4-[3,5-Bis(trimethylsilyl)benzamido] benzoic acid inhibits angiogenesis in colon cancer through reduced expression of vascular endothelial growth factor.

4-[3,5-bis(trimethylsilyl)benzamido] Benzoic acid (TAC-101) has potent antiproliferative, antiangiogenic, and antitumor effects in vitro and in vivo. These effects might be due to TAC-101 binding to retinoic acid receptor alpha (RAR-alpha) and interfering with the binding of activator protein-1 (AP-1) to DNA. However, little is known about the detailed mechanism of TAC-101 function. We investigated the mechanism of the antiangiogenic effect of TAC-101 using a rat hepatic metastatic model in vivo and DLD-1 human colon cancer cells in vitro. Liver metastases were induced by portal injection of RCN-9 rat colonic cancer cells into F344 rats. TAC-101 (8 mg/kg) was orally administered 5 days per week for 4 weeks and then hepatic tumors were immunohistochemically evaluated for microvessel density (MVD) and vascular endothelial growth factor (VEGF). TAC-101 significantly reduced both MVD and VEGF expression. Northern blot analysis and ELISA indicated that TAC-101 efficiently inhibited production of VEGF mRNA and protein in DLD-1 cells in a time- and dose-dependent manner. These findings suggest that TAC-101 may inhibit progression and metastasis in colon cancer by interfering with tumor production of VEGF.