Abstract:Targeted radionuclide therapy (TRT) is a promising strategy to treat different types of cancer. TRT relies on a targeting vector used to deliver a therapeutic radionuclide specifically to the tumour site. Several low molecular weight ligands targeting the prostate-specific membrane antigen (PSMA) have been synthesized, but their pharmacokinetic properties still need to be optimized. Hereby, we describe the synthesis of new conjugates, featuring the cleavable linkers Gly-Tyr-Lys (GYK) and Met-Val-Lys (MVK), to … Show more
“…While the reference compound [ 111 In]In-Ex4 displayed high stability with 80% intact tracer after 24 h, Ex4 derivatives equipped with a cleavable linker quickly displayed the generation of an unidentified secondary peak in the HPLC chromatogram. Based on previous accounts (Murce et al 2023 ; Bendre et al 2020 ), we speculated that the observed secondary peak is caused by the oxidation of methionine. Though the generation of the sulfoxide M(O)VK has been shown to impair the recognition by neprilysin, Bendre et al ( 202 0) found that it still resulted in a significant reduction of the kidney retention, in fact even higher than the one obtained with the non-oxidized version.…”
Section: Discussionmentioning
confidence: 65%
“…1 A, B). In fact, apart from MVK, which is the most frequently employed cleavable linker in conjunction with radiotracers, a big arsenal of other linking sequences have been described including amongst others: MI (Uehara et al 2018 , 2014 ), MWK and MFK (Zhang et al 2021 ), GYK (Murce et al 2023 ) and GFK (Suzuki et al 2018 ). Fig.…”
Background
Peptidic radiotracers are preferentially excreted through the kidneys, which often results in high persistent renal retention of radioactivity, limiting or even preventing therapeutic clinical translation of these radiotracers. Exendin-4, which targets the glucagon-like-peptide 1 receptor (GLP-1R) overexpressed in insulinomas and in congenital hyperinsulinism, is an example thereof. The use of the tripeptide MVK, which is readily cleaved between methionine and valine by neprilysin at the renal brush border membrane, already showed promising results in reducing kidney uptake as reported in the literature. Based on our previous findings we were interested how linker variants with multiple copies of the MV-motive influence renal washout of radiolabelled exendin-4.
Results
Three exendin-4 derivatives, carrying either one MVK, a MV-MVK or a MVK-MVK linker were synthesized and compared to a reference compound lacking a cleavable linker. In vivo results of a biodistribution in GLP-1R overexpressing tumour bearing mice at 24 h post-injection demonstrated a significant reduction (at least 57%) of renal retention of all 111In-labeled exendin-4 compounds equipped with a cleavable linker compared to the reference compound. While the insertion of the single linker MVK led to a reduction in kidney uptake of 70%, the dual approach with the linker MV-MVK slightly, but not significantly enhanced this effect, with 77% reduction in kidney uptake compared to the reference. In vitro IC50 and cell uptake studies were conducted and demonstrated that though the cleavable linkers negatively influenced the affinity towards the GLP-1R, cell uptake remained largely unaffected, except for the MV-MVK cleavable linker conjugate, which displayed lower cell uptake than the other compounds. Importantly, the tumour uptake in the biodistribution study was not significantly affected with 2.9, 2.5, 3.2 and 1.5% iA/g for radiolabelled Ex4, MVK-Ex4, MV-MVK-Ex4 and MVK-MVK-Ex4, respectively.
Conclusion
Cleavable linkers are highly efficient in reducing the radioactivity burden in the kidney. Though the dual linker approach using the instillation of MV-MVK or MVK-MVK between exendin-4 and the radiometal chelator did not significantly outperform the single cleavable linker MVK, further structural optimization or the combination of different cleavable linkers could be a stepping stone in reducing radiation-induced nephrotoxicity.
