Breast cancer is a leading cause of death among women in the USA. The efficacy of existing anticancer
therapeutics can be improved by targeting them through conjugation with
ligands binding to cellular receptors. Recently, we developed a novel drug targeting strategy based on the use of pre-selected
cancer-specific 'fusion pVIII
proteins' (fpVIII), as targeting
ligands. To study the efficiency of this approach in animal models, we developed a panel of
breast cancer cell-binding phages as a source of targeted fpVIIIs. Two landscape phage
peptide libraries (8-mer f8/8 and 9-mer f8/9) were screened to isolate 132 phage variants that recognize
breast carcinoma cells MCF-7 and ZR-75-1 and internalize into the cells. When tested for their interaction with the
breast cancer cells in comparison with
liver cancer cells HepG2, human mammary cells MCF-10A cells and serum, 16 of the phage probes selectively interacted with the
breast cancer cells whereas 32 bound both breast and
liver cancer cells. The most prominent
cancer-specific phage
DMPGTVLP, demonstrating sub-nanomolar Kd in interaction with target cells, was used for affinity chromatography of cellular membrane molecules to reveal its potential binding receptor. The isolated
protein was identified by direct sequencing as cellular surface
nucleolin. This conclusion was confirmed by inhibition of the phage-cell interaction with
nucleolin antibodies. Other prominent phage binders VPTDTDYS, VEEGGYIAA, and DWRGDSMDS demonstrate consensus motifs common to previously identified
cancer-specific
peptides. Isolated phage
proteins exhibit inherent binding specificity towards
cancer cells, demonstrating the functional activity of the selected fused
peptides. The selected phages, their
peptide inserts and intact fusion
proteins can serve as promising
ligands for the development of targeted nanomedicines and their study in model mice with xenograft of human cells MCF-7 and ZR-75-1.