Evaluation of ¹¹¹In-Labelled Exendin-4 Derivatives Containing Different Meprin β-Specific Cleavable Linkers

Abstract

BackgroundCleavable linkers, which are specifically cleaved by defined conditions or enzymes, are powerful tools that can be used for various purposes. Amongst other things, they have been successfully used to deliver toxic payloads as prodrugs into target tissues. In this work novel linker sequences targeting meprin β, a metalloprotease expressed in the kidney brush-border membrane, were designed and included in the sequence of three radiolabelled exendin-4 derivatives. As radiolabelled exendin-4 derivatives strongly accumulate in the kidneys, we hypothesised that specific cleavage of the radiolabelled moiety at the kidney brush-border membrane would allow easier excretion of the activity into the urine and therefore improve the pharmacological properties of the peptide.ResultsThe insertion of a cleavable linker did not negatively influence the in vitro properties of the peptides. They showed a good affinity to the GLP-1 receptor expressed in CHL cells, a high internalisation and sufficiently high stability in fresh human blood plasma. In vitro digestion with recombinant meprin β rapidly metabolised the corresponding linker sequences. After 60 min the majority of the corresponding peptides were digested and at the same time the anticipated fragments were formed. The peptides were also quickly metabolised in CD1 nu/nu mouse kidney homogenates. Immunofluorescence staining of meprin β in kidney sections confirmed the expression of the protease in the kidney brush-border membrane. Biodistribution in GLP-1 receptor positive tumour-xenograft bearing mice revealed high specific uptake of the 111In-labelled tracers in receptor positive tissue. Accumulation in the kidneys, however, was still high and comparable to the lead compound 111In-Ex4NOD40.ConclusionIn conclusion, we show that the concept of cleavable linkers specific for meprin β is feasible, as the peptides are rapidly cleaved by the enzyme while retaining their biological properties.

Exendin‐4 analogs in insulinoma theranostics

“…Other strategies to reduce renal uptake are introduction of a cleavable linker to allow renal excretion of the radionuclides, 80 inhibition of neutral endopeptidases to increase metabolic stability of the peptide in the circulation, 79,[81][82][83][84] and incorporation of highly lipophilic groups 34 (efficacies of these strategies are summarized in Table 5). Furthermore, groups have conjugated exendin to PEG, [85][86][87] albumin, 88 an albumin binding domain, 89 a nonglycosylated human Fc fragment, 90 or nanoparticles [91][92][93] to increase circulation time.…”

Radiosynthesis and evaluation of an 18F–labeled silicon containing exendin-4 peptide as a PET probe for imaging insulinoma

“…An important aspect is the kidney uptake which is very high with the radiometal labeled exendin derivatives (Jodal et al 2015 ; Jodal et al 2017 ). We observed a dramatic reduction with our compound but with a comparable uptake in receptor positive tissues.…”

Low kidney uptake of GLP-1R-targeting, beta cell-specific PET tracer, 18F-labeled [Nle14,Lys40]exendin-4 analog, shows promise for clinical imaging

“…Melis et al [43] showed that high radiation doses of [ 111 In]DTPA-Lys 40 -exendin-4 caused nephrotoxicity in mice. Several approaches have been tested to overcome high uptake of exendin-based tracers in the kidneys, including co-administration of competitive inhibitors of reabsorption [5–7], addition of metabolizable linkers [8, 9], or modifications in the size, charge, or structure of the tracer [44, 45]. Those attempts have been crucial in finding ways to improve the imaging accuracy, decrease the risk of nephrotoxicity, and improve the efficacy of peptide receptor radionuclide therapy.…”

“…Some success has been achieved in efforts to reduce the renal radioactivity of various radiolabeled peptides. For example, some studies co-administered amifostine, albumin derivatives, poly-glutamic acid, or Gelofusine [5–7] to limit renal uptake; and others used cleavable linkers, to allow excretion of radioactive metabolites into the urine [8, 9]. …”