The biology and function of fibroblasts in cancer

FSP1-positive fibroblasts are adipogenic niche and regulate adipose homeostasis

Adipocyte progenitors reside in the stromal vascular fraction (SVF) of adipose tissues that are composed of fibroblasts, immune cells, and endothelial cells. It remains to be elucidated how the SVF regulates adipocyte progenitor fate determination and adipose homeostasis. Here, we report that fibroblast-specific protein-1 (FSP1)⁺ fibroblasts in the SVF are essential to adipose homeostasis. FSP1⁺ fibroblasts, devoid of adipogenic potential, are adjacent to the preadipocytes in the SVF. Ablation of FSP1⁺ fibroblasts in mice severely diminishes fat content of adipose depots. Activation of canonical Wnt signaling in the FSP1⁺ fibroblasts results in gradual loss of adipose tissues and resistance to diet-induced obesity. Alterations in the FSP1⁺ fibroblasts reduce platelet-derived growth factor (PDGF)-BB signaling and result in the loss of preadipocytes. Reduced PDGF-BB signaling, meanwhile, impairs the adipogenic differentiation capability of preadipocytes by regulating matrix metalloproteinase (MMP) expression, extracellular matrix remodeling, and the activation of Yes-associated protein (YAP) signaling. Thus, FSP1⁺ fibroblasts are an important niche essential to the maintenance of the preadipocyte pool and its adipogenic potential in adipose homeostasis.

White adipose tissue (WAT), which consists mostly of adipocytes, is not only a passive energy storage but also an active metabolic and endocrine organ in the body. The importance of maintaining proper adipose mass is emphasized by the fact that both adipose tissue excess—in obese individuals—and deficiency have adverse metabolic consequences. In order to maintain the number of adipocytes, there is a continuous turnover from preadipocytes in adults. Like any other adult stem cells and progenitor cells, cell fate and differentiation capability of preadipocytes are tightly regulated by a highly specialized niche. However, what constitutes the preadipocyte niche, and how the niche regulates preadipocyte function and adipose homeostasis, remain poorly known. In this study, we have identified fibroblast-specific protein-1 (FSP1)⁺ fibroblasts in the WAT stromal vascular fraction (SVF) of mice as the niche for preadipocytes. We show that FSP1⁺ fibroblasts with aberrant Wnt signaling fail to maintain the preadipocyte pool and its differentiation potential, resulting in loss of adipose tissue. We conclude that FSP1⁺ fibroblasts are a niche for preadipocytes and regulate adipose tissue homeostasis in adult mice.

Photosensitizer-Encapsulated Ferritins Mediate Photodynamic Therapy against Cancer-Associated Fibroblasts and Improve Tumor Accumulation of Nanoparticles

Nanoparticles have been widely tested as drug delivery carriers or imaging agents, largely because of their ability to selectively accumulate in tumors through the enhanced permeability and retention (EPR) effect. However, studies show that many tumors afford a less efficient EPR effect and that many nanoparticles are trapped in the perivascular region after extravasation and barely migrate into tumor centers. This is to a large degree attributed to the dense tumor extracellular matrix (ECM), which functions as a physical barrier to prevent efficient nanoparticle extravasation and diffusion. In this study, we report a photodynamic therapy (PDT) approach to enhance tumor uptake of nanoparticles. Briefly, we encapsulate ZnF16Pc, a photosensitizer, into ferritin nanocages, and then conjugate to the surface of the ferritin a single chain viable fragment (scFv) sequence specific to fibroblast activation protein (FAP). FAP is a plasma surface protein widely upregulated in cancer-associated fibroblasts (CAFs), which is a major source of the ECM fiber components. We found that the scFv-conjugated and ZnF16Pc-loaded ferritin nanoparticles (scFv-Z@FRT) can mediate efficient and selective PDT, leading to eradication of CAFs in tumors. When tested in bilateral 4T1 tumor models, we found that the tumor accumulation of serum albumin (BSA), 10 nm quantum dots (QDs), and 50 nm QDs was increased by 2-, 3.5-, and 18-fold after scFv-Z@FRT mediated PDT. Our studies suggest a novel and safe method to enhance the delivery of nanoparticles to tumors.

Improving knowledge on the activation of bone marrow fibroblasts in MGUS and MM disease through the automatic extraction of genes via a nonnegative matrix factorization approach on gene expression profiles

Background

Multiple myeloma (MM) is a cancer of terminally differentiated plasma that is part of a spectrum of blood diseases. The role of the micro-environment is crucial for MM clonal evolution.

Methods

This paper describes the analysis carried out on a limited number of genes automatically extracted by a nonnegative matrix factorization (NMF) based approach from gene expression profiles of bone marrow fibroblasts of patients with monoclonal gammopathy of undetermined significance (MGUS) and MM.

Results

Automatic exploration through NMF, combined with a motivated post-processing procedure and a pathways analysis of extracted genes, allowed to infer that a functional switch is required to lead fibroblasts to acquire pro-tumorigenic activity in the progression of the disease from MGUS to MM.

Conclusion

The extracted biologically relevant genes may be representative of the considered clinical conditions and may contribute to a deeper understanding of tumor behavior.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1589-1) contains supplementary material, which is available to authorized users.

A positive feedback loop bi-stably activates fibroblasts

Although fibroblasts are dormant in normal tissue, they exhibit explosive activation during wound healing and perpetual activation in pathologic fibrosis and cancer stroma. The key regulatory network controlling these fibroblast dynamics is still unknown. Here, we report that Twist1, a key regulator of cancer-associated fibroblasts, directly upregulates Prrx1, which, in turn, increases the expression of Tenascin-C (TNC). TNC also increases Twist1 expression, consequently forming a Twist1-Prrx1-TNC positive feedback loop (PFL). Systems biology studies reveal that the Twist1-Prrx1-TNC PFL can function as a bistable ON/OFF switch and regulates fibroblast activation. This PFL can be irreversibly activated under pathologic conditions, leading to perpetual fibroblast activation. Sustained activation of the Twist1-Prrx1-TNC PFL reproduces fibrotic nodules similar to idiopathic pulmonary fibrosis in vivo and is implicated in fibrotic disease and cancer stroma. Considering that this PFL is specific to activated fibroblasts, Twist1-Prrx1-TNC PFL may be a fibroblast-specific therapeutic target to deprogram perpetually activated fibroblasts.

The Role of Desmoplasia and Stromal Fibroblasts on Anti-cancer Drug Resistance in a Microengineered Tumor Model

Introduction

Cancer associated fibroblasts (CAFs) are known to participate in anti-cancer drug resistance by upregulating desmoplasia and pro-survival mechanisms within the tumor microenvironment. In this regard, anti-fibrotic drugs (i.e., tranilast) have been repurposed to diminish the elastic modulus of the stromal matrix and reduce tumor growth in presence of chemotherapeutics (i.e., doxorubicin). However, the quantitative assessment on impact of these stromal targeting drugs on matrix stiffness and tumor progression is still missing in the sole presence of CAFs.

Methods

We developed a high-density 3D microengineered tumor model comprised of MDA-MB-231 (highly invasive breast cancer cells) embedded microwells, surrounded by CAFs encapsulated within collagen I hydrogel. To study the influence of tranilast and doxorubicin on fibrosis, we probed the matrix using atomic force microscopy (AFM) and assessed matrix protein deposition. We further studied the combinatorial influence of the drugs on cancer cell proliferation and invasion.

Results

Our results demonstrated that the combinatorial action of tranilast and doxorubicin significantly diminished the stiffness of the stromal matrix compared to the control. The two drugs in synergy disrupted fibronectin assembly and reduced collagen fiber density. Furthermore, the combination of these drugs, condensed tumor growth and invasion.

