Overhauser Enhanced Magnetic Resonance Imaging (OMRI)

a)代谢MRI分析前列腺癌的糖酵解途径：使用丙酮酸的超极化（HP） MRI可以成像动力学重要的生物能量途径，如有氧糖酵解或氧化磷酸化。由于恶性细胞通过有氧糖酵解处理葡萄糖/丙酮酸，而正常细胞则依赖于氧化磷酸化，因此该成像允许使用超极化示踪剂的13C MRI无创地对体内感兴趣的区域进行生化分析。超极化桥接了体内13C MRI所需的4级灵敏度。两株人前列腺癌细胞（DU145和PC3）作为异种移植物生长。异种移植物体内[1-13C]丙酮酸全身输送后，用超极化[1-13C]-丙酮酸磁共振成像（MRSI）测量丙酮酸转化为乳酸的情况。用质谱法对异种移植肿瘤进行稳态代谢组学分析，用质子（1H）核磁共振成像（MRSI）测量稳态乳酸浓度。用FX-11抑制乳酸脱氢酶（LDH）后评估肿瘤生长情况。与PC3相比，DU145肿瘤表现出丙酮酸向乳酸转化的增强，具有超极化[1-13C]-丙酮酸MRSI，并且对LDH抑制的相应敏感性更高。我们发现前列腺癌的超极化[1-13C]-丙酮酸MRSI磁共振光谱成像（MRSI）可以预测靶向Warburg效应的疗效。b) 13c标记的5-5-二甲基-1-吡咯啉- n -氧化物的合成和评价，目的是利用超极化13C-MRI在体内检测活性氧：5,5-二甲基-1-吡咯啉- n -氧化物（DMPO）是一种自旋诱捕剂，经常用于体外检测活性氧（ROS）。在本研究中，我们合成了13C标记的DMPO用于13C MR信号增加10000倍以上的超极化13C- mri，并研究了13C标记的DMPO结合超极化13C- mri检测体内ROS的可行性。DMPO在C5位置进行13c标记，并进行氘化以延长T1弛豫时间。5-13C-DMPO-d9的总产率为15%。超极化的5- 13c - dpo -d9在13c光谱上在76 ppm处呈现单峰，在磷酸盐缓冲液中T1弛豫时间为60秒。将超极化5-13C- dpo -d9溶液注射到放置在3T扫描仪上的小鼠体内，每1秒采集一次13C光谱，在活体小鼠体内检测到5-13C- dpo -d9的信号，超极化5-13C- dpo -d9在小鼠体内的13C信号T1衰减为29秒。13C化学位移成像显示5-13C- dpo -d9在静脉注射后1分钟内分布在小鼠体内。5- 13c - dpo -d9在心脏/肺和肾脏中检测到较强的信号，而在肝脏中的信号相对于其他器官较小。结果表明，超极化5-13C-DMPO-d9在小鼠体内提供了足够的可检测的13C信号，可以应用于一些疾病模型，评估其在体内检测ROS的能力。c)小鼠胰腺肿瘤异种移植物微环境的分子成像指导放疗或缺氧激活前药的治疗策略：胰腺导管腺癌（pancreatic ductal adenocarmicoma， PDAC）的特点是缺氧壁龛，导致治疗抵抗。因此，对肿瘤氧合和代谢谱的研究将有助于改进治疗策略。在这里，我们证明了两种成像生物标志物预测肿瘤对治疗反应差异的能力：1)EPR成像测量的氧分压（pO2）；2)超极化13C MRI测定[1-13C]丙酮酸代谢率。三种不同治疗敏感性的人类PDAC异种移植物（Hs766t、MiaPaCa-2和Su.86.86）在小鼠体内生长。成熟肿瘤Hs766t、MiaPaCa-2和Su.86.86的中位pO2分别为9.1、11.1和17.6mmHg，丙酮酸转化为乳酸的速率分别为2.72、2.28和1.98 min-1 （n=6）。结果与质谱和组织学分析定量测量的代谢产物稳态数据一致，表明Hs766t和MiaPaca-2肿瘤的糖酵解和缺氧特征。分步放射治疗（5gy x 5）导致肿瘤生长延迟16%。和18。在MiaPaca-2和Su.86.86肿瘤中分别为6天。低氧Hs766t肿瘤。吉西他滨，一线化疗，或缺氧激活的前药TH-302治疗对Hs766t肿瘤更有效。和25。(2)比MiaPaCa-2(2。和6。天)和苏86.86(4)。0.7天)肿瘤。总之，这些结果证明了分子成像生物标志物能够预测PDAC对放射治疗和TH-302治疗的反应。

a) Metabolic MRI to profile prostate cancer to target glycolytic pathways: Hyperpolarized (HP) MRI using pyruvate allows imaging kinetics of important bio-energetic pathways such as aerobic glycolysis or oxidative phosphorylation. Since malignant cells process glucose/pyruvate through aerobic glycolysis vs normal cells which rely on oxidative phosphorylation, this imaging allowed biochemically profiling regions of interest in vivo non-invasively using 13C MRI using hyperpolarized tracers. Hyperpolarization bridges the 4-orders in sensitivity needed for 13C MRI in vivo. Two human prostate cancer cell lines (DU145 and PC3) were grown as xenografts. The conversion of pyruvate to lactate in xenografts was measured with hyperpolarized [1-13C]-pyruvate MRSI after systemic delivery of [1-13C] pyruvic acid. Steady state metabolomic analysis of xenograft tumors was performed with mass spectrometry and steady state lactate concentrations were measured with proton (1H) MRSI. Tumor growth was assessed after lactate dehydrogenase (LDH) inhibition with FX-11. DU145 tumors demonstrated an enhanced conversion of pyruvate to lactate with hyperpolarized [1-13C]-pyruvate MRSI compared to PC3, and a corresponding greater sensitivity to LDH inhibition. We showed that hyperpolarized [1-13C]-pyruvate MRSI magnetic resonance spectroscopic imaging (MRSI) of prostate cancer predicts efficacy of targeting the Warburg effect. b) Synthesis and evaluation of 13C-labeled 5-5-dimethyl-1-pyrroline-N-oxide aimed at in vivo detection of reactive oxygen species