PET/CT Imaging of Human TNFα Using [89Zr]Certolizumab Pegol in a Transgenic Preclinical Model of Rheumatoid Arthritis

Immuno-PET Imaging of TNF-α in Colitis Using 89Zr-DFO-infliximab

Tumor necrosis factor-alpha (TNF-α) neutralization has become increasingly important in the treatment of inflammatory bowel diseases (IBD). A series of monoclonal antibodies were approved in the clinic for anti-TNF-α therapy. However, a comprehensive assessment of TNF-α levels throughout the colon, which facilitates the diagnosis of IBD and predicts anti-TNF-α efficacy, remains challenging. Here, we radiolabeled infliximab with long-lived radionuclides ⁸⁹Zr for immuno-positron emission tomography (PET) imaging of TNF-α in vivo. The increased TNF-α level was detected in the inflammatory colon of the dextran sodium sulfate-induced colitis mice. The immuno-PET imaging of ⁸⁹Zr-desferrioxamine-infliximab reveals a high uptake (7.1 ± 0.3%ID/g) in the inflammatory colon, which is significantly higher than in the healthy control and blocked groups. The colon-to-muscle ratio reached more than 10 and was maintained at a high level for 10 h after injection. The ex vivo biodistribution study also verified the superior uptake in the inflammatory colon. This study provides an in vivo immune-PET approach to molecular imaging of the pro-inflammatory cytokine TNF-α. It is promising in diagnosing and predicting efficacy in both IBD and other autoimmune diseases.

A glance into the future of diagnosis and treatment of spondyloarthritis

The last two decades have seen major developments in the field of spondyloarthritis (SpA), but there are still important unmet needs to address. In the future, we envisage important advances in the diagnosis and treatment of SpA. In the diagnosis of SpA, the use of online and social media tools will increase awareness of the disease and facilitate the referral of patients to rheumatology clinics. In addition, more specific diagnostic tests will be available, especially advanced imaging methods and new biomarkers. This will allow most patients to be diagnosed at an early stage of the disease. In the treatment of SpA, an increasing number of novel treatment targets can be expected, most of which will be directed against intracellular enzymes. We hope to see more strategy trials shaping treatment pathways in SpA and accommodating principals of precision medicine. Approved treatment options will be available for both axial and peripheral SpA. We also hope to intervene not only at the inflammation level but also at the level of underlying immunological processes that might be associated with a higher probability of long-standing remission if not a cure. Finally, artificial intelligence techniques will allow for the analysis of large-scale data to answer relevant research questions for the diagnosis and management of patients with SpA.

Systematic Review: Targeted Molecular Imaging of Angiogenesis and Its Mediators in Rheumatoid Arthritis

Extensive angiogenesis is a characteristic feature in the synovial tissue of rheumatoid arthritis (RA) from a very early stage of the disease onward and constitutes a crucial event for the development of the proliferative synovium. This process is markedly intensified in patients with prolonged disease duration, high disease activity, disease severity, and significant inflammatory cell infiltration. Angiogenesis is therefore an interesting target for the development of new therapeutic approaches as well as disease monitoring strategies in RA. To this end, nuclear imaging modalities represent valuable non-invasive tools that can selectively target molecular markers of angiogenesis and accurately and quantitatively track molecular changes in multiple joints simultaneously. This systematic review summarizes the imaging markers used for single photon emission computed tomography (SPECT) and/or positron emission tomography (PET) approaches, targeting pathways and mediators involved in synovial neo-angiogenesis in RA.

