Murine precision-cut liver slices (PCLS): a new tool for studying tumor microenvironments and cell signaling ex vivo

Adhesion of pancreatic tumor cell clusters by desmosomal molecules enhances early liver metastases formation

Desmosomes are intercellular adhesion complexes providing mechanical coupling and tissue integrity. Previously, a correlation of desmosomal molecule expression with invasion and metastasis formation in several tumor entities was described together with a relevance for circulating tumor cell cluster formation. Here, we investigated the contribution of the desmosomal core adhesion molecule desmoglein-2 (DSG2) to the initial steps of liver metastasis formation by pancreatic cancer cells using a novel ex vivo liver perfusion mouse model. We applied the pancreatic ductal adenocarcinoma cell line AsPC-1 with and without a knockout (KO) of DSG2 and generated mouse lines with a hepatocyte-specific KO of the known interacting partners of DSG2 (DSG2 and desmocollin-2). Liver perfusion with DSG2 KO AsPC-1 cells led to smaller circulating cell clusters and a reduced number of cells adhering to murine livers compared to control cells. While this was independent of the expression levels of desmosomal adhesion molecules in hepatocytes, we show that increased cluster size of cancer cells, which correlates with stronger cell-cell adhesion and expression of desmosomal molecules, is a major factor contributing to the early phase of metastatic spreading. In conclusion, impaired desmosomal adhesion results in reduced circulating cell cluster size, which is relevant for seeding and attachment of metastatic cells to the liver.

Multiscale transport and 4D time-lapse imaging in precision-cut liver slices (PCLS)

Background

Monitoring cellular processes across different levels of complexity, from the cellular to the tissue scale, is important for understanding tissue structure and function. However, it is challenging to monitor and estimate these structural and dynamic interactions within three-dimensional (3D) tissue models.

Objective

The aim of this study was to design a method for imaging, tracking, and quantifying 3D changes in cell morphology (shape and size) within liver tissue, specifically a precision-cut liver slice (PCLS). A PCLS is a 3D model of the liver that allows the study of the structure and function of liver cells in their native microenvironment.

Methods

Here, we present a method for imaging liver tissue during anisosmotic exposure in a multispectral four-dimensional manner. Three metrics of tissue morphology were measured to quantify the effects of osmotic stress on liver tissue. We estimated the changes in the volume of whole precision cut liver slices, quantified the changes in nuclei position, and calculated the changes in volumetric responses of tissue-embedded cells.

Results

During equilibration with cell-membrane-permeating and non-permeating solutes, the whole tissue experiences shrinkage and expansion. As nuclei showed a change in position and directional displacement under osmotic stress, we demonstrate that nuclei could be used as a probe to measure local osmotic and mechanical stress. Moreover, we demonstrate that cells change their volume within tissue slices as a result of osmotic perturbation and that this change in volume is dependent on the position of the cell within the tissue and the duration of the exposure.

Conclusion

The results of this study have implications for a better understanding of multiscale transport, mechanobiology, and triggered biological responses within complex biological structures.

In Vitro Models for the Study of Liver Biology and Diseases: Advances and Limitations

In vitro models of liver (patho)physiology, new technologies, and experimental approaches are progressing rapidly. Based on cell lines, induced pluripotent stem cells or primary cells derived from mouse or human liver as well as whole tissue (slices), such in vitro single- and multicellular models, including complex microfluidic organ-on-a-chip systems, provide tools to functionally understand mechanisms of liver health and disease. The International Society of Hepatic Sinusoidal Research (ISHSR) commissioned this working group to review the currently available in vitro liver models and describe the advantages and disadvantages of each in the context of evaluating their use for the study of liver functionality, disease modeling, therapeutic discovery, and clinical applicability.

