title: Bifunctional phage-based pretargeted imaging of human prostate carcinoma.
abstract: BACKGROUND
  Two-step and three-step pretargeting systems utilizing biotinylated prostate tumor-homing bacteriophage (phage) and (111)In-radiolabeled streptavidin or biotin were developed for use in cancer radioimaging. The in vivo selected prostate carcinoma-specific phage (G1) displaying up to five copies of the peptide IAGLATPGWSHWLAL was the focus of the present study.
  
  
  METHODS
  The ability of G1 phage to extravasate and target prostate tumor cells was investigated using immunohistochemistry. G1 phages were biotinylated, streptavidin was conjugated to diethylenetriaminepentaacetic acid (DTPA) and biotin was conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). Biodistribution studies and single-photon emission computed tomography (SPECT)/CT imaging of xenografted PC-3 tumors via two-step pretargeted (111)In-labeled streptavidin and three-step pretargeted (111)In-labeled biotin were performed in SCID mice to determine the optimal pretargeting method.
  
  
  RESULTS
  The ability of G1 phage to extravasate the vasculature and bind directly to human PC-3 prostate carcinoma tumor cells in vivo was demonstrated via immunocytochemical analysis. Comparative biodistribution studies of the two-step and three-step pretargeting strategies indicated increased PC-3 human prostate carcinoma tumor uptake in SCID mice of 4.34+/-0.26 %ID g(-1) at 0.5 h postinjection of (111)In-radiolabeled biotin (utilized in a three-step protocol) compared to 0.67+/-0.06 %ID g(-1) at 24 h postinjection of (111)In radiolabeled streptavidin (employed in a two-step protocol). In vivo SPECT/CT imaging of xenografted PC-3 tumors in SCID mice with the three-step pretargeting method was superior to that of the two-step pretargeting method, and, importantly, blocking studies demonstrated specificity of tumor uptake of (111)In-labeled biotin in the three-step pretargeting scheme.
  
  
  CONCLUSIONS
  This study demonstrates the use of multivalent bifunctional phage in a three-step pretargeting system for prostate cancer radioimaging.
authors.affiliation: Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA. newtonj@missouri.edu
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Newton-Northup
authors.forename: Said D
authors.initials: SD
authors.lastname: Figueroa
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Quinn
authors.forename: Susan L
authors.initials: SL
authors.lastname: Deutscher
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001435:Bacteriophages / Q000378:metabolism*; D045744:Cell Line, Tumor; D005119:Extravasation of Diagnostic and Therapeutic Materials; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D053758:Nanoparticles; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D010455:Peptides