RT Journal Article SR Electronic T1 Clinical-Scale Radiolabeling of a Humanized Anticarcinoembryonic Antigen Monoclonal Antibody, hMN-14, with Residualizing 131I for Use in Radioimmunotherapy JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 153 OP 159 VO 46 IS 1 A1 Serengulam V. Govindan A1 Gary L. Griffiths A1 Rhona Stein A1 Philip Andrews A1 Robert M. Sharkey A1 Hans J. Hansen A1 Ivan D. Horak A1 David M. Goldenberg YR 2005 UL http://jnm.snmjournals.org/content/46/1/153.abstract AB Radiolabeling of monoclonal antibodies (mAbs) with an intracellularly trapped form of 131I (residualizing 131I) involves radioiodinating a small molecular entity, conjugating it to the mAb, and purification. Column purifications are impractical during procedures involving multi-gigabecquerel levels of radioactivity. The goal of this study was to develop a simple, remote, “1-pot” method of radiolabeling and purification for the scaled-up radioiodination of a humanized anti–carcinoembryonic antigen (CEA) mAb, humanized MN-14 (hMN-14; labetuzumab), with an optimized residualizing 131I moiety, 131I-IMP-R4. IMP-R4 is MCC-Lys(MCC)-Lys(X)-d-Tyr-d-Lys(X)-OH, where MCC is 4-(N-maleimidomethyl)-cyclohexane-1-carbonyl and X is 1-((4-thiocarbonylamino)benzyl)-diethylenetriaminepentaacetic acid. Methods: An IODO-GEN-based remote labeling system was used. IMP-R4 was radioiodinated (0.13 μmol per 3.7 GBq of 131I) at a pH of 7.0–7.4 and conjugated to disulfide-reduced hMN-14 after quenching of unused reactive 131I. The product was purified by stirring for 5 min with a 20% (w/v) suspension of an anion-exchange resin and sterilely filtered into a sealed vial. Human serum albumin was added at a final concentration of 1%–2.5%. Immunoreactivity was determined by mixing with CEA and determining the complexation level by size-exclusion high-pressure liquid chromatography. Two control radiolabelings, either with unreduced hMN-14 or with IMP-R4 omitted, also were performed. Results: In 18 radiolabelings with 131I in the range of 2.04–4.81 GBq (55–130 mCi), yields of 59.9% ± 7.9% (mean ± SD) at specific activities of 200 ± 26 MBq/mg (5.4 ± 0.7 mCi/mg) were obtained, with ≥95% of the radioactivity being associated with hMN-14 and with ≤4% aggregation. Similar yields were obtained in a subset of radiolabelings (n = 7) with >3.7 GBq of 131I. The immunoreactivities of the preparations were typically >95%. Nonspecific incorporation in the absence of IMP-R4 was 0.5%, whereas that obtained with unreduced IgG was ∼8%, possibly because of conjugation of IMP-R4 at lysine sites. The process also removed >99% of the quenching reagent used. Radiolabelings performed with freshly prepared solutions or lyophilized preparations produced similar yields, a result that suggested the option for a single-use kit design. Conclusion: Efficient removal of 131I-IMP-R4 and quenched 131I by 5 min of stirring with anion-exchange resin renders a multi-gigabecquerel–level preparation of 131I-IMP-R4-hMN-14 safe, convenient, and practical.