Dataset Information

Cholecystokinin-2 Receptor Targeting with Novel C-terminally Stabilized HYNIC-Minigastrin Analogs Radiolabeled with Technetium-99m.

ABSTRACT: The high overexpression of cholecystokinin-2 receptors (CCK2R) in tumors, such as medullary thyroid carcinoma, allows for highly specific diagnostic and therapeutic targeting with radiolabeled peptide probes derived from natural ligands for the receptor. Based on the ideal imaging characteristics, high availability and low cost of technetium-99m (^99mTc)-labeled radiopharmaceuticals we have developed two hydrazinonicotinic acid (HYNIC) conjugated minigastrin analogs allowing labeling at high specific activity. The CCK2R targeting peptide conjugates show specific amino acid substitutions in the C-terminal receptor-specific sequence with the aim to increase stability and tumor targeting. The CCK2R affinity and the cell uptake of the new radioligands were analyzed using A431 human epidermoid carcinoma cells stably transfected with human CCK2R and mock transfected cells. Metabolic studies in BALB/c mice revealed a high resistance against enzymatic degradation for both radioligands. Biodistribution studies in tumor-xenografted athymic BALB/c nude mice at 1 h and 4 h p.i. showed that the two ^99mTc-labeled compounds showed varying uptake in receptor expressing organs, stomach and pancreas (1.3?10.4% IA/g), as well as kidneys, the main route of excretion (7.8?19.9% IA/g). The tumor uptake in A431-CCK2R xenografts was 24.75 ± 4.38% IA/g for [^99mTc]Tc-HYNIC-MGS5 and 42.48 ± 6.99% IA/g for [^99mTc]Tc-HYNIC-MGS11 at 4 h p.i., whereas the tumor-to-kidney ratio was comparable (2.6?3.3). On demand availability and potential application for radioguided surgery of a ^99mTc-labeled minigastrin analog support the further evaluation of these highly promising new compounds.

SUBMITTER: Klingler M

PROVIDER: S-EPMC6469167 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:BackgroundSomatostatin receptor targeting radiopeptides are successfully being used to image, stage, and monitor patients with neuroendocrine tumours. They are exclusively agonists that internalise upon binding to the relevant receptor. According to recent reports, antagonists may be preferable to agonists. To date, 99mTc-labelled somatostatin receptor antagonists have attracted little attention. Here, we report on a new somatostatin receptor subtype 2 (sst2) antagonist, SS-01 (p-Cl-Phe-cyclo(D-Cys-Tyr-D-Trp-Lys-Thr-Cys)D-Tyr-NH2), with the aim of developing 99mTc-labelled ligands for SPECT/CT imaging. SS-01 was prepared using Fmoc solid-phase synthesis and subsequently coupled to the chelators 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 6-carboxy-1,4,8,11-tetraazaundecane (N4), and 6-hydrazinonicotinic acid (HYNIC) to form the corresponding peptide-chelator conjugates SS-03, SS-04, and SS-05, respectively. SS-04 and SS-05 were radiolabelled with 99mTc and SS-03 with 177Lu. Binding affinity and antagonistic properties were determined using autoradiography and immunofluorescence microscopy. Biodistribution and small animal SPECT/CT studies were performed on mice bearing HEK293-rsst2 xenografts.ResultsThe conjugates showed low nanomolar sst2 affinity and antagonistic properties. 177Lu-DOTA-SS-01 (177Lu-SS-03) and 99mTc-N4-SS-01 (99mTc-SS-04) demonstrated high cell binding and low internalisation, whereas 99mTc-HYNIC/edda-SS-01 (99mTc-SS-05) showed practically no cellular uptake in vitro. The 99mTc-SS-04 demonstrated impressive tumour uptake at early time points, with 47% injected activity per gram tumour (%IA/g) at 1 h post-injection. The tumour uptake persisted after 4 h and was 32.5 %IA/g at 24 h. The uptake in all other organs decreased much more rapidly leading to high tumour-to-normal organ ratios, which was reflected in high-contrast SPECT/CT images.ConclusionsThese data indicate a very promising 99mTc-labelled sst2-targeting antagonist. The results demonstrate high sensitivity of the 99mTc-labelling strategy, which was shown to strongly influence the receptor affinity, contrary to corresponding agonists. 99mTc-SS-04 exhibits excellent pharmacokinetics and imaging properties and appears to be a suitable candidate for SPECT/CT clinical translation.

Project description:BACKGROUND:Among the many peptide receptor systems, gastrin-releasing-peptide (GRP) receptors, the mammalian equivalent of bombesin (BN) receptors, are potential targets for diagnosis and therapy of breast tumors due to their overexpression in various frequently occurring human cancers. The aim of this study was to synthesize and comparative evaluation of 99mTc-labeled new BN peptide analogs. Four new BN analogs, HYNIC-Asp[PheNle]BN(7-14)NH2, BN1; HYNIC-Pro-Asp[TyrMet]BN(7-14)NH2, BN2; HYNIC-Asp-Asn[Lys-CHAla-Nle]BN(7-14)NH2, BN3; and DOMA-GABA[Pro-Tyr-Nle]BN(7-14)NH2, BN4 were synthesized and biologically evaluated for targeted imaging of GRP receptor-positive breast-tumors. METHODS:Solid-phase synthesis using Fmoc-chemistry was adopted for the synthesis of peptides. BN1-BN4 analogs were better over the standard Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH2 (BNS). Lipophilicity, serum stability, internalization, and binding affinity studies were carried out using 99mTc-labeled analogs. Biodistribution and imaging analyses were performed on MDA-MB-231 cell-induced tumor-bearing mice. BN-analogs induced angiogenesis; tumor formation and GRP-receptor-expression were confirmed by histology and immunohistochemistry analyses of tumor sections and important tissue sections. RESULTS:All the analogs displayed ≥ 97% purity after the HPLC purification. BN-peptide-conjugates exhibited high serum stability and significant binding affinity to GRP-positive tumor; rapid internalization/externalization in/from MDA-MB-231 cells were noticed for the BN analogs. BN4 and BN3 exhibited higher binding affinity, stability than BN1 and BN2. Highly specific in vivo uptakes to the tumor were clearly visualized by scintigraphy; rapid excretion from non-target tissues via kidneys suggests a higher tumor-to-background ratio. BN4, among all the analogs, stimulates the expression of angiogenic markers to a maximum. CONCLUSION:Considering its most improved pharmacological characteristics, BN4 is thus considered as most promising probes for early non-invasive diagnosis of GRP receptor-positive breast tumors.

Dataset Information

Cholecystokinin-2 Receptor Targeting with Novel C-terminally Stabilized HYNIC-Minigastrin Analogs Radiolabeled with Technetium-99m.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets