Reassessment of Diethylenetriaminepentaacetic Acid (DTPA) as a Chelating Agent for Indium-111 Labeling of Polypeptides Using a Newly Synthesized Monoreactive DTPA Derivative

Abstract

Previous studies on indium-111 (111In) labeling of polypeptides and peptides using cyclic diethylenetriaminepentaacetic dianhydride (cDTPA) as a bifunctional chelating agent (BCA) have indicated that DTPA might be a useful BCA for 111In labeling of polypeptides at high specific activities when DTPA can be incorporated without inducing intra- or intermolecular cross-linking. To investigate this hypothesis, a monoreactive DTPA derivative with a maleimide group as the peptide binding site (MDTPA) was designed and synthesized. A monoclonal antibody (OST7, IgG1) was used as a model polypeptide, and conjugation of MDTPA with OST7, 111In radiolabeling of MDTPA-OST7, and the stability of 111In-MDTPA-OST7 were investigated using cDTPA and benzyl-EDTA derivatives as references. SDS-PAGE analysis demonstrated that while cDTPA induced intramolecular cross-linking, no such undesirable side reactions were observed with MDTPA. MDTPA generated 111In-labeled OST7 with high radiochemical yields at higher specific activities than those produced using cDTPA and benzyl-EDTA derivatives as the BCAs. Incubation of each 111In-labeled OST7 in human serum indicated that MDTPA generated 111In-labeled OST7 of much higher and a little lower stability than those derived from cDTPA and benzyl-EDTA derivatives, respectively. These findings indicated that the low in vivo stability of cDTPA-conjugated antibody reported previously is not attributable to low stability of 111In-DTPA but to formation of intramolecular cross-linking during cDTPA conjugation reactions. The present study also indicated that MDTPA and its precursor, the tetra-tert-butyl derivative of DTPA, would be useful BCAs for 111In radiolabeling of polypeptides that have rapid blood clearance with high specific activities.

Synthesis of a Covalent Epirubicin-(C3-amide)-Anti-HER2/neuImmunochemotherapeutic Utilizing a UV-Photoactivated Anthracycline Intermediate

“…6,39 In the preparation of some covalent immunochemotherapeutics, relatively higher anthracycline-immunoglobulin molar-incorporation-indexes results in only modest declines in immunoreactivity (e.g., 86% for a 73:1 ratio) but disproportionate declines in anti-neoplastic activity down to potency levels substantially lower than those found with nonconjugated ''free'' anthracycline. 39 However, in contrast to succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SMCC), 7,107-109 EMCH, [8][9][10]26,142,143 or PMPI 30,[110][111][112] the utilization of succinimidyl 4,4-azipentanoate allows greater flexibility for increasing the chemotherapeutic molarincorporation-index while synthesizing covalent immunochemotherapeutics without the simultaneous creation of harsher reaction conditions. Therefore the major risk of compromising the biological integrity (antigen binding avidity) of epirubicin-(C 3 -amide)-[anti-HER2/neu] synthesized with succinimidyl 4,4-azipentanoate is almost entirely associated with introducing too many chemotherapeutic moieties into the Fab antigen bindings regions of the immunoglobulin molecule.…”

Synthesis and biological evaluation ofS-[11C]methylated mercaptoimidazole piperazinyl derivatives as potential radioligands for imaging 5-HT1Areceptors by positron emission tomography (PET)

“…Secondary amine 6 was prepared by protection of the primary amine group as a trifluoroacetylamide followed by mono methylation with dimethylsulfate and subsequent removal of the amine protecting group under moderate basic conditions. 28 The overall chemical yield for the three steps was 68%.…”

Radiolabeling Strategies for Tumor-Targeting Proteinaceous Drugs

“…However Hnatowich et al overcame this by using gel chromatography in order to separate the lead product [86]. These negatives have led to the synthesis of DTPA derivatives such as tetra-t-Bu-DTPA (see Figure 6) [87] which contains only one free carboxy group, thus eliminating the possibility of forming double substituted DTPA derivatives [88]. An advantage of this BFC is its use in solid phase synthesis owing to its high solubility in a variety of solvents.…”