Effects of administration route on uptake kinetics of ¹⁸F‑sodium fluoride positron emission tomography in mice

 Zaniah N. Gonzalez‑Galofre^1,2, Carlos J. Alcaide‑Corral^1,2 & Adriana A. S. Tavares^1,2

¹British Heart Foundation/University of Edinburgh Centre for Cardiovascular Science

²Edinburgh Imaging, University of Edinburgh, Little France Campus, Edinburgh

³British Heart Foundation/University of Edinburgh Centre for Cardiovascular Science

 https://doi.org/10.1038/s41598-021-85073-0

Summary

¹⁸F-sodium fluoride (¹⁸F-NaF) is a positron emission tomography (PET) radiotracer widely used in skeletal imaging and has also been proposed as a biomarker of active calcification in atherosclerosis. Like most PET radiotracers, ¹⁸F-NaF is typically administered intravenously. 

However, in small animal research intravenous administrations can be challenging, because partial paravenous injection is common due to the small calibre of the superficial tail veins and repeat administrations via tail veins can lead to tissue injury therefore limiting the total number of longitudinal scanning points. In this paper, the feasibility of using intra-peritoneal route of injection of 18F-NaF to study calcification in mice was studied by looking at the kinetic and uptake profiles of normal soft tissues and bones versus intravascular injections.

In soft tissue, the ¹⁸F-NaF perfusion phase changes depending on the type on injection route, whereas the uptake phase is similar regardless of the administration route. In bone tissue standardised uptake value (SUV), standardised uptake value ratio (SUVr) and uptake constant (Ki) measures were not significantly different between the three administration routes.

 Authors have concluded that, intra-peritoneal injection is a valid and practical alternative to the intra-vascular injections in small-animal ¹⁸F-NaF PET imaging and provides equivalent pharmacokinetic data. Furthermore, their data show that CT outcomes report on sites of stablished calcification whereas PET measures sites of higher complexity and active calcification.

Results from nanoScan PET/CT

Mice received an intra-vascular or intra-peritoneal injection of ¹⁸F-NaF as follows: intra-arterial administration (8.68 ± 3.94 MBq, mean ± SD, n = 7) via femoral artery; intra-venous administration via femoral vein (7.43 ± 4.69 MBq, mean ± SD, n = 6); and intra-peritoneal administration (7.85 ± 2.18 MBq, mean ± SD, n = 6). Immediately post-radiotracer administration, a 60 min whole-body emission scan was obtained. PET data was reconstructed into 6 × 30 s, 3 × 60 s, 2 × 120 s, 10 × 300 s frames using Mediso’s iterative Tera-Tomo 3D reconstruction algorithm and the following settings: 4 iterations, 6 subsets, full detector model, low regularisation, spike filter on, voxel size 0.4 mm and 400–600 keV energy window.

Figure 1.  Representative examples of biodistribution of ¹⁸F-sodium fluoride (NaF) after femoral artery, femoral vein and intra peritoneal injections presented as average sagittal section images between 45 and 60 min post-injection (A). Mean time-activity curves of the vena cava (B), heart (C), lungs (D), liver (E) and kidneys (F) after femoral, artery, femoral vein or intraperitoneal (IP) injection. Error bars represent one SEM. SUV standardised uptake value.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

 Hee-Jeong Yang¹, Decheng Wang^{2 , 3} , Xin Wen^{2 , 3} ,Danielle M. Weiner^{1 , 4} and Laura E. Via^{1 , 4 , 5 , *}

¹ Tuberculosis Research Section, Laboratory of Clinical Immunology and Microbiology, Division of Intramural Research (DIR), National Institute of Allergy and Infectious Disease (NIAID), National Institutes of Health (NIH), Bethesda, MD, United States,

² Medical College, China Three Gorges University, Yichang, China,

³ Institute of Infection and Inflammation, China Three Gorges University, Yichang, China,

⁴ Tuberculosis Imaging Program, DIR, NIAID, NIH, Bethesda, MD, United States,

⁵ Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa

 doi: 10.3389/fcimb.2021.613149

Abstract

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb’s development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound’s effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound’s development. 

Results from MultiScan LFER PET/CT

Tuberculosis Imaging group under the direction of Laura E. Via is using 2 MultiScan LFER PET/CT scanner for studying tuberculosis on Rabbit, Common Marmoset and Rhesus Macaque at National Institute of Allergy and Infectious Diseases.

In this substantial comprehensive review, the researchers also compared these 3 animal models in respect of PET/CT imaging:

• In longitudinal studies that combined PET/CT imaging, using FDG injected IV as a probe for metabolic activity, FDG concentrated in metabolically active regions within the Mtb HN878 lesions as they developed, but as necrosis progressed, the acellular centers of granulomas and cavities accumulated less FDG due to the lack of live cells (Figure 3A)
• NHP models are amenable to most diagnostic and therapeutic methods used in clinical studies, such as medical imaging (Figures 3B, C), serial blood sampling, and bronchoalveolar lavage (BAL) sampling for pharmacokinetic monitoring within an individual (Lewinsohn et al., 2006; Lin et al., 2013; Via et al., 2013). As serial imaging is feasible, methods to follow both individual lesion development and regression PI have been developed

Figure 3. FDG PET/CTs of a rabbit (A), marmoset (B), and rhesus macaque (C) with cavitary disease. The animals were infected for 69 to 90 days with M. tuberculosis at the time of imaging. Cavities (blue arrows) have been partially emptied of their necrotic contents and filled with air indicated by a darker central region in the lesions (lower density) surrounded by lighter walls (higher density). The scales show the range of CT Hounsfield units from higher to low density in shades of gray (+400 to −1000) on the left and FDG uptake in PET standard uptake units/body weight from high to low uptake in bright yellow to red to black (14 to 0) on the right. The width of the animal’s midsection is indicated with a bar and label to highlight the difference in size of the three animals.

Sigma-1 Receptor Positron Emission Tomography: A New Molecular Imaging Approach Using (S)-(−)-[18F]Fluspidine in Glioblastoma

Magali Toussaint ¹, Winnie Deuther-Conrad ¹, Mathias Kranz ^{1 2 3}, Steffen Fischer ¹, Friedrich-Alexander Ludwig ¹, Tareq A Juratli ⁴, Marianne Patt ⁵, Bernhard Wünsch ⁶, Gabriele Schackert ⁴, Osama Sabri ⁵, Peter Brust ¹

¹ Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Research site Leipzig, 04318 Leipzig, Germany.

² PET Imaging Center, University Hospital of North Norway (UNN), 9009 Tromsø, Norway.

³ Nuclear Medicine and Radiation Biology Research Group, The Arctic University of Norway, 9009 Tromsø, Norway.

⁴ Department of Neurosurgery, Technische Universität Dresden (TUD), University Hospital Carl Gustav Carus, 01307 Dresden, Germany.

⁵ Department of Nuclear Medicine, University Hospital Leipzig, 04318 Leipzig, Germany.

⁶ Institute of Pharmaceutical and Medicinal Chemistry, University of Münster, 48149 Münster, Germany.

https://doi.org/10.3390/molecules25092170

Summary

Glioblastoma multiforme (GBM) is the most common primary tumors of the central nervous system. The survival rate for patients with GBM is dramatically low compared to patients with other brain tumor types. An important aspect contributing to this poor outcome is the genetic heterogeneity of GBM, which translates into heterogeneous expression patterns of potentially druggable targets. Hence the understanding of how spatiotemporal patterns evolve and change during pathogenesis would help to develop new targeted therapies, and biomarkers for treatment response.

The sigma-1 receptor (sig1R), an endoplasmic reticulum chaperone protein, is involved in signaling pathways assumed to control the proliferation of cancer cells and thus could serve as candidate for molecular characterization of GBM. The authors have used a selective sig1R ligand (S)-(−)-[18F]fluspidine to test this hypothesis with PET noninvasive molecular imaging.

In conclusion, the data obtained in the U87-MG mouse model of GBM along with the detection of sig1R in human GBM tissue for the first time by a PET radioligand, indicate not only the relevance of this target but also the suitability of (S)-(−)-[18F]fluspidine for sig1R-targeted cancer research and drug development.

Results from nanoScan PET/MRI

• Dynamic PET imaging showed that the uptake of (S)-(−)-[18F]fluspidine has higher retention in the tumor region compared to the CL at 60 min p.i., with SUVs of 0.38 and 0.28, respectively (Figure 4.)

Figure 4. PET/MR imaging of sig1R in mice with orthotopic xenograft of human GBM cells (U87-MG). Average time-activity curves after i.v. administration of (S)-(−)-[18F]fluspidine of the tumor (red dots) and the contralateral (black squares) regions of interest (n = 3). Statistical test: Student t-test, * p < 0.05.

• The early dynamic PET images between 2 and 9 min after injection show a heterogeneous uptake of (S)-(−)-[18F]fluspidine into the tumor (Figure 5D, upper panel), which may be caused by reduced blood supply to the tumor center. The PET image at later time points (45 to -60 min p.i.; Figure 5D, lower panel) pictures a more homogenous uptake of the tracer, along with a low slope, reflecting an accumulation.

Figure 5. (D) Representatives coronal PET/MR images of U87-MG tumor-bearing mouse after i.v. administration of (S)-(−)-[18F]fluspidine. The upper panel exhibits the distribution of (S)-(−)-[18F]fluspidine at early times p.i. (averaged time frames from 2 to 9 min), and the lower panel exhibits the distribution of (S)-(−)-[18F]fluspidine at later times (averaged time frames from 45 to 60 min). The regions-of-interest (ROIs) were delineated on the T2-weighted MR images and then applied on the PET data to generate the regional TACs.

