title: Identification of a Peptide fromIn vivoBacteriophage Display with Homology to EGFL6: A Candidate Tumor Vasculature Ligand in Breast Cancer.
abstract: BACKGROUND
  A crucial step in tumorigenesis is the recruitment of novel vasculature to the site of neoplasia. Currently, a number of high throughput techniques are employed to identify genes, mRNA and proteins that are aberrantly expressed in tumor vasculature. One drawback of such techniques is the lack of functionalin vivodata that they provide. Bacteriophage (phage) display has been demonstratedin vivoto select peptides that home to tumors and tumor vasculature. The peptides can be compared to sequences of putative cancer-related proteins, in order to identify novel proteins essential for tumorigenesis.
  
  
  OBJECTIVE
  It was hypothesized that anin vivoselection for phage which targeted human breast cancer xenografts could identify peptides with homology to cancer-related proteins forin vivoimaging of breast cancer.
  
  
  METHODS
  Following four rounds ofin vivoselection in human MDA-MB-435 breast cancer xenografted mice, peptide 3-G03 was discovered with significant homology to a putative secreted protein termed EGFL6. Egfl6 mRNA is upregulated in several transcriptomic analyses of human cancer biopsies, and the protein may play a role in tumor vascularization.
  
  
  RESULTS
  Egfl6 mRNA expression was demonstrated in MDA-MB-435 cells and EGFL6 protein was secreted from these cells. Based on homology of 3-G03 to EGFL6, an EGFL6 peptide was synthesized and shown to target MDA-MB-435 cells. EGFL6 peptide was radiolabeled with111In and analyzed for biodistribution and tumor imaging capabilities. Single photon emission computed tomography imaging revealed uptake of the peptide in a manner consistent with other tumor vasculature targeting agents.
authors.affiliation: Research Service, Harry S. Truman Veterans Memorial Hospital, Columbia, MO, USA ; Department of Biochemistry, University of Missouri, Columbia, MO, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Larimer
authors.affiliation: Research Service, Harry S. Truman Veterans Memorial Hospital, Columbia, MO, USA ; Department of Biochemistry, University of Missouri, Columbia, MO, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Deutscher
keywords: Breast cancer; EGFL6; Molecular imaging; Peptides; Phage display; SPECT/CT; Tumor vasculature