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

Abstract

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 microM were measured with cell counts and compared to control cells. HUVEC-C had an ED50 approximately 3.5 microM with approximately 27% inhibition of cell growth whereas RSE-1 had an ED50 approximately 2.2 microM with approximately 50% inhibition of cell growth compared with controls. The lowest concentration with maximal effect was 10.0 microM 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, antiangiotumor 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.