Investigation of the inhibitory mechanism of the hepatic metastasis in the colorectal carcinoma by synthesic retinoid, TAC-101

肝转移是影响结直肠癌预后的重要因素之一。这表明，更有效地抑制结肠癌的进展和转移将显著改善预后。最近，维甲酸(RA)已被证明是一种潜在的强大的抗癌药物，并在几种类型的癌症治疗中发挥作用。维甲酸对肿瘤的作用机制可能与其对肿瘤细胞增殖和分化的影响有关。4-[3，5-双(三甲基硅基)苯甲酰胺]苯甲酸是一种新型的维甲酸衍生物，与维甲酸受体-α和-β具有特异的结合亲和力。TAC-101在体内外具有明显的抗增殖、抗血管生成和抗肿瘤作用。然而，TAC-101的具体作用机制尚不清楚，因此，我们对TAC-101的抗血管生成和诱导细胞凋亡的机制进行了研究。POR-…诱导肝转移的实验研究在F344大鼠体内更多地注射RCN-9大鼠结肠癌细胞。每周5天口服TAC-101，连续4周，免疫组织化学检测肝肿瘤微血管密度(MVD)和血管内皮生长因子(VEGF)的表达。细胞凋亡指数(A.I.)用免疫组织化学方法检测肝肿瘤组织中单链DNA的表达。用免疫组织化学方法检测细胞增殖指数、Fas和Fas配体的表达。此外，应用流式细胞仪检测TAC-101对DLD-1人结肠癌细胞株的凋亡作用，发现TAC-101可显著降低微血管密度和血管内皮生长因子的表达。Northern印迹分析和ELISA法结果表明，TAC-101能有效抑制DLD-1细胞中VEGFmRNA和蛋白的表达，并呈时间和剂量依赖关系。TAC-101可显著降低肝转移瘤的PI，升高AI。TAC-101对Fas配体的表达没有影响，但明显增加了转移瘤中Fas的表达。此外，TAC-101在体外以时间依赖的方式诱导DLD-1细胞早期凋亡，这些结果提示TAC-101可能通过干扰肿瘤血管内皮生长因子的产生来抑制结肠癌的进展和转移。此外，TAC-101可能部分通过上调Fas的表达诱导细胞凋亡。较少

The presence of hepatic metastasis is one of the most important prognostic factors in colorectal cancer. This suggests that more effective suppressor of the progression and metastasis of colon cancer would significantly improve prognosis. Recently, RA (retinoic acid) has shown to be a potentially powerful anti-cancer agent, and acts in several types of cancer therapy. The mechanism of RA's affect on tumors appears to be related to its effects on proliferation and differentiation of tumor cells. 4-[3,5-bis (trimethylsilyl) benzamido] benzoic acid (TAC-101) is a novel retinobenzoic acid derivative and has a specific binding affinity to the retinoic acid receptors (RAR)-α and -β. TAC-101 has potent anti-proliferative, anti-angiogenic, and anti-tumor effects in vitro and in vivo. However, little is known about the detailed mechanism of TAC-101 function.Here, we investigate the mechanism of the anti-angiogenic effect and apoptosis induction of TAC-101. Hepatic metastases were induced by por … More tal injection of RCN-9 rat colonic cancer cells into F344 rats. TAC-101 was orally administered 5 days per week for four weeks, then liver tumors were immunohistochemically evaluated for microvascular density (MVD) and vascular endothelial growth factor (VEGF). Apoptotic index (A.I.) in the hepatic tumors was evaluated using immunohistochemistry for single-stranded DNA. The proliferative index (P.I.), Fas and Fas ligand were also immunohistochemically evaluated. Moreover, evaluation of apoptosis by TAC-101 in vitro using FACScan analysis was performed in the DLD-1 human colon cancer cell line.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. TAC-101 significantly decreased P. I. but increased A. I. in the hepatic metastatic tumors. TAC-101 did not affect the expression of Fas ligand, but obviously increased the expression of Fas in the metastatic tumors. Moreover, TAC-101 induced early apoptosis in DLD-1 cells in a time dependent manner in vitro.These findings suggest that TAC-101 may inhibit progression and metastasis in colon cancer by interfering with tumor production of VEGF. Moreover, TAC-101 may induced apoptosis partially through enhanced Fas expression. Less