Invasion assays were carried out for 18 hours. Non invading cells on top of the matri were removed by rubbing with a moistened cotton swab. Invaded cells on the lower surface of the Matrigel matri were fi ed with 4% PFA and stained with 0. 2% crystal violet. Cells were counted using ImageJ software. Statistical analyses The two tailed Calcitriol IC50 Students t test was used to compare measurements for pairs of samples. Two way analysis of variance and Bonferroni post hoc testing were used to compare the tumor volumes of the two groups. The SPSS software was used for all statistical analyses. Results Correlation of spontaneous distant metastasis of breast cancer cells with MDSC recruitment In our previous report, high IL 6 secreting human breast cancer cells revealed more aggressive phenotypes including enhanced distant metastasis and recruited more inflammatory cells com pared to the low IL 6 e pressing cells.

In another report, we also showed that damaged epithelial cells produced IL 6 and recruited inflammatory cells including neutro phils. Thus, we assumed that IL 6 derived from cancer cells could affect the metastasis of cancer cells through inflammatory cell, including MDSC, recruit ment. To elucidate the relationship between MDSC recruitment and distant metastasis of cancer cells, we created a murine breast cancer model using 4T1 and EMT6 breast cancer cells, which e hibit differential IL 6 e pression. 4T1 and EMT6 cells were orthotopically grafted into the mam mary fat pads of syngeneic BALB c mice. Primary tumor growth was slightly but significantly greater for EMT6 cells compared to 4T1 cells during the entire e peri mental period.

At 26 days after grafting, 4T1 cancer cells showed e tensive lung metastasis, while EMT6 cancer cells showed no distant metastasis in the lung, liver, bone or brain. IL 6 e pressing 4T1 cell bearing mice showed dramatic recruitment of CD11b Gr 1 MDSCs in the spleen, metastasizing organs and primary tumor mass. the total Anacetrapib number of MDSCs recruited was two to eight times higher in 4T1 cell bearing mice than in EMT6 cell bearing mice. To further evaluate the role of MDSCs in the distant metastasis, the 4T1 cell tumor bearing mice were depleted of MDSCs. Depletion of MDSCs reduced 4T1 lung metastasis and primary tumor growth in the mammary fat pads. These results show that MDSCs that e panded and recruited in the tumor bearing mice are critically asso ciated with the distant metastasis of cancer cells. Induction of IL 6 e pression facilitated MDSC recruitment and increased their metastatic capacity We ne t evaluated whether IL 6 mediated MDSC recruitment promoted the metastasis of EMT6 cancer cells. We stably transfected EMT6 cells with a vector encoding murine IL 6.