Human Pancreatic Ductal Epithelial Research Articles

Abstract C065: Base excision repair pathway regulates transcription-replication conflicts in pancreatic ductal adenocarcinoma

Abstract Oncogenic mutations (such as in KRAS) can dysregulate transcription and replication leading to transcription conflicts (TRCs). Unresolved TRCs can cause lethal DNA damage. Here, we sought to investigate the causal role of oncogenic mutations in regulating TRCs in pancreatic ductal adenocarcinoma (PDAC). Further, we characterize the adaptive pathways that mitigate TRCs for PDAC survival. Human PDAC demonstrated 30-120-fold higher levels of TRC genomic signature compared to breast, colon and lung cancer (p<0.001). Gene expression analysis demonstrated high levels of known TRC resolution factors in human tumors compared to normal tissues. TRCs as measured by RNAPII-PCNA proximity ligation assay were significantly enriched in human PDAC cells (Panc-1, BxPC3, MiaPaca2) compared to immortalized normal HPNE cells (p<0.001). Similarly transcriptomic complexes were enriched in nascent DNA immunoprecipitates from Panc1 cells but not HPNE cells. Ectopic expression of oncogenic KRAS(G12D) in human pancreatic ductal epithelial (HPNE) cells enhanced TRCs, and TRC-related DNA:RNA hybrids (R-loops). Inhibition of KRAS or downstream effectors abrogated TRCs in Panc1 and MiaPaca2 cells. An siRNA screen identified several factors in the base-excision repair (BER) pathway as regulators of TRCs. Sub-lethal exposure to hydrogen peroxide enhanced TRCs, whereas N-acetyl cysteine abrogated TRCs. These findings were validated by a pharmacologic approach using inhibitors of APE1 endonuclease in BER pathway (Methoxyamine and CRT). Mechanistic studies revealed that BER pathway inhibition severely altered RNA polymerase II dynamics at nascent DNA; causing RNAPII trapping and contributing to enhanced TRCs. The ensuing DNA damage activated Chk2-ATR pathway but not Chk1-ATM pathway. Co-treatment with ATR inhibitor (VX970, 10-80nM) and BER inhibitor (methoxyamine, 6-12mM) at clinically relevant doses, synergistically enhanced DNA damage and reduced clonogenic survival in PDAC cells. The study uncovers a novel role of BER pathway defects and oxidative DNA damage in promoting TRCs. Our studies provide mechanistic insights into the regulation of TRCs in PDAC which has implications for genome instability and therapy in PDAC. Citation Format: Fan Meng, Anup K. Singh, Tiane Li, Marc Attiyeh, Fatemeh Kohram, Terence Williams, Yilun Liu, Mustafa Raoof. Base excision repair pathway regulates transcription-replication conflicts in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C065.

Fatty acids abrogate the growth-suppressive effects induced by inhibition of cholesterol flux in pancreatic cancer cells

BackgroundDespite therapeutic advances, the prognosis of pancreatic ductal adenocarcinoma (PDAC) remains extremely poor. Metabolic reprogramming is increasingly recognized as a key contributor to tumor progression and therapy resistance in PDAC. One of the main metabolic changes essential for tumor growth is altered cholesterol flux. Targeting cholesterol flux appears an attractive therapeutic approach, however, the complex regulation of cholesterol balance in PDAC cells remains poorly understood.MethodsThe lipid content in human pancreatic duct epithelial (HPDE) cells and human PDAC cell lines (BxPC-3, MIA PaCa-2, and PANC-1) was determined. Cells exposed to eight different inhibitors targeting different regulators of lipid flux, in the presence or absence of oleic acid (OA) stimulation were assessed for changes in viability, proliferation, migration, and invasion. Intracellular content and distribution of cholesterol was assessed. Lastly, proteome profiling of PANC-1 exposed to the sterol O-acyltransferase 1 (SOAT1) inhibitor avasimibe, in presence or absence of OA, was performed.ResultsPDAC cells contain more free cholesterol but less cholesteryl esters and lipid droplets than HPDE cells. Exposure to different lipid flux inhibitors increased cell death and suppressed proliferation, with different efficiency in the tested PDAC cell lines. Avasimibe had the strongest ability to suppress proliferation across the three PDAC cell lines. All inhibitors showing cell suppressive effect disturbed intracellular cholesterol flux and increased cholesterol aggregation. OA improved overall cholesterol balance, reduced free cholesterol aggregation, and reversed cell death induced by the inhibitors. Treatment with avasimibe changed the cellular proteome substantially, mainly for proteins related to biosynthesis and metabolism of lipids and fatty acids, apoptosis, and cell adhesion. Most of these changes were restored by OA.ConclusionsThe study reveals that disturbing the cholesterol flux by inhibiting the actions of its key regulators can yield growth suppressive effects on PDAC cells. The presence of fatty acids restores intracellular cholesterol balance and abrogates the alternations induced by cholesterol flux inhibitors. Taken together, targeting cholesterol flux might be an attractive strategy to develop new therapeutics against PDAC. However, the impact of fatty acids in the tumor microenvironment must be taken into consideration.

