89Zr-DFO-Cetuximab as a Molecular Imaging Agent to Identify Cetuximab Resistance in Head and Neck Squamous Cell Carcinoma

89Zr-panitumumab PET imaging for preoperative assessment of ameloblastoma in a PDX model

Accurate assessment of tumor margins with specific, non-invasive imaging would result in the preservation of healthy tissue and improve long-term local tumor control, thereby reducing the risk of recurrence. Overexpression of epidermal growth factor receptor (EGFR) has been used in other cancers as an imaging biomarker to identify cancerous tissue. We hypothesize that expression of EGFR in ameloblastomas may be used to specifically visualize tumors. The aims of this study are to measure the specificity of radiolabeled ⁸⁹Zr-panitumumab (an EGFR antibody) in vivo using patient-derived xenograft (PDX) models of ameloblastoma and positron emission tomography/computed tomography (PET/CT) scans. In PDX of ameloblastomas from four patients (AB-36, AB-37, AB-39 AB-53), the biodistribution of ⁸⁹Zr-panitumumab was measured 120 h post-injection and was reported as the injected dose per gram of tissue (%ID/g; AB-36, 40%; AB-37, 62%; AB-39 18%; AB-53, 65%). The radiolabeled %ID/g was significantly greater in tumors of ⁸⁹Zr-panitumumab-treated mice that did not receive unlabeled panitumumab as a blocking control for AB-36, AB-37, and AB-53. Radiolabeled anti-EGFR demonstrates specificity for ameloblastoma PDX tumor xenografts, we believe ⁸⁹Zr-panitumumab is an attractive target for pre-surgical imaging of ameloblastomas. With this technology, we could more accurately assess tumor margins for the surgical removal of ameloblastomas.

Advances in nuclear medicine-based molecular imaging in head and neck squamous cell carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are often aggressive, making advanced disease very difficult to treat using contemporary modalities, such as surgery, radiation therapy, and chemotherapy. However, targeted therapy, e.g., cetuximab, an epidermal growth factor receptor inhibitor, has demonstrated survival benefit in HNSCC patients with locoregional failure or distant metastasis. Molecular imaging aims at various biomarkers used in targeted therapy, and nuclear medicine-based molecular imaging is a real-time and non-invasive modality with the potential to identify tumor in an earlier and more treatable stage, before anatomic-based imaging reveals diseases. The objective of this comprehensive review is to summarize recent advances in nuclear medicine-based molecular imaging for HNSCC focusing on several commonly radiolabeled biomarkers. The preclinical and clinical applications of these candidate imaging strategies are divided into three categories: those targeting tumor cells, tumor microenvironment, and tumor angiogenesis. This review endeavors to expand the knowledge of molecular biology of HNSCC and help realizing diagnostic potential of molecular imaging in clinical nuclear medicine.

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.

Immune-Directed Molecular Imaging Biomarkers

Imaging has played a critical role in the management of patients with cancer. Novel therapies are emerging rapidly; however, they are effective only in some patients. With the advent of new targeted therapeutics and immunotherapy, the limitations of conventional imaging methods are becoming more evident. FDG-PET imaging is restricted to the optimal assessment of immune therapies. There is a critical unmet need for pharmacodynamic and prognostic imaging biomarkers. Radiolabeled antibodies or small molecules can allow for specific assessment of targets in expression and concentration. Several such imaging agents have been under preclinical development. Early human studies with radiolabeled monoclonal antibodies or small molecules targeted to the epidermal growth factor receptor pathway have shown potential; targeted imaging of CA19.9 and CA-IX and are being further explored. Immune-directed imaging agents are highly desirable as biomarkers and preliminary studies with radiolabeled antibodies targeting immune mechanisms appear promising. While novel agents are being developed, larger well-designed studies are needed to validate the role of these agents as biomarkers in the clinical management of patients.

Physiologic constraints of using exosomes in vivo as systemic delivery vehicles

Systemic delivery of exosomes meets hurdles which had not been elucidated using live molecular imaging for their biodistribution. Production and uptake of endogenous exosomes are expected to be nonspecific and specific, respectively, where external stimuli of production of exosomes and their quantitative degree of productions are not understood. Despite this lack of understanding of basic physiology of in vivo behavior of exosomes including their possible paracrine or endocrine actions, many engineering efforts are taken to develop therapeutic vehicles. Especially, the fraction of exosomes’ taking the routes of waste disposal and exerting target actions are not characterized after systemic administration. Here, we reviewed the literature about in vivo distribution and disposal/excretion of exogenous or endogenous exosomes and, from these limited resources of knowledge currently available, summarized the knowledge and the uncertainties of exosomes on physiologic standpoints. An eloquent example of the investigations to understand the roles and confounders of exosomes’ action in the brain was highlighted with emphasis on the recent discovery of brain lymphatics and hypothesis of glymphatic/lymphatic clearance pathways in diseases as well as in physiologic processes. The possibility of delivering therapeutic exosomes through the systemic circulation, across blood-brain barriers and finally to target cells such as microglia, astrocytes and/or neurons is a good testbed in which the investigators can formulate problems to solve for both understanding (science) and application (engineering).