Novel Cu-64-Labeled NOTA-Conjugated Lactam-Cyclized Alpha-Melanocyte-Stimulating Hormone Peptides with Enhanced Tumor to Kidney Uptake Ratios

The aim of this study was to evaluate the effect of linker on tumor targeting and biodistribution of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) {Cu-64-1,4,7-triazacyclononane-1,4,7-triyl-triacetic acid-polyethylene glycol-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2} and Cu-64-NOTA-AocNle-CycMSH(hex) {Cu-64-NOTA-8-aminooctanoic acid-Nle-CycMSH(hex)} on melanoma-bearing mice. NOTA-PEG(2)Nle-CycMSH(hex) and NOTA-AocNle-CycMSH(hex) were synthesized and purified by HPLC. The melanocortin-1 (MC1) receptor binding affinities of the peptides were examined on B16/F10 melanoma cells. The biodistributions of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) and Cu-64-NOTA-AocNle-CycMSH(hex) were determined on B16/F10 melanoma-bearing C57 mice. The melanoma imaging property of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) was further examined on B16/F10 melanoma-bearing C57 mice because of its higher melanoma uptake than Cu-64-NOTA-AocNle-CycMSH(hex). The IC50 values of NOTA-PEG(2)Nle-CycMSH(hex) and NOTA-AocNle-CycMSH(hex) were 1.24 ?? 0.07 and 2.75 +/- 0.48 nM on B10/F10 melanoma cells. Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) and Cu-64-NOTA-AocNle-CycMSH(hex) were readily prepared with more than 90% radiolabeling yields and showed MC1R-specific binding on B16/F10 cells. Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) exhibited higher tumor uptake than Cu-64-NOTA-AocNle-CycMSH(hex) at 0.5, 2, 4, and 24 h post-injection. The tumor uptake of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) was 16.23 +/- 0.42, 19.59 +/- 1.48, 12.83 +/- 1.69, and 8.78 +/- 2.29% ID/g at 0.5, 2, 4, and 24 h post-injection, respectively. Normal organ uptake of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) was lower than 2% ID/g at 2 h post-injection except for kidney uptake. The renal uptake of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) was 3.66 +/- 0.52, 3.27 +/- 0.52, and 1.47 +/- 0.56 ID/g at 2, 4, and 24 h post-injection, respectively. Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) showed high tumor to normal organ uptake ratios after 2 h post-injection. The B16/F10 melanoma lesions could be clearly visualized by positron emission tomography (PET) using Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) as an imaging probe at 2 h post-injection. High tumor uptake and low kidney uptake of Cu-64-NOTA-PEG(2)Nle-CycMSH(hex) underscored its potential as an MC1R-theranostic peptide for melanoma and therapy.