Information SAR439859 (compound 43d) is an orally available and nonsteroidal selectiveestrogen receptordegrader (SERD) with potential antineoplastic activity. SAR439859 is a potentestrogen receptor (ER)antagonist with EC50 of 0.2 nM for ERα degradation. Targets ERα (Cell-free assay) 0.2 nM(EC50) In vitro SAR439859 is a novel, orally bioavailable SERD with potent antagonist and degradation activities against both wild-type and mutant Y537S ER. Driven by its fluoropropyl pyrrolidinyl side chain, SAR439859 has demonstrated broader and superior ER antagonist and degrader activities across a large panel of ER+ cells, including inhibition of ER signaling and tumor cell growth. In vivo SAR439859 shows promising antitumor activity in breast cancer mice xenograft models. In vivo treatment with SAR439859 demonstrates significant tumor regression in ER+ breast cancer models, including MCF7-ESR1 wild-type and mutant-Y537S mouse tumors, and HCI013, a patient-derived tamoxifen-resistant xenograft tumor. Cell Research(from reference) Cell lines：LCC2 cells, MCF7 cells Concentrations：0.01-1000 nM Incubation Time：7 days, 4 hours