Imaging Diagnostic and Therapeutic Targets: Human Epidermal Growth Factor Receptor 2

Detection of HER2 expression using 99mTc-NM-02 nanobody in patients with breast cancer: a non-randomized, non-blinded clinical trial

BACKGROUND

99mTc radiolabeled nanobody NM-02 (99mTc-NM-02) is a novel single photon emission computed tomography (SPECT) probe with a high affinity and specificity for human epidermal growth factor receptor 2 (HER2). In this study, a clinical imaging trial was conducted to investigate the relationship between 99mTc-NM-02 uptake and HER2 expression in patients with breast cancer.

METHODS

Thirty patients with pathologically confirmed breast cancer were recruited and imaged with both 99mTc-NM-02 SPECT/computed tomography (CT) and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT. According to the treatment conditions before recruitment, patients were divided into two groups, the newly diagnosed group (n = 24) and the treated group (n = 6). The maximal standard uptake value (SUVmax) of 18F-FDG and SUVmax and mean SUV (SUVmean) of 99mTc-NM-02 in the lesions were determined to analyze the relationship with HER2 expression.

RESULTS

No meaningful relationship was observed between 18F-FDG uptake and HER2 expression in 30 patients with breast cancer. 99mTc-NM-02 uptake was positively correlated with HER2 expression in the newly diagnosed group, but no correlation was observed in the treated group. 99mTc-NM-02 uptake in HER2-positive lesions was lower in those with effective HER2-targeted therapy compared with the newly diagnosed group. 99mTc-NM-02 SPECT/CT detected brain and bone metastases of breast cancer with a different imaging pattern from 18F-FDG PET/CT. 99mTc-NM-02 showed no non-specific uptake in inflamed tissues and revealed intra- and intertumoral HER2 heterogeneity by SPECT/CT imaging in 9 of the 30 patients with breast cancer.

CONCLUSIONS

99mTc-NM-02 SPECT/CT has the potential for visualizing whole-body HER2 overexpression in untreated patients, making it a promising method for HER2 assessment in patients with breast cancer.

TRIAL REGISTRATION

NCT04674722, Date of registration: December 19, 2020.

Phase II Trial Assessing the Repeatability and Tumor Uptake of [68Ga]Ga-HER2 Single-Domain Antibody PET/CT in Patients with Breast Carcinoma

Human epidermal growth factor receptor 2 (HER2) status is used for decision-making in breast carcinoma treatment. The status is obtained through immunohistochemistry or in situ hybridization. These two methods have the disadvantage of necessitating tissue sampling, which is prone to error due to tumor heterogeneity or interobserver variability. Whole-body imaging might be a solution to map HER2 expression throughout the body. Methods: Twenty patients with locally advanced or metastatic breast carcinoma (5 HER2-positive and 15 HER2-negative patients) were included in this phase II trial to assess the repeatability of uptake quantification and the extended safety of the [68Ga]Ga-NOTA-anti-HER2 single-domain antibody (sdAb). The tracer was injected, followed by a PET/CT scan at 90 min. Within 8 d, the procedure was repeated. Blood samples were taken for antidrug antibody (ADA) assessment and liquid biopsies. On available tissues, immunohistochemistry, in situ hybridization, and mass spectrometry were performed to determine the correlation of HER2 status with uptake values measured on PET. If relevant preexisting [18F]FDG PET/CT images were available (performed as standard of care), a comparison was made. Results: With a repeatability coefficient of 21.8%, this imaging technique was repeatable. No clear correlation between PET/CT uptake values and pathology could be established, as even patients with low levels of HER2 expression showed moderate to high uptake. Comparison with [18F]FDG PET/CT in 16 patients demonstrated that in 7 patients, [68Ga]Ga-NOTA-anti-HER2 shows interlesional heterogeneity within the same patient, and [18F]FDG uptake did not show the same heterogeneous uptake in all patients. In some patients, the extent of disease was clearer with the [68Ga]Ga-NOTA-anti-HER2-sdAb. Sixteen adverse events were reported but all without a clear relationship to the tracer. Three patients with preexisting ADAs did not show adverse reactions. No new ADAs developed. Conclusion: [68Ga]Ga-NOTA-anti-HER2-sdAb PET/CT imaging shows similar repeatability to [18F]FDG. It is safe for clinical use. There is tracer uptake in cancer lesions, even in patients previously determined to be HER2-low or -negative. The tracer shows potential in the assessment of interlesional heterogeneity of HER2 expression. In a subset of patients, [68Ga]Ga-NOTA-anti-HER2-sdAb uptake was seen in lesions with no or low [18F]FDG uptake. These findings support further clinical development of [68Ga]Ga-NOTA-anti-HER2-sdAb as a PET/CT tracer in breast cancer patients.

PET/CT and SPECT/CT Imaging of HER2-Positive Breast Cancer

HER2 (Human Epidermal Growth Factor Receptor 2)-positive breast cancer is characterized by amplification of the HER2 gene and is associated with more aggressive tumor growth, increased risk of metastasis, and poorer prognosis when compared to other subtypes of breast cancer. HER2 expression is therefore a critical tumor feature that can be used to diagnose and treat breast cancer. Moving forward, advances in HER2 in vivo imaging, involving the use of techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT), may allow for a greater role for HER2 status in guiding the management of breast cancer patients. This will apply both to patients who are HER2-positive and those who have limited-to-minimal immunohistochemical HER2 expression (HER2-low), with imaging ultimately helping clinicians determine the size and location of tumors. Additionally, PET and SPECT could help evaluate effectiveness of HER2-targeted therapies, such as trastuzumab or pertuzumab for HER2-positive cancers, and specially modified antibody drug conjugates (ADC), such as trastuzumab-deruxtecan, for HER2-low variants. This review will explore the current and future role of HER2 imaging in personalizing the care of patients diagnosed with breast cancer.

Molecular imaging as biomarker for treatment response and outcome in breast cancer

Molecular imaging, such as positron emission tomography (PET), is increasingly used as biomarker to predict and assess treatment response in breast cancer. The number of biomarkers is expanding with specific tracers for tumour characteristics throughout the body and this information can be used to aid the decision-making process. These measurements include metabolic activity using [18F]fluorodeoxyglucose PET ([18F]FDG-PET), oestrogen receptor (ER) expression using 16α-[18F]Fluoro-17β-oestradiol ([18F]FES)-PET and human epidermal growth factor receptor 2 (HER2) expression using PET with radiolabelled trastuzumab (HER2-PET). In early breast cancer, baseline [18F]FDG-PET is frequently used for staging, but limited subtype-specific data reduce its usefulness as biomarker for treatment response or outcome. Early metabolic change on serial [18F]FDG-PET is increasingly used in the neo-adjuvant setting as dynamic biomarker to predict pathological complete response to systemic therapy, potentially allowing de-intensification or step-up intensification of treatment. In the metastatic setting, baseline [18F]FDG-PET and [18F]FES-PET can be used as biomarker to predict treatment response, in triple-negative and ER-positive breast cancer, respectively. Metabolic progression on repeated [18F]FDG-PET appears to precede progressive disease on standard evaluation imaging; however, subtype-specific studies are limited and more prospective data are needed before implementation in clinical practice. Even though (repeated) [18F]FDG-PET, [18F]FES-PET and HER2-PEt all show promising results as biomarkers to predict therapy response and outcome, for eventual integration into clinical practice, future studies will have to clarify at what timepoint this integration has to optimally take place.

