111In-labeled galectin-3-targeting peptide as a SPECT agent for imaging breast tumors.
Galectin-3 is a member of the galectin family of beta-galactoside-binding animal lectins. Galectin-3 is overexpressed in a wide range of neoplasms and is associated with tumor growth and metastases. Given this fact, radiolabeled galectin-3-targeting molecules may be useful for the noninvasive imaging of tumors expressing galectin-3, as well as for targeted radionuclide therapy. In this study, the tumor cell-targeting and SPECT properties of a galectin-3-avid peptide identified from bacteriophage display were evaluated in human breast carcinoma cells and in human breast tumor-bearing mice.


METHODS
The galectin-3-avid peptide G3-C12 (ANTPCGPYTHDCPVKR) was synthesized with a Gly-Ser-Gly (GSG) linker at the amino terminus. After conjugation with 1,4,7,10-tetra-azacyclododecane-N,N',N''N'''-tetraacetic acid (DOTA), the peptide was labeled with (111)In. The radiochemical purity and stability of the compound was assessed by high-performance liquid chromatography. MDA-MB-435 human breast carcinoma cells expressing galectin-3 were used to characterize the in vitro binding properties of the radiolabeled compound. SCID mice bearing MDA-MB-435 xenografts were used as an in vivo model for biodistribution and imaging studies with the (111)In-labeled peptide.


RESULTS
(111)In-DOTA(GSG)-G3-C12 bound specifically to galectin-3-expressing MDA-MB-435 cells. The radiolabeled peptide was stable in serum and was found intact in excreted urine for at least 1 h. Competitive binding experiments indicated that the radiolabeled peptide exhibited an inhibitory concentration of 50% of 200.00+/-6.70 nM for cultured breast carcinoma cells. In vivo biodistribution studies revealed that tumor uptake was 1.2+/-0.24, 0.75+/-0.05, and 0.6+/-0.04 (mean +/- SD) percentage injected dose per gram at 30 min, 1.0 h, and 2.0 h after injection of the radiotracer, respectively. SPECT/CT studies with (111)In-DOTA(GSG)-G3-C12 showed excellent tumor uptake and contrast in the tumor-bearing mice. Specificity of peptide binding was demonstrated by successful blocking (52%) of in vivo tumor uptake of (111)In-DOTA(GSG)-G3-C12 in the presence of its nonradiolabeled counterpart at 2 h after injection.


CONCLUSIONS
This study demonstrated the successful use of a new radiolabeled peptide for the noninvasive imaging of galectin-3-positive breast tumors. This peptide may be a promising candidate for future clinical applications.
Kumar
Senthil R
SR
Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA.
Deutscher
Susan L
SL
D000595:Amino Acid Sequence; D000818:Animals; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry; D005260:Female; D037502:Galectin 3 / Q000378:metabolism*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D007205:Indium Radioisotopes; D051379:Mice; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D013194:Staining and Labeling; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014057:Tomography, X-Ray Computed
D002614:Chelating Agents; D037502:Galectin 3; D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D010455:Peptides; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid