Different chemo- and endocrino-sensitivity of MCF-7 cells with or without estradiol supplement in vitro

The sensitivity of MCF-7 cells to tamoxifen (TAM) and mitomycin C (MMC) was assessed in rapidly and slowly growing cells with or without estradiol supplementation, respectively. The growth of MCF-7 was inhibited by MMC in a concentration-dependent manner with or without estradiol (E2) supplementation. Preincubation with MMC suppressed subsequent E2 stimulated growth of MCF-7. TAM inhibited the growth of MCF-7 supplemented with E2 and preincubation with TAM prevented subsequent E2 stimulated growth of MCF-7. However, TAM did not inhibit the growth of MCF-7 cells in E2 free medium. These results suggested that MMC may be more effective than TAM on breast cancer cells in the dormant or slow-growth phase.