Detection of HER2-Positive Metastases in Patients with HER2-Negative Primary Breast Cancer Using 89Zr-Trastuzumab PET/CT

ImmunoPET of CD146 in Orthotopic and Metastatic Breast Cancer Models

The overexpression of CD146 in breast cancer is considered a hallmark of tumor progression and metastasis, particularly in triple negative breast cancer. Aimed at imaging differential CD146 expressions in breast cancer, a noninvasive method for predictive prognosis and diagnosis was investigated using a ⁶⁴Cu-labeled CD146-specific monoclonal antibody, YY146. CD146 expression was screened in human breast cancer cell lines using Western blotting. Binding ability was evaluated using flow cytometry and immunofluorescent staining. YY146 was conjugated with 1,4,7-triazacyclononane-triacetic acid (NOTA) and radiolabeled with ⁶⁴Cu following standard procedures. Serial PET or PET/CT imaging was performed in orthotopic and metastatic breast cancer tumor models. Biodistribution was performed after the final time point of imaging. Finally, tissue immunofluorescent staining and hematoxylin and eosin (H&E) staining were performed on tumor tissues. The MDA-MB-435 cell line showed the highest CD146 expression level, whereas MCF-7 had the lowest level at the cellular level. ImmunoPET showed that MDA-MB-435 orthotopic tumors had high and clear radioactive accumulation after the administration of ⁶⁴Cu-NOTA-YY146. The tumor uptake of ⁶⁴Cu-NOTA-YY146 in MDA-MB-435 was significantly higher than that in MCF-7 and nonspecific IgG control groups (P < 0.01). Biodistribution verified the PET imaging results. For metastatic models, ⁶⁴Cu-NOTA-YY146 allowed for the visualization of high radioactivity accumulation in metastatic MDA-MB-435 tumors, which was confirmed by ex vivo biodistribution of lung tissues. H&E staining proved the successful building of metastatic tumor models. Immunofluorescent staining verified the differential expression of CD146 in orthotopic tumors. Therefore, ⁶⁴Cu-NOTA-YY146 could be used as an immunoPET probe to visualize CD146 in the breast cancer model and is potentially useful for cancer diagnosis, prognosis prediction, and monitoring therapeutic response.

Improved image reconstruction of 89Zr-immunoPET studies using a Bayesian penalized likelihood reconstruction algorithm

Purpose

The aim of this study was to evaluate the use of a Bayesian penalized likelihood reconstruction algorithm (Q.Clear) for ⁸⁹Zr-immunoPET image reconstruction and its potential to improve image quality and reduce the administered activity of ⁸⁹Zr-immunoPET tracers.

Methods

Eight ⁸⁹Zr-immunoPET whole-body PET/CT scans from three ⁸⁹Zr-immunoPET clinical trials were selected for analysis. On average, patients were imaged 6.3 days (range 5.0–8.0 days) after administration of 69 MBq (range 65–76 MBq) of [⁸⁹Zr]Zr-DFO-daratumumab, [⁸⁹Zr]Zr-DFO-pertuzumab, or [⁸⁹Zr]Zr-DFO-trastuzumab. List-mode PET data was retrospectively reconstructed using Q.Clear with incremental β-values from 150 to 7200, as well as standard ordered-subset expectation maximization (OSEM) reconstruction (2-iterations, 16-subsets, a 6.4-mm Gaussian transaxial filter, “heavy” z-axis filtering and all manufacturers’ corrections active). Reduced activities were simulated by discarding 50% and 75% of original counts in each list mode stream. All reconstructed PET images were scored for image quality and lesion detectability using a 5-point scale. SUV_max for normal liver and sites of disease and liver signal-to-noise ratio were measured.

Results

Q.Clear reconstructions with β = 3600 provided the highest scores for image quality. Images reconstructed with β-values of 3600 or 5200 using only 50% or 25% of the original counts provided comparable or better image quality scores than standard OSEM reconstruction images using 100% of counts.

Conclusion

The Bayesian penalized likelihood reconstruction algorithm Q.Clear improved the quality of ⁸⁹Zr-immunoPET images. This could be used in future studies to improve image quality and/or decrease the administered activity of ⁸⁹Zr-immunoPET tracers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00352-z.

The emerging role of radionuclide molecular imaging of HER2 expression in breast cancer

Targeting of human epidermal growth factor type 2 (HER2) using monoclonal antibodies, antibody-drug conjugates and tyrosine kinase inhibitors extends survival of patients with HER2-expressing metastatic breast cancer. High expression of HER2 is a predictive biomarker for such specific treatment. Accurate determination of HER2 expression level is necessary for stratification of patients to targeted therapy. Non-invasive in vivo radionuclide molecular imaging of HER2 has a potential of repetitive measurements, addressing issues of heterogeneous expression and conversion of HER2 status during disease progression or in response to therapy. Imaging probes based of several classes of targeting proteins are currently in preclinical and early clinical development. Both preclinical and clinical data suggest that the most promising are imaging agents based on small proteins, such as single domain antibodies or engineered scaffold proteins. These agents permit a very specific high-contrast imaging at the day of injection.

Review: PET imaging with macro- and middle-sized molecular probes

Recent progress in radiolabeling of macro- and middle-sized molecular probes has been extending possibilities to use PET molecular imaging for dynamic application to drug development and therapeutic evaluation. Theranostics concept also accelerated the use of macro- and middle-sized molecular probes for sharpening the contrast of proper target recognition even the cellular types/subtypes and proper selection of the patients who should be treated by the same molecules recognition. Here, brief summary of the present status of immuno-PET, and then further development of advanced technologies related to immuno-PET, peptidic PET probes, and nucleic acids PET probes are described.

Targeting and imaging of HER2 overexpression tumor with a new peptide-based 68Ga-PET radiotracer

Human epidermal growth factor receptor 2 (HER2) overexpression, as a predictive biomarker, is associated with more tumor aggressiveness and worse clinical outcomes in cancer, whereas it's accurate identification has led to the choice of effective treatments in many patients. In this study, a peptide-based PET probe (⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY) was developed for imaging HER2 expression in tumors. The DOTA-(Ser)₃-LTVSPWY was labeled with ⁶⁸Ga and then was evaluated in vitro with HER2-positive SKOV-3 cell line; moreover, the in vivo biodistribution and PET/CT imaging were performed in xenografted tumor-bearing nude mice. The ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY displayed the high radiochemical purity greater than 95% and good stability in normal saline and human serum. The cellular binding experiments showed that the cell uptake in HER2-positive ovarian cancer cells could be effectively blocked by non-labeled peptide. The K_d and B_max values for radiolabeled peptide were obtained at 2.5 ± 0.6 nM and (3.4 ± 0.2) × 10⁵ sites per cell, respectively. Biodistribution study demonstrated that tumor-to-blood and tumor-to-muscle ratios were about 1.73 ± 0.36 and 3.78 ± 0.17 at 120 min after the injection of the radiolabeled peptide, respectively. Tumor imaging by PET/CT exhibited high contrast tumor image at 60 min after injection in animal models. Consequently, the results were indicative of the specific accumulation of ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY peptide in HER2-positive tumors and the suitability of its application as a PET probe for the diagnosis of HER2-overexpression tumor.

Polyazamacrocycle Ligands Facilitate 89Zr Radiochemistry and Yield 89Zr Complexes with Remarkable Stability

Over the last three decades, the chemistry of zirconium has facilitated antibody development and the clinical management of disease in the precision medicine era. Scientists have harnessed its reactivity, coordination chemistry, and nuclear chemistry to develop antibody-based radiopharmaceuticals incorporating zirconium-89 (⁸⁹Zr: t_1/2 = 78.4 h, β⁺: 22.8%, E_β+max = 901 keV; EC: 77%, E_γ = 909 keV) to improve disease detection, identify patients for individualized therapeutic interventions. and monitor their response to those interventions. However, release of the ⁸⁹Zr⁴⁺ ion from the radiopharmaceutical remains a concern, since it may confound the interpretation of clinical imaging data, negatively affect dosimetric calculations, and hinder treatment planning. In this report, we relate our novel observations involving the use of polyazamacrocycles as zirconium-89 chelators. We describe the synthesis and complete characterization of zirconium 2,2',2″,2‴-(1,4,7,10-tetraazacyclotridecane-1,4,7,10-tetrayl)tetraacetic acid (Zr-TRITA), zirconium 3,6,9,15-Tetraazabicyclo[9.3.1] pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (Zr-PCTA), and zirconium 2,2',2″-(1,4,7-triazacyclononane-1,4,7-triyl)triacetic acid (Zr-NOTA). In addition, we elucidate the solid-state structure of each complex using single-crystal X-ray diffraction analysis. Finally, we found that [⁸⁹Zr]Zr-PCTA and [⁸⁹Zr]Zr-NOTA demonstrate excellent stability in vitro and in vivo and provide a rationale for these observations. These innovative findings have the potential to guide the development of safer and more robust immuno-PET agents to improve precision medicine applications.

Nanobodies as non-invasive imaging tools

Antibodies and antibody fragments have found wide application for therapeutic and diagnostic purposes. Single-domain antibody fragments, also known as 'heavy-chain variable domains' or 'nanobodies', are a recent addition to the toolbox. Discovered some 30 years ago, nanobodies are the smallest antibody-derived fragments that retain antigen-binding properties. Their small size, stability, specificity, affinity and ease of manufacture make them appealing for use as imaging agents in the laboratory and the clinic. With the recent surge in immunotherapeutics and the success of cancer immunotherapy, it is important to be able to image immune responses and cancer biomarkers non-invasively to allocate resources and guide the best possible treatment of patients with cancer. This article reviews recent advances in the application of nanobodies as cancer imaging agents. While much work has been done in preclinical models, first-in-human applications are beginning to show the value of nanobodies as imaging agents.

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.

A preclinical PET dual-tracer imaging protocol for ER and HER2 phenotyping in breast cancer xenografts

BACKGROUND

Nuclear medicine is on the constant search of precision radiopharmaceutical approaches to improve patient management. Although discordant expression of the estrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER2) in breast cancer is a known dilemma for appropriate patient management, traditional tumor sampling is often difficult or impractical. While 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG)-positron emission tomography (PET) is an option to detect subclinical metastases, it does not provide phenotype information. Radiolabeled antibodies are able to specifically target expressed cell surface receptors. However, their long circulating half-lives (days) require labeling with long-lived isotopes, such as 89Zr, in order to allow sufficient time for tracer clearance from the blood compartment and to accumulate adequately in target tumors and, thus, generate high-quality PET images. The aim of this study was to develop a dual-tracer PET imaging approach consisting of a fast-clearing small molecule and a slow-clearing antibody. This approach was evaluated in a model consisting of mice harboring separate breast cancer xenografts with either an ER+/HER2- or ER-/HER2+ phenotype, comparable to human metastatic disease with intertumor heterogeneity. Lastly, the aim of our study was to determine the feasibility of specifically identifying these two important phenotypes in an acceptable time window.

METHODS

Female nude mice were subcutaneously implanted on opposite shoulders with the ER+/HER2- and ER-/HER2+ MCF-7 and JIMT-1 tumor cell lines, respectively. A second model was developed consisting of mice implanted orthotopically with either MCF-7 or JIMT-1 cells. Pharmacokinetic analysis, serial PET imaging, and biodistribution were first performed for [89Zr]Zr-DFO-trastuzumab (89Zr-T) up to 8 days post-injection (p.i.) in JIMT-1 bearing mice. Region-of-interest (ROI) and biodistribution-derived uptake (% injected-activity/gram of tissue [%IA/g]) values and tumor-to-background ratios were obtained. Results were compared in order to validate ROI and identify early time points that provided high contrast tumor images. For the dual-tracer approach, cohorts of tumor-bearing mice were then subjected to sequential tracer PET imaging. On day 1, mice were administered 4-fluoro-11β-methoxy-16α-[18F]-fluoroestradiol (4FMFES) which targets ER and imaged 45 min p.i. This was immediately followed by the injection of 89Zr-T. Mice were then imaged on day 3 or day 7. ROI analysis was performed, and uptake was calculated in tumors and selected healthy organs for all radiotracers. Quality of tumor targeting for all tracers was evaluated by tumor contrast visualization, tumor and normal tissue uptake, and tumor-to-background ratios.

RESULTS

89Zr-T provided sufficiently high tumor and low background uptake values that furnished high contrast tumor images by 48 h p.i. For the dual-tracer approach, 4FMFES provided tumor uptake values that were significantly increased in MCF-7 tumors. When 89Zr-T-PET was combined with 18F-4FMFES-PET, the entire dual-tracer sequential-imaging procedure provided specific high-quality contrast images of ER+/HER2- MCF-7 and ER-/HER2+ JIMT-1 tumors for 4FMFES and 89Zr-T, respectively, as short as 72 h from start to finish.

CONCLUSIONS

This protocol can provide high contrast images of tumors expressing ER or HER2 within 3 days from injection of 4FMFES to final scan of 89Zr-T and, hence, provides a basis for future dual-tracer combinations that include antibodies.

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.

Impact of 68Ga-NOTA-MAL-MZHER2 PET imaging in advanced gastric cancer patients and therapeutic response monitoring

PURPOSE

Clinical PET imaging of human epidermal growth factor receptor 2 (HER2) can noninvasively detect HER2 overexpression in lesions. A novel ⁶⁸Ga-NOTA-MAL-MZHER2 (⁶⁸Ga-HER2) affibody was developed for clinical PET/CT, and its safety, tissue dosimetry, ability to detect HER2-positive lesions, and utility for HER2-targeted therapy in patients with advanced gastric cancer (AGC) were evaluated.

METHODS

Thirty-four patients with AGC (23 with HER2-positive and 11 with HER2-negative primary lesions) were included and underwent PET/CT after an injection of approximately 3.7 MBq/kg body weight ⁶⁸Ga-HER2 affibody. Thirteen patients (8 HER2-positive and 5 HER2-negative patients) were scanned at 1, 2, and 3 h post-injection to determine the best imaging timepoint, and the remaining patients were scanned at the optimized timepoint. All patients underwent standard ¹⁸F-FDG PET/CT within 7 d to identify viable lesions. The SUV_max of lesions larger than 1.0 cm were analyzed. Five lesion maxima were analyzed for each organ.

RESULTS

(1) The ⁶⁸Ga-HER2 affibody was safe and effective, and optimal image contrast was observed 2 h post-injection; the average effective absorbed dose was 0.0215 mSv/MBq. (2) The HER2-positive group had significantly higher ⁶⁸Ga-HER2 affibody uptake than the HER2-negative group (SUV_max 10.7 ± 12.5 vs 3.8 ± 1.7, p = 0.005). The specificity and sensitivity were 100 and 55.4%, respectively, with a SUV_max cutoff value of 6.6. The SUV_max of the lesions ranged from 1.6 to 73.0, suggesting heterogeneity in HER2 expression. (3) ⁶⁸Ga-HER2 affibody uptake showed an organ-dependent difference in patients with HER2-positive expression. Bone metastases had the highest uptake (SUV_max 40.5 ± 24.9), followed by liver metastases (SUV_max 11.9 ± 3.9) and lymph node metastases (SUV_max 5.6 ± 3.7), while the uptake in other lesions, including in the primary lesion, was relatively lower (SUV_max 7.3 ± 3.7). (4) Patients receiving therapy had a non-significantly lower lesion SUV_max than patients not receiving therapy (SUV_max 8.8 ± 4.9 vs 11.8 ± 15.2) (p = 0.253). Additionally, the ⁶⁸Ga-HER2 affibody detected positive lesions in 1/11 patients with HER2-negative primary gastric cancer, which was confirmed by second generation gene sequencing. (5) Moreover, ten patients underwent baseline PET/CT followed by targeted anti-HER2 therapy. Patients with lesions showing high avidity to the ⁶⁸Ga-HER2 affibody showed longer progression-free survival (PFS) than those with lesions showing low avidity (4-9 m vs 2-3 m).

CONCLUSION

⁶⁸Ga-HER2 affibody PET/CT is a feasible method to noninvasively detect the HER2 status in AGC patients and enable early detection with a low dose. Ongoing anti-HER2 therapy did not influence ⁶⁸Ga-HER2 affibody imaging, which allowed repeated evaluations to monitor the HER2 status after anti-HER2 therapy. This method provides an in vivo understanding of AGC biology that will ultimately help oncologists improve individualized therapy plans.

