The vitamin A family can significantly decrease the expression of ERβ of ERs positive breast cancer cells in the presence or absence of ER ligands and paclitaxel

Taxanes have high activity against breast cancer cells either as the single agent or in combination with other anticancer compounds. The aim of the study was to determine the effects of vitamin A compounds on the cytotoxic action of paclitaxel and on the expression of ERs in the MCF-7 breast cancer cells. Retinol and beta-carotene, but not retinoids, added to the culture exerted an effect on paclitaxel activity. However, only beta-carotene significantly reduced the percentage of proliferating cells (40.36% +/- 5.64, p < 0.01). We observed that vitamin A and its derivatives combined with paclitaxel and estradiol decreased the percentage of proliferating cells, but only in comparison to estradiol group, whereas retinol and lycopene administered together with paclitaxel and tamoxifen decrease significantly the percentage of proliferatin cells (36.85% +/- 4.71, p < 0.0001 and 37.22% +/- 1.59, p < 0.0001 respectively, compared with paclitaxel group). We have shown that paclitaxel increases the expression of ER alpha and ER beta mRNA in MCF-7 line. The strongest effect of transcription inhibition ER alpha (2.5 times) and especially ER beta (10 times) was observed after addition of 9-cis retinoic acid and paclitaxel. This data suggests a synergistic effect of the compounds on ER beta down-regulation. Our results support the use of retinoid is treatment of ER positive breast cancer patients.