Antiproliferative steroidal glycosides from Digitalis ciliata

Two new compounds, a furostanol glycoside (1) and a pregnane glycoside (4), along with eight known compounds, belonging to the classes of spirostane (2,3), pregnane (5-7) and cardenolide (8-10) glycosides, were isolated from the seeds of Digitalis ciliata. Their structures were elucidated by 1D and 2D-NMR experiments as well as ESI-MS analysis. For the first time pregnane glycosides of the diginigenin series have been isolated from D. ciliata. The cytotoxic effects of compounds 1-10 on cell viability of several cancer cell lines, namely human breast cancer (MCF-7), human glioblastoma (T98G), human lung adenocarcinoma (A549), human colon carcinoma (HT-29), and human prostate cancer (PC-3) cell lines were evaluated. Compounds 1, 4, 7 and 8 showed antiproliferative effects against MCF-7, HT-29 and A549 cancer cells with IC₅₀ values ranging from 8.3 to 20 μM. The effects of compounds 1-10 on cell proliferation were evaluated on these three cancer cell lines by cell cycle analysis of DNA content using flow cytometry. Compounds 7, 8 and 10 induced significant changes in G₂/M cell cycle phase of all analyzed cells. The obtained results indicate that compounds 7, 8 and 10 are cytostatic compounds effective in reducing cell proliferation by inducing accumulation of the cells in the G₂/M phase of the cell cycle.