Creating RNA aptamers to modulate function of human estrogen receptor alpha

A significant number of breast cancers are estrogen receptor (ER)-positive and treatable by ER antagonists. The human estrogen receptor (hER)alpha protein is composed of multiple domains and bears multiple sites that interact with other factors or elements. However, all ER antagonists currently in use target the ligand-binding pocket of ER. We hypothesized that some other sites on hER alpha may be validated as new drug targets for treating breast cancer and other estrogenopathies. To test this hypothesis, we used RNA aptamers as a means for modulation of hER alpha function through specific protein surface occlusion.;Two classes of high affinity RNA aptamers have been developed for unliganded full-length hERalpha using the method of in vitro selection. Class I aptamers bind to both isoforms of hER, alpha and beta, with similar affinities, while a Class II aptamer only binds to hERalpha with high affinity. These results suggested that the two classes bind to different sites on hER alpha. To study the efficacy of the aptamers in breast cancer cell lines, genetic systems have been constructed to produce aptamers through transcription from synthetic genes delivered into the cells. In the ER-positive breast cancer cell line MCF7, the expressed aptamers reduced hER alpha-driven luciferase gene activity by 30-50%. The specific interaction between hER alpha and aptamers in vivo has been proven using an RNA pull-down assay and an RNA co-immunoprecipitation assay.