Current Perspectives on 89Zr-PET Imaging

⁸⁹Zr is an emerging radionuclide that plays an essential role in immuno-positron emission tomography (PET) imaging. The long half-life of ⁸⁹Zr (t_1/2 = 3.3 days) is favorable for evaluating the in vivo distribution of monoclonal antibodies. Thus, the use of ⁸⁹Zr is promising for monitoring antibody-based cancer therapies. Immuno-PET combines the sensitivity of PET with the specificity of antibodies. A number of studies have been conducted to investigate the feasibility of ⁸⁹Zr immuno-PET imaging for predicting the efficacy of radioimmunotherapy and antibody therapies, imaging target expression, detecting target-expressing tumors, and the monitoring of anti-cancer chemotherapies. In this review, we summarize the current status of PET imaging using ⁸⁹Zr in both preclinical and clinical studies by highlighting the use of immuno-PET for the targets of high clinical relevance. We also present ⁸⁹Zr-PET applications other than immuno-PET, such as nanoparticle imaging and cell tracking. Finally, we discuss the limitations and the ongoing research being performed to overcome the remaining hurdles.

Identification of HER2-Positive Metastases in Patients with HER2-Negative Primary Breast Cancer by Using HER2-targeted 89Zr-Pertuzumab PET/CT

Background Human epidermal growth factor receptor 2 (HER2)-targeted therapies are successful in patients with HER2-positive malignancies; however, spatial and temporal heterogeneity of HER2 expression may prevent identification of optimal patients for these therapies. Purpose To determine whether imaging with the HER2-targeted PET tracer zirconium 89 (⁸⁹Zr)-pertuzumab can depict HER2-positive metastases in women with HER2-negative primary breast cancer. Materials and Methods From January to June 2019, women with biopsy-proven HER2-negative primary breast cancer and biopsy-proven metastatic disease were enrolled in a prospective clinical trial (ClinicalTrials.gov NCT02286843) and underwent ⁸⁹Zr-pertuzumab PET/CT for noninvasive whole-biopsy evaluation of potential HER2-positive metastases. ⁸⁹Zr-pertuzumab-avid foci that were suspicious for HER2-positive metastases were tissue sampled and examined by pathologic analysis to document HER2 status. Results Twenty-four women (mean age, 55 years ± 11 [standard deviation]) with HER2-negative primary breast cancer were enrolled. Six women demonstrated foci at ⁸⁹Zr-pertuzumab PET/CT that were suspicious for HER2-positive disease. Of these six women, three had biopsy-proven HER2-positive metastases, two had pathologic findings that demonstrated HER2-negative disease, and one had a fine-needle aspirate with inconclusive results. Conclusion Human epidermal growth factor receptor 2 (HER2)-targeted imaging with zirconium 89-pertuzumab PET/CT was successful in detecting HER2-positive metastases in women with HER2-negative primary breast cancer. This demonstrates the ability of targeted imaging to identify patients for targeted therapies that might not otherwise be considered. © RSNA, 2020 Online supplemental material is available for this article. See the editorial by Mankoff and Pantel in this issue.

Up-regulation of hypoxia-inducible factor antisense as a novel approach to treat ovarian cancer

Ovarian cancer (OC) is estimated to kill ~14,000 women in the United States in 2019. Current chemotherapies to treat OC initially show therapeutic efficacy but frequently drug resistance develops, at which point therapies with alternative targets are needed. Herein, we are describing a novel approach to sensitize these tumors to standard chemotherapies by increasing the transcription of hypoxia-inducible factor antisense.

Methods: Genome-wide Bru-seq analysis was performed to fully capture the nascent transcriptional signature of OC cells treated with the gp130 inhibitor, SC144. In vitro and in vivo analysis, including characterization of hypoxia and select protein expression, combination with standard of care chemotherapy and antitumor efficacy were performed to assess the biological activity of SC144 on induction of hypoxia in OC cells.

Results: Bru-seq analysis of OVCAR8 cells treated with SC144 shows upregulation of hypoxia related genes. In addition, transcription of hypoxia-inducible factor antisense (HIF1A-AS2) was induced that in turn reduced expression of HIF-1α and simultaneously increased expression of NDRG1. Furthermore, we observed decreased protein levels of EGFR, Met, c-Myc, cyclin D1, MMP-2, MMP-9 and TF, and phosphorylation of Src and P130-cas. SC144-induced alterations of HIF-1α and NDRG1 were also confirmed in prostate cancer cells. Ciclopirox olamine (CPX) induces a cellular transcriptional profile comparable to SC144, suggesting a similar cellular mechanism of action between these two compounds. In addition, SC144 sensitized OC cells to olaparib, carboplatin and cisplatin, and shows better in vivo efficacy than CPX.

Conclusion: Induction of hypoxic stress responses through inhibition of gp130 represents a novel approach to design effective anticancer treatments in combination with standard-of-care chemotherapy in OC and the efficacy reported here strongly supports their clinical development.

Insight into the Development of PET Radiopharmaceuticals for Oncology

While the development of positron emission tomography (PET) radiopharmaceuticals closely follows that of traditional drug development, there are several key considerations in the chemical and radiochemical synthesis, preclinical assessment, and clinical translation of PET radiotracers. As such, we outline the fundamentals of radiotracer design, with respect to the selection of an appropriate pharmacophore. These concepts will be reinforced by exemplary cases of PET radiotracer development, both with respect to their preclinical and clinical evaluation. We also provide a guideline for the proper selection of a radionuclide and the appropriate labeling strategy to access a tracer with optimal imaging qualities. Finally, we summarize the methodology of their evaluation in in vitro and animal models and the road to clinical translation. This review is intended to be a primer for newcomers to the field and give insight into the workflow of developing radiopharmaceuticals.

Interactions Between Tumor Biology and Targeted Nanoplatforms for Imaging Applications

Although considerable efforts have been conducted to diagnose, improve, and treat cancer in the past few decades, existing therapeutic options are insufficient, as mortality and morbidity rates remain high. Perhaps the best hope for substantial improvement lies in early detection. Recent advances in nanotechnology are expected to increase the current understanding of tumor biology, and will allow nanomaterials to be used for targeting and imaging both in vitro and in vivo experimental models. Owing to their intrinsic physicochemical characteristics, nanostructures (NSs) are valuable tools that have received much attention in nanoimaging. Consequently, rationally designed NSs have been successfully employed in cancer imaging for targeting cancer-specific or cancer-associated molecules and pathways. This review categorizes imaging and targeting approaches according to cancer type, and also highlights some new safe approaches involving membrane-coated nanoparticles, tumor cell-derived extracellular vesicles, circulating tumor cells, cell-free DNAs, and cancer stem cells in the hope of developing more precise targeting and multifunctional nanotechnology-based imaging probes in the future.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

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.

CD38-targeted Immuno-PET of Multiple Myeloma: From Xenograft Models to First-in-Human Imaging

Background Current measurements of multiple myeloma disease burden are suboptimal. Daratumumab is a monoclonal antibody that targets CD38, an antigen expressed on nearly all myeloma cells. Purpose To demonstrate preclinical and first-in-human application of an antibody composed of the native daratumumab labeled with the positron-emitting radionuclide zirconium 89 (⁸⁹Zr) through the chelator deferoxamine (DFO), or ⁸⁹Zr-DFO-daratumumab, for immunologic PET imaging of multiple myeloma. Materials and Methods ⁸⁹Zr-DFO-daratumumab was synthesized by conjugating ⁸⁹Zr to daratumumab with DFO. A murine xenograft model using CD38-positive OPM2 multiple myeloma cells was used to evaluate CD38-specificity of ⁸⁹Zr-DFO-daratumumab. Following successful preclinical imaging, a prospective phase I study of 10 patients with multiple myeloma was performed. Study participants received 74 MBq (2 mCi) of intravenous ⁸⁹Zr-DFO-daratumumab. Each participant underwent four PET/CT scans over the next 8 days, as well as blood chemistry and whole-body counts, to determine safety, tracer biodistribution, pharmacokinetics, and radiation dosimetry. Because ⁸⁹Zr has a half-life of 78 hours, only a single administration of tracer was needed to obtain all four PET/CT scans. Results ⁸⁹Zr-DFO-daratumumab was synthesized with radiochemical purity greater than 99%. In the murine model, substantial bone marrow uptake was seen in OPM2 mice but not in healthy mice, consistent with CD38-targeted imaging of OPM2 multiple myeloma cells. In humans, ⁸⁹Zr-DFO-daratumumab was safe and demonstrated acceptable dosimetry. ⁸⁹Zr-DFO-daratumumab uptake was visualized at PET in sites of osseous myeloma. Conclusion These data demonstrate successful CD38-targeted immunologic PET imaging of multiple myeloma in a murine model and in humans. © RSNA, 2020 Online supplemental material is available for this article.

