CXCR4 and neoplasm: A trophic effect of the PVN was mediated by endothelial cell-derived CXCL12 [8] and was blocked by treatment with the CXCR4 antagonist AMD3100, depletion of CXCL12 in endothelial cells or overexpression of G-protein coupled receptor kinase 3, a negative regulator of the CXCL12 receptor, CXCR4, in tumor cells [12].