future developments to more closely mimic pathologic events in tumors.

Emerging Roles of Electrospun Nanofibers in Cancer Research

This article reviews the recent progress of electrospun nanofibers in cancer research. It begins with a brief introduction to the emerging potential of electrospun nanofibers in cancer research. Next, a number of recent advances on the important features of electrospun nanofibers critical for cancer research are discussed including the incorporation of drugs, control of release kinetics, orientation and alignment of nanofibers, and the fabrication of 3D nanofiber scaffolds. This article further highlights the applications of electrospun nanofibers in several areas of cancer research including local chemotherapy, combinatorial therapy, cancer detection, cancer cell capture, regulation of cancer cell behavior, construction of in vitro 3D cancer model, and engineering of bone microenvironment for cancer metastasis. This progress report concludes with remarks on the challenges and future directions for design, fabrication, and application of electrospun nanofibers in cancer diagnostics and therapeutics.

Structural characterization, immune regulation and antioxidant activity of a new heteropolysaccharide from Cantharellus cibarius Fr

A new heteropolysaccharide was extracted and purified from the fruiting bodies of Cantharellus cibarius Fr. The Cantharellus cibarius Fr. polysaccharide (CC-1) had a molecular weight of 61,056 kDa and was mainly formed of the glucose and xylose at ratio of 5:1. Structure identification of CC-1 was analysed by a combined application of total hydrolysis, high performance liquid chromatography (HPLC), methylation analysis, gas chromatography-mass spectrometry (GC-MS), infrared (IR) spectra and nuclear magnetic resonance (NMR) spectroscopy. The experimental results showed that CC-1 had a backbone of 1,4-linked-β-D-glucose which branched at O-6 and the branches were mainly composed of 6→1)-α-D-xylopyranose residue. CC-1 exhibited significant in vitro antioxidant effect and proliferation effect of immune cells. The activity study showed CC-1 has ability to clear the ABTS⁺ free radical and DPPH⁻ free radical in a certain range of concentration. The proliferation activity of the immune cells showed that the proliferation effect on B cells was very significant (P<0.001) in the concentration of 0.625–80 mg/ml; and the effect of T cell proliferation was also very significant (P<0.001) in the concentration of 5–20 mg/ml. The result of this study introduced Cantharellus cibarius Fr. as a possible valuable source in exhibiting unique immunoregulatory and antioxidant properties.

Role of Microenvironment in Glioma Invasion: What We Learned from In Vitro Models

The invasion properties of glioblastoma hamper a radical surgery and are responsible for its recurrence. Understanding the invasion mechanisms is thus critical to devise new therapeutic strategies. Therefore, the creation of in vitro models that enable these mechanisms to be studied represents a crucial step. Since in vitro models represent an over-simplification of the in vivo system, in these years it has been attempted to increase the level of complexity of in vitro assays to create models that could better mimic the behaviour of the cells in vivo. These levels of complexity involved: 1. The dimension of the system, moving from two-dimensional to three-dimensional models; 2. The use of microfluidic systems; 3. The use of mixed cultures of tumour cells and cells of the tumour micro-environment in order to mimic the complex cross-talk between tumour cells and their micro-environment; 4. And the source of cells used in an attempt to move from commercial lines to patient-based models. In this review, we will summarize the evidence obtained exploring these different levels of complexity and highlighting advantages and limitations of each system used.

Three-dimensional cell culture: A powerful tool in tumor research and drug discovery

In previous years, three-dimensional (3D) cell culture technology has become a focus of research in tumor cell biology, using a variety of methods and materials to mimic the in vivo microenvironment of cultured tumor cells ex vivo. These 3D tumor cells have demonstrated numerous different characteristics compared with traditional two-dimensional (2D) culture. 3D cell culture provides a useful platform for further identifying the biological characteristics of tumor cells, particularly in the drug sensitivity area of the key points of translational medicine. It promises to be a bridge between traditional 2D culture and animal experiments, and is of great importance for further research in the field of tumor biology. In the present review, previous 3D cell culture applications, focusing on anti-tumor drug susceptibility testing, are summarized.