First-in-human immunoPET imaging of HIV-1 infection using 89Zr-labeled VRC01 broadly neutralizing antibody

A major obstacle to achieving long-term antiretroviral (ART) free remission or functional cure of HIV infection is the presence of persistently infected cells that establish a long-lived viral reservoir. HIV largely resides in anatomical regions that are inaccessible to routine sampling, however, and non-invasive methods to understand the longitudinal tissue-wide burden of HIV persistence are urgently needed. Positron emission tomography (PET) imaging is a promising strategy to identify and characterize the tissue-wide burden of HIV. Here, we assess the efficacy of using immunoPET imaging to characterize HIV reservoirs and identify anatomical foci of persistent viral transcriptional activity using a radiolabeled HIV Env-specific broadly neutralizing antibody, ⁸⁹Zr-VRC01, in HIV-infected individuals with detectable viremia and on suppressive ART compared to uninfected controls (NCT03729752). We also assess the relationship between PET tracer uptake in tissues and timing of ART initiation and direct HIV protein expression in CD4 T cells obtained from lymph node biopsies. We observe significant increases in ⁸⁹Zr-VRC01 uptake in various tissues (including lymph nodes and gut) in HIV-infected individuals with detectable viremia (N = 5) and on suppressive ART (N = 5) compared to uninfected controls (N = 5). Importantly, PET tracer uptake in inguinal lymph nodes in viremic and ART-suppressed participants significantly and positively correlates with HIV protein expression measured directly in tissue. Our strategy may allow non-invasive longitudinal characterization of residual HIV infection and lays the framework for the development of immunoPET imaging in a variety of other infectious diseases.

EANM recommendations based on systematic analysis of small animal radionuclide imaging in inflammatory musculoskeletal diseases

Inflammatory musculoskeletal diseases represent a group of chronic and disabling conditions that evolve from a complex interplay between genetic and environmental factors that cause perturbations in innate and adaptive immune responses. Understanding the pathogenesis of inflammatory musculoskeletal diseases is, to a large extent, derived from preclinical and basic research experiments. In vivo molecular imaging enables us to study molecular targets and to measure biochemical processes non-invasively and longitudinally, providing information on disease processes and potential therapeutic strategies, e.g. efficacy of novel therapeutic interventions, which is of complementary value next to ex vivo (post mortem) histopathological analysis and molecular assays. Remarkably, the large body of preclinical imaging studies in inflammatory musculoskeletal disease is in contrast with the limited reports on molecular imaging in clinical practice and clinical guidelines. Therefore, in this EANM-endorsed position paper, we performed a systematic review of the preclinical studies in inflammatory musculoskeletal diseases that involve radionuclide imaging, with a detailed description of the animal models used. From these reflections, we provide recommendations on what future studies in this field should encompass to facilitate a greater impact of radionuclide imaging techniques on the translation to clinical settings.

Quantitative Tissue Pharmacokinetics and EPR Effect of AGuIX Nanoparticles: A Multimodal Imaging Study in an Orthotopic Glioblastoma Rat Model and Healthy Macaque

AGuIX are emerging radiosensitizing nanoparticles (NPs) for precision radiotherapy (RT) under clinical evaluation (Phase 2). Despite being accompanied by MRI thanks to the presence of gadolinium (Gd) at its surface, more sensitive and quantifiable imaging technique should further leverage the full potential of this technology. In this study, it is shown that ⁸⁹ Zr can be labeled on such NPs directly for positron emission tomography (PET) imaging with a simple and scalable method. The stability of such complexes is remarkable in vitro and in vivo. Using a glioblastoma orthotopic rat model, it is shown that injected ⁸⁹ Zr-AGuIX is detectable inside the tumor for at least 1 week. Interestingly, the particles seem to efficiently infiltrate the tumor even in necrotic areas, which places great hope for the treatment of radioresistant tumor. Lastly, the first PET/MR whole-body imaging is performed in non-human primate (NHP), which further demonstrates the translational potential of these bimodal NP.

Recent Progress in the Molecular Imaging of Nonalcoholic Fatty Liver Disease

Pathological fibrosis of the liver is a landmark feature in chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Diagnosis and assessment of progress or treatment efficacy today requires biopsy of the liver, which is a challenge in, e.g., longitudinal interventional studies. Molecular imaging techniques such as positron emission tomography (PET) have the potential to enable minimally invasive assessment of liver fibrosis. This review will summarize and discuss the current status of the development of innovative imaging markers for processes relevant for fibrogenesis in liver, e.g., certain immune cells, activated fibroblasts, and collagen depositions.

