Anti-growth action on mouse mammary and prostate glands of a monoclonal antibody to prolactin receptor

Monoclonal antibody (PrR-7A) against purified PRL receptor was used in the following studies. When PRL receptor was chromatographed on affinity columns containing PrR-7A antibody or monoclonal antibody against hemocyanin, which served as a control, PRL receptor was bound to the column containing PrR-7A antibody, but not to the column containing control antibody. When solubilized PRL receptor was incubated with PrR-7A antibody, the specific binding of the receptor was reduced 52%. Female mice were treated with the carcinogen, 7,12-dimethylbenz[α]anthracene, and during the succeeding 48 weeks were treated weekly with PrR-7A antibody or control antibody. In the control group 13% developed mammary carcinomas, and 16% developed moderate-to-severe intraductal hyperplasia. No mammary carcinomas were found in the mice treated with PrR-7A antibody, and only 8% of the mice had moderate-to-severe intraductal hyperplasia. Male mice made hyperprolactinemic by implanted pituitary glands were treated weekly with PrR-7A or control antibody. After 7 weeks of treatment, the mean weight of the prostates of mice treated with PrR-7A antibody was 8 ± 1.1 mg (mean ± SE), and that of mice treated with control antibody was 27 ± 3.6 mg. Similar differences were seen in the protein and DNA content of the prostates. These results indicate that PrR-7A antibody is directed against PRL receptor and that immunization with this antibody reduces the incidence of PRL-dependent mammary tumors and preneoplastic ductal hyperplasia and prevents PRL-induced hyperplasia of the prostate.