Design of a mucin-selective protease for targeted degradation of cancer-associated mucins

Targeted protein degradation is an emerging strategy for the elimination of classically undruggable proteins. Here, to expand the landscape of targetable substrates, we designed degraders that achieve substrate selectivity via recognition of a discrete peptide and glycan motif and achieve cell-type selectivity via antigen-driven cell-surface binding. We applied this approach to mucins, O-glycosylated proteins that drive cancer progression through biophysical and immunological mechanisms. Engineering of a bacterial mucin-selective protease yielded a variant for fusion to a cancer antigen-binding nanobody. The resulting conjugate selectively degraded mucins on cancer cells, promoted cell death in culture models of mucin-driven growth and survival, and reduced tumor growth in mouse models of breast cancer progression. This work establishes a blueprint for the development of biologics that degrade specific protein glycoforms on target cells.

Mechanosensitive hormone signaling promotes mammary progenitor expansion and breast cancer risk

Tissue stem-progenitor cell frequency has been implicated in tumor risk and progression, but tissue-specific factors linking these associations remain ill-defined. We observed that stiff breast tissue from women with high mammographic density, who exhibit increased lifetime risk for breast cancer, associates with abundant stem-progenitor epithelial cells. Using genetically engineered mouse models of elevated integrin mechanosignaling and collagen density, syngeneic manipulations, and spheroid models, we determined that a stiff matrix and high mechanosignaling increase mammary epithelial stem-progenitor cell frequency and enhance tumor initiation in vivo. Augmented tissue mechanics expand stemness by potentiating extracellular signal-related kinase (ERK) activity to foster progesterone receptor-dependent RANK signaling. Consistently, we detected elevated phosphorylated ERK and progesterone receptors and increased levels of RANK signaling in stiff breast tissue from women with high mammographic density. The findings link fibrosis and mechanosignaling to stem-progenitor cell frequency and breast cancer risk and causally implicate epidermal growth factor receptor-ERK-dependent hormone signaling in this phenotype.

The microenvironment dictates glycocalyx construction and immune surveillance

Efforts to identify anti-cancer therapeutics and understand tumor-immune interactions are built with in vitro models that do not match the microenvironmental characteristics of human tissues. Using in vitro models which mimic the physical properties of healthy or cancerous tissues and a physiologically relevant culture medium, we demonstrate that the chemical and physical properties of the microenvironment regulate the composition and topology of the glycocalyx. Remarkably, we find that cancer and age-related changes in the physical properties of the microenvironment are sufficient to adjust immune surveillance via the topology of the glycocalyx, a previously unknown phenomenon observable only with a physiologically relevant culture medium.

Tissue tension permits β-catenin phosphorylation to drive mesoderm specification in human embryonic stem cells

The role of morphogenetic forces in cell fate specification is an area of intense interest. Our prior studies suggested that the development of high cell-cell tension in human embryonic stem cells (hESC) colonies permits the Src-mediated phosphorylation of junctional β-catenin that accelerates its release to potentiate Wnt-dependent signaling critical for initiating mesoderm specification. Using an ectopically expressed nonphosphorylatable mutant of β-catenin (Y654F), we now provide direct evidence that impeding tension-dependent Src-mediated β-catenin phosphorylation impedes the expression of Brachyury (T) and the epithelial-to-mesenchymal transition (EMT) necessary for mesoderm specification. Addition of exogenous Wnt3a or inhibiting GSK3β activity rescued mesoderm expression, emphasizing the importance of force dependent Wnt signaling in regulating mechanomorphogenesis. Our work provides a framework for understanding tension-dependent β-catenin/Wnt signaling in the self-organization of tissues during developmental processes including gastrulation.

Uptake of tumor-derived microparticles induces metabolic reprogramming of macrophages in the early metastatic lung

Pre-metastatic niche formation is a critical step during the metastatic spread of cancer. One way by which primary tumors prime host cells at future metastatic sites is through the shedding of tumor-derived microparticles as a consequence of vascular sheer flow. However, it remains unclear how the uptake of such particles by resident immune cells affects their phenotype and function. Here, we show that ingestion of tumor-derived microparticles by macrophages induces a rapid metabolic and phenotypic switch that is characterized by enhanced mitochondrial mass and function, increased oxidative phosphorylation, and upregulation of adhesion molecules, resulting in reduced motility in the early metastatic lung. This reprogramming event is dependent on signaling through the mTORC1, but not the mTORC2, pathway and is induced by uptake of tumor-derived microparticles. Together, these data support a mechanism by which uptake of tumor-derived microparticles induces reprogramming of macrophages to shape their fate and function in the early metastatic lung.

A convolutional neural network STIFMap reveals associations between stromal stiffness and EMT in breast cancer

Intratumor heterogeneity associates with poor patient outcome. Stromal stiffening also accompanies cancer. Whether cancers demonstrate stiffness heterogeneity, and if this is linked to tumor cell heterogeneity remains unclear. We developed a method to measure the stiffness heterogeneity in human breast tumors that quantifies the stromal stiffness each cell experiences and permits visual registration with biomarkers of tumor progression. We present Spatially Transformed Inferential Force Map (STIFMap) which exploits computer vision to precisely automate atomic force microscopy (AFM) indentation combined with a trained convolutional neural network to predict stromal elasticity with micron-resolution using collagen morphological features and ground truth AFM data. We registered high-elasticity regions within human breast tumors colocalizing with markers of mechanical activation and an epithelial-to-mesenchymal transition (EMT). The findings highlight the utility of STIFMap to assess mechanical heterogeneity of human tumors across length scales from single cells to whole tissues and implicates stromal stiffness in tumor cell heterogeneity.

