Organotypic culture assays for murine and human primary and metastatic-site tumors

Claudin 7 suppresses invasion and metastasis through repression of a smooth muscle actin program

Metastasis initiates when cancer cells escape from the primary tumor, which requires changes to intercellular junctions. Claudins are transmembrane proteins that form the tight junction, and their expression is reduced in aggressive breast tumors. However, claudins' roles during breast cancer metastasis remain unclear. We used gain- and loss-of-function genetics in organoids isolated from murine breast cancer models to establish that Cldn7 suppresses invasion and metastasis. Transcriptomic analysis revealed that Cldn7 knockdown induced smooth muscle actin (SMA)-related genes and a broader mesenchymal phenotype. We validated our results in human cell lines, fresh human tumor tissue, bulk RNA-seq, and public single-cell RNA-seq data. We consistently observed an inverse relationship between Cldn7 expression and expression of SMA-related genes. Furthermore, knockdown and overexpression of SMA-related genes demonstrated that they promote breast cancer invasion. Our data reveal that Cldn7 suppresses breast cancer invasion and metastasis through negative regulation of SMA-related and mesenchymal gene expression.

Neuronal substance P drives metastasis through an extracellular RNA-TLR7 axis

Tumour innervation is associated with worse patient outcomes in multiple cancers1,2, which suggests that it may regulate metastasis. Here we observed that highly metastatic mouse mammary tumours acquired more innervation than did less-metastatic tumours. This enhanced innervation was driven by expression of the axon-guidance molecule SLIT2 in tumour vasculature. Breast cancer cells induced spontaneous calcium activity in sensory neurons and elicited release of the neuropeptide substance P (SP). Using three-dimensional co-cultures and in vivo models, we found that neuronal SP promoted breast tumour growth, invasion and metastasis. Moreover, patient tumours with elevated SP exhibited enhanced lymph node metastatic spread. SP acted on tumoral tachykinin receptors (TACR1) to drive death of a small population of TACR1high cancer cells. Single-stranded RNAs (ssRNAs) released from dying cells acted on neighbouring tumoural Toll-like receptor 7 (TLR7) to non-canonically activate a prometastatic gene expression program. This SP- and ssRNA-induced Tlr7 gene expression signature was associated with reduced breast cancer survival outcomes. Therapeutic targeting of this neuro-cancer axis with the TACR1 antagonist aprepitant, an approved anti-nausea drug, suppressed breast cancer growth and metastasis in multiple models. Our findings reveal that tumour-induced hyperactivation of sensory neurons regulates multiple aspects of metastatic progression in breast cancer through a therapeutically targetable neuropeptide/extracellular ssRNA sensing axis.

Using Microfluidics to Align Matrix Architecture and Generate Chemokine Gradients Promotes Directional Branching in a Model of Epithelial Morphogenesis

The mechanical cue of fiber alignment plays a key role in the development of various tissues in the body. The ability to study the effect of these stimuli in vitro has been limited previously. Here, we present a microfluidic device capable of intrinsically generating aligned fibers using the microchannel geometry. The device also features tunable interstitial fluid flow and the ability to form a morphogen gradient. These aspects allow for the modeling of complex tissues and to differentiate cell response to different stimuli. To demonstrate the abilities of our device, we incorporated luminal epithelial cysts into our device and induced growth factor stimulation. We found the mechanical cue of fiber alignment to play a dominant role in cell elongation and the ability to form protrusions was dependent on cadherin-3. Together, this work serves as a springboard for future potential with these devices to answer questions in developmental biology and complex diseases such as cancers.

Development of Injectable Thermosensitive Nanocomposite Hydrogel for Ratiometric Drug Delivery to Treat Drug Resistant Chondrosarcoma In Vivo

Chondrosarcoma(CS), a prevalent primary malignant bone tumor, frequently exhibits chemotherapy resistance attributed to upregulated anti-apoptosis pathways such as the Bcl-2 family. In this manuscript, a new strategy is presented to augment chemosensitivity and mitigate systemic toxicity by harnessing a nano-enabled drug delivery hydrogel platform. The platform utilizes "PLGA-PEG-PLGA", an amphiphilic triblock copolymer combining hydrophilic polyethylene glycol (PEG) and hydrophobic polylactide glycolide (PLGA) blocks, renowned for its properties conducive to crafting a biodegradable, temperature-sensitive hydrogel. This platform is tailored to encapsulate a ratiometrically designed dual-loaded liposomes containing a first-line chemo option for CS, Doxorubicin (Dox), plus a calculated amount of small molecule inhibitor for anti-apoptotic Bcl-2 pathway, ABT-737. In vitro and in vivo evaluations demonstrate successful Bcl-2 suppression, resulting in the restoration of Dox sensitivity, evident through impeded tumor growth and amplified necrosis rates at the tumor site. This delivery system showcases remarkable thermal responsiveness, injectability, and biodegradability, all finely aligned with the clinical demands of CS treatment. Collectively, this study introduces a transformative avenue for tackling drug resistance in CS chemotherapy, offering significant clinical potential.

Intra- and Interpatient Drug Response Heterogeneity Exist in Patients Undergoing Cytoreductive Surgery and Hyperthermic Intraperitoneal Chemotherapy for Nongynecologic Cancers

BACKGROUND

Select patients with peritoneal metastases are treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC). We assayed for intra- and interpatient drug response heterogeneity through testing of patient-derived tumor organoids (PDTOs).

METHODS

PDTOs were generated from CRS/HIPEC patients from December 2021 to September 2022 and subjected to an in vitro HIPEC drug screen. Drug response was assessed with a cell viability assay and cleaved caspase-3 staining.

RESULTS

A total of 31 patients were consented for tissue collection. Viable tissue was harvested from 23, and PDTO generation was successful in 13 (56%). PDTOs were analyzed from six appendiceal, three colorectal, two small bowel, one gastric, and one adrenal tumor. Drug screen results were generated in as few as 7 days (62%), with an average time of 12 days. Most patients received mitomycin-C (MMC) intraoperatively (n = 9); however, in only three cases was this agent considered the optimal choice in vitro. Three sets of PDTOs were resistant (defined as > 50% PDTO viability) to all agents tested and two were pan-sensitive (defined as 3 or more agents with < 50% PDTO viability). In three patients, organoids were generated from multiple metastatic sites and intrapatient drug response heterogeneity was observed.

