Design, Synthesis, and Evaluation of Near Infrared Fluorescent Multimeric RGD Peptides for Targeting Tumors

Abstract

Molecular interactions between RGD peptides and integrins are known to mediate many biological and pathological processes. This has led to an increased interest in the development of RGD compounds with high affinity and improved selectivity for integrin receptors. In this study, we synthesized and evaluated a series of multimeric RGD compounds constructed on a dicarboxylic acid-containing near-infrared (NIR) fluorescent dye (cypate) for tumor targeting. An array of NIR fluorescent RGD compounds was prepared efficiently, including one RGD monomer (cypate-(RGD)(2)-NH(2)), two RGD dimers (cypate-(RGD)(2)-NH(2) and cypate-(RGD-NH(2))(2)), one trimer (cypate-(RGD)(3)-NH(2)), two tetramers (cypate-(RGD)(4)-NH(2) and cypate-[(RGD)(2)-NH(2)](2)), one hexamer (cypate-[(RGD)(3)-NH(2)](2)), and one octamer (cypate-[(RGD)(4)-NH(2)](2)). The binding affinity of the multimeric RGD compounds for alpha(v)beta(3) integrin receptor (ABIR) showed a remarkable increase relative to the monomer cypate-RGD-NH(2). Generally, the divalent linear arrays of the multimeric RGD units bound the ABIR with slightly higher affinity than their monovalent analogues. These results suggest that the receptor binding affinity was not only dependent on the number of RGD moieties but also on the spatial alignments of the pendant peptides. Internalization of the compounds by ABIR-positive tumor cells (A549) was monitored by NIR fluorescence microscopy. The data showed that endocytosis of the octameric RGD derivative was significantly higher by comparison to other compounds in this study. In vivo noninvasive optical imaging and biodistribution data showed that the compounds were retained in A549 tumor tissue. These results clearly demonstrated that an array of simple RGD tripeptides on a NIR fluorescent dye core can be recognized by ABIR. Optimization of the spatial alignment of the RGD moieties through careful molecular design and library construction could induce multivalent ligand-receptor interactions useful for in vivo tumor imaging and tumor-targeted therapy.

Migfilin, a Molecular Switch in Regulation of Integrin Activation

“…S5, a punctate and a uniform fluorescent pattern. Similar patterns have been described in the literature of cells in which modified peptides have been taken up by cells (50,51). Similar micrographs were also obtained with A5 cells stably expressing ␣IIb␤3 (not shown).…”

Cell-penetrating and cell-targeting peptides in drug delivery

“…On the other hand, a dimeric ligand could also bind to two adjacent receptors, thus increasing the overall strength of the apparent affinity of the two receptors. It has to be pointed out that initial multimerization of targeting sequences have been made by repeating two or more adjacent recognition sequences [145] and this feature strengthens the hypothesis of a higher local concentration, since it appears unlikely that two adjacent receptors could bind to two sequences so closely linked along the same primary sequence. One might definitely solve this issue by modifying the length of the linker joining the two monomers.…”

18F-labeled mini-PEG spacered RGD dimer (18F-FPRGD2): synthesis and microPET imaging of αvβ3 integrin expression

“…In the clinical setting, 18 F-galacto-RGD also showed tumor uptake in certain cancer patients, yet the standardized uptake values were suboptimal owing to the relatively low α v β 3 binding affinity of the monomeric RGD peptide and the imperfect pharmacokinetics [6]. Therefore, we and others have developed a series of dimeric and multimeric RGD peptides to improve the integrin α v β 3 targeting efficacy [7][8][9][10][11][12][13][14][15][16][17][18][19]. One tracer in particular, 18 F-fluorobenzoyl-E[c(RGDyK)] 2 ( 18 F-FB-E[c(RGDyK)] 2 , denoted as 18 F-FRGD2, Fig.…”