Ectopic overexpression of Sonic Hedgehog (Shh) induces stromal expansion and metaplasia in the adult murine pancreas

Mechanisms and therapeutic potential of the hedgehog signaling pathway in cancer

A sort of major malignant disease, cancer can compromise human health wherever. Some mechanisms of the occurrence and evolution of cancer still seem elusive even now. Consequently, the therapeutic strategies for cancer must continually evolve. The hedgehog signaling pathway, a critical mediator in the normal development of numerous organs and the pathogenesis of cancer, is typically quiescent but is aberrantly activated in several malignancies. Extensive research has delineated that the aberrant activity of the hedgehog signaling pathway, whether autocrine or paracrine, is implicated in the initiation and progression of various neoplasms, including medulloblastoma (MB), basal cell carcinoma (BCC) and so on. Thus, notably Smo inhibitors, the opening of inhibitors of the hedgehog signaling pathway has become a topic of research attention. This review aims to summarize four aberrant activation pathways and the influence of hedgehog signaling pathway associated chemicals on tumor formation and development. Additionally, it will explore the therapeutic potential of targeted interventions in the hedgehog signaling pathway for cancer treatment.

Cancer-associated fibroblasts as therapeutic targets for cancer: advances, challenges, and future prospects

Research into cancer treatment has been mainly focused on developing therapies to directly target cancer cells. Over the past decade, extensive studies have revealed critical roles of the tumour microenvironment (TME) in cancer initiation, progression, and drug resistance. Notably, cancer-associated fibroblasts (CAFs) have emerged as one of the primary contributors in shaping TME, creating a favourable environment for cancer development. Many preclinical studies have identified promising targets on CAFs, demonstrating remarkable efficacy of some CAF-targeted treatments in preclinical models. Encouraged by these compelling findings, therapeutic strategies have now advanced into clinical evaluation. We aim to provide a comprehensive review of relevant subjects on CAFs, including CAF-related markers and targets, their multifaceted roles, and current landscape of ongoing clinical trials. This knowledge can guide future research on CAFs and advocate for clinical investigations targeting CAFs.

A Quick Guide to CAF Subtypes in Pancreatic Cancer

Pancreatic cancer represents one of the most desmoplastic malignancies and is characterized by an extensive deposition of extracellular matrix. The latter is provided by activated cancer-associated fibroblasts (CAFs), which are abundant cells in the pancreatic tumor microenvironment. Many recent studies have made it clear that CAFs are not a singular cellular entity but represent a multitude of potentially dynamic subgroups that affect tumor biology at several levels. As mentioned before, CAFs significantly contribute to the fibrotic reaction and the biomechanical properties of the tumor, but they can also modulate the local immune environment and the response to targeted, chemo or radiotherapy. As the number of known and emerging CAF subgroups is steadily increasing, it is becoming increasingly difficult to keep up with these developments and to clearly discriminate the cellular subsets identified so far. This review aims to provide a helpful overview that enables readers to quickly familiarize themselves with field of CAF heterogeneity and to grasp the phenotypic, functional and therapeutic distinctions of the various stromal subpopulations.

Developmental function of Piezo1 in mouse submandibular gland morphogenesis

Mechanically activated factors are important in organogenesis, especially in the formation of secretory organs, such as salivary glands. Piezo-type mechanosensitive ion channel component 1 (Piezo1), although previously studied as a physical modulator of the mechanotransduction, was firstly evaluated on its developmental function in this study. The detailed localization and expression pattern of Piezo1 during mouse submandibular gland (SMG) development were analyzed using immunohistochemistry and RT-qPCR, respectively. The specific expression pattern of Piezo1 was examined in acinar-forming epithelial cells at embryonic day 14 (E14) and E16, which are important developmental stages for acinar cell differentiation. To understand the precise function of Piezo1 in SMG development, siRNA against Piezo1 (siPiezo1) was employed as a loss-of-function approach, during in vitro organ cultivation of SMG at E14 for the designated period. Alterations in the histomorphology and expression patterns of related signaling molecules, including Bmp2, Fgf4, Fgf10, Gli1, Gli3, Ptch1, Shh, and Tgfβ-3, were examined in acinar-forming cells after 1 and 2 days of cultivation. Particularly, altered localization patterns of differentiation-related signaling molecules including Aquaporin5, E-cadherin, Vimentin, and cytokeratins would suggest that Piezo1 modulates the early differentiation of acinar cells in SMGs by modulating the Shh signaling pathway.

Cancer-Associated Fibroblast Diversity Shapes Tumor Metabolism in Pancreatic Cancer

Despite extensive research, the 5-year survival rate of pancreatic cancer (PDAC) patients remains at only 9%. Patients often show poor treatment response, due partly to a highly complex tumor microenvironment (TME). Cancer-associated fibroblast (CAF) heterogeneity is characteristic of the pancreatic TME, where several CAF subpopulations have been identified, such as myofibroblastic CAFs (myCAFs), inflammatory CAFs (iCAFs), and antigen presenting CAFs (apCAFs). In PDAC, cancer cells continuously adapt their metabolism (metabolic switch) to environmental changes in pH, oxygenation, and nutrient availability. Recent advances show that these environmental alterations are all heavily driven by stromal CAFs. CAFs and cancer cells exchange cytokines and metabolites, engaging in a tight bidirectional crosstalk, which promotes tumor aggressiveness and allows constant adaptation to external stress, such as chemotherapy. In this review, we summarize CAF diversity and CAF-mediated metabolic rewiring, in a PDAC-specific context. First, we recapitulate the most recently identified CAF subtypes, focusing on the cell of origin, activation mechanism, species-dependent markers, and functions. Next, we describe in detail the metabolic crosstalk between CAFs and tumor cells. Additionally, we elucidate how CAF-driven paracrine signaling, desmoplasia, and acidosis orchestrate cancer cell metabolism. Finally, we highlight how the CAF/cancer cell crosstalk could pave the way for new therapeutic strategies.

Hedgehog Signaling Pathway Proteins in Prognosis of Pancreatic Ductal Adenocarcinoma and Its Differentiation From Chronic Pancreatitis

OBJECTIVES

The Hedgehog signaling pathway (Hh) probably plays a role in development and progression of pancreatic ductal adenocarcinoma (PDAC).

METHODS

In our study, 114 patients (83 with PDAC and 31 with chronic pancreatitis [CP]) after pancreatic surgery were enrolled. The immunoexpression of Sonic hedgehog (Shh), Smoothened (Smo), and Glioblastoma transcription factor 1 (Gli1) and Ki-67 were detected in tissue specimens.

RESULTS

Mean (standard deviation) immunoexpression of all Hh pathway molecules was significantly higher in PDAC than in CP patients: Shh, 2.24 (0.57) versus 1.17 (0.25) (P < 0.01); Smo, 2.62 (0.34) versus 1.21 (0.23) (P < 0.01); and Gli1, 1.74 (0.74) versus 1.15 (0.72) (P < 0.01). Patients with a lower expression level (z score <0) of Shh and Ki-67 have longer overall survival when compared with z score >0 (15.97 vs 8.53 months [P = 0.0087] and 15.20 vs 5.53 months [P = 0.0004], respectively). In addition, Shh sensitivity in PDAC detection was 84.3%; specificity, 93.5%; positive predictive value, 97.2%; and negative predictive value, 69%.

CONCLUSIONS

Our results suggest the prognostic role of the Hh pathway in PDAC and a role in the differential diagnosis with CP.

Forebrain Shh overexpression improves cognitive function and locomotor hyperactivity in an aneuploid mouse model of Down syndrome and its euploid littermates

Down syndrome (DS) is the leading genetic cause of intellectual disability and causes early-onset dementia and cerebellar hypoplasia. The prevalence of attention deficit hyperactivity disorder is elevated in children with DS. The aneuploid DS mouse model "Ts65Dn" shows prominent brain phenotypes, including learning and memory deficits, cerebellar hypoplasia, and locomotor hyperactivity. Previous studies indicate that impaired Sonic hedgehog (Shh) signaling contributes to neurological phenotypes associated with DS and neurodegenerative diseases. However, because of a lack of working inducible Shh knock-in mice, brain region-specific Shh overexpression and its effects on cognitive function have not been studied in vivo. Here, with Gli1-LacZ reporter mice, we demonstrated that Ts65Dn had reduced levels of Gli1, a sensitive readout of Shh signaling, in both hippocampus and cerebellum at postnatal day 6. Through site-specific transgenesis, we generated an inducible human Shh knock-in mouse, TRE-bi-hShh-Zsgreen1 (TRE-hShh), simultaneously expressing dually-lipidated Shh-Np and Zsgreen1 marker in the presence of transactivator (tTA). Double transgenic mice "Camk2a-tTA;TRE-hShh" and "Pcp2-tTA;TRE-hShh" induced Shh overexpression and activated Shh signaling in a forebrain and cerebellum, respectively, specific manner from the perinatal period. Camk2a-tTA;TRE-hShh normalized locomotor hyperactivity and improved learning and memory in 3-month-old Ts65Dn, mitigated early-onset severe cognitive impairment in 7-month-old Ts65Dn, and enhanced spatial cognition in euploid mice. Camk2a-tTA;TRE-hShh cohort maintained until 600days old showed that chronic overexpression of Shh in forebrain from the perinatal period had no effect on longevity of euploid or Ts65Dn. Pcp2-tTA;TRE-hShh did not affect cognition but mitigated the phenotype of cerebellar hypoplasia in Ts65Dn. Our study provides the first in vivo evidence that Shh overexpression from the perinatal period protects DS brain integrity and enhances learning and memory in normal mice, indicating the broad therapeutic potential of Shh ligand for other neurological conditions. Moreover, the first inducible hShh site-specific knock-in mouse could be widely used for spatiotemporal Shh signaling regulation.

Inhibition of Hedgehog Signaling Alters Fibroblast Composition in Pancreatic Cancer

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease characterized by an extensive fibroinflammatory stroma, which includes abundant cancer-associated fibroblast (CAF) populations. PDAC CAFs are heterogeneous, but the nature of this heterogeneity is incompletely understood. The Hedgehog pathway functions in PDAC in a paracrine manner, with ligands secreted by cancer cells signaling to stromal cells in the microenvironment. Previous reports investigating the role of Hedgehog signaling in PDAC have been contradictory, with Hedgehog signaling alternately proposed to promote or restrict tumor growth. In light of the newly discovered CAF heterogeneity, we investigated how Hedgehog pathway inhibition reprograms the PDAC microenvironment.

EXPERIMENTAL DESIGN

We used a combination of pharmacologic inhibition, gain- and loss-of-function genetic experiments, cytometry by time-of-flight, and single-cell RNA sequencing to study the roles of Hedgehog signaling in PDAC.

RESULTS

We found that Hedgehog signaling is uniquely activated in fibroblasts and differentially elevated in myofibroblastic CAFs (myCAF) compared with inflammatory CAFs (iCAF). Sonic Hedgehog overexpression promotes tumor growth, while Hedgehog pathway inhibition with the smoothened antagonist, LDE225, impairs tumor growth. Furthermore, Hedgehog pathway inhibition reduces myCAF numbers and increases iCAF numbers, which correlates with a decrease in cytotoxic T cells and an expansion in regulatory T cells, consistent with increased immunosuppression.

CONCLUSIONS

Hedgehog pathway inhibition alters fibroblast composition and immune infiltration in the pancreatic cancer microenvironment.

Hedgehog signaling promotes angiogenesis directly and indirectly in pancreatic cancer

INTRODUCTION

The inhibition of Hedgehog (Hh) signaling in pancreatic ductal adenocarcinoma (PDAC) reduces desmoplasia and promotes increased vascularity. In contrast to these findings, the Hh ligand Sonic Hedgehog (SHH) is a potent proangiogenic factor in non-tumor models. The aim of this study was to determine the molecular mechanisms by which SHH affects the tumor stroma and angiogenesis.

