Abstract 2372: Mechanisms of microRNA-21 dysregulation in pancreatic ductal adenocarcinoma (PDAC)

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy with tumorigenesis largely driven by a nearly ubiquitous activating KRAS (mKRAS) mutation. Thus far efforts to target mKRAS have been largely unsuccessful due to compensatory mechanisms and associated toxicity. MicroRNAs (miRNAs) are short non-coding RNAs that represent a novel avenue to target KRAS effector function through post-transcriptional regulation. We recently described dysregulation of miRNA-21 (miR-21) in transgenic KrasG12D/+;Trp53R172H/+;Pdx-1-Cre (KPC) mice as a cell- and compartment-specific regulator of tumor epithelial cells. Here we report on the use of human models to elucidate the underlying mechanisms responsible for cellular phenotypes defined by KPC modeling. Experimental Procedures: The Cancer Genome Atlas (TCGA) was leveraged to computationally identify putative targets of miR-21 and additional pathways of interest for transcriptional and functional experiments. Concurrently, de-novo patient-derived organoid (PDO) models were generated from core biopsies and surgical resection specimens and expanded in Matrigel for current experiments. miR-21 expression in five PDO cell lines is profiled using qPCR. Stable knock-down of miR-21 is explored using lentiviral constructs in PDOs and cancer associated fibroblasts (CAFs) for use in a co-culture models to examine the mechanisms of action of miR-21 and investigating messenger RNA targets (mRNA) of miR-21. We have simultaneously used TCGA to examine targets of miR-21 and identify pathways of interest for further transcriptional and functional experiments. Results: Analysis of TCGA PDAC cohort examined 48 putative targets of miR-21. Decreases in the target mRNA levels of these 48 targets were heterogenous. Prominently, an inverse relationship was identified between miR-21 expression and the expression of one of its target mRNAs: programmed cell death protein 4 (PDCD4). Gene set enrichment analysis is underway to identify additional biologic targets of interest. Evaluation of miR-21 expression in PDO and matched CAF cell lines demonstrated robust and repeatable miR-21 identification as well as stability of knocked down miR-21 expression following transduction with a lentiviral miR-21 inhibitor construct. Conclusions: We previously demonstrated that miR-21 appears to be an early and reliable molecular marker of pancreatic neoplasia. The lack of global inverse relationship between miR-21 and target messenger RNA expression suggests more complexity to this regulation or bias from TCGA cohort, as the majority of patients in this cohort have early stage disease. These findings warrant additional mechanistic evaluation of specific targets such as PDCD4, which may have significant biologic importance and insight into our previously described phenotype. PDOs are powerful models for these mechanistic studies. Citation Format: Jacquelyn W. Zimmerman, Richard A. Burkhart, Elana J. Fertig, Elizabeth M. Jaffee. Mechanisms of microRNA-21 dysregulation in pancreatic ductal adenocarcinoma (PDAC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2372.