Inhibition of CXCR7 prevents the AMC-mediated MM tumor growth. (A) Number of circulating AMCs at 0, 7, 14, 21, and 28 days after subcutaneous implantation of ALZET osmotic pumps 1002 (replaced at day 14), 2002 (replaced at day 14), and 2004 loaded with POL9626 in healthy SCID-bg mice. (B) Pharmacokinetic analysis of the levels of POL9626 in plasma over 4 weeks after implantation of the different pumps. The effect of POL9626 (delivered by 2004 osmotic pump) on MM tumor growth by BLI as detected at 28, 35, and 42 days after injection of MM cells; as shown in quantification of BLI (C) and images (D). (E) Pharmacokinetic analysis of the levels of POL9626 in plasma of the treatment group. (F) Compound 1 and POL6926 triggered association of β-arrestin with CXCR7 in a concentration-dependent manner.