Pancreatic Ductal Adenocarcinoma Cell Lines Research Articles

Abstract C032: De novo pyrimidine biosynthesis inhibition synergizes with BCL-XL targeting in pancreatic cancer

Abstract Oncogenic KRAS, the genetic driver of 90% of PDAC, induces a metabolic rewiring characterized, in part, by dependency on de novo pyrimidine biosynthesis. Dihydroorotate dehydrogenase (DHODH) is the enzymatic ‘chokepoint’ of the de novo pyrimidine biosynthesis pathway and an in vivo metabolic liability in pancreatic ductal adenocarcinoma (PDAC). Targeting enzymes in the de novo pyrimidine synthesis pathway such as dihydroorotate dehydrogenase (DHODH) with clinically available inhibitor brequinar (BQ) starved the tumor of nucleotide synthesis and restrained growth of PDAC cells in vitro. However, therapeutic resistance limited BQ long-term effects in PDAC xenografts, which suggests compensatory pathways and that combinatorial strategies are required for enhanced efficacy. Here, we integrated a mass spectrometry (MS)-based quantitative temporal proteomics workflow, LC/MS- based metabolomics and in vitro and in vivo drug-anchored CRISPR/Cas9 genetic screens to identify compensatory pathways to DHODH inhibition (DHODHi) and targets for combination strategies. We demonstrate that DHODHi alters the apoptotic regulatory proteome thereby enhancing sensitivity to inhibitors of the anti-apoptotic BCL2L1 (BCL-XL) protein. Combinatorial regimens with DHODH and BCL-XL inhibition synergistically induce apoptosis in PDAC cell lines and patient-derived PDAC organoids. In vivo DHODH inhibition with Brequinar and BCL-XL degradation with DT2216, a proteolysis targeting chimera (PROTAC), significantly inhibits the growth of PDAC tumors. Our data defines mechanisms of adaptation to DHODH inhibition and identifies a combination therapy strategy in PDAC. Citation Format: huan zhang, Qijia yu, Naiara Santana-Codina, Clara Poupault, Claudia Campos, Xingping Qin, Aparna Padhye, Nicole Sindoni, Miljan Kuljanin, Junning Wang, Matthew J. Dorman, Andrew J. Aguirre, Stephanie K. Dougan, Kristopher A. Sarosiek, Joseph D. Mancias. De novo pyrimidine biosynthesis inhibition synergizes with BCL-XL targeting 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 C032.

Abstract A076: LINE-1 ORF1p mimics viral innate immune evasion mechanisms in pancreatic cancer

Abstract Aberrant expression of repeat elements displaying viral mimicry is a common feature found in both mouse models and human pancreatic ductal adenocarcinoma (PDAC). However, cancer cells must employ mechanisms to manage this "viral" repeat element load to avoid triggering innate immune responses. Here, we demonstrate that the long interspersed nuclear element 1 (LINE-1) ORF1 protein (ORF1p) in PDAC cells plays a role in shielding repeat RNAs from activating pathogen recognition receptor (PRR)-mediated antiviral responses, independent of retrotransposition. Suppression of ORF1p using lentiviral shRNA induces innate immune responses through the PRRs, RIG-I and MAVS (double-stranded RNA sensors). Interestingly, PDAC cell lines with low ORF1p lack these two receptors, suggesting convergent mechanisms to suppress PRR signaling. Furthermore, RNA immunoprecipitation sequencing (RIP-seq) demonstrates ORF1p association with repeat RNA, including LINE and SINE elements that typically trigger antiviral responses. Subcellular localization of ORF1p in processing bodies (p-bodies) reveals specific interaction with MOV10, a dsRNA helicase crucial for antiviral responses. Loss of ORF1p results in significant growth reduction in vitro and in vivo, which supports ORF1p as a potential immune oncology therapeutic target. Altogether, our results demonstrate a novel function of ORF1p in shielding cytoplasmic repeat RNA from PRR sensing, shedding light on how PDAC cells evade host immune responses triggered by viral-like repeat RNA. Citation Format: Eunae You, Bidish Patel, Alexandra Rojas, Siyu Sun, Natalie Ho, Ildiko Phillips, Michael Raabe, Yuhui Song, Katherine Xu, Joshua Kocher, Peter Richieri, Martin Taylor, Linda Nieman, Benjamin Greenbaum, David Ting. LINE-1 ORF1p mimics viral innate immune evasion mechanisms 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 A076.

Abstract C073: FOLFIRINOX with Glycogen Synthase Kinase-3 Beta (GSK-3β) Inhibitor Elraglusib and Transforming Growth Factor- β (TGFβ) Inhibitor Losartan in Untreated Metastatic Pancreatic Ductal Adenocarcinoma(PDAC): Interim analysis of safety cohort

