Fig. 6

CD11b⁺Gr-1⁺ MDSCs increased breast cancer extravasation and survival via PDGF-BB. CM of CD11b⁺Gr-1⁺ MDSC isolated from the lungs of CXCL17-treated or 4T1-bearing mice (n = 5) increased transendothelial migration (a) and colony formation (b) of 4T1 cells. rmPDGF enhanced 4T1 cell transendothelial migration (c) and colony formation (d). Blockade of PDGFR-β prevented transendothelial migration (e) and colony formation (f) of 4T1 cells induced by CM of CD11b⁺Gr-1⁺ MDSCs. CD11b⁺Gr-1⁺ MDSC isolation and the collection of their CMs have been described in the legend of Fig. 2. C166 cells were seeded 8-μm pore collagen-coated inserts for confluent monolayer, and PKH26-labeled 4T1 cells (1 × 10⁵/insert) were seeded onto C166 confluent monolayer inserts, and the CM of CD11b⁺Gr-1⁺ MDSCs (50%) or rmPDGF-BB protein (20 ng/ml) were placed in the bottom well as chemoattractant. The migration of cancer cells was assessed by a fluorescence microscope. For colony formation analysis, 4T1 cells were treated with different CMs (50%) or PDGF-BB (20 ng/ml), and the colonies counted after staining. g PDGFR inhibitor imatinib decreased lung metastasis in mice (n = 6 per group). h H&E staining of lung sections. Representative lung tissue sections were stained with H&E and photographed at × 100 magnification. Results are representative of at least three independent experiments and each value is the mean ± SD of three determinations. *Significant difference between the two test groups (p < 0.05)