While the switch from RGD to RAD in RGD-Lys-(Arg11)CCMSH decreased the αvβ3 integrin receptor binding affinity by 248-fold, surprisingly, the switch from RGD to RAD dramatically enhanced the MC1 receptor binding affinity of RAD-Lys-(Arg11)CCMSH as compared to RGD-Lys-(Arg11)CCMSH (0.3 vs. 2.0 nM) in M21 melanoma cells [114]. Here, RRAD is linked to melanoma.