Development of novel tumor imaging agents with phage-display combinatorial peptide libraries.
OBJECTIVE
Current radiologic methods do not provide sufficient information for unambiguous diagnosis and prognosis of cancer. The present investigation sought to address this deficiency by developing a system for designing novel small molecules targeted against tumor-specific molecules for use as radionuclide imaging agents.


METHODS
Part of a tumor-specific receptor, purified recombinant epidermal growth factor receptor (EGFR), variant III, extracellular domain (rEGFRvIII-ecd), was used as the target in the selection of EGFRvIII-specific peptide ligands from random peptide bacteriophage (phage) display libraries. After three rounds of screening, phage isolates were tested for binding affinity with an enzyme-linked immunosorbent assay. Positive phage were sequenced, and the peptides were synthesized and tested for binding affinity with a surface plasmon resonance assay.


RESULTS
Affinity screening identified 49 peptide-expressing phage that showed enhanced binding to the variant receptor compared with wild-type EGFR. Free peptides from the two phage isolates exhibiting the most favorable binding were tested for target binding. One of these demonstrated a binding affinity for rEGFRvIII-ecd in the 30-nmol/L range.


CONCLUSIONS
These data suggest that phage display libraries may be very useful in the design of novel, high-affinity tumor imaging agents.
Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Michael J
MJ
Campa
Scott B
SB
Serlin
Edward F
EF
Patz
D000345:Affinity Labels / Q000138:chemical synthesis* / Q000378:metabolism; D020650:Combinatorial Chemistry Techniques; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000302:isolation & purification / Q000378:metabolism; D007089:Image Enhancement / Q000379:methods; D008958:Models, Molecular; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism; D019151:Peptide Library; D011485:Protein Binding; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
D000345:Affinity Labels; D029968:Escherichia coli Proteins; D019151:Peptide Library; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; D066246:ErbB Receptors