Inhibition of Peripheral Aromatization of Androstenedione to Estrone in Postmenopausal Women with Breast Cancer Using Δ1Testololactone*

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Abstract
To determine if Δ1-testololactone can inhibit the peripheral aromatization of androstenedione (Δ), nine postmenopausal women with metastatic breast cancer were studied before and after 2 weeks of therapy with 250 mg of the drug, given every 6 h by mouth. The conversion ratio of Δ to estrone (E1) was significantly reduced (P < 0.005) from a mean (±SE) of 0.0098 ± 0.0025 before to 0.0009 ± 0.0005 after treatment. The drug's effect on the metabolism of Δ seemed to be specific since significant changes in the MCR of Δ and in the conversion ratio to testosterone were not observed. That this inhibition of peripheral aromatization had an effect on Ei metabolism was shown by the significant decrease (P < 0.01) of mean serum E1 levels from 22 ± 3 pg⁄ml before to 12 ± 1 pg⁄ml after treatment. Serum estradiol levels rose slightly from 8 ± 0.8 to 12 ± 4 pg⁄ml. Serum Δ and testosterone levels were unchanged by therapy. These data are consistent with the concept that Δ1-testololactone is a potent inhibitor of peripheral aromatization of Δ to E1. This mechanism could explain the antitumor properties of this compound.