Preparation of clinical-grade (89) Zr-panitumumab as a positron emission tomography biomarker for evaluating epidermal growth factor receptor-targeted therapy

Advances in PET/CT Imaging for Breast Cancer

One out of eight women will be affected by breast cancer during her lifetime. Imaging plays a key role in breast cancer detection and management, providing physicians with information about tumor location, heterogeneity, and dissemination. In this review, we describe the latest advances in PET/CT imaging of breast cancer, including novel applications of 18F-FDG PET/CT and the development and testing of new agents for primary and metastatic breast tumor imaging and therapy. Ultimately, these radiopharmaceuticals may guide personalized approaches to optimize treatment based on the patient's specific tumor profile, and may become a new standard of care. In addition, they may enhance the assessment of treatment efficacy and lead to improved outcomes for patients with a breast cancer diagnosis.

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.

Novel Receptor Tyrosine Kinase Pathway Inhibitors for Targeted Radionuclide Therapy of Glioblastoma

Glioblastoma (GB) remains the most fatal brain tumor characterized by a high infiltration rate and treatment resistance. Overexpression and/or mutation of receptor tyrosine kinases is common in GB, which subsequently leads to the activation of many downstream pathways that have a critical impact on tumor progression and therapy resistance. Therefore, receptor tyrosine kinase inhibitors (RTKIs) have been investigated to improve the dismal prognosis of GB in an effort to evolve into a personalized targeted therapy strategy with a better treatment outcome. Numerous RTKIs have been approved in the clinic and several radiopharmaceuticals are part of (pre)clinical trials as a non-invasive method to identify patients who could benefit from RTKI. The latter opens up the scope for theranostic applications. In this review, the present status of RTKIs for the treatment, nuclear imaging and targeted radionuclide therapy of GB is presented. The focus will be on seven tyrosine kinase receptors, based on their central role in GB: EGFR, VEGFR, MET, PDGFR, FGFR, Eph receptor and IGF1R. Finally, by way of analyzing structural and physiological characteristics of the TKIs with promising clinical trial results, four small molecule RTKIs were selected based on their potential to become new therapeutic GB radiopharmaceuticals.

Cetuximab PET delineated changes in cellular distribution of EGFR upon dasatinib treatment in triple negative breast cancer

Background

At least 50% of triple negative breast cancer (TNBC) overexpress the epidermal growth factor receptor, EGFR, which paved the way for clinical trials investigating its blockade. Outcomes remained dismal stemming from mechanisms of resistance particularly the nuclear cycling of EGFR, which is enhanced by Src activation. Attenuation of Src reversed nuclear translocation, restoring EGFR to the cell surface. Herein, we hypothesize that changes in cellular distribution of EGFR upon Src inhibition with dasatinib can be annotated through the EGFR immunopositron emission tomography (immunoPET) radiotracer, [⁸⁹Zr]Zr-cetuximab.

Methods

Nuclear and non-nuclear EGFR levels of dasatinib-treated vs. untreated MDA-MB-231 and MDA-MB-468 cells were analyzed via immunoblots. Both treated and untreated cells were exposed to [⁸⁹Zr]Zr-cetuximab to assess binding at 4 °C and 37 °C. EGFR-positive MDA-MB-231, MDA-MB-468, and a patient-derived xenograft were treated with dasatinib or vehicle followed by cetuximab PET imaging to compare EGFR levels. After imaging, the treated mice were separated into two groups: one cohort continued with dasatinib with the addition of cetuximab while the other cohort received dasatinib alone. Correlations between the radiotracer uptake vs. changes in tumor growth and EGFR expression from immunoblots were analyzed.

Results

Treated cells displayed higher binding of [⁸⁹Zr]Zr-cetuximab to the cell membrane at 4 °C and with greater internalized activity at 37 °C vs. untreated cells. In all tumor models, higher accumulation of the radiotracer in dasatinib-treated groups was observed compared to untreated tumors. Treated tumors displayed significantly decreased pSrc (Y416) with retained total Src levels compared to control. In MDA-MB-468 and PDX tumors, the analysis of cetuximab PET vs. changes in tumor volume showed an inverse relationship where high tracer uptake in the tumor demonstrated minimal tumor volume progression. Furthermore, combined cetuximab and dasatinib treatment showed better tumor regression compared to control and dasatinib-only-treated groups. No benefit was achieved in MDA-MB-231 xenografts with the addition of cetuximab, likely due to its KRAS-mutated status.

Conclusions

Cetuximab PET can monitor effects of dasatinib on EGFR cellular distribution and potentially inform treatment response in wild-type KRAS TNBC.

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.

Imaging EGFR and HER3 through 89Zr-labeled MEHD7945A (Duligotuzumab)

Tumor resistance to treatment paved the way toward the development of single agent drugs that target multiple molecular signatures amplified within the malignancy. The discovered crosstalk between EGFR and HER3 as well as the role of HER3 in mediating EGFR resistance made these two receptor tyrosine kinases attractive targets. MEHD7945A or duligotuzumab is a single immunotherapy agent that dually targets both molecular signatures. In this study, a positron emission tomography (PET) companion diagnostic to MEHD7945A is reported and evaluated in pancreatic cancer. Tumor accretion and whole body pharmacokinetics of 89Zr-MEHD7945A were established. Specificity of the probe for EGFR and/or HER3 was further examined.

Immuno-PET Imaging of 89Zr Labeled Anti-PD-L1 Domain Antibody

Recently, various immuno-PET tracers based on monoclonal antibodies (mAbs), engineered scaffold proteins, and peptides were developed to target either programmed cell death protein 1 (PD-1) or programmed cell death ligand 1 (PD-L1), showing promise in assessment of immune checkpoints. We sought to develop an immunotherapeutic agent based PET probe that enables real-time assessment of PD-L1 expression and evaluation of antibody drug biodistribution to select eligible candidates for anti-PD-1/PD-L1 immunotherapies. KN035, a 79.6 kDa size anti-PD-L1 domain antibody under analysis in clinical trials, was used to develop the immuno-PET probe, ⁸⁹Zr-Df-KN035. Immuno-PET studies were performed to monitor PD-L1 levels in nude mice bearing LN229 xenografts with positive expression for PD-L1, and to evaluate the whole-body biodistribution in healthy non-human primates (NHPs). LN229 xenografts were markedly visualized from 24 h after injection of ⁸⁹Zr-Df-KN035, with elevated accumulation persisting for up to 120 h. Tumor radioactivity was notably reduced in the presence of excess KN035. Mouse ex vivo biodistribution studies performed at 24 and 120 h revealed tumor-to-muscle ratios as high as 5.64 ± 0.65 and 7.70 ± 1.37, respectively. In the NHP model, PET imaging demonstrated low background. The liver and kidney showed moderate accumulation with the highest SUV_mean value of 1.15 ± 0.15 and 2.13 ± 0.10 at 72 h, respectively. The spleen, lymph nodes, and salivary glands were also slightly visualized. In conclusion, ⁸⁹Zr-Df-KN035, a novel anti-PD-L1 domain antibody-based probe, shows the feasibility of noninvasive in vivo evaluation of PD-L1 expression. This work further provides a template for immunotherapeutic agent based imaging to evaluate human PD-L1 expression and to augment our understanding of therapeutic agent biodistribution, leading to better therapeutic strategies in the future.

Dosimetry and first human experience with 89Zr-panitumumab

89Zr-panitumumab is a novel immuno-PET radiotracer. A fully humanized IgG2 antibody, panitumumab binds with high affinity to the extracellular ligand binding domain of EGFR. Immuno-PET with radiolabeled panitumumab is a non-invasive method that could characterize EGFR expression in tumors and metastatic lesions. It might also assist in selecting patients likely to benefit from targeted therapy as well as monitor response and drug biodistribution for dosing guidance. Our objective was to calculate the maximum dosing for effective imaging with minimal radiation exposure in a small subset. Three patients with metastatic colon cancer were injected with approximately 1 mCi (37 MBq) of 89Zr-panitumumab IV. Whole body static images were then obtained at 2-6 hours, 1-3 days and 5-7 days post injection. Whole organ contours were applied to the liver, kidneys, spleen, stomach, lungs, bone, gut, heart, bladder and psoas muscle. From these contours, time activity curves were derived and used to calculate mean resident times which were used as input into OLINDA 1.1 software for dosimetry estimates. The whole body effective dose was estimated between 0.264 mSv/MBq (0.97 rem/mCi) and 0.330 mSv/MBq (1.22 rem/mCi). The organ which had the highest dose was the liver which OLINDA estimated between 1.9 mGy/MBq (7.2 rad/mCi) and 2.5 mGy/MBq (9 rad/mCi). The effective dose is within range of extrapolated estimates from mice studies. 89Zr-panitumumab appears safe and dosimetry estimates are reasonable for clinical imaging.

Zirconium-89 labeled antibodies: a new tool for molecular imaging in cancer patients

Antibody based positron emission tomography (immuno-PET) imaging is of increasing importance to visualize and characterize tumor lesions. Additionally, it can be used to identify patients who may benefit from a particular therapy and monitor the therapy outcome. In recent years the field is focused on ⁸⁹Zr, a radiometal with near ideal physical and chemical properties for immuno-PET. In this review we will discuss the production of  ⁸⁹Zr, the bioconjugation strategies, and applications in (pre-)clinical studies of  ⁸⁹Zr-based immuno-PET in oncology. To date, ⁸⁹Zr-based PET imaging has been investigated in a wide variety of cancer-related targets. Moreover, clinical studies have shown the feasibility for ⁸⁹Zr-based immuno-PET to predict and monitor treatment, which could be used to tailor treatment for the individual patient. Further research should be directed towards the development of standardized and robust conjugation methods and improved chelators to minimize the amount of released Zr⁴⁺ from the antibodies. Additionally, further validation of the imaging method is required. The ongoing development of new ⁸⁹Zr-labeled antibodies directed against novel tumor targets is expected to expand applications of  ⁸⁹Zr-labeled immuno-PET to a valuable method in the medical imaging.