Abstract 2979: Inhibition of palladin in cancer associated fibroblast impedes pancreatic ductal adenocarcinoma associated desmoplasia
Authors: Alexander Jennifer I. , Cukierman Edna 
Published: July 2017

Pancreatic Ductal Adenocarcinoma (PDAC) claims 97% of patient lives in less than 5 years after diagnosis. Treatment of PDAC is challenged by the collagen-rich, highly dense, fibrous-like extracellular matrix (ECM) known as desmoplasia. Desmoplasia is initiated by activated cancer associated fibroblasts (CAFs) and disseminates throughout the stromal compartment in a vicious cycle involving alterations to the physical/structural and biochemical pathways in neighboring naïve fibroblasts that ultimately enriches the CAF population. This desmoplastic-ECM (D-ECM) encapsulates the tumor mass, thereby limiting therapeutic perfusion. Paradoxically, ablation of D-ECM induces a more aggressive PDAC progression.

Although the underlying biology remains unclear, the D-ECM is a consequence of cytoskeletal rearrangements occurring amid the CAFs. The goal of this study is to delineate the cytoskeleton dynamics engaged as a potential mechanism to restore the innate tumor-suppressive properties of a normal ECM. As such, this study focuses on the actin cross-linker palladin which has been identified as an independent prognostic marker in PDAC progression. We postulate palladin has an isoform-specific role in PDAC desmoplasia as well as cancer progression.

Using an in vivo-mimetic 3D fibroblast-derived ECM model, we explore the isoform-specific role of palladin during D-ECM onset as well as during D-ECM-induced CAF activation in PDAC patient derived CAFs in which the major palladin isoforms (isoforms 3 and 4) were knocked out via CRISPR/Cas9 gene editing. Using these cells, we examined the activation status of the CAFs while characterizing the ECM produced via quantitative immunoblots, real-time polymerase chain reaction, and detailed microscopy analyses. We then validated the effects of palladin knockout CAFs activity in influencing kras mutated cancer cells’ metabolic activity, invasion and proliferation.

Our data indicates palladin isoforms 3 and 4 expression are necessary to drive CAF activation as well as perpetuate the D-ECM phenotype whereby knockdown of either isoform prevents CAF activation while limiting cancer cell behavior. Additionally, the ECMs produced by the palladin knockout CAFs were no longer capable of activating naïve fibroblast in addition to decreasing the inherent aggressive nature of kras-mutant cancer cells. These results are similar to previous findings regarding the restrictive nature of a normal ECM on CAF activation and cancer cell behavior.

These findings suggest that palladin isoforms 3 and 4 are required for desmoplastic onset and D-ECM-induced fibroblastic activation and cancer cell progression. Together, these results propose manipulation of specific palladin isoforms could signify a strategy to restore a normal tumor-suppressive stroma in PDAC.

Citation Format: Jennifer I. Alexander, Edna Cukierman. Inhibition of palladin in cancer associated fibroblast impedes pancreatic ductal adenocarcinoma associated desmoplasia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2979. doi:10.1158/1538-7445.AM2017-2979