Nitromifene is an effective antagonist of the ability of calmodulin (CM) to activate cyclic nucleotide phosphodiesterase. Nitromifene inhibits MCF 7 cell proliferation to 70% of that in drug-free controls, at 0.5 μM and 1.0 μM concentrations. Nitromifene is clearly more effective than other metabolites, at higher concentrations. Specifically, bound estradiol is displaced from intact MCF 7 cells by Nitromifene .