Lipophilic and cationic gallium-68 chelates for mitochondrial imaging
File(s)
Author(s)
Smith, Adam James
Type
Thesis or dissertation
Abstract
This thesis details the synthesis and radiolabelling of gallium-68-labelled radiotracers for mitochondrial imaging, as well as their uptake in in vitro and ex vivo biological models. These tracers are designed to be cationic such that they are taken up into mitochondria in a manner dependant on their mitochondrial membrane potential, and lipophilic such that they can pass through lipid bilayer membranes.
The synthesis of novel gallium chelators is described in Chapter 3. Starting with triarylphosphonium (TAP)-functionalised DO3A as a base case, DO2A-based variants were synthesised due to their novelty in the literature, using TAP and aryl functionalisation to provide tracers with a range of cationic charges and lipophilicities. Bridged cyclens were also explored with a view to exploiting their preorganisation and complex stability, whilst work into synthesising HBED-based chelators was unsuccessful due to low stability of the chelators.
The radiolabelling of the chelators with generator-produced gallium-68 is described in Chapter 4. DO3A-based ligands were found to radiolabel in near-quantitative RCY as one species after heating at 100 °C for 30 min. After changing the radiolabelling buffer, near quantitative RCYs were achieved for the DO2A-based compounds, however HPLC showed that these tracers exist as multiple species. Altering reaction conditions revealed that these species exist as kinetic/thermodynamic pairs, although it was not possible to completely isolate a single species. Log D values of -1.81, -0.28 and -0.07 were obtained for DO3A-TXP, DO2A-TXP and DO2A-Xy compounds respectively. Quantitative RCY was obtained for diacid functionalised bridged cyclen, although its log D was lower than that of unchelated gallium.
The three candidate radiotracers discussed previously were taken forward to testing in biological models, the results of which are described in Chapter 5. The cardiac uptake of the radiotracers was determined ex vivo using an isolated perfused heart model and mitochondrial membrane potential decoupler challenge. Both DO2A-TXP and DO2A-Xy showed a significant change in uptake upon mitochondrial challenge, although it was found that log D alone is not an exact predictor of myocardial uptake. In vitro tumour cell uptake was also assessed for DO3A-TXP, showing a significant increase in uptake compared to unchelated gallium.
Chapter 6 summarises the overall conclusions of the thesis and suggests further work in this area. Chapter 7 provides experimental procedures.
The synthesis of novel gallium chelators is described in Chapter 3. Starting with triarylphosphonium (TAP)-functionalised DO3A as a base case, DO2A-based variants were synthesised due to their novelty in the literature, using TAP and aryl functionalisation to provide tracers with a range of cationic charges and lipophilicities. Bridged cyclens were also explored with a view to exploiting their preorganisation and complex stability, whilst work into synthesising HBED-based chelators was unsuccessful due to low stability of the chelators.
The radiolabelling of the chelators with generator-produced gallium-68 is described in Chapter 4. DO3A-based ligands were found to radiolabel in near-quantitative RCY as one species after heating at 100 °C for 30 min. After changing the radiolabelling buffer, near quantitative RCYs were achieved for the DO2A-based compounds, however HPLC showed that these tracers exist as multiple species. Altering reaction conditions revealed that these species exist as kinetic/thermodynamic pairs, although it was not possible to completely isolate a single species. Log D values of -1.81, -0.28 and -0.07 were obtained for DO3A-TXP, DO2A-TXP and DO2A-Xy compounds respectively. Quantitative RCY was obtained for diacid functionalised bridged cyclen, although its log D was lower than that of unchelated gallium.
The three candidate radiotracers discussed previously were taken forward to testing in biological models, the results of which are described in Chapter 5. The cardiac uptake of the radiotracers was determined ex vivo using an isolated perfused heart model and mitochondrial membrane potential decoupler challenge. Both DO2A-TXP and DO2A-Xy showed a significant change in uptake upon mitochondrial challenge, although it was found that log D alone is not an exact predictor of myocardial uptake. In vitro tumour cell uptake was also assessed for DO3A-TXP, showing a significant increase in uptake compared to unchelated gallium.
Chapter 6 summarises the overall conclusions of the thesis and suggests further work in this area. Chapter 7 provides experimental procedures.
Version
Open Access
Date Issued
2018-12
Date Awarded
2019-03
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Long, Nicholas
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/L015226/1
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)