CONCLUSIONS

Both intra- and interpatient drug response heterogeneity exist in patients undergoing CRS/HIPEC for nongynecologic abdominal cancers. Caution must be used when interpreting patient response to chemotherapeutic agents based on a single site of testing in those with metastatic disease.

Deep-Learning-Based Nanomechanical Vibration for Rapid and Label-Free Assay of Epithelial Mesenchymal Transition

Cancer is a profound danger to our life and health. The classification and related studies of epithelial and mesenchymal phenotypes of cancer cells are key scientific questions in cancer research. Here, we investigated cancer cell colonies from a mechanical perspective and developed an assay for classifying epithelial/mesenchymal cancer cell colonies using the biomechanical fingerprint in the form of "nanovibration" in combination with deep learning. The classification method requires only 1 s of vibration data and has a classification accuracy of nearly 92.5%. The method has also been validated for the screening of anticancer drugs. Compared with traditional methods, the method has the advantages of being nondestructive, label-free, and highly sensitive. Furthermore, we proposed a perspective that subcellular structure influences the amplitude and spectrum of nanovibrations and demonstrated it using experiments and numerical simulation. These findings allow internal changes in the cell colony to be manifested by nanovibrations. This work provides a perspective and an ancillary method for cancer cell phenotype diagnosis and promotes the study of biomechanical mechanisms of cancer progression.

Leader cells mechanically respond to aligned collagen architecture to direct collective migration

Leader cells direct collective migration through sensing cues in their microenvironment to determine migration direction. The mechanism by which leader cells sense the mechanical cue of organized matrix architecture culminating in a mechanical response is not well defined. In this study, we investigated the effect of organized collagen matrix fibers on leader cell mechanics and demonstrate that leader cells protrude along aligned fibers resulting in an elongated phenotype of the entire cluster. Further, leader cells show increased mechanical interactions with their nearby matrix compared to follower cells, as evidenced by increased traction forces, increased and larger focal adhesions, and increased expression of integrin-α2. Together our results demonstrate changes in mechanical matrix cues drives changes in leader cell mechanoresponse that is required for directional collective migration. Our findings provide new insights into two fundamental components of carcinogenesis, namely invasion and metastasis.

Exploring the interaction between extracellular matrix components in a 3D organoid disease model to replicate the pathophysiology of breast cancer

In vitro models are necessary to study the pathophysiology of the disease and the development of effective, tailored treatment methods owing to the complexity and heterogeneity of breast cancer and the large population affected by it. The cellular connections and tumor microenvironments observed in vivo are often not recapitulated in conventional two-dimensional (2D) cell cultures. Therefore, developing 3D in vitro models that mimic the complex architecture and physiological circumstances of breast tumors is crucial for advancing our understanding of the illness. A 3D scaffold-free in vitro disease model mimics breast cancer pathophysiology by allowing cells to self-assemble/pattern into 3D structures, in contrast with other 3D models that rely on artificial scaffolds. It is possible that this model, whether applied to breast tumors using patient-derived primary cells (fibroblasts, endothelial cells, and cancer cells), can accurately replicate the observed heterogeneity. The complicated interactions between different cell types are modelled by integrating critical components of the tumor microenvironment, such as the extracellular matrix, vascular endothelial cells, and tumor growth factors. Tissue interactions, immune cell infiltration, and the effects of the milieu on drug resistance can be studied using this scaffold-free 3D model. The scaffold-free 3D in vitro disease model for mimicking tumor pathophysiology in breast cancer is a useful tool for studying the molecular basis of the disease, identifying new therapeutic targets, and evaluating treatment modalities. It provides a more physiologically appropriate high-throughput platform for screening large compound library in a 96-384 well format. We critically discussed the rapid development of personalized treatment strategies and accelerated drug screening platforms to close the gap between traditional 2D cell culture and in vivo investigations.

Cancer-Associated Fibroblast-Like Tumor Cells Remodel the Ewing Sarcoma Tumor Microenvironment

PURPOSE

Despite limited genetic and histologic heterogeneity, Ewing sarcoma (EwS) tumor cells are transcriptionally heterogeneous and display varying degrees of mesenchymal lineage specification in vitro. In this study, we investigated if and how transcriptional heterogeneity of EwS cells contributes to heterogeneity of tumor phenotypes in vivo.

EXPERIMENTAL DESIGN

Single-cell proteogenomic-sequencing of EwS cell lines was performed and integrated with patient tumor transcriptomic data. Cell subpopulations were isolated by FACS for assessment of gene expression and phenotype. Digital spatial profiling and human whole transcriptome analysis interrogated transcriptomic heterogeneity in EwS xenografts. Tumor cell subpopulations and matrix protein deposition were evaluated in xenografts and patient tumors using multiplex immunofluorescence staining.

RESULTS

We identified CD73 as a biomarker of highly mesenchymal EwS cell subpopulations in tumor models and patient biopsies. CD73+ tumor cells displayed distinct transcriptional and phenotypic properties, including selective upregulation of genes that are repressed by EWS::FLI1, and increased migratory potential. CD73+ cells were distinguished in vitro and in vivo by increased expression of matrisomal genes and abundant deposition of extracellular matrix (ECM) proteins. In epithelial-derived malignancies, ECM is largely deposited by cancer-associated fibroblasts (CAF), and we thus labeled CD73+ EwS cells, CAF-like tumor cells. Marked heterogeneity of CD73+ EwS cell frequency and distribution was detected in tumors in situ, and CAF-like tumor cells and associated ECM were observed in peri-necrotic regions and invasive foci.

CONCLUSIONS

EwS tumor cells can adopt CAF-like properties, and these distinct cell subpopulations contribute to tumor heterogeneity by remodeling the tumor microenvironment. See related commentary by Kuo and Amatruda, p. 5002.

