Isolation of cell specific peptide ligands using fluorescent bacterial display libraries

Methods for identifying and producing cell specific affinity reagents are critical in cell detection, separation, and therapeutic delivery applications, yet remain difficult and time consuming. To address these limitations, a rapid and quantitative screening approach was developed using intrinsically fluorescent bacterial display peptide libraries and fluorescence-activated cell sorting (FACS). High-throughput screening of fluorescent libraries yielded a panel of peptide ligands mediating specific recognition of human breast cancer tumor cells. Clonal populations of fluorescent, peptide-displaying bacteria enabled single-step, fluorescent labeling of the target cells for cytometry and microscopy analysis. Isolated peptides could be categorized into several distinct groups possessing strong consensus sequences with as many as six identities. Importantly, individual clones exhibited high specificity target cell binding, with more than 80-fold increased binding to tumor cells (ZR-75-1) relative to cell lines derived from healthy tissue (HMEC, MCF-10A). Fluorescent display libraries thus provide a powerful new methodology for parallel identification of cell specific affinity ligands.