17-BETA-HYDROXYSTEROID OXIDOREDUCTASE ACTIVITY IN INTACT-CELLS SIGNIFICANTLY DIFFERS FROM CLASSICAL ENZYMOLOGY ANALYSIS

This paper summarizes our most recent results of steroid enzyme studie s on cultured breast and endometrial cancer cells. It deals mainly wit h estrogen 17 beta-hydroxysteroid oxidoreductase (17 beta HSOR) activi ty, which presides over estradiol (E(2)) and estrone (E(1)) interconve rsion, a major metabolic pathway of estrogens. Assessment of either th e oxidative or reductive component of 17 beta HSOR was carried out on intact cells by means of an original approach based on reverse phase-h igh performance liquid chromatography and radioactive detection on lin e. This system allows the continuous monitoring of both precursor degr adation and formation of several radiometabolites to assess rates and direction of steroid metabolism. Overall, hormone-responsive, estrogen receptor (ER)-positive cells, regardless of whether they were derived from breast (MCF7) or endometrial (Ishikawa) tumor tissues, showed a prevalence for reductive metabolism (E(1)-->E(2)), whilst oxidative pa thways (E(2)-->E(1)) were largely dominant in non-responsive, ER-poor mammary (MDA-MB231) and endometrial (HEC-1A) cells. The above estimate s of 17 beta HSOR activity were at variance with those obtained using the classical enzymology approach, not only in quantitative terms (bei ng markedly lower using intact cell analysis), but also because the pr evalent direction of estrogen metabolism was often reversed. Although striking methodological differences may well account for this discrepa ncy, intact cell analysis is undoubtedly more similar to the in vivo s tate than the artificial requirements of classical enzymology procedur es.