A non-human primate model for stable chronic Parkinson’s disease induced by MPTP administration based on individual behavioral quantification

https://doi.org/10.1016/j.jneumeth.2018.10.037

Summary

Parkinson’s disease (PD) is a neurodegenerative disease that affects about 3% of the population over 65 years of age. PD is characterized by a selective loss of dopaminergic neurons accompanied by movement disorders, including rigidity, bradykinesia, akinesia, tremors, and postural instability.

The authors aimed to develop a MPTP-induced chronic NHP model with stable symptoms by adjusting MPTP treatment based on individual behavioral quantification using a video-based analysis system. To validate this strategy, they assessed a parkinsonian behavior score, an immunohistochemistry Western blot, and PET imaging of dopamine transporter (DAT) with [¹⁸F] N-(3-fluoropropyl)-2ß-carboxymethoxy-3β-(4-iodophenyl) nortropane (¹⁸F-FP-CIT).

The authors stated that the novel strategy of MPTP administration based on global activity evaluations using a video-based analysis system provides an important conceptual advance of this method for the development of chronic NHP PD models.

Results from nanoScan PET/CT

Mediso’s nanoScan PET/CT with 16cm bore size, 12 cm transaxial and 10 cm axial Field of View (FOV) were suitable to execute PET/CT scans in cynomolgus monkeys (Macaca fascicularis). Furthermore high spatial and temporal resolution of PET allowed to determine the dopamine transporter biding potential (BP) in different striatal sub-regions.

Following a CT scan for attenuation correction, 185 MBq 18 F-FP-CIT in 1.5 ml saline was injected intravenously via the saphenous vein. To monitor presynaptic dopamine transporter activity in vivo, serial 18F-FP-CIT PET imaging was performed after MPTP administration.

• The biding potential analysis revealed that the 18F-FP-CIT BP were significantly reduced in all sub-regions of the striatum at 8, 16, 24, 32,40 and 48 weeks following the first MPTP administration (Fig. 4A and 4B).
• Monkeys with fewer striatal DAT tended to have lower global activity (GA), indicating that a decrease in GA reflects damage in dopaminergic neurons.
• The severity of Parkinsonian symptoms and the loss rates of DAT in each striatal sub-region did not correlate with the total dose of MPTP, indicating that a fixed MPTP dose is not a good strategy for development of chronic NHP PD models

Fig. 4. (A) Representative 18F-FP-CIT PET images fused with individual MRI. (B) Histogram representing 18F-FP-CIT binding potential (BP) in the MPTP-injection group. (#P < 0.05, *P<0.01 vs. baseline). (C) Histogram representing time activity curve. The radiotracer uptake in each region of interest was estimated as the standardized uptake value (SUV), which was calculated as decay-corrected activity per milliliter of tissue volume per injected radiotracer activity per body mass ([kBq/mL]/[kBq/g]). Ant, anterior; binding potential, BP; Ext, external; pallidum, globus pallidus; Int, internal; Post, posterior.

Adjuvanting a subunit SARS-CoV-2 nanoparticle vaccine to induce protective immunity in non-human primates

 https://www.biorxiv.org/content/10.1101/2021.02.10.430696v1

Summary

Despite of the success of messenger RNA vaccines against SARS-CoV-2, a wider portfolio of different vaccine candidates would be needed to stop COVID-19 pandemic. In particular, vaccinating infants and the elderly could benefit from the use of subunit vaccine platforms with a demonstrable history of safety and efficacy in such populations.

Subunit vaccines include only a fragment of a pathogen which can still induce the immune system. Although, the production of these types of vaccines are safer than producing attenuated pathogen, they often require adjuvants to enhance the immune response for long term protection.

In this extensive research collaboration, the authors demonstrate the capacity of a subunit vaccine under clinical development, containing the SARS-CoV-2 Spike protein receptor binding domain displayed on a two component protein nanoparticle (RBD-NP). They assessed the immunogenicity and protective efficacy of RBD-NP vaccination using five different clinically relevant adjuvants in non-human primates.

Among the tested adjuvants, AS03, an alpha-tocopherol-containing squalene-based oil-in-water emulsion, and CpG 1018 (with Alum), a Toll-like receptor 9 agonist formulated in Alum, were the most promising adjuvants.

The team concluded that the neutralizing antibody response by the RBD-NP/AS03 vaccination was durable. The study results can also help in the development of subunit vaccines to combat the ongoing pandemic.

Results from  MultiScan LFER PET/CT

The researchers in University of Pittsburgh School of Medicine evaluated inflammation in the lung tissues with no adjuvant, AS03 and CpG-Alum on pre and post challenge days using MultiScan LFER PET/CT

• Vaccinated animals showed FDG uptake, to a much lesser extent than the control animals (Fig. 3e and f)

  

  Fig 3 e, Inflammation in the lungs of two animals from each group indicated in the legend, pre-challenge (day 0) and post-challenge (day 4 or 5 after infection), measured using PET-CT scans. f, Representative PET-CT images of lungs from one animal in each group. PET signal is scaled 0 to 15 SUV.

Copper‑67 radioimmunotheranostics for simultaneous immunotherapy and immuno‑SPECT

Guiyang Hao¹, Tara Mastren¹, William Silvers¹, Gedaa Hassan¹, Orhan K. Öz¹ &

Xiankai Sun^1,2

1 Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.