Recent advances in organotypic tissue slice cultures for anticancer drug development

Organotypic tissue slice culture is established from animal or patient tissues and cultivated in an in vitro ecosystem. This technique has made countless contributions to anticancer drug development due to the vast number of advantages, such as the preservation of the cell repertoire and immune components, identification of invasive ability of tumors, toxicity determination of compounds, quick assessment of therapeutic efficacy, and high predictive performance of drug responses. Importantly, it serves as a reliable tool to stratify therapeutic responders from nonresponders and select the optimal standard-of-care treatment regimens for personalized medicine, which is expected to become a potent platform and even the gold standard for anticancer drug screening of individualization in the near future.

Drug Repurposing by Tumor Tissue Editing

The combinatory use of drugs for systemic cancer therapy commonly aims at the direct elimination of tumor cells through induction of apoptosis. An alternative approach becomes the focus of attention if biological changes in tumor tissues following combinatory administration of regulatorily active drugs are considered as a therapeutic aim, e.g., differentiation, transdifferentiation induction, reconstitution of immunosurveillance, the use of alternative cell death mechanisms. Editing of the tumor tissue establishes new biological ‘hallmarks’ as a ‘pressure point’ to attenuate tumor growth. This may be achieved with repurposed, regulatorily active drug combinations, often simultaneously targeting different cell compartments of the tumor tissue. Moreover, tissue editing is paralleled by decisive functional changes in tumor tissues providing novel patterns of target sites for approved drugs. Thus, agents with poor activity in non-edited tissue may reveal new clinically meaningful outcomes. For tissue editing and targeting edited tissue novel requirements concerning drug selection and administration can be summarized according to available clinical and pre-clinical data. Monoactivity is no pre-requisite, but combinatory bio-regulatory activity. The regulatorily active dose may be far below the maximum tolerable dose, and besides inhibitory active drugs stimulatory drug activities may be integrated. Metronomic scheduling often seems to be of advantage. Novel preclinical approaches like functional assays testing drug combinations in tumor tissue are needed to select potential drugs for repurposing. The two-step drug repurposing procedure, namely establishing novel functional systems states in tumor tissues and consecutively providing novel target sites for approved drugs, facilitates the systematic identification of drug activities outside the scope of any original clinical drug approvals.

Evaluation of a Three-Dimensional Primary Human Hepatocyte Spheroid Model: Adoption and Industrialization for the Enhanced Detection of Drug-Induced Liver Injury

Drug-induced liver injury is a leading cause of compound attrition during both preclinical and clinical drug development, and early strategies are in place to tackle this recurring problem. Human-relevant in vitro models that are more predictive of hepatotoxicity hazard identification, and that could be employed earlier in the drug discovery process, would improve the quality of drug candidate selection and help reduce attrition. We present an evaluation of four human hepatocyte in vitro models of increasing culture complexity (i.e., two-dimensional (2D) HepG2 monolayers, hepatocyte sandwich cultures, three-dimensional (3D) hepatocyte spheroids, and precision-cut liver slices), using the same tool compounds, viability end points, and culture time points. Having established the improved prediction potential of the 3D hepatocyte spheroid model, we describe implementing this model into an industrial screening setting, where the challenge was matching the complexity of the culture system with the scale and throughput required. Following further qualification and miniaturization into a 384-well, high-throughput screening format, data was generated on 199 compounds. This clearly demonstrated the ability to capture a greater number of severe hepatotoxins versus the current routine 2D HepG2 monolayer assay while continuing to flag no false-positive compounds. The industrialization and miniaturization of the 3D hepatocyte spheroid complex in vitro model demonstrates a significant step toward reducing drug attrition and improving the quality and safety of drugs, while retaining the flexibility for future improvements, and has replaced the routine use of the 2D HepG2 monolayer assay at GlaxoSmithKline.