METHODS

Mice bearing three different xenografted human PDAC (n = 5/group) were treated with neutralizing antibodies to SHH. After treatment for 7 days, tumors were evaluated and the expression of 38 pro- and antiangiogenic factors was assessed in the tumor cells and their stroma. The effect of SHH on the regulation of pro- and antiangiogenic factors in fibroblasts and its impact on endothelial cells was then further assessed in in vitro model systems.

RESULTS

Inhibition of SHH affected tumor growth, stromal content, and vascularity. Its effect on the Hh signaling pathway was restricted to the stromal compartment of the three cancers. SHH-stimulated angiogenesis indirectly through the reduction of antiangiogenic THBS2 and TIMP2 in stromal cells. An additional direct effect of SHH on endothelial cells depended on the presence of VEGF.

CONCLUSION

Inhibition of Hh signaling reduces tumor vascularity, suggesting that Hh plays a role in the maintenance or formation of the tumor vasculature. Whether the reduction in tumor growth and viability seen in the epithelium is a direct consequence of Hh pathway inhibition, or indirectly caused by its effect on the stroma and vasculature, remains to be evaluated.

Role of Tumor and Stroma-Derived IGF/IGFBPs in Pancreatic Cancer

Pancreatic cancer (PC) is the utmost stroma-rich cancer, which is accompanied by fibrotic reactions that stimulate interactions between tumor cells and stroma to promote tumor progression. Considerable research evidence denotes that insulin-like growth factor (IGF)/IGF binding proteins (IGFBP) signaling axis facilitate tumor growth, metastasis, drug resistance, and thereby facilitate PC into an advanced stage. The six members of IGFBPs were initially considered as passive carriers of free IGFs; however, current evidence revealed their functions beyond the endocrine role in IGF transport. Though numerous efforts have been made in blocking IGF/IGFBPs, the targeted therapies remain unsuccessful due to the complexity of tumor-stromal interactions in the pancreas. In this review, we explore the emerging evidence of the various roles of the tumor as well as stroma derived IGF/IGFBPs and highlight as a novel therapeutic target against PC progression.

Inflammatory and Senescent Phenotype of Pancreatic Stellate Cells Induced by Sqstm1 Downregulation Facilitates Pancreatic Cancer Progression

Pancreatic ductal adenocarcinoma (PDAC) has unique microenvironment with extensive infiltration of fibroblasts, which are mainly derived from the resident pancreatic stellate cells (PaSCs). As activated PaSCs constitute a major contributor to pancreatic cancer progression, the mechanisms underlying their activation have been being intensively studied. Previous studies showed that Sequestosome-1 (sqstm1) can modulate the functional status of fibroblasts in cancer. Here, we further delineated the role of sqstm1 in PaSCs. The analysis of PDAC patient samples revealed reduction of sqstm1 expression in activated PaSCs in both mRNA and protein level. Downregulated sqstm1 via shRNA in PaSCs led to an inflammatory and senescent phenotype with increased IL8, CXCL1, and CXCL2 expression. Further analysis demonstrated that increased intracellular reactive oxygen species level contributed to the senescence in sqstm1-downregulated PaSCs. This was mediated via impaired NRF2 activity since reduced sqstm1 resulted in accumulation of KEAP1. Meanwhile, we found that sqstm1 degradation caused by enhanced autophagy was not associated with transformation of senescent phenotype. At last, the data revealed that sqstm1-downregulated PaSCs promoted pancreatic tumor cell growth, invasion, and macrophage phenotype transformation. Collectively, the current study indicated that sqstm1 controlled transformation of senescent phenotype of PaSCs, which in turn is pro-tumorigenic.

