The endocrine background of human renal cell carcinoma. V. Binding of the highly potent androgen methyltrienolone (R 1881) by tumour cytosol.

The binding of methyltrienolone (R 1881, 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-trien-3-one), a highly active synthetic androgen, by cytosol preparations from human renal cell carcinoma was investigated. High-affinity, low-capacity binding components for R 1881 were detected in 3 out of 8 tumours analysed. The apparent dissociation constant of the R 1881-binder complexes was found to be in the range of 1.1-2.3 x 10(-9) mol/l. The number of binding sites in the positive tumours varied from 2.1 to 9.7 fmol/mg cytosol protein. Studies of binding specificity indicated a requirement for androgens. It is concluded that these binding components may be hormone receptors. If in consecutive studies this hypothesis holds true, progestins, most widely used in hormonal therapy of metastatic renal cancer, may possibly act on the tumour tissue by inhibiting the secretion of gonadotropins, thus lowering the blood levels of eventually growth-promoting.