title: Synthesis, metal chelate stability studies, and enzyme digestion of a peptide-linked DOTA derivative and its corresponding radiolabeled immunoconjugates.
abstract: By directly coupling a tetrapeptide to DOTA through an amide bond, we synthesized a novel DOTA derivative, DOTA-glycylglycylglycyl-L-p-nitrophenylalanine amide. We converted this new precursor bifunctional chelating agent to DOTA-glycylglycylglycyl-L-p-isothiocyanatophenylalanine++ + and conjugated it to monoclonal antibody Lym-1. Serum stability studies show that the radiolabeled conjugates are kinetically inert under physiological conditions. The rates of loss of radiometals in human serum are 0.1 +/- 0.1% per day for InIII, 0.02 +/- 0.15% per day for YIII, and 0.3 +/- 0.2% per day for CuII labeled immunoconjugates. In the presence of the liver enzyme cathepsin B, an in vitro digestion of 114mIn-labeled conjugate yields a small fragment containing 114mIn. Characterization of the cleavage products shows that this liver enzyme hydrolyzes the peptide linkage before the phenylalanine residue, freeing the In-DOTA-triglycine complex from the conjugate. However, the liver enzyme cathepsin D does not cleave the linkage over the span of 7 days.
authors.affiliation: Department of Chemistry, University of California, Davis 95616-0935.
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: C F
authors.initials: CF
authors.lastname: Meares
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies / Q000737:chemistry; D002401:Cathepsin B / Q000737:chemistry; D002402:Cathepsin D / Q000737:chemistry; D002614:Chelating Agents / Q000138:chemical synthesis* / Q000494:pharmacology; D006571:Heterocyclic Compounds / Q000097:blood / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D006573:Heterocyclic Compounds, 1-Ring; D006801:Humans; D006868:Hydrolysis; D007553:Isotope Labeling; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry*
chemical_list: D000906:Antibodies; D002614:Chelating Agents; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D009842:Oligopeptides; D010455:Peptides; C083918:DOTA-glycyl-glycyl-glycyl-(4-nitrophenyl)alanine amide; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D002401:Cathepsin B; D002402:Cathepsin D