Immunomodulatory Activity of 3β,6β‐Dihydroxyolean‐12‐en‐27‐oic Acid in Tumor‐Bearing Mice

3β,6β‐Dihydroxyolean‐12‐en‐27‐oic acid ( 1 ) is a pentacyclic triterpenoid isolated from the rhizomes of Astilbe chinensis. To evaluate the in vivo antitumor potential and to elucidate its immunological mechanisms, effect of 1 on the growth of mouse‐transplantable tumors, and the immune response in naive and tumor‐bearing mice were investigated. The mice inoculated with mouse tumor cell lines were orally treated with 1 at the doses of 40, 60, and 80 mg/kg for 10 days. The effects of 1 on the growth of mouse‐transplantable S180 sarcoma and H22 hepatoma, splenocyte proliferation, cytotoxic T lymphocyte (CTL) activity, natural killer (NK) cell activity, and production of interleukin‐2 (IL‐2) from splenocytes in S180‐bearing mice were measured. Furthermore, the effect of 1 on 2,4‐dinitrofluorobenzene (DNFB)‐induced delayed‐type hypersensitivity (DTH) reactions and the sheep red blood cell (SRBC)‐induced antibody response in naive mice were also studied. Compound 1 could not only significantly inhibit the growth of mouse transplantable S180 sarcoma and H22 hepatoma, increase splenocytes proliferation, CTL and NK cell activity, and the level of IL‐2 secreted by splenocytes in tumor‐bearing mice, but also remarkably promote the DTH reaction and enhance anti‐SRBC antibody titers in naive mice. These results suggested that 1 could improve both cellular and humoral immune response, and could act as antitumor agent with immunomodulatory activity.