Abstract PO-113: The prolyl isomerase PIN1 plays a critical role in fibroblast differentiation states to support pancreatic cancer

PIN1 is a phosphorylation-directed prolyl isomerase that alters the conformation and, therefore, the function of many proteins. PIN1 overexpression in cancer contributes to cancer cell-intrinsic phenotypes including cellular proliferation and migration. While its pro-tumor functions have generated interest in therapeutic targeting of PIN1 for cancer treatment, the effects of PIN1 inhibition on tumor-associated stromal phenotypes have not yet been studied. We assessed pancreatic cancer xenografts and genetically engineered p48-Cre; LSL-KrasG12D; p53R172H (KPC) mice that were treated with small molecule PIN1 inhibitors or crossed into a full body PIN1 knockout (Pin1−/−), and found that PIN1 inhibition or loss decreased tumor growth and extended overall survival. To interrogate a direct role for PIN1 in the stroma, we orthotopically injected a KPC cell line into syngeneic Pin1+/+ or Pin1−/− hosts and found dramatic reduction of tumor cell growth in Pin1−/− hosts. Further analysis of the Pin1−/− tumor microenvironment revealed decreased expression of alpha-SMA, a marker of myofibroblastic cancer associated fibroblasts (myCAFs), as well as decreased ECM deposition and/or organization. Pancreatic stellate cells (PSCs) activated in the tumor microenvironment play a major role in the deposition of ECM and secrete growth factors to support tumor cell proliferation and survival. We, therefore, interrogated the role of PIN1 in PSCs. We found that loss of PIN1 in PSCs inhibits TGF-beta-induced stellate cell activation into a myofibroblast phenotype. Single cell ATAC-seq analysis demonstrated that a subset of TGF-beta responsive changes to chromatin accessibility are impaired in the absence of PIN1, and suggests that specific transcription factor families may play a role in the PIN1-dependent response to TGF-beta. Further analysis of PSCs or CAFs with PIN1 loss indicated that, at baseline, these cells express gene programs consistent with the recently described antigen presenting CAFs (apCAFs). Finally, in addition to changes in cellular state and plasticity, we found that loss of PIN1 alters PSC secretion of paracrine factors that support oncogenic phenotypes. For example, PSCs with loss of PIN1 have reduced expression of HGF and increased expression of VEGF, resulting in altered cancer cell and vascular phenotypes. This work establishes a role for PIN1 in regulating fibroblast function and suggests that targeting PIN1 in cancer will have a broad anti-tumor effect. Our ongoing work continues to use 2D co-cultures, heterotypic 3D bioprinted tissues, and in vivo mouse models to interrogate the precise mechanisms by which PIN1 controls fibroblast phenotypes and impact of these changes on tumor phenotypes and outcomes. Citation Format: Ellen M. Langer, Isabel A. English, Vidhi Shah, Kevin MacPherson, Kayleigh M. Kresse, Brittany L. Allen-Petersen, Colin J. Daniel, Mara H. Sherman, Andrew Adey, Rosalie C. Sears. The prolyl isomerase PIN1 plays a critical role in fibroblast differentiation states to support pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-113.