Retinoic acid-induced pancreatic stellate cell quiescence reduces paracrine Wnt-β-catenin signaling to slow tumor progression

Expression of Aldehyde Dehydrogenase 1A1 (ALDH1A1) as a Prognostic Biomarker in Colorectal Cancer Using Immunohistochemistry

Background

The expression of aldehyde dehydrogenase 1A1 (ALDH1A1) is increased in several human tumors, including colorectal carcinoma (CRC). The aim of this study was to compare the expression ALDH1A1 in CRC tumor tissue compared with non-tumor adjacent tissue (NAT), using immunohistochemistry (IHC), and to determine whether the expression of the ALDH1A1 protein was associated with prognostic factors in CRC.

Material/Methods

Formalin-fixed paraffin-embedded (FFPE) tissue from 424 patients diagnosed with CRC, and 196 matched NATs were used to prepare tissue microarrays (TMAs). IHC was performed using an immunoperoxidase method with a primary polyclonal rabbit anti-ALDH1A1 antibody. The IHC scores by light microscopy were the staining intensity (scored from 0–3) multiplied by the percentage area of positive immunostaining within the visual field (scored from 0–4). Associations between tumor expression levels of ALDH1A1 and patient clinicopathological characteristics, including tumor grade, size, and TNM stage at surgery were analyzed.

Results

ALDH1A1 protein expression was significantly increased in CRC tissues compared with matched NATs. In patients with CRC, increased expression of the ALDH1A1 protein was significantly associated with the presence of lymph node metastasis: 64.28% in N0 cases; 75.49% in N1 cases; and 82.14% in N2 cases, (P=0.002). Univariate and multivariate analysis showed that ALDH1A1 expression was an independent prognostic marker for CRC (P<0.001).

Conclusions

Using IHC, the expression of the ALDH1A1 protein in CRC tissues was significantly associated with the presence of lymph node metastases and might be a potential prognostic marker in patients with CRC.

Targeting galectin-1 inhibits pancreatic cancer progression by modulating tumor-stroma crosstalk

Pancreatic ductal adenocarcinoma (PDA) remains one of the most lethal tumor types, with extremely low survival rates due to late diagnosis and resistance to standard therapies. A more comprehensive understanding of the complexity of PDA pathobiology, and especially of the role of the tumor microenvironment in disease progression, should pave the way for therapies to improve patient response rates. In this study, we identify galectin-1 (Gal1), a glycan-binding protein that is highly overexpressed in PDA stroma, as a major driver of pancreatic cancer progression. Genetic deletion of Gal1 in a Kras-driven mouse model of PDA (Ela-Kras^G12Vp53^-/- ) results in a significant increase in survival through mechanisms involving decreased stroma activation, attenuated vascularization, and enhanced T cell infiltration leading to diminished metastasis rates. In a human setting, human pancreatic stellate cells (HPSCs) promote cancer proliferation, migration, and invasion via Gal1-driven pathways. Moreover, in vivo orthotopic coinjection of pancreatic tumor cells with Gal1-depleted HPSCs leads to impaired tumor formation and metastasis in mice. Gene-expression analyses of pancreatic tumor cells exposed to Gal1 reveal modulation of multiple regulatory pathways involved in tumor progression. Thus, Gal1 hierarchically regulates different events implicated in PDA biology including tumor cell proliferation, invasion, angiogenesis, inflammation, and metastasis, highlighting the broad therapeutic potential of Gal1-specific inhibitors, either alone or in combination with other therapeutic modalities.

Fibroblast drug scavenging increases intratumoural gemcitabine accumulation in murine pancreas cancer

OBJECTIVE

Desmoplasia and hypovascularity are thought to impede drug delivery in pancreatic ductal adenocarcinoma (PDAC). However, stromal depletion approaches have failed to show clinical responses in patients. Here, we aimed to revisit the role of the tumour microenvironment as a physical barrier for gemcitabine delivery.

DESIGN

Gemcitabine metabolites were analysed in LSL-KrasG12D/+ ; LSL-Trp53R172H/+ ; Pdx-1-Cre (KPC) murine tumours and matched liver metastases, primary tumour cell lines, cancer-associated fibroblasts (CAFs) and pancreatic stellate cells (PSCs) by liquid chromatography-mass spectrometry/mass spectrometry. Functional and preclinical experiments, as well as expression analysis of stromal markers and gemcitabine metabolism pathways were performed in murine and human specimen to investigate the preclinical implications and the mechanism of gemcitabine accumulation.

RESULTS

Gemcitabine accumulation was significantly enhanced in fibroblast-rich tumours compared with liver metastases and normal liver. In vitro, significantly increased concentrations of activated 2',2'-difluorodeoxycytidine-5'-triphosphate (dFdCTP) and greatly reduced amounts of the inactive gemcitabine metabolite 2',2'-difluorodeoxyuridine were detected in PSCs and CAFs. Mechanistically, key metabolic enzymes involved in gemcitabine inactivation such as hydrolytic cytosolic 5'-nucleotidases (Nt5c1A, Nt5c3) were expressed at low levels in CAFs in vitro and in vivo, and recombinant expression of Nt5c1A resulted in decreased intracellular dFdCTP concentrations in vitro. Moreover, gemcitabine treatment in KPC mice reduced the number of liver metastases by >50%.

CONCLUSIONS

Our findings suggest that fibroblast drug scavenging may contribute to the clinical failure of gemcitabine in desmoplastic PDAC. Metabolic targeting of CAFs may thus be a promising strategy to enhance the antiproliferative effects of gemcitabine.

Reshaping the Tumor Stroma for Treatment of Pancreatic Cancer

Pancreatic cancer is accompanied by a fibrotic reaction that alters interactions between tumor cells and the stroma to promote tumor progression. Consequently, strategies to target the tumor stroma might be used to treat patients with pancreatic cancer. We review recently developed approaches for reshaping the pancreatic tumor stroma and discuss how these might improve patient outcomes. We also describe relationships between the pancreatic tumor extracellular matrix, the vasculature, the immune system, and metabolism, and discuss the implications for the development of stromal compartment-specific therapies.

Zeb1 in Stromal Myofibroblasts Promotes Kras-Driven Development of Pancreatic Cancer

The transcription factor Zeb1 has been identified as a crucial player in Kras-dependent oncogenesis. In pancreatic ductal adenocarcinoma (PDAC), Zeb1 is highly expressed in myofibroblasts and correlates with poor prognosis. As Kras mutations are key drivers in PDAC, we aimed here to assess the necessity of Zeb1 for Kras-driven PDAC and to define the role of Zeb1-expressing myofibroblasts in PDAC development. Genetically engineered mice with conditional pancreatic Kras^G12D and Trp53 mutations (KPC) were crossed with Zeb1 haploinsufficient mice (Z^+/-). Extensive PDAC was prominent in all 20-week-old KPC;Z^+/+ mice, whereas only low-grade precursor lesions were detected in age-matched KPC;Z^+/- littermates, with PDAC developing eventually in KPC;Z^+/- aged animals. Zeb1 expression in myofibroblasts occurred early in tumorigenesis and Zeb1 haploinsufficiency retarded native expansion of stromal myofibroblasts during precursor-to-cancer progression. Zeb1 downregulation in mPSC repressed their activated gene profile, impaired their migratory and proliferative activity, and attenuated their tumor-supporting features. Conditioned media from Z^+/+ mouse-activated (myofibroblast-like) pancreatic stellate cells (mPSC) boosted Ras activity in pancreatic cancer cells carrying mutant Kras; this effect was not observed when using conditioned media from Z^+/- mPSC, revealing a paracrinal cooperative axis between Zeb1-expressing PSC and oncogenic Kras-bearing tumor cells. We conclude that Zeb1-expressing stromal myofibroblasts enable a heterotypic collaboration with the Kras-fated epithelial compartment, thus supporting pancreatic malignancy.Significance: Zeb1 expression in stromal myofibroblasts supports PDAC development via collaboration with the epithelial compartment bearing oncogenic Kras mutations. Cancer Res; 78(10); 2624-37. ©2018 AACR.

The critical roles of activated stellate cells-mediated paracrine signaling, metabolism and onco-immunology in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignant diseases worldwide. It is refractory to conventional treatments, and consequently has a documented 5-year survival rate as low as 7%. Increasing evidence indicates that activated pancreatic stellate cells (PSCs), one of the stromal components in tumor microenvironment (TME), play a crucial part in the desmoplasia, carcinogenesis, aggressiveness, metastasis associated with PDAC. Despite the current understanding of PSCs as a "partner in crime" to PDAC, detailed regulatory roles of PSCs and related microenvironment remain obscure. In addition to multiple paracrine signaling pathways, recent research has confirmed that PSCs-mediated tumor microenvironment may influence behaviors of PDAC via diverse mechanisms, such as rewiring metabolic networks, suppressing immune responses. These new activities are closely linked with treatment and prognosis of PDAC. In this review, we discuss the recent advances regarding new functions of activated PSCs, including PSCs-cancer cells interaction, mechanisms involved in immunosuppressive regulation, and metabolic reprogramming. It's clear that these updated experimental or clinical studies of PSCs may provide a promising approach for PDAC treatment in the near future.

Stromal remodeling by the BET bromodomain inhibitor JQ1 suppresses the progression of human pancreatic cancer

Inhibitors of bromodomain and extraterminal domain (BET) proteins, a family of chromatin reader proteins, have therapeutic efficacy against various malignancies. However, the detailed mechanisms underlying the anti-tumor effects in distinct tumor types remain elusive. Here, we show a novel antitumor mechanism of BET inhibition in pancreatic ductal adenocarcinoma (PDAC). We found that JQ1, a BET inhibitor, decreased desmoplastic stroma, a hallmark of PDAC, and suppressed the growth of patient-derived tumor xenografts (PDX) of PDACs. In vivo antitumor effects of JQ1 were not always associated with the JQ1 sensitivity of respective PDAC cells, and were rather dependent on the suppression of tumor-promoting activity in cancer-associated fibroblasts (CAFs). JQ1 inhibited Hedgehog and TGF-β pathways as potent regulators of CAF activation and suppressed the expression of α-SMA, extracellular matrix, cytokines, and growth factors in human primary CAFs. Consistently, conditioned media (CM) from CAFs promoted the proliferation of PDAC cells along with the activation of ERK, AKT, and STAT3 pathways, though these effects were suppressed when CM from JQ1-treated CAFs was used. Mechanistically, chromatin immunoprecipitation experiments revealed that JQ1 reduced TGF-β–dependent gene expression by disrupting the recruitment of the transcriptional machinery containing BET proteins. Finally, combination therapy with gemcitabine plus JQ1 showed greater efficacy than gemcitabine monotherapy against PDAC in vivo. Thus, our results reveal BET proteins as the critical regulators of CAF-activation and also provide evidence that stromal remodeling by epigenetic modulators can be a novel therapeutic option for PDAC.

Experimental models of pancreatic cancer desmoplasia

Desmoplasia is a fibro-inflammatory process and a well-established feature of pancreatic cancer. A key contributor to pancreatic cancer desmoplasia is the pancreatic stellate cell. Various in vitro and in vivo methods have emerged for the isolation, characterization, and use of pancreatic stellate cells in models of cancer-associated fibrosis. In addition to cell culture models, genetically engineered animal models have been established that spontaneously develop pancreatic cancer with desmoplasia. These animal models are currently being used for the study of pancreatic cancer pathogenesis and for evaluating therapeutics against pancreatic cancer. Here, we review various in vitro and in vivo models that are being used or have the potential to be used to study desmoplasia in pancreatic cancer.

Modulating the Tumor Microenvironment to Enhance Tumor Nanomedicine Delivery

Nanomedicines including liposomes, micelles, and nanoparticles based on the enhanced permeability and retention (EPR) effect have become the mainstream for tumor treatment owing to their superiority over conventional anticancer agents. Advanced design of nanomedicine including active targeting nanomedicine, tumor-responsive nanomedicine, and optimization of physicochemical properties to enable highly effective delivery of nanomedicine to tumors has further improved their therapeutic benefits. However, these strategies still could not conquer the delivery barriers of a tumor microenvironment such as heterogeneous blood flow, dense extracellular matrix, abundant stroma cells, and high interstitial fluid pressure, which severely impaired vascular transport of nanomedicines, hindered their effective extravasation, and impeded their interstitial transport to realize uniform distribution inside tumors. Therefore, modulation of tumor microenvironment has now emerged as an important strategy to improve nanomedicine delivery to tumors. Here, we review the existing strategies and approaches for tumor microenvironment modulation to improve tumor perfusion for helping more nanomedicines to reach the tumor site, to facilitate nanomedicine extravasation for enhancing transvascular transport, and to improve interstitial transport for optimizing the distribution of nanomedicines. These strategies may provide an avenue for the development of new combination chemotherapeutic regimens and reassessment of previously suboptimal agents.

ETV4 collaborates with Wnt/β-catenin signaling to alter cell cycle activity and promote tumor aggressiveness in gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most common sarcoma, often resulting from a KIT or platelet-derived growth factor receptor alpha (PDGFRA) mutation. The lineage transcription factor ETV1 is expressed similarly in GISTs regardless of malignant potential. Although the related transcription factor ETV4 has been associated with metastasis and tumor progression in other cancers, its role in GIST is unknown. In this study, we found that ETV4 levels were high in a subset of human GISTs and correlated with high mitotic rate. Through Gene Set Enrichment Analysis in selected human GISTs, we identified a relationship between ETV4 levels and β-catenin signaling, especially in advanced GISTs. GIST specimens with high ETV4 levels overexpressed cell cycle regulating genes and had aberrant activation of the canonical Wnt pathway. In human GIST cell lines, ETV4 RNA interference suppressed cell cycle genes and Wnt/β-catenin signaling. ETV4 knockdown also reduced tumor cell proliferation, invasion, and tumor growth in vivo. Conversely, ETV4 overexpression increased cyclin D1 expression and Wnt/β-catenin signaling. Moreover, we determined that ETV4 knockdown destabilized nuclear β-catenin and increased its degradation via COP1, an E3 ligase involved in both ETV4 and β-catenin turnover. Aberrant accumulation of ETV4 and nuclear β-catenin was found in patient derived xenografts created from metastatic GISTs that became resistant to tyrosine kinase inhibitors. Collectively, our findings highlight the significance of ETV4 expression in GIST and identify ETV4 as a biomarker in human GISTs.

Reprogramming pancreatic stellate cells via p53 activation: A putative target for pancreatic cancer therapy

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an extremely dense fibrotic stroma, which contributes to tumor growth, metastasis, and drug resistance. During tumorigenesis, quiescent pancreatic stellate cells (PSCs) are activated and become major contributors to fibrosis, by increasing growth factor signaling and extracellular matrix deposition. The p53 tumor suppressor is known to restrict tumor initiation and progression through cell autonomous mechanisms including apoptosis, cell cycle arrest, and senescence. There is growing evidence that stromal p53 also exerts anti-tumor activity by paracrine mechanisms, though a role for stromal p53 in PDAC has not yet been described. Here, we demonstrate that activation of stromal p53 exerts anti-tumor effects in PDAC. We show that primary cancer-associated PSCs (caPSCs) isolated from human PDAC express wild-type p53, which can be activated by the Mdm2 antagonist Nutlin-3a. Our work reveals that p53 acts as a major regulator of PSC activation and as a modulator of PDAC fibrosis. In vitro, p53 activation by Nutlin-3a induces profound transcriptional changes, which reprogram activated PSCs to quiescence. Using immunofluorescence and lipidomics, we have also found that p53 activation induces lipid droplet accumulation in both normal and tumor-associated fibroblasts, revealing a previously undescribed role for p53 in lipid storage. In vivo, treatment of tumor-bearing mice with the clinical form of Nutlin-3a induces stromal p53 activation, reverses caPSCs activation, and decreases fibrosis. All together our work uncovers new functions for stromal p53 in PDAC.

Three-dimensional organotypic matrices from alternative collagen sources as pre-clinical models for cell biology

Organotypic co-cultures bridge the gap between standard two-dimensional culture and mouse models. Such assays increase the fidelity of pre-clinical studies, to better inform lead compound development and address the increasing attrition rates of lead compounds within the pharmaceutical industry, which are often a result of screening in less faithful two-dimensional models. Using large-scale acid-extraction techniques, we demonstrate a step-by-step process to isolate collagen I from commercially available animal byproducts. Using the well-established rat tail tendon collagen as a benchmark, we apply our novel kangaroo tail tendon collagen as an alternative collagen source for our screening-ready three-dimensional organotypic co-culture platform. Both collagen sources showed equal applicability for invasive, proliferative or survival assessment of well-established cancer models and clinically relevant patient-derived cancer cell lines. Additional readouts were also demonstrated when comparing these alternative collagen sources for stromal contributions to stiffness, organization and ultrastructure via atomic force microscopy, second harmonic generation imaging and scanning electron microscopy, among other vital biological readouts, where only minor differences were found between the preparations. Organotypic co-cultures represent an easy, affordable and scalable model to investigate drug responses within a physiologically relevant 3D platform.

