An inorganic kit-based approach to F-18 labeling of biomolecules for multimodal fluorescence/PET imaging

分子成像是非侵入性临床诊断的关键工具之一，并开辟了个性化患者治疗的可能性。特别是正电子发射断层扫描（PET）正在迅速扩展，新的PET成像中心目前正在英国各地安装。生物医学研究提供了越来越多的靶向体内疾病部位的活性分子，因此原则上可以通过标记正电子发射同位素来发挥显像剂的作用。然而，18-F- fdg是目前临床唯一常规使用的PET示踪剂，尽管18-F放射性核素广泛可用。这主要是由于多步骤程序的复杂性，需要专门的设备来制作18-F标记显像剂。目前的标记方法也可能对敏感生物分子有害，因此通常标记小前体分子，然后将其附着在活性生物分子上以产生显像剂。该项目将为敏感生物分子开发一种新的18- f标记方法，该方法使用金属铝结合氟化物，而不是迄今为止采用的主要方法碳氟键形成。一步标记程序将允许临床医生将18- f -氟化物直接添加到含有生物分子的制备试剂盒中，以制备显像剂。在标记中使用特殊聚合物珠具有实现比传统溶液方法更高的标记前体与未标记前体比率的潜力。这样做的优点是在体内提供更好的对比，并减少由未标记的过量生物分子的存在引起的患者反应问题。所涉及的化学反应不需要专门的设备，更快的、基于工具包的方法有助于最大限度地减少辐射工作人员对放射性核素的暴露。为了实现我们的目标，我们正在设计氟化物的金属结合位点，以便在不损害敏感生物分子和蛋白质的条件下进行放射性标记。我们还建议将这种方法与附加感兴趣的生物分子的方法结合起来，以保持其到达体内目标部位的能力。此外，我们提出的化合物本质上是荧光的，因此潜在的显像剂也可以在活细胞中使用荧光显微镜进行评估，因为PET成像本身没有必要的分辨率来观察像细胞这样小的东西中的复合物的行为。通过提供更好的标记，我们的新系统将有助于发现新的有效生物分子，并促进在临床上采用正电子发射断层扫描，而不需要昂贵的专业设备。铝所涉及的配体化学的最后一个好处是，它也有可能与其他金属PET放射性核素一起使用。

Molecular imaging is one of the key tools for non-invasive clinical diagnosis and opens up the possibility of personalising patient treatment. Positron Emission Tomography (PET) in particular is expanding rapidly and new PET imaging centres are currently being installed across the UK. Biomedical research provides increasing numbers of active molecules that target disease sites in the body and thus could in principle function as imaging agents by labeling with a positron emitting isotope. However, 18-F-FDG is currently the only routinely used PET tracer in the clinic, despite the wide availability of the 18-F radionuclide. This is mainly due to the complexity of the multistep-procedures requiring specialized equipment to make the 18-F labeled imaging agents. The current labeling methods also can be harmful to sensitive biomolecules and thus a small precursor molecule is often labeled that is then attached to an active biomolecule to create the imaging agent. This project will develop a new 18-F-labeling method for sensitive biomolecules which uses the metal aluminium to bind fluoride, rather than carbon-fluorine bond formation which has been the main approach adopted hitherto. The one step labeling procedure will allow clinicians to add the 18-F-fluoride directly into a prepared kit containing the biomolecule in order to prepare the imaging agent. The use of special polymer beads in the labeling has the potential of achieving a higher ratio of labeled to unlabeled precursor than conventional solution methods. This has the advantage of giving better contrast in-vivo and reducing the problems of patient reaction caused by the presence of unlabelled excess biomolecule. The chemistry involved requires no specialised equipment and the faster, kit-based method helps to minimise the exposure of radiation workers to the radionuclide. To achieve our aim, we are designing metal binding sites for fluoride that will allow radiolabeling under conditions that do not harm sensitive biomolecules and proteins. We also propose to combine this approach with methods to attach biomolecules of interest in a way that preserves their ability to reach the target site in the body. Additionally, the compounds we propose are intrinsically fluorescent, so that the potential imaging agents can also be evaluated in living cells using fluorescence microscopy, since PET imaging on its own does not have the resolution necessary to observe the behaviour of the complexes in something as small as a cell. By offering much improved labeling, our new system will facilitate the discovery of new potent biomolecules and facilitate the adoption of Positron Emission Tomography in the clinic without the need for expensive, specialized equipment. A final benefit of the ligand chemistry involved for aluminium is that it also has the potential to be used with other metallic PET radionuclides.