(A) In vitro, DA inhibits VEGFA-induced pro–MMP-9 synthesis in CD45^–VEGFR2⁺ BM cells. Pro–MMP-9 was assayed from supernatants of cultured CD45^–VEGFR2⁺ BM cells by sandwich ELISA. CD45^–VEGFR2⁺ cells were isolated from BM of normal mice using MACS cell-sorting system and cultured overnight in serum-free medium with VEGFA, VEGFA plus DA, and VEGFA plus eticlopride plus DA. Synthesis of pro–MMP-9 was found to be significantly increased in supernatants from cells treated with VEGFA, which was normalized in cells treated with VEGFA plus DA. *P < 0.05. However, treatment with eticlopride (DA D₂ receptor antagonist) prior to DA administration abrogated the effect of DA. Results are mean ± SEM for 4 separate experiments. (B) Western blot analysis of CD45^–VEGFR2⁺ BM cells showed considerably increased phosphorylation of ERK1/ERK2 in tumor-bearing mice compared with normal controls, whereas DA treatment inhibited phosphorylation. In D₂^(–/–) plus tumor-bearing animals, CD45^–VEGFR2⁺ BM cells showed increased phosphorylation, but DA treatment had no effect. (C) When CD45^–VEGFR2⁺ EPCs isolated from BM of normal animals were cultured overnight in presence of VEGFA, increased phosphorylation of ERK1/ERK2 was observed in Western blot analysis when compared with the untreated cells. However, the phosphorylation was significantly inhibited within 15 minutes of DA treatment, showing that DA inhibits VEGFA-induced phosphorylation of ERK1/ERK2. An antibody against total ERK was used to determine equal loading. Figures are representative of 4 separate blots.