Embedded Bioprinting of Breast Tumor Cells and Organoids Using Low-Concentration Collagen-Based Bioinks

Bioinks for 3D bioprinting of tumor models should not only meet printability requirements but also accurately maintain and support phenotypes of tumor surrounding cells to recapitulate key tumor hallmarks. Collagen is a major extracellular matrix protein for solid tumors, but low viscosity of collagen solution has made 3D bioprinted cancer models challenging. This work produces embedded, bioprinted breast cancer cells and tumor organoid models using low-concentration collagen I based bioinks. The biocompatible and physically crosslinked silk fibroin hydrogel is used to generate the support bath for the embedded 3D printing. The composition of the collagen I based bioink is optimized with a thermoresponsive hyaluronic acid-based polymer to maintain the phenotypes of both the noninvasive epithelial and invasive breast cancer cells, as well as cancer-associated fibroblasts. Mouse breast tumor organoids are bioprinted using optimized collagen bioink to mimic in vivo tumor morphology. A vascularized tumor model is also created using a similar strategy, with significantly enhanced vasculature formation under hypoxia. This study shows the great potential of embedded bioprinted breast tumor models utilizing a low-concentration collagen-based bioink for advancing the understanding of tumor cell biology and facilitating drug discovery research.

A T Cell-Engaging Tumor Organoid Platform for Pancreatic Cancer Immunotherapy

Pancreatic ductal adenocarcinoma (PDA) is a clinically challenging disease with limited treatment options. Despite a small percentage of cases with defective mismatch DNA repair (dMMR), PDA is included in the most immune-resistant cancer types that are poorly responsive to immune checkpoint blockade (ICB) therapy. To facilitate drug discovery combating this immunosuppressive tumor type, a high-throughput drug screen platform is established with the newly developed T cell-incorporated pancreatic tumor organoid model. Tumor-specific T cells are included in the pancreatic tumor organoids by two-step cell packaging, fully recapitulating immune infiltration in the immunosuppressive tumor microenvironment (TME). The organoids are generated with key components in the original tumor, including epithelial, vascular endothelial, fibroblast and macrophage cells, and then packaged with T cells into their outside layer mimicking a physical barrier and enabling T cell infiltration and cytotoxicity studies. In the PDA organoid-based screen, epigenetic inhibitors ITF2357 and I-BET151 are identified, which in combination with anti-PD-1 based therapy show considerably greater anti-tumor effect. The combinatorial treatment turns the TME from immunosuppressive to immunoactive, up-regulates the MHC-I antigen processing and presentation, and enhances the effector T cell activity. The standardized PDA organoid model has shown great promise to accelerate drug discovery for the immunosuppressive cancer.

Carcinoma-associated fibroblast-like tumor cells remodel the Ewing sarcoma tumor microenvironment

Tumor heterogeneity is a major driver of cancer progression. In epithelial-derived malignancies, carcinoma-associated fibroblasts (CAFs) contribute to tumor heterogeneity by depositing extracellular matrix (ECM) proteins that dynamically remodel the tumor microenvironment (TME). Ewing sarcomas (EwS) are histologically monomorphous, mesenchyme-derived tumors that are devoid of CAFs. Here we identify a previously uncharacterized subpopulation of transcriptionally distinct EwS tumor cells that deposit pro-tumorigenic ECM. Single cell analyses revealed that these CAF-like cells differ from bulk EwS cells by their upregulation of a matrisome-rich gene signature that is normally repressed by EWS::FLI1, the oncogenic fusion transcription factor that underlies EwS pathogenesis. Further, our studies showed that ECM-depositing tumor cells express the cell surface marker CD73, allowing for their isolation ex vivo and detection in situ. Spatial profiling of tumor xenografts and patient biopsies demonstrated that CD73 ⁺ EwS cells and tumor cell-derived ECM are prevalent along tumor borders and invasive fronts. Importantly, despite loss of EWS::FLI1-mediated gene repression, CD73 ⁺ EwS cells retain expression of EWS::FLI1 and the fusion-activated gene signature, as well as tumorigenic and proliferative capacities. Thus, EwS tumor cells can be reprogrammed to adopt CAF-like properties and these transcriptionally and phenotypically distinct cell subpopulations contribute to tumor heterogeneity by remodeling the TME.

Triple negative breast tumors contain heterogeneous cancer cells expressing distinct KRAS-dependent collective and disseminative invasion programs

Inter-patient and intra-tumoral heterogeneity complicate the identification of predictive biomarkers and effective treatments for basal triple negative breast cancer (b-TNBC). Invasion is the initiating event in metastasis and can occur by both collective and single-cell mechanisms. We cultured primary organoids from a b-TNBC genetically engineered mouse model in 3D collagen gels to characterize their invasive behavior. We observed that organoids from the same tumor presented different phenotypes that we classified as non-invasive, collective and disseminative. To identify molecular regulators driving these invasive phenotypes, we developed a workflow to isolate individual organoids from the collagen gels based on invasive morphology and perform RNA sequencing. We next tested the requirement of differentially regulated genes for invasion using shRNA knock-down. Strikingly, KRAS was required for both collective and disseminative phenotypes. We then performed a drug screen targeting signaling nodes upstream and downstream of KRAS. We found that inhibition of EGFR, MAPK/ERK, or PI3K/AKT signaling reduced invasion. Of these, ERK inhibition was striking for its ability to potently inhibit collective invasion and dissemination. We conclude that different cancer cells in the same b-TNBC tumor can express different metastatic molecular programs and identified KRAS and ERK as essential regulators of collective and single cell dissemination.

Multimodal Techniques to Study Tumor Growth, Basement Membrane Breaching, and Invasion in 3D Matrices

Cancer-derived organoids and three-dimensional (3D) extracellular matrix (ECM) are taking center stage as in vitro models to study neoplastic cell behavior, since they recapitulate the heterogeneous cellular composition of tumors and their extracellular environment. In combination with imaging and molecular/biochemical techniques, 3D organoid models have contributed substantially to our knowledge about the cellular and molecular mechanisms that regulate the growth of tumors and invasion into the surrounding tissue. We here outline a set of protocols that describe culturing of cancer-derived organoids in 3D matrices and various strategies that allow modeling of tumor growth, tumor cell penetration into basement membranes, and invasion into Collagen I-rich ECM. Furthermore, we specify protocols for subsequent handling of organoids cultured in 3D ECM for confocal microscopy and analysis of gene expression at the protein and mRNA level. Although we here use breast cancer-derived organoids, these protocols can be directly applied or adapted for organoids derived from other cancer types or healthy tissues. Thus, in addition to investigating cell behavior of multiple cancer types, the combination of protocols described here may be used to study processes such as cell differentiation and migration during homeostasis and normal development.

