Visualisation of in vivo protein synthesis during mycobacterial infection through [⁶⁸Ga]Ga-DOTA-puromycin µPET/MRI

Radiolabelled puromycin analogues will allow the quantification of protein synthesis through nuclear medicine-based imaging. A particularly useful application could be the non-invasive longitudinal visualisation of mycobacterial activity through direct quantification of puromycin binding. This study assesses the value of [⁶⁸Ga]Ga-DOTA-puromycin in the visualisation of mycobacteria through positron emission tomography combined with magnetic resonance imaging (µPET/MRI). The radiopharmaceutical was produced by previously published and validated methods. [⁶⁸Ga]Ga-DOTA-Puromycin imaging was performed on severe immunodeficient mice infected with Bacille Calmette-Guérin-derived M. Bovis (BCG). Acute and chronic infection stages were examined by µPET/MRI. A follow-up group of animals acted as controls (animals bearing S. aureus-derived infection and sterile inflammation) to assess tracer selectivity. [⁶⁸Ga]Ga-DOTA-puromycin-µPET/MRI images revealed the acute, widespread infection within the right upper shoulder and armpit. Also, [⁶⁸Ga]Ga-DOTA-puromycin signal sensitivity measured after a 12-week period was lower than that of [¹⁸F]FDG-PET in the same animals. A suitable correlation between normalised uptake values (NUV) and gold standard histopathological analysis confirms accurate tracer accumulation in viable bacteria. The radiopharmaceutical showed infection selectivity over inflammation but accumulated in both M. Bovis and S. Aureus, lacking pathogen specificity. Overall, [⁶⁸Ga]Ga-DOTA-puromycin exhibits potential as a tool for non-invasive protein synthesis visualization, albeit without pathogen selectivity.