Stiff matrix induces exosome secretion to promote tumour growth

Tissue fibrosis and extracellular matrix (ECM) stiffening promote tumour progression. The mechanisms by which ECM regulates its contacting cells have been extensively studied. However, how stiffness influences intercellular communications in the microenvironment for tumour progression remains unknown. Here we report that stiff ECM stimulates the release of exosomes from cancer cells. We delineate a molecular pathway that links stiff ECM to activation of Akt, which in turn promotes GTP loading to Rab8 that drives exosome secretion. We further show that exosomes generated from cells grown on stiff ECM effectively promote tumour growth. Proteomic analysis revealed that the Notch signalling pathway is activated in cells treated with exosomes derived from tumour cells grown on stiff ECM, consistent with our gene expression analysis of liver tissues from patients. Our study reveals a molecular mechanism that regulates exosome secretion and provides insight into how mechanical properties of the ECM control the tumour microenvironment for tumour growth.

Extracellular Matrix Glycation and Crosslinking in Mammary Tumor Progression

Breast cancer progression is accompanied by profound extracellular matrix (ECM) remodeling. A greater abundance of aligned fibrillar collagen is characteristic of invasive and aggressive breast cancers and has been associated with elevated activity of collagen crosslinking enzymes, such as lysyl oxidase (LOX) and lysyl hydroxylases (LH) and the formation of more mature collagen matrix crosslinks. Aligned collagen fibers can facilitate metastatic dissemination of tumor cells, and LOX inhibitors have been used to inhibit tumor progression and metastasis in experimental models. Thus, a better understanding of how matrix crosslinking alters tumor cell phenotypes, and behaviors would improve our ability to effectively treat aggressive metastatic breast cancer. Herein described is an experimental approach to glycate and crosslink a collagen-I/basement membrane extract ECM to study the impact of ECM crosslinking on mammary tumor progression in vivo. Moreover, glycation of collagen by sugars to form advanced glycation end products naturally occurs during aging, extending the potential relevance of this approach to research on mechanisms of aging involved in disease progression.

Novel cryo-tomography workflow reveals nanometer-scale responses of epithelial cells to matrix stiffness and dimensionality

Matrix stiffness and dimensionality have been shown to be major determinants of cell behavior. However, a workflow for examining nanometer-scale responses of the associated molecular machinery is not available. Here, we describe a comprehensive, quantitative workflow that permits the analysis of cells responding to mechanical and dimensionality cues in their native state at nanometer scale by cryogenic electron tomography. Using this approach, we quantified distinct cytoskeletal nanoarchitectures and vesicle phenotypes induced in human mammary epithelial cells in response to stiffness and dimensionality of reconstituted basement membrane. Our workflow closely recapitulates the microenvironment associated with acinar morphogenesis and identified distinct differences in situ at nanometer scale. Using drug treatment, we showed that molecular events and nanometer-scale rearrangements triggered by engagement of apical cell receptors with reconstituted basement membrane correspond to changes induced by reduction of cortical tension. Our approach is fully adaptable to any kind of stiffness regime, extracellular matrix composition, and drug treatment.

Abstract C051: Ceramide signaling regulates PDA aggression through exosome reprogramming of the stroma

Ceramide is a bioactive lipid signaling molecule that regulates multiple cellular processes influencing pancreatic tumor progression and drug response. The pleiotropic role of ceramide signaling in cancer includes modulation of exosome biogenesis and secretion. Smpd3 encodes an enzyme that generates ceramide through hydrolysis of sphingomyelin. Employing the KPC mouse model of pancreatic cancer, we demonstrated that Smpd3 regulates exosome biogenesis in pancreatic ductal adenocarcinoma (PDA) cells and is pro-tumorigenic during PDA progression. Ablation of Smdp3 in KPC mice significantly extends survival by 19% when compared to KPC; Smpd3wt/wt controls. KPC; Smpd3f/f mice display significantly less PanIN and tumor burden compared to KPC; Smpd3wt/wt controls. Lipidomics analysis of epithelial cell lines generated from end-stage pancreatic tumors of KPC; Smpd3f/f and KPC; Smpd3wt/wt mice demonstrated an alteration in hundreds of lipid species including ceramides, triacylglycerides, sphingomyelins, and phosphatidylcholines. Analysis of RNA-seq data of these epithelial cell lines showed a switching of primary tumors from the predominant more aggressive basal-like subtype seen in KPC; Smpd3wt/wt mice to classical in KPC; Smpd3f/f mice. Pathways analysis of our RNA-seq dataset showed an enrichment for genes involved in cellular mechanics and regulation of the tumor microenvironment. To query if Smpd3-generated exosomes have a direct effect on pancreatic tumor progression, we injected KPC; Smpd3wt/wt and KPC; Smpd3f/f mice with exosomes isolated from KPC; Smpd3f/f and KPC; Smpd3wt/wt PDA cell lines. Injection of exosomes derived from KPC; Smpd3f/f mice significantly extended survival of both Smpd3wt/wt and KPC; Smpd3f/f mice when compared to injection of exosomes isolated from KPC; Smpd3wt/wt mice, suggesting an anti-tumorigenic effect of exosomes isolated from Smpd3-deficient PDA cell lines. We observed a decrease in extracellular matrix collagen abundance and fewer activated stellate cells and fibroblasts in KPC; Smpd3f/f compared to control KPC; Smpd3wt/wt pancreata. Abrogation of Smpd3 expression also affected immune cell infiltration, as demonstrated by a significant increase in iNOS+ F4/80+ double positive macrophages in KPC; Smpd3f/f pancreata when compared to KPC; Smpd3wt/wt pancreata. Loss of Smpd3 resulted in a significant reduction in CD31+ endothelial cells in pancreatic tumors of KPC; Smpd3f/f mice when compared to KPC; Smpd3wt/wt mice, which may influence the ability of chemotherapeutics to enter pancreatic tumors. Our patient data demonstrate that high SMPD3 expression in surgically resected, treatment naive PDA significantly correlated with longer patient survival when patients received adjuvant chemotherapy, more than 95% of which was gemcitabine. Collectively, our data show that ceramide-dependent exosomes promote tumorigenesis, specifically activation of stellate cells and fibroblasts – which may in turn induce a stiff, fibrotic, proinflammatory tumor microenvironment that also impedes vasculature formation.

