Identification of a new prostate-specific cyclic peptide with the bacterial FliTrx system.

UNLABELLED Peptides are useful tools for directing radioisotopes into tumors. We evaluated the ability of a bacterial peptide display system to isolate new prostate tumor-specific peptides. METHODS We used the bacterial FliTrx system to identify a new cyclic peptide that binds to prostate carcinoma. Serum stability and binding affinities of the (125)I-labeled peptide were tested. Furthermore, the (131)I-labeled peptide was used to evaluate its biodistribution. RESULTS Several peptides showing a potential consensus motif were identified. The new peptide MM-2 is stable in serum for up to 24 h. It binds to PC-3 cells, and this binding can be inhibited more than 70% with the unlabeled peptide. Binding to human umbilical vein endothelial cells (HUVECs) and PNT-2 cells is weaker, and competition (27%) in HUVECs is less efficient. The biodistribution showed moderate accumulation in tumor. CONCLUSION Bacterial peptide display, an alternative to phage peptide display, can allow the identification of specific binding and stable peptides.