A 3D Biomimetic Model of Tissue Stiffness Interface for Cancer Drug Testing

Extracellular matrix regulation of cell spheroid invasion in a 3D bioprinted solid tumor-on-a-chip

Tumor organoids and tumors-on-chips can be built by placing patient-derived cells within an engineered extracellular matrix (ECM) for personalized medicine. The engineered ECM influences the tumor response, and understanding the ECM-tumor relationship accelerates translating tumors-on-chips into drug discovery and development. In this work, we tuned the physical and structural characteristics of ECM in a 3D bioprinted soft-tissue sarcoma microtissue. We formed cell spheroids at a controlled size and encapsulated them into our gelatin methacryloyl (GelMA)-based bioink to make perfusable hydrogel-based microfluidic chips. We then demonstrated the scalability and customization flexibility of our hydrogel-based chip via engineering tools. A multiscale physical and structural data analysis suggested a relationship between cell invasion response and bioink characteristics. Tumor cell invasive behavior and focal adhesion properties were observed in response to varying polymer network densities of the GelMA-based bioink. Immunostaining assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) helped assess the bioactivity of the microtissue and measure the cell invasion. The RT-qPCR data showed higher expressions of HIF-1α, CD44, and MMP2 genes in a lower polymer density, highlighting the correlation between bioink structural porosity, ECM stiffness, and tumor spheroid response. This work is the first step in modeling STS tumor invasiveness in hydrogel-based microfluidic chips. STATEMENT OF SIGNIFICANCE: We optimized an engineering protocol for making tumor spheroids at a controlled size, embedding spheroids into a gelatin-based matrix, and constructing a perfusable microfluidic device. A higher tumor invasion was observed in a low-stiffness matrix than a high-stiffness matrix. The physical characterizations revealed how the stiffness is controlled by the density of polymer chain networks and porosity. The biological assays revealed how the structural properties of the gelatin matrix and hypoxia in tumor progression impact cell invasion. This work can contribute to personalized medicine by making more effective, tailored cancer models.

Modelling the complex nature of the tumor microenvironment: 3D tumor spheroids as an evolving tool

Cancer remains a serious burden in society and while the pace in the development of novel and more effective therapeutics is increasing, testing platforms that faithfully mimic the tumor microenvironment are lacking. With a clear shift from animal models to more complex in vitro 3D systems, spheroids emerge as strong options in this regard. Years of development have allowed spheroid-based models to better reproduce the biomechanical cues that are observed in the tumor-associated extracellular matrix (ECM) and cellular interactions that occur in both a cell-cell and cell-ECM manner. Here, we summarize some of the key cellular interactions that drive tumor development, progression and invasion, and how successfully are these interactions recapitulated in 3D spheroid models currently in use in the field. We finish by speculating on future advancements in the field and on how these can shape the relevance of spherical 3D models for tumor modelling.

Application of three-dimensional (3D) bioprinting in anti-cancer therapy

Three-dimensional (3D) bioprinting is a novel technology that enables the creation of 3D structures with bioinks, the biomaterials containing living cells. 3D bioprinted structures can mimic human tissue at different levels of complexity from cells to organs. Currently, 3D bioprinting is a promising method in regenerative medicine and tissue engineering applications, as well as in anti-cancer therapy research. Cancer, a type of complex and multifaceted disease, presents significant challenges regarding diagnosis, treatment, and drug development. 3D bioprinted models of cancer have been used to investigate the molecular mechanisms of oncogenesis, the development of cancers, and the responses to treatment. Conventional 2D cancer models have limitations in predicting human clinical outcomes and drug responses, while 3D bioprinting offers an innovative technique for creating 3D tissue structures that closely mimic the natural characteristics of cancers in terms of morphology, composition, structure, and function. By precise manipulation of the spatial arrangement of different cell types, extracellular matrix components, and vascular networks, 3D bioprinting facilitates the development of cancer models that are more accurate and representative, emulating intricate interactions between cancer cells and their surrounding microenvironment. Moreover, the technology of 3D bioprinting enables the creation of personalized cancer models using patient-derived cells and biomarkers, thereby advancing the fields of precision medicine and immunotherapy. The integration of 3D cell models with 3D bioprinting technology holds the potential to revolutionize cancer research, offering extensive flexibility, precision, and adaptability in crafting customized 3D structures with desired attributes and functionalities. In conclusion, 3D bioprinting exhibits significant potential in cancer research, providing opportunities for identifying therapeutic targets, reducing reliance on animal experiments, and potentially lowering the overall cost of cancer treatment. Further investigation and development are necessary to address challenges such as cell viability, printing resolution, material characteristics, and cost-effectiveness. With ongoing progress, 3D bioprinting can significantly impact the field of cancer research and improve patient outcomes.

The response and resistance to drugs in ovarian cancer cell lines in 2D monolayers and 3D spheroids

Ovarian cancer is the most common type of gynecologic cancer. One of the leading causes of high mortality is chemoresistance, developed primarily or during treatment. Different mechanisms of drug resistance appear at the cellular and cancer tissue organization levels. We examined the differences in response to the cytotoxic drugs CIS, MTX, DOX, VIN, PAC, and TOP using 2D (two-dimensional) and 3D (three-dimensional) culture methods. We tested the drug-sensitive ovarian cancer cell line W1 and established resistant cell lines to appropriate cytotoxic drugs. The following qualitative and quantitative methods were used to assess: 1) morphology - inverted microscope and hematoxylin & eosin staining; 2) viability - MTT assay; 3) gene expression - a quantitative polymerase chain reaction; 4) identification of proteins - immunohistochemistry, and immunofluorescence. Our results indicate that the drug-sensitive and drug-resistant cells cultured in 3D conditions exhibit stronger resistance than the cells cultured in 2D conditions. A traditional 2D model shows that drug resistance of cancer cells is caused mainly by changes in the expression of genes encoding ATP-binding cassette transporter proteins, components of the extracellular matrix, "new" established genes related to drug resistance in ovarian cancer cell lines, and universal marker of cancer stem cells. Whereas in a 3D model, the drug resistance in spheroids can be related to other mechanisms such as the structure of the spheroid (dense or loose), the cell type (necrotic, quiescent, proliferating cells), drug concentrations or drug diffusion into the dense cellular/ECM structure.

Biomimetic Human Lung Alveolar Interstitium Chip with Extended Longevity

Determining the mechanistic causes of lung diseases, developing new treatments thereof, and assessing toxicity whether from chemical exposures or engineered nanomaterials would benefit significantly from a preclinical human lung alveolar interstitium model of physiological relevance. The existing preclinical models have limitations because they fail to replicate the key anatomical and physiological characteristics of human alveoli. Thus, a human lung alveolar interstitium chip was developed to imitate key alveolar microenvironmental factors including an electrospun nanofibrous membrane as the analogue of the basement membrane for co-culture of epithelial cells with fibroblasts embedded in 3D collagenous gels, physiologically relevant interstitial matrix stiffness, interstitial fluid flow, and 3D breathing-like mechanical stretch. The biomimetic chip substantially improved the epithelial barrier function compared to transwell models. Moreover, the chip having a gel made of a collagen I-fibrin blend as the interstitial matrix sustained the interstitium integrity and further enhanced the epithelial barrier, resulting in a longevity that extended beyond eight weeks. The assessment of multiwalled carbon nanotube toxicity on the chip was in line with the animal study.

Balance between the cell viability and death in 3D

Cell death is a phenomenon, frequently perceived as an absolute event for cell, tissue and the organ. However, the rising popularity and complexity of such 3D multicellular 'tissue building blocks' as heterocellular spheroids, organoids, and 'assembloids' prompts to revise the definition and quantification of cell viability and death. It raises several questions on the overall viability of all the cells within 3D volume and on choosing the appropriate, continuous, and non-destructive viability assay enabling for a single-cell analysis. In this review, we look at cell viability and cell death modalities with attention to the intrinsic features of such 3D models as spheroids, organoids, and bioprints. Furthermore, we look at emerging and promising methodologies, which can help define and understand the balance between cell viability and death in dynamic and complex 3D environments. We conclude that the recent innovations in biofabrication, biosensor probe development, and fluorescence microscopy can help answer these questions.

Mechanobiology of cancer cell responsiveness to chemotherapy and immunotherapy: Mechanistic insights and biomaterial platforms

Mechanical forces are central to how cancer treatments such as chemotherapeutics and immunotherapies interact with cells and tissues. At the simplest level, electrostatic forces underlie the binding events that are critical to therapeutic function. However, a growing body of literature points to mechanical factors that also affect whether a drug or an immune cell can reach a target, and to interactions between a cell and its environment affecting therapeutic efficacy. These factors affect cell processes ranging from cytoskeletal and extracellular matrix remodeling to transduction of signals by the nucleus to metastasis of cells. This review presents and critiques the state of the art of our understanding of how mechanobiology impacts drug and immunotherapy resistance and responsiveness, and of the in vitro systems that have been of value in the discovery of these effects.

Extracellular matrix stiffness mediates radiosensitivity in a 3D nasopharyngeal carcinoma model

Purpose

Radiotherapy is one of the essential treatment modalities for nasopharyngeal carcinoma (NPC), however, radioresistance still poses challenges. Three-dimensional (3D) tumor culture models mimic the in vivo growth conditions of cells more accurately than 2D models. This study is to compare the tumor biological behaviors of NPC cells in 2D, On-Surface 3D and Embedded 3D systems, and to investigate the correlation between radioresistance and extracellular matrix (ECM) stiffness.

Methods

The morphology and radioresistance of the human NPC cell line CNE-1 were observed in 2D and 3D systems. The CCK-8 assay, wounding healing assays, flow cytometry, soft agar assays, and western blot analysis were used to evaluate differences in biological behaviors such as proliferation, migration, cell cycle distribution, and stem cell activity. Different ECM stiffness systems were established by co-blending collagen and alginate in varying proportions. ECM stiffness was evaluated by compressive elastic moduli measurement and colony formation assay was used to assess radioresistance of NPC cells in systems with different ECM stiffness after irradiation.

Results

Compared to 2D models, the morphology of NPC cells in 3D culture microenvironments has more in common with in vivo tumor cells and 3D cultured NPC cells exhibit stronger radioresistance. Integrin β1 but not the epithelial-to-mesenchymal transition pathway in 3D models boost migration ability. Cell proliferation was enhanced, the proportion of tumor stem cells was increased, and G1/S phase arrest occurred in 3D models. NPC cells cultured in softer ECM systems (with low alginate proportions) exhibit striking resistance to ionizing radiation.

Conclusion

The tumor biological behaviors of NPC cells in 3D groups were obviously different from that of 2D. Radioresistance of NPC cells increased with the stiffness of ECM decreasing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02787-5.

Substrate viscosity impairs temozolomide-mediated inhibition of glioblastoma cells' growth

BACKGROUND

The mechanical state of the extracellular environment of the brain cells considerably affects their phenotype during the development of central nervous system (CNS) pathologies, and when the cells respond to drugs. The reports on the evaluation of the viscoelastic properties of different brain tumors have shown that both tissue stiffness and viscosity can be altered during cancer development. Although a compelling number of reports established the role of substrate stiffness on the proliferation, motility, and drug sensitivity of brain cancer cells, there is a lack of parallel data in terms of alterations in substrate viscosity.

METHODS

Based on viscoelasticity measurements of rat brain samples using strain rheometry, polyacrylamide (PAA) hydrogels mimicking elastic and viscous parameters of the tissues were prepared. Optical microscopy and flow cytometry were employed to assess the differences in glioblastoma cells morphology, proliferation, and cytotoxicity of anticancer drug temozolomide (TZM) due to increased substrate viscosity.

RESULTS

Our results indicate that changes in substrate viscosity affect the proliferation of untreated glioma cells to a lesser extent, but have a significant impact on the apoptosis-associated depolarization of mitochondria and level of DNA fragmentation. This suggests that viscosity sensing and stiffness sensing machinery can activate different signaling pathways in glioma cells.

CONCLUSION

Collected data indicate that viscosity should be considered an important parameter in in vitro polymer-based cell culture systems used for drug screening.

Increased Stiffness Downregulates Focal Adhesion Kinase Expression in Pancreatic Cancer Cells Cultured in 3D Self-Assembling Peptide Scaffolds

The focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that participates in integrin-mediated signal transduction and contributes to different biological processes, such as cell migration, survival, proliferation and angiogenesis. Moreover, FAK can be activated by autophosphorylation at position Y397 and trigger different signaling pathways in response to increased extracellular matrix stiffness. In addition, FAK is overexpressed and/or hyperactivated in many epithelial cancers, and its expression correlates with tumor malignancy and invasion potential. One of the characteristics of solid tumors is an over deposition of ECM components, which generates a stiff microenvironment that promotes, among other features, sustained cell proliferation and survival. Researchers are, therefore, increasingly developing cell culture models to mimic the increased stiffness associated with these kinds of tumors. In the present work, we have developed a new 3D in vitro model to study the effect of matrix stiffness in pancreatic ductal adenocarcinoma (PDAC) cells as this kind of tumor is characterized by a desmoplastic stroma and an increased stiffness compared to its normal counterpart. For that, we have used a synthetic self-assembling peptide nanofiber matrix, RAD16-I, which does not suffer a significant degradation in vitro, thus allowing to maintain the same local stiffness along culture time. We show that increased matrix stiffness in synthetic 3D RAD16-I gels, but not in collagen type I scaffolds, promotes FAK downregulation at a protein level in all the cell lines analyzed. Moreover, even though it has classically been described that stiff 3D matrices promote an increase in pFAK^Y397/FAK proteins, we found that this ratio in soft and stiff RAD16-I gels is cell-type-dependent. This study highlights how cell response to increased matrix stiffness greatly depends on the nature of the matrix used for 3D culture.

