紫檀芪對Heregulin-β1誘導之人類乳癌細胞侵襲能力的影響

國人十大死亡原因的首位為惡性腫瘤，其中乳癌是導致女性癌症致死率的第四位，癌症致死的主因在於癌細胞的擴散。因此，能有效的抑制乳癌細胞侵襲及轉移的發生機制，對於治療預後不良的乳癌患者將具有重大意義。乳癌細胞中，HER2接受器常有基因擴大表現的現象，進而促使癌細胞不斷的進行分化、增殖、血管新生以及轉移；而HRG-β1是屬於表皮生長因子-ligand家族中的成員，在乳癌組織中同樣具有過度表現的情形，可誘發細胞膜上HER family的訊息傳遞，因此在乳癌生成的過程中扮演非常重要的角色。基質金屬蛋白酶 (matrix metalloproteinases, MMPs)，是一群鋅依賴性的蛋白質水解酵素，目前發現的種類已超過20種，此群酵素幾乎能降解細胞外基質的所有成份，因此被認為與癌細胞之侵襲與轉移息息相關。研究發現，乳癌的復發或轉移和HER family 所引起的MMP-9過度表現具有相關性。植物多酚類之一的白藜蘆醇 (resveratrol) 證實具有抗發炎、抗氧化、抗腫瘤轉移等多種生物活性。近來，發現紫檀芪(pterostilbene)為白藜蘆醇的結構類似物，推測和白藜蘆醇可能具有類似的生理活性。目前初步研究已知紫檀芪可促使癌細胞產生凋亡，其在抗癌作用機制中仍不清楚。因此，本研究主要目的是想探討紫檀芪是否具有類似白藜蘆醇的抗腫瘤轉移的作用。在本研究中發現，紫檀芪對HRG-β1刺激人類乳癌細胞株MCF-7侵犯及轉移的能力皆具有濃度依賴性的抑制效果。另外，在明膠水解試驗及西方墨點法個別分析MMP-9的酵素活性及蛋白表現中也呈現相同的抑制趨勢。實驗結果發現，紫檀芪可明顯降低人類乳癌細胞中HER2/HER3蛋白質酪胺酸的磷酸化，並且會減少彼此形成複合體的情形。綜合以上結果，本研究發現紫檀芪確實具有抑制乳癌細胞轉移的能力，但詳細作用機轉仍需要更多研究來證實。

In Taiwan, breast cancer is one of the highly dangerous causes of death for females due to tumor metastasis and invasion which can be up-regulated by growth factor receptor such as human epidermal growth factor receptor 2 (HER2). Matrix metalloproteinases (MMPs), a group of zinc-dependent endopeptidases which degrade a variety of extracellular matrix components, have been considered to promote tumor metastasis and invasion. Among them, the expression of MMP-9 mediated by HER2 or its related ligand such as heregulin-β1 (HRG-β1, a combinatorial ligand for the HER3 and HER4 receptors can transactivate HER2 receptor) has been shown to be highly associated with breast cancer metastasis, suggesting that MMP-9 may be an accessible target for improving the health of breast cancer patients under metastatic progression.Pterostilbene, a dimethyl ether analogue of resveratrol, exerts its cancer chemopreventive activity similar to resveratrol by inhibiting cancer cell proliferation and inducing apoptosis. Recent study has shown that resveratrol blocks HRG-β1-modulated MMP-9 expression and invasion in human breast cancer cells, raising the possibility that pterostilbene might prevent cancer cell metastasis or invasion. To this end, the effects of pterostilbene on HRG-β1-mediated cell invasion in MCF-7 human breast cancer cells were examined. In this study, we found that pterostilbene reduced HRG-β1-mediated cell invasion and migration in a dose-dependent manner in MCF-7 cells, demonstrated by transwell assay and wound healing assay, respectively. Soft agar assay shows that pterostilbene inhibited HRG-β1-stimulated tumorigenicity of MCF-7 cells. Pterostilbene also inhibited the enzyme activity and protein expression of MMP-9 by HRG-β1, analyzed by gelatin zymography and western blotting, respectively. Furthermore, pterostilbene clearly decreased either HER2 or HER3 tyrosine phosphorylation, and interrupted the formation of heterodimer between HER2 and HER3 in HRG-β1-treated MCF-7 cells.Taken together, our present results indicate that pterostilbene has an inhibitory potential on HRG-β1-mediated cell invasion and metastasis of breast cancer cells, which might be attributed to inhibition of MMP-9 expression and HER2 signaling by pterostilbene. However, the detailed mechanisms by which pterostilbene down-regulates MMP-9 expression and cell invasion require further study.