Ascorbate-based biomarkers for predicting radiation response in prostate cancer

描述（由申请人提供）：在过去的十年中，使用超极化（HP）13C光谱表征体内代谢方面取得了显着的进展，对人类癌症的诊断和治疗具有深远的影响。大多数研究都集中在乳酸脱氢酶（LDH）对[1-13C]丙酮酸的代谢上，这种代谢在癌症中发生的程度更大，并且与小鼠前列腺肿瘤模型中的病理分级相关。尽管动态核极化 (DNP) 的分子要求相当严格，但已经开发了几种额外的超极化 13C 试剂，它们是 pH（13C 碳酸氢盐）、己糖代谢（[2-13C] 果糖）和坏死（[1,4-13C] 富马酸盐）的潜在标记。最近，我们开发了氧化还原传感器 [1-13C] 脱氢抗坏血酸 (DHA)，它是维生素 C 的氧化版本，与葡萄糖具有相同的吸收机制。这种新探针展示了在体内快速还原为 [1-13C] 维生素 C，并且是用于实现 R01 提案特定目标的主要药剂。在拟议的项目中，这种新探针用于解决肿瘤的氧化还原适应问题，肿瘤会积累大量的谷胱甘肽和其他抗氧化剂，从而赋予对ROS依赖性疗法（包括放射疗法）的抵抗力。选择前列腺癌是因为（1）放射治疗是主要治疗方法（2）一些体外研究表明谷胱甘肽和其他氧化还原成分与耐药性有关，（3）缺乏疾病侵袭性的非侵入性生物标志物。我们使用高分辨率魔角旋转 (HR-MAS) NMR 对原发性前列腺癌细胞进行的初步 1H 研究表明 GSH 水平较高，而使用 HP [1-13C] DHA 的体内小鼠研究表明已知富含 GSH 的器官（包括肝脏、肾脏和大脑）减少。此外，文献中的大量报告已证实 DHA 还原为 VitC 是 GSH 介导的。然而，其他氧化还原机制当然也可能用于体内观察到的 HP [1-13C] DHA 的减少，我们的第一项研究将确定涉及哪些细胞氧化还原（或运输）成分（具体目标 1）。然后，我们将转向验证使用 HP [1- 13C] DHA 来确定癌症侵袭性并预测小鼠前列腺癌 (TRAMP) 模型中放射治疗的反应的研究（具体目标 2）。最后，我们将这种新的 13C 探针与相关的 18F 抗坏血酸盐以及[2-脱氧-2-18F]氟-D-葡萄糖 (FDG) 进行比较，后者是绝大多数临床正电子发射断层扫描 (PET) 研究中使用的放射性同位素（具体目标 3）。我们预计 HP 13C MRI 将成为补充现有分子成像方法（包括 PET）的重要技术，而比较研究（采用结构或机械相关的探针）对于验证这两种模式非常重要。我们追求 18F 抗坏血酸的理由 探针具有双重作用：(1) 确定基于抗坏血酸的 PET 探针是否表现出与 HP [1-13C] DHA 相似的体内特性；(2) 比较 PET 和 HP 方法预测前列腺癌肿瘤侵袭性/治疗反应的能力。

DESCRIPTION (provided by applicant): Remarkable progress has been made over the last decade in the characterization of in vivo metabolism using hyperpolarized (HP) 13C spectroscopy, with profound implications for the diagnosis and treatment of human cancers. The majority of studies have focused on metabolism of [1-13C] pyruvate by lactate dehydrogenase (LDH), which occurs to a larger extent in cancer and has been correlated with pathologic grade in a murine prostate tumor model. Although the molecular requirements of dynamic nuclear polarization (DNP) are rather strict, several additional hyperpolarized 13C agents have been developed that are potential markers for pH (13C bicarbonate), hexose metabolism ([2-13C] fructose), and necrosis ([1,4-13C] fumarate). More recently, we have developed the redox sensor [1-13C] dehydroascorbate (DHA), an oxidized version of Vitamin C that shares an uptake mechanism with glucose. This new probe demonstrates rapid in vivo reduction to [1-13C] Vitamin C, and is the principal agent used for the Specific Aims of this R01 proposal. In the proposed project, this new probe is employed to address the redox adaptation of tumors, which accumulate large quantities of GSH and other antioxidants, conferring resistance to therapies that are ROS- dependent, including radiation. Prostate cancer was chosen since (1) radiation therapy is a mainstay of treatment (2) several in vitro studies have implicated GSH and other redox components in resistance and (3) non-invasive biomarkers for disease aggressiveness are lacking. Our preliminary 1H studies on primary prostate cancer cells using high resolution magic-angle spinning (HR-MAS) NMR indicate high levels of GSH, and in vivo murine studies using HP [1-13C] DHA demonstrate reduction in organs that are known to be rich in GSH, including the liver, kidneys, and brain. Furthermore, numerous reports in the literature have established that reduction of DHA to VitC is GSH-mediated. However, other redox mechanisms are certainly possible for the reduction of HP [1-13C] DHA observed in vivo, and our first studies will determine which cellular redox (or transport) components are involved (Specific Aim 1). We will then turn to studies validating the use of HP [1- 13C] DHA to determine cancer aggressiveness, and predict response to radiation therapy in a murine prostate cancer (TRAMP) model (Specific Aim 2). Finally, we will compare this new 13C probe to related 18F ascorbates as well as to [2-deoxy-2-18F] fluoro-D-glucose (FDG), the radioisotope used in the vast majority of clinical positron emission tomography (PET) studies (Specific Aim 3). We anticipate HP 13C MRI emerging as an important technology to complement existing molecular imaging methods, including PET, and comparative studies (employing structurally or mechanistically related probes) will be important to validate both modalities. Our justification for pursuing 18F ascorbate probes is twofold: (1) to determine whether ascorbate-based PET probes demonstrate similar in vivo characteristics to HP [1-13C] DHA and (2) to compare the ability of PET and HP methods to predict tumor aggressiveness/ treatment response in prostate cancer.