Estrone-N-O-C1-amido (ERα ligand 1) is an estrogen ligand derived from Estrone that specifically binds to estrogen receptor α (ERα). Through a linker, Estrone-N-O-C1-amido (ERα ligand 1) forms a complex with the cIAP1 ligand Bestatin, leading to the creation of SNIPER[1].