Inhibition of CXCR7 reverses tube formation induced by MM. (A) Representative images of the effect of POL9626 (50 nM) on the HUVEC tube formation induced by CM from MM1.S cells (non-CM was used a control). (B) Quantification of the length of tubes formed due to MM CM with or without the presence of POL9626 (50 nM), normalized to the length of tubes formed in non-CM. (C) Representative images of the effect of POL9626 (50 nM) on the tube formation of HUVECs induced by coculture with MM1.S cells, and the direct cell-adhesion of MM cells to the formed tubes. (D) Following activation of HUVECs with MM cells, the effect of CXCR7 inhibition on downstream signaling in HUVECells was shown by immunoblotting.