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Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model.

ABSTRACT: Positron emission tomography (PET) is an attractive imaging tool to localize and quantify tracer biodistribution. ImmunoPET with an intact mAb typically requires two to four days to achieve optimized tumor-to-normal ratios. Thus, a positron emitter with a half-life of two to four days such as zirconium-89 [(89)Zr] (t1/2: 78.4 h) is ideal. We have developed an antibody-based, long-lived immunoPET tracer (89)Zr-Desferrioxamine-p-SCN (Df-Bz-NCS)-rituximab (Zr-iPET) to image tumor for longer durations in a humanized CD20-expressing transgenic mouse model. To optimize the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab, multiple radiolabelings were performed. Radiochemical yield, purity, immunoreactivity, and stability assays were carried out to characterize the Zr-iPET for chemical and biological integrity. This tracer was used to image transgenic mice that express the human CD20 on their B cells (huCD20TM). Each huCD20TM mouse received a 7.4 MBq/dose. One group (n = 3) received a 2 mg/kg predose (blocking) of cold rituximab 2 h prior to (89)Zr-iPET; the other group (n = 3) had no predose (nonblocking). Small animal PET/CT was used to image mice at 1, 4, 24, 48, 72, and 120 h. Quality assurance of the (89)Zr-iPET demonstrated NCS-Bz-Df: antibody ratio (c/a: 1.5 ± 0.31), specific activity (0.44-1.64 TBq/mol), radiochemical yield (>70%), and purity (>98%). The Zr-iPET immunoreactivity was >80%. At 120 h, Zr-iPET uptake (% ID/g) as mean ± STD for blocking and nonblocking groups in spleen was 3.2 ± 0.1% and 83.3 ± 2.0% (p value <0.0013.). Liver uptake was 1.32 ± 0.05% and 0.61 ± 0.001% (p value <0.0128) for blocking and nonblocking, respectively. The small animal PET/CT image shows the spleen specific uptake of Zr-iPET in mice at 120 h after tracer injection. Compared to the liver, the spleen specific uptake of Zr-iPET is very high due to the expression of huCD20. We optimized the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab. These radioimmunoconjugate lots were stable up to 5 days in serum in vitro. The present study showed that (89)Zr is well-suited for mAbs to image cancer over an extended period of time (up to 5 days).

SUBMITTER: Natarajan A

PROVIDER: S-EPMC3459285 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model.

Natarajan Arutselvan A Habte Frezghi F Gambhir Sanjiv S SS

Bioconjugate chemistry 20120611 6

Positron emission tomography (PET) is an attractive imaging tool to localize and quantify tracer biodistribution. ImmunoPET with an intact mAb typically requires two to four days to achieve optimized tumor-to-normal ratios. Thus, a positron emitter with a half-life of two to four days such as zirconium-89 [(89)Zr] (t1/2: 78.4 h) is ideal. We have developed an antibody-based, long-lived immunoPET tracer (89)Zr-Desferrioxamine-p-SCN (Df-Bz-NCS)-rituximab (Zr-iPET) to image tumor for longer duratio ...[more]

