Amino Acid Transport and the Biology of Human Gliomas

描述（申请人提供）：胶质瘤是最常见、最致命的原发性脑肿瘤。对于许多患者来说，顽固性头痛和癫痫发作是早期症状。癫痫发作源于肿瘤相关的“瘤周”脑，在低级别胶质瘤中尤其常见，高达90%的患者表现为自发复发性癫痫发作，或通常难以治疗的“瘤周癫痫”。在此资助的前一个资助周期中形成的中心假设认为癫痫发作是由神经胶质瘤故意释放谷氨酸到肿瘤周围的大脑引起的，引起异常的神经元谷氨酸受体激活，并且随着时间的推移，谷氨酸导致肿瘤相关的大脑区域变得过度兴奋。据推测，谷氨酸作为胱氨酸摄取到肿瘤细胞的强制性副产物通过xc- (SXC)胱氨酸-谷氨酸交换器系统释放。此外，肿瘤可能会选择邻近的星形胶质细胞或招募小胶质细胞释放谷氨酸。这些细胞中的谷氨酸释放是否以及如何在机制上参与癫痫发作的启动是本提案的主要问题。这个问题将通过比较由高或低表达的SXC、shRNA沉默或药物抑制的人类异种移植物产生的荷瘤小鼠的癫痫表型来解决。脑电图/视频监测将记录癫痫发作的时间过程，期望减少SXC表达延迟癫痫发作并降低癫痫发作的严重程度。为了研究神经元高兴奋性背后的细胞变化，包括神经递质受体和转运体的表达和功能，将对已知癫痫状态的动物急性脑切片进行生物物理研究。这些结果将通过对300多名人类胶质瘤患者的活检和组织微阵列进行生化和免疫组织化学分析来补充，以寻找参与谷氨酸释放、再摄取或分解代谢的蛋白质的变化。如果谷氨酸在癫痫发作中的作用得到证实，FDA批准的两种药物磺胺氮嗪和Talampanel可以抑制谷氨酸释放或谷氨酸受体，应该可以快速转化为临床治疗。以往的胶质瘤研究几乎完全集中在高级别胶质瘤上，因此本研究的新目标是关注更有效地治疗低级别胶质瘤的瘤周癫痫发作，这是一个重大的临床挑战。

DESCRIPTION (provided by applicant): Glioma is the most common and deadly primary brain tumor. For many patients intractable headaches and epileptic seizures are early symptoms. Seizures arise from tumor associated "peritumoral" brain and are particularly common in low grade gliomas where up to 90% of patients present with spontaneous recurring seizures, or "peritumoral epilepsy" that is often refractory to treatment. The central hypothesis developed during the previous funding cycle of this grant posits that seizures are caused by the deliberate release of glutamate from gliomas into the peritumoral brain, causing abnormal neuronal glutamate receptor activation, and, over time, glutamate causes tumor associated brain regions to become hyperexcitable. It is hypothesized that glutamate is released as an obligatory by-product of cystine uptake into tumor cells via the system xc- (SXC) cystine-glutamate exchanger. In addition, the tumor may co-opt adjacent astrocytes or recruit microglial cells to release glutamate. Whether and how glutamate release from either of these cells is mechanistically involved in seizure initiation is the principle question of this proposal. This question will be addressed by comparing the seizure phenotype of tumor bearing mice generated from human xenografts with high or low SXC expression, shRNA silencing or pharmacological inhibition. The time-course of seizure development will be documented by EEG/video monitoring with the expectation that reduced SXC expression delays seizure onset and reduces seizure severity. To study cellular changes underlying the neuronal hyperexcitability, including neurotransmitter receptor and transporter expression and function, acute brain slices from animals with known seizure status will be studied biophysically. These results will be complemented by biochemical and immunohistochemical analysis of biopsies and tissue micro arrays from over 300 human glioma patients to search for changes in proteins involved in glutamate release, reuptake or catabolism. If a role for glutamate in seizure initiatio is confirmed, the availability of two FDA approved drugs, Sulfasalazine and Talampanel that inhibit either glutamate release or glutamate receptors should allow for a rapid translation towards clinical treatment of patients. Previous glioma research has almost exclusively focused on high grade gliomas and hence a novel objective of this study is a focus on a more effective management of peritumoral seizures in low grade gliomas, which present a significant clinical challenge.