Radiochemical Targeting and Imaging Group
Group Leader |
Scientific Officers |
The Radiochemical Targeting and Imaging Group focuses on the development of molecular imaging approaches to study cancer biology and therapy. The research themes include the development of imaging paradigms for cell death, angiogenesis, cell proliferation and drug pharmacokinetics. In addition, we are also developing microfluidic technology applied to PET radiochemistry.
- Cell Death
- A major goal of our research is to develop a non-invasive method for identifying and quantifying cell death in vivo. The approach taken is to radiolabel annexin V (Anx5), a protein that binds to phosphatidylserine (PS) exposed on apoptotic cells, with iodine-124 for PET imaging. We have developed a novel method of producing Anx5 fused to maltose-binding protein (MBP), and shown that directly iodinated MBP-Anx5 binds to apoptotic cells in vivo. We compared I-MBP-Anx5 with several other analogues in terms of PS binding ability, and determined that the accumulation of radiolabelled annexin was directly proportional to histologically-derived apoptotic density. We have shown that negative control molecules did not bind to PS in vitro nor in vivo, whilst annexin V analogues were able to identify apoptotic lesions. In vivo data have shown that directly labeled proteins showed at least a 2-fold greater uptake than their indirectly labeled counterparts. We are currently investigating the use of these analogues to image apoptosis in xenograft models.
- Cell Proliferation
- In a clinical setting, we have been studying the efficacy of anti-cancer therapy through functional imaging of changes in tumour metabolic activity using the PET tracer [18F]FDG. Such metabolic changes however, are not only a reflection of cancerous cells but also represent metabolic activity of other cells/tissues, (e.g. macrophages and inflammatory leasions). We have therefore been working on the development of more specific markers, namely PET nucleoside analogues as markers of DNA synthesis and hence cell proliferation. In non-small cell lung cancer (NSCLC) models (H460 & H596), we have been investigating the thymidine analogues, [124I]-IUdR, [124I]-FIAU and [18F]-FLT as markers of S-phase activity of the cell cycle. Like thymidine, [124I]-IUdR was appreciably incorporated into DNA, whilst both [124I]-FIAU and [18F]-FLT were minimally associated with the DNA fraction of cells, but showed good correlation with thymidine kinase enzyme activity. We are currently investigating a 'wash-out' strategy, using [124I]-IUdR to image tumour cell growth in NSCLC patients. In order to overcome the instability of the N-glycosidic bond, we are investigating the development of other analogues including FLT, as potential stable markers of cell proliferation.
- Anti-angiogenic Therapy
- Targeting integrin receptor provides the potential for anti-angiogenic therapy of a number of tumours. In collaboration with the CR-UK Department of Medical Oncology, we have been developing PET labeled mono-clonal antibodies specifically targeted against αV α3/5 integrins. We have demonstrated that the PET analogue showed specific binding to A375.S2 human melanoma cells expressing the αV α3/5 integrins. In a rat-bearing melanoma xenograft model, the radiolabelled protein localised predominantly to the tumour with minimum uptake in the rest of the tissues indicating specific binding to those cells over-expressing the integrin receptors. Further in-vivo studies are underway and this will provide the platform for a planned phase-1 clinical pharmacokinetic (PK) imaging study.
- Microfluidics
- Tracer level PET radiochemical syntheses are amenable to miniaturisation because these are carried out at levels (micro-nano-molar quantities and micro-liter volumes) compatible with microfluidic technology. Such an approach offers advantages, including ultra-high radiotracer concentration, specific activity and enhanced speed of labelling. We have demonstrated the application of a microfabricated reaction system to PET radiochemistry which we term microfluidic PET. Importantly, we have achieved the rapid radioiodination of, the apoptosis marker Annexin V and the anti-cancer drug doxorubicin using a simple microreactor chip, in a similar yield and quality to conventional radiosynthesis. These studies indicate that PET radiochemical reactions on a microfluidic 'chip' produce a radiolabelled product of equivalent purity and yield, at the experimental scale, to current methods.
- Drug Pharmacokinetics
- Using PET imaging, we are investigating, drug delivery and targeting approaches to maximize drug concentration in tumours, relative to normal tissues, in order to measure the efficiency of chemotherapy. We have developed a PET analogue of the anti-cancer drug doxorubicin ([124I]-DOXIB) and studied its kinetics in the presence and absence of a polymer delivery vehicle. We observed a 25-fold increase in [124I]-DOXIB uptake kinetics in MCF-7 cells in the presence of the carrier as compared to [124I]-DOXIB alone. This results suggest that the presence of the polymer carrier can significantly and selectively increase the cellular uptake of [124I]-DOXIB. The development of the PET analogue will allow us to demonstrate this proof of principle in vivo by imaging the pharmacokinetics of [124I]-DOXIB in the presence and absence of the carrier.