Project 3: Metabolic imaging of TERT expression

摘要 端粒酶逆转录酶（TERT）使端粒延长，这是连续细胞生长所必需的。 增殖与TERT启动子中的激活突变相关的TERT表达，在人结肠癌中观察到。 几乎所有的胶质母细胞瘤和少突胶质细胞瘤病例。这使得端粒酶逆转录酶成为最常见的基因改变 以及一个新的治疗靶点。因此，非侵入性的TERT表达成像可以帮助 在区分假进展和复发性胶质瘤方面，并提供了一种非侵入性生物标志物， 通过TERT抑制剂评估治疗功效。然而，迄今为止，没有平移成像方法用于 已经报道了TERT表达。项目3的目标是通过开发 代谢成像生物标志物的TERT表达。我们的方法是基于以前的报告， TERT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， 确定其他代谢改变具体来说，我们发现1H磁共振光谱 （MRS）-可检测的谷胱甘肽水平和13 C MRS-可检测的超极化代谢 脱羟基抗坏血酸与维生素C的比率在表达TERT的细胞中升高。此外，超极化13 C MRS- 通过磷酸戊糖途径生成6-磷酸葡萄糖酸的葡萄糖和葡内酯的可检测流量是 天冬氨酸和磷酸腺苷的水平也会升高。因此，我们假设， 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 实质和肿瘤细胞，其中TERT表达通过治疗沉默。我们将检验这一假设 如下在目标1中，我们将确定1H MRS和超极化13 C MRS代谢成像生物标志物， 通过研究仅在它们的TERT状态上不同的细胞系， 如果MRS可检测的与氧化还原相关的代谢生物标志物的水平以及其他代谢变化可以 区分TERT表达细胞和TERT非表达细胞。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通过使用具有以下特征的小鼠模型来监测体内TERT表达： 原位表达TERT的脑肿瘤，通过遗传和/或药理学途径抑制TERT表达 方法，并确定是否可以使用1H和/或超极化13 C MRS评估这种抑制 氧化还原的生物标志物。如果细胞研究表明其他代谢途径也受到TERT的调节， 在体内进行研究。在目标3中，我们将通过以下方式研究将TERT表达与代谢联系起来的机制： 评估已知与TERT表达相关的细胞过程，并确定这些过程是否 与氧化还原相关的代谢途径或其他MRS可检测的 代谢途径的改变。我们的研究有望导致可翻译的MRS检测代谢 这是一种可以改善神经胶质瘤患者治疗和预后的TERT表达生物标志物。

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.