title: 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).
authors.affiliation: Molecular Imaging Program at Stanford (MIPS), Department of Radiology and.
authors.forename: Arutselvan
authors.initials: A
authors.lastname: Natarajan
authors.forename: Frezghi
authors.initials: F
authors.lastname: Habte
authors.forename: Sanjiv S
authors.initials: SS
authors.lastname: Gambhir
mesh_terms: D000818:Animals; D058846:Antibodies, Monoclonal, Murine-Derived / Q000737:chemistry / Q000493:pharmacokinetics; D018951:Antigens, CD20 / Q000235:genetics; D045744:Cell Line, Tumor; D003676:Deferoxamine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D015870:Gene Expression; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000493:pharmacokinetics; D017879:Isothiocyanates / Q000737:chemistry / Q000493:pharmacokinetics; D008223:Lymphoma / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000235:genetics / Q000628:therapy; D051379:Mice; D008819:Mice, Nude; D008822:Mice, Transgenic; D049268:Positron-Emission Tomography / Q000379:methods*; D000069283:Rituximab; D014018:Tissue Distribution; D015040:Zirconium / Q000737:chemistry / Q000493:pharmacokinetics
chemical_list: C549125:4-isothiocyanatobenzyl-desferrioxamine; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D018796:Immunoconjugates; D017879:Isothiocyanates; D000069283:Rituximab; D015040:Zirconium; D003676:Deferoxamine