Three-dimensionally engineered biomimetic tissue models forin vitrodrug evaluation: delivery, efficacy and toxicity

The Role of Biomimetic Hypoxia on Cancer Cell Behaviour in 3D Models: A Systematic Review

Simple Summary

Cancer remains one of the leading causes of death worldwide. The advancements in 3D tumour models provide in vitro test-beds to study cancer growth, metastasis and response to therapy. We conducted this systematic review on existing experimental studies in order to identify and summarize key biomimetic tumour microenvironmental features which affect aspects of cancer biology. The review noted the significance of in vitro hypoxia and 3D tumour models on epithelial to mesenchymal transition, drug resistance, invasion and migration of cancer cells. We highlight the importance of various experimental parameters used in these studies and their subsequent effects on cancer cell behaviour.

Abstract

The development of biomimetic, human tissue models is recognized as being an important step for transitioning in vitro research findings to the native in vivo response. Oftentimes, 2D models lack the necessary complexity to truly recapitulate cellular responses. The introduction of physiological features into 3D models informs us of how each component feature alters specific cellular response. We conducted a systematic review of research papers where the focus was the introduction of key biomimetic features into in vitro models of cancer, including 3D culture and hypoxia. We analysed outcomes from these and compiled our findings into distinct groupings to ascertain which biomimetic parameters correlated with specific responses. We found a number of biomimetic features which primed cancer cells to respond in a manner which matched in vivo response.

From tissue engineering to engineering tissues: the role and application of in vitro models

This review defines and explores the engineering process and the multifaceted potential and limitations of models within the biomedical field.

Disentangling the fibrous microenvironment: designer culture models for improved drug discovery

INTRODUCTION

Standard high-throughput screening (HTS) assays rarely identify clinically viable 'hits', likely because cells do not experience physiologically realistic culture conditions. The biophysical nature of the extracellular matrix has emerged as a critical driver of cell function and response and recreating these factors could be critically important in streamlining the drug discovery pipeline.

AREAS COVERED

The authors review recent design strategies to understand and manipulate biophysical features of three-dimensional fibrous tissues. The effects of architectural parameters of the extracellular matrix and their resulting mechanical behaviors are deconstructed; and their individual and combined impact on cell behavior is examined. The authors then illustrate the potential impact of these physical features on designing next-generation platforms to identify drugs effective against breast cancer.

EXPERT OPINION

Progression toward increased culture complexity must be balanced against the demanding technical requirements for high-throughput screening; and strategies to identify the minimal set of microenvironmental parameters needed to recreate disease-relevant responses must be specifically tailored to the disease stage and organ system being studied. Although challenging, this can be achieved through integrative and multidisciplinary technologies that span microfabrication, cell biology, and tissue engineering.

An integrated cell printing system for the construction of heterogeneous tissue models

A new three-dimensional (3D) cell printing system was developed and investigated to organize multiple cells/biomaterials with a control precision within 100 μm. This system can be used for the in vitro construction of heterogeneous tissue models. The proposed printing system was achieved by the integration of extrusion printing and alternating viscous and inertial force jetting (AVIFJ) techniques using dual-nozzle switching. In this technique, hydrogels containing high cell densities were extruded using extrusion printing, while droplets containing single cells were precisely manipulated using AVIFJ. The droplets that contained single cells were at the scale of pico-liters and could be accurately positioned at the micron scale. Stable hydrogel structures with adjustable diameters were also printed, with cell viabilities exceeding 90% after printing. A heterogeneous tumor model that contained spheroids and human umbilical vein endothelial cells (HUVECs) was then constructed using the established integrated cell printing system in a stepwise or simultaneous fashion. HUVEC-loaded droplets were observed to locate around the preformed tumor spheroids as designed. Cells and spheroids in the model maintained high cell viability and sustained growth throughout the culture period. The ELISA results of albumin production also proved that the spheroids maintained increased cellular function during the culture. These results demonstrated the feasibility of this integrated 3D printing system for the engineering of in vitro heterogeneous tissue models for future biological and pathological studies. STATEMENT OF SIGNIFICANCE: Addressing the challenge of multi-scale printing in the construction of heterogeneous tissue models, a new 3D cell printing system was developed to organize cells/biomaterials of a control precision within 100 μm. AVIFJ was integrated with extrusion printing, thereby achieving the construction of cell interactions between single cells and spheroids, the manipulation of single cells in a 3D microenvironment with high accuracy, and the real-time on-demand printing. The printed heterogeneous tumor model maintained cell viability, sustained cell growth, and increased cell function during 7 days of culture. We believed that this work would benefit the production of functional artificial tissues, enabling the construction of more biomimetic cell arrangements and microenvironment to support cell functions.

Review on biofabrication and applications of heterogeneous tumor models

Resolving the origin and development of tumor heterogeneity has proven to be a crucial challenge in cancer research. In vitro tumor models have been widely used for both scientific and clinical research. Currently, tumor models based on 2D cell culture, animal models, and 3D cell-laden constructs are widely used. Heterogeneous tumor models, which consist of more than one cell type and mimic cell-cell as well as cell-matrix interactions, are attracting increasing attention. Heterogeneous tumor models can serve as pathological models to study the microenvironment and tumor development such as tumorigenesis, invasiveness, and malignancy. They also provide disease models for drug screening and personalized therapy. In this review, the current techniques, models, and oncological applications regarding 3D heterogeneous tumor models are summarized and discussed.

Biomaterial-based delivery systems of nucleic acid for regenerative research and regenerative therapy

Regenerative medicine is a new and promising medical method aiming at treating patients with defective or dysfunctional tissues by maintaining or enhancing the biological activity of cells. The development of biomaterial-based technologies, such as cell scaffolds and carriers for drug delivery system, are highly required to promote the regenerative research and regenerative therapy. Nucleic acids are one of the most feasible factors to efficiently modify the biological activity of cells. The effective and stable delivery of nucleic acids into cells is highly required to succeed in the modification. Biomaterials-based non-viral carriers or biological carriers, like exosomes, play an important role in the efficient delivery of nucleic acids. This review introduces the examples of regenerative research and regenerative therapy based on the delivery of nucleic acids with biomaterials technologies and emphasizes their importance to accomplish regenerative medicine.

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Modifying the activity of cells is important for regenerative medicine.

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Various nucleic acids regulate gene expression to modify the activity of cells.

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Intracellular delivery system is vital to the nucleic acids-based modification.

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Biomaterials are useful for the intracellular delivery of nucleic acids.

New Advances in the Study of Bone Tumors: A Lesson From the 3D Environment

Bone primary tumors, such as osteosarcoma, are highly aggressive pediatric tumors that in 30% of the cases develop lung metastasis and are characterized by poor prognosis. Bone is also the third most common metastatic site in patients with advanced cancer and once tumor cells become homed to the skeleton, the disease is usually considered incurable, and treatment is only palliative. Bone sarcoma and bone metastasis share the same tissue microenvironment and niches. 3D cultures represent a new promising approach for the study of interactions between tumor cells and other cellular or acellular components of the tumor microenvironment (i.e., fibroblasts, mesenchymal stem cells, bone ECM). Indeed, 3D models can mimic physiological interactions that are crucial to modulate response to soluble paracrine factors, tumor drug resistance and aggressiveness and, in all, these innovative models might be able of bypassing the use of animal-based preclinical cancer models. To date, both static and dynamic 3D cell culture models have been shown to be particularly suited for screening of anticancer agents and might provide accurate information, translating in vitro cell cultures into precision medicine. In this mini-review, we will summarize the current state-of-the-art in the field of bone tumors, both primary and metastatic, illustrating the different methods and techniques employed to realize 3D cell culture systems and new results achieved in a field that paves the way toward personalized medicine.