Citation Format: Audrey M. Hendley, Atsushi Urano, Xianlu L. Peng, Sudipta Ashe, Natanya R. Kerper, Tuan A. Phu, Martin Ng, Simone Giacometti, David I. Berrios, Gun H. Jang, Jen J. Yeh, Steven Gallinger, David K. Chang, Andrew V. Biankin, Valerie M. Weaver, Grace E. Kim, David W. Dawson, Robert L. Raffai, Matthias Hebrok. Ceramide signaling regulates PDA aggression through exosome reprogramming of the stroma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C051.

ECM dimensionality tunes actin tension to modulate endoplasmic reticulum function and spheroid phenotypes of mammary epithelial cells

Patient-derived organoids and cellular spheroids recapitulate tissue physiology with remarkable fidelity. We investigated how engagement with a reconstituted basement membrane in three dimensions (3D) supports the polarized, stress resilient tissue phenotype of mammary epithelial spheroids. Cells interacting with reconstituted basement membrane in 3D had reduced levels of total and actin-associated filamin and decreased cortical actin tension that increased plasma membrane protrusions to promote negative plasma membrane curvature and plasma membrane protein associations linked to protein secretion. By contrast, cells engaging a reconstituted basement membrane in 2D had high cortical actin tension that forced filamin unfolding and endoplasmic reticulum (ER) associations. Enhanced filamin-ER interactions increased levels of PKR-like ER kinase effectors and ER-plasma membrane contact sites that compromised calcium homeostasis and diminished cell viability. Consequently, cells with decreased cortical actin tension had reduced ER stress and survived better. Consistently, cortical actin tension in cellular spheroids regulated polarized basement membrane membrane deposition and sensitivity to exogenous stress. The findings implicate cortical actin tension-mediated filamin unfolding in ER function and underscore the importance of tissue mechanics in organoid homeostasis.

Low lamin A levels enhance confined cell migration and metastatic capacity in breast cancer

Aberrations in nuclear size and shape are commonly used to identify cancerous tissue. However, it remains unclear whether the disturbed nuclear structure directly contributes to the cancer pathology or is merely a consequence of other events occurring during tumorigenesis. Here, we show that highly invasive and proliferative breast cancer cells frequently exhibit Akt-driven lower expression of the nuclear envelope proteins lamin A/C, leading to increased nuclear deformability that permits enhanced cell migration through confined environments that mimic interstitial spaces encountered during metastasis. Importantly, increasing lamin A/C expression in highly invasive breast cancer cells reflected gene expression changes characteristic of human breast tumors with higher LMNA expression, and specifically affected pathways related to cell-ECM interactions, cell metabolism, and PI3K/Akt signaling. Further supporting an important role of lamins in breast cancer metastasis, analysis of lamin levels in human breast tumors revealed a significant association between lower lamin A levels, Akt signaling, and decreased disease-free survival. These findings suggest that downregulation of lamin A/C in breast cancer cells may influence both cellular physical properties and biochemical signaling to promote metastatic progression.

Mechanosensitive Steroid Hormone Signaling and Cell Fate

Mechanical forces collaborate across length scales to coordinate cell fate during development and the dynamic homeostasis of adult tissues. Similarly, steroid hormones interact with their nuclear and nonnuclear receptors to regulate diverse physiological processes necessary for the appropriate development and function of complex multicellular tissues. Aberrant steroid hormone action is associated with tumors originating in hormone-sensitive tissues and its disruption forms the basis of several therapeutic interventions. Prolonged perturbations to mechanical forces may further foster tumor initiation and the evolution of aggressive metastatic disease. Recent evidence suggests that steroid hormone and mechanical signaling intersect to direct cell fate during development and tumor progression. Potential mechanosensitive steroid hormone signaling pathways along with their molecular effectors will be discussed in this context.

Abstract SY23-01: Targeting the reciprocal interplay between inflammation, fibrosis, and pro-tumor immunity

Tumors are characterized by increased levels of remodeled and crosslinked extracellular matrix (ECM) proteins that progressively stiffen the tissue stroma. Transformed cells exhibit a perturbed oncogene-stimulated and ECM-tuned mechanophenotype that further stimulates ECM remodeling and stiffening. We have been exploring how these aberrant cell and tissue level forces arise and by what means these forces contribute to malignancy and metastasis, and how they promote tumor recurrence and treatment resistance. We use two and three dimensional culture models with tuned ECM stiffness, as well as transgenic and syngeneic mouse models, human PDX models and human biospecimens, in which ECM crosslinking and stiffness and integrin mechanosignaling are manipulated and quantified. Our work has thus far revealed that the tumor ECM is progressively remodeled, and stiffened, primarily by stromal fibroblasts. We determined that infiltrating pro-tumorigenic myeloid cells secrete factors that stimulate stromal fibroblasts to remodel and crosslink the ECM and that this occurs quite early during tumor evolution. The stromal-fibroblast stiffened ECM thereafter disrupts tissue organization, promotes cell growth and survival and drives cell invasion. The stiffened tumor stroma additionally drives angiogenesis, and activates STAT3 to increase expression of cytokines and chemokines that further stimulate immune cell infiltration. The stiffened ECM thereafter reprograms the infiltrating myeloid cells by altering integrin adhesions and TGFβ SMAD signaling to induce an ECM synthetic metabolic phenotype in the myeloid cells. The metabolically reprogrammed myeloid cells ultimately compromise arginine tissue availability and increase tissue levels of ornithine that severely disrupt CD8 T cell tissue infiltration and perturb their anti-tumor function to accelerate tumor aggression and metastatic dissemination. I will discuss the dynamic and reciprocal interplay between tissue tension and innate and acquired immunity. I will then present data to show how ECM stiffness is able to promote tumor aggression and metastasis by dysregulating anti-tumor immunity. I will end with a short discussion regarding approaches to design therapies informed by these results to improve cancer treatment.

