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Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer characterized by late diagnosis, lack of early symptoms and extensive metastasis. One of the foremost reasons for such startling statistics is the presence of a subpopulation of highly plastic stem-like cells within the tumor called cancer stem cells (CSCs). We have previously identified a distinct subset of these CSCs within the invasive front of patient tumors. This subset, called migrating cancer stem cells (miCSCs), is characterized by CD133+CXCR4+ expression and determines the metastatic phenotype of pancreatic cancer. Therefore, targeting CXCR4 may represent a potential therapeutic approach to lower metastatic burden in PDAC. Here, we examined the effect of endogenous human peptides EPI-X4 and other derivatives thereof as CXCR4 antagonist on (i) patient-derived primary pancreatic cancer cells and (ii) tumor-stroma crosstalk by using a dual culture system with pancreatic stellate cells. We established these peptides as novel therapeutic strategy for combating the metastatic activity of pancreatic cancer using combinatorial therapeutic approaches and testing different in vivo delivery system such as peptide fatty-acid (FA) conjugates and silica nanoparticles (Si-NP). Our results show that EPI-X4 as well as its derivatives (e.g., JM#21) strongly inhibited migratory capacity of primary pancreatic cancer cells towards the CXCR4 ligand CXCL12 in vitro. Thereby, JM#21 was identified as the most potent EPI-X4 derivate. Mechanistical analysis by western blot, gene expression and immunofluorescence revealed that JM#21 increased Cadherin-1 expression by suppression of Snail1 via inactivation of SHH pathway. Moreover, JM#21 decreased CXCL12-induced phosphorylation of AKT and IKBa as well as NANOG expression, which further suppressed self-renewal capacity and EMT in the tumor cells. Strikingly, JM#21 sensitized selected cell lines towards gemcitabine and paclitaxel. Furthermore, FA conjugated and Si-NP encapsulated JM#21 restricted miCSCs maintenance which was predominantly regulated via stellate cell secreted CXCL12. In serum conditions, both FA conjugated, and Si-NP encapsulated JM#21 was found to be stable and active, proving as a valuable delivery system for in vivo studies. In conclusion, our study reveals that targeting CXCR4/CXCL12 signaling axis using human endogenous EPI-X4 derivates particularly JM#21 inhibits tumor-stroma crosstalk which is paramount for the propagation and maintenance of miCSC. Particularly, we demonstrate, in both mechanistic and preclinical set up, that these peptides abrogate the metastatic capacity of patient-derived pancreatic cancer cells by selective targeted elimination of miCSCs. Moreover, tumor cells show increased susceptibility towards conventional treatment strategies enforcing EPI-X4 derivate as a novel combinatory therapy to treat metastatic pancreatic cancer. Citation Format: Kanishka Tiwary, Mirja Harms, Bastian Beitzinger, Roman Schmid, Syeda Inaas, Karolin Walter, Alexander Kleger, Mika Lindén, Thomas Seufferlein, Jan Münch, Patrick Christian Hermann. CXCR4 targeting endogenous human peptides eliminate migrating cancer stem cells by disrupting tumor-stroma crosstalk in pancreatic ductal adenocarcinomas [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B034.

