Tamoxifen and Colchicine Alter Mitochondrial Respiration toInduce Cell Death in Low-metastatic Breast Cancer Cells

Background: Breast cancer cells exhibit mitochondrial respiration-mediated metabolic heterogeneity and tumour aggressiveness. Tamoxifen and Colchicine are known to interfere with oxidative stress in breast cancer cells. However, their role in regulating mitochondrial respiration remains poorly understood. Methods: MCF7 and MDA-MB-231 cells were used to analyse the metabolic modulatory effects of Tamoxifen and Colchicine. The roles of Tamoxifen and Colchicine in regulating ROS production, mitochondrial membrane potential, mitochondrial membrane integrity, and oxidative phosphorylation were assessed using ROS assay, JC-1 assay, and high-resolution respirometry, respectively. Their effects on mitochondrial biogenesis and mitochondria-dependent cytotoxicity were analysed using flow cytometry and confocal microscopy. Results: Tamoxifen and Colchicine exhibited cytotoxic effects by reducing ROS production, depolarising mitochondrial membrane potential, decreasing oxygen consumption, and inhibiting mitochondrial respiration. They specifically downregulated pyruvate-mediated mitochondrial respiration, preventing N-linked state mitochondrial respiration and reducing complex I activity. Colchicine demonstrated mitochondrialindependent cytotoxic effects, whereas Tamoxifen did not. Neither drug impacted mitochondrial membrane integrity. Tamoxifen and Colchicine decreased leak respiration, inhibited proton and electron transfer, and prevented non-phosphorylating electron transfer, potentially due to reduced complex I activity. Tamoxifen significantly inhibits mitochondrial biogenesis and induces a mitochondrial-dependent cell death pathway. In contrast, Colchicine had a low impact on mitochondrial biogenesis and induced a mitochondrial-independent cell death pathway. Discussion: Tamoxifen and colchicine suppress complex I–driven mitochondrial respiration in breast cancer cells, reducing oxidative phosphorylation–associated aggressiveness. Notably, only tamoxifen links this metabolic inhibition to impaired mitochondrial biogenesis and mitochondria-dependent cytotoxicity. Conclusion: Tamoxifen and colchicine downregulate mitochondrial respiration and biogenesis, while only tamoxifen induces mitochondrial-dependent cytotoxicity.