Mitochondrial uncoupling, energy substrate utilization, and brown adipose tissue as therapeutic targets in cancer

Mitochondria play a central role in regulating cellular energy metabolism, redox homeostasis, and biosynthesis. Mitochondrial uncoupling, through the alteration in the permeability of the inner mitochondrial membrane (IMM) to the leak of protons without adenosine triphosphate (ATP) synthesis, regulates thermogenesis, glucose and lipid metabolism, and reactive oxygen species (ROS) generation. In brown adipose tissue (BAT), proton leak via uncoupling protein 1 (UCP1) is essential for thermogenesis and has been shown to improve systemic glucose homeostasis, and recent studies indicate that BAT activation can also suppress tumor growth by competing with cancer cells for glucose. Several small-molecule mitochondrial uncouplers have demonstrated anticancer effects in preclinical models, although endogenous UCPs-particularly UCP2-are often upregulated in tumors, where they may support tumor growth by buffering ROS and increasing metabolic flexibility. These seemingly contradictory observations highlight the context-dependent effects of mitochondrial uncoupling in cancer. Here, we review current understanding of mitochondrial uncoupling mechanisms, the roles of UCP isoforms, and the metabolic interplay between BAT, cancer cells, and the tumor microenvironment, with a focus on therapeutic implications.