Mytoxin B and Myrothecine A Induce Apoptosis in Human Hepatocarcinoma Cell Line SMMC-7721 via PI3K/Akt Signaling Pathway

Trichothecene macrolides comprise a class of valuable leading compounds in developing anticancer drugs, however, there are few reports concerning their anticancer mechanisms, especially the anticancer mechanism of the 10,13-cyclotrichothecane derivatives that are found mainly in symbiotic fungi. In vitro anticancer activity of two trichothecene macrolides mytoxin B and myrothecine A against the human hepatocarcinoma cell line SMMC-7721 was investigated in the present study. MTT assay showed that mytoxin B and myrothecine A inhibited the proliferation of SMMC-7721 cells in dose- and time-dependent manners. Annexin V-FITC/PI dual staining assay revealed that mytoxin B and myrothecine A both could induce SMMC-7721 cells apoptosis in a dose-dependent manner. The decreased expression level of anti-apoptotic protein Bcl-2 and the increased expression level of pro-apoptotic protein Bax were observed apparently in Western blot analysis. The reduced ratio of Bcl-2/Bax further confirmed the apoptosis-inducing effect of mytoxin B and myrothecine A on SMMC-7721 cells. Moreover, the expression levels of caspases-3, -8, and -9, and cleaved caspases-3, -8, and -9 were all upregulated in both mytoxin B and myrothecine A-treated cells in Western blot analysis, which indicated that both compounds might induce SMMC-7721 cells apoptosis through not only the death receptor pathway but also the mitochondrial pathway. Finally, mytoxin B and myrothecine A were found to reduce the activity of PI3K/Akt signaling pathway that was similar to the effect of LY294002 (a potent and specific PI3K inhibitor), suggesting that both mytoxin B and myrothecine A might induce SMMC-7721 cells apoptosis via PI3K/Akt pathway.

Cytotoxic trichothecene macrolides from the endophyte fungus Myrothecium roridum

A new cytotoxic roridin-type trichothecene macrolide named epiroridin acid (1) and two known compounds epiroridin E (2) and mytoxin B (3) were isolated from the liquid culture of Myrothecium roridum A553, which was isolated from the medicinal plant Pogostemon cablin. The structure of the new macrolide (1) was elucidated by extensive spectroscopic measurements (UV, IR, MS, and 1D and 2D NMR) analyses. All isolated compounds (1-3) were evaluated for their cytotoxic activities against SF-268, MCF-7, NCI-H460, and HepG-2 tumor cell lines. The new compound (1) exhibited well cytotoxicity against the four selected tumor cell lines.