The recently reported "starburst dendrimer"1,2 and "arborol"3 systems provide unimolecular prototypes that allow for both endo-receptor and exo-supramolecular controlled molecular morphogenesis.9 This present communication describes the use
The positron emitter zirconium-89 ((89)Zr) has very attractive properties for positron emission tomography (PET) imaging of intact monoclonal antibodies (mAbs) using immuno-PET. This protocol describes the step-by-step procedure for the facile radiolabeling of mAbs or other proteins with (89)Zr using p-isothiocyanatobenzyl-desferrioxamine (Df-Bz-NCS). First, Df-Bz-NCS is coupled to the lysine-NH(2) groups of a mAb at pH 9.0 (pre-modification), followed by purification using gel filtration. Next, the pre-modified mAb is labeled at room temperature by the addition of [(89)Zr]Zr-oxalic acid solution followed by purification using gel filtration. The entire process of pre-modification, radiolabeling and purification steps will take about 2.5 h.
PurposeImmuno-PET is an emerging imaging tool for the selection of high potential antibodies (mAbs) for imaging and therapy. The positron emitter zirconium-89 (89Zr) has attractive characteristics for immuno-PET with intact mAbs. Previously, we have described a multi-step procedure for stable coupling of 89Zr to mAbs via the bifunctional chelate (BFC) tetrafluorophenol-N-succinyldesferal (TFP-N-sucDf). To enable widespread use of 89Zr-immuno-PET, we now introduce the novel BFC p-isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS) and compare its performance in 89Zr-immuno-PET with the reference BFC TFP-N-sucDf.MethodsThree mAbs were premodified with Df-Bz-NCS and labeled with 89Zr at different pHs to assess the reaction kinetics and robustness of the radiolabeling. Stability of both 89Zr-Df-Bz-NCS- and 89Zr-N-sucDf-conjugates was evaluated in different buffers and human serum. Comparative biodistribution and PET studies in tumor-bearing mice were undertaken.ResultsThe selected conjugation conditions resulted in a chelate:mAb substitution ratio of about 1.5:1. Under optimal radiolabeling conditions (pH between 6.8–7.2), the radiochemical yield was >85% after 60 min incubation at room temperature, resulting in radioimmunoconjugates with preserved integrity and immunoreactivity. The new radioimmunoconjugate was very stable in serum for up to 7 days at 37°C, with <5% 89Zr release, and was equally stable compared to the reference conjugate when stored in the appropriate buffer at 4°C. In biodistribution and imaging experiments, the novel and the reference radioimmunoconjugates showed high and similar accumulation in tumors in nude mice.ConclusionsThe novel Df-Bz-NCS BFC allows efficient and easy preparation of optimally performing 89Zr-labeled mAbs, facilitating further exploration of 89Zr-immuno-PET as an imaging tool.
Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 mM(-1) s(-1) at pH 9 to 7.0 mM(-1) s(-1) at pH 5 as a result of acid-catalyzed dissociation of the nitrophenol from the lanthanide. The nitrophenol group in Gd(NP-DO3AM) does not dissociate from the metal center even at pH 5; therefore, the very modest increase in relaxivity in this complex must be ascribed to an increase in prototropic exchange rate of the bound water and/or phenolic protons.
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