Recent advances in cell-laden 3D bioprinting: materials, technologies and applications

Fabrication of 3D scaffolds with patient-specific designs, high structural and component complexity, and rapid on-demand production at a low-cost by printing technique has attracted ever-increasing interests in tissue engineering. Cell-laden 3D bioprinting offers good prospects for future organ transplantation. Compared with nonbiological 3D printing, cell-laden 3D bioprinting involves more complex factors, including the choice of printing materials, the strategy of gelling, cell viability and technical challenges. Although cell-populated 3D bioprinting has so many complex factors, it has proven to be a useful and exciting tool with wide potential applications in regenerative medicine to generate a variety of transplantable tissues. In this review, we first overview the bioprinting materials, gelling strategies and some major applications of cell-laden 3D bioprinting, with main focus on the recent advances and current challenges of the field. Finally, we propose some future directions of the cell-populated 3D bioprinting in tissue engineering and regenerative medicine.

[Formula: see text]

In this review, we first overview the bioprinting materials, gelling strategies and some major applications of cell-populated 3D bioprinting, with main focus on the recent advances and current challenges of the field. Finally, we propose some future directions of the cell-laden 3D bioprinting in tissue engineering and regenerative medicine.

PNIPAAm-co-Jeffamine® (PNJ) scaffolds as in vitro models for niche enrichment of glioblastoma stem-like cells

Glioblastoma (GBM) is the most common adult primary brain tumor, and the 5-year survival rate is less than 5%. GBM malignancy is driven in part by a population of GBM stem-like cells (GSCs) that exhibit indefinite self-renewal capacity, multipotent differentiation, expression of neural stem cell markers, and resistance to conventional treatments. GSCs are enriched in specialized niche microenvironments that regulate stem phenotypes and support GSC radioresistance. Therefore, identifying GSC-niche interactions that regulate stem phenotypes may present a unique target for disrupting the maintenance and persistence of this treatment resistant population. In this work, we engineered 3D scaffolds from temperature responsive poly(N-isopropylacrylamide-co-Jeffamine M-1000® acrylamide), or PNJ copolymers, as a platform for enriching stem-specific phenotypes in two molecularly distinct human patient-derived GSC cell lines. Notably, we observed that, compared to conventional neurosphere cultures, PNJ cultured GSCs maintained multipotency and exhibited enhanced self-renewal capacity. Concurrent increases in expression of proteins known to regulate self-renewal, invasion, and stem maintenance in GSCs (NESTIN, EGFR, CD44) suggest that PNJ scaffolds effectively enrich the GSC population. We further observed that PNJ cultured GSCs exhibited increased resistance to radiation treatment compared to GSCs cultured in standard neurosphere conditions. GSC radioresistance is supported in vivo by niche microenvironments, and this remains a significant barrier to effectively treating these highly tumorigenic cells. Taken in sum, these data indicate that the microenvironment created by synthetic PNJ scaffolds models niche enrichment of GSCs in patient-derived GBM cell lines, and presents tissue engineering opportunities for studying clinically important behaviors such as radioresistance in vitro.

Expression of CD133 in endometrial cancer cells and its implications

Cancer stem cells are an attractive therapeutic target for cancer. The present study examined stem cell characteristics of CD133+ cells isolated from endometrial cancer. Phenotypic characteristics, proliferation, migration, anchorage-independent growth, chemoresistance, gene expression profile and tumorigenicity of CD133+ tumor cells were assessed. Primary tumor exhibited immunoreactivity for CD133. Endometrial CD133+ tumor cells enhanced proliferation rate, colony formation, chemotaxis migration ability, and chemoresistance to cisplatin, paclitaxel, and doxorubicin than CD133- cells. CD133+ cells expressed more cancer stem cells markers such as EpCAM, aldehyde dehydrogenase 1 and insulin-like growth factor-1 receptor than CD133- cells. Moreover, CD133+ cells also increased expression of embryonic stem cell markers including oct4, nanog, sox2, and cmyc than CD133- cells. Finally, CD133+ tumor cells could generate xenograft but not CD133- tumor cells. CD133 and Ki67 were extensively expressed in the xenograft. In conclusion, endometrial CD133+ tumor cells displayed cancer stem cell characteristics and might represent a valuable tool for identifying endometrial cancer stem cells and hence a potential therapeutic target.