Organotypic-liver slide culture systems to explore the role of extracellular vesicles in pancreatic cancer metastatic behavior and guide new therapeutic approaches

Introduction: Recent studies suggested that extracellular vesicles (EVs) play a role both in the metastatic niche formation and in the progression of several tumors, including pancreatic cancer. In particular, the effects of EVs on metastasis should be studied in model systems that take into account both the tumor cells and the metastatic site/tumor microenvironment. Studies with labeled EVs or EV-secreting cells in ex vivo models will reflect the physiological and pathological functions of EVs. The organotypic-tissue slide culture systems can fulfill such a role.Areas covered: This review provides an overview of available organotypic-culture slide systems. We specifically focus on the assay system of liver culture-slides in combination with pancreatic tumors, which can be modulated to test the efficacy of new therapeutic approaches.Expert opinion: The intercellular exchange of EVs has emerged as a biologically relevant phenomenon to drive cancer metastasis. However, further models need to be developed to better elucidate the functional roles of EVs. The use of novel organotypic slide culture systems provides the opportunity to explore the role of EVs in the metastatic behavior of pancreatic cancer, decreasing the use of costly and cumbersome organoid or animal models.

Best Practices and Progress in Precision-Cut Liver Slice Cultures

Thirty-five years ago, precision-cut liver slices (PCLS) were described as a promising tool and were expected to become the standard in vitro model to study liver disease as they tick off all characteristics of a good in vitro model. In contrast to most in vitro models, PCLS retain the complex 3D liver structures found in vivo, including cell–cell and cell–matrix interactions, and therefore should constitute the most reliable tool to model and to investigate pathways underlying chronic liver disease in vitro. Nevertheless, the biggest disadvantage of the model is the initiation of a procedure-induced fibrotic response. In this review, we describe the parameters and potential of PCLS cultures and discuss whether the initially described limitations and pitfalls have been overcome. We summarize the latest advances in PCLS research and critically evaluate PCLS use and progress since its invention in 1985.

Organotypic platform for studying cancer cell metastasis

Metastasis is the leading cause of mortality in cancer patients. To migrate to distant sites, cancer cells would need to adapt their behaviour in response to different tissue environments. Thus, it is essential to study this process in models that can closely replicate the tumour microenvironment. Here, we evaluate the use of organotypic liver and brain slices to study cancer metastasis. Morphological and viability parameters of the slices were monitored daily over 3 days in culture to assess their stability as a realistic 3D tissue platform for in vitro metastatic assays. Using these slices, we evaluated the invasion of MDA-MB-231 breast cancer cells and of a subpopulation that was selected for increased motility. We show that the more aggressive invasion of the selected cells likely resulted not only from their lower stiffness, but also from their lower adhesion to the surrounding tissue. Different invasion patterns in the brain and liver slices were observed for both subpopulations. Cells migrated faster in the brain slices (with an amoeboid-like mode) compared to in the liver slices (where they migrated with mesenchymal or collective migration-like modes). Inhibition of the Ras/MAPK/ERK pathway increased cell stiffness and adhesion forces, which resulted in reduced invasiveness. These results illustrate the potential for organotypic tissue slices to more closely mimic in vivo conditions during cancer cell metastasis than most in vitro models.

Patient-Derived Organoids as a Model for Cancer Drug Discovery

In the search for the ideal model of tumours, the use of three-dimensional in vitro models is advancing rapidly. These are intended to mimic the in vivo properties of the tumours which affect cancer development, progression and drug sensitivity, and take into account cell–cell interactions, adhesion and invasiveness. Importantly, it is hoped that successful recapitulation of the structure and function of the tissue will predict patient response, permitting the development of personalized therapy in a timely manner applicable to the clinic. Furthermore, the use of co-culture systems will allow the role of the tumour microenvironment and tissue–tissue interactions to be taken into account and should lead to more accurate predictions of tumour development and responses to drugs. In this review, the relative merits and limitations of patient-derived organoids will be discussed compared to other in vitro and ex vivo cancer models. We will focus on their use as models for drug testing and personalized therapy and how these may be improved. Developments in technology will also be considered, including the use of microfluidics, 3D bioprinting, cryopreservation and circulating tumour cell-derived organoids. These have the potential to enhance the consistency, accessibility and availability of these models.