Abstract Introduction: Epithelial-mesenchymal transition (EMT) is one of the key drivers of aggressive biology and development of chemoresistance in PDAC. Inhibition of glycogen synthase kinase 3β (GSK3β) may offer a promising novel approach for modulating dynamic EMT plasticity to overcome resistance to FOLFIRINOX (5-Fluororuacil, Irinotecan, Oxaliplatin, FFX). Methods: Cell line panels comprising both epithelial (E) and quasi-mesenchymal (QM) subtypes were used and treated with IC50 (0.3125 mM) and IC100 (1.25 mM) doses of elraglusib (ELR). Gene expression patters in response to treatment were analyzed using bulk RNA sequencing. 6 patients in the safety run-in cohort of NCT05077800 treated with standard doses of FFX, ELR and losartan were included in this interim analysis. Biopsy specimens were processed for RNA-in situ hybridization (RNA-ISH), a clinically validated assay, and Nanostring (GeoMx) spatial transcriptomics. Results: In preclinical models, exposure to the higher IC100 (1.25 mM) doses of ELR in the QM cell lines caused a shift in transcriptional expression patterns similar to the E cell line, with strong downregulation of EMT. FFX exposure alone in QM cell lines was associated with significant resistance, but addition of ELR (even at IC50 dose) caused a synergistic effect with decreased cell viability. However, in the E cell lines, there was no benefit from addition of ELR. In the safety cohort, clinical results are encouraging with a long-term (>6 month) response in 3/6 patients. 2/6 achieved partial response, 1/6 had stable disease. Nanostring (GeoMx) spatial transcriptomic profiling on available biopsy samples showed significant global gene expression changes before and after treatment. There were concordant changes in 97 differentially expressed genes (DEGs) within the epithelial compartment with treatment, similar to ELR induced changes in PDAC cell lines, with a shift in transcriptional expression patterns from QM to E subtype. Gene set enrichment analysis demonstrated downregulation of the EMT pathway, as well as decreased TGF-β signaling. RNA-ISH analysis on baseline biopsy samples showed that the two partial (best) responders had higher degrees of QM marker expression (82.58% and 63.76%). The regimen was well tolerated with no dose limiting toxicity noted in the safety cohort. Conclusion: Our experiments demonstrate that the E subtype PDAC cell lines are inherently sensitive to FFX chemotherapy with no added advantage with GSK3β inhibition. Meanwhile, GSK3β inhibition in QM cell lines induces mesenchymal to epithelial transition, thereby rendering it sensitive to FFX. The data from our safety cohort provide a clinical proof of concept that GSK-3β inhibition with ELR, in combination with FFX, may be an effective therapeutic strategy in metastatic PDAC. NCT05077800 is currently enrolling. Citation Format: Priyadarshini Pathak, Eric Lin, Ildiko Phillips, David Ting, Colin Weekes. FOLFIRINOX with Glycogen Synthase Kinase-3 Beta (GSK-3β) Inhibitor Elraglusib and Transforming Growth Factor- β (TGFβ) Inhibitor Losartan in Untreated Metastatic Pancreatic Ductal Adenocarcinoma(PDAC): Interim analysis of safety cohort [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 C073.

Abstract C037: Characterization of cysteine dependency implicates glutathione metabolism as a critical adaptation axis in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a deadly cancer that is highly malignant and lethal. The treatment options are limited, contributing to its high mortality rate. PDAC is known to have profound metabolic alterations that enable its growth and survival. Here, we screened for amino acid dependency in PDAC cell lines and found that the cells cluster into cysteine highly dependent, moderately dependent, and independent cells. In the highly dependent cells, cysteine deprivation reduces viability by ∼90%, which could be rescued by glutathione (GSH) supplementation. Metabolomics revealed that cysteine deprivation led to GSH depletion, suggesting an impairment in the GSH pathway machinery in these cells. Consistently, most metabolite intermediates in the GSH pathway are downregulated in the cysteine-reliant PDAC cell lines compared to cell lines that resist cysteine deprivation, and those cells showed higher sensitivity to oxidative stress induction. Bioinformatics analysis of multiple PDAC tumor gene expression datasets indicated that the GSH pathway is strongly upregulated in PDAC and correlates with proliferation, metastasis, and oncogenic KRAS upregulation. Using CRISPR/Cas9, we found that the knockout of GSH genes enhanced sensitivity to oxidative stress. Our data implicate the GSH pathway as a critical nexus to be targeted to overcome metabolic adaptation in PDAC. Citation Format: Chiamaka J Ezeh, Matthew H Ward, Chesta Jain, Verodia Charlestin, Daeho D Kim, Andrew Yang, Maya Nassif, Nneka Mbah, Peter Sajjakulnukit, Anthony Andren, Li Zhang, Marina Pasca di Magliano, Costas A Lyssiotis, Zeribe C Nwosu. Characterization of cysteine dependency implicates glutathione metabolism as a critical adaptation axis 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 C037.

Abstract A049: Collagen-driven kinome reprogramming reveals unique, actionable DDR1-signaling dependencies in pancreatic cancer cells

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDA) is the 3rd most common cause of cancer death in the United States, with a 5-year survival rate of only 13%, in part due to late detection and metastatic dissemination at early stages of progression. Most PDA tumors exhibit a dense fibro-inflammatory stroma consisting of fibroblasts, immune cells, and a dense collagen-rich extracellular matrix (ECM) that regulate disease progression. How distinct collagens (COLs) influence PDA progression remains unclear. COLs signal via specific cell surface receptors, of which the Discoidin Domain Receptors (DDRs) constitute a unique family of collagen-binding receptor tyrosine kinases (RTKs). DDR1 is expressed by PDA cancer cells, while DDR2 is expressed by mesenchymal cells. DDR1 is activated by both basement membrane COL (e.g. COL4) and fibrillar COLs (e.g. COLs 1, 2, 11). Compared to most RTKs, relatively little is understood about differential ligand activation and signaling downstream of DDRs. Our working hypothesis is that switches in ECM collagen composition over the course of PDA progression induce changes in DDR1-intracellular signaling cascades, which may reveal unexplored therapeutic susceptibilities to target and eliminate PDA cancer cells. Methods and Recent Advances: Using genetically engineered mouse models of PDA, we previously found that genetic ablation of Ddr1 impedes tumor progression, blocking the transition from well-differentiated to poorly-differentiated adenocarcinoma and, as a result, metastasis. Moreover, we showed that xenografts of DDR1-expressing human PDA cell lines display enhanced tumor growth exclusively when implanted within a COL1 scaffold. Leveraging an innovative high-throughput kinase-activity mapping (HT-KAM) platform and kinase network resource database (PhosphoAtlas), we started investigating mechanisms of differential activation of DDR1 by distinct COLs, including COL1 and COL11, which is an understudied fibrillar collagen that is prominent in the stroma of late-stage, metastatic PDA. New, Unpublished Findings: Using several PDA cell line models with or without DDR1 expression, our results indicate that DDR1 activates two distinct signaling networks: (1) a conserved, coordinated response that is modestly activated by COL1 but is hyperactivated by COL11 (e.g., ERBB, AKT, MEK/ERK, SRC), and (2) a unique set of phospho-signaling nodes that are only induced by COL11 –and not COL1 (e.g., specific RTKs and PKCs). Several of these kinases are associated with cancer cell proliferation and survival, as well as EMT induction, in part illuminating the malignancy-promoting effects of DDR1 in late-stage PDA in response to changes in COL composition. Conclusion: Differential activation of DDR1 represents a new paradigm on how distinct fibrillar COLs within the TME may drive PDA cell signaling. We are actively exploring how distinct COLs differentially regulate PDA tumor growth and metastatic behavior via DDR1, and how specific kinase-targeting interventions may prevent malignant phenotypes or induce tumor cell death. Citation Format: Anjum Sohail, Yeonjoo Hwang, Denise P Munoz, Yoshihiro Ishikawa, Rafael Fridman, Howard Crawford, Jean-Philippe Coppe. Collagen-driven kinome reprogramming reveals unique, actionable DDR1-signaling dependencies in pancreatic cancer cells [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 A049.

