Abstract

ErbB-2 is a type 1 receptor tyrosine kinase over-expressed on ~30% of breast cancers and is an attractive target for the development of new diagnostic and therapeutic agents. In this study, an ErbB-2-targeting peptide, KCCYSL, previously isolated using bacteriophage display, was radiolabeled with [99mTc(H2O)3(CO)3]+ and examined for breast cancer in vitro cell binding and in vivo biodistribution and breast cancer imaging propensities. KCCYSL peptide was synthesized with the chelates diaminopropionc acid (DAP), Nα-histidinyl acetic acid [(NαHis)Ac], and 4-Ala-1,2-3-Triazol-1-acetic acid [(Ala-Triazol)Ac] at its amino-terminus via a gly-ser-gly (GSG) spacer and radiolabeled with [99mTc(H2O)3(CO)3]+. Radiolabeled peptide binding to cultured human MDA-MB-435 breast carcinoma cells was examined. Biodistribution and single photon emission computed tomography (SPECT)/CT imaging of the radiolabeled peptides were evaluated in female SCID mice bearing human MDA-MB-435 breast tumors. Results demonstrated that 99mTc(CO)3-DAP-GSG-KCCYSL, 99mTc(CO)3-(NαHis)Ac-GSG-KCCYSL and 99mTc(CO)3- (Ala-Triazol)Ac-GSG-KCCYSL were stable and bound to MDA-MB-435 cells. In vivo biodistribution studies revealed that tumor uptake of 99mTc(CO)3-DAP-GSG-KCCYSL was 1.67 ±0.16, 1.25 ±0.61, 0.88 ±0.12, 0.30 ±0.06 % ID/g at 1, 2, 4, and 24 h post injection, respectively. Tumor uptake of 99mTc(CO)3-(NαHis)Ac-GSG-KCCYSL was 0.76 ±0.13, 0.75 ±0.40, 0.33 ±0.08, 0.16 ±0.02 % ID/g at 1, 2, 4, and 24 h post injection, respectively. Tumor uptake of 99mTc(CO)3-(Ala- Triazol)Ac-GSG-KCCYSL was 1.15 ±0.12, 0.63 ±0.09, 0.30 ±0.02, 0.09 ±0.02 % ID/g at 1, 2, 4, and 24 h post injection, respectively. SPECT/CT studies showed tumor selective uptake of the peptides in the tumor-bearing mice. Specific uptake was confirmed by competitive receptor blocking studies. 99mTc(CO)3-DAP-GSG-KCCYSL and 99mTc(CO)3-(Ala-Triazol)Ac-GSG-KCCYSL may be better as imaging agents due to their higher tumor to non-target uptake ratios than 99mTc(CO)3-(NαHis)Ac-GSG-KCCYSL.

Keywords: Breast cancer, click chemistry, ErbB-2, peptide, radioimaging, technetium, tricarbonyl, [99mTc(CO)]-Radiolabeled, ErbB-2-Targeting Peptides, Breast Carcinoma Imaging, type 1 receptor tyrosine kinase, chelates diaminopropionc acid (DAP), N-histidinyl acetic acid [(NHis)Ac], a gly-ser-gly (GSG), (SPECT)/CT imaging, Technetium-99m, single photon computed emission tomography, diaminopropionc acid, BBN analogues, epidermal growth factor receptor, phosphatidylinositol 3-kinase, murine monoclonal antibody, trastuzumab, pertuzumab, human breast carcinoma cells, Novabiochem, Genzyme, Azidoacetic acid, Cell Lines, Cell Culture, Laemmli Buffer, Peptide Synthesis, trifluoroacetic acid, thioanisole, phenol, High Performance Liquid, HPLC, Liquid Chromatography-Mass Spectrometry, preparative HPLC, Thin Layer Chromatography, phosphate-buffered solution