Antibody-based tumor vascular theranostics targeting endosialin/TEM1 in a new mouse tumor vascular model

Tumor endothelial marker 1 (TEM1, endosialin) is a tumor vascular marker with significant diagnostic and therapeutic potential. However, in vivo small animal models to test affinity reagents specifically targeted to human (h)TEM1 are limited. We describe a new mouse tumor model where tumor vascular endothelial cells express hTEM1 protein. Methods: Immortalized murine endothelial cells MS1 were engineered to express hTEM1 and firefly luciferase and were inoculated in nude mice either alone, to form hemangioma-like endothelial grafts, or admixed with ID8 ovarian tumor cells, to form chimeric endothelial-tumor cell grafts. MORAb-004, a monoclonal humanized IgG₁ antibody specifically recognizing human TEM1 was evaluated for targeted theranostic applications, i.e., for its ability to affect vascular grafts expressing hTEM1 as well as being a tool for molecular positron emission tomography (PET) imaging. Results: Naked MORAb-004 treatment of mice bearing angioma grafts or chimeric endothelial-tumor grafts significantly suppressed the ability of hTEM1-positive endothelial cells, but not control endothelial cells, to form grafts and dramatically suppressed local angiogenesis. In addition, highly efficient radioiodination of MORAb-004 did not impair its affinity for hTEM1, and [¹²⁴I]-MORAb-004-PET enabled non-invasive visualization of tumors enriched with hTEM1-positive, but not hTEM1 negative vasculature with high degree of specificity and sensitivity. Conclusion: The development of a new robust endothelial graft model expressing human tumor vascular proteins will help accelerate the development of novel theranostics targeting the tumor vasculature, which exhibit affinity specifically to human targets but not their murine counterparts. Our results also demonstrate the theranostic potential of MORAb-004 as PET imaging tracer and naked antibody therapy for TEM1-positive tumor.     

Manganese in PET imaging: Opportunities and challenges

Several radionuclides of the transition metal manganese are known and accessible. Three of them, ⁵¹Mn, ^52mMn, and ^52gMn, are positron emitters that are potentially interesting for positron emission tomography (PET) applications and, thus, have caught the interest of the radiochemical/radiopharmaceutical and nuclear medicine communities. This mini‐review provides an overview of the production routes and physical properties of these radionuclides. For medical imaging, the focus is on the longer‐living ^52gMn and its application for the radiolabelling of molecules and other entities exhibiting long biological half‐lives, the imaging of manganese‐dependent biological processes, and the development of bimodal PET/magnetic resonance imaging (MRI) probes in combination with paramagnetic ^natMn as a contrast agent.     

Radioimmunoconjugates for treating cancer: recent advances and current opportunities

Introduction: Radioimmunoconjugates have been used for 30 years to diagnose and treat cancer. For many years, the use of these therapeutic tools has been limited to haematological disorders, such as non-Hodgkin’s lymphoma, given that they have only had a moderate effect on solid tumours.

Areas covered: Recently, several strategies have revived the potential therapeutic application for radioimmunoconjugates. In this review, the authors review the advances in immunological engineering to develop new tools like monoclonal antibodies and their derivatives. Then, the authors summarize the development of radionuclides, the use of recombinant antibodies, pretargeting approaches, and dose fractionation techniques, providing opportunities for both therapeutic and diagnostic applications.

Expert opinion: Radioimmunoconjugates used in nuclear medicine have entered a new era of development. These advances give rise to a variety of opportunities in the management of various cancers, where the radiolabelled antibodies may be particularly useful in immuno-specific phenotypic imaging e.g. companion diagnostics. Concerning therapeutic applications, radioimmunoconjugates have demonstrated their efficacy in the treatment of both haematological malignancies and solid tumours. Recent procedural developments are of great interest in optimising oncological targeted therapies. In the field of cancer theranostics, we believe that radioimmunoconjugated compounds are likely to play a large part in near future.     

Current and potential applications of positron emission tomography for multiple myeloma and plasma cell disorders

Fluorine-18 (18F)-fluorodeoxyglucose (FDG) positron emission tomography (PET) allows evaluation of elevated glucose metabolism in malignancies. There has been increasing interest in FDG PET/CT for plasma cell disorders since the International Myeloma Working Group outlined multiple applications of this imaging modality, including distinguishing smoldering myeloma from active multiple myeloma, confirmation of solitary plasmacytoma, and multiple indications in patients with known multiple myeloma, including determining extent of initial disease, monitoring therapy response, and detection of residual disease following therapy. The field of molecular imaging is now shifting focus from evaluation of metabolism to targeted evaluation of specific tumor markers. Targeted PET imaging targeted of CXCR4 and CD38 has advanced into translational clinical trials, bringing us closer to powerful imaging options for myeloma. In this review we discuss the current applications of FDG PET/CT in plasma cell disorders, as well as advances in targeted PET imaging.     