KRAS Oncogenic Signaling Extends beyond Cancer Cells to Orchestrate the Microenvironment

KRAS is one of the most frequently mutated oncogenes in cancer, being a potent initiator of tumorigenesis, a strong inductor of malignancy, and a predictive biomarker of response to therapy. Despite the large investment to understand the effects of KRAS activation in cancer cells, pharmacologic targeting of KRAS or its downstream effectors has not yet been successful at the clinical level. Recent studies are now describing new mechanisms of KRAS-induced tumorigenesis by analyzing its effects on the components of the tumor microenvironment. These studies revealed that the activation of KRAS on cancer cells extends to the surrounding microenvironment, affecting the properties and functions of its constituents. Herein, we discuss the most emergent perspectives on the relationship between KRAS-mutant cancer cells and their microenvironment components. Cancer Res; 78(1); 7-14. ©2017 AACR.

The Stromal Niche for Epithelial Stem Cells: A Template for Regeneration and a Brake on Malignancy

Stromal restraint of cancer growth and progression-emerging as a widespread phenomenon in epithelial cancers such as bladder, pancreas, colon, and prostate-appears rooted in stromal cell niche activity. During normal tissue repair, stromal niche signals, often Hedgehog-induced, promote epithelial stem cell differentiation as well as self-renewal, thus specifying a regenerating epithelial pattern. In the case of cancerous tissue, stromal cell-derived differentiation signals in particular may provide a brake on malignant growth. Understanding and therapeutic harnessing of the role of stroma in cancer restraint may hinge on our knowledge of the signaling programs elaborated by the stromal niche.

A sesquiterpene lactone from Siegesbeckia glabrescens suppresses Hedgehog/Gli-mediated transcription in pancreatic cancer cells

Pancreatic cancer is aggressive and therefore difficult to treat; however, continued efforts have been made with the aim of developing an effective therapy against the disease. The Hedgehog (Hh) signaling pathway is reportedly involved in the proliferation and survival of pancreatic cancer cells. The transcription factor glioma-associated oncogene (Gli) is a key component of the Hh signaling pathway and the primary effector of pancreatic cancer development. Inhibiting Gli is a proven therapeutic strategy for this disease. The present study examined the regulation of Gli and the expression of its target genes to identify an inhibitor of the Sonic Hh (Shh) pathway. A germacranolide sesquiterpene lactone (GSL) was isolated from Siegesbeckia glabrescens as an inhibitor of Gli-mediated transcription. The results demonstrated that GSL inhibited Shh-induced osteoblast differentiation and Gli homolog 1 (Gli1)-mediated transcriptional activity in mesenchymal C3H10T1/2 stem cells. Furthermore, GSL suppressed Gli-mediated transcriptional activity in human pancreatic cancer PANC-1 and AsPC-1 cells, which resulted in reduced cancer cell proliferation and downregulated expression of the Gli-target genes, Gli1 and cyclin D1. A sesquiterpene lactone from S. glabrescens may therefore serve as a candidate for the treatment of Hh/Gli-dependent pancreatic cancer.

Oncogenic KRAS Regulates Tumor Cell Signaling via Stromal Reciprocation

Oncogenic mutations regulate signaling within both tumor cells and adjacent stromal cells. Here, we show that oncogenic KRAS (KRAS(G12D)) also regulates tumor cell signaling via stromal cells. By combining cell-specific proteome labeling with multivariate phosphoproteomics, we analyzed heterocellular KRAS(G12D) signaling in pancreatic ductal adenocarcinoma (PDA) cells. Tumor cell KRAS(G12D) engages heterotypic fibroblasts, which subsequently instigate reciprocal signaling in the tumor cells. Reciprocal signaling employs additional kinases and doubles the number of regulated signaling nodes from cell-autonomous KRAS(G12D). Consequently, reciprocal KRAS(G12D) produces a tumor cell phosphoproteome and total proteome that is distinct from cell-autonomous KRAS(G12D) alone. Reciprocal signaling regulates tumor cell proliferation and apoptosis and increases mitochondrial capacity via an IGF1R/AXL-AKT axis. These results demonstrate that oncogene signaling should be viewed as a heterocellular process and that our existing cell-autonomous perspective underrepresents the extent of oncogene signaling in cancer. VIDEO ABSTRACT.