Modeling Physiologic Microenvironments in Three-Dimensional Microtumors Maintains Brain Tumor Initiating Cells

Development of effective novel anti-tumor treatments will require improved in vitro models that incorporate physiologic microenvironments and maintain intratumoral heterogeneity, including tumor initiating cells. Brain tumor initiating cells (BTIC) are a target for cancer therapy, because BTICs are highly tumorigenic and contribute to tumor angiogenesis, invasion, and therapeutic resistance. Current leading studies rely on BTIC isolation from patient-derived xenografts followed by propagation as neurospheres. As this process is expensive and time-consuming, we determined whether three-dimensional microtumors were an alternative in vitro method for modeling tumor growth via BITC maintenance and/or enrichment. Brain tumor cells were grown as neurospheres or as microtumors produced using the human-derived biomatrix HuBiogel™ and maintained with physiologically relevant microenvironments. BITC percentages were determined using cell surface marker expression, label retention, and neurosphere formation capacity. Our data demonstrate that expansion of brain tumor cells as hypoxic and nutrient-restricted microtumors significantly increased the percentage of both CD133+ and CFSEhigh cells. We further demonstrate that BTIC-marker positive cells isolated from microtumors maintained neurosphere formation capacity in the in vitro limiting dilution assay and tumorigenic potential in vivo. These data demonstrate that microtumors can be a useful three-dimensional biological model for the study of BTIC maintenance and targeting.

Bi-functional oxidized dextran–based hydrogel inducing microtumors: An in vitro three-dimensional lung tumor model for drug toxicity assays

Cancer is a serious death causing disease having 8.2 million deaths in 2012. In the last decade, only about 10% of chemotherapeutic compounds showed productivity in drug screening. Two-dimensional culture assays are the most common in vitro drug screening models, which do not precisely model the in vivo condition for reliable preclinical drug screening. Three-dimensional scaffold–based cell cultures perhaps mimic tumor microenvironment and recapitulate physiologically more relevant tumor. This study was carried out to develop bi-functional oxidized dextran–based cell instructive hydrogel that provides three-dimensional environment to cancer cells for inducing microtumor. Oxidized dextran was blended with thiolated chitosan to fabricate an in situ self-gelable hydrogel (modified dextran–chitosan) in a one-step process. The hydrogels characterization revealed cross-linked network structure with highly porous structure and water absorption. The modified dextran–chitosan hydrogel showed reduced hydrophobicity and has reduced protein absorption, which resulted in changing the A549 cell adhesiveness, and encouraged them to form microtumor. The cells were proliferated in clusters having spherical morphology with randomly oriented stress fiber and large nucleus. Further microtumors were studied for hypoxia where reactive oxygen species generation demonstrated 15-fold increase as compared to monolayer culture. Drug-sensitivity results showed that microtumors generated on modified dextran–chitosan hydrogel showed resistance to doxorubicin with having 33%–58% increased growth than two-dimensional monolayer model at concentrations of 25–100 µM. In summary, the modified dextran–chitosan scaffold can provide surface chemistry that induces three-dimensional microtumors with physiologically relevant properties to in vivo tumor including growth, morphology, extracellular matrix production, hypoxic phenotype, and drug response. This model can be potentially utilized for drug toxicity studies and cancer disease modeling to understand tumor phenotype and progression.

