A paracrine requirement for hedgehog signalling in cancer

Hedgehog signaling stimulates the formation of proliferating Müller glia-derived progenitor cells in the chick retina

Müller glia can be stimulated to de-differentiate and become proliferating progenitor cells that regenerate neurons in the retina. The signaling pathways that regulate the formation of proliferating Müller glia-derived progenitor cells (MGPCs) are beginning to be revealed. The purpose of this study was to investigate whether Hedgehog (Hh) signaling influences the formation of MGPCs in the chick retina. We find that Hh signaling is increased in damaged retinas where MGPCs are known to form. Sonic Hedgehog (Shh) is normally present in the axons of ganglion cells, but becomes associated with Müller glia and MGPCs following retinal damage. Activation of Hh signaling with recombinant human SHH (rhShh) or smoothened agonist (SAG) increased levels of Ptch1, Gli1, Gli2, Gli3, Hes1 and Hes5, and stimulated the formation of proliferating MGPCs in damaged retinas. In undamaged retinas, SAG or rhShh had no apparent effect upon the Müller glia. However, SAG combined with FGF2 potentiated the formation of MGPCs, whereas SAG combined with IGF1 stimulated the nuclear migration of Müller glia, but not the formation of MGPCs. Conversely, inhibition of Hh signaling with KAAD-cyclopamine, Gli antagonists or antibody to Shh reduced numbers of proliferating MGPCs in damaged and FGF2-treated retinas. Hh signaling potentiates Pax6, Klf4 and cFos expression in Müller glia during the formation of MGPCs. We find that FGF2/MAPK signaling recruits Hh signaling into the signaling network that drives the formation of proliferating MGPCs. Our findings implicate Hh signaling as a key component of the network of signaling pathways that promote the de-differentiation of Müller glia and proliferation of MGPCs.

Genetics and Biology of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma remains a clinical challenge. Thus far, enlightenment on the downstream activities of Kras, the tumor's unique metabolic needs, and how the stroma and immune system affect it have remained untranslated to the clinical practice. Given the numbers of diverse therapies in development and a growing knowledge about how to evaluate these systems preclinically and clinically, this is expected to change significantly and for the better over the next 5 years.

Pancreatic cancer stromal biology and therapy

Pancreatic cancer is one of the most lethal malignancies. Significant progresses have been made in understanding of pancreatic cancer pathogenesis, including appreciation of precursor lesions or premalignant pancreatic intraepithelial neoplasia (PanINs), description of sequential transformation from normal pancreatic tissue to invasive pancreatic cancer and identification of major genetic and epigenetic events and the biological impact of those events on malignant behavior. However, the currently used therapeutic strategies targeting tumor epithelial cells, which are potent in cell culture and animal models, have not been successful in the clinic. Presumably, therapeutic resistance of pancreatic cancer is at least in part due to its drastic desmoplasis, which is a defining hallmark for and circumstantially contributes to pancreatic cancer development and progression. Improved understanding of the dynamic interaction between cancer cells and the stroma is important to better understanding pancreatic cancer biology and to designing effective intervention strategies. This review focuses on the origination, evolution and disruption of stromal molecular and cellular components in pancreatic cancer, and their biological effects on pancreatic cancer pathogenesis.

The presence of primary cilia in cancer cells does not predict responsiveness to modulation of smoothened activity

Primary cilia are microtubule-based organelles that regulate smoothened-dependent activation of the GLI transcription factors in canonical hedgehog signaling. In many cancers, primary cilia are markedly decreased or absent. The lack of primary cilia may inhibit or alter canonical hedgehog signaling and, thereby, interfere in the cellular responsiveness to modulators of smoothened activity. Clinical trials of smoothened antagonists for cancer treatment have shown the best response in basal cell carcinomas, with limited response in other solid tumors. To determine whether the presence or absence of primary cilia in cancer cells will predict their responsiveness to modulation of smoothened activity, we compared the ability of an agonist and/or inhibitor of smoothened (SAG and SANT1, respectively) to modulate GLI-mediated transcription, as measured by GLI1 mRNA level or GLI-luciferase reporter activity, in non-cancer cells with primary cilia (ovarian surface epithelial cells and breast fibroblasts), in cancer cells that cannot assemble primary cilia (MCF7, MDA-MB-231 cell lines), and in cancer cells with primary cilia (SKOV3, PANC1 cell lines). As expected, SAG and SANT1 resulted in appropriate modulation of GLI transcriptional activity in ciliated non-cancer cells, and failed to modulate GLI transcriptional activity in cancer cells without primary cilia. However, there was also no modulation of GLI transcriptional activity in either ciliated cancer cell line. SAG treatment of SKOV3 induced localization of smoothened to primary cilia, as assessed by immunofluorescence, even though there was no increase in GLI transcriptional activity, suggesting a defect in activation of SMO in the primary cilia or in steps later in the hedgehog pathway. In contrast to SKOV3, SAG treatment of PANC1 did not cause the localization of smoothened to primary cilia. Our data demonstrate that the presence of primary cilia in the cancer epithelial cells lines tested does not indicate their responsiveness to smoothened activation or inhibition.

