Gallium-68-NODASA-Functionalized D-Lysine Radiosynthesis and first-line in vitro characterization - a potential PET imaging agent for infection

The advancement of new Positron Emission Tomography (PET) radiotracers for differentiating bacterial infections from sterile inflammation is essential for accurate diagnosis and treatment monitoring. D-amino acid-based probes have shown promise for bacterial imaging due to their selective peptidoglycan incorporation. However, host enzyme-mediated racemization of radiolabeled D-amino acids and limited tissue penetration of fluorescence signal of fluorescent D-amino acids limits their in vivo performance. Herein, we report the successful chemical synthesis, optimized radiosynthesis, and the required first-line in vitro characterization of [68Ga]Ga-NDL-1 (NDL = NODASA D-lysine; NODASA = 1,4,7-triazacyclononane-1-succinic acid-4,7-diacetic acid) (the L-isomeric compound, aka. [68Ga]Ga-NLL-1 was evaluated in parallel as the control). Robust radiolabeling was achieved within 60 minutes using the optimized radiolabeling method, featuring the consistent production of very good radiochemical yields (81.7 ± 3.2%), apparent molar activities (17.1 ± 0.8 GBq/µmol) and with excellent radiochemical purities (97.7 ± 0.5%), free of 68Ga-colloids; therefore, deemed suitable for future intravenous administration and micro-PET imaging applications. [68Ga]Ga-NDL-1 was highly stable during prolonged incubation in the presence of 1000-times excess of EDTA (>93%) as well as a during a 2-hour exposure to plasma (>97%). [68Ga]Ga-NLL-1 and [68Ga]Ga-NDL-1 showed minimal overall blood cell binding (<12%) or plasma protein binding (<15%). Results justify further investigation of [68Ga]Ga-NDL-1 as a potential PET imaging agent of infection.