Figure 4. Prior radiation is permissive for metastatic lung colonization in tumor-free mice.

(A) MMTV/PyVmT cells in 100-mm dishes in serum-free medium were treated with 1.25–7.5 Gy. Cell-conditioned medium was collected 72 hours later, and TGF-β1 levels were determined by ELISA as described in Methods. (B) MMTV/PyVmT cells stably expressing luciferase were injected via tail vein in virgin female FVB mice. Where indicated, mice received 10 Gy to the thorax 1 hour prior to injection of cells. Cancer cells in lungs were visualized by mouse bioluminescence 2 weeks after inoculation (top). In some cases, lungs were surgically removed after administration of d-luciferin and imaged ex vivo (bottom). Controls are shown on the left and irradiated mice are shown on the right. (C) Representative lung whole mounts (top) and H&E sections of lungs (bottom; original magnification, ×100) from control and irradiated mice. (D) Quantification of surface lung metastasis (left) and lung weight (right) in control and irradiated mice. Data are mean ± SD of 5 mice per group in 2 independent experiments. **P < 0.01, ***P < 0.001 versus control.