Pancreatic Ductal Adenocarcinoma Cell Survival Research Articles

A pancreatic cancer organoid incorporating macrophages reveals the correlation between the diversity of tumor-associated macrophages and cancer cell survival

Pancreatic ductal adenocarcinoma (PDAC) is a progressive cancer with a poor prognosis. It contains a complex tumor microenvironment (TME) that includes various stromal cell types. Comprehending cellular communications within the TME is difficult due to a lack of research models that can recapitulate human PDAC-TME. Previously, we recapitulated, in part, the PDAC-TME containing a diversity of cancer-associated fibroblasts (CAFs) in vitro. This was done by establishing a PDAC organoid by co-culturing patient-derived cancer cells with human induced pluripotent stem cell (hiPSC)-derived mesenchymal and endothelial cells, which was designated the fused pancreatic cancer organoid (FPCO). We further incorporated macrophages derived from the THP-1 cell line, which are the source of tumor-associated macrophages (TAMs), a major TME component, into FPCO, which was designated M0-FPCO. Bulk RNA sequencing (RNAseq) analysis revealed that macrophages in M0-FPCO (FPCO-Mac) lost their pro-inflammatory features but acquired pro-angiogenic features. Consistently, the formation of an endothelial cell network was enhanced in M0-FPCO. Single-cell RNA-seq (scRNA-seq) analysis revealed that M0-FPCO contained five TAM subpopulations similar to the corresponding TAM in human PDAC tissue in the integrated analysis, including SPP1+-TAM, which has been correlated with tumor angiogenesis and cell proliferation. Focusing on PDAC cells, we found that they could survive longer within the organoid in the presence of TAM. Consistent with the prolonged proliferation and survival of PDAC cells, PDAC subclusters were characterized by proliferative features, such as increased M0-FPCO. Therefore, by establishing a PDAC organoid with macrophages, we recapitulated the diversity of TAMs and identified the role of TAM in endothelial network formation as well as in the modulation of PDAC cell properties. SignificancePDAC organoids, including macrophages using hiPSC, showed that PDAC-TAM has angiogenic features and contributes to PDAC cell survival.

Abstract C038: Cancer-associated fibroblasts maintain critical pancreatic cancer cell lipid homeostasis in the tumor microenvironment

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy whose abundant cancer-associated fibroblasts (CAFs) create a hallmark “desmoplasia” that severely limits oxygen and nutrient delivery. Hypoxia inhibits oxygen-dependent metabolic processes. For example, unsaturated lipid biosynthesis relies on oxygen to maintain desaturase enzymatic activities. Here, we investigated the mechanisms by which PDAC cells maintain lipid homeostasis under these conditions. Exogenous unsaturated lipids, rather than de novo synthesis, sustain PDAC cell viability by relieving endoplasmic reticulum (ER) stress under nutrient scarcity. Furthermore, CAFs are less hypoxic than adjacent malignant cells in vivo due to proximal blood vessel accessibility, nominating them as a potential source of these obligatory species. CAF-conditioned medium promoted PDAC cell survival upon nutrient and oxygen deprivation, an effect reversed by delipidation. We determined that lysophosphatidylcholines (LPCs) are particularly enriched in CAF-conditioned medium and preferentially taken up by PDAC cells, where they are converted to phosphatidylcholines (PCs) to sustain membrane integrity. Inhibiting LPC to PC conversion reversed the ability of exogenous unsaturated LPCs to sustain cancer cell survival and restrain ER stress in vitro and in vivo. Collectively, these results reveal a critical lipid cross-feeding mechanism enabling PDAC cell survival and identify an innovative approach to targeting this metabolic dependency. Efforts to target lipid crosstalk between CAFs and PDAC cells will be discussed. Citation Format: Xu Han, Michelle Burrows, Laura C Kim, Jimmy Xu, Will Vostrejs, Tran Ngoc Van Le, Yanqing Jiang, Edna Cukierman, Reiss Binder Kim, Ben Z Stanger, Clementina Mesaros, Brian Keith, Celeste Simon. Cancer-associated fibroblasts maintain critical pancreatic cancer cell lipid homeostasis in the tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C038.