Conclusion

In this work, we utilized a 3D microengineered model to tease apart the role of tranilast and doxorubicin in the sole presence of CAFs on desmoplasia, tumor growth and invasion. Our study lay down a ground work on better understanding of the role of biomechanical properties of the matrix on anti-cancer drug efficacy in the presence of single class of stromal cells.

Present and future of cancer immunotherapy: A tumor microenvironmental perspective

Modulation of the tumor microenvironment is becoming an increasingly popular research topic in the field of immunotherapy, and studies regarding immune checkpoint blockades and cancer immunotherapy have pushed cancer immunotherapy to a climax. Simultaneously, the manipulation of the immune regulatory pathway can create an effective immunotherapy strategy; however, the tumor microenvironment serves an important role in suppressing the antitumor immunity by its significant heterogeneity. A number of patients with cancer do not have a good response to monotherapy approaches; therefore, combination strategies are required to achieve optimal therapeutic benefits. Targeting the tumor microenvironment may provide a novel strategy for immunotherapy, break down the resistance of conventional cancer therapy and produce the foundation for personalized precision medicine. The present review summarized the research regarding cancer immunotherapy from the perspective of how the tumor microenvironment affects the immune response, with the aim of proposing a novel strategy for cancer immunotherapy and combination therapy.

Role of RAC3 coactivator in the adipocyte differentiation

RAC3 is a member of the p160 family of steroid receptor coactivators and it is highly expressed in several human cancers, contributing to enhanced cell proliferation and cellular transformation. In this work, we have studied the role of RAC3 in adipogenesis in L-929 cells. Adipogenesis is a highly regulated process, involving cell cycle arrest and changes in the gene expression pattern required for morphological remodelling. We found that RAC3 expression levels are downregulated during adipocyte differentiation induced by specific stimulus. In addition, cells constitutively expressing low levels of RAC3 (shRNA), showed enhanced adipocyte differentiation which was evidenced by the early detection of the adipocyte markers Perilipin, PPARγ and Oil Red O staining. Moreover, RAC3 downregulation favoured cell arrest and autophagy. Early and late autophagy inhibitors blocked adipocyte differentiation in control cells, but partially inhibited shRAC3 differentiation, demonstrating that although autophagy is required for adipogenesis, additional signals could be trigged by RAC3 downregulation. We conclude that RAC3 is a key regulator of adipogenesis, since its downregulation generates the cellular arrest and autophagic responses that are required steps for this process.

Radiation-Induced Myofibroblasts Promote Tumor Growth via Mitochondrial ROS-Activated TGFβ Signaling

Fibroblasts are a key stromal cell in the tumor microenvironment (TME) and promote tumor growth via release of various growth factors. Stromal fibroblasts in cancer, called cancer-associated fibroblasts (CAF), are related to myofibroblasts, an activated form of fibroblast. While investigating the role of stroma fibroblasts on radiation-related carcinogenesis, it was observed following long-term fractionated radiation (FR) that the morphology of human diploid fibroblasts changed from smaller spindle shapes to larger flat shapes. These cells expressed smooth muscle actin (α-SMA) and platelet-derived growth factor receptors, markers of myofibroblasts and CAFs, respectively. Long-term FR induces progressive damage to the fibroblast nucleus and mitochondria via increases in mitochondrial reactive oxygen species (ROS) levels. Here, it is demonstrated that long-term FR-induced α-SMA-positive cells have decreased mitochondrial membrane potential and activated oxidative stress responses. Antioxidant N-acetyl cysteine suppressed radiation-induced mitochondrial damage and generation of myofibroblasts. These results indicate that mitochondrial ROS are associated with the acquisition of myofibroblasts after long-term FR. Mechanistically, mitochondrial ROS activated TGFβ signaling which in turn mediated the expression of α-SMA in radiation-induced myofibroblasts. Finally, in vivo tumor growth analysis in a human tumor xenograft model system revealed that long-term FR-induced myofibroblasts promote tumor growth by enhancing angiogenesis.Implications: Radiation affects malignant cancer cells directly and indirectly via molecular alterations in stromal fibroblasts such as activation of TGFβ and angiogenic signaling pathways. Mol Cancer Res; 16(11); 1676-86. ©2018 AACR.

Stellate Cells in Tissue Repair, Inflammation, and Cancer

Stellate cells are resident lipid-storing cells of the pancreas and liver that transdifferentiate to a myofibroblastic state in the context of tissue injury. Beyond having roles in tissue homeostasis, stellate cells are increasingly implicated in pathological fibrogenic and inflammatory programs that contribute to tissue fibrosis and that constitute a growth-permissive tumor microenvironment. Although the capacity of stellate cells for extracellular matrix production and remodeling has long been appreciated, recent research efforts have demonstrated diverse roles for stellate cells in regulation of epithelial cell fate, immune modulation, and tissue health. Our present understanding of stellate cell biology in health and disease is discussed here, as are emerging means to target these multifaceted cells for therapeutic benefit.

Targeting Delivery of Lidocaine and Cisplatin by Nanogel Enhances Chemotherapy and Alleviates Metastasis

Tumor growth inhibition and adverse effect reduction together with metastasis alleviation are still the challenges that need to be overcome in cancer chemotherapy. Combinational therapy provides an alternative solution for these challenges. Nanoparticles are the ideal carriers for combinational therapy due to their versatile drug loading capacities and versatile tumor-targeting strategies. In this study, a cRGDfk modified nanogel system has been utilized to coload lidocaine, a voltage-gated Na⁺ channels inhibitor, and cisplatin, a common anticancer drug to obtain a tumor-targeted dual drugs-loaded nanogel system. The introduction of lidocaine not only promotes the cisplatin-induced apoptosis in vitro and in vivo but also alleviates the metastasis of MDA-MB-231 breast cancer cells in the mouse model. Besides, the body weight loss caused by cisplatin has also been relieved, and higher dose with less body weight loss can be achieved, which indicated the adverse effect caused by cisplatin-mediated chemotherapy has been alleviated. Furthermore, the introduction of peptide segment-cRGDfk, which presents high affinity to α_vβ₃ integrin, further increases the enrichment of drug-loaded nanogel in the tumor site. It favors the primary tumor growth inhibition. The results demonstrate the coloading of lidocaine and cisplatin by ligand-modified nanogels is a promising strategy for α_vβ₃ integrin-overexpressing breast cancer combinational therapy.

Mutual concessions and compromises between stromal cells and cancer cells: driving tumor development and drug resistance

BACKGROUND

Various cancers have been found to be associated with heterogeneous and adaptive tumor microenvironments (TMEs) and to be driven by the local TMEs in which they thrive. Cancer heterogeneity plays an important role in tumor cell survival, progression and drug resistance. The diverse cellular components of the TME may include cancer-associated fibroblasts, adipocytes, pericytes, mesenchymal stem cells, endothelial cells, lymphocytes and other immune cells. These components may support tumor development through the secretion of growth factors, evasion from immune checkpoints, metabolic adaptations, modulations of the extracellular matrix, activation of oncogenes and the acquisition of drug resistance. Here, we will address recent advances in our understanding of the molecular mechanisms underlying stromal-tumor cell interactions, with special emphasis on basic and pre-clinical information that may facilitate the design of novel personalized cancer therapies.

CONCLUSIONS

This review presents a holistic view on the translational potential of the interplay between stromal cells and cancer cells. This interplay is currently being employed for the development of promising preclinical and clinical biomarkers, and the design of small molecule inhibitors, antibodies and small RNAs for (combinatorial) cancer treatment options. In addition, nano-carriers, tissue scaffolds and 3-D based matrices are being developed to precisely and safely deliver these compounds.

