Aspirin as a potential drug repurposing candidate targeting estrogen receptor alpha in breast cancer: a molecular dynamics and in-vitro study

Estrogen receptor alpha (ER alpha) is expressed by 70% of breast cancers (BCs). Any deregulation in ER alpha signaling is crucial for the initiation and progression of BC. Because of development of resistance to anti-estrogenic compounds, repurposing existing drugs is an apt strategy to avoid a long drug-discovery process. Substantial epidemiologic evidence suggests that Aspirin use reduces the risk of different cancers including BC, while its role as an adjuvant or a possible antineoplastic agent in cancer treatment is being investigated. In this study, we attempted to explore possibilities of ER alpha inhibition by Aspirin which may act through competitive binding to the ligand binding domain (LBD) of ER alpha. A list of 48 ER alpha-LBD crystal structures bound with agonists, antagonists, and selective ER modulators (SERMs) was thoroughly analysed to determine interaction patterns specific to each ligand category. Exhaustive docking and 500 ns molecular dynamics (MD) studies were performed on three ER alpha - Aspirin complexes generated using agonist, antagonist, and SERM-bound crystal structures. Besides, three ER alpha crystal structures bound to agonist, antagonist, and SERM respectively were also subjected to MD simulations. Aspirin showed good affinity to LBD of ER alpha. Comparative analyses of binding patterns, conformational changes and molecular interaction profiles from the docking results and MD trajectories suggests that Aspirin was most stable in complex generated using SERM bound crystal structure of ER alpha and showed interactions with Gly-521, Ala-350, Leu-525 and Thr-347 like SERMs. In addition, in-vitro assays, qPCR, and immunofluorescent assay demonstrated the decline in the expression of ER alpha in MCF-7 upon treatment with Aspirin. These preliminary bioinformatical and in-vitro findings may form the basis to consider Aspirin as a potential candidate for targeting ER alpha, especially in tamoxifen-resistant cancers.