Inhibitory effect of glycyrrhizin on experimental pulmonary metastasis in mice inoculated with B16 melanoma

The pulmonary metastasis of B16 melanoma cells has been shown to be influenced by tumor-associated T helper type 2 cells (Th2 cells). Glycyrrhizin (GR), an active component of licorice roots, has been described as an inducer of CD4⁺ CD28⁺ TCRα/β⁺ T cells, which are capable of counteracting Th2 cytokine production by Th2 cells. In the present study, the anti-metastatic effect of GR in mice implanted with highly metastatic B16F10 melanoma cells was investigated. When mice inoculated with B16F10 melanoma cells (1 × 10⁵ cells/mouse, i.v.) were treated with GR (10 mg/kg) 1, 3, 5 and 7 days after the tumor inoculation, the incidence of metastases decreased on average; 48 colonies were found in the GR-treated group and 208 in the saline-treated group. Similarly, 84% of metastases were inhibited in these mice after they were inoculated with splenic CD4⁺ T cells from mice treated with GR (GR-CD4⁺ T cells). These results suggest that GR inhibits the pulmonary metastases of B16 melanoma through the regulation of tumor-associated Th2 cells.