A novel RGD-conjugated alpha-MSH hybrid peptide for melanoma therapy

Objectives Arg-Gly-Asp (RGD)-containing peptide could induce apoptosis after the peptide entered into the cells. The purpose of this study was to determine whether RGD-conjugated alpha-melanocyte stimulating hormone (α-MSH) hybrid peptide could be used to target melanocortin-1 (MC1) receptor for melanoma therapy.

Methods The RGD motif {cyclic(Arg-Gly-Asp-DTyr-Asp)} was coupled to [Cys^3,4,10, D-Phe⁷, Arg¹¹]α-MSH_3-13 {(Arg¹¹)CCMSH} to generate RGD-Lys-(Arg¹¹)CCMSH hybrid peptide. The MC1 receptor binding affinity of RGD-Lys-(Arg¹¹)CCMSH was determined in B16/F1 melanoma cells. The internalization and efflux, melanoma targeting and pharmacokinetic properties and SPECT/CT imaging of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH were determined in B16/F1 cells and B16/F1 melanoma-bearing C57 mice.

Results RGD-Lys-(Arg¹¹)CCMSH displayed 2.1 nM receptor binding affinity in B16/F1 cells. ^99mTc-RGD-Lys-(Arg¹¹)CCMSH was prepared with >95% radiolabeling yield. ^99mTc-RGD-Lys-(Arg¹¹)CCMSH showed rapid internalization and extended retention in B16/F1 cells. The cellular uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH was MC1 receptor-mediated. ^99mTc-RGD-Lys-(Arg¹¹)CCMSH exhibited high tumor uptake (14.83±2.94 %ID/g 2 h post-injection) and prolonged tumor retention (7.59±2.04 %ID/g 24 h post-injection) in B16/F1 melanoma-bearing mice. The uptakes for non-target organs were generally low except for the kidneys. Flank melanoma tumors were clearly imaged using ^99mTc-RGD-Lys-(Arg¹¹)CCMSH as an imaging probe 2 h post-injection.

Conclusions Favorable melanoma targeting property of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH warranted further evaluation of ¹⁸⁸Re-labeled α-MSH hybrid peptides as novel therapeutic peptides for melanoma treatment.