We have recently reported that red ginseng acidic
polysaccharide (
RGAP), isolated from Korean red ginseng (Panax ginseng C.A. Meyer), shows immunomodulatory and antitumor activities, mainly mediated by the
nitric oxide (NO) production of macrophages. This compound may be used in
cancer therapy alone or in combination with other chemotherapeutic agents. The synergistic effect of
RGAP and
paclitaxel (
taxol) was evaluated to develop new
biological response modifiers in
cancer therapy. The present study demonstrates a synergistic antitumor effect of
RGAP and
paclitaxel in mice transplanted with
sarcoma 180 and
B16 melanoma. Combined treatment with
paclitaxel (5 or 15 mg/kg) and
RGAP (25 mg/kg) resulted in a 28.6 or 42.8 % increase in the life span of ICR mice bearing
sarcoma 180 tumor cells, while no obvious effect was seen on sole
paclitaxel treatment. When a combination of
paclitaxel (10 mg/kg) and
RGAP (100 mg/kg) was administered to C57BL/6 mice implanted with
B16 melanoma, the
tumor weight per mouse also decreased by 76.3 %, suggesting that
RGAP may be used as an adjuvant in medicinal applications of
paclitaxel. The augmented antitumor effect of
paclitaxel is supposed to be the result of the immunomodulating antitumor effect of
RGAP.
RGAP, having B cell specific mitogenic activity, induced the secretion of
interleukin-6 (IL-6) in spleen cells in a concentration-dependent manner (5 to 500 microg/microL).
RGAP also restored the proliferation of splenocytes and NK cell activity suppressed by
paclitaxel. Flow cytometric analysis of splenocytes in mice treated with
paclitaxel showed a significant increase of CD11b+ cells. Additionally, a synergistic effect of
RGAP and
paclitaxel was found to effect an increased tumoricidal activity of macrophages. The above results suggest that clinical trials of
RGAP as an adjuvant in
cancer chemotherapy of
paclitaxel are highly feasible.