Identification, Characterization, and Optimization of Integrin αvβ₆-Targeting Peptides from a One-Bead One-Compound (OBOC) Library: Towards the Development of Positron Emission Tomography (PET) Imaging Agents.

Yng Tang,Ryan Davis,Julie Sutcliffe,Tanushree Ganguly

doi:10.3390/molecules24020309

Yng Tang, Ryan Davis + Show 2 more

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https://doi.org/10.3390/molecules24020309

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Abstract

The current translation of peptides identified through the one-bead one-compound (OBOC) technology into positron emission tomography (PET) imaging agents is a slow process, with a major delay between ligand identification and subsequent lead optimization. This work aims to streamline the development process of 18F-peptide based PET imaging agents to target the integrin αvβ6. By directly identify αvβ6–targeting peptides from a 9-mer 4-fluorobenzoyl peptide library using the on-bead two-color (OBTC) cell-screening assay, a total of 185 peptide beads were identified and 5 beads sequenced for further evaluation. The lead peptide 1 (VGDLTYLKK(FB), IC50 = 0.45 ± 0.06 μM, 25% stable in serum at 1 h) was further modified at the N-, C-, and bi-termini. C-terminal PEGylation increased the metabolic stability (>95% stable), but decreased binding affinity (IC50 = 3.7 ± 1 μM) was noted. C-terminal extension (1i, VGDLTYLKK(FB)KVART) significantly increased binding affinity for integrin αvβ6 (IC50 = 0.021 ± 0.002 μM), binding selectivity for αvβ6-expressing cells (3.1 ± 0.8:1), and the serum stability (>99% stable). Our results demonstrate the challenges in optimizing OBOC-derived peptides, indicate both termini of 1 are sensitive to modifications, and show that further modification of 1 is necessary to demonstrate utility as an 18F-peptide imaging agent.

Highlights

The expanding use of positron emission tomography (PET) imaging in oncology to aid in early detection, more accurate diagnosis, and patient treatment stratification has led to an increased demand of novel peptide-based molecular imaging agents [1]
This work utilized the one-bead one-compound (OBOC) technology, applied the on-bead two-color (OBTC) fluorescent cell screening assay, and provided a framework for optimization of OBOC-derived peptides to streamline the development of 18 F-peptide based imaging agents for PET
To expedite the development of peptide identified from OBOC library into useful imaging agents, we eliminated the need of post-screening modification by designing a 4-fluorobenzoyl peptide library, improved the traditional on-bead manual library screening using OBTC fluorescent cell-screening, and further improved the binding affinity, selectivity, and serum stability of the lead peptide using numerous strategies, including N, C, and bi-terminal modifications

Summary

Introduction

The expanding use of positron emission tomography (PET) imaging in oncology to aid in early detection, more accurate diagnosis, and patient treatment stratification has led to an increased demand of novel peptide-based molecular imaging agents [1]. Peptides are attractive as imaging agents for several reasons, including favorable pharmacokinetic properties, such as high target affinity, good tumor penetration, rapid non-specific clearance, and minimal immunogenicity [2]. Molecules 2019, 24, 309; doi:10.3390/molecules24020309 www.mdpi.com/journal/molecules (e.g., 97% positron emission), and the ease of production with high yield and molar activity for PET imaging [4]. Combinatorial libraries, such as the one-bead one-compound (OBOC) and phage display, have provided indispensable tools for rapid identification of peptides for a given biological target, especially those expressed on the cell surface [5]. The current translation of OBOC-derived peptides from bench to bedside remains a slow process [11]

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