Tunable three-dimensional engineered prostate cancer tissues for in vitro recapitulation of heterogeneous in vivo prostate tumor stiffness

In this manuscript we report the establishment and characterization of a three-dimensional in vitro, coculture engineered prostate cancer tissue (EPCaT) disease model based upon and informed by our characterization of in vivo prostate cancer (PCa) xenograft tumor stiffness. In prostate cancer, tissue stiffness is known to impact changes in gene and protein expression, alter therapeutic response, and be positively correlated with an aggressive clinical presentation. To inform an appropriate stiffness range for our in vitro model, PC-3 prostate tumor xenografts were established. Tissue stiffness ranged from 95 to 6,750 Pa. Notably, xenograft cell seeding density significantly impacted tumor stiffness; a two-fold increase in the number of seeded cells not only widened the tissue stiffness range throughout the tumor but also resulted in significant spatial heterogeneity. To fabricate our in vitro EPCaT model, PC-3 castration-resistant prostate cancer cells were co-encapsulated with BJ-5ta fibroblasts within a poly(ethylene glycol)-fibrinogen matrix augmented with excess poly(ethylene glycol)-diacrylate to modulate the matrix mechanical properties. Encapsulated cells temporally remodeled their in vitro microenvironment and enrichment of gene sets associated with tumorigenic progression was observed in response to increased matrix stiffness. Through variation of matrix composition and culture duration, EPCaTs were tuned to mimic the wide range of biomechanical cues provided to PCa cells in vivo; collectively, a range of 50 to 10,000 Pa was achievable. Markedly, this also encompasses published clinical PCa stiffness data. Overall, this study serves to introduce our bioinspired, tunable EPCaT model and provide the foundation for future PCa progression and drug development studies. STATEMENT OF SIGNIFICANCE: The development of cancer models that mimic the native tumor microenvironment (TME) complexities is critical to not only develop effective drugs but also enhance our understanding of disease progression. Here we establish and characterize our 3D in vitro engineered prostate cancer tissue model with tunable matrix stiffness, that is inspired by this study's spatial characterization of in vivo prostate tumor xenograft stiffness. Notably, our model's mimicry of the TME is further augmented by the inclusion of matrix remodeling fibroblasts to introduce cancer-stromal cell-cell interactions. This study addresses a critical unmet need in the field by elucidating the prostate tumor xenograft stiffness range and establishing a foundation for recapitulating the biomechanics of site-of-origin and soft tissue metastatic prostate tumors in vitro.

Glioblastoma spheroid growth and chemotherapeutic responses in single and dual-stiffness hydrogels

Glioblastoma (GBM) is the deadliest brain tumor for which there is no cure. Bioengineered GBM models, such as hydrogel-encapsulated spheroids, that capture both cell-cell and cell-matrix interactions could facilitate testing of much needed therapies. Elucidation of specific microenvironment properties on spheroid responsiveness to therapeutics would enhance the usefulness of GBM models as predictive drug screening platforms. Here, GBM spheroids consisting of U87 or patient-derived GBM cells were encapsulated in soft (∼1 kPa), stiff (∼7 kPa), and dual-stiffness polyethylene glycol-based hydrogels, with GBM spheroids seeded at the stiffness interface. Spheroids were cultured for 7 days and examined for viability, size, invasion, laminin expression, hypoxia, proliferation, and response to the chemotherapeutic temozolomide (TMZ). We noted excellent cell viability in all hydrogels, and higher infiltration in soft compared to stiff hydrogels for U87 spheroids. In dual gels spheroids mostly infiltrated away from the stiffness interface with minimal crossing over it and some individual cell migration along the interface. U87 spheroids were equally responsive to TMZ in the soft and stiff hydrogels, but cell viability in the spheroid periphery was higher than the core for stiff hydrogels whereas the opposite was true for soft hydrogels. HIF1A expression was higher in the core of spheroids in the stiff hydrogels, while there was no difference in cell proliferation between spheroids in the stiff vs soft hydrogels. Patient-derived GBM spheroids did not show stiffness-dependent drug responses. U87 cells showed similar laminin expression in soft and stiff hydrogels with higher expression in the spheroid periphery compared to the core. Our results indicate that microenvironment stiffness needs to be considered in bioengineered GBM models including those designed for use in drug screening applications. STATEMENT OF SIGNIFICANCE: Recent work on tumor models engineered for use in drug screening has highlighted the potential of hydrogel-encapsulated spheroids as a simple, yet effective platform that show drug responses similar to native tumors. It has also been shown that substrate stiffness, in vivo and in vitro, affects cancer cell responses to drugs. This is particularly important for glioblastoma (GBM), the deadliest brain cancer, as GBM cells invade by following the stiffer brain structures such as white matter tracks and the perivascular niche. Invading cells have also been associated with higher resistance to chemotherapy. Here we developed GBM spheroid models using soft, stiff and dual-stiffness hydrogels to explore the connection between substrate stiffness, spheroid invasion and drug responsiveness in a controlled environment.

Materials-driven approaches to understand extrinsic drug resistance in cancer

Metastatic cancer has a poor prognosis, because it is broadly disseminated and associated with both intrinsic and acquired drug resistance. Critical unmet needs in effectively killing drug resistant cancer cells include overcoming the drug desensitization characteristics of some metastatic cancers/lesions, and tailoring therapeutic regimens to both the tumor microenvironment and the genetic profiles of the resident cancer cells. Bioengineers and materials scientists are developing technologies to determine how metastatic sites exclude therapies, and how extracellular factors (including cells, proteins, metabolites, extracellular matrix, and abiotic factors) at metastatic sites significantly affect drug pharmacodynamics. Two looming challenges are determining which feature, or combination of features, from the tumor microenvironment drive drug resistance, and what the relative impact is of extracellular signals vs. intrinsic cell genetics in determining drug response. Sophisticated systems biology tools that can de-convolve a crowded network of signals and responses, as well as controllable microenvironments capable of providing discrete and tunable extracellular cues can help us begin to interrogate the high dimensional interactions governing drug resistance in patients.

3D modeling in cancer studies

The tumor microenvironment contributes significantly to tumor initiation, progression, and resistance to chemotherapy. Much of our understanding of the tumor and its microenvironment is developed using various methods of cell culture. Throughout the last two decades, research has increasingly shown that 3D cell culture systems can remarkably recapitulate the complexity of tumor architecture and physiology compared to traditional 2D models. Unlike the flat culture system, these novel models enabled more cell-cell and cell-extracellular matrix interactions. By mimicking in vivo microenvironment, 3D culture systems promise to become accurate tools ready to be used in diagnosis, drug screening, and personalized medicine. In this review, we discussed the importance of 3D culture in simulating the tumor microenvironment and focused on the effects of cancer cell-microenvironment interactions on cancer behavior, resistance, proliferation, and metastasis. Finally, we assessed the role of 3D cell culture systems in the contexts of drug screening. 2D culture system is used to study cancer cell growth, progression, behavior, and drug response. It provides contact between cells and supports paracrine crosstalk between host cells and cancer cells. However, this system fails to simulate the architecture and the physiological aspects of in vivo tumor microenvironment due to the absence of cell-cell/ cell-ECM interactions as well as unlimited access to O₂ and nutrients, and the absence of tumor heterogeneity. Recently advanced research has led researchers to generate 3D culture system that can better recapitulate the in vivo environment by providing hypoxic medium, facilitating cell-cell and cell-ECM, interactions, and recapitulating heterogeneity of the tumor. Several approaches are used to maintain and expand cancer cells in 3D culture systems such as tumor spheroids (cell aggregate that mimics the in vivo growth of tumor cells), scaffold-based approaches, bioreactors, microfluidic derives, and organoids. 3D systems are currently used for disease modeling and pre-clinical drug testing.

