Synthesis of deuterium- and tritium-labeled 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-diene-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- 3 H]-4-OHA in the ovarian microsomal incubations. Conversion of [6,7- 3 H]-4-OHA to 4-hydroxyestrone was approximately 0.1%. The major metabolite of [6,7- 3 H]-4-OHA in vivo identified in the free, neutral fraction of rat blood was 3β-hydroxyandrostane-4,17-dione. This metabolite accounted for approximately 5% of the total radioactivity in the blood, whereas 4-OHT accounted for only 0.1%. 4-OHT inhibited in vitro ovarian aromatization by 59%, but 3β-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.