Complex roles of the stroma in the intrinsic resistance to gemcitabine in pancreatic cancer: where we are and where we are going

Pancreatic ductal adenocarcinoma (PDAC) is among the most devastating human malignancies. The poor clinical outcome in PDAC is partly attributed to a growth-permissive tumor microenvironment. In the PDAC microenvironment, the stroma is characterized by the development of extensive fibrosis, with stromal components outnumbering pancreatic cancer cells. Each of the components within the stroma has a distinct role in conferring chemoresistance to PDAC, and intrinsic chemoresistance has further worsened this pessimistic prognosis. The nucleoside analog gemcitabine (GEM) is usually the recommended first-line chemotherapeutic agent for PDAC patients and is given alone or in combination with other agents. The mechanisms of intrinsic resistance to GEM are an active area of ongoing research. This review highlights the important role the complex structure of stroma in PDAC plays in the intrinsic resistance to GEM and discusses whether antistroma therapy improves the efficacy of GEM. The addition of antistroma therapy combined with GEM is expected to be a novel therapeutic strategy with significant survival benefits for PDAC patients.

Overexpression of p16ink4a regulates the Wnt/β‑catenin signaling pathway in pancreatic cancer cells

The pathogenesis and etiology of pancreatic cancer remain to be fully elucidated; therefore, associated investigations are required to improve the outcome and prognosis of patients. In the present study, the effects of the overexpression of p16ink4a on the Wnt/β‑catenin signaling pathway were investigated in pancreatic cancer cell lines. Two pancreatic cancer cell lines, Bxpc‑3 and Miapaca‑2, characterized by low expression of p16ink4a, were transfected with the pc‑DNA3.0‑p16ink4a plasmid. After 24 h, Reverse transcription‑polymerase chain reaction and western blot analyses were performed to evaluate the expression of p16ink4a, β‑catenin, which is a key molecule in the Wnt/β‑catenin signaling pathway, c‑myc and cyclin D1, which are molecules downstream of β‑catenin. The expression of p16ink4a was significantly upregulated in the transfected cells. Consequently, the expression of β‑catenin was inhibited, whereas the expression levels of c‑myc and cyclin D1 were not altered significantly. The increased expression of p16ink4a may affect the activity of Wnt/β‑catenin signaling through modulation of the expression of β‑catenin. The results of the present study provide information for the future development of targeted treatments for pancreatic cancer.

Human epicardial adipose tissue-derived and circulating secreted frizzled-related protein 4 (SFRP4) levels are increased in patients with coronary artery disease

Background

Previous studies have demonstrated that secreted frizzled-related protein 4 (SFRP4) is associated with impaired glucose and triglyceride metabolism in patients with stable coronary artery disease. In the present study, we investigated human epicardial adipose tissue (EAT)-derived and circulating SFRP4 levels in patients with coronary artery disease (CAD).

Methods

Plasma samples and adipose biopsies from EAT and subcutaneous adipose tissue (SAT) were collected from patients with CAD (n = 40) and without CAD (non-CAD, n = 30) during elective cardiac surgery. The presence of CAD was identified by coronary angiography. SFRP4 mRNA and protein expression levels in adipose tissue were detected by quantitative real-time PCR and immunohistochemistry, respectively. Plasma SFRP4 concentrations were measured by an enzyme-linked immunosorbent assay (ELISA). Correlation analysis and multivariate linear regression analysis were used to determine the association of SFRP4 expression with atherosclerosis as well as clinical risk factors.

Results

SFRP4 mRNA and protein expression levels were significantly lower in EAT than in paired SAT in patients with and without CAD (all P < 0.05). Compared to non-CAD patients, CAD patients had higher SFRP4 expression levels in EAT (both mRNA and protein levels) and in plasma. Multivariate linear regression analysis showed that CAD was an independent predictor of SFRP4 expression levels in EAT (beta = 0.442, 95% CI 0.030–0.814; P = 0.036) and in plasma (beta = 0.300, 95% CI 0.056–0.545; P = 0.017). SAT-derived SFRP4 mRNA levels were independently associated with fasting insulin levels (beta = 0.382, 95% CI 0.008–0.756; P = 0.045). In addition, plasma SFRP4 levels were positively correlated with BMI (r = 0.259, P = 0.030), fasting insulin levels (r = 0.306, P = 0.010) and homeostasis model assessment of insulin resistance (HOMA-IR) values (r = 0.331, P = 0.005).

Conclusions

EAT-derived and circulating SFRP4 expression levels were increased in patients with CAD. EAT SFRP4 mRNA levels and plasma SFRP4 concentrations were independently associated with the presence of CAD.

Pancreatic cancer stroma: controversies and current insights

Pancreatic cancer is characterized by a dense stromal response. The stroma includes a heterogeneous mass of cells, including pancreatic stellate cells, fibroblasts, immune cells and nerve cells, as well as extracellular matrix proteins, cytokines and growth factors, which interact with the tumor cells. Previous research has indicated that stromal elements contribute to tumor growth and aggressiveness. However, recent studies suggest that some elements of the stroma may actually restrain the tumor. This review focuses on the complex interactions between the stromal microenvironment and tumor cells, discussing molecular mechanisms and potential future diagnostic and therapeutic approaches by targeting the stroma.

Pancreatic Stellate Cells Have Distinct Characteristics From Hepatic Stellate Cells and Are Not the Unique Origin of Collagen-Producing Cells in the Pancreas

OBJECTIVES

The origin of collagen-producing myofibroblasts in pancreatic fibrosis is still controversial. Pancreatic stellate cells (PSCs), which have been recognized as the pancreatic counterparts of hepatic stellate cells (HSCs), are thought to play an important role in the development of pancreatic fibrosis. However, sources of myofibroblasts other than PSCs may exist because extensive studies of liver fibrosis have uncovered myofibroblasts that did not originate from HSCs. This study aimed to characterize myofibroblasts in an experimental pancreatic fibrosis model in mice.

METHODS

We used transgenic mice expressing green fluorescent protein via the collagen type I α1 promoter and induced pancreatic fibrosis with repetitive injections of cerulein.

RESULTS

Collagen-producing cells that are negative for glial fibrillary acidic protein (ie, not derived from PSCs) exist in the pancreas. Pancreatic stellate cells had different characteristics from those of HSCs in a very small possession of vitamin A using mass spectrometry and a low expression of lecithin retinol acyltransferase. The microstructure of PSCs was entirely different from that of HSCs using flow cytometry and electron microscopy.

CONCLUSIONS

Our study showed that characteristics of PSCs are different from those of HSCs, and myofibroblasts in the pancreas might be derived not only from PSCs but also from other fibrogenic cells.

Human pancreatic stellate cells modulate 3D collagen alignment to promote the migration of pancreatic ductal adenocarcinoma cells

A hallmark of pancreatic ductal adenocarcinoma (PDAC) is the ability for cancer cells to aggressively infiltrate and navigate through a dense stroma during the metastatic process. Key features of the PDAC stroma include an abundant population of activated pancreatic stellate cells (PSCs) and highly aligned collagen fibers; however, important questions remain regarding how collagen becomes aligned and what the biological manifestations are. To better understand how PSCs, aligned collagen, and PDAC cells might cooperate during the transition to invasion, we utilized a microchannel-based in vitro tumor model and advanced imaging technologies to recreate and examine in vivo-like heterotypic interactions. We found that PSCs participate in a collaborative process with cancer cells by orchestrating the alignment of collagen fibers that, in turn, are permissive to enhanced cell migration. Additionally, direct contact between PSCs, collagen, and PDAC cells is critical to invasion and co-migration of both cell types. This suggests PSCs may accompany and assist in navigating PDAC cells through the stromal terrain. Together, our data provides a new role for PSCs in stimulating the metastatic process and underscores the importance of collagen alignment in cancer progression.

