Ascorbate-based biomarkers for predicting radiation response in prostate cancer

描述（由申请人提供）：在过去十年中，在使用超极化（HP）13 C光谱表征体内代谢方面取得了显著进展，对人类癌症的诊断和治疗具有深远意义。大多数研究集中于乳酸脱氢酶（LDH）对[1- 13 C]丙酮酸的代谢，这在癌症中发生的程度更大，并且与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，但已开发了几种额外的超极化13 C试剂，它们是pH（13 C碳酸氢盐）、己糖代谢（[2- 13 C]果糖）和坏死（[1，4 - 13 C]富马酸盐）的潜在标志物。最近，我们开发了氧化还原传感器[1- 13 C]脱氢抗坏血酸（DHA），这是一种氧化形式的维生素C，与葡萄糖具有相同的摄取机制。该新探针证明在体内可快速还原为[1- 13 C]维生素C，是用于本R 01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，肿瘤积累了大量的GSH和其他抗氧化剂，从而对ROS依赖性疗法（包括辐射）产生抗性。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和其他氧化还原组分与耐药性有关，以及（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，使用HP [1- 13 C] DHA进行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，文献中的许多报告已经确定，DHA还原为VitC是GSH介导的。然而，在体内观察到的HP [1- 13 C] DHA的还原肯定有其他氧化还原机制，我们的第一项研究将确定涉及哪些细胞氧化还原（或转运）组分（具体目标1）。然后，我们将转向验证HP [1- 13 C] DHA用于确定癌症侵袭性的研究，并预测小鼠前列腺癌（TRAMP）模型对放射治疗的反应（具体目标2）。最后，我们将比较这种新的13 C探针与相关的18 F抗坏血酸盐以及[2-脱氧-2-18 F]氟-D-葡萄糖（FDG），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（特定目标3）。我们预计HP 13 C MRI将成为补充现有分子成像方法（包括PET）的重要技术，并且比较研究（采用结构或机械相关的探针）对于验证两种方法都很重要。我们追求18F抗坏血酸盐的理由 探针是双重的：（1）确定基于抗坏血酸盐的PET探针是否表现出与HP [1- 13 C] DHA相似的体内特征，和（2）比较PET和HP方法预测前列腺癌中肿瘤侵袭性/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.