Abstract 4102: Mesenchymal stem cells induce epithelial-to-mesenchymal transition (EMT) in metastatic SP cells in pancreatic cancer

Abstract

Abstract In malignant cells, some reports demonstrated that Side population (SP) cells expressed tumor-initiating activity, chemotherapy resistance and metastatic potential. We previously reported that SP cells play a pivotal role of local invasion and in vivo liver metastasis in pancreatic cancer (Int-J-Cancer 124:2771, 2009). The augmentation of metastatic activity in SP cells appeared to relate to epithelial-to-mesenchymal transition (EMT), as SP cells were highly responsive to TGF-beta-mediated EMT and local invasion. However, the mechanisms by which SP cells undergo EMT in vivo remains unknown. Cancer associate fibroblasts (CAFs) have recently been implicated in important aspects of epithelial solid tumor biology, considered migrate to tumor sites and contribute to neoplastic progression, tumor growth, angiogenesis, and invasion/metastasis. In addition, recent reports have demonstrated that CAFs are derived from hematopoietic precursor/stem cells from bone marrow. Thus, bone marrow derived mesenchymal stem cells (MSCs) would be an attractive candidate for CAFs which enhance cancer metastasis by mediating EMT. The AIM of present study is to examine whether bone marrow-derived MSCs have ability to mediate EMT of pancreatic cancer SP cells. METHODS: Human bone marrow-derived MSCs were isolated by flowcytometry. Panc-1 cells were co-cultured with or without MSCs, and tumorigenesity was compared by implantation into NOD/SCID mice. Either unsorted panc-1 cells or Panc-1-derived SP cells were co-cultured in the presence or absence of MSCs using transwell culture dish for 7 days. Invasion activity was assessed by using matrigel invasion assay. In addition, real-time PCR experiments were performed to quantitate E-cadherin mRNA levels. RESULTS: When Panc-1 cells were mixed with MSCs and co-injected into NOD/SCID mice, tumorigenic activity was enhanced as compared to single injection of the equivalent number of cancer cells. In vitro co-culturing with MSCs changed the shape of Panc-1-derived SP cells to spindle-like appearance. The cell-to-cell contact underwent loosely, these morphological changes were consistent with EMT. E-cadherin mRNA levels were decreased after co-culturing. In addition, SP cell matrigel invasion activity was enhanced by co-culturing with MSCs. Similar results were observed in SP cells when EMT was induced by incubation in the presence of TGF-beta, a known inducer of EMT. It was surprising that when SP cells were co-incubated with MSCs, most of the cells fell into non-SP fraction by re-analysis of Hoechst33342 staining. This alteration was reversible as the cells recovered SP-phenotype by removing the MSCs. In CONCLUSION, MSC-derived soluble factors may induce EMT which is concordant with augmentation of invasion activity in metastatic SP cells. The SP-phenotype appears to be transient and reversible, which could be regulated by MSC-derived factors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4102.