open access

Vol 19, No 2 (2016)
Original articles
Published online: 2016-07-29
Submitted: 2016-07-21
Accepted: 2016-07-23
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Oxidation of methionine — is it limiting the diagnostic properties of 99mTc-labeled Exendin-4, a Glucagon-Like Peptide-1 receptor agonist?

Barbara Janota, Urszula Karczmarczyk, Ewa Laszuk, Piotr Garnuszek, Renata Mikołajczak
DOI: 10.5603/NMR.2016.0021
·
Pubmed: 27479787
·
Nucl. Med. Rev 2016;19(2):104-110.

open access

Vol 19, No 2 (2016)
Original articles
Published online: 2016-07-29
Submitted: 2016-07-21
Accepted: 2016-07-23

Abstract

BACKGROUND: Preliminary clinical evaluation of 99mTc-EDDA/HYNIC-Met14-Exendin-4 showed that the complex offers new diagnostic possibilities for insulinoma and MTC. Exendin-4 contains methionine at position 14 in the amino acid chain, which may be oxidized to methionine sulfoxide and, from the pharmaceutical point of view, the oxidized moiety becomes an undesired impurity in the final radioactive preparation. Therefore, the aim of this study was to investigate the influence of commonly used methods to eliminate the effect of methionine oxidation in peptides, i.e. the replacement of methionine by norleucine (Nle) and the addition of L-methionine, on the in vitro stability and the biodistribution.

MATERIAL AND METHODS: 99mTc-EDDA/HYNIC-Met14-Exendin-4, 99mTc-EDDA/HYNIC-Nle14-Exendin-4, 99mTc-EDDA/HYNIC-Met14-Ex­endin-4 with the addition of L-methionine and an oxidized form of Exendin-4, i.e. 99mTc-EDDA/HYNIC-Met14(ox)-Exendin-4 were compared in vivo with 68Ga-NODAGA-Nle14-Exendin-4 in normal Wistar rats. The stability and lipophilicity were determined in vitro.

RESULTS: Biodistribution studies confirmed the specific uptake of all tested complexes in the GLP-1 positive organs: lungs, pancreas and stomach. The uptake of 99mTc-EDDA/HYNIC-Met14-Exendin-4 with the addition of L-methionine and for 68Ga-NODAGA-Nle14-Exendin-4 at 1h p.i. was around 2-fold higher than that of 99mTc-EDDA/HYNIC-Met14-Exendin-4 and 99mTc-EDDA/HYNIC-Nle14-Exendin-4.

CONCLUSION: Although the substitution of methionine by norleucine in the HYNIC-Exendin-4 did not result in improved bio­distribution, the use of L-methionine, as the excipient that inhibits the oxidation of methionine in the peptide chain resulted in higher lung/blood and stomach/blood uptake ratios. Our results confirmed that methionine at position 14 of amino acid chain of Exendin-4 plays an important role in the interaction with GLP-1 receptor positive tissue.

Abstract

BACKGROUND: Preliminary clinical evaluation of 99mTc-EDDA/HYNIC-Met14-Exendin-4 showed that the complex offers new diagnostic possibilities for insulinoma and MTC. Exendin-4 contains methionine at position 14 in the amino acid chain, which may be oxidized to methionine sulfoxide and, from the pharmaceutical point of view, the oxidized moiety becomes an undesired impurity in the final radioactive preparation. Therefore, the aim of this study was to investigate the influence of commonly used methods to eliminate the effect of methionine oxidation in peptides, i.e. the replacement of methionine by norleucine (Nle) and the addition of L-methionine, on the in vitro stability and the biodistribution.

MATERIAL AND METHODS: 99mTc-EDDA/HYNIC-Met14-Exendin-4, 99mTc-EDDA/HYNIC-Nle14-Exendin-4, 99mTc-EDDA/HYNIC-Met14-Ex­endin-4 with the addition of L-methionine and an oxidized form of Exendin-4, i.e. 99mTc-EDDA/HYNIC-Met14(ox)-Exendin-4 were compared in vivo with 68Ga-NODAGA-Nle14-Exendin-4 in normal Wistar rats. The stability and lipophilicity were determined in vitro.

RESULTS: Biodistribution studies confirmed the specific uptake of all tested complexes in the GLP-1 positive organs: lungs, pancreas and stomach. The uptake of 99mTc-EDDA/HYNIC-Met14-Exendin-4 with the addition of L-methionine and for 68Ga-NODAGA-Nle14-Exendin-4 at 1h p.i. was around 2-fold higher than that of 99mTc-EDDA/HYNIC-Met14-Exendin-4 and 99mTc-EDDA/HYNIC-Nle14-Exendin-4.

CONCLUSION: Although the substitution of methionine by norleucine in the HYNIC-Exendin-4 did not result in improved bio­distribution, the use of L-methionine, as the excipient that inhibits the oxidation of methionine in the peptide chain resulted in higher lung/blood and stomach/blood uptake ratios. Our results confirmed that methionine at position 14 of amino acid chain of Exendin-4 plays an important role in the interaction with GLP-1 receptor positive tissue.

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Keywords

68Ga-NODAGA-Nle14-Exendin-4, 99mTc-EDDA/HYNIC-Met14-Exendin-4, 99mTc-EDDA/HYNIC-Nle14-Exendin-4, L-methionine, GLP-1, methionine sulfoxide

About this article
Title

Oxidation of methionine — is it limiting the diagnostic properties of 99mTc-labeled Exendin-4, a Glucagon-Like Peptide-1 receptor agonist?

Journal

Nuclear Medicine Review

Issue

Vol 19, No 2 (2016)

Pages

104-110

Published online

2016-07-29

DOI

10.5603/NMR.2016.0021

Pubmed

27479787

Bibliographic record

Nucl. Med. Rev 2016;19(2):104-110.

Keywords

68Ga-NODAGA-Nle14-Exendin-4
99mTc-EDDA/HYNIC-Met14-Exendin-4
99mTc-EDDA/HYNIC-Nle14-Exendin-4
L-methionine
GLP-1
methionine sulfoxide

Authors

Barbara Janota
Urszula Karczmarczyk
Ewa Laszuk
Piotr Garnuszek
Renata Mikołajczak

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