In addition, we show that imipramine inhibits the growth of ER + breast cancers by inhibiting the estrogen receptor- α (ER-α) signaling….To determine whether imipramine can sensitize cells to effects of tamoxifen, we performed short-term viability assays with various doses of tamoxifen plus vehicle or tamoxifen plus imipramine in MCF7-TamR cells. The combination therapy significantly inhibited cell viability compared to tamoxifen treatment alone.