CHANGES IN RADIATION SENSITIVITY AND STEROID-RECEPTOR CONTENT INDUCEDBY HORMONAL AGENTS AND IONIZING-RADIATION IN BREAST-CANCER CELLS IN-VITRO

Possible influences of tamoxifen and estradiol on in vitro radiation s ensitivity and cellular receptor content after irradiation and/or tamo xifen treatment were studied in breast cancer cell lines; estrogen rec eptor (ER) and progesterone receptor (PgR) positive cell lines MCF-7 a nd MCF-7/TAM(R)-1 and the ER and PgR negative cell line MDA-MB-231, Th e tamoxifen resistant MCF-7/TAM(R)-1 cells were more resistant to ioni zing radiation than the MCF-7 and MDA-MB-231 cells, Exposure to tamoxi fen made the MCF-7 cells more radiation resistant, while estradiol mad e the MDA-MB-231 cells more radiation sensitive, A radiation dose of 6 Gy reduced the ER content in cytosol in both MCF-7 and MCF-7/TAM(R)-1 cells, but brought no alterations to the PgR content, In MCF-7/TAM(R) -1 cells tamoxifen exposure significantly increased the ER and reduced the PgR content, an effect not observed in the MCF-7 cells, To conclu de, the present study indicates that irradiation and tamoxifen may mod ify the ER and PgR content in cytosol in breast cancer cells. Hormonal treatment may alter the radiation sensitivity, even in ER negative ce lls, suggesting that hormonal agents may act both via receptor and non -receptor binding mechanisms.