2 Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.

ttps://www.nature.com/articles/s41598-021-82812-1

Introduction

Copper-67 is useful from both therapeutic and diagnostic standpoints due to its medium energy beta particle, gamma emissions, and 2.6-day half-life. Moreover, since copper radioisotopes are chemically identical, the same radiopharmaceutical can be used for ⁶⁴Cu PET imaging to pre-screen of patients and ⁶⁷Cu based radionuclide therapy. For these reasons, the usage of ⁶⁷Cu in radiotherapy has long been arisen. However until now, its widespread use has been limited by unreliable supplies, cost, and difficulty in obtaining therapeutic quantities. The recent breakthrough of copper-67 production provides an opportunity to reassess its use in radiotherapy.

Summary

In this work, Xiankai Sun and his co-workers have evaluated and demonstrated the practical use of ⁶⁷Cu in radioimmunotherapy. To demonstrate the concept, human epidermal growth factor receptor 2 (HER2) antibody, pertuzumab, was labeled with ⁶⁷Cu isotope. The radiolabeling efficiency was two-order of magnitude higher compared to literature reports. Mice bearing HER2+ xenografts showed ⁶⁷Cu-dose dependent tumor-growth inhibition from ⁶⁷Cu-labeled-Pertuzumab co-administered with trastuzumab. Moreover, authors visualized and measured [⁶⁷Cu]Cu-NOTA-Pertuzumab uptake quantitatively by SPECT imaging.

Results from nanoSPECT/CT

Thanks to technological advances of Mediso's SPECT/CT, researchers were able to perform quantitative data analysis.

• All the tumors were clearly visualized with [⁶⁷Cu]Cu-NOTA-Pertuzumab on both day 2 and day 5 post injection (Fig. 4A).
• Quantitative tumor uptake from the SPECT imaging data are presented as absolute radioactivity concentration (μCi/mL) (Fig. 4B)

Figure 4. SPECT/CT imaging results. (A) Representative maximum intensity projection (MIP)  SPECT/CT images of HCC1954 HER2+ tumor-bearing mice injected with [⁶⁷Cu]Cu-NOTA-Pertuzumab (Group 2, 3, 4, and 5) at day 2 and 5 post the start of treatment (yellow arrows indicate the tumors); (B) Actual radioactivity concentration in tumors (MBq/mL) on Day 2 and 5 (without decay correction).

PD-1 blockade exacerbates Mycobacterium tuberculosis infection in rhesus macaques

Keith D Kauffman, Shunsuke Sakai, Nickiana E Lora, Sivaranjani Namasivayam, Paul J Baker, Olena Kamenyeva, Taylor W Foreman, Christine E Nelson, Deivide Oliveira-de-Souza, Caian L. Vinhaes, Ziv Yaniv, Cecilia S Lindestam Arleham, Alessandro Sette, Gordon J Freeman, Rashida Moore, the NIAID/DIR Tuberculosis Imaging Program, Alan Sher, Katrin D Mayer-Barber, Bruno B Andrade, Juraj Kabat, Laura E Via, Daniel L Barber

 doi: 10.1126/sciimmunol.abf3861,  BioRxiv 

Summary

PD-1 (programmed death-1) is a coinhibitory receptor primarily expressed on activated CD4 and CD8 T cells that has been shown to limit the function of pathogen-specific T cells during chronic infection. The reactive expression of PD-L1 (PD-1 receptor ligand) on cancer cells turns off the T cells that are trying to attack the tumor. Therefore, blockade of PD-1 receptor or its ligands with monoclonal antibodies (mAbs) has become an attractive target in cancer therapy. Recognition of this pathway has led to suggestions that anti–PD-1 therapy might also boost T cell immunity in chronic infections including tuberculosis.

In this recent Science Immunology publication, Kauffman et al. examined the role of PD-1 during Mycobacterium tuberculosis (Mtb) infection of rhesus macaques. It was shown that the PD-1 blockade increased the number and functionality of Mtb-specific CD8 T cells, but not CD4 cells and was associated with increases in proinflammatory cytokines. However, animals treated with anti–PD-1 monoclonal antibody developed worse disease and higher granuloma bacterial loads compared with isotype control–treated monkeys.

These data indicate that negative regulation of immune responses is a critical aspect of host resistance to Mtb infection. Also, these findings suggest that the anti-PD-1 cancer therapy needs to be used cautiously in patients with a history of Mtb exposure.

Results from MultiScan LFER

Mediso MultiScan™ Large Field of view Extreme Resolution (LFER) PET/CT system was used to follow the course of Mycobacterium tuberculosis (Mtb) infection in rhesus macaques. The animals were imaged before infection and every 2 weeks after infection beginning at 4 weeks for a maximum of eight PET-CT scans. [18F] FDG was injected intravenously (1 mCi/kg), and after 60 minutes incubation time a 20-min PET scan was acquired.

