Evaluation of Re/99mTc-labeled somatostatin receptor-targeting peptide complexes synthesized via direct metal cyclization
Author:
Makris George1, Li Yawen2, Gallazzi Fabio23, Kuchuk Marina1, Wang Jing14, Lewis Michael R.56, Jurisson Silvia S.2, Hennkens Heather M.12
Affiliation:
1. Research Reactor Center, University of Missouri , Columbia , MO 65211 , USA 2. Department of Chemistry , University of Missouri , Columbia , MO 65211 , USA 3. Molecular Interactions Core, University of Missouri , Columbia , MO 65211 , USA 4. Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics , Mianyang , Sichuan 621900 , P. R. China 5. Department of Veterinary Medicine and Surgery , University of Missouri , Columbia , MO 65211 , USA 6. Research Service, Harry S. Truman Memorial Veterans’ Hospital , Columbia , MO 65201 , USA
Abstract
Abstract
With interest in the development of somatostatin receptor (SSTR) targeting agents for potential application in diagnostic SPECT imaging (99mTc) or Peptide Radionuclide Receptor Therapy (PRRT, 186Re or 188Re) of neuroendocrine tumors, we present herein 99mTc/Re (radio)complexes synthesized by the integrated (radio)labeling approach of peptide cyclization via metal complexation. In particular, we utilized the potent SSTR2 peptide antagonist sequence DOTA-4-NO2-Phe-c(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH2 (DOTA-sst2-ANT) and report the syntheses and in vitro evaluations of its respective [99mTc]Tc/Re-cyclized peptides ([99mTc]Tc/Re-cyc-DOTA-sst2-ANT). The Re-cyc-DOTA-sst2-ANT complex was synthesized via an on-resin Re(V)-cyclization reaction using the ReOCl3(PPh3)2 precursor and consisted of three isomers characterized by LC–ESI-MS. The [99mTc]Tc-cyclized analogue was prepared via a ligand exchange reaction of the [99mTc][TcO]3+ core through a [99mTc]Tc-glucoheptonate intermediate with linear DOTA-sst2-ANT and was characterized by comparative HPLC studies against Re-cyc-DOTA-sst2-ANT. Good in vitro binding affinity was demonstrated in SSTR-expressing cells (AR42J) by the Re-cyc-DOTA-sst2-ANT major isomer, similar to the potent binder Lu-DOTA-sst2-ANT, in which the Lu metal was complexed by the bifunctional chelator DOTA versus via peptide cyclization. [99mTc]Tc-cyc-DOTA-sst2-ANT was obtained in high radiochemical yield, also with an elution pattern of three isomers observed by HPLC analysis, which were comparable yet not identical to those of Re-cyc-DOTA-sst2-ANT. The [99mTc]Tc-tracer complex was shown to be hydrophilic, and stability studies at 4 h demonstrated that it remained intact in both PBS and in rat serum, with low non-specific rat serum protein binding, while exhibiting more moderate stability in 1 mM cysteine. These findings demonstrate that direct Re/[99mTc]Tc-cyclization of DOTA-sst2-ANT is feasible and may be used as an alternative approach to the bifunctional chelate labeling strategy. However, given that the non-radioactive (Re) and radiotracer (99mTc) analogues are not identical and both form isomeric products in equilibrium, additional design modifications will be necessary prior to in vivo application of [99mTc]Tc/Re-cyc-DOTA-sst2-ANT.
Funder
University of Missouri Research Council Institution of Nuclear Physics and Chemistry Foundation China Scholarship Council
Publisher
Walter de Gruyter GmbH
Subject
Physical and Theoretical Chemistry
Reference30 articles.
1. Maecke, H. R., Reubi, J. C. Somatostatin receptors as targets for nuclear medicine imaging and radionuclide treatment. J. Nucl. Med. 2011, 52, 841–844; https://doi.org/10.2967/jnumed.110.084236. 2. Barbieri, F., Bajetto, A., Pattarozzi, A., Gatti, M., Würth, R., Thellung, S., Corsaro, A., Villa, V., Nizzari, M., Florio, T. Peptide receptor targeting in cancer: the somatostatin paradigm. Int. J. Pept 2013, 2013, 926295; https://doi.org/10.1155/2013/926295. 3. Fani, M., Peitl, P., Velikyan, I. Current status of radiopharmaceuticals for the theranostics of neuroendocrine neoplasms. Pharmaceuticals 2017, 10, 30; https://doi.org/10.3390/ph10010030. 4. Eychenne, R., Bouvry, C., Bourgeois, M., Loyer, P., Benoist, E., Lepareur, N. Overview of radiolabeled somatostatin analogs for cancer imaging and therapy. Molecules 2020, 25, 4012; https://doi.org/10.3390/molecules25174012. 5. Ginj, M., Zhang, H., Waser, B., Cescato, R., Wild, D., Wang, X., Erchegyi, J., Rivier, J., Mäcke, H. R., Reubi, J. C. Radiolabeled somatostatin receptor antagonists are preferable to agonists for in vivo peptide receptor targeting of tumors. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 16436–16441; https://doi.org/10.1073/pnas.0607761103.
|
|