Radiolabeled pertuzumab for imaging of human epidermal growth factor receptor 2 expression in ovarian cancer

Evaluation of 177Lu-Labeled Pertuzumab F(ab')2 Fragments for HER2-Positive Cancer Targeting: A Comparative In Vitro and In Vivo Study

Background: Radiolabeled antibody fragments present a promising opportunity as theranostic agents, offering distinct advantages over whole antibodies. In this study, the authors investigate the potential of [177Lu]Lu-DTPA-F(ab')2-pertuzumab as a theranostic agent for precise targeting of human epidermal growth factor receptor 2 (HER2)-positive cancers. Additionally, the authors aim to quantitatively assess the binding synergism in the presence of cold trastuzumab. Materials and Methods: F(ab')2-pertuzumab was prepared by pepsin digestion and conjugated with a bifunctional chelator. The immunoconjugate was radiolabeled with 177Lu and characterized by chromatography techniques. Binding parameters (affinity, specificity, and immunoreactivity) and cellular binding enhancement studies were evaluated in HER2-overexpressing and triple-negative cell lines. The in vivo enhancement in tumor uptake of the radiolabeled immunoformulation was assessed in severe combined immunodeficient (SCID) mice bearing tumors, both in the presence and absence of unlabeled trastuzumab. Results: The formulation of [177Lu]Lu-DTPA-F(ab')2-pertuzumab could be prepared in high yields and with consistent radiochemical purity, ensuring reproducibility. Comprehensive in vitro and in vivo evaluation studies confirmed high specificity and immunoreactivity of the formulation toward HER2 receptors. Binding synergism of radiolabeled pertuzumab fragments in the presence of trastuzumab to HER2 receptors was observed. Conclusions: The radioformulation of [177Lu]Lu-DTPA-F(ab')2-pertuzumab holds great promise as a targeted approach for addressing HER2-positive cancers. A potentially effective strategy to amplify therapeutic efficacy involves dual epitope targeting by combining radiolabeled pertuzumab with cold trastuzumab.

Dive into the details of radionuclide antibody conjugates: what role do EPR effects and LETs of different radionuclides play?

Radionuclide antibody conjugate (RAC) is a promising diagnostic and therapeutic tool. It combines radionuclides and antibodies by connecting arms and chelating agents, offering precise targeting and potent killing of tumor cells. However, further development and optimization of this radiopharmaceutical is needed to enhance the ultimate substantive efficacy for clinical translation. In this issue of AJNMMI, Strand et al. evaluated the enhanced permeability effect and different linear energy transfer (LET) of radionuclides in a prostate cancer xenograft model. The results showed that specific targeting might negatively influence normal organ uptake when targeting secreted antigens and different LETs of radionuclides might have diverse effects on receptor expression and cell proliferation in tumors. The findings provide new thinking for the development of antibody-based radiopharmaceuticals.

Expression and Therapeutic Targeting of TROP-2 in Treatment-Resistant Prostate Cancer

PURPOSE

Men with metastatic castration-resistant prostate cancer (mCRPC) frequently develop resistance to androgen receptor signaling inhibitor (ARSI) treatment; therefore, new therapies are needed. Trophoblastic cell-surface antigen (TROP-2) is a transmembrane protein identified in prostate cancer and overexpressed in multiple malignancies. TROP-2 is a therapeutic target for antibody-drug conjugates (ADC).

EXPERIMENTAL DESIGN

TROP-2 gene (TACSTD2) expression and markers of treatment resistance from prostate biopsies were analyzed using data from four previously curated cohorts of mCRPC (n = 634) and the PROMOTE study (dbGaP accession phs001141.v1.p1, n = 88). EPCAM or TROP-2-positive circulating tumor cells (CTC) were captured from peripheral blood for comparison of protein (n = 15) and gene expression signatures of treatment resistance (n = 40). We assessed the efficacy of TROP-2-targeting agents in a mouse xenograft model generated from prostate cancer cell lines.

