A perfusable 3D cell-matrix tissue culture chamber for in situ evaluation of nanoparticle vehicle penetration and transport

Engineering next generation vascularized organoids

Organoids are self-organizing 3D cell culture models that are valuable for studying the mechanisms underlying both development and disease in multiple species, particularly, in humans. These 3D engineered tissues can mimic the structure and function of human organs in vitro. Methods to generate organoids have substantially improved to better resemble, in various ways, their in vivo counterpart. One of the major limitations in current organoid models is the lack of a functional vascular compartment. Here we discuss methodological approaches to generating perfusable blood vessel networks in organoid systems. Inclusion of perfused vascular compartments markedly enhances the physiological relevance of organoid systems and is a critical step in the establishment of next generation, higher-complexity in vitro systems for use in developmental, clinical, and drug-development settings.

Chirality-enhanced transport and drug delivery of graphene nanocarriers to tumor-like cellular spheroid

Chirality, defined as "a mirror image," is a universal geometry of biological and nonbiological forms of matter. This geometry of molecules determines how they interact during their assembly and transport. With the development of nanotechnology, many nanoparticles with chiral geometry or chiroptical activity have emerged for biomedical research. The mechanisms by which chirality originates and the corresponding synthesis methods have been discussed and developed in the past decade. Inspired by the chiral selectivity in life, a comprehensive and in-depth study of interactions between chiral nanomaterials and biological systems has far-reaching significance in biomedicine. Here, we investigated the effect of the chirality of nanoscale drug carriers, graphene quantum dots (GQDs), on their transport in tumor-like cellular spheroids. Chirality of GQDs (L/D-GQDs) was achieved by the surface modification of GQDs with L/D-cysteines. As an in-vitro tissue model for drug testing, cellular spheroids were derived from a human hepatoma cell line (i.e., HepG2 cells) using the Hanging-drop method. Our results reveal that the L-GQDs had a 1.7-fold higher apparent diffusion coefficient than the D-GQDs, indicating that the L-GQDs can enhance their transport into tumor-like cellular spheroids. Moreover, when loaded with a common chemotherapy drug, Doxorubicin (DOX), via π-π stacking, L-GQDs are more effective as nanocarriers for drug delivery into solid tumor-like tissue, resulting in 25% higher efficacy for cancerous cellular spheroids than free DOX. Overall, our studies indicated that the chirality of nanocarriers is essential for the design of drug delivery vehicles to enhance the transport of drugs in a cancerous tumor.

In Vitro Models of Biological Barriers for Nanomedical Research

Nanoconstructs developed for biomedical purposes must overcome diverse biological barriers before reaching the target where playing their therapeutic or diagnostic function. In vivo models are very complex and unsuitable to distinguish the roles plaid by the multiple biological barriers on nanoparticle biodistribution and effect; in addition, they are costly, time-consuming and subject to strict ethical regulation. For these reasons, simplified in vitro models are preferred, at least for the earlier phases of the nanoconstruct development. Many in vitro models have therefore been set up. Each model has its own pros and cons: conventional 2D cell cultures are simple and cost-effective, but the information remains limited to single cells; cell monolayers allow the formation of cell–cell junctions and the assessment of nanoparticle translocation across structured barriers but they lack three-dimensionality; 3D cell culture systems are more appropriate to test in vitro nanoparticle biodistribution but they are static; finally, bioreactors and microfluidic devices can mimicking the physiological flow occurring in vivo thus providing in vitro biological barrier models suitable to reliably assess nanoparticles relocation. In this evolving context, the present review provides an overview of the most representative and performing in vitro models of biological barriers set up for nanomedical research.

Innovations in lymph node targeting nanocarriers

Lymph nodes are secondary lymphoid tissues in the body that facilitate the co-mingling of immune cells to enable and regulate the adaptive immune response. They are also tissues implicated in a variety of diseases, including but not limited to malignancy. The ability to access lymph nodes is thus attractive for a variety of therapeutic and diagnostic applications. As nanotechnologies are now well established for their potential in translational biomedical applications, their high relevance to applications that involve lymph nodes is highlighted. Herein, established paradigms of nanocarrier design to enable delivery to lymph nodes are discussed, considering the unique lymph node tissue structure as well as lymphatic system physiology. The influence of delivery mechanism on how nanocarrier systems distribute to different compartments and cells that reside within lymph nodes is also elaborated. Finally, current advanced nanoparticle technologies that have been developed to enable lymph node delivery are discussed.

Self-Assembled Hexagonal Superparamagnetic Cone Structures for Fabrication of Cell Cluster Arrays

In this study, we demonstrated that arrays of cell clusters can be fabricated by self-assembled hexagonal superparamagnetic cone structures. When a strong out-of-plane magnetic field was applied to the ferrofluid on a glass substrate, it will induce the magnetic poles on the upper/lower surfaces of the continuous ferrofluid to increase the magnetostatic energy. The ferrofluid will then experience hydrodynamic instability and be split into small droplets with cone structures because of the compromising surface tension energy and magnetostatic energy to minimize the system's total energy. Furthermore, the ferrofluid cones were orderly self-assembled into hexagonal arrays to reach the lowest energy state. After dehydration of these liquid cones to form solid cones, polydimethylsiloxane was cast to fix the arrangement of hexagonal superparamagnetic cone structures and prevent the leakage of magnetic nanoparticles. The U-343 human neuronal glioblastoma cells were labeled with magnetic nanoparticles through endocytosis in co-culture with a ferrofluid. The number of magnetic nanoparticles internalized was (4.2 ± 0.84) × 10⁶ per cell by the cell magnetophoresis analysis. These magnetically labeled cells were attracted and captured by hexagonal superparamagnetic cone structures to form cell cluster arrays. As a function of the solid cone size, the number of cells captured by each hexagonal superparamagnetic cone structure was increased from 48 to 126 under a 2000 G out-of-plane magnetic field. The local magnetic field gradient of the hexagonal superparamagnetic cone was 117.0-140.9 G/mm from the cell magnetophoresis. When an external magnetic field was applied, we observed that the number of protrusions of the cell edge decreased from the fluorescence images. It showed that the local magnetic field gradient caused by the hexagonal superparamagnetic cones restricted the cell growth and migration.

Real-Time Ratiometric Imaging of Micelles Assembly State in a Microfluidic Cancer-on-a-Chip

The performance of supramolecular nanocarriers as drug delivery systems depends on their stability in the complex and dynamic biological media. After administration, nanocarriers are challenged by physiological barriers such as shear stress and proteins present in blood, endothelial wall, extracellular matrix, and eventually cancer cell membrane. While early disassembly will result in a premature drug release, extreme stability of the nanocarriers can lead to poor drug release and low efficiency. Therefore, comprehensive understanding of the stability and assembly state of supramolecular carriers in each stage of delivery is the key factor for the rational design of these systems. One of the main challenges is that current 2D in vitro models do not provide exhaustive information, as they fail to recapitulate the 3D tumor microenvironment. This deficiency in the 2D model complexity is the main reason for the differences observed in vivo when testing the performance of supramolecular nanocarriers. Herein, we present a real-time monitoring study of self-assembled micelles stability and extravasation, combining spectral confocal microscopy and a microfluidic cancer-on-a-chip. The combination of advanced imaging and a reliable 3D model allows tracking of micelle disassembly by following the spectral properties of the amphiphiles in space and time during the crucial steps of drug delivery. The spectrally active micelles were introduced under flow and their position and conformation continuously followed by spectral imaging during the crossing of barriers, revealing the interplay between carrier structure, micellar stability, and extravasation. Integrating the ability of the micelles to change their fluorescent properties when disassembled, spectral confocal imaging and 3D microfluidic tumor blood vessel-on-a-chip resulted in the establishment of a robust testing platform suitable for real-time imaging and evaluation of supramolecular drug delivery carrier's stability.

