Targeting of hepatocellular carcinoma with glypican-3-targeting peptide ligand.

Hepatocellular carcinoma is a common malignancy. The carcinoma cells express glypican-3 (GPC-3) on the cell membrane. GPC-3 is also expressed in melanoma cells. Therefore, GPC-3 might be a potential target for tumor imaging or therapy. Here, proteomic mass spectrometry was used to identify peptides that target GPC-3-expressing tumors. A mammalian expression vector expressing a FLAG-GPC-3 fusion protein was cloned for immunoprecipitation. With the use of liposomes, the vector was transfected into HepG2 (HepG2/FLAG-GPC-3) and HEK 293 cells, and the transfected cell lines were selected with geneticin. HepG2/FLAG-GPC-3 cells were used for immunoprecipitation of FLAG-GPC-3 fusion protein. Seven peptide candidates (L1-L7) were selected for GPC-3-targeting ligands by mass spectrometric analysis. The L5 peptide with 14 amino acids (Arg-Leu-Asn-Val-Gly-Gly-Thr-Tyr-Phe-Leu-Thr-Thr-Arg-Gln) showed selective binding to the GPC-3-expressing tumor cells, as did a shortened L5 peptide (L5-2) with seven amino acids (Tyr-Phe-Leu-Thr-Thr-Arg-Gln). These peptide ligands have potential as targeting moieties to GPC-3-expressing tumors for diagnostic and/or therapeutic purposes.