Retinoic Acid affects Lung Adenocarcinoma growth by inducing differentiation via GATA6 activation and EGFR and Wnt inhibition

A fundamental task in cancer research aims at the identification of new pharmacological therapies that can affect tumor growth. Differentiation therapy might exploit this function not only for hematological diseases, such as acute promyelocytic leukemia (APML) but also for epithelial tumors, including lung cancer. Here we show that Retinoic Acid (RA) arrests in vitro and in vivo the growth of Tyrosine Kinase Inhibitors (TKI) resistant Non Small Cell Lung Cancer (NSCLC). In particular, we found that RA induces G0/G1 cell cycle arrest in TKI resistant NSCLC cells and activates terminal differentiation programs by modulating the expression of GATA6, a key transcription factor involved in the physiological differentiation of the distal lung. In addition, our results demonstrate that RA inhibits EGFR and Wnt signaling activation, two pathways involved in NSCLC progression. Furthermore, we uncovered a novel mechanism in NSCLC that shows how RA exerts its function; we found that RA-mediated GATA6 activation is necessary for EGFR and Wnt inhibition, thus leading to 1) increased differentiation and 2) loss of proliferation. All together, these findings prove that differentiation therapy might be feasible in TKI resistant NSCLCs, and shed light on new targets to define new pharmacological therapies.

Chemotherapy and tumor microenvironment of pancreatic cancer

Pancreatic cancer is an extremely dismal malignance. Chemotherapy has been widely applied to treat this intractable tumor. It has exclusive tumor microenvironment (TME), characterized by dense desmoplasia and profound infiltrations of immunosuppressive cells. Interactions between stromal cells and cancer cells play vital roles to affect the biological behaviors of pancreatic cancer. Targeting the stromal components of pancreatic cancer has shown promising results. In addition to the direct toxic effects of chemotherapeutic drugs on cancer cells, they can also remodel the TME, eventually affecting their efficacy. Herein, we reviewed the following four aspects; (1) clinical landmark advances of chemotherapy in pancreatic cancer, since 2000; (2) interactions and mechanisms between stromal cells and pancreatic cancer cells; (3) remodeling effects and mechanisms of chemotherapy on TME; (4) targeting stromal components in pancreatic cancer.

The pancreatic cancer microenvironment: A true double agent

The tumor microenvironment in pancreatic cancer is a complex balance of pro- and anti-tumor components. The dense desmoplasia consists of immune cells, extracellular matrix, growth factors, cytokines, and cancer associated fibroblasts (CAF) or pancreatic stellate cells (PSC). There are a multitude of targets including hyaluronan, angiogenesis, focal adhesion kinase (FAK), connective tissue growth factor (CTGF), CD40, chemokine (C-X-C motif) receptor 4 (CXCR-4), immunotherapy, and Vitamin D. The developing clinical therapeutics will be reviewed.

Cancer Manipulation of Host Physiology: Lessons from Pancreatic Cancer

Homeostasis is a fundamental property of living organisms enabling the human body to withstand internal and external insults. In several chronic diseases, and especially in cancer, many homeostatic mechanisms are deranged. Pancreatic cancer in particular is notorious for its ability to invoke an intense fibroinflammatory stromal reaction facilitating its progression and resistance to treatment. In the past decade, several seminal discoveries have elucidated previously unrecognized modes of commandeering the host's defense systems. Here we review novel discoveries in pancreatic cancer immunobiology and attempt to integrate the notion of deranged homeostasis in the pathogenesis of this disease. We also highlight areas of controversy and obstacles that need to be overcome, hoping to further our mechanistic insight into this malignancy.

The role of stromal cancer-associated fibroblasts in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer generally refractory to conventional treatments. Cancer-associated fibroblasts (CAFs) are cellular components of the desmoplastic stroma characteristic to the tumor that contributes to this treatment resistance. Various markers for CAFs have been explored including palladin and CD146 that have prognostic and functional roles in the pathobiology of PDAC. Mechanisms of CAF-tumor cell interaction have been described including exosomal transfer and paracrine signaling mediated by cytokines such as GM-CSF and IL-6. The role of downstream signaling pathways including JAK/STAT, mTOR, sonic hedge hog (SHH), and NFkB have also been shown to play an important function in PDAC-CAF cross talk. The role of autophagy and other metabolic effects on each cell type within the tumor have also been proposed to play roles in facilitating CAF secretory function and enhancing tumor growth in a low-glucose microenvironment. Targeting the stroma has gained interest with multiple preclinical and clinical trials targeting SHH, JAK2, and methods of either exploiting the secretory capability of CAFs to enhance drug delivery or inhibiting it to prevent its influence on cancer cell chemoresistance. This review summarizes the most recent progress made in understanding stromal formation; its contribution to tumor proliferation, invasion, and metastasis; its role in chemoresistance; and potential therapeutic strategies on the horizon.

Challenges and Opportunities in Modeling Pancreatic Cancer

The ability to faithfully model complex processes lies at the heart of experimental biology. Although a reductionist approach necessarily reduces this complexity, it is nevertheless required for untangling the contributions and interactions of the various system components. It has long been appreciated that cancer is a complex process that involves positive and negative interactions between tumor cells, normal host tissue, and the associated cells of the tumor microenvironment. However, accurate models for studying these complex interactions in vitro have remained elusive. We seek to generate models of mouse and human pancreatic cancer that are relevant to disease biology and useful for elucidating poorly understood facets of this deadly disease. The ability to model, manipulate, and predict the therapeutic response of an individual's disease outside their body represents the promise of precision medicine. Therefore, these models are patient-specific and allow the identification of new biomarkers and novel treatment modalities for rapid translation to the clinic. In this perspective we will discuss recent advances in modeling pancreatic cancer in vitro, the discoveries these models have enabled, and future challenges and opportunities awaiting further investigation.

Distinct populations of inflammatory fibroblasts and myofibroblasts in pancreatic cancer

Pancreatic stellate cells (PSCs) differentiate into cancer-associated fibroblasts (CAFs) that produce desmoplastic stroma, thereby modulating disease progression and therapeutic response in pancreatic ductal adenocarcinoma (PDA). However, it is unknown whether CAFs uniformly carry out these tasks or if subtypes of CAFs with distinct phenotypes in PDA exist. We identified a CAF subpopulation with elevated expression of α-smooth muscle actin (αSMA) located immediately adjacent to neoplastic cells in mouse and human PDA tissue. We recapitulated this finding in co-cultures of murine PSCs and PDA organoids, and demonstrated that organoid-activated CAFs produced desmoplastic stroma. The co-cultures showed cooperative interactions and revealed another distinct subpopulation of CAFs, located more distantly from neoplastic cells, which lacked elevated αSMA expression and instead secreted IL6 and additional inflammatory mediators. These findings were corroborated in mouse and human PDA tissue, providing direct evidence for CAF heterogeneity in PDA tumor biology with implications for disease etiology and therapeutic development.

Unravelling the pharmacologic opportunities and future directions for targeted therapies in gastro-intestinal cancers Part 1: GI carcinomas

Until the 1990s, cytotoxic chemotherapy has been the cornerstone of medical therapy for gastrointestinal (GI) cancers. Better understanding of the molecular biology of cancer cell has led to the therapeutic revolution of targeted therapies, i.e. monoclonal antibodies or small molecule inhibitors directed against proteins that are specifically overexpressed or mutated in cancer cells. These agents being more specific to cancer cells were expected to be less toxic than cytotoxic agents. Targeted agents have provided clinical benefit in many GI cancer types. For example, antiangiogenics and anti-EGFR therapies have significantly improved survival of patients affected by metastatic colorectal cancer and have deeply changed the therapeutic strategy in this disease. However, their effects have sometimes been disappointing, due to intrinsic or acquired resistance mechanisms (e.g., RAS mutation for anti-EGFR therapies), or to an activity restricted to some tumour settings (e.g., lack of activity in other cancer types, or on the microscopic residual disease in adjuvant setting). Many studies are negative in overall population but positive in some specific patient subgroups (e.g., trastuzumab in HER2-positive gastric cancer), illustrating the importance of patient selection and early identification of predictive biomarkers of response to these therapies. We propose a comprehensive two-part review providing a panoramic approach of the successes and failures of targeted agents in GI cancers to unravel the pharmacologic opportunities and future directions for these agents in GI oncology. In this first part, we will focus on adenocarcinomas and squamous cell carcinomas, for which targeted therapies are mostly used in combination with chemotherapy.

BET inhibitors block pancreatic stellate cell collagen I production and attenuate fibrosis in vivo

The fibrotic reaction, which can account for over 70%-80% of the tumor mass, is a characteristic feature of human pancreatic ductal adenocarcinoma (PDAC) tumors. It is associated with activation and proliferation of pancreatic stellate cells (PSCs), which are key regulators of collagen I production and fibrosis in vivo. In this report, we show that members of the bromodomain and extraterminal (BET) family of proteins are expressed in primary PSCs isolated from human PDAC tumors, with BRD4 positively regulating, and BRD2 and BRD3 negatively regulating, collagen I expression in primary cancer-associated PSCs. We show that the inhibitory effect of pan-BET inhibitors on collagen I expression in primary cancer-associated PSCs is through blocking of BRD4 function. Importantly, we show that FOSL1 is repressed by BRD4 in primary cancer-associated PSCs and negatively regulates collagen I expression. While BET inhibitors do not affect viability or induce PSC apoptosis or senescence, BET inhibitors induce primary cancer-associated PSCs to become quiescent. Finally, we show that BET inhibitors attenuate stellate cell activation, fibrosis, and collagen I production in the EL-KrasG12D transgenic mouse model of pancreatic tumorigenesis. Our results demonstrate that BET inhibitors regulate fibrosis by modulating the activation and function of cancer-associated PSCs.