Characterization and In Vivo Validation of a Three-Dimensional Multi-Cellular Culture Model to Study Heterotypic Interactions in Colorectal Cancer Cell Growth, Invasion and Metastasis

Colorectal cancer (CRC) is the third cause of cancer-related mortality in industrialized countries. Local invasion and metastasis formation are events associated with poor prognosis for which today there are no effective therapeutic options. Invasion and metastasis are strongly modulated by cells of the tumor microenvironment (TME), in particular fibroblasts and endothelial cells. Unraveling interactions between tumor cells and cells of the TME may identify novel mechanisms and therapeutic targets to prevent or treat metastasis. We report here the development and in vivo validation of a 3D tumor spheroid model to study the interactions between CRC cells, fibroblasts and endothelial cells in vitro. Co-cultured fibroblasts promoted SW620 and HCT116 CRC spheroid invasion, and this was prevented by the SRC and FGFR kinase inhibitors Dasatinib and Erdafitinib, respectively. To validate these findings in vivo, we injected SW620 cells alone or together with fibroblasts orthotopically in the caecum of mice. Co-injection with fibroblasts promoted lung metastasis growth, which was fully reversed by treatment with Dasatinib or Erdafitinib. Co-culture of SW620 or HCT116 CRC spheroids with endothelial cells suppressed spheroid growth while it had no effect on cancer cell migration or invasion. Consistent with this in vitro effect, co-injected endothelial cells significantly inhibited primary tumor growth in vivo. From these experiments we conclude that effects on cancer cell invasion and growth induced by co-cultured TME cells and drug treatment in the 3D spheroid model in vitro, are predictive of in vivo effects. The 3D spheroid model may be considered as an attractive model to study the effect of heterotypic cellular interactions and drug activities on cancer cells, as animal testing alternative. This model may be adapted and further developed to include different types of cancer and host cells and to investigate additional functions and drugs.

Perspective: bidirectional exosomal transport between cancer stem cells and their fibroblast-rich microenvironment during metastasis formation

Carcinomas are complex structures composed of hierarchically organized distinct cell populations such as cancer stem cells and non-stem (bulk) cancer cells. Their genetic/epigenetic makeup and the dynamic interplay between the malignant cell populations and their stromal fibroblasts are important determinants of metastatic tumor invasion. Important mediators of these interactions are the small, membrane-enclosed extracellular vesicles, in particular exosomes. Both cancer cell and fibroblast-derived exosomes carry a set of regulatory molecules, including proteins and different species of RNA, which cooperatively support metastatic tumor spread. Here, we briefly overview potential links between cancer stem cells and the exosome-mediated fibroblast-enriched metastatic niche formation to discuss their role in the promotion of tumor growth and metastatic expansion in breast carcinoma models.

TGFβ, Fibronectin and Integrin α5β1 Promote Invasion in Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most frequent human cancer and is becoming an important health problem in an aging population. Based on their clinical and histological characteristics, thick BCC are typically divided into low-risk nodular and high-risk infiltrative subtypes, although the underlying mechanisms are poorly understood. We have identified molecular mechanisms that explain the aggressiveness of high-risk infiltrative BCC, with a potential direct clinical impact. In this study, we first show that fibroblasts, transforming growth factor-β, and fibronectin are found preferentially in infiltrative human BCC. This allowed us to develop in vivo models for the study of infiltrative BCC, which in turn let us confirm the role of transforming growth factor-β in inducing peritumoral fibronectin deposition and tumor infiltration. We then show that fibronectin promotes adhesion and migration of BCC cell lines through integrin α5β1-mediated phosphorylation of focal adhesion kinase. Fittingly, both inhibition of integrin α5β1 and phospho-focal adhesion kinase prevent fibronectin-induced migration of BCC cells in vitro as well as BCC infiltration in vivo. Altogether, our results open important insights into the pathogenesis of aggressive infiltrative BCC and identify integrin α5β1 or focal adhesion kinase inhibition as promising strategies for the treatment of advanced BCC.

The cancer matrisome: From comprehensive characterization to biomarker discovery

Tumor progression and dissemination critically depend on support from the tumor microenvironment, the ensemble of cellular and acellular components surrounding and interacting with tumor cells. The extracellular matrix (ECM), the complex scaffolding of hundreds of proteins organizing cells in tissues, is a major component of the tumor microenvironment. It orchestrates cellular processes including proliferation, migration, and invasion, that are highly dysregulated during cancer progression. Alterations in ECM abundance, integrity, and mechanical properties have been correlated with poorer prognosis for cancer patients. Yet the ECM proteome, or "matrisome," of tumors remained until recently largely unexplored. This review will present the recent developments in computational and proteomic technologies that have allowed the comprehensive characterization of the ECM of different tumor types and microenvironmental niches. These approaches have resulted in the definition of protein signatures distinguishing tumors from normal tissues, tumors of different stages, primary from secondary tumors, and tumors from other diseased states such as fibrosis. Moreover, recent studies have demonstrated that the levels of expression of certain genes encoding ECM and ECM-associated proteins is prognostic of cancer patient survival and can thus serve as biomarkers. Last, proteomic studies have permitted the identification of novel ECM proteins playing functional roles in cancer progression. Such proteins have the potential to be exploited as therapeutic targets.

PEDF regulates plasticity of a novel lipid-MTOC axis in prostate cancer-associated fibroblasts

Prostate tumors make metabolic adaptations to ensure adequate energy and amplify cell cycle regulators, such as centrosomes, to sustain their proliferative capacity. It is not known whether cancer-associated fibroblasts (CAFs) undergo metabolic re-programming. We postulated that CAFs augment lipid storage and amplify centrosomal or non-centrosomal microtubule-organizing centers (MTOCs) through a pigment epithelium-derived factor (PEDF)-dependent lipid-MTOC signaling axis. Primary human normal prostate fibroblasts (NFs) and CAFs were evaluated for lipid content, triacylglycerol-regulating proteins, MTOC number and distribution. CAFs were found to store more neutral lipids than NFs. Adipose triglyceride lipase (ATGL) and PEDF were strongly expressed in NFs, whereas CAFs had minimal to undetectable levels of PEDF or ATGL protein. At baseline, CAFs demonstrated MTOC amplification when compared to 1-2 perinuclear MTOCs consistently observed in NFs. Treatment with PEDF or blockade of lipogenesis suppressed lipid content and MTOC number. In summary, our data support that CAFs have acquired a tumor-like phenotype by re-programming lipid metabolism and amplifying MTOCs. Normalization of MTOCs by restoring PEDF or by blocking lipogenesis highlights a previously unrecognized plasticity in centrosomes, which is regulated through a new lipid-MTOC axis.This article has an associated First Person interview with the first author of the paper.

Crosstalk between Notch, HIF-1α and GPER in Breast Cancer EMT

The Notch signaling pathway acts in both physiological and pathological conditions, including embryonic development and tumorigenesis. In cancer progression, diverse mechanisms are involved in Notch-mediated biological responses, including angiogenesis and epithelial-mesenchymal-transition (EMT). During EMT, the activation of cellular programs facilitated by transcriptional repressors results in epithelial cells losing their differentiated features, like cell–cell adhesion and apical–basal polarity, whereas they gain motility. As it concerns cancer epithelial cells, EMT may be consequent to the evolution of genetic/epigenetic instability, or triggered by factors that can act within the tumor microenvironment. Following a description of the Notch signaling pathway and its major regulatory nodes, we focus on studies that have given insights into the functional interaction between Notch signaling and either hypoxia or estrogen in breast cancer cells, with a particular focus on EMT. Furthermore, we describe the role of hypoxia signaling in breast cancer cells and discuss recent evidence regarding a functional interaction between HIF-1α and GPER in both breast cancer cells and cancer-associated fibroblasts (CAFs). On the basis of these studies, we propose that a functional network between HIF-1α, GPER and Notch may integrate tumor microenvironmental cues to induce robust EMT in cancer cells. Further investigations are required in order to better understand how hypoxia and estrogen signaling may converge on Notch-mediated EMT within the context of the stroma and tumor cells interaction. However, the data discussed here may anticipate the potential benefits of further pharmacological strategies targeting breast cancer progression.

