Effect of 4-hydroxyphenylretinamide and retinoic acid on proliferation and cell cycle of cultured human breast cancer cells.

The synthetic retinoid 4-hydroxyphenylretinamide (HPR) showed antiproliferative effect on cultured human breast cancer cells, which were sensitive to retinoic acid (RA) too. Investigation of the cell cycle by flow cytophotometry showed a significant increase of cells in the S-phase of the cell cycle after 24 hours of RA treatment, whereas HPR did not show this effect. After 4-7 days of retinoid treatment, the percentage of resting cells increased. The influence on the cell cycle and the antiproliferative effect were more pronounced for RA than for HPR treatment in both cell lines investigated (ZR-75.1 and 734 B).