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体内癌症成像探索性/开发补助金（R21）的回应。目的是探索磁共振成像（MRI）中的磁铁矿（由趋磁细菌产生）用于诊断癌症和跟踪癌症转移的潜力。拟议的工作与公共卫生有关，因为它旨在改善癌症成像，早期癌症检测和监测癌症治疗。它与美国国家癌症研究所癌症成像项目的使命一致雅阁，并且完全响应PA-06-371，因为它“专注于体内癌症成像，用于检测、诊断和监测对治疗的反应”。趋磁细菌将用于靶向肿瘤;它们的磁铁矿可以提供阳性MRI对比度，与阴性对比度相比，这对于解剖学研究来说是上级的。此外，与目前将MRI造影剂靶向肿瘤的努力不同，递送剂（即，肿瘤中的趋磁细菌）不会稀释造影剂。目的1将研究原位和转移性小鼠肿瘤的趋磁细菌的定植，使用MRI和生物发光成像（BLI）;为了实现后者，细菌将被修饰以表达细菌荧光素酶。这种双探头模式将使细菌的跟踪高度可靠。将使用专用小动物7 T扫描仪进行MRI，并使用IVIS系统进行BLI。重要的是，趋磁细菌在肿瘤中分裂时产生磁铁矿，以防止造影剂稀释。为了研究这种倾向，在没有铁的情况下生长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。由于这些细菌具有有效的铁摄取系统，并且可以预期肿瘤环境富含铁，因此假设这是可能的，并且将使用如上所述的双重追踪策略进行探索。由于阳性MRI对比度上级，目标2将比较两种阳性对比度MRI技术与趋磁细菌：非共振激发，空间频谱射频脉冲;和磁化率诱导梯度标测。将在体外和体内评价这些技术定量趋磁细菌的能力。细菌系统可能在临床上造成危害。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。将使用可靶向并杀死肿瘤细胞的细胞因子诱导的杀伤（CIK）细胞。磁铁矿生产所需的基因将使用慢病毒系统转导到CIK细胞中。将通过阳性对比MRI在体外和体内比较铁摄取和磁铁矿形成。这些结果有望表明，编码磁铁矿的基因可以作为一种强大的报告系统来跟踪癌症，并可以通过细菌或CIK细胞传递到肿瘤。公共卫生相关性：这项工作将为癌症的早期检测、癌症转移和治疗评估开发一种新的敏感和安全的方法。由于所有这些方面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，所描述的方法还可以具有其他与健康相关的益处。

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.