Improving therapeutic potential of non-viral minimized DNA vectors

The tragic deaths of three patients in a recent AAV-based X-linked myotubular myopathy clinical trial highlight once again the pressing need for safe and reliable gene delivery vectors. Non-viral minimized DNA vectors offer one possible way to meet this need. Recent pre-clinical results with minimized DNA vectors have yielded promising outcomes in cancer therapy, stem cell therapy, stem cell reprograming, and other uses. Broad clinical use of these vectors, however, remains to be realized. Further advances in vector design and production are ongoing. An intriguing and promising potential development results from manipulation of the specific shape of non-viral minimized DNA vectors. By improving cellular uptake and biodistribution specificity, this approach could impact gene therapy, DNA nanotechnology, and personalized medicine.

Biocompatibility of Biomaterials for Nanoencapsulation: Current Approaches

Nanoencapsulation is an approach to circumvent shortcomings such as reduced bioavailability, undesirable side effects, frequent dosing and unpleasant organoleptic properties of conventional drug delivery systems. The process of nanoencapsulation involves the use of biomaterials such as surfactants and/or polymers, often in combination with charge inducers and/or ligands for targeting. The biomaterials selected for nanoencapsulation processes must be as biocompatible as possible. The type(s) of biomaterials used for different nanoencapsulation approaches are highlighted and their use and applicability with regard to haemo- and, histocompatibility, cytotoxicity, genotoxicity and carcinogenesis are discussed.

Magnetically Triggered Release of Entrapped Bioactive Proteins from Thermally Responsive Polymer-Coated Iron Oxide Nanoparticles for Stem-Cell Proliferation

Nanoparticles could conceal bioactive proteins during therapeutic delivery, avoiding side effects. Superparamagnetic iron oxide nanoparticles (SPIONs) coated with a temperature-sensitive polymer were tested for protein release. We show that coated SPIONs can entrap test proteins and release them in a temperature-controlled manner in a biological system. Magnetically heating SPIONs triggered protein release at bulk solution temperatures below the polymer transition. The entrapped growth factor Wnt3a was inactive until magnetically triggered release, upon which it could increase mesenchymal stem cell proliferation. Once the polymer transition will be chemically adjusted above body temperature, this system could be used for targeted cell stimulation in model animals and humans.

Polymeric vehicles for nucleic acid delivery

Polymeric vehicles are versatile tools for therapeutic gene delivery. Many polymers-when assembled with nucleic acids into vehicles-can protect the cargo from degradation and clearance in vivo, and facilitate its transport into intracellular compartments. Design options in polymer synthesis yield a comprehensive range of molecules and resulting vehicle formulations. These properties can be manipulated to achieve stronger association with nucleic acid cargo and cells, improved endosomal escape, or sustained delivery depending on the application. Here, we describe current approaches for polymer use and related strategies for gene delivery in preclinical and clinical applications. Polymer vehicles delivering genetic material have already achieved significant therapeutic endpoints in vitro and in animal models. From our perspective, with preclincal assays that better mimic the in vivo environment, improved strategies for target specificity, and scalable techniques for polymer synthesis, the impact of this therapeutic approach will continue to expand.

Nanofibrillar Cellulose as an Enzymatically and Flow Driven Degradable Scaffold for Three-Dimensional Tissue Engineering

Nanofibrillar cellulose as a naturally biocompatible scaffold material is very promising for tissue engineering. It is shear thinning but has the downside of not being degradable in animals, it can only be degraded by cellulase enzymes. In this study, a newly developed bioreactor was used to culture fibroblast spheroids under flow conditions inside nanocellulose hydrogels with and without the presence of cellulase. The aim was to control the tissue size and ideally find a match between degradation and tissue formation within this promising material. Both the concentration of cellulase and the flow rate were varied and their influence on the activity and growth of fibroblast clusters was assessed. Cluster diameters, degradation, metabolic activity, and tissue production increase with higher cellulase concentration, although concentrations above 1 g/l does not have an additional benefit. Flow leads to more viable cells, more proliferation and migration, leading to overall larger tissue constructs compared to static conditions. This is most likely due to the shear thinning effect of flow on cellulose nanofibrils (CNFs) in addition to the increased nutrient supply through perfusion. At a constant cellulase concentration of 1 g/l, a flow of 2 ml/min proved to be optimal for tissue production. Therefore, degradation in combination with flow leads to more effective tissue production in CNF hydrogels, which is a very potent scaffold material for tissue engineering.

In vitro vascularized liver and tumor tissue microenvironments on a chip for dynamic determination of nanoparticle transport and toxicity

This paper presents the development of a vascularized breast tumor and healthy or tumorigenic liver microenvironments-on-a-chip connected in series. This is the first description of a vascularized multi tissue-on-a-chip microenvironment for modeling cancerous breast and cancerous/healthy liver microenvironments, to allow for the study of dynamic and spatial transport of particles. This device enables the dynamic determination of vessel permeability, the measurement of drug and nanoparticle transport, and the assessment of the associated efficacy and toxicity to the liver. The platform is utilized to determine the effect of particle size on the spatiotemporal diffusion of particles through each microenvironment, both independently and in response to the circulation of particles in varying sequences of microenvironments. The results show that when breast cancer cells were cultured in the microenvironments they had a 2.62-fold higher vessel porosity relative to vessels within healthy liver microenvironments. Hence, the permeability of the tumor microenvironment increased by 2.35- and 2.77-fold compared with a healthy liver for small and large particles, respectively. The extracellular matrix accumulation rate of larger particles was 2.57-fold lower than smaller particles in a healthy liver. However, the accumulation rate was 5.57-fold greater in the breast tumor microenvironment. These results are in agreement with comparable in vivo studies. Ultimately, the platform could be utilized to determine the impact of the tissue or tumor microenvironment, or drug and nanoparticle properties, on transport, efficacy, selectivity, and toxicity in a dynamic, and high-throughput manner for use in treatment optimization.

