title: Poly(ethylene glycol)-conjugated anti-EGF receptor antibody C225 with radiometal chelator attached to the termini of polymer chains.
abstract: Several biological barriers, including significant liver uptake, limit the clinical application of radiolabeled antibodies in radioimmunoscintigraphy. Here, a general approach is described for radiolabeling of monoclonal antibodies conjugated with poly(ethylene glycol) (PEG). This strategy is demonstrated with C225, a monoclonal antibody directed against epidermal growth factor (EGF) receptor. We synthesized a heterofunctional PEG with one end attached to a radiometal chelator, diethylenetriaminepentaacetic acid (DTPA), and the other end to a protected thiol group, S-acetylthioacetate. After a deprotection step, the resulting DTPA-PEG-SH was conjugated to maleimide-activated C225 to yield DTPA-PEG-C225 conjugate. Characterization of DTPA-PEG-C225 with immunoprecipitation and Western blot analysis revealed that the conjugate was biologically active in binding to the EGF receptor in A431 cells. Competitive EGF receptor binding assay in MDA-MB-468 cells showed that DTPA-PEG-C225, with up to 60% of the amino groups in C225 substituted, retained 66% of C225's binding affinity. Moreover, DTPA-PEG-C225 with increasing degrees of NH(2) substitution from 20% to 70% retained the activity of C225 to induce apoptosis in DiFi cells. More importantly, DTPA-PEG-C225 demonstrated less nonspecific interaction than DTPA-C225. Pharmacokinetic analysis using (111)In-labeled compounds revealed narrower steady-state distribution of (111)In-DTPA-PEG-C225 than (111)In-DTPA-C225, probably due to reduced nonspecific binding of PEG-modified antibody to tissues. The terminal half-life (t(1/2,)(gamma)) of (111)In-DTPA-PEG-C225, 21.1 h, was shorter than that of (111)In-DTPA-C225, 52.9 h. These data suggest that (111)In-DTPA-PEG-C225 may provide better imaging characteristics than (111)In-DTPA-C225, and that using PEG as a linker between the monoclonal antibody and DTPA may be a promising strategy in optimizing the imaging characteristics of immunoscintigraphic agents.
authors.affiliation: Department of Diagnostic Radiology and Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: X
authors.initials: X
authors.lastname: Wen
authors.forename: Q P
authors.initials: QP
authors.lastname: Wu
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: Z
authors.initials: Z
authors.lastname: Fan
authors.forename: C
authors.initials: C
authors.lastname: Charnsangavej
authors.forename: S
authors.initials: S
authors.lastname: Wallace
authors.forename: D
authors.initials: D
authors.lastname: Chow
authors.forename: C
authors.initials: C
authors.lastname: Li
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology; D001666:Binding Sites, Antibody / Q000502:physiology; D001667:Binding, Competitive / Q000502:physiology; D000068818:Cetuximab; D002614:Chelating Agents / Q000737:chemistry; D066246:ErbB Receptors / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry*; D004369:Pentetic Acid / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D016719:Radioimmunodetection; D012680:Sensitivity and Specificity; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D002614:Chelating Agents; D007205:Indium Radioisotopes; D011108:Polymers; D011092:Polyethylene Glycols; D004369:Pentetic Acid; D066246:ErbB Receptors; D000068818:Cetuximab