Attachment of
tumor cells to the endothelium (EC) under flow conditions is critical for migration of
tumor cells out of the vascular system to establish
metastases. We found that neutrophils (PMN) increased
melanoma cell extravasation. Endogenous
IL-8 liberated from
melanoma cells or from PMN induced by
melanoma cells contributed to PMN-facilitated
melanoma cell arrest on the EC in the microcirculation. Functional blocking of
IL-8 receptors on PMN or neutralizing soluble
IL-8 in the
tumor circulation decreased the level of CD11b/CD18 up-regulation on PMN and subsequently reduced
melanoma cell extravasation. We also found that targeting mutant V600EB-Raf interrupted
melanoma cell extravasation in vitro and subsequent lung
metastasis development in vivo. B-Raf encodes a RAS-regulated
kinase that mediates cell growth and malignant transformation
kinase pathway activation. Results showed that inhibition of V600EB-Raf reduced
IL-8 secretion from
melanoma cells and reduced the capacity of
IL-8 production from the tumor microenvironment involving PMN. Furthermore, reduction in
intercellular adhesion molecule-1 (ICAM-1) expression on
melanoma cells was found after V600EB-Raf knockdown. These results provide new evidence for the complex role of secreted
chemokine and PMN-
melanoma adhesion in the recruitment of metastatic
cancer cells to the EC, which are significant in fostering new approaches to
cancer treatment through anti-inflammatory
therapeutics.