A new semi-synthetic sapogenol derivative inducing regulated necrosis

Since saponin’s antitumor potency is relatively weak, researchers focus on their semi-synthetic modification to obtain structures with higher potencies. With the same motivation, we prepared a cytotoxic sapogenol derivative (AG-08) from cycloastragenol. Our preliminary studies revealed that AG-08 induced primarily necrotic cell death along with autophagic inhibition. Furthermore, immunoblotting experiments demonstrated that AG-08 promoted cleavage of various proteins such as ATGs, p62, and PARP-1.

The main goals of this study were to verify anti-cancer potential of AG-08 and investigate its possible mechanism(s). Firstly, cytotoxicity of AG-08 on 13 human cell lines was examined and IC₅₀ values were found to be between 2.3±0.035 to 10.18±0.509 µM with no selectivity towards cancer and normal cells. Since AG-08 induced cleavage of various proteins, we investigated the effect of several protease inhibitors on the cell death. Inhibitors of calpain-1, general caspases, cathepsin B/L/S, and caspase 8 partially alleviated cell death with 1.52, 1.55, 1.38 and 1.24-fold, respectively, whereas cathepsin D/E inhibitors did not cause any significant change. Our results from autophagy and lysosomal proteases studies prompted us to evaluate the integrity of lysosomes in live cells. Our lysotracker staining data suggested that AG-08 may be an inducer of lysosomal membrane permeabilization. In conclusion, AG-08 is a potent cytotoxic agent possessing necrotic cell death and autophagy inhibitory properties. Further studies are in progress to clarify complete mechanism of AG-08.