Segmentation and Tracking of Mammary Epithelial Organoids in Brightfield Microscopy

We present an automated and deep-learning-based workflow to quantitatively analyze the spatiotemporal development of mammary epithelial organoids in two-dimensional time-lapse (2D+t) sequences acquired using a brightfield microscope at high resolution. It involves a convolutional neural network (U-Net), purposely trained using computer-generated bioimage data created by a conditional generative adversarial network (pix2pixHD), to infer semantic segmentation, adaptive morphological filtering to identify organoid instances, and a shape-similarity-constrained, instance-segmentation-correcting tracking procedure to reliably cherry-pick the organoid instances of interest in time. By validating it using real 2D+t sequences of mouse mammary epithelial organoids of morphologically different phenotypes, we clearly demonstrate that the workflow achieves reliable segmentation and tracking performance, providing a reproducible and laborless alternative to manual analyses of the acquired bioimage data.

Role of Patient-Derived Models of Cancer in Translational Oncology

Cancer is a heterogeneous disease. Each individual tumor is unique and characterized by structural, cellular, genetic and molecular features. Therefore, patient-derived cancer models are indispensable tools in cancer research and have been actively introduced into the healthcare system. For instance, patient-derived models provide a good reproducibility of susceptibility and resistance of cancer cells against drugs, allowing personalized therapy for patients. In this article, we review the advantages and disadvantages of the following patient-derived models of cancer: (1) PDC-patient-derived cell culture, (2) PDS-patient-derived spheroids and PDO-patient-derived organoids, (3) PDTSC-patient-derived tissue slice cultures, (4) PDX-patient-derived xenografts, humanized PDX, as well as PDXC-PDX-derived cell cultures and PDXO-PDX-derived organoids. We also provide an overview of current clinical investigations and new developments in the area of patient-derived cancer models. Moreover, attention is paid to databases of patient-derived cancer models, which are collected in specialized repositories. We believe that the widespread use of patient-derived cancer models will improve our knowledge in cancer cell biology and contribute to the development of more effective personalized cancer treatment strategies.

The miR-181 family regulates colonic inflammation through its activity in the intestinal epithelium

The intestinal epithelium is a key physical interface that integrates dietary and microbial signals to regulate nutrient uptake and mucosal immune cell function. The transcriptional programs that regulate intestinal epithelial cell (IEC) quiescence, proliferation, and differentiation have been well characterized. However, how gene expression networks critical for IECs are posttranscriptionally regulated during homeostasis or inflammatory disease remains poorly understood. Herein, we show that a conserved family of microRNAs, miR-181, is significantly downregulated in IECs from patients with inflammatory bowel disease and mice with chemical-induced colitis. Strikingly, we showed that miR-181 expression within IECs, but not the hematopoietic system, is required for protection against severe colonic inflammation in response to epithelial injury in mice. Mechanistically, we showed that miR-181 expression increases the proliferative capacity of IECs, likely through the regulation of Wnt signaling, independently of the gut microbiota composition. As epithelial reconstitution is crucial to restore intestinal homeostasis after injury, the miR-181 family represents a potential therapeutic target against severe intestinal inflammation.

Clinical applications of 3D normal and breast cancer organoids: A review of concepts and methods

While mouse models and two-dimensional (2D) cell culture systems have dominated as research tools for cancer biology, three-dimensional (3D) cultures have gained traction as a new approach that retains features of in vivo biology within an in vitro system. Over time, 3D culture systems have evolved from spheroids and tumorspheres to organoids, and by doing so, they have become more complex and representative of original tissue. Such technological improvements have mostly benefited the study of heterogeneous solid tumors, like those found in breast cancer (BC), by providing an attractive avenue for scalable drug testing and biobank generation. Experimentally, organoids have been used in the BC field to dissect mechanisms related to cellular invasion and metastasis-and through co-culture methods-epithelial interactions with stromal and immune cells. In addition, organoid studies of wild-type mouse models and healthy donor samples have provided insight into the basic developmental cellular and molecular biology of the mammary gland, which may inform one's understanding of the initial stages of cancer development and progression.

Organoids in gastrointestinal diseases: from experimental models to clinical translation

We are entering an era of medicine where increasingly sophisticated data will be obtained from patients to determine proper diagnosis, predict outcomes and direct therapies. We predict that the most valuable data will be produced by systems that are highly dynamic in both time and space. Three-dimensional (3D) organoids are poised to be such a highly valuable system for a variety of gastrointestinal (GI) diseases. In the lab, organoids have emerged as powerful systems to model molecular and cellular processes orchestrating natural and pathophysiological human tissue formation in remarkable detail. Preclinical studies have impressively demonstrated that these organs-in-a-dish can be used to model immunological, neoplastic, metabolic or infectious GI disorders by taking advantage of patient-derived material. Technological breakthroughs now allow to study cellular communication and molecular mechanisms of interorgan cross-talk in health and disease including communication along for example, the gut-brain axis or gut-liver axis. Despite considerable success in culturing classical 3D organoids from various parts of the GI tract, some challenges remain to develop these systems to best help patients. Novel platforms such as organ-on-a-chip, engineered biomimetic systems including engineered organoids, micromanufacturing, bioprinting and enhanced rigour and reproducibility will open improved avenues for tissue engineering, as well as regenerative and personalised medicine. This review will highlight some of the established methods and also some exciting novel perspectives on organoids in the fields of gastroenterology. At present, this field is poised to move forward and impact many currently intractable GI diseases in the form of novel diagnostics and therapeutics.

Role of adipose tissue-derived cytokines in the progression of inflammatory breast cancer in patients with obesity

BACKGROUND

Inflammatory breast cancer (IBC) represents a deadly aggressive phenotype of breast cancer (BC) with a unique clinicopathological presentation and low survival rate. In fact, obesity represents an important risk factor for BC. Although several studies have identified different cellular-derived and molecular factors involved in IBC progression, the role of adipocytes remains unclear. Cancer-associated adipose tissue (CAAT) expresses a variety of adipokines, which contribute to tumorigenesis and the regulation of cancer stem cell (CSC). This research investigated the potential effect of the secretome of CAAT explants from patients with BC on the progression and metastasis of the disease.

