Role of inflammatory monocyte mobilization in growth of liver metastasis in a murine model of metastatic pancreatic cancer.

Abstract

299 Background: Pancreatic cancer (PC) is currently the fourth leading cause of death and the mortality rate approaches 100% due to early metastatic spread. Liver is the most common site of metastasis in PC. Our group and others have shown that PC induces cellular changes in the liver which include increase in inflammatory monocyte and macrophage population, long before development of metastasis. Based on our preliminary data, we developed a murine model of metastatic PC to study the role of chemotherapy in addition to novel IM blocking agents in established PC metastasis. Methods: We implanted spontaneously derived murine PC cell line (KCKO) orthotopically in the tail of pancreas of WT mice. 10 days after tumor implantation, there was an increase in infiltrating IM and macrophages in the liver by flow-cytometry and IHC. There was also an upregulation of genes associated with development of metastasis and recruitment of myeloid cells i.e. CCL2, CSF1, s100a4, s100a8, CXCL12, LOX, VEGF-A (P<0.01) by RT-PCR. However, there was no evidence of tumor metastasis at this stage in the liver. We removed the primary tumor on day 10. At this time, mice were injected with βluc-KCKO in the inferior pole of the spleen which was removed. Liver metastases were detectable by bioluminescence in 100% mice after 15 days of splenic injection. Results: Mice with established liver metastasis were randomized to treatment with CCR2i, FOLFIRINOX, CCR2i and CCR2i+FOLFIRINOX or vehicle. Mice were treated for 4 weeks and were imaged biweekly in-order to quantify tumor burden in the liver. Mice were sacrificed after 4 weeks and flow-cytometry studies were performed on peripheral blood, bone marrow and liver. The peripheral blood IM were significantly increased in mice bearing liver metastasis. However, CCR2i efficiently blocked the recruitment of IM and macrophages in liver (p<0.01). The burden of liver metastasis was significantly decreased after four weeks of treatment. Interestingly, the lowest tumor burden was found in livers of mice treated with combination of CCR2i and FOLFIRINOX. Conclusions: We demonstrate that CCR2i in combination with FOLFIRINOX decreases macrophages in the liver and impairs growth of liver metastasis.