Growth of MCF-7 breast cancer cells and efficacy of anti-angiogenic agents in a hydroxyethyl chitosan/glycidyl methacrylate hydrogel

Background

Breast cancer negatively affects women’s health worldwide. The tumour microenvironment plays a critical role in tumour initiation, proliferation, and metastasis. Cancer cells are traditionally grown in two-dimensional (2D) cultures as monolayers on a flat solid surface lacking cell–cell and cell–matrix interactions. These experimental conditions deviate from the clinical situation. Improved experimental systems that can mimic the in vivo situation are required to discover new therapies, particularly for anti-angiogenic agents that mainly target intercellular factors and play an essential role in treating some cancers.

Methods

Chitosan can be modified to construct three-dimensional (3D) tumour models. Here, we report an in vitro 3D tumour model using a hydroxyethyl chitosan/glycidyl methacrylate (HECS–GMA) hydrogel produced by a series of chitosan modifications. Parameters relating to cell morphology, viability, proliferation, and migration were analysed using breast cancer MCF-7 cells. In a xenograft model, secretion of angiogenesis-related growth factors and the anti-angiogenic efficacy of Endostar and Bevacizumab in cells grown in HECS–GMA hydrogels were assessed by immunohistochemistry.

Results

Hydroxyethyl chitosan/glycidyl methacrylate hydrogels had a highly porous microstructure, mechanical properties, swelling ratio, and morphology consistent with a 3D tumour model. Compared with a 2D monolayer culture, breast cancer MCF-7 cells residing in the HECS–GMA hydrogels grew as tumour-like clusters in a 3D formation. In a xenograft model, MCF-7 cells cultured in the HECS–GMA hydrogels had increased secretion of angiogenesis-related growth factors. Recombinant human endostatin (Endostar), but not Bevacizumab (Avastin), was an effective anti-angiogenic agent in HECS–GMA hydrogels.

Conclusions

The HECS–GMA hydrogel provided a 3D tumour model that mimicked the in vivo cancer microenvironment and supported the growth of MCF7 cells better than traditional tissue culture plates. The HECS–GMA hydrogel may offer an improved platform to minimize the gap between traditional tissue culture plates and clinical applicability. In addition, the anti-angiogenic efficacy of drugs such as Endostar and Bevacizumab can be more comprehensively studied and assessed in HECS–GMA hydrogels.

Chitosan promotes cancer progression and stem cell properties in association with Wnt signaling in colon and hepatocellular carcinoma cells

Cancer stem cells (CSCs), a small population of cancer cells, have been considered to be the origin of cancer initiation, recurrence, and metastasis. Tumor microenvironment provides crucial signals for CSCs to maintain stem cell properties and promotes tumorigenesis. Therefore, establishment of an appropriate cell culture system to mimic the microenvironment for CSC studies is an important issue. In this study, we grew colon and hepatocellular carcinoma (HCC) cells on chitosan membranes and evaluated the tumor progression and the CSC properties. Experimental results showed that culturing cancer cells on chitosan increased cell motility, drug resistance, quiescent population, self-renewal capacity, and the expression levels of stemness and CSC marker genes, such as OCT4, NANOG, CD133, CD44, and EpCAM. Furthermore, we demonstrated that chitosan might activate canonical Wnt/β-catenin-CD44 axis signaling in CD44^positive colon cancer cells and noncanonical Wnt-STAT3 signaling in CD44^negative HCC cells. In conclusion, chitosan as culture substrates activated the essential signaling of CSCs and promoted CSC properties. The chitosan culture system provides a convenient platform for the research of CSC biology and screening of anticancer drugs.

Integrating the glioblastoma microenvironment into engineered experimental models

Glioblastoma (GBM) is the most lethal cancer originating in the brain. Its high mortality rate has been attributed to therapeutic resistance and rapid, diffuse invasion - both of which are strongly influenced by the unique microenvironment. Thus, there is a need to develop new models that mimic individual microenvironmental features and are able to provide clinically relevant data. Current understanding of the effects of the microenvironment on GBM progression, established experimental models of GBM and recent developments using bioengineered microenvironments as ex vivo experimental platforms that mimic the biochemical and physical properties of GBM tumors are discussed.

Research on human glioma stem cells in China

Research on human glioma stem cells began early in the 21^st century and since then has become a rapidly growing research field with the number of publications increasing year by year. The research conducted by our diverse group of investigators focused primarily on cell culture techniques, molecular regulation, signaling pathways, cancer treatment, the stem cell microenvironment and the cellular origin and function of glioma stem cells. In particular, we put forward our view that there are inverse or forward transformations among neural stem cells, glial cells and glioma stem cells in glioma tissues under certain conditions. Based on the background of the progress of international research on human glioma stem cells, we aim to share our progress and current findings of human glioma stem cell research in China with colleagues around the world.

Culture on 3D Chitosan-Hyaluronic Acid Scaffolds Enhances Stem Cell Marker Expression and Drug Resistance in Human Glioblastoma Cancer Stem Cells

The lack of in vitro models that support the growth of glioblastoma (GBM) stem cells (GSCs) that underlie clinical aggressiveness hinders developing new, effective therapies for GBM. While orthotopic patient-derived xenograft models of GBM best reflect in vivo tumor behavior, establishing xenografts is a time consuming, costly, and frequently unsuccessful endeavor. To address these limitations, a 3D porous scaffold composed of chitosan and hyaluronic acid (CHA) is synthesized. Growth and expression of the cancer stem cell (CSC) phenotype of the GSC GBM6 taken directly from fresh xenogratfs grown on scaffolds or as adherent monolayers is compared. While 2D adherent cultures grow as monolayers of flat epitheliod cells, GBM6 cells proliferate within pores of CHA scaffolds as clusters of self-adherent ovoid cells. Growth on scaffolds is accompanied by greater expression of genes that mediate epithelial-mesenchymal transition and maintain a primitive, undifferentiated phenotype, hallmarks of CSCs. Scaffold-grown cells also display higher expression of genes that promote resistance to hypoxia-induced oxidative stress. In accord, scaffold-grown cells show markedly greater resistance to clinically utilized alkylating agents compared to adherent cells. These findings suggest that our CHA scaffolds better mimic in vivo biological and clinical behavior and provide insights for developing novel individualized treatments.

3D Porous Chitosan-Alginate Scaffolds Promote Proliferation and Enrichment of Cancer Stem-Like Cells

Cancer stem cells are increasingly becoming a primary target for new cancer treatment development. The ability to study their transient behavior in vitro will provide the opportunity for high-throughput testing of more effective therapies. We have previously demonstrated the use of 3D porous chitosan-alginate (CA) scaffolds to promote cancer stem-like cell (CSC) proliferation and enrichment in glioblastoma. Here we use 3D porous CA scaffolds to promote cancer stem-like cell enrichment in cell lines from prostate, liver, and breast cancers, and investigate the proliferation, morphology, and gene expressions of cells cultured in CA scaffolds as compared to 2D controls. The 3D CA scaffold cultures for all three cancer types showed reduced proliferation, formation of tumor spheroids, and increased expression of CSC associated mark genes (CD133 and NANOG), as opposed to monolayers. Additionally, we present a putative mechanism for the cancer stem-like cell enrichment on CA scaffolds. This study demonstrates that the cancer stem-like cell enrichment in CA scaffolds is a robust process that is not restricted to particular cancer types.

3D bioprinted glioma stem cells for brain tumor model and applications of drug susceptibility

Glioma is still difficult to treat because of its high malignancy, high recurrence rate, and high resistance to anticancer drugs. An alternative method for research of gliomagenesis and drug resistance is to use in vitro tumor model that closely mimics the in vivo tumor microenvironment. In this study, we established a 3D bioprinted glioma stem cell model, using modified porous gelatin/alginate/fibrinogen hydrogel that mimics the extracellular matrix. Glioma stem cells achieved a survival rate of 86.92%, and proliferated with high cellular activity immediately following bioprinting. During the in vitro culture period, the printed glioma stem cells not only maintained their inherent characteristics of cancer stem cells (Nestin), but also showed differentiation potential (glial fibrillary acidic protein and β-tubulin III). In order to verify the vascularization potential of glioma stem cells, tumor angiogenesis biomarker, vascular endothelial growth factor was detected by immunohistochemistry, and its expression increased from week one to three during the culture period. Drug-sensitivity results showed that 3D printed tumor model was more resistant to temozolomide than 2D monolayer model at TMZ concentrations of 400-1600 μg ml^-1. In summary, 3D bioprinted glioma model provides a novel alternative tool for studying gliomagenesis, glioma stem cell biology, drug resistance, and anticancer drug susceptibility in vitro.

Screening glioma stem cells in U251 cells based on the P1 promoter of the CD133 gene

Cluster of differentiation (CD)133 is an important cell surface marker of glioma stem cells (GSCs). The transcription of the CD133 gene is controlled by five alternative promoters (P1, P2, P3, P4 and P5), which are expressed in a tissue-specific manner. In the present study, gene recombination technology was used to construct two types of gene expression vectors that contained the P1 promoter of the CD133 gene, which regulated either the neomycin-resistance gene or the herpes simplex virus thymidine kinase (HSV-TK) gene. Following the stable transfection of U251 glioblastoma cells with these two gene vectors, the cells expressing the P1 promoter that regulated the neomycin-resistance gene were named CD133 (+) cells, while the cells expressing the P1 promoter regulating the HSV-TK gene were called CD133 (−) cells. The expression of CD133 was detected by flow cytometry and reverse transcription-quantitative polymerase chain reaction. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess cell proliferation ability, while the cell cycle was analyzed by flow cytometry, and a clone formation test was performed to evaluate the invasive capability of the cells. The results demonstrated that, due to CD133 expression, the cell proliferation ability and the invasive capability of CD133 (+) cells were significantly higher than those of CD133 (−) cells. In conclusion, the present study successfully established a novel method of screening GSCs in U251 cells based on the P1 promoter of the CD133 gene.

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.

An alginate-based platform for cancer stem cell research

As the primary determinants of the clinical behaviors of human cancers, the discovery of cancer stem cells (CSCs) represents an ideal target for novel anti-cancer therapies (Kievit et al., 2014). Notably, CSCs are difficult to propagate in vitro, which severely restricts the study of CSC biology and the development of therapeutic agents. Emerging evidence indicates that CSCs rely on a niche that controls their differentiation and proliferation, as is the case with normal stem cells (NSCs). Replicating the in vivo CSC microenvironment in vitro using three-dimensional (3D) porous scaffolds can provide means to effectively generate CSCs, thus enabling the discovery of CSC biology. This paper presents our study on a novel alginate-based platform for mimicking the CSC niche to promote CSC proliferation and enrichment. In this study, we used a versatile mouse 4T1 breast cancer model to independently evaluate the matrix parameters of a CSC niche - including the material's mechanical properties, cytokine immobilization, and the composition of the extracellular matrix's (ECM's) molecular impact - on CSC proliferation and enrichment. On this basis, the optimal stiffness and concentration of hyaluronic acid (HA), as well as epidermal growth factor and basic fibroblast growth factor immobilization, were identified to establish the platform for mimicking the 4T1 breast CSCs (4T1 CSCs) niche. The 4T1 CSCs obtained from the platform show increased expression of the genes involved in breast CSC and NSC, as compared to general 2D or 3D culture, and 4T1 CSCs were also demonstrated to have the ability to quickly form a subcutaneous tumor in homologous Balb/c mice in vivo. In addition, the platform can be adjusted according to different parameters for CSC screening. Our results indicate that our platform offers a simple and efficient means to isolate and enrich CSCs in vitro, which can help researchers better understand CSC biology and thus develop more effective therapeutic agents to treat cancer.

STATEMENT OF SIGNIFICANCE

As the primary determinants of the clinical behaviors of human cancers, the discovery of cancer stem cells (CSCs) represents an ideal target for novel anti-cancer therapies. However, CSCs are difficult to propagate in vitro, which severely restricts the study of CSC biology and the development of therapeutic agents. Emerging evidence indicates that CSCs rely on a niche that controls their differentiation and proliferation, as is the case with normal stem cells (NSCs). Replicating the in vivo CSC microenvironment in vitro using three-dimensional (3D) porous scaffolds can provide means to effectively generate CSCs, thus enabling the discovery of CSC biology. In our study, a novel alginate-based platform were developed for mimicking the CSC niche to promote CSC proliferation and enrichment.

Tumor-Initiating Cells: Emerging Biophysical Methods of Isolation

The discovery and subsequent isolation of tumor-initiating cells (TICs), a small population of highly tumorigenic and drug-resistant cancer cells also called cancer stem cells (CSCs), have revolutionized our understanding of cancer. TICs are isolated using various methodologies, including selection of surface marker expression, ALDH activity, suspension culture, and chemotherapy/drug resistance. These methods have several drawbacks, including their variability, lack of robustness and scalability, and low specificity. Alternative methods of purification take advantage of biophysical properties of TICs including their adhesion and stiffness. This review will provide a brief overview of TIC biology as well as review the most important methods of TIC isolation with a focus on biophysical methods of TIC purification.

A double-network poly(Nɛ-acryloyl L-lysine)/hyaluronic acid hydrogel as a mimic of the breast tumor microenvironment

To mimic the structure of breast tumor microenvironment, novel double-network poly(Nɛ-acryloyl L-lysine)/hyaluronic acid (pLysAAm/HA) hydrogels were fabricated by a two-step photo-polymerization process for in vitro three-dimensional (3D) cell culture. The morphology, mechanical properties, swelling and degradation behaviors of pLysAAm/HA hydrogels were investigated. The growth behavior and function of MCF-7 cells cultured on the hydrogels and standard 2D culture plates were compared. The results showed that pLysAAm/HA hydrogels had a highly porous microstructure with a double network and that their mechanical properties, swelling ratio and degradation rate depended on the degree of methacrylation of HA. The results of in vitro studies revealed that the pLysAAm/HA hydrogels could support MCF-7 cell adhesion, promote cell proliferation, and induce the diversification of cell morphologies and overexpression of VEGF, IL-8 and bFGF. The MCF-7 cells cultured on 3D hydrogels showed significantly increased migration and invasion abilities as compared to 2D-cultured cells. Preliminary in vivo results confirmed that the 3D culture of MCF-7 cells resulted in greater tumorigenesis than their 2D culture. These results indicate that the pLysAAm/HA hydrogels can provide a 3D microenvironment for MCF-7 cells that is more representative of the in vivo breast cancer.

STATEMENT OF SIGNIFICANCE

Traditional 2D cell cultures cannot ideally represent their in vivo physiological conditions. In this work, we reported a method for preparing double-network poly(Nɛ-acryloyl L-lysine)/hyaluronic acid hydrogel, and demonstrated its suitability for use in mimicing breast tumor microenvironment. Results showed the prepared hydrogels had controllable mechanical properties, swelling ratio and degradation rate. The MCF-7 cells cultured in hydrogels expressed much higher levels of pro-angiogenic growth factors and displayed significantly enhanced migration and invasion abilities. The tumorigenic capability of MCF-7 cells pre-cultured in 3D hydrogels was enhanced significantly. Therefore, the novel hydrogel may provide a more physiologically relevant 3D in vitro model for breast cancer research. To our knowledge, this is the first report assessing a HA-based double-network hydrogel used as a tumor model.

Modeling tumor microenvironments using custom-designed biomaterial scaffolds

The dominant roles of the tumor microenvironment in regulating tumor formation, progression, and metastasis have driven the application of tissue engineering strategies in cancer biology. Highly dynamic and reciprocal communication of tumor cells with their surroundings suggests that studying cancer in custom-designed biomaterial scaffolds may lead to novel therapeutic targets and therapeutic regimens more reliably than traditional monolayer tissue culture models. As tissue engineering becomes progressively more successful in recapitulating the native tumor environment, critical insights into mechanisms of tumor resistance may be elucidated, to impact clinical practice, drug development, and biological research. We review here the recent developments in the use of custom-designed biomaterial scaffolds for modeling human tumors.

