Immortalized bovine pancreatic duct cells become tumorigenic after transfection with mutant k-ras

RAS-targeted cancer therapy: Advances in drugging specific mutations

Rat sarcoma (RAS), as a frequently mutated oncogene, has been studied as an attractive target for treating RAS-driven cancers for over four decades. However, it is until the recent success of kirsten-RAS (KRAS)^G12C inhibitor that RAS gets rid of the title "undruggable". It is worth noting that the therapeutic effect of KRAS^G12C inhibitors on different RAS allelic mutations or even different cancers with KRAS^G12C varies significantly. Thus, deep understanding of the characteristics of each allelic RAS mutation will be a prerequisite for developing new RAS inhibitors. In this review, the structural and biochemical features of different RAS mutations are summarized and compared. Besides, the pathological characteristics and treatment responses of different cancers carrying RAS mutations are listed based on clinical reports. In addition, the development of RAS inhibitors, either direct or indirect, that target the downstream components in RAS pathway is summarized as well. Hopefully, this review will broaden our knowledge on RAS-targeting strategies and trigger more intensive studies on exploiting new RAS allele-specific inhibitors.

Porcine pancreatic ductal epithelial cells transformed with KRASG12D and SV40T are tumorigenic

We describe our initial studies in the development of an orthotopic, genetically defined, large animal model of pancreatic cancer. Primary pancreatic epithelial cells were isolated from pancreatic duct of domestic pigs. A transformed cell line was generated from these primary cells with oncogenic KRAS and SV40T. The transformed cell lines outperformed the primary and SV40T immortalized cells in terms of proliferation, population doubling time, soft agar growth, transwell migration and invasion. The transformed cell line grew tumors when injected subcutaneously in nude mice, forming glandular structures and staining for epithelial markers. Future work will include implantation studies of these tumorigenic porcine pancreatic cell lines into the pancreas of allogeneic and autologous pigs. The resultant large animal model of pancreatic cancer could be utilized for preclinical research on diagnostic, interventional, and therapeutic technologies.

Loss of canonical Smad4 signaling promotes KRAS driven malignant transformation of human pancreatic duct epithelial cells and metastasis

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer death in North America. Activating KRAS mutations and Smad4 loss occur in approximately 90% and 55% of PDAC, respectively. While their roles in the early stages of PDAC development have been confirmed in genetically modified mouse models, their roles in the multistep malignant transformation of human pancreatic duct cells have not been directly demonstrated. Here, we report that Smad4 represents a barrier in KRAS-mediated malignant transformation of the near normal immortalized human pancreatic duct epithelial (HPDE) cell line model. Marked Smad4 downregulation by shRNA in KRAS^G12V expressing HPDE cells failed to cause tumorigenic transformation. However, KRAS-mediated malignant transformation occurred in a new HPDE-TGF-β resistant (TβR) cell line that completely lacks Smad4 protein expression and is resistant to the mito-inhibitory activity of TGF-β. This transformation resulted in tumor formation and development of metastatic phenotype when the cells were implanted orthotopically into the mouse pancreas. Smad4 restoration re-established TGF-β sensitivity, markedly increased tumor latency by promoting apoptosis, and decreased metastatic potential. These results directly establish the critical combination of the KRAS oncogene and complete Smad4 inactivation in the multi-stage malignant transformation and metastatic progression of normal human HPDE cells.

Transdifferentiation of tadpole pancreatic acinar cells to duct cells mediated by Notch and stromelysin-3

The tadpole pancreas has differentiated acinar cells but an underdeveloped ductal system. At the climax of metamorphosis thyroid hormone (TH) induces the tadpole acinar cells to dedifferentiate to a progenitor state. After metamorphosis is complete the exocrine pancreas redifferentiates in the growing frog forming a typical vertebrate pancreas including a complex ductal system. A micro array analysis found that TH up regulates stromelysin 3 (ST3, matrix metalloproteinase 11) in the exocrine pancreas at metamorphic climax. Transgenic tadpoles were prepared with an elastase promoter driving either the ST3 gene or the constitutively active form of Notch (IC). Expression of the transgenes was controlled by the tetracycline system. A few days after either of these transgenes is activated by doxycycline the pancreatic acinar cells turn into duct-like cells. This transdetermination occurs without cell division since both acinar and ductal markers can be visualized transiently in the same cell. We propose that remodeling of the tadpole acinar cells is initiated when ST3 is up regulated by TH. Stromelysin-3 then cleaves and activates Notch.