RESULTS

We demonstrated that TACSTD2 is expressed in mCRPC from luminal and basal tumors but at lower levels in patients with neuroendocrine prostate cancer. Patients previously treated with ARSI showed no significant difference in TACSTD2 expression, whereas patients with detectable AR-V7 expression showed increased expression. We observed that TROP-2 can serve as a cell surface target for isolating CTCs, which may serve as a predictive biomarker for ADCs. We also demonstrated that prostate cancer cell line xenografts can be targeted specifically by labeled anti-TROP-2 agents in vivo.

CONCLUSIONS

These results support further studies on TROP-2 as a therapeutic and diagnostic target for mCRPC.

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.

Immunotherapeutic Approaches in Ovarian Cancer

Ovarian cancer (OC) is gynecological cancer, and diagnosis and treatment are continuously advancing. Next-generation sequencing (NGS)-based diagnoses have emerged as novel methods for identifying molecules and pathways in cancer research. The NGS-based applications have expanded in OC research for early detection and identification of aberrant genes and dysregulation pathways, demonstrating comprehensive views of the entire transcriptome, such as fusion genes, genetic mutations, and gene expression profiling. Coinciding with advances in NGS-based diagnosis, treatment strategies for OC, such as molecular targeted therapy and immunotherapy, have also advanced. Immunotherapy is effective against many other cancers, and its efficacy against OC has also been demonstrated at the clinical phase. In this review, we describe several NGS-based applications for therapeutic targets of OC, and introduce current immunotherapeutic strategies, including vaccines, checkpoint inhibitors, and chimeric antigen receptor (CAR)-T cell transplantation, for effective diagnosis and treatment of OC.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Advances in the Application of Radionuclide-Labeled HER2 Affibody for the Diagnosis and Treatment of Ovarian Cancer

Human epidermal growth factor receptor 2 (HER2) is a highly expressed tumor marker in epithelial ovarian cancer, and its overexpression is considered to be a potential factor of poor prognosis. Therefore, monitoring the expression of HER2 receptor in tumor tissue provides favorable conditions for accurate localization, diagnosis, targeted therapy, and prognosis evaluation of cancer foci. Affibody has the advantages of high affinity, small molecular weight, and stable biochemical properties. The molecular probes of radionuclide-labeled HER2 affibody have recently shown broad application prospects in the diagnosis and treatment of ovarian cancer; the aim is to introduce radionuclides into the cancer foci, display systemic lesions, and kill tumor cells through the radioactivity of the radionuclides. This process seamlessly integrates the diagnosis and treatment of ovarian cancer. Current research and development of new molecular probes of radionuclide-labeled HER2 affibody should focus on overcoming the deficiencies of non-specific uptake in the kidney, bone marrow, liver, and gastrointestinal tract, and on reducing the background of the image to improve image quality. By modifying the amino acid sequence; changing the hydrophilicity, surface charge, and lipid solubility of the affibody molecule; and using different radionuclides, chelating agents, and labeling conditions to optimize the labeling method of molecular probes, the specific uptake of molecular probes at tumor sites will be improved, while reducing radioactive retention in non-target organs and obtaining the best target/non-target value. These measures will enable the clinical use of radionuclide-labeled HER2 affibody molecular probes as soon as possible, providing a new clinical path for tumor-specific diagnosis, targeted therapy, and efficacy evaluation. The purpose of this review is to describe the application of radionuclide-labeled HER2 affibody in the imaging and treatment of ovarian cancer, including its potential clinical value and dilemmas.

Advances in aptamer-based nuclear imaging

Aptamers are short oligonucleotides that bind to specific target molecules. They have been extensively explored in biomedical applications, including biosensing, medical imaging, and disease treatment. Their adjustable affinity for specific biomarkers stimulates more translational efforts, such as nuclear imaging of tumors in preclinical and clinical settings. In this review, we present recent advances of aptamer-based nuclear imaging and compare aptamer tracers with other biogenic probes in forms of peptides, nanobodies, monoclonal antibodies, and antibody fragments. Fundamental properties of aptamer-based radiotracers are highlighted and potential directions to improve aptamer's imaging performance are discussed. Despite many translational obstacles to overcome, we envision aptamers to be a versatile tool for cancer nuclear imaging in the near future.