(C) Example PET-CT image from isotype control– (top) or PD-1 (bottom)–treated animals. (D) Fold change over week 4 value of total lung standardized uptake value (SUV) in isotype control (left) and PD-1–treated (right) animals.

Blood-triggered generation of platinum nanoparticle functions as an anti-cancer agent

 Xin Zeng, Jie Sun, Suping Li, Jiyun Shi, Han Gao, Wei Sun Leong, Yiqi Wu, Minghui Li, Chengxin Liu, Ping Li, Jing Kong, Yi-Zhou Wu, Guangjun Nie, Yuming Fu, Gen Zhang

  https://doi.org/10.1038/s41467-019-14131-z 

Summary

Despite the large amount of research on the effects of metal nanoparticles (NPs) in nature and medicine, there has been very limited application in the clinic due to their potential toxicity, cost, and ethical hurdles of research in humans.

In this Nature Communications article, the authors have discovered that platinum (Pt) nanoparticles (NPs) are generated in vivo in human blood when a patient is treated with cisplatin, a powerful anti-cancer agent. They have shown that the self-assembled Pt NPs form rapidly, accumulate in tumors, and remain in the body for an extended period. Furthermore, the Pt NPs by themselves act as anti-cancer agent, but the tumor inhibitory activity is greatly increased when the nanoparticles are loaded with a chemotherapeutic drug, daunorubicin (DNR). The Daunorubicin loaded nanoparticles appeared to be effective even in daunorubicin-resistant models.

 The authors proposed that in vivo-generated metal NPs represent a biocompatible drug delivery platform for chemotherapy resistant tumor treatment. 

Results from nanoScan SPECT/CT

Authors have used nanoScan SPECT/CT to create high resolution images to track the tumor targeting dynamics of the nanoparticles in vivo.

Human-derived Pt NPs were labeled with 125-I and 500 μCi 125I-Pt NPs was directly injected into DNR-resistant K562-xenografted nude mice. The images were acquired for 30 min at 1, 4, 24 and 48 h time point.

The radioactive signal accumulated in the tumor regions, peaking at 24 h and remaining apparent at 48 h P.I. (Fig. 4f), indicating that the Pt NPs were efficiently taken up by the tumors.

Figure 4. f NanoScan SPECT/CT imaging of 125I-Pt NPs in DNR-resistant K562 cell-xenografted nude mice (n = 5) at 1, 4, 24 and 48 h after intravenous injection of the NPs. The arrows and dotted circles indicate the tumors. MIP: Maximum Intensity Projection.

Synthesis, in vitro and in vivo evaluation of 11C-O-methylated arylpiperazines as potential serotonin 1A (5-HT_1A) receptor antagonist radiotracers

Vidya Narayanaswami, Junchao Tong, Ferdinando Fiorino, Beatrice Severino, Rosa Sparaco, Elisa Magli, Flavia Giordano, Peter M. Bloomfield, Jaya Prabhakaran3, J. John Mann, Neil Vasdev, Kenneth Dahl and S. Dileep Kumar

 https://doi.org/10.1186/s41181-020-00096-8

Peter M. Bloomfield and his colleague, Junchao Tong, from Centre for Addiction and Mental Health (CAMH), Toronto, Ontario have used Mediso nanoScan PET/MR 3T for testing candidate serotonin receptor radioligands in this publication. 

Summary

Clinical importance of 5-HT_1A receptors in the pathogenesis of several psychiatric and neurodegenerative disorders has promoted development of carbon-11 and fluorine-18 labeled radiotracers for in vivo positron emission tomography (PET). The gold standard PET imaging agent limited its widespread use. 

The purpose of the current study was to develop and characterize a radioligand with suitable characteristics for imaging 5-HT_1A receptors in the brain. The authors have reported the in vitro pharmacological characterization, radiosynthesis and preliminary in vivo PET imaging of three new 5-HT_1A receptor arylpiperazine based ligands in rats (DF-100 (1), DF-300 (2) and DF-400 (3)). 

They concluded DF-400 represents a promising O-methylated lead candidate which if subjected to structural alterations, may either lead to improved selectivity for 5-HT_1A receptors or may assist in the development of the first PET radioligand for α1-adrenergic receptors. 

Results from nanoScan PET/MRI 3T

• Dynamic PET studies in rats demonstrated negligible brain uptake of [11C] DF100 (1) and [11C] DF-300 (2). In contrast, significant brain uptake of [11C] DF400 (3) was observed.