Radiopharmaceuticals for Breast Cancer and Neuroendocrine Tumors: Two Examples of How Tissue Characterization May Influence the Choice of Therapy

Molecular medicine has gained clinical relevance for the detection and staging of oncological diseases, to guide therapy decision making and for therapy follow-up due to the availability of new highly sensitive hybrid imaging camera systems and the development of new tailored radiopharmaceuticals that target specific molecules. The knowledge of the expression of different receptors on the primary tumor and on metastases is important for both therapeutic and prognostic purposes and several approaches are available aiming to achieve personalized medicine in different oncological diseases. In this review, we describe the use of specific radiopharmaceuticals to image and predict therapy response in breast cancer and neuroendocrine tumors since they represent a paradigmatic example of the importance of tumoral characterization of hormonal receptors in order to plan a tailored treatment. The most attractive radiopharmaceuticals for breast cancer are 16α-[¹⁸F]-fluoro-17β-estradiol for PET assessment of the estrogen expression, radiolabeled monoclonal antibody trastuzumab to image the human epidermal growth factor receptor 2, but also the imaging of androgen receptors with [¹⁸F]-fluorodihydrotestosterone.

Affibody Molecules as Targeting Vectors for PET Imaging

Affibody molecules are small (58 amino acids) engineered scaffold proteins that can be selected to bind to a large variety of proteins with a high affinity. Their small size and high affinity make them attractive as targeting vectors for molecular imaging. High-affinity affibody binders have been selected for several cancer-associated molecular targets. Preclinical studies have shown that radiolabeled affibody molecules can provide highly specific and sensitive imaging on the day of injection; however, for a few targets, imaging on the next day further increased the imaging sensitivity. A phase I/II clinical trial showed that ⁶⁸Ga-labeled affibody molecules permit an accurate and specific measurement of HER2 expression in breast cancer metastases. This paper provides an overview of the factors influencing the biodistribution and targeting properties of affibody molecules and the chemistry of their labeling using positron emitters.

Preclinical pharmacokinetic, biodistribution, radiation dosimetry, and toxicity studies of 99mTc-HYNIC-(Ser)3-LTVPWY: A novel HER2-targeted peptide radiotracer

Accurate assessment of the HER2 expression is an essential issue for predicting response to anti-HER2 therapy in breast cancer patients. The aim of this study was to evaluate ^99mTc-HYNIC-(Ser)₃-LTVPWY (^99mTc-HYNIC-LY) peptide as a novel HER2-targeted radiolabeled peptide in healthy mice to examine the applicability of this imaging agent in a first-in-human clinical trial. To this end, pharmacokinetic and dosimetry studies were performed according to the ICH guideline M3 (R2) with ^99mTc-HYNIC-LY. To estimate the radiation-absorbed doses in humans, the accumulated activity in each mouse organ was calculated based on biodistribution data. In addition, toxicology assessment was performed based on mortality events, body weights, and serum biochemical, hematological, and histopathological assays. The pharmacokinetic study showed rapid blood clearance. Based on the results of biodistribution study, the highest radioactivity was observed in the kidneys. The projected absorbed doses to the kidneys, liver, lungs, stomach, and spleen were obtained as 1.70E-02, 1.42E-02, 1.02E-02, 8.62E-03, and 8.34E-03 mSv/MBq, respectively. The results also revealed that serum biochemical and hematological parameters were in the normal range. No significant morphologic alterations were observed in the liver, kidneys, and spleen tissues. Consequently, the results were indicative of the suitability of ^99mTc-HYNIC-LY peptide for advancement to a first-in-human clinical trial.

Hypoxia Attenuates Trastuzumab Uptake and Trastuzumab-Emtansine (T-DM1) Cytotoxicity through Redistribution of Phosphorylated Caveolin-1

The antibody-drug conjugate trastuzumab-emtansine (T-DM1) offers an additional treatment option for patients with HER2-amplified tumors. However, primary and acquired resistance is a limiting factor in a significant subset of patients. Hypoxia, a hallmark of cancer, regulates the trafficking of several receptor proteins with potential implications for tumor targeting. Here, we have investigated how hypoxic conditions may regulate T-DM1 treatment efficacy in breast cancer. The therapeutic effect of T-DM1 and its metabolites was evaluated in conjunction with biochemical, flow cytometry, and high-resolution imaging studies to elucidate the functional and mechanistic aspects of hypoxic regulation. HER2 and caveolin-1 expression was investigated in a well-annotated breast cancer cohort. We find that hypoxia fosters relative resistance to T-DM1 in HER2⁺ cells (SKBR3 and BT474). This effect was not a result of deregulated HER2 expression or resistance to emtansine and its metabolites. Instead, we show that hypoxia-induced translocation of caveolin-1 from cytoplasmic vesicles to the plasma membrane contributes to deficient trastuzumab internalization and T-DM1 chemosensitivity. Caveolin-1 depletion mimicked the hypoxic situation, indicating that vesicular caveolin-1 is indispensable for trastuzumab uptake and T-DM1 cytotoxicity. In vitro studies suggested that HER2 and caveolin-1 are not coregulated, which was supported by IHC analysis in patient tumors. We find that phosphorylation-deficient caveolin-1 inhibits trastuzumab internalization and T-DM1 cytotoxicity, suggesting a specific role for caveolin-1 phosphorylation in HER2 trafficking. IMPLICATIONS: Together, our data for the first time identify hypoxic regulation of caveolin-1 as a resistance mechanism to T-DM1 with potential implications for individualized treatment of breast cancer.

Examining the evolving utility of 18FDG-PET/CT in breast cancer recurrence

Many studies have demonstrated the utility of ¹⁸fluorodeoxyglucose-positron emission tomography/computed tomography (¹⁸FDG-PET/CT) scan in evaluating breast cancer recurrence in subsets of patients based on age, histological subtype and cancer stage to guide response to conventional chemoradiation guidelines during treatment of metastatic breast cancer disease. This literature review focuses on the breakthrough of ¹⁸FDG-PET/CT imaging within the paradigm of breast cancer oncology centered toward improving risk stratification and prognostication of disease relapse based on cancer molecular phenotypes, tumor markers, early metabolic activity and response to neoadjuvant chemotherapy (NAC). The authors consider the rapid shift toward biomarker based molecular tracers to quantify treatment response and pathologic complete response with more recent imaging modalities such as dedicated breast positron emission tomography (dbPET), and the advantages afforded by this multisystem approach.

The Influence of Glycans-Specific Bioconjugation on the FcγRI Binding and In vivo Performance of 89Zr-DFO-Pertuzumab

Rationale: The overwhelming majority of radioimmunoconjugates are produced via random conjugation methods predicated on attaching bifunctional chelators to the lysines of antibodies. However, this approach inevitably produces poorly defined and heterogeneous immunoconjugates because antibodies have several lysines distributed throughout their structure. To circumvent this issue, we have previously developed a chemoenzymatic bioconjugation strategy that site-specifically appends cargoes to the biantennary heavy chain glycans attached to C_H2 domains of the immunoglobulin's Fc region. In the study at hand, we explore the effects of this approach to site-specific bioconjugation on the Fc receptor binding and in vivo behavior of radioimmunoconjugates.

Methods: We synthesized three desferrioxamine (DFO)-labeled immunoconjugates based on the HER2-targeting antibody pertuzumab: one using random bioconjugation methods (DFO-^nsspertuzumab) and two using variants of our chemoenzymatic protocol (DFO-^sspertuzumab-EndoS and DFO-^sspertuzumab-βGal). Subsequently, we characterized these constructs and evaluated their ability to bind HER2, human FcγRI (huFcγRI), and mouse FcγRI (muFcγRI). After radiolabeling the immunoconjugates with zirconium-89, we conducted PET imaging and biodistribution studies in two different mouse models of HER2-expressing breast cancer.

Results: MALDI-ToF and SDS-PAGE analysis confirmed the site-specific nature of the bioconjugation, and flow cytometry and surface plasmon resonance (SPR) revealed that all three immunoconjugates bind HER2 as effectively as native pertuzumab. Critically, however, SPR experiments also illuminated that DFO-^sspertuzumab-EndoS possesses an attenuated binding affinity for huFcγRI (17.4 ± 0.3 nM) compared to native pertuzumab (4.7 ± 0.2 nM), DFO-^nsspertuzumab (4.1 ± 0.1 nM), and DFO-^sspertuzumab-βGal (4.7 ± 0.2 nM). ImmunoPET and biodistribution experiments in athymic nude mice bearing HER2-expressing BT474 human breast cancer xenografts yielded no significant differences in the in vivo behavior of the radioimmunoconjugates. Yet experiments in tumor-bearing humanized NSG mice revealed that ⁸⁹Zr-DFO-^sspertuzumab-EndoS produces higher activity concentrations in the tumor (111.8 ± 39.9 %ID/g) and lower activity concentrations in the liver and spleen (4.7 ± 0.8 %ID/g and 13.1 ± 4.0 %ID/g, respectively) than its non-site-specifically labeled cousin, a phenomenon we believe stems from the altered binding of the former to huFcγRI.

Conclusion: These data underscore that this approach to site-specific bioconjugation not only produces more homogeneous and well-defined radioimmunoconjugates than traditional methods but may also improve their in vivo performance in mouse models by reducing binding to FcγRI.

HER2-Targeted PET Imaging and Therapy of Hyaluronan-Masked HER2-Overexpressing Breast Cancer

Human epidermal growth factor receptor 2 (HER2) is a biomarker in breast cancer, and its overexpression is required to initiate therapies using HER2-targeted antibodies. Although trastuzumab is one of the most effective therapeutic antibodies in HER2-overexpressing breast cancer, a significant number of patients do not benefit from this therapy due to inherent or acquired resistance mechanisms. One reported mechanism of resistance is the steric hindering effect caused by the polymeric complex formed between hyaluronan and CD44, thus preventing trastuzumab from binding to HER2. Hyaluronan/CD44 contributes as an obstacle for trastuzumab to bind HER2, but it is also involved in HER2 internalization. In this study, we used zirconium-89 (⁸⁹Zr)-labeled trastuzumab immunoPET to investigate whether degradation of hyaluronan can resensitize HER2-overexpressing breast cancer cells to trastuzumab. Targeted degradation of endogenously produced hyaluronan and inhibition of its synthesis were achieved by treating trastuzumab-resistant JIMT1 breast cancer cells with hyaluronidase (HLX) and 4-methylumbelliferone (4MU). The 4MU/HLX treatment reduced HER2 internalization by depleting hyaluronan/CD44 and the caveolin-1 (CAV1) endocytic protein, resulting in enhanced membrane-bound ⁸⁹Zr-labeled trastuzumab. 4MU/HLX enhanced trastuzumab tumor uptake, as evidenced by increased tumor binding of the ⁸⁹Zr-labeled trastuzumab in JIMT1 tumor xenografts. In vitro mechanistic studies demonstrated a decrease in HER2-mediated oncogenic signaling upon cell treatment with 4MU/HLX. Importantly, 4MU/HLX enhanced trastuzumab efficacy in JIMT1 xenografts. These data showed the utility of ⁸⁹Zr-labeled trastuzumab as a PET imaging agent to monitor the affinity of the antibody to HER2 during CD44/hyaluronan-specific inhibition with the overall goal of improving trastuzumab therapy.

In vitro cytotoxicity of Auger electron-emitting [67Ga]Ga-trastuzumab

Introduction

Molecular radiotherapy exploiting short-range Auger electron-emitting radionuclides has potential for targeted cancer treatment and, in particular, is an attractive option for managing micrometastatic disease. Here, an approach using chelator-trastuzumab conjugates to target radioactivity to breast cancer cells was evaluated as a proof-of-concept to assess the suitability of ⁶⁷Ga as a therapeutic radionuclide.

Methods

THP-trastuzumab and DOTA-trastuzumab were synthesised and radiolabelled with Auger electron-emitters ⁶⁷Ga and ¹¹¹In, respectively. Radiopharmaceuticals were tested for HER2-specific binding and internalisation, and their effects on viability (dye exclusion) and clonogenicity of HER2-positive HCC1954 and HER2–negative MDA-MB-231 cell lines was measured. Labelled cell populations were studied by microautoradiography.

Results

Labelling efficiencies for [⁶⁷Ga]Ga-THP-trastuzumab and [¹¹¹In]In-DOTA-trastuzumab were 90% and 98%, respectively, giving specific activities 0.52 ± 0.16 and 0.61 ± 0.11 MBq/μg (78–92 GBq/μmol). At 4 nM total antibody concentration and 200 × 10³ cells/mL, [⁶⁷Ga]Ga-THP-trastuzumab showed higher percentage of cell association (10.7 ± 1.3%) than [¹¹¹In]In-DOTA-trastuzumab (6.2 ± 1.6%; p = 0.01). The proportion of bound activity that was internalised did not differ significantly for the two tracers (62.1 ± 1.4% and 60.8 ± 15.5%, respectively). At 100 nM, percentage cell binding of both radiopharmaceuticals was greatly reduced compared to 4 nM and did not differ significantly between the two (1.2 ± 1.0% [⁶⁷Ga]Ga-THP-trastuzumab and 0.8 ± 0.9% for [¹¹¹In]In-DOTA-trastuzumab). Viability and clonogenicity of HER2-positive cells decreased when each radionuclide was incorporated into cells by conjugation with trastuzumab, but not when the same level of radioactivity was confined to the medium by omitting the antibody conjugation, suggesting that ⁶⁷Ga needs to be cell-bound or internalised for a therapeutic effect. Microautoradiography showed that radioactivity bound to individual cells varied considerably within the population.

Conclusions

[⁶⁷Ga]Ga-THP-trastuzumab reduced cell viability and clonogenicity only when cell-bound, suggesting ⁶⁷Ga holds promise as a therapeutic radionuclide as part of a targeted radiopharmaceutical. The causes and consequences of non-homogeneous uptake among the cell population should be explored.

PET imaging of a 68Ga labeled modified HER2 affibody in breast cancers: from xenografts to patients

OBJECTIVE

Overexpression of human epidermal growth factor receptor-2 (HER2) in breast cancers provides promising opportunities for imaging and targeted therapy. Developing HER2 targeted positron emission tomography (PET) probes might be benefit for management of the disease. Small high-affinity scaffold proteins, affibodies, are ideal vectors for imaging HER2 overexpressed tumors. Despite of the initial success on development of 18F labeled ZHER2:342 affibody, the tedious synthesis producers, low yields and unfavorable pharmacokinetics may hinder the clinical use. 68Ga is an attractive positron emitter for PET imaging. A simple preparation of 68Ga labeled ZHER2:342 analog, 68Ga-NOTA-MAL-Cys-MZHER2:342, was reported in the study. The in vivo performances of the tracer for assessing HER2 status in breast cancers were also evaluated.

METHODS

NOTA-MAL conjugated Cys-MZHER2:342 was radiolabeled with 68Ga. The probe was evaluated by in vitro tests including stability and cell binding studies in breast cancer cells with different HER2 levels. In vivo evaluation was performed in mice bearing tumors using microPET imaging and biodistribution experiments. A PET/CT imaging study was initially performed in patients with breast cancers.

RESULTS

The tracer was synthesized in a straightforward chelation method with satisfactory non-decay corrected yield (81±5%) and radiochemical purity (>95%). In vivo micro-PET imaging showed that HER2 high levels expressed BT474 xenografts were more clear visualized than HER2 low levels expressed MCF-7 tumors (16.12 ± 2.69 ID%/g vs 1.32 ± 0.19 ID%/g at 1 h post-injection). The outcome was consistent with the immunohistochemical analysis. No significant radioactivity was accumulated in healthy tissues (less than 2% ID/g) except kidneys. In a preliminary clinical study, 68Ga-NOTA-MAL-Cys-MZHER2:342 PET imaging allowed more high-contrast detection of HER2 positive primary tumors (maximum standardized uptake value = 2.16±0.27) than those in HER2 negative primary focus (maximum standardized uptake value = 0.32±0.05). No detectable side-effects were found.