Abstract IA-06: Elucidation of metabolic resistance mechanisms to RAS inhibition

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by KRAS- and autophagy-dependent growth. We previously determined that concurrent inhibition of autophagy, using the lysosomal inhibitor chloroquine (CQ), and of ERK, using a small molecule ERK inhibitor (ERKi), synergistically suppressed the growth of pancreatic ductal adenocarcinoma (PDAC) cell lines and patient xenograft-derived (PDX) organoids in vitro and PDX tumors in vivo. Our findings provided the rationale for our initiation of Phase I and Phase I/II clinical trials evaluating the combination of MEKi (binimetinib; NCT04132505) or ERKi (LY3214996; NCT04386057) with hydroxychloroquine (HCQ) in PDAC. We have extended these findings and determined that the combined inhibition of KRASG12C or KRASG12D and autophagy was effective in KRAS-mutant cancers. Our ongoing studies are centered on developing additional combinations for targeting metabolic resistance mechanisms to KRAS or ERK MAPK targeted therapies. First, we performed a CRISPR/Cas-9 mediated genetic loss-of-function screen in the presence of CQ to determine additional sensitizers to autophagy inhibition. Top sensitizers included multiple facilitators of the DNA damage response, mTOR pathway components, and genes involved in the upstream regulation of the autophagy pathway. Additionally, we identified PIKfyve, a lipid kinase critical for the recycling dynamics of lysosomes, as an essential autophagy-related gene in PDAC cells. PIKfyve inhibition with apilimod resulted in a potent reduction of autophagic flux and growth. Importantly, PIKfyve inhibition blocked the compensatory increases in autophagic flux associated both with MEK inhibition and with direct RAS inhibition. Accordingly, combined inhibition of PIKfyve and either the RAS ERK-MAPK pathway or RAS itself showed robust growth suppression across a panel of KRAS-mutant PDAC models. Growth suppression was due, in part, to potentiated cell cycle arrest and induction of apoptosis following loss of IAP proteins. We conclude that concurrent inhibition of RAS and PIKfyve is a synergistic, cytotoxic combination that may represent a novel therapeutic strategy for PDAC. In a parallel line of investigation, we determined that autophagic signaling is temporally regulated following RAS pathway inhibition, peaking at 48-72 hours, and returning to basal levels by 7 days. Interestingly, we found that as autophagic upregulation subsides, another nutrient scavenging pathway, macropinocytosis, increases. We hypothesize that further dissection of the dynamic regulation of autophagy and macropinocytosis will improve current anti-nutrient scavenging treatment strategies. We conclude that concurrent suppression of multiple metabolic processes, to block compensatory rebound activities, will be needed for effective PDAC treatment. Citation Format: Jonathan M. DeLiberty, Ryan Robb, Mallory K. Roach, Sarah E. Ackermann, Runying Yang, Noah L. Pieper, Khalilah E. Taylor, Scott Bang, Elisa Baldelli, Emanuel F. Petricoin III, John P. Morris IV, Clint A. Stalnecker, Kirsten L. Bryant. Elucidation of metabolic resistance mechanisms to RAS inhibition [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 IA-06.

Abstract C065: PlastiNet: Understanding the Epithelial - Mesenchymal Transition Through Graphical Attention in Spatial Transcriptomics

Abstract Plasticity in tumor cells represents the ability of cancer cells to transition between different phenotypic states, including epithelial and mesenchymal states, known as the epithelial-mesenchymal transition (EMT). This transition is critical for processes such as invasion, metastasis, and resistance to therapy. Understanding the dynamics of plasticity and the extrinsic factors influencing state transitions may be crucial for improving therapeutic strategies and patient outcomes. However, deciphering the complex interactions and factors driving these state changes remains challenging. We introduce PlastiNet, a graphical attention-based network (GAT) designed to create spatially aware embeddings that enable the identification of cellular neighborhoods and the plasticity spectrum, despite gene panel limitations. PlastiNet incorporates both self-attention and neighbor-attention mechanisms in its GAT. This approach allows us to account for the influence of surrounding cells in determining the state of a target cell. We validated our model by constructing differentiation paths in healthy colon data, starting from stem cell signatures. The attention mechanisms highlighted known interactions, such as those between fibroblasts and epithelial cells. When applied to pancreatic ductal adenocarcinoma (PDAC) tumors, PlastiNet identified the SPP1-CD44 axis as a potential mediator in the classical-to-basal transition of tumor cells. To further explore the impact of CD44, particularly the isoform switch that occurs during EMT, we studied a patient-derived a PDAC cell line using single-cell RNA sequencing (scRNAseq) and Multiplexed Arrays Isoform Sequencing (Mas-Iso-Seq) to analyze cells spanning a range of the plasticity spectrum. Looping this analysis back to spatial transcriptomics data, we observed that the signature associated with CD44v8-10 or CD44s isoforms is co-localized with the SPP1 ligand, suggesting a spatially confined interaction. This finding underscores the potential of PlastiNet to generate hypotheses directly from patient-derived samples, offering new insights into the cellular mechanisms driving tumor plasticity. PlastiNet effectively constructs spatially aware embeddings that capture the dynamics of tumor cell plasticity. By identifying key interactions and extrinsic factors, this method opens new avenues for understanding and potentially targeting the mechanisms underlying tumor progression and treatment resistance. Citation Format: Izabella L Zamora, Milan Parikh, Samuel Wright, Lynn Bi, Bidish Patel, Dana Pe’er, David Ting, Nir Hacohen, Arnav Mehta. PlastiNet: Understanding the Epithelial - Mesenchymal Transition Through Graphical Attention in Spatial Transcriptomics [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 C065.

Abstract B090: Evaluating the molecular determinants of PDAC racial health disparities

Abstract Pancreatic cancer is the 3rd leading cause of cancer-related deaths, with a 5-year survival rate of just 13%. Pancreatic ductal adenocarcinoma (PDAC), accounting for over 90% of pancreatic malignancies, has the highest incidence rate, mortality rate, and shortest survival times in non- Hispanic Black (defined here as African and/or African American ancestry) patients compared to other races. To identify molecular features that may contribute to racial health disparities in PDAC, we used quantitative mass spectrometry to determine the proteomic signatures unique to tumor racial origin in a cohort of 30 Caucasian and 12 African American patients. This analysis of the bulk tumor proteome revealed 183 proteins were differentially expressed between these groups. The protein with the highest expression in tumors from Black patients relative to Whites was Ring Finger Protein 2 (RNF2) that acts as an epigenetic transcriptional repressor in developmental processes pertaining to cellular differentiation. To determine the molecular pathways in PDAC regulated by RNF2, chromatin immunoprecipitation and sequencing (ChIP-seq) was performed on MIA-PaCa2 and a primary PDAC cell line derived from a Black patient to identify binding sites for RNF2 in PDAC cells. From the 1,142 replicated peaks identified, RNF2 peaks were localized over the transcription start site of 644 unique transcripts, including GATA6, which is an important determinant in PDAC subtype delineation with higher GATA6 expression associated with the less aggressive and more chemosensitive Classical subtype. Modulating RNF2 levels/activity by exogenous expression, short hairpin RNA (shRNA) knockdown, and small molecule inhibition confirms that GATA6 is a target of RNF2 repression in PDAC. Multi-omic (transcriptomic, proteomic, and phosphoproteomic) characterization was performed on MIA-PaCa2 cells with CRISPR-Cas9 knockout (KO) of RNF2. Differential gene expression (DE) analysis revealed changes in platinum drug resistance, EMT, and innate immune response, which are characteristic of the aggressive Inflammatory PDAC subtype we previously reported using proteomics. Total and phospho-proteomics corroborated these results identifying changes in DNA repair, inflammation response, TNFα mediated signaling, and apoptotic signaling. These results reflect the enrichment of Inflammatory subtype markers in tumors originating in Black patients. In agreement with these results, RNF2 KO shows a significant reduction in migration, as well as an increase in sensitivity to oxaliplatin. Our work identifies differences in the underlying proteome of PDAC tumors associated with tumor racial origin and describes how elevated expression of RNF2 in PDACs from Black patients contribute to inflammation and subtype delineation. This study delineates the associations between tumor racial origin, subtype specification, and response to therapy that could mitigate PDAC health disparities and be broadly applied across all PDAC patients. Citation Format: Anthony E Johansen-Sallee, Alexa M Barber, Henry C.-H. Law, Vignesh Vudatha, Jose Trevino, Nicholas T Woods. Evaluating the molecular determinants of PDAC racial health disparities [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 B090.

Abstract C012: Overcoming Cell Subtype-Specific Adaptive Resistance to KRAS G12D Inhibition in KRAS G12D-Mutant Pancreatic Cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) has a 5-year survival rate of only 12%, with limited treatment options. Oncogenic KRAS mutations drive PDAC tumor progression, which occur in the majority of PDAC tumors. KRAS G12D is the most common KRAS mutation, found in 36% of PDAC cases, which is associated with the worst clinical outcomes. Mutant-selective KRAS G12D inhibitors (KRASi G12D), such as MRTX1133, have recently demonstrated initial responses in KRAS G12D-mutant preclinical models. However, mechanisms of adaptive resistance to KRAS G12D inhibition are largely under-investigated and novel therapeutic strategies to overcome drug resistance are urgently needed. Results: Adaptive RAS signaling reactivation was found to dampen KRAS G12D inhibition in a library of KRAS G12D PDAC cell lines, thereby minimizing drug efficacy. Quantitative downstream analyses of drug combination screening using a KRAS G12D cell line library further identified this adaption to KRAS inhibition was cell subtype specific. Fibroblast growth factor receptor (FGFRs) drove adaptive RAS reactivation specifically in mesenchymal PDAC cells, which are aggressive, and intrinsically resistant to KRASi. In contrast, epithelial growth factor receptor (EGFR) reactivated RAS G12D signaling in epithelial cells, which are sensitive to KRASi G12D. Genetic and pharmacological inhibition of FGFR1 or FGFR2 improved drug efficacy by decreasing FGFR-mediated RAS reactivation specifically in mesenchymal PDAC lines. Pharmacological blockade of EGFR enhanced drug efficacy by inhibiting EGFR-mediated RAS reactivation specifically in epithelial PDAC lines. Furthermore, low-concentration of a novel pan- RAS inhibitor, which inhibits both wild-type and mutant RAS, completely abrogated MAPK signaling and significantly improved efficacy, when combined with KRASi G12D, suggesting a pro-survival dependency on wild-type RAS as a compensatory mechanism in response to KRAS G12D inhibition. Conclusion: Upstream RTK-mediated adaptive RAS signaling re-activation in response to KRAS inhibition in PDAC is cell subtype specific. Complete inhibition of RAS signaling by overcoming adaptive RAS rebound improves efficacy of KRASi G12D. Citation Format: Qingxiang (Nick) Lin, Alvin Morales, Haley Barnes, Ryan Bruce Corcoran. Overcoming Cell Subtype-Specific Adaptive Resistance to KRAS G12D Inhibition in KRAS G12D-Mutant 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 C012.