Status of acute systemic toxicity testing requirements and data uses by U.S. regulatory agencies

Acute systemic toxicity data are used by a number of U.S. federal agencies, most commonly for hazard classification and labeling and/or risk assessment for acute chemical exposures. To identify opportunities for the implementation of non-animal approaches to produce these data, the regulatory needs and uses for acute systemic toxicity information must first be clarified. Thus, we reviewed acute systemic toxicity testing requirements for six U.S. agencies (Consumer Product Safety Commission, Department of Defense, Department of Transportation, Environmental Protection Agency, Food and Drug Administration, Occupational Safety and Health Administration) and noted whether there is flexibility in satisfying data needs with methods that replace or reduce animal use. Understanding the current regulatory use and acceptance of non-animal data is a necessary starting point for future method development, optimization, and validation efforts. The current review will inform the development of a national strategy and roadmap for implementing non-animal approaches to assess potential hazards associated with acute exposures to industrial chemicals and medical products. The Acute Toxicity Workgroup of the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM), U.S. agencies, non-governmental organizations, and other stakeholders will work to execute this strategy.

Comparative studies of cellular viability levels on 2D and 3D in vitro culture matrices

In this study, the cellular viability and function of immortalized human cervical and dermal cells are monitored and compared in conventional 2D and two commercial 3D membranes, Collagen and Geltrex, of varying working concentration and volume. Viability was monitored with the aid of the Alamar Blue assay, cellular morphology was monitored with confocal microscopy, and cell cycle studies and cell death mechanism studies were performed with flow cytometry. The viability studies showed apparent differences between the 2D and 3D culture systems, the differences attributed in part to the physical transition from 2D to 3D environment causing alterations to effective resazurin concentration, uptake and conversion rates, which was dependent on exposure time, but also due to the effect of the membrane itself on cellular function. These effects were verified by flow cytometry, in which no significant differences in viable cell numbers between 2D and 3D systems were observed after 24 h culture. The results showed the observed effect was different after shorter exposure periods, was also dependent on working concentration of the 3D system and could be mediated by altering the culture vessel size. Cell cycle analysis revealed cellular function could be altered by growth on the 3D substrates and the alterations were noted to be dependent on 3D membrane concentration. The use of 3D culture matrices has been widely interpreted to result in "improved viability levels" or "reduced" toxicity or cellular "resistance" compared to cells cultured on traditional 2D systems. The results of this study show that cellular health and viability levels are not altered by culture in 3D environments, but their normal cycle can be altered as indicated in the cell cycle studies performed and such variations must be accounted for in studies employing 3D membranes for in vitro cellular screening.

Perfused human hepatocyte microtissues identify reactive metabolite-forming and mitochondria-perturbing hepatotoxins

Hepatotoxins cause liver damage via many mechanisms but the formation of reactive metabolites and/or damage to liver mitochondria are commonly implicated. We assess 3D human primary hepatocyte microtissues as a platform for hepatotoxicity studies with reactive metabolite-forming and mitochondria-perturbing compounds. We show that microtissues formed from cryopreserved human hepatocytes had bile canaliculi, transcribed mRNA from genes associated with xenobiotic metabolism and expressed functional cytochrome P450 enzymes. Hierarchical clustering was used to distinguish dose-dependent hepatotoxicity elicited by clozapine, fialuridine and acetaminophen (APAP) from control cultures and less liver-damaging compounds, olanzapine and entecavir. The regio-isomer of acetaminophen, N-acetyl-meta-aminophenol (AMAP) clustered with the hepatotoxic compounds. The principal metabolites of APAP were formed and dose-dependent changes in metabolite profile similar to those seen in patient overdose was observed. The toxicological profile of APAP was indistinguishable from that of AMAP, confirming AMAP as a human hepatotoxin. Tissue oxygen consumption rate was significantly decreased within 2h of exposure to APAP or AMAP, concomitant with glutathione depletion. These data highlight the potential utility of perfused metabolically functional human liver microtissues in drug development and mechanistic toxicology.

Development and Characterization of In Vitro Human Oral Mucosal Equivalents Derived from Immortalized Oral Keratinocytes

Tissue-engineered oral mucosal equivalents (OME) are being increasingly used to measure toxicity, drug delivery, and to model oral diseases. Current OME mainly comprise normal oral keratinocytes (NOK) cultured on top of a normal oral fibroblasts-containing matrix. However, the commercial supply of NOK is limited, restricting widespread use of these mucosal models. In addition, NOK suffer from poor longevity and donor-to-donor variability. Therefore, we constructed, characterized, and tested the functionality of OME based on commercial TERT2-immortalized oral keratinocytes (FNB6) to produce a more readily available alternative to NOK-based OME. FNB6 OME cultured at an air-to-liquid interface for 14 days exhibited expression of differentiation markers cytokeratin 13 in the suprabasal layers and cytokeratin 14 in basal layer of the epithelium. Proliferating cells were restricted to the basal epithelium, and there was immuno-positive expression of E-cadherin confirming the presence of established cell-to-cell contacts. The histology and expression of these structural markers paralleled those observed in the normal oral mucosa and NOK-based models. On stimulation with TNFα and IL-1, FNB6 OME displayed a similar global gene expression profile to NOK-based OME, with increased expression of many common pro-inflammatory molecules such as chemokines (CXCL8), cytokines (IL-6), and adhesion molecules (ICAM-1) when analyzed by gene array and quantitative PCR. Similarly, pathway analysis showed that both FNB6 and NOK models initiated similar intracellular signaling on stimulation. Gene expression in FNB6 OME was more consistent than NOK-based OME that suffered from donor variation in response to stimuli. Mucosal equivalents based on immortalized FNB6 cells are accessible, reproducible and will provide an alternative animal experimental system for studying mucosal drug delivery systems, host-pathogen interactions, and drug-induced toxicity.

Evaluating Biomaterial- and Microfluidic-Based 3D Tumor Models

Cancer is a major cause of morbidity and mortality worldwide, with a disease burden estimated to increase over the coming decades. Disease heterogeneity and limited information on cancer biology and disease mechanisms are aspects that 2D cell cultures fail to address. Here, we review the current ‘state-of-the-art’ in 3D tissue-engineering (TE) models developed for, and used in, cancer research. We assess the potential for scaffold-based TE models and microfluidics to fill the gap between 2D models and clinical application. We also discuss recent advances in combining the principles of 3D TE models and microfluidics, with a special focus on biomaterials and the most promising chip-based 3D models.

Evaluation of surrogate tissues as indicators of drug activity in a melanoma skin model

The development of novel cancer treatments is a challenging task, partly because results from model systems often fail to predict drug efficacy in humans, and also tumors are often inaccessible for biochemical analysis, preventing effective monitoring of drug activity in vivo. Utilizing a model system, we evaluated the use of drug-induced DNA damage in surrogate tissues as indicators of drug efficacy. Samples of a commercially available melanoma skin model (Mattek MLNM-FT-A375) containing keratinocyte and fibroblast layers with melanoma nodules were subjected to various chemotherapeutic regimens for one, four, or eight days. At these times they were analyzed for DNA double-stranded breaks (γH2AX foci) and apoptosis (TUNEL). A wide range of drug responses in both tumor and normal tissues were observed and cataloged. For the melanoma, the most common drug response was apoptosis. The basal keratinocyte layer, which was the most reliable indicator of drug response in the melanoma skin model, responded with γH2AX foci formation that was abrupt and transient. The relationships between tumor and surrogate tissue drug responses are complex, indicating that while surrogate tissue drug responses may be useful clinical tools, careful control of variables such as the timing of sampling may be important in interpreting the results.

