Estramustine-binding protein in malignant glioma in rat

Estramustine is a chemotherapeutic drug, used in the treatment of prostatic carcinoma. In the prostate, it binds specifically to a 46 kDa glycoprotein called estramustine-binding protein (EMBP), which consists of three polype ptide components; C1, C2, and C3, each coded for by a specific gene. Expres sion of EMBP and binding of estramustine has also been detected in malignan t glioma in both rats and humans. Elevated levels of this protein in astroc ytoma have proved to correlate with poor prognosis. In the present work, ex pression of all three polypeptide components of EMBP was confirmed in an or thotopic rat glioma model with nested reverse transcriptase PCR and Western blot (molecular weights of 8, 10, and 12 kDa). Specific binding of estramu stine with a K-d of 40 for male and 50 for female rats, and a total number of binding sites of 0.7 and 0.4 pmol/mg proteins for male and female rats r espectively, was demonstrated with Scatchard plot analysis. These binding c haracteristics are similar to those of prostatic EMBP. Further studies to e lucidate how EMBP expression affects the effect of estramustine treatment, and its putative prognostic value is of special clinical interest. The conf irmation of BMBP expression in BT4C rat glioma demonstrates its suitability as a model system for such studies.