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| Formula | C25H22O2 |
| Molar mass | 354.449 g·mol−1 |
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Etacstil (developmental code names GW-5638, DPC974) is an orally active, nonsteroidal, combined selective estrogen receptor modulator (SERM) and selective estrogen receptor degrader (SERD) that was developed for the treatment of estrogen receptor-positive breast cancer. [1] [2] [3] It was shown to overcome antiestrogen (tamoxifen, aromatase inhibitor, fulvestrant) resistance in breast cancer by altering the shape of the estrogen receptor, thus exhibiting SERD properties. [4] [5] [6] [7] [8] Etacstil is a tamoxifen derivative and one of the first drugs to overcome tamoxifen-resistance. It is the predecessor of GW-7604, [3] [9] [10] of which etacstil is a prodrug (GW-7604 being the 4-hydroxy metabolite of etacstil). [11] This is analogous to the case of tamoxifen being a prodrug of afimoxifene (4-hydroxytamoxifen). [11]
Etacstil was developed in the early 1990s by Duke University, Glaxo Wellcome, and later, Dupont. [12] [13] In 2001, Bristol Myers-Squibb (BMS) acquired Dupont, and for non-scientific, corporate reasons, closed the trial and abandoned the release of etacstil and its metabolite GW-7604. [6] [9] [12]
After many dormant years, a recent resurgence of interest in SERDs has led to the development of brilanestrant, a structural analogue of etacstil. [9]
{{cite journal}}: CS1 maint: DOI inactive as of September 2025 (link)