p-Isothiocyanatobenzyl-desferrioxamine: a new bifunctional chelate for facile radiolabeling of monoclonal antibodies with zirconium-89 for immuno-PET imaging

Abstract

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.

Positive Progress in ImmunoPET—Not Just a Coincidence

“…2 As mentioned in the preceding section, the physical half-life (t 1/2 ) of the radionuclide should be matched to the biological half-life of the protein to which it is being conjugated. For example, the short-lived (t 1/2 ¼ 110 minutes) 18 F pairs well with affibodies and diabodies, whereas the longer-lived (t 1/2 ¼ 100.2 hours) 124 I is typically more appropriate for intact antibodies. Success has been seen with unconventional pairings, however, resulting in many comparison studies involving different combinations of radionuclides and targeting molecules.…”

“…The extremely short half-life (110 minutes) of 18 F precludes its use for labeling of large targeting molecules, but makes the radionuclide an ideal match for smaller diabodies and affibodies. The fact that 18 F is often more readily available than other positron emitters because of its routine use in the clinical setting, and the ability to perform same-day PET imaging with 18 F-labeled probes make diabodies and affibodies labeled with 18 F two new exciting classes of imaging agents.…”

“…In this study, both high radiochemical purity (>99%) and high specific activity (470-1195 Ci/mmol zirconium) were achieved. On the radiolabeling side, Perk et al 18 have accomplished easier and faster 89 Zr labeling by using a novel chelate. In a previous study, Verel et al 19 modified desferrioxamine B (Df ) to produce tetrafluorophenol-Nsuccinyldesferal (TFP-N-sucDf ).…”

“…5 Additional factors to consider when choosing a radionuclide include cost and accessibility. Because 18 F is the most commonly used positron emitter in the clinical setting, it is often readily available. Because of its short half-life, however, 18 F is not a feasible option if the cyclotron is not on the same site as or close to the radiolabeling and imaging facilities.…”

“…Because 18 F is the most commonly used positron emitter in the clinical setting, it is often readily available. Because of its short half-life, however, 18 F is not a feasible option if the cyclotron is not on the same site as or close to the radiolabeling and imaging facilities. Longer-lived radioisotopes that are produced commercially offer the advantage of transportation from remote locations, but unfortunately availability is sometimes limited.…”