Early elevations of RAS protein level and activity are critical for the development of PDAC in the context of inflammation

The KRASG12D mutation was believed to be locked in a GTP-bound form, rendering it fully active. However, recent studies have indicated that the presence of mutant KRAS alone is insufficient; it requires additional activation through inflammatory stimuli to effectively drive the development of pancreatic ductal adenocarcinoma (PDAC). It remains unclear to what extent RAS activation occurs during the development of PDAC in the context of inflammation. Here, in a mouse model with the concurrent expression of KrasG12D/+ and inflammation mediator IKK2 in pancreatic acinar cells, we showed that, compared to KRASG12D alone, the cooperative interaction between KRASG12D and IKK2 rapidly elevated both the protein level and activity of KRASG12D and NRAS in a short term. This high level was sustained throughout the rest phase of PDAC development. These results suggest that inflammation not only rapidly augments the activity but also the protein abundance, leading to an enhanced total amount of GTP-bound RAS (KRASG12D and NRAS) in the early stage. Notably, while KRASG12D could be further activated by IKK2, not all KRASG12D proteins were in the GTP-bound state. Overall, our findings suggest that although KRASG12D is not fully active in the context of inflammation, concurrent increases in both the protein level and activity of KRASG12D as well as NRAS at the early stage by inflammation contribute to the rise in total GTP-bound RAS.

Kras mutation rate precisely orchestrates ductal derived pancreatic intraepithelial neoplasia and pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related death in the United States. Despite the high prevalence of Kras mutations in pancreatic cancer patients, murine models expressing the oncogenic mutant Kras (Krasmut) in mature pancreatic cells develop PDAC at a low frequency. Independent of cell of origin, a second genetic hit (loss of tumor suppressor TP53 or PTEN) is important for development of PDAC in mice. We hypothesized ectopic expression and elevated levels of oncogenic mutant Kras would promote PanIN arising in pancreatic ducts. To test our hypothesis, the significance of elevating levels of K-Ras and Ras activity has been explored by expression of a CAG driven LGSL-KrasG12V allele (cKras) in pancreatic ducts, which promotes ectopic Kras expression. We predicted expression of cKras in pancreatic ducts would generate neoplasia and PDAC. To test our hypothesis, we employed tamoxifen dependent CreERT2 mediated recombination. Hnf1b:CreERT2;KrasG12V (cKrasHnf1b/+) mice received 1 (Low), 5 (Mod) or 10 (High) mg per 20 g body weight to recombine cKras in low (cKrasLow), moderate (cKrasMod), and high (cKrasHigh) percentages of pancreatic ducts. Our histologic analysis revealed poorly differentiated aggressive tumors in cKrasHigh mice. cKrasMod mice had grades of Pancreatic Intraepithelial Neoplasia (PanIN), recapitulating early and advanced PanIN observed in human PDAC. Proteomics analysis revealed significant differences in PTEN/AKT and MAPK pathways between wild type, cKrasLow, cKrasMod, and cKrasHigh mice. In conclusion, in this study, we provide evidence that ectopic expression of oncogenic mutant K-Ras in pancreatic ducts generates early and late PanIN as well as PDAC. This Ras rheostat model provides evidence that AKT signaling is an important early driver of invasive ductal derived PDAC.

Abstract 4711: Novel mechanism involved in the regulation ofoncogenic Axl receptor tyrosine kinase in cancer

Background: Oncogenic receptor tyrosine kinase Axl is overexpressed and plays an important role in multiple human cancers. However the mechanisms of Axl overexpression in cancer remain unclear. This study is to investigate the mechanisms that regulate Axl expression in pancreatic cancer.

Experimental procedures: The interactions between HPK1, Axl and c-Cbl were examined using co-immunoprecipitation and immunoblotting. Inhibitors of endocytic pathway and immunofluorescence were used to examine the underlying mechanisms of HPK1-mediated Axl degradation. The functional significance of HPK1-mediated Axl degradation in the invasive capability of pancreatic ductal adenocarcinoma (PDAC) cells and it downstream signaling pathways were examined using HPK1 stable PDAC cells. Immunohistochemistry was used to examine the in vivo correlation between HPK1 and Axl in human pancreatic intraepithelial neoplasia. The RNA sequencing data of HPK1 and Axl expression and survival data of 176 pancreatic cancer patients in the Cancer Genome Atlas (TCGA) database were downloaded from the Human Protein Atlas (https://www.proteinatlas.org). The expression of HPK1 and Axl was categorized as low or high using the cutoff values set by TCGA (3.42 for HPK1 and 14.09 for Axl). Survival analysis were performed using the Kaplan-Meier method and the log-rank test was used to evaluate the statistical significance of differences.

Results: We identified Axl as a novel HPK1-interacting protein and demonstrated for the first time that HPK1 down-regulated Axl and decreased the half-life of Axl protein. HPK1-mediated Axl degradation was inhibited by leupeptin, baflomycin A1 and monensin which inhibit endocytic pathway. HPK1 accelerates the movement of Axl from the plasma membrane onto endosomes in pancreatic cancer cells after treated with Gas6. HPK1 increased the binding of Axl to c-Cbl, promoted Axl ubiquitination, decreased Axl signaling including phospho-Akt and phospho-Erk, and decreased the invasion capability of pancreatic cancer. More importantly, we showed that Axl expression inversely correlated with HPK1 expression in human pancreatic intraepithelial neoplasia (P=0.005). Low expression of HPK1 and high expression of Axl correlated significantly with poor survival in patients with PDAC (P<0.001).

Conclusions: Our results suggest a novel tumor suppressor mechanism of HPK1 in which it targets Axl for degradation via the endocytic pathway. Loss of HPK1 may contribute to Axl overexpression and enhance its downstream signaling and tumor invasion in pancreatic cancer.

Citation Format: Hua Wang, Xianzhou Song, Hironari Akasaka, Reza Abbasgholizadeh, Ji-Hyun Shin, Craig D. Logsdon, Anirban Maitra, Andrew J. Bean, Huamin Wang. Novel mechanism involved in the regulation ofoncogenic Axl receptor tyrosine kinase in cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4711.

Transgenic Expression of PRSS1R122H Sensitizes Mice to Pancreatitis

BACKGROUND & AIMS

Mutations in the trypsinogen gene (PRSS1) cause human hereditary pancreatitis. However, it is not clear how mutant forms of PRSS1 contribute to disease development. We studied the effects of expressing mutant forms of human PRSS1 in mice.

METHODS

We expressed forms of PRSS1 with and without the mutation encoding R122H (PRSS1^R122H) specifically in pancreatic acinar cells under control of a full-length pancreatic elastase gene promoter. Mice that did not express these transgenes were used as controls. Mice were given injections of caerulein to induce acute pancreatitis or injections of lipopolysaccharide to induce chronic pancreatitis. Other groups of mice were fed ethanol or placed on a high-fat diet to induce pancreatitis. Pancreata were collected and analyzed by histology, immunoblots, real-time polymerase chain reaction, and immunohistochemistry. Trypsin enzymatic activity and chymotrypsin enzymatic activity were measured in pancreatic homogenates. Blood was collected and serum amylase activity was measured.

RESULTS

Pancreata from mice expressing transgenes encoding PRSS1 or PRSS1^R122H had focal areas of inflammation; these lesions were more prominent in mice that express PRSS1^R122H. Pancreata from mice that express PRSS1 or PRSS1^R122H had increased levels of heat shock protein 70 and nuclear factor (erythroid-derived 2)-like 2, and reduced levels of chymotrypsin C compared with control mice. Increased expression of PRSS1 or PRSS1^R122H increased focal damage in pancreatic tissues and increased the severity of acute pancreatitis after caerulein injection. Administration of lipopolysaccharide exacerbated inflammation in mice that express PRSS1^R122H compared to mice that express PRSS1 or control mice. Mice that express PRSS1^R122H developed more severe pancreatitis after ethanol feeding or a high-fat diet than mice that express PRSS1 or control mice. Pancreata from mice that express PRSS1^R122H had more DNA damage, apoptosis, and collagen deposition and increased trypsin activity and infiltration by inflammatory cells than mice that express PRSS1 or control mice.

CONCLUSIONS

Expression of a transgene encoding PRSS1^R122H in mice promoted inflammation and increased the severity of pancreatitis compared with mice that express PRSS1 or control mice. These mice might be used as a model for human hereditary pancreatitis and can be studied to determine mechanisms of induction of pancreatitis by lipopolysaccharide, ethanol, or a high-fat diet.

Hematopoietic progenitor kinase 1 down-regulates the oncogenic receptor tyrosine kinase AXL in pancreatic cancer

The oncogenic receptor tyrosine kinase AXL is overexpressed in cancer and plays an important role in carcinomas of multiple organs. However, the mechanisms of AXL overexpression in cancer remain unclear. In this study, using HEK293T, Panc-1, and Panc-28 cells and samples of human pancreatic intraepithelial neoplasia (PanIN), along with several biochemical approaches and immunofluorescence microscopy analyses, we sought to investigate the mechanisms that regulate AXL over-expression in pancreatic ductal adenocarcinoma (PDAC). We found that AXL interacts with hematopoietic progenitor kinase 1 (HPK1) and demonstrate that HPK1 down-regulates AXL and decreases its half-life. The HPK1-mediated AXL degradation was inhibited by the endocytic pathway inhibitors leupeptin, bafilomycin A1, and monensin. HPK1 accelerated the movement of AXL from the plasma membrane to endosomes in pancreatic cancer cells treated with the AXL ligand growth arrest-specific 6 (GAS6). Moreover, HPK1 increased the binding of AXL to the Cbl proto-oncogene (c-Cbl); promoted AXL ubiquitination; decreased AXL-mediated signaling, including phospho-AKT and phospho-ERK signaling; and decreased the invasion capability of PDAC cells. Importantly, we show that AXL expression inversely correlates with HPK1 expression in human PanINs and that patients whose tumors have low HPK1 and high AXL expression levels have shorter survival than those with low AXL or high HPK1 expression (p < 0.001). Our results suggest that HPK1 is a tumor suppressor that targets AXL for degradation via the endocytic pathway. HPK1 loss of function may contribute to AXL overexpression and thereby enhance AXL-dependent downstream signaling and tumor invasion in PDAC.

Oncogenic KRAS Reduces Expression of FGF21 in Acinar Cells to Promote Pancreatic Tumorigenesis in Mice on a High-Fat Diet

BACKGROUND & AIMS

Obesity is a risk factor for pancreatic cancer. In mice, a high-fat diet (HFD) and expression of oncogenic KRAS lead to development of invasive pancreatic ductal adenocarcinoma (PDAC) by unknown mechanisms. We investigated how oncogenic KRAS regulates the expression of fibroblast growth factor 21, FGF21, a metabolic regulator that prevents obesity, and the effects of recombinant human FGF21 (rhFGF21) on pancreatic tumorigenesis.

METHODS

We performed immunohistochemical analyses of FGF21 levels in human pancreatic tissue arrays, comprising 59 PDAC specimens and 45 nontumor tissues. We also studied mice with tamoxifen-inducible expression of oncogenic KRAS in acinar cells (Kras^G12D/+ mice) and fElas^CreERT mice (controls). Kras^G12D/+ mice were placed on an HFD or regular chow diet (control) and given injections of rhFGF21 or vehicle; pancreata were collected and analyzed by histology, immunoblots, quantitative polymerase chain reaction, and immunohistochemistry. We measured markers of inflammation in the pancreas, liver, and adipose tissue. Activity of RAS was measured based on the amount of bound guanosine triphosphate.

RESULTS

Pancreatic tissues of mice expressed high levels of FGF21 compared with liver tissues. FGF21 and its receptor proteins were expressed by acinar cells. Acinar cells that expressed Kras^G12D/+ had significantly lower expression of Fgf21 messenger RNA compared with acinar cells from control mice, partly due to down-regulation of PPARG expression-a transcription factor that activates Fgf21 transcription. Pancreata from Kras^G12D/+ mice on a control diet and given injections of rhFGF21 had reduced pancreatic inflammation, infiltration by immune cells, and acinar-to-ductal metaplasia compared with mice given injections of vehicle. HFD-fed Kras^G12D/+ mice given injections of vehicle accumulated abdominal fat, developed extensive inflammation, pancreatic cysts, and high-grade pancreatic intraepithelial neoplasias (PanINs); half the mice developed PDAC with liver metastases. HFD-fed Kras^G12D/+ mice given injections of rhFGF21 had reduced accumulation of abdominal fat and pancreatic triglycerides, fewer pancreatic cysts, reduced systemic and pancreatic markers of inflammation, fewer PanINs, and longer survival-only approximately 12% of the mice developed PDACs, and none of the mice had metastases. Pancreata from HFD-fed Kras^G12D/+ mice given injections of rhFGF21 had lower levels of active RAS than from mice given vehicle.

CONCLUSIONS

Normal acinar cells from mice and humans express high levels of FGF21. In mice, acinar expression of oncogenic KRAS significantly reduces FGF21 expression. When these mice are placed on an HFD, they develop extensive inflammation, pancreatic cysts, PanINs, and PDACs, which are reduced by injection of FGF21. FGF21 also reduces the guanosine triphosphate binding capacity of RAS. FGF21 might be used in the prevention or treatment of pancreatic cancer.

Small interfering RNAs (siRNAs) in cancer therapy: a nano-based approach

Cancer is one of the most complex diseases that has resulted in multiple genetic disorders and cellular abnormalities. Globally, cancer is the most common health concern disease that is affecting human beings. Great efforts have been made over the past decades in biology with the aim of searching novel and more efficient tools in therapy. Thus, small interfering RNAs (siRNAs) have been considered one of the most noteworthy developments which are able to regulate gene expression following a process known as RNA interference (RNAi). RNAi is a post-transcriptional mechanism that involves the inhibition of gene expression through promoting cleavage on a specific area of a target messenger RNA (mRNA). This technology has shown promising therapeutic results for a good number of diseases, especially in cancer. However, siRNA therapeutics have to face important drawbacks in therapy including stability and successful siRNA delivery in vivo. In this regard, the development of effective siRNA delivery systems has helped addressing these issues by opening novel therapeutic windows which have allowed to build up important advances in Nanomedicine. In this review, we discuss the progress of siRNA therapy as well as its medical application via nanoparticle-mediated delivery for cancer treatment.

Obesogenic high-fat diet heightens aerobic glycolysis through hyperactivation of oncogenic KRAS

Oncogenic KRAS plays a vital role in controlling tumor metabolism by enhancing aerobic glycolysis. Obesity driven by chronic consumption of high-fat diet (HFD) is a major risk factor for oncogenic KRAS-mediated pancreatic ductal adenocarcinoma (PDAC). However, the role of HFD in KRAS-mediated metabolic reprogramming has been obscure. Here, by using genetically engineered mouse models expressing an endogenous level of KRASG12D in pancreatic acinar cells, we demonstrate that hyperactivation of KRASG12D by obesogenic HFD, as compared to carbohydrate-rich diet, is responsible for enhanced aerobic glycolysis that associates with critical pathogenic responses in the path towards PDAC. Ablation of Cox-2 attenuates KRAS hyperactivation leading to the reversal of both aggravated aerobic glycolysis and high-grade dysplasia under HFD challenge. Our data highlight a pivotal role of the cooperative interaction between obesity-ensuing HFD and oncogenic KRAS in driving the heightened aerobic glycolysis during pancreatic tumorigenesis and suggest that in addition to directly targeting KRAS and aerobic glycolysis pathway, strategies to target the upstream of KRAS hyperactivation may bear important therapeutic value.

Transgenic expression of cyclooxygenase-2 in pancreatic acinar cells induces chronic pancreatitis

Replacement of the exocrine parenchyma by fibrous tissue is a main characteristic of chronic pancreatitis. Understanding the mechanisms of pancreatic fibrogenesis is critical for the development of preventive and therapeutic interventions. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme for prostaglandin synthesis, is expressed in patients with chronic pancreatitis. However, it is unknown whether COX-2 can cause chronic pancreatitis. To investigate the roles of pancreatic acinar COX-2 in fibrogenesis and the development of chronic pancreatitis, COX-2 was ectopically expressed specifically in pancreatic acinar cells in transgenic mice. Histopathological changes and expression levels of several profibrogenic factors related to chronic pancreatitis were evaluated. COX-2 was expressed in the pancreas of the transgenic mice, as detected by Western blot analysis. Immunohistochemical staining showed COX-2 was specifically expressed in pancreatic acinar cells. COX-2 expression led to progressive changes in the pancreas, including pancreas megaly, persistent inflammation, collagen deposition, and acinar-to-ductal metaplasia. Quantitative RT-PCR and immunostaining showed that profibrogenic factors were upregulated and pancreatic stellate cells were activated in the COX-2 transgenic mice. Expression of COX-2 in pancreatic acinar cells is sufficient to induce chronic pancreatitis. Targeting this pathway may be valuable in the prevention of chronic pancreatitis. NEW & NOTEWORTHY COX-2 expression is observed in pancreatic tissues of human chronic pancreatitis. In this study, we showed that COX-2 expression caused the development of chronic pancreatitis in transgenic mice, supporting the idea that COX-2 inhibition may be an effective preventive and therapeutic strategy.

Suppression of stromal-derived Dickkopf-3 (DKK3) inhibits tumor progression and prolongs survival in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, and it is unclear whether its stromal infiltrate contributes to its aggressiveness. Here, we demonstrate that Dickkopf-3 (DKK3) is produced by pancreatic stellate cells and is present in most human PDAC. DKK3 stimulates PDAC growth, metastasis, and resistance to chemotherapy with both paracrine and autocrine mechanisms through NF-κB activation. Genetic ablation of DKK3 in an autochthonous model of PDAC inhibited tumor growth, induced a peritumoral infiltration of CD8+ T cells, and more than doubled survival. Treatment with a DKK3-blocking monoclonal antibody inhibited PDAC progression and chemoresistance and prolonged survival. The combination of DKK3 inhibition with immune checkpoint inhibition was more effective in reducing tumor growth than either treatment alone and resulted in a durable improvement in survival, suggesting that DKK3 neutralization may be effective as a single targeted agent or in combination with chemotherapy or immunotherapy for PDAC.

Galectin-3 Mediates Tumor Cell-Stroma Interactions by Activating Pancreatic Stellate Cells to Produce Cytokines via Integrin Signaling

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is characterized by activated pancreatic stellate cells (PSCs), abundance of extracellular matrix (ECM), and production of cytokines and chemokines. Galectin 3 (GAL3), a β-galactoside-specific lectin, contributes to PDAC development but its effects on the stroma and cytokine production are unclear.

METHODS

The effect of recombinant human GAL3 (rGAL3) on activation of PSCs, production of cytokines, and ECM proteins was determined by proliferation, invasion, cytokine array, and quantitative polymerase chain reaction. We assessed co-cultures of PDAC cells with GAL3 genetic alterations with PSCs. Production of interleukin 8 (IL8) and activities of nuclear factor (NF)-κB were determined by enzyme-linked immunosorbent assay and luciferase reporter analyses. We studied the effects of inhibitors of NF-κB and integrin-linked kinase (ILK) on pathways activated by rGAL3.

RESULTS

In analyses of the Gene Expression Omnibus database and our dataset, we observed higher levels of GAL3, IL8, and other cytokines in PDAC than in nontumor tissues. Production of IL8, granulocyte-macrophage colony-stimulating factor, chemokine ligand 1, and C-C motif chemokine ligand 2 increased in PSCs exposed to rGAL3 compared with controls. Culture of PSCs with PDAC cells that express different levels of GAL3 resulted in proliferation and invasion of PSCs that increased with level of GAL3. GAL3 stimulated transcription of IL8 through integrin subunit beta 1 (ITGB1) on PSCs, which activates NF-κB through ILK. Inhibitors of ILK or NF-κB or a neutralizing antibody against ITGB1 blocked transcription and production of IL8 from PSCs induced by rGAL3. The GAL3 inhibitor significantly reduced growth and metastases of orthotopic tumors that formed from PDAC and PSC cells co-implanted in mice.

CONCLUSION

GAL3 activates PSC cells to produce inflammatory cytokines via ITGB1signaling to ILK and activation of NF-κB. Inhibition of this pathway reduced growth and metastases of pancreatic orthotopic tumors in mice.

Identification of a Specific Vimentin isoform that Induces an Antibody Response in Pancreatic Cancer

Pancreatic cancer has a poor prognosis, in part due to lack of early detection. The identification of circulating tumor antigens or their related autoantibodies provides a means for early cancer diagnosis. We have used a proteomic approach to identify proteins that commonly induce a humoral response in pancreatic cancer. Proteins from a pancreatic adenocarcinoma cell line (Panc-1) were subjected to two-dimensional PAGE, followed by Western blot analysis in which individual sera were tested for autoantibodies. Sera from 36 newly diagnosed patients with pancreatic cancer, 18 patients with chronic pancreatitis and 15 healthy subjects were analyzed. Autoantibodies were detected against a protein identified by mass spectrometry as vimentin, in sera from 16/36 patients with pancreatic cancer (44.4%). Only one of 18 chronic pancreatitis patients and none of the healthy controls exhibited reactivity against this vimentin isoform. Interestingly, none of several other isoforms of vimentin detectable in 2-D gels exhibited reactivity with patient sera. Vimentin protein expression levels were investigated by comparing the integrated intensity of spots visualized in 2-D PAGE gels of various cancers. Pancreatic tumor tissues showed greater than a 3-fold higher expression of total vimentin protein than did the lung, colon, and ovarian tumors that were analyzed. The specific antigenic isoform was found at 5–10 fold higher levels. The detection of autoantibodies to this specific isoform of vimentin may have utility for the early diagnosis of pancreatic cancer.

The immune system in cancer metastasis: friend or foe?

Metastatic disease is the leading cause of death among cancer patients and involves a complex and inefficient process. Every step of the metastatic process can be rate limiting and is influenced by non-malignant host cells interacting with the tumor cell. Over a century ago, experiments first indicated a link between the immune system and metastasis. This phenomenon, called concomitant immunity, indicates that the primary tumor induces an immune response, which may not be sufficient to destroy the primary tumor, but prevents the growth of a secondary tumor or metastases. Since that time, many different immune cells have been shown to play a role in both inhibiting and promoting metastatic disease. Here we review classic and new observations, describing the links between the immune system and metastasis that inform the development of cancer therapies.

RAGE maintains high levels of NFκB and oncogenic Kras activity in pancreatic cancer

Oncogenic KRas activity is central to several cancer types including pancreatic ductal adenocarcinoma (PDAC) but has been determined to be "undruggable". Recent studies have indicated that oncogenic KRas is not constitutively active but relies on a feed-forward stimulatory mechanism involving NFκB mediated inflammation. In the current study, we investigated the role of the receptor for advanced glycation end-products (RAGE) in maintaining oncogenic signaling in PDAC. We observed that there was a shift in the levels of specific RAGE isoforms and altered cellular localization in PDAC. Furthermore, inhibition of RAGE using a pharmacological antagonist, FPS-ZM1, or a blocking antibody, decreased phosphorylation of IKBα and inhibited Erk activity down-stream of Kras in PDAC cell lines. In vivo, inhibition of RAGE using FPS-ZM1 reduced the growth of PDAC syngeneic orthotopic xenografts and prolonged survival. These data indicate that RAGE plays a central role in maintaining inflammatory signaling in PDAC that benefits tumor growth. These observations support the development of approaches to inhibit the carcinogenic actions of Kras indirectly by blocking the mechanisms which maintain its activity.

Abstract 2961: Targeting stromal-derived Dickkopf-3 (DKK3) for the treatment of pancreatic ductal adenocarcinoma (PDAC)

Introduction: We and others have shown that pancreatic stellate cells (PSCs) in the tumor-associated stroma of PDAC promote tumor progression and resistance to therapy but the precise mechanisms are unclear. We investigated the role of PSC-derived DKK3, a member of the Dickkopf family of glycoproteins, in PDAC progression, metastasis and response to chemotherapy.

Methods: We evaluated expression of DKK3 in human PDAC tissue and cell lines, human PSCs and in a genetically engineered mouse model (GEMM) of PDAC. The paracrine and autocrine effects of DKK3 on PDAC and PSCs were examined by treatment with exogenous DKK3 and gain- and loss of function assays for proliferation, migration, invasion, and gemcitabine-induced apoptosis. The effects of DKK3 on PDAC progression and metastasis were determined by shRNA neutralization and genetic ablation in orthotopic xenograft models and the KPC autochthonous model of PDAC. We developed novel monoclonal antibodies (mAbs) against DKK3 and tested their ability to neutralize DKK3 and prolong survival in mouse models of PDAC.

Results: DKK3 was expressed at 4.5 times higher levels in human PDAC by Affymetrix profiling compared to normal pancreas and was present in 99% (118/119) of samples on a tissue microarray with moderate to high expression in 59%. In a GEMM of PDAC, DKK3 appeared early with preneoplastic PanIN lesions with increased expression in invasive carcinoma. DKK3 was strongly expressed by PSCs with minimal to no expression in PDAC cells and knockdown by shRNA reduced PSC proliferation and migration by 60% and 84% compared to controls (p&lt;0.001). Treatment of Panc1 and BxPC3 cells with DKK3 stimulated migration and invasion by 100-300% (p&lt;0.001) and proliferation of DKK3-silenced Panc1 cells was decreased by 80% (p&lt;0.001). Overexpression of DKK3 in L3.6pl cells increased colony formation in gemcitabine by &gt;90% (p&lt;0.001) with 65% reduction in apoptosis (p&lt;0.01), indicating that DKK3 contributes to PDAC resistance to chemotherapy. When we ablated DKK3 in KPC mice by breeding with DKK3-knockout mice, tumor growth was inhibited and survival increased by 45% (p=0.0002). In addition, fewer PanIN lesions developed in DKK3-null mice suggesting that DKK3 may contribute to the early developmental stages of PDAC. DKK3 neutralizing mAbs abrogated DKK3-mediated induction of PDAC cell migration, invasion and resistance to gemcitabine in vitro. Furthermore, treatment with DKK3 mAb significantly inhibited primary tumor growth, reduced peritoneal metastases and prolonged survival in an orthotopic model of PDAC by 43% compared to control mAb (p=0.005; HR 0.24, 95% CI 0.01-0.30).

Conclusions: These data are the first report, to our knowledge, of a tumor-promoting function of DKK3 and our results suggest that neutralization of DKK3 may be an effective approach as a primary treatment for PDAC and to enhance responsiveness to chemotherapy.

Citation Format: Liran Zhou, Hongmei Husted, Todd Moore, Mason Lu, Defeng Deng, Yan Liu, Vijaya Ramachandran, Thiruvengadam Arumugam, Baoan Ji, Huamin Wang, Jeffrey E. Lee, Craig D. Logsdon, Rosa F. Hwang. Targeting stromal-derived Dickkopf-3 (DKK3) for the treatment of pancreatic ductal adenocarcinoma (PDAC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2961. doi:10.1158/1538-7445.AM2017-2961

Abstract 1837: High Ras activity promotes neoplasia in pancreatic ductal cells

Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal malignancy and is the third leading cause of cancer-related deaths in the United States. Next generation sequencing efforts have revealed KRAS mutations occur in over 99% of pancreatic ductal adenocarcinomas and are thought to be the initiating mutation for pancreatic cancer. Despite the high prevalence of KRAS mutations in pancreatic cancer patients, murine models expressing endogenous levels of mutant Kras in pancreatic cells do not develop PDAC. A number of publications have revealed that acinar cells are more sensitive to early neoplastic lesion formation in the presence of Kras mutations than ductal cells. In these models, a second genetic hit (loss of tumor suppressor TP53, SMAD4 or CDKN) is required for the development of invasive PDAC, including transforming pancreatic ductal cells. Recent data has revealed a novel role for high levels of Ras activity in acinar cells in the tranformation of this cell type to PDAC (Ji, B., 2009). We hypothesized based on other preliminary data that high levels of Ras activity would transform ductal cells. To test this hypothesis, we studied the role of constitutively active high levels of Kras activity in acinar and ductal cells by expressing an inducible KrasG12V allele in Ptf1a:CreERT2 (acinar cell specific) and Hnf1b:CreERT2 (ductal cell specific) mice. Similar to previously published work, high levels of Ras activity in acinar cells resulted in PDAC and a remarkably low survival time of 10 days after mice were injected with tamoxifen. Mice with elevated Ras activity in ductal cells needed to be euthanized two weeks after tamoxifen injection and manifested a cancer cachexic phenotype. Histological analysis of these mice revealed high grade oncocytic intraductal neoplasia and the phenotype extended throughout the pancreatobiliary ducts. Western blot analysis of human PDAC and Cholangiocarcinoma tissue revealed similar levels of Ras activity to our murine models, confirming human equivalent high Ras expression to both animal models. Oncocytic tumors are characterized by an abundance of mitochondria. Thus, we are currently studying metabolic alterations and mitochondria accumulation in ductal and acinar cells expressing high Ras activity. Our goal is to determine how mitochondrial alterations play a role in progression or inhibition of tumors in ductal vs acinar cells.

