Repurposing Diclofenac as an Anticancer Agent: Suppression of Breast Cancer and Progression through EPAS1-EFNA1 Regulation

Introduction: Breast cancer, the most common female malignant tumor, endangers women’s health. Traditional anticancer drugs often lead to resistance, so new therapeutics are urgently needed. This study explored the anti-tumor mechanism of diclofenac in breast cancer. Methods: Diclofenac’s effects on breast cancer cell proliferation, migration, invasion, and apoptosis were assessed via in vitro (MTT, Colony formation, Transwell, Wound healing, Flow cytometry, Immunofluorescence) and in vivo (Xenograft model) assays. RNA-seq identified diclofenac’s target. EFNA1 expression was analyzed by RNA-seq, qRT-PCR, and Western blot. The luciferase assay investigated diclofenac-mediated EFNA1 transcriptional regulation; overexpression strategies validated EFNA1’s involvement in mediating diclofenac’s anticancer activities. Results: Diclofenac inhibited proliferation, migration, and invasion, and induced apoptosis in T47D and MDA-MB-231 cells, and suppressed xenograft growth. It reduced EFNA1 expression by impairing EPAS1 binding to the EFNA1 promoter’s -1353~-782 region; EFNA1 overexpression abrogated diclofenac’s anti-tumor effects, confirming EFNA1 as a critical mediator of diclofenac’s effects. Discussion: Our findings reveal that diclofenac exerts anti-breast cancer effects by targeting EFNA1 via EPAS1-mediated transcriptional regulation. It not only provides novel insights into the COX-independent anticancer mechanism of diclofenac but also highlights EFNA1 as a potential therapeutic target for breast cancer, although further in vivo validation and larger-cohort studies are warranted. Conclusion: Diclofenac inhibits breast cancer progression by down-regulating EFNA1 through impairing EPAS1 binding to its promoter. These findings support repurposing diclofenac into an established and readily accessible medication as a promising and cost-effective agent for breast cancer treatment, while also underscoring EFNA1’s potential role in guiding treatment stratification.