In vitro Cytotoxic Activities and Molecular Mechanisms of Angelica shikokiana Extract and its Isolated Compounds

Background: Angelica shikokiana is a Japanese medicinal herb that is included among food and drug preparations protecting against cancer; however, there is no previous report about the cytotoxicity of A. shikokiana or its bioactive compounds.

Objective: This study was designed to investigate the cytotoxic activities of A. shikokiana methanol extract (AME) and its isolated compounds and to identify the molecular mechanisms of the cytotoxicity.

Materials and methods: Cytotoxicity and selectivity was investigated by measuring the IC50 values on five cancer cell lines; human hepatocellular carcinoma, rhabdomyosarcoma (RD), colorectal carcinoma, human epithelioma and human breast adenocarcinoma and one normal cell line; human lung fibroblasts. The effects on tubulin polymerization and histone deacetylase 8 (HDAC8), were examined to determine the mechanism of cytotoxicity. Docking study was designed to examine the binding affinity to the target molecules.

Results: Methanol extract and some of its isolated coumarins and flavonoids showed potent, selective cytotoxicity against cancer cell lines. AME and all isolated compounds inhibited tubulin polymerization. Angelicin and kaempferol-3-O-rutinoside were the most active compounds. Phenolic compounds and furanocoumarins showed binding affinity to colchicine binding site rather than the vinblastine binding site of tubulin microtubules. On the other side, quercetin, kaempferol, luteolin, chlorogenic acid, and methyl chlorogenate exhibited the strongest activity against HDAC8 and the highest affinity to trichostatin A binding site.

Conclusion: These findings provide the first scientific evidence of the cytotoxicity of AME through inhibition of tubulin polymerization and HDAC8 activity through its coumarin and flavonoid content.

Summary: The present study provides for the first time a clue for the cytotoxic activities of the AME. Our results indicate that the cytotoxic activities are partially related to the ability of AME to inhibit tubulin polymerization and HDAC8 activity. Isolated compounds; Angelicin and kaempferol-3-O-rutinoside showed the strongest inhibition of tubulin polymerization through binding to colchicine binding domain of tubulin microtubules. Phenolic compounds; quercetin, luteolin, kaempferol, chlorogenic acid and methyl chlorogenate exhibited a strong inhibition of HDAC8 through binding to TSA binding site. This, however, further detailed pharmacological and in vivo studies should be the next step in evaluating the cytotoxic activities of AME and its active compounds that are currently ongoing. Abbreviations used: AME: Methanol extract of the aerial part of A. shikokiana, HDACs: Histone deacetylases,HDAC8: Histone deacetylase 8.