CONCLUSION

In summary, this study indicates the significant efficiency of the 68Ga labeled HER2 affibody. Preclinical and clinical studies support the possibility of monitoring HER2 levels in breast cancers using 68Ga-NOTA-MAL-Cys-MZHER2:342.

ADVANCES IN KNOWLEDGE

The research investigated the feasibility of a 68Ga labeled HER2 affibody modified with a hydrophilic linker for breast cancer PET imaging. Favorable outcomes showed that the probe might be valuable for determining HER2 status of the disease.

HER2-targeted multimodal imaging of anaplastic thyroid cancer

Clinical management of anaplastic thyroid cancer (ATC) is very challenging due to its dedifferentiation and aggressiveness. We aim to develop HER2-targeted multimodal imaging approaches and assess the diagnostic efficacies of these molecular imaging probes in preclinical ATC models. Flow cytometry was used to detect HER2 expression status in thyroid cancer cell lines. We then developed a HER2-specific immunoPET imaging probe ⁸⁹Zr-Df-pertuzumab by radiolabeling a HER-2 specific monoclonal antibody (mAb) pertuzumab with ⁸⁹Zr (t_1/2=78.4 h) and a fluorescent imaging probe IRDye 800CW-pertuzumab. The diagnostic efficacies of the probes were assessed in subcutaneous and orthotopic ATC models, followed by ex vivo biodistribution profile and immunofluorescence staining studies. HER2 was highly expressed on the surface of all the four primary thyroid cancer cell lines examined, which included two ATC cell lines (i.e., 8505C and THJ-16T). PET imaging with ⁸⁹Zr-Df-pertuzumab clearly visualized all the subcutaneous ATCs with a peak tumor uptake of 20.23±6.44 %ID/g (n=3), whereas the highest tumor uptake of the nonspecific probe ⁸⁹Zr-Df-IgG in subcutaneous ATC models was 6.30±0.95 %ID/g (n=3). More importantly, ⁸⁹Zr-Df-pertuzumab PET imaging strategy readily delineated all the orthotopic ATCs with a peak tumor uptake of 24.93±8.53 %ID/g (n=3). We also suggested that Cerenkov luminescence imaging (CLI) using ⁸⁹Zr-Df-pertuzumab and fluorescence imaging using IRDye 800CW-pertuzumab are useful tools for image-guided removal of ATCs. We demonstrate that HER2 is a promising biomarker for ATC, and multimodal imaging using ⁸⁹Zr-Df-pertuzumab and IRDye 800CW-pertuzumab is useful for identifying HER2-postive ATCs.

CUTseq is a versatile method for preparing multiplexed DNA sequencing libraries from low-input samples

Current multiplexing strategies for massively parallel sequencing of genomic DNA mainly rely on library indexing in the final steps of library preparation. This procedure is costly and time-consuming, because a library must be generated separately for each sample. Furthermore, library preparation is challenging in the case of fixed samples, such as DNA extracted from formalin-fixed paraffin-embedded (FFPE) tissues. Here we describe CUTseq, a method that uses restriction enzymes and in vitro transcription to barcode and amplify genomic DNA prior to library construction. We thoroughly assess the sensitivity and reproducibility of CUTseq in both cell lines and FFPE samples, and demonstrate an application of CUTseq for multi-region DNA copy number profiling within single FFPE tumor sections, to assess intratumor genetic heterogeneity at high spatial resolution. In conclusion, CUTseq is a versatile and cost-effective method for library preparation for reduced representation genome sequencing, which can find numerous applications in research and diagnostics.

Genomics DNA library preparation from formalin-fixed paraffin-embedded tissues is challenging. Here the authors describe CUTseq that uses restriction enzymes and in vitro amplification to barcode samples for reduced representation genome sequencing.

Total-Body PET and Highly Stable Chelators Together Enable Meaningful 89Zr-Antibody PET Studies up to 30 Days After Injection

The use of ⁸⁹Zr-antibody PET imaging to measure antibody biodistribution and tissue pharmacokinetics is well established, but current PET systems lack the sensitivity needed to study ⁸⁹Zr-labeled antibodies beyond 2-3 isotope half-lives (7-10 d), after which a poor signal-to-noise ratio is problematic. However, studies across many weeks are desirable to better match antibody circulation half-life in human and nonhuman primates. These studies investigated the technical feasibility of using the primate mini-EXPLORER PET scanner, making use of its high sensitivity and 45-cm axial field of view, for total-body imaging of ⁸⁹Zr-labeled antibodies in rhesus monkeys up to 30 d after injection. Methods: A humanized monoclonal IgG antibody against the herpes simplex viral protein glycoprotein D (gD) was radiolabeled with ⁸⁹Zr via 1 of 4 chelator-linker combinations (benzyl isothiocyanate-DFO [DFO-Bz-NCS], where DFO is desferrioxamine B; DFO-squaramide; DFO*-Bz-NCS, where DFO* is desferrioxamine*; and DFO*-squaramide). The pharmacokinetics associated with these 4 chelator-linker combinations were compared in 12 healthy young male rhesus monkeys (∼1-2 y old, ∼3 ± 1 kg). Each animal was initially injected intravenously with unlabeled antibody in a peripheral vessel in the right arm (10 mg/kg, providing therapeutic-level antibody concentrations), immediately followed by approximately 40 MBq of one of the ⁸⁹Zr-labeled antibodies injected intravenously in a peripheral vessel in the left arm. All animals were imaged 6 times over a period of 30 d, with an initial 60-min dynamic scan on day 0 (day of injection) followed by static scans of 30-45 min on approximately days 3, 7, 14, 21, and 30, with all acquired using a single bed position and images reconstructed using time-of-flight list-mode ordered-subsets expectation maximization. Activity concentrations in various organs were extracted from the PET images using manually defined regions of interest. Results: Excellent image quality was obtained, capturing the initial distribution phase in the whole-body scan; later time points showed residual ⁸⁹Zr mainly in the liver. Even at 30 d after injection, representing approximately 9 half-lives of ⁸⁹Zr and with a total residual activity of only 20-40 kBq in the animal, the image quality was sufficient to readily identify activity in the liver, kidneys, and upper and lower limb joints. Significant differences were noted in late time point liver uptake, bone uptake, and whole-body clearance between chelator-linker types, whereas little variation (±10%) was observed within each type. Conclusion: These studies demonstrate the ability to image ⁸⁹Zr-radiolabeled antibodies up to 30 d after injection while maintaining satisfactory image quality, as provided by the primate mini-EXPLORER with high sensitivity and long axial field of view. Quantification demonstrated potentially important differences in the behavior of the 4 chelators. This finding supports further investigation.

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.

HER-2 status of circulating tumor cells in a metastatic breast cancer cohort: A comparative study on characterization techniques

Background

Personalized targeted treatment in metastatic breast cancer relies on accurate assessment of molecular aberrations, e.g. overexpression of Human Epidermal growth factor Receptor 2 (HER-2). Molecular interrogation of circulating tumor cells (CTCs) can provide an attractive alternative for real-time biomarker assessment. However, implementation of CellSearch-based HER-2 analysis has been limited. Immunofluorescent (IF) image interpretation is crucial, as different HER-2 categories have been described. Major questions in CTC research are how these IF categories reflect gene expression and amplification, and if we should consider ‘medium’ HER-2 expressing CTCs for patient selection.

Methods

Tumor cells from spiked cell lines (n = 8) and CTCs (n = 116 samples) of 85 metastatic breast cancer patients were enriched using CellSearch. Comparative analysis of HER-2 expression by IF imaging (ACCEPT, DEPArray, and visual scoring) with qRT-PCR and HER-2/neu FISH was performed.

