Development of HER2-Targeted Theranostics for Diagnosis and Treatment of Breast Cancer

Abstract

A library of peptides targeting HER2 was established from in silico docking analysis of a pool of over 8000 preliminary sequences based on a recently developed anti-HER2 peptide KSPNPRF. The library has been synthesized by solid-phase Fmoc protocol and evaluated for their binding affinities. The peptides have a common core sequence, PNP, flanked by various amino acids and conjugated to a Cy5.5 fluorescent dye via a PEG4-K linker. Six peptides of this library have been evaluated by a magnetic beads-based fluorescence binding assay and compared to the reference KSPNPRF and a scrambled control peptide developed by the same group. With this assay, we found a KD of 49 nM for the reference, while the affinities of the six peptides of the library ranged from ~40 nM to ~2 μM. However due to the ambiguity of the data analysis, these values need to be further validated. We also report the development of a surface plasmon resonance protocol to evaluate the peptide library. For this, we have immobilised biotinylated HER2 on a streptavidin-coated chip and assessed the effect of the protein type, sensor chip, and regeneration conditions on the quality of the measurements of the KSP*, scrambled control peptide and Herceptin. While the SPR signal is sufficient, further investigations are needed to reduce non-specific binding and improve the signal quality.