Expression of polymeric immunoglobulin receptor and stromal activity in pancreatic ductal adenocarcinoma

BACKGROUND/OBJECTIVES

Polymeric immunoglobulin receptor (pIgR) traffics Immunoglobulins (IgA and IgM) through epithelial cells in normal mucosae but neither are expressed in the normal pancreas. Recent work from our laboratory suggested pIgR may be upregulated in pancreatic ductal adenocarcinoma (PDAC). Our aim was to assess the role of pIgR in human PDAC.

METHODS

pIgR expression was manipulated (siRNA and shRNA) in cell lines to evaluate its subsequent effect on cell behaviour in 2D assays as well as 3D organotypics models. Tissue Microarrays of 88 patients with PDAC were analysed after pIgR, αSMA, E-Cadherin and Picrosirius Red staining to assess their role as a combined bio-marker panel.

RESULTS

Cytokines such as interleukin 4 (IL4) and Tumour Necrosis Factor (TNFα) could not modulate pIgR expression in PDAC cell lines despite this effect being seen in other studies. Down-regulation in pIgR expression in Capan1 cancer cell line resulted in reduction of cellular proliferation, adhesion and migration in 2D assays. In 3D physiomimetic organotypic models, pIgR downregulation resulted in reduced cancer cell invasion, alteration of apico-basal polarity and diminished stromal activity. In human PDAC, decreased E-cadherin expression correlates with increased pIgR expression through pancreatic intra-epithelial neoplasia (PanIN) progression. In combination with enhanced stromal indices (α-smooth muscle action (SMA) and Picrosirius red), low pIgR scores had a trend towards better survival.

CONCLUSION

pIgR may be involved in PDAC progression and may be linked stromal activity. Further work on its precise role is mandated in in vivo models, to understand its influence on cancer progression.

Matrix-regulated integrin αvβ5 maintains α5β1-dependent desmoplastic traits prognostic of neoplastic recurrence

Desmoplasia, a fibrotic mass including cancer-associated fibroblasts (CAFs) and self-sustaining extracellular matrix (D-ECM), is a puzzling feature of pancreatic ductal adenocarcinoma (PDACs). Conflicting studies have identified tumor-restricting and tumor-promoting roles of PDAC-associated desmoplasia, suggesting that individual CAF/D-ECM protein constituents have distinguishable tumorigenic and tumor-repressive functions. Using 3D culture of normal pancreatic versus PDAC-associated human fibroblasts, we identified a CAF/D-ECM phenotype that correlates with improved patient outcomes, and that includes CAFs enriched in plasma membrane-localized, active α₅β₁-integrin. Mechanistically, we established that TGFβ is required for D-ECM production but dispensable for D-ECM-induced naïve fibroblast-to-CAF activation, which depends on α_vβ₅-integrin redistribution of pFAK-independent active α₅β₁-integrin to assorted endosomes. Importantly, the development of a simultaneous multi-channel immunofluorescence approach and new algorithms for computational batch-analysis and their application to a human PDAC panel, indicated that stromal localization and levels of active SMAD2/3 and α₅β₁-integrin distinguish patient-protective from patient-detrimental desmoplasia and foretell tumor recurrences, suggesting a useful new prognostic tool.

DOI:http://dx.doi.org/10.7554/eLife.20600.001

Tumors are not entirely made out of cancerous cells. They contain many other components – referred to as tumor stroma – that may either encourage or hinder the tumor’s growth. Tumor stroma includes non-cancerous cells and a framework of fibrous sugary proteins, called the extracellular matrix, which surround and signal to cells while providing physical support.

In the most common and aggressive form of pancreatic cancer, the stroma often makes up the majority of the tumor’s mass. Sometimes the stroma of these pancreatic tumors can protect the cancer cells from anti-cancer drugs. Researchers have therefore been interested in finding out exactly which aspects of the tumor stroma shield and support cancer cells, and which impede their growth and progression. Answering these questions could make it possible to develop new drugs that will change a tumor-supporting stroma into one that hinders the tumor’s growth and spread.

The most abundant cells in the stroma of pancreatic tumors are called cancer-associated fibroblasts. Healthy specialized fibroblasts – known as pancreatic stellate cells – help to build and maintain the ‘normal’ extracellular matrix and so these cells normally restrict a tumor’s development. However, cancer cells can adapt healthy fibroblasts into cancer-associated fibroblasts, which produce an altered extracellular matrix that could allow the tumor to grow.

Franco-Barraza et al. have now compared healthy and cancer-associated fibroblasts from patients’ pancreatic tumors. One of the main differences between these two cell types was the location of the activated form of a molecule called α₅β₁-integrin. Healthy fibroblasts, in a normal extracellular matrix, have active α₅β₁-integrin on the surface of the cell. However, a number of tumor-promoting signals, including some from the altered extracellular matrix, could force the active α₅β₁-integrins to relocate inside the fibroblasts instead. In further experiments, where the activated integrin was retained at the cell surface, the fibroblasts were able to resist the influence of the cancer-associated extracellular matrix. Then again, if the active α₅β₁-integrins were directed inside the cells, healthy cells turned into cancer-associated fibroblasts.

With this information in hand, Franco-Barraza et al. examined tumor samples from over a hundred pancreatic cancer patients using a new microscopy-based technique that distinguishes cancer cells from stroma cells. The analysis confirmed the pattern observed in the laboratory: those patients who appeared to produce more normal extracellular matrix and have active α₅β₁-integrin localized mostly to the surface of the cells survived longer without the cancer returning than those patients who lacked these stroma traits. Samples from patients with kidney cancer also showed similar results and, as before, an altered extracellular matrix was linked to a worse outcome of the disease.

Together these findings suggest that if future studies uncover ways to relocate or maintain active α₅β₁-integrin to the cell surface of fibroblasts they could lead to new treatments to restrict the growth of tumors in cancer patients.

DOI:http://dx.doi.org/10.7554/eLife.20600.002

Whole Exome Sequencing in Psoriasis Patients Contributes to Studies of Acitretin Treatment Difference

Psoriasis vulgaris is an immune-mediated inflammatory skin disease. Although acitretin is a widely used synthetic retinoid for moderate to severe psoriasis, little is known about patients’ genetics in response to this drug. In this study, 179 patients were enrolled in either the discovery set (13 patients) or replication set (166 patients). The discovery set was sequenced by whole exome sequencing and sequential validation was conducted in the replication set by MassArray assays. Four SNPs (single nucleotide polymorphisms) (rs1105223T>C in CRB2, rs11086065A>G in ANKLE1, rs3821414T>C in ARHGEF3, rs1802073 T>G in SFRP4) were found to be significantly associated with acitretin response in either co-dominant or dominant models via multivariable logistic regression analysis, while CRB2 rs1105223CC (OR = 4.10, 95% CI = 1.46–11.5, p = 0.007) and ANKLE1 rs11086065AG/GG (OR = 2.76, 95% CI = 1.42–5.37, p = 0.003) were associated with no response to acitretin after 8-week treatment. Meanwhile, ARHGEF3 rs3821414CT/CC (OR = 0.25, 95% CI = 0.10–0.68, p = 0.006) and SFRP4 rs1802073GG/GT (OR = 2.40, 95% CI, 1.23–4.70, p = 0.011) were associated with a higher response rate. Four new genetic variations with potential influences on the response to acitretin were found in this study which may serve as genetic markers for acitretin in psoriasis patients.

