A liver microphysiological system of tumor cell dormancy and inflammatory responsiveness is affected by scaffold properties

Liver 'organ on a chip'

The liver plays critical roles in both homeostasis and pathology. It is the major site of drug metabolism in the body and, as such, a common target for drug-induced toxicity and is susceptible to a wide range of diseases. In contrast to other solid organs, the liver possesses the unique ability to regenerate. The physiological importance and plasticity of this organ make it a crucial system of study to better understand human physiology, disease, and response to exogenous compounds. These aspects have impelled many to develop liver tissue systems for study in isolation outside the body. Herein, we discuss these biologically engineered organoids and microphysiological systems. These aspects have impelled many to develop liver tissue systems for study in isolation outside the body. Herein, we discuss these biologically engineered organoids and microphysiological systems.

Functional hepatocyte clusters on bioactive blend silk matrices towards generating bioartificial liver constructs

The creation of in vitro functional hepatic tissue simulating micro-environmental niche of native liver is a keen area of research due to its demand in bioartificial liver (BAL) and cell-based tissue engineering. Here, we investigated the potential of novel blend (BA) silk scaffold fabricated by blending mulberry (Bombyx mori, BM) silk fibroin with cell adhesion motif (RGD) rich non-mulberry (Antheraea assamensis, AA) silk fibroin, in generating a functional liver construct. Three-dimensional (3D) porous silk scaffolds (BM, AA and BA) were physico-chemically characterized and functionally evaluated using human hepatocarcinoma cells (HepG2) and primary neonatal rat hepatocytes. The growth and distribution of hepatocytes within the scaffolds were tracked by FESEM, alamar blue proliferation assay and live/dead staining. Hemocompatible BA scaffolds supported the formation of high density hepatocyte clusters, facilitating cell-matrix and cell-cell interactions. Blend scaffolds evinced enhanced liver-specific functions of cultured hepatocytes in terms of albumin synthesis, urea synthesis and cytochrome P450 enzyme activity over 21 days. Subcutaneous implantation of scaffolds demonstrated minimal macrophage infiltration in blend scaffolds. These findings substantiate that the integral property of blend (BA) scaffold offers a befitting environment by influencing spheroidal growth of hepatocytes with enhanced biological activity. Collectively, the present study provides a new 3D bio-matrix niche for growing functional liver cells that would have future prospects in BAL as well as regenerative medicine.

STATEMENT OF SIGNIFICANCE

An end stage liver disease called cirrhosis perturbs the self-healing ability and physiological functions of liver. Due to the scarcity of healthy donors, a functional in vitro hepatic construct retaining the liver-specific functions is in great demand for its prospects in bioartificial liver (BAL) and cell-based tissue engineering. Physicochemical attributes of a matrix influence the behavior of cultured hepatocytes in terms of attachment, morphology and functionality. Mulberry and non-mulberry silk fibroin presents unique amino acid sequence with difference in hydrophobicity and crystallinity. Considering this, the present study focuses on the development of a suitable three-dimensional (3D) bioactive matrix incorporating both mulberry silk fibroin and cell adhesion motif (RGD) rich non-mulberry silk fibroin. Porous silk blend scaffolds facilitated the formation of hepatocyte clusters with enhanced liver-specific functions emphasizing both cell-cell and cell-matrix interactions. Hemocompatibility and integral property of blend scaffolds offers a biological niche for seeding functional liver cells that would have future prospects in biohybrid devices.

Tumor Metastasis in the Microcirculation

Tumor cell metastasis through blood circulation is a complex process and is one of the great challenges in cancer research as metastatic spread is responsible for ∼90% of cancer-related mortality. Tumor cell intravasation into, arrest and adhesion at, and extravasation from the microvessel walls are critical steps in metastatic spread. Understanding these steps may lead to new therapeutic concepts for tumor metastasis. Vascular endothelium forming the microvessel wall and the glycocalyx layer at its surface are the principal barriers to and regulators of the material exchange between circulating blood and body tissues. The cleft between adjacent endothelial cells is the principal pathway for water and solute transport through the microvessel wall in health. Recently, this cleft has been found to be the location for tumor cell adhesion and extravasation. The blood-flow-induced hydrodynamic factors such as shear rates and stresses, shear rate and stress gradients, as well as vorticities, especially at the branches and turns of microvasculatures, also play important roles in tumor cell arrest and adhesion. This chapter therefore reports the current advances from in vivo animal studies and in vitro culture cell studies to demonstrate how the endothelial integrity or microvascular permeability, hydrodynamic factors, microvascular geometry, cell adhesion molecules, and surrounding extracellular matrix affect critical steps of tumor metastasis in the microcirculation.

