Roles of inducible cyclooxvgenase-2 in angiogenesis and its significance of therapeutic targets

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Angiogenesis in chronic glanuloma formed around sponge discs implanted into subcutaneous tissues of rats was increased over a 14-day experimental period. In sponge granuloma, mRNA of COX-1 was constitutively expressed, whereas that of COX-2 was increased with neovascularization in pararell with that of vascular endothelial growth factor (VEGF). Topical injections of bFGF increased the expression of COX-2 mRNA without affecting that of COX-1 mRNA. The angiogenesis with bFGF was inhibited by indomethacin or selective COX-2 inhibitors, NS-398, nimesulide, and JTE-522. The expression of VEGF mRNA in the granuloma was also enhanced by bFGF, and was reduced by NS-398. The enhanced angiogenesis by bFGF was significantly inhibited by topical injections of VEGF anti-sense oligonucleotide. These results suggested that COX-2 may enhance the neovascularization in sponge granuloma by PG-mediated expression of VEGF, and that a COX-2 inhibitor would facilitate the management of conditions involving a … More ngiogenesis. Using prostaglandin (PG) receptor knockout mice, we have evaluated a role of PGs in tumor-associated angiogenesis and tumor growth, and identified PG receptors involved. Sarcoma-180 cells implanted in wild type mice (WT) formed a tumor with extensive angiogenesis, which was greatly suppressed by specific inhibitors for cyclooxygenase(COX)-2 but not for COX-1. Angiogenesis in sponge implantation model, which can mimic tumor-stromal angiogenesis, was markedly suppressed in mice lacking EP3 (EP3-/-) with reduced expression of vascular endothelial growth factor (VEGF) around the sponge implants. Further, implanted tumor growth (sarcoma-180, Lewis lung carcinoma) was markedly suppressed in EP3-/-, in which tumor-associated angiogenesis was also reduced. Immunohistochemical analysis revealed that major VEGF-expressing cells in the stroma were CD3/Mac-1 double-negative fibroblasts, and that VEGF-expression in the stroma was markedly reduced in EP3-/-, compared with WT. These results demonstrate significance of host stromal PGE2-EP3 receptor signaling in tumor angiogenesis. An EP3 receptor antagonist may be a candidate of chemopreventive agents effective for malignant tumors. Less