Abstract C066: Identifying Transcriptional Drivers of Plasticity in Pancreatic Cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains a deadly disease with few effective treatments. Even with the advent of mutationally-directed therapies targeting the KRAS oncogene, PDAC transcriptional plasticity remains a major mechanism of therapeutic resistance. As a result, there is a desperate need to develop additional strategies to treat this deadly disease. In addition to the canonical genomic alterations in KRAS, TP53, CDKN2A, and SMAD4, PDAC tumors exhibit diverse transcriptional programs, or "cell states," with prognostic implications: PDAC tumors in the “classical state” are more responsive to upfront chemotherapy and have better outcomes, while those in the “basal state” are more aggressive with poorer prognoses. Currently, PDAC cell states are not used to direct therapy. Cell state is an integrative property shaped by both cell-intrinsic (e.g., mutations, epigenetics) and cell-extrinsic (e.g., tumor microenvironment) factors. In our prior work, single-cell analyses of clinical PDAC samples demonstrated notable cell state heterogeneity and plasticity. In addition, longitudinal monitoring of patient-derived organoids showed that cells can shift from classical to basal or coexpressor states as the environment changes, and that these cell states can drastically influence drug response. However, it remains unknown which signaling and transcriptional pathways induce basal or classical states, and whether these gene regulatory networks can be targeted therapeutically. Thus, there is a pressing need to devise scalable methods to determine essential drivers for prognostically relevant cancer cell states.Here, we aim to systematically and unbiasedly identify transcription factors (TFs) that drive basal and classical cell states in PDAC. We have successfully established a high-throughput screening pipeline to 1) over-express all human TF isoforms in a pooled format within a cohort of PDAC models; 2) sort cells using antibodies against state-specific cell surface markers; and 3) perform single-cell RNA sequencing on sorted cells to nominate individual TFs or combinations that induce specific cell state transitions. Preliminary results identify both previously reported (e.g., GATA4) and new TFs that can induce the classical state. By overexpressing TFs individually or in combination, we are able to engineer PDAC cell line models that more faithfully reflect the transcriptional phenotypes observed in patient tumors. Ultimately, we aim to use this approach to construct high-fidelity isogenic but state-variant PDAC models for use both in therapeutic screening and as a substrate for investigating mechanisms governing cancer cell state plasticity. Citation Format: Yuzhou Evelyn Tong, Aswanth Mahalingam, Walaa E Katan, Julia Joung, Alex K Shalek, Peter S Winter, Srivatsan Raghavan. Identifying Transcriptional Drivers of Plasticity 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 C066.

Abstract PR-16: Evaluating direct KRASQ61H inhibition in pancreatic cancer models

Abstract KRASQ61 mutations are associated with the worst prognosis among the various KRAS mutational subtypes of pancreatic ductal adenocarcinoma (PDAC). RMC-7977 is a RAS(ON) multi-selective noncovalent inhibitor with broad spectrum activity against oncogenic RAS mutants and wild-type RAS. The related investigational agent RMC-6236 is currently undergoing clinical trials. Binary complexes of CypA: RMC-7977 bind equipotently to multiple KRAS mutational subtypes however RMC-7977 is less potent at inhibiting growth in KRASQ61H-mutant cell lines. In contrast, RM-047 is a preclinical RAS(ON) Q61H-selective inhibitor tool compound. We evaluated direct KRASQ61H inhibition using both RMC-7977 and RM-047 in cell culture models. We found that in KRASQ61H-rescued RASless mouse embryonic fibroblasts (MEFs), RM-047 inhibited ERK activity and suppressed growth more potently than RMC-7977. Conversely, in a panel of KRASQ61H-mutant PDAC cell lines, RM-047 was less potent than RMC-7977 in two out of three KRASQ61H-mutant PDAC cell lines. Furthermore, we discovered that ERK activity rapidly rebounded with treatment in KRASQ61H-mutant PDAC cell lines, whereas ERK activity remained suppressed in KRASQ61H-rescued RASless MEFS lacking WT RAS alleles. Our analysis of DepMap data indicated that among the KRAS mutational subtypes frequently found in pancreatic cancer, KRASQ61H is the least dependent on KRAS for survival. This suggests that in a KRASQ61H-mutant PDAC setting, additional factors such as WT RAS expression may mediate growth. From our KRAS drug-anchored CRISPR loss-of-function screens, we found that the loss of EGFR sensitized cells to KRAS inhibition, particularly in a KRASQ61H-dependent context. Therefore, we combined erlotinib, an FDA-approved EGFR inhibitor, with either RM-047 or RMC-7977, and found that the addition of erlotinib prevented ERK rebound activity and synergized with RM-047 or RMC-7977 to reduce growth in KRASQ61H-mutant PDAC cell lines. These data provide insights into mechanisms by which KRASQ61H-mutant PDAC may be less dependent on KRAS for survival and further support the clinical evaluation of combined EGFR and RAS(ON) inhibition as a potential therapeutic strategy in the treatment of PDAC patients harboring KRASQ61H mutations. Citation Format: Szu-Aun Long, Amber M Amparo, Haley Todd, Grace Goodhart, Syed A Ahmad, Andrew M Waters. Evaluating direct KRAS inhibition in pancreatic cancer models [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 PR-16.

