tissue distribution of GLP1 by PET vs Autoradiography

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Comparison of the Tissue Distribution of a Long-Circulating Glucagon-like Peptide-1 Agonist Determined by Positron Emission Tomography and Quantitative Whole-Body Autoradiography

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tissue distribution of GLP1 by PET vs Autoradiography

Comparison of the Tissue Distribution of a Long-Circulating Glucagon-like Peptide-1 Agonist Determined by Positron Emission Tomography and Quantitative Whole-Body Autoradiography

by Eduardo Felipe Alves Fernandes, Jonas Wilbs, Rene Raavé, Christian Borch Jacobsen, Hanne Toftelund, Hans Helleberg, Milou Boswinkel, Sandra Heskamp, Magnus Bernt Frederik Gustafsson, and Inga Bjørnsdottir


ACS Pharmacol. Transl. Sci. 2022, 5, 8, 616–624. doi: 10.1021/acsptsci.2c00075

Abstract

Positron emission tomography (PET) is a molecular imaging modality that enables non-invasive visualization of tracer distribution and pharmacology. Recently, peptides with long half-lives allowed once-a-week dosing of glucagon-like peptide-1 receptor (GLP-1R) agonists with therapeutic applications in diabetes and obesity. PET imaging for such long-lived peptides is hindered by the typically used short-lived radionuclides. Zirconium-89 (89Zr) emerged as a promising PET radionuclide with a sufficiently long half-life to be applied for biodistribution studies of long-circulating biomolecules. A comparison between the biodistribution profiles obtained via 89Zr-PET and the current standard, quantitative whole-body autoradiography (QWBA), will be valuable for the development of novel peptide drugs. We determined the PET biodistribution of a 89Zr-labeled acylated peptide agonist of GLP-1R and compared it to the profile obtained by QWBA using analogous tritiated tracers for up to 1 week after administration. The plasma metabolic profile was obtained and identification was done for the tritiated tracers. We found that, at early time points, the biodistribution profiles agreed between PET and QWBA. At the latertime points, the 89Zr tracer remained primarily trapped in the kidneys. The introduction of desferrioxamine (DFO) chelator reduced the peptide stability, and UPLC-MS analysis identified a circulating metabolite arising from DFO hydrolysis. Kidney accumulation of radiolabeled peptides and DFO metabolic instability may compromise biodistribution studies using 89Zr-PET to support the development of new biopharmaceuticals. PET and QWBA biodistribution data correlated well during the absorption phase, but new and more stable 89Zr chelators are needed for a more accurate description of the elimination phase.

Tissue distribution of GLP1 by PET vs Autoradiography
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Manual vs AI based segmentation for dosimetry

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Manual Versus Artificial Intelligence-Based Segmentations as a Pre-processing Step in Whole-body PET Dosimetry Calculations
 

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Manual vs AI based segmentation for Dosimetry

Manual Versus Artificial Intelligence-Based Segmentations as a Pre-processing Step in Whole-body PET Dosimetry Calculations

by Joyce van Sluis, Walter Noordzij, Elisabeth G. E. de Vries, Iris C. Kok, Derk Jan A. de Groot, Mathilde Jalving, Marjolijn N. Lub-de Hooge, Adrienne H. Brouwers & Ronald Boellaard 


Mol Imaging Biol (2022). doi: 10.1007/s11307-022-01775-5

Abstract

Purpose
As novel tracers are continuously under development, it is important to obtain reliable radiation dose estimates to optimize the amount of activity that can be administered while keeping radiation burden within acceptable limits.

Organ segmentation is required for quantification of specific uptake in organs of interest and whole-body dosimetry but is a time-consuming task which induces high interobserver variability. Therefore, we explored using manual segmentations versus an artificial intelligence (AI)-based automated segmentation tool as a pre-processing step for calculating whole-body effective doses to determine the influence of variability in volumetric whole-organ segmentations on dosimetry.