89Zr-cetuximab PET imaging in patients with advanced colorectal cancer

Monoclonal antibodies (mAbs) against the epidermal growth factor receptor (EGFR) are used in the treatment of advanced colorectal cancer (mCRC). Approximately 50% of patients benefit despite patient selection for RAS wild type (wt) tumors. Based on the hypothesis that tumor targeting is required for clinical benefit of anti-EGFR treatment, biodistribution and tumor uptake of ⁸⁹Zr-cetuximab by Positron Emission Tomography (PET), combining the sensitivity of PET with the specificity of cetuximab for EGFR was evaluated. Ten patients with wt K-RAS mCRC received 37 ± 1 MBq ⁸⁹Zr-cetuximab directly (<2 h) after the first therapeutic dose of cetuximab. PET-scans were performed from 1 hour to 10 days post injection (p.i.). Biodistribution was determined for blood and organs. Uptake in tumor lesions was quantified by Standardized Uptake Value (SUV) and related to response. In 6 of 10 patients ⁸⁹Zr-cetuximab uptake in tumor lesions was detected. Four of 6 patients with ⁸⁹Zr-cetuximab uptake had clinical benefit, while progressive disease was observed in 3 of 4 patients without ⁸⁹Zr-cetuximab uptake. Taken together, tumor uptake of ⁸⁹Zr-cetuximab can be visualized by PET imaging. The strong relation between uptake and response warrants further clinical validation as an innovative selection method for cetuximab treatment in patients with wt RAS mCRC.     

ImmunoPET/MR imaging allows specific detection of Aspergillus fumigatus lung infection in vivo

Invasive pulmonary aspergillosis (IPA) is a life-threatening lung disease caused by the fungus Aspergillus fumigatus, and is a leading cause of invasive fungal infection-related mortality and morbidity in patients with hematological malignancies and bone marrow transplants. We developed and tested a novel probe for noninvasive detection of A. fumigatus lung infection based on antibody-guided positron emission tomography and magnetic resonance (immunoPET/MR) imaging. Administration of a [⁶⁴Cu]DOTA-labeled A. fumigatus-specific monoclonal antibody (mAb), JF5, to neutrophil-depleted A. fumigatus-infected mice allowed specific localization of lung infection when combined with PET. Optical imaging with a fluorochrome-labeled version of the mAb showed colocalization with invasive hyphae. The mAb-based newly developed PET tracer [⁶⁴Cu]DOTA-JF5 distinguished IPA from bacterial lung infections and, in contrast to [¹⁸F]FDG-PET, discriminated IPA from a general increase in metabolic activity associated with lung inflammation. To our knowledge, this is the first time that antibody-guided in vivo imaging has been used for noninvasive diagnosis of a fungal lung disease (IPA) of humans, an approach with enormous potential for diagnosis of infectious diseases and with potential for clinical translation.Despite the success of therapeutics fighting against especially bacteria and fungi, infectious diseases still remain one of the main causes of death worldwide (1). Beside effective therapeutics, the early and reliable differential diagnosis of infectious diseases is of utmost importance; here noninvasive imaging can have a huge impact. Imaging of infectious diseases is an emerging field still in its infancy, but is nevertheless attracting considerable attention from many disciplines in biomedical research, as well as in patient care. There are several challenging aspects of imaging infectious diseases, not at least the clear and reliable differentiation between bacterial, fungal, and viral infection needed for the best treatment options. Furthermore, infection is typically linked to inflammation, which makes it mandatory to use pathogen specific imaging probes to definitively and rapidly diagnose the causative agent of the infectious disease.Invasive pulmonary aspergillosis (IPA) is a frequently fatal lung disease of neutropenic patients caused by the ubiquitous airborne fungus Aspergillus fumigatus. As a leading cause of death in hematological malignancy and hematopoietic stem cell transplant patients, the fungus accounts for the majority of the >200,000 life-threatening infections annually with an associated mortality rate of 30–90% (2). Diagnosis of IPA is a major challenge as clinical manifestations of the disease (febrile episodes unresponsive to antibiotics, pulmonary infiltrates and radiological abnormalities) are nonspecific, and methods for the detection of circulating biomarkers such as β-d-glucan or galactomannan (GM) in the bloodstream lack specificity or sensitivity (3). For this reason, culture of the fungus from lung biopsy tissues remains the gold standard test for IPA diagnosis (4), but this invasive procedure lacks sensitivity, delays diagnosis, and is frequently not possible in neutropenic patients. Recently, detection of A. fumigatus GM or mannoprotein antigens in bronchoalveolar lavage (BAL) has shown enormous promise for the early detection of the disease especially when combined with point-of-care diagnostics (5). However, BAL recovery is similarly intrusive and so a sensitive, specific, and minimally invasive test that is amenable to repeated application is needed to allow diagnostic-driven treatment with antifungal drugs. Such a test should be able to discriminate between active lung infection caused by hyphal proliferation of the fungus and inactive spores that are a common component of inhaled air. Conventional imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) are able to produce high contrast images of all structures within the human body but they are not able to distinguish between invasive fungal infections and those caused by other microorganisms, or to discriminate these from cancer tissues (6, 7). Molecular imaging using positron emission tomography (PET) is able to define the metabolic properties of living cells as well as their molecular structures when suitable radiolabeled tracers are used (8). Here, we use a radiolabeled monoclonal antibody (mAb) specific to the active growth phase of A. fumigatus to diagnose IPA in a neutropenic animal model of the disease with PET/MRI. Our work shows that antibody-based immunoPET can be used successfully to noninvasively identify this challenging lung disease.