Identification of C10 biotinylated camptothecin (CPT-10-B) binding peptides using T7 phage display screen on a QCM device.

A peptide sequence that can bind to camptothecin (CPT), a natural cytotoxic compound, was screened for using a T7 phage display system combined with a cuvette type quartz crystal microbalance (QCM) device. In this screen, after only 10min of monitoring of the interaction between injected T7 phage pool with immobilized C10 biotinylated CPT (CPT-10-B) on a gold electrode surface, six different kinds of phage (A-F) were identified as judged by the size of PCR product on agarose gel electrophoresis. Injection of each single phage (A-E) pool individually caused a frequency decrease, suggesting interaction with the immobilized CPT-10-B. In addition, the peptide sequence displayed on phages A-C is consistent with chemical and biological studies of the interaction of CPTs with topoisomerase I (TopI), human E prostanoid receptor third cytoplasmic polypeptide, and a series of esterases. The efficacy of T7 phage display screening for small molecules on QCM devices, target discovery from primary peptide sequence, and application of this strategy to various drug-like small molecules are discussed.