Relation between sonic hedgehog pathway gene polymorphisms and basal cell carcinoma development in the Polish population

In recent decades, increases have been observed in the incidence of nonmelanoma skin cancers, including basal cell carcinoma (BCC) and squamous cell carcinoma. BCC is the most common neoplasm in Caucasian populations. Sonic hedgehog (Shh) pathway impairment plays a key role in BCC pathogenesis, and there is evidence that Shh pathway genetic variations may predispose to BCC development. We genotyped 22 single-nucleotide polymorphisms (SNPs) in 4 Shh pathway genes: SHH, GLI, SMO, and PTCH. The study group consisted of 142 BCC patients and 142 age-matched, sex-matched healthy subjects (controls). SNPs were assessed using the PCR-RFLP method. The genotype distribution for the polymorphisms in the rs104894049 331 A/T SHH, rs104894040 349 T/C SHH, and rs41303402 385 G/A SMO genes differed significantly between the BCC patients and the controls. The presence of CC genotype in the SHH rs104894040 349 T/C polymorphism was linked to the highest risk of BCC development (OR 87.9, p < 0.001). Other genotypes, such as the TT in SHH rs104894049 331 A/T and the GG in SMO rs41303402 385 G/A also statistically raised the risk of BCC, but these associations were weaker. Other investigated polymorphisms showed no statistical differences between patients and controls. The results obtained testify to the importance of the SHH and SMO gene polymorphisms in skin cancerogenesis. These results mainly underline the potential role of SHH3 rs104894040 349 T/C gene polymorphism in the development of skin basal cell carcinomas in patients of Polish origin.

SMO expression in colorectal cancer: associations with clinical, pathological, and molecular features

BACKGROUND

Smoothened, frizzled family receptor (SMO) is an important component of the hedgehog signaling pathway, which has been implicated in various human carcinomas. However, clinical, molecular, and prognostic associations of SMO expression in colorectal cancer remain unclear.

METHODS

Using a database of 735 colon and rectal cancers in the Nurse's Health Study and the Health Professionals Follow-up Study, we examined the relationship of tumor SMO expression (assessed by immunohistochemistry) to prognosis, and to clinical, pathological, and tumor molecular features, including mutations of KRAS, BRAF, and PIK3CA, microsatellite instability, CpG island methylator phenotype (CIMP), LINE-1 methylation, and expression of phosphorylated AKT and CTNNB1.

RESULTS

SMO expression was detected in 370 tumors (50 %). In multivariate logistic regression analysis, SMO expression was independently inversely associated with phosphorylated AKT expression [odds ratio (OR) 0.48; 95 % confidence interval (CI) 0.34-0.67] and CTNNB1 nuclear localization (OR 0.48; 95 % CI 0.35-0.67). SMO expression was not significantly associated with colorectal cancer-specific or overall survival. However, in CIMP-high tumors, but not CIMP-low/0 tumors, SMO expression was significantly associated with better colorectal cancer-specific survival (log-rank P = 0.012; multivariate hazard ratio, 0.36; 95 % CI 0.13-0.95; P interaction = 0.035, for SMO and CIMP status).

CONCLUSIONS

Our data reveal novel potential associations between the hedgehog, the WNT/CTNNB1, and the PI3K (phosphatidylinositol-4,5-bisphosphonate 3-kinase)/AKT pathways, supporting pivotal roles of SMO and hedgehog signaling in pathway networking. SMO expression in colorectal cancer may interact with tumor CIMP status to affect patient prognosis, although confirmation by future studies is needed.

