Selective estrogen receptor degrader

A selective estrogen receptor degrader or downregulator is a type of drug that selectively binds to the estrogen receptor and induces its degradation, and thus causes its downregulation. SERDs are used in the treatment of estrogen receptor-positive breast cancer, particularly in cases where tumors have developed resistance to other forms of endocrine therapy, such as selective estrogen receptor modulators or aromatase inhibitors.
The mechanism of action of SERDs involves binding to the estrogen receptor, leading to a conformational change that facilitates recruitment of cellular machinery to degrade the receptor protein. By promoting degradation of the estrogen receptor, SERDs effectively inhibit estrogen signaling within cancer cells, thereby suppressing tumor growth.
A common SERD used in clinical practice is fulvestrant. Fulvestrant is administered as an intramuscular injection and is indicated for the treatment of advanced breast cancer in postmenopausal women whose cancer has progressed following anti-estrogen therapy.
As of 2016 the only marketed SERD was fulvestrant. As of November 2016 other SERDs under development include brilanestrant and elacestrant. The clinical success of fulvestrant led to efforts to discover and develop a parallel drug class of selective androgen receptor degraders.

Investigational

Fulvestrant requires intramuscular injections once every two weeks. In response, pharmaceutical companies are currently developing oral SERDs. Among products in development are:
Monofunction hydrophobic tag degradation:

The oral SERDs target ER-positive/HER2-negative breast cancer and are tested as monotherapy and in combination with other drugs such as the CDK inhibitor palbociclib.