Engineering hydrogels for personalized disease modeling and regenerative medicine

Technological innovations and advances in scientific understanding have created an environment where data can be collected, analyzed, and interpreted at scale, ushering in the era of personalized medicine. The ability to isolate cells from individual patients offers tremendous promise if those cells can be used to generate functional tissue replacements or used in disease modeling to determine optimal treatment strategies. Here, we review recent progress in the use of hydrogels to create artificial cellular microenvironments for personalized tissue engineering and regenerative medicine applications, as well as to develop personalized disease models. We highlight engineering strategies to control stem cell fate through hydrogel design, and the use of hydrogels in combination with organoids, advanced imaging methods, and novel bioprinting techniques to generate functional tissues. We also discuss the use of hydrogels to study molecular mechanisms underlying diseases and to create personalized in vitro disease models to complement existing pre-clinical models. Continued progress in the development of engineered hydrogels, in combination with other emerging technologies, will be essential to realize the immense potential of personalized medicine. STATEMENT OF SIGNIFICANCE: In this review, we cover recent advances in hydrogel engineering strategies with applications in personalized medicine. Specifically, we focus on material systems to expand or control differentiation of patient-derived stem cells, and hydrogels to reprogram somatic cells to pluripotent states. We then review applications of hydrogels in developing personalized engineered tissues. We also highlight the use of hydrogel systems as personalized disease models, focusing on specific examples in fibrosis and cancer, and more broadly on drug screening strategies using patient-derived cells and hydrogels. We believe this review will be a valuable contribution to the Special Issue and the readership of Acta Biomaterialia will appreciate the comprehensive overview of the utility of hydrogels in the developing field of personalized medicine.

The Extracellular Matrix in Pancreatic Cancer: Description of a Complex Network and Promising Therapeutic Options

The stroma is a relevant player in driving and supporting the progression of pancreatic ductal adenocarcinoma (PDAC), and a large body of evidence highlights its role in hindering the efficacy of current therapies. In fact, the dense extracellular matrix (ECM) characterizing this tumor acts as a natural physical barrier, impairing drug penetration. Consequently, all of the approaches combining stroma-targeting and anticancer therapy constitute an appealing option for improving drug penetration. Several strategies have been adopted in order to target the PDAC stroma, such as the depletion of ECM components and the targeting of cancer-associated fibroblasts (CAFs), which are responsible for the increased matrix deposition in cancer. Additionally, the leaky and collapsing blood vessels characterizing the tumor might be normalized, thus restoring blood perfusion and allowing drug penetration. Even though many stroma-targeting strategies have reported disappointing results in clinical trials, the ECM offers a wide range of potential therapeutic targets that are now being investigated. The dense ECM might be bypassed by implementing nanoparticle-based systems or by using mesenchymal stem cells as drug carriers. The present review aims to provide an overview of the principal mechanisms involved in the ECM remodeling and of new promising therapeutic strategies for PDAC.

Hydroxyethyl chitosan hydrogels for enhancing breast cancer cell tumorigenesis

Polysaccharide hydrogels are promising candidate matrices for recapitulating the characteristics of extracellular matrix (ECM) in breast tumors in terms of their structure and composition. Herein, to obtain an ECM-mimetic matrix, hydroxyethyl chitosan (HECS) hydrogels were prepared through Schiff-base crosslinking reaction using dialdehyde hyaluronic acid as crosslinker. The obtained HECS hydrogels displayed a highly porous structure, a stiffness comparable to that of breast tissue, and a fast water-absorption speed. The amount of crosslinker had great effects on the swelling and rheological behaviors of the HECS hydrogels. Preliminary results from in vitro biological assessments confirmed that MCF-7 cells incubated within HECS hydrogels preferred to grow into three-dimensional spheroids. Importantly, the cells displayed enhanced migrative capability and upregulated expression levels of MMP-2, TGF-β and VEGF in comparison to two-dimension cultured cells. Hence, the HECS hydrogels show great promise as a biomimetic ECM in constructing breast tumor models.

In-vitro tumor microenvironment models containing physical and biological barriers for modelling multidrug resistance mechanisms and multidrug delivery strategies

The complexity and heterogeneity of the three-dimensional (3D) tumor microenvironment have brought challenges to tumor studies and cancer treatment. The complex functions and interactions of cells involved in tumor microenvironment have led to various multidrug resistance (MDR) and raised challenges for cancer treatment. Traditional tumor models are limited in their ability to simulate the resistance mechanisms and not conducive to the discovery of multidrug resistance and delivery processes. New technologies for making 3D tissue models have shown the potential to simulate the 3D tumor microenvironment and identify mechanisms underlying the MDR. This review overviews the main barriers against multidrug delivery in the tumor microenvironment and highlights the advances in microfluidic-based tumor models with the success in simulating several drug delivery barriers. It also presents the progress in modeling various genetic and epigenetic factors involved in regulating the tumor microenvironment as a noticeable insight in 3D microfluidic tumor models for recognizing multidrug resistance and delivery mechanisms. Further correlation between the results obtained from microfluidic drug resistance tumor models and the clinical MDR data would open up avenues to gain insight into the performance of different multidrug delivery treatment strategies.

3D Cancer Models: The Need for a Complex Stroma, Compartmentalization and Stiffness

The use of tissue-engineered 3D models of cancer has grown in popularity with recent advances in the field of cancer research. 3D models are inherently more biomimetic compared to 2D cell monolayers cultured on tissue-culture plastic. Nevertheless 3D models still lack the cellular and matrix complexity of native tissues. This review explores different 3D models currently used, outlining their benefits and limitations. Specifically, this review focuses on stiffness and collagen density, compartmentalization, tumor-stroma cell population and extracellular matrix composition. Furthermore, this review explores the methods utilized in different models to directly measure cancer invasion and growth. Of the models evaluated, with PDX and in vivo as a relative "gold standard", tumoroids were deemed as comparable 3D cancer models with a high degree of biomimicry, in terms of stiffness, collagen density and the ability to compartmentalize the tumor and stroma. Future 3D models for different cancer types are proposed in order to improve the biomimicry of cancer models used for studying disease progression.

3D Cell Culture: Recent Development in Materials with Tunable Stiffness

It is widely accepted that three-dimensional cell culture systems simulate physiological conditions better than traditional 2D systems. Although extracellular matrix components strongly modulate cell behavior, several studies underlined the importance of mechanosensing in the control of different cell functions such as growth, proliferation, differentiation, and migration. Human tissues are characterized by different degrees of stiffness, and various pathologies (e.g., tumor or fibrosis) cause changes in the mechanical properties through the alteration of the extracellular matrix structure. Additionally, these modifications have an impact on disease progression and on therapy response. Hence, the development of platforms whose stiffness could be modulated may improve our knowledge of cell behavior under different mechanical stress stimuli. In this review, we have analyzed the mechanical diversity of healthy and diseased tissues, and we have summarized recently developed materials with a wide range of stiffness.