Abstract B092: PP2A activation alters macropinosome processing in pancreatic cancer cells leading to metabolic stress and cancer cell death

Abstract The majority of pancreatic ductal adenocarcinoma (PDAC) patients present with late-stage, metastatic disease that is often resistant to therapeutics, resulting in the lowest survival rate of all major cancers. Metabolic rewiring in response to oncogenic signals plays a critical role in PDAC cell survival, tumor growth, and metastasis. In contrast to normal epithelial cells, these metabolic alterations make PDAC tumors dependent on glutamine and glucose for survival, highlighting a unique metabolic vulnerability that can be therapeutically exploited. However, during times of nutrient stress, PDAC cells can circumvent this vulnerability by engulfing extracellular fluids to replenish amino acids, including glutamine, in a process called, macropinocytosis. Macropinocytosis occurs downstream of oncogenic KRAS, a small GTPase that is almost universally mutated in PDAC patients. The inhibition of macropinocytosis in vivo reduces PDAC tumor growth, underscoring the importance of this pathway to cancer cell survival. However, the signaling mechanisms that regulate this process and the contribution of macropinocytic signaling to aggressive cancer phenotypes remains poorly understood. Protein phosphatase 2A (PP2A) is a heterotrimeric complex that reguates a wide variety of cell signaling pathways, inlcuding KRAS, and is commonly deregulated in human PDAC tumors. Recently, PP2A has been implicated as an important regulator of macropinocytosis, but the mechanism by which this occurs is unknown. We demosntrate that suppression of PP2A accelerates the formation of KRAS-driven precursor lesions in an in vivo mouse model of PDAC, implicating PP2A as a critical regulator of mutant KRAS phenotypes. Here, we show that acute PP2A activation prevents the fusion of macropinosomes with the lysosome, robbing PDAC cells of critical metabolic nutrients and driving cell death. Furthermore, we find PP2A associates with the lipid kinase, PIKfyve, a key regulator of macropinosome-lysosome fusion. Finally, we determined that PP2A activating compounds can function synergistically with metabolic inhibitors, support a new therapeutic strategy in this aggressive and deadly cancer. Together, our results implicate PP2A as a critical suppressor of PDAC metabolic plasticity and highlight the use of PP2A activating compounds to prevent PDAC nutrient scavenging. Citation Format: Garima Baral, Claire M Pfeffer, Indiraa Doraivel, Sara N Filippelli, Brittany N Heil, Brittany L Allen-Petersen. PP2A activation alters macropinosome processing in pancreatic cancer cells leading to metabolic stress and cancer cell death [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B092.

Abstract C019: A novel SDC1-targeted therapeutic antibody inhibits macropinocytosis and induces anti-tumor immunity in pancreatic cancer

Abstract Given that the mutated KRAS oncogene (KRAS*) dominates the genetic landscape of pancreatic ductal adenocarcinoma (PDAC), the development of KRAS* inhibitors represents a significant breakthrough in PDAC therapy. However, emerging evidence suggests that PDAC may eventually overcome its dependency on KRAS* and develop resistance to KRAS* inhibitor treatment. Our laboratory is dedicated to uncovering novel, accessible therapeutic targets that govern the mechanisms essential for KRAS*- driven PDAC cell survival. Our recent work has identified Syndecan1 (SDC1), a major heparan sulfate proteoglycan, as a critical mediator of KRAS* activity, promoting nutrient salvaging and fueling cancer cell growth, even in cases where PDAC cells have evaded KRAS* targeted therapy. Our finding positions SDC1 as a promising new therapeutic target for PDAC therapy. In our pursuit of new therapeutic approaches that can directly and specifically target SDC1 activity, we have successfully developed a monoclonal antibody against SDC1 (22B mAb), which exhibits remarkable sensitivity and specificity for human SDC1. Our results indicate that 22B mAb exerts substantial inhibition of PDAC cell growth in vitro and desirable tumor inhibitory effects in vivo in murine PDAC tumors and human PDAC cell-derived xenograft tumors. Interrogation of mechanism of actions further demonstrates that 22B elicits both direct effect in inhibiting macropinocytosis to block nutrient salvage of PDAC cells and indirect effect in inducing antibody-dependent cellular cytotoxicity (ADCC) to eliminate tumor cells. Notably, our 22B mAb synergizes with KRAS* inhibitors, chemotherapy, or immunotherapy, resulting in significantly enhanced therapeutic effects. In summary, our 22B mAb represents the first in class of anti-SDC1 antibody that not only directly targets the PDAC cells but also elicits immune cell-mediated killing. Additionally, our antibody holds the potential for developing new anti-PDAC therapeutic strategies, including antibody drug conjugates with cytotoxic or radionuclides payloads, for SDC1 targeted therapy/theranostics in PDAC. Thus, our newly developed 22B therapeutic antibody provides an alternate strategy for PDAC treatment and opens up new research horizons in therapeutic targeting of SDC1 in other malignancies characterized by aberrant SDC1 expression. Citation Format: Zecheng Yang, Madelaine S Theardy, Shuaitong Chen, Yongkun Wei, Mitsunobu Takeda, Xiaofei Wang, Jun Yao, Jennifer Li, Jangho Park, Yangxi Zheng, Long T Vien, Laura Bover, Haoqiang Ying, Wantong Yao. A novel SDC1-targeted therapeutic antibody inhibits macropinocytosis and induces anti-tumor immunity in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C019.