Cisplatin-activated PAI-1 secretion in the cancer-associated fibroblasts with paracrine effects promoting esophageal squamous cell carcinoma progression and causing chemoresistance

Preoperative chemotherapy is a promising strategy for the treatment of esophageal squamous cell carcinoma (ESCC). Acquired resistance to chemotherapy is a major obstacle in improving patient prognosis. Cancer-associated fibroblasts (CAFs) are the primary components of the tumor microenvironment and play a crucial role in tumor development; these cells are also potential therapeutic targets for cancer. Using protein arrays, we identified a key secreted cytokine, PAI-1, from CAFs pretreated with cisplatin that was induced after DNA damage of CAFs. The PAI-1 in the tumor microenvironment promoted tumor growth and attenuated the effects of cisplatin treatment. Extracellular PAI-1 activated the AKT and ERK1/2 signaling pathways and inhibited caspase-3 activity and reactive oxygen species accumulation. Tiplaxtinin as a PAI-1 inhibitor could play synergistic effects with cisplatin in vitro and in vivo. In clinical samples, ESCC patients with high expression of PAI-1 in CAFs presented a significantly worse progression-free survival. Taken together, our results showed that PAI-1 secreted from cisplatin-activated CAFs promoted tumor growth and reduced the effects of cisplatin in a paracrine manner, establishing a preclinical rationale to target this cytokine to further improve the clinical response of esophageal squamous cell carcinoma.

Phenotype molding of stromal cells in the lung tumor microenvironment

Cancer cells are embedded in the tumor microenvironment (TME), a complex ecosystem of stromal cells. Here, we present a 52,698-cell catalog of the TME transcriptome in human lung tumors at single-cell resolution, validated in independent samples where 40,250 additional cells were sequenced. By comparing with matching non-malignant lung samples, we reveal a highly complex TME that profoundly molds stromal cells. We identify 52 stromal cell subtypes, including novel subpopulations in cell types hitherto considered to be homogeneous, as well as transcription factors underlying their heterogeneity. For instance, we discover fibroblasts expressing different collagen sets, endothelial cells downregulating immune cell homing and genes coregulated with established immune checkpoint transcripts and correlating with T-cell activity. By assessing marker genes for these cell subtypes in bulk RNA-sequencing data from 1,572 patients, we illustrate how these correlate with survival, while immunohistochemistry for selected markers validates them as separate cellular entities in an independent series of lung tumors. Hence, in providing a comprehensive catalog of stromal cells types and by characterizing their phenotype and co-optive behavior, this resource provides deeper insights into lung cancer biology that will be helpful in advancing lung cancer diagnosis and therapy.

Multiple liver insults synergize to accelerate experimental hepatocellular carcinoma

The urgent unmet need for hepatocellular carcinoma (HCC) therapies is addressed here by characterising a novel mouse model of HCC in the context of ongoing liver damage and overnutrition. Male C57Bl/6J mice were treated with diethylnitrosamine (DEN) and thioacetamide (TAA), and some were provided with an atherogenic high fat diet (HFD). Inflammation, steatosis, fibrosis, 87 genes, liver lesions and intratumoural leukocyte subsets were quantified up to 24 weeks of age. Adding HFD to DEN/TAA increased fibrosis, steatosis and inflammation, and the incidence of both HCC and non-HCC dysplastic lesions. All lesions contained α-SMA positive fibroblasts. Macrophage marker F4/80 was not significantly different between treatment groups, but the macrophage-associated genes Arg-1 and Cd47 were differentially expressed. Fibrosis, cancer and cell death associated genes were upregulated in DEN/TAA/HFD livers. Fewer Kupffer cells and plasmacytoid dendritic cells were in tumours compared to control liver. In conclusion, combining a hepatotoxin with an atherogenic diet produced more intrahepatic tumours, dysplastic lesions and fibrosis compared to hepatotoxin alone. This new HCC model provides a relatively rapid means of examining primary HCC and potential therapies in the context of multiple hepatotoxins including those derived from overnutrition.

IL-6 Mediates Cross-Talk between Tumor Cells and Activated Fibroblasts in the Tumor Microenvironment

The tumor microenvironment (TME) plays a major role in the pathogenesis of multiple cancer types, including upper-gastrointestinal (GI) cancers that currently lack effective therapeutic options. Cancer-associated fibroblasts (CAF) are an essential component of the TME, contributing to tumorigenesis by secreting growth factors, modifying the extracellular matrix, supporting angiogenesis, and suppressing antitumor immune responses. Through an unbiased approach, we have established that IL-6 mediates cross-talk between tumor cells and CAF not only by supporting tumor cell growth, but also by promoting fibroblast activation. As a result, IL-6 receptor (IL6Rα) and downstream effectors offer opportunities for targeted therapy in upper-GI cancers. IL-6 loss suppressed tumorigenesis in physiologically relevant three-dimensional (3D) organotypic and 3D tumoroid models and murine models of esophageal cancer. Tocilizumab, an anti-IL6Rα antibody, suppressed tumor growth in vivo in part via inhibition of STAT3 and MEK/ERK signaling. Analysis of a pan-cancer TCGA dataset revealed an inverse correlation between IL-6 and IL6Rα overexpression and patient survival. Therefore, we expanded evaluation of tocilizumab to head and neck squamous cell carcinoma patient-derived xenografts and gastric adenocarcinoma xenografts, demonstrating suppression of tumor growth and altered STAT3 and ERK1/2 gene signatures. We used small-molecule inhibitors of STAT3 and MEK1/2 signaling to suppress tumorigenesis in the 3D organotypic model of esophageal cancer. We demonstrate that IL6 is a major contributor to the dynamic cross-talk between tumor cells and CAF in the TME. Our findings provide a translational rationale for inhibition of IL6Rα and downstream signaling pathways as a novel targeted therapy in oral-upper-GI cancers.Significance: These findings demonstrate the interaction of esophageal cancer and cancer-associated fibroblasts through IL-6 signaling, providing rationale for a novel therapeutic approach to target these cancers. Cancer Res; 78(17); 4957-70. ©2018 AACR.

Fibrosis in metastatic lymph nodes is clinically correlated to poor prognosis in colorectal cancer

Background

Tumor microenvironment including fibrosis has a pivotal role in cancer growth and distant metastasis. Fibrosis is a known risk factor for carcinogenesis, but its biological role in disease invasion and metastasis in colorectal cancer (CRC) remains unclear. In particular, there is no report on how fibrosis of metastatic lymph nodes (MLNs) in CRC contributes to prognosis.

Methods

We reviewed 94 colorectal adenocarcinoma patients with MLNs who underwent colectomy. Both the primary tumors and MLNs were analyzed for alpha-smooth muscle actin (α-SMA) expression and collagen deposition.

Results

Higher α-SMA expression and collagen deposition in MLNs were associated with significantly shorter relapse-free survival and overall survival in CRC patients. α-SMA expression in MLNs (HR, 1.53; p = 0.034) was independent predictive factor of overall survival in multivariate Cox proportional hazards regression analysis of clinicopathological factors. In the Stage III patient subgroup, α-SMA expression in MLNs was a strong prognostic marker (HR, 3.01; p = 0.006). On the other hand, higher α-SMA expression and collagen deposition in primary tumors were associated with short overall survival, but they were not significant factors in multivariate Cox regression analyses. In MLNs, the podoplanin signals co-localized with α-SMA expression and were confirmed by the dual immunofluorescence staining, implying that the MLN stromal cells were fibroblastic reticular cells.

Conclusion

Both high collagen deposition and high α-SMA expression in MLNs predicted poor prognosis in CRC.

Inhibition of integrin αVβ6 changes fibril thickness of stromal collagen in experimental carcinomas

Background

Chemotherapeutic efficacy can be improved by targeting the structure and function of the extracellular matrix (ECM) in the carcinomal stroma. This can be accomplished by e.g. inhibiting TGF-β1 and -β3 or treating with Imatinib, which results in scarcer collagen fibril structure in xenografted human KAT-4/HT29 (KAT-4) colon adenocarcinoma.

Methods

The potential role of α_Vβ₆ integrin-mediated activation of latent TGF-β was studied in cultured KAT-4 and Capan-2 human ductal pancreatic carcinoma cells as well as in xenograft carcinoma generated by these cells. The monoclonal α_Vβ₆ integrin-specific monoclonal antibody 3G9 was used to inhibit the α_Vβ₆ integrin activity.

Results

Both KAT-4 and Capan-2 cells expressed the α_Vβ₆ integrin but only KAT-4 cells could utilize this integrin to activate latent TGF-β in vitro. Only when Capan-2 cells were co-cultured with human F99 fibroblasts was the integrin activation mechanism triggered, suggesting a more complex, fibroblast-dependent, activation pathway. In nude mice, a 10-day treatment with 3G9 reduced collagen fibril thickness and interstitial fluid pressure in KAT-4 but not in the more desmoplastic Capan-2 tumors that, to achieve a similar effect, required a prolonged 3G9 treatment. In contrast, a 10-day direct inhibition of TGF-β1 and -β3 reduced collagen fibril thickness in both tumor models.

Conclusion

Our data demonstrate that the α_Vβ₆-directed activation of latent TGF-β plays a pivotal role in modulating the stromal collagen network in carcinoma, but that the sensitivity to α_Vβ₆ inhibition depends on the simultaneous presence of alternative paths for latent TGF-β activation and the extent of desmoplasia.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0249-7) contains supplementary material, which is available to authorized users.

Croix B. Tumor stroma-targeted antibody-drug conjugate triggers localized anticancer drug release

Although nonmalignant stromal cells facilitate tumor growth and can occupy up to 90% of a solid tumor mass, better strategies to exploit these cells for improved cancer therapy are needed. Here, we describe a potent MMAE-linked antibody-drug conjugate (ADC) targeting tumor endothelial marker 8 (TEM8, also known as ANTXR1), a highly conserved transmembrane receptor broadly overexpressed on cancer-associated fibroblasts, endothelium, and pericytes. Anti-TEM8 ADC elicited potent anticancer activity through an unexpected killing mechanism we term DAaRTS (drug activation and release through stroma), whereby the tumor microenvironment localizes active drug at the tumor site. Following capture of ADC prodrug from the circulation, tumor-associated stromal cells release active MMAE free drug, killing nearby proliferating tumor cells in a target-independent manner. In preclinical studies, ADC treatment was well tolerated and induced regression and often eradication of multiple solid tumor types, blocked metastatic growth, and prolonged overall survival. By exploiting TEM8+ tumor stroma for targeted drug activation, these studies reveal a drug delivery strategy with potential to augment therapies against multiple cancer types.

Transforming growth factor-β modulates pancreatic cancer associated fibroblasts cell shape, stiffness and invasion

BACKGROUND

Tumor microenvironment consists of the extracellular matrix (ECM), stromal cells, such as fibroblasts (FBs) and cancer associated fibroblasts (CAFs), and a myriad of soluble factors. In many tumor types, including pancreatic tumors, the interplay between stromal cells and the other tumor microenvironment components leads to desmoplasia, a cancer-specific type of fibrosis that hinders treatment. Transforming growth factor beta (TGF-β) and CAFs are thought to play a crucial role in this tumor desmoplastic reaction, although the involved mechanisms are unknown.

METHODS

Optical/fluorescence microscopy, atomic force microscopy, image processing techniques, invasion assay in 3D collagen I gels and real-time PCR were employed to investigate the effect of TGF-β on normal pancreatic FBs and CAFs with regard to crucial cellular morphodynamic characteristics and relevant gene expression involved in tumor progression and metastasis.

RESULTS

CAFs present specific myofibroblast-like characteristics, such as α-smooth muscle actin expression and cell elongation, they also form more lamellipodia and are softer than FBs. TGF-β treatment increases cell stiffness (Young's modulus) of both FBs and CAFs and increases CAF's (but not FB's) elongation, cell spreading, lamellipodia formation and spheroid invasion. Gene expression analysis shows that these morphodynamic characteristics are mediated by Rac, RhoA and ROCK expression in CAFs treated with TGF-β.

CONCLUSIONS

TGF-β modulates CAFs', but not FBs', cell shape, stiffness and invasion.

GENERAL SIGNIFICANCE

Our findings elucidate on the effects of TGF-β on CAFs' behavior and stiffness providing new insights into the mechanisms involved.

Cancer-Stimulated CAFs Enhance Monocyte Differentiation and Protumoral TAM Activation via IL6 and GM-CSF Secretion

Purpose: M2-type TAMs are increasingly implicated as a crucial factor promoting metastasis. Numerous cell types dictate monocyte differentiation into M2 TAMs via a complex network of cytokine-based communication. Elucidating critical pathways in this network can provide new targets for inhibiting metastasis. In this study, we focused on cancer cells, CAFs, and monocytes as a major node in this network.Experimental Design: Monocyte cocultures with cancer-stimulated CAFs were used to investigate differentiation into M2-like TAMs. Cytokine array analyses were employed to discover the CAF-derived regulators of differentiation. These regulators were validated in primary CAFs and bone marrow-derived monocytes. Orthotopic, syngeneic colon carcinoma models using cotransplanted CAFs were established to observe effects on tumor growth and metastasis. To confirm a correlation with clinical evidence, meta-analyses were employed using the Oncomine database.Results: Our coculture studies identify IL6 and GM-CSF as the pivotal signals released from cancer cell-activated CAFs that cooperate to induce monocyte differentiation into M2-like TAMs. In orthotopic, syngeneic colon carcinoma mouse models, cotransplanted CAFs elevated IL6 and GM-CSF levels, TAM infiltration, and metastasis. These pathologic effects were dramatically reversed by joint IL6 and GM-CSF blockade. A positive correlation between GM-CSF and IL6 expression and disease course was observed by meta-analyses of the clinical data.Conclusions: Our studies indicate a significant reappraisal of the role of IL6 and GM-CSF in metastasis and implicate CAFs as the "henchmen" for cancer cells in producing an immunosuppressive tumor ecological niche. Dual targeting of GM-CSF and IL6 is a promising new approach for inhibiting metastasis. Clin Cancer Res; 24(21); 5407-21. ©2018 AACR.

