title: Effect of chelator conjugation level and injection dose on tumor and organ uptake of 111In-labeled MORAb-009, an anti-mesothelin antibody.
abstract: BACKGROUND
  Radiolabeling of a monoclonal antibody (mAb) with a metallic radionuclide requires the conjugation of a bifunctional chelator to the mAb. The conjugation, however, can alter the physical and immunological properties of the mAb, consequently affecting its tumor-targeting pharmacokinetics. In this study, we investigated the effect of the amount of 2-(p-isothiocyanatobenzyl)-cyclohexyl-diethylenetriamine-pentaacetic acid (CHX-A″) conjugated to MORAb-009, a mAb directed against mesothelin, and the effect of MORAb dose on the biodistribution of (111)In-labeled MORAb-009.
  
  
  METHODS
  We used nude mice bearing the A431/K5 tumor as a mesothelin-positive tumor model and the A431 tumor as a mesothelin-negative control. To find the optimal level of CHX-A″ conjugation, CHX-A″-MORAb-009 conjugates with 2.4, 3.5 and 5.5 CHX-A″ molecules were investigated. To investigate the effect of injected MORAb-009 dose on neutralizing the shed mesothelin in the circulation, biodistribution studies were performed after the intravenous co-injection of (111)In-labeled MORAb-009 (2.4 CHX-A″/MORAb-009) with three different doses: 0.2, 2 and 30 μg of MORAb-009.
  
  
  RESULTS
  The tumor uptake in A431/K5 tumor was four times higher than that in A431 tumor, indicating that the tumor uptake in A431/K5 was mesothelin mediated. The conjugate with 5.5 CHX-A″ showed a lower isoelectric point (pI) and lower immunoreactivity (IR) than the 2.4 CHX-A″ conjugate. These differences were reflected in the biodistribution of the (111)In label. The (111)In-labeled MORAb-009 conjugated with 2.4 CHX-A″ produced higher tumor uptake and lower liver and spleen uptakes than the 5.5 CHX-A″ conjugate. The biodistribution studies also revealed that the tumor uptake was significantly affected by the injected MORAb-009 dose and tumor size. The 30-μg dose produced higher tumor uptake than the 0.2- and 2-μg doses, whereas the 30-μg dose produced lower liver and spleen uptakes than the 0.2-μg dose.
  
  
  CONCLUSIONS
  This study demonstrates that the number of chelate conjugation and the injected dose are two important parameters to achieve high tumor and low non-target organ uptake of (111)In-labeled MORAb-009. This study also suggests that the injected dose of mAb could be individualized based on the tumor size or the blood level of shed antigen in a patient to achieve the ideal tumor-to-organ radioactivity ratios.
authors: Radiopharmaceutical Laboratory, Division of Nuclear Medicine, Department of Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, MD 20892, USA.
authors: In Soo
authors: IS
authors: Shin
authors: Sang-Myung
authors: SM
authors: Lee
authors: Hyung Sub
authors: HS
authors: Kim
authors: Zhengsheng
authors: Z
authors: Yao
authors: Celeste
authors: C
authors: Regino
authors: Noriko
authors: N
authors: Sato
authors: Kenneth T
authors: KT
authors: Cheng
authors: Raffit
authors: R
authors: Hassan
authors: Melissa F
authors: MF
authors: Campo
authors: Earl F
authors: EF
authors: Albone
authors: Peter L
authors: PL
authors: Choyke
authors: Ira
authors: I
authors: Pastan
authors: Chang H
authors: CH
authors: Paik
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000493:pharmacokinetics*; D002614:Chelating Agents / Q000493:pharmacokinetics*; D004307:Dose-Response Relationship, Radiation; D058851:GPI-Linked Proteins / Q000378:metabolism*; D007205:Indium Radioisotopes / Q000493:pharmacokinetics*; D017879:Isothiocyanates / Q000493:pharmacokinetics*; D008099:Liver / Q000378:metabolism; D000090204:Mesothelin; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000378:metabolism*; D004369:Pentetic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D013154:Spleen / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D002614:Chelating Agents; D058851:GPI-Linked Proteins; D007205:Indium Radioisotopes; D017879:Isothiocyanates; C000715528:Msln protein, mouse; C085678:N-(2-amino-3-(4-isothiocyanatophenyl)propyl)cyclohexane-1,2-diamine-N,N',N',N'',N''-pentaacetic acid; C526187:amatuximab; D004369:Pentetic Acid; D000090204:Mesothelin