ABSTRACT
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-Aâ³) 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-Aâ³ conjugation, CHX-Aâ³-MORAb-009 conjugates with 2.4, 3.5 and 5.5 CHX-Aâ³ 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-Aâ³/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-Aâ³ showed a lower isoelectric point (pI) and lower immunoreactivity (IR) than the 2.4 CHX-Aâ³ conjugate. These differences were reflected in the biodistribution of the (111)In label. The (111)In-labeled MORAb-009 conjugated with 2.4 CHX-Aâ³ produced higher tumor uptake and lower liver and spleen uptakes than the 5.5 CHX-Aâ³ 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.
Subject(s)
Antibodies, Monoclonal/pharmacokinetics , Chelating Agents/pharmacokinetics , GPI-Linked Proteins/metabolism , Indium Radioisotopes/pharmacokinetics , Isothiocyanates/pharmacokinetics , Neoplasms, Experimental/metabolism , Pentetic Acid/analogs & derivatives , Animals , Antibodies, Monoclonal/administration & dosage , Dose-Response Relationship, Radiation , Liver/metabolism , Mesothelin , Mice , Mice, Nude , Pentetic Acid/pharmacokinetics , Spleen/metabolism , Tissue DistributionABSTRACT
The influence of age on B lymphocyte phenotype and function in DBA/2J mice was examined. The B cells of this strain express the endogenous minor lymphocyte stimulatory (Mls) retroviral superantigen (SAg) Mls-1a permitting assessment of age-related changes in cognate B cell-T cell interaction. Relative to young DBA/2J mice (< 8 months), old mice (> 17 months) had greater numbers of B cells expressing high levels of IgM and low levels of the CD11b and CD5 antigens characteristic of B-1 B cells. As measured by the T cell proliferative response to Mls, the B cells from old DBA/2J mice had reduced ability to present SAg. Upon interaction with Mls-activated T cells, old B cells secreted more IgM while young B cells made more IgG1, IgG3, and IgG2a. DBA/2J BCL functioned poorly as Mls APCs and made considerably less serum Ig. T cells from old mice exhibited a lower response to SAg and were less capable of promoting B cell differentiation. These results indicate that aging influences the cellular collaboration necessary for humoral immunity.
