Abstract 1690: Tumor-educated macrophages promote tumor growth and peritoneal metastasis in an orthotopic nude mouse model of human pancreatic cancer

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Abstract There is a strong association between poor survival and increased macrophage density in many cancers. In the current study, we determined whether macrophages from tumor-bearing mice (tumor-educated macrophages) had greater tumor-promoting capability than macrophages from non-tumor-bearing mice. Ten transgenic nude mice ubiquitously-expressing GFP were injected subcutaneously with the human pancreatic cancer cell line, BXPC3 stably expressing RFP. GFP-expressing macrophages from tumor-bearing transgenic GFP mice were harvested and defined as “tumor-educated macrophages”. Macrophages were also harvested from transgenic GFP mice (n=10) without subcutaneous tumors and identified as “naïve macrophages.” Three groups of mice were studied: 1) A control group without addition of macrophages (n=10); 2) A naïve group, with weekly intraperitoneal (ip) injection of 106 naïve macrophages per mouse (n=10); and 3) A tumor-educated group, with weekly ip injection of 106 tumor-educated macrophages per mouse (n=10). The study ended with termination of the tumor-educated group after 8 weeks due to a pre-morbid state identified in all mice. At this time, all mice in each of the three study arms were terminated, imaging was performed, and total tumor weight was obtained. In the control group, the average primary tumor weighed 668 mg; only three mice (30%) developed peritoneal metastases with an average weight of 241 mg. The naïve-macrophage group had an average tumor weight of 823 mg (p=0.51); 50% developed peritoneal metastases with an average weight of 975 mg (p=0.029). The tumor-educated-macrophage group had an average primary tumor weight of 2095 mg (p=0.001); 75% of mice developed peritoneal metastases with an average weight of 2135 mg (p=0.008). When comparing naïve- to tumor-educated- groups, primary tumor weight was significantly greater in the tumor-educated group (p=0.003), and the average weight of metastasis was 2.2 times greater in the tumor educated group, however this did not reach statistical significance (p = 0.17). When comparing naïve- to tumor-educated-groups, there was no statistically significant difference with regard to body weight (p=0.87), or weight of metastasis (p=0.68); however primary tumor weight was significantly greater in the tumor-educated group (p=0.013). Tumor-educated-macrophages specifically promote tumor growth progression in an orthotopic nude mouse model of pancreatic cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1690. doi:1538-7445.AM2012-1690