Procedures
PET/CT data of six patients undergoing imaging with 89Zr-labelled pembrolizumab were included. Manual organ segmentations were performed, using in-house developed software, and biodistribution information was obtained. Based on the activity biodistribution information, residence times were calculated. The residence times served as input for OLINDA/EXM version 1.0 (Vanderbilt University, 2003) to calculate the whole-body effective dose (mSv/MBq).

Subsequently, organ segmentations were performed using RECOMIA, a cloud-based AI platform for nuclear medicine and radiology research. The workflow for calculating residence times and whole-body effective doses, as described above, was repeated.

Results
Data were acquired on days 2, 4, and 7 post-injection, resulting in 18 scans. Overall analysis time per scan was approximately 4 h for manual segmentations compared to ≤ 30 min using AI-based segmentations. Median Jaccard similarity coefficients between manual and AI-based segmentations varied from 0.05 (range 0.00–0.14) for the pancreas to 0.78 (range 0.74–0.82) for the lungs. Whole-body effective doses differed minimally for the six patients with a median difference in received mSv/MBq of 0.52% (range 0.15–1.95%).

Conclusion
This pilot study suggests that whole-body dosimetry calculations can benefit from fast, automated AI-based whole organ segmentations.

Manual vs AI based segmentation for dosimetry
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Quantify tumor CD8 cell infiltration

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Head-to-head comparison of nuclear imaging techniques to quantify tumor CD8+ T cell infiltration (conference abstract)

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quantify tumor CD8+ T-cell infiltration

Head-to-head comparison of nuclear imaging techniques to quantify tumor CD8+ T cell infiltration 

by Gerwin Sandker, René Raavé, Ines Antunes, Peter Wierstra, Iris Hagemans, Milou Boswinkel, Gerben Franssen, Janneke Molkenboer-Kuenen, Johan Bussink, Gosse Adema, Erik Aarntzen, Martijn Verdoes, Sandra Heskamp


EMIM 2022 Conference Abstract

Abstract

Background: 
CD8+ T cells are key effector cells in anti-tumor immune responses. Immunotherapies (re)activating these cells are promising cancer treatments. Prevalent immune-related adverse effects and high costs combined with limited treatment responses necessitate biomarkers predicting response. Previous studies have shown that nuclear imaging techniques with radiolabeled anti-CD8 antibodies, IL2 and ex vivo labeled cells can be used to noninvasively evaluate the whole-body and tumor residing distribution of CD8+ T cells over time. In this study, we perform a head-to-head comparison of these techniques.
Methods: 
C57BL/6 mice bearing B16F10/ova tumors were randomized in 3 groups (n=10) to receive either: 1) 89Zr-labeled DFO-conjugated Fc-silent anti-CD8 antibodies (89Zr-antiCD8lala), 2) from donor mice isolated and ex vivo 89Zr-oxine labeled OT1 T cells (89Zr-OT1), or 3) 18F-labeled RESCA-IL2 (18F-IL2). Mice were injected intravenously with 89Zr-antiCD8lala 72 hours, 89Zr-OT1 48 hours, and 18F-IL2 directly before PET/CT scanning and dissection. Additionally, 89Zr-OT1 mice were PET/CT scanned 24 hours after injection. Following dissection, relevant tissues were collected for ex vivo biodistribution analysis. Next, tumors were halved for subsequent immunohistochemistry and autoradiography evaluation, and flow cytometric analysis to evaluate the number of CD8+ T cells. 
Results/Discussion: 
Preliminary data analysis suggests tumor uptake of 89Zr-antiCD8lala, 89Zr-OT1 and 18F-IL2 above background levels. Furthermore, uptake of 89Zr-antiCD8lala and 89Zr-OT1 was observed in the spleen and lymph nodes. (Figure 1 A and B) 18F-IL2 accumulation was observed in spleen, lung and the excretory organs. (Figure 1 C) The uptake of 89Zr-antiCD8lala and 18F-IL2 in lymphoid organs indicates their target specificity, whereas the uptake of 89Zr-OT1 indicates that the OT1 T cells were viable and retained their migratory ability.
Conclusions: 
Preliminary data analysis suggests quantifiable tumor uptake of each tracer. Further analysis will investigate the correlations between the quantified PET signal and the number of CD8+ T cells in the tumor as determined by flow cytometry. Moreover, immunohistochemistry for CD8 will be performed to investigate the spatial correlation with autoradiographic images.

