[Experimental study of the 6-day subrenal capsule assay by cyclophosphamide pretreatment]

For the purpose to suppress the host immune reaction in subrenal capsule assay (SRCA) using normal immunocompetent mice, the effects of cyclophosphamide (CPM) pre-treatment (CPM 180 mg/kg day-1 s.c.) were compared with cyclosporine A (CSA) treatment (CSA 60 mg/kg s.c. daily). CPM and CSA suppressed host reaction until day 6 and day 12, respectively. However, in the histological evaluation of day 6 tumor, there was no difference between two groups. Mouse serum levels of CPM were measured by a bioassay as indicated by the cytotoxicity against P388 cells, to evaluate its residual activity against implanted tumor. No cytotoxicity was observed in the serum of 36 hr. after CPM injection. The antitumor activities of several chemotherapeutic agents against serially transplanted human esophageal cancer xenograft (IMEs-1) in untreated control group and CPM pre-treated group of SRCA were compared with the subcutaneous transplantation assay in nude mice. In all agents, the drug activities in CPM pre-treated group were similar to that in nude mice assay system. The increase of toxicity in CPM pre-treated group was very light. The immunosuppressive activity of CPM were also tested in 14 clinical samples. CPM suppressed the host reaction satisfactorily in all samples. These results suggest the usefulness of CPM pretreatment for suppressing the host reaction in SRCA.