C-X-C chemokine receptor 4 (CXCR4) is a receptor for the stromal cell-derived factor-1 (SDF-1) which is designated as chemokine ligand 12 (CXCL12). It is involved in cell progression, hematopoiesis, cancer, HIV entry, and rheumatoid arthritis. FC 131 is an inhibitor of CXCR4 activation by SDF-1 (IC50 = 4.5 nM) and also blocks HIV-induced cytopathogenicity (EC50 = 73 nM). FC 131 derivatives can be used for imaging CXCR4 and elucidating its function.
