Abstract 1721: A steroid-based drug that binds estrogen receptor beta can inhibit cancer cell proliferation by blocking chromosome replication

Abstract

Abstract Our approach for developing a cancer therapeutic is based on the notion that the estrogen receptors alpha (ER-alpha) and beta (ER-beta) function in opposing manners towards events involved in controlling cell growth and proliferation. If the proposed inhibitory function of ER-beta is accurate, we predict that treatment of cancer cells with an ER-beta agonist may lead to cessation of cell division and potentially to cell death. Towards that end, we have discovered a family of first-in-class compounds for treating cancer that function by blocking chromosome replication in rapidly dividing cells. NDC-1022 and NDC-1308 are estradiol analogs which vary only in the length of the 6-alkoxyalkyl group at the carbon 6 position. Importantly, the length of the 6-alkoxyalkyl group may impact the function of the compounds since in silico modeling studies predict a difference in how the side-chains of NDC-1022 and NDC-1308 are bound within the ligand binding sites of ER-alpha and ER-beta. To understand the mechanism of action for these compounds, competitive binding studies were carried out with either recombinant human ER-alpha or ER-beta in the presence of labeled estradiol. The results show that the NDC compounds preferentially bind to the ER-beta receptor compared to the ER-alpha receptor. To determine how the NDC compounds affect cell growth, 201T NSCLC cells were incubated with 100 µm of NDC-1022. After 48 hours, NDC-1022 caused a reversible cell cycle arrest at G0/G1 for the majority of cells. The level of cytotoxicity was determined by treating 14 different human tumor cell lines with a serial dilution of the NDC compounds. The EC50 data suggests that NDC-1308 (10-20 uM) is about 3 to 8.5-fold more potent than NDC-1022 (30-85 uM). We propose that this difference in potency is due to NDC-1308 making additional non-polar interactions within the receptor ligand binding sites compared to NDC-1022. Finally, gene expression studies were carried out using microarray to identify the mechanism of action for cytotoxicity. Three human tumor cell lines (A549-lung, SKOV-3-ovary, and Panc-1- pancreatic) were treated with the NDC compounds for 24 hours. Both NDC-1022 and NDC-1308 exhibit a substantial reduction in the transcription of 27 genes critical for chromosome replication, a cellular process exaggerated in most cancer cells and therefore a relevant therapeutic target. We conclude that NDC-1022 and NDC-1308 impact all rapidly growing cells without regard to any underlying mutation and therefore could be used to treat a wide range of cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1721.