Pantoprazole and riluzole target H+/K+-ATPases and pH-sensitive K+ channels in pancreatic cancer cells.

Pancreatic ductal adenocarcinoma (PDAC) remains the most lethal cancer type. PDAC is characterized by fibrotic, hypoxic, and presumably acidic tumor microenvironment (TME). Acidic TME is an important player in tumor development, progression, aggressiveness, and chemoresistance. The dysregulation of ductal ion transporters/channels might contribute to extracellular pH (pHe) acidification and PDAC progression. Our aim was to test whether H+/K+-ATPases and pH-sensitive K+ channels contribute to these processes and could be targeted by clinically approved drugs. We used human pancreatic cancer cells adapted to various pHe conditions and grown in monolayers and spheroids. First, we created cells expressing pHoran4 at the outer plasma membrane and showed that pantoprazole, the H+/K+-ATPase inhibitor, alkalinized pHe. Second, we used FluoVolt to monitor the membrane voltage (Vm) and showed that riluzole hyperpolarized Vm, most likely by opening of pH-sensitive K+ channels such as TREK-1. Third, we show that pantoprazole and riluzole inhibited cell proliferation and viability of monolayers and spheroids of cancer cells adapted to various pHe conditions. Most importantly, combination of the two drugs had significantly larger inhibitory effects on PDAC cell survival. We propose that co-targeting H+/K+-ATPases and pH-sensitive K+ channels by re-purposing of pantoprazole and riluzole could provide novel acidosis-targeted therapies of PDAC.

Potential role of lipophagy impairment for anticancer effects of glycolysis-suppressed pancreatic ductal adenocarcinoma cells

Although increased aerobic glycolysis is common in various cancers, pancreatic ductal adenocarcinoma (PDAC) cells can survive a state of glycolysis suppression. We aimed to identify potential therapeutic targets in glycolysis-suppressed PDAC cells. By screening anticancer metabolic compounds, we identified SP-2509, an inhibitor of lysine-specific histone demethylase 1A (LSD1), which dramatically decreased the growth of PDAC PANC-1 cells and showed an anti-tumoral effect in tumor-bearing mice. The growth of glycolysis-suppressed PANC-1 cells was also inhibited by another LSD1 inhibitor, OG-L002. Similarly, the other two PDAC cells (PK-1 and KLM-1) with suppressed glycolysis exhibited anticancer effects against SP-2509. However, the anticancer effects on PDAC cells were unrelated to LSD1. To investigate how PDAC cells survive in a glycolysis-suppressed condition, we conducted proteomic analyses. These results combined with our previous findings suggested that glucose-starvation causes PDAC cells to enhance mitochondrial oxidative phosphorylation. In particular, mitochondrial fatty acid metabolism was identified as a key factor contributing to the survival of PDAC cells under glycolysis suppression. We further demonstrated that SP-2509 and OG-L002 disturbed fatty acid metabolism and induced lipid droplet accumulation through the impairment of lipophagy, but not bulk autophagy. These findings indicate a significant potential association of lipophagy and anticancer effects in glycolysis-suppressed PDAC cells, offering ideas for new therapeutic strategies for PDAC by dual inhibition of glycolysis and fatty acids metabolism.

Progesterone receptor potentiates macropinocytosis through CDC42 in pancreatic ductal adenocarcinoma

Endocrine receptors play an essential role in tumor metabolic reprogramming and represent a promising therapeutic avenue in pancreatic ductal adenocarcinoma (PDAC). PDAC is characterized by a nutrient-deprived microenvironment. To meet their ascendant energy demands, cancer cells can internalize extracellular proteins via macropinocytosis. However, the roles of endocrine receptors in macropinocytosis are not clear. In this study, we found that progesterone receptor (PGR), a steroid-responsive nuclear receptor, is highly expressed in PDAC tissues obtained from both patients and transgenic LSL-KrasG12D/+; LSL-Trp53R172H/+; PDX1-cre (KPC) mice. Moreover, PGR knockdown restrained PDAC cell survival and tumor growth both in vitro and in vivo. Genetic and pharmacological PGR inhibition resulted in a marked attenuation of macropinocytosis in PDAC cells and subcutaneous tumor models, indicating the involvement of this receptor in macropinocytosis regulation. Mechanistically, PGR upregulated CDC42, a critical regulator in macropinocytosis, through PGR-mediated transcriptional activation. These data deepen the understanding of how the endocrine system influences tumor progression via a non-classical pathway and provide a novel therapeutic option for patients with PDAC.

