Project 3: Metabolic imaging of TERT expression

摘要 端粒酶逆转录酶(TERT)使端粒延长，这是连续细胞所必需的 扩散。观察到与激活TERT启动子突变相关的TERT表达 几乎所有的胶质母细胞瘤和少突胶质细胞瘤病例。这使得TERT成为最常见的基因改变 和一种新的治疗靶点。因此，对TERT表达的非侵入性成像可能有助于 在鉴别假性进展和复发胶质瘤方面，并提供了一种非侵入性生物标志物 端粒酶逆转录酶抑制剂的疗效评价。然而，到目前为止，还没有转换成像方法来 TERT的表达已有报道。项目3的目标是通过开发 TERT表达的代谢成像生物标志物。我们的方法是基于之前的报告显示 TERT的表达与细胞氧化还原的控制有关，我们的初步数据证实了这一发现和 确定额外的代谢变化。具体地说，我们发现1H磁共振波谱 (MRS)可检测的谷胱甘肽水平和超极化的~(13)C MRS可检测的代谢 在表达TERT的细胞中，脱羟基抗坏血酸与维生素C的比例升高。此外，超极化~(13)C-MRS- 葡萄糖和葡萄糖内酯通过磷酸戊糖途径转化为6-磷酸葡萄糖酸盐的可检测通量为 天冬氨酸和腺苷磷酸水平升高。因此我们假设先进的 MRS代谢成像可用于区分表达TERT的胶质瘤细胞和正常脑组织 实质组织和肿瘤细胞中TERT的表达因治疗而沉默。我们将检验这一假设 具体如下。在目标1中，我们将识别1H MRS和超极化13C MRS代谢成像生物标记物 通过研究仅在TERT状态上不同的细胞系并确定 如果与氧化还原和其他代谢变化相关的MRS可检测代谢生物标志物的水平可以 区分表达TERT和不表达TERT的细胞。在目标2中，我们将确定MRS是否- 可检测的氧化还原生物标志物可用于监测体内TERT的表达，方法是使用 原位表达TERT的脑肿瘤，通过遗传和/或药物抑制TERT的表达 方法，并确定这种抑制是否可以用1H和/或超极化13C MRS来评估 氧化还原的生物标志物。如果细胞研究表明其他新陈代谢途径受到TERT的调节，这些途径也将 在活体内被研究。在目标3中，我们将通过以下方式研究TERT表达与代谢之间的联系机制 评估已知与TERT表达相关的细胞过程并确定这些过程 与氧化还原相关的代谢途径或其他MRS可检测到的变化有机械联系 TERT改变了代谢途径。我们的研究有望导致可翻译的MRS-可检测的代谢 TERT表达的生物标记物可以改善胶质瘤患者的治疗和预后。

ABSTRACT Telomerase reverse transcriptase (TERT) enables telomere elongation that is essential for continuous cell proliferation. TERT expression that is associated with activating mutations in the TERT promoter, is observed in virtually all glioblastoma and oligodendroglioma cases. This makes TERT the most common genetic alteration in brain tumors, and a novel therapeutic target. Noninvasive imaging of TERT expression could therefore help in distinguishing between pseudo-progression and recurrent glioma, and provide a noninvasive biomarker for assessment of treatment efficacy by TERT inhibitors. However, to date, no translational imaging approaches for TERT expression have been reported. The goal of Project 3 is to address this critical need by developing metabolic imaging biomarkers of TERT expression. Our approach is based on previous reports showing that TERT expression is associated with control of cellular redox, and our preliminary data confirming this finding and identifying additional metabolic alterations. Specifically, we have found that 1H magnetic resonance spectroscopy (MRS)-detectable levels of glutathione and the 13C MRS-detectable metabolism of hyperpolarized dehydroxyascorbate to vitamin C, are elevated in TERT-expressing cells. Additionally, hyperpolarized 13C MRS- detectable fluxes of glucose and gluconolactone via the pentose phosphate pathway to 6-phosphogluconate are elevated, as are the levels of aspartate and adenosine phosphates. We therefore hypothesize that advanced MRS metabolic imaging could be used to distinguish glioma cells expressing TERT from normal brain parenchyma and from tumor cells in which TERT expression is silenced by treatment. We will test this hypothesis as follows. In Aim 1 we will identify 1H MRS and hyperpolarized 13C MRS metabolic imaging biomarkers that are associated with TERT expression by investigating cell lines that differ only in their TERT status and determining if levels of MRS-detectable metabolic biomarkers associated with redox, and other metabolic changes can distinguish TERT-expressing from TERT non-expressing cells. In Aim 2 we will determine whether MRS- detectable biomarkers of redox can be used to monitor TERT expression in vivo by using mouse models with orthotopic TERT-expressing brain tumors, inhibiting TERT expression via genetic and/or pharmacological approaches, and determining if this inhibition can be assessed using 1H and/or hyperpolarized 13C MRS biomarkers of redox. If cell studies show that other metabolic pathways are modulated by TERT, these will also be investigated in vivo. In Aim 3 we will investigate mechanisms linking TERT expression with metabolism by assessing cellular processes known to be associated with TERT expression and determining if these processes are mechanistically linked to changes in redox-associated metabolic pathways or other MRS-detectable metabolic pathways altered by TERT. Our study is expected to lead to translatable MRS-detectable metabolic biomarkers of TERT expression that could improve glioma patient treatment and outcome.