Radiolabeled Antibodies for Cancer Imaging and Therapy

Simple Summary

Monoclonal antibodies (mAbs) have the ability to specifically target tumor-cell antigens. This unique property has led to their use in the delivery of radioisotopes to tumor sites (scintigraphic imaging and radioimmunotherapy (RIT)). The choice of the radionuclide depends on its unique physical properties and intended use. Using radiolabeled mAbs with imaging techniques provides critical data that are essential for predicting side effects and determining an optimal antibody dose and treatment schedule. While RIT has been successful in the management of hematological malignancies, the treatment of solid tumors remains challenging. Various strategies are being investigated to improve the efficacy of RIT in solid tumors.

Abstract

Radioimmunoconjugates consist of a monoclonal antibody (mAb) linked to a radionuclide. Radioimmunoconjugates as theranostics tools have been in development with success, particularly in hematological malignancies, leading to approval by the US Food and Drug Administration (FDA) for the treatment of non-Hodgkin’s lymphoma. Radioimmunotherapy (RIT) allows for reduced toxicity compared to conventional radiation therapy and enhances the efficacy of mAbs. In addition, using radiolabeled mAbs with imaging methods provides critical information on the pharmacokinetics and pharmacodynamics of therapeutic agents with direct relevance to the optimization of the dose and dosing schedule, real-time antigen quantitation, antigen heterogeneity, and dynamic antigen changes. All of these parameters are critical in predicting treatment responses and identifying patients who are most likely to benefit from treatment. Historically, RITs have been less effective in solid tumors; however, several strategies are being investigated to improve their therapeutic index, including targeting patients with minimal disease burden; using pre-targeting strategies, newer radionuclides, and improved labeling techniques; and using combined modalities and locoregional application. This review provides an overview of the radiolabeled intact antibodies currently in clinical use and those in development.

ImmunoPET of trophoblast cell-surface antigen 2 (Trop-2) expression in pancreatic cancer

PURPOSE

Without a standard test for pancreatic carcinomas, this highly lethal disease is normally diagnosed at its advanced stage, leading to a low survival rate of patients. Trophoblast cell-surface antigen 2 (Trop-2), a transmembrane glycoprotein, is associated with cell proliferation and highly expressed in most of solid epithelial tumors, including pancreatic cancer. A non-invasive method of imaging Trop-2 would greatly benefit clinical diagnosis and monitoring of pancreatic cancer. In the current study, ⁸⁹Zr-labeled anti-Trop-2 antibody (AF650) was recruited for the systemic evaluation of Trop-2 as an immunoPET target for pancreatic cancer imaging.

METHODS

AF650 was conjugated with desferrioxamine (DFO) and then radiolabeled with ⁸⁹Zr. Trop-2 expression levels were determined in three pancreatic cancer cell lines (BxPC-3, MIA PaCa-2, and AsPC-1) via western blot, flow cytometry, saturation binding assay, and immunofluorescence staining. The targeting capacity of ⁸⁹Zr-DFO-AF650 was evaluated in mouse models with subcutaneous xenograft of pancreatic cancers via PET imaging and bio-distribution studies. In addition, a Trop-2-positive orthotopic cancer model was recruited for further validating the targeting specificity of ⁸⁹Zr-DFO-AF650.

