Abstract 5719: Tumor-suppressive stromal activity of pro-fibrogenic microRNA-21 in initiation and progression of K-Ras-driven mouse models of pancreatic cancer
Authors: Schipper Josh , Jackson Brooke , Beddows Ian , Kenyon Elizabeth , Powell Katie , Robertson Neil , Hostetter Galen , Kiupel Matti , Moore Anna , Conejo-Garcia Jose , sempere Lorenzo 
Published: September 2020

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is a recalcitrant and lethal disease with an overall 5-year survival rate of less than 8%. The abundance and heterogeneity of cancer-associated fibroblasts (CAFs) in a highly desmoplastic tumor microenvironment are unique features of PDAC. Therapeutic strategies aimed at indiscriminately eliminating CAFs have failed in clinical trials. The opposing tumor-restraining or tumor-promoting role of distinct CAFs subpopulations of has emerged as a new paradigm in PDAC basic and translational research. Understanding how the composition of these distinct CAF subpopulations is affected by and interferes with current treatments is a key question to solve in order to obtain more effective and durable clinical responses. Genetic studies in K-Ras-driven genetically engineered mouse models (GEMMs) indicate that α-smooth muscle actin-expressing (SMA+) CAFs have a predominant tumor-restraining role. Here, we studied global loss of pro-fibrotic non-coding regulatory microRNA-21 (miR-21) in PDAC GEMMs. We generated mouse strains carrying wild type or knockout alleles of Mir-21 in a well-characterized K-Ras-driven, p53-deleted PDAC model (LSL-KrasG12D; p53lox/+;Pdx1-Cre, KPC). Even though miR-21 expression was upregulated in cancer cells and cancer-associated fibroblasts in KPC tumors, global loss of miR-21 activity did not inhibit tumor growth. Strikingly, loss of miR-21 accelerated tumor initiation via mucinous cystic neoplastic lesions and progression to locally advanced invasive carcinoma from which animals precipitously succumbed at an early age. We uncovered a cell-autonomous requirement of miR-21 activity for induction of tumor-restraining SMA+ CAFs, whose absence led to a profound remodeling of the stroma and massive infiltrate of tumor-promoting immune cells. Low miR-21 expression negatively correlated with a fibroblast gene expression signature and positively with an immune cell gene expression signature in TCGA PDAC data set (n = 156) mirroring findings in GEMMs. In vitro and in vivo isograft experiments showed that miR-21 activity was dispensable for cancer cell growth, but required for complete execution of TGF-β-mediated programs. Our results suggest that modulation of miR-21 activity may provide a novel therapeutic opportunity to affect the composition of CAF subpopulations. We will present our genetic and pharmacological approaches to modulate stromal activity of miR-21 in established disease in order to enhance current chemotherapy and/or immunotherapy treatments.
Citation Format: Josh Schipper, Brooke Jackson, Ian Beddows, Elizabeth Kenyon, Katie Powell, Neil Robertson, Galen Hostetter, Matti Kiupel, Anna Moore, Jose Conejo-Garcia, Lorenzo sempere. Tumor-suppressive stromal activity of pro-fibrogenic microRNA-21 in initiation and progression of K-Ras-driven mouse models of pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5719.