Inhibition of ankyrin-B expression reduces growth and invasion of human pancreatic ductal adenocarcinoma

BACKGROUND

In spite of the increasing knowledge of the molecular pathology of pancreatic ductal adenocarcinoma (PDAC), treatment of this tumor still remains an unresolved problem. Thus, the identification of 'novel' genes involved in pancreatic tumor progression is essential for early diagnosis and new treatment regimens of PDAC. Ankyrin-B (ANK2) was identified as being overexpressed in PDAC in a previous study by our group. ANK2 overexpression has been described in several tumors; however, the function of ANK2 in pancreatic carcinoma has not been elucidated.

MATERIALS AND METHODS

In the present study, we confirmed ANK2 overexpression in PDAC and analyzed the effects of ANK2 knockdown in the pancreatic tumor cell line PANC-1.

RESULTS

ANK2 silencing reduced the activity of FAK, ERK1/2 and p38. Decreased ANK2 expression restrained migration and invasive potential of PANC-1 cells. Moreover, silencing of ANK2 decreased the proliferation of the pancreatic tumor cells and reduced their tumorigenicity in vitro and in vivo.

CONCLUSION

Our results demonstrate that silencing of ANK2 expression reduced the malignant phenotype of pancreatic cancer cells, indicating that ANK2 represents a potential target for therapy of pancreatic cancer.

Autoantibodies against the exocrine pancreas in autoimmune pancreatitis: gene and protein expression profiling and immunoassays identify pancreatic enzymes as a major target of the inflammatory process

OBJECTIVES

Autoimmune pancreatitis (AIP) is thought to be an immune-mediated inflammatory process, directed against the epithelial components of the pancreas. The objective was to identify novel markers of disease and to unravel the pathogenesis of AIP.

METHODS

To explore key targets of the inflammatory process, we analyzed the expression of proteins at the RNA and protein level using genomics and proteomics, immunohistochemistry, western blot, and immunoassay. An animal model of AIP with LP-BM5 murine leukemia virus-infected mice was studied in parallel. RNA microarrays of pancreatic tissue from 12 patients with AIP were compared with those of 8 patients with non-AIP chronic pancreatitis.

RESULTS

Expression profiling showed 272 upregulated genes, including those encoding for immunoglobulins, chemokines and their receptors, and 86 downregulated genes, including those for pancreatic proteases such as three trypsinogen isoforms. Protein profiling showed that the expression of trypsinogens and other pancreatic enzymes was greatly reduced. Immunohistochemistry showed a near-loss of trypsin-positive acinar cells, which was also confirmed by western blotting. The serum of AIP patients contained high titers of autoantibodies against the trypsinogens PRSS1 and PRSS2 but not against PRSS3. In addition, there were autoantibodies against the trypsin inhibitor PSTI (the product of the SPINK1 gene). In the pancreas of AIP animals, we found similar protein patterns and a reduction in trypsinogen.

CONCLUSIONS

These data indicate that the immune-mediated process characterizing AIP involves pancreatic acinar cells and their secretory enzymes such as trypsin isoforms. Demonstration of trypsinogen autoantibodies may be helpful for the diagnosis of AIP.

Reactive Oxygen Species And Lung Tumorigenesis By Mutant K-ras: A Working Hypothesis

Wild-type K-ras is tumor suppressive in mouse lung, but mutant K-ras is actively oncogenic. Thus, the mutant protein must acquire new, dominant protumorigenic properties. Generation of reactive oxygen species could be one such property. The authors demonstrate increased peroxides in lung epithelial cells (E10)-transfected with mutant hK-ras(va112). An associated increase in DNA damage (comet assay) correlates with increased cyclooxygenase-2 protein. This DNA damage is completely abrogated by a specific cyclooxygenase-2 inhibitor (SC58125) or by a cell-permeable modified catalase. Literature is reviewed regarding generation of reactive oxygen and cyclooxygenase-2 induction by ras, cyclooxygenase-2 release of DNA-damaging reactive oxygen, and involvement of cyclooxygenase-2 and reactive oxygen in lung cancer

Remodeling the exocrine pancreas at metamorphosis in Xenopus laevis

At metamorphosis the Xenopus laevis tadpole exocrine pancreas remodels in two stages. At the climax of metamorphosis thyroid hormone (TH) induces dedifferentiation of the entire exocrine pancreas to a progenitor state. The organ shrinks to 20% of its size, and approximately 40% of its cells die. The acinar cells lose their zymogen granules and approximately 75% of their RNA. The mRNAs that encode exocrine-specific proteins (including the transcription factor Ptf1a) undergo almost complete extinction at climax, whereas PDX-1, Notch-1, and Hes-1, genes implicated in differentiation of the progenitor cells, are activated. At the end of spontaneous metamorphosis when the endogenous TH has reached a low level, the pancreas begins to redifferentiate. Exogenous TH induces the dedifferentiation phase but not the redifferentation phase. The tadpole pancreas lacks the mature ductal system that is found in adult vertebrate pancreases, including the frog. Exocrine pancreases of transgenic tadpoles expressing a dominant negative form of the TH receptor controlled by the elastase promoter are resistant to TH. They do not shrink when subjected to TH. Their acinar cells do not dedifferentiate at climax, nor do they down-regulate exocrine-specific genes or activate Notch-1 and Hes-1. Even 2 months after metamorphosis these frogs have not developed a mature ductal system and the acinar cells are abnormally arranged. The TH-dependent dedifferentiation of the tadpole acinar cells at climax is a necessary step in the formation of a mature frog pancreas.

Medical treatment of pancreatic cancer

Pancreatic carcinoma is a devastating disease with the worst prognosis of all solid tumors; the only cure is surgery. The vast majority of patients are inoperable at the time of diagnosis and require palliative treatment. With a median survival time oscillating around 6 months, indicating an almost complete resistance to conventional cytotoxic and radiation therapy, there is ample room for improvement. Therefore, pancreatic carcinoma has been used to trial many new substances and novel concepts. All aspects of palliative antitumor treatment will be presented in detail and discussed. Finally, some outlooks are given into the future of pancreatic cancer treatment.

Genes and proteins differentially expressed during in vitro malignant transformation of bovine pancreatic duct cells

Pancreatic carcinoma has an extremely bad prognosis due to lack of early diagnostic markers and lack of effective therapeutic strategies. Recently, we have established an in vitro model recapitulating the first steps in the carcinogenesis of the pancreas. SV40 large T antigen-immortalized bovine pancreatic duct cells formed intrapancreatic adenocarcinoma tumors on k-ras(mut) transfection after orthotopic injection in the nude mouse pancreas. Here we identified genes and proteins differentially expressed in the course of malignant transformation using reciprocal suppression subtractive hybridization and 2D gel electrophoresis and mass spectrometry, respectively. We identified 34 differentially expressed genes, expressed sequence tags, and 15 unique proteins. Differential expression was verified for some of the genes or proteins in samples from pancreatic carcinoma. Among these genes and proteins, the majority had already been described either to be influenced by a mutated ras or to be differentially expressed in pancreatic adenocarcinoma, thus proving the feasibility of our model. Other genes and proteins (e.g., BBC1, GLTSCR2, and rhoGDIalpha), up to now, have not been implicated in pancreatic tumor development. Thus, we were able to establish an in vitro model of pancreatic carcinogenesis, which enabled us to identify genes and proteins differentially expressed during the early steps of malignant transformation.

Immortalization of pancreatic stellate cells as an in vitro model of pancreatic fibrosis: deactivation is induced by matrigel and N-acetylcysteine

Tissue fibrosis is one of the characteristics of chronic pancreatitis and pancreatic adenocarcinoma. Activated pancreatic stellate cells (PSC) play a central role in this process. However, analysis of the molecular mechanisms leading to PSC activation is hampered by the lack of an established human PSC line. To overcome this problem, we immortalized and characterized primary human PSC. The cells were isolated by the outgrowth method and were immortalized by transfection with SV40 large T antigen and human telomerase (hTERT). Primary human PSC served as controls. An immortalized line, RLT-PSC, was analyzed for the expression of stellate cell markers. Moreover, the effects of transforming growth factor beta 1(TGFbeta1) or platelet-derived growth factor stimulation and of cultivation on basement membrane components or N-acetylcysteine (NAC) treatment on gene and protein expression and proliferation were analyzed. Immortal RLT-PSC cells retained the phenotype of activated PSC proven by the expression of alpha-smooth muscle actin (alphaSMA), vimentin, desmin and glial fibrillary acidic protein (GFAP). TGFbeta1 treatment upregulated the expression of alphaSMA, collagen type I (Col I), fibronectin and TGFbeta1. Incubation of RLT-PSC cells and primary human activated PSC on Matrigel plus NAC treatment resulted in a deactivated phenotype as evidenced by a decrease of alphaSMA, connective tissue growth factor and Col I expression and by a decreased proliferation of the cells. Moreover, this treatment restored the ability of the cells to store vitamin A in cytoplasmic vesicles. In conclusion, we have established an immortal pancreatic stellate cell line, without changing the characteristic phenotype. Importantly, we were able to demonstrate that besides soluble factors, the matrix surrounding PSC plays a pivotal role in the maintenance of the activation process of PSC. Cultivation of activated PSC on a reconstituted basement membrane plus treatment with NAC was able to deactivate the cells, thus pointing to the possibility of an antifibrosis therapy in chronic pancreatitis.

5-Lipoxygenase, a Marker for Early Pancreatic Intraepithelial Neoplastic Lesions

Pancreatic cancer has an abysmal prognosis because of late diagnosis. Therefore, it is important to identify risk factors if we are to be able to prevent and detect this cancer in an early, noninvasive stage. Pancreatic intraepithelial neoplasias (PanIN) are the precursor lesions which could be an ideal target for chemoprevention. This study shows up-regulation of 5-lipoxygenase (5-LOX) in all grades of human PanINs and early lesions of pancreatic cancer in two different animal models (EL-Kras mice and N-nitrosobis(2-oxopropyl)amine-treated hamsters) by immunohistochemistry. The results were consistent in all tissues examined, including seven chronic pancreatitis patients, four pancreatic cancer patients, one multiorgan donor, nine EL-Kras mice, and three N-nitrosobis(2-oxopropyl)amine-treated hamsters, all with PanINs. Overexpression of 5-LOX in NIH3T3 cells resulted in greater sensitivity of these cells to the growth inhibitory effects of the 5-LOX inhibitor Rev5901. These findings provide evidence that 5-LOX plays a key role in the development of pancreatic cancer. Furthermore, the lipoxygenase pathway may be a target for the prevention of this devastating disease.

In vitro modeling of human pancreatic duct epithelial cell transformation defines gene expression changes induced by K-ras oncogenic activation in pancreatic carcinogenesis

Genetic analysis of pancreatic ductal adenocarcinomas and their putative precursor lesions, pancreatic intraepithelial neoplasias (PanIN), has shown a multistep molecular paradigm for duct cell carcinogenesis. Mutational activation or inactivation of the K-ras, p16(INK4A), Smad4, and p53 genes occur at progressive and high frequencies in these lesions. Oncogenic activation of the K-ras gene occurs in >90% of pancreatic ductal carcinoma and is found early in the PanIN-carcinoma sequence, but its functional roles remain poorly understood. We show here that the expression of K-ras(G12V) oncogene in a near diploid HPV16-E6E7 gene immortalized human pancreatic duct epithelial cell line originally derived from normal pancreas induced the formation of carcinoma in 50% of severe combined immunodeficient mice implanted with these cells. A tumor cell line established from one of these tumors formed ductal cancer when implanted orthotopically. These cells also showed increased activation of the mitogen-activated protein kinase, AKT, and nuclear factor-kappaB pathways. Microarray expression profiling studies identified 584 genes whose expression seemed specifically up-regulated by the K-ras oncogene expression. Forty-two of these genes have been reported previously as differentially overexpressed in pancreatic cancer cell lines or primary tumors. Real-time PCR confirmed the overexpression of a large number of these genes. Immunohistochemistry done on tissue microarrays constructed from PanIN and pancreatic cancer samples showed laminin beta3 overexpression starting in high-grade PanINs and occurring in >90% of pancreatic ductal carcinoma. The in vitro modeling of human pancreatic duct epithelial cell transformation may provide mechanistic insights on gene expression changes that occur during multistage pancreatic duct cell carcinogenesis.