Novel HER2-Targeted Peptide for NIR-II Imaging of Tumor

Molecular targets serve a crucial role in drug development. Herein, we discovered a novel peptide that can specifically target the human epidermal growth factor receptor 2 (HER2) and thus named it Herceptide. In our study, Herceptide was conjugated to the near-infrared fluorescent dye indocyanine green (ICG) to obtain a probe, ICG-Herceptide. Importantly, specific binding to HER2 was revealed by molecular docking, surface plasmon resonance analysis, and competition assays. The probe showed high binding affinity (K_D = 1.03 nM) and fast binding property (k_on = 0.44 min^-1). In vivo near-infrared window two (NIR-II, 1000-1700 nm) imaging in HER2-overexpressed SKOV3 tumor-bearing mice demonstrated a high tumor-to-normal tissue signal ratio (T/N = 7.3) at 8 h postinjection. In the blocking study, ICG-Herceptide coinjected with Herceptide only showed a weak tumor signal. In other HER2 high-expression tumors, such as non-small-cell lung cancer A549 and gastric cancer MKN45, the tumor-to-normal tissue signal ratios (T/N) were 4.1 and 4.7, respectively. In contrast, HER2 low-expression tumor MDAMB231 shows no imaging contrast between the tumor and normal tissues. Furthermore, tumor resection was successfully performed under the guidance of the ICG-Herceptide-based NIR-II imaging in subcutaneous SKOV3 mice models. The biocompatibility study indicated that the probe had no observable toxicity to cells and tissues. Overall, these results demonstrate that ICG-Herceptide is a promising optical probe for the diagnosis and localization of HER2-overexpressing tumors. Moreover, Herceptide is a novel HER2-targeting peptide and can be further used for developing theranostic agents.

Molecular imaging of HER2 receptor: Targeting HER2 for imaging and therapy in nuclear medicine

Targeting HER 2 for imaging and therapy in nuclear medicine has been used with a special emphasis on developing more powerful radiopharmaceuticals. Zirconium-89 plays an essential role in immune PET imaging so was used labeled with anti-HER2 antibody (Trastuzumab and Pertuzumab). Also there were attempts with other PET tracers as Cuprum-64 and Galium-68, as well as SPECT radiopharmaceuticals Indium-111 and Technetium- 99m. Regarding antibody pharmacokinetic that is not quite appropriate for imaging acquisition, several smaller molecules with shorter residence times have been developed. These molecules called nanobody, affibody, minibody do not compromize HER2 receptor affinity and specificity. Excess of Trastuzumab do not block the affinity of labeled affibodies. Silica nanoparticles have been conjugated to anti-HER2 antibodies to enable targeting of HER2 expressing cells with potential of drug delivery carry for antitumor agents and b(beta) or a(alfa) emitting radioisotopes commonly used for radionuclide therapy, as Iodine-131, Lutetium-177, Yttrium-90, Rhenium-188 and Thorium-277.

The Evolution of Targeted Radionuclide Diagnosis of HER2-Positive Breast Cancer

This review examines the evolution of the radionuclide diagnosis of HER2-positive breast cancer using various compounds as a targeting module in clinical practice: from full-length antibodies to a new group of small synthetic proteins called alternative scaffold proteins. This topic is of especial relevance today in view of the problems attendant to the detection of breast cancer with HER2/neu overexpression, which, in most cases, introduce errors in the treatment of patients. The results of clinical studies of radiopharmaceuticals based on affibody molecules, ADAPTs, and DARPins for SPECT and PET have demonstrated good tolerability of the compounds, their rapid excretion from the body, and the possibility to differentiate tumor sites depending on the HER2/neu status. This indicates that targeted radionuclide diagnosis holds promise and the need to continue research in this direction.

Multimodal Imaging Technology Effectively Monitors HER2 Expression in Tumors Using Trastuzumab-Coupled Organic Nanoparticles in Patient-Derived Xenograft Mice Models

Trastuzumab is a monoclonal antibody targeting human epidermal growth factor 2 (HER2), which has been successfully used in the treatment of patients with breast cancer and gastric cancer; however, problems concerning its cardiotoxicity, drug resistance, and unpredictable efficacy still remain. Herein, we constructed novel organic dopamine–melanin nanoparticles (dMNs) as a carrier and then surface-loaded them with trastuzumab to construct a multifunctional nanoprobe named Her-PEG-dMNPs. We used micro-PET/CT and PET/MRI multimodality imaging to evaluate the retention effect of the nanoprobe in HER2 expression in gastric cancer patient-derived xenograft (PDX) mice models after labeling of the radionuclides ⁶⁴Cu or ¹²⁴I and MRI contrast agent Mn²⁺. The nanoprobes can specifically target the HER2-expressing SKOV-3 cells in vitro (3.61 ± 0.74 vs. 1.24 ± 0.43 for 2 h, P = 0.002). In vivo, micro-PET/CT and PET/MRI showed that the ¹²⁴I-labeled nanoprobe had greater contrast and retention effect in PDX models than unloaded dMNPs as carrier (1.63 ± 0.07 vs. 0.90 ± 0.04 at 24 h, P = 0.002), a similarity found in ⁶⁴Cu-labeled Her-PEG-dMNPs. Because ¹²⁴I has a longer half-life and matches the pharmacokinetics of the nanoparticles, we focused on the further evaluation of ¹²⁴I-Her-PEG-dMNPs. Furthermore, immunohistochemistry staining confirmed the overexpression of HER2 in the animal model. This study developed and validated novel HER2-specific multimodality imaging nanoprobes for quantifying HER2 expression in mice. Through the strong retention effect of the tumor site, it can be used for the promotion of monoclonal antibody treatment effect and process monitoring.

Design, Synthesis and Binding Affinity Evaluation of Cytochrome P450 1B1 Targeted Chelators

BACKGROUND

Cytochrome P450 1B1 (CYP1B1) is specifically expressed in a variety of tumors which makes it a promise imaging target of tumor.

