Nitromifene is an antagonist of estrogen receptor (ER). IC50 & Target: ER^[1] In Vitro: Nitromifene is an antagonist of estrogen receptor (ER). At 0.5 μM and 1.0 μM concentrations, Nitromifene inhibits MCF 7 cell proliferation to 70% of that in drug-free controls. At higher concentrations, Nitromifene is clearly more effective than other metabolites. Specifically bound estradiol is displaced from intact MCF 7 cells by Nitromifene. Nitromifene is an effective antagonist of the ability of calmodulin (CM) to activate cyclic nucleotide phosphodiesterase^[1].