RESULTS

BxPC-3 cells expressed high levels of Trop-2, while AsPC-1 and MIA PaCa-2 cells expressed low levels of Trop-2. Additionally, ⁸⁹Zr-DFO-AF650 exhibited high specificity to Trop-2 in BxPC-3 cells (K_d = 22.34 ± 2.509 nM). In subcutaneous xenograft models, about 28.8 ± 7.63%ID/g tracer accumulated in the BxPC-3 tumors at 120 h post injection, which was much higher than those reaching MIA PaCa-2 (6.76 ± 2.08%ID/g) and AsPC-1 (3.51 ± 0.69%ID/g) tumors (n = 4). More importantly, ⁸⁹Zr-DFO-AF650 could efficiently distinguish primary tumors in the orthotopic BxPC-3 cancer model, showing high correlation between PET imaging and bio-distribution and sensitivity.

CONCLUSIONS

⁸⁹Zr-DFO-AF650 can be effectively used to detect pancreatic cancer via Trop-2-mediated immunoPET in vivo, clearly revealing the great potential of Trop-2-based non-invasive imaging in pancreatic cancer detection and treatment monitoring.

Evaluation of Liquid Biopsy in Patients with HER2-Positive Breast Cancer

Breast cancer is one of the common malignant tumors, and liquid biopsy has become a hot spot for clinical testing. To clarify the detection effect of liquid biopsy in breast cancer, we collected peripheral blood of HER2-positive (human epidermal growth factor receptor 2-positive) patients. Circulating tumor cells (CTCs) were isolated and analyzed. HER2 expression on CTCs was detected. The results showed that in the 198 HER2-positive samples, the CTC detection rate was 79.8% (158/198), and the mean number of CTCs was 21, ranging from 1 to 63/7.5 mL peripheral blood. Only 41.1% (65/158) of patients had histology and CTC HER2 status consistent with the remaining 58.9% (93/158) of patients, although their histological HER2 was positive, and CTC HER2 was negative. Our study confirmed the value of CTC HER2 real-time status testing in HER2-positive breast cancer patients. The inconsistency in HER2 status between CTCs and histology may be related to the time interval between CTCs and histological HER2 detection, suggesting that real-time HER2 detection is necessary for histological HER2-positive patients.

Review: Radionuclide Molecular Imaging Targeting HER2 in Breast Cancer with a Focus on Molecular Probes into Clinical Trials and Small Peptides

As the most frequently occurring cancer worldwide, breast cancer (BC) is the leading cause of cancer-related death in women. The overexpression of HER2 (human epidermal growth factor receptor 2) is found in about 15% of BC patients, and it is often associated with a poor prognosis due to the effect on cell proliferation, migration, invasion, and survival. As a result of the heterogeneity of BC, molecular imaging with HER2 probes can non-invasively, in real time, and quantitatively reflect the expression status of HER2 in tumors. This will provide a new approach for patients to choose treatment options and monitor treatment response. Furthermore, radionuclide molecular imaging has the potential of repetitive measurements, and it can help solve the problem of heterogeneous expression and conversion of HER2 status during disease progression or treatment. Different imaging probes of targeting proteins, such as monoclonal antibodies, antibody fragments, nanobodies, and affibodies, are currently in preclinical and clinical development. Moreover, in recent years, HER2-specific peptides have been widely developed for molecular imaging techniques for HER2-positive cancers. This article summarized different types of molecular probes targeting HER2 used in current clinical applications and the developmental trend of some HER2-specific peptides.

