Glucose-6-phosphate dehydrogenase deficiency accelerates pancreatic acinar-to-ductal metaplasia

Activating mutations in KRAS extensively reprogram cellular metabolism to support the continuous growth, proliferation, and survival of pancreatic tumors. Targeting these metabolic dependencies are promising approaches for the treatment of established tumors. However, metabolic reprogramming is required early during tumorigenesis to provide transformed cells selective advantage towards malignancy. Acinar cells can give rise to pancreatic tumors through acinar-to-ductal metaplasia (ADM). Dysregulation of pathways that maintain acinar homeostasis accelerate tumorigenesis. During ADM, acinar cells transdifferentiate to duct-like cells, a process driven by oncogenic KRAS. The metabolic reprogramming that is required for the transdifferentiation in ADM is unclear. We performed transcriptomic analysis on mouse acinar cells undergoing ADM and found metabolic programs are globally enhanced, consistent with the transition of a specialized cell to a less differentiated phenotype with proliferative potential. Indeed, we and others have demonstrated how inhibiting metabolic pathways necessary for ADM can prevent transdifferentiation and tumorigenesis. Here, we also find NRF2-target genes are differentially expressed during ADM. Among these, we focused on the increase in the gene coding for NADPH-producing enzyme, Glucose-6-phosphate dehydrogenase (G6PD). Using established mouse models of KrasG12D-driven pancreatic tumorigenesis and G6PD-deficiency, we find that mutant G6pd accelerates ADM and pancreatic intraepithelial neoplasia. Acceleration of cancer initiation with G6PD-deficiency is dependent on its NADPH-generating function in reactive oxygen species (ROS) management, as opposed to other outputs of the pentose phosphate pathway. Together, this work provides new insights into the function of metabolic pathways during early tumorigenesis.

Uridine-derived ribose fuels glucose-restricted pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a lethal disease notoriously resistant to therapy1,2. This is mediated in part by a complex tumour microenvironment3, low vascularity4, and metabolic aberrations5,6. Although altered metabolism drives tumour progression, the spectrum of metabolites used as nutrients by PDA remains largely unknown. Here we identified uridine as a fuel for PDA in glucose-deprived conditions by assessing how more than 175 metabolites impacted metabolic activity in 21 pancreatic cell lines under nutrient restriction. Uridine utilization strongly correlated with the expression of uridine phosphorylase 1 (UPP1), which we demonstrate liberates uridine-derived ribose to fuel central carbon metabolism and thereby support redox balance, survival and proliferation in glucose-restricted PDA cells. In PDA, UPP1 is regulated by KRAS-MAPK signalling and is augmented by nutrient restriction. Consistently, tumours expressed high UPP1 compared with non-tumoural tissues, and UPP1 expression correlated with poor survival in cohorts of patients with PDA. Uridine is available in the tumour microenvironment, and we demonstrated that uridine-derived ribose is actively catabolized in tumours. Finally, UPP1 deletion restricted the ability of PDA cells to use uridine and blunted tumour growth in immunocompetent mouse models. Our data identify uridine utilization as an important compensatory metabolic process in nutrient-deprived PDA cells, suggesting a novel metabolic axis for PDA therapy.

Pancreatic cancer: Advances and challenges

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers. Significant efforts have largely defined major genetic factors driving PDAC pathogenesis and progression. Pancreatic tumors are characterized by a complex microenvironment that orchestrates metabolic alterations and supports a milieu of interactions among various cell types within this niche. In this review, we highlight the foundational studies that have driven our understanding of these processes. We further discuss the recent technological advances that continue to expand our understanding of PDAC complexity. We posit that the clinical translation of these research endeavors will enhance the currently dismal survival rate of this recalcitrant disease.

Arginase 1 is a key driver of immune suppression in pancreatic cancer

An extensive fibroinflammatory stroma rich in macrophages is a hallmark of pancreatic cancer. In this disease, it is well appreciated that macrophages are immunosuppressive and contribute to the poor response to immunotherapy; however, the mechanisms of immune suppression are complex and not fully understood. Immunosuppressive macrophages are classically defined by the expression of the enzyme Arginase 1 (ARG1), which we demonstrated is potently expressed in pancreatic tumor-associated macrophages from both human patients and mouse models. While routinely used as a polarization marker, ARG1 also catabolizes arginine, an amino acid required for T cell activation and proliferation. To investigate this metabolic function, we used a genetic and a pharmacologic approach to target Arg1 in pancreatic cancer. Genetic inactivation of Arg1 in macrophages, using a dual recombinase genetically engineered mouse model of pancreatic cancer, delayed formation of invasive disease, while increasing CD8+ T cell infiltration. Additionally, Arg1 deletion induced compensatory mechanisms, including Arg1 overexpression in epithelial cells, namely Tuft cells, and Arg2 overexpression in a subset of macrophages. To overcome these compensatory mechanisms, we used a pharmacological approach to inhibit arginase. Treatment of established tumors with the arginase inhibitor CB-1158 exhibited further increased CD8+ T cell infiltration, beyond that seen with the macrophage-specific knockout, and sensitized the tumors to anti-PD1 immune checkpoint blockade. Our data demonstrate that Arg1 drives immune suppression in pancreatic cancer by depleting arginine and inhibiting T cell activation.

Barriers and opportunities for gemcitabine in pancreatic cancer therapy

Pancreatic ductal adenocarcinoma (PDA) has become one of the leading causes of cancer-related deaths across the world. A lack of durable responses to standard-of-care chemotherapies renders its treatment particularly challenging and largely contributes to the devastating outcome. Gemcitabine, a pyrimidine antimetabolite, is a cornerstone in PDA treatment. Given the importance of gemcitabine in PDA therapy, extensive efforts are focusing on exploring mechanisms by which cancer cells evade gemcitabine cytotoxicity, but strategies to overcome them have not been translated into patient care. Here, we will introduce the standard treatment paradigm for patients with PDA, highlight mechanisms of gemcitabine action, elucidate gemcitabine resistance mechanisms, and discuss promising strategies to circumvent them.

An Optimized Enzyme-Nucleobase Pair Enables In Vivo RNA Metabolic Labeling with Improved Cell-Specificity

Current transcriptome-wide analyses have identified a growing number of regulatory RNA with expression that is characterized in a cell-type-specific manner. Herein, we describe RNA metabolic labeling with improved cell-specificity utilizing the in vivo expression of an optimized uracil phosphoribosyltransferase (UPRT) enzyme. We demonstrate improved selectivity for metabolic incorporation of a modified nucleobase (5-vinyuracil) into nascent RNA, using a battery of tests. The selective incorporation of vinyl-U residues was demonstrated in 3xUPRT LM2 cells through validation with dot blot, qPCR, LC-MS/MS and microscopy analysis. We also report using this approach in a metastatic human breast cancer mouse model for profiling cell-specific nascent RNA.