Frequency of K-ras mutations in pancreatic intraductal neoplasias associated with pancreatic ductal adenocarcinoma and chronic pancreatitis: a meta-analysis

Molecular analyses have demonstrated mutations in the K-ras gene at codon 12 in the majority of pancreatic ductal adenocarcinomas (PDACs). In order to determine whether the K-ras mutation rate increases parallel to the grade of dysplasia in duct lesions, we performed a meta-analysis of the studies published between 1988 and 2003 that provide information on K-ras mutations in hyperplastic and dysplastic duct lesions in the pancreas. The described duct lesions were reclassified according to the nomenclature for pancreatic intraepithelial neoplasia (PanIN), and the molecular methods for detecting K-ras were reviewed. In PanIN lesions from pancreata of patients with PDAC, there was a stepwise increase in K-ras mutations that correlated with the grade of dysplasia of the PanIN lesion. K-ras mutations were found in 36%, 44%, and 87% of PanIN-1a, 1b, and 2-3 lesions, respectively (trend statistic P <.001). Mutation-enriched polymerase chain reaction (PCR) resulted in higher rates of K-ras mutations in PanIN than plain PCR did. The incidence of K-ras mutations in PanIN lesions associated with chronic pancreatitis (CP) or normal pancreas was low (around 10%). In CP, K-ras mutations were only found after a disease duration of 3 years. The correlation of the incidence of K-ras mutations with the grade of dysplasia in PanIN and the occurrence of these mutations in CP with a duration of more than 3 years underlines the importance of this genetic change for the development of PDAC.

Transgenic expression of CCK2 receptors sensitizes murine pancreatic acinar cells to carcinogen-induced preneoplastic lesions formation

In humans, initial events of pancreatic carcinogenesis remain unknown, and the question of whether this cancer, which has a ductal phenotype, exclusively arises from duct cells has been raised. Previous studies have demonstrated that transgenic expression of the CCK2 receptor in acinar cells of ElasCCK2 mice plays a role in the development of pancreatic neoplasia. The aim of our study was to examine initial steps of carcinogenesis in ElasCCK2 mice, adding a supplementary defect by using a chemical carcinogen, azaserine. Results of posttreatment sequential immunohistochemical examinations and quantifications demonstrate that mice responded to azaserine. Transition of acinar cells into duct-like cells expressing Pdx1 and gastrin, as well as proliferation of acinar cells, were transiently observed in both transgenic and control mice. The carcinogen also induced formation of preneoplastic lesions, adenomas, exhibiting properties of autonomous growth. Importantly, expression of the CCK2 receptor increased the susceptibility of pancreas to azaserine. Indeed, treated ElasCCK2 mice exhibited larger areas of pancreatic acinar-ductal transition, increased cellular proliferation as well as larger adenomas areas vs. control mice. These amplified responses may be related to auto/paracrine stimulation of CCK2 receptor by gastrin expressed in newly formed duct-like cells. Our results demonstrate that activation of CCK2 receptor and azaserine result in cumulative effects to favor the emergence of a risk situation that is a potential site for initiation of carcinogenesis.

Successful growth and characterization of mouse pancreatic ductal cells: functional properties of the Ki-RAS(G12V) oncogene

BACKGROUND & AIMS

The Ki-RAS oncogene is altered in pancreatic ductal neoplasms. Pancreatic ductal cells (PDCs) were purified from cytokeratin 19 (K19)-Ki-RAS(G12V) transgenic mice and control littermates to identify properties of Ki-Ras activation in a cell-type-specific context. Because Ki-RAS mutation has prognostic significance in patients treated with radiation, we studied the influence of Ki-RAS status on radiation survival.

METHODS

Pancreatic ductal fragments from mice with Ki-RAS(G12V) mutation or wild-type (WT)-Ki-RAS were cultured. Growth curves, electron microscopy, flow cytometry, and analysis of signaling and cell-cycle proteins were established. Farnesyltransferase inhibitor (FTI) treatment with R115777 before and after irradiation was used to determine the effect of Ki-Ras farnesylation on cell survival.

RESULTS

PDCs from WT and K19-Ki-RAS(G12V) mice had features of ductal cells with formation of 3-dimensional structures on collagen without differences in morphology, growth, and cell-cycle distribution. This may result from up-regulation of p16INK4 and p27(Kip1) and lack of hyperstimulation of the mitogen-activated protein kinase pathway in Ki-RAS(G12V) PDCs. No differences in radiation survival between Ki-RAS(G12V) PDCs and WT PDCs were observed. However, Ki-RAS(G12V) PDCs expressing mutant p53(V143A) had enhanced survival compared with WT PDCs transduced with p53(V143A). R115777 treatment sensitized Ki-RAS(G12V) PDCs and Ki-RAS(G12V)/p53(V143A) PDCs, but not WT PDCs.

CONCLUSIONS

Novel characterization of murine WT PDCs and Ki-RAS(G12V) PDCs is described. Induction of cell-cycle regulators and lack of mitogen-activated protein kinase hyperstimulation likely are responsible for constraining activated Ki-RAS(G12V)-mediated proliferation. Because its activation was required for sensitization by an FTI, R115777 may be useful against pancreatic tumors expressing oncogenic Ki-Ras.

Conditional transformation of mouse pancreatic epithelial cells: an in vitro model for analysis of genetic events in pancreatocarcinogenesis

Pancreatic ductal adenocarcinomas arise through the accumulation of certain genetic alterations including ras, p16, p53, and DPC4. We found that activation of ras and inactivation of p53 could cooperatively induce in vitro tumorigenicity in conditionally immortalized pancreatic epithelial (IMPE) cells. IMPE cells were established from transgenic mice bearing a temperature-sensitive mutant SV40 Large T (LT) antigen. IMPE cells grew continuously under permissive conditions (33 degrees C with interferon-gamma), but rapidly suffered growth arrest under non-permissive conditions (39 degrees C without interferon-gamma). The cells showed strong expression of E-cadherin and beta-catenin as epithelial markers, and cytokeratin 19, a specific ductal cell marker. Cell proliferation under permissive conditions was associated with down-regulation of p21 expression through inactivation of p53 after overexpression of LT antigen. Intriguingly, the shift from the permissive to non-permissive culture conditions caused G2/M arrest of IMPE cells. Although the cells did not form colonies when cultured in soft agar without activation of ras, cells with ras activation via an adenovirus vector formed colonies under permissive conditions. These findings suggest that activation of ras and inactivation of p53 can cooperatively induce anchorage-independent growth of IMPE cells. This cell line might be useful for studying the processes involved in pancreatocarcinogenesis.

Gene expression profiles of microdissected pancreatic ductal adenocarcinoma

In a search for new molecular markers of pancreatic ductal adenocarcinoma (PDAC), we compared the gene expression profiles of seven pancreatic carcinomas and one carcinoma of the papilla Vateri with those of duct cells from three non-neoplastic pancreatic tissues. In addition, the human pancreatic duct cell line and five PDAC cell lines (AsPC-1, BxPC-3, Capan-1, Capan-2, HPAF) were examined. RNA was extracted from microdissected tissue or cultured cell lines and analysed using a custom-made Affymetrix Chip containing 3023 genes, of which 1000 were known to be tumour associated. Hierarchical clustering revealed 81 differentially expressed genes. Of all the genes, 26 were downregulated in PDAC and 14 were upregulated in PDAC. In PDAC cell lines versus normal pancreatic duct cells, 21 genes were downregulated and 20 were upregulated. Of these 81 differentially expressed genes, 15 represented human genes previously implicated in the tumourigenesis of PDAC. From the genes that were so far not known to be associated with PDAC tumorigenesis, we selected ADAM9 for further validation because of its distinct overexpression in tumour tissue. Using immunohistochemistry, the over-expressed gene, ADAM9, was present in 70% of the PDACs analysed. In conclusion, using microarray technology we were able to identify a set of genes whose aberrant expression was associated with PDAC and may be used to target the disease.