Biotransformation of bufadienolides by cell suspension cultures of Saussurea involucrata

► Six bufadienolides were obtained by biotransformation using cell suspension cultures of Saussurea involucrata. ► A Δ1-reduction was observed for the first time in the biotransformation of bufadienolides. ► The compounds showed potent cytotoxic activities against human hepatoma (HepG2) and breast cancer (MCF-7) cell lines with IC50 values of 0.05-0.50 μM.