Quantify tumor CD8+ T-cell infiltration
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In vivo PET of 89Zr-PLGA-NH2 labelled Monocytes

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In Vivo PET Imaging of Monocytes Labeled with [89Zr]Zr-PLGA-NH2 Nanoparticles in Tumor and Staphylococcus aureus Infection Models

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PET  of Monocytes IN tUMOR AND INFECTION MODEL

In Vivo PET Imaging of Monocytes Labeled with [89Zr]Zr-PLGA-NH2 Nanoparticles in Tumor and Staphylococcus aureus Infection Models

by Massis Krekorian, Kimberley R. G. Cortenbach ,Milou Boswinkel, Annemarie Kip, Gerben M. Franssen, Andor Veltien, Tom W. J. Scheenen, René Raavé, Nicolaas Koen van Riessen, Mangala Srinivas, Ingrid Jolanda M. de Vries, Carl G. Figdor, Erik H. J. G. Aarntzen and Sandra Heskamp


Cancers 2021, 13(20), 5069. doi: 10.3390/cancers13205069

Abstract

Non-invasive imaging biomarkers (IBs) are warranted to enable improved diagnostics and follow-up monitoring of interstitial lung disease (ILD) including drug-induced ILD (DIILD). Of special interest are IB, which can characterize and differentiate acute inflammation from fibrosis. The aim of the present study was to evaluate a PET-tracer specific for Collagen-I, combined with multi-echo MRI, in a rat model of DIILD. Rats were challenged intratracheally with bleomycin, and subsequently followed by MRI and PET/CT for four weeks. PET imaging demonstrated a significantly increased uptake of the collagen tracer in the lungs of challenged rats compared to controls. This was confirmed by MRI characterization of the lesions as edema or fibrotic tissue. The uptake of tracer did not show complete spatial overlap with the lesions identified by MRI. Instead, the tracer signal appeared at the borderline between lesion and healthy tissue. Histological tissue staining, fibrosis scoring, lysyl oxidase activity measurements, and gene expression markers all confirmed establishing fibrosis over time. In conclusion, the novel PET tracer for Collagen-I combined with multi-echo MRI, were successfully able to monitor fibrotic changes in bleomycin-induced lung injury. The translational approach of using non-invasive imaging techniques show potential also from a clinical perspective.

Pet of Monocytes in tumor and infection model
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Dual-Labeled Immunoconjugates for PET/NIRF

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Site-Specific, Platform-Based Conjugation Strategy for the Synthesis of Dual-Labeled Immunoconjugates for Bimodal PET/NIRF Imaging of HER2-Positive Tumors

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dual-labelled Immunoconjugates for PET/NIRF

Site-Specific, Platform-Based Conjugation Strategy for the Synthesis of Dual-Labeled Immunoconjugates for Bimodal PET/NIRF Imaging of HER2-Positive Tumors

by Pierre Adumeau, René Raavé, Milou Boswinkel, Sandra Heskamp, Hans J. C. T. Wessels, Alain J. van Gool, Mathieu Moreau, Claire Bernhard, Laurène Da Costa, Victor Goncalves, and Franck Denat


