IMAGING PROSTATE CANCER BY MRI/PET WITH PSMA-TARGETED PROBES

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 本项目的目标是合成和表征PSMA靶向的纳米缀合物;评估纳米缀合物在正常和前列腺肿瘤荷瘤小鼠中的体内行为;并将纳米缀合物应用于前列腺癌的非侵入性MRI/PET成像。 在美国，前列腺癌（PCa）一直是男性癌症相关死亡的第二大原因。目前，美国癌症协会建议每年进行前列腺特异性抗原检测和直肠指检，以根据其种族和家族史在特定年龄段早期发现PCa。 尽管常规PSA筛查已被引入PCa的诊断超过二十年，并可能已成为最常见的癌症临床试验，但关于PSA筛查的益处和正常PSA值的上限仍存在争议。另一方面，常规经直肠超声进行的PCa活检不能保证PCa的明确分期，因为PCa可能是等回声的，与周围组织无法区分。因此，开发高灵敏度、高特异性的前列腺癌无创检测新技术具有重要意义。在非侵入性成像方式中，计算机断层扫描（CT）传统上用于评估局部PCa的程度，最近磁共振成像（MRI）也加入了临床实践，以更准确地对PCa进行分期，因为MRI技术的快速发展。因为CT和MRI是典型的解剖成像技术，所以与功能/代谢成像模态（诸如正电子发射断层扫描（PET））相比，它们固有地缺乏灵敏度。然而，最常用的PET放射性药物18F-FDG在识别PCa（直到PCa变成转移性的）方面不太成功，因为它在检测其他肿瘤方面是成功的，这是因为PCa的低糖酵解速率和由于18F-FDG通过尿液的正常排泄而导致的高背景。迄今为止，PET在前列腺癌中的作用尚未确定。本提案的目标是探索一种新的方法，将联合收割机结合MRI和PET的优势，用于PCa的诊断成像和分期。 我们建议将正电子发射同位素掺杂到超顺磁性氧化铁纳米颗粒中，制成纳米级的MRI/PET双探针，通过多模态（解剖MRI+功能PET）分子成像方法检测PCa，从而显著提高PCa诊断的灵敏度和特异性。 在该提案中，我们选择砷-74，因为其端点正电子能量低（0.94 MeV），可提供更高的PET空间分辨率，并且其半衰期相对较长（17.77天），使我们能够执行制作双模态成像探头的程序。从长远来看，长半衰期还允许这种成像探针的全球递送。 两种前列腺特异性膜抗原（PSMA）靶向分子（一种新的PSMA单克隆抗体和一种新的PSMA靶向RNA适体）将用于构建PSMA靶向纳米缀合物。使用两种前列腺癌细胞系C4-2和PC-3细胞的三种动物模型（股内、皮下和原位）将用于本提案中的成像探针评价，因为C4-2是表达PSMA的雄激素应答细胞，PC-3是将用作阴性对照的无PSMA的AIPCa细胞。 该项目安排了两个具体目标： 目标一77/74 As掺杂的氧化铁纳米颗粒的制备/表征和PSMA靶向纳米缀合物的构建;和目的II.通过常规生物分布和小动物MRI和PET成像方法在PCa异种移植小鼠模型中评价PSMA靶向纳米缀合物。 在目标I中，我们将建立制备葡聚糖涂覆的77/74 As掺杂的氧化铁纳米颗粒和PSMA靶向纳米缀合物的方案。我们计划通过将两种靶向分子共价连接到尺寸为25 nm和35 nm的葡聚糖涂层的77/74 As掺杂的氧化铁纳米颗粒来制备四种PSMA靶向纳米缀合物，用于目标II中的研究。将通过将纳米缀合物与新鲜大鼠血清孵育48小时并进行后续放射性HPLC分析来确定体外稳定性。将通过常规生物分布方法在C4-2和PC-3异种移植模型（皮下在侧腹）中评价纳米缀合物的肿瘤靶向性质。在两种C4-2异种移植模型（原位和股内）中，通过小动物MRI和PET成像进一步评估显示出体外和体内最佳行为以及肿瘤靶向特性的纳米缀合物，以检测局部和转移性肿瘤。将生物分布和小动物成像结果与相应的PSA数据进行比较。我们预计PSMA靶向纳米缀合物将能够作为双模态成像探针，并为PCa检测提供比单模态成像方法和PSA测试更高的灵敏度和特异性。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this project is to synthesize and characterize PSMA-targeted nano-conjugates; evaluate in vivo behavior of the nanoconjugates in normal and prostate tumor bearing mice; and apply the nanoconjugates to noninvasive MRI/PET imaging of prostate cancer. In the United States, prostate cancer (PCa) has been consistently the second leading cause of cancer-related deaths of men. Currently the American Cancer Society recommends annual checkups with the prostate-specific antige test and the digital rectal examination for the early detection of PCa in men at certain ages based on their ethnic groups and family history. Although the routine PSA-based screening has been introduced to the diagnosis of PCa over two decades and has become probably the most common clinical test of cancer, it is still in debate about the benefit of the PSA screening and the upper limit of normal PSA values. On the other hand, the PCa biopsies routinely performed with transrectal ultrasound cannot warrant a definitive stage of PCa because PCa can be isoechoic and indistinguishable from the surrounding tissues. Therefore it is of great significance to develop new techniques for the non-invasive detection of PCa with high sensitivity and specificity. Among the non-invasive imaging modalities, computed tomography (CT) has been traditionally used to evaluate the extent of local PCa, more recently magnetic resonance imaging (MRI) has also joined the clinical practices for more accurate staging of PCa as the MRI techniques rapidly evolve. Because CT and MRI are typically anatomical imaging techniques, they are inherently short of sensitivity as compared to the functional/metabolic imaging modalities, such as positron emission tomography (PET). However, the most commonly used PET radiopharmaceutical, 18F-FDG, is not quite successful at identifying PCa (until PCa becomes metastatic) as it is in the detection of other tumors because of the low glycolytic rate of PCa and high background due to the normal excretion of 18F-FDG through urine. To date, the role of PET in prostate cancer has not been established. The goal of this proposal is to explore a new approach that will combine the advantages of MRI and PET for the diagnostic imaging and staging of PCa. We propose to dope positron-emitting isotopes to superparamagnetic iron oxide nanoparticle to make nanosized dual MRI/PET probes for the detection of PCa by multi-modality (anatomical MRI plus functional PET) molecular imaging approaches, so that the sensitivity and specificity of PCa diagnosis could be significantly improved. In this proposal, we choose arsenic-74 due to its low endpoint positron energy (0.94 MeV) that provides higher spatial resolution of PET, and its relatively long half-life (17.77 days) that allows us to carry out the procedures of making the dual-modality imaging probes. In perspective, the long half-life also allows global delivery of such imaging probes. Two prostate specific membrane antigen (PSMA) targeting molecules (a new PSMA monoclonal antibody and a novel PSMA-targeting RNA aptamer) will be used to construct the PSMA-targeted nano-conjugates. Three animal models (intra-femoral, subcutaneous, and orthotopic) using two prostate cancer cell lines, C4-2 and PC-3 cells, will be used for the imaging probe evaluations in this proposal, because C4-2 is an androgen responsive cell expressing PSMA and PC-3 is PSMA-devoid AIPCa cell that will serve as negative control. Two specific objectives are arranged in this project: Objective I. Preparation/characterization of 77/74As-doped iron oxide nanoparticles and construction of PSMA-targeted nano-conjugates; and Objective II. Evaluation of the PSMA-targeted nano-conjugates in PCa xenograft mouse models via the conventional biodistribution and small animal MRI and PET imaging methods. In Objective I, we will establish protocols to prepare dextran-coated 77/74As-doped iron oxide nanoparticles and PSMA-targeted nano-conjugates. We plan to make four PSMA-targeted nano-conjugates by covalently attaching the two targeting molecules to the dextran-coated 77/74As-doped iron oxide nanoparticles with sizes of 25 nm and 35 nm, for the studies in the Objective II. The in vitro stability will be determined by incubating the nano-conjugates with fresh rat serum over 48 h and follow-up radio-HPLC analysis. The tumor-targeting property of the nano-conjugates will be evaluated in C4-2 and PC-3 xenograft models (subcutaneously in the flank) by the conventional biodistribution method. The nano-conjugates that show optimal behavior in vitro and in vivo and tumor-targeting property will be further evaluated by small animal MRI and PET imaging in two C4-2 xenograft models (orthotopic and intra-femoral) for the detection of localized and metastatic tumors. Both biodistribution and small animal imaging results will be compared with the respective PSA data. We anticipate the PSMA-targeted nano-conjugates will be able to serve as dual-modality imaging probes and provide higher sensitivity and specificity for PCa detection than either of the single-modality imaging approaches and the PSA test.