Celecoxib potentiates ribociclib-induced apoptosis and anti-tumor activity by co-targeting COX-2/NF-κB and PI3K/AKT/mTOR pathways in hormone receptor-positive/HER2-negative breast cancer.

Hormone receptor‐positive/HER2‐negative (HR+/HER2−) breast cancer accounts for the majority of breast tumours, and cyclin‑dependent kinase 4/6 (CDK4/6) inhibitors such as ribociclib have improved patient outcomes. However, their benefit is limited by resistance and dose‑limiting toxicities, while COX‑2-associated inflammatory signaling and downstream NF‑κB and PI3K/AKT/mTOR pathways contribute to cancer cell survival. We therefore examined whether the clinically available COX‑2 inhibitor celecoxib enhances ribociclib’s anti‑tumour activity in preclinical HR+/HER2− models, primarily through in vitro mechanistic evaluation. HR+/HER2− breast cancer cells were treated with celecoxib, ribociclib or both, and cell viability, clonogenic growth, cell‑cycle distribution and apoptosis were assessed alongside RT‑qPCR and western blotting. Drug interactions were analyzed using Chou–Talalay synergy analysis. Celecoxib plus ribociclib significantly reduced proliferation and colony formation compared with single agents and yielded combination index values < 1 in multiple dose pairs, indicating synergy. The combination increased sub-G1 and Annexin V-positive cells, reduced mRNA levels of CDK1, CDK6, CCND1, CCNE1/E2, and CDC25A, and lowered p-Rb, cyclin D1, CDK4, CDK1, and E2F1 protein expression. BAX increased and BCL-2 decreased. IL1B, IL6, and TNF transcripts, p-p65, COX-2, p-PI3K, p-AKT, and p-mTOR were also reduced. In an orthotopic MCF7 xenograft model, combined treatment was associated with greater tumour growth suppression and lower Ki‑67, p‑Rb, COX‑2 and p‑AKT expression than monotherapy, without additional toxicity under the experimental conditions tested. These findings show that celecoxib is associated with enhanced ribociclib‑induced apoptosis and anti‑tumour activity, accompanied by coordinated modulation of cell-cycle, apoptotic, inflammatory, and survival pathways. To our knowledge, this is the first report of a celecoxib–CDK4/6 inhibitor combination in HR+/HER2− breast cancer, providing a mechanistic basis for further evaluation in more biologically robust preclinical models.