Pancreatic stellate cell: Pandora's box for pancreatic disease biology

Pancreatic stellate cells (PSCs) were identified in the early 1980s, but received much attention after 1998 when the methods to isolate and culture them from murine and human sources were developed. PSCs contribute to a small proportion of all pancreatic cells under physiological condition, but are essential for maintaining the normal pancreatic architecture. Quiescent PSCs are characterized by the presence of vitamin A laden lipid droplets. Upon PSC activation, these perinuclear lipid droplets disappear from the cytosol, attain a myofibroblast like phenotype and expresses the activation marker, alpha smooth muscle actin. PSCs maintain their activated phenotype via an autocrine loop involving different cytokines and contribute to progressive fibrosis in chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC). Several pathways (e.g., JAK-STAT, Smad, Wnt signaling, Hedgehog etc.), transcription factors and miRNAs have been implicated in the inflammatory and profibrogenic function of PSCs. The role of PSCs goes much beyond fibrosis/desmoplasia in PDAC. It is now shown that PSCs are involved in significant crosstalk between the pancreatic cancer cells and the cancer stroma. These interactions result in tumour progression, metastasis, tumour hypoxia, immune evasion and drug resistance. This is the rationale for therapeutic preclinical and clinical trials that have targeted PSCs and the cancer stroma.

Pancreatic cancer: Stroma and its current and emerging targeted therapies

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human malignancies with a 5-year survival rate of 8%. Dense, fibrotic stroma associated with pancreatic tumors is a major obstacle for drug delivery to the tumor bed and plays a crucial role in pancreatic cancer progression. Targeting stroma is considered as a potential therapeutic strategy to improve anti-cancer drug efficacy and patient survival. Although numerous stromal depletion therapies have reached the clinic, they add little to overall survival and are often associated with toxicity. Furthermore, increasing evidence suggests the anti-tumor properties of stroma. Its complete ablation enhanced tumor progression and reduced survival. Consequently, efforts are now focused on developing stromal-targeted therapies that normalize the reactive stroma and avoid the extremes: stromal abundance vs. complete depletion. In this review, we summarized the state of current and emerging anti-stromal targeted therapies, with major emphasis on the role of miRNAs in PDAC stroma and their potential use as novel therapeutic agents to modulate PDAC tumor-stromal interactions.

ER stress protein AGR2 precedes and is involved in the regulation of pancreatic cancer initiation

The mechanisms of initiation of pancreatic ductal adenocarcinoma (PDAC) are still largely unknown. In the present study, we analysed the role of anterior gradient-2 (AGR2) in the earliest stages of pancreatic neoplasia. Immunohistochemical analysis of chronic pancreatitis (CP) and peritumoral areas in PDAC tissues showed that AGR2 was present in tubular complexes (TC) and early pancreatic intraepithelial neoplasia (PanINs). Moreover, AGR2 was also found in discrete subpopulations of non-transformed cells neighbouring these pre-neoplastic lesions. In primary cells derived from human patient-derived xenograft (PDX) model, flow-cytometry revealed that AGR2 was overexpressed in pancreatic cancer stem cells (CSC) compared with non-stem cancer cells. In LSL-Kras^G12D;Pdx1-Cre (KC) mouse model Agr2 induction preceded the formation of pre-neoplastic lesions and their development was largely inhibited by Agr2 deletion in engineered LSL-Kras^G12D;Pdx1-Cre; Agr2^−/− mice. In vitro, AGR2 expression was stimulated by tunicamycin-induced endoplasmic reticulum (ER) stress in both KRAS wild-type normal pancreas cells, as well as in KRAS mutated pancreatic cancer cells and was essential for ER homoeostasis. The unfolded protein response proteins GRP78, ATF6 and XBP1s were found expressed in CP and PDAC peritumoral tissues, but in contrast to AGR2, their expression was switched off during TC and PanIN formation. Real-time PCR and ELISA analyses showed that ER stress induced a pro-inflammatory phenotype in pancreatic normal, cancer and stellate cells. Moreover, AGR2 expression was inducible by paracrine transfer of ER stress and pro-inflammation between different pancreatic cell types. Our findings demonstrate that AGR2 induced in ER-stressed and inflammatory pre-neoplastic pancreas is a potential marker of cancer progenitor cells with an important functional role in PDAC initiation.

Prognostic role and correlation of CA9, CD31, CD68 and CD20 with the desmoplastic stroma in pancreatic ductal adenocarcinoma

We assessed the prognostic value of hypoxia (carbonic anhydrase 9; CA9), vessel density (CD31), with macrophages (CD68) and B cells (CD20) that can interact and lead to immune suppression and disease progression using scanning and histological mapping of whole-mount FFPE pancreatectomy tissue sections from 141 primarily resectable pancreatic ductal adenocarcinoma (PDAC) samples treated with surgery and adjuvant chemotherapy. Their expression was correlated with clinicopathological characteristics, and overall survival (OS), progression-free survival (PFS), local progression-free survival (LPFS) and distant metastases free-survival (DMFS), also in the context of stroma density (haematoxylin-eosin) and activity (alpha-smooth muscle actin). The median OS was 21 months after a mean follow-up of 20 months (range, 2-69 months). The median tumor surface area positive for CA9 and CD31 was 7.8% and 8.1%, respectively. Although total expression of these markers lacked prognostic value in the entire cohort, nevertheless, high tumor compartment CD68 expression correlated with worse PFS (p = 0.033) and DMFS (p = 0.047). Also, high CD31 expression predicted for worse OS (p = 0.004), PFS (p = 0.008), LPFS (p = 0.014) and DMFS (p = 0.004) in patients with moderate density stroma. High stromal and peripheral compartment CD68 expression predicted for significantly worse outcome in patients with loose and moderate stroma density, respectively. Altogether, in contrast to the current notion, hypoxia levels in PDAC appear to be comparable to other malignancies. CD31 and CD68 constitute prognostic markers in patient subgroups that vary according to tumor compartment and stromal density. Our study provides important insight on the pathophysiology of PDAC and should be exploited for future treatments.

Leveraging Mechanisms Governing Pancreatic Tumorigenesis To Reduce Pancreatic Cancer Mortality

Pancreatic ductal adenocarcinoma (PDA) is a devastating malignancy with limited and modest clinical treatments. High-throughput technologies and accurate disease models now provide a comprehensive picture of the diverse molecular signaling pathways and cellular processes governing PDA tumorigenesis. Central among these is oncogenic KRAS, a mediator of cellular plasticity, metabolic reprogramming, and inflammatory and paracrine signaling required for tumor development and maintenance. Biological aggressiveness is further conferred by a highly fibrotic and immunosuppressive PDA microenvironment that also acts as a barrier to effective drug delivery. The regulation of these mechanisms and their implications for early cancer detection, chemoprevention and therapy are discussed.

Pancreatic stellate cells regulate blood vessel density in the stroma of pancreatic ductal adenocarcinoma

BACKGROUND/OBJECTIVES

The vascular heterogeneity of pancreatic ductal adenocarcinoma (PDAC) has never been characterised. We analysed the heterogeneous vascular density of human PDAC along with its prognostic correlation.

METHODS

Tissue Microarrays of 87 patients with different pancreatico-biliary pathologies were analysed in an automated manner (Ariol™) after CD31 staining to assess vascular density in juxta-tumoral and panstromal compartments. In vitro and ex vivo assays were carried out to assess the role of PSC.

RESULTS

PDAC has a distinct vascular density and distribution of vessels compared to cholangiocarcinoma. The PDAC juxta-tumoral stroma was hypovascular and the normal adjacent rim was hypervascular compared to the panstromal compartment. These features adversely affected patient prognosis, suggesting a model for spatio-temporal PDAC evolution. Mice aortic rings and 3D organotypic cultures demonstrated pro- and anti-angiogenic signalling from activated PSC and cancer cells respectively. ATRA-induced quiescence suppressed the pro-angiogenic activity of PSC.

CONCLUSION

Human PDAC has variable vascularity at microscopic level suggesting that novel stromal directed therapies would need to be determined by pathological characteristics.

Senescence in hepatic stellate cells as a mechanism of liver fibrosis reversal: a putative synergy between retinoic acid and PPAR-gamma signalings

Hepatic stellate cells (HSCs), also known as perisinusoidal cells, are pericytes found in the perisinusoidal space of the liver. HSCs are the major cell type involved in liver fibrosis, which is the formation of scar tissue in response to liver damage. When the liver is damaged, stellate cells can shift into an activated state, characterized by proliferation, contractility and chemotaxis. The activated HSCs secrete collagen scar tissue, which can lead to cirrhosis. Recent studies have shown that in vivo activation of HSCs by fibrogenic agents can eventually lead to senescence of these cells, which would contribute to reversal of fibrosis although it may also favor the insurgence of liver cancer. HSCs in their non-active form store huge amounts of retinoic acid derivatives in lipid droplets, which are progressively depleted upon cell activation in injured liver. Retinoic acid is a metabolite of vitamin A (retinol) that mediates the functions of vitamin A, generally required for growth and development. The precise function of retinoic acid and its alterations in HSCs has yet to be elucidated, and nonetheless in various cell types retinoic acid and its receptors (RAR and RXR) are known to act synergistically with peroxisome proliferator-activated receptor gamma (PPAR-gamma) signaling through the activity of transcriptional heterodimers. Here, we review the recent advancements in the understanding of how retinoic acid signaling modulates the fibrogenic potential of HSCs and proposes a synergistic combined action with PPAR-gamma in the reversal of liver fibrosis.

