Inhibition of Estrogen Tumorigenesis in the Syrian Golden Hamster Kidney by Antiestrogens

Abstract

Both 8S and 4S estrogen-binding components were identified following sucrose gradient analyses in untreated and either diethylstilbestrol (DES)-primed or 17β-estradiol-primed Syrian golden hamster renal cytosols homogenized in the presence of 5% glycerol. The 8S estrogen-binding moiety increased in the untransformed kidney with continued hormone treatment. The concentration of total estrogen receptor in hamster renal cytosols was enhanced from 6.1 ±0.9 fmol/mg protein in untreated hamsters to 20.7±2.5 fmol/mg protein (SEM) in DES-treated hamsters. Binding equilibrium measurements (K_a) for the kidney estrogen binder in DES-primed hamsters was estimated to be 2.4×10¹⁰ M⁻¹. The antiestrogens nafoxidine and enclomiphene but not 1-(ρ-2-diethylaminoethoxyphenyl)-1-phenyl-2-ρ-methoxyphenyl ethanol (MER-25) appreciably inhibited the binding activity of the tritiated estradiol, particularly in the 8S region of the gradient, at five hundredfold excess radioinert antiestrogen concentrations. Injection of these antiestrogens for 3 days into previously estrogen-treated hamsters yielded competition profiles in the renal cytosols of these animals consistent with those found after in vitro incubation. Simuitaneous treatment with antiestrogens such as either nafoxidine or enclomiphene and DES completely suppressed the induction of renal carcinoma in the hamster by estrogen. The presence of tumor foci was ascertained by histochemical staining in fresh-frozen sections for esterase activity, i.e., very low levels in tumor foci compared to high levels in adjacent untransformed renal cortex. This observation was consistent with gel electrophoretic data that indicated a marked decline in individual esterase activity in extracts of pure renal tumor compared to normal kidney. In contrast, MER-25 did not inhibit renal tumorigenesis in the hamster in the presence of DES under similar conditions. Therefore, the ability of these antiestrogens to block renal tumorigenesis in the presence of estrogen correlated well with the antiestrogen competition data for the renal estrogen receptor in DES-treated hamsters.