Steroidal glycosides from Ornithogalum thyrsoides bulbs and their cytotoxicity toward HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells

Ornithogalum thyrsoides Jacq belongs to the Asparagaceae family and is cultivated for ornamental purposes. The authors have previously reported several cholestane- and spirostan-type steroidal glycosides from O. thyrsoides. Conventional TLC analysis of the methanolic bulb extract of O. thyrsoides suggested the presence of unprecedented compounds; therefore, a detailed phytochemical investigation of the extract was performed and 35 steroidal glycosides (1-35), including 21 previously undescribed ones (1-21) were collected. The structures of 1-21 were determined mainly by analyses of their 1H and 13C NMR spectra with the aid of two-dimensional NMR spectroscopy. The isolated compounds were classified into three distinct groups: furostan-type (1, 2, 8-12, and 22), spirostan-type (3-7 and 23-26), and cholestane-type (13-21 and 27-35). Although the C/D-ring junction of the steroidal skeleton is typically trans-oriented, except for some cardiotonic and pregnane-type steroidal derivatives, 7 possess a cis C/D-ring junction. This is the first reported instance of such a configuration in spirostan-type steroidal derivatives, marking it as a finding of significant interest. Compounds 1-35 were evaluated for cytotoxicity against HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells. Compounds 3-6, 9, 17-21, 23-25, and 30-35 demonstrated cytotoxicity in a dose-dependent manner with IC50 values ranging from 0.000086 to 18 μM and from 0.00014 to 37 μM toward HL-60 and SBC-3 cells, respectively. Compound 19, which is obtained in a good yield and shows relatively potent cytotoxicity among the undescribed compounds, induces apoptosis in HL-60 cells, accompanied by arresting the cell cycle of HL-60 cells at the G2/M phase. In contrast, 19 causes oxidative stress-associated necrosis in SBC-3 cells. The cytotoxic mechanism of 19 is different between HL-60 and SBC-3 cells.