Metabolic Interplay between Tumour Cells and Cancer-Associated Fibroblasts (CAFs) under Hypoxia versus Normoxia

The growth of tumour cells is closely related to cancer-associated fibroblasts (CAFs) present within their microenvironment. CAFs, the most abundant cells in tumour stroma, secrete growth factors that play pivotal roles in tumour cell proliferation, metabolism, angiogenesis and metastasis. Tumour cells adapt to rapid environmental changes from normoxia to hypoxia through metabolic interplay with CAFs. In this mini review, we discuss the role of lactate dehydrogenases (LDHs) and monocarboxylate transporters (MCTs) on the metabolic interplay between tumour cells and CAFs under hypoxia compared to normoxia. The LDHs catalyse the interchange of lactate and pyruvate, whereas MCTs facilitate the influx and efflux of monocarboxylates, especially lactate and pyruvate. To sum up, tumour cells switch their metabolic state between glycolysis and oxidative phosphorylation through metabolic interplay with CAFs, which exhibit the Warburg effect under hypoxia and reverse Warburg effect under normoxia.

BMP7 Signaling in TGFBR2-Deficient Stromal Cells Provokes Epithelial Carcinogenesis

Deregulated transforming growth factor-β (TGFβ) signaling is a common feature of many epithelial cancers. Deletion of TGFβ receptor type 2 (TGFBR2) in fibroblast specific protein-1 (FSP1)-positive stromal cells induces squamous cell carcinoma in the murine forestomach, implicating fibroblast-derived hepatocyte growth factor (HGF) as the major driver of the epithelium carcinogenesis. Prior to cancer development, hyperproliferative FSP1⁺ fibroblasts lacking TGFBR2 accumulate in the forestomach, disrupting the regulatory signaling cross-talk with the forestomach epithelium. Here, concurrent loss in TGFBR2 and SMAD4 completely abrogates the development of forestomach cancer. Bone morphogenic protein-7 (BMP7) was highly upregulated in forestomach cancer tissue, activating Smad1/5/8 signaling, cell proliferation, and HGF production in TGFBR2-deficient FSP1⁺ fibroblasts. This stimulation by BMP7 was lost in the combined TGFBR2 and SMAD4 double knockout fibroblasts, which included a profound decrease in HGF expression. Thus, Smad4-mediated signaling is required to initiate epithelial carcinogenesis subsequent to TGFBR2 deletion in FSP1⁺ fibroblasts.Implications: These findings reveal a complex cross-talk between epithelial cells and the stroma, wherein Smad4 is required to elicit squamous cell carcinomas in the forestomach of mice with TGFBR2-deficient stromal cells. Mol Cancer Res; 16(10); 1568-78. ©2018 AACR.

Targeting the NRG1/HER3 pathway in tumor cells and cancer-associated fibroblasts with an anti-neuregulin 1 antibody inhibits tumor growth in pre-clinical models of pancreatic cancer

Neuregulin 1 (NRG1), a ligand for HER3 and HER4 receptors, is secreted by both pancreatic tumor cells (PC) and cancer-associated fibroblasts (CAFs), the latter representing the most abundant compound of pancreatic stroma. This desmoplastic stroma contributes to Pancreatic Ductal Adenocarcinoma (PDAC) aggressiveness and therapeutic failure by promoting tumor progression, invasion and resistance to chemotherapies. In the present work, we aimed at disrupting the complex crosstalk between PC and CAF in order to prevent tumor cell proliferation. To do so, we demonstrated the promising tumor growth inhibitory effect of the 7E3, an original antibody directed to NRG1. This antibody promotes antibody dependent cellular cytotoxicity in NRG1-positive PC and CAFs and inhibits NRG1-associated signaling pathway induction, by blocking NRG1-mediated HER3 activation. Moreover, 7E3 inhibits migration and growth of pancreatic cancer cells co-cultured with CAFs, both in vitro and in vivo using orthotopic pancreatic tumor xenografts. Our preclinical results demonstrate that the anti-NRG1 antibody 7E3 could represent a promising approach to target pancreatic stroma and cancer cells, thereby providing novel therapeutic options for PDAC.

Altered p53 functionality in cancer-associated fibroblasts contributes to their cancer-supporting features

Within the tumor microenvironment, cancer cells coexist with noncancerous adjacent cells that constitute the tumor microenvironment and impact tumor growth through diverse mechanisms. In particular, cancer-associated fibroblasts (CAFs) promote tumor progression in multiple ways. Earlier studies have revealed that in normal fibroblasts (NFs), p53 plays a cell nonautonomous tumor-suppressive role to restrict tumor growth. We now wished to investigate the role of p53 in CAFs. Remarkably, we found that the transcriptional program supported by p53 is altered substantially in CAFs relative to NFs. In agreement, the p53-dependent secretome is also altered in CAFs. This transcriptional rewiring renders p53 a significant contributor to the distinct intrinsic features of CAFs, as well as promotes tumor cell migration and invasion in culture. Concordantly, the ability of CAFs to promote tumor growth in mice is greatly compromised by depletion of their endogenous p53. Furthermore, cocultivation of NFs with cancer cells renders their p53-dependent transcriptome partially more similar to that of CAFs. Our findings raise the intriguing possibility that tumor progression may entail a nonmutational conversion ("education") of stromal p53, from tumor suppressive to tumor supportive.

The TGFβ-induced lncRNA TBILA promotes non-small cell lung cancer progression in vitro and in vivo via cis-regulating HGAL and activating S100A7/JAB1 signaling

Long non-coding RNAs (lncRNAs) play critical roles in multiple cellular processes in non-small cell lung cancer (NSCLC); however, the involvement of lncRNAs in the transforming growth factor-beta (TGFβ) signaling pathway, the critical tumor cell epithelial-mesenchymal transition (EMT) and metastasis pathway, remains poorly understood. To address this issue, we compared the lncRNAs expression patterns of NSCLC cells treated with and without TGFβ1 treatment. We observed that one of the most prominent hits, TGFβ-induced lncRNA (TBILA), promoted NSCLC progression and was upregulated in tumor tissues. Upregulated TBILA promotes human germinal center-associated lymphoma (HGAL) expression by binding to the Smad transcription factor complex, thereby enhancing RhoA activation. In addition, TBILA induces the S100A7-c-Jun activation domain-binding protein 1 (JAB1) pathway by binding to nuclear S100A7 and enhances pro-survival pathways in NSCLC. These findings have provided us with a new perspective regarding the regulation of the TGFβ signaling pathway in NSCLC and suggest that the lncRNA TBILA can serve as a target for anticancer therapies.

Extracellular vesicle-mediated cell-cell communication in haematological neoplasms

Crosstalk between bone marrow tumour cells and surrounding cells, including bone marrow mesenchymal stromal cells (BM-MSCs), endothelial cells and immune cells, is important for tumour growth in haematological neoplasms. In addition to conventional signalling pathways, extracellular vesicles (EVs), which are endosome-derived vesicles containing proteins, mRNAs, lipids and miRNAs, can facilitate modulation of the bone marrow microenvironment without directly contacting non-tumourous cells. In this review, we discuss the current understanding of EV-mediated cell-cell communication in haematological neoplasms, particularly leukaemia and multiple myeloma. We highlight the actions of tumour and BM-MSC EVs in multiple myeloma. The origin of EVs, their tropism and mechanism of EV transfer are emerging issues that need to be addressed in EV-mediated cell-cell communication in haematological neoplasms.This article is part of the discussion meeting issue 'Extracellular vesicles and the tumour microenvironment'.