A Bioreactor Technology for Modeling Fibrosis in Human and Rodent Precision-Cut Liver Slices

Precision cut liver slices (PCLSs) retain the structure and cellular composition of the native liver and represent an improved system to study liver fibrosis compared to two-dimensional mono- or co-cultures. The aim of this study was to develop a bioreactor system to increase the healthy life span of PCLSs and model fibrogenesis. PCLSs were generated from normal rat or human liver, or fibrotic rat liver, and cultured in our bioreactor. PCLS function was quantified by albumin enzyme-linked immunosorbent assay (ELISA). Fibrosis was induced in PCLSs by transforming growth factor beta 1 (TGFβ1) and platelet-derived growth factor (PDGFββ) stimulation ± therapy. Fibrosis was assessed by gene expression, picrosirius red, and α-smooth muscle actin staining, hydroxyproline assay, and soluble ELISAs. Bioreactor-cultured PCLSs are viable, maintaining tissue structure, metabolic activity, and stable albumin secretion for up to 6 days under normoxic culture conditions. Conversely, standard static transwell-cultured PCLSs rapidly deteriorate, and albumin secretion is significantly impaired by 48 hours. TGFβ1/PDGFββ stimulation of rat or human PCLSs induced fibrogenic gene expression, release of extracellular matrix proteins, activation of hepatic myofibroblasts, and histological fibrosis. Fibrogenesis slowly progresses over 6 days in cultured fibrotic rat PCLSs without exogenous challenge. Activin receptor-like kinase 5 (Alk5) inhibitor (Alk5i), nintedanib, and obeticholic acid therapy limited fibrogenesis in TGFβ1/PDGFββ-stimulated PCLSs, and Alk5i blunted progression of fibrosis in fibrotic PCLS. Conclusion: We describe a bioreactor technology that maintains functional PCLS cultures for 6 days. Bioreactor-cultured PCLSs can be successfully used to model fibrogenesis and demonstrate efficacy of antifibrotic therapies.

From in vitro to ex vivo: subcellular localization and uptake of graphene quantum dots into solid tumors

Among various nanoparticles tested for pharmacological applications over the recent years, graphene quantum dots (GQDs) seem to be promising candidates for the construction of drug delivery systems due to their superior biophysical and biochemical properties. The subcellular fate of incorporated nanomaterial is decisive for transporting pharmaceuticals into target cells. Therefore a detailed characterization of the uptake of GQDs into different breast cancer models was performed. The demonstrated accumulation inside the endolysosomal system might be the reason for the particles' low toxicity, but has to be overcome for cytosolic or nuclear drug delivery. Furthermore, the penetration of GQDs into precision-cut mammary tumor slices was studied. These constitute a far closer to reality model system than monoclonal cell lines. The constant uptake into the depth of the tissue slices underlines the systems' potential for drug delivery into solid tumors.

Transcriptomic Analysis Reveals Priming of The Host Antiviral Interferon Signaling Pathway by Bronchobini® Resulting in Balanced Immune Response to Rhinovirus Infection in Mouse Lung Tissue Slices

Rhinovirus (RV) is the predominant virus causing respiratory tract infections. Bronchobini^® is a low dose multi component, multi target preparation used to treat inflammatory respiratory diseases such as the common cold, described to ease severity of symptoms such as cough and viscous mucus production. The aim of the study was to assess the efficacy of Bronchobini^® in RV infection and to elucidate its mode of action. Therefore, Bronchobini^®’s ingredients (BRO) were assessed in an ex vivo model of RV infection using mouse precision-cut lung slices, an organotypic tissue capable to reflect the host immune response to RV infection. Cytokine profiles were assessed using enzyme-linked immunosorbent assay (ELISA) and mesoscale discovery (MSD). Gene expression analysis was performed using Affymetrix microarrays and ingenuity pathway analysis. BRO treatment resulted in the significant suppression of RV-induced antiviral and pro-inflammatory cytokine release. Transcriptome analysis revealed a multifactorial mode of action of BRO, with a strong inhibition of the RV-induced pro-inflammatory and antiviral host response mediated by nuclear factor kappa B (NFkB) and interferon signaling pathways. Interestingly, this was due to priming of these pathways in the absence of virus. Overall, BRO exerted its beneficial anti-inflammatory effect by priming the antiviral host response resulting in a reduced inflammatory response to RV infection, thereby balancing an otherwise excessive inflammatory response.