ATRA mechanically reprograms pancreatic stellate cells to suppress matrix remodelling and inhibit cancer cell invasion

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a dismal survival rate. Persistent activation of pancreatic stellate cells (PSCs) can perturb the biomechanical homoeostasis of the tumour microenvironment to favour cancer cell invasion. Here we report that ATRA, an active metabolite of vitamin A, restores mechanical quiescence in PSCs via a mechanism involving a retinoic acid receptor beta (RAR-β)-dependent downregulation of actomyosin (MLC-2) contractility. We show that ATRA reduces the ability of PSCs to generate high traction forces and adapt to extracellular mechanical cues (mechanosensing), as well as suppresses force-mediated extracellular matrix remodelling to inhibit local cancer cell invasion in 3D organotypic models. Our findings implicate a RAR-β/MLC-2 pathway in peritumoural stromal remodelling and mechanosensory-driven activation of PSCs, and further suggest that mechanical reprogramming of PSCs with retinoic acid derivatives might be a viable alternative to stromal ablation strategies for the treatment of PDAC.

Persistent activation of pancreatic stellate cells (PSCs) can perturb the biomechanical homeostasis of the tumour microenvironment. Here the authors show that all-trans retinoic acid reduces retinoic acid receptor beta dependent-actomyosin contractility and restores mechanical quiescence in PSCs.

BCL9L expression in pancreatic neoplasia with a focus on SPN: a possible explanation for the enigma of the benign neoplasia

BACKGROUND

Solid pseudopapillary neoplasms of the pancreas (SPN) are rare tumors affecting mainly women. They show an activating mutation in CTNNB1, the gene for β-catenin, and consequently an overactivation of the Wnt/β-catenin pathway. This signaling pathway is implied in the pathogenesis of various aggressive tumors, including pancreatic adenocarcinomas (PDAC). Despite this, SPN are characterized by an unusually benign clinical course. Attempts to explain this lack of malignancy have led to the discovery of an aberrant expression of the transcription factor FLI1 in SPN.

METHODS

In 42 primary pancreatic tumors the RNA-expression of the FLI1 targets DKK1, INPP5D, IGFBP3 and additionally two members of the Wnt/β-catenin pathway, namely BCL9 and BCL9L, was investigated using quantitative real time PCR. Expression of these genes was evaluated in SPN (n = 18), PDAC (n = 12) and the less aggressive intraductal papillary mucinous neoplasm IPMN (n = 12) and compared to normal pancreatic tissue. Potential differences between the tumor entities were evaluated using students t-test.

RESULTS

The results demonstrated a differential RNA-expression of BCL9L with a lack of expression in SPN (p < 0.001), RNA levels similar to normal tissue in IPMN and increased expression in PDAC (p < 0.04). Further, overexpression of the cyclin D1 inhibitor INPP5D in IPMN (p < 0.0001) was found. PDAC, on the other hand, showed the highest expression of IGFBP3 (p < 0.00001) with the gene still being significantly overexpressed in IPMN (p < 0.001). Nevertheless the difference in expression was significant between PDAC and IPMN (p < 0.05) and IGFBP3 RNA levels were significantly higher in PDAC and IPMN than in SPN (p < 0.0001 and p < 0.02, resp.).

CONCLUSIONS

This study demonstrates a significantly decreased expression of the β-catenin stabilizing gene BCL9L in SPN as a first clue to the possible reasons for the astonishingly benign behavior of this entity. In contrast, high expression of the gene was detected in PDAC supporting the connection between BCL9L expression and tumor malignancy in pancreas neoplasias. IPMN, accordingly, showed intermediate expression of BCL9L, but instead demonstrated a high expression of the cyclin D1 inhibitor INPP5D, possibly contributing to the better prognosis of this neoplasia compared to PDAC.

ATRA modulates mechanical activation of TGF-β by pancreatic stellate cells

The hallmark of pancreatic ductal adenocarcinoma (PDAC) is abundant desmoplasia, which is orchestrated by pancreatic stellate cells (PSCs) and accounts for the majority of the stroma surrounding the tumour. Healthy PSCs are quiescent, but upon activation during disease progression, they adopt a myofibroblast-contractile phenotype and secrete and concomitantly reorganise the stiff extracellular matrix (ECM). Transforming growth factor β (TGF-β) is a potent activator of PSCs, and its activation requires spatiotemporal organisation of cellular and extracellular cues to liberate it from an inactive complex with latent TGF-β binding protein (LTBP). Here we study the mechanical activation of TGF-β by PSCs in vitro by investigating LTBP-1 organisation with fibrillar fibronectin and show that all trans-retinoic acid (ATRA), which induces PSC quiescence, down-regulates the ability of PSCs to mechanically organise LTBP-1 and activate TGF-β through a mechanism involving myosin II dependent contractility. Therefore, ATRA inhibits the ability of PSCs to mechanically release active TGF-β, which might otherwise act in an autocrine manner to sustain PSCs in an active state and a tumour-favouring stiff microenvironment.

Anti-stromal treatment together with chemotherapy targets multiple signalling pathways in pancreatic adenocarcinoma

Stromal targeting for pancreatic ductal adenocarcinoma (PDAC) is rapidly becoming an attractive option, due to the lack of efficacy of standard chemotherapy and increased knowledge about PDAC stroma. We postulated that the addition of stromal therapy may enhance the anti-tumour efficacy of chemotherapy. Gemcitabine and all-trans retinoic acid (ATRA) were combined in a clinically applicable regimen, to target cancer cells and pancreatic stellate cells (PSCs) respectively, in 3D organotypic culture models and genetically engineered mice (LSL-Kras(G12D) (/+) ;LSL-Trp53(R172H) (/+) ;Pdx-1-Cre: KPC mice) representing the spectrum of PDAC. In two distinct sets of organotypic models as well as KPC mice, we demonstrate a reduction in cancer cell proliferation and invasion together with enhanced cancer cell apoptosis when ATRA is combined with gemcitabine, compared to vehicle or either agent alone. Simultaneously, PSC activity (as measured by deposition of extracellular matrix proteins such as collagen and fibronectin) and PSC invasive ability were both diminished in response to combination therapy. These effects were mediated through a range of signalling cascades (Wnt, hedgehog, retinoid, and FGF) in cancer as well as stellate cells, affecting epithelial cellular functions such as epithelial-mesenchymal transition, cellular polarity, and lumen formation. At the tissue level, this resulted in enhanced tumour necrosis, increased vascularity, and diminished hypoxia. Consequently, there was an overall reduction in tumour size. The enhanced effect of stromal co-targeting (ATRA) alongside chemotherapy (gemcitabine) appears to be mediated by dampening multiple signalling cascades in the tumour-stroma cross-talk, rather than ablating stroma or targeting a single pathway. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Quantitative analysis of 3D extracellular matrix remodelling by pancreatic stellate cells

Extracellular matrix (ECM) remodelling is integral to numerous physiological and pathological processes in biology, such as embryogenesis, wound healing, fibrosis and cancer. Until recently, most cellular studies have been conducted on 2D environments where mechanical cues significantly differ from physiologically relevant 3D environments, impacting cellular behaviour and masking the interpretation of cellular function in health and disease. We present an integrated methodology where cell-ECM interactions can be investigated in 3D environments via ECM remodelling. Monitoring and quantification of collagen-I structure in remodelled matrices, through designated algorithms, show that 3D matrices can be used to correlate remodelling with increased ECM stiffness observed in fibrosis. Pancreatic stellate cells (PSCs) are the key effectors of the stromal fibrosis associated to pancreatic cancer. We use PSCs to implement our methodology and demonstrate that PSC matrix remodelling capabilities depend on their contractile machinery and β1 integrin-mediated cell-ECM attachment.

Targeting stromal microenvironment in pancreatic ductal adenocarcinoma: controversies and promises

Pancreatic cancer is a highly lethal disease. Conventional therapeutics targeting pancreas cancer cell compartment using cytotoxics improved patient survival but at the expense of significant toxicity. Microscopically, the tumor is characterized by thick desmoplastic stroma that surrounds islands of pancreatic cancer cells. The tumor microenvironment has been found to play important roles in carcinogenesis, the development of drug resistance, and mediating immunosuppression. The understanding the tumor-stromal interaction has led to the development of novel therapeutic approaches. Here, we review the strategies that are currently in (or, near to) clinical evaluation and the underlying preclinical rationales.

