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
polypeptide components; C1, C2, and C3, each coded for by a specific gene. Expression of
EMBP and binding of
estramustine has also been detected in
malignant glioma in both rats and humans. Elevated levels of this
protein in
astrocytoma have proved to correlate with poor prognosis. In the present work, expression of all three
polypeptide components of
EMBP was confirmed in an orthotopic rat
glioma model with nested
reverse transcriptase PCR and Western blot (molecular weights of 8, 10, and 12 kDa). Specific binding of
estramustine with a Kd 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 respectively, was demonstrated with Scatchard plot analysis. These binding characteristics are similar to those of prostatic
EMBP. Further studies to elucidate how
EMBP expression affects the effect of
estramustine treatment, and its putative prognostic value is of special clinical interest. The confirmation of BMBP expression in BT4C rat
glioma demonstrates its suitability as a model system for such studies.