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Journal of Biomedicine and Biotechnology
Volume 2012 (2012), Article ID 368075, 8 pages
http://dx.doi.org/10.1155/2012/368075
Research Article

1 1 1 I n -Labeled Cystine-Knot Peptides Based on the Agouti-Related Protein for Targeting Tumor Angiogenesis

1Department of Nuclear Medicine, Shanghai Sixth Peopleโ€™s Hospital, Shanghai Jiao Tong University, Shanghai 200233, China
2Molecular Imaging Program at Stanford (MIPS), Department of Radiology, Stanford Cancer Institute, and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, CA 94305, USA
3Department of Bioengineering, Stanford Cancer Institute, and Bio-X Program, Stanford University, Stanford, CA 94305, USA

Received 14 December 2011; Revised 29 January 2012; Accepted 30 January 2012

Academic Editor: David J. Yang

Copyright ยฉ 2012 Lei Jiang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Agouti-related protein (AgRP) is a 4-kDa cystine-knot peptide of human origin with four disulfide bonds and four solvent-exposed loops. The cell adhesion receptor integrin ๐›ผ v ๐›ฝ 3 is an important tumor angiogenesis factor that determines the invasiveness and metastatic ability of many malignant tumors. AgRP mutants have been engineered to bind to integrin ๐›ผ v ๐›ฝ 3 with high affinity and specificity using directed evolution. Here, AgRP mutants 7C and 6E were radiolabeled with 111In and evaluated for in vivo targeting of tumor integrin ๐›ผ v ๐›ฝ 3 receptors. AgRP peptides were conjugated to the metal chelator 1, 4, 7, 10-tetra-azacyclododecane- N, N ๎…ž , N ๎…ž ๎…ž , N ๎…ž ๎…ž ๎…ž -tetraacetic acid (DOTA) and radiolabeled with 111In. The stability of the radiopeptides 111In-DOTA-AgRP-7C and 111In-DOTA-AgRP-6E was tested in phosphate-buffered saline (PBS) and mouse serum, respectively. Cell uptake assays of the radiolabeled peptides were performed in U87MG cell lines. Biodistribution studies were performed to evaluate the in vivo performance of the two resulting probes using mice bearing integrin-expressing U87MG xenograft tumors. Both AgRP peptides were easily labeled with 111In in high yield and radiochemical purity (>99%). The two probes exhibited high stability in phosphate-buffered saline and mouse serum. Compared with 111In-DOTA-AgRP-6E, 111In-DOTA-AgRP-7C showed increased U87MG tumor uptake and longer tumor retention ( 5 . 7 4 ยฑ 1 . 6 0 and 1 . 2 9 ยฑ 0 . 0 2 %ID/g at 0.5 and 24 h, resp.), which was consistent with measurements of cell uptake. Moreover, the tumor uptake of 111In-DOTA-AgRP-7C was specifically inhibited by coinjection with an excess of the integrin-binding peptidomimetic c(RGDyK). Thus, 111In-DOTA-AgRP-7C is a promising probe for targeting integrin ๐›ผ v ๐›ฝ 3 positive tumors in living subjects.