Technetium-99m-labeled Arg-Gly-Asp-conjugated alpha-melanocyte stimulating hormone hybrid peptides for human melanoma imaging☆

Abstract 

Introduction

The purpose of this study was to examine whether ^99mTc-labeled Arg-Gly-Asp (RGD)-conjugated alpha-melanocyte stimulating hormone (α-MSH) hybrid peptide targeting both melanocortin-1 (MC1) and α_vβ₃ integrin receptors was superior in melanoma targeting to ^99mTc-labeled α-MSH or RGD peptide targeting only the MC1 or α_vβ₃ integrin receptor.

Methods

RGD-Lys-(Arg¹¹)CCMSH, RAD-Lys-(Arg¹¹)CCMSH and RGD-Lys-(Arg¹¹)CCMSHscramble were designed to target both MC1 and α_vβ₃ integrin receptors, MC1 receptor only and α_vβ₃ integrin receptor only, respectively. The MC1 or α_vβ₃ integrin receptor binding affinities of three peptides were determined in M21 human melanoma cells. The melanoma targeting properties of ^99mTc-labeled RGD-Lys-(Arg¹¹)CCMSH, RAD-Lys-(Arg¹¹)CCMSH and RGD-Lys-(Arg¹¹)CCMSHscramble were determined in M21 human melanoma-xenografted nude mice. Meanwhile, the melanoma uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH was blocked with various non-radiolabeled peptides in M21 melanoma xenografts.

Results

RGD-Lys-(Arg¹¹)CCMSH displayed 2.0 and 403 nM binding affinities to both MC1 and α_vβ₃ integrin receptors, whereas RAD-Lys-(Arg¹¹)CCMSH or RGD-Lys-(Arg¹¹)CCMSHscramble lost their α_vβ₃ integrin receptor binding affinity by greater than 248-fold or MC1 receptor binding affinity by more than 100-fold, respectively. The melanoma uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH was 2.49 and 2.24 times (P < .05) the melanoma uptakes of ^99mTc-RAD-Lys-(Arg¹¹)CCMSH and ^99mTc-RGD-Lys-(Arg¹¹)CCMSHscramble at 2 h post-injection, respectively. Either RGD or (Arg¹¹)CCMSH peptide co-injection could block 42% and 57% of the tumor uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH, whereas the coinjection of RGD+(Arg¹¹)CCMSH peptide mixture could block 66% of the tumor uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH.

Conclusions

Targeting both MC1 and α_vβ₃ integrin receptors enhanced the melanoma uptake of ^99mTc-RGD-Lys-(Arg¹¹)CCMSH in M21 human melanoma xenografts. Flank M21 human melanoma tumors were clearly visualized by single photon emission computed tomography/computed tomographic imaging using ^99mTc-RGD-Lys-(Arg¹¹)CCMSH as an imaging probe, highlighting its potential use as a dual-receptor-targeting imaging probe for human melanoma detection.

Keywords: Arg-Gly-Asp-conjugated, Alpha-melanocyte stimulating hormone hybrid peptide, Dual receptor-targeting human melanoma imaging