Underlying Causes and Therapeutic Targeting of the Inflammatory Tumor Microenvironment

Historically, the link between chronic inflammation and cancer has long been speculated. Only more recently, pre-clinical and epidemiologic data as well as clinical evidence all point to the role of the tumor microenvironment as inextricably connected to the neoplastic process. The tumor microenvironment (TME), a complex mix of vasculature, inflammatory cells, and stromal cells is the essential "soil" helping to modulate tumor potential. Increasingly, evidence suggests that chronic inflammation modifies the tumor microenvironment, via a host of mechanisms, including the production of cytokines, pro-inflammatory mediators, angiogenesis, and tissue remodeling. Inflammation can be triggered by a variety of different pressures, such as carcinogen exposure, immune dysfunction, dietary habits, and obesity, as well as genetic alterations leading to oncogene activation or loss of tumor suppressors. In this review, we examine the concept of the tumor microenvironment as related to both extrinsic and intrinsic stimuli that promote chronic inflammation and in turn tumorigenesis. Understanding the common pathways inherent in an inflammatory response and the tumor microenvironment may shed light on new therapies for both primary and metastatic disease. The concept of personalized medicine has pushed the field of oncology to drill down on the genetic changes of a cancer, in the hopes of identifying individually targeted agents. Given the complexities of the tumor microenvironment, it is clear that effective oncologic therapies will necessitate targeting not only the cancer cells, but their dynamic relationship to the tumor microenvironment as well.

Sleeping Beauty and the Microenvironment Enchantment: Microenvironmental Regulation of the Proliferation-Quiescence Decision in Normal Tissues and in Cancer Development

Cells from prokaryota to the more complex metazoans cease proliferating at some point in their lives and enter a reversible, proliferative-dormant state termed quiescence. The appearance of quiescence in the course of evolution was essential to the acquisition of multicellular specialization and compartmentalization and is also a central aspect of tissue function and homeostasis. But what makes a cell cease proliferating even in the presence of nutrients, growth factors, and mitogens? And what makes some cells "wake up" when they should not, as is the case in cancer? Here, we summarize and discuss evidence showing how microenvironmental cues such as those originating from metabolism, extracellular matrix (ECM) composition and arrangement, neighboring cells and tissue architecture control the cellular proliferation-quiescence decision, and how this complex regulation is corrupted in cancer.

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

The composition of prostate core matrisome in vivo and in vitro unveiled by mass spectrometric analysis

BACKGROUND

The composition and organization of extracellular matrix (ECM) are important regulators of cell behavior. In particular in the prostate, this central role of the ECM is further stressed by the fact that several potential markers of prostate stem cells are matrix receptors.

METHODS

We established 12 fibroblastic cell lines from cancerous and non-cancerous areas of six prostates and allowed the cells to produce ECM under cell culture conditions. We also performed a proteome wide analysis of the ECM components by mass spectrometry. To study the in vitro activation of fibroblastic cells we compared the differences between the ECM produced in cell culture by six non-cancerous-tissue-derived fibroblasts and the in vivo matrisome from the corresponding non-cancerous tissue of prostate.

RESULTS

Our results suggest that at tissue level the ECM is mainly produced by fibroblastic cells and that it contains standard collagen I fibrils and fibril-associated proteins. Beaded-filament forming collagen VI is also abundant and basement membranes potentially contain five laminin subtypes and collagens XV and XVIII. As the main finding, we also detected differences when in vivo and in vitro matrisomes were compared. Only 65 out of 206 proteins were found to be common for both in vivo and in vitro samples. Majority of the 55 proteins, which were solely detected in in vivo samples, were considered to be plasma derived. Eighty-six proteins were solely found from in vitro fibroblast-derived ECM, and most of them were related to matrix remodeling or growth factor action, proposing that the activation of fibroblasts in cell culture may remarkably modify their gene expression profile. Finally, in comparison to traditional 2D in vitro cell culture, the ECM composition of 3D spheroid culture was analyzed. The matrisome in spheroid culture did not resemble the in vivo ECM more closely than in monolayer culture.

CONCLUSIONS

Artificial activation of ECM remodeling seems to be a distinctive feature in in vitro models. In conclusion the constitution of ECM produced by prostate derived fibroblasts in vitro is similar, but not identical to the prostate ECM in vivo as shown here by mass spectrometric analysis.

Known and novel roles of the MET oncogene in cancer: a coherent approach to targeted therapy

The MET oncogene encodes an unconventional receptor tyrosine kinase with pleiotropic functions: it initiates and sustains neoplastic transformation when genetically altered ('oncogene addiction') and fosters cancer cell survival and tumour dissemination when transcriptionally activated in the context of an adaptive response to adverse microenvironmental conditions ('oncogene expedience'). Moreover, MET is an intrinsic modulator of the self-renewal and clonogenic ability of cancer stem cells ('oncogene inherence'). Here, we provide the latest findings on MET function in cancer by focusing on newly identified genetic abnormalities in tumour cells and recently described non-mutational MET activities in stromal cells and cancer stem cells. We discuss how MET drives cancer clonal evolution and progression towards metastasis, both ab initio and under therapeutic pressure. We then elaborate on the use of MET inhibitors in the clinic with a critical appraisal of failures and successes. Ultimately, we advocate a rationale to improve the outcome of anti-MET therapies on the basis of thorough consideration of the entire spectrum of MET-mediated biological responses, which implicates adequate patient stratification, meaningful biomarkers and appropriate clinical end points.

Hypoxic Signalling in Tumour Stroma

Hypoxia is a common feature in solid tumors and is associated with cancer progression. The main regulators of the hypoxic response are hypoxia-inducible transcription factors (HIFs) that guide the cellular adaptation to hypoxia by gene activation. The actual oxygen sensing is performed by HIF prolyl hydroxylases (PHDs) that under normoxic conditions mark the HIF-α subunit for degradation. Cancer progression is not regulated only by the cancer cells themselves but also by the whole tumor microenvironment, which consists of cellular and extracellular components. Hypoxic conditions also affect the stromal compartment, where stromal cells are in close contact with the cancer cells. The important function of HIF in cancer cells has been shown by many animal models and described in hundreds of reviews, but less in known about PHDs and even less PHDs in stromal cells. Here, we review hypoxic signaling in tumors, mainly in the tumor stroma, with a focus on HIFs and PHDs.

Immune therapies in pancreatic ductal adenocarcinoma: Where are we now?

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers, mostly due to its resistance to treatment. Of these, checkpoint inhibitors (CPI) are inefficient when used as monotherapy, except in the case of a rare subset of tumors harboring microsatellite instability (< 2%). This inefficacy mainly resides in the low immunogenicity and non-inflamed phenotype of PDAC. The abundant stroma generates a hypoxic microenvironment and drives the recruitment of immunosuppressive cells through cancer-associated-fibroblast activation and transforming growth factor β secretion. Several strategies have recently been developed to overcome this immunosuppressive microenvironment. Combination therapies involving CPI aim at increasing tumor immunogenicity and promoting the recruitment and activation of effector T cells. Ongoing studies are therefore exploring the association of CPI with vaccines, oncolytic viruses, MEK inhibitors, cytokine inhibitors, and hypoxia- and stroma-targeting agents. Adoptive T-cell transfer is also under investigation. Moreover, translational studies on tumor tissue and blood, prior to and during treatment may lead to the identification of biomarkers with predictive value for both clinical outcome and response to immunotherapy.

Synergistic tumor microenvironment targeting and blood-brain barrier penetration via a pH-responsive dual-ligand strategy for enhanced breast cancer and brain metastasis therapy

Cancer associated fibroblasts (CAFs) which shape the tumor microenvironment (TME) and the presence of blood brain barrier (BBB) remain great challenges in targeting breast cancer and its brain metastasis. Herein, we reported a strategy using PTX-loaded liposome co-modified with acid-cleavable folic acid (FA) and BBB transmigrating cell penetrating peptide dNP2 peptide (cFd-Lip/PTX) for enhanced delivery to orthotopic breast cancer and its brain metastasis. Compared with single ligand or non-cleavable Fd modified liposomes, cFd-Lip exhibited synergistic TME targeting and BBB transmigration. Moreover, upon arrival at the TME, the acid-cleavable cFd-Lip/PTX showed sensitive cleavage of FA, which reduced the hindrance effect and maximized the function of both FA and dNP2 peptide. Consequently, efficient targeting of folate receptor (FR)-positive tumor cells and FR-negative CAFs was achieved, leading to enhanced anti-tumor activity. This strategy provides a feasible approach to the cascade targeting of TME and BBB transmigration in orthotopic and metastatic cancer treatment.