METHODS

This study established an ex-vivo culture of CAAT excised from IBC (n = 13) vs. non-IBC (n = 31) patients with obesity and profiled their secretome using a cytokine antibody array. Furthermore, the quantitative PCR (qPCR) methodology was used to validate the levels of predominant cytokines at the transcript level after culture in a medium conditioned by CAAT. Moreover, the impact of the CAAT secretome on the expression of epithelial-mesenchymal transition (EMT) and cells with stem cell (CSC) markers was studied in the non-IBC MDA-MB-231 and the IBC SUM-149 cell lines. The statistical differences between variables were evaluated using the chi-squared test and unpaired a Student's t-test.

RESULTS

The results of cytokine array profiling revealed an overall significantly higher level of a panel of 28 cytokines secreted by the CAAT ex-vivo culture from IBC patients with obesity compared to those with non-IBC. Of note, interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemo-attractant protein 1 (MCP-1) were the major adipokines secreted by the CAAT IBC patients with obesity. Moreover, the qPCR results indicated a significant upregulation of the IL-6, IL-8, and MCP-1 mRNAs in CAAT ex-vivo culture of patients with IBC vs. those with non-IBC. Intriguingly, a qPCR data analysis showed that the CAAT secretome secretions from patients with non-IBC downregulated the mRNA levels of the CD24 CSC marker and of the epithelial marker E-cadherin in the non-IBC cell line. By contrast, E-cadherin was upregulated in the SUM-149 cell.

CONCLUSIONS

This study identified the overexpression of IL-6, IL-8, and MCP-1 as prognostic markers of CAAT from patients with IBC but not from those with non-IBC ; moreover, their upregulation might be associated with IBC aggressiveness via the regulation of CSC and EMT markers. This study proposed that targeting IL-6, IL-8, and MCP-1 may represent a therapeutic option that should be considered in the treatment of patients with IBC.

Triple-negative breast cancer metastasis involves complex epithelial-mesenchymal transition dynamics and requires vimentin

Triple-negative breast cancer (TNBC) is an aggressive subtype associated with early metastatic recurrence and worse patient outcomes. TNBC tumors express molecular markers of the epithelial-mesenchymal transition (EMT), but its requirement during spontaneous TNBC metastasis in vivo remains incompletely understood. We demonstrated that spontaneous TNBC tumors from a genetically engineered mouse model (GEMM), multiple patient-derived xenografts, and archival patient samples exhibited large populations in vivo of hybrid E/M cells that lead invasion ex vivo while expressing both epithelial and mesenchymal characteristics. The mesenchymal marker vimentin promoted invasion and repressed metastatic outgrowth. We next tested the requirement for five EMT transcription factors and observed distinct patterns of utilization during invasion and colony formation. These differences suggested a sequential activation of multiple EMT molecular programs during the metastatic cascade. Consistent with this model, our longitudinal single-cell RNA analysis detected three different EMT-related molecular patterns. We observed cancer cells progressing from epithelial to hybrid E/M and strongly mesenchymal patterns during invasion and from epithelial to a hybrid E/M pattern during colony formation. We next investigated the relative epithelial versus mesenchymal state of cancer cells in both GEMM and patient metastases. In both contexts, we observed heterogeneity between and within metastases in the same individual. We observed a complex spectrum of epithelial, hybrid E/M, and mesenchymal cell states within metastases, suggesting that there are multiple successful molecular strategies for distant organ colonization. Together, our results demonstrate an important and complex role for EMT programs during TNBC metastasis.

Patient-derived organoids identify an apico-basolateral polarity switch associated with survival in colorectal cancer

The metastatic progression of cancer remains a major issue in patient treatment. Yet, the molecular and cellular mechanisms underlying this process remains unclear. Here, we use primary explants and organoids from patients harboring mucinous colorectal carcinoma (MUC CRC), a poor prognosis histological form of digestive cancers, to study the architecture, invasive behavior and chemoresistance of tumor cell intermediates. We report that these tumors maintain a robust apico-basolateral polarity as they spread in the peritumoral stroma or organotypic collagen-I gels. We identified two distinct topologies: MUC CRCs either display a conventional "apical-in" polarity or, more frequently, harbor an inverted "apical-out" topology. Transcriptomic analyses combined with interference experiments on organoids showed that TGFb and focal adhesion signaling pathways are the main drivers of polarity orientation. Finally, this apical-out topology is associated with increased resistance to chemotherapeutic treatments in organoids and decreased patient survival in the clinic. Thus, patient-derived organoids have the potential to bridge histological, cellular and molecular analyses to decrypt onco-morphogenic programs and stratify cancer patients.

DOT1L Is a Novel Cancer Stem Cell Target for Triple-Negative Breast Cancer

PURPOSE

Although chemotherapies kill most cancer cells, stem cell-enriched survivors seed metastasis, particularly in triple-negative breast cancers (TNBC). TNBCs arise from and are enriched for tumor stem cells. Here, we tested if inhibition of DOT1L, an epigenetic regulator of normal tissue stem/progenitor populations, would target TNBC stem cells.

EXPERIMENTAL DESIGN

Effects of DOT1L inhibition by EPZ-5676 on stem cell properties were tested in three TNBC lines and four patient-derived xenograft (PDX) models and in isolated cancer stem cell (CSC)-enriched ALDH1+ and ALDH1- populations. RNA sequencing compared DOT1L regulated pathways in ALDH1+ and ALDH1- cells. To test if EPZ-5676 decreases CSC in vivo, limiting dilution assays of EPZ-5676/vehicle pretreated ALDH1+ and ALDH1- cells were performed. Tumor latency, growth, and metastasis were evaluated. Antitumor activity was also tested in TNBC PDX and PDX-derived organoids.

RESULTS

ALDH1+ TNBC cells exhibit higher DOT1L and H3K79me2 than ALDH1-. DOT1L maintains MYC expression and self-renewal in ALDH1+ cells. Global profiling revealed that DOT1L governs oxidative phosphorylation, cMyc targets, DNA damage response, and WNT activation in ALDH1+ but not in ALDH1- cells. EPZ-5676 reduced tumorspheres and ALDH1+ cells in vitro and decreased tumor-initiating stem cells and metastasis in xenografts generated from ALDH1+ but not ALDH1- populations in vivo. EPZ-5676 significantly reduced growth in vivo of one of two TNBC PDX tested and decreased clonogenic 3D growth of two other PDX-derived organoid cultures.

CONCLUSIONS

DOT1L emerges as a key CSC regulator in TNBC. Present data support further clinical investigation of DOT1L inhibitors to target stem cell-enriched TNBC.

Leucyl-tRNA synthetase is a tumour suppressor in breast cancer and regulates codon-dependent translation dynamics

Tumourigenesis and cancer progression require enhanced global protein translation^1–3. Such enhanced translation is caused by oncogenic and tumour suppressive events that drive the synthesis and activity of translational machinery^4,5. Here we report the surprising observation that leucyl-tRNA synthetase (LARS) becomes repressed during mammary cell transformation and in human breast cancer. Monoallelic genetic deletion of LARS in mouse mammary glands enhanced breast cancer tumour formation and proliferation. LARS repression reduced the abundance of select leucine tRNA isoacceptors, leading to impaired leucine codon-dependent translation of growth suppressive genes including epithelial membrane protein 3 (EMP3) and gamma-glutamyltransferase 5 (GGT5). Our findings uncover a tumour suppressive tRNA synthetase and reveal that dynamic repression of a specific tRNA synthetase—along with its downstream cognate tRNAs—elicits a downstream codon-biased translational gene network response that enhances breast tumour formation and growth.

Instructive Hydrogels for Primary Tumor Cell Culture: Current Status and Outlook

Primary tumor organoids (PTOs) growth in hydrogels have emerged as an important in vitro model that recapitulates many characteristics of the native tumor tissue, and have important applications in fundamental cancer research and for the development of useful therapeutic treatment. This paper begins with reviewing the methods of isolation of primary tumor cells. Then, recent advances on the instructive hydrogels as biomimetic extracellular matrix for primary tumor cell culture and construction of PTO models are summarized. Emerging microtechnology for growth of PTOs in microscale hydrogels and the applications of PTOs are highlighted. This paper concludes with an outlook on the future directions in the investigation of instructive hydrogels for PTO growth.

Protocol for Studying Embryonic Mammary Gland Branching Morphogenesis Ex Vivo

Mammary gland development starts during embryogenesis, and the process continues after birth. During development, the mammary gland undergoes massive morphological and physiological alterations including growth, invasion, and branching morphogenesis providing an ideal model for stem cell and cancer biology studies. Great efforts have been made in understanding mammary gland development during puberty and adulthood; however, the process during embryogenesis is still elusive. One reason is that the tools to study tissue dynamics during development are limited, which is partially due to the lack of an ex vivo culture method. Here we describe an updated organ culture protocol of the murine embryonic mammary gland. This powerful tool allows monitoring of growth and branching morphogenesis of mammary gland ex vivo by live imaging. In addition, we introduce a novel method for culturing intact, stroma-free mammary rudiments from late gestation mouse embryos in 3D in Matrigel. This approach can be used to identify the direct stromal cues for branching morphogenesis.

Single Organoids Droplet-Based Staining Method for High-End 3D Imaging of Mammary Organoids

In the last decade, organoids became a tremendously popular technique in developmental and cancer biology for their high pathophysiological relevance to in vivo models with the advantage of easier manipulation, real-time observation, potential for high-throughput studies, and reduced ethical issues. Among other fundamental biological questions, mammary organoids have helped to reveal mechanisms of mammary epithelial morphogenesis, mammary stem cell potential, regulation of lineage specification, mechanisms of breast cancer invasion or resistance to therapy, and their regulation by stromal microenvironment. To exploit the potential of organoid technology to the fullest, together with optimal organoid culture protocols, visualization of organoid architecture and composition in high resolution in three dimensions (3D) is required. Whole-mount imaging of immunolabeled organoids enables preservation of the 3D cellular context, but conventional confocal microscopy of organoid cultures struggles with the large organoid sample size and relatively long distance from the objective to the organoid due to the 3D extracellular matrix (ECM) that surrounds the organoid. We have overcome these issues by physical separation of single organoids with their immediate stroma from the bulk ECM. Here we provide a detail protocol for the procedure, which entails single organoid collection and droplet-based staining and clearing to allow visualization of organoids in the greatest detail.

In-Depth Comparison of Matrigel Dissolving Methods on Proteomic Profiling of Organoids

Patient-derived organoids recently emerged as promising ex vivo 3D culture models recapitulating histological and molecular characteristics of original tissues, thus proteomic profiling of organoids could be valuable for function investigation and clinical translation. However, organoids are usually cultured in murine Matrigel (served as scaffolds and matrix), which brings an issue to separate organoids from Matrigel. Because of the complex compositions of Matrigel and thousands of identical peptides shared between Matrigel and organoids, insufficiently dissolved Matrigel could influence proteomic analysis of organoids in multiple ways. Thus, how to dissolve Matrigel matrix and recovery organoid cells efficiently is vital for sample preparation. Here, we comprehensively compared three popular Matrigel dissolving methods (cell recovery solution, dispase, and PBS–EDTA buffer) and investigated the effect of undissolved Matrigel proteins on proteomic profiles of organoids. By integrative analysis of label-free proteomes of Matrigel and stable isotope labeling by amino acids in cell culture proteomes of organoids collected by three methods, respectively, we found that dispase showed an optimal efficiency, with the highest peptide yield and the highest incorporation ratio of stable isotope labeling by amino acids in cell culture labels (97.1%), as well as with the least potential Matrigel contaminants. To help analysis of proteomic profiles of organoids collected by the other two methods, we identified 312 high-confidence Matrigel contaminants, which could be filtered out to attenuate Matrigel interference with minimal loss of biological information. Together, our study identifies bioinformatics and experimental approaches to eliminate interference of Matrigel contaminants efficiently, which will be valuable for basic and translational proteomic research using organoid models.

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A comprehensive comparison of Matrigel dissolving methods on organoid proteomics.

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Matrigel leftover influences protein identification and quantification for organoids.

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Dispase is a satisfying method for proteomic sample preparation of organoids.

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Exclusion of high-confidence Matrigel contaminants attenuates Matrigel interference.

In Vitro Magnetic Techniques for Investigating Cancer Progression

Worldwide, there are currently around 18.1 million new cancer cases and 9.6 million cancer deaths yearly. Although cancer diagnosis and treatment has improved greatly in the past several decades, a complete understanding of the complex interactions between cancer cells and the tumor microenvironment during primary tumor growth and metastatic expansion is still lacking. Several aspects of the metastatic cascade require in vitro investigation. This is because in vitro work allows for a reduced number of variables and an ability to gather real-time data of cell responses to precise stimuli, decoupling the complex environment surrounding in vivo experimentation. Breakthroughs in our understanding of cancer biology and mechanics through in vitro assays can lead to better-designed ex vivo precision medicine platforms and clinical therapeutics. Multiple techniques have been developed to imitate cancer cells in their primary or metastatic environments, such as spheroids in suspension, microfluidic systems, 3D bioprinting, and hydrogel embedding. Recently, magnetic-based in vitro platforms have been developed to improve the reproducibility of the cell geometries created, precisely move magnetized cell aggregates or fabricated scaffolding, and incorporate static or dynamic loading into the cell or its culture environment. Here, we will review the latest magnetic techniques utilized in these in vitro environments to improve our understanding of cancer cell interactions throughout the various stages of the metastatic cascade.

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.

Deciphering Organoids: High-Dimensional Analysis of Biomimetic Cultures

Organoids are self-organising stem cell-derived ex vivo cultures widely adopted as biomimetic models of healthy and diseased tissues. Traditional low-dimensional experimental methods such as microscopy and bulk molecular analysis have generated remarkable biological insights from organoids. However, as complex heterocellular systems, organoids are especially well-positioned to take advantage of emerging high-dimensional technologies. In particular, single-cell methods offer considerable opportunities to analyse organoids at unprecedented scale and depth, enabling comprehensive characterisation of cellular processes and spatial organisation underpinning organoid heterogeneity. This review evaluates state-of-the-art analytical methods applied to organoids, discusses the latest advances in single-cell technologies, and speculates on the integration of these two rapidly developing fields.

Collective metastasis: coordinating the multicellular voyage

The metastatic process is arduous. Cancer cells must escape the confines of the primary tumor, make their way into and travel through the circulation, then survive and proliferate in unfavorable microenvironments. A key question is how cancer cells overcome these multiple barriers to orchestrate distant organ colonization. Accumulating evidence in human patients and animal models supports the hypothesis that clusters of tumor cells can complete the entire metastatic journey in a process referred to as collective metastasis. Here we highlight recent studies unraveling how multicellular coordination, via both physical and biochemical coupling of cells, induces cooperative properties advantageous for the completion of metastasis. We discuss conceptual challenges and unique mechanisms arising from collective dissemination that are distinct from single cell-based metastasis. Finally, we consider how the dissection of molecular transitions regulating collective metastasis could offer potential insight into cancer therapy.

Morphological screening of mesenchymal mammary tumor organoids to identify drugs that reverse epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) has been implicated in conferring stem cell properties and therapeutic resistance to cancer cells. Therefore, identification of drugs that can reprogram EMT may provide new therapeutic strategies. Here, we report that cells derived from claudin-low mammary tumors, a mesenchymal subtype of triple-negative breast cancer, exhibit a distinctive organoid structure with extended "spikes" in 3D matrices. Upon a miR-200 induced mesenchymal-epithelial transition (MET), the organoids switch to a smoother round morphology. Based on these observations, we developed a morphological screening method with accompanying analytical pipelines that leverage deep neural networks and nearest neighborhood classification to screen for EMT-reversing drugs. Through screening of a targeted epigenetic drug library, we identified multiple class I HDAC inhibitors and Bromodomain inhibitors that reverse EMT. These data support the use of morphological screening of mesenchymal mammary tumor organoids as a platform to identify drugs that reverse EMT.

Mechano-induced cell metabolism promotes microtubule glutamylation to force metastasis

Mechanical signals from the tumor microenvironment modulate cell mechanics and influence cell metabolism to promote cancer aggressiveness. Cells withstand external forces by adjusting the stiffness of their cytoskeleton. Microtubules (MTs) act as compression-bearing elements. Yet how cancer cells regulate MT dynamic in response to the locally constrained environment has remained unclear. Using breast cancer as a model of a disease in which mechanical signaling promotes disease progression, we show that matrix stiffening rewires glutamine metabolism to promote MT glutamylation and force MT stabilization, thereby promoting cell invasion. Pharmacologic inhibition of glutamine metabolism decreased MT glutamylation and affected their mechanical stabilization. Similarly, decreased MT glutamylation by overexpressing tubulin mutants lacking glutamylation site(s) decreased MT stability, thereby hampering cancer aggressiveness in vitro and in vivo. Together, our results decipher part of the enigmatic tubulin code that coordinates the fine-tunable properties of MT and link cell metabolism to MT dynamics and cancer aggressiveness.

Engineering a 3D collective cancer invasion model with control over collagen fiber alignment

Prior to cancer cell invasion, the structure of the extracellular matrix (ECM) surrounding the tumor is remodeled, such that circumferentially oriented matrix fibers become radially aligned. This predisposed radially aligned matrix structure serves as a critical regulator of cancer invasion. However, a biomimetic 3D model recapitulating a tumor's behavioral response to these ECM structures is not yet available. In this study, we have developed a phase-specific, force-guided method to establish a 3D dual topographical tumor model in which each tumor spheroid/organoid is surrounded by radially aligned collagen I fibers on one side and circumferentially oriented fibers on the opposite side. A coaxial rotating cylinder system was employed to construct the dual fiber topography and to pre-seed tumor spheroids/organoids within a single device. This system enables the application of different force mechanisms in the nucleation and elongation phases of collagen fiber polymerization to guide fiber alignment. In the nucleation phase, fiber alignment is enhanced by a horizontal laminar Couette flow driven by the inner cylinder rotation. In the elongation phase, fiber growth is guided by a vertical gravitational force to form a large aligned collagen matrix gel (35 × 25 × 0.5 mm) embedded with >1000 tumor spheroids. The fibers above each tumor spheroid are radially aligned along the direction of gravitational force in contrast to the circumferentially oriented fibers beneath each tumor spheroid/organoid, where the presence of the tumor interferes with the gravity-induced fiber alignment. After tumor invasion, there are more disseminated multicellular clusters on the radially aligned side, compared to the side of the tumor spheroid/organoid facing circumferentially oriented fibers. These results indicate that our 3D dual topographical model recapitulates the preference of tumors to invade and disseminate along radially aligned fibers. We anticipate that this 3D dual topographical model will have broad utility to those studying collective tumor invasion and that it has the potential to identify cancer invasion-targeted therapeutic agents.

