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).
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Authors | Arutselvan Natarajan, Frezghi Habte, Sanjiv S Gambhir |
Journal | Bioconjugate chemistry
(Bioconjug Chem)
Vol. 23
Issue 6
Pg. 1221-9
(Jun 20 2012)
ISSN: 1520-4812 [Electronic] United States |
PMID | 22621257
(Publication Type: Journal Article, Research Support, N.I.H., Extramural)
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Chemical References |
- 4-isothiocyanatobenzyl-desferrioxamine
- Antibodies, Monoclonal, Murine-Derived
- Antigens, CD20
- Immunoconjugates
- Isothiocyanates
- Rituximab
- Zirconium
- Deferoxamine
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Topics |
- Animals
- Antibodies, Monoclonal, Murine-Derived
(chemistry, pharmacokinetics)
- Antigens, CD20
(genetics)
- Cell Line, Tumor
- Deferoxamine
(analogs & derivatives, chemistry, pharmacokinetics)
- Gene Expression
- Humans
- Immunoconjugates
(chemistry, pharmacokinetics)
- Isothiocyanates
(chemistry, pharmacokinetics)
- Lymphoma
(diagnosis, diagnostic imaging, genetics, therapy)
- Mice
- Mice, Nude
- Mice, Transgenic
- Positron-Emission Tomography
(methods)
- Rituximab
- Tissue Distribution
- Zirconium
(chemistry, pharmacokinetics)
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