Monoclonal antibody based radiopharmaceuticals for imaging and therapy

The concept of personalized medicine has been steadily growing for the past decades. Monoclonal antibodies (mAbs) are undoubtedly playing an important role in the transition away from conventional medical practice to a more tailored approach to deliver the best therapy with the highest safety margin to a specific patient. In certain instances, mAbs and antibody drug conjugates (ADCs) may represent the preferred therapeutic option for several types of cancers due to their high specificity and affinity to the antigen. Monoclonal antibodies can be labeled with specific radionuclides well-suited for PET (Positron Emission Tomography) or gamma camera scintigraphy. The use of radiolabeled mAbs allows the interrogation of specific biomarkers and assessment of tumor heterogeneity in vivo by a single diagnostic imaging scan that includes the whole-body in the field-of-view. Moreover, the same mAb can then be radiolabeled with an analogous radionuclide for the delivery of beta-minus radiation or alpha-particles as part of a radioimmunotherapy (RIT) approach. However, the path to develop, validate, and implement mAb-based radiopharmaceuticals from bench-to-bedside is complex due to the extensive pre-clinical experiments and toxicological studies required, and the necessity of labor-intensive clinical trials that often require multi-time-point imaging and blood draws for internal radiation dosimetry and pharmacokinetics. As more mAb-based radiopharmaceuticals have been developed and evaluated, the opportunities and limitations offered by mAbs have become better defined. Our aim with this manuscript is therefore to provide an overview of the recent advances in the development of mAb-based radiopharmaceuticals and their clinical applications in Oncology.

Next-Generation Molecular Imaging of Thyroid Cancer

An essential aspect of thyroid cancer (TC) management is personalized and precision medicine. Functional imaging of TC with radioiodine and [18F]FDG has been frequently used in disease evaluation for several decades now. Recently, advances in molecular imaging have led to the development of novel tracers based on aptamer, peptide, antibody, nanobody, antibody fragment, and nanoparticle platforms. The emerging targets-including HER2, CD54, SHP2, CD33, and more-are promising targets for clinical translation soon. The significance of these tracers may be realized by outlining the way they support the management of TC. The provided examples focus on where preclinical investigations can be translated. Furthermore, advances in the molecular imaging of TC may inspire the development of novel therapeutic or theranostic tracers. In this review, we summarize TC-targeting probes which include transporter-based and immuno-based imaging moieties. We summarize the most recent evidence in this field and outline how these emerging strategies may potentially optimize clinical practice.

HER2-directed antibodies, affibodies and nanobodies as drug-delivery vehicles in breast cancer with a specific focus on radioimmunotherapy and radioimmunoimaging

PURPOSE

The aim of the present paper is to review the role of HER2 antibodies, affibodies and nanobodies as vehicles for imaging and therapy approaches in breast cancer, including a detailed look at recent clinical data from antibody drug conjugates and nanobodies as well as affibodies that are currently under development.

RESULTS

Clinical and preclinical studies have shown that the use of monoclonal antibodies in molecular imaging is impaired by slow blood clearance, associated with slow and low tumor uptake and with limited tumor penetration potential. Antibody fragments, such as nanobodies, on the other hand, can be radiolabelled with short-lived radioisotopes and provide high-contrast images within a few hours after injection, allowing early diagnosis and reduced radiation exposure of patients. Even in therapy, the small radioactively labeled nanobodies prove to be superior to radioactively labeled monoclonal antibodies due to their higher specificity and their ability to penetrate the tumor.

CONCLUSION

While monoclonal antibodies are well established drug delivery vehicles, the current literature on molecular imaging supports the notion that antibody fragments, such as affibodies or nanobodies, might be superior in this approach.

PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology

The human epidermal growth factor receptor family (EGFR-family, other designations: HER family, RTK Class I) is strongly linked to oncogenic transformation. Its members are frequently overexpressed in cancer and have become attractive targets for cancer therapy. To ensure effective patient care, potential responders to HER-targeted therapy need to be identified. Radionuclide molecular imaging can be a key asset for the detection of overexpression of EGFR-family members. It meets the need for repeatable whole-body assessment of the molecular disease profile, solving problems of heterogeneity and expression alterations over time. Tracer development is a multifactorial process. The optimal tracer design depends on the application and the particular challenges of the molecular target (target expression in tumors, endogenous expression in healthy tissue, accessibility). We have herein summarized the recent preclinical and clinical data on agents for Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) imaging of EGFR-family receptors in oncology. Antibody-based tracers are still extensively investigated. However, their dominance starts to be challenged by a number of tracers based on different classes of targeting proteins. Among these, engineered scaffold proteins (ESP) and single domain antibodies (sdAb) show highly encouraging results in clinical studies marking a noticeable trend towards the use of smaller sized agents for HER imaging.

Virus-Mimicking Nanoparticles for Targeted Near Infrared Fluorescence Imaging of Intraperitoneal Ovarian Tumors in Mice

Ovarian cancer is the most lethal malignancy affecting the female reproductive system. Identification and removal of all ovarian intraperitoneal tumor deposits during the intraoperative surgery is important towards preventing cancer recurrence and ultimately improving patient survival. Herein, we investigate the effectiveness of virus mimicking nanoparticles, derived from genome-depleted plant-infecting brome mosaic virus, and doped with near infrared (NIR) brominated cyanine dye BrCy106-NHS, for targeted NIR fluorescence imaging of intraperitoneal ovarian tumors. We refer to these nanoparticles as optical viral ghosts (OVGs). We functionalized the OVGs with antibodies against HER2 receptor, a biomarker over-expressed in ovarian cancers. We injected functionalized OVGs, non-functionalized OVGs, and non-encapsulated BrCy106-NHS intravenously in mice implanted with ovarian intraperitoneal tumors. Tumors were extracted at 2, 6, and 24 h post-injection, and quantitatively analyzed using NIR fluorescence imaging. Fluorescence emission from tumors associated with the injection of the functionalized OVGs continued to increase between 2 and 24 h post-injection. At 24 h timepoint, the average spectrally-integrated fluorescence emission from homogenized tumors containing functionalized-OVGs was about 3.5 and 19.5 times higher than those containing non-functionalized OVGs or non-encapsulated BrCy106-NHS, respectively. Similarly, by using the functionalized-OVGs, the imaging signal-to-noise ratio at 24 h timepoint was enhanced by approximately threefold and sevenfold as compared to non-functionalized OVGs and the non-encapsulated dye, respectively. These functionalized virus-mimicking NIR nano-constructs could potentially be used for intraoperative visualization of ovarian tumors implants.

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.

Ovarian Cancer Targeted Theranostics

Ovarian cancer is a leading cause of death from gynecological malignancies. Although the prognosis is quite favorable if detected at an early stage, the vast majority of cases are diagnosed at an advanced stage, when 5-year survival rates are only 30–40%. Most recurrent ovarian tumors are resistant to traditional therapies underscoring the need for new therapeutic options. Theranostic agents, that combine diagnostic and therapeutic capabilities, are being explored to better detect, diagnose and treat ovarian cancer. To minimize morbidity, improve survival rates, and eventually cure patients, new strategies are needed for early detection and for delivering specifically anticancer therapies to tumor sites. In this review we will discuss various molecular imaging modalities and targets that can be used for imaging, therapeutic and theranostic agent development for improved diagnosis and treatment of ovarian cancer.

64Cu-Labeled Aptamers for Tumor-Targeted Radionuclide Delivery

Aptamers are a class of oligonucleotides with high binding affinity and specificity with their targets. Additionally, aptamers are nontoxic, very thermally stable, and able to reversibly undergo denaturation and have a small size. Cancer-related aptamers can be used for tumor-targeted drug delivery, such as to deliver diagnostic and therapeutic radionuclides to target cancers. We describe the process for preparing a ⁶⁴Cu-labeled modified A10 aptamer to target prostate cancer by conjugating and radiolabeling. The modified A10 aptamer was conjugated with p-SCN-Bn-NOTA as the chelator. Following this, the aptamer can be radiolabeled with the ⁶⁴Cu radioisotope. NOTA was selected as the chelator of choice due to its commercial availability and widely demonstrated in vivo stability with the ⁶⁴Cu radioisotope. Using this system, prostate cancer could potentially be targeted for noninvasive imaging using positron emission tomography (PET). Closely following this protocol allows many aptamers to be successfully radiolabeled to accurately and quantitatively trace their distribution in vivo for a wide range of medical applications.