Differential integrated stress response and asparagine production drive symbiosis and therapy resistance of pancreatic adenocarcinoma cells

The pancreatic tumor microenvironment drives deregulated nutrient availability. Accordingly, pancreatic cancer cells require metabolic adaptations to survive and proliferate. Pancreatic cancer subtypes have been characterized by transcriptional and functional differences, with subtypes reported to exist within the same tumor. However, it remains unclear if this diversity extends to metabolic programming. Here, using metabolomic profiling and functional interrogation of metabolic dependencies, we identify two distinct metabolic subclasses among neoplastic populations within individual human and mouse tumors. Furthermore, these populations are poised for metabolic cross-talk, and in examining this, we find an unexpected role for asparagine supporting proliferation during limited respiration. Constitutive GCN2 activation permits ATF4 signaling in one subtype, driving excess asparagine production. Asparagine release provides resistance during impaired respiration, enabling symbiosis. Functionally, availability of exogenous asparagine during limited respiration indirectly supports maintenance of aspartate pools, a rate-limiting biosynthetic precursor. Conversely, depletion of extracellular asparagine with PEG-asparaginase sensitizes tumors to mitochondrial targeting with phenformin.

Metabolic requirement for GOT2 in pancreatic cancer depends on environmental context

Mitochondrial glutamate-oxaloacetate transaminase 2 (GOT2) is part of the malate-aspartate shuttle, a mechanism by which cells transfer reducing equivalents from the cytosol to the mitochondria. GOT2 is a key component of mutant KRAS (KRAS*)-mediated rewiring of glutamine metabolism in pancreatic ductal adenocarcinoma (PDA). Here, we demonstrate that the loss of GOT2 disturbs redox homeostasis and halts proliferation of PDA cells in vitro. GOT2 knockdown (KD) in PDA cell lines in vitro induced NADH accumulation, decreased Asp and α-ketoglutarate (αKG) production, stalled glycolysis, disrupted the TCA cycle, and impaired proliferation. Oxidizing NADH through chemical or genetic means resolved the redox imbalance induced by GOT2 KD, permitting sustained proliferation. Despite a strong in vitro inhibitory phenotype, loss of GOT2 had no effect on tumor growth in xenograft PDA or autochthonous mouse models. We show that cancer-associated fibroblasts (CAFs), a major component of the pancreatic tumor microenvironment (TME), release the redox active metabolite pyruvate, and culturing GOT2 KD cells in CAF conditioned media (CM) rescued proliferation in vitro. Furthermore, blocking pyruvate import or pyruvate-to-lactate reduction prevented rescue of GOT2 KD in vitro by exogenous pyruvate or CAF CM. However, these interventions failed to sensitize xenografts to GOT2 KD in vivo, demonstrating the remarkable plasticity and differential metabolism deployed by PDA cells in vitro and in vivo. This emphasizes how the environmental context of distinct pre-clinical models impacts both cell-intrinsic metabolic rewiring and metabolic crosstalk with the TME.

Multiomic characterization of pancreatic cancer-associated macrophage polarization reveals deregulated metabolic programs driven by the GM-CSF-PI3K pathway

The pancreatic ductal adenocarcinoma microenvironment is composed of a variety of cell types and marked by extensive fibrosis and inflammation. Tumor-associated macrophages (TAMs) are abundant, and they are important mediators of disease progression and invasion. TAMs are polarized in situ to a tumor promoting and immunosuppressive phenotype via cytokine signaling and metabolic crosstalk from malignant epithelial cells and other components of the tumor microenvironment. However, the specific distinguishing features and functions of TAMs remain poorly defined. Here, we generated tumor-educated macrophages (TEMs) in vitro and performed detailed, multiomic characterization (i.e., transcriptomics, proteomics, metabolomics). Our results reveal unique genetic and metabolic signatures of TEMs, the veracity of which were queried against our in-house single-cell RNA sequencing dataset of human pancreatic tumors. This analysis identified expression of novel, metabolic TEM markers in human pancreatic TAMs, including ARG1, ACLY, and TXNIP. We then utilized our TEM model system to study the role of mutant Kras signaling in cancer cells on TEM polarization. This revealed an important role for granulocyte–macrophage colony-stimulating factor (GM-CSF) and lactate on TEM polarization, molecules released from cancer cells in a mutant Kras-dependent manner. Lastly, we demonstrate that GM-CSF dysregulates TEM gene expression and metabolism through PI3K–AKT pathway signaling. Collectively, our results define new markers and programs to classify pancreatic TAMs, how these are engaged by cancer cells, and the precise signaling pathways mediating polarization.

Hyaluronic acid fuels pancreatic cancer cell growth

Rewired metabolism is a hallmark of pancreatic ductal adenocarcinomas (PDA). Previously, we demonstrated that PDA cells enhance glycosylation precursor biogenesis through the hexosamine biosynthetic pathway (HBP) via activation of the rate limiting enzyme, glutamine-fructose 6-phosphate amidotransferase 1 (GFAT1). Here, we genetically ablated GFAT1 in human PDA cell lines, which completely blocked proliferation in vitro and led to cell death. In contrast, GFAT1 knockout did not preclude the growth of human tumor xenografts in mice, suggesting that cancer cells can maintain fidelity of glycosylation precursor pools by scavenging nutrients from the tumor microenvironment. We found that hyaluronic acid (HA), an abundant carbohydrate polymer in pancreatic tumors composed of repeating N-acetyl-glucosamine (GlcNAc) and glucuronic acid sugars, can bypass GFAT1 to refuel the HBP via the GlcNAc salvage pathway. Together, these data show HA can serve as a nutrient fueling PDA metabolism beyond its previously appreciated structural and signaling roles.

Asparagine couples mitochondrial respiration to ATF4 activity and tumor growth

Mitochondrial respiration is critical for cell proliferation. In addition to producing ATP, respiration generates biosynthetic precursors, such as aspartate, an essential substrate for nucleotide synthesis. Here, we show that in addition to depleting intracellular aspartate, electron transport chain (ETC) inhibition depletes aspartate-derived asparagine, increases ATF4 levels, and impairs mTOR complex I (mTORC1) activity. Exogenous asparagine restores proliferation, ATF4 and mTORC1 activities, and mTORC1-dependent nucleotide synthesis in the context of ETC inhibition, suggesting that asparagine communicates active respiration to ATF4 and mTORC1. Finally, we show that combination of the ETC inhibitor metformin, which limits tumor asparagine synthesis, and either asparaginase or dietary asparagine restriction, which limit tumor asparagine consumption, effectively impairs tumor growth in multiple mouse models of cancer. Because environmental asparagine is sufficient to restore tumor growth in the context of respiration impairment, our findings suggest that asparagine synthesis is a fundamental purpose of tumor mitochondrial respiration, which can be harnessed for therapeutic benefit to cancer patients.

