Non-invasive imaging of tumor-associated macrophage infiltration to colon cancer in living mice using an enhanced luciferase reporter gene

Objectives Tumor-associated macrophage are known to affect the cancer progression through modulation of immune function, angiogenesis, and cell metastasis. The aim of this study is to visualize the macrophage migration toward tumors lesion in living mice using a colon cancer cells expressing a renilla luciferase gene and macrophage expressing an enhanced firefly luciferase gene.

Methods Murine macrophage Raw264.7 cells expressing an enhanced firefly luciferase gene (Raw264.7/effluc) and murine colon cancer CT26 cells expressing a renilla luciferase gene (CT26/Rluc) were established. CT26/Rluc cells (5x104 cells/well) were plated in 96-well plate with or without Raw264.7/effluc cells (1x104 cells/well) and then Rluc activity was measured at 24 h. CT26/Rluc cells were challenged to right thigh of Balb/C mice for animal tumor model. When tumor mass were detected, Raw264.7/effluc cells were intravenously transferred to mice and bioluminescent imaging (BLI) imaging was done at indicated times. Tumor and draining inguinal lymph node were excised and ex vivo BLI was acquired at day 7 post-transfer of Raw264.7/effluc.

Results BLI signals for Rluc gene were significantly increased when CT26/Rluc cells were co-cultured for 24 hours with Raw264.7/effluc cells compared with when CT26/Rluc cells were cultured alone (P=0.025). Early distribution of Raw264.7/effluc cells were visualized in the lung and spleen and BLI signals emitted from Raw264.7/effluc cells were observed in tumor lesion from day 1 until day 7 post-transfer of Raw264.7/effluc. Also ex vivo BLI exhibited the migration of Raw264.7/effluc cells into both tumor periphery and draining inguinal lymph nodes.

Conclusions We successfully demonstrated that reporter macrophage Raw264.7/effluc can not only promote the proliferation of CT26 colon cancer cells in vitro but also migrate into tumor periphery in vivo animal model.

Research Support This work was supported by the grant No. RTI04-01-01 from the Regional Technology Innovation Program of the Ministry of Knowledge Economy(MKE), by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MEST, NRF-2009-0078234), by a grant of the Korea Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (A111345), by National Nuclear R&D Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (No.2012M2A2A7014020), by a grant of the Korea Healthcare technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea (A091224) and by Kyungpook National University Research Fund, 2013.