Site-specific conjugation for the synthesis of radiopharmaceuticals
File(s)
Author(s)
Yue, Tom
Type
Thesis
Abstract
This thesis aims to expand on the current toolbox of site-specific conjugation methods available to radiochemists, facilitating the development of well-defined radioconjugates of antibodies for diagnostic positron-emission tomography (PET) imaging.
Firstly, the utility of a methionine-specific oxaziridine-based conjugation method (ReACT platform) for attaching radiometal chelators to biomolecules was demonstrated. This method was simple to implement, yielding high conjugation efficiencies. Model biomolecule conjugates prepared via this strategy were successfully radiolabelled with 89Zr, 68Ga and 111In with high radiochemical conversions. The synthesis of an oxaziridine-based bifunctional chelator to facilitate one-step conjugation was explored and showcased the intricate synthetic challenges associated with oxaziridines. The investigation of N-alkyl oxaziridines to enhance the stability of methionine sulfimide conjugates revealed the need for a delicate balance between controlling oxaziridine reactivity and ensuring sulfimide stability.
Application of the ReACT platform for the preparation of site-specifically modified 68Ga-labelled radioimmunoconjugates was also demonstrated, employing the trastuzumab Fab fragment as an example. In vitro and in vivo experiments showed high stabilities of the resulting 68Ga-Fab radioconjugates, where their high affinities towards the HER2 receptor are retained. Comparison between a Fab derivative labelled at the antigen binding site and a Fab labelled at an optimised conjugation site elucidated the importance of managing and optimising the conjugation site for achieving optimal imaging outcomes.
Finally, the utility of the π-clamp conjugation method to site-specifically radiolabel biomolecules was explored, employing octreotate as a model substrate. An [18F]AlF-based prosthetic group approach was explored, demonstrating its potential for pre-labelling peptides. Direct labelling approaches employing 18F and 68Ga demonstrated excellent site-specific modification and radiolabelling efficiencies. In vitro evaluation of a π-clamp-conjugated 68Ga-octreotate derivative demonstrated the high stability and affinity of the resulting radioconjugate. Concurrently, in vivo experiments demonstrated the tag’s influence on enhancing hepatic clearance and prolonging circulation half-life, highlighting its potential strategic use in certain scenarios.
Firstly, the utility of a methionine-specific oxaziridine-based conjugation method (ReACT platform) for attaching radiometal chelators to biomolecules was demonstrated. This method was simple to implement, yielding high conjugation efficiencies. Model biomolecule conjugates prepared via this strategy were successfully radiolabelled with 89Zr, 68Ga and 111In with high radiochemical conversions. The synthesis of an oxaziridine-based bifunctional chelator to facilitate one-step conjugation was explored and showcased the intricate synthetic challenges associated with oxaziridines. The investigation of N-alkyl oxaziridines to enhance the stability of methionine sulfimide conjugates revealed the need for a delicate balance between controlling oxaziridine reactivity and ensuring sulfimide stability.
Application of the ReACT platform for the preparation of site-specifically modified 68Ga-labelled radioimmunoconjugates was also demonstrated, employing the trastuzumab Fab fragment as an example. In vitro and in vivo experiments showed high stabilities of the resulting 68Ga-Fab radioconjugates, where their high affinities towards the HER2 receptor are retained. Comparison between a Fab derivative labelled at the antigen binding site and a Fab labelled at an optimised conjugation site elucidated the importance of managing and optimising the conjugation site for achieving optimal imaging outcomes.
Finally, the utility of the π-clamp conjugation method to site-specifically radiolabel biomolecules was explored, employing octreotate as a model substrate. An [18F]AlF-based prosthetic group approach was explored, demonstrating its potential for pre-labelling peptides. Direct labelling approaches employing 18F and 68Ga demonstrated excellent site-specific modification and radiolabelling efficiencies. In vitro evaluation of a π-clamp-conjugated 68Ga-octreotate derivative demonstrated the high stability and affinity of the resulting radioconjugate. Concurrently, in vivo experiments demonstrated the tag’s influence on enhancing hepatic clearance and prolonging circulation half-life, highlighting its potential strategic use in certain scenarios.
Version
Open Access
Date Issued
2023-10-24
Date Awarded
01/03/2024
License URL
Advisor
Long, Nicholas
Ma, Michelle
Sponsor
Schrödinger Scholarship Scheme
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)