Inhibition of Hedgehog Signaling Alters Fibroblast Composition in Pancreatic Cancer

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSIONS

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

Purine metabolism regulates DNA repair and therapy resistance in glioblastoma

Intratumoral genomic heterogeneity in glioblastoma (GBM) is a barrier to overcoming therapy resistance. Treatments that are effective independent of genotype are urgently needed. By correlating intracellular metabolite levels with radiation resistance across dozens of genomically-distinct models of GBM, we find that purine metabolites, especially guanylates, strongly correlate with radiation resistance. Inhibiting GTP synthesis radiosensitizes GBM cells and patient-derived neurospheres by impairing DNA repair. Likewise, administration of exogenous purine nucleosides protects sensitive GBM models from radiation by promoting DNA repair. Neither modulating pyrimidine metabolism nor purine salvage has similar effects. An FDA-approved inhibitor of GTP synthesis potentiates the effects of radiation in flank and orthotopic patient-derived xenograft models of GBM. High expression of the rate-limiting enzyme of de novo GTP synthesis is associated with shorter survival in GBM patients. These findings indicate that inhibiting purine synthesis may be a promising strategy to overcome therapy resistance in this genomically heterogeneous disease.

Targeting genotype-independent abnormalities may overcome therapy resistance in glioblastoma despite intratumoral genomic heterogeneity. Here, the authors show that glioblastoma radiation resistance is promoted by purine metabolism and can be overcome by inhibitors of purine synthesis.

Endoplasmic reticulum-associated degradation regulates mitochondrial dynamics in brown adipocytes

The endoplasmic reticulum (ER) engages mitochondria at specialized ER domains known as mitochondria-associated membranes (MAMs). Here, we used three-dimensional high-resolution imaging to investigate the formation of pleomorphic "megamitochondria" with altered MAMs in brown adipocytes lacking the Sel1L-Hrd1 protein complex of ER-associated protein degradation (ERAD). Mice with ERAD deficiency in brown adipocytes were cold sensitive and exhibited mitochondrial dysfunction. ERAD deficiency affected ER-mitochondria contacts and mitochondrial dynamics, at least in part, by regulating the turnover of the MAM protein, sigma receptor 1 (SigmaR1). Thus, our study provides molecular insights into ER-mitochondrial cross-talk and expands our understanding of the physiological importance of Sel1L-Hrd1 ERAD.

Regulatory T-cell Depletion Alters the Tumor Microenvironment and Accelerates Pancreatic Carcinogenesis

Regulatory T cells (Treg) are abundant in human and mouse pancreatic cancer. To understand the contribution to the immunosuppressive microenvironment, we depleted Tregs in a mouse model of pancreatic cancer. Contrary to our expectations, Treg depletion failed to relieve immunosuppression and led to accelerated tumor progression. We show that Tregs are a key source of TGFβ ligands and, accordingly, their depletion reprogramed the fibroblast population, with loss of tumor-restraining, smooth muscle actin-expressing fibroblasts. Conversely, we observed an increase in chemokines Ccl3, Ccl6, and Ccl8 leading to increased myeloid cell recruitment, restoration of immune suppression, and promotion of carcinogenesis, an effect that was inhibited by blockade of the common CCL3/6/8 receptor CCR1. Further, Treg depletion unleashed pathologic CD4+ T-cell responses. Our data point to new mechanisms regulating fibroblast differentiation in pancreatic cancer and support the notion that fibroblasts are a heterogeneous population with different and opposing functions in pancreatic carcinogenesis. SIGNIFICANCE: Here, we describe an unexpected cross-talk between Tregs and fibroblasts in pancreatic cancer. Treg depletion resulted in differentiation of inflammatory fibroblast subsets, in turn driving infiltration of myeloid cells through CCR1, thus uncovering a potentially new therapeutic approach to relieve immunosuppression in pancreatic cancer.See related commentary by Aykut et al., p. 345.This article is highlighted in the In This Issue feature, p. 327.

Tissue of origin dictates GOT1 dependence and confers synthetic lethality to radiotherapy

BACKGROUND

Metabolic programs in cancer cells are influenced by genotype and the tissue of origin. We have previously shown that central carbon metabolism is rewired in pancreatic ductal adenocarcinoma (PDA) to support proliferation through a glutamate oxaloacetate transaminase 1 (GOT1)-dependent pathway.

METHODS

We utilized a doxycycline-inducible shRNA-mediated strategy to knockdown GOT1 in PDA and colorectal cancer (CRC) cell lines and tumor models of similar genotype. These cells were analyzed for the ability to form colonies and tumors to test if tissue type impacted GOT1 dependence. Additionally, the ability of GOT1 to impact the response to chemo- and radiotherapy was assessed. Mechanistically, the associated specimens were examined using a combination of steady-state and stable isotope tracing metabolomics strategies and computational modeling. Statistics were calculated using GraphPad Prism 7. One-way ANOVA was performed for experiments comparing multiple groups with one changing variable. Student's t test (unpaired, two-tailed) was performed when comparing two groups to each other. Metabolomics data comparing three PDA and three CRC cell lines were analyzed by performing Student's t test (unpaired, two-tailed) between all PDA metabolites and CRC metabolites.

RESULTS

While PDA exhibits profound growth inhibition upon GOT1 knockdown, we found CRC to be insensitive. In PDA, but not CRC, GOT1 inhibition disrupted glycolysis, nucleotide metabolism, and redox homeostasis. These insights were leveraged in PDA, where we demonstrate that radiotherapy potently enhanced the effect of GOT1 inhibition on tumor growth.

CONCLUSIONS

Taken together, these results illustrate the role of tissue type in dictating metabolic dependencies and provide new insights for targeting metabolism to treat PDA.

Metabolism Drives Carcinogenesis and Maintenance of Pancreatic Tumors

In this issue of Cancer Discovery, Carrer and colleagues find that early events in pancreatic tumorigenesis are driven by altered acetyl-CoA metabolism, where targeting this axis in established cancer models impairs tumor growth. This work provides new insights into the roles of acetyl-CoA in pancreatic cancer and underscores the value of studying early events in carcinogenesis to yield new treatment strategies.See related article by Carrer et al., p. 416.

