Effects of immunosuppressive acidic protein on DMBA-induced pancreatic cancer in rats.

In order to determine the effect of immunosuppressive acidic protein (IAP) on the formation of pancreatic carcinoma, rats of the Sprague-Dawley strain were embedded with 7,12-dimethyl-benzanthracene (DMBA) in the pancreas with and without administration of IAP. In these animals, the growth of pancreatic cancer was studied both immunologically and histologically. Tumor was induced in 51 animals (85%) of 60 treated with embedding of 1 mg DMBA alone. Tumors began to appear from the 16th week after the embedding. Among animals in which tumor was induced, tubular adenocarcinoma and pleomorphic carcinoma accounted for 55% of the cases. When administration of IAP was combined, the period required for development of tumor was shortened. It became shorter with increases in the dosage and frequency of administration of IAP. In animals which received IAP in a mean dose of 75 mg/kg the area showing cancerous changes appeared as early as at the 8th week after the embedding of DMBA. A significant increase in the volume of tumors was seen in the group treated with IAP as compared to the group not treated with IAP. Animals which received IAP in increasing doses and frequencies showed an accelerated increase in the volume of the tumors which underwent cancerous changes. IAP was eliminated from the serum of rats within 72 hr after the administration, and acid protein was clearly recovered from the serum when tumors proliferated. These findings indicate that the acceleration of carcinogenesis in DMBA-induced pancreatic carcinoma may be attributable to the immunosuppressive effect of IAP administered and tend to be dependent on the dosage and frequency of its administration in the early phase of tumor induction.