SPECT/CT Imaging of the Novel HER2-Targeted Peptide Probe ^99mTc-HYNIC-H6F in Breast Cancer Mouse Models

Abstract

Overexpression of human epidermal growth factor receptor 2 (HER2) plays important roles in tumorigenesis and tumor progression in breast cancer. Nuclear imaging of HER2 expression in tumors might detect all HER2-positive tumors throughout the body and guide HER2-targeted therapies for patients. We therefore aimed to develop a HER2-targeted peptide probe for breast cancer imaging. A novel SPECT imaging probe, 99m Tc-HYNIC-H6F, was prepared and then evaluated in breast cancer animal models. Methods: The HER2-targeted peptide H6F (YLFFVFER) was conjugated with the bifunctional chelator hydrazinonicotinamide (HYNIC). 99m Tc-HYNIC-H6F was prepared, and the in vivo characteristics of 99m Tc-HYNIC-H6F were investigated in MDA-MB-453 (HER2-positive) and MDA-MB-231 (HER2-negative) models using small-animal SPECT/CT. Moreover, to investigate the specificity of the H6F peptide toward HER2 and the potential applications in monitoring therapies involving trastuzumab, unlabeled H6F and trastuzumab were used as blocking agents in cell competition studies and SPECT imaging. Results: A standard tricine/trisodium triphenylphosphine-3,39,3$-trisulfonate labeling procedure demonstrated that the radiochemical purity was greater than 95%. 99m Tc-HYNIC-H6F displayed excellent HER2-binding specificity both in vitro and in vivo. SPECT/ CT imaging revealed that the MDA-MB-453 tumors were clearly visualized (percentage injected dose per gram, 3.58 6 0.01 at 30 min after injection), whereas the signals in HER2-negative MDA-MB-231 tumors were much lower (0.73 6 0.22 at 30 min after injection). Tumor uptake of MDA-MB-453 was blocked by the coinjection of excess H6F but not by excess trastuzumab. Conclusion: The 99m Tc-HYNIC-H6F peptide probe specifically accumulates in HER2-positive tumors and is therefore promising for the diagnosis of HER2-positive cancers. Because 99m Tc-HYNIC-H6F and trastuzumab target different regions of the HER2 receptor, this radiotracer also has great potential for monitoring the therapeutic efficacy of trastuzumab by rechecking the expression level of HER2 without blocking effect during therapy. Br east cancer is the most frequent cancer and the second leading cause of cancer death among women worldwide. The great progress in breast cancer screening and early diagnosis in recent decades has significantly increased life expectancy and patient quality of life (1,2). The best-studied tumor-associated antigen in breast cancer is human epidermal growth factor receptor 2 (HER2), which is positive in approximately 20%-30% of all breast cancers (3-5). Moreover, overexpression of HER2 is also characterized as a major negative prognostic factor that is associated with higher mortality in early-stage disease, increased incidence of metastasis, and reduced time to relapse (6-8). Trastuzumab (Herceptin; Genentech), the first approved HER2-targeted humanized monoclonal antibody, is the standard-of-care treatment for patients with HER2-positive breast cancer. In several trials, trastuzumab has proven effective in combination with...

Targeting Peptide‐Based Probes for Molecular Imaging and Diagnosis

“…Many factors are related to excretion ability, such as shape, size, surface charge, and hydrophilicity . Small molecules (size <6 nm, molecular weight <40 kDa) are generally accepted to be renally eliminated . Typically, bioactive peptides containing several to <50 amino acids have low molecular weights.…”

“…Newly developed HER2‐targeting peptides such as peptide 2Rs15d, which was designed as an antibody fragment, and peptide H6, which was selected from a library, are typical examples . Since the epithelial–mesenchymal transition (EMT) is involved in tumor progression, it is meaningful to monitor the epithelial‐derived markers with these peptide probes . Third, cancer stem cells (CSCs) have been proven to be related to initial tumorigenesis.…”

“…A) HER2‐targeting peptide H6 conjugated with a radionuclide for in vivo targeted SPECT imaging (top). Reproduced with permission . Copyright 2017, Society of Nuclear Medicine and Molecular Imaging.…”

99mTc-HYNIC-(tricine/EDDA)-FROP peptide for MCF-7 breast tumor targeting and imaging

“…In recent years developing a peptide-based radiopharmaceuticals due to certain favorable properties for the detection of breast cancer are increased. Previously technetium-99m labeled alpha-M2 [ 8 ], H6F [ 9 ], TP1623 [ 10 ], PI [ 11 ] and EC peptide [ 12 ] are used as a molecular imaging agent for breast cancer.…”

Radioiodinated Small-Molecule Tyrosine Kinase Inhibitor for HER2-Selective SPECT Imaging

“…Radionuclide-based molecular imaging techniques such as PET and SPECT may represent an appropriate tool to obtain real-time, noninvasive, and quantitative information about HER2 expression in vivo with high sensitivity (8)(9)(10)(11)(12). So far, several radiolabeled HER2-targeted imaging probes have been assessed, including anti-HER2 antibodies (13)(14)(15) or their fragments (16), single-domain antibodies (17), diabodies (18), Affibody molecules (Affibody AB) (19,20), and high-affinity peptide ligands (21,22). Although most have shown high accumulation in tumor tissues, imaging with these large-molecule radiotracers has limitations due to the unfavorable receptor binding kinetics compared with their systemic clearance (23,24).…”