Fibroblasts in the Tumor Microenvironment: Shield or Spear?

Tumorigenesis is a complex process involving dynamic interactions between malignant cells and their surrounding stroma, including both the cellular and acellular components. Within the stroma, fibroblasts represent not only a predominant cell type, but also a major source of the acellular tissue microenvironment comprising the extracellular matrix (ECM) and soluble factors. Normal fibroblasts can exert diverse suppressive functions against cancer initiating and metastatic cells via direct cell-cell contact, paracrine signaling by soluble factors, and ECM integrity. The loss of such suppressive functions is an inherent step in tumor progression. A tumor cell-induced switch of normal fibroblasts into cancer-associated fibroblasts (CAFs), in turn, triggers a range of pro-tumorigenic signals accompanied by distraction of the normal tissue architecture, thus creating an optimal niche for cancer cells to grow extensively. To further support tumor progression and metastasis, CAFs secrete factors such as ECM remodeling enzymes that further modify the tumor microenvironment in combination with the altered adhesive forces and cell-cell interactions. These paradoxical tumor suppressive and promoting actions of fibroblasts are the focus of this review, highlighting the heterogenic molecular properties of both normal and cancer-associated fibroblasts, as well as their main mechanisms of action, including the emerging impact on immunomodulation and different therapy responses.

Aberrant upregulation of KLK10 promotes metastasis via enhancement of EMT and FAK/SRC/ERK axis in PDAC

Pancreatic Ductal Adenocarcinoma (PADC) metastasis is the leading cause of morality of this severe malignant tumor. Proteases are key players in the degradation of extracellular matrix which promotes the cascade of tumor metastasis. As a kind of serine proteases, the kallikrein family performs vital function on the cancer proteolysis scene, which have been proved in diverse malignant tumors. However, the specific member of kallikrein family and its function in PDAC remain unexplored. In this study, by data mining of GEO datasets, we have identified KLK10 is upregulated gene in PDAC. We found that KLK10 was significantly overexpressed in tissues of pancreatic intraepithelial neoplasia (PanIN) and PDAC from Pdx1-Cre; LSL-KrasG12D/+ mice (KC) and Pdx1-Cre; LSL-KrasG12D/+; LSL-Trp53R172H/+ mice (KPC) by immunohistochemical analysis. Moreover, KLK10 is extremely elevated in the PDAC tissues, especially that from the PDAC patients with lymphatic and distant metastasis. Aberrant KLK10 expression is significantly correlated with poor prognosis and shorter survival by univariable and multivariable analysis. Functionally, knockdown of KLK10 observably inhibits invasion and metastatic phenotype of PDAC cells in vitro and metastasis in vivo. In addition, blockade of KLK10 attenuates epithelial-mesenchymal transition and activation of FAK-SRC-ERK signaling, which explains the mechanism of KLK10 in promoting metastasis. Collectively, KLK10 should be considered as a promising biomarker for diagnosis and potential target for therapy in PDAC.

The ULK3 Kinase Is Critical for Convergent Control of Cancer-Associated Fibroblast Activation by CSL and GLI

The connection between signaling pathways activating cancer-associated fibroblasts (CAFs) remains to be determined. Metabolic alterations linked to autophagy have also been implicated in CAF activation. CSL/RBPJ, a transcriptional repressor that mediates Notch signaling, suppresses the gene expression program(s), leading to stromal senescence and CAF activation. Deregulated GLI signaling can also contribute to CAF conversion. Here, we report that compromised CSL function depends on GLI activation for conversion of human dermal fibroblasts into CAFs, separately from cellular senescence. Decreased CSL upregulates the expression of the ULK3 kinase, which binds and activates GLI2. Increased ULK3 also induces autophagy, which is unlinked from GLI and CAF activation. ULK3 upregulation occurs in the CAFs of several tumor types, and ULK3 silencing suppresses the tumor-enhancing properties of these cells. Thus, ULK3 links two key signaling pathways involved in CAF conversion and is an attractive target for stroma-focused anti-cancer intervention.

Oesophageal Stem Cells and Cancer

Oesophageal cancer remains one of the least explored malignancies. However, in recent years its increasing incidence and poor prognosis have stimulated interest from the cancer community to understand the pathways to the initiation and progression of the disease.

Critical understanding of the molecular processes controlling changes in stem cell fate and the cross-talk with their adjacent stromal neighbours will provide essential knowledge on the mechanisms that go awry in oesophageal carcinogenesis. Advances in lineage tracing techniques have represented a powerful tool to start understanding changes in oesophageal cell behaviour in response to mutations and mutagens that favour tumour development.

Environmental cues constitute an important factor in the aetiology of oesophageal cancer. The oesophageal epithelium is a tissue exposed to harsh conditions that not only damage the DNA of epithelial cells but also result in an active stromal reaction, promoting tumour progression. Ultimately, cancer represents a complex interplay between malignant cells and their microenvironment. Indeed, increasing evidence suggests that the accumulation of somatic mutations is not the sole cause of cancer. Instead, non-cell autonomous components, coming from the stroma, can significantly contribute from the earliest stages of tumour formation.

The realisation that stromal cells play an important role in cancer has transformed this cellular compartment into an attractive and emerging field of research. It is becoming increasingly clear that the tumour microenvironment provides unique opportunities to identify early diagnostic and prognostic markers, as well as potential therapeutic strategies that may synergise with those targeting tumour cells.

This chapter compiles recent observations on oesophageal epithelial stem cell biology, and how environmental and micro-environmental changes may lead to oesophageal disease and cancer.

Hyaluronan, Cancer-Associated Fibroblasts and the Tumor Microenvironment in Malignant Progression

This review summarizes the roles of CAFs in forming a “cancerized” fibrotic stroma favorable to tumor initiation and dissemination, in particular highlighting the functions of the extracellular matrix component hyaluronan (HA) in these processes. The structural complexity of the tumor and its host microenvironment is now well appreciated to be an important contributing factor to malignant progression and resistance-to-therapy. There are multiple components of this complexity, which include an extensive remodeling of the extracellular matrix (ECM) and associated biomechanical changes in tumor stroma. Tumor stroma is often fibrotic and rich in fibrillar type I collagen and hyaluronan (HA). Cancer-associated fibroblasts (CAFs) are a major source of this fibrotic ECM. CAFs organize collagen fibrils and these biomechanical alterations provide highways for invading carcinoma cells either under the guidance of CAFs or following their epithelial to mesenchymal transition (EMT). The increased HA metabolism of a tumor microenvironment instructs carcinoma initiation and dissemination by performing multiple functions. The key effects of HA reviewed here are its role in activating CAFs in pre-malignant and malignant stroma, and facilitating invasion by promoting motility of both CAFs and tumor cells, thus facilitating their invasion. Circulating CAFs (cCAFs) also form heterotypic clusters with circulating tumor cells (CTC), which are considered to be pre-cursors of metastatic colonies. cCAFs are likely required for extravasation of tumors cells and to form a metastatic niche suitable for new tumor colony growth. Therapeutic interventions designed to target both HA and CAFs in order to limit tumor spread and increase response to current therapies are discussed.