Bioconjugate Chem. 2022, 33, 3, 530–540. doi: 10.1021/acs.bioconjchem.2c00049

Abstract

Because positron emission tomography (PET) and optical imaging are very complementary, the combination of these two imaging modalities is very enticing in the oncology field. Such bimodal imaging generally relies on imaging agents bearing two different imaging reporters. In the bioconjugation field, this is mainly performed by successive random conjugations of the two reporters on the protein vector, but these random conjugations can alter the vector properties. In this study, we aimed at abrogating the heterogeneity of the bimodal imaging immunoconjugate and mitigating the impact of multiple random conjugations. A trivalent platform bearing a DFO chelator for 89Zr labeling, a NIR fluorophore, IRDye800CW, and a bioconjugation handle was synthesized. This bimodal probe was site-specifically grafted to trastuzumab via glycan engineering. This new bimodal immunoconjugate was then investigated in terms of radiochemistry, in vitro and in vivo, and compared to the clinically relevant random equivalent. In vitro and in vivo, our strategy provides several improvements over the current clinical standard. The combination of site-specific conjugation with the monomolecular platform reduced the heterogeneity of the final immunoconjugate, improved the resistance of the fluorophore toward radiobleaching, and reduced the nonspecific uptake in the spleen and liver compared to the standard random immunoconjugate. To conclude, the strategy developed is very promising for the synthesis of better defined dual-labeled immunoconjugates, although there is still room for improvement. Importantly, this conjugation strategy is highly modular and could be used for the synthesis of a wide range of dual-labeled immunoconjugates.

Dual-Labeled Immunoconjugates for PET/NIRF
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AI based segmentation for dosimetry

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Manual versus artificial intelligence-based segmentations as a pre-processing step in whole-body dosimetry calculations (conference abstract)

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Manual vs AI based segmentation for dosimetry

Manual versus artificial intelligence-based segmentations as a pre-processing step in whole-body dosimetry calculations

by Joyce van Sluis, Walter Noordzij, Lars Edenbrandt, Elisabeth G. E. de Vries, Adrienne H. Brouwers, and Ronald Boellaard


Poster presentation at the EANM 2021 conference

Abstract

Aim/Introduction

Over the last decades, labelling of monoclonal antibodies (MAbs) with zirconium-89 (89Zr) allowed whole body assessment of MAb distribution and tumour targeting over time with molecular imaging. The main advantage of 89Zr is the long half-life of 78.4 h matching the pharmacokinetic behaviour of antibodies, making it suitable for labelling of MAbs.     
The long physical half-life of 89Zr and the long biological half-life of MAbs may cause high radiation burden and/or limits the amount of activity that can be administered, which in turn limits image quality. It is therefore important to obtain reliable radiation dose estimates to optimize the amount of activity that can be administered while keeping radiation burden within acceptable limits.
Organ segmentation is required for whole-body dosimetry but is a very time-consuming task. Therefore, we explored the possibility of using an AI based automated segmentation tool as a pre-processing step for calculating the organ and whole-body effective doses. 

Materials and Methods

Retrospective PET/CT data of six patients undergoing treatment with 89Zr-labelled pembrolizumab were included in this study. Manual organ segmentations were performed using in-house developed software and biodistribution information was obtained. Using the activity biodistribution information, residence times were calculated. The obtained residence times served as input for OLINDA XLM version 1.0 (Vanderbilt University, 2003) to calculate the effective dose per organ as well as the whole-body effective dose (mSv/MBq) according to ICRP60 and ICRP103 guidelines.     
Subsequently, organ segmentations were also performed using Recomia, a cloud-based AI platform for nuclear medicine and radiology research. The workflow for calculating residence times and whole-body effective doses, as described above, was repeated. 

Results

Patient data were obtained at three different time-points, day 2, 4, and 7 postinjecton, resulting in 18 PET/CT scans. Overall analysis time was approximately half a workday for manual segmentations compared to ≤30 min using Recomia. Whole-body effective doses differed minimally for the six patients with a median difference in received mSv/MBq of 0.49% (range 0.12 – 1.58%) according to ICRP60 and 0.52% (range 0.15 – 1.95%) according to ICRP103.

Conclusion

These first results suggest that whole-body dosimetry calculations can benefit from fast automated AI based whole-organ segmentations using Recomia. As newly developed MAbs are quickly emerging in anti-cancer therapy, whole-body effective doses for these different therapeutic agents can be assessed quickly and efficiently.

Manual vs AI based segmentation for dosimetry
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Zr-Pembro to assess PD-1 block in patients

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89Zr-pembrolizumab imaging as a non-invasive approach to assess clinical response to PD-1 blockade in cancer

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89Zr-Pembrolizumab to assess clinical PD-1 Block

89Zr-pembrolizumab imaging as a non-invasive approach to assess clinical response to PD-1 blockade in cancer

by II.C.Kok, J.S.Hooiveld, P.P.van de Donk, D.Giesen, E.L.van der Veen, M.N.Lub-de Hooge, A.H.Brouwers, T.J.N.Hiltermann, A.J.van der Wekken, L.B.M.Hijmering-Kappelle, W.Timens, S.G.Elias, G.A.P.Hospers, H.J.M.Groen, W.Uyterlinde, B.van der Hiel, J.B.Haanen, D.J.A.de Groot, M.Jalving, E.G.E.de Vries


Annals of Oncology. 2022, 33(1), 80. doi: 10.1016/j.annonc.2021.10.213

Abstract

Background
Programmed cell death protein 1 (PD-1) antibody treatment is standard of care for melanoma and non-small-cell lung cancer (NSCLC). Accurately predicting which patients will benefit is currently not possible. Tumor uptake and biodistribution of the PD-1 antibody might play a role. Therefore, we carried out a positron emission tomography (PET) imaging study with zirconium-89 (89Zr)-labeled pembrolizumab before PD-1 antibody treatment.

Patients and methods
Patients with advanced or metastatic melanoma or NSCLC received 37 MBq (1 mCi) 89Zr-pembrolizumab (∼2.5 mg antibody) intravenously plus 2.5 or 7.5 mg unlabeled pembrolizumab. After that, up to three PET scans were carried out on days 2, 4, and 7. Next, PD-1 antibody treatment was initiated. 89Zr-pembrolizumab tumor uptake was calculated as maximum standardized uptake value (SUVmax) and expressed as geometric mean. Normal organ uptake was calculated as SUVmean and expressed as a mean. Tumor response was assessed according to (i)RECIST v1.1.

Results
Eighteen patients, 11 with melanoma and 7 with NSCLC, were included. The optimal dose was 5 mg pembrolizumab, and the optimal time point for PET scanning was day 7. The tumor SUVmax did not differ between melanoma and NSCLC (4.9 and 6.5, P = 0.49). Tumor 89Zr-pembrolizumab uptake correlated with tumor response (P trend = 0.014) and progression-free (P = 0.0025) and overall survival (P = 0.026). 89Zr-pembrolizumab uptake at 5 mg was highest in the spleen with a mean SUVmean of 5.8 (standard deviation ±1.8). There was also 89Zr-pembrolizumab uptake in Waldeyer's ring, in normal lymph nodes, and at sites of inflammation.

Conclusion
89Zr-pembrolizumab uptake in tumor lesions correlated with treatment response and patient survival. 89Zr-pembrolizumab also showed uptake in lymphoid tissues and at sites of inflammation.

89Zr-Pembrolizumab to clinically assess PD-1 blockade
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Uptake of Pembrolizumab in lymphoid organs

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89Zr-pembrolizumab biodistribution is influenced by PD-1-mediated uptake in lymphoid organs

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Uptake of Pembrolizumab in lymphoid organs 

89Zr-pembrolizumab biodistribution is influenced by PD-1-mediated uptake in lymphoid organs

Elly L van der Veen, Danique Giesen, Linda Pot-de Jong, Annelies Jorritsma-Smit, Elisabeth G E De Vries, and Marjolijn N Lub-de Hooge

 

J Immunother Cancer. 2020; 8(2): e000938. doi: 10.1136/jitc-2020-000938

Abstract

Background
To better predict response to immune checkpoint therapy and toxicity in healthy tissues, insight in the in vivo behavior of immune checkpoint targeting monoclonal antibodies is essential. Therefore, we aimed to study in vivo pharmacokinetics and whole-body distribution of zirconium-89 (89Zr) labeled programmed cell death protein-1 (PD-1) targeting pembrolizumab with positron-emission tomography (PET) in humanized mice.

Methods
Humanized (huNOG) and non-humanized NOG mice were xenografted with human A375M melanoma cells. PET imaging was performed on day 7 post 89Zr-pembrolizumab (10 µg, 2.5 MBq) administration, followed by ex vivo biodistribution studies. Other huNOG mice bearing A375M tumors received a co-injection of excess (90 µg) unlabeled pembrolizumab or 89Zr-IgG4 control (10 µg, 2.5 MBq). Tumor and spleen tissue were studied with autoradiography and immunohistochemically including PD-1.

Results
PET imaging and biodistribution studies showed high 89Zr-pembrolizumab uptake in tissues containing human immune cells, including spleen, lymph nodes and bone marrow. Tumor uptake of 89Zr-pembrolizumab was lower than uptake in lymphoid tissues, but higher than uptake in other organs. High uptake in lymphoid tissues could be reduced by excess unlabeled pembrolizumab. Tracer activity in blood pool was increased by addition of unlabeled pembrolizumab, but tumor uptake was not affected. Autoradiography supported PET findings and immunohistochemical staining on spleen and lymph node tissue showed PD-1 positive cells, whereas tumor tissue was PD-1 negative.

Conclusion
89Zr-pembrolizumab whole-body biodistribution showed high PD-1-mediated uptake in lymphoid tissues, such as spleen, lymph nodes and bone marrow, and modest tumor uptake. Our data may enable evaluation of 89Zr-pembrolizumab whole-body distribution in patients.
 

Uptake of Pembrolizumab in lymphoid organs
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Bimodal PET/NIRF imaging of HER-2 tumors

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Site-specific, platform-based dual-labeled immunoconjugate for bimodal PET/NIRF imaging of HER2-positive tumors

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Biomodal PET/NIRF Imaging of her-2 tumors

Site-specific, platform-based dual-labeled immunoconjugate for bimodal PET/NIRF imaging of HER2-positive tumors

Pierre Adumeau, René Raavé, Milou Boswinkel, Sandra Heskamp, Mathieu Moreau, Claire Bernhard, Laurène Da Costa, Victor Goncalves, Franck Denat


EMIM Conference 2020

Abstract

Introduction 
Immuno-PET/NIRF imaging is very promising for cancer therapy, as it allows non-invasive localization of the tumor and its image-guided resection. The mostly used strategy to synthesize such dual-labeled conjugates relies on a double, sequential random conjugation of the fluorophore and the radionuclide/chelator with the antibody. However, the random conjugation leads to high heterogeneity and potential loss of bioactivity and these phenomena are exponentially amplified by sequential modifications. Therefore, there is a need for a better dual-labeling strategy for PET/NIRF imaging.

Results/Discussion 
The trivalent platform BCN-DFO-IR800 was obtained in a five steps synthetic route with a global yield of 5%. Trastuzumab-N3, obtained through chemoenzymatic glycoengineering, was efficiently conjugated with the trivalent platform, leading to trastss-DFO/IR800 with a degree of labeling (DOL) of 2.0 (theoretical maximum). Trastrd-DFO/IR800 was synthesized with comparable DOL for the sake of comparison.
Radiolabeling of the conjugates with 89Zr yielded the radioconjugates with high yield, purity and specific activity (RCY >95%, RCP >99%, SA >50 MBq/mg).
The site-specific conjugate displayed lesser aggregation over time than its random cousin (after 7 days in PBS: 5.0±0.1 % vs 12.7±5.2 % for trastss-DFO/IR800 and trastrd-DFO/IR800, respectively). Fluorescence intensity of the site-specific conjugate also showed an improved stability compared to the random conjugate, the first displaying 90±1 % of the initial fluorescence intensity after 7 days in PBS, with only 25±3 % for trastrd-DFO/IR800.

