Identification Of Vascular-binding Peptide GX1 Receptors And Their Expression In Gastric Cancer And Colon Cancer

【Background】Gastric cancer remains quite a common malignancy and counts among the most important causes of cancer-related death worldwide. Conventional treatments for gastric cancer are surgery, radiation and chemotherapy. Antivascular therapy provides a promising method for anticancer therapy.In 2004, our lab successfully completed the research of"Screeening Specific Peptides Binding to Vasculature of Human Gastric Cancer Using Phage Display C7C Peptide Library", and obtained a specific peptide GNSNPKS (GX1) for the vasculature of gastric cancer. Preliminary experiments suggested that there was an increase in the number of GX1 phage in gastric cancer xenograft compared with control organs, including brain, heart, liver, spleen and kidney. This peptide might be a candidate for targeting the vascular of gastric cancer.【Aims】To investigate the expression of vascular-binding peptide GX1 receptors in gastric cancer and colon cancer and their relations with pathological characteristics of tumors; to identify possible receptors of vascular-binding peptide GX1.【Methods】①GX1 phage was used as the first antibody to detect the expression of vascular-binding peptide GX1 receptors in gastric cancer and colon cancer and their relations with pathological characteristics of tumors by immunohistochemical analysis.②GX1 phage was used as the primary antibody to screen a human microvascular endothelial cell cDNA library to detect receptors of GX1. After sequencing the positive cDNA fragments, DNA homology analysis was performed according to GenBank.【Results】①GX1 receptors was found to present in vascular of gastric cancer tissues, including 67% cases of well-diiferentiated tissues, 74% cases of moderate-diiferentiated tissues and 92% cases of poor-diiferentiated tissues. Expression of GX1 receptors was also detected in vascular of colon cancer tissues, including 19% cases of well-diiferentiated tissues, 24% cases of moderate-diiferentiated tissues and 30% cases of poor-diiferentiated tissues. Moreover, the expression of GX1 receptors in gastric cancer was significantly higher than that in colon cancer. Statistical analysis showed that there was significant correlation between the expression of GX1 receptors and the differentiation of gastric cancer.②About 2.0×106 phage clones in primary cDNA library were screened by GX1 phage. After three rounds of selection, 43 phage clones were characterized as positive clones.③Sequence analysis and on-line homology analysis revealed that these 43 positive cDNA fragments (designated as C1-C43) belonged to 13 genes. C1, C4, C7, C9, C11, C14, C15 and C20 shared the same homologous gene, PON2. C2, C5, C10, C12, C13, C21 and C24 shared the same homologous gene, SEC13L1. C22, C23, C27, C28, C31 and C33 shared the same homologous gene, HSBP1. Inserts C6, C25, C34 and C42 shared the same size and sequence, homologous to LAMR1. Inserts C3, C26, C29 and C35 shared the same size and sequence, homologous to RPL37A. C16, C17, C30 and C36 shared the same homologous gene, NUDT21. The other homologous gene were as following: ATG5, MMP1, GLO1, SLC25A25, PQBP1, APLP2 and AES. As GX1 was received and identified by screening phage displayed peptide library in vivo, its receptors were assumed to locate at cell membrane. Thus, the roles of PON2 and SEC13L1, which located at cell membrane, need further research.【Conclusions】①GX1 phage was found bind specifically to the blood vessel of gastric cancer and colon cancer. The expression of GX1 receptors in gastric cancer was higher than that in colon cancer, and the expression of GX1 receptors in poor-diiferentiated gastric cancer was significantly higher than that in moderate-diiferentiated and well-diiferentiated gastric cancer. Therefore, we suspected that GX1 peptide could bind specifically to the endothelial cells of blood vessel, and might be used as an effective tool in the anti-angiogenesis therapy.②GX1 receptors might belong to 13 genes. As receptors of GX1 was assumed to locate at cell membrane. The roles of PON2 and SEC13L1, which located at cell membrane, need further research. They might be considered as potential novel targets for vascular targeting therapy.