Pancreatic cancer is a fatal disease and is one of the most aggressive and metastatic malignancies worldwide. The dissemination of tumor cells is the prerequisite of metastases and correlates with a loss of epithelial differentiation and the acquisition of a migratory phenotype, a hallmark of malignant tumor progression. Migrating cancer stem cells (miCSCs) characterized by CD133+ and CXCR4+ expression play a pivotal role in malignant tumor formation, have been reported to form the invasive front of the metastasis and in silico analysis showed that both CSCs and miCSCs are significantly upregulated in PDAC. However, the regulatory pattern maintaining these CSCs and especially miCSCs in PDAC remains widely elusive. Thus, this study further helps to unravel pathways responsible for maintenance of CSC (CD133+) and miCSC (CD133+ CXCR4+) population. To identify key signaling pathways responsible for both CSCs and miCSCs maintenance, we first generated a protein-protein interaction network using STRING database. Afterwards, we validated these signaling pathway(s) involved in aiding CSC and miCSC population by performing shRNA mediated knockdown of key signaling proteins in different patient-derived pancreatic cancer cell lines. Moreover, we interrogated the involvement of the tumor-stroma crosstalk in the regulation of these pathways by co-culturing tumor cells with pancreatic stellate cells. Protein-protein interaction network incorporating relevant factors involved in EMT, stemness, as well as SHH, NF-kB and AKT signaling pathway identified a strong link between the CXCL12/CXCR4 signaling axis and BMI1. Migration assay, sphere formation assay and western blot upon shRNA mediated knockdown of either CXCR4 and/or BMI1 ascertained BMI1 as a key player downstream of the CXCL12/CXCR4 axis to mechanistically effect both EMT and stemness. Pathway focused gene expression analysis as well as ELISA and immunofluorescence for CXCL12 and actin filaments, respectively, revealed the indispensable nature of tumor-stroma crosstalk on promoting CSC and miCSC population through the chemokine CXCL12. In addition, co-culture systems revealed that particularly pancreatic stellate cells play a significant role in maintaining both CSCs and miCSCs population as well as their characteristic phenotype including but not limited to chemotherapy resistance. Taken together, our results obtained in this study established mechanistically that the CXCL12/CXCR4 signaling pathway driven by tumor-stroma crosstalk not only enhances but also maintains both CSCs and miCSCs in pancreatic ductal adenocarcinomas through BMI1 ultimately promoting metastases and therapeutic resistance. Citation Format: Kanishka Tiwary, Anton Lahusen, Syeda Inaas, Stefanie Hauff, Karolin Walter, Alexander Kleger, Thomas Seufferlein, Bruno Sainz Jr., Patrick Christian Hermann. CXCL12 / CXCR4 signaling enhances and sustains migrating cancer stem cells via BMI1 in pancreatic ductal adenocarcinomas [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B035.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies with a devastating 5-year survival rate of 11%. A lack of durable responses to standard-of-care chemotherapy combinations renders its treatment particularly challenging and largely contributes to the devastating prognosis. Gemcitabine, a pyrimidine anti-metabolite, is a cornerstone in PDAC therapy, but resistance remains a major hurdle. Multiple mechanisms of chemoresistance have been suggested to be mediated by rewired metabolism in PDAC cells. Accordingly, we hypothesize that metabolic reprogramming can be targeted to re-sensitize PDAC tumors to anti-metabolite chemotherapy. To define the spectrum of targetable metabolic and transcriptomic programs that drive cell-intrinsic resistance to gemcitabine, we established organoids from treatment-naïve PDAC patients. Gemcitabine high versus low responders, as assessed by dose response viability assays, were selected for metabolomic profiling and RNA sequencing. To define real-time reprogramming during the acquisition of resistance, we generated gemcitabine resistant murine pancreatic cancer cell lines and collected a time course series of metabolomic and transcriptomic datasets of sensitive, intermediate resistant and resistant cells. Integration of these dataset through a systems biology approach to define primary and de novo resistance is being used to characterize metabolic gemcitabine resistance mechanisms. These are functionally validated to provide novel approaches to re-sensitize resistant PDAC cells to gemcitabine in vitro and in vivo. The improvement of current chemotherapy combinations represents a promising approach, with potential to immediately translate into a clinical benefit and improve survival in this deadly disease. Citation Format: Alica Katrin Beutel, Rima Singh, Cecily Anaraki, Gregory Tong, Thomas Martinez, Alexander Kleger, Zeljka Jutric, Christopher James Halbrook. Targeting gemcitabine resistance in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr PR023.

