Wide spectrum of steroids serving as substrates for the formation of lipoidal derivatives in ZR-75-1 human breast cancer cells.

Recently, several natural steroids have been found to be esterified to long-chain fatty acids (FAE) in various mammalian tissues. The purpose of the present study was to determine the ability of a series of 3H-labeled steroids to serve as substrates for the formation and accumulation of such non-polar derivatives in intact cells, using the hormone-responsive ZR-75-1 human breast cancer cell line as model. All 14 steroids tested were found to be converted, directly or following further metabolism, to lipoidal ester derivatives. The percentage of intracellular steroids recovered as FAE derivatives was usually substantial (14-90%), especially in the case of C-19 steroids (75-90%). The composition of the lipoidal steroid fractions recovered from the labeled cell extracts was characterized by chromatographic comparison with synthetic steroid FAEs and by saponification of the steroid FAEs and identification of the released steroidal moieties. Following metabolism, most steroid substrates were converted into multiple lipoidal esters. Furthermore, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol, as well as androst-5-ene-3 beta, 17 beta-diol formed lipoidal diesters in addition to the monoester form. The high level of intracellular steroid FAE accumulation reported in this study suggests that these yet poorly known steroid derivatives may play important functions in the regulation of steroid hormone metabolism and action.