title: Synthesis and in vitro evaluation of an 111In-labeled ST-peptide enterotoxin (ST) analogue for specific targeting of guanylin receptors on human colonic cancers.
abstract: BACKGROUND
  Human colonic cancer cells are known to express guanylate cyclase C (GC-C) receptors for guanylin and uroguanylin. E. coli ST is a peptide with high metabolic stability that specifically binds to GC-C receptors. An in vitro evaluation of a new synthetic indium-111 labeled ST conjugate for specific targeting of human colonic cancers that express GC-C receptors was performed.
  
  
  METHODS
  A DOTA conjugated ST analogue DOTA-NCS-6-Ahx-Phe19-ST[1-19] (DOTA-NCS-ST) was synthesized and labeled with indium-111. The non-radioactive indium analogue (In-DOTA-NCS-ST) was also prepared in macroscopic quantities. 111In-DOTA-NCS-ST was produced as a single species (>80% RCP) and purified by HPLC. Human colon cancer CaCO-2 and T-84 cells were used to evaluate the in vitro IC50 values for GC-C receptor binding and determine the cell uptake and retention of radioactivity.
  
  
  RESULTS
  The DOTA-NCS-ST and In-DOTA-NCS-ST conjugates exhibit high in vitro binding affinity for GC-C receptors with IC50 values <10 nM. The in vitro cell binding studies with the 111In-DOTA-NCS-ST conjugate demonstrated that 111In-label ST internalizes in human colon cancer cells and exhibits long-term retention.
  
  
  CONCLUSIONS
  The combination of radiolabeling efficacy and specific in vitro cell uptake and retention suggests that the DOTA-NCS-ST construct holds potential for the development of diagnostic or therapeutic radiopharmaceuticals labeled with trivalent radiometals for specific targeting of human colonic cancers.
authors.affiliation: Department of Radiology, University of Missouri-Columbia, 65211, USA.
authors.forename: H
authors.initials: H
authors.lastname: Gali
authors.forename: G L
authors.initials: GL
authors.lastname: Sieckman
authors.forename: T J
authors.initials: TJ
authors.lastname: Hoffman
authors.forename: G E
authors.initials: GE
authors.lastname: Kiefer
authors.forename: D T
authors.initials: DT
authors.lastname: Chin
authors.forename: L R
authors.initials: LR
authors.lastname: Forte
authors.forename: W A
authors.initials: WA
authors.lastname: Volkert
mesh_terms: D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism*; D004768:Enterotoxins / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins; D006162:Guanylate Cyclase; D006573:Heterocyclic Compounds, 1-Ring / Q000138:chemical synthesis* / Q000378:metabolism*; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry; D008969:Molecular Sequence Data; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D006573:Heterocyclic Compounds, 1-Ring; C440168:In-DOTA-NSC-ST; D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C034151:heat stable toxin (E coli); D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled