The endocrine background of human renal cell carcinoma. III. Role of inhibitors of R 5020 binding in tumour cytosol.

Abstract

Cytosol preparations obtained from 9 different human renal cell carcinomas were investigated for the eventual presence of progestin-binding inhibitors which might offer an explanation for the previous failure to demonstrate high receptor levels in the tumour tissue. The inhibitory potency of these preparations was estimated by measuring the decrease of R 5020 binding to uterine progestin receptors in the presence of tumour cytosol. Interestingly, cytosol from human renal cell carcinoma was found to contain progestin-binding inhibitors. The average inhibition of R-5020-receptor interaction amounted to 46%. In only 1 out of 9 cases, binding was completely suppressed. In order to circumvent the inhibitory reaction potentially occurring in cell-free systems, R-5020-binding studies additionally were performed in cell suspension. Out of 7 carcinomas studied using this assay system, 5 did not contain any specific progestin-binding entities. In 1 tumour, receptor-atypical non-saturable binding was observed. Only in isolated cells prepared from 1 other carcinoma, could slight indications for the presence of low concentrations of progestin receptors be detected.