TfR Binding Peptide Screened by Phage Display Technology - Characterization to Target Cancer Cells

Purpose: To screen an hTfR affinity peptide and investigate its activity in vitro.
Methods: hTfR affinity phage clones were screened from 7-mer phage display library, and their binding ability evaluated by enzyme-linked immunosorbent assay (ELISA). A competitive assay was performed to discover the peptide BP9 (BP9) binding site on the cells. The inhibitory effect of BP9 on the cells was determined using thiazolyl blue (MTT) assay. EGFP-BP9 fusion protein was expressed in E. coli, and its binding and localization on cells were determined by fluorescence microscopy and confocal microscopy, respectively.
Results: After three rounds of panning, recovery efficiency was 48-fold higher than that of the first round. The peptide BP9 sharing 2 identical amino acids to Tf showed high-affinity to hTfR, and possessed strong proliferation inhibition ratio on different tumour cells of 70 % (HepG2 cells)/77 % (SMMC-7221 cells) at a concentration of 0.1 mM, and 85 % (HepG2 cells)/81 % (SMMC-7221 cells) at a concentration of 0.001 mM for 48 h. The recombinant protein EGFP–BP9 could bind to tumour cells and gain entry via the endocytic pathway.
Conclusion: BP9 can bind to TfR and inhibit the proliferation of the tumour cells over-expressing TfR. The DNA sequence coding for BP9 was able to target the macromolecule to combine with TfR. BP9 may possess potential applications in cancer therapy.

Keywords
Peptide; hTfR; Transferrin receptor; Phage display technology; Enhanced green fluorescence protein; Target; Cancer cells