OBJECTIVE

We aimed to design and synthesize CYP1B1 targeted chelators for the potential application in positron emission tomography (PET) imaging of tumor.

METHODS

1,4,7-triazacyclononane-1,4-diiacetic acid (NODA) was connected to the CYP1B1 selective inhibitor we developed before through polyethylene glycol (PEG) linkers with different lengths. The inhibitory activities of chelators 6a-c against CYP1 family were evaluated by 7-ethoxyresorufin o-deethylation (EROD) assay. The manual docking between the chelators and the CYP1B1 are conducted subsequently. To determine the binding affinities of 6a-c to CYP1B1 in cells, we further performed a competition study at the cell level.

RESULTS

Among three chelators, 6a with the shortest linker showed the best inhibitory activity against CYP1B1. In the following molecular simulation study, protein-inhibitor complex of 6a showed the nearest F-heme distance which is consistent with the results of enzymatic assay. Finally, the cell based competitive assay proved the binding affinity of 6a-c to CYP1B1 enzyme.

CONCLUSION

We designed and synthesized a series of chelators which can bind to CYP1B1 enzyme in cancer cells.To our knowledge, this work is the first attempt to construct CYP1B1 targeted chelators for radiolabeling and we hope it will prompt the application of CYP1B1 imaging in tumor detection.

Preclinical Evaluation of 99mTc-ZHER2:41071, a Second-Generation Affibody-Based HER2-Visualizing Imaging Probe with a Low Renal Uptake

Radionuclide imaging of HER2 expression in tumours may enable stratification of patients with breast, ovarian, and gastroesophageal cancers for HER2-targeting therapies. A first-generation HER2-binding affibody molecule [^99mTc]Tc-ZHER2:V2 demonstrated favorable imaging properties in preclinical studies. Thereafter, the affibody scaffold has been extensively modified, which increased its melting point, improved storage stability, and increased hydrophilicity of the surface. In this study, a second-generation affibody molecule (designated ZHER2:41071) with a new improved scaffold has been prepared and characterized. HER2-binding, biodistribution, and tumour-targeting properties of [^99mTc]Tc-labelled ZHER2:41071 were investigated. These properties were compared with properties of the first-generation affibody molecules, [^99mTc]Tc-ZHER2:V2 and [^99mTc]Tc-ZHER2:2395. [^99mTc]Tc-ZHER2:41071 bound specifically to HER2 expressing cells with an affinity of 58 ± 2 pM. The renal uptake for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 was 25–30 fold lower when compared with [^99mTc]Tc-ZHER2:2395. The uptake in tumour and kidney for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 in SKOV-3 xenografts was similar. In conclusion, an extensive re-engineering of the scaffold did not compromise imaging properties of the affibody molecule labelled with ^99mTc using a GGGC chelator. The new probe, [^99mTc]Tc-ZHER2:41071 provided the best tumour-to-blood ratio compared to HER2-imaging probes for single photon emission computed tomography (SPECT) described in the literature so far. [^99mTc]Tc-ZHER2:41071 is a promising candidate for further clinical translation studies.

Characterization and clinical significance of the CADM1/HER2/STAT3 axis in serous ovarian tumors

The subtypes of serous ovarian tumors (SOTs), including benign serous cystadenoma, serous borderline tumor (SBT), low-grade serous ovarian carcinoma (LGSC), and high-grade serous ovarian carcinoma (HGSC), remain poorly understood. Herein, we aimed to characterize the cell adhesion molecule 1 (CADM1)/signal transducer and activator of transcription 3 (STAT3)/human epidermal growth factor receptor 2 (HER2) axis and identify its clinical significance in patients with serous cystadenoma, SBT, LGSC, and HGSC.The immunohistochemical expression of CADM1, HER2, and STAT3 was assessed in 180 SOT specimens, and its association with clinical data was determined.High levels of CADM1 expression were detected in 100% of serous cystadenomas and 83.33% of SBTs, while a loss of CADM1 expression was observed in 44% of LGSCs and 72.5% of HGSCs. Relative to the levels in benign cystadenomas and SBTs, higher levels of HER2 and STAT3 expression were observed in LGSCs and aggressive HGSCs. Furthermore, the expression profile of the CADM1/HER2/STAT3 axis was significantly associated with histologic type, International Federation of Gynecology and Obstetrics stage, and lymph node metastasis in patients with SOT.Our study identified the changes in the CADM1/HER2/STAT3 axis that were closely associated with the clinical behavior of SOTs. These molecular data may provide new insights into SOT carcinogenesis and aid in the diagnosis and treatment of patients with SOT.

Imaging of HER2-Positive Tumors in NOD/SCID Mice with Pertuzumab Fab-Hexahistidine Peptide Immunoconjugates Labeled with [99mTc]-(I)-Tricarbonyl Complex

PURPOSE

Molecular imaging of tumor HER2 expression may allow patient selection for HER2-targeted therapies. Our aim was to introduce hexahistidine (His₆) peptides into pertuzumab Fab to enable labeling with the [^99mTc(CO)₃(H₂O)₃]⁺ complex and study these radioimmunoconjugates for microSPECT/CT imaging of HER2-positive tumor xenografts in mice.

PROCEDURES

Fab were produced by papain digestion of pertuzumab and reacted with sulfo-SMCC for conjugation to His₆-containing peptides (CGYGGHHHHHH). His₆-peptide conjugation was measured by a radiometric assay. His₆-pertuzumab Fab were labeled at 0.4-1.0 MBq/μg with [^99mTc(CO)₃(H₂O)₃]⁺ for 1 h at 37 °C. HER2 immunoreactivity was assessed in a direct (saturation) binding assay using HER2-overexpressing SK-BR-3 human breast cancer (BC) cells. MicroSPECT/CT and biodistribution studies were performed in NOD/SCID mice with HER2-positive s.c. SK-OV-3 human ovarian cancer, or MDA-MB-361 or MDA-MB-231 human BC xenografts at 4 or 24 h post i.v. injection of [^99mTc]His₆-pertuzumab Fab (29-49 MBq, 70 μg). The specificity of tumor uptake was assessed by comparison to irrelevant [^99mTc]Fab 3913 in SK-OV-3 tumor-bearing mice.