Targeting FTO Suppresses Pancreatic Carcinogenesis via Regulating Stem Cell Maintenance and EMT Pathway

N6-methyladenosine (m6A) is the most prevalent post-transcriptional RNA modification regulating cancer self-renewal. However, despite its functional importance and prognostic implication in tumorigenesis, the relevance of FTO, an m6A eraser, in pancreatic cancer (PC) remains elusive. Here, we establish the oncogenic role played by FTO overexpression in PC. FTO is upregulated in PC cells compared to normal human pancreatic ductal epithelial (HPDE) cells. Both RNAi depletion and CS1-mediated pharmacological inhibition of FTO caused a diminution of PC cell proliferation via cell cycle arrest in the G1 phase and p21cip1 and p27kip1 induction. While HPDE cells remain insensitive to CS1 treatment, FTO overexpression confers enhancements in growth, motility, and EMT transition, thereby inculcating tumorigenic properties in HPDE cells. Notably, shRNA-mediated FTO depletion in PC cells impairs their mobility and invasiveness, leading to EMT reversal. Mechanistically, this was associated with impaired tumorsphere formation and reduced expression of CSCs markers. Furthermore, FTO depletion in PC cells weakened their tumor-forming capabilities in nude mice; those tumors had increased apoptosis, decreased proliferation markers, and MET conversion. Collectively, our study demonstrates the functional importance of FTO in PC and the maintenance of CSCs via EMT regulation. Thus, FTO may represent an attractive therapeutic target for PC.

Dynamic Interplay between Structural Variations and 3D Genome Organization in Pancreatic Cancer.

Structural variations (SVs) are the greatest source of variations in the genome and can lead to oncogenesis. However, the identification and interpretation of SVs in human cancer remain technologically challenging. Here, long‐read sequencing is first employed to depict the signatures of structural variations in carcinogenesis of human pancreatic ductal epithelium. Then widespread reprogramming of the 3D chromatin architecture is revealed by an in situ Hi‐C technique. Integrative analyses indicate that the distribution pattern of SVs among the 3D genome is highly cell‐type specific and the bulk remodeling effects of SVs in the chromatin organization partly depend on intercellular genomic heterogeneity. Meanwhile, contact domains tend to minimize these disrupting effects of SVs within local adjacent genomic regions to maintain overall stability. Notably, complex genomic rearrangements involving two key driver genes CDKN2A and SMAD4 are identified, and their influence on the expression of oncogenes MIR31HG, MYO5B, etc., are further elucidated from both a linear view and 3D perspective. Overall, this work provides a genome‐wide resource and highlights the impact, complexity, and dynamicity of the interplay between structural variations and high‐order chromatin organization, which expands the current understanding of the pathogenesis of SVs in human cancer.

Pancreatic ductal adenocarcinoma cells employ integrin α6β4 to form hemidesmosomes and regulate cell proliferation

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis due to its aggressive progression, late detection and lack of druggable driver mutations, which often combine to result in unsuitability for surgical intervention. Together with activating mutations of the small GTPase KRas, which are found in over 90% of PDAC tumours, a contributory factor for PDAC tumour progression is formation of a rigid extracellular matrix (ECM) and associated desmoplasia. This response leads to aberrant integrin signalling, and accelerated proliferation and invasion. To identify the integrin adhesion systems that operate in PDAC, we analysed a range of pancreatic ductal epithelial cell models using 2D, 3D and organoid culture systems. Proteomic analysis of isolated integrin receptor complexes from human pancreatic ductal epithelial (HPDE) cells predominantly identified integrin α6β4 and hemidesmosome components, rather than classical focal adhesion components. Electron microscopy, together with immunofluorescence, confirmed the formation of hemidesmosomes by HPDE cells, both in 2D and 3D culture systems. Similar results were obtained for the human PDAC cell line, SUIT-2. Analysis of HPDE cell secreted proteins and cell-derived matrices (CDM) demonstrated that HPDE cells secrete a range of laminin subunits and form a hemidesmosome-specific, laminin 332-enriched ECM. Expression of mutant KRas (G12V) did not affect hemidesmosome composition or formation by HPDE cells. Cell-ECM contacts formed by mouse and human PDAC organoids were also assessed by electron microscopy. Organoids generated from both the PDAC KPC mouse model and human patient-derived PDAC tissue displayed features of acinar-ductal cell polarity, and hemidesmosomes were visible proximal to prominent basement membranes. Furthermore, electron microscopy identified hemidesmosomes in normal human pancreas. Depletion of integrin β4 reduced cell proliferation in both SUIT-2 and HPDE cells, reduced the number of SUIT-2 cells in S-phase, and induced G1 cell cycle arrest, suggesting a requirement for α6β4-mediated adhesion for cell cycle progression and growth. Taken together, these data suggest that laminin-binding adhesion mechanisms in general, and hemidesmosome-mediated adhesion in particular, may be under-appreciated in the context of PDAC.Proteomic data are available via ProteomeXchange with the identifiers PXD027803, PXD027823 and PXD027827.

Giant obscurin regulates migration and metastasis via RhoA-dependent cytoskeletal remodeling in pancreatic cancer.