PMID: 22621257

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Project description:BackgroundThere are remarkable genetic differences between animal major histocompatibility complex (MHC) systems and the human leukocyte antigen (HLA) system. HLA transgenic humanized mouse model systems offer a much better method to study the HLA-A-related principal mechanisms for vaccine development and HLA-A-restricted responses against infection in human.MethodsA recombinant gene encoding the chimeric HLA-A30 monochain was constructed. This HHD molecule contains the following: α1-α2 domains of HLA-A30, α3 and cytoplasmic domains of H-2Db , linked at its N-terminus to the C-terminus of human β2m by a 15-amino-acid peptide linker. The recombinant gene encoding the chimeric HLA-A30 monochain cassette was introduced into bacterial artificial chromosome (BAC) CH502-67J3 containing the HLA-A01 gene locus by Red-mediated homologous recombination. Modified BAC CH502-67J3 was microinjected into the pronuclei of wild-type mouse oocytes. This humanized mouse model was further used to assess the immune responses against influenza A virus (H1N1) pdm09 clinically isolated from human patients. Immune cell population, cytokine production, and histopathology in the lung were analyzed.ResultsWe describe a novel human β2m-HLA-A30 (α1α2)-H-2Db (α3 transmembrane cytoplasmic) (HHD) monochain transgenic mouse strain, which contains the intact HLA-A01 gene locus including 49 kb 5'-UTR and 74 kb 3'-UTR of HLA-A01*01. Five transgenic lines integrated into the large genomic region of HLA-A gene locus were obtained, and the robust expression of exogenous transgene was detected in various tissues from A30-18# and A30-19# lines encompassing the intact flanking sequences. Flow cytometry revealed that the introduction of a large genomic region in HLA-A gene locus can influence the immune cell constitution in humanized mice. Pdm09 infection caused a similar immune response among HLA-A30 Tg humanized mice and wild-type mice, and induced the rapid increase of cytokines, including IFN-γ, TNF-α, and IL-6, in both HLA-A30 humanized Tg mice and wild-type mice. The expression of HLA-A30 transgene was dramatically promoted in tissues from A30-9# line at 3 days post-infection (dpi).ConclusionsWe established a promising preclinical research animal model of HLA-A30 Tg humanized mouse, which could accelerate the identification of novel HLA-A30-restricted epitopes and vaccine development, and support the study of HLA-A-restricted responses against infection in humans.

Project description:PurposeIt is well known that cancers exploit immune checkpoints (programmed death 1 receptor (PD-1) and its ligand (PD-L1)) to evade anti-tumor immune responses. Although immune checkpoint (IC) blockade is a promising approach, not all patients respond. Hence, imaging of tumor-infiltrating lymphocytes (TILs) is of high specific interest, as they are known to express PD-1 during activation and subsequent exhaustion in the tumor microenvironment and are thought to be potentially predictive of therapeutic responses to IC blockade.ProceduresWe developed immune-tracers for positron emission tomography (PET) to image hPD-1 status of human peripheral blood mononuclear cells (hPBMCs) adoptively transferred to NOD-scid IL-2Rγnull (NSG) mice (hNSG) bearing A375 human skin melanoma tumors. The anti-PD-1 human antibody (IgG; keytruda) was labeled with either Zr-89 or Cu-64 radiometals to image PD-1-expressing human TILs in vivo.Results[89Zr] Keytruda (groups = 2; NSG-ctl (control) and hNSG-nblk (non-blocking), n = 3-5, 3.2 ± 0.4 MBq/15-16 μg/200 μl) and [64Cu] Keytruda (groups = 3; NSG-ctl, NSG-blk (blocking), and hNSG-nblk; n = 4, 7.4 ± 0.4 MBq /20-25 μg/200 μl) were administered in mice. PET-CT scans were performed over 1-144 h ([89Zr] Keytruda) and 1-48 h ([64Cu] Keytruda) on mice. hNSG mice exhibited a high tracer uptake in the spleen, lymphoid organs and tumors. At 24 h, human TILs homing into melanoma of hNSG-nblk mice exhibited high signal (mean %ID/g ± SD) of 3.8 ± 0.4 ([89Zr] Keytruda), and 6.4 ± 0.7 ([64Cu] Keytruda), which was 1.5- and 3-fold higher uptake compared to NSG-ctl mice (p = 0.01), respectively. Biodistribution measurements of hNSG-nblk mice performed at 144 h ([89Zr] Keytruda) and 48 h ([64Cu] Keytruda) p.i. revealed tumor to muscle ratios as high as 45- and 12-fold, respectively.ConclusionsOur immunoPET study clearly demonstrates specific imaging of human PD-1-expressing TILs within the tumor and lymphoid tissues. This suggests these anti-human-PD-1 tracers could be clinically translatable to monitor cancer treatment response to IC blockade therapy.

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Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model.

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Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model.

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