Evaluation of an internalizing monoclonal antibody labeled using N-succinimidyl 3-[131I]iodo-4-phosphonomethylbenzoate ([131I]SIPMB), a negatively charged substituent bearing acylation agent.
Monoclonal antibodies such as L8A4, reactive with the epidermal growth factor receptor variant III, internalize after receptor binding resulting in proteolytic degradation by lysosomes. Labeling internalizing mAbs requires the use of methodologies that result in the trapping of labeled catabolites in tumor cells after intracellular processing. Herein we have investigated the potential utility of N-succinimidyl-3-[131I]iodo-4-phosphonomethylbenzoate ([131I]SIPMB), an acylation agent that couples the corresponding negatively charged acid [131I]IPMBA to the protein, for this purpose. Biodistribution studies demonstrated that [131I]IPMBA cleared rapidly from normal tissues and exhibited thyroid levels < or =0.1% injected dose, consistent with a low degree of dehalogenation. Biodistribution experiments in athymic mice bearing subcutaneous D-256 human glioma xenografts were performed to compare L8A4 labeled using [131I]SIPMB to L8A4 labeled with 125I using both the analogous positively charged acylation agent N-succinimidyl-4-guanidinomethyl-3-[125I]iodobenzoate ([125I]SGMIB) and Iodogen. Tumor uptake of [131I]SIPMB-L8A4 (41.9+/-3.5% ID/g) was nearly threefold that of L8A4 labeled using Iodogen (14.0+/-1.1% ID/g) after 2 days, and tumor to tissue ratios remained uniformly high throughout with [131I]SIPMB-L8A4. Thyroid uptake increased for the Iodogen labeled mAb (3.55+/-0.36 %ID at 5 days) whereas that of [131I]SIPMB labeled mAb remained low (0.21+/-0.04% ID at 5 days). In the second biodistribution, L8A4 labeled using [131I]SIPMB and [125I]SGMIB showed no difference in normal tissue uptake and had nearly identical tumor uptake ([131I]SIPMB, 41.8+/-14.2% ID/g; [125I]SGMIB, 41.6+/-15.8% ID/g, at 4 days). These results suggest that [131I]SIPMB may be a viable acylation agent for the radioiodination of internalizing mAbs.
Shankar
Sriram
S
Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USA.
Vaidyanathan
Ganesan
G
Affleck
Donna J
DJ
Peixoto
Katia
K
Bigner
Darell D
DD
Zalutsky
Michael R
MR
D000215:Acylation; D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D001565:Benzoates / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D005240:Feasibility Studies; D005260:Female; D005910:Glioma / Q000378:metabolism* / Q000532:radiotherapy; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009928:Organ Specificity; D016499:Radioimmunotherapy / Q000379:methods*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000627:therapeutic use; D013388:Succinimides / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D001565:Benzoates; C478639:N-succinimidyl 3-((131)I)iodo-4-phosphonomethylbenzoate; D019275:Radiopharmaceuticals; D013388:Succinimides