Comparative binding specificity of methyltrienolone in human and rat prostate

Area of Science:

• Endocrinology
• Andrology
• Prostate Cancer Research

Background:

• Benign prostatic hyperplasia (BPH) is a common condition in aging men.
• Steroid hormone receptors play a crucial role in prostate physiology and pathology.
• Understanding androgen and progesterone receptor binding in the prostate is vital for therapeutic development.

Purpose of the Study:

• To characterize the binding kinetics of methyltrienolone (R 1881) in human hyperplastic prostate cytosol.
• To compare the binding specificity of R 1881 in human versus rat prostate tissue.
• To investigate the presence and quantity of progesterone-binding components in human hyperplastic prostate.

Main Methods:

• Crude human hyperplastic prostate cytosol was incubated with radiolabeled methyltrienolone (3H-R 1881).
• Charcoal assay was employed to determine radioligand binding.
• Competition assays were performed using various unlabeled steroids, including R 1881, R 5020, progesterone, dihydrotestosterone (DHT), and 17 alpha-methyl-DHT.
• Apparent association constants (Ka) and binding site numbers were calculated.

Main Results:

• Maximum binding of 3H-R 1881 in human hyperplastic prostate cytosol occurred within 2-3 hours at 0°C, with a decline over 96 hours.
• Human prostate binding of 3H-R 1881 was competed by low concentrations of R 1881, R 5020, and progesterone, and high concentrations of DHT and 17 alpha-methyl-DHT.
• Rat prostate binding showed a different profile, with low concentrations of DHT and 17 alpha-methyl-DHT being effective competitors, and only high concentrations of progesterone and R 5020.
• The apparent association constant (Ka) for R 1881 was 0.2-0.4 X 10(9) L/mol, with 101-158 fmol binding sites per mg protein.

Conclusions:

• Human hyperplastic prostate cytosol exhibits significant binding for methyltrienolone (R 1881).
• These findings support the presence of substantial progesterone-binding components in human hyperplastic prostate tissue.
• The distinct binding characteristics between human and rat prostate suggest species-specific receptor interactions.