Citation Format: Valerie M. Weaver. Targeting the reciprocal interplay between inflammation, fibrosis, and pro-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY23-01.

Screening of organoids derived from patients with breast cancer implicates the repressor NCOR2 in cytotoxic stress response and antitumor immunity

Resistance to antitumor treatment contributes to patient mortality. Functional proteomic screening of organoids derived from chemotherapy-treated patients with breast cancer identified nuclear receptor corepressor 2 (NCOR2) histone deacetylase as an inhibitor of cytotoxic stress response and antitumor immunity. High NCOR2 in the tumors of patients with breast cancer predicted chemotherapy refractoriness, tumor recurrence and poor prognosis. Molecular studies revealed that NCOR2 inhibits antitumor treatment by regulating histone deacetylase 3 (HDAC3) to repress interferon regulatory factor 1 (IRF-1)-dependent gene expression and interferon (IFN) signaling. Reducing NCOR2 or impeding its epigenetic activity by modifying its interaction with HDAC3 enhanced chemotherapy responsiveness and restored antitumor immunity. An adeno-associated viral NCOR2-HDAC3 competitor potentiated chemotherapy and immune checkpoint therapy in culture and in vivo by permitting transcription of IRF-1-regulated proapoptosis and inflammatory genes to increase IFN-γ signaling. The findings illustrate the utility of patient-derived organoids for drug discovery and suggest that targeting stress and inflammatory-repressor complexes such as NCOR2-HDAC3 could overcome treatment resistance and improve the outcome of patients with cancer.

Immunosuppressive glycoproteins associate with breast tumor fibrosis and aggression

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Increased sialoglycoprotein expression in high fibrosis regions and in TNBC.

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Cancer cells are the primary biosynthetic source of sialoglycoproteins.

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Immunosuppressive SIGLEC-positive myeloid cells are increased in TNBC.

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Immunosuppressive Siglec ligands are increased in high fibrosis regions.

Tumors feature elevated sialoglycoprotein content. Sialoglycoproteins promote tumor progression and are linked to immune suppression via the sialic acid-Siglec axis. Understanding factors that increase sialoglycoprotein biosynthesis in tumors could identify approaches to improve patient response to immunotherapy. We quantified higher levels of sialoglycoproteins in the fibrotic regions within human breast tumor tissues. Human breast tumor subtypes, which are more fibrotic, similarly featured increased sialoglycoprotein content. Further analysis revealed the breast cancer cells as the primary cell type synthesizing and secreting the tumor tissue sialoglycoproteins and confirmed that the more aggressive, fibrotic breast cancer subtypes expressed the highest levels of sialoglycoprotein biosynthetic genes. The more aggressive breast cancer subtypes also featured greater infiltration of immunosuppressive SIGLEC7, SIGLEC9, and SIGLEC10-pos myeloid cells, indicating that triple-negative breast tumors had higher expression of both immunosuppressive Siglec receptors and their cognate ligands. The findings link sialoglycoprotein biosynthesis and secretion to tumor fibrosis and aggression in human breast tumors. The data suggest targeting of the sialic acid-Siglec axis may comprise an attractive therapeutic target particularly for the more aggressive HER2+ and triple-negative breast cancer subtypes.

NCI's publication affiliation conundrum: Reframing innovation to incentivize an equitable path for advocate representation

Advocacy engagement has been at the forefront of National Cancer Institute (NCI) efforts to advance scientific discoveries and transform medical interventions. Nonetheless, the journey for advocates has been uneven. Case in Point: NCI publication affiliation rules of engagement pose unique equity challenges while raising questions about structural representation in biomedical research. Abiding by the core rationale that publication affiliation should be tailored to employment status, the NCI has systematically denied research advocate volunteers the opportunity to specifically list NCI as an institutional affiliation on academic publications. Unpacking advocate NCI publication affiliation restrictions and its links with advocacy heritage preservation and convergent science goals poses unique diversity, equity, and inclusion challenges and opportunities. Improving the quality of structural representation in biomedical research requires new theories of action and flexible planning to advance, promote and build capacity for strategic advocacy inclusion and equity within publication affiliation initiatives. Here we highlight several opportunities for how leadership might formulate a radically different vision for NCI's approach. This perspective interrogates the best way forward for ensuring that biomedical employee and volunteer advocate workforce publication affiliation intersections are characterized by increased creativity and representation parity. Imbuing the scientist and clinical researcher archetype with social dimensions, we join NCI critical thinkers in urging employees, funded academics, and volunteer citizen scientists to collectively assume the role as paladins of science and integrity who view the triumphs of making a difference in science alongside the social responsibility of promoting transdisciplinary professionalism and the democratization of science.

Adhesion-mediated mechanosignaling forces mitohormesis

Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.

Autophagy in stromal fibroblasts promotes tumor desmoplasia and mammary tumorigenesis

In this study, Rudnick et al. use mouse mammary cancer models and syngeneic transplantation assays to demonstrate that genetic ablation of stromal fibroblast autophagy significantly impedes fundamental elements of the stromal desmoplastic response, including collagen and proinflammatory cytokine secretion, extracellular matrix stiffening, and neoangiogenesis. Their findings suggest the efficacy of autophagy inhibition is shaped by the ability of host stromal fibroblast autophagy to support tumor desmoplasia.

Autophagy inhibitors are currently being evaluated in clinical trials for the treatment of diverse cancers, largely due to their ability to impede tumor cell survival and metabolic adaptation. More recently, there is growing interest in whether and how modulating autophagy in the host stroma influences tumorigenesis. Fibroblasts play prominent roles in cancer initiation and progression, including depositing type 1 collagen and other extracellular matrix (ECM) components, thereby stiffening the surrounding tissue to enhance tumor cell proliferation and survival, as well as secreting cytokines that modulate angiogenesis and the immune microenvironment. This constellation of phenotypes, pathologically termed desmoplasia, heralds poor prognosis and reduces patient survival. Using mouse mammary cancer models and syngeneic transplantation assays, we demonstrate that genetic ablation of stromal fibroblast autophagy significantly impedes fundamental elements of the stromal desmoplastic response, including collagen and proinflammatory cytokine secretion, extracellular matrix stiffening, and neoangiogenesis. As a result, autophagy in stromal fibroblasts is required for mammary tumor growth in vivo, even when the cancer cells themselves remain autophagy-competent . We propose the efficacy of autophagy inhibition is shaped by this ability of host stromal fibroblast autophagy to support tumor desmoplasia.

Targeting acid ceramidase inhibits YAP/TAZ signaling to reduce fibrosis in mice

Hepatic stellate cells (HSCs) drive hepatic fibrosis. Therapies that inactivate HSCs have clinical potential as antifibrotic agents. We previously identified acid ceramidase (aCDase) as an antifibrotic target. We showed that tricyclic antidepressants (TCAs) reduce hepatic fibrosis by inhibiting aCDase and increasing the bioactive sphingolipid ceramide. We now demonstrate that targeting aCDase inhibits YAP/TAZ activity by potentiating its phosphorylation-mediated proteasomal degradation via the ubiquitin ligase adaptor protein β-TrCP. In mouse models of fibrosis, pharmacologic inhibition of aCDase or genetic knockout of aCDase in HSCs reduces fibrosis, stromal stiffness, and YAP/TAZ activity. In patients with advanced fibrosis, aCDase expression in HSCs is increased. Consistently, a signature of the genes most down-regulated by ceramide identifies patients with advanced fibrosis who could benefit from aCDase targeting. The findings implicate ceramide as a critical regulator of YAP/TAZ signaling and HSC activation and highlight aCDase as a therapeutic target for the treatment of fibrosis.

Tissue mechanics in stem cell fate, development, and cancer

Cells in tissues experience a plethora of forces that regulate their fate and modulate development and homeostasis. Cells sense mechanical cues through localized mechanoreceptors or by influencing cytoskeletal or plasma membrane organization. Cells translate force and modulate their behavior through a process termed mechanotransduction. Cells tune their tension upon exposure to chronic force by engaging cellular machinery that modulates actin tension, which in turn stimulates matrix remodeling and stiffening and alters cell-cell adhesions until cells achieve a state of tensional homeostasis. Loss of tensional homeostasis can be induced through oncogene activity and/or tissue fibrosis, accompanies tumor progression, and is associated with increased cancer risk. The mechanical stresses that develop in tumors can also foster the mesenchymal-like transdifferentiation of cells to induce a stem-like phenotype that contributes to their aggression, metastatic dissemination, and treatment resistance. Thus, strategies that ameliorate tumor mechanics may comprise an effective strategy to prevent aggressive tumor behavior.

EPH/EPHRIN regulates cellular organization by actomyosin contractility effects on cell contacts

EPH/EPHRIN signaling is essential to many aspects of tissue self-organization and morphogenesis, but little is known about how EPH/EPHRIN signaling regulates cell mechanics during these processes. Here, we use a series of approaches to examine how EPH/EPHRIN signaling drives cellular self-organization. Contact angle measurements reveal that EPH/EPHRIN signaling decreases the stability of heterotypic cell:cell contacts through increased cortical actomyosin contractility. We find that EPH/EPHRIN-driven cell segregation depends on actomyosin contractility but occurs independently of directed cell migration and without changes in cell adhesion. Atomic force microscopy and live cell imaging of myosin localization support that EPH/EPHRIN signaling results in increased cortical tension. Interestingly, actomyosin contractility also nonautonomously drives increased EPHB2:EPHB2 homotypic contacts. Finally, we demonstrate that changes in tissue organization are driven by minimization of heterotypic contacts through actomyosin contractility in cell aggregates and by mouse genetics experiments. These data elucidate the biomechanical mechanisms driving EPH/EPHRIN-based cell segregation wherein differences in interfacial tension, regulated by actomyosin contractility, govern cellular self-organization.

Membrane Tension Locks In Pluripotency

In this issue of Cell Stem Cell, De Belly et al. (2021) and Bergert et al. (2021) reveal that membrane tension regulates the pluripotent state via endocytosis-mediated ERK signaling. These findings advance our understanding of naive pluripotency and highlight how cell mechanics are intertwined with molecular signaling to drive cell fate decisions.

Single-cell transcriptome analysis defines heterogeneity of the murine pancreatic ductal tree

To study disease development, an inventory of an organ's cell types and understanding of physiologic function is paramount. Here, we performed single-cell RNA-sequencing to examine heterogeneity of murine pancreatic duct cells, pancreatobiliary cells, and intrapancreatic bile duct cells. We describe an epithelial-mesenchymal transitory axis in our three pancreatic duct subpopulations and identify osteopontin as a regulator of this fate decision as well as human duct cell dedifferentiation. Our results further identify functional heterogeneity within pancreatic duct subpopulations by elucidating a role for geminin in accumulation of DNA damage in the setting of chronic pancreatitis. Our findings implicate diverse functional roles for subpopulations of pancreatic duct cells in maintenance of duct cell identity and disease progression and establish a comprehensive road map of murine pancreatic duct cell, pancreatobiliary cell, and intrapancreatic bile duct cell homeostasis.

Matrix compliance permits NF-κB activation to drive therapy resistance in breast cancer

Triple-negative breast cancers (TNBCs) are associated with poor survival mediated by treatment resistance. TNBCs are fibrotic, yet little is known regarding how the extracellular matrix (ECM) evolves following therapy and whether it impacts treatment response. Analysis revealed that while primary untreated TNBCs are surrounded by a rigid stromal microenvironment, chemotherapy-resistant residual tumors inhabit a softer niche. TNBC organoid cultures and xenograft studies showed that organoids interacting with soft ECM exhibit striking resistance to chemotherapy, ionizing radiation, and death receptor ligand TRAIL. A stiff ECM enhanced proapoptotic JNK activity to sensitize cells to treatment, whereas a soft ECM promoted treatment resistance by elevating NF-κB activity and compromising JNK activity. Treatment-resistant residual TNBCs residing within soft stroma had elevated activated NF-κB levels, and disengaging NF-κB activity sensitized tumors in a soft matrix to therapy. Thus, the biophysical properties of the ECM modify treatment response, and agents that modulate stiffness-dependent NF-κB or JNK activity could enhance therapeutic efficacy in patients with TNBC.

Tumour-associated macrophages drive stromal cell-dependent collagen crosslinking and stiffening to promote breast cancer aggression

Stromal stiffening accompanies malignancy, compromises treatment and promotes tumour aggression. Clarifying the molecular nature and the factors that regulate stromal stiffening in tumours should identify biomarkers to stratify patients for therapy and interventions to improve outcome. We profiled lysyl hydroxylase-mediated and lysyl oxidase-mediated collagen crosslinks and quantified the greatest abundance of total and complex collagen crosslinks in aggressive human breast cancer subtypes with the stiffest stroma. These tissues harbour the highest number of tumour-associated macrophages, whose therapeutic ablation in experimental models reduced metastasis, and decreased collagen crosslinks and stromal stiffening. Epithelial-targeted expression of the crosslinking enzyme, lysyl oxidase, had no impact on collagen crosslinking in PyMT mammary tumours, whereas stromal cell targeting did. Stromal cells in microdissected human tumours expressed the highest level of collagen crosslinking enzymes. Immunohistochemical analysis of biopsies from a cohort of patients with breast cancer revealed that stromal expression of lysyl hydroxylase 2, an enzyme that induces hydroxylysine aldehyde-derived collagen crosslinks and stromal stiffening, correlated significantly with disease specific mortality. The findings link tissue inflammation, stromal cell-mediated collagen crosslinking and stiffening to tumour aggression and identify lysyl hydroxylase 2 as a stromal biomarker.

Leveraging microenvironmental synthetic lethalities to treat cancer

Treatment resistance leads to cancer patient mortality. Therapeutic approaches that employ synthetic lethality to target mutational vulnerabilities in key tumor cell signaling pathways have proven effective in overcoming therapeutic resistance in some cancers. Yet, tumors are organs composed of malignant cells residing within a cellular and noncellular stroma. Tumor evolution and resistance to anticancer treatment are mediated through a dynamic and reciprocal dialogue with the tumor microenvironment (TME). Accordingly, expanding tumor cell synthetic lethality to encompass contextual synthetic lethality has the potential to eradicate tumors by targeting critical TME circuits that promote tumor progression and therapeutic resistance. In this Review, we summarize current knowledge about the TME and discuss its role in treatment. We outline the concept of tumor cell-specific synthetic lethality and describe therapeutic approaches to expand this paradigm to leverage TME synthetic lethality to improve cancer therapy.

Stiff stroma increases breast cancer risk by inducing the oncogene ZNF217

Women with dense breasts have an increased lifetime risk of malignancy that has been attributed to a higher epithelial density. Quantitative proteomics, collagen analysis, and mechanical measurements in normal tissue revealed that stroma in the high-density breast contains more oriented, fibrillar collagen that is stiffer and correlates with higher epithelial cell density. microRNA (miR) profiling of breast tissue identified miR-203 as a matrix stiffness-repressed transcript that is downregulated by collagen density and reduced in the breast epithelium of women with high mammographic density. Culture studies demonstrated that ZNF217 mediates a matrix stiffness- and collagen density-induced increase in Akt activity and mammary epithelial cell proliferation. Manipulation of the epithelium in a mouse model of mammographic density supported a causal relationship between stromal stiffness, reduced miR-203, higher levels of the murine homolog Zfp217, and increased Akt activity and mammary epithelial proliferation. ZNF217 was also increased in the normal breast epithelium of women with high mammographic density, correlated positively with epithelial proliferation and density, and inversely with miR-203. The findings identify ZNF217 as a potential target toward which preexisting therapies, such as the Akt inhibitor triciribine, could be used as a chemopreventive agent to reduce cancer risk in women with high mammographic density.

Pancreatic ductal adenocarcinoma progression is restrained by stromal matrix

Desmoplasia describes the deposition of extensive extracellular matrix and defines primary pancreatic ductal adenocarcinoma (PDA). The acellular component of this stroma has been implicated in PDA pathogenesis and is being targeted therapeutically in clinical trials. By analyzing the stromal content of PDA samples from numerous annotated PDA data sets and correlating stromal content with both anatomic site and clinical outcome, we found PDA metastases in the liver, the primary cause of mortality to have less stroma, have higher tumor cellularity than primary tumors. Experimentally manipulating stromal matrix with an anti-lysyl oxidase like-2 (anti-LOXL2) antibody in syngeneic orthotopic PDA mouse models significantly decreased matrix content, led to lower tissue stiffness, lower contrast retention on computed tomography, and accelerated tumor growth, resulting in diminished overall survival. These studies suggest an important protective role of stroma in PDA and urge caution in clinically deploying stromal depletion strategies.

Mechanical Tension Promotes Formation of Gastrulation-like Nodes and Patterns Mesoderm Specification in Human Embryonic Stem Cells

Embryogenesis is directed by morphogens that induce differentiation within a defined tissue geometry. Tissue organization is mediated by cell-cell and cell-extracellular matrix (ECM) adhesions and is modulated by cell tension and tissue-level forces. Whether cell tension regulates development by modifying morphogen signaling is less clear. Human embryonic stem cells (hESCs) exhibit an intrinsic capacity for self-organization, which motivates their use as a tractable model of early human embryogenesis. We engineered patterned substrates that recapitulate the biophysical properties of the early embryo and mediate the self-organization of "gastrulation-like" nodes in cultured hESCs. Tissue geometries that generated local nodes of high cell-adhesion tension directed the spatial patterning of the BMP4-dependent "gastrulation-like" phenotype by enhancing phosphorylation and junctional release of β-catenin to promote Wnt signaling and mesoderm specification. Furthermore, direct force application via mechanical stretching promoted BMP-dependent mesoderm specification, confirming that tissue-level forces can directly regulate cell fate specification in early human development.

Derivation of a nuclear heterogeneity image index to grade DCIS

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Abnormalities in cell nuclear morphology is a hallmark of cancer.

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Changes in nuclear morphology are utilized by pathologists in tumor grading.

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Heterogeneity in DCIS grade may influence invasive progression.

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Current pathological assessment of DCIS does not incorporate heterogeneity.

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I mage analysis is a supplemental tool for pathologists to quantitatively grade DCIS.

Abnormalities in cell nuclear morphology are a hallmark of cancer. Histological assessment of cell nuclear morphology is frequently used by pathologists to grade ductal carcinoma in situ (DCIS). Objective methods that allow standardization and reproducibility of cell nuclear morphology assessment have potential to improve the criteria needed to predict DCIS progression and recurrence. Aggressive cancers are highly heterogeneous. We asked whether cell nuclear morphology heterogeneity could be incorporated into a metric to classify DCIS. We developed a nuclear heterogeneity image index to objectively, and quantitatively grade DCIS. A whole-tissue cell nuclear morphological analysis, that classified tumors by the worst ten percent in a duct-by-duct manner, identified nuclear size ranges associated with each DCIS grade. Digital image analysis further revealed increasing heterogeneity within ducts or between ducts in tissues of worsening DCIS grade. The findings illustrate how digital image analysis comprises a supplemental tool for pathologists to objectively classify DCIS and in the future, may provide a method to predict patient outcome through analysis of nuclear heterogeneity.

Proteoglycans as Mediators of Cancer Tissue Mechanics

Proteoglycans are a diverse group of molecules which are characterized by a central protein backbone that is decorated with a variety of linear sulfated glycosaminoglycan side chains. Proteoglycans contribute significantly to the biochemical and mechanical properties of the interstitial extracellular matrix where they modulate cellular behavior by engaging transmembrane receptors. Proteoglycans also comprise a major component of the cellular glycocalyx to influence transmembrane receptor structure/function and mechanosignaling. Through their ability to initiate biochemical and mechanosignaling in cells, proteoglycans elicit profound effects on proliferation, adhesion and migration. Pathologies including cancer and cardiovascular disease are characterized by perturbed expression of proteoglycans where they compromise cell and tissue behavior by stiffening the extracellular matrix and increasing the bulkiness of the glycocalyx. Increasing evidence indicates that a bulky glycocalyx and proteoglycan-enriched extracellular matrix promote malignant transformation, increase cancer aggression and alter anti-tumor therapy response. In this review, we focus on the contribution of proteoglycans to mechanobiology in the context of normal and transformed tissues. We discuss the significance of proteoglycans for therapy response, and the current experimental strategies that target proteoglycans to sensitize cancer cells to treatment.

Don't sugarcoat it: How glycocalyx composition influences cancer progression

Buffone and Weaver discuss how the structure of the backbones and glycans of the tumor glycocalyx governs cell–matrix interactions and directs cancer progression.

Mechanical interactions between tumors and the extracellular matrix (ECM) of the surrounding tissues have profound effects on a wide variety of cellular functions. An underappreciated mediator of tumor–ECM interactions is the glycocalyx, the sugar-decorated proteins and lipids that act as a buffer between the tumor and the ECM, which in turn mediates all cell-tissue mechanics. Importantly, tumors have an increase in the density of the glycocalyx, which in turn increases the tension of the cell membrane, alters tissue mechanics, and drives a more cancerous phenotype. In this review, we describe the basic components of the glycocalyx and the glycan moieties implicated in cancer. Next, we examine the important role the glycocalyx plays in driving tension-mediated cancer cell signaling through a self-enforcing feedback loop that expands the glycocalyx and furthers cancer progression. Finally, we discuss current tools used to edit the composition of the glycocalyx and the future challenges in leveraging these tools into a novel tractable approach to treat cancer.

Abstract A49: A dual blockade of N-CoR2- and immune checkpoints induces complete remissions in treatment-refractory tumors

Background: The majority of human malignant tumors are resistant or only partially respond to conventional chemotherapy (C/T) or immunotherapy (I/T) such as immune checkpoint inhibitors (ICIs). Irrespective of the treatments, efficient tumor-cell killing requires amplification of inflammatory signaling, which, however, is tightly regulated by various “checkpoint” mechanisms evolved by epithelial cells to prevent excessive tissue damage induced by virus and immune attack. Novel approaches to disable theses conserved and cell-intrinsic inflammation checkpoints may provide breakthrough and “tumor-agnostic” strategies to circumvent the innate treatment resistance to unleash the full potential of C/T and I/T in treatment-refractory and highly lethal malignant tumors, such as triple-negative breast cancer (TNBC), pancreatic ductal adenocarcinoma (PDAC), and glioblastoma multiform (GBM).

