Synthesis of deuterium- and tritium-labelled 4-hydroxyandrostene-3,17-dione, an aromatase inhibitor, and its metabolism in vitro and in vivo in the rat.

The metabolism of the aromatase inhibitor-4-hydroxyandrostenedione (4-OHA) was studied in vitro and in vivo in the rat. To accomplish this, deuterium- and tritium-labeled 4-OHA were prepared from 4-hydroxyandrosta-4, 6-dione-3,17-dione. The latter was synthesized from 4-androstene-3,17-dione. Using deuterated 4-OHA in in vitro incubations of rat ovarian microsomes, 4-hydroxytesterone (4-OHT) was identified by gas chromatography/mass spectroscopy as the major metabolite. 4-OHT constituted approximately 20% of the total radioactivity from [6,7-3H]-4-OHA in the ovarian microsomal incubations. Conversion of [6,7-3H]-4-OHA to 4-hydroxyesterone was approximately 0.1%. The major metabolite of [6, 7-3H]-4-OHA in vivo identified in the free, neutral fraction of rat blood was 3 beta-hydroxyandrostane-4,17-dione. The metabolite accounted for approximately 5% of the total radio-activity in the blood, Whereas 4-OHT accounted for only 0.1%, 4-OHT inhibited in vitro ovarian aromatization by 59%, but 3 beta-hydroxyandrostane-4-17-dione had little effect. It was concluded that the in vivo effects of 4-OHA previously reported are largely due to its own activity although additional effects of its metabolic products cannot be excluded.