Application of 3-D Microfluidic Models for Studying Mass Transport Properties of the Tumor Interstitial Matrix

The physical remodeling associated with cancer progression results in barriers to mass transport in the tumor interstitial space. This hindrance ultimately affects the distribution of macromolecules that govern cell fate and potency of cancer therapies. Therefore, knowing how specific extracellular matrix (ECM) and cellular components regulate transport in the tumor interstitium could lead to matrix normalizing strategies that improve patient outcome. Studies over the past decades have provided quantitative insights into interstitial transport in tumors by characterizing two governing parameters: (1) molecular diffusivity and (2) hydraulic conductivity. However, many of the conventional techniques used to measure these parameters are limited due to their inability to experimentally manipulate the physical and cellular environments of tumors. Here, we examine the application and future opportunities of microfluidic systems for identifying the physiochemical mediators of mass transport in the tumor ECM. Further advancement and adoption of microfluidic systems to quantify tumor transport parameters has potential to bridge basic science with translational research for advancing personalized medicine in oncology.

Microfluidics for Cancer Nanomedicine: From Fabrication to Evaluation

Self-assembled drug delivery systems (sDDSs), made from nanocarriers and drugs, are one of the major types of nanomedicines, many of which are in clinical use, under preclinical investigation, or in clinical trials. One of the hurdles of this type of nanomedicine in real applications is the inherent complexity of their fabrication processes, which generally lack precise control over the sDDS structures and the batch-to-batch reproducibility. Furthermore, the classic 2D in vitro cell model, monolayer cell culture, has been used to evaluate sDDSs. However, 2D cell culture cannot adequately replicate in vivo tissue-level structures and their highly complex dynamic 3D environments, nor can it simulate their functions. Thus, evaluations using 2D cell culture often cannot correctly correlate with sDDS behaviors and effects in humans. Microfluidic technology offers novel solutions to overcome these problems and facilitates studying the structure-performance relationships for sDDS developments. In this Review, recent advances in microfluidics for 1) fabrication of sDDSs with well-defined physicochemical properties, such as size, shape, rigidity, and drug-loading efficiency, and 2) fabrication of 3D-cell cultures as "tissue/organ-on-a-chip" platforms for evaluations of sDDS biological performance are in focus.

Comparison of conventional and advanced in vitro models in the toxicity testing of nanoparticles

Humans are exposed to a wide variety of nanoparticles (NPs) present in the environment, in consumer, health and medical products, and in food. Conventional cytotoxicity testing compared to animal testing is less expensive, faster and avoids ethical problems at the expense of a lower predictive value. New cellular models and exposure conditions have been developed to overcome the limitations of conventional cell culture and obtain more predictive data. The use of three-dimensional culture, co-culture and inclusion of mechanical stimulation can provide physiologically more relevant culture conditions. These systems are particularly relevant for oral, respiratory and intravenous exposure to NPs and it may be assumed that physiologically relevant application of the NPs can improve the predictive value of in vitro testing. Various groups have used advanced culture and exposure systems, but few direct comparisons between data from conventional cultures and from advanced systems exist. In silico models may present another option to predict human health risk by NPs without using animal studies. In the absence of validation, the question whether these alternative models provide more predictive data than conventional testing remains elusive.

Preventing Obstructions of Nanosized Drug Delivery Systems by the Extracellular Matrix

Although nanosized drug delivery systems are promising tools for the treatment of severe diseases, the extracellular matrix (ECM) constitutes a major obstacle that endangers therapeutic success. Mobility of diffusing species is restricted not only by small pore size (down to as low as 3 nm) but also by electrostatic interactions with the network. This article evaluates commonly used in vitro models of ECM, analytical methods, and particle types with respect to their similarity to native conditions in the target tissue. In this cross-study evaluation, results from a wide variety of mobility studies are analyzed to discern general principles of particle-ECM interactions. For instance, cross-linked networks and a negative network charge are essential to reliably recapitulate key features of the native ECM. Commonly used ECM mimics comprised of one or two components can lead to mobility calculations which have low fidelity to in vivo results. In addition, analytical methods must be tailored to the properties of both the matrix and the diffusing species to deliver accurate results. Finally, nanoparticles must be sufficiently small to penetrate the matrix pores (ideally R_d/p < 0.5; d = particle diameter, p = pore size) and carry a neutral surface charge to avoid obstructions. Larger (R_d/p >> 1) or positively charged particles are trapped.

Tunable Collagen Microfluidic Platform to Study Nanoparticle Transport in the Tumor Microenvironment

This chapter describes the motivation and protocol for creating a perfused 3D microfluidic in vitro platform representative of the tumor microenvironment to study nanoparticle transport. The cylindrical vascularized tumor platform described consists of a central endothelialized microchannel surrounded by a collagen hydrogel matrix containing cancer cells. This system can be employed to investigate key nanoparticle transport events in the tumor such as extravasation, diffusion within the extracellular matrix, and nanoparticle uptake. This easily manufactured tumor platform can be used for novel nanoparticle refinement focused on optimizing nanoparticle features such as size, shape, and functionalization method. This can yield ideal nanoparticles with properties that facilitate increased transport within the tumor microenvironment, leading to more effective nanoparticle-based treatments for cancer including nanoparticle-based drug delivery systems.

Magnetic forces enable controlled drug delivery by disrupting endothelial cell-cell junctions

The vascular endothelium presents a major transport barrier to drug delivery by only allowing selective extravasation of solutes and small molecules. Therefore, enhancing drug transport across the endothelial barrier has to rely on leaky vessels arising from disease states such as pathological angiogenesis and inflammatory response. Here we show that the permeability of vascular endothelium can be increased using an external magnetic field to temporarily disrupt endothelial adherens junctions through internalized iron oxide nanoparticles, activating the paracellular transport pathway and facilitating the local extravasation of circulating substances. This approach provides a physically controlled drug delivery method harnessing the biology of endothelial adherens junction and opens a new avenue for drug delivery in a broad range of biomedical research and therapeutic applications.

The transportation of large molecules through the vascular endothelium presents a major challenge for in vivo drug delivery. Here, the authors demonstrate the potential of using external magnetic fields and magnetic nanoparticles to enhance the local extravasation of circulating large molecules.

Mimicking Tumors: Toward More Predictive In Vitro Models for Peptide- and Protein-Conjugated Drugs

Macromolecular drug candidates and nanoparticles are typically tested in 2D cancer cell culture models, which are often directly followed by in vivo animal studies. The majority of these drug candidates, however, fail in vivo. In contrast to classical small-molecule drugs, multiple barriers exist for these larger molecules that two-dimensional approaches do not recapitulate. In order to provide better mechanistic insights into the parameters controlling success and failure and due to changing ethical perspectives on animal studies, there is a growing need for in vitro models with higher physiological relevance. This need is reflected by an increased interest in 3D tumor models, which during the past decade have evolved from relatively simple tumor cell aggregates to more complex models that incorporate additional tumor characteristics as well as patient-derived material. This review will address tissue culture models that implement critical features of the physiological tumor context such as 3D structure, extracellular matrix, interstitial flow, vascular extravasation, and the use of patient material. We will focus on specific examples, relating to peptide-and protein-conjugated drugs and other nanoparticles, and discuss the added value and limitations of the respective approaches.