Key players in pancreatic cancer-stroma interaction: Cancer-associated fibroblasts, endothelial and inflammatory cells

Pancreatic cancer (PC) is the most aggressive type of common cancers, and in 2014, nearly 40000 patients died from the disease in the United States. Pancreatic ductal adenocarcinoma, which accounts for the majority of PC cases, is characterized by an intense stromal desmoplastic reaction surrounding the cancer cells. Cancer-associated fibroblasts (CAFs) are the main effector cells in the desmoplastic reaction, and pancreatic stellate cells are the most important source of CAFs. However, other important components of the PC stroma are inflammatory cells and endothelial cells. The aim of this review is to describe the complex interplay between PC cells and the cellular and non-cellular components of the tumour stroma. Published data have indicated that the desmoplastic stroma protects PC cells against chemotherapy and radiation therapy and that it might promote the proliferation and migration of PC cells. However, in animal studies, experimental depletion of the desmoplastic stroma and CAFs has led to more aggressive cancers. Hence, the precise role of the tumour stroma in PC remains to be elucidated. However, it is likely that a context-dependent therapeutic modification, rather than pure depletion, of the PC stroma holds potential for the development of new treatment strategies for PC patients.

Pharmacological targeting of the protein synthesis mTOR/4E-BP1 pathway in cancer-associated fibroblasts abrogates pancreatic tumour chemoresistance

Pancreatic ductal adenocarcinoma (PDAC) is extremely stroma-rich. Cancer-associated fibroblasts (CAFs) secrete proteins that activate survival and promote chemoresistance of cancer cells. Our results demonstrate that CAF secretome-triggered chemoresistance is abolished upon inhibition of the protein synthesis mTOR/4E-BP1 regulatory pathway which we found highly activated in primary cultures of α-SMA-positive CAFs, isolated from human PDAC resections. CAFs selectively express the sst1 somatostatin receptor. The SOM230 analogue (Pasireotide) activates the sst1 receptor and inhibits the mTOR/4E-BP1 pathway and the resultant synthesis of secreted proteins including IL-6. Consequently, tumour growth and chemoresistance in nude mice xenografted with pancreatic cancer cells and CAFs, or with pieces of resected human PDACs, are reduced when chemotherapy (gemcitabine) is combined with SOM230 treatment. While gemcitabine alone has marginal effects, SOM230 is permissive to gemcitabine-induced cancer cell apoptosis and acts as an antifibrotic agent. We propose that selective inhibition of CAF protein synthesis with sst1-directed pharmacological compounds represents an anti-stromal-targeted therapy with promising chemosensitization potential.

Retinoids in the pancreas

Retinoids (vitamin A and its natural and synthetic analogs) are required by most tissues for maintaining the normal health of the tissue. This is certainly true for the pancreas. The recent literature is convincing that retinoids are needed by the adult to assure normal pancreatic endocrine functions, especially those of the α- and β-cells. It is also well established that retinoids are required to insure normal pancreas development in utero, including the development of the endocrine pancreas. The actions of retinoids for maintaining normal pancreatic islet functions has drawn considerable research interest from investigators interested in understanding and treating metabolic disease. Pancreatic retinoids are also of interest to investigators studying the origins of pancreatic disease, including the development of pancreatic fibrosis and its sequelae. This research interest is focused on pancreatic stellate cells (PSCs) which store retinoids and possess the metabolic machinery needed to metabolize retinoids. The literature on pancreatic disease and retinoids suggests that there is an association between impairments in pancreatic retinoid storage and metabolism and the development of pancreatic disease. These topics will be considered in this review.

The prognostic role of desmoplastic stroma in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an abundant desmoplastic stroma. We examined the prognostic value of stroma density and activity in patients with resectable PDAC treated with surgery and adjuvant gemcitabine-based chemotherapy. FFPE-tissue from the pancreatectomy of 145 patients was immunohistochemically stained for haematoxylin-eosin and Masson's trichrome to assess stroma density, and alpha-smooth muscle actin (αSMA) expression for activated pancreatic stellate cells. Their expression was correlated with clinicopathological characteristics as well as overall survival (OS), progression-free survival (PFS), local progression-free survival (LPFS) and distant metastases free-survival (DMFS). After a mean follow-up of 20 months (range, 2-69 months), the median OS was 21 months and the 3-year OS was 35.7%. In multivariate analysis, highly-dense stroma was an independent prognostic parameter for OS (p = 0.001), PFS (p = 0.007), LPFS (p = 0.001) and DMFS (p = 0.002), while αSMA expression lacked significance. Interestingly, highly-dense stroma retained significance for the four clinical endpoints only in early (pT1-2) but not late (pT3-4) stage tumors. Additionally, late pT-stage (pT3-4), the presence of lymph node metastases (pN+ vs pN0), perineural/neural invasion and administration of adjuvant chemotherapy also correlated with prognosis in multivariate analysis. Altogether, stroma density constitutes an independent prognostic marker in PDAC patients treated with adjuvant chemotherapy. Our findings highlight the dynamic complexity of desmoplasia and indicate that highly-dense stroma is correlated with better outcome. Further validation of the prognostic value of stroma as a biomarker and its role in PDAC patients after adjuvant chemotherapy is warranted and will be performed in a prospective study.

Targeting Transcriptional and Epigenetic Reprogramming in Stromal Cells in Fibrosis and Cancer

The basis of many human diseases arises from both genetic and epigenetic regulation. Recent advances in the understanding of the mechanisms underlying transcriptional and epigenetic regulation and their prevalence as contributors to a diverse range of human diseases have led us to focus on transcription and epigenetic changes in a variety of human disease conditions. Specifically, our recent studies in liver fibrosis and pancreatic cancer have demonstrated that the epigenetic regulation in hepatic stellate cells (HSCs) and pancreatic stellate cells (PSCs) significantly contributes to the progress in such diseases and presents great therapeutic potential. We show that the vitamin D receptor (VDR) acts as a master genomic suppressor in both HSC and PSC activation. The studies also have demonstrated that the VDR ligand reduces fibrosis and inflammation in a murine liver fibrosis and pancreatitis model. Although our current studies focus on characterizing the roles of VDR and regulatory regions within gene promoters and regulatory enhancers, we have expanded our effort to epigenetic mechanisms as major determinants of gene activation and repression in order to develop potential therapeutics to modulate stroma-associated pathologies including inflammation, fibrosis, and cancer.

Retinoic Acid Ameliorates Pancreatic Fibrosis and Inhibits the Activation of Pancreatic Stellate Cells in Mice with Experimental Chronic Pancreatitis via Suppressing the Wnt/β-Catenin Signaling Pathway

Pancreatic fibrosis, a prominent feature of chronic pancreatitis (CP), induces persistent and permanent damage in the pancreas. Pancreatic stellate cells (PSCs) provide a major source of extracellular matrix (ECM) deposition during pancreatic injury, and persistent activation of PSCs plays a vital role in the progression of pancreatic fibrosis. Retinoic acid (RA), a retinoid, has a broad range of biological functions, including regulation of cell differentiation and proliferation, attenuating progressive fibrosis of multiple organs. In the present study, we investigated the effects of RA on fibrosis in experimental CP and cultured PSCs. CP was induced in mice by repetitive cerulein injection in vivo, and mouse PSCs were isolated and activated in vitro. Suppression of pancreatic fibrosis upon administration of RA was confirmed based on reduction of histological damage, α-smooth muscle actin (α-SMA) expression and mRNA levels of β-catenin, platelet-derived growth factor (PDGF)-Rβ transforming growth factor (TGF)-βRII and collagen 1α1 in vivo. Wnt 2 and β-catenin protein levels were markedly down-regulated, while Axin 2 expression level was up-regulated in the presence of RA, both in vivo and in vitro. Nuclear translation of β-catenin was significantly decreased following RA treatment, compared with cerulein-induced CP in mice and activated PSCs. Furthermore, RA induced significant PSC apoptosis, inhibited proliferation, suppressed TCF/LEF-dependent transcriptional activity and ECM production of PSC via down-regulation of TGFβRII, PDGFRβ and collagen 1α1 in vitro. These results indicate a critical role of the Wnt/β-catenin signaling pathway in RA-induced effects on CP and PSC regulation and support the potential of RA as a suppressor of pancreatic fibrosis in mice.