Abstract A054: PP2A activation alters macropinosome processing in pancreatic cancer cells leading to metabolic stress and cancer cell death

Abstract The majority of pancreatic ductal adenocarcinoma (PDAC) patients present with late-stage, metastatic disease that is often resistant to therapeutics, resulting in the lowest survival rate of all major cancers. Metabolic rewiring in response to oncogenic signals plays a critical role in PDAC cell survival, tumor growth, and metastasis. In contrast to normal epithelial cells, these metabolic alterations make PDAC tumors dependent on glutamine for survival, highlighting a unique metabolic vulnerability that can be therapeutically exploited. However, during times of nutrient stress, PDAC cells can circumvent this vulnerability by engulfing extracellular fluids to replenish amino acids, including glutamine, in a process called, macropinocytosis. Macropinocytosis occurs downstream of oncogenic KRAS, a small GTPase that is almost universally mutated in PDAC patients. The inhibition of macropinocytosis in vivo reduces PDAC tumor growth, underscoring the importance of this pathway to cancer cell survival. However, the signaling mechanisms that regulate this process and the contribution of macropinocytic signaling to aggressive cancer phenotypes remains poorly understood. Protein phosphatase 2A (PP2A) is a heterotrimeric complex that regulates a wide variety of cell signaling pathways, including KRAS, and is commonly deregulated in human PDAC tumors. Recently, PP2A has been implicated as an important regulator of macropinocytosis, but the mechanism by which this occurs is unknown. We demonstrate that the genetic loss of the specific PP2A subunit, B56a, accelerates the formation of KRAS-driven pancreatic lesions in an in vivo mouse model, implicating this subunit as a critical negative regulator of KRAS phenotypes during PDAC progression. Here, we show that acute PP2A-B56a activation prevents the fusion of macropinosomes with lysosomes, robbing PDAC cells of critical metabolic nutrients and driving cell death. Consistent with these findings, PP2A activation also reduces glutamine levels and suppresses oxidative phosphorylation. Finally, we determined that PP2A activating compounds can function synergistically with metabolic inhibitors, supporting a new therapeutic strategy in this aggressive and deadly cancer. Together, our results implicate PP2A as a critical suppressor of PDAC metabolic plasticity and highlight the use of PP2A activating compounds to prevent PDAC nutrient scavenging. Citation Format: Garima Baral, Claire M. Pfeffer, Indiraa Doraivel, Brittany L. Allen-Petersen. PP2A activation alters macropinosome processing in pancreatic cancer cells leading to metabolic stress and cancer cell death [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 A054.

Heme Oxygenase-1 Inhibition Modulates Autophagy and Augments Arsenic Trioxide Cytotoxicity in Pancreatic Cancer Cells.

Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent form, accounting for more than 90% of all pancreatic malignancies. In a previous study, we found that hypoxia and chemotherapy induced expression of Heme Oxygenase-1 (HO-1) in PDAC cells and tissues. Arsenic trioxide (ATO) is the first-line chemotherapeutic drug for acute promyelocytic leukemia (APL). ATO increases the generation of reactive oxidative species (ROS) and induces apoptosis in treated cells. The clinical use of ATO for solid tumors is limited due to severe systemic toxicity. In order to reduce cytotoxic side effects and resistance and improve efficacy, it has become increasingly common to use combination therapies to treat cancers. In this study, we used ATO-sensitive and less sensitive PDAC cell lines to test the effect of combining HO-1 inhibitors (SnPP and ZnPP) with ATO on HO-1 expression, cell survival, and other parameters. Our results show that ATO significantly induced the expression of HO-1 in different PDAC cells through the p38 MAPK signaling pathway. ROS production was confirmed using the oxygen-sensitive probes DCFH and DHE, N-acetyl cysteine (NAC), an ROS scavenger, and oxidized glutathione levels (GSSG). Both ATO and HO-1 inhibitors reduced PDAC cell survival. In combined treatment, inhibiting HO-1 significantly increased ATO cytotoxicity, disrupted the GSH cycle, and induced apoptosis as measured using flow cytometry. ATO and HO-1 inhibition modulated autophagy as shown by increased expression of autophagy markers ATG5, p62, and LC3B in PDAC cells. This increase was attenuated by NAC treatment, indicating that autophagy modulation was through an ROS-dependent mechanism. In conclusion, our work explored new strategies that could lead to the development of less toxic and more effective therapies against PDAC by combining increased cellular stress and targeting autophagy.