Current Challenges toward In Vitro Cellular Validation of Inorganic Nanoparticles

An impressive development has been achieved toward the production of well-defined "smart" inorganic nanoparticles, in which the physicochemical properties can be controlled and predicted to a high degree of accuracy. Nanoparticle design is indeed highly advanced, multimodal and multitargeting being the norm, yet we do not fully understand the obstacles that nanoparticles face when used in vivo. Increased cooperation between chemists and biochemists, immunologists and physicists, has allowed us to think outside the box, and we are slowly starting to understand the interactions that nanoparticles undergo under more realistic situations. Importantly, such an understanding involves awareness about the limitations when assessing the influence of such inorganic nanoparticles on biological entities and vice versa, as well as the development of new validation strategies.

Microfluidic Biopsy Trapping Device for the Real-Time Monitoring of Tumor Microenvironment

The tumor microenvironment is composed of cellular and stromal components such as tumor cells, mesenchymal cells, immune cells, cancer associated fibroblasts and the supporting extracellular matrix. The tumor microenvironment provides crucial support for growth and progression of tumor cells and affects tumor response to therapeutic interventions. To better understand tumor biology and to develop effective cancer therapeutic agents it is important to develop preclinical platforms that can faithfully recapitulate the tumor microenvironment and the complex interaction between the tumor and its surrounding stromal elements. Drug studies performed in vitro with conventional two-dimensional cancer cell line models do not optimally represent clinical drug response as they lack true tumor heterogeneity and are often performed in static culture conditions lacking stromal tumor components that significantly influence the metabolic activity and proliferation of cells. Recent microfluidic approaches aim to overcome such obstacles with the use of cell lines derived in artificial three-dimensional supportive gels or micro-chambers. However, absence of a true tumor microenvironment and full interstitial flow, leads to less than optimal evaluation of tumor response to drug treatment. Here we report a continuous perfusion microfluidic device coupled with microscopy and image analysis for the assessment of drug effects on intact fresh tumor tissue. We have demonstrated that fine needle aspirate biopsies obtained from patient-derived xenograft models of adenocarcinoma of the lung can successfully be analyzed for their response to ex vivo drug treatment within this biopsy trapping microfluidic device, wherein a protein kinase C inhibitor, staurosporine, was used to assess tumor cell death as a proof of principle. This approach has the potential to study tumor tissue within its intact microenvironment to better understand tumor response to drug treatments and eventually to choose the most effective drug and drug combination for individual patients in a cost effective and timely manner.

Radionuclide I-131 Labeled Albumin-Paclitaxel Nanoparticles for Synergistic Combined Chemo-radioisotope Therapy of Cancer

Development of biocompatible/biodegradable materials with multiple functionalities via simple methods for cancer combination therapy has attracted great attention in recent years. Herein, paclitaxel (PTX), a popular anti-tumor chemotherapeutic drug, is used to induce the self-assembly of human serum albumin (HSA) pre-labeled with radionuclide I-131, obtaining 131I-HSA-PTX nanoparticles for combined chemotherapy and radioisotope therapy (RIT) of cancer. Such 131I-HSA-PTX nanoparticles show prolonged blood circulation time, high tumor specific uptake and excellent intra-tumor penetration ability. Interestingly, as revealed by in vivo photoacoustic imaging and ex vivo immunofluorescence staining, PTX delivered into the tumor by HSA-nanoparticle transportation can remarkably enhance the tumor local oxygen level and suppress the expression of HIF-1α, leading to greatly relieved tumor hypoxia. As the results, the combined in vivo chemotherapy & RIT with 131I-HSA-PTX nanoparticles in the animal tumor model offers excellent synergistic therapeutic efficacy, likely owing to the greatly modulated tumor microenvironment associated with PTX-based chemotherapy. Therefore, in this work, a simple yet effective therapeutic agent is developed for synergistic chemo-RIT of cancer, promising for future clinic translations in cancer treatment.

Dynamics of nanoparticle diffusion and uptake in three-dimensional cell cultures

This study aims at elucidating the effect of three-dimensional (3D) extracellular matrix on cell behaviour and nanoparticle (NP) diffusion and its consequences on NP cellular uptake mechansims. For this purpose, human dermal fibroblasts (HDF) and human fibrosarcoma (HT1080) cell lines were grown within a 3D collagen gel and exposed to model polystyrene (PS) NPs of controlled size (44 and 100nm). Results indicate that, in 3D, cell morphology dramatically changes compared to standard 2D cultures and NP diffusion within the matrix is hampered by the interaction with the collagen fibres. As a consequence, NP cellular uptake, modeled with equations describing the stoichiometric exchange between NPs and cell membrane, is significantly slowed down in 3D and in the case of 100 nm NPs, in part due to the hampered diffusion of NPs in collagen gel compared to their transport in standard cell culture medium. Furthermore, our outcomes point at a significant contribution of the cytoskeleton assembly, in particular actin microfilaments, in governing the uptake of PS NPs in a 3D environment, and also that the macropinocytosis process is preserved and is mainly involved in the internalization of PS NPs in a 3D environment. However, depending on cell type and nanoparticle size, other endocytic pathways are also implicated when moving from 2D to 3D culture systems. This work highlights the importance of studying the nano-bio interaction in experimental models that resembles in vivo conditions in order to better predict the therapeutic efficacy of drug delivery systems.

Nanomedicine based curcumin and doxorubicin combination treatment of glioblastoma with scFv-targeted micelles: In vitro evaluation on 2D and 3D tumor models

NF-κB is strongly associated with poor prognosis of different cancer types and an important factor responsible for the malignant phenotype of glioblastoma. Overcoming chemotherapy-induced resistance caused by activation of PI3K/Akt and NF-κB pathways is crucial for successful glioblastoma therapy. We developed an all-in-one nanomedicine formulation for co-delivery of a chemotherapeutic agent (topoisomerase II inhibitor, doxorubicin) and a multidrug resistance modulator (NF-κB inhibitor, curcumin) for treatment of glioblastoma due to their synergism. Both agents were incorporated into PEG-PE-based polymeric micelles. The glucose transporter-1 (GLUT1) is overexpressed in many tumors including glioblastoma. The micellar system was decorated with GLUT1 antibody single chain fragment variable (scFv) as the ligand to promote blood brain barrier transport and glioblastoma targeting. The combination treatment was synergistic (combination index, CI of 0.73) against U87MG glioblastoma cells. This synergism was improved by micellar encapsulation (CI: 0.63) and further so with GLUT1 targeting (CI: 0.46). Compared to non-targeted micelles, GLUT1 scFv surface modification increased the association of micelles (>20%, P<0.01) and the nuclear localization of doxorubicin (∼3-fold) in U87MGcells, which also translated into enhanced cytotoxicity. The increased caspase 3/7 activation by targeted micelles indicates successful apoptosis enhancement by combinatory treatment. Moreover, GLUT1 targeted micelles resulted in deeper penetration into the 3D spheroid model. The increased efficacy of combination nanoformulations on the spheroids compared to a single agent loaded, or to non-targeted formulations, reinforces the rationale for selection of this combination and successful utilization of GLUT1 scFv as a targeting agent for glioblastoma treatment.