Running the Light: Nucleotide Metabolism Drives Bypass of Senescence in Cancer

Senescence is engaged in response to oncogenes to suppress proliferation. Cancers rewire metabolism to facilitate proliferation; however, it is not well appreciated how this enables senescence bypass. Recent work by Buj et al. demonstrates that loss of the tumor suppressor p16 engages a mTORC1-dependent increase in nucleotide pools to override senescence.

Inhibiting the Hexosamine Biosynthetic Pathway Lowers O-GlcNAcylation Levels and Sensitizes Cancer to Environmental Stress

The amounts of the intracellular glycosylation, O-GlcNAc modification, are increased in essentially all tumors when compared to healthy tissue, and lowering O-GlcNAcylation levels results in reduced tumorigenesis and increased cancer cell death. Therefore, the pharmacological reduction of O-GlcNAc may represent a therapeutic vulnerability. The most direct approach to this goal is the inhibition of O-GlcNAc transferase (OGT), the enzyme that directly adds the modification to proteins. However, despite some recent success, this enzyme has proven difficult to inhibit. An alternative strategy involves starving OGT of its sugar substrate UDP-GlcNAc by targeting enzymes of the hexosamine biosynthetic pathway (HBP). Here, we explore the potential of the rate-determining enzyme of this pathway, glutamine fructose-6-phosphate amidotransferase (GFAT). We first show that CRISPR-mediated knockout of GFAT results in inhibition of cancer cell growth in vitro and a xenograft model that correlates with O-GlcNAcylation levels. We then demonstrate that pharmacological inhibition of GFAT sensitizes a small panel of cancer cells to undergo apoptosis in response to diamide-induced oxidative stress. Finally, we find that GFAT expression and O-GlcNAc levels are increased in a spontaneous mouse model of liver cancer. Together these experiments support the further development of inhibitors of the HBP as an indirect approach to lowering O-GlcNAcylation levels in cancer.

Abstract 4549: Macrophage-epithelial metabolic crosstalk impairs chemotherapy in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) remains a leading cause of cancer related death, contrasting a relatively low incidence rate. A principle barrier in PDA treatment is the physiology of the tumors, characterized by a densely fibrotic stroma, rich with immune cell infiltration including macrophages. Macrophages are polarized by environmental cues which dictate their function. In PDA, macrophages within the tumor (tumor associated macrophages, or TAMs) are strongly immunosuppressive, inhibiting both infiltration and activation of cytotoxic T-cells. Additionally, TAMs have been shown to drive resistance to chemotherapy, though the mechanism for which remains unclear.

Several pathways have been described by which PDA cells recruit and polarize macrophages into TAMs, and the effects that TAMs have on the tumor microenvironment. These pathways have largely focused on signaling proteins, however, metabolic byproducts also influence the behavior of immune cells within the tumor microenvironment. To explore potential metabolic crosstalk, we have profiled the metabolic factors exchanged between PDA cells and TAMs. Among these, we have found that TAMs release metabolites which can regulate the response of PDA cells to chemotherapy. Importantly, this response is consistent across several murine and patient-derived pancreatic cancer cell lines, and this metabolite release appears to be a general property of anti-inflammatory macrophage metabolism. We further validated these findings in vivo, using a combination of pharmacological and genetic models to modulate myeloid cells within the tumor microenvironment. Taken together, these data suggest that further development of interventions which target either PDA-mediated polarization of TAMs or TAM-mediated inhibition of chemotherapy represent opportunities to improve the efficacy of currently available treatment options.

Citation Format: Christopher J. Halbrook, Corbin Pontious, Ilya Kovalenko, Laura Lapienyte, Stephan Dreyer, Yaqing Zhang, Barbara Nelson, Hanna Hong, Daivid Chang, Jennifer P. Morton, Marina Pasca di Magliano, Costas A. Lyssiotis. Macrophage-epithelial metabolic crosstalk impairs chemotherapy in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4549.

Macrophage-Released Pyrimidines Inhibit Gemcitabine Therapy in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by abundant infiltration of tumor-associated macrophages (TAMs). TAMs have been reported to drive resistance to gemcitabine, a frontline chemotherapy in PDA, though the mechanism of this resistance remains unclear. Profiling metabolite exchange, we demonstrate that macrophages programmed by PDA cells release a spectrum of pyrimidine species. These include deoxycytidine, which inhibits gemcitabine through molecular competition at the level of drug uptake and metabolism. Accordingly, genetic or pharmacological depletion of TAMs in murine models of PDA sensitizes these tumors to gemcitabine. Consistent with this, patients with low macrophage burden demonstrate superior response to gemcitabine treatment. Together, these findings provide insights into the role of macrophages in pancreatic cancer therapy and have potential to inform the design of future treatments. Additionally, we report that pyrimidine release is a general function of alternatively activated macrophage cells, suggesting an unknown physiological role of pyrimidine exchange by immune cells.

ATDC is required for the initiation of KRAS-induced pancreatic tumorigenesis

Pancreatic adenocarcinoma (PDA) is an aggressive disease driven by oncogenic KRAS and characterized by late diagnosis and therapeutic resistance. Here we show that deletion of the ataxia-telangiectasia group D-complementing (Atdc) gene, whose human homolog is up-regulated in the majority of pancreatic adenocarcinoma, completely prevents PDA development in the context of oncogenic KRAS. ATDC is required for KRAS-driven acinar-ductal metaplasia (ADM) and its progression to pancreatic intraepithelial neoplasia (PanIN). As a result, mice lacking ATDC are protected from developing PDA. Mechanistically, we show ATDC promotes ADM progression to PanIN through activation of β-catenin signaling and subsequent SOX9 up-regulation. These results provide new insight into PDA initiation and reveal ATDC as a potential target for preventing early tumor-initiating events.

Fine-Tuning Mitochondrial Dysfunction and Reductive Carboxylation

Metabolic processes within cells are dynamically interconnected. If mitochondria become defective, cells must rewire their metabolism to survive. Here we highlight recent work by Gaude et al. that used a tunable model of mitochondrial dysfunction combined with metabolic tracing and in silico analyses to define these compensatory pathways.

Tumor cross-talk networks promote growth and support immune evasion in pancreatic cancer

In the event of an injury, normal tissues exit quiescent homeostasis and rapidly engage a complex stromal and immune program. These tissue repair responses are hijacked and become dysregulated in carcinogenesis to form a growth-supportive tumor microenvironment. In pancreatic ductal adenocarcinoma (PDA), which remains one of the deadliest major cancers, the microenvironment is a key driver of tumor maintenance that impedes many avenues of therapy. In this review, we outline recent efforts made to uncover the microenvironmental cross-talk mechanisms that support pancreatic cancer cells, and we detail the strategies that have been undertaken to help overcome these barriers.

Menin regulates the serine biosynthetic pathway in Ewing sarcoma

Developmental transcription programs are epigenetically regulated by multi-protein complexes, including the menin- and MLL-containing trithorax (TrxG) complexes, which promote gene transcription by depositing the H3K4me3 activating mark at target gene promoters. We recently reported that in Ewing sarcoma, MLL1 (lysine methyltransferase 2A, KMT2A) and menin are overexpressed and function as oncogenes. Small molecule inhibition of the menin-MLL interaction leads to loss of menin and MLL1 protein expression, and to inhibition of growth and tumorigenicity. Here, we have investigated the mechanistic basis of menin-MLL-mediated oncogenic activity in Ewing sarcoma. Bromouridine sequencing (Bru-seq) was performed to identify changes in nascent gene transcription in Ewing sarcoma cells, following exposure to the menin-MLL interaction inhibitor MI-503. Menin-MLL inhibition resulted in early and widespread reprogramming of metabolic processes. In particular, the serine biosynthetic pathway (SSP) was the pathway most significantly affected by MI-503 treatment. Baseline expression of SSP genes and proteins (PHGDH, PSAT1, and PSPH), and metabolic flux through the SSP were confirmed to be high in Ewing sarcoma. In addition, inhibition of PHGDH resulted in reduced cell proliferation, viability, and tumor growth in vivo, revealing a key dependency of Ewing sarcoma on the SSP. Loss of function studies validated a mechanistic link between menin and the SSP. Specifically, inhibition of menin resulted in diminished expression of SSP genes, reduced H3K4me3 enrichment at the PHGDH promoter, and complete abrogation of de novo serine and glycine biosynthesis, as demonstrated by metabolic tracing studies with ¹³ C-labeled glucose. These data demonstrate that the SSP is highly active in Ewing sarcoma and that its oncogenic activation is maintained, at least in part, by menin-dependent epigenetic mechanisms involving trithorax complexes. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mutant p53R270H drives altered metabolism and increased invasion in pancreatic ductal adenocarcinoma

Pancreatic cancer is characterized by nearly universal activating mutations in KRAS. Among other somatic mutations, TP53 is mutated in more than 75% of human pancreatic tumors. Genetically engineered mice have proven instrumental in studies of the contribution of individual genes to carcinogenesis. Oncogenic Kras mutations occur early during pancreatic carcinogenesis and are considered an initiating event. In contrast, mutations in p53 occur later during tumor progression. In our model, we recapitulated the order of mutations of the human disease, with p53 mutation following expression of oncogenic Kras. Further, using an inducible and reversible expression allele for mutant p53, we inactivated its expression at different stages of carcinogenesis. Notably, the function of mutant p53 changes at different stages of carcinogenesis. Our work establishes a requirement for mutant p53 for the formation and maintenance of pancreatic cancer precursor lesions. In tumors, mutant p53 becomes dispensable for growth. However, it maintains the altered metabolism that characterizes pancreatic cancer and mediates its malignant potential. Further, mutant p53 promotes epithelial-mesenchymal transition (EMT) and cancer cell invasion. This work generates new mouse models that mimic human pancreatic cancer and expands our understanding of the role of p53 mutation, common in the majority of human malignancies.

This study shows that sequential mutations in Kras and Trp53 collaborate in pancreatic cancer and establishes effects of interrupting mutant Trp53 at different tumor stages.

Pancreatic HIF2α Stabilization Leads to Chronic Pancreatitis and Predisposes to Mucinous Cystic Neoplasm

BACKGROUND & AIMS

Tissue hypoxia controls cell differentiation in the embryonic pancreas, and promotes tumor growth in pancreatic cancer. The cellular response to hypoxia is controlled by the hypoxia-inducible factor (HIF) proteins, including HIF2α. Previous studies of HIF action in the pancreas have relied on loss-of-function mouse models, and the effects of HIF2α expression in the pancreas have remained undefined.

METHODS

We developed several transgenic mouse models based on the expression of an oxygen-stable form of HIF2α, or indirect stabilization of HIF proteins though deletion of von Hippel-Lindau, thus preventing HIF degradation. Furthermore, we crossed both sets of animals into mice expressing oncogenic KrasG12D in the pancreas.

RESULTS

We show that HIF2α is not expressed in the normal human pancreas, however, it is up-regulated in human chronic pancreatitis. Deletion of von Hippel-Lindau or stabilization of HIF2α in mouse pancreata led to the development of chronic pancreatitis. Importantly, pancreatic HIF1α stabilization did not disrupt the pancreatic parenchyma, indicating that the chronic pancreatitis phenotype is specific to HIF2α. In the presence of oncogenic Kras, HIF2α stabilization drove the formation of cysts resembling mucinous cystic neoplasm (MCN) in humans. Mechanistically, we show that the pancreatitis phenotype is linked to expression of multiple inflammatory cytokines and activation of the unfolded protein response. Conversely, MCN formation is linked to activation of Wnt signaling, a feature of human MCN.

CONCLUSIONS

We show that pancreatic HIF2α stabilization disrupts pancreatic homeostasis, leading to chronic pancreatitis, and, in the context of oncogenic Kras, MCN formation. These findings provide new mouse models of both chronic pancreatitis and MCN, as well as illustrate the importance of hypoxia signaling in the pancreas.

Employing Metabolism to Improve the Diagnosis and Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma is on pace to become the second leading cause of cancer-related death. The high mortality rate results from a lack of methods for early detection and the inability to successfully treat patients once diagnosed. Pancreatic cancer cells have extensively reprogrammed metabolism, which is driven by oncogene-mediated cell-autonomous pathways, the unique physiology of the tumor microenvironment, and interactions with non-cancer cells. In this review, we discuss how recent efforts delineating rewired metabolic networks in pancreatic cancer have revealed new in-roads to develop detection and treatment strategies for this dreadful disease.

PDX1 dynamically regulates pancreatic ductal adenocarcinoma initiation and maintenance

Aberrant activation of embryonic signaling pathways is frequent in pancreatic ductal adenocarcinoma (PDA), making developmental regulators therapeutically attractive. Here we demonstrate diverse functions for pancreatic and duodenal homeobox 1 (PDX1), a transcription factor indispensable for pancreas development, in the progression from normal exocrine cells to metastatic PDA. We identify a critical role for PDX1 in maintaining acinar cell identity, thus resisting the formation of pancreatic intraepithelial neoplasia (PanIN)-derived PDA. Upon neoplastic transformation, the role of PDX1 changes from tumor-suppressive to oncogenic. Interestingly, subsets of malignant cells lose PDX1 expression while undergoing epithelial-to-mesenchymal transition (EMT), and PDX1 loss is associated with poor outcome. This stage-specific functionality arises from profound shifts in PDX1 chromatin occupancy from acinar cells to PDA. In summary, we report distinct roles of PDX1 at different stages of PDA, suggesting that therapeutic approaches against this potential target need to account for its changing functions at different stages of carcinogenesis. These findings provide insight into the complexity of PDA pathogenesis and advocate a rigorous investigation of therapeutically tractable targets at distinct phases of PDA development and progression.

