Exendin-4 Derivatives with an Albumin-Binding Moiety Show Decreased Renal Retention and Improved GLP-1 Receptor Targeting

Abstract

The glucagon-like peptide-1 receptor (GLP-1R) is highly and specifically expressed on the pancreatic β-cells. It plays an important role in glucose metabolism as well as in β-cell-derived diseases like diabetes, insulinoma, or congenital and adult hyperinsulinemic hypoglycemia. Radiolabeled exendin-4, a ligand of GLP-1R, has routinely been used in clinics to image insulinomas. However, its major drawback is the high kidney accumulation. Here, we show that the addition of an albumin-binding moiety (ABM) to radiolabeled exendin-4 results in a significant reduction of kidney uptake while retaining its high affinity and specificity to GLP-1R. The four tested peptides were shown to have high affinity to the GLP-1 receptor (IC50 of 3.7 ± 0.6 to 15.1 ± 0.8 nM). The radiolabeled derivatives were taken up into cells efficiently, internalizing between 39 ± 2 and 56 ± 2% after 2 h. Thus, the derivatives with ABM outperformed the reference peptide with its IC50 of 22.5 ± 2.9 nM and internalization of 41 ± 4%. Stability in human blood plasma was slightly enhanced by the addition of the albumin binder. In biodistribution studies, the radioligands exhibited an improved target-to-kidney ratio in comparison to the reference peptide of up to seven-fold. This was confirmed qualitatively in single-photon-emission computed tomography (SPECT)/CT imaging. This study demonstrated in vitro and in vivo that the addition of an ABM to radiolabeled exendin-4 strongly decreased kidney accumulation while retaining affinity to GLP-1R. Thus, exendin-4 derivatives with an albumin-binding moiety could present a viable class of diagnostic tracers for the detection of insulinomas and other GLP-1R-positive tissue in clinical application.

Innovative imaging of insulinoma: the end of sampling? A review

“…The major drawback of radiolabeled exendin-4 is the high kidney accumulation, which might limit in some cases, accurate diagnosis -for example in the tail region of the pancreas -and in addition the application of targeted radionuclide therapy. A number of strategies were tested to circumvent renal accumulation (Jansen et al 2019), with the most recent ones being: (a) the use the nephroprotective agent succinylated gelatin (Gelofusine©), which combined with 111 In-exendin-4 in humans reduced kidney uptake (Buitinga et al 2019), (b) conjugation of an albumin-binding moiety (ABM) to the radiolabeled exendin-4, which resulted in a significant reduction of kidney uptake while retaining its high affinity and specificity to GLP-1R in a preclinical model (Kaeppeli et al 2019) and (c) introduction of a cleavable linker between the peptide sequence and the chelator, which is cleaved by brush border membrane enzymes allowing this way rapid excretion from urine, thus significantly reducing renal uptake, in a preclinical model (Zhang et al 2019).…”

Development of an 111In-Labeled Glucagon-Like Peptide-1 Receptor-Targeting Exendin-4 Derivative that Exhibits Reduced Renal Uptake

“…In a previous study, a 4-(4-iodophenyl)­butyric acid derivative (an ALB moiety) was directly conjugated with exendin-4 via a specific residue ([ 111 In]­In-Ex4-ABM-4) . The introduction of the ALB moiety into the exendin-4 derivative significantly decreased its renal accumulation, as was found in previous studies involving ligands targeting CA-IX and FR; however, in mice, the kidneys were visualized more clearly than tumors on SPECT imaging performed with [ 111 In]­In-Ex4-ABM-4.…”

“…Recently, small albumin binder (ALB) molecules, e.g., 4-(4-iodophenyl)­butyric acid and Evans blue, have been utilized to improve the pharmacokinetics of radioligands . The introduction of an ALB moiety into radioligands targeting biomolecules that are overexpressed in tumors, which enabled endogenous albumin to be used as a reversible carrier for drug delivery, resulted in enhanced tumor accumulation and reduced renal accumulation of the radioligands. , In addition, Kaeppeli et al reported that the direct introduction of an ALB moiety at a specific residue of exendin-4 (lysine or glutamic acid) produced a radiotracer that exhibited significantly reduced renal accumulation, but its renal accumulation was still higher than its tumor accumulation, and hence, imaging small pancreatic tail lesions would clearly be difficult. Thus, ALB-conjugated exendin-4 derivatives are currently of limited clinical use.…”

Structure–Activity Relationships and Pharmacokinetics of 111In-Labeled Glucagon-like Peptide-1 Receptor-Targeting Exendin-4 Derivatives Conjugated with Albumin Binder Moieties

“…These findings corresponded with those of the biodistribution study (Figure ). Kaeppeli et al previously described an exendin-4-based radioligand, which was directly conjugated with iodophenylbutyric acid as an ALB moiety via a specific residue of an exendin-4 scaffold ([ 111 In]­In-Ex4-ABM-4) . [ 111 In]­In-Ex4-ABM-4 showed increased tumor accumulation and decreased renal accumulation compared with its non-ALB-conjugated counterpart, as was demonstrated in previous studies of radioligands targeting CA-IX and folate receptors; , however, SPECT imaging performed with [ 111 In]­In-Ex4-ABM-4 resulted in greater accumulation of radioactivity in the kidneys than in tumors in mice.…”