Conclusion 
This is the first example of a platform-based, site-specific PET/NIRF conjugate. This strategy gives complete control over the dual-labeling of antibody. The preliminary results have demonstrated the in vitro superiority of our conjugate over the classical random bimodal conjugate. We expect these results to translate into a superior in vivo behavior of the site-specific conjugate. In vivo experiment results will be presented at the conference.
 

Bimodal PET/NIRF Imaging of HER-2 Tumors
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Development of IL2 derived PET tracer

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Development and Evaluation of Interleukin-2–Derived Radiotracers for PET Imaging of T Cells in Mice

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IL2 PET Tracers for imaging mouse T-cells

Development and Evaluation of Interleukin-2–Derived Radiotracers for PET Imaging of T Cells in Mice

Elly L. van der Veen, Frans V. Suurs, Frederik Cleeren, Guy Bormans, Philip H. Elsinga, Geke A.P. Hospers, Marjolijn N. Lub-de Hooge, Elisabeth G.E. de Vries, Erik F.J. de Vries and Inês F. Antunes

Journal of Nuclear Medicine Sept. 2020, 6(9) 1355-1360; DOI:10.2967/jnumed.119.238782

Abstract

Recently, N-(4-18F-fluorobenzoyl)-interleukin-2 (18F-FB-IL2) was introduced as a PET tracer for T cell imaging. However, production is complex and time-consuming. Therefore, we developed 2 radiolabeled IL2 variants, namely aluminum 18F-fluoride-(restrained complexing agent)-IL2 (18F-AlF-RESCA-IL2) and 68Ga-gallium-(1,4,7-triazacyclononane-4,7-diacetic acid-1-glutaric acid)-IL2 (68Ga-Ga-NODAGA-IL2), and compared their in vitro and in vivo characteristics with 18F-FB-IL2. 

Methods: Radiolabeling of 18F-AlF-RESCA-IL2 and 68Ga-Ga-NODAGA-IL2 was optimized, and stability was evaluated in human serum. Receptor binding was studied with activated human peripheral blood mononuclear cells (hPBMCs). Ex vivo tracer biodistribution in immunocompetent BALB/cOlaHsd (BALB/c) mice was performed at 15, 60, and 90 min after tracer injection. In vivo binding characteristics were studied in severe combined immunodeficient (SCID) mice inoculated with activated hPBMCs in Matrigel. Tracer was injected 15 min after hPBMC inoculation, and a 60-min dynamic PET scan was acquired, followed by ex vivo biodistribution studies. Specific uptake was determined by coinjection of tracer with unlabeled IL2 and by evaluating uptake in a control group inoculated with Matrigel only. 

Results: 68Ga-Ga-NODAGA-IL2 and 18F-AlF-RESCA-IL2 were produced with radiochemical purity of more than 95% and radiochemical yield of 13.1% ± 4.7% and 2.4% ± 1.6% within 60 and 90 min, respectively. Both tracers were stable in serum, with more than 90% being intact tracer after 1 h. In vitro, both tracers displayed preferential binding to activated hPBMCs. Ex vivo biodistribution studies on BALB/c mice showed higher uptake of 18F-AlF-RESCA-IL2 than of 18F-FB-IL2 in liver, kidney, spleen, bone, and bone marrow. 68Ga-Ga-NODAGA-IL2 uptake in liver and kidney was higher than 18F-FB-IL2 uptake. In vivo, all tracers revealed uptake in activated hPBMCs in SCID mice. Low uptake was seen after a blocking dose of IL2 and in the Matrigel control group. In addition, 18F-AlF-RESCA-IL2 yielded the highest-contrast PET images of target lymph nodes. 

Conclusion: Production of 18F-AlF-RESCA-IL2 and 68Ga-Ga-NODAGA-IL2 is simpler and faster than that of 18F-FB-IL2. Both tracers showed good in vitro and in vivo characteristics, with high uptake in lymphoid tissue and hPBMC xenografts.

IL2 PET TRACERS FOR IMAGING MOUSE T-CELLS
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