RESULTS

SDS-PAGE analysis demonstrated cleavage of pertuzumab to produce Fab, which eluted as a single peak with a retention time of 13.8 min on SE-HPLC. Fab were conjugated to 2.1 ± 0.5 His₆ peptides and labeled with [^99mTc(CO)₃(H₂O)₃]⁺ to a radiochemical purity of 92-97 % at 0.4-0.8 MBq/μg. [^99mTc]His₆-pertuzumab Fab exhibited saturable and specific binding to SK-BR-3 cells with a K_D = 51.3 ± 5.2 × 10^-9 M and B_max = 3.5 ± 0.1 × 10⁶ receptors/cell. SK-OV-3 tumors were imaged at 4 and 24 h p.i [^99mTc]His₆-pertuzumab Fab. Tumor uptake at 24 h p.i. was 4.1 ± 0.6 %ID/g, which was 13-fold significantly greater than [^99mTc]Fab 3913 (0.3 ± 0.0 %ID/g; P < 0.01). MicroSPECT/CT imaged HER2-overexpressing MDA-MB-361 tumors but not MDA-MB-231 tumors with low HER2 expression. Tumor uptake was 5.2-fold significantly greater at 24 h p.i. in MDA-MB-361 than MDA-MB-231 tumors (3.2 ± 0.1 %ID/g vs. 0.8 ± 0.1 %ID/g; P < 0.05).

CONCLUSIONS

MicroSPECT/CT with [^99mTc]His₆-pertuzumab Fab imaged tumors in NOD/SCID mice that exhibited intermediate or high HER2 expression, but not tumors with low HER2. [^99mTc]His₆-pertuzumab Fab is promising for SPECT imaging of tumor HER2 expression.

Developing PEGylated Reversed D-Peptide as a Novel HER2-Targeted SPECT Imaging Probe for Breast Cancer Detection

Human epidermal growth factor receptor-2 (HER2)-enriched breast cancer is characterized by strong invasiveness, high recurrence rate, and poor prognosis. HER2-specific imaging can help screening right patients for appropriate HER2-targeted therapies. Previously, we have developed a ^99mTc-labeled HER2-targeted H6 peptide for SPECT imaging of breast cancer. However, the poor metabolic stability and high gallbladder uptake hamper its clinical application. In this study, a retro-inverso D-peptide of H6 (RDH6) was designed to increase the metabolic stability. PEGylation was used to improve its water solubility and in vivo pharmacokinetics. The results showed that the D-amino acids in ^99mTc-PEG₄-RDH6 brought better metabolic stability than ^99mTc-PEG₄-H6, thus achieving higher tumor uptake. As the length of the PEG chain increases, the hydrophilicity of the probes gradually increased, which may also be the main cause for the decreased liver uptake. Compared with radiotracers modified by PEG₄ and PEG₁₂, ^99mTc-PEG₂₄-RDH6 had a comparable tumor uptake and the lowest liver radioactivity. The SPECT imaging demonstrated that ^99mTc-PEG₂₄-RDH6 could specifically distinguish HER2-positive tumors from HER2-negative tumors with better imaging contrast, which thus has the potential for clinical screening of HER2-positive breast patients.

Phase I Study of 99mTc-ADAPT6, a Scaffold Protein-Based Probe for Visualization of HER2 Expression in Breast Cancer

Radionuclide molecular imaging of human epidermal growth factor receptor type 2 (HER2) expression may help to stratify breast and gastroesophageal cancer patients for HER2-targeting therapies. Albumin-binding domain-derived affinity proteins (ADAPTs) are a new type of small (46-59 amino acids) protein useful as probes for molecular imaging. The aim of this first-in-humans study was to evaluate the biodistribution, dosimetry, and safety of the HER2-specific ^99mTc-ADAPT6. Methods: Twenty-nine patients with primary breast cancer were included. In 22 patients with HER2-positive (n = 11) or HER2-negative (n = 11) histopathology, an intravenous injection of 385 ± 125 MBq of ^99mTc-ADAPT6 was performed, randomized to an injected protein mass of either 500 μg (n = 11) or 1,000 μg (n = 11). Planar scintigraphy followed by SPECT imaging was performed after 2, 4, 6, and 24 h. An additional cohort (n = 7) was injected with 165 ± 29 MBq (injected protein mass, 250 μg), and imaging was performed after 2 h only. Results: Injections of ^99mTc-ADAPT6 were well tolerated at all mass levels and not associated with adverse effects. ^99mTc-ADAPT6 cleared rapidly from the blood and most other tissues. The normal organs with the highest accumulation were the kidney, liver, and lung. Effective doses were 0.009 ± 0.002 and 0.010 ± 0.003 mSv/MBq for injected protein masses of 500 and 1,000 μg, respectively. Injection of 500 μg resulted in excellent discrimination between HER2-positive and HER2-negative tumors as early as 2 h after injection (tumor-to-contralateral breast ratio, 37 ± 19 vs. 5 ± 2; P < 0.01). The tumor-to-contralateral breast ratios for HER2-positive tumors were significantly (P < 0.05) higher for an injected mass of 500 μg than for either 250 or 1,000 μg. Conclusion: Injections of ^99mTc-ADAPT6 are safe and associated with low absorbed and effective doses. A protein dose of 500 μg is preferable for discrimination between tumors with high and low expression of HER2. Further studies are justified to evaluate whether ^99mTc-ADAPT6 can be used as an imaging probe to stratify patients for HER2-targeting therapy in areas where PET imaging is not readily available.

Imaging using radiolabelled targeted proteins: radioimmunodetection and beyond

The use of radiolabelled antibodies was proposed in 1970s for staging of malignant tumours. Intensive research established chemistry for radiolabelling of proteins and understanding of factors determining biodistribution and targeting properties. The use of radioimmunodetection for staging of cancer was not established as common practice due to approval and widespread use of [¹⁸F]-FDG, which provided a more general diagnostic use than antibodies or their fragments. Expanded application of antibody-based therapeutics renewed the interest in radiolabelled antibodies. RadioimmunoPET emerged as a powerful tool for evaluation of pharmacokinetics of and target engagement by biotherapeutics. In addition to monoclonal antibodies, new radiolabelled engineered proteins have recently appeared, offering high-contrast imaging of expression of therapeutic molecular targets in tumours shortly after injection. This creates preconditions for noninvasive determination of a target expression level and stratification of patients for targeted therapies. Radiolabelled proteins hold great promise to play an important role in development and implementation of personalised targeted treatment of malignant tumours. This article provides an overview of biodistribution and tumour-seeking features of major classes of targeting proteins currently utilized for molecular imaging. Such information might be useful for researchers entering the field of the protein-based radionuclide molecular imaging.

First In-Human Medical Imaging with a PASylated 89Zr-Labeled Anti-HER2 Fab-Fragment in a Patient with Metastatic Breast Cancer

Purpose

PASylation® offers the ability to systematically tune and optimize the pharmacokinetics of protein tracers for molecular imaging. Here we report the first clinical translation of a PASylated Fab fragment (⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀) for the molecular imaging of tumor-related HER2 expression.

Methods

A patient with HER2-positive metastatic breast cancer received 37 MBq of ⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀ at a total mass dose of 70 μg. PET/CT was carried out 6, 24, and 45 h after injection, followed by image analysis of biodistribution, normal organ uptake, and lesion targeting.

