Characterization and Measurement of the Androgen Receptor in Human Benign Prostatic Hyperplasia and Prostatic Carcinoma

Abstract

[6,7-³H]Methyltrienolone (R 1881) has been used as ligand to measure and characterize the androgen receptor in human benign prostatic hyperplasia and prostatic carcinoma. [³H]R 1881 was bound with high affinity and low capacity to cytosol from six out of nine specimens of transvesically enucleated benign prostatic hyperplasia and from two specimens of prostate carcinoma obtained by Veenema biopsy or transvesical enucleation. The dissociation constant of the [³H]R 1881-receptor complex was in the range of 0.3–1.8 × 10⁻⁹M and the number of binding sites 9–26 fmoles/mg protein. [³H]R 1881 was displaced from its binding sites on the receptor by 5α-dihydrotestosterone and testosterone; much less efficient competitors were LS 1727, cyproterone acetate, 17β-estradiol, R 5020, 5α-androstane-3α,17β-diol and progesterone, whereas 4-androstene-3,17-dione, cyproterone, estramustine and cortisol did not compete. The receptor was stable at 0 C but was degraded rapidly (t_½ = 14 min) at 37 C. The rate of dissociation of the [³H]R 1881-receptor complex increased at higher temperatures (t_½ = 810 and 50 min at 0 C and 37 C, respectively). The [³H]R 1881-receptor complex had an isoelectric point of about pH 5. 5α-[³H]Dihydrotestosterone was found to be an unsuitable ligand in assays of the androgen receptor in benign prostatic hyperplasia since this steroid also binds to testosterone-binding globulin that probably contaminates all prostate cytosol preparations. Furthermore, 5α-[³H]dihydrotestosterone was rapidly metabolized in prostate cytosol, even at 0 C, whereas [³H]R 1881 was not. Electroresected specimens did not contain detectable levels of androgen receptor, probably due to heat denaturation.