One of the hallmarks of human pancreatic ductal adenocarcinoma (PDAC) is its pronounced type I collagenrich fibrotic reaction. Although recent reports have shown that the fibrotic reaction can limit the efficacy of gemcitabine chemotherapy, the underlying mechanisms remain poorly understood. In this article, we show that the type I collagen allows PDAC cells to override checkpoint arrest induced by gemcitabine. Relative to cells grown on tissue culture plastic, PDAC cells grown in 3-dimensional collagen microenvironment have minimal Chk1 phosphorylation and continue to proliferate in the presence of gemcitabine. Collagen increases membrane type 1 matrix metalloproteinase (MT1-MMP)-dependent ERK1/2 phosphorylation to limit the effect of gemcitabine. Collagen also increases MT1-MMP-dependent high mobility group A2 (HMGA2) expression, a nonhistone DNA-binding nuclear protein involved in chromatin remodeling and gene transcription, to attenuate the effect of gemcitabine. Overexpression of MT1-MMP in the collagen microenvironment increases ERK1/2 phosphorylation and HMGA2 expression, and thereby further attenuates gemcitabine-induced checkpoint arrest. MT1-MMP also allows PDAC cells to continue to proliferate in the presence of gemcitabine in a xenograft mouse model. Clinically, human tumors with increased MT1-MMP show increased HMGA2 expression. Overall, our data show that collagen upregulation of MT1-MMP contributes to gemcitabine resistance in vitro and in a xenograft mouse model, and suggest that targeting MT1-MMP could be a novel approach to sensitize pancreatic tumors to gemcitabine. Cancer Res; 71(3); 1019-28. Ó2010 AACR.

Purpose To assess the clinical and pathological significance of mast cell infiltration in human pancreatic cancer and evaluate crosstalk between mast cells and cancer cells in vitro. Experimental Design Immunohistochemistry for tryptase was performed on 53 pancreatic cancer specimens. Mast cell counts were correlated with clinical variables and survival. Serum tryptase activity from cancer patients was compared to patients with benign pancreatic disease. In vitro, the effect of pancreatic cancer conditioned media on mast cell migration was assessed. The effect of conditioned media from the human mast cell line, LAD-2, on cancer and normal ductal cell proliferation was assessed by thymidine incorporation. Matrigel invasion assays were used to evaluate the effect of mast cell conditioned media on cancer cell invasion in the presence and absence of a matrix metalloproteinase inhibitor, GM6001. Results Mast cell infiltration was significantly increased in pancreatic cancer compared to normal pancreatic tissue [11.4±6.7vs.2.0±1.4(p<0.001)]. Increased infiltrating mast cells correlated with higher grade tumors (p<0.0001) and worse survival. Patients with pancreatic cancer had elevated serum tryptase activity (p<0.05). In vitro, AsPC1 and PANC-1 cells induced mast cell migration. Mast cell conditioned media induced pancreatic cancer cell migration, proliferation and invasion but had no effect on normal ductal cells. Furthermore, the effect of mast cells on cancer cell invasion was in large part MMP-dependent. Conclusions Tumor infiltrating mast cells are associated with worse prognosis in pancreatic cancer. In vitro, the interaction between mast cells and pancreatic cancer cells promote tumor growth and invasion.