Sulfamoylation of 2-methoxyestradiol (2-MeOE2) was shown previously to enhance its potency as an anti-proliferative agent against breast cancer cell lines and its in vitro anti-angiogenic activity. 2-Methoxyestradiol-3,17-O,O-bis-sulfamate (2-MeOE2bisMATE) inhibits cell cycle progression and proliferation in both normal and drug resistant breast, ovarian and prostate cancer cell lines. A C-17 modified analogue of 2-MeOE2bisMATE, 2-methoxy-3-O-sulfamoyl-17β-cyanomethyl estra-1,3,5-triene (2-MeOE2CyMATE), displays enhanced anti-proliferative activity. In this study we assessed the anti-tumor potential of a non-sulfamoylated derivative of 2-MeOE2CyMATE, 2-methoxy-17β-cyanomethyl estra-1,3,5-triene (2-MeOE2Cy), in a range of tumor cell lines and in an in vitro model of angiogenesis. 2-MeOE2Cy is a potent inhibitor of A2780 (ovarian ER-ve), LNCaP (prostate AR+ve), PC3 (prostate AR-ve) and MCF-7 (breast ER+ve) cell proliferation with IC50 values between 330nM-430nM. Treatment of cells and subsequent compound removal indicated that the effects of 2-MeOE2Cy on cell proliferation are irreversible, in contrast to 2-MeOE2. Previously it has been shown that a sulfamoylated derivative of 2-methoxyestrone (2-methoxyestrone-3-O-sulfamate) blocks paclitaxel-stimulated tubulin assembly, in contrast to 2-MeOE2, which did not block paclitaxel-stimulated tubulin assembly in this study. Despite lacking a sulfamate group, 2-MeOE2Cy inhibited paclitaxel-stimulated tubulin assembly. Furthermore, like 2-MeOE2bisMATE and 2-MeOE2CyMATE, 2-MeOE2Cy causes G2/M cell cycle arrest and subsequent apoptosis. The apoptosis is in part mediated by phosphorylation and inactivation of the anti-apoptotic protein BCL-2. Furthermore, 2-MeOE2Cy inhibits the proliferation of endothelial cells, indicating that this compound may possess anti-angiogenic potential. To further explore this possibility we used an in vitro co-culture model of angiogenesis, in which endothelial cells form vessel-like structures when cultured with fibroblasts. In this assay 100nM 2-MeOE2Cy completely inhibited the vessel formation, verifying the potential anti-angiogenic activity of this compound. In conclusion, 2-MeOE2Cy could have considerable therapeutic potential for the treatment of a variety of cancers as it would; target both the tumor and its blood supply; the C-17 modification should make it resistant to metabolism and inactivation; and finally, in vitro this compound is more potent than the well established anti-cancer agent 2-MeOE2.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]