Sonic hedgehog processing and release are regulated by glypican heparan sulfate proteoglycans

All Hedgehog morphogens are released from producing cells, despite being synthesized as N- and C-terminally lipidated molecules, a modification that firmly tethers them to the cell membrane. We have previously shown that proteolytic removal of both lipidated peptides, called shedding, releases bioactive Sonic hedgehog (Shh) morphogens from the surface of transfected Bosc23 cells. Using in vivo knockdown together with in vitro cell culture studies, we now show that glypican heparan sulfate proteoglycans regulate this process, through their heparan sulfate chains, in a cell autonomous manner. Heparan sulfate specifically modifies Shh processing at the cell surface, and purified glycosaminoglycans enhance the proteolytic removal of N- and C-terminal Shh peptides under cell-free conditions. The most likely explanation for these observations is direct Shh processing in the extracellular compartment, suggesting that heparan sulfate acts as a scaffold or activator for Shh ligands and the factors required for their turnover. We also show that purified heparan sulfate isolated from specific cell types and tissues mediates the release of bioactive Shh from pancreatic cancer cells, revealing a previously unknown regulatory role for these versatile molecules in a pathological context.

Cyclopamine-loaded core-cross-linked polymeric micelles enhance radiation response in pancreatic cancer and pancreatic stellate cells

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers. Cyclopamine (CPA), a potent inhibitor for sonic hedgehog pathway (SHH), shows great promises in PDAC treatment, including the disruption of tumor-associated stroma, and enhancement of radiation therapy. However, CPA is insoluble in water and therefore requires a nanometric delivery platform to achieve satisfactory performance. We herein encapsulated CPA in a core-cross-linked polymeric micelle system (M-CPA). M-CPA was combined with Cs-137 radiation and evaluated in vitro in PDAC cell lines and a human pancreatic stellate cell line. The results showed that M-CPA had higher cytotoxicity than CPA, abolished Gli-1 expression (a key component of SHH), and enhanced the radiation therapy of Cs-137. M-CPA radiosensitization correlated with its ability to disrupt the repair of radiation-induced DNA damage. These findings indicate that the combination therapy of M-CPA and radiation is an effective strategy to simultaneously treat pancreatic tumors and tumor-associated stroma.

Progress in the treatment of metastatic pancreatic cancer and the search for next opportunities

A growing number of therapeutic options are now available for patients with metastatic pancreatic cancer, informed by positive results from recently completed phase III clinical trials. These have led to modest, if not necessarily transformative, improvements in clinical outcomes. Although the standard of care for metastatic disease remains cytotoxic therapy, a variety of novel therapeutic approaches are currently under active investigation, several of which have already demonstrated encouraging results in phase I/II studies. The following three broad categories (with significant overlap among them) are highlighted here: stromal-depleting agents, immunotherapies, and signal transduction inhibitors. The mechanistic rationale, limitations, and promise of each of these strategies specific to pancreatic cancer are discussed, as are the aspects of this disease and this patient population that pose ongoing challenges in terms of both therapeutic management and biomarker-driven trial design.

New insights into pancreatic cancer stem cells

Pancreatic cancer (PC) has been one of the deadliest of all cancers, with almost uniform lethality despite aggressive treatment. Recently, there have been important advances in the molecular, pathological and biological understanding of pancreatic cancer. Even after the emergence of recent new targeted agents and the use of multiple therapeutic combinations, no treatment option is viable in patients with advanced cancer. Developing novel strategies to target progression of PC is of intense interest. A small population of pancreatic cancer stem cells (CSCs) has been found to be resistant to chemotherapy and radiation therapy. CSCs are believed to be responsible for tumor initiation, progression and metastasis. The CSC research has recently achieved much progress in a variety of solid tumors, including pancreatic cancer to some extent. This leads to focus on understanding the role of pancreatic CSCs. The focus on CSCs may offer new targets for prevention and treatment of this deadly cancer. We review the most salient developments in important areas of pancreatic CSCs. Here, we provide a review of current updates and new insights on the role of CSCs in pancreatic tumor progression with special emphasis on DclK1 and Lgr5, signaling pathways altered by CSCs, and the role of CSCs in prevention and treatment of PC.

Targeting of the Hedgehog pathway in myeloid malignancies: still a worthy chase?

Deregulated Hedgehog (Hh) signalling activity may be associated with a broad range of cancer types and hence has become an attractive target for therapeutic intervention. Although initial haematological interest focused on the therapeutic targeting of this pathway in chronic myeloid leukaemia), small molecule inhibitors targeting the Hh pathway are now being tested in a range of other myeloid disorders, including myelofibrosis, myelodysplasia and acute myeloid leukaemia. In this review we will evaluate the rationale for targeting of the Hh pathway in myeloid diseases and discuss the novel agents that have entered the clinical arena. We will discuss pre-clinical models, emerging clinical trial data, and suggest how these targeted therapies may address current unmet medical needs. Finally, we will explore potential limitations of these therapies due to the emergence of secondary resistance mechanisms and speculate on future developments within this arena.

Establishment of patient-derived xenograft models and cell lines for malignancies of the upper gastrointestinal tract

Background

The upper gastrointestinal tract is home to some of most notorious cancers like esophagogastric and pancreatic cancer. Several factors contribute to the lethality of these tumors, but one that stands out for both tumor types is the strong inter- as well as intratumor heterogeneity. Unfortunately, genetic tumor models do not match this heterogeneity, and for esophageal cancer no adequate genetic models exist. To allow for an improved understanding of these diseases, tissue banks with sufficient amount of samples to cover the extent of diversity of human cancers are required. Additionally, xenograft models that faithfully mimic and span the breadth of human disease are essential to perform meaningful functional experiments.

Methods

We describe here the establishment of a tissue biobank, patient derived xenografts (PDXs) and cell line models of esophagogastric and pancreatic cancer patients. Biopsy material was grafted into immunocompromised mice and PDXs were used to establish primary cell cultures to perform functional studies. Expression of Hedgehog ligands in patient tumor and matching PDX was assessed by immunohistochemical staining, and quantitative real-time PCR as well as flow cytometry was used for cultured cells. Cocultures with Hedgehog reporter cells were performed to study paracrine signaling potency. Furthermore, SHH expression was modulated in primary cultures using lentiviral mediated knockdown.

Results

We have established a panel of 29 PDXs from esophagogastric and pancreatic cancers, and demonstrate that these PDXs mirror several of the (immuno)histological and biochemical characteristics of the original tumors. Derived cell lines can be genetically manipulated and used to further study tumor biology and signaling capacity. In addition, we demonstrate an active (paracrine) Hedgehog signaling mode by both tumor types, the magnitude of which has not been compared directly in previous studies.

Conclusions

Our established PDXs and their matching primary cell lines retain important characteristics seen in the original tumors, and this should enable future studies to address the responses of these tumors to different treatment modalities, but also help in gaining mechanistic insight in how some tumors respond to certain regimens and others do not.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0469-1) contains supplementary material, which is available to authorized users.

Pancreatic cancer: from state-of-the-art treatments to promising novel therapies

Pancreatic cancer is expected to be the second deadliest malignancy in the USA by 2020. The survival rates for patients with other gastrointestinal malignancies have increased consistently during the past 30 years; unfortunately, however, the outcomes of patients with pancreatic cancer have not changed significantly. Although surgery remains the only curative treatment for pancreatic cancer, therapeutic strategies based on initial resection have not substantially improved the survival of patients with resectable disease over the past 25 years; presently, more than 80% of patients suffer disease relapse after resection. Preclinical evidence that pancreatic cancer is a systemic disease suggests a possible benefit for early administration of systemic therapy in these patients. In locally advanced disease, the role of chemoradiotherapy is increasingly being questioned, particularly considering the results of the LAP-07 trial. Novel biomarkers are clearly needed to identify subsets of patients likely to benefit from chemoradiotherapy. In the metastatic setting, FOLFIRINOX (folinic acid, 5-fluorouracil, irinotecan, and oxaliplatin), and nab-paclitaxel plus gemcitabine have yielded only modest improvements in survival. Thus, new treatments are urgently needed for patients with pancreatic cancer. Herein, we review the state-of-the-art of pancreatic cancer treatment, and the upcoming novel therapeutics that hold promise in this disease are also discussed.

Hedgehog signaling pathway is active in GBM with GLI1 mRNA expression showing a single continuous distribution rather than discrete high/low clusters

Hedgehog (Hh) signaling pathway is a valid therapeutic target in a wide range of malignancies. We focus here on glioblastoma multiforme (GBM), a lethal malignancy of the central nervous system (CNS). By analyzing RNA-sequencing based transcriptomics data on 149 clinical cases of TCGA-GBM database we show here a strong correlation (r = 0.7) between GLI1 and PTCH1 mRNA expression--as a hallmark of the canonical Hh-pathway activity in this malignancy. GLI1 mRNA expression varied in 3 orders of magnitude among the GBM patients of the same cohort showing a single continuous distribution-unlike the discrete high/low-GLI1 mRNA expressing clusters of medulloblastoma (MB). When compared with MB as a reference, the median GLI1 mRNA expression in GBM appeared 14.8 fold lower than that of the "high-Hh" cluster of MB but 5.6 fold higher than that of the "low-Hh" cluster of MB. Next, we demonstrated statistically significant up- and down-regulation of GLI1 mRNA expressions in GBM patient-derived low-passage neurospheres in vitro by sonic hedgehog ligand-enriched conditioned media (shh-CM) and by Hh-inhibitor drug vismodegib respectively. We also showed clinically achievable dose (50 μM) of vismodegib alone to be sufficient to induce apoptosis and cell cycle arrest in these low-passage GBM neurospheres in vitro. Vismodegib showed an effect on the neurospheres, both by down-regulating GLI1 mRNA expression and by inducing apoptosis/cell cycle arrest, irrespective of their relative endogenous levels of GLI1 mRNA expression. We conclude from our study that this single continuous distribution pattern of GLI1 mRNA expression technically puts almost all GBM patients in a single group rather than discrete high- or low-clusters in terms of Hh-pathway activity. That is suggestive of therapies with Hh-pathway inhibitor drugs in this malignancy without a need for further stratification of patients on the basis of relative levels of Hh-pathway activity among them.

Sonic hedgehog signaling in the lung. From development to disease

Over the past two decades, the secreted protein sonic hedgehog (SHH) has emerged as a critical morphogen during embryonic lung development, regulating the interaction between epithelial and mesenchymal cell populations in the airway and alveolar compartments. There is increasing evidence that the SHH pathway is active in adult lung diseases such as pulmonary fibrosis, asthma, chronic obstructive pulmonary disease, and lung cancer, which raises two questions: (1) What role does SHH signaling play in these diseases? and (2) Is it a primary driver of the disease or a response (perhaps beneficial) to the primary disturbance? In this review we aim to fill the gap between the well-studied period of embryonic lung development and the adult diseased lung by reviewing the hedgehog (HH) pathway during the postnatal period and in adult uninjured and injured lungs. We elucidate the similarities and differences in the epithelial-mesenchymal interplay during the fibrosis response to injury in lung compared with other organs and present a critical appraisal of tools and agents available to evaluate HH signaling.

Injury-stimulated Hedgehog signaling promotes regenerative proliferation of Drosophila intestinal stem cells

In response to injury, Hedgehog signaling regulates the production of Upd2 in enteroblasts, which in turn activates the JAK–STAT pathway to drive intestinal stem cell proliferation.