Obscurins, encoded by the OBSCN gene, are giant cytoskeletal proteins with structural and regulatory roles. Large scale omics analyses reveal that OBSCN is highly mutated across different types of cancer, exhibiting a 5-8% mutation frequency in pancreatic cancer. Yet, the functional role of OBSCN in pancreatic cancer progression and metastasis has to be delineated. We herein show that giant obscurins are highly expressed in normal pancreatic tissues, but their levels are markedly reduced in pancreatic ductal adenocarcinomas. Silencing of giant obscurins in non-tumorigenic Human Pancreatic Ductal Epithelial (HPDE) cells and obscurin-expressing Panc5.04 pancreatic cancer cells induces an elongated, spindle-like morphology and faster cell migration via cytoskeletal remodeling. Specifically, depletion of giant obscurins downregulates RhoA activity, which in turn results in reduced focal adhesion density, increased microtubule growth rate and faster actin dynamics. Although OBSCN knockdown is not sufficient to induce de novo tumorigenesis, it potentiates tumor growth in a subcutaneous implantation model and exacerbates metastasis in a hemispleen murine model of pancreatic cancer metastasis, thereby shortening survival. Collectively, these findings reveal a critical role of giant obscurins as tumor suppressors in normal pancreatic epithelium whose loss of function induces RhoA-dependent cytoskeletal remodeling, and promotes cell migration, tumor growth and metastasis.

Establishment of a Macrophage Phenotypic Switch Related Prognostic Signature in Patients With Pancreatic Cancer.

IntroductionMacrophage phenotype switch plays a vital role in the progression of malignancies. We aimed to build a prognostic signature by exploring the expression pattern of macrophage phenotypic switch related genes (MRGs) in the Cancer Genome Atlas (TCGA)—pancreatic adenocarcinoma (PAAD), Genotype-Tissue Expression (GTEx)-Pancreas, and Gene Expression Omnibus (GEO) databases.MethodsWe identified the differentially expressed genes between the PAAD and normal tissues. We used single factor Cox proportional risk regression analysis, Least Absolute Shrinkage and Selection Operator (LASSO) analysis, and multivariate Cox proportional hazard regression analysis to establish the prognosis risk score by the MRGs. The relationships between the risk score and immune landscape, “key driver” mutations and clinicopathological factors were also analyzed. Gene-set enrichment analysis (GSEA) analysis was also performed.ResultsWe detected 198 differentially expressed MRGs. The risk score was constructed based on 9 genes (KIF23, BIN1, LAPTM4A, ERAP2, ATP8B2, FAM118A, RGS16, ELMO1, RAPGEFL1). The median overall survival time of patients in the low-risk group was significantly longer than that of patients in the high-risk group (P < 0.001). The prognostic value of the risk score was validated in GSE62452 dataset. The prognostic performance of nomogram based on risk score was superior to that of TNM stage. And GSEA analysis also showed that the risk score was closely related with P53 signaling pathway, pancreatic cancer and T cell receptor signaling pathway. qRT-PCR assay showed that the expressions of the 9 MRGs in PDAC cell lines were higher than those in human pancreatic ductal epithelium cell line.ConclusionsThe nine gene risk score could be used as an independent prognostic index for PAAD patients. Further studies validating the prognostic value of the risk score are warranted.

Eicosapentaenoic Acid Inhibits KRAS Mutant Pancreatic Cancer Cell Growth by Suppressing Hepassocin Expression and STAT3 Phosphorylation.

Background: The oncogenic Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation was reported to be the signature genetic event in most cases of pancreatic ductal adenocarcinoma (PDAC). Hepassocin (HPS/FGL1) is involved in regulating lipid metabolism and the progression of several cancer types; however, the underlying mechanism of HPS/FGL1 in the KRAS mutant PDAC cells undergoing eicosapentaenoic acid (EPA) treatment remains unclear. Methods: We measured HPS/FGL1 protein expressions in a human pancreatic ductal epithelial (HPNE) normal pancreas cell line, a KRAS-wild-type PDAC cell line (BxPC-3), and KRAS-mutant PDAC cell lines (PANC-1, MIA PaCa-2, and SUIT-2) by Western blot methods. HEK293T cells were transiently transfected with corresponding KRAS-expressing plasmids to examine the level of HPS expression with KRAS activation. We knocked-down HPS/FGL1 using lentiviral vectors in SUIT-2 cells and measured the cell viability by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and clonogenicity assays. Furthermore, a lipidomic analysis was performed to profile changes in lipid metabolism after HPS/FGL1 knockdown. Results: We found that the HPS/FGL1 level was significantly upregulated in KRAS-mutated PDAC cells and was involved in KRAS/phosphorylated (p)-signal transduction and activator of transcription 3 (STAT3) signaling, and the knockdown of HPS/FGL1 in SUIT-2 cells decreased cell proliferation through increasing G2/M cell cycle arrest and cyclin B1 expression. In addition, the knockdown of HPS/FGL1 in SUIT-2 cells significantly increased omega-3 polyunsaturated fatty acids (PUFAs) and EPA production but not docosahexaenoic acid (DHA). Moreover, EPA treatment in SUIT-2 cells reduced the expression of de novo lipogenic protein, acetyl coenzyme A carboxylase (ACC)-1, and decreased p-STAT3 and HPS/FGL1 expressions, resulting in the suppression of cell viability. Conclusions: Results of this study indicate that HPS is highly expressed by KRAS-mutated PDAC cells, and HPS/FGL1 plays a crucial role in altering lipid metabolism and increasing cell growth in pancreatic cancer. EPA supplements could potentially inhibit or reduce ACC-1-involved lipogenesis and HPS/FGL1-mediated cell survival in KRAS-mutated pancreatic cancer cells.

Proteome-Wide Alterations of Asymmetric Arginine Dimethylation Associated With Pancreatic Ductal Adenocarcinoma Pathogenesis.

Arginine methylation catalyzed by protein arginine methyltransferases (PRMTs) performs essential roles in regulating cancer initiation and progression, but its implication in pancreatic ductal adenocarcinoma (PDAC) requires further elucidation. In this study, asymmetric dimethylarginine (ADMA)-containing peptides in PDAC cell line PANC-1 were identified by label-free quantitative proteomics combined with affinity purification, using human non-cancerous pancreatic ductal epithelium cell line HPDE6c7 as the control. In total, 289 ADMA sites in 201 proteins were identified in HPDE6c7 and PANC-1 cells, including 82 sites with lower dimethylation and 37 sites with higher dimethylation in PANC-1 cells compared with HPDE6c7 cells. These ADMA-containing peptides demonstrated significant enrichment of glycine and proline residues in both cell lines. Importantly, leucine residues were significantly enriched in ADMA-containing peptides identified only in HPDE6c7 cells or showing lower dimethylation in PANC-1 cells. ADMA-containing proteins were significantly enriched in multiple biological processes and signaling cascades associated with cancer development, such as spliceosome machinery, the Wnt/β-catenin, Hedgehog, tumor growth factor beta (TGF-β), and mitogen-activated protein kinase (MAPK) signaling pathways. Moreover, PDAC cell lines with enhanced cell viability showed lower PRMT4 protein abundance and global ADMA-containing protein levels compared with HPDE6c7. PRMT4 overexpression partially recovered ADMA-containing protein levels and repressed viability in PANC-1 cells. These results revealed significantly altered ADMA-containing protein profiles in human pancreatic carcinoma cells, which provided a basis for elucidating the pathogenic roles of PRMT-mediated protein methylation in pancreatic cancer.

Aberrant (pro)renin receptor expression induces genomic instability in pancreatic ductal adenocarcinoma through upregulation of SMARCA5/SNF2H

(Pro)renin receptor [(P)RR] has a role in various diseases, such as cardiovascular and renal disorders and cancer. Aberrant (P)RR expression is prevalent in pancreatic ductal adenocarcinoma (PDAC) which is the most common pancreatic cancer. Here we show whether aberrant expression of (P)RR directly leads to genomic instability in human pancreatic ductal epithelial (HPDE) cells. (P)RR-expressing HPDE cells show obvious cellular atypia. Whole genome sequencing reveals that aberrant (P)RR expression induces large numbers of point mutations and structural variations at the genome level. A (P)RR-expressing cell population exhibits tumour-forming ability, showing both atypical nuclei characterised by distinctive nuclear bodies and chromosomal abnormalities. (P)RR overexpression upregulates SWItch/Sucrose Non-Fermentable (SWI/SNF)-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a, member 5 (SMARCA5) through a direct molecular interaction, which results in the failure of several genomic stability pathways. These data reveal that aberrant (P)RR expression contributes to the early carcinogenesis of PDAC.

A KRAS-RAD18-miR-296-3p Regulated Network Mediates Radioresistance in Pancreatic Cancer Through Homologous Recombination

Pancreatic ductal adenocarcinoma (PDAC) is a relatively radioresistant disease, and inhibition of DNA homologous recombination (HR) repair in combination with radiation therapy (RT) is a potentially attractive strategy to overcome radioresistance. We have found that the expression of the HR protein RAD18 is increased upon induction of KRAS mutation and reduced following KRAS suppression. Therefore, we hypothesized targeting RAD18 in KRAS mutant PDAC with its predicted inhibitor, miR-296-3p, will increase radiosensitization. Standard clonogenic assays, γH2aX foci staining, HR-GFP reporter assay, and western blot analysis of DNA damage response proteins was performed in MIA-PaCa2 (MP2) and PANC-1 cells following knockdown of RAD18 in cells via short hairpin RNA (shRNA). Forced expression of miR-296-3p mimics was performed using lipofectamine transfection. Cells with or without stable knockdown of RAD18 were implanted subcutaneously in the hind limb of athymic nude mice and treated with sham radiation or radiation to a dose of 20 Gy in 5 daily fractions once tumors reached 100-150 mm3. Doxycycline treatment of KRAS inducible human pancreatic ductal epithelial (HPDE) cells increased both RAD18 protein and RNA expression. In contrast, knockdown of KRAS by siRNA reduced RAD18 protein and RNA expression in PANC-1 and MP2 cell lines (3.5 and 4.2-fold, respectively). Stable knockdown of RAD18 in MP2 and PANC-1 resulted in decreased radiation clonogenic survival in vitro (dose enhancement factor (DEF) = 1.52 and 1.51, respectively), decreased DNA repair after radiation as measured by increased number of γH2aX nuclear foci assay at 6, 12, and 24 hours (all p<0.05), decreased HR activation following DNA damage via a HR-GFP reporter assay (p = 0.039), and increased tumor growth delay following radiation in vivo (p<0.001). Overexpression of RAD18 resulted in increased radiation clonogenic survival (DEF = 0.88). We identified that miR-296-3p has a conserved target sequence complimentary to the 3’UTR region of the RAD18 mRNA. MiR-296-3p expression via qRT-PCR was absent in a panel of 6 KRAS mutant PDAC cell lines and highly expressed in 2 normal pancreatic cell lines. MiR-296-3p mimic transfection of the high RAD18 expressing PANC-1 and MP2 cells resulted in efficient knockdown of RAD18, which was confirmed through western blotting, qRT-PCR, and luciferase reporter assays. Following the transfection of miR-296-3p mimics into PANC-1 or MP2 cells, radiosensitization increased (DEF = 1.15 and 1.14, respectively), yH2aX nuclear foci remained elevated at 12 and 24 hours (p<0.05), and HR repair was reduced (p = 0.014). Herein, we show that KRAS mutation in PDAC positively regulates expression of the HR repair protein RAD18, and that modulation of RAD18 expression correlates with in vitro and in vivo radiosensitization through altered HR-mediated DNA repair. MiR-296-3p successfully reduced RAD18 expression and resulted in enhanced radiosensitization.

