Although it has been recognized that tumor microenvironment plays a pivotal role in cancer progression, little is known about how differences of microenvironment affect malignant characteristics of cancer cells. In the present study, we tried to investigate the roles of pancreatic tumor microenvironment by use of several mouse inoculation models. First, human pancreatic cancer SUIT-2 cells (parental cells) were inoculated into pancreas orthotopically or into subcutaneous tissue ectopically. In order to expose cancer cells to each microenvironment for long period, processes of inoculation and extraction of cancer cells from primary tumor were repeated. After 3 circles of inoculation, cancer cells were collected from primary tumors in each model and established as distinct cancer cell lines, that is, 3P cells from pancreas in the orthotopic model and 3sc cells from subcutaneous tissue in the ectopic model, respectively. Orthotopic inoculation of these established cells revealed that the 3sc cells, and more prominently the 3P cells, showed higher tumorigenicity in vivo than parental cells. In addition, the 3P cells specifically exhibited low E-cadherin expression and high invasiveness, suggesting that the 3P cells possessed the highest malignant characteristics. Next, gene expression profiles in these cells were examined. RNA-sequence analysis demonstrated that distinct signaling pathways were activated in the 3P or 3sc cells. Pathways associated with extracellular matrix disassembly or collagen catabolic process were commonly activated in the 3P and 3sc cells. On the other hand, pathways including stem cell development or axon guidance were activated only in the 3P cells. These findings suggested that interactions between cancer cells and pancreatic microenvironment are necessary to obtain highly malignant traits. We are currently focusing upon some molecules, which are expressed specifically in the 3P cells, and figuring out their roles in pancreatic cancer progression. Finally, we also tried to uncover the underlying mechanisms of developing highly malignant 3P cells. Two processes are expected to be involved; small fractions of highly malignant cancer cells were adapted to pancreatic microenvironment (“selection”) or parental cells were affected by pancreatic microenvironment (“education”). To address this hypothesis, several clones within the parental SUIT-2 cells were isolated and inoculated as described previously. Individual clones varied in their tumor-forming ability, indicating that heterogeneity is present amongst the parental cells. However, we found that the gene expression profile in each clone was altered after in vivo orthotopic inoculation, suggesting that pancreatic microenvironment may have influence on phenotype of cancer cells. Based on these observations, we postulated that not only “selection” process but “education” process is involved in establishment of highly malignant cancer cells.

Citation Format: Kei Takahashi, Shogo Ehata, Daizo Koinuma, Kohei Miyazono. Roles of tumor microenvironment in pancreatic cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5902. doi:10.1158/1538-7445.AM2017-5902