Influence of Linker Molecules in Hexavalent RGD Peptides on Their Multivalent Interactions with Integrin α_vβ₃

Abstract

Multivalent RGD peptides have been used as an excellent targeting vector to integrin α_vβ₃-positive tumors. However, little attention has been paid to the influence of linker molecules in multivalent RGD peptides on their dissociation kinetics from tumor cells. In this study, we evaluated the dissociation kinetics of ^99mTc-labeled hexavalent RGD peptides which have (CH₂-CH₂-O)_<i>n</i> (<i>n</i> = 4, [^99mTc][Tc(L1)₆]⁺ and <i>n</i> = 12, [^99mTc][Tc(L2)₆]⁺) or (_DPro-Gly)_<i>n</i> (<i>n</i> = 1, [^99mTc][Tc(L3)₆]⁺; <i>n</i> = 6, [^99mTc][Tc(L4)₆]⁺; and <i>n</i> = 9, [^99mTc][Tc(L5)₆]⁺) as a linker molecule. The results showed that [^99mTc][Tc(L4)₆]⁺ and [^99mTc][Tc(L5)₆]⁺ displayed slower dissociation kinetics and [^99mTc][Tc(L4)₆]⁺ showed exceptionally high <i>in vitro</i> cellular uptake (203.1 ± 16.7% dose/mg protein) and the highest tumor to blood ratio (138.1 ± 26.3 at 4 h p.i.) in tumor bearing nude mice. These findings indicate that the use of appropriate length of (_DPro-Gly)_<i>n</i> would maximize the binding of multivalent RGD peptides to clustered integrin α_vβ₃.