Advanced Multi-Dimensional Cellular Models as Emerging Reality to Reproduce In Vitro the Human Body Complexity

A hot topic in biomedical science is the implementation of more predictive in vitro models of human tissues to significantly improve the knowledge of physiological or pathological process, drugs discovery and screening. Bidimensional (2D) culture systems still represent good high-throughput options for basic research. Unfortunately, these systems are not able to recapitulate the in vivo three-dimensional (3D) environment of native tissues, resulting in a poor in vitro–in vivo translation. In addition, intra-species differences limited the use of animal data for predicting human responses, increasing in vivo preclinical failures and ethical concerns. Dealing with these challenges, in vitro 3D technological approaches were recently bioengineered as promising platforms able to closely capture the complexity of in vivo normal/pathological tissues. Potentially, such systems could resemble tissue-specific extracellular matrix (ECM), cell–cell and cell–ECM interactions and specific cell biological responses to mechanical and physical/chemical properties of the matrix. In this context, this review presents the state of the art of the most advanced progresses of the last years. A special attention to the emerging technologies for the development of human 3D disease-relevant and physiological models, varying from cell self-assembly (i.e., multicellular spheroids and organoids) to the use of biomaterials and microfluidic devices has been given.

Tissue engineered platforms for studying primary and metastatic neoplasm behavior in bone

Cancer is the second leading cause of death in the United States, claiming more than 560,000 lives each year. Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and young adults, while bone is a common site of metastasis for tumors initiating from other tissues. The heterogeneity, continual evolution, and complexity of this disease at different stages of tumor progression drives a critical need for physiologically relevant models that capture the dynamic cancer microenvironment and advance chemotherapy techniques. Monolayer cultures have been favored for cell-based research for decades due to their simplicity and scalability. However, the nature of these models makes it impossible to fully describe the biomechanical and biochemical cues present in 3-dimensional (3D) microenvironments, such as ECM stiffness, degradability, surface topography, and adhesivity. Biomaterials have emerged as valuable tools to model the behavior of various cancers by creating highly tunable 3D systems for studying neoplasm behavior, screening chemotherapeutic drugs, and developing novel treatment delivery techniques. This review highlights the recent application of biomaterials toward the development of tumor models, details methods for their tunability, and discusses the clinical and therapeutic applications of these systems.

Microfluidics and organ-on-a-chip technologies: A systematic review of the methods used to mimic bone marrow

Bone marrow (BM) is an organ responsible for crucial processes in living organs, e. g., hematopoiesis. In recent years, Organ-on-a-Chip (OoC) devices have been used to satisfy the need for in vitro systems that better mimic the phenomena occurring in the BM microenvironment. Given the growing interest in these systems and the diversity of developed devices, an integrative systematic literature review is required. We have performed this review, following the PRISMA method aiming to identify the main characteristics and assess the effectiveness of the devices that were developed to represent the BM. A search was performed in the Scopus, PubMed, Web of Science and Science Direct databases using the keywords (("bone marrow" OR "hematopoietic stem cells" OR "haematopoietic stem cells") AND ("organ in a" OR "lab on a chip" OR "microfluidic" OR "microfluidic*" OR ("bioreactor" AND "microfluidic*"))). Original research articles published between 2009 and 2020 were included in the review, giving a total of 21 papers. The analysis of these papers showed that their main purpose was to study BM cells biology, mimic BM niches, model pathological BM, and run drug assays. Regarding the fabrication protocols, we have observed that polydimethylsiloxane (PDMS) material and soft lithography method were the most commonly used. To reproduce the microenvironment of BM, most devices used the type I collagen and alginate. Peristaltic and syringe pumps were mostly used for device perfusion. Regarding the advantages compared to conventional methods, there were identified three groups of OoC devices: perfused 3D BM; co-cultured 3D BM; and perfused co-cultured 3D BM. Cellular behavior and mimicking their processes and responses were the mostly commonly studied parameters. The results have demonstrated the effectiveness of OoC devices for research purposes compared to conventional cell cultures. Furthermore, the devices have a wide range of applicability and the potential to be explored.

Matrix Stiffness-Regulated Growth of Breast Tumor Spheroids and Their Response to Chemotherapy

Interactions between tumor cells and the extracellular matrix (ECM) are an important factor contributing to therapy failure in cancer patients. Current in vitro breast cancer spheroid models examining the role of mechanical properties on spheroid response to chemotherapy are limited by the use of two-dimensional cell culture, as well as simultaneous variation in hydrogel matrix stiffness and other properties, e.g., hydrogel composition, pore size, and cell adhesion ligand density. In addition, currently used hydrogel matrices do not replicate the filamentous ECM architecture in a breast tumor microenvironment. Here, we report a collagen-alginate hydrogel with a filamentous architecture and a 20-fold variation in stiffness, achieved independently of other properties, used for the evaluation of estrogen receptor-positive breast cancer spheroid response to doxorubicin. The variation in hydrogel mechanical properties was achieved by altering the degree of cross-linking of alginate molecules. We show that soft hydrogels promote the growth of larger MCF-7 tumor spheroids with a lower fraction of proliferating cells and enhance spheroid resistance to doxorubicin. Notably, the stiffness-dependent chemotherapeutic response of the spheroids was temporally mediated: it became apparent at sufficiently long cell culture times, when the matrix stiffness has influenced the spheroid growth. These findings highlight the significance of decoupling matrix stiffness from other characteristics in studies of chemotherapeutic resistance of tumor spheroids and in development of drug screening platforms.

A 3D Bioprinter Specifically Designed for the High-Throughput Production of Matrix-Embedded Multicellular Spheroids

3D in vitro cancer models are important therapeutic and biological discovery tools, yet formation of matrix-embedded multicellular spheroids prepared in high-throughput (HTP), and in a highly controlled manner, remains challenging. This is important to achieve robust and statistically relevant data. Here, we developed an enabling technology consisting of a bespoke drop-on-demand 3D bioprinter capable of HTP printing of 96-well plates of spheroids. 3D multicellular spheroids are embedded inside a hydrogel matrix with precise control over size and cell number, with the intra-experiment variability of embedded spheroid diameter coefficient of variation being between 4.2% and 8.7%. Application of 3D bioprinting HTP drug screening was demonstrated with doxorubicin. Measurements of IC₅₀ values showed sensitivity to spheroid size, embedding, and how spheroids conform to the embedding, revealing parameters shaping biological responses in these models. Our study demonstrates the potential of 3D bioprinting as a robust HTP platform to screen biological and therapeutic parameters.

High-matrix-stiffness induces promotion of hepatocellular carcinoma proliferation and suppression of apoptosis via miR-3682-3p-PHLDA1-FAS pathway

Hepatocellular carcinoma (HCC) with malignant behaviors related to death causes distant metastasis and is the fourth primary cancer in the whole world, which has taken millions lives in Asian countries such as China. The novel miR-3682-3p involving high-expression-related poor prognosis in HCC tissues and cell lines indicate oncogenesis functions in vitro and in vivo. According to TCGA database, our group find several none-coding RNAs showing abnormal expression including miR-3682-3p, thus we originally confirmed the inhibition of proliferation and acceleration of apoptosis are enhanced in miR-3682-3p knock-down cell lines. Then, in nude mice transplantation assays, we found the suppressor behaviors, smaller nodules and lower speed of tumor expansion in model of injection of cell cultured and transfected shRNA-miR-3682-3p. A combination of databases (Starbase, Targetscan and MiRgator) illustrates miR-3682-3p targets PHLDA1, which shows negative correlation demonstrated by dual-luciferase reporter system. To make functional verification of PHLDA1, we upregulate the gene and rescue tests are established to confirm that miR-3682-3p suppresses PHLDA1 to promotion of cell growth. Rescue experiments finish making confirmation of relation of miR-3682-3p and PHLDA1 subsequently. Cirrhotic tissues illustrate strong correlation to higher miR-3682-3p and clinical features make the hint that high-extracellular-matrix-stiffness environment promotes such miRNA. Functional tests on different stiffness provide the proof of underlying mechanism. In conclusion, the overexpression of miR-3682-3p mediates PHLDA1 inhibition could impede apoptosis and elevate proliferation of HCC through high-extracellular-matrix-stiffness environment potentially.