Abstract C045: Targeting metabolic heterogeneity in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related death in the US. This poor prognosis is related to the complex tumor microenvironment and tumor heterogeneity that drives resistance to chemotherapy. Here the heterogeneity of the stromal, immune, and malignant epithelial cell populations enables signaling and metabolic crosstalk mechanisms that drive immune suppression and resistance to therapy. Recently, our group unveiled that multiple distinct metabolic subclasses of cancer cells coexist within individual PDAC tumors. Among these, two PDAC clonal populations can engage in metabolic symbiosis that supports mitochondrial metabolism. One subtype has a constitutively high integrated stress response (ISR), enabling resistance to mitochondrial inhibitors. Further, these cells release asparagine that supports the mitochondrial metabolism of the other subtype that are more sensitive to mitochondrial inhibition. Given these observations, we are developing approaches to disrupt this metabolic symbiosis. Clonal PDAC cells with constitutively active ISR exhibit increased sensitivity to inhibition of the redox activity of Redox factor 1/Apurinic-apyrimidinic endonuclease 1 (Ref-1). Importantly, this can be leveraged to disrupt the support of the mitochondrial metabolism of clonal symbiotic pairs. Moreover, polyclonal PDAC cell lines representative of the heterogeneity seen in PDAC patients show a highly synergistic response to the combination of Ref-1 redox inhibitors with mitochondrial inhibitors. These data suggest this treatment combination will be synergistic in polyclonal tumors that exist in most PDAC patients. Overall, these data have the potential to lead to new avenues to directly target heterogenous populations of cancer cells to treat pancreatic cancer- an urgent clinical need. Citation Format: Taryn Morningstar, Cecily Anaraki, Lorenzo Scipioni, Giulia Tedeschi, Michelle Digman, Aimee Edinger, Claus Jorgensen, Melissa Fishel, Christopher J Halbrook. Targeting metabolic heterogeneity in pancreatic ductal adenocarcinoma [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 C045.

Abstract B063: Elucidating treatment induced tumor antigen presentation in pancreatic cancer

Abstract Introduction Pancreatic ductal adenocarcinoma (PDAC), the most common form of pancreatic cancer, is projected to become the second leading cause of cancer-related deaths by 2030. The 5-year survival rate remains stubbornly low at just 13%. These discouraging statistics primarily stem from the lack of effective treatments till date. Despite the success of immunotherapy for several malignancies, immunotherapy for PDAC has yielded disappointing results alone or in combination with other therapies. Successful immunotherapy will require a deeper understanding of PDAC immunobiology and immune recognition of cancer during its progression, and treatment regimens. Immunosurveillance of cancer requires the presentation of peptide antigens on Major Histocompatibility complex class I (MHC-I). Understanding the repertoire of MHC-I associated peptides (pMHC-I), collectively termed as the “immunopeptidome”, is essential for anti-tumor immunity and successful immunotherapies. Using a collection of preclinical tools and human cell lines, we aim to uncover treatment induced antigens in PDAC that can be used for targeted immunotherapy approaches. Methods To understand the biogenesis of the immunopeptidome, our group has developed a novel genetically engineered mouse model (GEMM), which integrates inducible affinity tags on MHC-I (KbStrep) and ribosomes (RiboTag) into the Kras LSL-G12D/+ ; P53 fl/fl (KP) mouse model (KP/RiboMHC). This approach enabled us to precisely measure protein synthesis and antigen presentation in malignant PDAC cells in vivo with paired ribosome profiling and mass spectrometry based immunopeptidomics. In parallel we have employed a collection of human PDAC cell lines for immunopeptidomics analysis. About 93% of PDACs have KRAS mutation, with G12D mutation being the most common. In addition, PDAC is subjected to a deregulated metabolic milieu, with a strong dependence on glutamine utilization. Therefore, to examine treatment induced changes in PDAC antigen presentation, we examined the impact of KRAS inhibition (MRTX1133) and glutamine antagonism (6-diazo-5-oxo-L-norleucine, DON) on the biogenesis of the immunopeptidome in vitro and in vivo. Results Using our GEMM model, we have started to uncover MRTX1133 and DON induced alterations in protein synthesis and in pMHC-I repertoire in vivo using the KP/RiboMHC model and in vitro in mouse and human cell lines. We have identified unique antigen peptides that are induced by MRTX1133 and DON, including those derived from non-canonical translation events that were defined by ribosome profiling. Conclusions Our data demonstrates that KRAS inhibition with MRTX1133 or glutamine antagonism with DON reshapes the antigen landscape of PDAC. We are actively exploring which of the induced peptides harbor potential to mount an anti-tumor CD8+ T cell response. Collectively, these results could pave the way forward for rationally designed treatment regimens that pair targeted therapies with antigen specific immunotherapy in PDAC. Citation Format: Emma Adhikari, Andrew Weeden, Emily Brennan, Christopher Polera, Victoria lzumi, Bin Fang, John Koomen, Paul Stewart, Alex Jaeger. Elucidating treatment induced tumor antigen presentation 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 B063.

Abstract B044: Durable T-cell-mediated anti-tumor immune response to pancreatic cancer cells overexpressing interleukin 6

Abstract Tumor immune resistance contributes to low survivorship in patients with pancreatic ductal adenocarcinoma (PDAC). To understand how tumor-secreted factors might impact anti-tumor immunity, we developed a model of PDAC tumor overexpressing interleukin-6 (IL-6), a known driver of pancreatic tumorigenesis and cancer cachexia, in orthotopically implanted PDAC cancer cells (OT-PDACIL6). This model utilized codon-optimized IL6 to accurately detect tumor cells in the pancreas and distal organs via qPCR. OT-PDACIL6 tumors developed poorly- differentiated, infiltrative carcinomas, which were histologically similar to the PDAC cell line they were derived from (OT-PDACparental). Surprisingly, OT-PDACIL6 tumors were present at 5 days post implantation, but undetectable by histology or qPCR by 10 days post implantation. OT- PDACIL6 and sham mouse survival were equivalent (87.5%) at 76 days post-implantation. OT- PDACparental mortality was 100% at day 13. We concluded that OT-PDACIL6 tumors resolve spontaneously. IL-6 is well-established as a driver of cachexia, and we saw that OT-PDACIL6 tumors induced a rapid cachexia phenotype that began to resolve as the tumor was cleared. Plasma IL-6 levels tracked with tumor burden. At 5 days, plasma IL-6 was 100-fold higher in OT-PDACIL6 mice than in OT-PDACparental mice, but undetectable in OT-PDACIL6 mice after 12 days. We hypothesized that high levels of IL-6 were driving an anti-tumor immune response. To assess changes in tumor immune infiltrate that could lead to tumor clearance, we measured a broad range of immune cells using flow cytometry and immunofluorescent histology. At peak tumor burden, we observed exacerbated splenomegaly, and increased tumor-infiltrating T cells and NK cells in OT-PDACIL6 mice. T regulatory cells were decreased in OT-PDACIL6 tumors. CD4/CD8 antibody-based depletion prevented tumor clearance and significantly decreased survival of OT-PDACIL6 mice, indicating that T cells are necessary for IL-6-driven PDAC tumor clearance. We then tested whether the anti-tumor T cell response was durable using a secondary tumor challenge with PDACparental cells. This revealed that the anti-tumor T cell response elicited by mice bearing OT-PDACIL6 tumors was sufficient to prevent development of OT-PDACparental tumors, likely due to induction of long-term memory T cells during the initial tumor challenge. We assessed the effect of the anti-tumor immune response on metastases and found that PDACIL6 cells were detected by qPCR in lungs of 58% of mice at day 5, and not detected at day 12. We conclude that extremely high levels of tumor-derived IL-6 are sufficient to drive an anti-tumor T cell response that rapidly and durably clears the tumor. The combination of increased tumor-infiltrating T cells and decreased T regulatory cells are likely both important aspects of the immune response observed in OT-PDACIL6 mice. This surprising finding highlights the pleiotropic effects of IL-6, which is known to promote tumorigenesis and cachexia, and yet, in this work, is the driving force underlying tumor clearance. Citation Format: Paige C Arneson-Wissink, Alexandra Q Bartlett, Heike Mendez, Xinxia Zhu, Jessica Dickie, Matthew McWhorter, Peter R Levasseur, Parham Diba, Katelyn T Byrne, Gregory D Scott, Robert Eil, Aaron J Grossberg. Durable T-cell-mediated anti-tumor immune response to pancreatic cancer cells overexpressing interleukin 6 [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 B044.