Many adult tissues are maintained by resident stem cells that elevate their proliferation in response to injury. The regulatory mechanisms underlying regenerative proliferation are still poorly understood. Here we show that injury induces Hedgehog (Hh) signaling in enteroblasts (EBs) to promote intestinal stem cell (ISC) proliferation in Drosophila melanogaster adult midgut. Elevated Hh signaling by patched (ptc) mutations drove ISC proliferation noncell autonomously. Inhibition of Hh signaling in the ISC lineage compromised injury-induced ISC proliferation but had little if any effect on homeostatic proliferation. Hh signaling acted in EBs to regulate the production of Upd2, which activated the JAK–STAT pathway to promote ISC proliferation. Furthermore, we show that Hh signaling is stimulated by DSS through the JNK pathway and that inhibition of Hh signaling in EBs prevented DSS-stimulated ISC proliferation. Hence, our study uncovers a JNK–Hh–JAK–STAT signaling axis in the regulation of regenerative stem cell proliferation.

Crosstalk between epithelial and mesenchymal tissues in tumorigenesis and imaginal disc development

BACKGROUND

Cancers develop in a complex mutational landscape. Interaction of genetically abnormal cancer cells with normal stromal cells can modify the local microenvironment to promote disease progression for some tumor types. Genetic models of tumorigenesis provide the opportunity to explore how combinations of cancer driver mutations confer distinct properties on tumors. Previous Drosophila models of EGFR-driven cancer have focused on epithelial neoplasia.

RESULTS

Here, we report a Drosophila genetic model of EGFR-driven tumorigenesis in which the neoplastic transformation depends on interaction between epithelial and mesenchymal cells. We provide evidence that the secreted proteoglycan Perlecan can act as a context-dependent oncogene cooperating with EGFR to promote tumorigenesis. Coexpression of Perlecan in the EGFR-expressing epithelial cells potentiates endogenous Wg/Wnt and Dpp/BMP signals from the epithelial cells to support expansion of a mesenchymal compartment. Wg activity is required in the epithelial compartment, whereas Dpp activity is required in the mesenchymal compartment. This genetically normal mesenchymal compartment is required to support growth and neoplastic transformation of the genetically modified epithelial population.

CONCLUSIONS

We report a genetic model of tumor formation that depends on crosstalk between a genetically modified epithelial cell population and normal host mesenchymal cells. Tumorigenesis in this model co-opts a regulatory mechanism that is normally involved in controlling growth of the imaginal disc during development.

Sonic hedgehog and Gli1 expression predict outcome in resected pancreatic adenocarcinoma

PURPOSE

Aberrant activation of the hedgehog (Hh) pathway is implicated in pancreatic ductal adenocarcinoma (PDAC) tumorigenesis. We investigated the prognostic and predictive value of four Hh signaling proteins and of the tumor stromal density.

EXPERIMENTAL DESIGN

Using tissue microarray and immunohistochemistry, the expression of Shh, Gli1, SMO, and PTCH1 was assessed in 567 patients from three independent cohorts who underwent surgical resection for PDAC. In 82 patients, the tumor stromal index (SI) was calculated, and its association with overall survival (OS) and disease-free survival (DFS) was investigated.

RESULTS

Shh and Gli1 protein abundance were independent prognostic factors in resected PDACs; low expressors for those proteins experiencing a better OS and DFS. The combination of Shh and Gli1 levels was the most significant predictor for OS and defined 3 clinically relevant subgroups of patients with different prognosis (Gli1 and Shh low; HR set at 1 vs. 3.08 for Shh or Gli1 high vs. 5.69 for Shh and Gli1 high; P < 0.001). The two validating cohorts recapitulated the findings of the training cohort. After further stratification by lymph node status, the prognostic significance of combined Shh and Gli1 was maintained. The tumor SI was correlated with Shh levels and was significantly associated with OS (P = 0.023).

CONCLUSIONS

Shh and Gli1 are prognostic biomarkers for patients with resected PDAC.

Cooperative integration between HEDGEHOG-GLI signalling and other oncogenic pathways: implications for cancer therapy

The HEDGEHOG-GLI (HH-GLI) signalling is a key pathway critical in embryonic development, stem cell biology and tissue homeostasis. In recent years, aberrant activation of HH-GLI signalling has been linked to several types of cancer, including those of the skin, brain, lungs, prostate, gastrointestinal tract and blood. HH-GLI signalling is initiated by binding of HH ligands to the transmembrane receptor PATCHED and is mediated by transcriptional effectors that belong to the GLI family, whose activity is finely tuned by a number of molecular interactions and post-translation modifications. Several reports suggest that the activity of the GLI proteins is regulated by several proliferative and oncogenic inputs, in addition or independent of upstream HH signalling. The identification of this complex crosstalk and the understanding of how the major oncogenic signalling pathways interact in cancer is a crucial step towards the establishment of efficient targeted combinatorial treatments. Here we review recent findings on the cooperative integration of HH-GLI signalling with the major oncogenic inputs and we discuss how these cues modulate the activity of the GLI proteins in cancer. We then summarise the latest advances on SMO and GLI inhibitors and alternative approaches to attenuate HH signalling through rational combinatorial therapies.

Breast cancer cells promote a notch-dependent mesenchymal phenotype in endothelial cells participating to a pro-tumoral niche

Background

Endothelial cells (ECs) are responsible for creating a tumor vascular niche as well as producing angiocrine factors. ECs demonstrate functional and phenotypic heterogeneity when located under different microenvironments. Here, we describe a tumor-stimulated mesenchymal phenotype in ECs and investigate its impact on tumor growth, stemness, and invasiveness.

Methods

Xenograft tumor assay in NOD/SCID mice and confocal imaging were conducted to show the acquisition of mesenchymal phenotype in tumor-associated ECs in vivo. Immunocytochemistry, qPCR and flow cytometry techniques showed the appearance of mesenchymal traits in ECs after contact with breast tumor cell lines MDA-MB231 or MCF-7. Cell proliferation, cell migration, and sphere formation assays were applied to display the functional advantages of mesenchymal ECs in tumor growth, invasiveness, and enrichment of tumor initiating cells. qPCR and western blotting were used to investigate the mechanisms underlying EC mesenchymal transition.

Results

Our results showed that co-injection of ECs and tumor cells in NOD/SCID mice significantly enhanced tumor growth in vivo with tumor-associated ECs expressing mesenchymal markers while maintaining their intrinsic endothelial trait. We also showed that a mesenchymal phenotype is possibly detectable in human neoplastic breast biopsies as well as ECs pre-exposed to tumor cells (ECs^Mes) in vitro. The ECs^Mes acquired prolonged survival, increased migratory behavior and enhanced angiogenic properties. In return, ECs^Mes were capable of enhancing tumor survival and invasiveness. The mesenchymal phenotypes in ECs^Mes were the result of a contact-dependent transient phenomenon and reversed upon removal of the neoplastic contexture. We showed a synergistic role for TGFβ and notch pathways in this phenotypic change, as simultaneous inhibition of notch and TGFβ down-regulated Smad1/5 phosphorylation and Jag1^KD tumor cells were unable to initiate the process.

Conclusions

Overall, our data proposed a crosstalk mechanism between tumor and microenvironment where tumor-stimulated mesenchymal modulation of ECs enhanced the constitution of a transient mesenchymal/endothelial niche leading to significant increase in tumor proliferation, stemness, and invasiveness. The possible involvement of notch and TGFβ pathways in the initiation of mesenchymal phenotype may propose new stromal targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0386-3) contains supplementary material, which is available to authorized users.

Efficacy of Hedgehog pathway inhibitors in Basal cell carcinoma

Basal cell carcinoma (BCC) is the most commonly diagnosed cancer. While most BCCs are amenable to surgery, some tumors can reach a more advanced stage or metastasize, and become ineligible for surgical resection or radiotherapy. Abnormal activation of the Hedgehog (Hh) pathway is a key driver in BCC pathophysiology. Consequently, inhibitors of the Hh pathway have been developed. Molecules that inhibit the receptor protein Smoothened (SMO) are the most advanced in clinical development. Vismodegib is the first-in-class SMO inhibitor and has been approved in a number of countries for the treatment of metastatic or locally advanced BCC. Several molecules have demonstrated antitumoral activity, but treatment may be limited in duration by a number of side effects, and it is not yet established whether these agents are truly curative or whether continued treatment will be required. Resistance to SMO inhibition has been reported in the clinic for which incidence and mechanisms must be elucidated to inform future therapeutic strategies. Intermittent dosing regimens to improve tolerability, as well as neoadjuvant use of Hh pathway inhibitors, are currently under investigation. Here, we review the most recent outcomes obtained with Hh inhibitors under clinical investigation in BCC.

Hedgehog acyltransferase as a target in pancreatic ductal adenocarcinoma

Sonic Hedgehog (Shh) is abnormally expressed in pancreatic cancer and is associated with disease onset and progression. Inhibition of Shh signaling is thus an attractive clinical target for therapeutic intervention. Most efforts to block Shh signaling have focused on inhibitors of Smoothened, which target the canonical Shh signaling pathway. These approaches have met with limited success, in part due to development of resistance-conferring mutations and contributions from non-canonical signaling pathways. Here, we show that Hedgehog acyltransferase (Hhat), the enzyme responsible for the attachment of palmitate onto Shh, is a novel target for inhibition of Shh signaling in pancreatic cancer cells. Depletion of Hhat with lentivirally delivered small hairpin RNA decreased both anchorage-dependent and independent proliferation of human pancreatic cancer cells. In vivo, Hhat knockdown led to reduction of tumor growth in a mouse xenograft model of pancreatic cancer. RU-SKI 43, a small molecule inhibitor of Hhat recently developed by our group, reduced pancreatic cancer cell proliferation and Gli-1 activation through Smoothened-independent non-canonical signaling. In addition, RU-SKI 43 treatment inhibited two key proliferative pathways regulated by Akt and mTOR. This work demonstrates that Hhat has a critical role in pancreatic cancer and that a small molecule inhibitor of Hhat can successfully block pancreatic cancer cell proliferation. It also highlights the importance of developing optimized Hhat inhibitors to be used as therapeutics in pancreatic cancer, as well as in other malignancies characterized by Shh overexpression.

Pancreatic ductal adenocarcinoma: From genetics to biology to radiobiology to oncoimmunology and all the way back to the clinic

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death. Despite improvements in the clinical management, the prognosis of PDAC remains dismal. In the present comprehensive review, we will examine the knowledge of PDAC genetics and the new insights into human genome sequencing and clonal evolution. Additionally, the biology and the role of the stroma in tumour progression and response to treatment will be presented. Furthermore, we will describe the evidence on tumour chemoresistance and radioresistance and will provide an overview on the recent advances in PDAC metabolism and circulating tumour cells. Next, we will explore the characteristics and merits of the different mouse models of PDAC. The inflammatory milieu and the immunosuppressive microenvironment mediate tumour initiation and treatment failure. Hence, we will also review the inflammatory and immune escaping mechanisms and the new immunotherapies tested in PDAC. A better understanding of the different mechanisms of tumour formation and progression will help us to identify the best targets for testing in future clinical studies of PDAC.

