Chemopreventive Properties of Phytosterols and Maslinic Acid Extracted from Coleus tuberosus in Inhibiting the Expression of EBV Early‐Antigen in Raji Cells

Abstract Bioassay‐guided fractionation of a MeOH extract of tubers of Coleus tuberosus afforded the active anti‐tumor‐promoting compounds identified as the triterpenoid 2 α ,3 β ‐dihydroxyolean‐12‐en‐28‐oic acid (maslinic acid; CT2) and a phytosterol mixture (CT1). CT1 consists of stigmasterol (32%), β ‐sitosterol (40.3%), and campesterol (27.7%) as determined by capillary gas chromatography. CT1 and CT2 showed very strong anti‐tumor‐promoting activities at IC 50 0.7 μg/ml and 0.1 μg/ml, respectively, in a convenient, short‐term in vitro assay, i.e. , the inhibition of Epstein–Barr virus (EBV) activation induced by phorbol 12‐myristate 13‐acetate (PMA) and sodium butyrate. We report for the first time the anti‐tumor‐promoting activity of 2 α ,3 β ‐dihydroxyolean‐12‐en‐28‐oic acid and show that a mixture of stigmasterol, β ‐sitosterol, and campesterol is more potent than the individual components in inhibiting tumor‐promoting activity.