Homologous recombination deficiency (HRD) leads to DNA double strand breaks and can be exploited by the use of PARP inhibitors to induce synthetic lethality of cancer cells. Over the last years, the clinical utility of this therapeutic concept was successfully demonstrated in ovarian, breast, prostate and pancreatic cancer. Currently, the role of HRD is investigated in trials testing immune checkpoint blockers alone or in combination with PARP inhibitors. But the relationship between HRD and immune cell contexture in cancer is incompletely understood. Here, we analyzed the association of HRD with tumor mutational burden (TMB), immune cell composition and gene expression in 10,000 tumors of 32 solid cancer types from the TCGA project. For each of the tumors, the HRD sum score (HRDsum) was calculated from allele-specific copy numbers (derived from genotyping data) and the TMB was calculated from the missense mutation calls (derived from WES data). HRDsum and tumor mutational burden (TMB) correlated positively pan-cancer (R=0.42) and within most cancer types. By contrast, HRD was absent in ultra-hypermutated (TMB >= 100 mut/Mb) tumors. Ultra-hypermutation was typically associated with microsatellite instability (MSI) or POLE/POLD1 mutation. Significant positive correlation of the HRDsum and immune cell infiltration was observed pan-cancer, but only within a few cancer types. Significant positive correlation of HRDsum and the T-cell inflamed gene expression profile was observed only in 7 of 32 cancer types: in breast cancer, ovarian cancer, low grade glioma, testicular germ cell tumors and three kinds of kidney cancer. A functional genomics analysis was carried out by correlating genome-wide gene expression data (derived from RNA-Seq) with HRDsum. The resulting lists of significantly correlating genes were analyzed for enrichment of 50 hallmark gene sets (catalog H, MSigDB). We detected simultaneous enrichment of two proliferation-related categories, E2F_TARGETS and G2M_checkpoint, for 13 of the 32 cancer types (ACC, BLCA, BRCA, KIRC, KIRP, LGG, LIHC, LUAD, LUSC, MESO, PRAD, SARC, THYM). The study shows that HRD is associated with immunological activation of the tumor microenvironment only in a minority of cancer types. Our data support further studies of immune activating therapies in combination with immune checkpoint blockade in the not intrinsically activated cancer types and advocate to combine different genomic and transcriptomic biomarkers (including HRD and TMB) for comprehensive molecular diagnostics and therapy guidance. Citation Format: Jan Budczies, Klaus Kluck, Susanne Beck, Iordanis Ouralidis, Michael Allgäuer, Michael Menzel, Eugen Rempel, Daniel Kazdal, Lukas Perkhofer, Alexander Kleger, Peter Schirmacher, Thomas Seufferlein, Albrecht Stenzinger. HRD is inversely correlated with MSI and identifies immunologically cold tumors in most cancer types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 810.

Pancreatic ductal adenocarcinoma (PDAC) still presents with a dismal prognosis despite intense research. Better understanding of cellular homeostasis could identify druggable targets to improve therapy. Here we propose RAD50-interacting protein 1 (RINT1) as an essential mediator of cellular homeostasis in PDAC. In a cohort of resected PDAC, low RINT1 protein expression correlated significantly with better survival. Accordingly, RINT1 depletion caused severe growth defects in vitro associated with accumulation of DNA double-strand breaks (DSB), G2 cell cycle arrest, disruption of Golgi–endoplasmic reticulum homeostasis, and cell death. Time-resolved transcriptomics corroborated by quantitative proteome and interactome analyses pointed toward defective SUMOylation after RINT1 loss, impairing nucleocytoplasmic transport and DSB response. Subcutaneous xenografts confirmed tumor response by RINT1 depletion, also resulting in a survival benefit when transferred to an orthotopic model. Primary human PDAC organoids licensed RINT1 relevance for cell viability. Taken together, our data indicate that RINT1 loss affects PDAC cell fate by disturbing SUMOylation pathways. Therefore, a RINT1 interference strategy may represent a new putative therapeutic approach. Significance: These findings provide new insights into the aggressive behavior of PDAC, showing that RINT1 directly correlates with survival in patients with PDAC by disturbing the SUMOylation process, a crucial modification in carcinogenesis.

Pancreatic ductal adenocarcinomas (PDAC) harbor recurrent functional mutations of the master DNA damage response kinase ATM, which has been shown to accelerate tumorigenesis and epithelial–mesenchymal transition. To study how ATM deficiency affects genome integrity in this setting, we evaluated the molecular and functional effects of conditional Atm deletion in a mouse model of PDAC. ATM deficiency was associated with increased mitotic defects, recurrent genomic rearrangements, and deregulated DNA integrity checkpoints, reminiscent of human PDAC. We hypothesized that altered genome integrity might allow synthetic lethality-based options for targeted therapeutic intervention. Supporting this possibility, we found that the PARP inhibitor olaparib or ATR inhibitors reduced the viability of PDAC cells in vitro and in vivo associated with a genotype-selective increase in apoptosis. Overall, our results offered a preclinical mechanistic rationale for the use of PARP and ATR inhibitors to improve treatment of ATM-mutant PDAC. Cancer Res; 77(20); 5576–90. ©2017 AACR.