Bottom-Up Engineering of Well-Defined 3D Microtissues Using Microplatforms and Biomedical Applications

During the last decades, the engineering of well-defined 3D tissues has attracted great attention because it provides in vivo mimicking environment and can be a building block for the engineering of bioartificial organs. In this Review, diverse engineering methods of 3D tissues using microscale devices are introduced. Recent progress of microtechnologies has enabled the development of microplatforms for bottom-up assembly of diverse shaped 3D tissues consisting of various cells. Micro hanging-drop plates, microfluidic chips, and arrayed microwells are the typical examples. The encapsulation of cells in hydrogel microspheres and microfibers allows the engineering of 3D microtissues with diverse shapes. Applications of 3D microtissues in biomedical fields are described, and the future direction of microplatform-based engineering of 3D micro-tissues is discussed.

Facile fabrication of a 3D electrospun fibrous mat by ice-templating for a tumor spheroid culture

A 3D polycaprolactone fibrous mat was fabricated by using spherical ice as a template during electrospinning for stabilizing droplets in a spheroid culture.

Fabrication of functional 3D hepatic tissues with polarized hepatocytes by stacking endothelial cell sheets in vitro

Cell sheet stratification technology has been used for reconstituting highly functional three-dimensional (3D) hepatic tissues in vitro. Triple-layered hepatic tissues with a hepatocyte-specific polarity were fabricated by sandwiching a hepatocyte sheet (Hep sheet) between two endothelial cell (EC) sheets. The morphological and functional characteristics of the triple-layered hepatic construct (EC-Hep-EC) were evaluated and compared with those of a double-layered hepatic construct with a single EC sheet (Hep-EC) and a Hep sheet only. Transmission electron microscope (TEM) observations revealed that the extracellular matrix was observed to be deposited in the space between the ECs and hepatocytes on both the upper and lower sides of the hepatocytes in the EC-Hep-EC construct. Immunohistochemistry with basolateral (CD147) and apical [multidrug resistance-associated protein (MRP2)] membrane polarity markers clearly showed the recovery of in vivo-like hepatocyte polarization in the EC-Hep-EC group. In addition, hepatocyte-specific functions, including albumin secretion, ammonia removal and the induction of cytochrome P450, were also highly preserved. The presented technology for stratifying multiple cell sheets was simple in operation and successfully reproduced both the heterotypic/homotypic cell-cell and cell-matrix interactions with the inherent hepatocyte configurations, thus closely mimicking the in vivo environment. The triple-layered 3D hepatic constructs could therefore be valuable as a new experiment tool for drug-screening tests, an implantable tissue model for cell-based therapies and an efficient culture platform for bioartificial liver devices. Copyright © 2015 John Wiley & Sons, Ltd.

Life in 3D is never flat: 3D models to optimise drug delivery

The development of safe, effective and patient-acceptable drug products is an expensive and lengthy process and the risk of failure at different stages of the development life-cycle is high. Improved biopharmaceutical tools which are robust, easy to use and accurately predict the in vivo response are urgently required to help address these issues. In this review the advantages and challenges of in vitro 3D versus 2D cell culture models will be discussed in terms of evaluating new drug products at the pre-clinical development stage. Examples of models with a 3D architecture including scaffolds, cell-derived matrices, multicellular spheroids and biochips will be described. The ability to simulate the microenvironment of tumours and vital organs including the liver, kidney, heart and intestine which have major impact on drug absorption, distribution, metabolism and toxicity will be evaluated. Examples of the application of 3D models including a role in formulation development, pharmacokinetic profiling and toxicity testing will be critically assessed. Although utilisation of 3D cell culture models in the field of drug delivery is still in its infancy, the area is attracting high levels of interest and is likely to become a significant in vitro tool to assist in drug product development thus reducing the requirement for unnecessary animal studies.

Applying refinement to the use of mice and rats in rheumatoid arthritis research

Rheumatoid arthritis (RA) is a painful, chronic disorder and there is currently an unmet need for effective therapies that will benefit a wide range of patients. The research and development process for therapies and treatments currently involves in vivo studies, which have the potential to cause discomfort, pain or distress. This Working Group report focuses on identifying causes of suffering within commonly used mouse and rat ‘models’ of RA, describing practical refinements to help reduce suffering and improve welfare without compromising the scientific objectives. The report also discusses other, relevant topics including identifying and minimising sources of variation within in vivo RA studies, the potential to provide pain relief including analgesia, welfare assessment, humane endpoints, reporting standards and the potential to replace animals in RA research.

Robust and flexible fabrication of chemical micropatterns for tumor spheroid preparation

A robust and flexible approach is described for the straightforward preparation of multicellular tumor spheroids of controllable dimensions. The approach is based on a one-step plasma polymerization of the monomer allylamine carried out through conformal micropatterning physical masks that is used to deposit amine-rich (PolyAA) micrometer-scale features that promote cellular attachment and initiate the formation of multicellular spheroids. A simple backfilling step of the nonpolymerized poly(dimethylsiloxane) background with Pluronic F127 significantly reduced background cellular adhesion on the untreated substrate and, in turn, improved the quality of the spheroid formed. Tumor cells grown on the PolyAA/F127 patterned surfaces reliably formed multicellular spheroids within 24-48 h depending on the cell type. The dimension of the spheroids could be readily controlled by the dimension of the amine-rich micropatterns. This simple approach is compatible with the long-term culture of multicellular spheroids and their characterization with high-resolution optical microscopy. These features facilitate the development of on-chip assays, as demonstrated here for the study of the binding of transferrin-functionalized gold nanoparticles to multicellular tumor spheroids.

Superhydrophobic chips for cell spheroids high-throughput generation and drug screening

We suggest the use of biomimetic superhydrophobic patterned chips produced by a benchtop methodology as low-cost and waste-free platforms for the production of arrays of cell spheroids/microtissues by the hanging drop methodology. Cell spheroids have a wide range of applications in biotechnology fields. For drug screening, they allow studying 3D models in structures resembling real living tissues/tumors. In tissue engineering, they are suggested as building blocks of bottom-up fabricated tissues. We used the wettability contrast of the chips to fix cell suspension droplets in the wettable regions and evaluated on-chip drug screening in 3D environment. Cell suspensions were patterned in the wettable spots by three distinct methods: (1) by pipetting the cell suspension directly in each individual spot, (2) by the continuous dragging of a cell suspension on the chip, and (3) by dipping the whole chip in a cell suspension. These methods allowed working with distinct throughputs and degrees of precision. The platforms were robust, and we were able to have static or dynamic environments in each droplet. The access to cell culture media for exchange or addition/removal of components was versatile and opened the possibility of using each spot of the chip as a mini-bioreactor. The platforms' design allowed for samples visualization and high-content image-based analysis on-chip. The combinatorial analysis capability of this technology was validated by following the effect of doxorubicin at different concentrations on spheroids formed using L929 and SaOs-2 cells.

Novel Nystatin A₁ derivatives exhibiting low host cell toxicity and antifungal activity in an in vitro model of oral candidosis

Opportunistic oral infections caused by Candida albicans are frequent problems in immunocompromised patients. Management of such infections is limited due to the low number of antifungal drugs available, their relatively high toxicity and the emergence of antifungal resistance. Given these issues, our investigations have focused on novel derivatives of the antifungal antibiotic Nystatin A1, generated by modifications at the amino group of this molecule. The aims of this study were to evaluate the antifungal effectiveness and host cell toxicity of these new compounds using an in vitro model of oral candidosis based on a reconstituted human oral epithelium (RHOE). Initial studies employing broth microdilution, revealed that against planktonic C. albicans, Nystatin A1 had lower minimal inhibitory concentration than novel derivatives. However, Nystatin A1 was also markedly more toxic against human keratinocyte cells. Interestingly, using live/dead staining to assess C. albicans and tissue cell viability after RHOE infection, Nystatin A1 derivatives were more active against Candida with lower toxicity to epithelial cells than the parent drug. Lactate dehydrogenase activity released by the RHOE indicated a fourfold reduction in tissue damage when certain Nystatin derivatives were used compared with Nystatin A1. Furthermore, compared with Nystatin A1, colonisation of the oral epithelium by C. albicans was notably reduced by the new polyenes. In the absence of antifungal agents, confocal laser scanning microscopy showed that C. albicans extensively invaded the RHOE. However, the presence of the novel derivatives greatly reduced or totally prevented this fungal invasion.