Autophagy promotes malignant migration and invasion via miR-224-5p/BCL2 in pancreatic mucinous cystadenocarcinoma MCC1 cells.

The prognosis of invasive pancreatic mucinous cystadenocarcinoma (MCC) is poor, and the molecular mechanism underlying its development remains unclear. The present study aimed to explore the potential role of autophagy in pancreatic MCC. The results demonstrated an increase in autophagy signaling in pancreatic MCC tissues and the MCC1 cell line compared with adjacent tissues and normal human pancreatic ductal epithelium (HPDE) cells. In addition, abnormal autophagy activation facilitated the migration and invasion of MCC1 cells. MicroRNA (miR)-224-5p expression levels were significantly higher in MCC1 cells compared with those in HPDE cells. Treatment with rapamycin further demonstrated that high levels of autophagy elevated miR-224-5p expression in MCC1 cells in a time-dependent manner. BCL2 was identified as a downstream target gene of miR-224-5p, which binds to the 3′-untranslated region of BCL2. In addition, the results of the present study demonstrated that BCL2 knockdown reversed the inhibition of autophagy mediated by the miR-224-5p inhibitor. To the best of our knowledge, this is the first study to evaluate the role of autophagy in pancreatic MCC. Thus, these results suggested that autophagy may be hyperactivated in pancreatic MCC. In addition, the present study identified a positive feedback loop between autophagy signaling and miR-224-5p, which may promote the aggressive migration and invasion of MCC1. These results may provide a new insight into the relationship between autophagy and tumor metastasis in pancreatic MCC.

Downregulation of CDCA3 expression inhibits tumor formation in pancreatic cancer.

Downregulation of cell division cycle-associated 3 (CDCA3) markedly inhibited cell growth and induced apoptosis in tumors. However, the effect of CDCA3 in pancreatic cancer (PAC) was rarely investigated. Therefore, this study attempted to clarify the role of CDCA3 in PAC. The mRNA and protein expression of CDCA3 were examined in PAC cell lines and tumor tissues by using real-time quantitative PCR (RT-qPCR), western blotting (WB), and immunohistochemistry (IHC). The effects of CDCA3 downregulation on cell proliferation, apoptosis, and colony information were investigated through MTT assay, Annexin V-APC single staining cell apoptosis detection, and colony formation test. The microarray and ingenuity pathway analysis were employed to explore the potential regulatory relation. The tumor xenograft model was established for determining the effect of CDCA3 downregulation on the growth of PAC in vivo. The results showed that the expression of CDCA3 in tumor tissues was higher than that of normal tissues (p<0.05). In addition, the mRNA expression of CDCA3 was markedly increased in PANC-1 cells and SW 1990 cells when compared with human pancreatic duct epithelial (HPDE) cells (p<0.05). MTT assay showed that the cell proliferation of PANC-1 cells and SW 1990 cells was significantly inhibited after the lentivirus transfection of CDCA3 knockdown (p<0.05). Annexin V-APC apoptosis assays suggested that the apoptotic cell number was markedly increased in the shCDCA3 group compared to that in the shCtrl group in SW 1990 cells and PANC-1 cells (p<0.05). Meanwhile, the activity of caspase-3/7 was obviously elevated in the shCDCA3 group compared to the shCtrl group (p<0.05). The colony formation was notably inhibited in the shCDCA3 group relative to the shCtrl group in SW 1990 cells (p<0.05). Moreover, the tumor growth was evidently suppressed in the shCDCA3 group compared with the shCtrl group in vivo (p<0.05). These findings revealed that CDCA3 plays a crucial role in the progress of PCA by regulating cell apoptosis and proliferation, which may serve as a potential target for PAC treatment.

