Screening and identification of a renal carcinoma specific peptide from a phage display peptide library

Abstract

Background: Specific peptide ligands to cell surface receptors have been extensively used in tumor research and clinical applications. Phage display technology is a powerful tool for the isolation of cell-specific peptide ligands. To screen and identify novel markers for renal cell carcinoma, we evaluated a peptide that had been identified by phage display technology.

Methods: A renal carcinoma cell line A498 and a normal renal cell line HK-2 were used to carry out subtractive screening in vitro with a phage display peptide library. After three rounds of panning, there was an obvious enrichment for the phages specifically binding to the A498 cells, and the output/input ratio of phages increased about 100 fold. A group of peptides capable of binding specifically to the renal carcinoma cells were obtained, and the affinity of these peptides to the targeting cells and tissues was studied.

Results: Through a cell-based ELISA, immunocytochemical staining, immunohistochemical staining, and immunofluorescence, the Phage ZT-2 and synthetic peptide ZT-2 were shown to specifically bind to the tumor cell surfaces of A498 and incision specimens, but not to normal renal tissue samples.

Conclusion: A peptide ZT-2, which binds specifically to the renal carcinoma cell line A498 was selected from phage display peptide libraries. Therefore, it provides a potential tool for early diagnosis of renal carcinoma or targeted drug delivery in chemotherapy.

Figure 1

Evaluation by cell-ELISA of the binding selectivity of twenty phage clones. The selectivity values of five higher phage clone (ZT-2, ZT-4, ZT-8, ZT-9, and ZT-16), calculated by the formula mentioned in the text, were 3.15, 2.90, 2.95, 2.80, and 3.05, respectively. Therefore, clone ZT-2 appeared to bind more effectively than the other clones.

Figure 2

Immunocytochemical staining of A498 and control cells when bound with phage ZT-2. Cell-bound phages were detected using anti-M13 phage monoclonal antibody, secondary antibody, and ABC complex. The cells were stained with diaminobenzidine (DAB). (A) shows control cell (B) shows immunocytochemical staining of A498 cells when bound with phages without exogenous sequences (wild-type phage) (C) shows immunocytochemical staining of A498 cells when bound with unrelated phage (D) shows immunocytochemical staining of A498 cells when bound with phage ZT-2. Amplification × 200.

Figure 3

Immunohistochemical staining of renal carcinoma and nontumorous renal tissue sections when bound with ZT-2 peptide-fluorescein isothiocyanate. To investigate if the free ZT-2 peptide maintained its binding affinity to renal carcinoma cells, we made a synthetic peptide ZT-2 (QQPPMHLMSYAG) labeled with fluorescein isothiocyanate. (A) Immunohistochemical staining of renal carcinoma tissues when bound with phage ZT-2-FITC. The specific binding sites on tumor cells fluoresced green (B) Immunohistochemical staining of nontumorous renal tissues when bound with phage ZT-2 (C) a negative control section stained with random peptide-fluorescein isothiocyanate in renal carcinoma tissues. Magnification × 200.

Figure 4

Competitive inhibition of binding of the phage ZT-2 to A498 cells by the synthetic peptide ZT-2 QQPPMHLMSYAG. The average inhibition rates at different concentrations of the peptide are shown. When the concentration of the peptide ZT-2 reached more than 0.001 μM, a significant inhibition occurred.