Introduction of a Polyethylene Glycol Linker Improves Uptake of 67Cu-NOTA-Conjugated Lactam-Cyclized Alpha-Melanocyte-Stimulating Hormone Peptide in Melanoma

The aim of this study was to evaluate the effect of linker on tumor targeting and biodistribution of 67Cu-NOTA-PEG2Nle-CycMSHhex {67Cu-1,4,7-triazacyclononane-1,4,7-triyl-triacetic acid-polyethylene glycol-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2} and 67Cu-NOTA-GGNle-CycMSHhex {67Cu-NOTA-GlyGlyNle-CycMSHhex} on melanoma-bearing mice. NOTA-PEG2Nle-CycMSHhex and NOTA-GGNle-CycMSHhex were synthesized and purified by HPLC. The biodistribution of 67Cu-NOTA-PEG2Nle-CycMSHhex and 67Cu-NOTA-GGNle-CycMSHhex was determined in B16/F10 melanoma-bearing C57 mice. The melanoma imaging property of 67Cu-NOTA-PEG2Nle-CycMSHhex was further examined in B16/F10 melanoma-bearing C57 mice. 67Cu-NOTA-PEG2Nle-CycMSHhex exhibited higher tumor uptake than 67Cu-NOTA-GGNle-CycMSHhex at 2, 4, and 24 h post-injection. The tumor uptake of 67Cu-NOTA-PEG2Nle-CycMSHhex was 27.97 ± 1.98, 24.10 ± 1.83, and 9.13 ± 1.66% ID/g at 2, 4, and 24 h post-injection, respectively. Normal organ uptake of 67Cu-NOTA-PEG2Nle-CycMSHhex was lower than 2.6% ID/g at 4 h post-injection, except for kidney uptake. The renal uptake of 67Cu-NOTA-PEG2Nle-CycMSHhex was 6.43 ± 1.31, 2.60 ± 0.79, and 0.90 ± 0.18% ID/g at 2, 4, and 24 h post-injection, respectively. 67Cu-NOTA-PEG2Nle-CycMSHhex showed high tumor to normal organ uptake ratios after 2 h post-injection. The B16/F10 melanoma lesions could be clearly visualized by single photon emission computed tomography (SPECT) using 67Cu-NOTA-PEG2Nle-CycMSHhex as an imaging probe at 4 h post-injection. The favorable tumor targeting and biodistribution properties of 67Cu-NOTA-PEG2Nle-CycMSHhex underscored its potential as an MC1R-targeted therapeutic peptide for melanoma treatment.