Etacstil
Etacstil is an orally active, nonsteroidal, combined selective estrogen receptor modulator and selective estrogen receptor degrader that was developed for the treatment of estrogen receptor-positive breast cancer. It was shown to overcome antiestrogen resistance in breast cancer by altering the shape of the estrogen receptor, thus exhibiting SERD properties. Etacstil is a tamoxifen derivative and one of the first drugs to overcome tamoxifen-resistance. It is the predecessor of GW-7604, of which etacstil is a prodrug. This is analogous to the case of tamoxifen being a prodrug of afimoxifene.
Etacstil was developed in the early 1990s by Duke University, Glaxo Wellcome, and later, Dupont. In 2001, Bristol Myers-Squibb acquired Dupont, and for non-scientific, corporate reasons, closed the trial and abandoned the release of etacstil and its metabolite GW-7604.
After many dormant years, a recent resurgence of interest in SERDs has led to the development of brilanestrant, a structural analogue of etacstil.
