A Semi Rigid Novel Hydroxamate AMPED-Based Ligand for 89Zr PET Imaging.

Lisa Russelli,Lorenzo Tei,Markus Schwaiger,Loredana Leone,Sybille Reder,Francesco De Rose,Calogero D’Alessandria

doi:10.3390/molecules26195819

Lisa Russelli, Lorenzo Tei + Show 5 more

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https://doi.org/10.3390/molecules26195819

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Abstract

In this work, we designed, developed, characterized, and investigated a new chelator and its bifunctional derivative for 89Zr labeling and PET-imaging. In a preliminary study, we synthesized two hexadentate chelators named AAZTHAS and AAZTHAG, based on the seven-membered heterocycle AMPED (6-amino-6-methylperhydro-1,4-diazepine) with the aim to increase the rigidity of the 89Zr complex by using N-methyl-N-(hydroxy)succinamide or N-methyl-N-(hydroxy)glutaramide pendant arms attached to the cyclic structure. N-methylhydroxamate groups are the donor groups chosen to efficiently coordinate 89Zr. After in vitro stability tests, we selected the chelator with longer arms, AAZTHAG, as the best complexing agent for 89Zr presenting a stability of 86.4 ± 5.5% in human serum (HS) for at least 72 h. Small animal PET/CT static scans acquired at different time points (up to 24 h) and ex vivo organ distribution studies were then carried out in healthy nude mice (n = 3) to investigate the stability and biodistribution in vivo of this new 89Zr-based complex. High stability in vivo, with low accumulation of free 89Zr in bones and kidneys, was measured. Furthermore, an activated ester functionalized version of AAZTHAG was synthesized to allow the conjugation with biomolecules such as antibodies. The bifunctional chelator was then conjugated to the human anti-HER2 monoclonal antibody Trastuzumab (Tz) as a proof of principle test of conjugation to biologically active molecules. The final 89Zr labeled compound was characterized via radio-HPLC and SDS-PAGE followed by autoradiography, and its stability in different solutions was assessed for at least 4 days.

Highlights

A rapidly expanding number of radionuclides with a variety of half-lives, emission types, and energies for the application of radionuclide imaging are routinely produced.When choosing the most suitable radionuclide for a certain application, one should consider the decay properties and availability of the radionuclide, but it is of great importance that the physical half-life of the radionuclide matches the biological half-life of the vector molecule [1,2]
New pseudo-macrocyclic ligands for 89 Zr complexation for PET imaging were synthesized, in particular, two non-functionalized chelators, AAZTHAS and AAZTHAG, and one functionalized for conjugation to biomolecules, AAZTHAG-C5 -OTFP
A functionalized version of the AAZTHAG chelator was synthesized since it was confirmed that a longer spacer arm leads to a more stable 89 Zr-complex

Summary

Introduction

When choosing the most suitable radionuclide for a certain application, one should consider the decay properties and availability of the radionuclide, but it is of great importance that the physical half-life of the radionuclide matches the biological half-life of the vector molecule [1,2]. This biological half-life can be in the range of minutes (small organic molecules), hours (peptides, antibody fragments), or even days (full-size monoclonal antibodies). The nuclide should lead to a low activity isotope that can be eliminated from the organism

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