Equilenin

Equilenin is a B-ring unsaturated estrogen discovered in pregnant mare urine and is one of the major components of Premarin, a drug commonly used for estrogen replacement therapy. Equilenin binds to estrogen receptors in the body and exerts effects similar to endogenous estrogens. Equilenin weakly binds to and activates the aryl hydrocarbon receptor (AhR) to induce CYP1A1 expression. Equilenin exhibits high affinity for sex hormone-binding globulin (SHBG/SBP) and is metabolized by CYP1A1/1B1 to 4-hydroxy and 17β-dihydro derivatives. Equilenin is used in breast cancer-related research^[1][2][3]. In Vitro:Equilenin (10-300 μM; 1 h) directly binds to AhR in C57BL mice, and at high concentrations inhibits specific [³H]B (a) P binding by approximately 50%^[1].
Equilenin binds to SBP with an equilibrium association constant of approximately 6 × 10⁷ M^-1, which is strong enough to competitively displace the natural steroid DHT from the binding site^[2].
Equilenin (1-30 μM; 24 h) induces CYP1A1 mRNA expression in HepG2 cells in a concentration-dependent manner^[1].
Equilenin (1-30 μM; 24 h) activates transcription through the xenobiotic response element (XRE) in HepG2 cells^[1]. In Vivo:Equilenin (1-20 mg/kg/day; i.p.; for 3 consecutive days) dose-dependently induces CYP1A activity and CYP1A protein expression in the liver of C57BL mice^[1].
Equilenin (1-20 mg/kg/day; i.p.; intraperitoneal injection; 3 consecutive days) significantly induces CYP1A activity and protein expression in the liver of DBA2 mice at high doses^[1].
Equilenin (1-10 mg/L; immersion; 2 h) causes significant developmental toxicity and teratogenicity in developing medaka embryos, including malformations, mortality, and delayed hatching, accompanied by alterations in multiple gene expression pathways^[4].