Tramadol induced hypoxia signaling and paraptosis-like cell death in breast cancer cells via HIF-1α and ATF4 dependent pathways

OBJECTIVES: Tramadol, a clinically approved analgesic widely used for managing postoperative pain, has recently been shown to possess anticancer properties in several tumor models, especially in breast cancer. In this study, we explored the intricate molecular mechanisms by which tramadol induces cytotoxicity in breast cancer cell lines. METHODS: Two invasive ductal carcinoma lines MCF-7 and MDA-MB-231 were used to verify the molecular cytotoxicity of tramadol using cell viability analysis, flow cytometry analysis, real-time polymerase chain reaction, western blotting, Seahorse biogenetic, and transmission electron microscopy analyses. RESULTS: Our findings demonstrate that tramadol induces the normoxic stabilization and nuclear translocation of hypoxia-inducible factor- 1 alpha (HIF-1α) to activate hypoxia responsive genes. Concurrently, tramadol triggers endoplasmic reticulum (ER) stress and activates the p-eIF2α/ATF4/CHOP signaling axis, leading to the generation of reactive oxygen species, impaired autophagy, mitochondrial dysfunction, including mitochondrial membrane depolarization and the decline of ATP production, cytoplasmic vacuolization, and lipid droplet accumulation which is characteristics of paraptosis-like cell death. Notably, the knockout of HIF-1α or ATF4 significantly reduced tramadol-induced cytotoxicity, highlighting their crucial roles in mediating these cellular responses. CONCLUSION: Tramadol induced breast cancer cell death via paraptosis which highlights its therapeutic potential in targeting resistant cancer subtypes such as triple-negative breast cancer.