Ascorbate-based biomarkers for predicting radiation response in prostate cancer

描述(申请人提供)：在过去十年中，利用超极化(HP)~(13)C光谱学表征体内代谢已取得显著进展，对人类癌症的诊断和治疗具有深远的意义。大多数研究集中在乳酸脱氢酶(LDH)对[1-13C]丙酮酸的代谢，乳酸脱氢酶在癌症中存在较大程度，并与小鼠前列腺癌模型的病理分级相关。尽管动态核极化(DNP)的分子要求相当严格，但一些额外的超极化13C试剂已经被开发出来，它们是pH(13C重碳酸盐)、己糖代谢([2-13C]果糖)和坏死([1，4-13C]富马酸)的潜在标记物。最近，我们开发了氧化还原传感器[1-13C]脱氢抗坏血酸(DHA)，这是维生素C的氧化版本，与葡萄糖具有相同的摄取机制。这一新的探针显示了体内快速还原为[1-13C]维生素C，是用于R01提案特定目的的主要试剂。在拟议的项目中，这种新的探针被用来解决肿瘤的氧化还原适应问题，它积累了大量的GSH和其他抗氧化剂，使人对包括辐射在内的依赖ROS的治疗产生抵抗。选择前列腺癌是因为(1)放射治疗是治疗的主要手段；(2)几项体外研究表明GSH和其他氧化还原成分与耐药性有关；(3)缺乏反映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)核磁共振对原代前列腺癌细胞进行的初步1H研究表明，GSH水平很高，而使用HP[1-13C]DHA进行的小鼠体内研究表明，包括肝脏、肾脏和大脑在内的已知富含GSH的器官减少。此外，大量文献报道已证实DHA还原为VitC是由GSH介导的。然而，对于体内观察到的HP[1-13C]DHA的减少，其他氧化还原机制当然是可能的，我们的第一项研究将确定哪些细胞氧化还原(或运输)成分参与(特定目标1)。然后，我们将转向验证使用HP[1-13C]DHA来确定癌症侵袭性的研究，并在小鼠前列腺癌(TRAMP)模型中预测对放射治疗的反应(特定目标2)。最后，我们将把这种新的13C探针与相关的18F抗坏血酸以及[2-脱氧-2-18F]氟-D-葡萄糖(FDG)进行比较，FDG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(特定目标3)。我们预计，HP 13C MRI将成为补充现有分子成像方法(包括PET)的一项重要技术，比较研究(使用结构或机械相关的探针)将对验证这两种方法至关重要。我们追求18F抗坏血酸的理由 我们的研究包括两个方面：(1)确定基于抗坏血酸的PET探针是否表现出与HP[1-13C]DHA相似的体内特征；(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.