Inhibition of pulmonary metastasis of Lewis lung carcinoma by a glucan, Schizophyllan.

The effect of a glucan, Schizophyllan (SPG), on pulmonary metastases in syngeneic mice bearing Lewis lung carcinoma (3LL) was examined. As a model of pulmonary metastases, 3LL cells were implanted into the footpads of C57BL/6 mice, the resulting primary tumor was removed 9-10 days later. The inhibitory effect of SPG was evaluated from the number of pulmonary surface nodules on the lungs about 3 weeks after tumor implantation. SPG was found to have antimetastatic activity, which depended on its dose and time of injection. A single injection of 100 or 200 mg/kg or daily injections of 20 or 50 mg/kg of SPG after removal of the primary tumor markedly inhibited pulmonary metastases. Combined therapy with cyclophosphamide and SPG significantly prolonged the survival of mice with pulmonary metastases. Enhancement of the in vitro cytotoxic activity of peritoneal macrophages and bronchoalveolar or whole lung cells against 3LL cells was noted in SPG-treated mice on day 7 after a single intraperitoneal injection of 100 mg/kg SPG. Intravenous transfer of peritoneal macrophages activated with SPG inhibited the development of pulmonary micrometastases.