The presence in rat and human prostate of proteins that bind steroid-cytostatic complexes.

During studies on the uptake and distribution of estramustine phosphate (Estracyt) in the rat, a major protein in the rat ventral prostate was found that binds estramustine, estromustine, and several other steroid nitrogen mustard complexes. This protein, called estramustine-binding protein, shares many physicochemical characteristics with alpha-protein, prostatic-binding protein, and prostatein, each reported to constitute a major steroid-binding protein in the rat ventral prostate. There is every indication that these four names designate one and the same protein, the binding properties of which favor the binding of lipophilic compounds, and which has shown an affinity for estramustine and closely structure-related compounds that is 100- to 1000-fold higher than for the natural steroids. Also, the human prostate has been shown to take up and bind estramustine and estromustine. However, the binding entity (or entities) is still under intense investigation.