Imaging of Preclinical Endometrial Cancer Models for Monitoring Tumor Progression and Response to Targeted Therapy

Endometrial cancer is the most common gynecologic malignancy in industrialized countries. Most patients are cured by surgery; however, about 15% of the patients develop recurrence with limited treatment options. Patient-derived tumor xenograft (PDX) mouse models represent useful tools for preclinical evaluation of new therapies and biomarker identification. Preclinical imaging by magnetic resonance imaging (MRI), positron emission tomography-computed tomography (PET-CT), single-photon emission computed tomography (SPECT) and optical imaging during disease progression enables visualization and quantification of functional tumor characteristics, which may serve as imaging biomarkers guiding targeted therapies. A critical question, however, is whether the in vivo model systems mimic the disease setting in patients to such an extent that the imaging biomarkers may be translatable to the clinic. The primary objective of this review is to give an overview of current and novel preclinical imaging methods relevant for endometrial cancer animal models. Furthermore, we highlight how these advanced imaging methods depict pathogenic mechanisms important for tumor progression that represent potential targets for treatment in endometrial cancer.

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.

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.

ImmunoPET imaging of CD38 expression in hepatocellular carcinoma using 64Cu-labeled daratumumab

CD38 is expressed on the surface of many immune cells, which are closely associated with antitumor immunity and immune tolerance of tumor cells. Therefore, monitoring CD38 expression has gained great attention for tracking the progression of tumors and cancer treatment. Herein, we aim to develop a PET tracer using an anti-CD38 monoclonal antibody (daratumumab) to monitor CD38 expression in hepatocellular carcinoma (HCC). In this study, daratumumab was radiolabeled with ⁶⁴Cu (t_1/2=12.7 h) to obtain ⁶⁴Cu-NOTA-daratumumab. Relative CD38 expression in HepG2 and Huh7 HCC cell lines was assessed using western blot. The specificity of ⁶⁴Cu-NOTA-daratumumab to both cell lines was examined using an in vitro cell-binding assay. PET imaging in subcutaneous models of HCC was performed to evaluate the capability and specificity of ⁶⁴Cu-NOTA-daratumumab to target CD38 in vivo. Region-of-interest analysis and ex vivo biodistribution were performed to verify the tracer targeting capability of CD38. Through cellular studies of two HCC cell lines, CD38 expression was found to be higher in HepG2 and minimal in Huh7 cells. ⁶⁴Cu-NOTA-daratumumab showed relatively high affinity to CD38 (K_a=18.21 ± 1.74 nM), while the affinity of Huh7 was in the micromolar range for daratumumab binding to the cells (K_a=3.98 ± 0.87 μM). At 48 h post-injection, PET imaging of subcutaneous models with ⁶⁴Cu-NOTA-daratumumab revealed tumor uptakes of 12.23 ± 2.4 and 2.7 ± 1.2 %ID/g for HepG2 and Huh7, respectively (n=4), which correlated well with relative CD38 expression of the cells. Moreover, the ⁶⁴Cu-NOTA-IgG nonspecific analogue showed a significantly lower uptake in HepG2 subcutaneous model in mice, suggesting a specific binding of daratumumab with CD38 in vivo. Our cellular studies and PET imaging confirmed the capability and specificity of ⁶⁴Cu-NOTA-daratumumab for the imaging of CD38 in murine models of HCC. This study supports our claim that ⁶⁴Cu-NOTA-daratumumab is an effective PET tracer for the non-invasive evaluation of CD38 expression and sensitive detection of CD38-positive tumor lesions in HCC.

