Amino Acid Transport and the Biology of Human Gliomas

描述(申请人提供)：胶质瘤是最常见和最致命的原发脑肿瘤。对许多患者来说，顽固性头痛和癫痫发作是早期症状。癫痫发作发生在与肿瘤相关的“瘤周”脑中，在低级别胶质瘤中尤其常见，在低级别胶质瘤中，高达90%的患者存在自发性反复发作，或通常难以治疗的“瘤周癫痫”。在这笔赠款的前一个资金周期中提出的中心假说假设，癫痫发作是由于胶质瘤故意将谷氨酸释放到瘤周脑中，导致神经元谷氨酸受体异常激活，随着时间的推移，谷氨酸导致与肿瘤相关的大脑区域变得高度兴奋。推测谷氨酸通过XC-(SXC)胱氨酸-谷氨酸交换系统被释放到肿瘤细胞中，作为摄取胱氨酸的必备副产物。此外，肿瘤可能会吸收邻近的星形胶质细胞或招募小胶质细胞来释放谷氨酸。这项建议的主要问题是，这两个细胞中的任何一个释放谷氨酸是否以及如何机械地参与癫痫发作的启动。这个问题将通过比较高或低SXC表达、shRNA沉默或药物抑制的人异种移植瘤小鼠的癫痫表型来解决。癫痫发作发展的时间过程将通过脑电/视频监测记录下来，期望减少SXC的表达可以推迟癫痫发作并降低癫痫发作的严重程度。为了研究神经元超兴奋性的细胞变化，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的急性脑片进行生物物理学研究。这些结果将得到来自300多名人类胶质瘤患者的活检和组织微阵列的生化和免疫组织化学分析的补充，以寻找与谷氨酸释放、重新摄取或分解代谢有关的蛋白质的变化。如果证实谷氨酸在癫痫发作启动中的作用，FDA批准的两种药物柳氮磺吡啶和塔拉帕德的上市将抑制谷氨酸释放或谷氨酸受体，从而使患者的临床治疗得以快速转化。以往对胶质瘤的研究几乎都集中在高级别胶质瘤上，因此，本研究的一个新目标是更有效地处理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.