DT‐5461, a New Synthetic Lipid A Analogue, Inhibits Lung and Liver Metastasis of Tumor in Mice

We have investigated the antimetastatic effect of a new synthetic lipid A analogue, of low endo‐toxicity, DT‐5461, against two highly metastatic tumor cell lines, L5178Y‐ML25 T‐lymphoma and B16‐BL6 melanoma cells in mice. Four intermittent i.v. administrations of DT‐5461 at intervals of 4 days resulted in a significant inhibition of liver metastasis caused by i.v. injection of L5178Y‐ML25 cells and lung metastasis of B16‐BL6 cells in the experimental metastasis models. Intraperitoneal and intranasal administrations as well as i.v. administration of DT‐5461 were also effective in preventing lung metastasis of the melanoma cells. Multiple administrations of DT‐5461 before the surgical excision of primary tumors significantly reduced the number of lung colonies of melanoma cells and primary tumor size. Similarly, this treatment modality after the surgical excision of primary tumors showed a greater reduction of lung tumor colonies as compared with lipopolysaccharide, a synthetic lipid A (No. 506) and its analogue as well as untreated control in the spontaneous lung metastasis model. Furthermore, the group that received DT‐5461 after the inoculation of lymphoma or melanoma cells showed significantly enhanced survival rate compared with the untreated control. These results suggested that DT‐5461 may he therapeutically useful for the inhibition of tumor metastasis.