Hedgehog signalling-an essential pathway during embryonic pancreatic development, the misregulation of which has been implicated in several forms of cancer-may also be an important mediator in human pancreatic carcinoma [1][2][3][4][5][6][7][8] . Here we report that sonic hedgehog, a secreted hedgehog ligand, is abnormally expressed in pancreatic adenocarcinoma and its precursor lesions: pancreatic intraepithelial neoplasia (PanIN). Pancreata of Pdx-Shh mice (in which Shh is misexpressed in the pancreatic endoderm) develop abnormal tubular structures, a phenocopy of human PanIN-1 and -2. Moreover, these PanIN-like lesions also contain mutations in K-ras and overexpress HER-2/neu, which are genetic mutations found early in the progression of human pancreatic cancer. Furthermore, hedgehog signalling remains active in cell lines established from primary and metastatic pancreatic adenocarcinomas. Notably, inhibition of hedgehog signalling by cyclopamine induced apoptosis and blocked proliferation in a subset of the pancreatic cancer cell lines both in vitro and in vivo. These data suggest that this pathway may have an early and critical role in the genesis of this cancer, and that maintenance of hedgehog signalling is important for aberrant proliferation and tumorigenesis.Sonic hedgehog (SHH) is misexpressed in human adenocarcinoma and its precursor lesions. SHH expression was determined using in situ hybridization to detect SHH messenger RNA and immunohistochemistry (IHC) to detect the protein with an antibody directed against Competing interests statementThe authors declare that they have no competing financial interests. . Pancreatic tissues were obtained from 20 specimens resected for pancreatic cancer. Control pancreatic tissues with no evidence of abnormality or autolysis upon histological evaluation were obtained from autopsy specimens or from pancreatic resections for trauma. In normal adult human pancreata, no SHH was detected in the islets, acini or ductal epithelium (Fig. 1a). However, evaluation of pancreata from patients with adenocarcinoma reveals that SHH is aberrantly expressed in 70% of specimens. Normal ductal epithelium does not express detectable levels of SHH (Fig. 1b); however, as the ductal epithelium shows increasing degrees of atypia, PanIN-1 to -3 ( Fig. 1c-e), a higher expression of SHH is observed. SHH expression is also detected in the malignant epithelium of adenocarcinoma samples (Fig. 1f). This expression pattern was also confirmed by our in situ hybridization for SHH mRNA ( Supplementary Fig. 1). NIH Public AccessLoss of regulation in this pathway has been implicated in several human cancers 10,11 . Thus in order to determine the potential role of SHH misexpression in the adult human pancreas, pancreata from transgenic mice (gift of H. Edlund) in which Shh misexpression was driven by the pancreatic-specific Pdx-1 promoter were histologically and immunohistochemically analysed.A total of four pancreata from three-week-old Pdx-Shh mice were histologically evaluated by a gastro...

Pancreatic cancer is almost invariably associated with mutations in the KRAS gene, most commonly KRAS G12D , that result in a dominant-active form of the KRAS GTPase. However, how KRAS mutations promote pancreatic carcinogenesis is not fully understood, and whether oncogenic KRAS is required for the maintenance of pancreatic cancer has not been established. To address these questions, we generated two mouse models of pancreatic tumorigenesis: mice transgenic for inducible Kras G12D , which allows for inducible, pancreas-specific, and reversible expression of the oncogenic Kras G12D , with or without inactivation of one allele of the tumor suppressor gene p53. Here, we report that, early in tumorigenesis, induction of oncogenic Kras G12D reversibly altered normal epithelial differentiation following tissue damage, leading to precancerous lesions. Inactivation of Kras G12D in established precursor lesions and during progression to cancer led to regression of the lesions, indicating that Kras G12D was required for tumor cell survival. Strikingly, during all stages of carcinogenesis, Kras G12D upregulated Hedgehog signaling, inflammatory pathways, and several pathways known to mediate paracrine interactions between epithelial cells and their surrounding microenvironment, thus promoting formation and maintenance of the fibroinflammatory stroma that plays a pivotal role in pancreatic cancer. Our data establish that epithelial Kras G12D influences multiple cell types to drive pancreatic tumorigenesis and is essential for tumor maintenance. They also strongly support the notion that inhibiting Kras G12D , or its downstream effectors, could provide a new approach for the treatment of pancreatic cancer.

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The Kras gene is mutated to an oncogenic form in most pancreatic tumors. However, early attempts to use this molecule as a specific biomarker of the disease, or inhibit its activity as a cancer therapy, failed. This left a situation in which everyone was aware of the association between this important oncogene and pancreatic cancer, but no one knew what to do about it. Recent findings have changed this picture—many assumptions made about KRAS and its role in pancreatic cancer were found to be incorrect. Several factors have contributed to increased understanding of the activities of KRAS, including creation of genetically engineered mouse models, which have allowed for detailed analyses of pancreatic carcinogenesis in an intact animal with a competent immune system. Cancer genome sequencing projects have increased our understanding of the heterogeneity of individual tumors. We also have a better understanding of which oncogenes are important for tumor maintenance and are therefore called “drivers.” We review the advances and limitations of our knowledge about the role of Kras in development of pancreatic cancers and the important areas for future research.