TIMP1 down-regulation enhances gemcitabine sensitivity and reverses chemoresistance in pancreatic cancer

The therapeutic effect of gemcitabine (GEM) in pancreatic ductal adenocarcinoma (PDAC) is limited due to low drug sensitivity and high drug resistance. Tissue inhibitor of matrix metalloprotease 1 (TIMP1) is reportedly associated with GEM resistance in PDAC. However, the effect of TIMP1 down-regulation in combination with GEM treatment is unknown. We analyzed the expression of TIMP1 in human PDAC tissue using western blot, quantitative real-time polymerase chain reaction (qRT-PCR), and immunohistochemistry. TIMP1 was highly expressed in PDAC specimens. Kaplan-Meier survival analysis suggested that a higher level of TIMP1 was correlated with poorer overall survival in 103 PDAC patients. The mRNA and protein expression profiles of TIMP1 were explored in the HTERT-HPNE human pancreatic ductal epithelium cell line, five PDAC cell lines (MIA PaCa-2, PANC-1, BxPC-3, Capan2, and SW1990), and two GEM-resistant PDAC cell lines (MIA PaCa-2R and PANC-1R). Compared with HTERT-HPNE, TIMP1 was highly expressed in the PDAC cell lines. In addition, TIMP1 was upregulated in GEM-resistant PDAC cell lines compared with their parental cells. When TIMP1 was knocked-down using short hairpin RNA, GEM-induced cytotoxicity and apoptosis were increased, while colony formation was repressed in MIA PaCa-2, PANC-1, and their GEM-resistant cells. When Bax was activated by BAM7 or Bcl-2 was inhibited by venetoclax, CCK-8 assays demonstrated that GEM sensitivity was restored in GEM-resistant cells. When Bax was down-regulated by siRNA, CCK-8 assays verified that GEM sensitivity was decreased in PDAC cells. The observations that TIMP1 knockdown enhanced GEM sensitivity and reversed chemoresistance by inducing cells apoptosis indicated cooperative antitumor effects of shTIMP1 and GEM therapy on PDAC cells. The combination may be a potential strategy for PDAC therapy.

TGFβ Signaling Increases Net Acid Extrusion, Proliferation and Invasion in Panc-1 Pancreatic Cancer Cells: SMAD4 Dependence and Link to Merlin/NF2 Signaling.

Pancreatic ductal adenocarcinoma (PDAC) is a major cause of cancer-related death, with a 5-year survival of <10% and severely limited treatment options. PDAC hallmarks include profound metabolic acid production and aggressive local proliferation and invasiveness. This phenotype is supported by upregulated net acid extrusion and epithelial-to-mesenchymal transition (EMT), the latter typically induced by aberrant transforming growth factor-β (TGFβ) signaling. It is, however, unknown whether TGFβ-induced EMT and upregulation of acid extrusion are causally related. Here, we show that mRNA and protein expression of the net acid extruding transporters Na+/H+ exchanger 1 (NHE1, SLC9A1) and Na+, HCO cotransporter 1 (NBCn1, SLC4A7) are increased in a panel of human PDAC cell lines compared to immortalized human pancreatic ductal epithelial (HPDE) cells. Treatment of Panc-1 cells (which express SMAD4, required for canonical TGFβ signaling) with TGFβ-1 for 48 h elicited classical EMT with down- and upregulation of epithelial and mesenchymal markers, respectively, in a manner inhibited by SMAD4 knockdown. Accordingly, less pronounced EMT was induced in BxPC-3 cells, which do not express SMAD4. TGFβ-1 treatment elicited a SMAD4-dependent increase in NHE1 expression, and a smaller, SMAD4-independent increase in NBCn1 in Panc-1 cells. Consistent with this, TGFβ-1 treatment led to elevated intracellular pH and increased net acid extrusion capacity in Panc-1 cells, but not in BxPC-3 cells, in an NHE1-dependent manner. Proliferation was increased in Panc-1 cells and decreased in BxPC-3 cells, upon TGFβ-1 treatment, and this, as well as EMT per se, was unaffected by NHE1- or NBCn1 inhibition. TGFβ-1-induced EMT was associated with a 4-fold increase in Panc-1 cell invasiveness, which further increased ~10-fold upon knockdown of the tumor suppressor Merlin (Neurofibromatosis type 2). Knockdown of NHE1 or NBCn1 abolished Merlin-induced invasiveness, but not that induced by TGFβ-1 alone. In conclusion, NHE1 and NBCn1 expression and NHE-dependent acid extrusion are upregulated during TGFβ-1-induced EMT of Panc-1 cells. NHE1 upregulation is SMAD4-dependent, and SMAD4-deficient BxPC-3 cells show no change in pHi regulation. NHE1 and NBCn1 are not required for EMT per se or EMT-associated proliferation changes, but are essential for the potentiation of invasiveness induced by Merlin knockdown.