Precision-cut human liver slice cultures as an immunological platform

The liver is the central metabolic organ in the human body, and also plays an essential role in innate and adaptive immunity. While mouse models offer significant insights into immune-inflammatory liver disease, human immunology differs in important respects. It is not easy to address those differences experimentally. Therefore, to improve the understanding of human liver immunobiology and pathology, we have established precision-cut human liver slices to study innate immunity in human tissue. Human liver slices collected from resected livers could be maintained in ex vivo culture over a two-week period. Although an acute inflammatory response accompanied by signs of tissue repair was observed in liver tissue following slicing, the expression of many immune genes stabilized after day 4 and remained stable until day 15. Remarkably, histological evidence of pre-existing liver diseases was preserved in the slices for up to 7 days. Following 7 days of culture, exposure of liver slices to the toll-like receptor (TLR) ligands, TLR3 ligand Poly-I:C and TLR4 ligand LPS, resulted in a robust activation of acute inflammation and cytokine genes. Moreover, Poly-I:C treatment induced a marked antiviral response including increases of interferons IFNB, IL-28B and a group of interferon-stimulated genes. Therefore, precision-cut liver slices emerge as a valuable tool to study human innate immunity.

Emerging tumor spheroids technologies for 3D in vitro cancer modeling

Cancer is a leading cause of mortality and morbidity worldwide. Around 90% of deaths are caused by metastasis and just 10% by primary tumor. The advancement of treatment approaches is not at the same rhythm of the disease; making cancer a focal target of biomedical research. To enhance the understanding and prompts the therapeutic delivery; concepts of tissue engineering are applied in the development of in vitro models that can bridge between 2D cell culture and animal models, mimicking tissue microenvironment. Tumor spheroid represents highly suitable 3D organoid-like framework elucidating the intra and inter cellular signaling of cancer, like that formed in physiological niche. However, spheroids are of limited value in studying critical biological phenomenon such as tumor-stroma interactions involving extra cellular matrix or immune system. Therefore, a compelling need of tailoring spheroid technologies with physiologically relevant biomaterials or in silico models, is ever emerging. The diagnostic and prognostic role of spheroids rearrangements within biomaterials or microfluidic channel is indicative of patient management; particularly for the decision of targeted therapy. Fragmented information on available in vitro spheroid models and lack of critical analysis on transformation aspects of these strategies; pushes the urge to comprehensively overview the recent technological advancements (e.g. bioprinting, micro-fluidic technologies or use of biomaterials to attain the third dimension) in the shed of translationable cancer research. In present article, relationships between current models and their possible exploitation in clinical success is explored with the highlight of existing challenges in defining therapeutic targets and screening of drug efficacy.

Maintenance of high quality rat precision cut liver slices during culture to study hepatotoxic responses: Acetaminophen as a model compound

Precision cut liver slices (PCLiS) represent a promising tool in reflecting hepatotoxic responses. However, the culture of PCLiS varies considerably between laboratories, which can affect the performance of the liver slices and thus the experimental outcome. In this study, we describe an easily accessible culture method, which ensures optimal slice viability and functionality, in order to set the basis for reproducible and comparable PCLiS studies. The quality of the incubated rat PCLiS was assessed during a 24h culture period using ten readouts, which covered viability (lactate dehydrogenase-, aspartate transaminase- and glutamate dehydrogenase-leakage, ATP content) and functionality parameters (urea, albumin production) as well as histomorphology and other descriptive characteristics (protein content, wet weight, slice thickness). The present culture method resulted in high quality liver slices for 24h. Finally, PCLiS were exposed to increasing concentrations of acetaminophen to assess the suitability of the model for the detection of hepatotoxic responses. Six out of ten readouts revealed a toxic effect and showed an excellent mutual correlation. ATP, albumin and histomorphology measurements were identified as the most sensitive readouts. In conclusion, our results indicate that rat PCLiS are a valuable liver model for hepatotoxicity studies, particularly if they are cultured under optimal standardized conditions.

