2-methoxyestradiol induces cell cycle arrest and mitotic cell apoptosis in human vascular smooth muscle cells

It has been shown that 2-methoxyestradiol (2-ME) inhibits cell proliferation and DNA synthesis in human aortic smooth muscle cells. However, the cellular mechanisms underlying the antiproliferative activity of 2-ME are unclear. The present study was performed to explore the cellular mechanisms whereby 2-ME leads to growth inhibition and apoptosis of human smooth muscle cells. Our results demonstrate that at 1 hour of treatment, 1 micromol/L 2-ME induces multiple spindles, overamplified centrosomes, and multipolar cytokinesis, whereas 10 micromol/L 2-ME causes completely damaged spindle, disorientated centrosomes, and missegregated chromosomes. At 6 hours of treatment, the mitotic index was increased and reached a maximal level, and cells with 4N DNA content (4N cells) began to accumulate. The increased mitotic cells induced by 2-ME were apoptotic as detected by both annexin V and TUNEL staining. Blockage of cells in G(1/0) phase by thymidine prevented 2-ME-induced apoptosis. In addition, the increased mitotic index declined concurrently when even more 4N cells accumulated at 12 to 48 hours of treatment with 10 micromol/L 2-ME. Furthermore, in response to 2-ME, cells delayed entry into the next cell cycle and exhibited aneuploidy or micronuclei. Some aneuploidy cells continued to synthesize DNA. We conclude that 2-ME treatment not only arrests cells in mitosis and promotes mitotic cell apoptosis, but also causes cells to undergo "mitotic slippage" and endoreduplication. The induction of mitotic cell arrest and apoptosis may be a major cellular mechanism by which 2-ME inhibits proliferation of human smooth muscle cells.