Abstract C028: DKK3 in pancreatic cancer – Elucidating the roles of a double-edged sword
Authors: Srinivasan Dharini , Arnold Frank , Roger Elodie , Härle Anna , Melzer Michael , Hermann Patrick , Perkhofer Lukas , Gout Johann , Kleger Alexander 
Published: January 2024

Abstract
Pancreatic ductal adenocarcinoma (PDAC) remains a highly challenging disease with a poor prognosis due to high tumor heterogeneity, lack of diagnostic biomarkers and limited treatment options. Therefore, it is crucial to meticulously examine the intricate molecular mechanisms involved in the interplay between different cellular compartments 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 or without homozygous/heterozygous DKK3 deletion in both epithelial and stromal compartment and employed various in vitro and ex vivo systems to examine the stage and compartment-specific roles of DKK3 during PDAC progression. 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, shortened overall survival, and a higher liver metastasis incidence in the DKK3-null animals at the endpoint. Further characterization of isolated tumor cells underpinned 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 PDAC onset, 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 addressing the oncogenic dialog within PDAC tumors.
Citation Format: Dharini Srinivasan, Frank Arnold, Elodie Roger, Anna Härle, Michael Melzer, Patrick 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: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C028.