Using in vitro phage display to identify αvβ6-specific peptides as molecular imaging probes

Objectives The purpose of this study is to use the phage display technique to isolate novel ligands for the integrin αvβ6, a receptor that is over-expressed in many cancers and has been linked to elevated aggressiveness of the disease. Phage display offers a fast, high-throughput method of identifying peptide sequences with increased affinity for a specific target or biomarker.

Methods The positive and negative cell lines DX3/puro/β6 (αvβ6 positive) and DX3/puro (αvβ6 negative) were used as screens for αvβ6 -specific ligands. The phage library used displayed peptides with 7 randomized amino acid positions on its coat protein pIII. Phage display was conducted with four rounds of panning, each with a separate negative and positive screen to eliminate non-specific peptides. From these rounds of panning, three repeating peptides were isolated. These three peptides were synthesized on solid phase using standard Fmoc chemistry and characterized by HPLC. These sequences were subsequently radiolabeled with 4-[18F]fluorobenzoic acid (n=3).

Results The first peptide had a radiochemical purity of 76.7 ± 5.4% and radiochemical yield of 34.68 ± 8.94% decay corrected. The second peptide resulted in a radiochemical purity of 82.4 ± 12.7% and radiochemical yield of 41.56 ± 5.99% decay corrected. On average, the third peptide demonstrates a decay corrected radiochemical yield of 37% with a radiochemical purity of 80%.

Conclusions The αvβ6 -targeted peptides all resulted in high radiochemical yields. Further in vitro and in vivo screening of these peptides is ongoing.

Research Support Office of Science, United States Department of Energy grant DE-SC000206