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

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