Walking through trabecular meshwork biology: Toward engineering design of outflow physiology

According to the World Health Organization, glaucoma remains the second leading cause of blindness in the world. Glaucoma belongs to a group of optic neuropathies that is characterized by chronic degeneration of the optic nerve along with its supporting glia and vasculature. Despite significant advances in the field, there is no available cure for glaucoma. The trabecular meshwork has been implicated as the primary site for regulation of intraocular pressure, the only known modifiable factor in glaucoma development. In this review, we describe the current models for glaucoma studies, primary culture, anterior eye segments, and animal studies and their limitations. These models, especially anterior eye segments and animal tissues, often require careful interpretation given the inter-species variation and are cumbersome and expensive. The lack of an available in vitro 3D model to study trabecular meshwork cells and detailed mechanisms of their regulation of intraocular pressure has limited progress in the field of glaucoma research. In this paper, we review the current status of knowledge of the trabecular meshwork and how the current advances in tissue engineering techniques might be applied in an effort to engineer a synthetic trabecular meshwork as a 3D in vitro model to further advance glaucoma research. In addition, we describe strategies for selection and design of biomaterials for scaffold fabrication as well as extracellular matrix components to mimic and support the trabecular architecture. We also discuss possible uses for a bioengineered trabecular meshwork for both developing a fundamental understanding of trabecular meshwork biology as well as high-throughput screening of glaucoma drugs.

Engineering anisotropic biomimetic fibrocartilage microenvironment by bioprinting mesenchymal stem cells in nanoliter gel droplets

Over the past decade, bioprinting has emerged as a promising patterning strategy to organize cells and extracellular components both in two and three dimensions (2D and 3D) to engineer functional tissue mimicking constructs. So far, tissue printing has neither been used for 3D patterning of mesenchymal stem cells (MSCs) in multiphase growth factor embedded 3D hydrogels nor been investigated phenotypically in terms of simultaneous differentiation into different cell types within the same micropatterned 3D tissue constructs. Accordingly, we demonstrated a biochemical gradient by bioprinting nanoliter droplets encapsulating human MSCs, bone morphogenetic protein 2 (BMP-2), and transforming growth factor β1 (TGF- β1), engineering an anisotropic biomimetic fibrocartilage microenvironment. Assessment of the model tissue construct displayed multiphasic anisotropy of the incorporated biochemical factors after patterning. Quantitative real time polymerase chain reaction (qRT-PCR) results suggested genomic expression patterns leading to simultaneous differentiation of MSC populations into osteogenic and chondrogenic phenotype within the multiphasic construct, evidenced by upregulation of osteogenesis and condrogenesis related genes during in vitro culture. Comprehensive phenotypic network and pathway analysis results, which were based on genomic expression data, indicated activation of differentiation related mechanisms, via signaling pathways, including TGF, BMP, and vascular endothelial growth factor.

A 3-D artificial colon tissue mimic for the evaluation of nanoparticle-based drug delivery system

Functional engineered nanoparticles are promising drug delivery carriers. As the construction of a functional nanocarrier always needs the optimization of multiple technical variables, efficient in vitro high-throughput evaluation methods would help to shorten the development cycle. In the present study, we generated a tissue mimic of the colon of inflammatory bowel disease (IBD) patients. Generally, Caco-2 cells and THP-1 cells were grown in a 3-D matrix with different number, spatial distribution and specific extracellular cell matrix (ECM) composition according to real healthy and inflamed animal colon tissues. After interlerukin-1β/lipopolysaccharide (LPS) stimulation, the artificial model closely resembled the pathological features of IBD patient's colon, including massive cytokines and mucus production, epithelium defect and leukocytic infiltration. The tissue and cellular uptake of three different nanoparticles in the artificial model was similar to that in 2,4,6-trinitrobenzenesulfonic acid (TNBS) colitic mice. Most importantly, our artificial tissue can be placed into 96-well plates for high-throughput screening of drug delivery carriers for the treatment of IBD. Our study suggested a readily achievable way to improve current methodologies for the development of colon targeted drug delivery systems.

