In Vivo Phage Display And Characterization Of Peptides Specific To The Vasculature Of Gastric Cancer

Angiogenic vessels within solid tumor are distinct at molecular level to the normal endothelium. Such vascular 'addresses' may provide an effective mean by which systemically administered therapies can be targeted to tumor vessles. So selection of ligands that home to tumor vasculature plays very important roles in targeting therapies. In vivo phage display makes it possible to isolate unknown ligands that localize to the vasculature of specific tissues within a living organism. In this respect, in vivo phage display technology is well established as an important experimental approach in the identification of ligand-receptor pairs on tumor vessles.By screening in vivo from a phage-displayed peptide library, peptides which home specifically to vascular endothelial cells of gastric cancer xenografts were isolated for anti-angiogenesis therapies of the tumor.A mouse irnmunosuppressing model was established by pretreating with cyclophosphamide(CTX). Subrenal capsular assay (SRCA) was carried out simultaneously with fresh xenografts of human gastric cancer. Within 7daysafter SRCA the xenografts grew constantly, and there were many rumor cells and neovascularure under the kidney capsule.Through four biopanning procedures, phage were recovered and titered from xenografts and control tissues in each biopanning procedure. Phage proteins were detected in xenografts by immunohistochemistry. The result indicated that phage homing to gastric cancer xenografts was enriched, up to 3.4-fold of that recovered from brain tissue. Immunohistochemical staining for the homing phage revealed a specific vascular localization in gastric cancer xenografts 5 min after injection of the enriched phage.Then, 5 phage clones were selected from the fourth biopanning. Single chains of DNA were sequenced and amino acid sequences were deduced. The peptide sequence YESIRIGVAPSQ appeared most frequently. When individually tested, the phage recovered from gastric cancer xenografts was as 4.2 times as that from control tissue (brain), as 4.9 times as that from lung and as 5.4 times as that from heart.After four biopanning procedures , the phage that selectively bind to blood vessles in the tumor is obstained. The tumor-specific homing peptides may provide a molecular tool for targeting tumor vascularure in anti-angiogenesis therapies for cancer. The in vivo phage display approach used in our study was effective and applicable to select peptides homing to vascular endothelial cells.