Mirk kinase inhibition blocks the in vivo growth of pancreatic cancer cells

The Mirk/dyrk1B gene is upregulated and sometimes amplified in pancreatic ductal carcinomas. In poor microenvironmental conditions Mirk mediates cell survival by maintaining cancer cells in a largely quiescent, noncycling state and by decreasing toxic ROS levels through maintaining expression of a series of antioxidant genes. Premature entry into cycle, increased ROS levels, DNA damage, and apoptosis follow Mirk kinase depletion or inhibition. Mirk kinase inhibitor EHT5372 treated Panc1 spheroids lost quiescence markers coincident with an increase in cyclin A showing entry into cycle, and exhibited DNA damage, apoptosis and smaller size. EHT5372 treatment in vivo led to an increased fraction of Ki67 positive, cycling cells in Panc1 xenografts whose size was reduced. Pdx-1-cre LSL/KrasG12D/Ink4a/Arf null B6 mice always develop pancreatic cancer, allowing only 30% survival by 8 weeks, while each of the Mirk kinase inhibitor treated mice survived 8 weeks. Mirk inhibition led to a roughly four-fold increase in tumor αSMA-positive fibroblasts and large stromal collagen-rich infiltrates in the pancreas that can restrain tumor growth. The mTOR inhibitor RAD001 alone, or together with EHT5372, reduced pancreatic cancer size 30-fold, while the drug combination reduced the number of microscopic tumor foci 2-fold compared to RAD001 alone.

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

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.

Inhibition of Hedgehog signaling in the gastrointestinal tract: targeting the cancer microenvironment

This review summarizes emerging information regarding the Hedgehog (Hh) signaling pathway during neoplastic transformation in the gastrointestinal tract. Although there is a role for the well-established canonical pathway in which Hedgehog ligands interact with their receptor Patched, there is sufficient evidence that downstream components of the Hh pathway, e.g., Gli1, are hijacked by non-Hh signaling pathways to promote the conversion of the epithelium to dysplasia and carcinoma. We review the canonical pathway and involvement of primary cilia, and then focus on current evidence for Hh signaling in luminal bowel cancers as well as accessory organs, i.e., liver, pancreas and biliary ducts. We conclude that targeting the Hh pathway with small molecules, nutriceuticals and other mechanisms will likely require a combination of inhibitors that target Gli transcription factors in addition to canonical modulators such as Smoothened.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Mechanistic insights into self-reinforcing processes driving abnormal histogenesis during the development of pancreatic cancer

Pancreatic ductal adenocarcinoma, one of the most feared lethal and painful diseases, is increasing in incidence. The poor prognosis of pancreatic ductal adenocarcinoma-affected patients primarily is owing to our inability to develop effective therapies. Mechanistic studies of genetic, epigenetic, and cell-to-cell signaling events are providing clues to molecular pathways that can be targeted in an attempt to cure this disease. The current review article seeks to draw inferences from available mechanistic knowledge to build a theoretical framework that can facilitate these approaches. This conceptual model considers pancreatic cancer as a tissue disease rather than an isolated epithelial cell problem, which develops and progresses in large part as a result of three positive feedback loops: i) genetic and epigenetic changes in epithelial cells modulate their interaction with mesenchymal cells to generate a dynamically changing process of abnormal histogenesis, which drives more changes; ii) the faulty tissue architecture of neoplastic lesions results in unsynchronized secretion of signaling molecules by cells, which generates an environment that is poor in oxygen and nutrients; and iii) the increased metabolic needs of rapidly dividing cells serve as an evolutionary pressure for them to adapt to this adverse microenvironment, leading to the emergence of resistant clones. We discuss how these concepts can guide mechanistic studies, as well as aid in the design of novel experimental therapeutics.

Cancer Stem Cells, EMT, and Developmental Pathway Activation in Pancreatic Tumors

Pancreatic cancer is a disease with remarkably poor patient survival rates. The frequent presence of metastases and profound chemoresistance pose a severe problem for the treatment of these tumors. Moreover, cross-talk between the tumor and the local micro-environment contributes to tumorigenicity, metastasis and chemoresistance. Compared to bulk tumor cells, cancer stem cells (CSC) have reduced sensitivity to chemotherapy. CSC are tumor cells with stem-like features that possess the ability to self-renew, but can also give rise to more differentiated progeny. CSC can be identified based on increased in vitro spheroid- or colony formation, enhanced in vivo tumor initiating potential, or expression of cell surface markers. Since CSC are thought to be required for the maintenance of a tumor cell population, these cells could possibly serve as a therapeutic target. There appears to be a causal relationship between CSC and epithelial-to-mesenchymal transition (EMT) in pancreatic tumors. The occurrence of EMT in pancreatic cancer cells is often accompanied by re-activation of developmental pathways, such as the Hedgehog, WNT, NOTCH, and Nodal/Activin pathways. Therapeutics based on CSC markers, EMT, developmental pathways, or tumor micro-environment could potentially be used to target pancreatic CSC. This may lead to a reduction of tumor growth, metastatic events, and chemoresistance in pancreatic cancer.

Hepatitis B and C virus infections as possible risk factor for pancreatic adenocarcinoma

Pancreatic adenocarcinoma (PAC) is a very aggressive and lethal cancer, with a very poor prognosis, because of absence of early symptoms, advanced stage at presentation, early metastatic dissemination and lack of both specific tests to detect its growth in the initial phases and effective systemic therapies. To date, the causes of PAC still remain largely unknown, but multiple lines of evidence from epidemiological and laboratory researches suggest that about 15-20% of all cancers are linked in some way to chronic infection, in particular it has been shown that several viruses have a role in human carcinogenesis. The purpose of this report is to discuss the hypothesis that two well-known oncogenic viruses, Human B hepatitis (HBV) and Human C hepatitis (HCV) are a possible risk factor for this cancer. Therefore, with the aim to examine the potential link between these viruses and PAC, we performed a selection of observational studies evaluating this association and we hypothesized that some pathogenetic mechanisms involved in liver carcinogenesis might be in common with pancreatic cancer development in patients with serum markers of present or past HBV and HCV infections. To date the available observational studies performed are few, heterogeneous in design as well as in end-points and with not univocal results, nevertheless they might represent the starting-point for future larger and better designed clinical trials to define this hypothesized relationship. Should these further studies confirm an association between HBV/HCV infection and PAC, screening programs might be justified in patients with active or previous hepatitis B and C viral infection.

Hedgehog signaling: from the cuirass to the heart of pancreatic cancer

Exocrine pancreatic cancer is the fifth cause of cancer-related death in Europe and carries a very poor prognosis for all disease stages. To date no medical treatment has significantly increased patients' survival. One of the reasons for pancreatic cancer's chemoresistence is the complex tumor architecture: cancer cells are surrounded by a dense desmoplastic stroma that blocks drug delivery. Moreover, pancreatic cancer is characterized by a marked heterogeneity of cells, including cancer stem cells (CSCs) that act as tumor-initiating cells and hierarchically control the differentiated cancer cells. In particular, this subpopulation is resistant to classic cytotoxic therapies, and seems to be responsible for disease renewal. Hedgehog signaling (HH) is implicated in pancreatic gland development during embryogenesis and is reactivated during tumorigenesis and the maintenance of pancreatic cancer. Some studies demonstrated that the Hedgehog-secreted signaling proteins are overexpressed in both the stromal and CSCs pools, implying an abnormal activation of HH in the main compartment of pancreatic cancer. For this reason, the Hedgehog pathway could be an interesting target for clinical trials to increase drug concentration in neoplastic cells and hence deplete the stroma and directly kill tumor-initiating cells.

The interconnectedness of cancer cell signaling

The elegance of fundamental and applied research activities have begun to reveal a myriad of spatial and temporal alterations in downstream signaling networks affected by cell surface receptor stimulation including G protein-coupled receptors and receptor tyrosine kinases. Interconnected biochemical pathways serve to integrate and distribute the signaling information throughout the cell by orchestration of complex biochemical circuits consisting of protein interactions and covalent modification processes. It is clear that scientific literature summarizing results from both fundamental and applied scientific research activities has served to provide a broad foundational biologic database that has been instrumental in advancing our continued understanding of underlying cancer biology. This article reflects on historical advances and the role of innovation in the competitive world of grant-sponsored research.