Fig. 2 Uptake of [11C]3 (a); [11C]2 (b) and [11C]1 (c) in rat brain. Shown are TACs averaged for left and right brain (A: n = 3; B and C: n = 1) in SUV and summed (0–60 min) PET images in coronal, transverse and sagittal planes, respectively, through the thalamus. The spatially co-registered MR images (2D fast spin echo) show left-half ROIs including thalamus (blue), anterior cingulate cortex (red), hippocampus (green) and cerebellum (magenta) for the corresponding color-coded TACs

• Nevertheless, DF-400 displayed significant off-target binding attributed to α1-adrenergic receptors based on regional distribution (thalamus>hippocampus) and blocking studies

Fig. 2 Blocking of the uptake of [11C]3 in rat brain by WAY-100635 (a) and prazosin (b). Shown are TACs, averaged for left and right brain, (n = 1; solid: baseline; dashed: blocking) in SUV and summed (0–60 min) PET images in coronal, transverse and sagittal planes, respectively, through the thalamus at baseline and under blocking conditions. The three depicted left-half ROIs include thalamus (orange), hippocampus (red) and cerebellum (magenta) for the corresponding color-coded TACs

PET imaging of P2X₇R in the experimental autoimmune encephalomyelitis model of multiple sclerosis using [¹¹C]SMW139

https://doi.org/10.1186/s12974-020-01962-7

 Summary

Neuroinflammation plays a central role in a variety of pathologies affecting the central nervous system (CNS), such as multiple sclerosis (MS), Alzheimer’s and Parkinson’s disease. Microglia are major contributor in disease’s pathogenesis, although the exact role of microglia and their activation status during the disease process is not understood exactly.

In this article the process of neuroinflammation has been studied in Lewis rats with experimental autoimmune encephalomyelitis (EAE), an animal model for MS.

Mediso nanoScan PET/CT and nanoScan PET/MRI were used for non-invasive imaging of the activation status of microglia and the ability to identify a pro- or anti-inflammatory environment.

The authors have used a C-11 isotope labelled purinergic receptor (P2X₇R) ligand ([¹¹C]SMW139) for tracing microglial activity. They assessed the tracer’s potential for imaging neuroinflammation and its specific binding to P2X₇R. They also matched the molecular imaging result with autoradiography and immunohistochemistry.

The authors have shown that [11C]SMW139 is a promising PET tracer for imaging neuroinflammation and evaluating the dynamics of pro-inflammatory microglia in the brain.

Selected results from nanoScan PET/MRI and nanoScan PET/CT

• They evaluated the uptake of [¹¹C]SMW139 at the peak of inflammation and compared it to the uptake in the recovery phase.

Fig 1. Sagittal PET images extracted from the static reconstruction of the 5–45 min frame and showing [¹¹C]SMW139 uptake in the brain and spinal cord (arrows) of severe-relapsing (a), severe acute (b). Arrow heads are showing [¹¹C]SMW139 uptake in a brain draining lymph node

Fig 2. Sagittal PET images extracted from the static reconstruction of the 5–45 min frame and showing [¹¹C]SMW139 uptake in the brain and spinal cord (arrows) of relapsing EAE rat (peak of the disease (e), relapse (f), recovery (g)) and non-relapsing rat ( of the disease (h), no-relapse (i), recovery (j)). S.C. spinal cord, CB cerebellum, B.S. brain stem. Data are expressed as percent injected dose per milliliter (%ID/mL)

• They validated the specificity of [¹¹C]SMW139 tracer binding to the EAE tissue

Fig 3. Correlation between uptake of [¹¹C]SMW139 tracer in the brain of the EAE animal and the ex vivo immunostaining for IBA-1 and ED-1; Transversal (A) and sagittal (D) PET image section showing the uptake of the [¹¹C]SMW139 in the brain. The dotted purple circles or rectangles mark the area with the highest uptake. The green and red spots in the brain indicate a high accumulation of [¹¹C]SMW139; Immunostaining with IBA-1 (B, E) and CD68 (C, F) of the respective brain region post PET imaging showing high microglia activation in the same region where the high uptake of [¹¹C]SMW139 was observed by PET imaging.

Dendritic cell derived exosomes loaded with immunoregulatory cargo reprogram local immune responses and inhibit degenerative bone disease in vivo.

Elashiry, M. et al., Journal of Extracellular Vesicles 9, 1795362 (2020).

 doi: 10.1080/20013078.2020.1795362

Summary

This recently published study is the first demonstration of DC exosome-based therapy for a degenerative alveolar bone disease and provides the basis for a novel treatment strategy.

Periodontitis (PD) is a chronic bone disease that affects over 50% of the U.S. population. Severe PD lesions are infiltrated with B cells, macrophages, and dendritic cell (DC) clusters with CD4+T cells. The immune response can be shaped based on the maturation status of DCs, yet no effective immunomodulatory agent for PD has been identified. The goal of the current study was to characterize the immunobiology of DC derived exosome subtypes in vitro and in vivo and their ability to reprogram immune cells responsible for inflammatory bone loss.

The authors have used nanoScan SPECT/CT for imaging of exosome biodistribution in the murine periodontitis model.

