Selection of trypsin inhibitors in phage peptide library

Identification of novel peptide inhibitors for human trypsins

Human trypsin isoenzymes share extensive sequence similarity, but certain differences in their activity and susceptibility to inhibitors have been observed. Using phage display technology, we identified seven different peptides that bind to and inhibit the activity of trypsin-3, a minor trypsin isoform expressed in pancreas and brain. All of the peptides contain at least two of the amino acids tryptophan, alanine and arginine, whereas proline was found closer to the N-terminus in all but one peptide. All peptides contain two or more cysteines, suggesting a cyclic structure. However, we were able to make synthetic linear variants of these peptides without losing bioactivity. Alanine replacement experiments for one of the peptides suggest that the IPXXWFR motif is important for activity. By molecular modeling the same amino acids were found to interact with trypsin-3. The peptides also inhibit trypsin-1, but only weakly, if at all, trypsin-2 and -C. As trypsin is a highly active enzyme which can activate protease-activated receptors and enzymes that participate in proteolytic cascades involved in tumor invasion and metastasis, these peptides might be useful lead molecules for the development of drugs for diseases associated with increased trypsin activity.

Phage-displayed peptide ligands for pancreatic alpha-amylase cross-react with barley alpha-amylase

Peptide ligands that bind to pancreatic alpha-amylase were isolated from bacteriophage libraries displaying random 15-mer peptides by iterative affinity selection and amplification. The DNA sequences of selected clones from the final round of biopanning were determined. The two phage-display ligands with high-binding activities contained a high content of Arg, Tyr, and Trp residues with the short consensus sequence Arg-X-Tyr-Trp. These clones were shown to exhibit comparable binding interactions toward barley alpha-amylase based on transducing units titering and measurement of the dissociation constants.

Tumor targeting with a selective gelatinase inhibitor

Several lines of evidence suggest that tumor growth, angiogenesis, and metastasis are dependent on matrix metalloproteinase (MMP) activity. However, the lack of inhibitors specific for the type IV collagenase/gelatinase family of MMPs has thus far prevented the selective targeting of MMP-2 (gelatinase A) and MMP-9 (gelatinase B) for therapeutic intervention in cancer. Here, we describe the isolation of specific gelatinase inhibitors from phage display peptide libraries. We show that cyclic peptides containing the sequence HWGF are potent and selective inhibitors of MMP-2 and MMP-9 but not of several other MMP family members. Our prototype synthetic peptide, CTTHWGFTLC, inhibits the migration of human endothelial cells and tumor cells. Moreover, it prevents tumor growth and invasion in animal models and improves survival of mice bearing human tumors. Finally, we show that CTTHWGFTLC-displaying phage specifically target angiogenic blood vessels in vivo. Selective gelatinase inhibitors may prove useful in tumor targeting and anticancer therapies.

Selection of a cyclic nonapeptide inhibitor to alpha-chymotrypsin using a phage display peptide library

A cyclic nonapeptide library displayed on filamentous bacteriophages was selected 6 times against alpha-chymotrypsin (EC 3.4.21.1) at three different pH conditions (6.5, 7.0, and 7.5). Phage peptide clones from the sixth selection, at all three pH conditions, interacted more strongly with alpha-chymotrypsin than the original library and a wild-type phage did. DNA sequencing of the selected phage peptide clones showed that different cyclic nonapeptide sequences had been selected at the different pH conditions. The oxidized form of the synthetic peptide, Cys-Cys-Phe-Ser-Trp-Arg-Cys-Arg-Cys, selected at pH 7.5, could completely inhibit the enzymatic activity of alpha-chymotrypsin. The structurally related enzymes trypsin (bovine) and elastase (porcine) were only marginally inhibited by the same peptide under the same conditions. The inhibition constant for alpha-chymotrypsin was estimated to be 10(-6) M. Phage clones expressing this peptide had a lower affinity for phenylmethylsulfonylfluoride-modified alpha-chymotrypsin than for natural alpha-chymotrypsin as determined by an enzyme immunosorbent assay. This peptide phage clone was also competitively prevented from binding to alpha-chymotrypsin by the corresponding synthetic oxidized peptide. Collectively, the results suggest that the oxidized form of the selected peptide Cys-Cys-Phe- Ser-Trp-Arg-Cys-Arg-Cys interacts with the active site of alpha-chymotrypsin and acts as a specific inhibitor to the enzyme. To our knowledge, the selected sequence Cys-Cys-Phe-Ser-Trp-Arg-Cys-Arg-Cys has not been found in nature.