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Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens.

ABSTRACT: We recently developed 125I- and 211At-labeled monomer RGD peptides using a novel radiolabeling method. Both labeled peptides showed high accumulation in the tumor and exhibited similar biodistribution, demonstrating their usefulness for radiotheranostics. This study applied the labeling method to a dimer RGD peptide with the aim of gaining higher accumulation in tumor tissues based on improved affinity with αvβ3 integrin. We synthesized an iodine-introduced dimer RGD peptide, E[c(RGDfK)] (6), and an 125/131I-labeled dimer RGD peptide, E[c(RGDfK)]{[125/131I]c[RGDf(4-I)K]} ([125/131I]6), and evaluated them as a preliminary step to the synthesis of an 211At-labeled dimer RGD peptide. The affinity of 6 for αvβ3 integrin was higher than that of a monomer RGD peptide. In the biodistribution experiment at 4 h postinjection, the accumulation of [125I]6 (4.12 ± 0.42% ID/g) in the tumor was significantly increased compared with that of 125I-labeled monomer RGD peptide (2.93 ± 0.08% ID/g). Moreover, the accumulation of [125I]6 in the tumor was greatly inhibited by co-injection of an excess RGD peptide. However, a single injection of [131I]6 (11.1 MBq) did not inhibit tumor growth in tumor-bearing mice. We expect that the labeling method for targeted alpha therapy with 211At using a dimer RGD peptide could prove useful in future clinical applications.

SUBMITTER: Echigo H

PROVIDER: S-EPMC8539346 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens.

Echigo Hiroaki H Mishiro Kenji K Fuchigami Takeshi T Shiba Kazuhiro K Kinuya Seigo S Ogawa Kazuma K

Molecules (Basel, Switzerland) 20211010 20

We recently developed 125I- and 211At-labeled monomer RGD peptides using a novel radiolabeling method. Both labeled peptides showed high accumulation in the tumor and exhibited similar biodistribution, demonstrating their usefulness for radiotheranostics. This study applied the labeling method to a dimer RGD peptide with the aim of gaining higher accumulation in tumor tissues based on improved affinity with αvβ3 integrin. We synthesized an iodine-intro ...[more]

PMID: 34684688

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Project description:Over the last years Gallium-68 ((68)Ga) has received tremendous attention for labeling of radiopharmaceuticals for positron emission tomography (PET). (68)Ga labeling of biomolecules is currently based on bifunctional chelators containing aminocarboxylates (mainly DOTA and NOTA). We have recently shown that cyclic peptide siderophores have very good complexing properties for (68)Ga resulting in high specific activities and excellent metabolic stabilities, in particular triacetylfusarinine-C (TAFC). We postulated, that, starting from its deacetylated form (Fusarinine-C (FSC)) trimeric bioconjugates are directly accessible to develop novel targeting peptide based (68)Ga labeled radiopharmaceuticals. As proof of principle we report on the synthesis and (68)Ga-radiolabeling of a trimeric FSC-RGD conjugate, [(68)Ga]FSC-(RGD)3, targeting αvβ3 integrin, which is highly expressed during tumor-induced angiogenesis. Synthesis of the RGD peptide was carried out applying solid phase peptide synthesis (SPPS), followed by the coupling to the siderophore [Fe]FSC via in situ activation using HATU/HOAt and DIPEA. Subsequent demetalation allowed radiolabeling of FSC-(RGD)3 with (68)Ga. The radiolabeling procedure was optimized regarding peptide amount, reaction time, temperature as well buffer systems. For in vitro evaluation partition coefficient, protein binding, serum stability, αvβ3 integrin binding affinity, and tumor cell uptake were determined. For in vitro tests as well as for the biodistribution studies αvβ3 positive human melanoma M21 and αvβ3 negative M21-L cells were used. [(68)Ga]FSC-(RGD)3 was prepared with high radiochemical yield (>98%). Distribution coefficient was -3.6 revealing a hydrophilic character, and an IC50 value of 1.8±0.6 nM was determined indicating a high binding affinity for αvβ3 integrin. [(68)Ga]FSC-(RGD)3 was stable in PBS (pH7.4), FeCl3- and DTPA-solution as well as in fresh human serum at 37°C for 2hours. Biodistribution assay confirmed the receptor specific uptake found in vitro. Uptake in the αvβ3 positive tumor was 4.3% ID/g 60min p.i. which was 3-fold higher than the monomeric [(68)Ga]NODAGA-RGD. Tumor to blood ratio of approx. 8 and tumor to muscle ratio of approx. 7 were observed. [(68)Ga]FSC-(RGD)3 serves as an example for the feasibility of a novel class of bifunctional chelators based on cyclic peptide siderophores and shows excellent targeting properties for αvβ3 integrin in vivo for imaging tumor-induced neovascularization.

Dataset Information

Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens.

Publications

Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens.

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