Results

Images show a biodistribution typical for protein tracers, characterized by a prominent blood pool 6 h p.i., which decreased over time. Lesions were detectable as early as 24 h p.i. ⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀ was tolerated well.

Conclusion

This study demonstrates that a PASylated Fab tracer shows appropriate blood clearance to allow sensitive visualization of small tumor lesions in a clinical setting.

PET Imaging of Receptor Tyrosine Kinases in Cancer

Overexpression and/or mutations of the receptor tyrosine kinase (RTK) subfamilies, such as epidermal growth factor receptors (EGFR) and vascular endothelial growth factor receptors (VEGFR), are closely associated with tumor cell growth, differentiation, proliferation, apoptosis, and cellular invasiveness. Monoclonal antibodies (mAb) and tyrosine kinase inhibitors (TKI) specifically inhibiting these RTKs have shown remarkable success in improving patient survival in many cancer types. However, poor response and even drug resistance inevitably occur. In this setting, the ability to detect and visualize RTKs with noninvasive diagnostic tools will greatly refine clinical treatment strategies for cancer patients, facilitate precise response prediction, and improve drug development. Positron emission tomography (PET) agents using targeted radioactively labeled antibodies have been developed to visualize tumor RTKs and are changing clinical decisions for certain cancer types. In the present review, we primarily focus on PET imaging of RTKs using radiolabeled antibodies with an emphasis on the clinical applications of these immunoPET probes. Mol Cancer Ther; 17(8); 1625-36. ©2018 AACR.

Development of the Tumor-Specific Antigen-Derived Synthetic Peptides as Potential Candidates for Targeting Breast and Other Possible Human Carcinomas

The human epidermal growth factor receptor 2 (HER2) represents one of the most studied tumor-associated antigens for cancer immunotherapy. The receptors for HER2 are overexpressed in various human cancers, such as breast and ovarian cancer. The relatively low expression of this antigen on normal tissues makes it a clinically useful molecular target for tumor imaging and targeted therapy. HER2 overexpression is correlated with aggressive tumor behavior and poor clinical outcomes. Thus, HER2 has become an important prognostic and predictive factor, as well as a potential molecular target. Due to the heterogeneity of breast cancer and possible discordance in HER2 status between primary tumors and distant metastases, assessment of HER2 expression by noninvasive imaging is important. Molecular imaging of HER2 expression may provide essential prognostic and predictive information concerning disseminated cancer and aid in the selection of an optimal therapy. Another tumor-specific antigen is MUC1, which is silent on normal tissues, but overexpressed in almost all human epithelial cell cancers, including >90% of human breast, ovarian, pancreatic, colorectal, lung, prostate, and gastric cancers and is a promising tumor antigen with diagnostic as well as the therapeutic potential of cancer. Radiolabeled small peptide ligands are attractive as probes for molecular imaging, as they reach and bind the target receptor efficiently and clear from blood and non-target organs faster than bulky antibodies. In this study, HER2 and MUC1-based peptides were synthesized and preclinically evaluated in an effort to develop peptide-based SPECT radiopharmaceuticals derived from tumor-associated antigens for the detection of breast cancer. Our findings demonstrate that the tumor antigen peptides radiolabeled efficiently with ^99mTc and showed high metabolic stability in human plasma in vitro. The data from breast tumor cell binding confirmed the high affinity (in low nanomolar range) towards respective breast cancer cell lines. In healthy mice, ^99mTc-labeled peptides displayed favorable pharmacokinetics, with high excretion by the renal system. In tumor xenografts nude mice models, good uptake by the SKBR3, MCF7, and T47D tumors were found, with good tumor-to-blood and tumor to muscle ratios. Additionally, tumor lesions can be seen in γ-camera imaging. Our data suggest that based on its ability to detect HER2- and MUC1-positive breast cancer cells in vivo, ^99mTc-HER2 and ^99mTc-MUC1-targeted peptides may be promising tumor imaging probes and warrant further investigation.

Autophosphorylation of Orphan Receptor ERBB2 Can Be Induced by Extracellular Treatment with Mildly Alkaline Media

ErbB2 is an oncogene receptor tyrosine kinase linked to breast cancer. It is a member of the epidermal growth factor receptor (EGFR) minifamily. ErbB2 is currently viewed as an orphan receptor since, by itself, it does not bind EGF-like ligands and can be activated only when overexpressed in malignant cells or complexed with ErbB3, another member of the EGFR minifamily. Here, we report that ErbB2 can be activated by extracellular application of mildly alkaline (pH 8–9) media to ErbB2-transfected cells. We also show that the activation of the ErbB2 receptor by alkali is dose-dependent and buffer-independent. The endogenous ErbB2 receptor of A431 cell line can also undergo alkali-dependent autophosphorylation. Thus, we describe a novel ligand-independent mechanism of ErbB2 receptor activation.

Imaging of HER2 with [89Zr]pertuzumab in Response to T-DM1 Therapy

Background: The success of human epidermal growth factor receptor 2 (HER2)-targeted therapy depends on accurate characterization of HER2 expression, but current methods available have several limitations. This study aims to investigate the feasibility of [⁸⁹Zr]pertuzumab imaging to monitor early response to Ado-trastuzumab emtansine (T-DM1) therapy in mice bearing xenografts of HER2-positive breast cancer (BCa). Materials and Methods: Pertuzumab was conjugated to DFO-Bz-NCS and labeled with ⁸⁹Zr. Mice bearing BT-474 tumors were imaged with [⁸⁹Zr]pertuzumab and [¹⁸F]FDG before and after T-DM1 therapy. Results: Pertuzumab was successfully labeled with ⁸⁹Zr with a specific activity of 0.740 MBq/μg. Overall [¹⁸F]FDG images showed poor delineation of tumors. Using [¹⁸F]FDG-PET to measure tumor volume, the volume remained unchanged from 107.6 ± 20.7 mm³ before treatment to 89.87 ± 66.55 mm³ after treatment. In contrast, [⁸⁹Zr]pertuzumab images showed good delineation of HER2-positive tumors, allowing accurate detection of changes in tumor volume (from 243.80 ± 40.91 mm³ before treatment to 78.4 ± 40.43 mm³ after treatment). Conclusion: [⁸⁹Zr]pertuzumab may be an imaging probe for monitoring the response of HER2-positive BCa patients to T-DM1 therapy.

