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

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.

Positron Emission Tomography (PET) is a diagnostic molecular imaging technique performed daily in hospitals around the world. PET allows for non-invasive, in-vivo imaging and has become an important tool for the diagnosis of diseases such as Parkinson's, Alzheimer's and cancer. In addition, PET is being increasingly used by the pharmaceutical industry to speed up drug development. The ability to identify and accurately diagnose a patient at the onset of a disease greatly aids physicians in selecting the appropriate treatment, giving patients the best chance for survival. As medicine moves towards personalised treatment, the use of PET will play an increasingly important role. 18-F-fluorodeoxyglucose ([18F]FDG), is the most widely used PET radiotracer and has found multiple clinical applications. Despite [18F]FDG's ubiquitous use, it's synthesis requires dedicated automated units, requiring dedicated trained scientists to operate. The proposed research describes a novel, kit based method for the one-step labelling of sensitive proteins and antibodies with [18F]-fluoride. This new technique will benefit medicinal chemists in both academia and industry to radiolabel important bio-molecules in a rapid fashion and investigate their potential as new tracers for diseases. Protein-based radiotracers currently inaccessible using conventional chemistry could potentially be readily synthesised speeding up new radiotracer and drug discovery. The development of a kit-based technology will mean that research centres without easy access to radioactive isotopes and specialised automated synthesisers will be able perform radiochemistry opening up this important field to more researchers. Another advantage of the kit-based technology is the translation of a tracer from laboratory to the clinic. The simplicity of the system will mean no specialist equipment or trained radiochemists are needed, greatly reducing cost for hospitals. If successful, patients could benefit greatly. Firstly, as more radiotracers become available the ability to accurately and rapidly diagnose a greater number of diseases increases and thus patient prognosis improves. Secondly, due to the simple nature of the kit-based system and the relative in expense, this should allow more patients to get PET scans. Furthermore, shorter radiolabeling procedures reduce the radiation dose received by the person carrying out the formulation. These aspects are a major help for physicians to provide the correct medicines/treatment. Obviously this results in more efficient and better care for patients, overall improving their quality of life.