Discovery of a novel, covalent and heterobifunctional thioredoxin reductase inhibitor with antitumor activity

Reactive oxygen species (ROS) play a central role in cellular signaling and homeostasis. However, imbalances in ROS levels contribute to various pathologies, including cancer. Tumor cells often upregulate antioxidant systems, such as the thioredoxin reductase (TrxR) and glutathione (GSH) pathways, to buffer against oxidative stress. The identification of aberrant metabolism and ROS has generated excitement and promise as a hallmark targetable vulnerability of tumors. Unfortunately, despite tremendous academic and industry efforts, this promise remains unfulfilled. Here, we report the discovery of YS207, a first-in-class covalent heterobifunctional inhibitor of TrxR1 using the deubiquitinase-targeting chimera (DUBTAC) technology. YS207 is composed of TrxR1 recruiting moiety coupled to deubiquitinase recruiting moiety via a novel chemical linker resulting in stabilization of covalently inhibited TrxR1 for profound generation of therapeutic levels of ROS. YS207 treatment potently inhibited TrxR1 enzymatic activity in vitro and in vivo (IC 50 of 40nM & 700nM respectively). Mechanistically, YS207 elevated ROS levels, induced lipid peroxidation, and decreased intracellular GSH. Additionally, we observed profound alterations of the mitochondria including swelling, loss of cristae, increased electron density and prominent mitophagy, all characteristic of oxidative damage by using transmission electron microscopy (TEM). Rescue experiments with the ROS scavenger N-acetyl cysteine (NAC) confirmed that YS207-induced cell death was ROS-dependent. Large-scale PRISM profiling across 885 cancer cell lines revealed that sensitivity to YS207 strongly correlates with TrxR1 dependency, NADPH metabolism, and selenoprotein biosynthesis pathways. Notably, dual knockout of TrxR1 and GPX4 partially rescued YS207-induced cytotoxicity, underscoring a cooperative role in redox regulation. Further, we showed promising anti-tumor growth inhibitory activity of YS207 in xenograft models of lung cancer. Taken together, our results demonstrate that YS207 is a potent ROS modulator with potential antitumor activities through novel mechanism of action. We aim to pursue further development of this class of molecules in tumors with enhanced vulnerability to redox imbalance.