Hydrazine Derivatives as a Platform for Site-Specific Labelling of Peptides for in vivo Molecular Imaging of Disease

The 6-hydrazinonicotinyl group, known as HYNIC, is an attractive bifunctional coupling agent for preparing 99mTc-labeled peptides and proteins for medical imaging. Peptides are useful for imaging disease states such as cancer and inflammation because they take advantage of a distinct cellular target, such as a receptor, being present on the cell. Receptors are often over expressed on tumour cells. Peptides will bind to their receptors with high specificity and affinity. There is a recognized need to create well-de?ned polymer probes for in vivo and clinical PET and SPECT imaging to guide the development of new generation polymer therapeutics. In general the amount of radionuclide used in radiopharmaceuticals is small, so attaching the radionuclide to a polymer ensures that the radionuclide will be highly concentrated in the radiopharmaceutical. The number of binding sites is increased with the copolymer making it a viable choice for radiolabelling applications. The chances of successfully imaging the point of interest are therefore increased.

This thesis presents the synthesis of various HYNIC analogues that are capable of chelating technetium-99m in order to be attached to an amino acid and incorporated into a peptide sequence via solid phase peptide synthesis (SPPS) to image site-specific targets. While 6-HYNIC has been widely used, 2-HYNIC has not, and as such both of these were used in the synthesis of a number of derivatives. These derivatives were characterised by 1H and 13C NMR, FT-IR and melting point data was obtained for comparison with literature. A number of derivatives were successfully synthesised and purified with the aim of binding these to copolymer chains.

This work also presents the synthesis of a bifunctional copolymer (POEGMA-co-PAMA) which is biocompatible and can be attached to a HYNIC group and subsequently a peptide. This copolymer was synthesised using a controlled living radical polymerisation technique called Reversible Addition Fragmentation chain Transfer (RAFT). This technique was chosen due to its ability to synthesise polymers with predetermined molecular weights of complex architectures whilst maintaining control over polydispersity. Copolymers of varying compositions were synthesised and analysed by GPC and NMR. This method (once optimised) would allow for the copolymer to be labelled with technetium-99 for SPECT, providing an alternative bioconjugate synthetic route.