Background
Menopausal hormone therapy (MHT) is recommended for only five years to treat vasomotor symptoms and vulvovaginal atrophy because of safety issues with long-term treatment. We examined the ability of 2’, 3’, 4’-trihydroxychalcone (2’, 3’, 4’-THC) to modulate ERα-mediated responses on gene regulation and cell proliferation to identify drugs that can potentially overcome the adverse effects of estradiol (E2) in MHT so it can be used for long-term therapy to treat prolonged menopausal symptoms and prevent chronic diseases.
Methods
Transfection assays, quantitative real time-polymerase chain reaction, and microarrays were used to evaluate the effects of 2’, 3’, 4’-THC on gene regulation. Radioligand binding studies were used to determine if 2’, 3’, 4’-THC binds to ERα. The effects of 2’, 3’, 4’-THC on cell proliferation and the cell cycle were examined in MCF-7 breast cancer cells using growth curves and flow cytometry. Western blots were used to determine if 2’, 3’, 4’-THC alters the E2 activation of the MAPK pathway and degradation of ERα. Chromatin immunoprecipitation was used to measure ERα binding to genes.
Results
2’, 3’, 4’-THC produced a synergistic response of E2 activation of reporter and endogenous genes in U2OS osteosarcoma cells. Microarrays identified 824 genes that we termed reprogrammed genes because they were not regulated in U2OS-ERα cells unless the cells were treated with 2’, 3’, 4’-THC and E2 together. 2’, 3’, 4’-THC blocked the proliferation of MCF-7 cells by preventing the E2-induced stimulation of MAPK activity and c-MYC transcription. The antiproliferative mechanism of 2’, 3’, 4’-THC differs from selective estrogen receptor modulators (SERMs) since 2’, 3’, 4’-THC does not bind to E2 binding site in ERα like SERMs.
Conclusion
Our study identified 2’, 3’, 4’-THC as a reprogramming compound, because it changes the actions of E2 on gene regulation and cell proliferation without competing for the E2 binding site in ERα. The addition of a reprogramming compound such as 2’, 3’, 4’-THC to estrogens in MHT may offer a new strategy to overcome the adverse effects of estrogen in MHT through a reprogramming mechanism rather than an antagonist action.