using hyperpolarized 13C-MRI: 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) is a spin trap agent frequently used to detect reactive oxygen species (ROS) in vitro. In this study, we synthesized 13C-labeled DMPO to be applied to hyperpolarized 13C-MRI in which 13C MR signal increases more than 10000 folds, and investigated feasibility of in vivo ROS detection by the 13C-labeled DMPO combined with hyperpolarized 13C-MRI. DMPO was 13C-labeled at C5 position, and deuterated to prolong the T1 relaxation time. Overall yield achieved for 5-13C-DMPO-d9 was 15%. Hyperpolarized 5-13C-DMPO-d9 provided a single peak at 76 ppm on the 13C-spectrum, and the T1 relaxation time was 60 sec in phosphate buffer. The solution of hyperpolarized 5-13C-DMPO-d9 was injected into a mouse placed in a 3T scanner, and 13C-spectra was acquired every 1 sec. The signal of 5-13C-DMPO-d9 was detected in the living mouse body, and the T1 decay of 13C signal of hyperpolarized 5-13C-DMPO-d9 in the mouse body was 29 sec. 13C-chemical shift imaging revealed that 5-13C-DMPO-d9 was distributed through the mouse body in a minute after the intravenous injection. The strong signal of 5-13C-DMPO-d9 was detected in heart/lung and kidney, whereas the signal in liver was small compared to other organs. The results indicate hyperpolarized 5-13C-DMPO-d9 provided sufficient magnitude of the 13C signal to be detected in the mouse body, and can be applied to some disease models to evaluate the capability for detection of ROS in vivo. c) Molecular imaging of the microenvironment of pancreatic tumor xenografts in mice guides treatment strategy with radiotherapy- or hypoxia-activated prodrugs: Pancreatic ductal adenocarcinoma (PDAC) is characterized by hypoxic niches, leading to treatment resistance. Therefore, studies of tumor oxygenation and metabolic profiling will contribute to improved treatment strategies. Here, we demonstrated the ability of two imaging biomarkers to predict differences in tumor response to therapy: 1) partial oxygen pressure (pO2), measured by EPR imaging; and 2) [1-13C] pyruvate metabolism rate, measured by hyperpolarized 13C MRI. Three human PDAC xenografts with varying treatment sensitivity (Hs766t, MiaPaCa-2, and Su.86.86) were grown in mice. The median pO2 of the mature Hs766t, MiaPaCa-2, and Su.86.86 tumors was 9.1, 11.1, and 17.6mmHg, and the rate of pyruvate-to-lactate conversion was 2.72, 2.28, and 1.98 min-1, respectively(n=6, each). The results are in agreement with steady state data of matabolites quantitatively measured by mass spectroscopy and histological analysis indicating glycolytic and hypoxic profile in Hs766t and MiaPaca-2 tumors. Fractionated radiation therapy (5 Gy x 5) resulted in a tumor growth delay of 16. and 18. days in MiaPaca-2 and Su.86.86 tumors, respectively, compared to 6. days in hypoxic Hs766t tumors. Treatment with gemcitabine, a first-line chemotherapy, or the hypoxia-activated prodrug TH-302 was more effective against Hs766t tumors (20. and 25. days' increase in survival time, respectively) than MiaPaCa-2 (2. and 6. days) and Su.86.86 (4. and 0.7 days) tumors. Collectively, these results demonstrate the ability of molecular imaging biomarkers to predict the response of PDAC to treatment with radiation therapy and TH-302.