3D Miniaturization of Human Organs for Drug Discovery

"Engineered human organs" hold promises for predicting the effectiveness and accuracy of drug responses while reducing cost, time, and failure rates in clinical trials. Multiorgan human models utilize many aspects of currently available technologies including self-organized spherical 3D human organoids, microfabricated 3D human organ chips, and 3D bioprinted human organ constructs to mimic key structural and functional properties of human organs. They enable precise control of multicellular activities, extracellular matrix (ECM) compositions, spatial distributions of cells, architectural organizations of ECM, and environmental cues. Thus, engineered human organs can provide the microstructures and biological functions of target organs and advantageously substitute multiscaled drug-testing platforms including the current in vitro molecular assays, cell platforms, and in vivo models. This review provides an overview of advanced innovative designs based on the three main technologies used for organ construction leading to single and multiorgan systems useable for drug development. Current technological challenges and future perspectives are also discussed.

Inflammatory cytokine IL-8/CXCL8 promotes tumour escape from hepatocyte-induced dormancy

Background:

Breast cancers can recur after a long latency period following ‘successful’ primary treatments. Chronic inflammation significantly correlates with reduced diseased-free survival in breast cancer patients and could be a point of intervention to prevent recurrence. Liver is among the main sites of breast cancer recurrence. Thus, we hypothesise that inflammatory signals from hepatic stellate cells, the major inflammatory regulators in the sinusoid, could stimulate dormant cancer cells to emerge.

Methods:

We utilise in vitro co-culture of breast cancer cells with stellate cells and an ex vivo 3D human liver micro-physiologic system to identify stellate cells-derived factors that mediate tumour emergence.

Results:

Activated, but not quiescent, hepatic stellate cells secreted soluble factors to induce the proliferation of MCF7 and MDA-MB231 cancer cells. IL-8 and MCP-1 were highly secreted by the activated stellate cells and primary human non-parenchymal cells. IL-8 significantly reduced serum-starvation growth arrest on MDA-MB231 cells in vitro and increased cancer proliferation ex vivo. Blocking IL-8Rb/CXCR2 reduced IL-8-induced cancer growth and proliferation.

Conclusions:

Activated stellate cells can induce breast cancer emergence from dormancy in the liver by secreting inflammatory cytokines. Preventing liver inflammation or disrupting the subsequent key cytokines may prevent metastatic outgrowth.

Bi-directional exosome-driven intercommunication between the hepatic niche and cancer cells

BACKGROUND

Our understanding of the multiple roles exosomes play during tumor progression is still very poor and the contribution of the normal tissue derived exosomes in distant seeding and tumor outgrowth has also not been widely appreciated.

METHODS

Using our all-human liver microphysiological system (MPS) platform as a model to closely recapitulate the early metastatic events, we isolated exosomes from both tumor cells and liver microenvironment.

RESULTS

We observed that while priming of the hepatic niche (HepN) with MDA-231 breast cancer derived exosomes facilitated seeding of the cancer cells in the liver, subsequent tumor outgrowth was diminished; this was consistent with increased entry into dormancy. We found that hepatic niche (HepN) derived exosomes contribute significantly to the exosome pool and are distinguished from cancer derived exosomes based on their size, protein and miRNA content. By Ingenuity Pathway Analysis (IPA) of the miRNA content of the HepN, MDA-231/HepN and MDA-231 cells we showed that the HepN derived exosomes affect the breast cancer cells by suppressing pathways involved in cancer cell proliferation and invasion. More importantly exposure of MDA-231 and MDA-468 cells to purified normal HepN derived exosomes, induced changes in the cells consistent with a Mesenchymal to Epithelial reverting Transition (MErT). miRNA arrays performed on MDA-231 treated with Hum Hep/NPC derived exosomes showed significant changes in the levels of a select number of miRNAs involved in epithelial cell differentiation and miRNAs, such as miR186, miR23a and miR205, from our top and bottom bins have previously been reported to regulate E-cadherin transcription and MErT induction in various cancer types. Consistently HepN derived exosome treatment of breast and prostate cancer lines lead to a transient induction of E-cadherin and ZO-1 at the protein level and a more epithelial-like morphology of the cells.

