Inhibition of pulmonary metastasis by Nocardia rubra cell wall skeleton, with special reference to macrophage activation.

The antimetastatic activity of Nocardia rubra cell wall skeleton (N-CWS) with or without cyclophosphamide was examined in an experimental model of pulmonary metastasis induced by Lewis lung carcinoma in C57BL/6 mice. Lewis lung carcinoma cells were implanted into the footpads of mice, and the implanted tumors were removed 9 to 10 days later. Pulmonary metastatic nodules began to develop a few days after the implanted tumor was removed. The inhibitory effect of N-CWS was evaluated from the number of pulmonary surface nodules about 3 weeks after tumor implantation. The antimetastatic activity of N-CWS depended upon the dose, time, and route of its injection. Injection of N-CWS i.v. after removal of the implanted tumor caused the greatest inhibition of development of pulmonary metastases. Therapy with N-CWS plus cyclophosphamide prolonged significantly the survival of mice with metastases. The cytotoxic activities of peritoneal macrophages and macrophages in the lung against Lewis lung carcinoma cells were enhanced in mice treated with N-CWS. Injection i.v. of peritoneal macrophages activated with N-CWS inhibited pulmonary metastases. The role of macrophages in inhibition of micrometastasis in the lung is discussed.