Bioreactor-Based Tumor Tissue Engineering

This review focuses on modeling of cancer tumors using tissue engineering technology. Tumor tissue engineering (TTE) is a new method of three-dimensional (3D) simulation of malignant neoplasms. Design and development of complex tissue engineering constructs (TECs) that include cancer cells, cell-bearing scaffolds acting as the extracellular matrix, and other components of the tumor microenvironment is at the core of this approach. Although TECs can be transplanted into laboratory animals, the specific aim of TTE is the most realistic reproduction and long-term maintenance of the simulated tumor properties in vitro for cancer biology research and for the development of new methods of diagnosis and treatment of malignant neoplasms. Successful implementation of this challenging idea depends on bioreactor technology, which will enable optimization of culture conditions and control of tumor TECs development. In this review, we analyze the most popular bioreactor types in TTE and the emerging applications.

Sunflower Polymers for Folate-Mediated Drug Delivery

Polymeric delivery vehicles can improve the safety and efficacy of chemotherapy drugs by facilitating preferential tumor delivery. Polymer-drug conjugates are especially attractive carriers because additional formulation steps are not required during manufacturing, and drug release profiles can be altered based on linker choice. For clinical translation, these vehicles should also be reproducibly and controllably synthesized. Recently, we reported the development of a class of materials called "sunflower polymers," synthesized by controlled radical polymerization of hydrophilic "petals" from a cyclic multimacroinitiator "core". This synthesis strategy afforded control over the size of the polymer nanostructures based on their petal polymerization time. In this work, we demonstrate that particle size can be further tuned by varying the degree of polymerization of the cyclic core in addition to that of the petals. Additionally, we investigate the application of these materials for tumor-targeted drug delivery. We demonstrate that folate-targeted, doxorubicin-conjugated sunflower polymers undergo receptor-mediated uptake into cancer cells and pH-triggered drug release leading to cytotoxicity. These materials are attractive as drug carriers due to their discrete and small size, shielded drug cargo that can be triggered for release, and relative ease of synthesis.

Polymer nanostructures synthesized by controlled living polymerization for tumor-targeted drug delivery

The development of drug delivery systems based on well-defined polymer nanostructures could lead to significant improvements in the treatment of cancer. The design of these therapeutic nanosystems must account for numerous systemic and circulation obstacles as well as the specific pathophysiology of the tumor. Nanoparticle size and surface charge must also be carefully selected in order to maintain long circulation times, allow tumor penetration, and avoid clearance by the reticuloendothelial system (RES). Targeting ligands such as vitamins, peptides, and antibodies can improve the accumulation of nanoparticle-based therapies in tumor tissue but must be optimized to allow for intratumoral penetration. In this review, we will highlight factors influencing the design of nanoparticle therapies as well as the development of modern controlled "living" polymerization techniques (e.g. ATRP, RAFT, ROMP) that are leading to the creation of sophisticated new polymer architectures with discrete spatially-defined functional modules. These innovative materials (e.g. star polymers, polymer brushes, macrocyclic polymers, and hyperbranched polymers) combine many of the desirable properties of traditional nanoparticle therapies while substantially reducing or eliminating the need for complex formulations.

Cancer Associated Fibroblast-Derived Hepatocyte Growth Factor Inhibits the Paclitaxel-Induced Apoptosis of Lung Cancer A549 Cells by Up-Regulating the PI3K/Akt and GRP78 Signaling on a Microfluidic Platform

Tumor stroma and growth factors provide a survival environment to tumor cells and can modulate their chemoresistance by dysregulating several signal pathways. In this study, we fabricated a three-dimensional (3D) microfluidic chip using polydimethylsiloxane (PDMS) to investigate the impact of hepatocyte growth factor (HGF) from cancer-associated fibroblasts (CAF) on the Met/PI3K/AKT activation, glucose regulatory protein (GRP78) expression and the paclitaxel-induced A549 cell apoptosis. With a concentration gradient generator, the assembled chip was able to reconstruct a tumor microenvironment in vitro. We found high levels of HGF in the supernatants of CAF and the CAF matrix from the supernatants of activated HFL1 fibroblasts or HGF enhanced the levels of Met, PI3K and AKT phosphorylation and GRP78 expression in A549 cells cultured in a 3D cell chamber, which was abrogated by anti-HGF. Inhibition of Met attenuated the CAF matrix-enhanced PI3K/AKT phosphorylation and GRP78 expression while inhibition of PI3K reduced GRP78 expression, but not Met phosphorylation in A549 cells. Inhibition of GRP78 failed to modulate the CAF matrix-enhanced Met/PI3K/AKT phosphorylation in A549 cells. Furthermore, inhibition of PI3K or GRP78 enhanced spontaneous and paclitaxel-induced A549 cell apoptosis. Moreover, treatment with the CAF matrix inhibited spontaneous and medium or high dose of paclitaxel-induced A549 cell apoptosis. Inhibition of PI3K or GRP78 attenuated the CAF matrix-mediated inhibition on paclitaxel-induced A549 cell apoptosis. Our data indicated that HGF in the CAF matrix activated the Met/PI3K/AKT and up-regulated GRP78 expression, promoting chemoresistance to paclitaxel-mediated apoptosis in A549 cells. Our findings suggest that the microfluidic system may represent an ideal platform for signaling research and drug screening.

The effect of co-delivery of paclitaxel and curcumin by transferrin-targeted PEG-PE-based mixed micelles on resistant ovarian cancer in 3-D spheroids and in vivo tumors

Multicellular 3D cancer cell culture (spheroids) resemble to in vivo tumors in terms of shape, cell morphology, growth kinetics, gene expression and drug response. However, these characteristics cause very limited drug penetration into deeper parts of the spheroids. In this study, we used multi drug resistant (MDR) ovarian cancer cell spheroid and in vivo tumor models to evaluate the co-delivery of paclitaxel (PCL) and a potent NF-κB inhibitor curcumin (CUR). PCL and CUR were co-loaded into the polyethylene glycol-phosphatidyl ethanolamine (PEG-PE) based polymeric micelles modified with transferrin (TF) as the targeting ligand. Cytotoxicity, cellular association and accumulation into the deeper layers were investigated in the spheroids and compared with the monolayer cell culture. Comparing to non-targeted micelles, flow cytometry and confocal imaging proved significantly deeper and higher micelle penetration into the spheroids with TF-targeting. Both in monolayers and in spheroids, PCL cytotoxicity was significantly increased when co-delivered with CUR in non-targeted micelles or as single agent in TF-targeted micelles, whereas TF-modification of co-loaded micelles did not further enhance the cytotoxicity. In vivo tumor inhibition studies showed good correlation with the 3D cell culture experiments, which suggests the current spheroid model can be used as an intermediate model for the evaluation of co-delivery of anticancer compounds in targeted micelles.

Microfluidics for nano-pathophysiology

Nanotechnology-based drug delivery systems hold promise for innovative medical treatment of cancers. While drug materials are constantly under development, there are no practical cell-based models to assess whether these materials can reach the target tissue. Recently developed microfluidic systems have revolutionized cell-based experiments. In these systems, vascular endothelial cells and interstitium are set in microchannels that mimic microvessels. Drug permeability can be assayed in these blood vessel models under fluidic conditions that mimic blood flow. In this review, we describe device fabrication, disease model development, nanoparticle permeability assays, and the potential utility of these systems in the future.

Miniaturized pre-clinical cancer models as research and diagnostic tools

Cancer is one of the most common causes of death worldwide. Consequently, important resources are directed towards bettering treatments and outcomes. Cancer is difficult to treat due to its heterogeneity, plasticity and frequent drug resistance. New treatment strategies should strive for personalized approaches. These should target neoplastic and/or activated microenvironmental heterogeneity and plasticity without triggering resistance and spare host cells. In this review, the putative use of increasingly physiologically relevant microfabricated cell-culturing systems intended for drug development is discussed. There are two main reasons for the use of miniaturized systems. First, scaling down model size allows for high control of microenvironmental cues enabling more predictive outcomes. Second, miniaturization reduces reagent consumption, thus facilitating combinatorial approaches with little effort and enables the application of scarce materials, such as patient-derived samples. This review aims to give an overview of the state-of-the-art of such systems while predicting their application in cancer drug development.

Microfluidic chip-based technologies: emerging platforms for cancer diagnosis

The development of early and personalized diagnostic protocols is considered the most promising avenue to decrease mortality from cancer and improve outcome. The emerging microfluidic-based analyzing platforms hold high promises to fulfill high-throughput and high-precision screening with reduced equipment cost and low analysis time, as compared to traditional bulky counterparts in bench-top laboratories. This article overviewed the potential applications of microfluidic technologies for detection and monitoring of cancer through nucleic acid and protein biomarker analysis. The implications of the technologies in cancer cytology that can provide functional personalized diagnosis were highlighted. Finally, the future niches for using microfluidic-based systems in tumor screening were briefly discussed.

Color Doppler ultrasound and gamma imaging of intratumorally injected 500 nm iron-silica nanoshells

Perfluoropentane gas filled iron-silica nanoshells have been developed as stationary ultrasound contrast agents for marking tumors to guide surgical resection. It is critical to establish their long-term imaging efficacy, as well as biodistribution. This work shows that 500 nm Fe-SiO2 nanoshells can be imaged by color Doppler ultrasound over the course of 10 days in Py8119 tumor bearing mice. The 500 nm nonbiodegradable SiO2 and biodegradable Fe-SiO2 nanoshells were functionalized with diethylenetriamine pentaacetic acid (DTPA) ligand and radiolabeled with (111)In(3+) for biodistribution studies in nu/nu mice. The majority of radioactivity was detected in the liver and kidneys following intravenous (IV) administration of nanoshells to healthy animals. By contrast, after nanoshells were injected intratumorally, most of the radioactivity remained at the injection site; however, some nanoshells escaped into circulation and were distributed similarly as those given intravenously. For intratumoral delivery of nanoshells and IV delivery to healthy animals, little difference was seen between the biodistribution of SiO2 and biodegradable Fe-SiO2 nanoshells. However, when nanoshells were administered IV to tumor bearing mice, a significant increase was observed in liver accumulation of SiO2 nanoshells relative to biodegradable Fe-SiO2 nanoshells. Both SiO2 and Fe-SiO2 nanoshells accumulate passively in proportion to tumor mass, during intravenous delivery of nanoshells. This is the first report of the biodistribution following intratumoral injection of any biodegradable silica particle, as well as the first report demonstrating the utility of DTPA-(111)In labeling for studying silica nanoparticle biodistributions.

Microfluidic culture models to study the hydrodynamics of tumor progression and therapeutic response

The integration of tissue engineering strategies with microfluidic technologies has enabled the design of in vitro microfluidic culture models that better adapt to morphological changes in tissue structure and function over time. These biomimetic microfluidic scaffolds accurately mimic native 3D microenvironments, as well as permit precise and simultaneous control of chemical gradients, hydrodynamic stresses, and cellular niches within the system. The recent application of microfluidic in vitro culture models to cancer research offers enormous potential to aid in the development of improved therapeutic strategies by supporting the investigation of tumor angiogenesis and metastasis under physiologically relevant flow conditions. The intrinsic material properties and fluid mechanics of microfluidic culture models enable high-throughput anti-cancer drug screening, permit well-defined and controllable input parameters to monitor tumor cell response to various hydrodynamic conditions or treatment modalities, as well as provide a platform for elucidating fundamental mechanisms of tumor physiology. This review highlights recent developments and future applications of microfluidic culture models to study tumor progression and therapeutic targeting under conditions of hydrodynamic stress relevant to the complex tumor microenvironment.

Nanoparticle characterization: state of the art, challenges, and emerging technologies

Nanoparticles have received enormous attention as a promising tool to enhance target-specific drug delivery and diagnosis. Various in vitro and in vivo techniques are used to characterize a new system and predict its clinical efficacy. These techniques enable efficient comparison across nanoparticles and facilitate a product optimization process. On the other hand, we recognize their limitations as a prediction tool, due to inadequate applications and overly simplified test conditions. We provide a critical review of in vitro and in vivo techniques currently used for evaluation of nanoparticles and introduce emerging techniques and models that may be used complementarily.

An integrated microfluidic cell culture system for high-throughput perfusion three-dimensional cell culture-based assays: effect of cell culture model on the results of chemosensitivity assays

Although microfluidic cell culture systems are versatile tools for cellular assays, their use has yet to set in motion an evolutionary shift away from conventional cell culture methods. This situation is mainly due to technical hurdles: the operational barriers to the end-users, the lack of compatible detection schemes capable of reading out the results of a microfluidic-based cellular assay, and the lack of fundamental data to bridge the gap between microfluidic and conventional cell culture models. To address these issues, we propose a high-throughput, perfusion, three-dimensional (3-D) microfluidic cell culture system encompassing 30 microbioreactors. This integrated system not only aims to provide a user-friendly cell culture tool for biologists to perform assays but also to enable them to obtain precise data. Its technical features include (i) integration of a heater chip based on transparent indium tin oxide glass, providing stable thermal conditions for cell culturing; (ii) a microscale 3-D culture sample loading scheme that is both efficient and precise; (iii) a non-mechanical pneumatically driven multiplex medium perfusion mechanism; and (iv) a microplate reader-compatible waste medium collector array for the subsequent high throughput bioassays. In this study, we found that the 3-D culture sample loading method provided uniform sample loading [coefficient of variation (CV): 3.2%]. In addition, the multiplex medium perfusion mechanism led to reasonably uniform (CV: 3.6-6.9%) medium pumping rates in the 30 microchannels. Moreover, we used the proposed system to perform a successful cell culture-based chemosensitivity assay. To determine the effects of cell culture models on the cellular proliferation, and the results of chemosensitivity assays, we compared our data with that obtained using three conventional cell culture models. We found that the nature of the cell culture format could lead to different evaluation outcomes. Consequently, when establishing a cell culture model for in vitro cell-based assays, it might be necessary to investigate the fundamental physiological variations of the cultured cells in different culture systems to avoid any misinterpretation of data. As a whole, we have developed an integrated microfluidic cell culture system that overcomes several technical hurdles commonly encountered in the practical application of microfluidic cell culture systems, and we have obtained fundamental information to reconcile differences found with data acquired using conventional methods.

Development of an in vitro 3D tumor model to study therapeutic efficiency of an anticancer drug

The importance and advantages of three-dimensional (3D) cell cultures have been well-recognized. Tumor cells cultured in a 3D culture system as multicellular tumor spheroids (MTS) can bridge the gap between in vitro and in vivo anticancer drug evaluations. An in vitro 3D tumor model capable of providing close predictions of in vivo drug efficacy will enhance our understanding, design, and development of better drug delivery systems. Here, we developed an in vitro 3D tumor model by adapting the hydrogel template strategy to culture uniformly sized spheroids in a hydrogel scaffold containing microwells. The in vitro 3D tumor model was to closely simulate an in vivo solid tumor and its microenvironment for evaluation of anticancer drug delivery systems. MTS cultured in the hydrogel scaffold are used to examine the effect of culture conditions on the drug responses. Free MTS released from the scaffold are transferred to a microfluidic channel to simulate a dynamic in vivo microenvironment. The in vitro 3D tumor model that mimics biologically relevant parameters of in vivo microenvironments such as cell-cell and cell-ECM interactions, and a dynamic environment would be a valuable device to examine efficiency of anticancer drug and targeting specificity. These models have potential to provide in vivo correlated information to improve and optimize drug delivery systems for an effective chemotherapy.

Microfluidic 3D cell culture: potential application for tissue-based bioassays

Current fundamental investigations of human biology and the development of therapeutic drugs commonly rely on 2D monolayer cell culture systems. However, 2D cell culture systems do not accurately recapitulate the structure, function or physiology of living tissues, nor the highly complex and dynamic 3D environments in vivo. Microfluidic technology can provide microscale complex structures and well-controlled parameters to mimic the in vivo environment of cells. The combination of microfluidic technology with 3D cell culture offers great potential for in vivo-like tissue-based applications, such as the emerging organ-on-a-chip system. This article will review recent advances in the microfluidic technology for 3D cell culture and their biological applications.

Nucleic acid delivery: the missing pieces of the puzzle?

The delivery of genes or RNA interference (RNAi) agents can increase or decrease the expression of virtually any protein in a cell, and this process opens the path for cures to most diseases that afflict humans. However, the high molecular weight, anionic nature, and instability of nucleic acids in the presence of enzymes pose major obstacles to their delivery and frustrates their use as human therapies. This Account describes current ideas about the mechanisms in nonviral nucleic acid delivery and how lipidic and polymeric carriers can overcome some of the critical barriers to delivery. Over the last 20 years, researchers have developed a multitude of polymeric and lipidic vectors, but only a small fraction of these have progressed into clinical trials. None of these vectors has received FDA approval, which indicates that the current vectors do not yet have suitable properties for effective in vivo nucleic acid delivery. Nucleic acid delivery is a multistep process and inefficiencies at any stage result in a dramatic decrease in gene delivery or gene silencing. However, the majority of studies investigating synthetic vectors focus solely on optimization of endosomal escape. A small number of studies address how to improve uptake via targeted delivery, and an even smaller fraction examine the intracellular fate of the delivery systems and nucleic acid cargo. The internalization of genes into the cell nucleus remains an inefficient and mysterious process. In the case of DNA delivery, strategies are needed to increase and accelerate the migration of DNA through the cytoplasm and transport it through the nuclear membrane. siRNA delivery involves fewer barriers. siRNA is more readily released from the carrier and more resistant to enzymatic degradation, and its target is in the cytoplasm; hence, siRNA delivery systems are becoming a clinical reality. With regard to siRNA therapy, the exact cytoplasmic location of RNA-induced silencing complex (RISC) formation and activity is unknown, which makes specific targeting of the RISC for more efficient delivery difficult. Furthermore, we would like to identify the factors that favor the binding of siRNA to Ago-2. If we could understand how the half-life of siRNA and Ago-2/siRNA complex in the cytoplasm can be modulated without interfering with RISC functions that are essential for normal cell activity, we could increase siRNA delivery efficiency. In this Account, we review the current synthetic vectors and propose alternative strategies in a few cases. We also suggest how certain cellular mechanisms might be exploited to improve gene transfection and silencing. Finally, we discuss whether some carriers that deliver the siRNA to cells could also repackage the siRNA into exosomes. The exosomes would then transport the siRNA into a subsequent population of cells that manifest the siRNA effect. This piggy-back mechanism may be responsible for reported deep tissue siRNA effects using certain carriers.

A microfluidic system for investigation of extravascular transport and cellular uptake of drugs in tumors

Three-dimensional (3D) tumor models have been established in various microfluidic systems for drug delivery and resistance studies in vitro. However, one of the main drawbacks of these models is non-uniform distribution of cells, leaving regions with very low cell density within the 3D structures. As a result, molecular diffusion in the cell compartments is faster than that observed in solid tumors. To solve this problem, we developed a new technique for preparation of 3D tumor models in vitro. It was based on a microfluidic device containing three parallel channels separated by narrowly spaced posts. Tumor cells were loaded into the central channel at high density. To test the system, B16.F10 melanoma cells were perfusion-cultured overnight and the resulting 3D structure was characterized in terms of viability, density, and morphology of cells as well as transport properties of small fluorescent molecules. Immediately upon loading of tumor cells, the cell density was comparable to those observed in B16.F10 tumor tissues in vivo; and the viability of tumor cells was maintained through the overnight culture. The tumor model displayed low extracellular space and high resistance to diffusion of small molecules. For membrane-permeant molecules (e.g., Hoechst 33342), the rate of interstitial penetration was extremely slow, compared to membrane-impermeant molecules (e.g., sodium fluorescein). This versatile tumor model could be applied to in vitro studies of transport and cellular uptake of drugs and genes.

Migration dynamics of breast cancer cells in a tunable 3D interstitial flow chamber

The migration of cells such as leukocytes, tumor cells, and fibroblasts through 3D matrices is critical for regulating homeostasis and immunity and for driving pathogenesis. Interstitial flow through the extracellular matrix, which can substantially increase during inflammation and in the tumor microenvironment, can influence cell migration in multiple ways. Leukocytes and tumor cells are heterogeneous in their migration responses to flow, yet most 3D migration studies use endpoint measurements representing average characteristics. Here we present a robust new microfluidic device for 3D culture with live imaging under well-controlled flow conditions, along with a comparison of analytical methods for describing the migration behavior of heterogeneous cell populations. We then use the model to provide new insight on how interstitial flow affects MDA-MB-231 breast cancer cell invasion, phenomena that are not seen from averaged or endpoint measurements. Specifically, we find that interstitial flow increases the percentage of cells that become migratory, and increases migrational speed in about 20% of the cells. It also increases the migrational persistence of a subpopulation (5-10% of cells) in the positive or negative flow direction. Cells that migrated upstream moved faster but with less directedness, whereas cells that migrated in the direction of flow moved at slower speeds but with higher directedness. These findings demonstrate how fluid flow in the tumor microenvironment can enhance tumor cell invasion by directing a subpopulation of tumor cells in the flow direction; i.e., towards the draining lymphatic vessels, a major route of metastasis.

