Abstract 172: Pathophysiological role of microRNA-29 in pancreatic cancer stroma

Abstract

Dense fibrotic stroma associated with pancreatic ductal adenocarcinoma (PDAC) has been a major obstacle for drug delivery to the tumor bed and may impede attempts to slow down PDAC progression and metastasis. However, current anti-stromal drugs have not improved tumor response to chemotherapy or patient survival. Thus, a better understanding of the molecular mechanisms associated with tumor-stromal interactions is desperately needed to develop novel anti-stromal therapeutic approaches. MicroRNAs (miRNAs) are an abundant class of highly conserved, small non-coding RNAs that function as key regulators of eukaryotic gene expression and cellular homeostasis. miR-29 is known to play a paramount role in the fibrotic process of several organs by providing crucial functions downstream of pro-fibrotic signaling pathways such as TGF-β1 and regulating the expression of extracellular matrix (ECM) proteins, a major component in the PDAC stroma. Upregulation of TGF-β1 is commonly associated with PDAC pathogenesis and is known to activate stromal cells. Furthermore, vascular endothelial growth factor (VEGF) that stimulates tumor angiogenesis is a predicted target of miR-29. We hypothesize that miR-29 may be misregulated in TGF-β1 activated PDAC stromal cells and lead to excessive accumulation of ECM proteins and VEGF. Restored expression of miR-29 could be therapeutically beneficial to modulate tumor-stromal interactions. To understand the role of miR-29 in PDAC stroma, we examined miR-29 expression patterns in TGF-β1 activated stromal cells using qPCR/northern blot analysis and determined ECM and VEGF protein expression. In activated stromal cells, we observed loss of miR-29 in correlation with a significant increase in ECM and VEGF protein expression. In addition, in both murine and human PDAC samples, loss of miR-29 expression is associated with an increase in stromal percentage estimated by Sirius red stain. To evaluate the physiological role of miR-29 in stroma, we performed gain and loss-of-function studies by transfecting stromal cells with synthetic miR-29 mimics or locked nucleic acid, a miR-29 inhibitor. Overexpression of miR-29 in stromal cells suppressed matrix and VEGF protein expression, and conversely, depletion of miR-29 lead to their significant increase. Finally, to evaluate the effect of miR-29 overexpression in stromal cells on cancer colony growth, we directly co-cultured miR-29 transfected stromal cells with pancreatic cancer cells for 10 days, and subsequently, cancer colony number and stromal deposition was determined by crystal violet and Sirius red stains respectively. We observed a significant decrease in the number of cancer colonies and stromal accumulation in co-cultures. In conclusion, our results provide insight into the mechanistic role of miR-29 in PDAC stroma and its potential use as a novel anti-stromal therapeutic agent. Citation Format: Jason J. Kwon, Sarah C. Nabinger, Ravi K. Alluri, Zachary Vega, Smiti S. Sahu, Zahi Abdul Sater, Zhangsheng Yu, A Jesse Gore, Grzegorz Nalepa, Romil Saxena, Murray Korc, Janaiah Kota. Pathophysiological role of microRNA-29 in pancreatic cancer stroma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 172. doi:10.1158/1538-7445.AM2015-172