Peptide specifically binding to human medullary breast carcinoma Bcap-37 cells selected by phage display in vivo and its property as well as combination effect

Objective To investigate the property and the combination effect of the peptide specifically binding to human medullary breast cancer Bcap-37 cells by using phage display in vivo and to provide molecular targeting probe for early diagnosis of breast cancer. Methods The human medullary breast carcinoma Bcap-37 cells tumor-bearing nude mice model was prepared and three rounds in vivo were performed by using Ph.D.-C7CTM phage display peptide library. The distribution of screened phages in tumors and normal tissues was detected by using immunohistochemistry. The affinity of monoclonal phage to Bcap-37 cells was identified by using enzyme linked immunosorbent assay (ELISA). The positive monoclonal phage DNA was taken and sequenced, and the sequence with high repetition rate was selected to synthesize peptide by using chemical methods. Optical molecular probe was prepared and fluorescence molecular imaging was used to test its specificity and targeting ability for breast transplantation tumor of tumor-bearing nude mice in vivo. Results The recovery rate of phage in the third round screening in vivo was 107.2 times than that in the first round. Immunohistochemical results showed that the phages binding to the tumor tissues were increased successively with the increasing screening rounds in vivo. The number of phages binding to tumor tissues was more than that binding to normal tissues (lung, skeletal muscle, liver and kidney). The absorbancy (A) value of section scanning image in the tumor tissues was higher than that in the normal tissues, and the difference was statistically significant different (P < 0.05). ELISA results showed that 22 phages (affinity≥2) among the 50 randomly selected monoclonal phage were positive. After DNA sequencing analysis of the positive monoclonal phage, 4 repeat amino acid sequences were obtained. The fluorescein isothiocyanate-labelled (FITC)-CSPLNTRFC with the highest repetition rate was synthesized for FITC-CSPLNTRFC peptide. Bcap-37 cells tumor-bearing nude mice model assay in vivo showed that FITC-CSPLNTRFC peptide could significantly enriched in the breast xenograft tissues. Conclusion CSPLNTRFC peptide specifically binding to human medullary breast cancer Bcap-37 cells can be screened out successfully by using phage display in vivo, which will be helpful to vitro studies on the early diagnosis of breast cancer. Key words: Breast neoplasms; Peptide library; Phage display; Specifically binding peptide