Results from nanoScan SPECT/CT

Locally administrated exosomes showed higher affinity and slower clearance from periodontal tissues in the inflammatory, alveolar bone loss model. (A) SPECT CT live animal in vivo imaging of free, In-111 (left) or In-111-labelled, exosomes (right) in mice after the 24h IV administration. (B) Local delivery of free, In-111 (left) or In-111-labelled, exosomes (right) by injection in the palatal gingiva at the right side of maxilla was utilized. (C) Radioactivity in maxilla, relative to the total, when free or bound to DC EXO, was expressed as a percentage determined by using SPECT CT images. (D) Radioactivity in maxilla, relative to the total, when free or bound to DC EXO, was expressed as a percentage, in post-mortem isolated maxilla, determined by a gamma counter. Mice were subjected to ligature placement to induce inflammatory bone loss prior to imaging. Yellow arrows delineate maxilla, white arrows liver, spleen and other non-oral sites.

Introduction

We would like to introduce Professor Ali Arbab and his colleagues’ work in this blog. Professor Ali Arbab is the leader of the Tumor Angiogenesis Initiative, and director of the Core Imaging Facilities for Small Animals (CIFSA) in Augusta, GA. His research group interests are antiangiogenic therapy and vascular mimicry in glioblastoma (GBM) and breast cancer, targeting the tumor microenvironment of GBM and breast cancers as a better option to counter therapy resistance. Recently they have explored engineered exosomes as imaging and therapeutic probes to target immune-suppressive cells in tumor microenvironment. Professor Ali Arbab has 30 years of experience in imaging science involving MRI, SPECT, CT, ultrasound, and optical imaging modalities. The core facility provides MRI and optical imaging resources, and they also have a nanoScan SPECT/CT from Mediso. 

Publication

Rashid, M. H. et al. Generation of Novel Diagnostic and Therapeutic Exosomes to Detect and Deplete Protumorigenic M2 Macrophages. Advanced Therapeutics 3, 1900209 (2020).

Exosomes have emerged as potential tools for a drug delivery system that can target specific tissues or cells. M2 macrophages participate in immune suppression, epithelial to mesenchymal transition, invasion, angiogenesis, tumor progression, and subsequent metastasis foci formation. In their recent work they determined in vivo distribution of M2 macrophages with 111In-oxine-based radiolabeling of the targeted exosomes. The research demonstrated that M2 macrophage targeting therapeutic exosomes deplete M2 macrophages both in vitro and in vivo, and reduce tumor burden, increasing survival in a metastatic breast cancer model.

 nanoScan SPECT/CT was used to detect the biodistribution of 111In-oxine-labeled exosomes targeting CD206-positive M2 macrophages.

Figure 4.d from the publication, After 3 h of intravenous injection showed significant accumulation of M2-targeting exosome in tumor, lung, spleen, lymph node, and bones. 111In-oxine-labeled non-targeting exosomes (HEK293 exo) and CD206-positive M2 macrophage targeting exosomes (M2-targeting exo) were injected into the 4T1 tumor bearing mice. One group was treated with Clophosome to deplete macrophages. Yellow and green arrows denote lymph node and bone metastasis, respectively.

Southwest National Primate Research Center in Texas Biomedical Research, San Antonio has purchased Mediso’s multiscan LFER PET/CT scanner in early 2020. Mediso USA proudly post that Professor Deepak Kaushal and his co-workers used multiscan LFER PET/CT in their recently reported comprehensive work about the course of SARS-CoV-2 infection in nonhuman primate models.

multiscan LFER PET/CT features a 20 cm axial and 15 cm transaxial field of view with a 26 cm bore opening which allows the researcher to scan non-human primates (NHP) with sub-mm PET and even 150 um CT resolution.

preliminary report title: SARS-CoV-2 infection leads to acute infection with dynamic cellular and inflammatory flux in the lung that varies across nonhuman primate species June 5, 2020. https://doi.org/10.1101/2020.06.05.136481

Summary

The authors compare SARS-CoV-2 infection in three species of experimentally infected NHPs (rhesus macaques, baboons, and marmosets). They used a wide variety of methods to describe the course of disease such as clinical parameters of viral infection, viral RNA and viral protein detection, immune response, X-ray, CXR scoring, CT scanning and pathology.

Their results show all NHPs can be infected with SARS-CoV-2 but exhibit differential progression to COVID-19. Baboons exhibit moderate to severe pathology, macaques exhibit moderate pathology and marmosets exhibit mild pathology. They also summarize that rhesus macaques and baboons develop different, quantifiable disease attributes making them immediately available essential models to test new vaccines and therapies.

Results from multiscan LFER PET/CT

The report shows the importance of state-of-the-art, non-invasive imaging – cone beam CT scanning, and the application of innovative algorithms to identify the extent of lung involvement in pneumonia in developing models of COVID-19. CT image analysis provided a quantifiable metric data which enables testing efficacy of vaccines or the impact of therapeutic intervention. Lung hyperdensity and the CT abnormality score was used as a metric parameter to follow the onset of the disease. 

• Each NHP species was infected and followed over a 3-day period to describe the early signs of infection. Cone-beam CT scans showed evidence of moderate pneumonia, which progressed over 3 days (Figure 1). CT images were analyzed using the segmentation tool in VivoQuant (Invicro, Boston,MA). Lung hyperdensity and the CT abnormality score were used as a metric parameter to follow the course of the disease.

