title: Tumor and organ uptake of (64)Cu-labeled MORAb-009 (amatuximab), an anti-mesothelin antibody, by PET imaging and biodistribution studies.
abstract: OBJECTIVE
  To investigate the effect of the injection dose of MORAb-009 (amatuximab, an anti-mesothelin monoclonal antibody), the tumor size and the level of shed mesothelin on the uptake of the antibody in mesothelin-positive tumor and organs by biodistribution (BD) and positron emission tomography (PET) imaging studies.
  
  
  METHODS
  2-S-(4-Isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) was conjugated to amatuximab and labeled with (64)CuCl2 in 0.25 M acetate buffer, pH4.2. The resulting (64)Cu-NOTA-amatuximab was purified with a PD 10 column. To investigate the dose effect or the effect of tumor size, the BD was performed in groups of nude mice (n=5) with mesothelin-expressing A431/H9 tumors (range, 80-300 mm(3)) one day after iv injection of (64)Cu-NOTA-amatuximab (10 μCi) containing a total amatuximab dose of 2, 30, or 60 μg. The BD and PET imaging were also investigated 3, 24 and 48 h after injecting a total dose of 30 μg (10 μCi for BD), and 2 or 60 μg (300 μCi for PET), respectively.
  
  
  RESULTS
  Comparing the results of the BDs from three different injection doses, the major difference was shown in the uptake (%ID/g) of the radiolabel in tumor, liver and blood. The tumor uptake and blood retention from 30 and 60 μg doses were greater than those from 2 μg dose, whereas the liver uptake was smaller. The BD studies also demonstrated a positive correlation between tumor size (or the level of shed mesothelin in blood) and liver uptake. However, there was a negative correlation between tumor size (or the shed mesothelin level) and tumor uptake and between tumor size and blood retention. These findings were confirmed by the PET imaging study, which clearly visualized the tumor uptake with the radiolabel concentrated in the tumor core and produced a tumor to liver ratio of 1.2 at 24h post-injection with 60 μg amatuximab, whereas the injection of 2 μg amatuximab produced a tumor to liver ratio of 0.4 at 24h post-injection.
  
  
  CONCLUSIONS
  Our studies using a nude mouse model of A431/H9 tumor demonstrated that the injection of a high amatuximab dose (30 to 60 μg) could provide a beneficial effect in maximizing tumor uptake while maintaining minimum liver and spleen uptakes of the radiolabel, and in facilitating its penetration into the tumor core.
authors: Nuclear Medicine, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, 20892, USA. Electronic address: leejaeho@mail.nih.gov.
authors: Jae-Ho
authors: JH
authors: Lee
authors: Nuclear Medicine, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, 20892, USA.
authors: Heejung
authors: H
authors: Kim
authors: Nuclear Medicine, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, 20892, USA.
authors: Zhengsheng
authors: Z
authors: Yao
authors: Nuclear Medicine, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, 20892, USA.
authors: Sung-Jin
authors: SJ
authors: Lee
authors: Positron Emission Tomography Department, Clinical Center, NIH, Bethesda, MD, 20892, USA.
authors: Lawrence P
authors: LP
authors: Szajek
authors: Morphotek, Inc., Exton, PA, 19341, USA.
authors: Luigi
authors: L
authors: Grasso
authors: Laboratory of Molecular Biology, NCI, NIH, Bethesda, MD, 20892, USA.
authors: Ira
authors: I
authors: Pastan
authors: Nuclear Medicine, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, 20892, USA. Electronic address: cpaik@mail.nih.gov.
authors: Chang H
authors: CH
authors: Paik
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism / Q000493:pharmacokinetics*; D001692:Biological Transport; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes; D058851:GPI-Linked Proteins / Q000276:immunology*; D000090204:Mesothelin; D051379:Mice; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D003301:Copper Radioisotopes; D058851:GPI-Linked Proteins; C000715528:Msln protein, mouse; C526187:amatuximab; D000090204:Mesothelin
keywords: (64)Cu labeling; Amatuximab; Antibody; Mesothelin; NOTA; Tumor targeting