Cyclic bisdesmosides from Actinostemma lobatum MAXIM (Cucurbitaceae) and their in vitro cytotoxicity

Two new cyclic bisdesmosides elucidated as lobatoside L (1) and lobatoside M (2) and four known cyclic bisdesmosides (3-6) were isolated from Actinostemma lobatum MAXIM (Cucurbitaceae). Their structures were determined on the basis of spectroscopic analyses including IR, HR-FAB-MS, TOCSY, 1D- and 2D-NMR experiments and chemical reactions. The inhibitory effects of the six compounds on human Cancer cell growth (including esophageal squamous carcinoma cell line ECA109, lung Cancer cell line A549 and gastric Cancer cell line MGC-803) were determined using the MTT assay. The results revealed that the six compounds exhibited cytotoxicity against all the cell lines tested, and compounds 1, 3 and 5 showed significant activities in a dose dependent manner against all the cell lines, especially for compound 1 and 5, the IC(50) values for ECA-109 cells were 8.25 μM and 3.71 μM. The results demonstrated that compounds 1 and 5's activities are 2- and 4-fold that of cisplatin.