ALL-TRANS-RETINOIC ACID (ATRA)-INDUCED APOPTOSIS IS PRECEDED BY G(1) ARREST IN HUMAN MCF-7 BREAST-CANCER CELLS

In this study the effects of all-trans retinoic acid (ATRA) on cell cy cle and apoptosis of MCF-7 human breast cancer cells were investigated to elucidate the mechanisms underlying the antineoplastic potential o f this retinoid in breast cancer. The antiproliferative effect of ATRA was evaluated by DNA content measurements and dual-parameter flow cyt ometry of bromodeoxyuridine (BrdU) incorporation and of the expression of cell cycle-related proteins (Ki-67 as proliferation marker and sta tin as quiescence marker) vs DNA content. Apoptosis was also studied b y flow cytometry of either DNA content or Annexin V labelling. After 1 0(-6) M ATRA treatment, the fraction of S-phase cells decreased signif icantly, and cells accumulated in the G(0)/G(1) range of DNA contents. Dual-parameter flow cytograms showed a decrease in the percentage of Ki-67-labelled cells (after 10 days, only 20% of the cells were still positive for Ki-67 compared with 95% in controls), while the fraction of statin-positive cells increased slightly. From 3 days of treatment onwards, apoptosis was found to occur. These results show that ATRA-in duced inhibition of MCF-7 cell growth is related to two mechanisms, i. e. the block of cell proliferation, mostly in a pre-S phase, and the i nduction of apoptosis. These results should be taken into account when attempting to design treatment programmes that associate ATRA with an tineoplastic compounds of different cell cycle specificity.