Evaluation of a Novel Arg-Gly-Asp-Conjugated α-Melanocyte Stimulating Hormone Hybrid Peptide for Potential Melanoma Therapy

The purpose of this Study was to determine whether Arg-Gly-Asp (RGD)-conjugated alpha-melanocyte stimulating hormone (alpha-MSH) hybrid peptide could be employed to target melanocortin-1 (MC1) receptor for potential melanoma therapy. Methods: The RGD motif {cyclic(Arg-Gly-ASP-DTyr-Asp)) was coupled to [Cys(3.4.10), DPhe(7), Arg(II)]alpha-MSH(3-13) {(Arg(II))CCMSH} to generate RGD-Lys-(Arg(II))CCMSH hybrid peptide. The MC1 receptor binding affinity of RGD-Lys-(Arg(II))CCMSH was determined in B16/F1 melanoma cells. The internalization and efflux, melanoma targeting and pharmacokinetic properties and single photon emission computed tomography/CT (SPECT/CT) imaging of (99m)Tc-RGD-Lys-(Arg(II))CCMSH were determined in B16/F1 melanoma cells and melanoma-bearing C57 mice. Clonogenic cytotoxic effect of RGD-Lys-(Arg(II))CCMSH was examined in B16/F1 melanoma cells. Results: RGD-Lys-(Arg(II))CCMSH displayed 2.1 nM MC1 receptor binding affinity. (99m)Tc-RGD-Lys-(Arg(II))CCMSH showed rapid internalization andextended retention in B16/F1 cells. The cellular uptake of (99m)Tc-RGD-Lys-(Arg(II))CCMSH was MC1 receptor-mediated. (99m)Tc-RGD-Lys-(Arg(II))CCMSH exhibited high tumor uptake (14.83 +/- 2.94% ID/g 2 h postinjection) and prolonged tumor retention (7.59 +/- 2.04% ID/g 24 h post injection) in B16/F1 melanoma-bearing mice. Nontarget organ uptakes were generally low except for the kidneys. Whole-body clearance of (99m)Tc-RGD-Lys-(Arg(II))CCMSH was rapid, with approximately 62% of the injected radioactivity cleared through the urinary system by 2 h postinjection. Flank melanoma tumors were clearly imaged by small animal SPECT/CT using (99m)Tc-RGD-Lys-(Arg(II))CCMSH as an imaging probe 2 h postinjection. Single treatment (3 h incubation) with 100 nM of RGD-Lys-(Arg(II))CCMSH significantly (p < 0.05) decreased the clonogenic survival of B16/F1 cells by 65% compared to (he untreated control cells. Conclusion: Favorable melanoma targeting property of (99m)Tc-RGD-Lys-(Arg(II))CCMSH and remarkable cytotoxic effect of RGD-Lys-(Arg(II))CCMSH in B16/F1 cells warranted the further evaluation of (188)Re-labeled alpha-MSH hybrid peptides as novel therapeutic peptides for melanoma treatment once the strategies of amino acid coinjection or structural modification of peptide sequence substantially reduce the renal uptake.