Molecular imaging of HER2 expression in breast cancer patients using a novel peptide-based tracer 99mTc-HP-Ark2: a pilot study

Abstract

Background Due to the temporal and spatial heterogeneity of human epidermal growth factor receptor 2 (HER2) expression in breast tumors, immunohistochemistry (IHC) cannot accurately reflect the HER2 status in real time, which may cause misguided treatment decisions. HER2-specific imaging can noninvasively determine HER2 status in primary and metastatic tumors. In this study, HER2 expression in breast cancer patients was determined in vivo by SPECT/CT of 99mTc-HP-Ark2, comparing with PET/CT of 18F-FDG lesion by lesion. Methods A novel HER2-targeted peptide probe 99mTc-HP-Ark2 was constructed. Biodistribution and nanoScan SPECT/CT imaging were performed in mice models. The correlation between the quantified tumor uptake and HER2 expression in tumor cells was analyzed. In the pilot clinical study, a total of 34 breast cancer patients (mean age ± SD: 49 ± 10 y) suspected of having breast cancer according to mammography or ultrasonography were recruited at Peking Union Medical College Hospital, and 99mTc-HP-Ark2 SPECT/CT and 18F-FDG PET/CT were carried out with IHC and fluorescence in situ hybridization as validation. Results Small animal SPECT/CT of 99mTc-HP-Ark2 clearly identified tumors with different HER2 expression. The quantified tumor uptake and tumor HER2 expression showed a significant linear correlation (r = 0.932, P < 0.01). Among the 36 primary lesions in the 34 patients, when IHC (2 +) or IHC (3 +) was used as the positive evaluation criterion, 99mTc-HP-Ark2 SPECT/CT imaging with a tumor-to-background ratio of 1.44 as the cutoff value reflected the HER2 status with sensitivity of 89.5% (17/19), specificity of 88.2% (15/17) and accuracy of 88.9% (32/36), while the 18F-FDG PET/CT showed sensitivity of 78.9% (15/19), specificity of 70.6% (12/17) and accuracy of 75.0% (27/36). In particular, 100% of IHC (3 +) tumors were all identified by 99mTc-HP-Ark2 SPECT/CT imaging. Conclusion 99mTc-HP-Ark2 SPECT/CT can provide a specific, noninvasive evaluation of HER2 expression in breast cancer, showing great potential to guide HER2-targeted therapies in clinical practice. ClinicalTrials.gov Trial registration: NCT04267900. Registered 11th February 2020. Retrospectively registered, https://www.clinicaltrials.gov/ct2/results?pg=1&load=cart&id=NCT04267900.

Clinical application of 99mTc‐labeled peptides for tumor imaging: Current status and future directions

“…The selection of co-ligands is critical for determining the stability, lipophilicity, and biodistribution of 99m Tc-HYNIC conjugates [30]. Notably, the most widely used co-ligands currently are TPPTS (triphenylphosphine-3,3 0 ,3″-trisulfonic acid trisodium salt) and tricine, both of which exhibit excellent water solubility and form stable complexes [11,31,32]. More importantly, TPPTS itself also serves as a reducing agent, eliminating the need for additional reducing agents, such as stannous chloride, in the labeling process [33].…”

“…F I G U R E 1 0 Chemical structures of bombesin [1][2][3][4][5][6][7][8][9][10][11][12][13][14], 99m Tc-RP527, 99m Tc-demobesin 4, 99m Tc-DB15, and 99m Tc-maSSS-PEG 2 -RM26.…”

“…(a) Incorporation of unnatural amino acids: Peptides incorporating unnatural or D-amino acids are more resistant to enzymatic degradation, prolonging their biological half-life in the human body [10,11]. (b) Cyclization: Compared with their linear counterparts, cyclic peptides often exhibit enhanced metabolic stability and resistance to proteolytic degradation, thereby increasing their biological halflife [12].…”

“…Incorporation of unnatural amino acids: Peptides incorporating unnatural or D‐amino acids are more resistant to enzymatic degradation, prolonging their biological half‐life in the human body [10, 11].…”

“…To overcome these challenges, various strategies have been developed to enhance the in vivo stability, pharmacokinetics, and targeting capabilities of peptides. These techniques can be categorized as follows. Incorporation of unnatural amino acids: Peptides incorporating unnatural or D‐amino acids are more resistant to enzymatic degradation, prolonging their biological half‐life in the human body [10, 11]. Cyclization: Compared with their linear counterparts, cyclic peptides often exhibit enhanced metabolic stability and resistance to proteolytic degradation, thereby increasing their biological half‐life [12].…”