Figure 1. a) 3D Reconstruction of ROI volume representing the location of the lesion. b-d) represent images for quantification of the lung lesion with the green area representing normal intensity lung voxels (-850 HU to -500 HU), while red areas represent hyperdense voxels (-490 HU to 500 HU). (Image courtesy of Dr. Deepak Kaushal, Texas Biomedical Research) 

• They also performed detailed imaging of macaques in a 12-day longitudinal study. Similar to the acute study. imaging revealed a significant, progressive increase in the volume of lung involved in pneumonia at 6 dpi, which normalized by 12 dpi. 

• These results suggest that pneumonia in some older macaques may persist longer than in younger animals. Although there were several smaller changes observed in older animals, old and young animals both resolved the infection.

Introduction:

Small Animal Molecular imaging of infectious diseases in lung is becoming more and more important, especially at the time of COVID-19 outbreak. Dr. Sanjay K. Jain and his research group in Center for Infection and Inflammation Imaging Research (Ci3R, John Hopkins University) focuses on studying the pathogenesis of bacterial diseases, with a major focus on tuberculosis (TB). They have developed a pipeline of bacteria-specific PET-based imaging tracers. They also have developed imaging techniques to noninvasively determine antimicrobial penetration into infected lesions and understand lesions-specific host-responses. They translate their preclinical findings to the clinic and are testing some novel imaging tracers developed in their laboratory in human studies. For pre-clinical molecular imaging technique they are using Mediso nanoScan PET/CT, so they are able to follow kinetic changes of a drug distribution in high temporal resolution, and can locate sites of pathogen and inflammation in high spatial resolution.

The main challenge working with M. tuberculosis, and working with SARS-CoV-2 even, is that it requires Biosafety Level 3 (BSL-3) environment. Dr. Jain and his co-workers have developed sealed biocontainment chambers for mouse and rabbit compliant with BSL-3 requirements in house. The high versatility and open design of nanoScan PET/CT allowed them to install their chamber on the Mediso system. Working in a BSL-2 environment with a BSL-3 compatible chamber makes researcher’s life easier. For these reasons Mediso in collaboration with Dr. Jain has developed a commercially available BSL-3 compatible chamber for the PET/CT MultiCell™ imaging system, (see details below).

Clinical study findings supported by small animal imaging on Mediso nanoScan PET/CT

Ordonez et al. “Dynamic Imaging in Patients with Tuberculosis Reveals Heterogeneous Drug Exposures in Pulmonary Lesions.” Nature Medicine 26, no. 4 (April 2020): 529–34. (https://doi.org/10.1038/s41591-020-0770-2)

In this recent publication Ordonez et al. provided estimates on rifampin dosing, a first-line TB drug, required to achieve faster cure in 4 months. Newly identified patients were enrolled in a first-in-human study using dynamic [11C]rifampin positron emission tomography (PET) and computed tomography (CT). The findings from human studies were supported with small animal imaging using Mediso nanoScan PET/CT (extended data in publication Fig. 6). 

An interesting finding was that [¹¹C]rifampin exposures in human pulmonary TB lesions were low, were spatially compartmentalized and demonstrated between-patient and within-patient variability. [¹¹C]rifampin (tissue-to-plasma) AUC ratios demonstrate limited [¹¹C]rifampin exposure in lesions, with the lowest exposure noted in cavity walls, which paradoxically also have the highest bacterial burden. The pharmacokinetic studies conducted on a rabbit model also demonstrated limited and spatially compartmentalized [¹¹C]rifampin exposures in TB lesions, with the lowest exposures in cavity walls.

The authors hypothesize that tissue necrosis and presumably the fibrotic extracellular matrix surrounding cavitary tissues limited the ability for passive diffusion and rifampin penetration into these lesions, thus minimizing the spread.

Commercially available BSL-3 compliant imaging chamber from Mediso

Mediso has developed in collaboration with Dr. Sanjay K. Jain a commercially available BSL-3 compliant imaging chamber for MultiCell™ imaging system.

The advance of using this chamber is that the PET/CT scanner doesn’t have to be in BSL-3 laboratory, so the animal imaging and the scanner maintenance become much easier. Moreover, the scanner in a such setup can be used for non BSL-3 required animal studies also.

As a workflow, the animals are anesthetized in a BSL-3 environment and placed into the imaging chamber and then sealed. The outer surface of the chamber is decontaminated before caring to BSL-2 environment.

The chamber can be attached by one-click to the scanner’s docking stage without any further tube connection. The anesthesia gas flows in and out through a 0.3 um pore filter. The heating air is circulating only in the chamber’s wall, so there is no transit between the heating air compartment and the chamber space. For kinetic studies the animal is cannulated in BSL-3 and the tubing is led out through a sealed opening (see Figure 1.)

This practical solution provides a tenable and flexible mechanism for routine imaging and for implementing the more severe constraints necessitated by BSL-3 imaging procedures in a simple and expeditious manner.

Figure 1. MultiCell™ BSL-3 compliant imaging chamber