Development of Contrast Agents from Bacterial Magnetite for Targeting and Visuali

描述（由申请人提供）：该提案是对PA-06-371体内癌症成像探索/发展拨款（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。拟议的工作与公共卫生有关，因为它寻求改善癌症成像、早期癌症检测和监测癌症治疗。它符合美国国家癌症研究所癌症成像项目的使命，完全符合PA-06-371，因为它“专注于体内癌症成像，用于检测、诊断和监测治疗反应”。趋磁细菌将用于靶向肿瘤；它们的磁铁矿可以提供阳性MRI对比，与阴性对比相比，这在解剖学研究中是优越的。此外，与目前针对肿瘤的MRI造影剂不同，肿瘤中递送剂（即趋磁细菌）的复制不会稀释造影剂。目的1将利用MRI和生物发光成像（BLI）研究趋磁细菌在原位和转移性小鼠肿瘤中的定植；为了实现后者，将对细菌进行修饰以表达细菌荧光素酶。这种双探针方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使用IVIS系统。重要的是，趋磁细菌在肿瘤中分裂时产生磁铁矿，以防止造影剂的稀释。为了研究这种倾向，在没有铁的情况下培养的趋磁细菌将被用于靶向肿瘤，从而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MRI阳性对比是优越的，Aim 2将比较两种正对比MRI技术与趋磁细菌：非共振激励，与空间频谱射频脉冲；和敏感性诱导的梯度映射。这些技术量化趋磁细菌的能力将在体外和体内进行评估。细菌系统可能对临床造成危害。因此，Aim 3将开发一种哺乳动物细胞系统，将磁铁矿输送到肿瘤中。将使用能够靶向并杀伤肿瘤细胞的细胞因子诱导杀伤细胞（CIK）。使用慢病毒系统将产生磁铁矿所需的基因转导到CIK细胞中。铁摄取和磁铁矿形成将比较体外和体内的正对比MRI。这一结果有望表明，磁铁矿编码基因作为一种强大的癌症追踪报告系统，可以通过细菌或CIK细胞传递到肿瘤中。公共卫生相关性：这项工作将开发一种新的敏感和安全的方法，用于早期检测癌症、癌症转移和治疗评估。由于所有这些方面都对抗击癌症至关重要，这些研究解决了一个重要的公共卫生问题。从长远来看，上述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.