SPARC expression enhances cellular aggregation and resistance to gemcitabine in pancreatic cancer cells

EDGARDO SALVATIERRA; ELVIA RIVAS; LEANDRO GÜTTLEIN; EMILY ROBITSCHEK; ANDREA LLERA; OSVALDO PODHAJCER

Congreso; AACR Annual Meeting 2015; 2015

Pancreatic cancer (PaCa) is a very aggressive disease with a high mortality rate, characterized by a survival time of only few months after diagnosis. Pancreatic cancers also demonstrate great resistance to chemotherapeutic regimes, associated with an extensive desmoplastic reaction. The matricelular protein SPARC is involved in the interaction between the cell and the extracellular matrix, and its expression has been associated with worse prognosis in general, and in patients treated with gemcitabine. To evaluate its role in pancreatic cancer and chemotherapeutic resistance, we overexpressed SPARC in the SPARC-negative pancreatic cancer cells lines Miapaca2, Sw1990, and Panc1. The in vitro growth of two stable clones obtained from the different cell lines was compared with eGFP-transduced controls. No significant differences were observed in the 2D in vitro growth or the clonogenic capacity between pancreatic cancer cells expressing or not expressing SPARC. However, cell growth in 3D spheroid culture was markedly different. Indeed, SPARC-expressing cells exhibited more compact structures, with 45% reduction in spheroid size compared to control eGFP-expressing cells. This could partially be explained by the fact that the SPARC-expressing cells themselves exhibited more than 50% reduction in their size compared to the eGFP cells. While SPARC expression in pancreatic cancer cells did not affect Gemcitabine EC50 in 2D culture, SPARC-positive Panc1 and SW1990 cells exhibited six to ten times increased EC50 in 3D spheroids. Because the cell-cell interactions could potentially affect drug efficacy, and because increased resistance to gemcitabine has been associated with epithelial-mesenchymal transition (EMT), we analyzed the expression of EMT-associated genes (SNAI1 and OCLN), and genes also involved in cellular junctions (CDH1 and OCLN). SPARC-positive pancreatic cancer cells down regulated the expression of SNAI1 and CDH2, while CDH1 and OCLN were up-regulated Taken together, these data indicate that SPARC expression in PaCa cell lines diminishes cells size and modulates gemcitabine resistance in 3D models of cell culture, possibly through the modulation of epithelial genes related to cell-cell connections and EMT.