Targeting Occult Metastatic Disease: A Hematogenously Derived Xenograft Model of Human Pancreatic Tumor Growth in the Murine Liver.

198 Background: Most pancreatic cancer patients will die following surgery due to recurrent metastatic disease. Thus, better systemic therapies are needed to treat occult metastases to improve survival. We have developed a model of occult liver metastasis from pancreatic cancer in order to evaluate novel treatment strategies. Methods: Pancreatic cancer cells (MAD 09-366, 08-608, MPanc96) transduced with green fluorescent protein (GFP) and luciferase were injected into the spleens of athymic, nude mice to generate hepatic metastases. Ninety-six hours after injection, tumor-bearing mice were treated with MEK1/2 inhibitor (trametinib, 0.3mg/kg, daily), gemcitabine (100mg/kg, twice weekly), or vehicle control. Sequential bioluminescence imaging, flow cytometry, and histologic evaluation were used to assess hepatic tumor growth and behavior. Results: All injected cell lines generated hepatic metastases. Different cell lines exhibited different growth kinetics. MPanc96 injected mice demonstrated a 64% decrease in average luminescence from 6 to 72 hrs after injection followed by a 146-fold increase from 72hrs until sacrifice at 21 days. Extensive liver metastases were noted at necropsy. Flow cytometry analysis of digested mouse livers following MPanc96 injection revealed rapid clearance followed by sharp outgrowth of tumor cells that mirror the bioluminescent imaging data. MPanc96 injected mice treated with trametinib exhibited significant hepatic tumor growth inhibition relative to gemcitabine and control treated mice. At 21 days, trametinib treated mice demonstrated a 14.9-fold increase in average luminescence while on treatment compared to an 82.5-fold increased for gemcitabine treated mice (p = 0.028) and a 195.5-fold increase for control mice (p = 0.027). Conclusions: This in vivo model of pancreatic liver metastases has proven effective in assessing treatment effects on pancreatic metastatic growth. Trametinib appears to be a superior agent to gemcitabine at inhibiting metastatic pancreatic tumor growth and its effectiveness will be evaluated using this model with additional patient-derived tumor cell lines.