We report evidence indicating that the isoflavone genistein induces a dose-dependent antiproliferative effect in the human uterine adenocarcinoma cell lines HEC-1A, HEC-1B, AN3 CA and RL95-2. Cell growth inhibition resulted from a partial G2/M block and from the appearance of a hypodiploid DNA peak (reduction in nuclear DNA content), suggestive of apoptosis. In HEC-1A cells, we found that both cell cycle impairment and the appearance of a hypodiploid DNA peak were time-dependent, triggered by similar concentrations of the isoflavone and not affected by the presence of serum in the culture medium. However, while the genistein-induced cell cycle'arrest was fully reversible, the appearance of the hypodiploid DNA peak was not. To verify whether the appearance of a hypodiploid DNA peak corresponded to apoptosis, we used in situ end labelling (ISEL) and transmission electron microscopy (TEM) in HEC-1A cells. We found that a 48-h treatment with genistein induced ISEL positivity only in a minority of cells, while at 72 h the majority of cells were labelled. At this time TEM showed the typical ultrastructural features of apoptosis, including apoptotic bodies.
Because genistein inhibited tyrosine kinase (TK) and topoisomerase (Topo) II activity in HEC-1A cells and its effects were mimicked by structurally unrelated TK and Topo II inhibitors, we speculate that interactions with TK and Topo II are relevant for the antiproliferative effect of genistein. Conversely, the antiproliferative effect of genistein seems to be independent of its oestrogenic activity. Our data indicate that genistein inhibits the growth of uterine adenocarcinoma cell lines by inducing cell cycle arrest and apoptosis.
Endocrine-Related Cancer (1997) 4 203-218