Novel dual PET And fluorescent bioconjugation reagents for biomedical imaging

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

This thesis aims to develop dual-modality bioconjugation reagents for i) cancer Positron Emission Tomography (PET) imaging and fluorescence-guided surgery, and ii) multiscale direct cell tracking. Chapter 1 reviews the basic principles of PET and fluorescence, together with their advantages and limitations. Furthermore, the chapter emphasises the benefits of combining the two imaging modalities for medical applications. Chapter 2 outlines the characteristics and applications of four commonly used radionuclides of iodine in nuclear medicine. In addition, the chapter reviews the one-pot three-component click radioiodination chemistry that is used to synthesise the dual PET and fluorescent bioconjugation reagents in this thesis. Chapter 3 focuses on cancer diagnosis with PET and fluorescence-guided surgery. The chapter first reviews the current developments in both fields, together with the efforts to unite the two modalities. A generic dual PET and fluorescent labelling reagent, [124I]FIT-Succ was developed, using the abovementioned click radioiodination chemistry. This reagent enables a one-step installation of an iodine-124/fluorescein dual reporter to any antibody. When coupled with the carcinoembryonic antigen (CEA)-specific antibody A5B7, the affinity of the dual labelled A5B7 was preserved. In vitro fluorescence imaging of CEA overexpressing SW1222 cells indicated the specific binding of the dual labelled A5B7 to its antigens. The SW1222 xenografts in nude mice were clearly visualised by both PET/CT and ex vivo fluorescence imaging with excellent target-to-background contrast. Chapter 4 focuses on non-invasive direct cell tracking. The introduction addresses the current advancements and limitations of direct cell tracking methods. Also using click chemistry, this chapter demonstrates the development of dual nuclear and fluorescent labelling reagents for cell conjugation. Two thiol-targeting reagents - maleimide [124I]04 (or [124I]FIT-Mal) and dithiophenolmaleimide [124I]08 (or [124I]FIT-(PhS)2Mal) – and two primary amine targeting reagents - isothiocyanates [125I]10 (or [125I]FIT-NCS01) and [125I]17 (or [125I]FIT-NCS02)– were synthesised and validated in vitro. Among these, [124I]08 stood out to be the lead candidate for further evaluation. [124I]08 successfully labelled various cell lines through their membrane thiols in 22%-62% labelling efficiency with prolonged radiolabel retention and without compromising the cell viability and functions. Cell membrane localisation of [124I]08 was confirmed by confocal fluorescence imaging. Longitudinal monitoring of the in vivo distribution and migration of [124I]08 labelled Jurkat cells was accomplished with PET/CT imaging over 7 days. In conclusion, this thesis describes the successful development of two iodine-124/fluorescein based bioconjugation reagents [124I]FIT-Succ and [124I]08 for i) cancer PET imaging and fluorescence-guided surgery, and ii) multiscale direct cell tracking, respectively. The promising results prompt their further research towards clinical multimodality imaging applications.
Date of Award1 Feb 2021
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorRan Yan (Supervisor) & John Maher (Supervisor)

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