Anti‐Tumor Mechanism of Z‐100, an Immunomodulatory Arabinomannan Extracted from Mycobacterium tuberculosis Strain Aoyama B, on Pulmonary Metastases of B16F10 Melanoma: Restoration of Helper T Cell Responses via Suppression of Glucocorticoid‐Genesis

In the present study, the anti-tumor mechanism of Z-100 was investigated with the use of pulmonary metastasis of B16F10 melanoma. In B16F10 mice, Th1 cytokine production (IL-2, IFN-γ) was suppressed in comparison with normal mice. On the other hand, Th2 cytokine production (IL-4, IL-10) was increased in the B16F10 mice. The administration of Z-100 to B16F10 mice restored the balance of Th1/Th2 cell responses from the Th2 dominant state to the normal state. Z-100 significantly suppressed the pulmonary metastasis of B16F10 melanoma in a dose-dependent manner. These results suggest that Z-100 restored the breakdown of Th1 cell responses, resulting in the suppression of pulmonary metastasis of B16F10 melanoma. Moreover, Z-100 decreased the corticosterone levels, which is known to suppress the Th1 cell responses, in both serum specimens and splenic tissue, and the steroidogenic CYP11A1 mRNA expression in CD4+ T cells. These results suggest that a suppression of pulmonary metastasis and restoration of Th1/Th2 cell responses by Z-100 may be due to the decrease in the corticosterone levels and the steroidogenic CYP11A1 mRNA expression of CD4+ T cells in B16F10 mice. Further, the role of Th1 cytokine, IFN-γ, on these activities of Z-100 was examined. The suppressive effects of Z-100 on pulmonary metastasis and restoration of Th1/Th2 cell responses were eliminated by the administration of anti-IFN-γ mAb. Moreover, the suppressive effects of Z-100 on glucocorticoid-genesis were eliminated by the administration of anti-IFN-γ mAb. These results suggest that Z-100 restores the balance of Th1/Th2 cell responses via the suppression of glucocorticoid-genesis by Z-100-induced IFN-γ. IFN-γ acts as a key cytokine in anti-tumor activities of Z-100.