Notes: Ethisterone is an orally bioavailable synthetic progestin and a derivative of testosterone (Item Nos. ISO60154 / 15645) that binds to progesterone and androgen receptors (EC50s = 23 and 23.1 nM, respectively, in yeast).{40099} Ethisterone (1 µM) downregulates progesterone receptors in MCF-7 cells.{40098}