title: Preparation and in vivo evaluation of a novel stabilized linker for 211At labeling of protein.
abstract: Significant improvement of in vivo stability of 211At-labeled radioimmunoconjugates achieved upon employment of a recently reported new linker, succinimidyl N-2-(4-[211At]astatophenethyl)succinamate (SAPS), prompted additional studies of its chemistry. The 211At radiolabeling of succinimidyl N-2-(4-tributylstannylphenethyl)succinamate (1) was noted to decline after storage at -15 degrees C for greater than 6 months. Compound 1 was found to degrade via a ring closure reaction with the formation of N-2-(4-tributylstannylphenethyl)succinimide (3), and a modified procedure for the preparation of 1 was developed. The N-methyl structural analog of 1, succinimidyl N-2-(4-tributylstannylphenethyl)-N-methyl succinamate (SPEMS), was synthesized to investigate the possibility of improving the stability of reagent-protein linkage chemistry. Radiolabeling of SPEMS with 211At generates succinimidyl N-2-(4-[211At]astatophenethyl)-N-methyl succinamate (Methyl-SAPS), with yields being consistent for greater than 1 year. Radiolabelings of 1 and SPEMS with 125I generated succinimidyl N-2-(4-[125I]iodophenethyl)succinamate (SIPS) and succinimidyl N-2-(4-[125I]iodophenethyl)-N-methyl succinamate (Methyl-SIPS), respectively, and showed no decline in yields. Methyl-SAPS, SAPS, Methyl-SIPS and SIPS were conjugated to Herceptin for a comparative assessment in LS-174T xenograft-bearing mice. The conjugates of Herceptin with Methyl-SAPS or Methyl-SIPS demonstrated immunoreactivity equivalent to if not superior to the SAPS and SIPS paired analogs. The in vivo studies also revealed that the N-methyl modification resulted in a superior statinated product.
authors.affiliation: Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. vstalanov@msrce.howard.edu
authors.forename: Vladimir S
authors.initials: VS
authors.lastname: Talanov
authors.forename: Kayhan
authors.initials: K
authors.lastname: Garmestani
authors.forename: Celeste A S
authors.initials: CA
authors.lastname: Regino
authors.forename: Diane E
authors.initials: DE
authors.lastname: Milenic
authors.forename: Paul S
authors.initials: PS
authors.lastname: Plascjak
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Waldmann
authors.forename: Martin W
authors.initials: MW
authors.lastname: Brechbiel
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism* / Q000532:radiotherapy; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use; D001246:Astatine / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000532:radiotherapy; D003432:Cross-Linking Reagents / Q000737:chemistry; D004355:Drug Stability; D005079:Excipients / Q000737:chemistry; D006801:Humans; D007553:Isotope Labeling; D007554:Isotopes / Q000737:chemistry / Q000493:pharmacokinetics / Q000627:therapeutic use; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000627:therapeutic use; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; D005079:Excipients; D007554:Isotopes; D019275:Radiopharmaceuticals; D001246:Astatine