Systemic cyst(e)inase administration induces ferroptosis and synergizes with temozolomide in glioblastoma

Glioblastoma exhibits profound therapeutic resistance, driven by tumor heterogeneity and highly plastic glioma stem cells (GSCs). This study exploits GSC metabolic dependence on cysteine using systemic cyst(e)inase, a cysteine-degrading enzyme. In patient-derived GSCs and orthotopic xenograft models, cyst(e)inase potently inhibited GSC proliferation and extended animal survival by inducing ferroptosis. Mechanistically, cyst(e)inase triggered elevated reactive oxygen species (ROS), glutathione (GSH) depletion, and significant lipid peroxidation. Crucially, these effects were reversed by N-acetylcysteine (NAC), and lipid peroxidation was abrogated by the iron chelator deferoxamine (DFX), unequivocally confirming iron-dependent ferroptosis. Characteristic mitochondrial morphological changes further validated ferroptosis induction. Acyl-CoA synthetase long-chain family member-4 (ACSL4) was identified as essential for this process. Critically, cyst(e)inase synergized with temozolomide (TMZ), markedly enhancing its anti-tumor efficacy and prolonging survival, even in TMZ-resistant xenografts. These findings establish cysteine metabolism as a promising therapeutic target and position cyst(e)inase, especially with TMZ, as a potent strategy to overcome GBM resistance.