Modeling human carcinomas: physiologically relevant 3D models to improve anti-cancer drug development

Anti-cancer drug development is inefficient, mostly due to lack of efficacy in human patients. The high fail rate is partly due to the lack of predictive models or the inadequate use of existing preclinical test systems. However, progress has been made and preclinical models were improved or newly developed, which all account for basic features of solid cancers, three-dimensionality and heterotypic cell interaction. Here we give an overview of available in vivo and in vitro models of cancer, which meet the criteria of being 3D and mirroring human tumor-stroma interactions. We only focus on drug response models without touching models for pharmacokinetic and dynamic, toxicity or delivery aspects.

Pathological and molecular evaluation of pancreatic neoplasms

Pancreatic neoplasms are morphologically and genetically heterogeneous and include a wide variety of tumors ranging from benign to malignant with an extremely poor clinical outcome. Our understanding of these pancreatic neoplasms has improved significantly with recent advances in cancer sequencing. Awareness of molecular pathogenesis brings new opportunities for early detection, improved prognostication, and personalized gene-specific therapies. Here we review the pathological classification of pancreatic neoplasms from the molecular and genetic perspectives.

Epithelial Notch signaling is a limiting step for pancreatic carcinogenesis

Background

Pancreatic cancer is one of the deadliest human malignancies, with few therapeutic options. Re-activation of embryonic signaling pathways is commonly in human pancreatic cancer and provided rationale to explore inhibition of these pathways therapeutically. Notch signaling is important during pancreatic development, and it is re-activated in pancreatic cancer. The functional role of Notch signaling during pancreatic carcinogenesis has been previously characterized using both genetic and drug-based approaches. However, contrasting findings were reported based on the study design. In fact, Notch signaling has been proposed to act as tumor-promoter or tumor-suppressor. Given the availability of Notch inhibitors in the clinic, understanding how this signaling pathway contributes to pancreatic carcinogenesis has important therapeutic implications. Here, we interrogated the role of Notch signaling specifically in the epithelial compartment of the pancreas, in the context of a genetically engineered mouse model of pancreatic cancer.

Methods

To inhibit Notch signaling in the pancreas epithelium, we crossed a mouse model of pancreatic cancer based on pancreas-specific expression of mutant Kras with a transgenic mouse that conditionally expresses a dominant negative form of the Mastermind-like 1 gene. MAML is an essential co-activator of the canonical Notch signaling-mediated transcription. DNMAML encodes a truncated MAML protein that represses all canonical Notch mediated transcription in a cell autonomous manner, independent of which Notch receptor is activated. As a result, in mice co-expressing mutant Kras and DNMAML, Notch signaling is inhibited specifically in the epithelium upon Cre-mediated recombination. We explored the effect of epithelial-specific DNMAML expression on Kras-driven carcinogenesis both during normal aging and following the induction of acute pancreatitis.

Results

We find that DNMAML expression efficiently inhibits epithelial Notch signaling and delays PanIN formation. However, over time, loss of Notch inhibition allows PanIN formation and progression.

Conclusions

Epithelial-specific Notch signaling is important for PanIN initiation. Our findings indicate that PanIN formation can only occur upon loss of epithelial Notch inhibition, thus supporting an essential role of this signaling pathway during pancreatic carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-862) contains supplementary material, which is available to authorized users.

A loss-of-function mutation in PTCH1 suggests a role for autocrine hedgehog signaling in colorectal tumorigenesis

Hedgehog (Hh) signaling is largely suppressed in the normal differentiated tissues of the adult but activated in many cancers. The Hh pathway can either be activated by the expression of Hh ligands, or by mutations that cause constitutive, ligand-independent signaling. Colorectal cancer cells frequently express Hh ligands that are believed to exert paracrine effects on the stromal component of the tumor. Evidence for a more direct role of Hh signaling on the growth and evolution of colorectal cancer cell clones has been lacking. Here, we report a loss-of-function mutation of PTCH1, a tumor suppressor in the Hh pathway, in a colorectal cancer that exhibits transcriptional upregulation of the downstream Hh gene GLI1. This finding demonstrates that autocrine Hh signaling can provide a selective advantage to evolving tumors that arise in the colorectal epithelia, and suggests a definable group of colorectal cancer patients that could derive enhanced benefit from Hh pathway inhibitors.

Repurposing the antihelmintic mebendazole as a hedgehog inhibitor

The hedgehog (Hh) signaling pathway is activated in many types of cancer and therefore presents an attractive target for new anticancer agents. Here, we show that mebendazole, a benzamidazole with a long history of safe use against nematode infestations and hydatid disease, potently inhibited Hh signaling and slowed the growth of Hh-driven human medulloblastoma cells at clinically attainable concentrations. As an antiparasitic, mebendazole avidly binds nematode tubulin and causes inhibition of intestinal microtubule synthesis. In human cells, mebendazole suppressed the formation of the primary cilium, a microtubule-based organelle that functions as a signaling hub for Hh pathway activation. The inhibition of Hh signaling by mebendazole was unaffected by mutants in the gene that encodes human Smoothened (SMO), which are selectively propagated in cell clones that survive treatment with the Hh inhibitor vismodegib. Combination of vismodegib and mebendazole resulted in additive Hh signaling inhibition. Because mebendazole can be safely administered to adults and children at high doses over extended time periods, we propose that mebendazole could be rapidly repurposed and clinically tested as a prospective therapeutic agent for many tumors that are dependent on Hh signaling.

Blocking Hedgehog release from pancreatic cancer cells increases paracrine signaling potency

Members of the Hedgehog (Hh) family of morphogens play crucial roles in development but are also involved in the progression of certain types of cancer. Despite being synthesized as hydrophobic dually lipid-modified molecules, and thus being strongly membrane-associated, Hh ligands are able to spread through tissues and act on target cells several cell diameters away. Various mechanisms that mediate Hh release have been discussed in recent years; however, little is known about dispersion of this ligand from cancer cells. Using co-culture models in conjunction with a newly developed reporter system, we were able to show that different members of the ADAM family of metalloproteinases strongly contribute to the release of endogenous bioactive Hh from pancreatic cancer cells, but that this solubilization decreases the potency of cancer cells to signal to adjacent stromal cells in direct co-culture models. These findings imply that under certain conditions, cancer-cell-tethered Hh molecules are the more potent signaling activators and that retaining Hh on the surface of cancer cells can unexpectedly increase the effective signaling range of this ligand, depending on tissue context.

