Development of a Novel Long-Lived ImmunoPET Tracer for Monitoring Lymphoma Therapy in a Humanized Transgenic Mouse Model

Molecular Imaging Program at Stanford (MIPS), Department of Radiology and.
Bioconjugate Chemistry (Impact Factor: 4.51). 05/2012; 23(6). DOI: 10.1021/bc300039r
Source: PubMed


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] (t(1/2): 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).

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    • "The glycosylated phosphoprotein, CD20, is expressed on the surface of B-cell lymphomas, hairy leukemia, B-cell chronic lymphocytic leukemia, and melanoma cells. 89Zr-labeled antibodies directed against CD20 might be useful to measure and monitor the therapeutic effect of non-Hodgkin's lymphoma (NHL) therapy [18, 37]. The 89Zr-Desferrioxamine-rituximab, an antibody directed against CD20, specifically targeted the human CD20 antigen in a humanized CD20-expressing transgenic mouse model (huCD20TM). "
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    • "The anti-human GPC3 mAb (Clone 1G12, BioMosaics Inc., Burlington, VT) or non-targeting mouse IgG (Jackson ImmunoResearch, Inc.) were conjugated with desferrioxamine (DFO) and radiolabeled with 89 Zr (University of Wisconsin, Madison , WI) as previously described [27] [28]. The radiolabeled products, "
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    Biomaterials 05/2014; 35(25). DOI:10.1016/j.biomaterials.2014.04.089 · 8.56 Impact Factor
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    • "For example, the fluorine in BODIPY-FL could be exchanged for 18F for positron emission tomography (PET) imaging, or entirely replaced via bioorthogonal ligands or direct 18F attachment36373839. Alternatively, longer-lived isotopes such as Zirconium-89 could also be utilized in order to take full advantage of the probe's irreversible binding kinetics4041424344. Such molecules may be useful in clinical imaging-based tests for whole body distribution and inhibition of BTK. "
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