Dual inhibition of xCT and GGCT induces ferroptosis in glioblastoma cells by depleting cysteine and disrupting redox homeostasis

Glioblastoma is the most aggressive and treatment-resistant brain tumor. Ferroptosis, an iron-dependent form of regulated cell death caused by lipid peroxidation, has emerged as a promising therapeutic strategy; however, intrinsic resistance to ferroptosis limits its therapeutic efficacy. Here, we demonstrate that metabolic depletion of cysteine through dual inhibition of exogenous and endogenous sources represents a novel approach to overcome this resistance. While inhibition of xCT suppresses cystine uptake and induces ferroptosis, we identified γ-glutamylcyclotransferase (GGCT), a key enzyme in glutathione (GSH) degradation, as a metabolic compensation pathway that regenerates cysteine to sustain redox homeostasis. Blocking both xCT and GGCT synergistically depleted intracellular cysteine and GSH, leading to excessive accumulation of reactive oxygen species (ROS), lipid peroxidation, and ferroptotic cell death in glioblastoma cells. Importantly, dual inhibition markedly suppressed tumor growth in vivo and enhanced oxidative stress in tumor tissues, as evidenced by 4-hydroxynonenal accumulation. These findings uncover a previously unrecognized mechanism by which GGCT confers ferroptosis resistance by maintaining intracellular redox balance. Targeting the xCT-GGCT axis effectively disrupts redox homeostasis and eliminates metabolic plasticity that underlies ferroptosis resistance in glioblastoma. This study provides a mechanistic and translational rationale for developing dual inhibition of xCT and GGCT as a promising therapeutic strategy against this lethal and therapy-refractory cancer.