Stilbene Derivatives from the Leaves and Stems of Bletilla striata and their Cytotoxicity and Autophagy Activity

Two new compounds (1 and 2), together with five known (3–7) stilbene derivatives, were isolated from the leaves and stems of Bletilla striata. Their structures were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. Compounds 1 and 2 were evaluated for their cytotoxicity against five human tumor cell lines. Compound 1 showed cytotoxicity against SHSY5Y and MCF7 cells with IC50 values of 2.8 and 2.2 μM. Compound 2 showed cytotoxicity against SHSY5Y and MCF7 cells with IC50 values of 2.2 and 2.4 μM, respectively. Moreover, compound 1 was found to trigger both apoptosis and autophagy in Hela cells, as indicated by increased cleaved PARP and LC3B, respectively. The enhanced autophagy induced by compound 1 was further confirmed by imaging detection of more autophagosomes (mRFP–GFP–LC3+ puncta) and autolysosomes (mRFP–LC3+ puncta), as well as a low GFP/RFP fluorescence ratio of GFP-LC3-RFP. Signal pathway analysis indicated compound 1 might inhibit mTOR signaling to stimulate autophagy.