Protective and therapeutic efficacies of protein A on 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma.

Protein A of Staphylococcus aureus Cowan I is a powerful immunostimulating agent. Female Swiss Portan rats fed 7,12-dimethylbenz(alpha)anthrancene (DMBA) exhibited increased serum alkaline phosphatase activity, which returned to normal levels following eight weeks of treatment with 12 micrograms protein A subcutaneously. Protein A reduced the potential of tumor induction by DMBA as observed by the noninduction of tumors until three months after discontinuation of protein A administration. The total leukocyte count was not affected. Protein A treatment for six weeks of DMBA-induced mammary adenocarcinoma-bearing rats caused the increased serum alkaline phosphatase activity to decrease but not to normal levels, indicating regression but no disappearance of the tumors. The total leukocyte count of the tumor bearers was stimulated by protein A and increased 24 hours after protein A administration; however, in the fourth week of treatment it returned to normal levels. The leukocytosis suggests that protein A could cause tumor necrosis by an inflammatory reaction, edema, and cell destruction and thus tumor regression.