Novel positron emission tomography tracers for imaging of rheumatoid arthritis

Positron emission tomography (PET) is a nuclear imaging modality that relies on visualization of molecular targets in tissues, which is nowadays combined with a structural imaging modality such as computed tomography (CT) or Magnetic Resonance Imaging (MRI) and referred to as hybrid PET imaging. This technique allows to image specific immunological targets in rheumatoid arthritis (RA). Moreover, quantification of the PET signal enables highly sensitive monitoring of therapeutic effects on the molecular target. PET may also aid in stratification of the immuno-phenotype at baseline in order to develop personalized therapy. In this systematic review we will provide an overview of novel PET tracers, investigated in the context of RA, either pre-clinically, or clinically, that specifically visualize immune cells or stromal cells, as well as other factors and processes that contribute to pathology. The potential of these tracers in RA diagnosis, disease monitoring, and prediction of treatment outcome will be discussed. In addition, novel PET tracers established within the field of oncology that may be of use in RA will also be reviewed in order to expand the future opportunities of PET imaging in RA.

Molecular Imaging of Prostate Cancer Targeting CD46 Using ImmunoPET

PURPOSE

We recently identified CD46 as a novel therapeutic target in prostate cancer. In this study, we developed a CD46-targeted PET radiopharmaceutical, [⁸⁹Zr]DFO-YS5, and evaluated its performance for immunoPET imaging in murine prostate cancer models.

EXPERIMENTAL DESIGN

[⁸⁹Zr]DFO-YS5 was prepared and its in vitro binding affinity for CD46 was measured. ImmunoPET imaging was conducted in male athymic nu/nu mice bearing DU145 [AR^-, CD46⁺, prostate-specific membrane antigen-negative (PSMA^-)] or 22Rv1 (AR⁺, CD46⁺, PSMA⁺) tumors, and in NOD/SCID gamma mice bearing patient-derived adenocarcinoma xenograft, LTL-331, and neuroendocrine prostate cancers, LTL-331R and LTL-545.

RESULTS

[⁸⁹Zr]DFO-YS5 binds specifically to the CD46-positive human prostate cancer DU145 and 22Rv1 xenografts. In biodistribution studies, the tumor uptake of [⁸⁹Zr]DFO-YS5 was 13.3 ± 3.9 and 11.2 ± 2.5 %ID/g, respectively, in DU145 and 22Rv1 xenografts, 4 days postinjection. Notably, [⁸⁹Zr]DFO-YS5 demonstrated specific uptake in the PSMA- and AR-negative DU145 model. [⁸⁹Zr]DFO-YS5 also showed uptake in the patient-derived LTL-331 and -331R models, with particularly high uptake in the LTL-545 neuroendocrine prostate cancer tumors (18.8 ± 5.3, 12.5 ± 1.8, and 32 ± 5.3 %ID/g in LTL-331, LTL-331R, and LTL-545, respectively, at 4 days postinjection).

CONCLUSIONS

[⁸⁹Zr]DFO-YS5 is an excellent PET imaging agent across a panel of prostate cancer models, including in both adenocarcinoma and neuroendocrine prostate cancer, both cell line- and patient-derived xenografts, and both PSMA-positive and -negative tumors. It demonstrates potential for clinical translation as an imaging agent, theranostic platform, and companion biomarker in prostate cancer.