Abstract C64: C4BPA identified as a novel biomarker is associated with favorable outcome of patients with pancreatic cancer

Abstract Introduction: We have previously identified C4b-binding protein α-chain (C4BPA) as a serum biomarker for pancreatic ductal adenocarcinoma (PDAC). Serum C4BPA level was significantly higher, especially in the early stage of PDAC patients, than in healthy controls as well as in patients with pancreatitis and other malignancies (Br J Cancer 2016). C4BPA is known as a potent soluble inhibitor of the complement system; however, the functional role of C4BPA remains unknown during tumor progression. In this study, we investigated the clinical significance of C4BPA expression and explored the possibility of correlation between C4BPA and antitumoral immunity in PDAC progression. Materials and Methods: Immunohistochemistry (IHC) for C4BPA was performed in resected PDAC tissues. PDAC tissues were obtained from 172 consecutive patients who underwent pancreatectomy at the Department of General Surgery, Chiba University Hospital, Japan from January 2011 to December 2014. In in vitro experiments, we evaluated C4BPA expression in human pancreatic duct epithelial (HPDE) cell, 7 human PDAC cell lines, resected PDAC sample, and the adjacent normal pancreatic tissues. C4BPA is known as a soluble inhibitor of the complement system and an activating ligand for CD40, which alters tumor microenvironment. The binding of CD40 on B cells or macrophages activates antitumoral T cells and antigen-presenting cells and induces a variety of downstream effects. To elucidate the molecular mechanism, we have addressed the association between C4BPA and CD40 expression in PDAC cells. Results: In IHC analysis, we found that C4BPA was mainly expressed in the stroma surrounding PDAC cells. Based on the staining intensity, PDAC samples were categorized into two groups: 75 cases as a high-expression group and 97 cases as a low-expression group. The Kaplan-Meier analysis showed that patients with low C4BPA expression presented a significantly shorter disease-free (P=0.011) and overall survival time than those with high C4BPA expression (P=0.0016, log-rank test). On multivariate analyses, high venous invasion and low C4BPA expression were observed as an independent prognostic factor in patients with PDAC after curative surgery. In in vitro experiment, C4BPA was strongly expressed in human pancreatic duct epithelial (HPDE) cell line but not in PDAC cell lines by Western blotting. Now, we have confirmed C4BPA expression in frozen section of PDAC tissues and the adjacent normal pancreas tissues, and CD40 expression in various PDAC cell lines. Discussion: Our results suggested that low C4BPA expression in the stroma of PDAC is associated with unfavorable prognosis of PDAC patients. These results also suggested that C4BPA might play a role in the process of elimination and equilibrium phase based on the immunoediting theory. Citation Format: Kosuke Sasaki, Shigetsugu Takano, Hideyuki Yoshitomi, Kazuyuki Sogawa, Shingo Kagawa, Katsunori Furukawa, Tsukasa Takayashiki, Satoshi Kuboki, Daisuke Suzuki, Nozomu Sakai, Takashi Mishima, Eri Nakadai, Masayuki Ohtsuka. C4BPA identified as a novel biomarker is associated with favorable outcome of patients with pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C64.

Snail-Overexpression Induces Epithelial-mesenchymal Transition and Metabolic Reprogramming in Human Pancreatic Ductal Adenocarcinoma and Non-tumorigenic Ductal Cells.

The zinc finger transcription factor Snail is a known effector of epithelial-to-mesenchymal transition (EMT), a process that underlies the enhanced invasiveness and chemoresistance of common to cancerous cells. Induction of Snail-driven EMT has also been shown to drive a range of pro-survival metabolic adaptations in different cancers. In the present study, we sought to determine the specific role that Snail has in driving EMT and adaptive metabolic programming in pancreatic ductal adenocarcinoma (PDAC) by overexpressing Snail in a PDAC cell line, Panc1, and in immortalized, non-tumorigenic human pancreatic ductal epithelial (HPDE) cells. Snail overexpression was able to induce EMT in both pancreatic cell lines through suppression of epithelial markers and upregulation of mesenchymal markers alongside changes in cell morphology and enhanced migratory capacity. Snail-overexpressed pancreatic cells additionally displayed increased glucose uptake and lactate production with concomitant reduction in oxidative metabolism measurements. Snail overexpression reduced maximal respiration in both Panc1 and HPDE cells, with further reductions seen in ATP production, spare respiratory capacity and non-mitochondrial respiration in Snail overexpressing Panc1 cells. Accordingly, lower expression of mitochondrial electron transport chain proteins was observed with Snail overexpression, particularly within Panc1 cells. Modelling of 13C metabolite flux within both cell lines revealed decreased carbon flux from glucose in the TCA cycle in snai1-overexpressing Panc1 cells only. This work further highlights the role that Snail plays in EMT and demonstrates its specific effects on metabolic reprogramming of glucose metabolism in PDAC.

A drug‐repositioning screen for primary pancreatic ductal adenocarcinoma cells identifies 6‐thioguanine as an effective therapeutic agent for TPMT‐low cancer cells

Pancreatic cancer is one of the most difficult cancers to cure due to the lack of early diagnostic tools and effective therapeutic agents. In this study, we aimed to isolate new bioactive compounds that effectively kill pancreatic ductal adenocarcinoma (PDAC) cells, but not untransformed, human pancreatic ductal epithelial (HPDE) cells. To this end, we established four primary PDAC cell lines and screened 4141 compounds from four bioactive‐compound libraries. Initial screening yielded 113 primary hit compounds that caused over a 50% viability reduction in all tested PDAC cells. Subsequent triplicate, dose‐dependent analysis revealed three compounds with a tumor cell‐specific cytotoxic effect. We found that these three compounds fall into a single category of thiopurine biogenesis. Among them, 6‐thioguanine (6‐TG) showed an IC50 of 0.39–1.13 μm toward PDAC cells but had no effect on HPDE cells. We propose that this cancer selectivity is due to differences in thiopurine methyltransferase (TPMT) expression between normal and cancer cells. This enzyme is responsible for methylation of thiopurine, which reduces its cytotoxicity. We found that TPMT levels were lower in all four PDAC cell lines than in HPDE or Panc1 cells, and that knockdown of TPMT in HPDE or Panc1 cells sensitized them to 6‐TG. Lastly, we used a patient‐derived xenograft model to confirm that 6‐TG has a significant antitumor effect in combination with gemcitabine. Overall, our study presents 6‐TG as a strong candidate for use as a therapeutic agent against PDAC with low levels of TPMT.

Abstract 3501: Adipocytes sustain pancreatic cancer progression through a non-canonical WNT paracrine network inducing ROR2 nuclear shuttling

Abstract Background: Solid epidemiological evidences connect obesity with incidence, stage, and survival in pancreatic cancer. However, the underlying mechanistic basis linking adipocytes to pancreatic cancer progression remain largely elusive. We hypothesized that factors secreted by adipocytes could be responsible for epithelial-to-mesenchymal transition (EMT) induction and, in turn, a more aggressive phenotype in models of pancreatic preneoplastic lesions. Methods: We studied the role of factors secreted by two adipogenic model systems from primary human Bone Marrow Stromal Cells (hBMSC) in an in vitro experimental cell transformation model system of human pancreatic ductal epithelial (HPDE) cell stably expressing activated KRAS (HPDE/KRAS). Results: We measured a significant induction of EMT and aggressiveness in HPDE and HPDE/KRAS cell lines when cultured with medium conditioned by fully differentiated adipocytes (ADIPOCM) if compared with the same cells cultured with medium conditioned by hBMSC (hBMSCCM) from two different healthy donors. Several genes coding for soluble modulators of the non-canonical WNT signaling pathway, including FRZB, SFRP2, RSPO1, WNT5A and 5B were significantly overexpressed in fully differentiated adipocytes than in their respective in hBMSC. ADIPOCM induced the overexpression and the nuclear translocation of the Frizzled family member Receptor tyrosine kinase-like orphan receptor (Ror) 2 in HPDE and HPDE/KRAS cells. Vantictumab, an anti-Frizzled monoclonal antibody, reduced ROR2 nuclear translocation and in turn the EMT and aggressiveness in HPDE and HPDE/KRAS cells. Conclusions: We demonstrated that adipocytes could induce EMT and aggressiveness in models of pancreatic preneoplastic lesions by orchestrating a complex paracrine signaling of soluble modulators of the non-canonical WNT signaling pathway that determine, in turn, the activation and nuclear translocation of ROR2. This signaling pathway could represent a novel target for pancreatic cancer chemoprevention. Most importantly, these factors could serve as novel biomarkers to select a risk population among obese subjects for screening and, thus, early diagnosis of pancreatic cancer. Citation Format: Carmine Carbone, Geny Piro, Raffaela Santoro, Francesca Simionato, Valeria Merz, Camilla Zecchetto, Aldo Scarpa, Giampaolo Tortora, Davide Melisi. Adipocytes sustain pancreatic cancer progression through a non-canonical WNT paracrine network inducing ROR2 nuclear shuttling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3501.

Abstract 3068: Chronic alcohol exposure induces malignant transformation of pancreatic ductal epithelial cells and generates stem cell characteristics

Abstract Findings from epidemiologic studies and research with experimental animal models provide insights into alcohol toxicity-related disease pathogeneses. Epidemiologic data indicate that heavy drinking is associated with high risk of pancreatic cancer. However the molecular mechanisms by which chronic ethanol exposure changes pathophysiology of human pancreatic ductal epithelial (HPNE) cells is not well understood. Cancer stem cells (CSCs) play significant role in cellular transformation, and their emergence is responsible for cancer initiation, progression and metastasis. SATB2 is required for normal mammalian development; however, it is not expressed in normal adult cells. Inappropriate activation of SATB2 gene may cause malignant cellular transformation. SATB2 regulates transcription of pluripotency maintaining factors which are required for sustaining the stem cells capacity for self-renewal. The main goal of the paper is to examine the molecular mechanisms by which chronic alcohol consumption induces cellular transformation of HPNE cells. To investigate the role of SATB2 at an early step of cell transformation, we utilized HPNE cells to generate progenitor cells either by chronic ethanol exposure or overexpression with SATB2. Our data demonstrate that chronic exposure of HPNE cells to ethanol induces cellular transformation by upregulating SATB2. Furthermore, during ethanol-induced cell transformation, cells gain the phenotype of progenitor cells / CSCs and express pluripotency maintaining factors and epithelial-mesenchymal transition (EMT) markers. Suppression of SATB2 expression in ethanol-transformed HPNE cells inhibits stemness and EMT. SATB2 is highly expressed in pancreatic cancer tissues derived from human and KrasG12D mice. In conclusion, chronic ethanol exposure may contribute in pancreatic carcinogenesis by inducing the expression of SATB2 gene. Citation Format: We Yu, Yiming Ma, Sharmila Shankar, Rakesh K. Srivastava. Chronic alcohol exposure induces malignant transformation of pancreatic ductal epithelial cells and generates stem cell characteristics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3068.