Effect of chelator conjugation level and injection dose on tumor and organ uptake of 111In-labeled MORAb-009, an anti-mesothelin antibody

Nucl Med Biol. 2011 Nov;38(8):1119-27. doi: 10.1016/j.nucmedbio.2011.05.003. Epub 2011 Jul 7.


Introduction: 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.

Conclusion: 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.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Antibodies, Monoclonal / administration & dosage
  • Antibodies, Monoclonal / pharmacokinetics*
  • Chelating Agents / pharmacokinetics*
  • Dose-Response Relationship, Radiation
  • GPI-Linked Proteins / metabolism*
  • Indium Radioisotopes / pharmacokinetics*
  • Isothiocyanates / pharmacokinetics*
  • Liver / metabolism
  • Mice
  • Mice, Nude
  • Neoplasms, Experimental / metabolism*
  • Pentetic Acid / analogs & derivatives*
  • Pentetic Acid / pharmacokinetics
  • Spleen / metabolism
  • Tissue Distribution


  • Antibodies, Monoclonal
  • Chelating Agents
  • GPI-Linked Proteins
  • Indium Radioisotopes
  • Isothiocyanates
  • N-(2-amino-3-(4-isothiocyanatophenyl)propyl)cyclohexane-1,2-diamine-N,N',N',N'',N''-pentaacetic acid
  • amatuximab
  • Pentetic Acid
  • mesothelin