Evaluation of (68)Ga-Radiolabeled Peptides for HER2 PET Imaging

One in eight women will be diagnosed with breast cancer in their lifetime and approximately 25% of those cases will be HER2-positive. Current methods for diagnosing HER2-positive breast cancer involve using IHC and FISH from suspected cancer biopsies to quantify HER2 expression. HER2 PET imaging could potentially increase accuracy and improve the diagnosis of lesions that are not available for biopsies. Using two previously discovered HER2-targeting peptides, we modified each peptide with the chelator DOTA and a PEG(2) linker resulting in DOTA-PEG(2)-GSGKCCYSL (P5) and DOTA-PEG(2)-DTFPYLGWWNPNEYRY (P6). Each peptide was labeled with (68)Ga and was evaluated for HER2 binding using in vitro cell studies and in vivo tumor xenograft models. Both [(68)Ga]P5 and [(68)Ga]P6 showed significant binding to HER2-positive BT474 cells versus HER2-negative MDA-MB-231 cells ([(68)Ga]P5; 0.68 ± 0.20 versus 0.47 ± 0.05 p < 0.05 and [(68)Ga]P6; 0.55 ± 0.21 versus 0.34 ± 0.12 p < 0.01). [(68)Ga]P5 showed a higher percent injected dose per gram (%ID/g) binding to HER2-positive tumors two hours post-injection compared to HER2-negative tumors (0.24 ± 0.04 versus 0.12 ± 0.06; p < 0.05), while the [(68)Ga]P6 peptide showed significant binding (0.98 ± 0.22 versus 0.51 ± 0.08; p < 0.05) one hour post-injection. These results lay the groundwork for the use of peptides to image HER2-positive breast cancer.