Citation Format: Kanchan Singh, Melissa A. Pruski, Wasim A. Dar, Kishore Polireddy, John S. Bynon, Mamoun Younes, Anirban Maitra, Craig D. Logsdon, Jennifer M. Bailey. High Ras activity promotes neoplasia in pancreatic ductal cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1837. doi:10.1158/1538-7445.AM2017-1837

Lipocalin-2 Promotes Pancreatic Ductal Adenocarcinoma by Regulating Inflammation in the Tumor Microenvironment

Lipocalin-2 (LCN2) promotes malignant development in many cancer types. LCN2 is upregulated in patients with pancreatic ductal adenocarcinoma (PDAC) and in obese individuals, but whether it contributes to PDAC development is unclear. In this study, we investigated the effects of Lcn2 depletion on diet-induced obesity, inflammation, and PDAC development. Mice with acinar cell-specific expression of KrasG12D were crossed with Lcn2-depleted animals and fed isocaloric diets with varying amounts of fat content. Pancreas were collected and analyzed for inflammation, pancreatic intraepithelial neoplasia (PanIN), and PDAC. We also used a syngeneic orthotopic PDAC mouse model to study tumor growth in the presence or absence of Lcn2 expression. In addition, to understand the mechanistic role of how LCN2 could be mediating PDAC, we studied LCN2 and its specific receptor solute carrier family 22 member 17 (SLC22A17) in human pancreatic cancer stellate cells (PSC), key mediators of the PDAC stroma. Depletion of Lcn2 diminished extracellular matrix deposition, immune cell infiltration, PanIN formation, and tumor growth. Notably, it also increased survival in both obesity-driven and syngeneic orthotopic PDAC mouse models. LCN2 modulated the secretion of proinflammatory cytokines in PSC of the PDAC tumor microenvironment, whereas downregulation of LCN2-specific receptor SLC22A17 blocked these effects. Our results reveal how LCN2 acts in the tumor microenvironment links obesity, inflammation, and PDAC development. Cancer Res; 77(10); 2647-60. ©2017 AACR.

Chronic inflammation initiates multiple forms of K-Ras-independent mouse pancreatic cancer in the absence of TP53

Chronic inflammation (CI) is a risk factor for pancreatic cancer (PC) including the most common type, ductal adenocarcinoma (PDAC), but its role and the mechanisms involved are unclear. To investigate the role of CI in PC, we generated genetic mouse models with pancreatic specific CI in the presence or absence of TP53. Mice were engineered to express either cyclooxygenase-2 (COX-2) or IκB kinase-2 (IKK2), and TP53^+/+ or TP53^f/f specifically in adult pancreatic acinar cells by using a full-length pancreatic elastase promoter-driven Cre. Animals were followed for >80 weeks and pancreatic lesions were evaluated histologically and immunohistochemically. The presence of K-ras mutations was assessed by direct sequencing, locked nuclei acid (LNA)-based PCR, and immunohistochemistry. We observed that sustained COX-2/IKK2 expression caused histological abnormalities of pancreas, including increased immune cell infiltration, proliferation rate and DNA damage. A minority of animals with CI developed pre-neoplastic lesions, but cancer was not observed in any TP53^+/+ animals within 84 weeks. In contrast, all animals with CI-lacking TP53 developed various subtypes of PC, including acinar cell carcinoma, ductal adenocarcinoma, sarcomatoid carcinoma and neuroendocrine tumors, and all died within 65 weeks. No evidence of K-ras mutations was observed. Variations in the activity of the Hippo, pERK and c-Myc pathways were found in the diverse cancer subtypes. In summary, chronic inflammation is extremely inefficient at inducing PC in the presence of TP53. However, in the absence of TP53, CI leads to the development of several rare K-ras-independent forms of PC, with infrequent PDAC. This may help explain the rarity of PDAC in persons with chronic inflammatory conditions.

TM4SF1 Regulates Pancreatic Cancer Migration and Invasion In Vitro and In Vivo

BACKGROUND/AIMS

The cell surface protein transmembrane 4 L6 family member 1 (TM4SF1) has been detected in various tumors and plays a major role in the development of cancer. We aimed to investigate the effects of TM4SF1 on the migration and invasion of pancreatic cancer in vitro and in vivo and explore its related molecular mechanisms.

METHODS

qRT-PCR and immunohistochemical analyses were used to measure the expression of TM4SF1 in pancreatic cancer tissues and adjacent tissues. TM4SF1 was silenced using siRNA and shRNA to investigate the role of this protein in the proliferation and metastasis of pancreatic cancer cells. MTS and Transwell assays were used to examine the effect of TM4SF1 on pancreatic cancer cell lines. The expression and activity of MMP-2 and MMP-9 were determined by qRT-PCR, western blots and gelatin zymography. In vivo, orthotopic pancreatic tumor models were used to examine the formation of metastasis.

RESULTS

qRT-PCR and immunohistochemical analyses showed that TM4SF1 was highly expressed in pancreatic cancer tissues compared with the adjacent tissues. In in vitro experiments the silencing of TM4SF1 reduced cell migration and invasion and down-regulated the expression and activity of MMP-2 and MMP-9. However, no significant difference in cell proliferation was detected after silencing TM4SF1. Additionally, knocking down TM4SF1 decreased the formation of lung and liver metastases in orthotopic pancreatic tumor models.

CONCLUSION

Our results demonstrate that the expression of TM4SF1 is higher in pancreatic cancer tissues and pancreatic cancer cell lines than controls. Knockdown of TM4SF1 inhibited the migration and invasion of pancreatic cancer cells by regulating the expression and activity of MMP-2 and MMP-9, which suggests that TM4SF1 may play a significant role in metastasis in pancreatic cancer.

The Significance of Ras Activity in Pancreatic Cancer Initiation

The genetic landscape of pancreatic cancer shows nearly ubiquitous mutations of K-RAS. However, oncogenic K-Ras^mt alone is not sufficient to lead to pancreatic ductal adenocarcinoma (PDAC) in either human or in genetically modified adult mouse models. Many stimulants, such as high fat diet, CCK, LPS, PGE2 and others, have physiological effects at low concentrations that are mediated in part through modest increases in K-Ras activity. However, at high concentrations, they induce inflammation that, in the presence of oncogenic K-Ras expression, substantially accelerates PDAC formation. The mechanism involves increased activity of oncogenic K-Ras^mt. Unlike what has been proposed in the standard paradigm for the role of Ras in oncogenesis, oncogenic K-Ras^mt is now known to not be constitutively active. Rather, it can be activated by standard mechanisms similar to wild-type K-Ras, but its activity is sustained for a prolonged period. Furthermore, if the level of K-Ras activity exceeds a threshold at which it begins to generate its own activators, then a feed-forward loop is formed between K-Ras activity and inflammation and pathological processes including oncogenesis are initiated. Oncogenic K-Ras^mt activation, a key event in PDAC initiation and development, is subject to complex regulatory mechanisms. Reagents which inhibit inflammation, such as the Cox2 inhibitor celecoxib, block the feed-forward loop and prevent induction of PDAC in models with endogenous oncogenic K-Ras^mt. Increased understanding of the role of activating and inhibitory mechanisms on oncogenic K-Ras^mt activity is of paramount importance for the development of preventive and therapeutic strategies to fight against this lethal disease.

TM4SF1 Promotes Gemcitabine Resistance of Pancreatic Cancer In Vitro and In Vivo

Background

TM4SF1 is overexpressed in pancreatic ductal adenocarcinoma (PDAC) and affects the development of this cancer. Also, multidrug resistance (MDR) is generally associated with tumor chemoresistance in pancreatic cancer. However, the correlation between TM4SF1 and MDR remains unknown. This research aims to investigate the effect of TM4SF1 on gemcitabine resistance in PDAC and explore the possible molecular mechanism between TM4SF1 and MDR.

Methods

The expression of TM4SF1 was evaluated in pancreatic cancer cell lines and human pancreatic duct epithelial (HPDE) cell lines by quantitative RT-PCR. TM4SF1 siRNA transfection was carried out using Hiperfect transfection reagent to knock down TM4SF1. The transcripts were analyzed by quantitative RT-PCR, RT-PCR and western blotting for further study. The cell proliferation and apoptosis were obtained to investigate the sensitivity to gemcitabine of pancreatic cancer cells after silencing TM4SF1 in vitro. We demonstrated that cell signaling of TM4SF1 mediated chemoresistance in cancer cells by assessing the expression of multidrug resistance (MDR) genes using quantitative RT-PCR. In vivo, we used orthotopic pancreatic tumor models to investigate the effect of proliferation after silencing TM4SF1 by a lentivirus-mediated shRNA in MIA PaCa-2 cell lines.

Results

The mRNA expression of TM4SF1 was higher in seven pancreatic cancer cell lines than in HPDE cell lines. In three gemcitabine-sensitive cell lines (L3.6pl, BxPC-3, SU86.86), the expression of TM4SF1 was lower than that in four gemcitabine-resistant cell lines (MIA PaCa-2, PANC-1, Hs766T, AsPC-1). We evaluated that TM4SF1 was a putative target for gemcitabine resistance in pancreatic cancer cells. Using AsPC-1, MIA PaCa-2 and PANC-1, we investigated that TM4SF1 silencing affected cell proliferation and increased the percentages of cell apoptosis mediated by treatment with gemcitabine compared with cells which were treated with negative control. This resistance was associated with the expression of multidrug resistance genes including ABCB1 and ABCC1. In vivo, silencing of TM4SF1 in MIA PaCa-2 cell lines increased the effectiveness of gemcitabine-based treatment in orthotopic pancreatic tumor models evaluated using noninvasive bioluminescent imaging.

Conclusion

These findings suggest that TM4SF1 is a surface membrane antigen that is highly expressed in pancreatic cancer cells and increases the chemoresistance to gemcitabine. Thus, TM4SF1 may be a promising target to overcome the chemoresistance of pancreatic cancer.

Animal Models of Gastrointestinal and Liver Diseases. The difficulty of animal modeling of pancreatic cancer for preclinical evaluation of therapeutics

Pancreatic ductal adenocarcinoma (PDAC) is relatively rare but extremely lethal. Standard cytotoxic therapeutics provide little benefit. To date, newer targeted therapeutics have also not been highly successful. Often novel therapeutics that have appeared to perform well in preclinical models have failed in the clinic. Many factors contribute to these failures, but the one most often attributed is the shortcomings of the preclinical models. A plethora of animal models now exist for PDAC, including cell line xenografts, patient-derived xenografts, a wide variety of genetic mouse models, and syngeneic xenografts. These models have generated a tremendous amount of information useful for the understanding of PDAC. Yet none seems to well predict clinical outcomes of new treatments. This review will discuss how genetic instability and cellular heterogeneity make this disease so difficult to model accurately. We will also discuss the strengths and weaknesses of many of the popular models. Ultimately we will argue that there is no perfect model and that the best approach to understanding clinical performance is the use of multiple preclinical models with an understanding of their salient features.

Abstract 891: FGF21 prevents high fat diet-induced pancreatic cancer in mice expressing oncogenic Kras

The genetic landscape of pancreatic cancer shows nearly ubiquitous mutations of Kras. However, expression of mutant Kras alone is not sufficient to drive pancreatic ductal adenocarcinoma (PDAC) in adult mice. Obesity is a metabolic disorder and is a risk factor for PDAC. One of the main factors that contributes to the development of obesity is high-fat consumption. Recent studies have demonstrated that High-Fat-Diet (HFD) can promote oncogenic Kras mediated development of pancreatic intraepithelial neoplasia and PDAC. However, it is not clear why mice with oncogenic KrasG12D expression are predisposed to HFD mediated pancreatic carcinogenesis. Here, we report that Ras activity dramatically reduces the expression of fibroblast growth factor 21 (FGF21). FGF21 is a key mediator of fatty acid oxidation and lipid metabolism. Pharmacological doses of FGF21 lower serum free fatty acids and lead to weight loss in obese mice. FGF21 is highly expressed in pancreatic acinar cells and is a potential autocrine factor. High levels expression of FGFR1 and β-Klotho, key components for specific sites of FGF21 action, were observed on normal control mouse pancreatic acinar cells using both qRT-PCR and immunohistochemistry technics. FGF21 levels were dramatically reduced (∼6-fold) by Cre-mediated knock-in of oncogenic KrasG12D within one week and further decreased by more than 100-fold within 7 months. This effect of KrasG12D may have been mediated by decreased expression of pancreatic transcription factor Mist1, which was also observed. To dissect obesity and oncogenic KrasG12D mediated PDAC, we fed adult KrasG12D expressing mice with HFD or HFD+FGF21. We observed that KrasG12D expressing mice fed with HFD+FGF21 for 9 weeks significantly lower body weight and pancreatic triglyceride, as well as dramatically fewer PanIN lesions and tumor, compared with KrasG12D mice on a HFD without FGF21. FGF21 treatment extended survival of KrasG12D expressing mice on a HFD. Our results suggest that pancreas-derived FGF21 is an important metabolic regulator which is silenced by oncogenic KrasG12D expression and plays an important role in preventing HFD induced PDAC in KrasG12D expressing mice.

Citation Format: Weiqin Lu, Yaying Yang, Xiaojie Wang, Yan Liu, Yongde Luo, Robert A. Wolff, James L. Abbruzzese, Craig D. Logsdon. FGF21 prevents high fat diet-induced pancreatic cancer in mice expressing oncogenic Kras. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 891. doi:10.1158/1538-7445.AM2015-891

Abstract B24: Targeting pancreatic ductal adenocarcinoma acidic microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in the USA, accounting for ~40,000 deaths annually. The dismal prognosis for PDAC is largely due to its late diagnosis. Currently, the most sensitive diagnosis of PDAC requires invasive procedures, such as endoscopic ultrasonography, which has inherent risks and accuracy that is highly operator dependent. Here we took advantage of a general characteristic of solid tumors, the acidic microenvironment that is generated as a by-product of metabolism, to develop a novel approach of using pH (Low) Insertion Peptides (pHLIPs) for imaging of PDAC. We show that fluorescently labeled pHLIPs can localize and specifically detect PDAC in human xenografts as well as PDAC and PanIN lesions in genetically engineered mouse models. This novel approach may improve detection, differential diagnosis and staging of PDAC

Citation Format: Zobeida Cruz-Monserrate, Christina L. Roland, Defeng Deng, Thiruvengadam Arumugam, Anna Moshnikova, Oleg A. Andreev, Yana Reshetnyak, Craig D. Logsdon. Targeting pancreatic ductal adenocarcinoma acidic microenvironment. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B24.

New Blocking Antibodies against Novel AGR2-C4.4A Pathway Reduce Growth and Metastasis of Pancreatic Tumors and Increase Survival in Mice

Anterior gradient 2 (AGR2) promotes cancer growth, metastasis, and resistance to therapy via unknown mechanisms. We investigated the effects of extracellular AGR2 signaling through the orphan glycosylphosphatidylinositol-linked receptor C4.4A in pancreatic ductal adenocarcinoma (PDAC). Proliferation, migration, invasion, and apoptosis were measured using colorimetric, Boyden chamber, and FACS analyses. We developed blocking mAbs against AGR2 and C4.4A and tested their effects, along with siRNAs, on cancer cell functions and on orthotopic tumors in nude mice. Extracellular AGR2 stimulated proliferation, migration, invasion, and chemoresistance of PDAC cell lines. AGR2 interacted with C4.4A in cell lysates and mixtures of recombinant proteins. Knockdown of C4.4A reduced migration and resistance to gemcitabine. PDAC tissues, but not adjacent healthy pancreatic tissues, expressed high levels of AGR2 and C4.4A. AGR2 signaling through C4.4A required laminins 1 or 5 and integrin β1. Administration of antibodies against AGR2 and C4.4A reduced growth and metastasis and caused regression of aggressive xenograft tumors, leading to increased survival of mice. These data support a model in which AGR2 binds and signals via C4.4A in an autocrine loop and promotes the growth of pancreas tumors in mice. Blocking mAbs against AGR2 and C4.4A may have therapeutic potential against PDAC.

Preliminary evaluation of 1'-[(18)F]fluoroethyl-β-D-lactose ([(18)F]FEL) for detection of pancreatic cancer in nude mouse orthotopic xenografts

INTRODUCTION

Early detection of pancreatic cancer could save many thousands of lives. Non-invasive diagnostic imaging, including PET with [(18)F]FDG, has inadequate resolution for detection of small (2-3 mm) pancreatic tumours. We demonstrated the efficacy of PET imaging with an (18)F-labelled lactose derivative, [(18)F]FEDL, that targets HIP/PAP, a biomarker that is overexpressed in the peritumoural pancreas. We developed another analogue, 1-[(18)F]fluoroethyl lactose ([(18)F]FEL), which is simpler to synthesise, for the same application. We conducted a preliminary evaluation of the new probe and its efficacy in detecting orthotopic pancreatic carcinoma xenografts in mice.

METHODS

Xenografts were developed in nude mice by injecting L3.6 pl/GL(+) pancreatic carcinoma cells into the pancreas of each mouse. Tumour growth was monitored by bioluminescence imaging (BLI); accuracy of BLI tumour size estimates was verified by MRI in two representative mice. When the tumour size reached approximately 2-3mm, the animals were injected with [(18)F]FEL (3.7 MBq) and underwent static PET/CT scans. Blood samples were collected at 2, 5, 10, 20 and 60 min after [(18)F]FEL injection to track blood clearance. Following imaging, animals were sacrificed and their organs and tumours/pancreatic tissue were collected and counted on a gamma counter. Pancreas, including tumour, was frozen, sliced and used for autoradiography and immunohistochemical analysis of HIP/PAP expression.

RESULTS

Tumour growth was rapid, as observed by BLI and MRI. Blood clearance of [(18)F]FEL was bi-exponential, with half-lives of approximately 3.5 min and 40 min. Mean accumulation of [(18)F]FEL in the peritumoural pancreatic tissue was 1.29±0.295 %ID/g, and that in the normal pancreas of control animals was 0.090±0.101 %ID/g. [(18)F]FEL was cleared predominantly by the kidneys. Comparative analysis of autoradiographic images and immunostaining results demonstrated a correlation between [(18)F]FEL binding and HIP/PAP expression.

CONCLUSION

[(18)F]FEL may be useful for non-invasive imaging of early-stage pancreatic tumours by PET. The results warrant further studies.

Convergence of nanotechnology and cancer prevention: are we there yet?

Nanotechnology is emerging as a promising modality for cancer treatment; however, in the realm of cancer prevention, its full utility has yet to be determined. Here, we discuss the potential of integrating nanotechnology in cancer prevention to augment early diagnosis, precision targeting, and controlled release of chemopreventive agents, reduced toxicity, risk/response assessment, and personalized point-of-care monitoring. Cancer is a multistep, progressive disease; the functional and acquired characteristics of the early precancer phenotype are intrinsically different from those of a more advanced anaplastic or invasive malignancy. Therefore, applying nanotechnology to precancers is likely to be far more challenging than applying it to established disease. Frank cancers are more readily identifiable through imaging and biomarker and histopathologic assessment than their precancerous precursors. In addition, prevention subjects routinely have more rigorous intervention criteria than therapy subjects. Any nanopreventive agent developed to prevent sporadic cancers found in the general population must exhibit a very low risk of serious side effects. In contrast, a greater risk of side effects might be more acceptable in subjects at high risk for cancer. Using nanotechnology to prevent cancer is an aspirational goal, but clearly identifying the intermediate objectives and potential barriers is an essential first step in this exciting journey.

Cell surface lactate receptor GPR81 is crucial for cancer cell survival

The mechanisms that allow cancer cells to adapt to the typical tumor microenvironment of low oxygen and glucose and high lactate are not well understood. GPR81 is a lactate receptor recently identified in adipose and muscle cells that has not been investigated in cancer. In the current study, we examined GPR81 expression and function in cancer cells. We found that GPR81 was present in colon, breast, lung, hepatocellular, salivary gland, cervical, and pancreatic carcinoma cell lines. Examination of tumors resected from patients with pancreatic cancer indicated that 94% (148 of 158) expressed high levels of GPR81. Functionally, we observed that the reduction of GPR81 levels using shRNA-mediated silencing had little effect on pancreatic cancer cells cultured in high glucose, but led to the rapid death of cancer cells cultured in conditions of low glucose supplemented with lactate. We also observed that lactate addition to culture media induced the expression of genes involved in lactate metabolism, including monocarboxylase transporters in control, but not in GPR81-silenced cells. In vivo, GPR81 expression levels correlated with the rate of pancreatic cancer tumor growth and metastasis. Cells in which GPR81 was silenced showed a dramatic decrease in growth and metastasis. Implantation of cancer cells in vivo was also observed to lead to greatly elevated levels of GPR81. These data support that GPR81 is important for cancer cell regulation of lactate transport mechanisms. Furthermore, lactate transport is important for the survival of cancer cells in the tumor microenvironment. Cancer Res; 74(18); 5301-10. ©2014 AACR.

A high-fat diet activates oncogenic Kras and COX2 to induce development of pancreatic ductal adenocarcinoma in mice

BACKGROUND & AIMS

Obesity is a risk factor for pancreatic ductal adenocarcinoma (PDAC), but it is not clear how obesity contributes to pancreatic carcinogenesis. The oncogenic form of KRAS is expressed during early stages of PDAC development and is detected in almost all of these tumors. However, there is evidence that mutant KRAS requires an additional stimulus to activate its full oncogenic activity and that this stimulus involves the inflammatory response. We investigated whether the inflammation induced by a high-fat diet, and the accompanying up-regulation of cyclooxygenase-2 (COX2), increases Kras activity during pancreatic carcinogenesis in mice.

METHODS

We studied mice with acinar cell-specific expression of KrasG12D (LSL-Kras/Ela-CreERT mice) alone or crossed with COX2 conditional knockout mice (COXKO/LSL-Kras/Ela-CreERT). We also studied LSL-Kras/PDX1-Cre mice. All mice were fed isocaloric diets with different amounts of fat, and a COX2 inhibitor was administered to some LSL-Kras/Ela-CreERT mice. Pancreata were collected from mice and analyzed for Kras activity, levels of phosphorylated extracellular-regulated kinase, inflammation, fibrosis, pancreatic intraepithelial neoplasia (PanIN), and PDACs.

RESULTS

Pancreatic tissues from LSL-Kras/Ela-CreERT mice fed high-fat diets (HFDs) had increased Kras activity, fibrotic stroma, and numbers of PanINs and PDACs than LSL-Kras/Ela-CreERT mice fed control diets; the mice fed the HFDs also had shorter survival times than mice fed control diets. Administration of a COX2 inhibitor to LSL-Kras/Ela-CreERT mice prevented these effects of HFDs. We also observed a significant reduction in survival times of mice fed HFDs. COXKO/LSL-Kras/Ela-CreERT mice fed HFDs had no evidence for increased numbers of PanIN lesions, inflammation, or fibrosis, as opposed to the increases observed in LSL-Kras/Ela-CreERT mice fed HFDs.

CONCLUSIONS

In mice, an HFD can activate oncogenic Kras via COX2, leading to pancreatic inflammation and fibrosis and development of PanINs and PDAC. This mechanism might be involved in the association between risk for PDAC and HFDs.

Dietary energy balance modulation of Kras- and Ink4a/Arf+/--driven pancreatic cancer: the role of insulin-like growth factor-I

New molecular targets and intervention strategies for breaking the obesity-pancreatic cancer link are urgently needed. Using relevant spontaneous and orthotopically transplanted murine models of pancreatic cancer, we tested the hypothesis that dietary energy balance modulation impacts pancreatic cancer development and progression through an insulin-like growth factor (IGF)-I-dependent mechanism. In LSL-Kras(G12D)/Pdx-1-Cre/Ink4a/Arf(lox/+) mice, calorie restriction versus overweight- or obesity-inducing diet regimens decreased serum IGF-I, tumoral Akt/mTOR signaling, pancreatic desmoplasia, and progression to pancreatic ductal adenocarcinoma (PDAC), and increased pancreatic tumor-free survival. Serum IGF-I, Akt/mTOR signaling, and orthotopically transplanted PDAC growth were decreased in liver-specific IGF-I-deficient mice (vs. wild-type mice), and rescued with IGF-I infusion. Thus, dietary energy balance modulation impacts spontaneous pancreatic tumorigenesis induced by mutant Kras and Ink4a deficiency, the most common genetic alterations in human pancreatic cancer. Furthermore, IGF-I and components of its downstream signaling pathway are promising mechanistic targets for breaking the obesity-pancreatic cancer link.

A novel epigenetic CREB-miR-373 axis mediates ZIP4-induced pancreatic cancer growth

Changes in the intracellular levels of the essential micronutrient zinc have been implicated in multiple diseases including pancreatic cancer; however, the molecular mechanism is poorly understood. Here, we report a novel mechanism where increased zinc mediated by the zinc importer ZIP4 transcriptionally induces miR-373 in pancreatic cancer to promote tumour growth. Reporter, expression and chromatin immunoprecipitation assays demonstrate that ZIP4 activates the zinc-dependent transcription factor CREB and requires this transcription factor to increase miR-373 expression through the regulation of its promoter. miR-373 induction is necessary for efficient ZIP4-dependent enhancement of cell proliferation, invasion, and tumour growth. Further analysis of miR-373 in vivo oncogenic function reveals that it is mediated through its negative regulation of TP53INP1, LATS2 and CD44. These results define a novel ZIP4-CREB-miR-373 signalling axis promoting pancreatic cancer growth, providing mechanistic insights explaining in part how a zinc transporter functions in cancer cells and may have broader implications as inappropriate regulation of intracellular zinc levels plays an important role in many other diseases.

Roles for KRAS in pancreatic tumor development and progression

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.

Dynamic mast cell-stromal cell interactions promote growth of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) exists in a complex desmoplastic microenvironment, which includes cancer-associated fibroblasts [also known as pancreatic stellate cells (PSC)] and immune cells that provide a fibrotic niche that impedes successful cancer therapy. We have found that mast cells are essential for PDAC tumorigenesis. Whether mast cells contribute to the growth of PDAC and/or PSCs is unknown. Here, we tested the hypothesis that mast cells contribute to the growth of PSCs and tumor cells, thus contributing to PDAC development. Tumor cells promoted mast cell migration. Both tumor cells and PSCs stimulated mast cell activation. Conversely, mast cell-derived interleukin (IL)-13 and tryptase stimulated PSC proliferation. Treating tumor-bearing mice with agents that block mast cell migration and function depressed PDAC growth. Our findings suggest that mast cells exacerbate the cellular and extracellular dynamics of the tumor microenvironment found in PDAC. Therefore, targeting mast cells may inhibit stromal formation and improve therapy.

Plectin-1 Targeted AAV Vector for the Molecular Imaging of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is highly malignant disease that is the fourth leading cause of cancer-related death in the US. Gene therapy using AAV vectors to selectively deliver genes to PDAC cells is an attractive treatment option for pancreatic cancer. However, most AAV serotypes display a broad spectrum of tissue tropism and none of the existing serotypes specifically target PDAC cells. This study tests the hypothesis that AAV2 can be genetically re-engineered to specifically target PDAC cells by modifying the capsid surface to display a peptide that has previously been shown to bind plectin-1. Toward this end, a Plectin-1 Targeting Peptide (PTP) was inserted into the loop IV region of the AAV2 capsid, and the resulting capsid (AAV-PTP) was used in a series of in vitro and in vivo experiments. In vitro, AAV-PTP was found to target all five human PDAC cell lines tested (PANC-1, MIA PaCa-2, HPAC, MPanc-96, and BxPC-3) preferentially over two non-neoplastic human pancreatic cell lines (human pancreatic ductal epithelial and human pancreatic stellate cells). In vivo, mice bearing subcutaneous tumor xenografts were generated using the PANC-1 cell line. Once tumors reached a size of ∼1-2 mm in diameter, the mice were injected intravenously with luciferase reporter vectors packaged in the either AAV-PTP or wild type AAV2 capsids. Luciferase expression was then monitored by bioluminescence imaging on days 3, 7, and 14 after vector injection. The results indicate that the AAV-PTP capsid displays a 37-fold preference for PANC-1 tumor xenographs over liver and other tissues; whereas the wild type AAV2 capsid displays a complementary preference for liver over tumors and other tissues. Together, these results establish proof-of-principle for the ability of PTP-modified AAV capsids to selectively target gene delivery to PDAC cells in vivo, which opens promising new avenues for the early detection, diagnosis, and treatment of pancreatic cancer.

Abstract LB-187: Dietary energy balance modulation of Kras- and Ink4a/Arf+/-driven pancreatic cancer: the role of insulin-like growth factor-1

New molecular targets and intervention strategies for breaking the obesity-pancreatic cancer link are urgently needed. Using relevant murine spontaneous and orthotopically transplanted models of pancreatic cancer, we tested the hypothesis that dietary energy balance modulation impacts pancreatic cancer development and progression through an insulin-like growth factor (IGF) 1—dependent mechanism. In LSL-KrasG12D/Pdx-1-Cre/Ink4a/Arflox/+ mice, calorie restriction, versus overweight- or obesity-inducing diet regimens, decreased serum IGF-1, tumoral Akt/mammalian target of rapamycin (mTOR) signaling, pancreatic desmoplasia, and progression to pancreatic ductal adenocarcinoma (PDAC); and increased pancreatic tumor-free survival by 50%. Serum IGF-1, Akt/mTOR signaling, and orthotopically transplanted PDAC growth were decreased in liver-specific IGF-1—deficient mice (versus wild-type mice), and rescued with IGF-1 infusion. Thus, dietary energy balance modulation impacts spontaneous pancreatic tumorigenesis induced by mutant Kras and Ink4a/Arf deficiency, the most common genetic alterations in human pancreatic cancer. Furthermore, IGF-1 and components of its downstream signaling pathway are promising mechanistic targets for breaking the obesity-pancreatic cancer link.

Citation Format: Laura M. Lashinger, Lauren M. Harrison, Audrey J. Rasmussen, Craig D. Logsdon, Susan M. Fischer, Mark J. McArthur, Stephen D. Hursting. Dietary energy balance modulation of Kras- and Ink4a/Arf+/-driven pancreatic cancer: the role of insulin-like growth factor-1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-187. doi:10.1158/1538-7445.AM2013-LB-187

Prostaglandin E2 regulates pancreatic stellate cell activity via the EP4 receptor

OBJECTIVES

Pancreatic stellate cells are source of dense fibrotic stroma, a constant pathological feature of chronic pancreatitis and pancreatic adenocarcinoma. We observed correlation between levels of cyclooxygenase 2 (COX-2) and its product prostaglandin E2 (PGE2) and the extent of pancreatic fibrosis. The aims of this study were to delineate the effects of PGE2 on immortalized human pancreatic stellate cells (HPSCs) and to identify the receptor involved.

METHODS

Immunohistochemistry, reverse transcription-polymerase chain reaction and quantitative reverse transcription-polymerase chain reaction were used to assess COX-2, extracellular matrix, and matrix metalloproteinase gene expression. Eicosanoid profile was determined by liquid chromatography-tandem mass spectrometry. Human pancreatic stellate cell proliferation was assessed by MTS assay, migration by Boyden chamber assay, and invasion using an invasion chamber. Transient silencing was obtained by small interfering RNA.

RESULTS

Human pancreatic stellate cells express COX-2 and synthesize PGE2. Prostaglandin E2 stimulated HPSC proliferation, migration, and invasion and stimulated expression of both extracellular matrix and matrix metalloproteinase genes. Human pancreatic stellate cells expressed all 4 EP receptors. Only blocking the EP4 receptor resulted in abrogation of PGE2-mediated HPSC activation. Specificity of EP4 for the effects of PGE2 on stellate cells was confirmed using specific antagonists.

CONCLUSIONS

Our data indicate that PGE2 regulates pancreatic stellate cell profibrotic activities via EP4 receptor, thus suggesting EP4 receptor as useful therapeutic target for pancreatic cancer to reduce desmoplasia.

Pancreatic cancer-associated Cathepsin E as a drug activator

Pancreatic ductal adenocarcinoma (PDAC) is challenging to treat, and better means to detect and/or treat pancreatic cancer are urgently needed to save lives. Cathepsin E (Cath E) is a proteolytic enzyme highly expressed in PDAC. In this study, a novel approach using Cath E activation of a Cath E-specific prodrug was demonstrated. Specific activation of the prodrug is expected to kill pancreatic cancer cells without harming normal pancreatic cells. A novel 5-aminolevulinic acid (5-ALA) prodrug was custom-designed to be activated selectively by endogenous Cath E within the PDAC cells. The 5-ALA prodrug was incubated with Cath E-positive and -negative tumor cells and illuminated with various doses of light. In addition, mice genetically engineered to develop PDAC were injected intravenously with the 5-ALA prodrug, and the pancreas was treated with light irradiation. One day after treatment, PDAC tissue was assessed for apoptosis. The 5-ALA prodrug was activated within the Cath E-positive tumor but not in the normal pancreatic tissue. When used in combination with light treatment, it allowed delivery of selective photodynamic therapy (PDT) to the cancerous tissues, with minimal harm to the adjacent normal tissues. With this novel Cath E activation approach, it is possible to detect pancreatic cancer cells accurately and specifically impair their viability, while sparing normal cells. This treatment could result in fewer side effects than the non-specific treatments currently in use. Cath E is a specific and effective drug activator for PDAC treatment.

Oncogenic K-Ras requires activation for enhanced activity

Oncogenic Ras mutations are widely considered to be locked in a permanent 'On' state and 'constitutively active'. Yet, many healthy people have cells possessing mutant Ras without apparent harm, and in animal models mutant Ras causes transformation only after upregulation of Ras activity. Here, we demonstrate that oncogenic K-Ras is not constitutively active but can be readily activated by upstream stimulants to lead to prolonged strong Ras activity. These data indicate that in addition to targeting K-Ras downstream effectors, interventions to reduce K-Ras activation may have important cancer-preventive value, especially in patients with oncogenic Ras mutations. As other small G proteins are regulated in a similar manner, this concept is likely to apply broadly to the entire Ras family of molecules.

Designing and developing S100P inhibitor 5-methyl cromolyn for pancreatic cancer therapy

We have previously shown that the antiallergic drug cromolyn blocks S100P interaction with its receptor receptor for advanced glycation end product (RAGE) and improves gemcitabine effectiveness in pancreatic ductal adenocarcinoma (PDAC). However, the concentration required to achieve its effectiveness was high (100 μmol/L). In this study, we designed and synthesized analogs of cromolyn and analyzed their effectiveness compared with the parent molecule. An ELISA was used to confirm the binding of S100P with RAGE and to test the effectiveness of the different analogs. Analog 5-methyl cromolyn (C5OH) blocked S100P binding as well as the increases in NF-κB activity, cell growth, and apoptosis normally caused by S100P. In vivo C5OH systemic delivery reduced NF-κB activity to a greater extent than cromolyn and at 10 times lesser dose (50 mg vs. 5 mg). Treatment of mice-bearing syngeneic PDAC tumors showed that C5OH treatment reduced both tumor growth and metastasis. C5OH treatment of nude mice bearing orthotopic highly aggressive pancreatic Mpanc96 cells increased the overall animal survival. Therefore, the cromolyn analog, C5OH, was found to be more efficient and potent than cromolyn as a therapeutic for PDAC.

Adrenomedullin is up-regulated in patients with pancreatic cancer and causes insulin resistance in β cells and mice

BACKGROUND & AIMS

New-onset diabetes in patients with pancreatic cancer is likely to be a paraneoplastic phenomenon caused by tumor-secreted products. We aimed to identify the diabetogenic secretory product(s) of pancreatic cancer.

METHODS

Using microarray analysis, we identified adrenomedullin as a potential mediator of diabetes in patients with pancreatic cancer. Adrenomedullin was up-regulated in pancreatic cancer cell lines, in which supernatants reduced insulin signaling in beta cell lines. We performed quantitative reverse-transcriptase polymerase chain reaction and immunohistochemistry on human pancreatic cancer and healthy pancreatic tissues (controls) to determine expression of adrenomedullin messenger RNA and protein, respectively. We studied the effects of adrenomedullin on insulin secretion by beta cell lines and whole islets from mice and on glucose tolerance in pancreatic xenografts in mice. We measured plasma levels of adrenomedullin in patients with pancreatic cancer, patients with type 2 diabetes mellitus, and individuals with normal fasting glucose levels (controls).

RESULTS

Levels of adrenomedullin messenger RNA and protein were increased in human pancreatic cancer samples compared with controls. Adrenomedullin and conditioned media from pancreatic cell lines inhibited glucose-stimulated insulin secretion from beta cell lines and islets isolated from mice; the effects of conditioned media from pancreatic cancer cells were reduced by small hairpin RNA-mediated knockdown of adrenomedullin. Conversely, overexpression of adrenomedullin in mice with pancreatic cancer led to glucose intolerance. Mean plasma levels of adrenomedullin (femtomoles per liter) were higher in patients with pancreatic cancer compared with patients with diabetes or controls. Levels of adrenomedullin were higher in patients with pancreatic cancer who developed diabetes compared those who did not.

CONCLUSIONS

Adrenomedullin is up-regulated in patients with pancreatic cancer and causes insulin resistance in β cells and mice.

Study human pancreatic cancer in mice: how close are they?

Pancreatic cancer is the fourth leading cause of cancer deaths and is characterized by dismal prognosis. Xenograft and genetically engineered mouse (GEM) models have recapitulated critical elements of human pancreatic cancer, providing useful tools to probe the underlying cause of cancer etiology. In this review, we provide a brief description of the common genetic lesions that occur during the development of pancreatic cancer. Next, we describe the strengths and weaknesses of these two models and highlight key discoveries each has made. Although the relative merits of GEM and xenograft pancreatic cancer mouse models are subject to debate, both systems have and will continue to yield essential insights in understanding pancreatic cancer etiology. This information is critical for the development of new methods to screen, treat, and prevent pancreatic cancer.

Abstract B113: High Fat Diet Accelerates Development of Precancerous Lesions and Fibrosis in Mice Expressing mutant K-Ras in Pancreatic Acinar Cells

Background: Obesity is postulated to be a major risk factor for pancreatic ductal carcinoma (PDAC), which is the fourth deadliest cancer in the US. Although the association between obesity and pancreatic cancer has been reported, the molecular mechanisms are not yet known. Since K-Ras mutations are almost universal in PDAC, and we have recently shown that endogenous levels of oncogenic K-Ras make cells susceptible to otherwise benign levels of inflammation, we hypothesize that high fat intake can act as a persistent low level inflammatory mechanism capable of inducing PDAC in cells expressing a single copy of oncogenic K-Ras. In the current study, we examined the effects of high dietary fat on the development of precancerous lesions and fibrosis, as well as the activation of K-Ras signaling pathways in mice expressing mutant K-Ras in pancreatic acinar cells.

Methods: Transgenic mice LSL-K-Ras were cross with Ela-CreER (Pancreatic-Ras) and treated with tamoxifen to “knock-in” oncogenic K-Ras in adult pancreatic acinar cells. Pancreatic-Ras and littermate control mice were administered a low fat diet with 10.2% kcal fat or a high fat diet with 61.6% kcal fat for 30 days starting at 50 days of age. Mice were then sacrificed and analyzed histologically for fibrosis development, presence of precancerous lesions, and activation of K-Ras signaling pathways.

Results: Mice expressing endogenous levels of oncogenic K-Ras and fed a high fat diet developed abundant fibrosis, low grade precancerous lesions throughout the pancreas and had higher levels of phospho-ERK when compared to littermate controls and mice fed a low fat diet.

Conclusions: These findings suggest that consumption of high dietary fat acts as an inflammatory stimulus that enhances the activation of oncogenic K-Ras downstream signaling pathways, leading to the early development of precancerous lesions and fibrosis in the pancreas. Therefore, efforts aimed at inhibiting inflammation and K-Ras activation would be expected to prevent cancer development.

Citation Format: Zobeida Cruz-Monserrate, Bincy Philips, Baoan Ji, Jaroslaw Daniluk, Craig D. Logsdon. High-fat diet accelerates development of precancerous lesions and fibrosis in mice expressing mutant K-Ras in pancreatic acinar cells. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B113.

Detection of pancreatic cancer tumours and precursor lesions by cathepsin E activity in mouse models

BACKGROUND AND AIMS

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in the USA. Surgical resection is the only effective treatment; however, only 20% of patients are candidates for surgery. The ability to detect early PDAC would increase the availability of surgery and improve patient survival. This study assessed the feasibility of using the enzymatic activity of cathepsin E (Cath E), a protease highly and specifically expressed in PDAC, as a novel biomarker for the detection of pancreas-bearing pancreatic intraepithelial neoplasia (PanIN) lesions and PDAC.

METHODS

Pancreas from normal, chronic pancreatitis and PDAC patients was assessed for Cath E expression by quantitative real-time PCR and immunohistochemistry. Human PDAC xenografts and genetically engineered mouse models (GEMM) of PDAC were injected with a Cath E activity selective fluorescent probe and imaged using an optical imaging system.

RESULTS

The specificity of Cath E expression in PDAC patients and GEMM of pancreatic cancer was confirmed by quantitative real-time PCR and immunohistochemistry. The novel probe for Cath E activity specifically detected PDAC in both human xenografts and GEMM in vivo. The Cath E sensitive probe was also able to detect pancreas with PanIN lesions in GEMM before tumour formation.

CONCLUSIONS

The elevated Cath E expression in PanIN and pancreatic tumours allowed in-vivo detection of human PDAC xenografts and imaging of pancreas with PanIN and PDAC tumours in GEMM. Our results support the usefulness of Cath E activity as a potential molecular target for PDAC and early detection imaging.

Inhibition of the hedgehog pathway targets the tumor-associated stroma in pancreatic cancer

PURPOSE

The Hedgehog (Hh) pathway has emerged as an important pathway in multiple tumor types and is thought to be dependent on a paracrine signaling mechanism. The purpose of this study was to determine the role of pancreatic cancer-associated fibroblasts (human pancreatic stellate cells, HPSCs) in Hh signaling. In addition, we evaluated the efficacy of a novel Hh antagonist, AZD8542, on tumor progression with an emphasis on the role of the stroma compartment.

EXPERIMENTAL DESIGN

Expression of Hh pathway members and activation of the Hh pathway were analyzed in both HPSCs and pancreatic cancer cells. We tested the effects of Smoothened (SMO) inhibition with AZD8542 on tumor growth in vivo using an orthotopic model of pancreatic cancer containing varying amounts of stroma.

RESULTS

HPSCs expressed high levels of SMO receptor and low levels of Hh ligands, whereas cancer cells showed the converse expression pattern. HPSC proliferation was stimulated by Sonic Hedgehog with upregulation of downstream GLI1 mRNA. These effects were abrogated by AZD8542 treatment. In an orthotopic model of pancreatic cancer, AZD8542 inhibited tumor growth only when HPSCs were present, implicating a paracrine signaling mechanism dependent on stroma. Further evidence of paracrine signaling of the Hh pathway in prostate and colon cancer models is provided, demonstrating the broader applicability of our findings.

CONCLUSION

Based on the use of our novel human-derived pancreatic cancer stellate cells, our results suggest that Hh-targeted therapies primarily affect the tumor-associated stroma, rather than the epithelial compartment.

Met receptor tyrosine kinase signaling induces secretion of the angiogenic chemokine interleukin-8/CXCL8 in pancreatic cancer

At diagnosis, the majority of pancreatic cancer patients present with advanced disease when curative resection is no longer feasible and current therapeutic treatments are largely ineffective. An improved understanding of molecular targets for effective intervention of pancreatic cancer is thus urgent. The Met receptor tyrosine kinase is one candidate implicated in pancreatic cancer. Notably, Met is over expressed in up to 80% of invasive pancreatic cancers but not in normal ductal cells correlating with poor overall patient survival and increased recurrence rates following surgical resection. However the functional role of Met signaling in pancreatic cancer remains poorly understood. Here we used RNA interference to directly examine the pathobiological importance of increased Met signaling for pancreatic cancer. We show that Met knockdown in pancreatic tumor cells results in decreased cell survival, cell invasion, and migration on collagen I in vitro. Using an orthotopic model for pancreatic cancer, we provide in vivo evidence that Met knockdown reduced tumor burden correlating with decreased cell survival and tumor angiogenesis, with minimal effect on cell growth. Notably, we report that Met signaling regulates the secretion of the pro-angiogenic chemokine interleukin-8/CXCL8. Our data showing that the interleukin-8 receptors CXCR1 and CXCR2 are not expressed on pancreatic tumor cells, suggests a paracrine mechanism by which Met signaling regulates interleukin-8 secretion to remodel the tumor microenvironment, a novel finding that could have important clinical implications for improving the effectiveness of treatments for pancreatic cancer.

S100P-derived RAGE antagonistic peptide reduces tumor growth and metastasis

PURPOSE

The receptor for advanced glycation end products (RAGE) contributes to multiple pathologies, including diabetes, arthritis, neurodegenerative diseases, and cancer. Despite the obvious need, no RAGE inhibitors are in common clinical use. Therefore, we developed a novel small RAGE antagonist peptide (RAP) that blocks activation by multiple ligands.

EXPERIMENTAL DESIGN

RAGE and its ligands were visualized by immunohistochemical analysis of human pancreatic tissues, and siRNA was used to analyze their functions. Interactions between RAGE and S100P, S100A4, and HMGB-1 were measured by ELISA. Three S100P-derived small antagonistic peptides were designed, synthesized, and tested for inhibition of RAGE binding. The effects of the peptide blockers on NFκB-luciferase reporter activity was used to assess effects on RAGE-mediated signaling. The most effective peptide was tested on glioma and pancreatic ductal adenocarcinoma (PDAC) models.

RESULTS

Immunohistochemical analysis confirmed the expression of RAGE and its ligands S100P, S100A4, and HMGB-1 in human PDAC. siRNA silencing of RAGE or its ligands reduced the growth and migration of PDAC cells in vitro. The most effective RAP inhibited the interaction of S100P, S100A4, and HMGB-1 with RAGE at micromolar concentrations. RAP also reduced the ability of the ligands to stimulate RAGE activation of NFκB in cancer cells in vitro and in vivo. Importantly, systemic in vivo administration of RAP reduced the growth and metastasis of pancreatic tumors and also inhibited glioma tumor growth.

CONCLUSION

RAP shows promise as a tool for the investigation of RAGE function and as an in vivo treatment for RAGE-related disorders.

Abstract LB-425: An NF-κB pathway mediated positive feedback loop amplifies Ras activity to pathological levels in mice

Elevated Ras activity is critical for Ras induced tumorigenesis. However, the underlying mechanisms that lead to pathological levels of Ras activity are unclear. Here, we found that stimulation of Ras signaling by typical inflammatory stimuli was transient and had no long term sequelae in wild-type mice. In contrast, these stimuli generated prolonged Ras signaling and led to chronic inflammation and precancerous lesions (PanINs) in mice expressing endogenous levels of oncogenic K-Ras. The effects of inflammatory stimuli on oncogenic Ras expressing mice were disrupted by deleting IKK2 or inhibiting Cox-2. Likewise, the expression of active IKK2 or Cox-2, or treatments with LPS generated chronic inflammation and PanINs only in mice expressing oncogenic Ras. The data support that in the presence of oncogenic Ras, inflammatory stimuli trigger an NF-κB mediated positive feedback mechanism involving Cox-2 that amplifies Ras activity to pathological levels. Because a large portion of the adult human population possesses Ras mutations in tissues including colon, pancreas, and lung, disruption of this positive feedback loop may be an important strategy for cancer prevention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-425. doi:1538-7445.AM2012-LB-425

Abstract LB-504: Mast cell cytokines stimulate cancer-associated fibroblasts proliferation and promote pancreatic cancer progression

Objectives: Pancreatic ductal adenocarcinoma (PDAC) is a uniformly lethal disease and is notoriously resistant to most therapies. In patients, cancer cells exist in a complex microenvironment containing cancer-associated fibroblasts (pancreatic stellate cells, PSCs) and immune cells. These components provide a fibrotic niche that is an impediment to successful therapy. In our preliminary studies, we found that mast cells infiltrated at the tumor margin. This high infiltration of human mast cells into the tumor microenvironment was associated with poor survival. Mast cells were found to be essential to PDAC tumorigenesis in a mast cell-deficient Kitw-sh/w-sh mouse model compared to control mice. In addition, when we treated tumor-bearing mice with cromolyn, a mast cell stabilizer, tumor growth was depressed. How mast cells regulate the tumor microenvironment and contribute to PDAC tumorigenesis are unknown. We hypothesized that mast cell cytokines mediate cancer-associated fibroblasts proliferation that promotes PDAC progression. Methods: We measured mast cell infiltration in 16 normal human pancreas (NP), 26 pancreatic intraepithelial lesions (PanINs), and 25 PDAC patients’ tissue samples. In an in vitro co-culture system, we measured the crosstalk of human mast cells, PDAC cells, and PSCs. The effect of mast cell cytokine release on PDAC and PSC proliferation and migration was measured using conditioned medium. To determine the role of IL-1β, IL-13, and tryptase on PDAC and PSC proliferations, neutralizing antibodies were used. To determine whether inhibiting mast cell degranulation and cytokine production has a therapeutic effect in vivo, we treated tumor-bearing mice with masitinib, which is a tyrosine kinase inhibitor targeting c-KIT. Tumor sizes were measured by bioluminescence imaging. Results: Mast cell infiltration was associated with human malignancy progression (NP → PanIN, P &gt; 0.05; PanIN → PDAC, P &lt; 0.001), which was consistent with tryptase expression pattern in a spontaneous PDAC mouse model. In vitro, tumor cells promoted mast cell migration (P &lt; 0.05). PDAC cells and PSCs stimulated mast cell activation, as measured by degranulation and tryptase release (P &lt; 0.05). Conversely, mast cell-derived IL-13 stimulated PDAC proliferation (P &lt; 0.001). Strikingly, IL-1β, tryptase, or IL-13 from mast cells promoted PSC proliferation. In vivo, PDAC growth was significantly reduced by masitinib (P &lt; 0.01 vs saline control) in tumor-bearing mice. Conclusions: Mast cells promote PDAC progression. Tumor cells promote mast cell activation and migration to the tumor site. Once there, mast cell cytokines activate proliferation of both tumor cells and fibroblasts, potentially contributing to the fibrotic microenvironment found in PDAC. Therefore, therapy targeting mast cells cytokines, IL-1β, tryptase, or IL-13, may overcome stromal formation and improve PDAC therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-504. doi:1538-7445.AM2012-LB-504