Growth of human tumors in mice after short-term immunosuppression with procarbazine, cyclophosphamide, and antilymphocyte serum.

A simple combine treatment with immunosuppressive agents permitting the growth of human tumor xenografts in conventional mice is presented. It consists of two simultaneous applications of 90 mg of procarbazine (PCH) per kg and 30 mg of cyclophosphamide (CY) per kg, alternating with two doses of 0.15 ml/10 g of antilymphocyte serum (ALS) for 4 days before grafting. No postgraft treatment is used. With a take rate of 100%, at 60 days after subcutaneous transplantation into male C3H mice, fragments of a human colon adenocarcinoma had grown (on the average) into cherry-sized tumors. Two osteosarcomas, an Ewing sarcoma, and a bronchogenic carcinoma were also studied and grew similarly. Tumors could be established in the three tested mouse strains but grew better in male animals. Synergy of PCH and CY and ALS depends upon the alternating sequence of both drugs and ALS. The histology of the colon carcinoma and the Ewing sarcoma was unchanged as compared to the tumors growing in nude mice. In contrast, the osteosarcoma developed in a more differentiated fashion in the immunosuppressed mice. The presented model may serve as a screening system for anticancer drugs.