title: Near-infrared fluorescence imaging of gastrin releasing peptide receptor targeting in prostate cancer lymph node metastases.
abstract: BACKGROUND
  Development of high affinity and specificity molecular imaging probes that increase accuracy for early detection of lymph node (LN) metastases is important for improving survivorship in prostate cancer. We evaluated the specificity, sensitivity, and accuracy of fluorescence-labeled bombesin (BBN) peptides to detect LN and systematic metastases in orthotopic mouse models bearing gastrin releasing peptide receptor (GRPR)-positive human prostate cancer.
  
  
  METHODS
  PC-3 cells were orthotopically implanted in severe combined immunedeficient or thymic nude (nu/nu) male mice. Tumor growth was monitored using magnetic resonance imaging. Alexa Fluor 680 conjugated BBN[7-14]NH2 (AF680-BBN) peptides were administered intravenously at 4-7 weeks post-tumor-implantation. Near-infrared fluorescence (NIRF) imaging was performed for up to 6 hr post-injection. The imaging sensitivity and specificity were assessed by co-registration of AF680-BBN NIRF imaging and luciferase bioluminescence imaging of the PC-3/Luc+ orthotopic mouse model.
  
  
  RESULTS
  AF680-BBN showed a high binding affinity and selectivity to GRPR-positive cancer in vitro and in vivo. LN and peritoneal metastases were detected by NIRF imaging, and confirmed by histopathology. Tumor-to-muscle (T/M) ratio was the highest at 2-hr post-injection (4.12 ± 1.77). Blocking experiments, using unlabeled BBN as the inhibiting agent, significantly reduced the T/M ratio (1.64 ± 0.21, P = 0.02). AF680-BBN NIRF imaging had a sensitivity of 89.4%, specificity of 92.9%, and accuracy of 90.2% for the detection of metastases in mice.
  
  
  CONCLUSIONS
  [corrected] The studies suggest the potential of use and development of NIR-fluorescent BBN probes as site-directed agents to help improve the current detection and LN staging accuracy in prostate cancer.
authors.affiliation: Department of Radiology, University of Missouri, Columbia, Missouri 78229-3900, USA.
authors.forename: Quan-Yu
authors.initials: QY
authors.lastname: Cai
authors.forename: Ping
authors.initials: P
authors.lastname: Yu
authors.forename: Cynthia
authors.initials: C
authors.lastname: Besch-Williford
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Smith
authors.forename: Gary L
authors.initials: GL
authors.lastname: Sieckman
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Hoffman
authors.forename: Lixin
authors.initials: L
authors.lastname: Ma
mesh_terms: D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives*; D045744:Cell Line, Tumor; D005456:Fluorescent Dyes; D006651:Histocytochemistry; D006801:Humans; D008198:Lymph Nodes / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008819:Mice, Nude; D016513:Mice, SCID; D008856:Microscopy, Fluorescence; D010446:Peptide Fragments; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D018004:Receptors, Bombesin / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D005456:Fluorescent Dyes; D010446:Peptide Fragments; D018004:Receptors, Bombesin; C118536:bombesin (7-14); D001839:Bombesin