Etoposide is a plant alkaloid and an inhibitor of topoisomerase II (IC50 = 60.3 ?M).{21619,21623} It inhibits proliferation of a variety of adenocarcinoma cells (IC50s = 0.005-12,200 µM) and human umbilical vein endothelial (HUVEC) cells (IC50 = 0.249 µM).{21620} It reduces tumor growth in an Ma human embryonal carcinoma mouse xenograft model when administered at a dose of 25 mg/kg, an effect that is enhanced by concomitant administration of the immunosuppressant cyclosporin A (Item No. 12088).{47188} Etoposide also inhibits nuclear receptor coactivator 3 (IC50 = 2.48 µM).{21622} Formulations containing etoposide have been used in combination therapy in the treatment of cancer.