Testolactone is a synthetic antineoplastic agent that is structurally distinct from the androgen steroid nucleus in possessing a six-membered lactone ring in place of the usual five-membered carbocyclic D-ring. Despite some similarity to testosterone, testolactone has no in vivo androgenic effect. No other hormonal effects have been reported in clinical studies in patients receiving testolactone.
The principal action of testolactone is reported to be inhibition of steroid aromatase activity and the reduction in estrone synthesis that follows. Androstenedione, a 19-carbon steroid hormone produced in the adrenal glands and the gonads, is where estrone synthesis originates and is the source of estrogen in postmenopausal women. In vitro studies report that the aromatase inhibition may be noncompetitive and irreversible, and could possibly account for the persistence of this drug's effect on estrogen synthesis after drug withdrawal.
This drug is mainly used for treating various types of breast cancer in women who have been through menopause or whose ovaries no longer function. It works by blocking the production of estrogen, which helps prevent the growth of breast cancers that are activated by estrogen. It may also prevent tumor cells from being activated by other hormones. It also has been used to postpone precocious puberty because of its ability to block estrogen production.