Ultrasmall targeted nanoparticles with engineered antibody fragments for imaging detection of HER2-overexpressing breast cancer

Controlling the biodistribution of nanoparticles upon intravenous injection is the key to achieving target specificity. One of the impediments in nanoparticle-based tumor targeting is the inability to limit the trafficking of nanoparticles to liver and other organs leading to smaller accumulated amounts in tumor tissues, particularly via passive targeting. Here we overcome both these challenges by designing nanoparticles that combine the specificity of antibodies with favorable particle biodistribution profiles, while not exceeding the threshold for renal filtration as a combined vehicle. To that end, ultrasmall silica nanoparticles are functionalized with anti-human epidermal growth factor receptor 2 (HER2) single-chain variable fragments to exhibit high tumor-targeting efficiency and efficient renal clearance. This ultrasmall targeted nanotheranostics/nanotherapeutic platform has broad utility, both for imaging a variety of tumor tissues by suitably adopting the targeting fragment and as a potentially useful drug delivery vehicle.

Fluorine-18 Labeling of the HER2-Targeting Single-Domain Antibody 2Rs15d Using a Residualizing Label and Preclinical Evaluation

PURPOSE

Our previous studies with F-18-labeled anti-HER2 single-domain antibodies (sdAbs) utilized 5F7, which binds to the same epitope on HER2 as trastuzumab, complicating its use for positron emission tomography (PET) imaging of patients undergoing trastuzumab therapy. On the other hand, sdAb 2Rs15d binds to a different epitope on HER2 and thus might be a preferable vector for imaging in these patients. The aim of this study was to evaluate the tumor targeting of F-18 -labeled 2Rs15d in HER2-expressing breast carcinoma cells and xenografts.

PROCEDURES

sdAb 2Rs15d was labeled with the residualizing labels N-succinimidyl 3-((4-(4-[¹⁸F]fluorobutyl)-1H-1,2,3-triazol-1-yl)methyl)-5-(guanidinomethyl)benzoate ([¹⁸F]RL-I) and N-succinimidyl 4-guanidinomethyl-3-[¹²⁵I]iodobenzoate ([¹²⁵I]SGMIB), and the purity and HER2-specific binding affinity and immunoreactivity were assessed after labeling. The biodistribution of I-125- and F-18-labeled 2Rs15d was determined in SCID mice bearing subcutaneous BT474M1 xenografts. MicroPET/x-ray computed tomograph (CT) imaging of [¹⁸F]RL-I-2Rs15d was performed in this model and compared to that of nonspecific sdAb [¹⁸F]RL-I-R3B23. MicroPET/CT imaging was also done in an intracranial HER2-positive breast cancer brain metastasis model after administration of 2Rs15d-, 5F7-, and R3B23-[¹⁸F]RL-I conjugates.

RESULTS

[¹⁸F]RL-I was conjugated to 2Rs15d in 40.8 ± 9.1 % yield and with a radiochemical purity of 97-100 %. Its immunoreactive fraction (IRF) and affinity for HER2-specific binding were 79.2 ± 5.4 % and 7.1 ± 0.4 nM, respectively. [¹²⁵I]SGMIB was conjugated to 2Rs15d in 58.4 ± 8.2 % yield and with a radiochemical purity of 95-99 %; its IRF and affinity for HER2-specific binding were 79.0 ± 12.9 % and 4.5 ± 0.8 nM, respectively. Internalized radioactivity in BT474M1 cells in vitro for [¹⁸F]RL-I-2Rs15d was 43.7 ± 3.6, 36.5 ± 2.6, and 21.7 ± 1.2 % of initially bound radioactivity at 1, 2, and 4 h, respectively, and was similar to that seen for [¹²⁵I]SGMIB-2Rs15d. Uptake of [¹⁸F]RL-I-2Rs15d in subcutaneous xenografts was 16-20 %ID/g over 1-3 h. Subcutaneous tumor could be clearly delineated by microPET/CT imaging with [¹⁸F]RL-I-2Rs15d but not with [¹⁸F]RL-I-R3B23. Intracranial breast cancer brain metastases could be visualized after intravenous administration of both [¹⁸F]RL-I-2Rs15d and [¹⁸F]RL-I-5F7.

CONCLUSIONS

Although radiolabeled 2Rs15d conjugates exhibited lower tumor cell retention both in vitro and in vivo than that observed previously for 5F7, given that it binds to a different epitope on HER2 from those targeted by the clinically utilized HER2-targeted therapeutic antibodies trastuzumab and pertuzumab, F-18-labeled 2Rs15d has potential for assessing HER2 status by PET imaging after trastuzumab and/or pertuzumab therapy.

Optimized Molecular Design of ADAPT-Based HER2-Imaging Probes Labeled with 111In and 68Ga

Radionuclide molecular imaging is a promising tool for visualization of cancer associated molecular abnormalities in vivo and stratification of patients for specific therapies. ADAPT is a new type of small engineered proteins based on the scaffold of an albumin binding domain of protein G. ADAPTs have been utilized to select and develop high affinity binders to different proteinaceous targets. ADAPT6 binds to human epidermal growth factor 2 (HER2) with low nanomolar affinity and can be used for its in vivo visualization. Molecular design of ¹¹¹In-labeled anti-HER2 ADAPT has been optimized in several earlier studies. In this study, we made a direct comparison of two of the most promising variants, having either a DEAVDANS or a (HE)₃DANS sequence at the N-terminus, conjugated with a maleimido derivative of DOTA to a GSSC amino acids sequence at the C-terminus. The variants (designated DOTA-C⁵⁹-DEAVDANS-ADAPT6-GSSC and DOTA-C⁶¹-(HE)₃DANS-ADAPT6-GSSC) were stably labeled with ¹¹¹In for SPECT and ⁶⁸Ga for PET. Biodistribution of labeled ADAPT variants was evaluated in nude mice bearing human tumor xenografts with different levels of HER2 expression. Both variants enabled clear discrimination between tumors with high and low levels of HER2 expression. ¹¹¹In-labeled ADAPT6 derivatives provided higher tumor-to-organ ratios compared to ⁶⁸Ga-labeled counterparts. The best performing variant was DOTA-C⁶¹-(HE)₃DANS-ADAPT6-GSSC, which provided tumor-to-blood ratios of 208 ± 36 and 109 ± 17 at 3 h for ¹¹¹In and ⁶⁸Ga labels, respectively.