Materials and Methods: We designed and conducted integrated genomic and proteomic screening combined with molecular and functional studies to identify conserved anti-inflammatory pathways that mediate innate and cell-intrinsic resistance to C/T and I/T agents. Preclinical studies were used to validate a gene therapy strategy to disable the inflammation-checkpoint identified from this process.

Results: We uncovered that the cytotoxic and immunogenic death induced by C/T and I/T agents is constrained by repression of a toll-like receptor-2 (TLR-2)/TLR-3- and NF-kB-induced interferon regulatory factor-1 (IRF-1) and interferon (IFN)-gamma anti-viral response program in various malignant tumor cells, including breast cancer, PDAC and GBM. Loss- and gain-of-function studies implicated that co-repressor-2 (N-CoR2) co-translocated with NF-kB p50 into cell nuclei in response to therapy, wherein it serves as an epigenetic checkpoint of this inflammation program by mediating a histone deacetylase-dependent chromatin remodeling and repression of a specific panel of proinflammatory and proapoptotic genes. Thus, high N-CoR2 expression predicts treatment refractoriness and poor prognosis in neoadjuvant or adjuvant-treated breast cancer patients. Blockade of the epigenetic checkpoint function of N-CoR2 by a small decoy of N-CoR2 hypersensitized malignant cells to assorted C/T agents, death ligands, and IFN-gamma. Consistently, intratumoral delivery of the N-CoR2 checkpoint blockade dramatically potentiated systemic C/T and ICI therapies, including anti-PD-1 and anti-CTLA-4 antibodies, and completely halted tumor growth or induced remissions in orthotopic and patient-derived xenograft models of TNBC and GBM.

Conclusion: Our findings suggest that malignant tumors can access intrinsically conserved anti-inflammatory mechanisms that enable them to escape from C/T and I/T. As such, strategies that can override this defense program constitute novel antitumor gene therapies that may be applied to overcome resistance in treatment-refractory tumors and improve patient prognosis.

Citation Format: Kelvin Tsai, Valerie M. Weaver. A dual blockade of N-CoR2- and immune checkpoints induces complete remissions in treatment-refractory tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A49.

Fibrosis and cancer: A strained relationship

Tumors are characterized by extracellular matrix (ECM) deposition, remodeling, and cross-linking that drive fibrosis to stiffen the stroma and promote malignancy. The stiffened stroma enhances tumor cell growth, survival and migration and drives a mesenchymal transition. A stiff ECM also induces angiogenesis, hypoxia and compromises anti-tumor immunity. Not surprisingly, tumor aggression and poor patient prognosis correlate with degree of tissue fibrosis and level of stromal stiffness. In this review, we discuss the reciprocal interplay between tumor cells, cancer associated fibroblasts (CAF), immune cells and ECM stiffness in malignant transformation and cancer aggression. We discuss CAF heterogeneity and describe its impact on tumor development and aggression focusing on the role of CAFs in engineering the fibrotic tumor stroma and tuning tumor cell tension and modulating the immune response. To illustrate the role of mechanoreciprocity in tumor evolution we summarize data from breast cancer and pancreatic ductal carcinoma (PDAC) studies, and finish by discussing emerging anti-fibrotic strategies aimed at treating cancer.

Patterning the Geometry of Human Embryonic Stem Cell Colonies on Compliant Substrates to Control Tissue-Level Mechanics

Human embryonic stem cells demonstrate a unique ability to respond to morphogens in vitro by self-organizing patterns of cell fate specification that correspond to primary germ layer formation during embryogenesis. Thus, these cells represent a powerful tool with which to examine the mechanisms that drive early human development. We have developed a method to culture human embryonic stem cells in confined colonies on compliant substrates that provides control over both the geometry of the colonies and their mechanical environment in order to recapitulate the physical parameters that underlie embryogenesis. The key feature of this method is the ability to generate polyacrylamide hydrogels with defined patterns of extracellular matrix ligand at the surface to promote cell attachment. This is achieved by fabricating stencils with the desired geometric patterns, using these stencils to create patterns of extracellular matrix ligand on glass coverslips, and transferring these patterns to polyacrylamide hydrogels during polymerization. This method is also compatible with traction force microscopy, allowing the user to measure and map the distribution of cell-generated forces within the confined colonies. In combination with standard biochemical assays, these measurements can be used to examine the role mechanical cues play in fate specification and morphogenesis during early human development.

Controlled modelling of human epiblast and amnion development using stem cells

Early human embryonic development involves extensive lineage diversification, cell-fate specification and tissue patterning¹. Despite its basic and clinical importance, early human embryonic development remains relatively unexplained owing to interspecies divergence^2,3 and limited accessibility to human embryo samples. Here we report that human pluripotent stem cells (hPSCs) in a microfluidic device recapitulate, in a highly controllable and scalable fashion, landmarks of the development of the epiblast and amniotic ectoderm parts of the conceptus, including lumenogenesis of the epiblast and the resultant pro-amniotic cavity, formation of a bipolar embryonic sac, and specification of primordial germ cells and primitive streak cells. We further show that amniotic ectoderm-like cells function as a signalling centre to trigger the onset of gastrulation-like events in hPSCs. Given its controllability and scalability, the microfluidic model provides a powerful experimental system to advance knowledge of human embryology and reproduction. This model could assist in the rational design of differentiation protocols of hPSCs for disease modelling and cell therapy, and in high-throughput drug and toxicity screens to prevent pregnancy failure and birth defects.