MIP-2 induziert Proliferation aber nicht Vaskularisierung etablierter extrahepatischer Metastasen während endogeninduziertes MIP-2 nur die Etablierung dieser Metastasen stimuliert

Abstract

Background: Previous studies have shown that liver resection enhances intrahepatic engraftment of CXCR-2 expressing colorectal cancer cells by the action of the CXC chemokine macrophage inflammatory protein (MIP)-2. However, the effect of MIP-2 on extrahepatic metastasis is not known yet. With the use of a murine model, we studied how exogenously applied and liver resection-associated MIP-2 affects extrahepatic tumor cell engraftment and whether MIP-2 also stimulates the growth of already established metastases. Methods: Green fluorescent protein (GFP)-transfected CT26.WT colorectal cancer cells were implanted in dorsal skinfold chambers of syngeneic BALB/c mice. After 5 days, the tumors were locally exposed to 100 nM MIP-2 (MIP-2; n = 7). Tumors exposed to PBS served as controls (control; n = 8). To study the effect of MIP-2 on extrahepatic tumor cell engraftment after liver resection, additional animals underwent a 30 % hepatectomy. Animals were treated with a anti-MIP-2 antibody, starting at day 0 simultaneously with tumor cell implantation (Phx+mAB0). To study the effect of MIP-2 on established metastases, anti-MIP-2 treatment was initiated at day 5 after tumor cell implantation (Phx+mAB5). Hepatectomized animals without neutralization of MIP-2 served as sham controls (Phx). Tumor vascularization and growth as well as tumor cell migration, proliferation, apoptosis and CXCR- 2 expression were studied over 14 days using intravital fluorescence microscopy, histology and immunohisto- chemistry. Results: Exogenously applied MIP-2 induced CXCR2 expression and tumor cell proliferation leading to a significant acceleration of tumor growth compared to PBS-treated controls. MIP-2 did not affect dilation and permeability of the tumor microvessels. Accordingly, the angiogenic response was not affected, and the density of the established tumor microvascular network was even found decreased after MIP-2 exposure when compared to PBS controls. Functional inhibition of MIP-2 significantly delayed extrahepatic tumor cell engraftment (Phx+mAB0) but not the growth of established metastases (Phx+mAB5). The initial delay of engraftment was associated with a compensatory stimulation of vascularization and tumor cell migration when compared to controls. Further, inhibition of MIP-2 caused a slight reduction of the number of proliferating cells, but a significant (p < 0.05) diminution of tumor cell apoptosis. In both groups with antibody treatment, the number of CXCR-2 expressing tumor cells was found significantly reduced. Conclusion: With the use of a murine tumor model, we demonstrate that MIP-2 is involved especially in engraftment of CT.26 colorectal cancer cells at extrahepatic sites. The MIP-2/CXCR-2 signaling pathway may be a promising target for early antitumor therapy in patients undergoing liver resection.