Development of 64Cu-NOTA-Trastuzumab for HER2 Targeting: A Radiopharmaceutical with Improved Pharmacokinetics for Human Studies

The purpose of this study was to develop ⁶⁴Cu-labeled trastuzumab with improved pharmacokinetics for human epidermal growth factor receptor 2 (HER2). Methods: Trastuzumab was conjugated with SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu. Serum stability and immunoreactivity of ⁶⁴Cu-NOTA-trastuzumab were tested. Small-animal PET imaging and biodistribution studies were performed in a HER2-positive breast cancer xenograft model (BT-474). The internal dosimetry for experimental animals was determined using the image-based approach with the Monte Carlo N-particle code. Results: ⁶⁴Cu-NOTA-trastuzumab was prepared with high radiolabeling yield and radiochemical purity (>98%) and showed high stability in serum and good immunoreactivity. Uptake of ⁶⁴Cu-NOTA-trastuzumab was highest at 48 h after injection as determined by PET imaging and biodistribution results in BT-474 tumors. The blood radioactivity concentrations of ⁶⁴Cu-NOTA-trastuzumab decreased biexponentially with time in both mice with and mice without BT-474 tumor xenografts. The calculated absorbed dose of ⁶⁴Cu-NOTA-trastuzumab was 0.048 mGy/MBq for the heart, 0.079 mGy/MBq for the liver, and 0.047 mGy/MBq for the spleen. Conclusion: ⁶⁴Cu-NOTA-trastuzumab was effectively targeted to the HER2-expressing tumor in vitro and in vivo, and it exhibited a relatively low absorbed dose due to a short residence time. Therefore, ⁶⁴Cu-NOTA-trastuzumab could be applied to select the right patients and right timing for HER2 therapy, to monitor the treatment response after HER2-targeted therapy, and to detect distal or metastatic spread.

Molecular design of radiocopper-labelled Affibody molecules

The use of long-lived positron emitters ⁶⁴Cu or ⁶¹Cu for labelling of Affibody molecules may improve breast cancer patients’ stratification for HER-targeted therapy. Previous animal studies have shown that the use of triaza chelators for ⁶⁴Cu labelling of synthetic Affibody molecules is suboptimal. In this study, we tested a hypothesis that the use of cross-bridged chelator, CB-TE2A, in combination with Gly-Glu-Glu-Glu spacer for labelling of Affibody molecules with radiocopper would improve imaging contrast. CB-TE2A was coupled to the N-terminus of synthetic Affibody molecules extended either with a glycine (designation CB-TE2A-G-ZHER2:342) or Gly-Glu-Glu-Glu spacer (CB-TE2A-GEEE-ZHER2:342). Biodistribution and targeting properties of ⁶⁴Cu-CB-TE2A-G-ZHER2:342 and ⁶⁴Cu-CB-TE2A-GEEE-ZHER2:342 were compared in tumor-bearing mice with the properties of ⁶⁴Cu-NODAGA-ZHER2:S1, which had the best targeting properties in the previous study. ⁶⁴Cu-CB-TE2A-GEEE-ZHER2:342 provided appreciably lower uptake in normal tissues and higher tumor-to-organ ratios than ⁶⁴Cu-CB-TE2A-G-ZHER2:342 and ⁶⁴Cu-NODAGA-ZHER2:S1. The most pronounced was a several-fold difference in the hepatic uptake. At the optimal time point, 6 h after injection, the tumor uptake of ⁶⁴Cu-CB-TE2A-GEEE-ZHER2:342 was 16 ± 6%ID/g and tumor-to-blood ratio was 181 ± 52. In conclusion, a combination of the cross-bridged CB-TE2A chelator and Gly-Glu-Glu-Glu spacer is preferable for radiocopper labelling of Affibody molecules and, possibly, other scaffold proteins having high renal re-absorption.

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

One of the most clinically relevant molecular aberrations in breast cancer is overexpression of human epidermal growth factor receptor type 2 (HER2). We aimed to develop a radiolabeled tyrosine kinase inhibitor for HER2-targeted breast cancer imaging. In this study, a radioiodinated analog (^125/131I-IBA-CP) of the HER2-selective inhibitor CP724,714 was prepared and evaluated in HER2-positive or -negative subcutaneous human breast cancer xenografts. Methods: The CP724,714 analog IBA-CP was synthesized and assayed for its inhibitory activities against HER2 and 6 other tyrosine kinases. ^125/131I-IBA-CP was prepared using a copper-mediated radioiodination method with enhanced labeling yield and molar activity. In vitro biologic activity, including specific and nonspecific binding of ¹³¹I-IBA-CP to its HER2 kinase target, was assessed in different cell lines. In vivo small-animal ¹²⁵I-IBA-CP SPECT imaging and biodistribution studies were conducted on mice bearing HER2-positive, HER2-negative, or epidermal growth factor receptor (EGFR)-positive tumors. Nonradioactive IBA-CP and the EGFR inhibitor erlotinib were used as blocking agents to investigate the binding specificity and selectivity of ^125/131I-IBA-CP toward HER2 in vitro and in vivo. Additionally, ^125/131I-ICP was prepared by direct radioiodination of CP724,714 for comparison with ^125/131I-IBA-CP. Results: IBA-CP displayed superior in vitro inhibitory activity (half-maximal inhibitory concentration, 16 nM) and selectivity for HER2 over 6 other cancer-related tyrosine kinases. ^125/131I-IBA-CP was prepared in a typical radiochemical yield of about 65% (decay-corrected), radiochemical purity of more than 98%, and molar activity of 42 GBq/μmol at the end of synthesis. SPECT imaging revealed significantly higher uptake of ¹²⁵I-IBA-CP than of ¹²⁵I-ICP in the HER2-positive MDA-MB-453 tumors. Uptake in the HER2-negative MCF-7 tumors was much lower. Binding of ¹²⁵I-IBA-CP in the MDA-MB-453 tumors was blocked by coinjection with an excess amount of IBA-CP, but not by erlotinib. Conclusion: The radiolabeled HER2-selective inhibitor ^125/131I-IBA-CP is a promising probe for in vivo detection of HER2-positive tumors.

The prognostic value of volume-based parameters using 18F-FDG PET/CT in gastric cancer according to HER2 status

BACKGROUND

We aimed to find the clinical value of metastatic tumor burden evaluated with F18-FDG PET/CT in gastric cancer patients, considering the human epidermal growth factor receptor 2 (HER2) status.

METHODS

We retrospectively reviewed 124 patients with locally advanced or metastatic gastric cancer at Yonsei Cancer Center between January 2006 and December 2014 who had undergone baseline FDG PET/CT before first-line chemotherapy. We measured the maximum standardized uptake value from the primary tumor (SUV_max) and whole-body (WB) PET/CT parameters, including WB SUV_max, WB SUV_mean, WB metabolic tumor volume (WB MTV), and WB total lesion glycolysis (WB TLG), in all metabolically active metastatic lesions (SUV threshold ≥2.5 or 40% isocontour for ≤2.5), and we determined their association with patient survival outcomes.

RESULTS

SUV_max was higher in HER2-positive gastric cancers (median 12.1, range 3.4-34.6) compared to HER-2 negative (7.4, 1.6-39.1, P < 0.001). Among all patients, WB TLG > 600, which is indicative of a high metastatic tumor burden, showed worse progression-free survival (PFS) [hazard ratio (HR), 2.003; 95% CI, 1.300-3.086; P = 0.002] and overall survival (OS) (HR, 3.001; 95% CI, 1.950-4.618; P < 0.001) than did WB TLG ≤ 600. Among HER2-positive gastric cancer patients treated with trastuzumab, higher metabolic tumor burden predicted worse OS, but not PFS.

CONCLUSIONS

HER2-positive gastric cancers had higher SUV_max compared to HER2-negative gastric cancers. In both HER2-negative patients and -positive patients receiving trastuzumab, FDG PET/CT volume-based parameters may have a role in further stratifying the prognosis of stage IV gastric cancer.

Targeting HER2 in Nuclear Medicine for Imaging and Therapy

Since its discovery, the human epidermal growth factor 2 (HER2) has been extensively studied. Presently, there are 2 standard diagnostic techniques to assess HER2 status in biopsies: immunohistochemistry and fluorescence in situ hybridization. While these techniques have played an important role in the treatment of patients with HER2-positive cancer, they both require invasive biopsies for analysis. Moreover, the expression of HER2 is heterogeneous in breast cancer and can change over the course of the disease. Thus, the degree of HER2 expression in the small sample size of biopsied tumors at the time of analysis may not represent the overall status of HER2 expression in the whole tumor and in between tumor foci in the metastatic setting as the disease progresses. Unlike biopsy, molecular imaging using probes against HER2 allows for a noninvasive, whole-body assessment of HER2 status in real time. This technique could potentially select patients who may benefit from HER2-directed therapy and offer alternative treatments to those who may not benefit. Several antibodies and small molecules against HER2 have been labeled with different radioisotopes for nuclear imaging and/or therapy. This review presents the most recent advances in HER2 targeting in nuclear medicine focusing on preclinical and clinical studies.

Radioiodination of BODIPY and its application to a nuclear and optical dual functional labeling agent for proteins and peptides

In molecular imaging research, the development of multimodal imaging probes has recently attracted much attention. In the present study, we prepared radioiodinated BODIPY and applied it as a nuclear and optical dual functional labeling agent for proteins and peptides. We designed and synthesized [¹²⁵I]BODIPY with a N-hydroxysuccinimide (NHS) ester, and evaluated its utility as a nuclear and fluorescent dual labeling agent for proteins and peptides. In the radioiodination reaction of BODIPY-NHS with [¹²⁵I]NaI, [¹²⁵I]BODIPY-NHS was obtained at a 48% radiochemical yield. When we carried out the conjugation reaction of [¹²⁵I]BODIPY-NHS with bovine serum albumin (BSA) and RGD (Arg-Gly-Asp) peptide as a model protein and peptide, respectively, [¹²⁵I]BODIPY-BSA and [¹²⁵I]BODIPY-RGD peptide were successfully prepared at 98 and 82% radiochemical yields, respectively. Furthermore, we prepared [¹²³I]BODIPY-trastuzumab by this conjugation reaction and successfully applied it to single photon emission computed tomography (SPECT) imaging studies using tumor-bearing mice, suggesting that radioiodinated BODIPY-NHS serves as a dual functional labeling agent for proteins and peptides. Since iodine has various radioisotopes that can be used for SPECT and positron emission tomography (PET) imaging, biological research, and radiotherapy, the radioiodinated BODIPY may be extensively applicable from basic to clinical research.

Harnessing Integrative Omics to Facilitate Molecular Imaging of the Human Epidermal Growth Factor Receptor Family for Precision Medicine

Cancer is a growing problem worldwide. The cause of death in cancer patients is often due to treatment-resistant metastatic disease. Many molecularly targeted anticancer drugs have been developed against 'oncogenic driver' pathways. However, these treatments are usually only effective in properly selected patients. Resistance to molecularly targeted drugs through selective pressure on acquired mutations or molecular rewiring can hinder their effectiveness. This review summarizes how molecular imaging techniques can potentially facilitate the optimal implementation of targeted agents. Using the human epidermal growth factor receptor (HER) family as a model in (pre)clinical studies, we illustrate how molecular imaging may be employed to characterize whole body target expression as well as monitor drug effectiveness and the emergence of tumor resistance. We further discuss how an integrative omics discovery platform could guide the selection of 'effect sensors' - new molecular imaging targets - which are dynamic markers that indicate treatment effectiveness or resistance.

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

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, ^99mTc-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). ^99mTc-HYNIC-H6F was prepared, and the in vivo characteristics of ^99mTc-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-3,3',3″-trisulfonate labeling procedure demonstrated that the radiochemical purity was greater than 95%. ^99mTc-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 ± 0.01 at 30 min after injection), whereas the signals in HER2-negative MDA-MB-231 tumors were much lower (0.73 ± 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 ^99mTc-HYNIC-H6F peptide probe specifically accumulates in HER2-positive tumors and is therefore promising for the diagnosis of HER2-positive cancers. Because ^99mTc-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.

68Ga-PSMA-HBED-CC PET imaging in breast carcinoma patients

Background

To report on imaging findings using ⁶⁸Ga-PSMA-HBED-CC PET in a series of 19 breast carcinoma patients.

Methods

⁶⁸Ga-PSMA-HBED-CC PET imaging results obtained were compared to routinely performed staging examinations and analyzed as to lesion location and progesterone receptor status.

Results

Out of 81 tumor lesions identified, 84% were identified on ⁶⁸Ga-PSMA-HBED-CC PET. ⁶⁸Ga-PSMA-HBED-CC SUVmean values of distant metastases proved significantly higher (mean, 6.86, SD, 5.68) when compared to those of primary or local recurrences (mean, 2.45, SD, 2.55, p = 0.04) or involved lymph nodes (mean, 3.18, SD, 1.79, p = 0.011). SUVmean values of progesterone receptor-positive lesions proved not significantly different from progesterone receptor-negative lesions. SUV values derived from FDG PET/CT, available in seven patients, and ⁶⁸Ga-PSMA-HBED-CC PET/CT imaging proved weakly correlated (r = 0.407, p = 0.015).

Conclusions

⁶⁸Ga-PSMA-HBED-CC PET/CT imaging in breast carcinoma confirms the reported considerable variation of PSMA expression on human solid tumors using immunohistochemistry.

Molecular Imaging and Precision Medicine in Breast Cancer

Precision medicine, basing treatment approaches on patient traits and specific molecular features of disease processes, has an important role in the management of patients with breast cancer as targeted therapies continue to improve. PET imaging offers noninvasive information that is complementary to traditional tissue biomarkers, including information about tumor burden, tumor metabolism, receptor status, and proliferation. Several PET agents that image breast cancer receptors can visually demonstrate the extent and heterogeneity of receptor-positive disease and help predict which tumors are likely to respond to targeted treatments. This review presents applications of PET imaging in the targeted treatment of breast cancer.