Abstract A32: GFAT: The crossroads of glucose and glutamine metabolism in pancreatic cancer

Due to a lack of early detection methods and effective treatment strategies, pancreatic cancer is slated to become the second leading cause of cancer related death in the United States. Pancreatic ductal adenocarcinoma (PDA), the most common type of pancreatic cancer, is initiated almost universally by mutations in the Kras oncogene. Kras mutations rewire metabolism in the cancer cells by enhancing nutrient capture and facilitating metabolic pathways that support survival and proliferation in the austere tumor microenvironment. Among these pathways, we have previously demonstrated that mutant Kras drives glucose flux into the hexosamine biosynthetic pathway (HBP) through upregulation of the rate limiting enzyme, glutamine fructose-6-phosphate transaminase (GFAT). The HBP plays a well-established role in the generation of the precursor substrates in glycosylation. In addition to this, GFAT has a less well appreciated facet, as it requires input from both glucose and glutamine (Gln). Specifically, GFAT deamidates the terminal nitrogen on Gln and releases glutamate, which can serve as an anaplerotic carbon source for the TCA cycle. Accordingly, GFAT sits at a nexus in the metabolism of the two canonical nutrients used by proliferating cells.

Previous work from our group demonstrated that GFAT1 knockdown in mouse PDA cells results in the inhibition of colony formation and decreased growth of subcutaneous xenografts in mice. These results combined with the nearly ubiquitous nature of Kras mutations in pancreatic cancer, strongly indicate that targeting the HBP by inhibition of GFAT could offer a powerful new avenue of treatment for PDA. Utilizing a Cas9/CRISPR approach to modulate GFAT expression in human PDA cells, we have generated cell lines which require the addition of downstream HBP metabolites to maintain cell viability. We have also found several cell lines in which the loss of GFAT expression appears to have no impact on cell viability, suggesting novel mechanisms of glucose and Gln metabolism in these cells. In addition to validating GFAT as a therapeutic option in PDAC, we have also explored the utility of the GFAT reaction as an imaging tool. To accomplish this, we have developed a method to monitor the conversion of Gln to glutamate by magnetic resonance spectroscopy using hyperpolarized glutamine. We further assessed the importance of GFAT in this conversion utilizing our GFAT-/- cell lines. Taken together, these results highlight the benefit of working to understand the complex nature of metabolic rewiring in pancreatic cancer cells, where a further understanding of these pathways may lead to more effective early detection and therapeutic options.

Citation Format: Christopher J. Halbrook, Daniel M. Kremer, Lucia Salamanca-Cardona, Kayvan R. Keshari, Costas A. Lyssioitis.{Authors}. GFAT: The crossroads of glucose and glutamine metabolism in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A32.

Mitogen-activated Protein Kinase Kinase Activity Maintains Acinar-to-Ductal Metaplasia and Is Required for Organ Regeneration in Pancreatitis

BACKGROUND & AIMS

Mitogen-activated protein kinase (MAPK) signaling in the exocrine pancreas has been extensively studied in the context of pancreatic cancer, where its potential as a therapeutic target is limited by acquired drug resistance. However, its role in pancreatitis is less understood. We investigated the role of mitogen-activated protein kinase kinase (MEK)-initiated MAPK signaling in pancreatitis to determine the potential for MEK inhibition in treating pancreatitis patients.

METHODS

To examine the role of MEK signaling in pancreatitis, we used both genetic and pharmacologic approaches to inhibit the MAPK signaling pathway in a murine model of cerulein-induced pancreatitis. We generated mice harboring inducible short hairpins targeting the MEK isoforms Map2k1 and/or Map2k2 specifically in the pancreatic epithelium. We also used the MEK inhibitor trametinib to determine the efficacy of systemic inhibition in mice with pancreatitis.

RESULTS

We demonstrated an essential role for MEK signaling in the initiation of pancreatitis. We showed that both systemic and parenchyma-specific MEK inhibition in established pancreatitis induces epithelial differentiation and stromal remodeling. However, systemic MEK inhibition also leads to a loss of the proliferative capacity of the pancreas, preventing the restoration of organ mass.

CONCLUSIONS

MEK activity is required for the initiation and maintenance of pancreatitis. MEK inhibition may be useful in the treatment of chronic pancreatitis to interrupt the vicious cycle of destruction and repair but at the expense of organ regeneration.

Pancreatic stellate cells support tumour metabolism through autophagic alanine secretion

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease characterized by an intense fibrotic stromal response and deregulated metabolism. The role of the stroma in PDAC biology is complex and it has been shown to play critical roles that differ depending on the biological context. The stromal reaction also impairs the vasculature, leading to a highly hypoxic, nutrient-poor environment. As such, these tumours must alter how they capture and use nutrients to support their metabolic needs. Here we show that stroma-associated pancreatic stellate cells (PSCs) are critical for PDAC metabolism through the secretion of non-essential amino acids (NEAA). Specifically, we uncover a previously undescribed role for alanine, which outcompetes glucose and glutamine-derived carbon in PDAC to fuel the tricarboxylic acid (TCA) cycle, and thus NEAA and lipid biosynthesis. This shift in fuel source decreases the tumour’s dependence on glucose and serum-derived nutrients, which are limited in the pancreatic tumour microenvironment. Moreover, we demonstrate that alanine secretion by PSCs is dependent on PSC autophagy, a process that is stimulated by cancer cells. Thus, our results demonstrate a novel metabolic interaction between PSCs and cancer cells, in which PSC-derived alanine acts as an alternative carbon source. This finding highlights a previously unappreciated metabolic network within pancreatic tumours in which diverse fuel sources are used to promote growth in an austere tumour microenvironment.

Abstract A04: PI3K regulation of RAC1 is required for Kras-induced pancreatic tumorigenesis

Nearly all pancreatic ductal adenocarcinomas are caused by oncogenic mutations in the KRAS gene. Pharmacological inhibition of mutant KRAS has thus far been unsuccessful in the clinical setting, precipitating a need to understand the pathways downstream of KRAS which may prove more easily targeted with small molecule inhibitors. Here we show that PI3K p110α is absolutely required for pancreatic tumorigenesis while p110β is dispensable for this process. Surprisingly, ablation of p110α does not impair the ability of KRAS to activate AKT, demonstrating that AKT activation is not sufficient for transformation. Instead we find that p110α is required for robust activation of RAC1, a small GTPase required for pancreatic metaplasia. Consistent with this, our data show that p110α is necessary for regulating epithelial expression and activation of RAC-GEFs including Vav1, Tiam1 and Ect2. Ultimately, these results define the mechanistic role of p110α in pancreatic tumorigenesis and suggest selective inhibition of this PI3K isoform as a promising therapeutic approach to treating patients with pancreas cancer.

Citation Format: Kenneth K. Takeuchi, Eileen Carpenter, Claire Wu, Christopher J. Halbrook, Richard Z. Lin, Howard C. Crawford. PI3K regulation of RAC1 is required for Kras-induced pancreatic tumorigenesis. [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 A04.

Abstract A77: Investigating the role of ADAM10 in pancreatic tumor differentiation

Pancreatic adenocarcinoma (PDAC) is the 4th most common cause of cancer related deaths in the United States and has a dismal 5-year survival rate of 6%. This prognosis is attributed the disease’s fast and asymptomatic progression to metastasis, leading to late diagnosis upon which time there are few treatment options available. The A Disintegrin and Metalloproteinase (ADAM) family are sheddase proteins known to regulate cell adhesion and function. This regulation can allow ADAMs to influence the ability of tumor cells to disseminate from the primary tumor and metastasize to distant organs. ADAM10, which is seen to be up-regulated in both chronic pancreatitis and PDAC, cleaves a variety of substrates including several cell adhesion molecules such as L1-CAM, N-Cadherin, and E-Cadherin. Using a conditional knockout for ADAM10 in the Kras+/G12D;Ptf1a+/Cre (KC) mouse model of pancreatic cancer, we have observed an absence of metastasis when ADAM10 is genetically ablated. To investigate the potential role that ADAM10 plays in this, we used a shRNA approach to knock-down ADAM10 expression in various human pancreatic cancer cells lines. Analysis of these cell lines suggests a partial restoration of a less aggressive, differentiated phenotype, consistent with the increased longevity of the ADAM10 knockout KC mice.

Citation Format: Louise V. Peverley, Christopher J. Halbrook, Jason C. Hall, Christine M. Ardito, Howard C. Crawford. Investigating the role of ADAM10 in pancreatic tumor differentiation. [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 A77.

Abstract IA13: Acinar cell transdifferentiation sets the stage for early tumor heterogeneity

Prior to PanIN formation, acinar cells harboring oncogenic Kras gradually lose their acinar character and take on a ductal phenotype in a process known as acinar-to-ductal metaplasia. Rather than mimicking a normal pancreatic duct, metaplastic ducts take on a proliferative biliary progenitor phenotype, marked by the expression of SOX17 and PDX1 and the presence of numerous tuft cells, recently identified as a PanIN initiating cells. Manipulation of SOX17 and PDX1 in vivo reveal them to be a transdifferentiation promoter and suppressor, respectively, both greatly affecting tuft cell genesis and tumor formation. These opposing roles of developmental transcription factors during tumorigenesis implicate the usurpation of a differentiation program that significantly contributes to cellular heterogeneity within early pre-cancerous lesions of the pancreas.

Citation Format: Kenneth K. Takeuchi, Kathleen E. Delgiorno, Christopher J. Halbrook, Howard C. Crawford. Acinar cell transdifferentiation sets the stage for early tumor heterogeneity. [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 IA13.

Abstract A09: Notch signaling couples with Kras or PI3K to drive EGFR independent pancreatic acinar to ductal metaplasia

Almost all reported cases of pancreatic ductal adenocarcinoma, the most common form of pancreatic cancer, harbor an oncogenic Kras mutation. Recently, targeting oncogenic Kras to specific cell types in the adult pancreas has shown the acinar compartment to be more susceptible to neoplastic transformation than ductal cells. Acinar to ductal metaplasia (ADM) is a phenomenon where acinar cells undergo a morphological change and begin expressing markers normally found only in ductal cells while losing markers typical of acinar cells. ADM is highly proliferative with the potential to develop into pancreatic intraepithelial neoplasias, a precursor lesion to pancreatic cancer. Acinar cells harvested from mice expressing mutant Kras undergo spontaneous ADM when embedded in 3D collagen cultures, however, we and others have found the epidermal growth factor receptor (EGFR) is required for ADM induced by mutant Kras expression in vitro. Activation of EGFR by treatment of WT collagen embedded acinar cell explants with the EGFR ligand TGF-α has also been shown to induce ADM in a manner requiring Notch pathway activation. Furthermore, it has been demonstrated that expression of Notch2 intracellular domain (N2ICD) is sufficient to induce ADM in WT acinar cells. To directly investigate the relationship of the EGFR, Kras, and Notch signaling pathways in ADM, we examined the effect of Notch signaling in acinar cells harvested from EGFRf/f; Ptf1a+/Cre (EKO) mice, which harbor a pancreas specific deletion of EGFR. Surprisingly, we found that expression of N2ICD failed to induce ADM in acinar cells from EKO mice. We also observed that co-expression of a constitutively active p110α mutant or mutant Kras with N2ICD was able to rescue ADM in acinar cells from EKO mice, though neither was sufficient to drive ADM in the absence of N2ICD. Additionally, treatment of acinar cells from WT mice with either the p110α inhibitor Pik75 or the expression of a dominant negative mutant of the PI3K downstream target Rac1 reduced Erk1/2 phosphorylation, whereas expression of constitutively active p110α increased the level of Erk1/2 phosphorylation. These results demonstrate the importance of EGFR signaling in ADM, and identify the need to determine the mechanism of crosstalk between the PI3K and MAPK pathways in acinar cells.

Citation Format: Christopher J. Halbrook, Howard C. Crawford. Notch signaling couples with Kras or PI3K to drive EGFR independent pancreatic acinar to ductal metaplasia. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A09. doi: 10.1158/1557-3125.RASONC14-A09

PI3K regulation of RAC1 is required for KRAS-induced pancreatic tumorigenesis in mice

BACKGROUND & AIMS

New drug targets are urgently needed for the treatment of patients with pancreatic ductal adenocarcinoma (PDA). Nearly all PDAs contain oncogenic mutations in the KRAS gene. Pharmacological inhibition of KRAS has been unsuccessful, leading to a focus on downstream effectors that are more easily targeted with small molecule inhibitors. We investigated the contributions of phosphoinositide 3-kinase (PI3K) to KRAS-initiated tumorigenesis.

METHODS

Tumorigenesis was measured in the Kras(G12D/+);Ptf1a(Cre/+) mouse model of PDA; these mice were crossed with mice with pancreas-specific disruption of genes encoding PI3K p110α (Pik3ca), p110β (Pik3cb), or RAC1 (Rac1). Pancreatitis was induced with 5 daily intraperitoneal injections of cerulein. Pancreata and primary acinar cells were isolated; acinar cells were incubated with an inhibitor of p110α (PIK75) followed by a broad-spectrum PI3K inhibitor (GDC0941). PDA cell lines (NB490 and MiaPaCa2) were incubated with PIK75 followed by GDC0941. Tissues and cells were analyzed by histology, immunohistochemistry, quantitative reverse-transcription polymerase chain reaction, and immunofluorescence analyses for factors involved in the PI3K signaling pathway. We also examined human pancreas tissue microarrays for levels of p110α and other PI3K pathway components.

RESULTS

Pancreas-specific disruption of Pik3ca or Rac1, but not Pik3cb, prevented the development of pancreatic tumors in Kras(G12D/+);Ptf1a(Cre/+) mice. Loss of transformation was independent of AKT regulation. Preneoplastic ductal metaplasia developed in mice lacking pancreatic p110α but regressed. Levels of activated and total RAC1 were higher in pancreatic tissues from Kras(G12D/+);Ptf1a(Cre/+) mice compared with controls. Loss of p110α reduced RAC1 activity and expression in these tissues. p110α was required for the up-regulation and activity of RAC guanine exchange factors during tumorigenesis. Levels of p110α and RAC1 were increased in human pancreatic intraepithelial neoplasias and PDAs compared with healthy pancreata.

CONCLUSIONS

KRAS signaling, via p110α to activate RAC1, is required for transformation in Kras(G12D/+);Ptf1a(Cre/+) mice.

Identification and manipulation of biliary metaplasia in pancreatic tumors

BACKGROUND & AIMS

Metaplasias often have characteristics of developmentally related tissues. Pancreatic metaplastic ducts are usually associated with pancreatitis and pancreatic ductal adenocarcinoma. The tuft cell is a chemosensory cell that responds to signals in the extracellular environment via effector molecules. Commonly found in the biliary tract, tuft cells are absent from normal murine pancreas. Using the aberrant appearance of tuft cells as an indicator, we tested if pancreatic metaplasia represents transdifferentiation to a biliary phenotype and what effect this has on pancreatic tumorigenesis.

METHODS

We analyzed pancreatic tissue and tumors that developed in mice that express an activated form of Kras (Kras(LSL-G12D/+);Ptf1a(Cre/+) mice). Normal bile duct, pancreatic duct, and tumor-associated metaplasias from the mice were analyzed for tuft cell and biliary progenitor markers, including SOX17, a transcription factor that regulates biliary development. We also analyzed pancreatic tissues from mice expressing transgenic SOX17 alone (ROSA(tTa/+);Ptf1(CreERTM/+);tetO-SOX17) or along with activated Kras (ROSAtT(a/+);Ptf1a(CreERTM/+);tetO-SOX17;Kras(LSL-G12D;+)).

RESULTS

Tuft cells were frequently found in areas of pancreatic metaplasia, decreased throughout tumor progression, and absent from invasive tumors. Analysis of the pancreatobiliary ductal systems of mice revealed tuft cells in the biliary tract but not the normal pancreatic duct. Analysis for biliary markers revealed expression of SOX17 in pancreatic metaplasia and tumors. Pancreas-specific overexpression of SOX17 led to ductal metaplasia along with inflammation and collagen deposition. Mice that overexpressed SOX17 along with Kras(G12D) had a greater degree of transformed tissue compared with mice expressing only Kras(G12D). Immunofluorescence analysis of human pancreatic tissue arrays revealed the presence of tuft cells in metaplasia and early-stage tumors, along with SOX17 expression, consistent with a biliary phenotype.

CONCLUSIONS

Expression of Kras(G12D) and SOX17 in mice induces development of metaplasias with a biliary phenotype containing tuft cells. Tuft cells express a number of tumorigenic factors that can alter the microenvironment. Expression of SOX17 induces pancreatitis and promotes Kras(G12D)-induced tumorigenesis in mice.

Abstract 3030: Regulation of EGFR in pancreatic cancer

EGFR and EGFR ligand upregulation has been widely seen in both human chronic pancreatitis and pancreatic ductal adenocarcinoma (PDA) for many years; however the role of EGFR in PDA was poorly understood. Recently we and others have shown that genetic ablation of EGFR effectively prevents both spontaneous and cerulein induced tumorigenesis in the pancreas of the LSL-KrasG12D/+;Ptf1aCre/+ (KC) mouse model of pancreatic tumorigenesis. Pockets of EGFR upregulation localized in single acini of KC mice appear to precede pancreatic intraepithelial neoplasia (PanIN) formation in spontaneous tumorigenesis, coupled with a distinct spatially localized immune response. Ubiquitous EGFR upregulation is observed throughout the pancreas upon induction of pancreatitis in wild-type (WT) and KC mice, returning to normal levels in WT mice but continuing to increase along with the widespread tumorigenesis in cerulein treated KC mice. Comparison of cerulein treated KC mice with the EGFRf/f;LSL-KrasG12D/+;Ptf1aCre/+ mice (EKC), which are largely resistant to cerulein induced pancreatitis, offers an opportunity to identify signals in the KC mouse which could be responsible for the upregulation of EGFR and subsequent tumorigenesis.

Citation Format: Christopher J. Halbrook, Kenneth K. Takeuchi, Howard C. Crawford. Regulation of EGFR in pancreatic cancer. [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 3030. doi:10.1158/1538-7445.AM2013-3030

EGF receptor is required for KRAS-induced pancreatic tumorigenesis

Initiation of pancreatic ductal adenocarcinoma (PDA) is definitively linked to activating mutations in the KRAS oncogene. However, PDA mouse models show that mutant Kras expression early in development gives rise to a normal pancreas, with tumors forming only after a long latency or pancreatitis induction. Here, we show that oncogenic KRAS upregulates endogenous EGFR expression and activation, the latter being dependent on the EGFR ligand sheddase, ADAM17. Genetic ablation or pharmacological inhibition of EGFR or ADAM17 effectively eliminates KRAS-driven tumorigenesis in vivo. Without EGFR activity, active RAS levels are not sufficient to induce robust MEK/ERK activity, a requirement for epithelial transformation.