Breast cancer models: Engineering the tumor microenvironment

The mechanisms behind cancer initiation and progression are not clear. Therefore, development of clinically relevant models to study cancer biology and drug response in tumors is essential. In vivo models are very valuable tools for studying cancer biology and for testing drugs; however, they often suffer from not accurately representing the clinical scenario because they lack either human cells or a functional immune system. On the other hand, two-dimensional (2D) in vitro models lack the three-dimensional (3D) network of cells and extracellular matrix (ECM) and thus do not represent the tumor microenvironment (TME). As an alternative approach, 3D models have started to gain more attention, as such models offer a platform with the ability to study cell-cell and cell-material interactions parametrically, and possibly include all the components present in the TME. Here, we first give an overview of the breast cancer TME, and then discuss the current state of the pre-clinical breast cancer models, with a focus on the engineered 3D tissue models. We also highlight two engineering approaches that we think are promising in constructing models representative of human tumors: 3D printing and microfluidics. In addition to giving basic information about the TME in the breast tissue, this review article presents the state-of-the-art tissue engineered breast cancer models. STATEMENT OF SIGNIFICANCE: Involvement of biomaterials and tissue engineering fields in cancer research enables realistic mimicry of the cell-cell and cell-extracellular matrix (ECM) interactions in the tumor microenvironment (TME), and thus creation of better models that reflect the tumor response against drugs. Engineering the 3D in vitro models also requires a good understanding of the TME. Here, an overview of the breast cancer TME is given, and the current state of the pre-clinical breast cancer models, with a focus on the engineered 3D tissue models is discussed. This review article is useful not only for biomaterials scientists aiming to engineer 3D in vitro TME models, but also for cancer researchers willing to use these models for studying cancer biology and drug testing.

Bioengineered scaffolds for 3D culture demonstrate extracellular matrix-mediated mechanisms of chemotherapy resistance in glioblastoma

Originating in the brain, glioblastoma (GBM) is a highly lethal and virtually incurable cancer, in large part because it readily develops resistance to treatments. While numerous studies have investigated mechanisms enabling GBM cells to evade chemotherapy-induced apoptosis, few have addressed how their surrounding extracellular matrix (ECM) acts to promote their survival. Here, we employed a biomaterial-based, 3D culture platform to investigate systematically how interactions between patient-derived GBM cells and the brain ECM promote resistance to alkylating chemotherapies - including temozolomide, which is used routinely in clinical practice. Scaffolds for 3D culture were fabricated from hyaluronic acid (HA) - a major structural and bioactive component of the brain ECM - and functionalized with the RGD (arginine-glycine-aspartic acid) tripeptide to provide sites for integrin engagement. Data demonstrate that cooperative engagement of CD44, through HA, and integrin αV, through RGD, facilitates resistance to alkylating chemotherapies through co-activation of Src, which inhibited downstream expression of BCL-2 family pro-apoptotic factors. In sum, a bioengineered, 3D culture platform was used to gain new mechanistic insights into how ECM in the brain tumor microenvironment promotes resistance to chemotherapy and suggests potential avenues for the development of novel, matrix-targeted combination therapies designed to suppress chemotherapy resistance in GBM.

Hydrogel 3D in vitro tumor models for screening cell aggregation mediated drug response

Hydrogel-based 3D in vitro models comprising tumor ECM-mimetic biomaterials exhibit differential responses to therapeutics according to cancer cells cellular aggregation state.

Epithelial-mesenchymal transition of cancer cells using bioengineered hybrid scaffold composed of hydrogel/3D-fibrous framework

Cancer cells undergoing epithelial-mesenchymal transition (EMT) acquire stem cell-like phenotype associated with malignant behaviour, chemoresistance, and relapse. Current two-dimensional (2D) in-vitro culture models of tumorigenesis are inadequate to replicate the complexity of in-vivo microenvironment. Therefore, the generation of functional three-dimensional (3D) constructs is a fundamental prerequisite to form multi-cellular tumour spheroids for studying basic pathological mechanisms. In this study, we focused on two major points (i) designing and fabrication of 3D hybrid scaffolds comprising electrospun fibers with cancer cells embedded within hydrogels, and (ii) determining the potential roles of 3D hybrid scaffolds associated with EMT in cancer progression and metastasis. Our findings revealed that 3D hybrid scaffold enhances cell proliferation and induces cancer cells to undergo EMT, as demonstrated by significant up-regulation of EMT associated transcriptional factors including Snail1, Zeb1, and Twist2; and mesenchymal markers whereas epithelial marker, E-Cadherin was downregulated. Remarkably, this induction is independent of cancer cell-type as similar results were obtained for breast cancer cells, MDA-MB-231 and gastric cancer cells, MKN74. Moreover, the hybrid scaffolds enrich aggressive cancer cells with stem cell properties. We showed that our 3D scaffolds could trigger EMT of cancer cells which could provide a useful model for studying anticancer therapeutics against metastasis.

A Novel 3D in Vitro Tumor Model Based on Silk Fibroin/Chitosan Scaffolds To Mimic the Tumor Microenvironment

Drug development involves various evaluation processes to ascertain drug effects and rigorous analysis of biological indicators during in vitro preclinical studies. Two-dimensional (2D) cell cultures are commonly used in numerous in vitro studies, which are poor facsimiles of the in vivo conditions. Recently, three-dimensional (3D) tumor models mimicking the tumor microenvironment and reducing the use of experimental animals have been developed generating great interest to appraise tumor response to treatment strategies in cancer therapy. In this study, silk fibroin (SF) protein and chitosan (CS), two natural biomaterials, were chosen to construct the scaffolds of 3D cell models. Human non-small cell lung cancer A549 cells in the SF/CS scaffolds were found to have a great tendency to gather and form tumor spheres. A549 cell spheres in the 3D scaffolds showed biological and morphological characteristics much closer to the in vivo tumors. Besides, the cells in 3D models displayed better invasion ability and drug resistance than 2D models. Additionally, differences in drug-resistant and immune-related protein levels were found, which indicated that 3D models might resemble the real-life situation. These findings suggested that these 3D tumor models composed of SF/CS are promising to provide a valuable biomaterial platform in the evaluation of anticancer drugs.

Integration of hyper-compliant microparticles into a 3D melanoma tumor model

Multicellular spheroids provide a physiologically relevant platform to study the microenvironment of tumors and therapeutic applications, such as microparticle-based drug delivery. The goal of this study was to investigate the incorporation/penetration of compliant polyacrylamide microparticles (MPs), into either cancer or normal human cell spheroids. Incorporation of collagen-1-coated MPs (stiffness: 0.1 and 9 kPa; diameter: 15-30 µm) into spheroids (diameter ∼100 µm) was tracked for up to 22 h. Results indicated that cells within melanoma spheroids were more influenced by MP mechanical properties than cells within normal cell spheroids. Melanoma spheroids had a greater propensity to incorporate and displace the more compliant MPs over time. Mature spheroids composed of either cell type were able to recognize and integrate MPs. While many tumor models exist to study drug delivery and efficacy, the study of uptake and incorporation of cell-sized MPs into established spheroids/tissues or tumors has been limited. The ability of hyper-compliant MPs to successfully penetrate 3D tumor models with natural extracellular matrix deposition provides a novel platform for potential delivery of drugs and other therapeutics into the core of tumors and micrometastases.

Hydrogel microenvironments for cancer spheroid growth and drug screening

Multicellular cancer spheroids (MCSs) have emerged as a promising in vitro model that replicates many features of solid tumors in vivo. Biomimetic hydrogel scaffolds for MCS growth offer a broad spectrum of biophysical and biochemical cues that help to recapitulate the behavior of natural extracellular matrix, essential for regulating cancer cell behavior. This perspective highlights recent advances in the development of hydrogel environments for MCS growth, release, and drug screening. We review the use of different types of hydrogels for MCS growth, the effect of biophysical and biochemical cues on MCS fate, the isolation of MCSs from hydrogel scaffolds, the utilization of microtechnologies, and the applications of MCSs grown in hydrogels. We conclude with the discussion of new research directions in the development of hydrogels for MCS growth.

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.

Biomimetic tumor microenvironments based on collagen matrices

This review provides an overview of the current approaches to engineer defined 3D matrices for the investigation of tumor cell behaviorin vitro, with a focus on collagen-based fibrillar systems.

A biomaterial screening approach reveals microenvironmental mechanisms of drug resistance

Traditional drug screening methods lack features of the tumor microenvironment that contribute to resistance. Most studies examine cell response in a single biomaterial platform in depth, leaving a gap in understanding how extracellular signals such as stiffness, dimensionality, and cell-cell contacts act independently or are integrated within a cell to affect either drug sensitivity or resistance. This is critically important, as adaptive resistance is mediated, at least in part, by the extracellular matrix (ECM) of the tumor microenvironment. We developed an approach to screen drug responses in cells cultured on 2D and in 3D biomaterial environments to explore how key features of ECM mediate drug response. This approach uncovered that cells on 2D hydrogels and spheroids encapsulated in 3D hydrogels were less responsive to receptor tyrosine kinase (RTK)-targeting drugs sorafenib and lapatinib, but not cytotoxic drugs, compared to single cells in hydrogels and cells on plastic. We found that transcriptomic differences between these in vitro models and tumor xenografts did not reveal mechanisms of ECM-mediated resistance to sorafenib. However, a systems biology analysis of phospho-kinome data uncovered that variation in MEK phosphorylation was associated with RTK-targeted drug resistance. Using sorafenib as a model drug, we found that co-administration with a MEK inhibitor decreased ECM-mediated resistance in vitro and reduced in vivo tumor burden compared to sorafenib alone. In sum, we provide a novel strategy for identifying and overcoming ECM-mediated resistance mechanisms by performing drug screening, phospho-kinome analysis, and systems biology across multiple biomaterial environments.

3D collagen fibrillar microstructure guides pancreatic cancer cell phenotype and serves as a critical design parameter for phenotypic models of EMT

Pancreatic cancer, one of the deadliest cancers, is characterized by high rates of metastasis and intense desmoplasia, both of which are associated with changes in fibrillar type I collagen composition and microstructure. Epithelial to mesenchymal transition (EMT), a critical step of metastasis, also involves a change in extracellular matrix (ECM) context as cells detach from basement membrane (BM) and engage interstitial matrix (IM). The objective of this work was to develop and apply an in-vitro three-dimensional (3D) tumor-ECM model to define how ECM composition and biophysical properties modulate pancreatic cancer EMT. Three established pancreatic ductal adenocarcinoma (PDAC) lines were embedded within 3D matrices prepared with type I collagen Oligomer (IM) at various fibril densities to control matrix stiffness or Oligomer and Matrigel combined at various ratios while maintaining constant matrix stiffness. Evaluation of cell morphology and protein expression at both the cellular- and population-levels revealed a spectrum of matrix-driven EMT phenotypes that were dependent on ECM composition and architecture as well as initial PDAC phenotype. In general, exposure to fibrillar IM was sufficient to drive EMT, with cells displaying spindle-shaped morphology and mesenchymal markers, and non-fibrillar BM promoted more epithelial behavior. When cultured within low density Oligomer, only a subpopulation of epithelial BxPC-3 cells displayed EMT while mesenchymal MiaPaCa-2 cells displayed more uniform spindle-shaped morphologies and mesenchymal marker expression. Interestingly, as IM fibril density increased, associated changes in spatial constraints and matrix stiffness resulted in all PDAC lines growing as tight clusters; however mesenchymal marker expression was maintained. Collectively, the comparison of these results to other in-vitro tumor models highlights the role of IM fibril microstructure in guiding EMT heterogeneity and showcases the potential of standardized 3D matrices such as Oligomer to serve as robust platforms for mechanistic study of metastasis and creation of predictive drug screening models.

3D bioprinting for drug discovery and development in pharmaceutics

Successful launch of a commercial drug requires significant investment of time and financial resources wherein late-stage failures become a reason for catastrophic failures in drug discovery. This calls for infusing constant innovations in technologies, which can give reliable prediction of efficacy, and more importantly, toxicology of the compound early in the drug discovery process before clinical trials. Though computational advances have resulted in more rationale in silico designing, in vitro experimental studies still require gaining industry confidence and improving in vitro-in vivo correlations. In this quest, due to their ability to mimic the spatial and chemical attributes of native tissues, three-dimensional (3D) tissue models have now proven to provide better results for drug screening compared to traditional two-dimensional (2D) models. However, in vitro fabrication of living tissues has remained a bottleneck in realizing the full potential of 3D models. Recent advances in bioprinting provide a valuable tool to fabricate biomimetic constructs, which can be applied in different stages of drug discovery research. This paper presents the first comprehensive review of bioprinting techniques applied for fabrication of 3D tissue models for pharmaceutical studies. A comparative evaluation of different bioprinting modalities is performed to assess the performance and ability of fabricating 3D tissue models for pharmaceutical use as the critical selection of bioprinting modalities indeed plays a crucial role in efficacy and toxicology testing of drugs and accelerates the drug development cycle. In addition, limitations with current tissue models are discussed thoroughly and future prospects of the role of bioprinting in pharmaceutics are provided to the reader.

STATEMENT OF SIGNIFICANCE

Present advances in tissue biofabrication have crucial role to play in aiding the pharmaceutical development process achieve its objectives. Advent of three-dimensional (3D) models, in particular, is viewed with immense interest by the community due to their ability to mimic in vivo hierarchical tissue architecture and heterogeneous composition. Successful realization of 3D models will not only provide greater in vitro-in vivo correlation compared to the two-dimensional (2D) models, but also eventually replace pre-clinical animal testing, which has their own shortcomings. Amongst all fabrication techniques, bioprinting- comprising all the different modalities (extrusion-, droplet- and laser-based bioprinting), is emerging as the most viable fabrication technique to create the biomimetic tissue constructs. Notwithstanding the interest in bioprinting by the pharmaceutical development researchers, it can be seen that there is a limited availability of comparative literature which can guide the proper selection of bioprinting processes and associated considerations, such as the bioink selection for a particular pharmaceutical study. Thus, this work emphasizes these aspects of bioprinting and presents them in perspective of differential requirements of different pharmaceutical studies like in vitro predictive toxicology, high-throughput screening, drug delivery and tissue-specific efficacies. Moreover, since bioprinting techniques are mostly applied in regenerative medicine and tissue engineering, a comparative analysis of similarities and differences are also expounded to help researchers make informed decisions based on contemporary literature.

In vitro cancer cell-ECM interactions inform in vivo cancer treatment

The general progression of cancer drug development involves in vitro testing followed by safety and efficacy evaluation in clinical trials. Due to the expense of bringing candidate drugs to trials, in vitro models of cancer cells and tumor biology are required to screen drugs. There are many examples of drugs exhibiting cytotoxic behavior in cancer cells in vitro but losing efficacy in vivo, and in many cases, this is the result of poorly understood chemoresistant effects conferred by the cancer microenvironment. To address this, improved methods for culturing cancer cells in biomimetic scaffolds have been developed; along the way, a great deal about the nature of cancer cell-extracellular matrix (ECM) interactions has been discovered. These discoveries will continue to be leveraged both in the development of novel drugs targeting these interactions and in the fabrication of biomimetic substrates for efficient cancer drug screening in vitro.

Three-Dimensional Microfluidic Tri-Culture Model of the Bone Marrow Microenvironment for Study of Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) initiates and progresses in the bone marrow, and as such, the marrow microenvironment is a critical regulatory component in development of this cancer. However, ALL studies were conducted mainly on flat plastic substrates, which do not recapitulate the characteristics of marrow microenvironments. To study ALL in a model of in vivo relevance, we have engineered a 3-D microfluidic cell culture platform. Biologically relevant populations of primary human bone marrow stromal cells, osteoblasts and human leukemic cells representative of an aggressive phenotype were encapsulated in 3-D collagen matrix as the minimal constituents and cultured in a microfluidic platform. The matrix stiffness and fluidic shear stress were controlled in a physiological range. The 3-D microfluidic as well as 3-D static models demonstrated coordinated cell-cell interactions between these cell types compared to the compaction of the 2-D static model. Tumor cell viability in response to an antimetabolite chemotherapeutic agent, cytarabine in tumor cells alone and tri-culture models for 2-D static, 3-D static and 3-D microfluidic models were compared. The present study showed decreased chemotherapeutic drug sensitivity of leukemic cells in 3-D tri-culture models from the 2-D models. The results indicate that the bone marrow microenvironment plays a protective role in tumor cell survival during drug treatment. The engineered 3-D microfluidic tri-culture model enables systematic investigation of effects of cell-cell and cell-matrix interactions on cancer progression and therapeutic intervention in a controllable manner, thus improving our limited comprehension of the role of microenvironmental signals in cancer biology.

In vitro microtumors provide a physiologically predictive tool for breast cancer therapeutic screening

Many anti-cancer drugs fail in human trials despite showing efficacy in preclinical models. It is clear that the in vitro assays involving 2D monoculture do not reflect the complex extracellular matrix, chemical, and cellular microenvironment of the tumor tissue, and this may explain the failure of 2D models to predict clinical efficacy. We first optimized an in vitro microtumor model using a tumor-aligned ECM, a tumor-aligned medium, MCF-7 and MDA-MB-231 breast cancer spheroids, human umbilical vein endothelial cells, and human stromal cells to recapitulate the tissue architecture, chemical environment, and cellular organization of a growing and invading tumor. We assayed the microtumor for cell proliferation and invasion in a tumor-aligned extracellular matrix, exhibiting collagen deposition, acidity, glucose deprivation, and hypoxia. We found maximal proliferation and invasion when the multicellular spheroids were cultured in a tumor-aligned medium, having low pH and low glucose, with 10% fetal bovine serum under hypoxic conditions. In a 7-day assay, varying doses of fluorouracil or paclitaxel had differential effects on proliferation for MCF-7 and MDA-MB-231 tumor spheroids in microtumor compared to 2D and 3D monoculture. The microtumors exhibited a tumor morphology and drug response similar to published xenograft data, thus demonstrating a more physiologically predictive in vitro model.

Modulation of Huh7.5 spheroid formation and functionality using modified PEG-based hydrogels of different stiffness

Physical cues, such as cell microenvironment stiffness, are known to be important factors in modulating cellular behaviors such as differentiation, viability, and proliferation. Apart from being able to trigger these effects, mechanical stiffness tuning is a very convenient approach that could be implemented readily into smart scaffold designs. In this study, fibrinogen-modified poly(ethylene glycol)-diacrylate (PEG-DA) based hydrogels with tunable mechanical properties were synthesized and applied to control the spheroid formation and liver-like function of encapsulated Huh7.5 cells in an engineered, three-dimensional liver tissue model. By controlling hydrogel stiffness (0.1–6 kPa) as a cue for mechanotransduction representing different stiffness of a normal liver and a diseased cirrhotic liver, spheroids ranging from 50 to 200 μm were formed over a three week time-span. Hydrogels with better compliance (i.e. lower stiffness) promoted formation of larger spheroids. The highest rates of cell proliferation, albumin secretion, and CYP450 expression were all observed for spheroids in less stiff hydrogels like a normal liver in a healthy state. We also identified that the hydrogel modification by incorporation of PEGylated-fibrinogen within the hydrogel matrix enhanced cell survival and functionality possibly owing to more binding of autocrine fibronectin. Taken together, our findings establish guidelines to control the formation of Huh7.5 cell spheroids in modified PEGDA based hydrogels. These spheroids may serve as models for applications such as screening of pharmacological drug candidates.

The role of matrix compliance on cell responses to drugs and toxins: towards predictive drug screening platforms

Since the birth of tissue engineering, it has been redefined to include not only the development of tissues for clinical use, but also in vitro models for the study of tissue physiology and pathology. Great strides have been accomplished in the design of in vitro tissue models, yet one area in which they are underrepresented, but where they can have an immediate impact, is the development of platforms for drug screening. By providing more in vivo-like cell environments, such models could address the growing concerns about drug failures due to lack of efficacy or unexpected side effects. This review aims to address the interface between substrate compliance and cell responsiveness to toxins and drugs since compliance has been established as a major determinate of overall cell fate. Here, results from 2D substrates and 3D matrices are discussed. Additionally, examples of biomaterial-based high-throughput stiffness assays in drug screening are presented.

Matrigel: from discovery and ECM mimicry to assays and models for cancer research

The basement membrane is an important extracellular matrix that is found in all epithelial and endothelial tissues. It maintains tissue integrity, serves as a barrier to cells and to molecules, separates different tissue types, transduces mechanical signals, and has many biological functions that help to maintain tissue specificity. A well-defined soluble basement membrane extract, termed BME/Matrigel, prepared from an epithelial tumor is similar in content to authentic basement membrane, and forms a hydrogel at 24-37°C. It is used in vitro as a substrate for 3D cell culture, in suspension for spheroid culture, and for various assays, such as angiogenesis, invasion, and dormancy. In vivo, BME/Matrigel is used for angiogenesis assays and to promote xenograft and patient-derived biopsy take and growth. Studies have shown that both the stiffness of the BME/Matrigel and its components (i.e. chemical signals) are responsible for its activity with so many different cell types. BME/Matrigel has widespread use in assays and in models that improve our understanding of tumor biology and help define therapeutic approaches.