68Ga Radiolabeling of NODASA-Functionalized Phage Display–Derived Peptides for Prospective Assessment as Tuberculosis-Specific PET Radiotracers

Abstract

This research presents the development of positron emission tomography (PET) radiotracers for detecting Mycobacterium tuberculosis (MTB) for the diagnosis and monitoring of tuberculosis. Two phage display–derived peptides with proven selective binding to MTB were identified for development into PET radiopharmaceuticals: H8 (linear peptide) and PH1 (cyclic peptide). We sought to functionalize H8/PH1 with NODASA, a bifunctional chelator that allows complexation of PET-compatible radiometals such as gallium-68. Herein, we report on the chelator functionalization, optimized radiosynthesis, and assessment of the radiopharmaceutical properties of [⁶⁸Ga]Ga-NODASA-H8 and [⁶⁸Ga]Ga-NODASA-PH1. Robust radiolabeling was achieved using the established routine method, indicating consistent production of a radiochemically pure product (RCP ≥ 99.6%). For respective [⁶⁸Ga]Ga-NODASA-H8 and [⁶⁸Ga]Ga-NODASA-PH1, relatively high levels of decay-corrected radiochemical yield (91.2% ± 2.3%, 86.7% ± 4.0%) and apparent molar activity (A_m, 3.9 ± 0.8 and 34.0 ± 5.3 GBq/μmol) were reliably achieved within 42 min, suitable for imaging purposes. Notably, [⁶⁸Ga]Ga-NODASA-PH1 remained stable in blood plasma for up to 2 h, while [⁶⁸Ga]Ga-NODASA-H8 degraded within 30 min. For both ⁶⁸Ga peptides, minimal whole-blood cell binding and plasma protein binding were observed, indicating a favorable pharmaceutical behavior. [⁶⁸Ga]Ga-NODASA-PH1 is a promising candidate for further in vitro/in vivo evaluation as a tuberculosis-specific infection imaging agent.