Abstract 1582: Tumor-associated stromal cells increase malignancy of human colorectal cancers triggering EMT induction
Authors: Mele Valentina , Governa Valeria , Muraro Manuele G. , Glaus Garzon Jesus F. , Borsig Lubor , Daester Silvio , Droeser Raoul , Oertli Daniel , Zuber Markus , Rosso Raffaele , Spagnoli Giulio C. , Iezzi Giandomenica 
Published: July 2016

In the last decades it has been demonstrated that the stroma surrounding tumor not only provides mechanical support, but profoundly influences the outcome of the primary tumor and its possible relapse, impacting on proliferation, metastatic progression and resistance to therapies. Major components of the stroma in most types of human carcinomas are the Tumor-Associated Stromal Cells (TASC). Different sources have been proposed for this population, ranging from the resident fibroblasts to bone marrow-derived mesenchymal stromal cells (BM-MSC) recruited to the trans-differentiated epithelial and endothelial cells, but the scenario is still unclear. Moreover, TASC have an intrinsic heterogeneity, combined also with the presence of multiple subpopulations, and they share several markers with other cell subsets of the stroma, thus making the identification of this population, based on the expression of specific markers, an arduous task.

In this intricate context, we aim to address phenotypic and functional characterization of TASC isolated from colorectal cancer specimens, and to analyze TASC-mediated effects on CRC development and progression in vivo.

TASC were characterized for phenotype and differentiation capacity. Human CRC cells were cultured in the presence or absence of TASC for five days. After co-culture tumor cells were sorted by flow cytometry and evaluated for the expression of EMT-related genes by Real Time PCR and for in vitro invasiveness by chemoinvasion assay. Furthermore, their tumorigenicity and the metastatic potential were assessed upon subcutaneous and intracoecally injection in NOD/SCID mice. Developed tumors, metastatic foci and circulating tumor cells were assessed by histology, flow cytometry and Imaging Flow Cytometry.

Our results indicate that TASC resemble BM-MSC in morphology and phenotype. They also comprise a multipotent subpopulation that is able to differentiate into adipogenic and osteogenic lineage. After co-culture with CRC cells, TASC express membrane-bound TGF-β, through which they are capable to trigger epithelial-to-mesenchymal transition (EMT). Upon subcutaneous injection in NOD/SCID mice, tumor cells co-cultured or admixed with TASC before injection, show a faster growth kinetic and develop larger tumor masses as compared to tumor cells alone. Furthermore developed tumor masses are characterized by a higher vessel density. Notably, upon intracoecal injection TASC presence or conditioning leads to a higher metastatic formation in lungs and livers and an increased number of circulating tumor cells in the peripheral blood, most importantly comprising cells undergoing EMT.

Our data clearly show that the stromal component in the human colorectal cancer microenvironment increases the malignancy of tumor cells, by providing pro-mitogenic factors and by triggering EMT initiation in vitro and in vivo, thus promoting tumorigenicity and metastasis formation in vivo.

Citation Format: Valentina Mele, Valeria Governa, Manuele G. Muraro, Jesus F. Glaus Garzon, Lubor Borsig, Silvio Daester, Raoul Droeser, Daniel Oertli, Markus Zuber, Raffaele Rosso, Giulio C. Spagnoli, Giandomenica Iezzi. Tumor-associated stromal cells increase malignancy of human colorectal cancers triggering EMT induction. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1582.