Abstract A084: CDK12 inhibition drives mitotic catastrophe, triggering genome instability and innate immune response in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited therapies. In our screening using patient-derived organoids, we identified cyclin-dependent kinase 12 (CDK12) as a promising target in a subset of PDAC. Both pharmacological and genetic inhibition of CDK12 exerted potent antitumor activity in vitro and in vivo, inducing double-strand DNA breaks and apoptosis. CDK12 is a member of cyclin-dependent kinases that is involved in gene expression regulations at multiple levels. Recently, CDK12 has gained attention as a therapeutic target in several types of cancers including triple-negative breast cancer and Ewing sarcoma. However, little is known about the impact and possibility of CDK12 inhibition in pancreatic cancer treatment. As the lack of specific inhibitors that selectively target CDK12, studying CDK12 has long been challenging. To overcome this, we used CRISPR-Cas9 mediated genome editing to generate FKBP12F36V (dTAG) knock-in PDAC cell lines, enabling rapid elimination of endogenous CDK12 using a degrader against dTAG (dTAG-13). Quantitative-image-based cytometry and time lapse imaging showed that CDK12 ablation induces mitotic arrest, DNA damage and apoptosis (mitotic catastrophe). Specifically, loss of CDK12 kinase activity in the S phase was sufficient to slow DNA replication speed, leading to spindle assembly checkpoint activation and mitotic catastrophe. Importantly, cells that escaped mitotic death accumulate micronuclei, triggering immune response signaling that is mediated by the cGAS-STING-type I interferon pathway. Our results suggest that CDK12 is a promising target in a subset of PDAC patients, where CDK12 inhibition exerts antitumor activity both in cell autonomous and non-cell autonomous ways through inducing mitotic catastrophe as well as triggering immune response. Citation Format: Dosuke Iwadate, Keisuke Yamamoto, Hiroyuki Kato, Keisuke Tateishi, Mitsuhiro Fujishiro. CDK12 inhibition drives mitotic catastrophe, triggering genome instability and innate immune response 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 A084.

The pro-inflammatory cytokines IL-1β and IL-6 promote upregulation of the ST6GAL1 sialyltransferase in pancreatic cancer cells

The ST6GAL1 sialyltransferase is overexpressed in multiple cancers including pancreatic ductal adenocarcinoma (PDAC). ST6GAL1 adds an α2-6-linked sialic acid to N-glycosylated membrane receptors, which consequently modulates receptor structure and function. While many studies have investigated the effects of ST6GAL1 on cell phenotype, there is a dearth of knowledge regarding mechanisms that regulate ST6GAL1 expression. In the current study, we evaluated the regulation of ST6GAL1 by two pro-inflammatory cytokines, IL-1β and IL-6, that are abundant within the PDAC tumor microenvironment. Cytokine activity was monitored using the Suit-2 PDAC cell line and two Suit-2-derived metastatic subclones, S2-013 and S2-LM7AA. For all three cell models, treatment with IL-1β or IL-6 increased the expression of ST6GAL1 protein and mRNA. Specifically, IL-1β and IL-6 induced expression of the ST6GAL1 YZ mRNA isoform, which is driven by the P3 promoter. The ST6GAL1 H and X isoforms were not detected. Promoter reporter assays confirmed that IL-1β and IL-6 activated transcription from the P3 promoter. We then examined downstream signaling mechanisms. IL-1β is known to signal through the NFκB transcription factor, whereas IL-6 signals through the STAT3 transcription factor. CUT&RUN experiments revealed that IL-1β promoted the binding of NFκB to the ST6GAL1 P3 promoter, and IL-6 induced the binding of STAT3 to the P3 promoter. Finally, we determined that inhibitors of NFκB and STAT3 blocked the upregulation of ST6GAL1 stimulated by IL-1β and IL-6, respectively. Together, these results highlight a novel molecular pathway by which cytokines within the tumor microenvironment stimulate the upregulation of ST6GAL1 in PDAC cells.

