Theranostics 2014; 4(7):745-760. doi:10.7150/thno.7811

Research Paper

Dimerization of a Phage-Display Selected Peptide for Imaging of αvβ6- Integrin: Two Approaches to the Multivalent Effect

Ajay N. Singh1, Michael J. McGuire2, Shunzi Li2, Guiyang Hao1, Amit Kumar1, Xiankai Sun1,3,4✉, Kathlynn C. Brown2,4✉

1. Department of Radiology,
2. Department of Internal Medicine,
3. Advanced Imaging Research Center, and
4. The Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas.

Abstract

The integrin αvβ6 is an emerging biomarker for non-small cell lung cancer (NSCLC). An αvβ6-binding peptide was previously selected from a phage-displayed peptide library. Here, we utilize a multivalent design to develop a peptidic probe for positron emission tomography (PET) imaging of αvβ6+ NSCLC tumors. Multimeric presentation of this peptide, RGDLATLRQL, on a bifunctional copper chelator was achieved using two approaches: dimerization of the peptide followed by conjugation to the chelator (H2-D10) and direct presentation of two copies of the peptide on the chelator scaffold (H2-(M10)2). Binding affinities of the divalent peptide conjugates are four-fold higher than their monovalent counterpart (H2-M10), suggestive of multivalent binding. PET imaging using the bivalent 64Cu-labeled conjugates showed rapid and persistent accumulation in αvβ6+ tumors. By contrast, no significant accumulation was observed in αvβ6- tumors. Irrespective of the dimerization approach, all divalent probes showed three-fold higher tumor uptake than the monovalent probe, indicating the role of valency in signal enhancement. However, the divalent probes have elevated uptake in non-target organs, especially the kidneys. To abrogate nonspecific uptake, the peptide's N-terminus was acetylated. The resultant bivalent probe, 64Cu- AcD10, showed drastic decrease of kidney accumulation while maintaining tumor uptake. In conclusion, we developed an αvβ6-integrin specific probe with optimized biodistribution for noninvasive PET imaging of NSCLC. Further, we have demonstrated that use of multivalent scaffolds is a plausible method to improve library selected peptides, which would be suboptimal or useless otherwise, for imaging probe development.

Keywords: Lung Cancer, Molecular Imaging, Positron Emission Tomography, Integrin, Peptide.

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How to cite this article:
Singh AN, McGuire MJ, Li S, Hao G, Kumar A, Sun X, Brown KC. Dimerization of a Phage-Display Selected Peptide for Imaging of αvβ6- Integrin: Two Approaches to the Multivalent Effect. Theranostics 2014; 4(7):745-760. doi:10.7150/thno.7811. Available from http://www.thno.org/v04p0745.htm