Pancreatic ductal adenocarcinoma (PDA) constitutes a lethal disease that affects >30,000 people annually in the United States. Deregulation of Hedgehog signaling has been implicated in the pathogenesis of PDA. To gain insights into the role of the pathway during the distinct stages of pancreatic carcinogenesis, we established a mouse model in which Hedgehog signaling is activated specifically in the pancreatic epithelium. Transgenic mice survived to adulthood and developed undifferentiated carcinoma, indicating that epithelium-specific Hedgehog signaling is sufficient to drive pancreatic neoplasia but does not recapitulate human pancreatic carcinogenesis. In contrast, simultaneous activation of Ras and Hedgehog signaling caused extensive formation of pancreatic intraepithelial neoplasias, the earliest stages of human PDA tumorigenesis, and accelerated lethality. These results indicate the cooperation of Hedgehog and Ras signaling during the earliest stages of PDA formation. They also mark Hedgehog pathway components as relevant therapeutic targets for both early and advanced stages of pancreatic ductal neoplasia. Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer death in the United States (Hezel et al. 2006). Annually, its incidence closely matches its mortality, highlighting the inefficacy of existing treatment options (Jemal et al. 2006). Presently, surgical resection is the most effective therapeutic intervention, resulting in survival rates of ∼20% over 5 yr; however, most patients are diagnosed at advanced stages when removal of the cancer is not possible.Pancreatic intraepithelial neoplasias (PanINs) constitute the most common precursor lesions of PDA. PanIN lesions are classified based on histological changes and this histological classification correlates well with the presence of characteristic genetic alterations (Hruban et al. 2001), including mutations in KRAS, INK4A, TP53, and MADH4 (Boschman et al. 1994;Klimstra and Longnecker 1994;Hahn et al. 1996; Rozenblum et al. 1997;Wilentz et al. 2000;Maitra et al. 2003). Early PanINs (PanIN1A/B) are characterized by the change from a cuboidal duct epithelium to cells with columnar shape and by the accumulation of abundant supranuclear mucin. Higher-grade PanINs (PanIN2) show increasing alterations in the cellular architecture, including changes in cell polarity and nuclear atypia. PanIN3 lesions are considered carcinoma in situ. The cellular changes observed in these tumors are similar to invasive carcinoma; however, cells do not invade through the basement membrane.Previous studies by us and others (Berman et al. 2003;Thayer et al. 2003) have identified activation of the Hedgehog signaling pathway as a key event in the histogenesis of pancreatic cancer. The expression of the Hedgehog ligands SONIC and INDIAN HEDGEHOG (SHH, IHH), the transcriptional target gene PATCHED (PTC), and the essential pathway component SMOOTHENED (SMO) is undetectable in normal human pancreatic ducts. In contrast, a relative increase in the expression of ...

BackgroundPancreatic cancer is characterised by the accumulation of a fibro-inflammatory stroma. Within this stromal reaction, myeloid cells are a predominant population. Distinct myeloid subsets have been correlated with tumour promotion and unmasking of anti-tumour immunity.ObjectiveThe goal of this study was to determine the effect of myeloid cell depletion on the onset and progression of pancreatic cancer and to understand the relationship between myeloid cells and T cell-mediated immunity within the pancreatic cancer microenvironment.MethodsPrimary mouse pancreatic cancer cells were transplanted into CD11b-diphtheria toxin receptor (DTR) mice. Alternatively, the iKras* mouse model of pancreatic cancer was crossed into CD11b-DTR mice. CD11b+ cells (mostly myeloid cell population) were depleted by diphtheria toxin treatment during tumour initiation or in established tumours.ResultsDepletion of myeloid cells prevented KrasG12D-driven pancreatic cancer initiation. In pre-established tumours, myeloid cell depletion arrested tumour growth and in some cases, induced tumour regressions that were dependent on CD8+ T cells. We found that myeloid cells inhibited CD8+ T-cell anti-tumour activity by inducing the expression of programmed cell death-ligand 1 (PD-L1) in tumour cells in an epidermal growth factor receptor (EGFR)/mitogen-activated protein kinases (MAPK)-dependent manner.ConclusionOur results show that myeloid cells support immune evasion in pancreatic cancer through EGFR/MAPK-dependent regulation of PD-L1 expression on tumour cells. Derailing this crosstalk between myeloid cells and tumour cells is sufficient to restore anti-tumour immunity mediated by CD8+ T cells, a finding with implications for the design of immune therapies for pancreatic cancer.