Enhanced radiosensitivity of pancreatic cancer achieved through inhibition of Cyclin-dependent kinase 1

Background and purposeOvercoming radioresistance is a critical challenge in pancreatic ductal adenocarcinoma (PDAC). Our study investigates the targeting of Cyclin-dependent kinase-1 (CDK1) through genetic and pharmaceutical inhibition to radiosensitize PDAC cells. Materials and MethodsMass spectrometry and phosphoproteomics were used to analyze engineered radiation-resistant PDAC cell lines (MIA PaCa-2 and PANC-1) compared to parental controls. The TCGA PDAC database was queried for clinical outcomes and patients were dichotomized based on the median CDK1 mRNA expression. We generated a microRNA-based TET-on inducible shRNA to inhibit CDK1 expression in two PDAC cell lines. We used an orthotopic model of PDAC to test the radiation sensitivity of PDAC tumors with or without doxycycline treatment. We targeted CDK1 activation with a selective CDK1 inhibitor, RO-3306, followed by in vitro experiments employing immunoblotting, immunocytochemistry, and clonogenic assays. ResultsPhosphoproteomics analysis revealed that phospho-CDK1 (Tyr15) was significantly elevated in the resistant clones. We found that high CDK1 expression was associated with worse OS in PDAC patients. Radiation exposure increased CDK1 phosphorylation. In MIA PaCa-2 and PANC-1 cells, CDK1 inhibition synergized with radiation therapy to delay tumor growth in vivo. CDK1 inhibition via. RO-3306 resulted in a significant shift of cells into the G2/M phase and disrupted DNA repair after radiation exposure. In vitro, pre-treatment with RO-3306 led to enhanced radiosensitivity of PDAC cells. ConclusionCDK1 plays a crucial role in PDAC radioresistance. Targeting CDK1 with radiotherapy holds promise for further investigation in PDAC treatment.

Identification of TPI1 As a potential therapeutic target in pancreatic cancer with dependency of TP53 mutation using multi-omics analysis.

Mutations of KRAS, CDKN2A, TP53, and SMAD4 are the four major driver genes for pancreatic ductal adenocarcinoma (PDAC), of which mutations of KRAS and TP53 are the most frequently recognized. However, molecular-targeted therapies for mutations of KRAS and TP53 have not yet been developed. To identify novel molecular targets, we newly established organoids with the Kras mutation (KrasmuOR) and Trp53 loss of function using Cre transduction and CRISPR/Cas9 (Krasmu/p53muOR) from murine epithelia of the pancreatic duct in KrasLSL-G12D mice, and then analyzed the proteomic and metabolomic profiles in both organoids by mass spectrometry. Hyperfunction of the glycolysis pathway was recognized in Krasmu/p53muOR compared with KrasmuOR. Loss of function of triosephosphate isomerase (TPI1), which is involved in glycolysis, induced a reduction of cell proliferation in human PDAC cell lines with the TP53 mutation, but not in PDAC or in human fibroblasts without TP53 mutation. The TP53 mutation is clinically recognized in 70% of patients with PDAC. In the present study, protein expression of TPI1 and nuclear accumulation of p53 were recognized in the same patients with PDAC. TPI1 is a potential candidate therapeutic target for PDAC with the TP53 mutation.

The Exon Junction Complex component EIF4A3 plays a splicing-linked oncogenic role in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, underscoring the urgent need for in-depth biological research. The phenomenon of alternative RNA splicing dysregulation is a common hallmark in cancer, including PDAC, presenting new avenues for understanding and developing diagnostic and therapeutic tools. Our research focuses on EIF4A3, a core component of the Exon Junction Complex intimately linked to RNA splicing, and its role in PDAC. EIF4A3 is overexpressed in PDAC tissue and associated to clinical parameters of malignancy and poorer patient survival. Mechanistically, exploration of PDAC RNA-seq data unveiled the link of EIF4A3 to diverse malignancy processes, consistent with its association to key molecular pathways. EIF4A3 targeting in vitro decreased essential functional tumor features such as proliferation, migration, colony formation and sphere formation, while its in vivo targeting reduced tumor growth. EIF4A3 silencing in PDAC cell lines severely altered its transcriptional and spliceosomic landscapes, as shown by RNA-seq analyses, suggesting a role for EIF4A3 in maintaining RNA homeostasis. Our results indicate that EIF4A3 dysregulation in PDAC has a pleiotropic regulatory role on RNA biology, influencing key cellular functions. This paves the way to explore its potential as novel biomarker and actionable target candidate for this lethal cancer.

Darifenacin: a promising chitinase 3-like 1 inhibitor to tackle drug resistance in pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is among the most aggressive malignancies. Our previous work revealed Chitinase 3-like 1 (CHI3L1) involvement in PDAC resistance to gemcitabine, identifying it as a promising therapeutic target. Here, we aimed to identify putative CHI3L1 inhibitors and to investigate their chemosensitizing potential in PDAC. Docking analysis for CHI3L1 identified promising CHI3L1 inhibitors, including darifenacin (muscarinic receptor antagonist). PDAC cell lines (BxPC-3, PANC-1) and primary PDAC cells were used to evaluate darifenacin's effects on cell growth (Sulforhodamine B, SRB), alone or in combination with gemcitabine or gemcitabine plus paclitaxel. Cytotoxicity against normal immortalized pancreatic ductal cells (HPNE) was assessed. Recombinant protein was used to confirm the impact of darifenacin on CHI3L1-induced PDAC cellular resistance to therapy (SRB assay). Darifenacin's effect on Akt activation was analysed by ELISA. The association between cholinergic receptor muscarinic 3 (CHRM3) expression and therapeutic response was evaluated by immunohistochemistry of paraffin-embedded tissues from surgical resections of a 68 patients' cohort. In silico screening revealed the ability of darifenacin to target CHI3L1 with high efficiency. Darifenacin inhibited PDAC cell growth, with a GI50 of 26 and 13.6 µM in BxPC-3 and PANC-1 cells, respectively. These results were confirmed in primary PDAC-3 cells, while darifenacin showed no cytotoxicity against HPNE cells. Importantly, darifenacin sensitized PDAC cells to standard chemotherapies, reverted CHI3L1-induced PDAC cellular resistance to therapy, and decreased Akt phosphorylation. Additionally, high CHMR3 expression was associated with low therapeutic response to gemcitabine. This work highlights the potential of darifenacin as a chemosensitizer for PDAC treatment.