Immunolocalization of glioma-associated oncogene homolog 1 in non melanoma skin cancer

Glioma-associated oncogene homolog (GLI)1 is involved in controlling cell proliferation and angiogenesis. The aim of this work was to explore its possible role in non-melanoma skin cancer pathogenesis through its immunohistochemical (IHC) expression in skin biopsies of these diseases and correlating this expression with the clinico-pathological parameters of the studied cases. Seventy-six cutaneous specimens were studied; 30 cases with basal cell carcinoma (BCC), 30 cases with squamous cell carcinoma (SCC) and 16 normal skin samples, from age- and gender-matched subjects, as a control group. GLI1 was expressed in all BCC cases and in 60% of SCC cases. All SCC cases showed cytoplasmic, while 70% of BCC cases showed nucleocytoplasmic immunoreactivity. It was over expressed in BCC and SCC compared to normal skin (p = 0.01 and 0.0006, respectively). Higher Histo (H) score in BCC cases was significantly associated with female gender (p = 0.04), multiple lesions, desmoplastic stromal reaction and stromal angiogenesis (p < 0.001 for all). Higher H score in SCC cases was significantly associated with scalp location, nodular type, recurrent lesions, high tumor grade, lymphovascular invasion (p = 0.004 for all), inflammatory stromal reaction (p = 0.01), lymph node involvement and absence of calcification (p = 0.001 for both). In conclusion, GLI1 may play a role in BCC pathogenesis through its role in cell proliferation, migration, and angiogenesis. Its upregulation and cytoplasmic localization in SCC may suggest that its role in tumor pathogenesis is through mechanisms other than Hedgehog pathway activation. Further studies are needed to clarify the exact molecular basis of its oncogenic action.

Hedgehog signaling pathway: a novel target for cancer therapy: vismodegib, a promising therapeutic option in treatment of basal cell carcinomas

The Hedgehog signaling pathway is one of the major regulators of cell growth and differentiation during embryogenesis and early development. It is mostly quiescent in adults but inappropriate mutation or deregulation of the pathway is involved in the development of cancers. Therefore; recently it has been recognized as a novel therapeutic target in cancers. Basal cell carcinomas (BCC) and medulloblastomas are the two most common cancers identified with mutations in components of the hedgehog pathway. The discovery of targeted Hedgehog pathway inhibitors has shown promising results in clinical trials, several of which are still undergoing clinical evaluation. Vismodegib (GDC-0449), an oral hedgehog signaling pathway inhibitor has reached the farthest in clinical development. Initial clinical trials in basal cell carcinoma and medulloblastoma have shown good efficacy and safety and hence were approved by U.S. FDA for use in advanced basal cell carcinomas. This review highlights the molecular basis and the current knowledge of hedgehog pathway activation in different types of human cancers as well as the present and future prospects of the novel drug vismodegib.

Desmoplasia and chemoresistance in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) occurs mainly in people older than 50 years of age. Although great strides have been taken in treating PDAC over the past decades its incidence nearly equals its mortality rate and it was quoted as the 4th leading cause of cancer deaths in the U.S. in 2012. This review aims to focus on research models and scientific developments that help to explain the extraordinary resistance of PDAC towards current therapeutic regimens. Furthermore, it highlights the main features of drug resistance including mechanisms promoted by cancer cells or cancer stem cells (CSCs), as well as stromal cells, and the acellular components surrounding the tumor cells-known as peritumoral desmoplasia-that affects intra-tumoral drug delivery. Finally, therapeutic concepts and avenues for future research are suggested, based on the topics discussed.

Hedgehog signaling restrains bladder cancer progression by eliciting stromal production of urothelial differentiation factors

Hedgehog (Hh) pathway inhibitors are clinically effective in treatment of basal cell carcinoma and medulloblastoma, but fail therapeutically or accelerate progression in treatment of endodermally derived colon and pancreatic cancers. In bladder, another organ of endodermal origin, we find that despite its initial presence in the cancer cell of origin Sonic hedgehog (Shh) expression is invariably lost during progression to invasive urothelial carcinoma. Genetic blockade of stromal response to Shh furthermore dramatically accelerates progression and decreases survival time. This cancer-restraining effect of Hh pathway activity is associated with stromal expression of BMP signals, which stimulate urothelial differentiation. Progression is dramatically reduced by pharmacological activation of BMP pathway activity with low-dose FK506, suggesting an approach to management of human bladder cancer.

Dosage-dependent regulation of pancreatic cancer growth and angiogenesis by hedgehog signaling

Pancreatic cancer, a hypovascular and highly desmoplastic cancer, is characterized by tumor expression of Hedgehog (HH) ligands that signal to fibroblasts in the surrounding stroma that in turn promote tumor survival and growth. However, the mechanisms and consequences of stromal HH pathway activation are not well understood. Here, we show that the HH coreceptors GAS1, BOC, and CDON are expressed in cancer-associated fibroblasts. Deletion of two coreceptors (Gas1 and Boc) in fibroblasts reduces HH responsiveness. Strikingly, these fibroblasts promote greater tumor growth in vivo that correlates with increased tumor-associated vascularity. In contrast, deletion of all three coreceptors (Gas1, Boc, and Cdon) results in the near complete abrogation of HH signaling and a corresponding failure to promote tumorigenesis and angiogenesis. Collectively, these data identify a role for HH dosage in pancreatic cancer promotion and may explain the clinical failure of HH pathway blockade as a therapeutic approach in pancreatic cancer.

