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Cancer-associated fibroblasts (CAFs) in the cancer microenvironment play an essential role in metastasis. Differentiation of endothelial cells into CAFs is induced by cancer cell-derived exosomes secreted from cancer cells that transfer molecular signals to surrounding cells. Differentiated CAFs facilitate migration of cancer cells to different regions through promoting extracellular matrix (ECM) modifications. However, in vitro models in which endothelial cells exposed to cancer cell-derived exosomes secreted from various cancer cell types differentiate into CAFs or a microenvironmentally controlled model for investigating cancer cell invasion by CAFs have not yet been studied. In this study, we propose a three-dimensional in vitro cancer cell invasion model for real-time monitoring of the process of forming a cancer invasion site through CAFs induced by exosomes isolated from three types of cancer cell lines. The invasiveness of cancer cells with CAFs induced by cancer cell-derived exosomes (eCAFs) was significantly higher than that of CAFs induced by cancer cells (cCAFs) through physiological and genetic manner. In addition, different genetic tendencies of the invasion process were observed in the process of invading cancer cells according to CAFs. Our 3D microfluidic platform helps to identify specific interactions among multiple factors within the cancer microenvironment and provides a model for cancer drug development.

For decades, scientists have been using two-dimensional cell culture platforms for high-throughput drug screening of anticancer drugs. Growing evidence indicates that the results of anti-cancer drug screening vary with the cell culture microenvironment, and this variation has been proposed as a reason for the high failure rate of clinical trials. Since the culture condition-dependent drug sensitivity of anti-cancer drugs may negatively impact the identification of clinically effective drug candidates, more reliable in vitro cancer platforms are urgently needed. In this review article, we provide an overview of how cell culture conditions can alter drug efficacy and highlight the importance of developing more reliable cancer drug testing platforms for use in the drug discovery process. The environmental factors that can alter drug delivery and efficacy are reviewed. Based on these observations of chemoresistant tumor physiology, we summarize the recent advances in the fabrication of in vitro cancer models and the model-dependent cytotoxicity of anti-cancer drugs, with a particular focus on engineered environmental factors in these platforms. It is believed that more physiologically relevant cancer models can revolutionize the drug discovery process., Competing Interests: Conflict of Interest: The authors declare no conflict of interest.

Cancer-associated fibroblasts (CAFs) play a pivotal role in tumor growth, but very little has been known about its characteristics and origin. Recently, cancer-derived exosome has been suggested to transdifferentiate CAFs, by a new mechanism of endothelial to mesenchymal transition (EndMT), initiating angiogenic processes and triggering metastatic evolution. However, an enabling tool in vitro is yet to be developed to investigate complicated procedures of the EndMT and the transdifferentiation under reconstituted tumor microenvironment. Here we proposed an in vitro microfluidic model which enables to monitor a synergetic effect of complex tumor microenvironment in situ, including extracellular matrix (ECM), interstitial flow and environmental exosomes. The number of CAFs differentiated from human umbilical vein endothelial cells (HUVECs) increased with melanoma-derived exosomes, presenting apparent morphological and molecular changes with pronounced motility. Mesenchymal stem cell (MSC)-derived exosomes were found to suppress EndMT, induce angiogenesis and maintain vascular homeostasis, while cancer-derived exosomes promoted EndMT. Capabilities of the new microfluidic model exist in precise regulation of the complex tumor microenvironment and therefore successful reconstitution of 3D microvasculature niches, enabling in situ investigation of EndMT procedure between various cell types., Statement of Significance: This study presents an in vitro 3D EndMT model to understand the progress of the CAF generation by recapitulating the 3D tumor microenvironment in a microfluidic device. Both cancer-derived exosomes and interstitial fluid flow synergetically played a pivotal role in the EndMT and consequent formation of CAFs through a collagen-based ECM. Our approach also enabled the demonstration of a homeostatic capability of MSC-derived exosomes, ultimately leading to the recovery of CAFs back to endothelial cells. The in vitro 3D EndMT model can serve as a powerful tool to validate exosomal components that could be further developed to anti-cancer drugs., (Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

In this study, we demonstrate cell culture platforms that can provide a microenvironment similar to in vivo conditions so that in vivo-compatible drug testing results can be obtained from the in vitro experiments. To realize such in vivo microenvironment-mimetic platforms, different culture platforms such as a three-dimensional (3D) cell aggregate film, fluidic environment within a microfluidic system or extracellular matrix (ECM) coating were established. The tumor cell growth rate and sensitivity to doxorubicin (DOX) were studied using the glioblastoma cell line T98G. When 3 D spheroids were cultured, they grew significantly slower than under other culture conditions. When the cells were treated with DOX, the anticancer drug could not efficiently penetrate the 3 D spheroids to inhibit cell growth. When cultured on the Matrigel-coated culture vessel, T98G cells grew even in the presence of DOX, demonstrating chemoresistance. Nonetheless, in the 2D culture plate and in the microfluidic chip, cell growth decreased with DOX treatment and the binding ability was lost. These results indicate that the cells reacted differently to the same anticancer drug depending on the culture microenvironment. We believe that the development of a more physiologically relevant tumor cell culture platform will lead to more reliable antitumor drug responses.

Physiologically, brain tumors interact with surrounding vascular and glial cells, and change their responses to survive in brain tissue‐specific microenvironments. A major difficulty in brain tumor treatment is caused by the organism's high resistance to pharmaceutical drugs and poor blood–brain barrier (BBB) penetration. Therefore, mimicking the physiological environment of brain tumors on in vitro platforms can aid in predicting the cellular response to drugs. Here, an engineered 3D human glioblastoma in vitro platform that is integrated with a tricultured BBB is presented. First, the barrier function of the constructed BBB model and its reversibility are characterized, after administrating BBB‐opening agents through the microvasculature. The brain tumor cells that are cocultured in the BBB show a more aggressive growth pattern and high drug resistance, as well as secreting high concentrations of inflammatory cytokines. Finally, the delivery of BBB‐nonpenetrating drugs are promoted by chemically opening the BBB. The results of this study indicate that the platform can potentially study the physiology of the BBB, and monitor drug responses based on the interaction of the brain tumor and BBB. [ABSTRACT FROM AUTHOR]

Tumor cell heterogeneity with distinct phenotypes, genotypes, and epigenetic states as well as the complex tumor microenvironment is major challenges for cancer diagnosis and treatment. There have been substantial advances in our knowledge of tumor biology and in the capabilities of available biological analysis tools; however, the absence of physiologically relevant in vitro testing platforms limits our ability to gain an in‐depth understanding of the role of the tumor microenvironment in cancer pathology. In this review, recent advances in engineered tumor microenvironments to advance cancer research and drug discovery are presented, including tumor spheroids, microfluidic chips, paper scaffolds, hydrogel‐based engineered tissues, 3D bioprinted scaffolds, and multiscale topography. Furthermore, how these technologies address the specific characteristics of the native tumor microenvironment is described. Through the comparison of these biomimetic 3D tumor models to conventional 2D culture models, the validity and physiological relevance of these platforms for fundamental in vitro studies of the tumor biology, as well as their potential use in drug screening applications, is also discussed. [ABSTRACT FROM AUTHOR]