The effects of retinoid treatment and antiestrogens on the growth of T47D human breast cancer cells.

The ability of all-trans-retinoic acid, 13-cis-retinoic acid, the free acid of etretinate (RO 10-1670), the 'arotinoid' RO 13-6298 and its free acid RO 13-7410 to affect the growth of T47D human breast cancer cells in vitro was investigated. The growth of T47D cells was inhibited by all of the retinoids tested, with the arotinoids being up to 100 times more effective than all-trans-retinoic acid. The presence of cellular retinoic acid binding protein (cRABP) was indicated by the cellular uptake of [3H]all-trans-retinoic acid. Maximum binding was 460 fmol/micrograms DNA. All of the retinoids with a polar terminal free carboxyl group readily competed for the binding sites, but none of the retinoids competed for the estrogen or progesterone receptor. Co-treatment of the T47D cells with 0.1 microM all-trans-retinoic acid and either tamoxifen (1 microM) or hydroxytamoxifen (10 nM or 0.1 microM) produced an additive effect on growth inhibition. No such additive effect was observed when T47D cells were co-treated with arotinoids and antiestrogens. The results showed that the T47D cells can serve as a useful model in vitro to test the effects of the synthetic retinoids and antiestrogens on steroid receptor-positive human breast cancer.