The present study was focused on identifying
cancer cell-specific internalizing
ligands using a new kind of phage display library in which the linear or
cysteine-constrained random
peptides were at amino-terminus fusion to catalytically active P99
beta-lactamase molecules. The size and quality of libraries were comparable to other reported phage display systems. Several
cancer cell-specific binding and internalizing
beta-lactamase-
peptide fusion
ligands were isolated by selecting these libraries on the live BT-474 human
breast cancer cells. The identified
ligands shared several significant motifs, which showed their selectivity and possible binding to some common
cancer cell targets. The
beta-lactamase fusion made the whole process of clone screening efficient and simple. The
ligands selected from such libraries do not require
peptide synthesis and modifications, and can be used directly for applications that require
ligand tracking. In addition, the selected
beta-lactamase-
peptide ligands have a potential for their direct use in targeted
enzyme prodrug therapy. The
cancer-specific
peptides can also be adopted for other kinds of targeted delivery protocols requiring cell-specific affinity
reagents. This is first report on the selection of cell-internalized
enzyme conjugates using phage display technology, which opens the possibility for new fusion libraries with other relevant
enzymes.