Dual-stage growth factor release within 3D protein-engineered hydrogel niches promotes adipogenesis

Engineered biomimetic microenvironments from hydrogels are an emerging strategy to achieve lineage-specific differentiation in vitro. In addition to recapitulating critical matrix cues found in the native three-dimensional (3D) niche, the hydrogel can also be designed to deliver soluble factors that are present within the native inductive microenvironment. We demonstrate a versatile materials approach for the dual-stage delivery of multiple soluble factors within a 3D hydrogel to induce adipogenesis. We use a Mixing-Induced Two-Component Hydrogel (MITCH) embedded with alginate microgels to deliver two pro-adipogenic soluble factors, fibroblast growth factor 1 (FGF-1) and bone morphogenetic protein 4 (BMP-4) with two distinct delivery profiles. We show that dual-stage delivery of FGF-1 and BMP-4 to human adipose-derived stromal cells (hADSCs) significantly increases lipid accumulation compared with the simultaneous delivery of both growth factors together. Furthermore, dual-stage growth factor delivery within a 3D hydrogel resulted in substantially more lipid accumulation compared to identical delivery profiles in 2D cultures. Gene expression analysis shows upregulation of key adipogenic markers indicative of brown-like adipocytes. These data suggest that dual-stage release of FGF-1 and BMP-4 within 3D microenvironments can promote the in vitro development of mature adipocytes.

The effect of network biology on drug toxicology

INTRODUCTION

The high failure rate of drug candidates due to toxicity, during clinical trials, is a critical issue in drug discovery. Network biology has become a promising approach, in this regard, using the increasingly large amount of biological and chemical data available and combining it with bioinformatics. With this approach, the assessment of chemical safety can be done across multiple scales of complexity from molecular to cellular and system levels in human health. Network biology can be used at several levels of complexity.

AREAS COVERED

This review describes the strengths and limitations of network biology. The authors specifically assess this approach across different biological scales when it is applied to toxicity.

EXPERT OPINION

There has been much progress made with the amount of data that is generated by various omics technologies. With this large amount of useful data, network biology has the opportunity to contribute to a better understanding of a drug's safety profile. The authors believe that considering a drug action and protein's function in a global physiological environment may benefit our understanding of the impact some chemicals have on human health and toxicity. The next step for network biology will be to better integrate differential and quantitative data.

Dogs and monkeys in preclinical drug development: the challenge of reducing and replacing

INTRODUCTION

Animal experimentation is a very contentious issue affecting reputation of drug industry. There are several reasons to forecast an increase in the number of dogs and monkeys used in safety and pharmacokinetic studies. This increase may trigger a strong reaction of the public opinion. There have been many proposals and initiatives to change the present approach to safety and metabolic studies. Tests based on new technologies, in vitro cell assays, stem cells, imaging, and computational systems, have the potential to anticipate effects in humans. Unfortunately, all these efforts and ideas have not changed standard approaches and regulatory expectations.

AREAS COVERED

This review looks at opportunities to reduce the number of dogs and monkeys currently used in pharmaceutical research. It also discusses present efforts and approaches, their strengths and potentials and the reasons why they may not fulfill expectations.

EXPERT OPINION

Unless the pharmaceutical industry gets more involved, an alternative paradigm of preclinical drug development is unlikely to be established in the foreseeable future. One can imagine a scenario where the political pressure against the use of dogs and monkeys in biomedical research becomes irresistible while alternative methods are not yet established. To avoid this situation, the pharmaceutical industry should take the lead and preclinical scientists at all levels need to influence decision makers and help develop new innovative approaches in drug safety evaluation.