Pancreatic cancer afflicts nearly 32,000 people in the USA yearly and has an extremely poor prognosis. The five-year survival rate is less than 5%, due largely to late presentation and resistance to standard therapies. Gemcitabine is currently the standard of care for unresectable tumors; however resistance to gemcitabine quickly emerges. To study mechanisms by which resistance arises in pancreatic tumors, we have isolated two gemcitabine resistant (GR) stable cell lines from the human pancreatic cancer line L3.6pl and AsPC-1. These cells were resistant to gemcitabine compared to the parental cell lines by 50 and 100 fold respectively. They were also resistant to EGFR and c-Met inhibition but were equally sensitive to oxaliplatin and 5-FU. GR cells were more migratory and invasive than parental cells lines. Because of the increased intrinsic migratory ability, we examined the status of c-Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF), as c-Met is activated in 70% of human pancreatic cancers. There was a constitutive increase in the phosphorylation of the c-Met receptor, in both cell lines, while total levels were unchanged. Addition of HGF to the GR cells did not further increase receptor phosphorylation. Also, while the parental cell lines could be stimulated to migrate and invade with HGF, no change in migration or invasion was noted with addition of HGF to the GR cells. While c-Met activation was not associated with increased Src or Akt phosphorylation, GR cells acquired changes characteristic of epithelial to mesenchymal transition (EMT), including an increase in nuclear β-catenin and vimentin and a decrease in E-cadherin expression. As c-Met activation is associated with nuclear translocation of β-catenin and EGFR phosphorylation, our data suggest that c-Met activation may be an important mechanism leading to gemcitabine resistance, EGFR inhibitor resistance and tumor progression in pancreatic carcinoma. The mechanistic basis for c-Met activation is currently under investigation.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA