Identification of a bladder cancer-specific ligand using a combinatorial chemistry approach

Abstract

Objectives: To develop bladder cancer-specific ligands using a combinatorial chemistry approach.

Materials and methods: We performed a high-throughput one-bead one-compound combinatorial chemistry approach to identify ligands that bound to bladder transitional cell carcinoma cells. The whole-cell binding assay allowed successful identification of a few peptides that bound selectively to bladder cancer cells. Single cell suspensions derived from clinical bladder cancer specimens and cell lines were used to determine the binding specificity. Studies with mouse xenografts were performed to determine the in vivo binding and targeting efficiency, specificity, and biodistribution of one of the ligands.

Results: One cyclic peptide named PLZ4 (amino acid sequence: cQDGRMGFc) was identified that could selectively bind to bladder cancer cell lines and all of the 5 primary bladder cancer cells from human patients, but not to normal urothelial cells, cell mixtures from normal bladder specimens, fibroblasts, and blood cells. Comparison of PLZ4 binding to cell lines of different cancer origins showed that it was bladder cancer-specific (P < 0.05). PLZ4 could bind to tumor cells treated with urine at pH 6.0, but not to noncancerous cells collected from the urine of 4 patients actively being treated with intravesical Bacillus Calmette-Guerin therapy. In vivo and ex vivo imaging studies showed that PLZ4 linked to Cy5.5 fluorescent dye administered via tail vein injection was specifically taken up in mouse xenografts developed from excised fresh human bladder cancer specimens. Several ligands contain the same DGR motif, but only PLZ4 was bladder cancer-specific. We performed alanine walk and rainbow bead coding experiments, and found that the C-terminal GF residues were also important for cell binding and modulated the binding specificity.

Conclusions: PLZ4 has the potential to be used for targeted therapy and imaging detection during diagnosis and follow-up/surveillance of noninvasive and advanced bladder cancer.