“…While the reference compound [ 111 In]In-Ex4 displayed high stability with 80% intact tracer after 24 h, Ex4 derivatives equipped with a cleavable linker quickly displayed the generation of an unidentified secondary peak in the HPLC chromatogram. Based on previous accounts (Murce et al 2023 ; Bendre et al 2020 ), we speculated that the observed secondary peak is caused by the oxidation of methionine. Though the generation of the sulfoxide M(O)VK has been shown to impair the recognition by neprilysin, Bendre et al ( 202 0) found that it still resulted in a significant reduction of the kidney retention, in fact even higher than the one obtained with the non-oxidized version.…”
Section: Discussionmentioning
confidence: 65%
“…1 A, B). In fact, apart from MVK, which is the most frequently employed cleavable linker in conjunction with radiotracers, a big arsenal of other linking sequences have been described including amongst others: MI (Uehara et al 2018 , 2014 ), MWK and MFK (Zhang et al 2021 ), GYK (Murce et al 2023 ) and GFK (Suzuki et al 2018 ). Fig.…”
Background
Peptidic radiotracers are preferentially excreted through the kidneys, which often results in high persistent renal retention of radioactivity, limiting or even preventing therapeutic clinical translation of these radiotracers. Exendin-4, which targets the glucagon-like-peptide 1 receptor (GLP-1R) overexpressed in insulinomas and in congenital hyperinsulinism, is an example thereof. The use of the tripeptide MVK, which is readily cleaved between methionine and valine by neprilysin at the renal brush border membrane, already showed promising results in reducing kidney uptake as reported in the literature. Based on our previous findings we were interested how linker variants with multiple copies of the MV-motive influence renal washout of radiolabelled exendin-4.
Results
Three exendin-4 derivatives, carrying either one MVK, a MV-MVK or a MVK-MVK linker were synthesized and compared to a reference compound lacking a cleavable linker. In vivo results of a biodistribution in GLP-1R overexpressing tumour bearing mice at 24 h post-injection demonstrated a significant reduction (at least 57%) of renal retention of all 111In-labeled exendin-4 compounds equipped with a cleavable linker compared to the reference compound. While the insertion of the single linker MVK led to a reduction in kidney uptake of 70%, the dual approach with the linker MV-MVK slightly, but not significantly enhanced this effect, with 77% reduction in kidney uptake compared to the reference. In vitro IC50 and cell uptake studies were conducted and demonstrated that though the cleavable linkers negatively influenced the affinity towards the GLP-1R, cell uptake remained largely unaffected, except for the MV-MVK cleavable linker conjugate, which displayed lower cell uptake than the other compounds. Importantly, the tumour uptake in the biodistribution study was not significantly affected with 2.9, 2.5, 3.2 and 1.5% iA/g for radiolabelled Ex4, MVK-Ex4, MV-MVK-Ex4 and MVK-MVK-Ex4, respectively.
Conclusion
Cleavable linkers are highly efficient in reducing the radioactivity burden in the kidney. Though the dual linker approach using the instillation of MV-MVK or MVK-MVK between exendin-4 and the radiometal chelator did not significantly outperform the single cleavable linker MVK, further structural optimization or the combination of different cleavable linkers could be a stepping stone in reducing radiation-induced nephrotoxicity.
In the context of molecularly targeted radiotherapy, dosimetry concerns in off-target tissues are a major limitation to the more wide-spread application of radiopharmaceuticals to treat diseases like cancer. Reducing off-target accumulation of radionuclides in background tissues, whilst maintaining high and specific uptake in disease sites and improving the therapeutic window, requires rethinking common radiotracer design concepts. This article explores ways in which innovative radiotracer chemistry (the making and breaking of bonds) is used to modify interactions with the host organism to control excretion profiles and dosimetry at the tissue-specific level.
Targeted radionuclide therapy (TRT) is a promising strategy to treat different types of cancer. TRT relies on a targeting vector used to deliver a therapeutic radionuclide specifically to the tumour site. Several low molecular weight ligands targeting the prostate-specific membrane antigen (PSMA) have been synthesized, but their pharmacokinetic properties still need to be optimized. Hereby, we describe the synthesis of new conjugates, featuring the cleavable linkers Gly-Tyr-Lys (GYK) and Met-Val-Lys (MVK), to reduce the dose delivered to the kidneys. Compounds were synthesized by solid-phase peptide synthesis (SPPS) and obtained in greater than 95% chemical purity. Radiolabelling was performed with both In-111 and Lu-177 to validate potential use of the compounds as both imaging and therapeutic agents. Radiochemical purity greater than 80% was obtained for both nuclides, but significant radiolysis was observed for the methionine-containing analogue. The results obtained thus far with the GYK-PSMA conjugate could warrant further biological investigations.
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