[Estracyt (estradiol-nitrogen mustard complex)--estramustine binding protein and its specificity]

Estracyt (estramustine phosphate) is a nitrogen mustard derivative of estradiol-17 beta which is rapidly dephosphorylated to yield estramustine. Estramustine is metabolized to estromustine mainly in the liver. Both estramustine and estromustine are retained in rat prostate with a high degree of specificity. This retention is due to the binding of estramustine and/or estromustine to a protein called EMBP (estramustine binding protein). When estimated by HPLC, the molecular weights of these estramustine binding components in rat prostate are 45,000-50,000 and 25,000-30,000, respectively. HPLC and glycerol density gradient analysis clearly demonstrated the occurrence of EMBP in a cytosol preparation from human prostatic cancer tissue. When estimated by HPLC, the molecular weights of estramustine binding components are 45,000 and 25,000 daltons, respectively. In addition, results of effectiveness of Estracyt studied under a cooperative research group in Japan, are reported in this paper. Effectiveness was evaluated at 3 months of the treatment on 121 patients with untreated prostatic cancer (Study I) and 95 patients with reactivated cancer (Study II), at 12 months of the treatment on 68 patients in Study I and 85 patients in Study II, and at 24 months on 37 patients in Study I and 23 patients in Study II. At 3 months of the treatment, Estracyt was effective in 89% of untreated prostatic cancers, and 38% of reactivated prostatic cancers. At 24 months of the treatment, this drug was effective in 65% of untreated prostatic cancers and 30% of reactivated ones. Estracyt is especially recommended as a first-choice drug for both the untreated patients with poorly differentiated adenocarcinoma and reactivated cancer.