Extracellular-signal regulated kinase (Erk1/2), mitogen-activated protein kinase-activated protein kinase 2 (MK2) and tristetraprolin (TTP) comprehensively regulate injury-induced immediate early gene (IEG) response in in vitro liver organ culture

Differentiated hepatocytes are long-lived and normally do not undergo cell division, however they have the unique capacity to autonomously decide their replication fate after liver injury. In this context, the key players of liver regeneration immediately after injury have not been adequately studied. Using an in vitro liver culture system, we show that after liver injury, p38 mitogen-activated protein kinase (p38MAPK), mitogen-activated protein kinase-activated protein kinase 2 (MK2) and extracellular-signal regulated kinase (Erk)1/2 were activated within 15 min and continued to be phosphorylated for more than 2h. Both p38MAPK and Erk1/2 were activated at the edge of the cut as well as on the liver surface where the mesothelial cell sheet expresses several cytokines. Notably, in human liver Erk1/2 was also activated under the mesothelial cell sheet shortly after liver resections. Furthermore, in in vitro liver slice culture immediate early genes (IEGs) were upregulated within 1-2 h and the S phase marker proliferation-cell-nuclear-antigen (PCNA) appeared 24 h after injury. Although Erk1/2 was activated after injury, in MK2 depleted liver a set of IEGs, such as Dusp1, Cox2, or c-Myc and proliferation marker gene Ki67 were not induced. In addition, in immortalized hepatocyte cells, THLE-2, the same subset of genes was upregulated upon stimulation with lipopolysaccharide (LPS), but not in the presence of MK2 inhibitor. The protein level of tristetraprolin (TTP), a substrate for MK2 that plays a role in mRNA degradation, was increased in the presence of MK2 inhibitor. In this context, the depletion of TTP gene rescued Dusp1, Cox2, or c-Myc upregulation in the presence of MK2 inhibitor. These data imply that MK2 pathway is positively involved in Erk1/2 induced IEG response after liver injury. These data also suggest that in vitro liver culture may be a useful tool for measuring the proliferation potential of hepatocytes in individual liver.

Depletion of three combined THOC5 mRNA export protein target genes synergistically induces human hepatocellular carcinoma cell death

Hepatocellular carcinoma (HCC) is a frequent form of cancer with a poor prognosis and with limited possibilities of medical intervention. It has been shown that over 100 putative driver genes are associated with multiple recurrently altered pathways in HCC, suggesting that multiple pathways will need to be inhibited for any therapeutic method. mRNA processing is regulated by a complex RNA-protein network that is essential for the maintenance of homeostasis. THOC5, a member of mRNA export complex, has a role in less than 1% of mRNA processing, and is required for cell growth and differentiation, but not for cell survival in normal fibroblasts, hepatocytes and macrophages. In this report, we show that 50% depletion of THOC5 in human HCC cell lines Huh7 and HepG2 induced apoptosis. Transcriptome analysis using THOC5-depleted cells revealed that 396 genes, such as transmembrane BAX inhibitor motif containing 4 (TMBIM4), transmembrane emp24-like trafficking protein 10 (Tmed10) and D-tyrosyl-tRNA deacylase 2 (Dtd2) genes were downregulated in both cell lines. The depletion of one of these THOC5 target genes in Huh7 or HepG2 did not significantly induce cell death, suggesting that these may be fine tuners for HCC cell survival. However, the depletion of a combination of these genes synergistically increased the number of TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling)-positive HCC. It must be noted that the depletion of these genes did not induce cell death in the hepatocyte cell line, THLE-2 cells. THOC5 expression was enhanced in 78% of cytological differentiation grading G2 and G3 tumor in primary HCC. Furthermore, the expression of a putative glycoprotein, Tmed10, is correlated to THOC5 expression level in primary HCCs, suggesting that this protein may be a novel biomarker for HCC. These data imply that the suppression of the multiple THOC5 target genes may represent a novel strategy for HCC therapy.