Imlunestrant CAS# 2408840-26-4

Imlunestrant is a potent, orally bioavailable selective estrogen receptor degrader (SERD) that works on both wild-type (WT) and mutated ESR1 (ERα) (e.g. Y537S, Y537N, E380Q) forms. In vitro, it shows high binding affinity: ~0.64 nM for WT ERα, ~2.8 nM for Y537S mutant. It degrades WT ERα and mutants (e.g. Y537N) in cells with IC₅₀s of ~3.0 nM (WT) and ~9.6 nM (mutant). In breast cancer cell panels, nearly all ER+ cell lines (11/12) have IC₅₀ <100 nM; ER– lines are largely insensitive. It also suppresses ER-mediated transcription (e.g. progesterone receptor gene expression) and cell proliferation, both as monotherapy and in combination with standard agents (CDK4/6 inhibitors like abemaciclib; PI3K inhibitor alpelisib; mTOR inhibitor everolimus), showing synergy or additive inhibition depending on the cell line.