Development and Biodistribution of a Nerve Growth Factor Radioactive Conjugate for PET Imaging.
Mol Imaging Biol 2023;
25:977-988. [PMID:
36692661 DOI:
10.1007/s11307-023-01805-w]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 01/16/2023] [Accepted: 01/16/2023] [Indexed: 01/25/2023]
Abstract
PURPOSE
The purpose of these studies was to develop a nerve growth factor (NGF) radiometal-chelator conjugate to determine the biodistribution and brain uptake of NGF by positron emission tomography/computerized tomography (PET-CT).
PROCEDURES
Purified NGF from llama seminal plasma was conjugated with FITC, and the chelator NOTA or DFO. NGF conjugates were evaluated for bioactivity. NOTA- and DFO-conjugated NGF were radiolabeled with gallium-68 or zirconium-89 ([68 Ga]GaCl3, half-life = 68 min; [89Zr]Zr(oxalate)4, half-life = 3.3 days). [89Zr]Zr-NGF was evaluated for biodistribution (0.5, 1, or 24 h), PET imaging (60 min), and brain autoradiography in mice.
RESULTS
Cell-based in vitro assays confirmed that the NGF conjugates maintained NGF receptor-binding and biological activity. Zirconium-89 and gallium-68 radiolabeling showed a high efficiency; however, only[89Zr]Zr-NGF was stable in vitro. Biodistribution studies showed that, as with most small proteins < 70 kDa, [89Zr]Zr-NGF uptake was predominantly in the kidney and was cleared rapidly with almost complete elimination of NGF at 24 h. Dynamic PET imaging from 0-60 min showed a similar pattern to ex vivo biodistribution with some transient liver uptake. Interestingly, although absolute brain uptake was very low, at 24 h after treatment, cerebral cortex uptake was higher than any other brain area examined and blood.
CONCLUSIONS
We conclude that conjugation of DFO to NGF through a thiourea linkage allows effective radiolabeling with zirconium-89 while maintaining NGF bioactivity. Following intravenous administration, the radiolabeled NGF targets non-neuronal tissues (e.g., kidney, liver), and although absolute brain uptake was very low, the brain uptake that was observed was restricted to the cortex.
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