Gallium-68-NODASA-functionalized D-lysine radiosynthesis and first-line in vitro characterization-a potential PET imaging agent for infection

Abstract

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.