Organoids in cancer research: a review for pathologist-scientists

The use of three-dimensional (3D) culture models for cancer research has expanded greatly in recent years, with studies in almost every tumor type addressing a wide variety of research questions. Multiple distinct 3D culture approaches are now available, each with its own advantages and disadvantages, as well as most effective applications. In this review, we focus on one of these 3D culture models, organoids, in which multicellular units are isolated from primary or metastatic tumors and cultured in extracellular matrix gels. Organoids can be studied in acute cultures for short times after isolation, or passaged and biobanked for long-term use. We define this model system and describe some key studies in which organoid culture models were used to investigate cellular strategies and molecular mechanisms driving cancer initiation and progression, highlighting research questions for which this model is particularly well suited. In addition, as interest in implementing organoid systems continues to expand, we discuss key considerations in developing a new organoid research program. Our goal is to demonstrate the power and utility of organoid models and provide guidance for investigators who are considering implementation of these models in their own research programs. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Engineering confining microenvironment for studying cancer metastasis

The physical microenvironment of cells plays a fundamental role in regulating cellular behavior and cell fate, especially in the context of cancer metastasis. For example, capillary deformation can destroy arrested circulating tumor cells while the dense extracellular matrix can form a physical barrier for invading cancer cells. Understanding how metastatic cancer cells overcome the challenges brought forth by physical confinement can help in developing better therapeutics that can put a stop to this migratory stage of the metastatic cascade. Numerous in vivo and in vitro assays have been developed to recapitulate the metastatic processes and study cancer cell migration in a confining microenvironment. In this review, we summarize some of the representative techniques and the exciting new findings. We critically review the advantages, as well as challenges associated with these tools and methodologies, and provide a guide on the applications that they are most suited for. We hope future efforts that push forward our current understanding on metastasis under confinement can lead to novel and more effective diagnostic and therapeutic strategies against this dreaded disease.

Neuroblastoma Invasion Strategies Are Regulated by the Extracellular Matrix

Neuroblastoma is a paediatric malignancy of the developing sympathetic nervous system. About half of the patients have metastatic disease at the time of diagnosis and a survival rate of less than 50%. Our understanding of the cellular processes promoting neuroblastoma metastases will be facilitated by the development of appropriate experimental models. In this study, we aimed to explore the invasion of neuroblastoma cells and organoids from patient-derived xenografts (PDXs) grown embedded in 3D extracellular matrix (ECM) hydrogels by time-lapse microscopy and quantitative image analysis. We found that the ECM composition influenced the growth, viability and local invasion of organoids. The ECM compositions induced distinct cell behaviours, with Matrigel being the preferred substratum for local organoid invasion. Organoid invasion was cell line- and PDX-dependent. We identified six distinct phenotypes in PDX-derived organoids. In contrast, NB cell lines were more phenotypically restricted in their invasion strategies, as organoids isolated from cell line-derived xenografts displayed a broader range of phenotypes compared to clonal cell line clusters. The addition of FBS and bFGF induced more aggressive cell behaviour and a broader range of phenotypes. In contrast, the repression of the prognostic neuroblastoma marker, MYCN, resulted in less aggressive cell behaviour. The combination of PDX organoids, real-time imaging and the novel 3D culture assays developed herein will enable rapid progress in elucidating the molecular mechanisms that control neuroblastoma invasion.

Optimal, Large-Scale Propagation of Mouse Mammary Tumor Organoids

Tumor organoids mimic the architecture and heterogeneity of in vivo tumors and enable studies of collective interactions between tumor cells as well as with their surrounding microenvironment. Although tumor organoids hold significant promise as cancer models, they are also more costly and labor-intensive to cultivate than traditional 2D cell culture. We sought to identify critical factors regulating organoid growth ex vivo, and to use these observations to develop a more efficient organoid expansion method. Using time-lapse imaging of mouse mammary tumor organoids in 3D culture, we observed that outgrowth potential varies non-linearly with initial organoid size. Maximal outgrowth occurred in organoids with a starting size between ~10 to 1000 cells. Based on these observations, we developed a suspension culture method that maintains organoids in the ideal size range, enabling expansion from 1 million to over 100 million cells in less than 2 weeks and less than 3 hours of hands-on time. Our method facilitates the rapid, cost-effective expansion of organoids for CRISPR based studies and other assays requiring a large amount of organoid starting material.

Metastatic behavior analyses of tetraspanin TM4SF5-expressing spheres in three-dimensional (3D) cell culture environment

Cancer metastasis involves diverse cellular functions via bidirectional communications between intracellular and extracellular spaces. To achieve development of the anti-metastatic drugs, one needs to consider the efficacy and mode of action (MOA) of the drug candidates to block the metastatic potentials of cancerous cells. Rather than under two-dimensional environment, investigation of the metastatic potentials under three-dimensional environment would be much pharmaceutically beneficent, since it can mimic the in vivo tumor lesions in cancer patients, leading to allowance of drug candidates analyzed in the 3D culture systems to lower failure rates during the anti-metastatic drug development. Here we have reviewed on the analyses of metastatic potentials of certain cancer models in 3D culture systems surrounded with extracellular matrix proteins, which could be supported by TM4SF5- and/or EMT-mediated actions. We particularly focused the initial events of the cancer metastasis, such as invasive outgrowth and dissemination from the cancer cell masses, spheroids, embedded in the 3D gel culture systems. This review summarizes the significance of tetraspanin TM4SF5 and Snail1 that are related to EMT in the metastatic potentials explored in the 3D gel systems.