Development of Contrast Agents from Bacterial Magnetite for Targeting and Visuali

描述(由申请人提供)：本提案是对PA-06-371关于体内癌症成像探索/发展资助(R21)的回应。目的是探索磁铁矿(由趋磁细菌产生)在磁共振成像(MRI)中诊断癌症和追踪癌症转移的潜力。这项拟议的工作与公共健康相关，因为它寻求改善癌症成像、早期癌症检测和监测癌症治疗。它与国家癌症研究所癌症成像计划的使命一致，并完全响应PA-06-371，因为它“专注于(S)体内癌症成像，用于检测、诊断和监测治疗反应”。趋磁细菌将被用于靶向肿瘤；它们的磁铁矿可以提供阳性的MRI对比度，与负对比度相比，这在解剖学研究中是优越的。此外，与目前针对肿瘤靶向MRI造影剂的努力不同，在肿瘤中复制递送剂(即趋磁细菌)不会稀释造影剂。目的1利用磁共振成像和生物发光成像(BLI)技术，研究趋磁细菌在小鼠原位肿瘤和转移性肿瘤中的定植情况；为了实现生物发光成像，对细菌进行修饰以表达细菌荧光素酶。这种双探针模式将使细菌的跟踪高度可靠。MRI将使用专用的小动物7T扫描仪进行，BLI将使用IVIS系统进行。重要的是，磁性细菌在肿瘤分裂时产生磁铁矿，以防止对比剂的稀释。为了研究这种倾向，不含铁的趋磁细菌将被用于靶向肿瘤，从而能够确定肿瘤内是否可能形成磁铁矿。由于这些细菌具有强大的铁摄取系统，并且肿瘤环境可以预期是富含铁的，因此假设这是可能的，并将使用上述双重跟踪策略进行探索。由于阳性MRI对比度更好，Aim 2将比较两种阳性对比度MRI技术与趋磁细菌：空间频谱射频脉冲的非共振激发；以及磁化率诱导的梯度映射。这些技术量化趋磁细菌的能力将在体外和体内进行评估。细菌系统在临床上可能会造成危险。因此，AIM 3将开发一种哺乳动物细胞系统，将磁铁输送到肿瘤。将使用细胞因子诱导的杀伤(CIK)细胞，这种细胞可以靶向并杀死肿瘤细胞。生产磁铁矿所需的基因(S)将使用慢病毒系统导入CIK细胞。铁摄取和磁铁矿的形成将在体外和体内通过阳性对比磁共振成像进行比较。预计结果将显示，磁铁编码基因是追踪癌症的强大报告系统，并可通过细菌或CIK细胞传递到肿瘤。公共卫生相关性：拟议的工作将开发一种新的敏感和安全的方法，用于癌症的早期检测、癌症转移和治疗评估。由于所有这些方面都是抗击癌症的关键，这些研究解决了一个重要的公共卫生问题。从长远来看，所描述的方法还可以带来其他与健康相关的好处。

DESCRIPTION (provided by applicant): This proposal is in response to PA-06-371 for an In vivo cancer imaging exploratory/developmental grant (R21). The objective is to explore the potential of magnetite (produced by magnetotactic bacteria) in magnetic resonance imaging (MRI) for diagnosing cancer and tracking cancer metastasis. The proposed work is relevant to public health as it seeks to improve cancer imaging, early cancer detection, and monitoring cancer treatment. It is in accord with the mission of the Cancer Imaging Program of the National Cancer Institute, and is fully responsive to PA-06-371, as it "focuse(s) on in vivo cancer imaging for detection, diagnosis, and monitoring of response to therapy". Magnetotactic bacteria will be used to target tumors; their magnetite can provide a positive MRI contrast, which, compared to negative contrast, is superior for anatomical studies. Furthermore, unlike the current efforts to target MRI contrast agents to tumors, replication of the delivery agent (i.e., the magnetotactic bacteria) in tumors will not dilute the contrasting agent. Aim 1 will investigate the colonization of orthotopic and metastatic mouse tumors by magnetotactic bacteria, using both MRI and bioluminescence imaging (BLI); to accomplish the latter, the bacteria will be modified to express bacterial luciferase. This dual probe modality will make the tracking of the bacteria highly reliable. MRI will be performed using a dedicated small-animal 7T scanner, and BLI using the IVIS system. It is important that the magnetotatic bacteria generate magnetite as they divide in tumors so as to prevent the dilution of the contrast agent. To investigate this propensity, magnetotactic bacteria grown without iron will be used to target tumors, permitting determination of whether magnetite formation is possible within the tumors. As these bacteria possess potent iron uptake systems, and the tumor environment can be expected to be iron-rich, it is hypothesized that this is possible and will be explored using the dual tracking strategy as above. Since positive MRI contrast is superior, Aim 2 will compare two positive contrast MRI techniques with magnetotactic bacteria: off-resonance excitation, with spatial- spectral radio frequency pulses; and susceptibility-induced gradient mapping. The ability of these techniques to quantify magnetotactic bacteria will be evaluated both in vitro and in vivo. A bacterial system may pose hazards in the clinic. Therefore, Aim 3 will develop a mammalian cell system to deliver magnetite to tumors. Cytokine induced killer (CIK) cells, which can target and kill tumor cells, will be used. The gene(s) required for magnetite production will be transduced into the CIK cells using a lentiviral system. Iron uptake and magnetite formation will be compared in vitro and in vivo by positive- contrast MRI. The results are expected to show that magnetite-encoding genes serve as a powerful reporter system for tracking cancer and can be delivered to tumors through bacteria or CIK cells. PUBLIC HEALTH RELEVANCE: The proposed work will develop a novel sensitive and safe method for early detection of cancer, cancer metastasis, and treatment evaluation. Since all these aspects are critical to fight cancer, these studies address an important public health issue. In the long run, the approach described can also have other health related benefits.