Quantitative Imaging in Inflammatory Arthritis: Between Tradition and Innovation

Radiologic imaging is crucial for diagnosing and monitoring rheumatic inflammatory diseases. Particularly the emerging approach of precision medicine has increased the interest in quantitative imaging. Extensive research has shown that ultrasound allows a quantification of direct signs such as bone erosions and synovial thickness. Dual-energy X-ray absorptiometry and high-resolution peripheral quantitative computed tomography (CT) contribute to the quantitative assessment of secondary signs such as osteoporosis or lean mass loss. Magnetic resonance imaging (MRI), using different techniques and sequences, permits in-depth evaluations. For instance, the perfusion of the inflamed synovium can be quantified by dynamic contrast-enhanced imaging or diffusion-weighted imaging, and cartilage injury can be assessed by mapping (T1ρ, T2). Furthermore, the increased metabolic activity characterizing the inflammatory response can be reliably assessed by hybrid imaging (positron emission tomography [PET]/CT, PET/MRI). Finally, advances in intelligent systems are pushing forward quantitative imaging. Complex mathematical algorithms of lesions' segmentation and advanced pattern recognition are showing promising results.

Positron Emission Tomography Imaging of Functional Transforming Growth Factor β (TGFβ) Activity and Benefit of TGFβ Inhibition in Irradiated Intracranial Tumors

PURPOSE

Transforming growth factor β (TGFβ) promotes cell survival by endorsing DNA damage repair and mediates an immunosuppressive tumor microenvironment. Thus, TGFβ activation in response to radiation therapy is potentially targetable because it opposes therapeutic control. Strategies to assess this potential in the clinic are needed.

METHODS AND MATERIALS

We evaluated positron emission tomography (PET) to image ⁸⁹Zr -fresolimumab, a humanized TGFβ neutralizing monoclonal antibody, as a means to detect TGFβ activation in intracranial tumor models. Pathway activity of TGFβ was validated by immunodetection of phosphorylated SMAD2 and the TGFβ target, tenascin. The contribution of TGFβ to radiation response was assessed by Kaplan-Meier survival analysis of mice bearing intracranial murine tumor models GL261 and SB28 glioblastoma and brain-adapted 4T1 breast cancer (4T1-BrA) treated with TGFβ neutralizing monoclonal antibody, 1D11, and/or focal radiation (10 Gy).

RESULTS

⁸⁹Zr-fresolimumab PET imaging detected engineered, physiological, and radiation-induced TGFβ activation, which was confirmed by immunostaining of biological markers. GL261 glioblastoma tumors had a greater PET signal compared with similar-sized SB28 glioblastoma tumors, whereas the widespread PET signal of 4T1-BrA intracranial tumors was consistent with their highly dispersed histologic distribution. Survival of mice bearing intracranial tumors treated with 1D11 neutralizing antibody alone was similar to that of mice treated with control antibody, whereas 1D11 improved survival when given in combination with focal radiation. The extent of survival benefit of a combination of radiation and 1D11 was associated with the degree of TGFβ activity detected by PET.

CONCLUSIONS

This study demonstrates that ⁸⁹Zr-fresolimumab PET imaging detects radiation-induced TGFβ activation in tumors. Functional imaging indicated a range of TGFβ activity in intracranial tumors, but TGFβ blockade provided survival benefit only in the context of radiation treatment. This study provides further evidence that radiation-induced TGFβ activity opposes therapeutic response to radiation.

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.

Design and Challenges of Radiopharmaceuticals

This review describes general concepts with regard to radiopharmaceuticals for diagnostic or therapeutic applications that help to understand the specific challenges encountered during the design, (radio)synthesis, in vitro and in vivo evaluation and clinical translation of novel radiopharmaceuticals. The design of a radiopharmaceutical requires upfront decisions with regard to combining a suitable vector molecule with an appropriate radionuclide, considering the type and location of the molecular target, the desired application, and the time constraints imposed by the relatively short half-life of radionuclides. Well-designed in vitro and in vivo experiments allow nonclinical validation of radiotracers. Ultimately, in combination with a limited toxicology package, the radiotracer becomes a radiopharmaceutical for clinical evaluation, produced in compliance with regulatory requirements for medicines for intravenous (IV) injection.