牛樟芝菌絲體中4-Acetylantroquinonol B提升抑制肝癌幹細胞之免疫機制

Abstract

牛樟芝以護肝聞名，本研究室過去發現其菌絲體萃取之泛醌類衍生物4-acetylantroquinonol B（4-AAQB）具有抑制肝癌細胞HepG2良好功效，IC50 為0.1 ppm (μg/mL)，但在4-AAQB對於肝癌幹細胞與免疫系統的影響仍不清楚。免疫系統為腫瘤發展上必需克服的難題，腫瘤可藉由分泌免疫逃避激素、馴化免疫系統、隱蔽抗原辨識部位等方式，來躲避免疫系統的攻擊，甚至利用免疫系統協助其發展。有許多癌症幹細胞已被定義為腫瘤起始細胞(tumor-initiating cell)，被視為發展腫瘤免疫抑制（tumor- derived immunosuppression）的重要因素。另外，在腫瘤免疫中，樹突細胞為扮演抗原呈現連結非特異性與特異性毒殺腫瘤的重要角色，針對癌症幹細胞研究的樹突疫苗可望作為腫瘤治療發展的重要目標。因此，本研究為探討牛樟芝機能性成分4-AAQB對肝癌幹細胞與免疫機能的影響。研究結果顯示，4-AAQB可以抑制HepG2肝癌幹細胞標誌EpCAM與AFP，且相較於類似的活性化合物antroquinonol ( AQ ) 具有更好的效果。4-AAQB能顯著使EpCAM及β-catenin表現量下降，抑制腫瘤細胞的成瘤性與免疫逃避細胞激素的分泌，顯示4-AAQB具有防制肝癌幹細胞發展與免疫逃避的潛力。在免疫活性評估方面，4-AAQB可促進單核球與巨噬細胞的增生，相較於AQ可顯著的提升未成熟樹突細胞的吞噬作用並促進相關免疫激素IFN-γ、IL-2、TNF-α的分泌，在共培養肝癌幹細胞與未成熟樹突細胞下，4-AAQB可以促進EpCAM+ HepG2肝癌幹細胞與未成熟態樹突細胞彼此的MHC class I與II表現，以及增強偕同刺激分子CD80和刺激免疫活化細胞激素IFN-γ和TNF-α的分泌，顯示出良好的抗原呈現作用。綜合以上結果，本研究證實了4-AAQB相對於AQ擁有更好的腫瘤幹細胞抑制和免疫促進能力，並可以提升樹突細胞對於肝癌幹細胞的辨識力，因此我們可以結論，牛樟芝菌絲體萃取物4-AAQB具有活化免疫系統與預防肝癌發生與發展的潛力。

Antrodia cinnamomea is famous for its liver protection function. In our laboratory, 4-acetylantroquinonol B (4-AAQB), a ubiquinone derivative extracted from the mycelium of Antrodia cinnamomea, was found to be able to inhibit the growth of HepG2 cells with IC50 of 0.1 μg/mL. However, its impact on liver cancer stem cells and the immune system remains unclear. The immune system is a hurdle factor for tumor development. The cancer cells must develop immune escape ability in order to grow continuously. Cancer cells can secrete a variety of immune escape cytokines, domesticate immune system and hidden antigen recognition sites to evade the attack of the immune system and even use the immune system to help their development. Many cancer stem cells are defined as tumor-initiating cells, which are considered as an important factor for multi-potential development of tumor-derived immune-suppression. In tumor immunity, dendritic cells play an important role in the link between nonspecific and specific tumor poisoning. Therefore, this study aimed to investigate the effects of 4-AAQB on immune responses of hepatoma stem cells and dendritic cells. The results showed that 4-AAQB can inhibit EpCAM, AFP and related pathways of hepatocellular carcinoma stem cells, and has more potent activity than the analogous active compound antroquinonol (AQ). 4-AAQB can significantly decrease the expression of β-catenin, inhibit the tumorigenicity and decrease the secretion of immune escape related cytokines, indicating that 4-AAQB has the potential to inhibit the immune escape of hepatocellular carcinoma stem cells. Moreover, 4-AAQB can stimulate the proliferation of immune cells and promote the endocytosis and the secretion of IFN-γ、IL-2、TNF-α of immature dendritic cells. When the immature dendritic cells were co-cultured with EpCAM+ HepG2 cells, 4-AAQB enhanced the expression of MHC class I and II on the surface of liver cancer stem cells and dendritic cells, increased the expression of costimulatory molecules CD80 of dendritic cells and cytokines related to immune activation. The aforementioned results show that 4-AAQB has the potential to activate the immune system thus prevent the development of liver cancer stem cells.