| Autor: |
Joosten L; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Frielink C; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Jansen TJP; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Lobeek D; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Andreae F; Forschungs- und Entwicklungs GmbH, piCHEM, Parkring 3, 8074 Grambach, Austria., Konijnenberg M; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Heskamp S; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Gotthardt M; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands., Brom M; Department of Medical Imaging, Nuclear Medicineof Medical Imaging, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands. |
| Abstrakt: |
PET imaging of the glucagon-like peptide-1 receptor (GLP-1R) using radiolabeled exendin is a promising imaging method to detect insulinomas. However, high renal accumulation of radiolabeled exendin could hamper the detection of small insulinomas in proximity to the kidneys and limit its use as a radiotherapeutic agent. Here, we report two new exendin analogues for GLP-1R imaging and therapy, designed to reduce renal retention by incorporating a cleavable methionine-isoleucine (Met-Ile) linker. We examined the renal retention and insulinoma targeting properties of these new exendin analogues in a nude mouse model bearing subcutaneous GLP-1R-expressing insulinomas. NOTA or DOTA was conjugated via a methionine-isoleucine linker to the C-terminus of exendin-4 (NOTA-MI-exendin-4 or DOTA-MI-exendin-4). NOTA- and DOTA-exendin-4 without the linker were used as references. The affinity for GLP-1R was determined in a competitive binding assay using GLP-1R transfected cells. Biodistribution of [ 68 Ga]Ga-NOTA-exendin-4, [ 68 Ga]Ga-NOTA-MI-exendin-4, [ 177 Lu]Lu-DOTA-exendin-4, and [ 177 Lu]Lu-DOTA-MI-exendin-4 was determined in INS-1 tumor-bearing BALB/c nude mice, and PET/CT was acquired to visualize renal retention and tumor targeting. For all tracers, dosimetric calculations were performed to determine the kidney self-dose. The affinity for GLP-1R was in the low nanomolar range (<11 nM) for all peptides. In vivo biodistribution revealed a significantly lower kidney uptake of [ 68 Ga]Ga-NOTA-MI-exendin-4 at 4 h post-injection (p.i.) (34.2 ± 4.2 %IA/g), compared with [ 68 Ga]Ga-NOTA-exendin-4 (128 ± 10 %IA/g). Accumulation of [ 68 Ga]Ga-NOTA-MI-exendin-4 in the tumor was 25.0 ± 8.0 %IA/g 4 h p.i., which was similar to that of [ 68 Ga]Ga-NOTA-exendin-4 (24.9 ± 9.3 %IA/g). This resulted in an improved tumor-to-kidney ratio from 0.2 ± 0.0 to 0.8 ± 0.3. PET/CT confirmed the findings in the biodistribution studies. The kidney uptake of [ 177 Lu]Lu-DOTA-MI-exendin-4 was 39.4 ± 6.3 %IA/g at 24 h p.i. and 13.0 ± 2.5 %IA/g at 72 h p.i., which were significantly lower than those for [ 177 Lu]Lu-DOTA-exendin-4 (99.3 ± 9.2 %IA/g 24 h p.i. and 45.8 ± 3.9 %IA/g 72 h p.i.). The uptake in the tumor was 7.8 ± 1.5 and 11.3 ± 2.0 %IA/g 24 h p.i. for [ 177 Lu]Lu-DOTA-MI-exendin-4 and [ 177 Lu]Lu-DOTA-exendin-4, respectively, resulting in improved tumor-to-kidney ratios for [ 177 Lu]Lu-DOTA-MI-exendin-4. The new exendin analogues with a Met-Ile linker showed 2-3-fold reduced renal retention and improved tumor-to-kidney ratios compared with their reference without the Met-Ile linker. Future studies should demonstrate whether [ 68 Ga]Ga-NOTA-MI-exendin-4 results in improved detection of small insulinomas in close proximity to the kidneys with PET/CT. [ 177 Lu]Lu-DOTA-MI-exendin-4 might open a window of opportunity for exendin-based radionuclide therapy. |
