In vivo imaging of human colorectal cancer using radiolabeled analogs of the uroguanylin peptide hormone.
BACKGROUND
Uroguanylin is an endogenous peptide agonist that binds to the guanylate cyclase C receptor (GC-C). GC-C is overexpressed in human colorectal cancer (CRC), and exposure of GC-C-expressing cells to GC-C agonists results in cell cycle arrest and/or apoptosis, highlighting the therapeutic potential of such compounds. This study describes the first use of radiolabeled uroguanylin analogs for in vivo detection of CRC.


METHODS
The peptides uroguanylin and E(3)-uroguanylin were N-terminally labeled with the DOTA chelating group via NHS ester activation and characterized by RP-HPLC, ESI-MS, and GC-C receptor binding assays. The purified conjugates were radiolabeled with In-111 and used for in vivo biodistribution and SPECT imaging studies. In vivo experiments were carried out using SCID mice bearing T84 human colorectal cancer tumor xenografts.


RESULTS
Alteration of the position 3 aspartate residue to glutamate resulted in increased affinity for GC-C, with IC(50) values of 5.0+/-0.3 and 9.6+/-2.9 nM for E(3)-uroguanylin and DOTA-E(3)-uroguanylin, respectively. In vivo, (111)In-DOTA-E(3)-uroguanylin demonstrated tumor uptake of 1.17+/-0.23 and 0.61+/-0.07% ID/g at 1 and 4 h post injection, respectively. The specificity of tumor localization was demonstrated by coinjection of 3 mg/kg unlabeled E(3)-uroguanylin, which reduced tumor uptake by 69%. Uptake in kidney, however, was dramatically higher for the uroguanylin peptides than for previously characterized radiolabeled E. coli heat-stable enterotoxin (STh) analogs targeting GC-C, and was also inhibited by coinjection of unlabeled peptide in a fashion not previously observed.


CONCLUSIONS
Use of uroguanylin-targeting vectors for in vivo imaging of colorectal cancers expressing GC-C resulted in tumor uptake that paralleled that of higher affinity heat-stable enterotoxin peptides, but also resulted in increased kidney uptake in vivo.
Harry S. Truman Memorial VA Hospital, Research Service Room A004, 800 Hospital Drive, Columbia, MO 65201, USA.
Dijie
D
Liu
Douglas
D
Overbey
Lisa D
LD
Watkinson
Said
S
Daibes-Figueroa
Timothy J
TJ
Hoffman
Leonard R
LR
Forte
Wynn A
WA
Volkert
Michael F
MF
Giblin
D000595:Amino Acid Sequence; D000818:Animals; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D005260:Female; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry / Q000493:pharmacokinetics; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics; D051379:Mice; D008813:Mice, Inbred ICR; D016513:Mice, SCID; D008969:Molecular Sequence Data; D045265:Natriuretic Peptides / Q000737:chemistry / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D014183:Transplantation, Heterologous
D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D045265:Natriuretic Peptides; D019275:Radiopharmaceuticals; C084362:uroguanylin; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid