Dual receptor-targeting ⁹⁹mTc-labeled Arg-Gly-Asp-conjugated Alpha-Melanocyte stimulating hormone hybrid peptides for human melanoma imaging.

INTRODUCTION

The aim of this study was to examine whether the substitution of the Lys linker with the aminooctanoic acid (Aoc) and polyethylene glycol (PEG) linker could substantially decrease the non-specific renal uptake of (99m)Tc-labeled Arg-Gly-Asp-conjugated α-melanocyte stimulating hormone (α-MSH) hybrid peptides.

METHODS

The RGD motif {Arg-Gly-Asp-DTyr-Asp} was coupled to [Cys(3,4,10), D-Phe(7), Arg(11)]α-MSH₃₋₁₃ via the Aoc or PEG₂ linker to generate RGD-Aoc-(Arg(11))CCMSH and RGD-PEG-(Arg(11))CCMSH. The biodistribution results of (99m)Tc-RGD-Aoc-(Arg(11))CCMSH and (99m)Tc-RGD-PEG₂-(Arg(11))CCMSH were examined in M21 human melanoma-xenografted nude mice.

RESULTS

The substitution of Lys linker with Aoc and PEG₂ linker significantly reduced the renal uptake of (99m)Tc-RGD-Aoc-(Arg(11))CCMSH and (99m)Tc-RGD-PEG₂-(Arg(11))CCMSH by 58% and 63% at 2h post-injection. The renal uptake of (99m)Tc-RGD-Aoc-(Arg(11))CCMSH and (99m)Tc-RGD-PEG₂-(Arg(11))CCMSH was 27.93 ± 3.98 and 22.01 ± 9.89% ID/g at 2 h post-injection. (99m)Tc-RGD-Aoc-(Arg(11))CCMSH displayed higher tumor uptake than (99m)Tc-RGD-PEG₂-(Arg(11))CCMSH (2.35 ± 0.12 vs. 1.71 ± 0.25% ID/g at 2 h post-injection). The M21 human melanoma lesions could be clearly visualized by SPECT/CT using (99m)Tc-RGD-Aoc-(Arg(11))CCMSH as an imaging probe.

CONCLUSIONS

The favorable effect of Aoc and PEG₂ linker in reducing the renal uptake provided a new insight into the design of novel dual receptor-targeting radiolabeled peptides.