In Vitro Performance of Published Glypican 3-Targeting Peptides TJ12P1 and L5 Indicates Lack of Specificity and Potency.

Background: Glypican 3 (GPC3), a plasma membrane heparan sulfate proteoglycan, is overexpressed on human hepatocellular carcinoma and may represent a promising biomarker. Several studies have reported peptides that selectively bind to GPC3 and could serve as scaffolds for imaging or therapeutic agents. Materials and Methods: We synthesized variants of two previously published peptides, DHLASLWWGTEL (TJ12P1) and RLNVGGTYFLTTRQ (L5), and evaluated their in vitro binding performance in paired isogenic cell lines, A431(GPC3(-)) and A431-GPC3(+) (G1), as well as the liver cancer cell line HepG2. Using flow cytometry and biolayer interferometry (BLI), we compared the binding of the TJ12P1 and L5 peptide variants to the binding of corresponding scrambled peptides having the same amino acid composition, but in random sequence. Results: While both peptides bound to G1 and HepG2, they also bound to A431. The corresponding scrambled peptides demonstrated greater apparent binding to both G1 and A431 than their specific counterparts. BLI confirmed lack of binding at 0.5-1 mu M for both peptides. Conclusions: We conclude that neither TJ12P1 nor L5 variant demonstrates selectivity for GPC3 at concentrations near the reported K-D, and that the peptides lack potency or are nonspecific, making them inadequate for use as imaging agents.