Results

Automated IF HER-2-profiling by DEPArray and ACCEPT delivered comparable results. There was a 98% agreement between 17 trained observers (visual scoring) and ACCEPT considering HER-2^neg and HER-2^high expressing CTCs. However, 89% of HER-2^med expressing CTCs by ACCEPT were scored negative by observers. HER-2^high expressing tumor cells demonstrated HER-2/neu gene amplification, whereas HER-2^neg and HER-2^med expressing tumor cells and CTCs by ACCEPT were copy-number neutral. All patients with HER-2-positive archival tumors had ≥1 HER-2^high expressing CTCs, while 80% of HER-2-negative patients did not. High relative gene expression of HER-2 measured on enriched CTC lysates correlated with having ≥1 HER-2^high expressing CTCs.

Conclusion

Automated images analysis has enormous potential for clinical implementation. HER-2 characterization and clinical trial design should be focused on HER-2^high expressing CTCs.

Advances in PET Diagnostics for Guiding Targeted Cancer Therapy and Studying In Vivo Cancer Biology

Purpose of the Review

We present an overview of recent advances in positron emission tomography (PET) diagnostics as applied to the study of cancer, specifically as a tool to study in vivo cancer biology and to direct targeted cancer therapy. The review is directed to translational and clinical cancer investigators who may not be familiar with these applications of PET cancer diagnostics, but whose research might benefit from these advancing tools.

Recent Findings

We highlight recent advances in 3 areas: (1) the translation of PET imaging cancer biomarkers to clinical trials; (2) methods for measuring cancer metabolism in vivo in patients; and (3) advances in PET instrumentation, including total-body PET, that enable new methodologies. We emphasize approaches that have been translated to human studies.

Summary

PET imaging methodology enables unique in vivo cancer diagnostics that go beyond cancer detection and staging, providing an improved ability to guide cancer treatment and an increased understanding of in vivo human cancer biology.

New advance in breast cancer pathology and imaging

The improvement of knowledge concerning the pathology of breast cancer could provide the rationale for the development of new imaging diagnostic protocols. Indeed, as for the microcalcifications, new histopathological markers can be used as target for in vivo early detection of breast cancer lesions by using molecular imaging techniques such as positron emission tomography. Specifically, the mutual contribution of these medical specialties can ‘nourish’ the dream of a personalized medicine that takes into account the intrinsic variability of breast cancer. In this review, we report the main discoveries concerning breast cancer pathology highlighting the possible cooperation between the departments of anatomic pathology and imaging diagnostics.

Novel insights into breast cancer progression and metastasis: A multidisciplinary opportunity to transition from biology to clinical oncology

According to the most recent epidemiological studies, breast cancer shows the highest incidence and the second leading cause of death in women. Cancer progression and metastasis are the main events related to poor survival of breast cancer patients. This can be explained by the presence of highly resistant to chemo- and radiotherapy stem cells in many breast tumor tissues. In this context, numerous studies highlighted the possible involvement of epithelial to mesenchymal transition phenomenon as biological program to generate cancer stem cells, and thus participate to both metastatic and drug resistance process. Therefore, the comprehension of mechanisms (both cellular and molecular) involved in breast cancer occurrence and progression can lay the foundation for the development of new diagnostic and therapeutical protocols. In this review, we reported the most important findings in the field of breast cancer highlighting the most recent data concerning breast tumor biology, diagnosis and therapy.

Temporal Modulation of HER2 Membrane Availability Increases Pertuzumab Uptake and Pretargeted Molecular Imaging of Gastric Tumors

Human epidermal growth factor receptor 2 (HER2) is used as a tumor biomarker and therapeutic target. Pertuzumab is an anti-HER2 antibody, and its binding to tumor cells requires HER2 to be present at the cell membrane. However, the cellular distribution of HER2 protein in gastric tumors is dynamic, and HER2 internalization decreases antibody binding to tumor cells. These features preclude the use of pretargeted strategies for molecular imaging and therapy. We explored the pharmacological modulation of HER2 endocytosis as a strategy to improve pertuzumab uptake in HER2-positive gastric tumors and allow the use of a pretargeted imaging approach. Methods: We conducted in vitro and in vivo studies with NCI-N87 gastric cancer cells to determine how HER2 endocytosis affects pertuzumab binding to tumor cells. Lovastatin, a clinically approved cholesterol-lowering drug, was used to modulate caveolae-mediated HER2 endocytosis. Results: Administration of lovastatin to NCI-N87 cancer cells resulted in significant accumulation of non-activated HER2 dimers at the cell surface. Pretreatment of NCI-N87 cells with lovastatin increased in vitro specific accumulation of membrane-bound ⁸⁹Zr-labeled pertuzumab. Lovastatin-enhanced pertuzumab tumor uptake was also observed in NCI-N87 gastric cancer xenografts, allowing tumor detection as early as 4 h and high-contrast images at 48 h after tracer administration via PET. Temporal enhancement of HER2 membrane availability by lovastatin allowed imaging of cell surface HER2 with transcyclooctene-conjugated antibodies and ¹⁸F-labeled tetrazine. Conclusion: Temporal pharmacological modulation of membrane HER2 may be clinically relevant and exploitable for pretargeted molecular imaging and therapy in gastric tumors.

Assessment of the Spatial Heterogeneity of Breast Cancers: Associations Between Computed Tomography and Immunohistochemistry

BACKGROUND

Tumour heterogeneity is considered an important mechanism of treatment failure. Imaging-based assessment of tumour heterogeneity is showing promise but the relationship between these mathematically derived measures and accepted 'gold standards' of tumour biology such as immunohistochemical measures is not established.

METHODS

A total of 20 women with primary breast cancer underwent a research dynamic contrast-enhanced computed tomography prior to treatment with data being available for 15 of these. Texture analysis was performed of the primary tumours to extract 13 locoregional and global parameters. Immunohistochemical analysis associations were assessed by the Spearman rank correlation.

RESULTS

Hypoxia-inducible factor-1α was correlated with first-order kurtosis (r = -0.533, P = .041) and higher order neighbourhood grey-tone difference matrix coarseness (r = 0.54, P = .038). Vascular maturity-related smooth muscle actin was correlated with higher order grey-level run-length long-run emphasis (r = -0.52, P = .047), fractal dimension (r = 0.613, P = .015), and lacunarity (r = -0.634, P = .011). Micro-vessel density, reflecting angiogenesis, was also associated with lacunarity (r = 0.547, P = .035).

CONCLUSIONS

The associations suggest a biological basis for these image-based heterogeneity features and support the use of imaging, already part of standard care, for assessing intratumoural heterogeneity.

What is the Best Radionuclide for Immuno-PET of Multiple Myeloma? A Comparison Study Between 89Zr- and 64Cu-Labeled Anti-CD138 in a Preclinical Syngeneic Model

Although positron emission tomography (PET) imaging with 18-Fluorodeoxyglucose (¹⁸F-FDG) is a promising technique in multiple myeloma (MM), the development of other radiopharmaceuticals seems relevant. CD138 is currently used as a standard marker for the identification of myeloma cells and could be used in phenotype tumor imaging. In this study, we used an anti-CD138 murine antibody (9E7.4) radiolabeled with copper-64 (⁶⁴Cu) or zirconium-89 (⁸⁹Zr) and compared them in a syngeneic mouse model to select the optimal tracers for MM PET imaging. Then, 9E7.4 was conjugated to TE2A-benzyl isothiocyanate (TE2A) and desferrioxamine (DFO) chelators for ⁶⁴Cu and ⁸⁹Zr labeling, respectively. ⁶⁴Cu-TE2A-9E7.4 and ⁸⁹Zr-DFO-9E7.4 antibodies were evaluated by PET imaging and biodistribution studies in C57BL/KaLwRij mice bearing either 5T33-MM subcutaneous tumors or bone lesions and were compared to ¹⁸F-FDG-PET imaging. In biodistribution and PET studies, ⁶⁴Cu-TE2A-9E7.4 and ⁸⁹Zr-DFO-9E7.4 displayed comparable good tumor uptake of subcutaneous tumors. On the bone lesions, PET imaging with ⁶⁴Cu-TE2A-9E7.4 and ⁸⁹Zr-DFO-9E7.4 showed higher uptake than with ¹⁸F-FDG-PET. Comparison of both 9E7.4 conjugates revealed higher nonspecific bone uptakes of ⁸⁹Zr-DFO-9E7.4 than ⁶⁴Cu-TE2A-9E7.4. Because of free ⁸⁹Zr’s tropism for bone when using ⁸⁹Zr-anti-CD138, ⁶⁴Cu-anti-CD138 antibody had the most optimal tumor-to-nontarget tissue ratios for translation into humans as a specific new imaging radiopharmaceutical agent in MM.

