Cysteine Depletion-induced Ferroptosis as a Therapeutic Vulnerability i

胶质母细胞瘤是成人中最恶性和最常诊断的原发性脑肿瘤， 中位生存期只有14到16个月2005年，Stupp方案改变了临床 关心的发现，化疗药物替莫唑胺（TMZ），加上 手术和放疗可以延长病人的生存期然而，新的治疗途径 仍然停滞不前，没有二线治疗选择显示出显着改善 在复发性GBM肿瘤中，对TMZ的耐药性是一致致命的。为此，我们努力改善 了解TMZ耐药疾病的分子机制，为患者提供潜在的 二线治疗选择，重点关注TMZ中半胱氨酸缺失诱导的铁凋亡- 耐药GBM。铁凋亡是一种铁依赖性的细胞死亡形式， 注意力作为一个有吸引力的途径，以消除其他耐药癌细胞。我们 初步数据支持了以前未表征的代谢酶在 诱导半胱氨酸耗竭诱导的铁凋亡。我们的发现强烈地表明伽马射线 （γ）-谷氨酰酶（γ-谷氨酰环化转移酶; GGCT）可降解半胱氨酸， 谷胱甘肽（GSH）的生产-γ-谷氨酰途径的主要目标。我们进一步表明， TMZ耐药细胞具有与对铁凋亡诱导的敏感性一致的变化，例如， 活性氧（ROS）、半胱氨酸摄取和半胱氨酸/谷氨酸反向转运蛋白增加 - xCT以及错误定位的核周线粒体。因此，我们试图重新利用 依布硒啉，一种以前被认为是谷胱甘肽的神经保护剂 过氧化物酶4（GPX 4）模拟物，但最近因其硒离子的能力而引起关注， 共价结合半胱氨酸。我们发现，神经保护剂依布硒啉已经 已被证明可以穿过血脑屏障-GBM治疗的主要障碍-特别是 体外靶向TMZ抗性GBM细胞。基于这些结果，我们建议进一步研究 通过GGCT的半胱氨酸再循环的作用及其作为治疗弱点的治疗潜力 在患者来源的异种移植物（PDX）TMZ抗性GBM原位临床前动物模型中。 最后，我们试图建立这种异常的半胱氨酸再循环的预后生物标志物， 临床胶质瘤标本中GGCTs酶活性的代谢副产物。总体而言，这 该提案将深入了解耐药GBM中铁凋亡诱导的新途径， 可能为其他耐药细胞中半胱氨酸缺失诱导的铁凋亡铺平道路。 癌的

Glioblastoma is the most malignant and commonly diagnosed primary brain tumor in adults with a dismal median overall survival of 14 to 16 months. In 2005 the Stupp regimen changed clinical care with the discovery that the chemotherapeutic drug temozolomide (TMZ), with the addition of surgery and radiation, could extend patient survival. However, new therapeutic avenues have remained stagnant and with no second-line therapeutic options showing significant improvement in recurrent GBM tumors, resistance to TMZ is uniformly fatal. To this end we sought to better understand the molecular mechanisms of TMZ-resistant disease to provide patients a potential second-line therapeutic option with a focus on cysteine depletion-induced ferroptosis in TMZ- resistant GBM. Ferroptosis is an iron-dependent form of cell death which has recently gained attention as an attractive avenue to eradicate otherwise drug resistant cancer cells. Our preliminary data support the role of a previously uncharacterized metabolic enzyme in the induction of cysteine depletion-induced ferroptosis. Our findings strongly suggest that the gamma (γ)-glutamyl enzyme (γ-glutamylcyclotransferase; GGCT) recycles cysteine and prevents glutathione (GSH) production – the main goal of the γ-glutamyl pathway. We further show that TMZ-resistant cells have changes consistent with a sensitivity to ferroptosis induction such as an increase in reactive oxygen species (ROS), cysteine uptake and the cysteine/glutamate antiporter – xCT, as well as mislocalized perinuclear mitochondria. Therefore, we sought to repurpose ebselen, a previously characterized neuroprotective agent that was thought to be a glutathione peroxidase 4 (GPX4) mimetic but has recently garnered attention for its selenium ion’s ability to covalently bind cysteines. We show that the neuroprotective agent ebselen which has already been shown to cross the blood brain barrier – a major hurdle for GBM treatment – specifically targets TMZ-resistant GBM cells in vitro. Based on these results, we propose to further investigate the role of cysteine recycling via GGCT and its therapeutic potential as a treatment vulnerability in patient-derived xenograft (PDX) TMZ-resistant GBM orthotopic pre-clinical animal models. Lastly, we seek to establish prognostic biomarkers of this aberrant cysteine recycling through a metabolic byproduct of GGCTs enzymatic activity in clinical glioma specimens. Overall, this proposal will give insight into a new avenue of ferroptosis induction in drug resistant GBM, and potentially pave the way for cysteine deprivation-induced ferroptosis in other drug resistant cancers.