Abstract 3870: TNF-MK2 signaling drives protective autophagy following MAPK pathway inhibition in pancreatic cancer

Abstract Targeting the oncogenic KRAS-RAF-MEK-ERK (MAPK) pathway has remain unsuccessful in the clinic for patients with pancreatic ductal adenocarcinoma (PDAC), a highly lethal cancer with few effective treatment options. To identify novel, effective therapeutic strategies, we investigated the impact of MEK and ERK inhibitors on production of inflammatory cytokines in PDAC cells. We found that both MEK and ERK inhibitors dramatically upregulated production of TNF, leading to activation of multiple TNF signaling pathways which include the pro-death and pro-survival NF-kB and p38.MK2 cascades. Silencing of TNF receptor 1 (TNFR1) abrogated the pro-apoptotic effect of MAPK inhibitors, suggesting that pro-death effect driven by TNF signaling is required for the therapeutic effect of MAPK inhibitors. However, targeting the NF-kB and MK2 pathways greatly augment the suppressive effect of MAPK inhibitors. Notably, the mechanisms via which MK2 promotes PDAC cell survival are mediated through phospho-activation of Heat shock protein 27 (Hsp27) and Beclin1, a critical mediator of autophagy. Intriguingly, silencing of TNFR1 abrogated induction of proactive autophagy following MAPK inhibition, strongly suggesting autocrine signaling as the inciting event of autophagy. Mechanistically, we showed that TNF signaling upregulate unfolded protein response (UPR) in PDAC cells, which is required for autophagy induction. Targeting MK2 abrogated transcription of key UPR genes and blocks subsequent autophagy. The combination of MK2 inhibitor ATI-450 and ERK inhibitor ulixertinib was more effective in curbing the growth of PDAC patient-derived xenograft in vivo and prolonged the survival of autochthonous PDAC mice (KPC model). Overall, our study provided novel insights on the mechanisms that drive protective autophagy following MAPK pathway inhibition and a rationale and feasible therapeutic combination that can be tested in clinical trials for PDAC patients. Citation Format: Iftikhar Ali Khawar, Qing Wei, Timothy Hung-Po Chen, Lin Lin, Patrick M. Grierson, Kian-Huat Lim. TNF-MK2 signaling drives protective autophagy following MAPK pathway inhibition in pancreatic cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3870.

Mechanisms of development and progression of pancreatic neoplasms.

Pancreatic ductal adenocarcinoma (PDAC) develops via dysplastic changes in the epithelia graded as low- and high-grade with accumulation of molecular alterations. Constitutive activation of mitogen-activated protein kinase (MAPK) contributed by attenuation of DUSP6 plays a key role in sustaining PDAC. Active MAPK induces various molecules that function as effectors to sustain PDAC. AURKA and SON are downstream effectors that contribute substantially to the proliferation and survival of PDAC cells and are potentially useful as therapeutic targets. Active MAPK also promote microRNAs that modulate the proliferation of PDAC cells and are useful as diagnostic markers. Familial pancreatic cancer kindreds in Japan show various germline mutations supposed to increase a pancreatic cancer risk. Intraductal papillary mucinous neoplasms (IPMNs) consist of dilated ducts lined by papillary neoplastic epithelia of various shapes and varying grades of atypia. Various papillae of IPMNs are classified into four subtypes that are associated with clinicopathological features, including patient prognosis. GNAS is a specific driver gene for the development of IPMN through gain-of-function mutations. Tracing of molecular alterations has elucidated the mechanism of progression of IPMN from dysplasia to carcinoma, as well as one type of papillae. Intraductal tubulopapillary neoplasms belong to a distinct class of pancreatic neoplasms.

IRAK4 Signaling Drives Resistance to Checkpoint Immunotherapy in Pancreatic Ductal Adenocarcinoma

Checkpoint immunotherapy is largely ineffective in pancreatic ductal adenocarcinoma (PDAC). The innate immune nuclear factor (NF)-κB pathway promotes PDAC cell survival and stromal fibrosis, and is driven by Interleukin-1 Receptor Associated Kinase-4 (IRAK4), but its impact on tumor immunity has not been directly investigated. We interrogated The Cancer Genome Atlas data to identify the correlation between NF-κB and T cell signature, and a PDAC tissue microarray (TMA) to correlate IRAK4 activity with CD8+ T cell abundance. We performed RNA sequencing (RNA-seq) on IRAK4-deleted PDAC cells, and single-cell RNA-seq on autochthonous KPC (p48-Cre/TP53f/f/LSL-KRASG12D) mice treated with an IRAK4 inhibitor. We generated conditional IRAK4-deleted KPC mice and complementarily used IRAK4 inhibitors to determine the impact of IRAK4 on T cell immunity. We found positive correlation between NF-κB activity, IRAK4 and T cell exhaustion from The Cancer Genome Atlas. We observed inverse correlation between phosphorylated IRAK4 and CD8+ T cell abundance in a PDAC tissue microarray. Loss of IRAK4 abrogates NF-κB activity, several immunosuppressive factors, checkpoint ligands, and hyaluronan synthase 2, all of which drive T cell dysfunction. Accordingly, conditional deletion or pharmacologic inhibition of IRAK4 markedly decreased tumor desmoplasia and increased the abundance and activity of infiltrative CD4+ and CD8+ T cells in KPC tumors. Single-cell RNA-seq showed myeloid and fibroblast reprogramming toward acute inflammatory responses following IRAK4 inhibition. These changes set the stage for successful combination of IRAK4 inhibitors with checkpoint immunotherapy, resulting in excellent tumor control and markedly prolonged survival of KPC mice. IRAK4 drives T cell dysfunction in PDAC and is a novel, promising immunotherapeutic target.

SUMO Modification of PAF1/PD2 Enables PML Interaction and Promotes Radiation Resistance in Pancreatic Ductal Adenocarcinoma.

RNA polymerase II-associated factor 1 (PAF1)/pancreatic differentiation 2 (PD2) is a core subunit of the human PAF1 complex (PAF1C) that regulates the RNA polymerase II function during transcriptional elongation. PAF1/PD2 has also been linked to the oncogenesis of pancreatic ductal adenocarcinoma (PDAC). Here, we report that PAF1/PD2 undergoes posttranslational modification (PTM) through SUMOylation, enhancing the radiation resistance of PDAC cells. We identified that PAF1/PD2 is preferentially modified by small ubiquitin-related modifier 1 (SUMO 1), and mutating the residues (K)-150 and 154 by site-directed mutagenesis reduces the SUMOylation. Interestingly, PAF1/PD2 was found to directly interact with the promyelocytic leukemia (PML) protein in response to radiation, and inhibition of PAF1/PD2 SUMOylation at K-150/154 affects its interaction with PML. Our results demonstrate that SUMOylation of PAF1/PD2 increased in the radiated pancreatic cancer cells. Furthermore, inhibition of SUMOylation or PML reduces the cell growth and proliferation of PDAC cells after radiation treatment. These results suggest that SUMOylation of PAF1/PD2 interacts with PTM for PDAC cell survival. Furthermore, abolishing the SUMOylation in PDAC cells enhances the effectiveness of radiotherapy. Overall, our results demonstrate a novel PTM and PAF1/PD2 interaction through SUMOylation, and inhibiting the SUMOylation of PAF1/PD2 enhance the therapeutic efficacy for PDAC.

YEATS2 regulates the activation of TAK1/NF-κB pathway and is critical for pancreatic ductal adenocarcinoma cell survival.

The prognosis of pancreatic ductal adenocarcinoma (PDAC) is poor despite diagnostic progress and new chemotherapeutic regimens. Constitutive activation of NF-κB is frequently observed in PDAC. In this study, we found that YEATS2, a scaffolding protein of ATAC complex, was highly expressed in human PDAC. Depletion of YEATS2 reduced the growth, survival, and tumorigenesis of PDAC cells. The binding of YEATS2 is crucial for maintaining TAK1 activation and NF-κB transcriptional activity. Of importance, our results reveal that YEATS2 promotes NF-κB transcriptional activity through modulating TAK1 abundance and directly interacting with NF-κB as a co-transcriptional factor.

Genetic Inactivation of Peroxiredoxin-I Impairs the Growth of Human Pancreatic Cancer Cells.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with few therapeutic options. The identification of new promising targets is, therefore, an urgent need. Using available transcriptomic datasets, we first found that Peroxiredoxin-1 gene (PRDX1) expression was significantly increased in human pancreatic tumors, but not in the other gastrointestinal cancers; its high expression correlated with shortened patient survival. We confirmed by immunostaining on mouse pancreata the increased Peroxiredoxin-I protein (PRX-I) expression in pancreatic neoplastic lesions and PDAC. To question the role of PRX-I in pancreatic cancer, we genetically inactivated its expression in multiple human PDAC cell lines, using siRNA and CRISPR/Cas9. In both strategies, PRX-I ablation led to reduced survival of PDAC cells. This was mainly due to an increase in the production of reactive oxygen species (ROS), accumulation of oxidative DNA damage (i.e., 8-oxoguanine), and cell cycle blockade at G2/M. Finally, we found that PRX-I ablation disrupts the autophagic flux in PDAC cells, which is essential for their survival. This proof-of-concept study supports a pro-oncogenic role for PRX-I in PDAC.

Macropinocytosis in Cancer-Associated Fibroblasts Is Dependent on CaMKK2/ARHGEF2 Signaling and Functions to Support Tumor and Stromal Cell Fitness.

Although pancreatic ductal adenocarcinoma (PDAC) cells are exposed to a nutrient-depleted tumor microenvironment, they can acquire nutrients via macropinocytosis, an endocytic form of protein scavenging that functions to support cancer metabolism. Here, we provide evidence that macropinocytosis is also operational in the pancreatic tumor stroma. We find that glutamine deficiency triggers macropinocytic uptake in pancreatic cancer-associated fibroblasts (CAF). Mechanistically, we decipher that stromal macropinocytosis is potentiated via the enhancement of cytosolic Ca2+ and dependent on ARHGEF2 and CaMKK2-AMPK signaling. We elucidate that macropinocytosis has a dual function in CAFs-it serves as a source of intracellular amino acids that sustain CAF cell fitness and function, and it provides secreted amino acids that promote tumor cell survival. Importantly, we demonstrate that stromal macropinocytosis supports PDAC tumor growth. These results highlight the functional role of macropinocytosis in the tumor stroma and provide a mechanistic understanding of how nutrient deficiency can control stromal protein scavenging. SIGNIFICANCE: Glutamine deprivation drives stromal macropinocytosis to support CAF cell fitness and provide amino acids that sustain PDAC cell survival. Selective disruption of macropinocytosis in CAFs suppresses PDAC tumor growth.This article is highlighted in the In This Issue feature, p. 1601.

AraC-FdUMP[10] Is a Next-Generation Fluoropyrimidine with Potent Antitumor Activity in PDAC and Synergy with PARG Inhibition.

AraC-FdUMP[10] (CF10) is a second-generation polymeric fluoropyrimidine that targets both thymidylate synthase (TS), the target of 5-fluorouracil (5-FU), and DNA topoisomerase 1 (Top1), the target of irinotecan, two drugs that are key components of FOLFIRNOX, a standard-of-care regimen for pancreatic ductal adenocarcinoma (PDAC). We demonstrated that F10 and CF10 are potent inhibitors of PDAC cell survival (in multiple cell lines including patient-derived lines) with IC50s in the nanomolar range and are nearly 1,000-fold more potent than 5-FU. The increased potency of CF10 relative to 5-FU correlated with enhanced TS inhibition and strong Top1 cleavage complex formation. Furthermore, CF10 displayed single-agent activity in PDAC murine xenografts without inducing weight loss. Through a focused drug synergy screen, we identified that combining CF10 with targeting the DNA repair enzyme, poly (ADP-ribose) glycohydrolase, induces substantial DNA damage and apoptosis. This work moves CF10 closer to a clinical trial for the treatment of PDAC. IMPLICATIONS: CF10 is a promising polymeric fluoropyrimidine with dual mechanisms of action (i.e., TS and Top1 inhibition) for the treatment of PDAC and synergizes with targeting of DNA repair. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/4/565/F1.large.jpg.

Abstract PO-017: Targeting NF-kB pathway through IRAK4 renders immune checkpoint blockade effective in pancreatic cancer

Abstract Effective immunotherapy in pancreatic ductal adenocarcinoma (PDAC) is impeded by multiple barriers in the tumor microenvironment. These include the dense extracellular matrix (ECM), excessive inhibitory myeloid cells, cytokines and chemokines, which collectively incapacitate anti-tumour T cells. Constitutive activation the NF-kB pathway is a mechanism that drives intrinsic survival of PDAC cells and stromal fibrosis, but its impact on anti-tumour immunity has not been investigated. Using The Cancer Genome Atlas database, we found that expression of RELA, a canonical NF-kB factor, in PDAC samples is associated with activated stroma and lower cytotoxic T cell signatures. In a PDAC tissue microarray, the staining intensity of activated IRAK4, the innate immune kinase that drives NF-kB signaling, negatively correlates with T cell abundance. Based on these findings, we investigated the immunological impact role of IRAK4 in PDAC. Transcriptomic analysis showed that ablation of IRAK4 in PDAC cells downregulates NF-kB and inflammatory signatures, and markedly decreases transcription of hyaluronan synthase 2 (HAS2). Accordingly, pharmacologic inhibition of IRAK4 significantly decreased intratumoral hyaluronan, as well as collagen, in autochthonous PDAC mice and potentiated standard chemotherapy. Furthermore, IRAK4 inhibition also significantly reduced production of several suppressive chemokines and checkpoint ligands PD-L1 and Nectin2, leading to revitalization of infiltrative CD4+ and CD8+ T cells. These effects were partly mediated through reduction of intratumoural hyaluronan, which we recapitulated with HAS inhibitor, 4-MU. Accordingly, combined IRAK4 inhibitors with immune checkpoint blockade (ICB) especially anti-CTLA4, were highly efficacious in abrogating tumour growth in autochthonous PDAC mice and doubling their survival. In summary, we showed that targeting the NF-kB pathway through IRAK4 renders ICB effective via multiple mechanisms and should be tested in clinical trials for PDAC patients. Citation Format: Daoxiang Zhang, Vikas Somani, Paarth B. Dodhiawala, Patrick M. Grierson, Lin Li, Kuljeet Seehra, Xiuting Liu, Brett L. Knolhoff, Marianna B. Ruzinova, David G. DeNardo, Kian-Huat Lim. Targeting NF-kB pathway through IRAK4 renders immune checkpoint blockade effective in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-017.

Docosahexaenoic acid inhibits the proliferation of Kras/TP53 double mutant pancreatic ductal adenocarcinoma cells through modulation of glutathione level and suppression of nucleotide synthesis.

The treatment of cancer cells obtained by blocking cellular metabolism has received a lot of attention recently. Previous studies have demonstrated that Kras mutation-mediated abnormal glucose metabolism would lead to an aberrant cell proliferation in human pancreatic ductal adenocarcinoma (PDAC) cells. Previous literature has suggested that consumption of fish oil is associated with lower risk of pancreatic cancer. In this study, we investigated the anti-cancer effects of docosahexaenoic acid (DHA) in human PDAC cells in vitro and in vivo. Omega-3 polyunsaturated fatty acids (PUFAs) such as DHA and eicosapentaenoic acid (EPA) significantly inhibited the proliferation of human PDAC cells. The actions of DHA were evaluated through an induction of cell cycle arrest at G1 phase and noticed a decreased expression of cyclin A, cyclin E and cyclin B proteins in HPAF-II cells. Moreover, it was found that co-treatment of DHA and gemcitabine (GEM) effectively induced oxidative stress and cell death in HPAF-II cells. Interestingly, DHA leads to an increased oxidative glutathione /reduced glutathione (GSSG/GSH) ratio and induced cell apoptosis in HPAF-II cells. The findings in the study showed that supplementation of GSH or N-Acetyl Cysteine (NAC) could reverse DHA-mediated cell death in HPAF-II cells. Additionally, DHA significantly increased cellular level of cysteine, cellular NADP/NADPH ratio and the expression of cystathionase (CTH) and SLCA11/xCT antiporter proteins in HPAF-II cells. The action of DHA was, in part, associated with the inactivation of STAT3 cascade in HPAF-II cells. Treatment with xCT inhibitors, such as erastin or sulfasalazine (SSZ), inhibited the cell survival ability in DHA-treated HPAF-II cells. DHA also inhibited nucleotide synthesis in HPAF-II cells. It was demonstrated in a mouse-xenograft model that consumption of fish oil significantly inhibited the growth of pancreatic adenocarcinoma and decreased cellular nucleotide level in tumor tissues. Furthermore, fish oil consumption induced an increment of GSSG/GSH ratio, an upregulation of xCT and CTH proteins in tumor tissues. In conclusion, DHA significantly inhibited survival of PDAC cells both in vitro and in vivo through its recently identified novel mode of action, including an increment in the ratio of GSSG/GSH and NADP/NADPH respectively, and promoting reduction in the levels of nucleotide synthesis.

Targeting the IκB Kinase Enhancer and Its Feedback Circuit in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease with an overall median 5-year survival rate of 8%. This poor prognosis is because of the development of resistance to chemotherapy and radiation therapy and lack of effective targeted therapies. IκB kinase enhancer (IKBKE) overexpression was previously implicated in chemoresistance. Because IKBKE is frequently elevated in PDAC and IKBKE inhibitors are currently in clinical trials, we evaluated IKBKE as a therapeutic target in this disease. Depletion of IKBKE was found to significantly reduce PDAC cell survival, growth, cancer stem cell renewal, and cell migration and invasion. Notably, IKBKE inhibitor CYT387 and IKBKE knockdown dramatically activated the MAPK pathway. Phospho-RTK array analyses showed that IKBKE inhibition leads to rapid upregulation of ErbB3 and IGF-1R expression, which results in MAPK-ERK pathway activation—thereby limiting the efficacy of IKBKE inhibitors. Furthermore, IKBKE inhibition leads to stabilization of FOXO3a, which is required for RTK upregulation on IKBKE inhibition. Finally, we demonstrated that the IKBKE inhibitors synergize with the MEK inhibitor trametinib to significantly induce cell death and inhibit tumor growth and liver metastasis in an orthotopic PDAC mouse model.