Inhibition of normal and experimental angiotumor endothelial cell proliferation and cell cycle progression by 2-methoxyestradiol

With rapid growth and metabolism, aggressive cancers require an extensive vascular network, termed tumor angiogenesis. The body produces a variety of natural angiogenic inhibitors, among which is the mammalian estrogen metabolite, 2-methoxyestradiol (2-MeOE₂). In this study, we compared the effects of 2-MeOE₂ on a human umbilical vein cell line (HUVEC- C) and on an immortal, angiotumor-producing rat sinusoidal endothelial cell line (RSE-1). In vitro, the effects of varying concentrations of 2-MeOE₂ from 0.01-100.0 μM were measured with cell counts and compared to control cells. HUVEC-C had an ED₅₀ -3.5 μM with ~27% inhibition of cell growth whereas RSE-1 had an ED₅₀ ~2.2 μM with ~50% inhibition of cell growth compared with controls. The lowest concentration with maximal effect was 10.0 μM 2-MeOE₂ for both cell lines. Using this concentration, flow cytometric analysis of cell cycles was performed with propidium iodide stained DNA of HUVEC-C and RSE-1 at 24 and 48 hr. Both demonstrated a significant (P < 0.0001) block at G₂M of the cell cycle. At 48 hr, HUVEC-C had 32% of cells in G₂M (control = 9% G₂M), and RSE-1 had 36% of cells in G₂M (control = 18% G₂M). These findings demonstrate a strong in vitro antiproliferative effect of 2-MeOE₂ on normal dividing endothelial as well as angiotumor cells mediated through a cell cycle-specific block at G₂M. The antiendothelial, antianglotumor effect of 2-MeOE₂ supports its potential as a therapeutic agent against solid organ cancers, benign or malignant vascular growths, and other pathologic states dependent on angiogenesis.