黑殭菌素 B (Destruxin B) 對大腸癌細胞 HT-29 之抑制效果及機制
黑殭菌素 (Destruxin) 是由昆蟲寄生性真菌 (entomogenous fungi) 之一 (Matarhizium anis opliae) 所分泌出的毒素，在已分離出的三十餘種中，本研究中採用的是由此一菌種分泌 的二次代謝物 Destruxin B(DB) 作為抗腫瘤製劑。 DB 對昆蟲具有毒性且運用在生物農 藥已有數年之久。在之前的研究中發現到在體外試驗或是活體試驗 DB 對於 DBA/2 老 鼠 L5178Y 淋巴癌細胞有抑制的效果。
本論文將探討由黑殭菌素 B (Destruxin B) 對人類大腸癌細胞株 HT-29 細胞造成生長抑 制或毒殺作用。由初期的實驗結果得知 HT-29 在高於 1.29uM DB 作用下可以有效的抑 制癌細胞生長。再利用 DNA 片段及 Annexin V 染色的方式更進一步地證實出 Destruxin B 會引起 HT-29 細胞死亡是經由細胞凋亡而來，而非壞死。再以西方點墨法的結果證 實 procaspase 3 和 PARP 蛋白降解有增加的情形，更能證實細胞是由於凋亡而死。 HT-2 9 在給於 DB 48 小時之後，可以由西方點墨的結果得知較上游的 caspase 9 表現進而使 得 cytochrome c 表現上升 ;Bcl-2 的表現減少， Bax 和 AIF 的增加更可以確定出 HT-29 經由 DB 作用後，會經由粒線體的內在路徑而走向細胞凋亡。此外，經由 DB 刺激下，可誘使 p53 的表現進而抑制 cyclin D1 與 CDK4 的表現而使得細胞週期停滯在 G0/G1 期。
此結果也與流式細胞儀的結果相吻合。 CDK2 、 cdc2 和 cyclin B 些微的減少也導致細 胞週期停滯在 S 和 G2/M 期。也由螢光顯微鏡的結果顯示出 DB 會使得 HT-29 產生一些 凋亡核質 (apoptotic nuclei) 也部份印證出由西方點墨法的結果。
綜合以上結果得知， DB 可以抑制人類大腸癌細胞株 HT-29 的生長是透過內在的細胞死 亡路徑及影響細胞週期的 G0/G1 期和部份的 S 和 G2/M 期所致。The Anti-Tumor Effects of Destruxin B on HT-29 Colorectal Cancer
Destruxins are second metabolic products form an entomogenous fungus, Mararhuzuim anisopliae.These s ubstances are toxic to insect and have been used as an insecticide for decades.Over thirty analogues of dest ruxins have been isolated by different laboratories;the one used in this study is Destruxin B (DB).The previ ous study in our laboratory revealed that DB has potent anti-tumor activity in mouse L5178Y lymphoma ce lls in DBA/2 mice both in vitro and in vivo experiments.
In this report,the HT-29 human colon adenocarcinoma cell line was used as a subject to evaluate its anti-tu mor activity and study the mechanism of the effect.The initial experimental results showed that DB possess es a potent growth suppression effect on HT-29 when the doses of DB higher than 1.29uM.Further Annexi n V staining and DNA fragmentation experimental results showed that the tumor cells apoptosis is one of t he major factor to cause the death of tumor cells.From the Western blot experimental results found that cas pase 3 activity and PARP degraded form of protein were increased, it confirmed the previous observations.
Caspase 9,one of the upstream caspase which is induced by cytochrome c was increased at 48 hours after D B treatment.The expression of some other signal proteins such as decreasing Bcl-2,increasing Bax and AIF confirmed the effect of DB is followed by the intrinsic pathway of apoptosis which is mediated by mitocho ndria.In addition,DB may enhance p53 protein expression which corresponded suppression cyclin D1 and CDK4 implied that DB may cause cell cycle arrest at G0/G1 phase.These results are accordant with the res ult from flow cytometry. The expression of CDK2,cdc2 and cyclin B showed a slightly decreasing at some points may explain that partially interfere the cell cycle at S and G2/M phase. Immuno-fluorescence stainin g results showed that DB treated HT-29 containing some apoptotic nuclei which may be and indirect evide nce to support the results from Western blot.
