靈芝醇抗癌機制的研究：抑制拓樸異構酶及引導肝癌細胞走向老化

Abstract

靈芝醇(Ganoderiol F；841)是萃取自鹿角靈芝具有四環結構的三帖類。在本實驗中發現，841可同時抑制拓樸異構酶I與拓樸異構酶IIα的活性。在肝癌(HepG2, Hep3B, Huh7)及血癌(K562)細胞的研究中，841可立即抑制細胞內DNA的合成，使細胞生長停止，而對正常的肺纖維母細胞影響較小，甚至完全不會影響到週邊血細胞的存活。更進一步發現，841可誘導肝癌細胞(HepG2)走向老化的命運。在誘導老化的分子機制上，我們觀察到p21及p16的表現量增加、p38及p53被活化、以及p53的負調節因子：SIRT-1與細胞週期調節因子：cyclin D1的減少。這是第一篇指出841可誘導癌細胞老化的研究。因此，具有選擇性抑制癌細胞及誘導老化能力的841也許將來能應用於癌症的治療上。另一方面，低劑量的841雖然不會影響到癌細胞的生長，但是卻可以抑制細胞內端粒酶的mRNA表現，也可降低Buthionine sulfoximine所造成的細胞毒性。由這些實驗推測，低劑量的841也許可以當作化學預防藥物來抑制細胞的癌化。

Ganoderiol F (841), a tetracyclic triterpene isolated from Ganoderma amboinense, was found to be inhibitors of both topoisomerase I and topoisomerase IIα. Treatment of human hepatoma HepG2, Hep3B, Huh7 cells, and leukemia K562 cells with 841 resulted in immediate inhibition of DNA synthesis and halt of cell growth. On the other hand, the growth of normal lung fibroblast MRC5 cells were less affected and peripheral blood mononuclear cells were unaffected by 841. Furthermore, a senescent phenotype was detected in 841-treated HepG2 cells. Molecular events of senescence, including increase of p21 and p16, activation of p38 and p53 and the decrease of SIRT-1 as well as cyclin D1, were observed. Our study is the first report about 841 functioning as a senescence inducer in cancer cells and the tumor selective cytostatic effect and senescence induction capability of 841 might have anticancer implications. Low dosage of 841 (<1 μM) did not affect the viability of HepG2 cells but caused a significant decrease in the mRNA expression of hTERT, a reverse transcriptase subunit of telomerase, and detoxification in buthionine sulfoximine-treated cell, suggesting that low-dose of 841 may function as chemopreventive agent and inhibit tumorigenesis.