Synthesis and ex vivo biological evaluation of gallium-68 labelled NODAGA chelates assessing cardiac uptake and retention

Radiolabelled lipophilic cations can be used to non-invasively report on mitochondrial dysfunction in diseases such as cardiovascular disease, cardiotoxicity and cancer. Several such lipophilic cations are currently used clinically to map myocardial perfusion using SPECT imaging. Since PET offers significant advantages over SPECT in terms of sensitivity, resolution and the capacity for dynamic imaging to allow pharmacokinetic modelling, we have synthesised and radiolabelled a series of NODAGA-based radiotracers, with triarylphosphonium-functionalisation, with gallium-68 to develop PET-compatible cationic complexes. To evaluate their capacity to report upon mitochondrial membrane potential, we assessed their pharmacokinetic profiles in isolated perfused rat hearts before and after mitochondrial depolarisation with the ionophore CCCP. All three tracers radiolabel with over 96% RCY, with log D-7.4 values above -0.4 observed for the most lipophilic example of this family of radiotracers. The candidate tracer [Ga-68]Ga4c exhibited non-preferential uptake in healthy cardiac tissue over CCCP-infused cardiac tissue. While this approach does show promise, the lipophilicity of this family of probes needs improving in order for them to be effective cardiac imaging agents.