C-X-C chemokine receptor type 4 (CXCR4) is a receptor for the stromal cell-derived factor-1 which is designated as chemokine ligand 12 (CXCL12). It is involved in cell progression, hematopoiesis, cancer, HIV entry, and rheumatoid arthritis. TC 14012 is an antagonist of CXCR4, blocking CXCR4-mediated HIV infection with an IC50 value of 19.3 nM. In addition, TC 14012 (100 μg/ml) inhibits CXCL12-induced phosphorylation of p42/44 MAPK and STAT3 in B cells from patients with chronic lymphocytic leukemia. This peptidomimetic is C-terminally amidated, resulting in high stability in serum. TC 14012 also activates CXCR7 (EC50 = 350 nM), resulting in the recruitment of β-arrestin and Erk ½ phosphorylation.