A rapid bead-based radioligand binding assay for the determination of target-binding fraction and quality control of radiopharmaceuticals

INTRODUCTION

Determination of the target-binding fraction (TBF) of radiopharmaceuticals using cell-based assays is prone to inconsistencies arising from several intrinsic and extrinsic factors. Here, we report a cell-free quantitative method of analysis to determine the TBF of radioligands.

METHODS

Magnetic beads functionalized with Ni-NTA or streptavidin were incubated with 1 μg of histidine-tagged or biotinylated antigen of choice for 15 min, followed by incubating 1 ng of the radioligand for 30 min. The beads, supernatant and wash fractions were measured for radioactivity on a gamma counter. The TBF was determined by quantifying the percentage of activity associated with the magnetic beads.

RESULTS

The described method works robustly with a variety of radioisotopes and class of molecules used as radioligands. The entire assay can be completed within 2 h.

CONCLUSION

The described method yields results in a rapid and reliable manner whilst improving and extending the scope of previously described bead-based radioimmunoassays.

ADVANCES IN KNOWLEDGE

Using a bead-based radioligand binding assay overcomes the limitations of traditional cell-based assays. The described method is applicable to antibody as well as non-antibody based radioligands and is independent of the effect of target antigen density on cells, the choice of radioisotope used for synthesis of the radioligand and the temperature at which the assay is performed.

IMPLICATIONS FOR PATIENT CARE

The bead-based radioligand binding assay is significantly easier to perform and is ideally suited for adoption by the radiopharmacy as a quality control method of analysis to fulfill the criteria for release of radiopharmaceuticals in the clinic. The use of this assay is likely to ensure a more reliable validation of radiopharmaceutical quality and result in fewer failed doses, which could ultimately translate to an efficient release of radiopharmaceuticals for administration to patients in the clinic.

Dual-isotope imaging allows in vivo immunohistochemistry using radiolabelled antibodies in tumours

While radiolabelled antibodies have found great utility as PET and SPECT imaging agents in oncological investigations, a notable shortcoming of these agents is their propensity to accumulate non-specifically within tumour tissue. The degree of this non-specific contribution to overall tumour uptake is highly variable and can ultimately lead to false conclusions. Therefore, in an effort to obtain a reliable measure of inter-individual differences in non-specific tumour uptake of radiolabelled antibodies, we demonstrate that the use of dual-isotope imaging overcomes this issue, enables true quantification of epitope expression levels, and allows non-invasive in vivo immunohistochemistry. The approach involves co-administration of (i) an antigen-targeting antibody labelled with zirconium-89 (89Zr), and (ii) an isotype-matched non-specific control IgG antibody labelled with indium-111 (111In). As an example, the anti-HER2 antibody trastuzumab was radiolabelled with 89Zr, and co-administered intravenously together with its 111In-labelled non-specific counterpart to mice bearing human breast cancer xenografts with differing HER2 expression levels (MDA-MB-468 [HER2-negative], MDA-MB-231 [low-HER2], MDA-MB-231/H2N [medium-HER2], and SKBR3 [high-HER2]). Simultaneous PET/SPECT imaging using a MILabs Vector4 small animal scanner revealed stark differences in the intratumoural distribution of [89Zr]Zr-trastuzumab and [111In]In-IgG, highlighting regions of HER2-mediated uptake and non-specific uptake, respectively. Normalisation of the tumour uptake values and tumour-to-blood ratios obtained with [89Zr]Zr-trastuzumab against those obtained with [111In]In-IgG yielded values which were most strongly correlated (R = 0.94; P = 0.02) with HER2 expression levels for each breast cancer type determined by Western blot and in vitro saturation binding assays, but not non-normalised uptake values. Normalised intratumoural distribution of [89Zr]Zr-trastuzumab correlated well with intratumoural heterogeneity HER2 expression.

Progress of Coordination and Utilization of Zirconium-89 for Positron Emission Tomography (PET) Studies

Radiometals have been commonly used in medical applications, and utilization of such metals continues to be an attractive research area. In particular, a variety of radiometals have been developed and implemented for molecular imaging. For such applications, ⁸⁹Zr has been one of the most interesting radiometals currently used for tumor targeting. Several chemical ligands were developed as ⁸⁹Zr chelators, and new coordinating methods have also been developed more recently. In addition, immuno-positron emission tomography (PET) studies using ⁸⁹Zr-labeled monoclonal antibodies have been performed by several scientists. In this review, recent advances to the coordination of ⁸⁹Zr and the utilization of ⁸⁹Zr in PET studies are described.

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.

Radiolabelled Aptamers for Theranostic Treatment of Cancer

Cancer has a high incidence and mortality rate worldwide, which continues to grow as millions of people are diagnosed annually. Metastatic disease caused by cancer is largely responsible for the mortality rates, thus early detection of metastatic tumours can improve prognosis. However, a large number of patients will also present with micrometastasis tumours which are often missed, as conventional medical imaging modalities are unable to detect micrometastases due to the lack of specificity and sensitivity. Recent advances in radiochemistry and the development of nucleic acid based targeting molecules, have led to the development of novel agents for use in cancer diagnostics. Monoclonal antibodies may also be used, however, they have inherent issues, such as toxicity, cost, unspecified binding and their clinical use can be controversial. Aptamers are a class of single-stranded RNA or DNA ligands with high specificity, binding affinity and selectivity for a target, which makes them promising for molecular biomarker imaging. Aptamers are presented as being a superior choice over antibodies because of high binding affinity and pH stability, amongst other factors. A number of aptamers directed to cancer cell markers (breast, lung, colon, glioblastoma, melanoma) have been radiolabelled and characterised to date. Further work is ongoing to develop these for clinical applications.

Dedicated Breast Gamma Camera Imaging and Breast PET: Current Status and Future Directions

Recent advances in nuclear medicine instrumentation have led to the emergence of improved molecular imaging techniques to image breast cancer: dedicated gamma cameras using γ-emitting ^99mTc-sestamibi and breast-specific PET cameras using ¹⁸F-fluorodeoxyglucose. This article focuses on the current role of such approaches in the clinical setting including diagnosis, assessing local extent of disease, monitoring response to therapy, and, for gamma camera imaging, possible supplemental screening in women with dense breasts. Barriers to clinical adoption and technologies and radiotracers under development are also discussed.

Nuclear Medicine Imaging Techniques for Detection of Skeletal Metastases in Breast Cancer

Bone is the most common site of metastases from advanced breast cancer. Whole-body bone scintigraphy has been most frequently used in the process of managing cancer patients; its advantage is that it provides rapid whole-body imaging for screening of osteoblastic or sclerotic/mixed bone metastases at reasonable cost. Recent advanced techniques, such as single-photon emission computed tomography (SPECT)/CT, quantitative analysis, and bone scan index, contribute to better understanding of the disease state. More recent advances in machines and PET drugs improve the staging of the skeleton with higher sensitivity and specificity.

Caveolin-1 mediates cellular distribution of HER2 and affects trastuzumab binding and therapeutic efficacy

Human epidermal growth factor receptor 2 (HER2) gene amplification and/or protein overexpression in tumors is a prerequisite for initiation of trastuzumab therapy. Although HER2 is a cell membrane receptor, differential rates of endocytosis and recycling engender a dynamic surface pool of HER2. Since trastuzumab must bind to the extracellular domain of HER2, a depressed HER2 surface pool hinders binding. Using in vivo biological models and cultures of fresh human tumors, we find that the caveolin-1 (CAV1) protein is involved in HER2 cell membrane dynamics within the context of receptor endocytosis. The translational significance of this finding is highlighted by our observation that temporal CAV1 depletion with lovastatin increases HER2 half-life and availability at the cell membrane resulting in improved trastuzumab binding and therapy against HER2-positive tumors. These data show the important role that CAV1 plays in the effectiveness of trastuzumab to target HER2-positive tumors.

Trastuzumab binding to tumor cells depends on the availability of HER2 at the cell membrane. Here the authors show that caveolin-1 (CAV1) regulates HER2 density at the cell membranes and that CAV1 gene knockdown or protein depletion via the cholesterol modulator lovastatin, increases trastuzumab binding and anti-tumor activity.

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.