Abstract A061: DKK3 in pancreatic cancer – Elucidating the roles of a double-edged sword
Authors: Srinivasan Dharini , Arnold Frank , Roger Elodie , Härle Anna , Melzer Michael K , Allgöwer Chantal , Hermann Patrick C , Perkhofer Lukas , Gout Johann , Kleger Alexander 
Published: September 2024

Abstract
Pancreatic ductal adenocarcinoma (PDAC) remains a highly challenging disease with a poor prognosis due to lack of diagnostic biomarkers and high tumor heterogeneity. Therefore, it is crucial to meticulously examine the intricate molecular mechanisms in PDAC. We previously identified DKK3 (Dickkopf-3) as a novel factor promoting organ regeneration during pancreatitis and established a previously unknown link between DKK3 and the Wnt and Hedgehog signaling. Given that pancreatitis is a significant risk factor for pancreatic cancer, we were motivated to investigate the potential role of DKK3 in PDAC development. We utilized PDAC mouse models driven by LSL-KrasG12D/+; Ptf1aCre/+ with wildtype, homozygous/heterozygous DKK3 deletion in both epithelial and stromal compartment while employing in vitro and ex vivo systems to examine the stage and compartment-specific roles of the same. Through a comprehensive and time-resolved analysis of tumor characteristics, we discovered that the loss of DKK3 led to rapid oncogenic transformation, marked by a significant increase in metaplasia and desmoplasia starting at an early stage (10 weeks). Ex vivo acinar-to-ductal metaplasia assay and rescue experiments with wildtype and DKK3-null acinar cells revealed that secreted DKK3 operates as a tumor suppressive roadblock in PDAC-initiating steps. This advanced preneoplastic stage translated into accelerated progression toward invasive tumors at 36 weeks, a shortened overall survival, and a higher liver metastasis incidence in the DKK3-null animals at the endpoint. Interestingly, transcriptomic analyses further validated our observation and revealed the involvement PI3-AKT signaling pathway as an underlying mechanism. Further characterization of isolated tumor cells confirmed our observations, revealing prominent mesenchymal features and enhanced migratory capacities upon loss of DKK3. Interestingly, DKK3-null PDACs exhibited a pronounced stroma remodeling with a myofibroblastic cancer-associated fibroblast-enriched environment, as well as an immunosuppressive stroma with abundant regulatory T cells and cytotoxic T cell depletion, as substantiated by coculture experiments. Intriguingly, while displaying similar phenotypic features to DKK3-null tumors, Dkk3+/- heterozygotes exhibited the most aggressive outcome. To further dissect this finding, we conducted a set of in silico approaches and immunostainings revealing persistent stromal DKK3 expression in DKK3- proficient PDACs. This suggested a possible dual role of DKK3 that could operate either as a friend or a foe depending on its spatiotemporal expression in PDAC. In line, in vitro systems demonstrated a distinct oncogenic effect of DKK3 on endpoint tumor cells, particularly promoting malignant cell migration. In summary, we propose that epithelial DKK3 exerts cell-autonomous tumor suppressive functions during the onset of PDAC, while stromal DKK3 acts as an oncogenic cue driving cancer progression. These findings highlight DKK3 as a promising biomarker and a novel therapeutic target for PDAC tumors.
Citation Format: Dharini Srinivasan, Frank Arnold, Elodie Roger, Anna Härle, Michael K Melzer, Chantal Allgöwer, Patrick C Hermann, Lukas Perkhofer, Johann Gout, Alexander Kleger. DKK3 in pancreatic cancer – Elucidating the roles of a double-edged sword [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 A061.