Enrichment of cancer stem cells by cotton fiber

In this study, a new, simple method for selecting and expanding CSCs was developed. In the system, PC12 cells were cultured on a supporting material of cotton fibers treated by NH₃ plasma.

Using carbohydrate-based biomaterials as scaffolds to control human stem cell fate

This review describes the current state and applications of several important and extensively studied natural polysaccharide and glycoprotein scaffolds that can control the stem cell fate.

Modeling the tumor microenvironment using chitosan-alginate scaffolds to control the stem-like state of glioblastoma cells

Better prediction of in vivo drug efficacy using in vitro models should greatly improve in vivo success. Here we utilize 3D highly porous chitosan-alginate complex scaffolds to probe how various components of the glioblastoma microenvironment including extracellular matrix and stromal cells affect tumor cell stem-like state.

Collaboration of 3D context and extracellular matrix in the development of glioma stemness in a 3D model

A hierarchy of cellular stemness exists in certain cancers, and any successful strategy to treat such cancers would have to eliminate the self-renewing tumor-initiating cells at the apex of the hierarchy. The cellular microenvironment, in particular the extracellular matrix (ECM), is believed to have a role in regulating stemness. In this work, U251 glioblastoma cells are cultured on electrospun polystyrene (ESPS) scaffolds coated with an array of 7 laminin isoforms to provide a 3D model for stem cell-related genes and proteins expression studies. We observed collaboration between 3D context and laminins in promoting glioma stemness. Depending on the laminin isoform presented, U251 cells cultured on ESPS scaffolds (3D) exhibited increased expression of stemness markers compared to those cultured on tissue culture polystyrene (2D). Our results indicate the influence of 3D (versus 2D) context on integrin expression, specifically, the upregulation of the laminin-binding integrins alpha 6 and beta 4. By a colony forming assay, we showed enhanced clonogenicity of cells grown on ESPS scaffolds in collaboration with laminins 411, 421, 511 and 521. Evaluation of patient glioma databases demonstrated significant enrichment of integrin and ECM pathway networks in tumors of worse prognosis, consistent with our observations. The present results demonstrate how 3D versus 2D context profoundly affects ECM signaling, leading to stemness.

3D Porous Chitosan-Alginate Scaffolds as an In Vitro Model for Evaluating Nanoparticle-Mediated Tumor Targeting and Gene Delivery to Prostate Cancer

Cationic nanoparticles (NPs) for targeted gene delivery are conventionally evaluated using 2D in vitro cultures. However, this does not translate well to corresponding in vivo studies because of the marked difference in NP behavior in the presence of the tumor microenvironment. In this study, we investigated whether prostate cancer (PCa) cells cultured in three-dimensional (3D) chitosan-alginate (CA) porous scaffolds could model cationic NP-mediated gene targeted delivery to tumors in vitro. We assessed in vitro tumor cell proliferation, formation of tumor spheroids, and expression of marker genes that promote tumor malignancy in CA scaffolds. The efficacy of NP-targeted gene delivery was evaluated in PCa cells in 2D cultures, PCa tumor spheroids grown in CA scaffolds, and PCa tumors in a mouse TRAMP-C2 flank tumor model. PCa cells cultured in CA scaffolds grew into tumor spheroids and displayed characteristics of higher malignancy as compared to those in 2D cultures. Significantly, targeted gene delivery was only observed in cells cultured in CA scaffolds, whereas cells cultured on 2D plates showed no difference in gene delivery between targeted and nontarget control NPs. In vivo NP evaluation confirmed targeted gene delivery, indicating that only CA scaffolds correctly modeled NP-mediated targeted delivery in vivo. These findings suggest that CA scaffolds serve as a better in vitro platform than 2D cultures for evaluation of NP-mediated targeted gene delivery to PCa.