Introduction of an 8-Aminooctanoic Acid Linker Enhances Uptake of ^99mTc-Labeled Lactam Bridge–Cyclized α-MSH Peptide in Melanoma

Abstract

The purpose of this study was to examine the effects of amino acid, hydrocarbon and polyethylene glycol (PEG) linkers on melanoma targeting and imaging properties of 99mTc-labeled lactam bridge-cyclized HYNIC-linker-Nle-CycMSHhex {hydrazinonicotinamide-linker-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2} peptides. Methods four novel peptides {HYNIC-GGGNle-CycMSHhex, HYNIC-GSGNle-CycMSHhex, HYNIC-PEG2Nle-CycMSHhex and HYNIC-AocNle-CycMSHhex} were designed and synthesized. The melanocortin-1 (MC1) receptor binding affinities of the peptides were determined in B16/F1 melanoma cells. The biodistribution of 99mTc(EDDA)-HYNIC-GGGNle-CycMSHhex, 99mTc(EDDA)-HYNIC-GSGNle-CycMSHhex, 99mTc(EDDA)-HYNIC-PEG2Nle-CycMSHhex and 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex were determined in B16/F1 melanoma-bearing C57 mice at 2 h post-injection to select a lead peptide for further evaluation. The melanoma targeting and imaging properties of 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex were further examined because of its high melanoma uptake. Results The IC50 values of HYNIC-GGGNle-CycMSHhex, HYNIC-GSGNle-CycMSHhex, HYNIC-PEG2Nle-CycMSHhex, and HYNIC-AocNle-CycMSHhex were 0.7 ± 0.1, 0.8 ± 0.09, 0.4 ± 0.08, and 0.3 ± 0.06 nM in B16/F1 melanoma cells, respectively. Among these four 99mTc-labeled peptides, 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex displayed the highest melanoma uptake (22.3 ± 1.72% ID/g) at 2 h post-injection. 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex exhibited high tumor to normal organ uptake ratios except for the kidneys. The tumor/kidney uptake ratios of 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex were 3.29, 3.63 and 6.78 at 2, 4 and 24 h post-injection. The melanoma lesions were clearly visualized by single photon emission computed tomography (SPECT)/CT using 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex as an imaging probe at 2 h post-injection. Conclusion High melanoma uptake and fast urinary clearance of 99mTc(EDDA)-HYNIC-AocNle-CycMSHhex highlighted its potential for metastatic melanoma detection in the future.

Imaging human melanoma using a novel Tc-99m-labeled lactam bridge-cyclized alpha-MSH peptide

“…Melanocortin-1 (MC1) receptor is a distinct molecular target due to its over-expression on murine and human melanoma cells. 2–6 Over the past several years, we and others have developed 99m Tc-labeled α-MSH peptides 7–14 to target the MC1 receptors for melanoma imaging, taking advantage of the ideal imaging properties of 99m Tc (140-keV γ-photon and 6 h half-life) and its wide application in nuclear medicine. Specifically, we have developed a novel class of 99m Tc-labeled lactam bridge-cyclized α-MSH peptides building upon the construct of GGNle-CycMSH hex {Gly-Gly-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH 2 } 10 .…”

“…14 Specifically, we inserted -GlyGlyGly- (GGG), -GlySerGly- (GSG), -Aoc- (8-aminooctanoic acid) and -PEG 2 -linkers between the HYNIC and Nle-CycMSH hex moiety to generate new HYNIC-linker-Nle-CycMSH hex peptides. The introduction of -GGG-, -GSG-, -Aoc- and -PEG 2 - linkers retained low nanomolar (0.3–0.8 nM) MC1 receptor binding affinities of the peptides.…”

Imaging Bradykinin B1 Receptor with68Ga-Labeled [des-Arg10]Kallidin Derivatives: Effect of the Linker on Biodistribution and Tumor Uptake

“…[31][32] Besides the previously tested linear carbon chain and polyethylene glycol, there are two other types of linkers, polyamino acid and the cationic 4-amino-(1-carboxymethyl)piperidine (Pip), that are also commonly used for the design of radio-peptides. [33][34][35][36][37][38] For comparison and in hopes to optimize the tumor-to-background contrast through the selection of linker, we synthesized two more analogs, 68 Ga-P04115 and 68 Ga-P04168 (Table 1 and Fig. 1), containing Gly-Gly and Pip, respectively as the linker.…”

Metastatic melanoma imaging using a novel Tc-99m-labeled lactam-cyclized alpha-MSH peptide

“…The B16/F1 melanoma lesions could be clearly visualized by single photon emission computed tomography (SPECT)/CT using 99m Tc(EDDA)-HYNIC-Aoc-Nle-CycMSH hex as an imaging probe. 21 …”

“…99m Tc(EDDA)-HYNIC-Aoc-Nle-CycMSH hex was readily prepared according to our published procedure 21 with greater than 95% radiolabeling yield, and was completely separated from the excess non-labeled peptide by RP-HPLC. The retention time of 99m Tc(EDDA)-HYNIC-Aoc-Nle-CycMSH hex and HYNIC-Aoc-Nle-CycMSH hex was 20 and 18 min, respectively.…”