Back to the drawing board: Re-thinking the role of GLI1 in pancreatic carcinogenesis

Aberrant activation of the transcription factor GLI1, a central effector of the Hedgehog (HH) pathway, is associated with several malignancies, including pancreatic ductal adenocarcinoma (PDAC), one of most deadly human cancers. GLI1 has been described as an oncogene in PDAC, making it a promising target for drug therapy. Surprisingly, clinical trials targeting HH/GLI1 axis in advanced PDAC were unsuccessful, leaving investigators questioning the mechanism behind these failures. Recent evidence suggests the loss of GLI1 in the later stages of PDAC may actually accelerate disease. This indicates GLI1 may play a dual role in PDAC, acting as an oncogene in the early stages of disease and a tumor-suppressor in the late stages.

Back to the drawing board: Re-thinking the role of GLI1 in pancreatic carcinogenesis

Aberrant activation of the transcription factor GLI1, a central effector of the Hedgehog (HH) pathway, is associated with several malignancies, including pancreatic ductal adenocarcinoma (PDAC), one of most deadly human cancers. GLI1 has been described as an oncogene in PDAC, making it a promising target for drug therapy. Surprisingly, clinical trials targeting HH/GLI1 axis in advanced PDAC were unsuccessful, leaving investigators questioning the mechanism behind these failures. Recent evidence suggests the loss of GLI1 in the later stages of PDAC may actually accelerate disease. This indicates GLI1 may play a dual role in PDAC, acting as an oncogene in the early stages of disease and a tumor-suppressor in the late stages.

Fibroblast heterogeneity in the cancer wound

Dr. Tuveson and colleagues provide a comprehensive review on the fundamental role of cancer-associated fibroblasts in shaping the tumor microenvironment and promoting tumor initiation and progression.

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Challenges and future directions in therapeutics for pancreatic ductal adenocarcinoma

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in the USA. The 5-year survival of < 5% has not changed in decades. In contrast to other major cancers, the incidence of PDAC is increasing.

AREAS COVERED

The aims of this paper are first to analyze why PDAC is so difficult to treat and, second, to suggest future directions for PDAC therapeutics. The authors provide an article that is based on a comprehensive search through MEDLINE and the clinicalTrials.gov website.

EXPERT OPINION

Progress has been made recently. Notably, FOLFIRINOX or nab-paclitaxel plus gemcitabine provide survival benefit over gemcitabine alone, which was previously the mainstay of therapy for PDAC. Most of the current trials are testing combinations of repurposed drugs rather than addressing key targets in the PDAC pathogenesis. It is clear that to really make an impact on this disease, it will be necessary to address three different problems with targeted therapeutics. First, it is important to eradicate PDAC stem cells that result in recurrence. Second, it is important to reduce the peritumoral stroma that provides the tumors with growth support and provides a barrier to access of therapeutic agents. Finally, it is important to address the marked cachexia and metabolic derangement that contribute to morbidity and mortality and further complicate therapeutic intervention.

Replaying evolutionary transitions from the dental fossil record

The evolutionary relationships of extinct species are ascertained primarily through the analysis of morphological characters. Character inter-dependencies can have a substantial effect on evolutionary interpretations, but the developmental underpinnings of character inter-dependence remain obscure because experiments frequently do not provide detailed resolution of morphological characters. Here we show experimentally and computationally how gradual modification of development differentially affects characters in the mouse dentition. We found that intermediate phenotypes could be produced by gradually adding ectodysplasin A (EDA) protein in culture to tooth explants carrying a null mutation in the tooth-patterning gene Eda. By identifying development-based character inter-dependencies, we show how to predict morphological patterns of teeth among mammalian species. Finally, in vivo inhibition of sonic hedgehog signalling in Eda null teeth enabled us to reproduce characters deep in the rodent ancestry. Taken together, evolutionarily informative transitions can be experimentally reproduced, thereby providing development-based expectations for character-state transitions used in evolutionary studies.

Stromal response to Hedgehog signaling restrains pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDA) is the most lethal of common human malignancies, with no truly effective therapies for advanced disease. Preclinical studies have suggested a therapeutic benefit of targeting the Hedgehog (Hh) signaling pathway, which is activated throughout the course of PDA progression by expression of Hh ligands in the neoplastic epithelium and paracrine response in the stromal fibroblasts. Clinical trials to test this possibility, however, have yielded disappointing results. To further investigate the role of Hh signaling in the formation of PDA and its precursor lesion, pancreatic intraepithelial neoplasia (PanIN), we examined the effects of genetic or pharmacologic inhibition of Hh pathway activity in three distinct genetically engineered mouse models and found that Hh pathway inhibition accelerates rather than delays progression of oncogenic Kras-driven disease. Notably, pharmacologic inhibition of Hh pathway activity affected the balance between epithelial and stromal elements, suppressing stromal desmoplasia but also causing accelerated growth of the PanIN epithelium. In striking contrast, pathway activation using a small molecule agonist caused stromal hyperplasia and reduced epithelial proliferation. These results indicate that stromal response to Hh signaling is protective against PDA and that pharmacologic activation of pathway response can slow tumorigenesis. Our results provide evidence for a restraining role of stroma in PDA progression, suggesting an explanation for the failure of Hh inhibitors in clinical trials and pointing to the possibility of a novel type of therapeutic intervention.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.

Fibroblast heterogeneity in the cancer wound

Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy.