Abstract PR03: Mesenchymal stem cells in pancreatic cancer possess unique properties in promoting tumor growth and metastasis

Background and Rationale: Pancreatic ductal adenocarcinoma (PDA) is one of the most stroma-rich cancers that exists. It is hypothesized that stroma contributes to the aggressive nature of PDA. There is strong evidence that mesenchymal stem cells (MSC) are recruited as part of the stroma to the tumor microenvironment. Studies in solid cancers of various organs including lung, stomach and ovaries have reported that MSCs are present in stroma within the cancer tissue and impact tumor biology. However, no published reports on role of MSC in PDA exist, therefore an opportunity exists to identify and functionally characterize MSC in pancreatic cancer and understand their contribution to pancreatic cancer biology. Experimental Design: Human pancreatic cancer associated fibroblasts (CAFs) from patient tumors (n=18) were isolated and grown in low passage cultures. The mesenchymal lineage of the CAF cultures was confirmed by KRAS mutational analysis of both the CAF cells and matching neoplastic epithelial cells. The purity of CAF cultures was also confirmed by immunostaining for immune (CD45) and epithelial (CK19) cell markers. An orthotopic model was established in which 105 GFP labeled tumor cells were mixed with either 105 DsRed labeled CAF or CAF-MSC cells and implanted into the pancreata of NOD-SCID mice (n= 6 mice per group). GFP labeled tumor cells and DsRed CAF/CAF-MSC cells injected alone served as the experimental controls. Growth kinetics and tumor metastasis between different groups were studied using bioluminescence animal imaging and weekly tumor monitoring. Once tumors formed, mice were sacrificed and tumor burden quantified. Blood was collected for analysis of circulating GFP+ tumor cells and RFP+ CAF or CAF-MSC cells. Protein cytokine arrays were performed to identify differentially expressed genes by CAF-MSCs. Results: Primary human CAF cultures were heterogeneous and each contained a unique population of MSCs, as defined by expression of MSC markers (CD90, CD49a, CD73 and CD44), the functional capacity to differentiate into bone, cartilage and adipose cells, and the ability to form colonies when plated at low densities. We observed that CAF-MSCs promoted tumor growth and metastasis to a significantly greater degree than bulk CAF cells, and only CAF-MSCs cells were capable of entering into the circulation. Using human protein cytokine arrays to explore the paracrine factors selectively secreted by CAF-MSC, we found that the cytokine GM-CSF was secreted selectively by CAF-MSCs and not CAFs (n=4). GM-CSF knockdown in CAF-MSCs using targeted shRNA compared to control shRNA resulted in a significant decrease in the development of metastasis in co-injection experiments with primary pancreatic cancer cells using an orthotopic model. Conclusions: Here we provide the first characterization of MSCs within the human PDA microenvironment. We find PDAs have a unique population of MSCs which confer specific biologic properties to PDA. These studies will help us to define important target molecules within the tumor microenvironment involved in key tumor-stromal interactions that may impact therapeutic approaches for patients. This abstract is also presented as Poster B2. Citation Format: Meghna Waghray, Guan Grace, Malica Yalamanchili, Lidong Wang, Michele Dziubinski, Mina Zeinali, Sunitha Nagrath, Diane Simeone. Mesenchymal stem cells in pancreatic cancer possess unique properties in promoting tumor growth and metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr PR03.