title: Dimerization of a phage-display selected peptide for imaging of αvβ6- integrin: two approaches to the multivalent effect.
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.
authors.affiliation: 1. Department of Radiology.
authors.forename: Ajay N
authors.initials: AN
authors.lastname: Singh
authors.affiliation: 2. Department of Internal Medicine.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McGuire
authors.affiliation: 2. Department of Internal Medicine.
authors.forename: Shunzi
authors.initials: S
authors.lastname: Li
authors.affiliation: 1. Department of Radiology.
authors.forename: Guiyang
authors.initials: G
authors.lastname: Hao
authors.affiliation: 1. Department of Radiology.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.affiliation: 1. Department of Radiology, ; 3. Advanced Imaging Research Center, and ; 4. The Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Xiankai
authors.initials: X
authors.lastname: Sun
authors.affiliation: 2. Department of Internal Medicine, ; 4. The Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Kathlynn C
authors.initials: KC
authors.lastname: Brown
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D001435:Bacteriophages / Q000235:genetics; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging*; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes / Q000493:pharmacokinetics*; D019281:Dimerization; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D019151:Peptide Library; D010455:Peptides / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D049268:Positron-Emission Tomography; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: D000951:Antigens, Neoplasm; D003301:Copper Radioisotopes; D016023:Integrins; D019151:Peptide Library; D010455:Peptides; D019275:Radiopharmaceuticals; C073878:integrin alphavbeta6
keywords: Integrin; Lung Cancer; Molecular Imaging; Peptide.; Positron Emission Tomography