The effect of ICI 164384 and beta-interferon on the growth and steroid receptor profile of breast cancer cell lines.

We investigated the effect of a concomitant treatment of ICI 164384 and B-interferon (beta-IFN) on the growth of estrogen-receptor-positive (ER+) and estrogen-receptor-negative (ER-) breast cancer cell lines and on their steroid receptor profiles. ICI 164384 reduced cell proliferation not only in ER+ but also in ER- cell lines and completely suppressed the stimulation induced by estradiol (E2) in hormone-sensitive cell lines, MCF7 and T47D. When associated with beta-IFN, ICI 164384 increased the inhibitory effect exerted by the low concentration of beta-IFN. Moreover, ICI 164384, singly or in association with beta-IFN, did not affect ER and PgR concentration in ER- cell lines, whereas in ER+ cell lines we observed an almost total disappearance of ER and PgR. In conclusion, our study seems to indicate that, although beta-IFN is able to control the proliferation of hormone-sensitive and hormone-independent subclones, it does not further improve the antiproliferative activity of ICI 164384. In contrast, the presence of ICI 164384, which does not induce the selection of resistant subclones under the same experimental conditions in which TAM does, may improve the efficacy of low concentration of beta-IFN and prevent the development of a secondary TAM-induced resistance.