Heart failure (HF) affects 64 million people globally and is a major driver of mortality and morbidity. Myocardial fibrosis, characterised by changes in collagen type I (COL1) and III (COL3), underpins the development of HF. In myocardial fibrosis, COL3 increases in the early stages of remodelling and is later replaced by COL1. Currently used cardiac magnetic resonance (CMR) imaging only provides indirect or surrogate measurements of myocardial fibrosis. Alternatively, molecular imaging enables direct imaging and quantification of fibrosis. But current imaging probes are limited to COL1. This thesis aims to develop and validate a new COL3-specific imaging probe to quantify and stage fibrosis in cardiac remodelling. The experimental pipeline used for developing and testing a new imaging probe involved a multi-step approach. Initially, candidate peptide sequences with the potential to bind to COL3 and COL1 were selected. Based on these sequences, molecular imaging probes were designed and synthesised. The probes were chemically characterised using in vitro binding assays, relaxivity studies, stability studies and biodistribution studies to select the most promising candidate(s) for initial in vivo testing. The lead probe(s) were compared in vivo in a model of vascular fibrosis to assess their imaging performance, specificity, and sensitivity in detecting COL3. Finally, the best-performing probe was used to study COL3 remodelling and to monitor the response to treatment in a murine model of cardiac fibrosis. In vitro binding assays showed that the probe had high affinity and specificity towards COL3. The probe had r1 relaxivity within the expected values for the molecular size of the probe and was stable in serum. PET/CT studies showed that the probe has favourable pharmacokinetics with fast blood clearance. Molecular CMR using the best performing probe enabled selective profiling of the natural turnover of COL3 after MI with the signal increasing at day 10 when COL3 is elevated and decreasing at day 21 as COL3 is replaced by COL1. Changes in COL3 remodelling following the treatment of mice with enalapril were also detected using this probe. The COL3 probe developed in the thesis is a significant contribution to the field of cardiac molecular imaging. It provides a non-invasive imaging tool to investigate the role of COL3 in cardiovascular fibrosis and to assess the effect of newly developed drugs in preclinical studies. Future clinical translation may enhance clinical decision-making, guide treatment strategies, and ultimately improve patient outcomes.
Developing a Collagen III Targeted MRI Probe for Molecular Imaging of Cardiac Fibrosis
Chaher, N. (Author). 1 Mar 2024
Student thesis: Doctoral Thesis › Doctor of Philosophy