Comparison of cytotoxicity and DNA damage potential induced by ent-kaurene diterpenoids from Isodon plant

The cytotoxicity of six ent-kaurene Diterpenoids isolated from the leaves of Isodon japonica (Burm.f.) Hara var. galaucocalyx (maxin) Hara was evaluated against three human tumour HepG2, GLC-82 and HL-60 cell lines through SRB assay, and their DNA damage potential (against HepG2 cell line) was assessed by comet assay. Among the six ent-kaurene Diterpenoids, Rabdosin B was most cytotoxic, followed by Oridonin, Epinodosin, Rabdosinate, Lasiokaurin and Epinodosinol. All of the six ent-kaurene Diterpenoids induced significant DNA damage (p < 0.05) to HepG2 cells in a time- and dose-dependent manner except Lasiokaurin and Eponodosinol at 6 µmol L⁻¹ for 24 h. The structure-activity relationships (SARs) were discussed and it was found that exo-methylene cyclopentanone in the molecular structure was important for maintaining the cytotoxicity and DNA damage potential of the compounds.-OAc group at site C-1 in Lasiokaurin had a higher stereospecific blockade, which made the compound have less cytotoxicity and DNA damage potential than Oridonin (-OH at C-1).