Dual-labeled pertuzumab for multimodality image-guided ovarian tumor resection

Pertuzumab is clinically employed in the treatment of cancers over-expressing human epidermal growth factor receptor 2 (HER2). Herein, we developed dual-labeled pertuzumab with a radionuclide (⁸⁹Zr) and a near-infrared fluorophore (IRDye 800CW) to investigate the feasibility of utilizing dual-labeled monoclonal antibodies (mAbs) with numerous imaging modalities for preoperative imaging and image-guided surgery in ovarian cancer models. MAbs were dually-labeled with ⁸⁹Zr and IRDye 800CW to generate ⁸⁹Zr-Df-pertuzumab-800CW or ⁸⁹Zr-Df-IgG-800CW. Serial positron emission tomography (PET) and near-infrared fluorescence (NIRF) images were acquired up to 72 hours after injection of dual-labeled mAbs to map the tracers' biodistributions. After the last time point, image-guided tumor resection was executed using different modalities (NIRF, Cerenkov luminescence [CL], and β particle imaging) and ex vivo studies including biodistribution assays and histology analysis were performed to confirm the in vivo imaging data. SKOV3 ovarian cancer cells showed high expression of HER2 and pertuzumab conjugated with Df and IRDye 800CW maintained its binding affinity for these cells. For PET imaging in subcutaneous xenograft ovarian cancer models, ⁸⁹Zr-Df-pertuzumab-800CW showed a significantly higher tumor-to-muscle ratio compared to the nonspecific ⁸⁹Zr-Df-IgG-800CW from 24 hours after injection through the last time point (72 h: 30.7 ± 7.4 vs. 7.5 ± 1.8, P < 0.01, n = 3-4). During image-guided surgery, three imaging modalities including NIRF, CL, and β particle imaging could detect ovarian cancer in both subcutaneous and orthotopic models and each exhibited its own imaging characteristics. In addition, ex vivo imaging and biodistribution studies as well as histology analysis corroborated the in vivo imaging results. Therefore, we concluded that this single radiolabeled tracer can provide all-in-one contrast for multiple imaging modalities. The dual-labeled mAbs may hold promise to be employed for image-guided tumor surgery as well as diagnosis and staging through balancing out the strengths and weaknesses of various modalities such as PET/CT, NIRF, CL, and β particle imaging.

Targeting Membrane Receptors of Ovarian Cancer Cells for Therapy

Ovarian cancer is a leading cause of death worldwide from gynecological malignancies, mainly because there are few early symptoms and the disease is generally diagnosed at an advanced stage. In addition, despite the effectiveness of cytoreductive surgery for ovarian cancer and the high response rates to chemotherapy, survival has improved little over the last 20 years. The management of patients with ovarian cancer also remains similar despite studies showing striking differences and heterogeneity among different subtypes. It is therefore clear that novel targeted therapeutics are urgently needed to improve clinical outcomes for ovarian cancer. To that end, several membrane receptors associated with pivotal cellular processes and often aberrantly overexpressed in ovarian cancer cells have emerged as potential targets for receptor-mediated therapeutic strategies including specific agents and multifunctional delivery systems based on ligand-receptor binding. This review focuses on the profiles and potentials of such strategies proposed for ovarian cancer treatment and imaging.

European research trends in nuclear medicine

Written by associate editors of the Annals of Nuclear Medicine, this invited review article is intended to offer our readers a condensed global view on the high-quality research work that has been published in Europe last year. We have divided this article into five sections. The first three sections from the oncology category include "[¹⁸F]fluorodeoxyglucose (FDG) positron-emission tomography (PET) for therapy monitoring in malignant lymphoma", "[¹⁸F]fluoromisonidazole (FMISO) PET for hypoxia", and "lymphoscintigraphy update". It is followed by a section on "amyloid PET for Alzheimer's disease" using [¹¹C]Pittsburgh Compound B (PiB) and [¹⁸F]florbetapir from the neurology category. The final section reviews three original articles in the field of "basic and translational molecular imaging" regardless of the category, which investigated new PET tracers such as L-4-borono-2-[¹⁸F]fluoro-phenylalanine (FBPA), O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) and ⁶⁴Cu-NOTA-pertuzumab in small animals. We hope that this review article will arouse greater interest in our readers in recent European research trends in the field of nuclear medicine.

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.