CONCLUSIONS

Collectively our data revealed a novel mechanism of regulation of the metastatic cascade, showing a well-orchestrated, timely controlled crosstalk between the cancer cells and the HepN and implicating for the first time the normal tissue/HepN derived exosomes in enabling seeding and entry into dormancy of the cancer cells at the metastatic site.

Integrated gut/liver microphysiological systems elucidates inflammatory inter-tissue crosstalk

A capability for analyzing complex cellular communication among tissues is important in drug discovery and development, and in vitro technologies for doing so are required for human applications. A prominent instance is communication between the gut and the liver, whereby perturbations of one tissue can influence behavior of the other. Here, we present a study on human gut‐liver tissue interactions under normal and inflammatory contexts, via an integrative multi‐organ platform comprising human liver (hepatocytes and Kupffer cells), and intestinal (enterocytes, goblet cells, and dendritic cells) models. Our results demonstrated long‐term (>2 weeks) maintenance of intestinal (e.g., barrier integrity) and hepatic (e.g., albumin) functions in baseline interaction. Gene expression data comparing liver in interaction with gut, versus isolation, revealed modulation of bile acid metabolism. Intestinal FGF19 secretion and associated inhibition of hepatic CYP7A1 expression provided evidence of physiologically relevant gut‐liver crosstalk. Moreover, significant non‐linear modulation of cytokine responses was observed under inflammatory gut‐liver interaction; for example, production of CXCR3 ligands (CXCL9,10,11) was synergistically enhanced. RNA‐seq analysis revealed significant upregulation of IFNα/β/γ signaling during inflammatory gut‐liver crosstalk, with these pathways implicated in the synergistic CXCR3 chemokine production. Exacerbated inflammatory response in gut‐liver interaction also negatively affected tissue‐specific functions (e.g., liver metabolism). These findings illustrate how an integrated multi‐tissue platform can generate insights useful for understanding complex pathophysiological processes such as inflammatory organ crosstalk. Biotechnol. Bioeng. 2017;114: 2648–2659. © 2017 Wiley Periodicals, Inc.

A Pathway to Personalizing Therapy for Metastases Using Liver-on-a-Chip Platforms

Metastasis accounts for most cancer-related deaths. The majority of solid cancers, including those of the breast, colorectum, prostate and skin, metastasize at significant levels to the liver due to its hemodynamic as well as tumor permissive microenvironmental properties. As this occurs prior to detection and treatment of the primary tumor, we need to target liver metastases to improve patients' outcomes. Animal models, while proven to be useful in mechanistic studies, do not represent the heterogeneity of human population especially in drug metabolism lack proper human cell-cell interactions, and this gap between animals and humans results in costly and inefficient drug discovery. This underscores the need to accurately model the human liver for disease studies and drug development. Further, the occurrence of liver metastases is influenced by the primary tumor type, sex and race; thus, modeling these specific settings will facilitate the development of personalized/targeted medicine for each specific group. We have adapted such all-human 3D ex vivo hepatic microphysiological system (MPS) (a.k.a. liver-on-a-chip) to investigate human micrometastases. This review focuses on the sources of liver resident cells, especially the iPS cell-derived hepatocytes, and examines some of the advantages and disadvantages of these sources. In addition, this review also examines other potential challenges and limitations in modeling human liver.

Biomimetic strategies to recapitulate organ specific microenvironments for studying breast cancer metastasis

The progression of breast cancer from the primary tumor setting to the metastatic setting is the critical event defining Stage IV disease, no longer considered curable. The microenvironment at specific organ sites is known to play a key role in influencing the ultimate fate of metastatic cells; yet microenvironmental mediated-molecular mechanisms underlying organ specific metastasis in breast cancer are not well understood. This review discusses biomimetic strategies employed to recapitulate metastatic organ microenvironments, particularly, bone, liver, lung and brain to elucidate the mechanisms dictating metastatic breast cancer cell homing and colonization. These biomimetic strategies include in vitro techniques such as biomaterial-based co-culturing techniques, microfluidics, organ-mimetic chips, bioreactor technologies, and decellularized matrices as well as cutting edge in vivo techniques to better understand the interactions between metastatic breast cancer cells and the stroma at the metastatic site. The advantages and disadvantages of these systems are discussed. In addition, how creation of biomimetic models will impact breast cancer metastasis research and their broad utility is explored.