Development of an integrated microfluidic perfusion cell culture system for real-time microscopic observation of biological cells

This study reports an integrated microfluidic perfusion cell culture system consisting of a microfluidic cell culture chip, and an indium tin oxide (ITO) glass-based microheater chip for micro-scale perfusion cell culture, and its real-time microscopic observation. The system features in maintaining both uniform, and stable chemical or thermal environments, and providing a backflow-free medium pumping, and a precise thermal control functions. In this work, the performance of the medium pumping scheme, and the ITO glass microheater were experimentally evaluated. Results show that the medium delivery mechanism was able to provide pumping rates ranging from 15.4 to 120.0 μL·min⁻¹. In addition, numerical simulation and experimental evaluation were conducted to verify that the ITO glass microheater was capable of providing a spatially uniform thermal environment, and precise temperature control with a mild variation of ±0.3 °C. Furthermore, a perfusion cell culture was successfully demonstrated, showing the cultured cells were kept at high cell viability of 95 ± 2%. In the process, the cultured chondrocytes can be clearly visualized microscopically. As a whole, the proposed cell culture system has paved an alternative route to carry out real-time microscopic observation of biological cells in a simple, user-friendly, and low cost manner.

Proliferation behavior of E. coli in a three-dimensional in vitro tumor model

Advances in genetic engineering of non-pathogenic Escherichia coli (E. coli) have made this organism an attractive candidate for gene delivery vehicle. However, proliferation and transport behaviors of E. coli in three-dimensional (3D) tumor environment are still unclear. To this end, we developed a novel microfluidics-based tumor model that permitted direct in situ visualization of E. coli in a 3D environment with densely packed tumor cells (B16.F10 or EMT6). The E. coli was engineered to co-express two proteins invasin and mCherry (inv(+)) so that they had the ability to enter mammalian cells and could be visualized via fluorescence microscopy. E. coli expressing mCherry alone (inv(-)) was used as the control counterpart. The inv(-) bacteria proliferated to a higher extent than inv(+) bacteria in both the 3D tumor model and a 2D monolayer culture model. Meanwhile, the proliferation appeared to be tumor cell type dependent since bacteria did not proliferate as well in the EMT6 model compared to the B16.F10 model. These differences in bacterial proliferation were likely to be caused by inhibitors secreted by tumor cells, as suggested by our data from the bacterial-tumor cell monolayer co-culture experiment. The bacterial proliferation provided a driving force for E. coli spreading in the 3D interstitial space of tumors. These findings are useful for researchers to develop novel strategies for improvement of bacteria-mediated oncolysis or gene delivery in cancer treatment.

Alginate-based microfluidic system for tumor spheroid formation and anticancer agent screening

We demonstrate a microfluidic system for long-term tumor cell culture and drug testing. Three-dimensional cell culture is critical in characterizing anticancer treatments since it may provide a better model than monolayer culture of tumor cells. Breast tumor cells were encapsulated within alginate which was gelled in situ within the microchannels. Tumor spheroid formation was observed several days after cell seeding, and various concentrations of doxorubicin were applied to the encapsulated cell aggregates. Drug effects on cell viability and proliferation were measured. In future, hydrogel-based microfluidic devices can comprise part of systems which replace labor intensive screening platforms currently implemented in the laboratory, and they address a need for improving preclinical testing of cancer cell sensitivity to anti-cancer drugs.

The delivery of doxorubicin to 3-D multicellular spheroids and tumors in a murine xenograft model using tumor-penetrating triblock polymeric micelles

Doxorubicin (DOX) is an effective chemotherapeutic against a wide range of solid tumors. However, its clinical use is limited by severe side effects such as cardiotoxicity as well as inherent and acquired drug resistance of tumors. DOX encapsulation within self-assembled polymeric micelles has the potential to decrease the systemic distribution of free drug and enhance the drug accumulation in the tumor via the enhanced permeability and retention (EPR). In this study, DOX was encapsulated in micelles composed of poly (ethylene oxide)-poly [(R)-3-hydroxybutyrate]-poly (ethylene oxide) (PEO-PHB-PEO) triblock copolymers. Micelle size, DOX loading and DOX release were characterized. To evaluate DOX activity, micelles were tested in both monolayer cell cultures and three-dimensional (3-D) multicellular spheroids (MCS) that mimic solid tumors. Antitumor activity in vivo was further studied with tumor-bearing mice. The micelles improved the efficiency of Dox penetration in 3-D MCS compared with free DOX. Efficient cell killing by Dox-micelles in both monolayer cells and 3-D MCS was also demonstrated. Finally, DOX-loaded micelles mediate efficient tumor delivery from tail vein injections to tumor-bearing mice with much less toxicity compared with free DOX.

A review of three-dimensional in vitro tissue models for drug discovery and transport studies

The use of animal models in drug discovery studies presents issues with feasibility and ethical concerns. To address these limitations, in vitro tissue models have been developed to provide a means for systematic, repetitive, and quantitative investigation of drugs. By eliminating or reducing the need for animal subjects, these models can serve as platforms for more tightly controlled, high-throughput screening of drugs and for pharmacokinetic and pharmacodynamic analyses of drugs. The focus of this review is three-dimensional (3D) tissue models that can capture cell-cell and cell-matrix interactions. Compared to the 2D culture of cell monolayers, 3D models more closely mimic native tissues since the cellular microenvironment established in the 3D models often plays a significant role in disease progression and cellular responses to drugs. A growing body of research has been published in the literature, which highlights the benefits of the 3D in vitro models of various tissues. This review provides an overview of some successful 3D in vitro models that have been developed to mimic liver, breast, cardiac, muscle, bone, and corneal tissues as well as malignant tissues in solid tumors.

A multichamber fluidic device for 3D cultures under interstitial flow with live imaging: development, characterization, and applications

Interstitial flow is an important biophysical cue that can affect capillary morphogenesis, tumor cell migration, and fibroblast remodeling of the extracellular matrix, among others. Current models that incorporate interstitial flow and that are suitable for live imaging lack the ability to perform multiple simultaneous experiments, for example, to compare effects of growth factors, extracellular matrix composition, etc. We present a nine-chamber radial flow device that allows simultaneous 3D fluidic experiments for relatively long-term culture with live imaging capabilities. Flow velocity profiles were characterized by fluorescence recovery after photobleaching (FRAP) for flow uniformity and estimating the hydraulic conductivity. We demonstrate lymphatic and blood capillary morphogenesis in fibrin gels over 10 days, comparing flow with static conditions as well as the effects of an engineered variant of VEGF that binds fibrin via Factor XIII. We also demonstrate the culture of contractile fibroblasts and co-cultures with tumor cells for modeling the tumor microenvironment. Therefore, this device is useful for studies of capillary morphogenesis, cell migration, contractile cells like fibroblasts, and multicellular cultures, all under interstitial flow.