RU49953

RU49953 is an experimental **small-molecule**, non-hormonal estradiol-derived steroid research compound developed by **Roussel-Uclaf** as a **P-glycoprotein modulator** intended to reverse **multidrug resistance** in cancer cells. It acts as a potent inhibitor of P-glycoprotein-mediated drug efflux and has been described as more effective than verapamil in preclinical systems, consistent with a role as a chemosensitizer for resistant tumors. Despite being an estradiol derivative, it was designed to be highly hydrophobic and to **avoid meaningful interaction with hormone receptors**, distinguishing it from classical endocrine agents. Available information supports preclinical research use in oncology and transporter biology, with no clear evidence of clinical development, regulatory approval, or commercialization.