High-level production of alpha-particle-emitting (211)At and preparation of (211)At-labeled antibodies for clinical use.
In vitro and in vivo studies in human glioma models suggest that the antitenascin monoclonal antibody 81C6 labeled with the 7.2-h-half-life alpha-particle emitter (211)At might be a valuable endoradiotherapeutic agent for the treatment of brain tumors. The purpose of this study was to develop methods for the production of high levels of (211)At and the radiosynthesis of clinically useful amounts of (211)At-labeled human/mouse chimeric 81C6 antibody.


METHODS
(211)At was produced through the (209)Bi(alpha, 2n)(211)At reaction using an internal target system and purified by a dry distillation process. Antibody labeling was accomplished by first synthesizing N-succinimidyl 3-[(211)At]astatobenzoate from the corresponding tri-n-butyl tin precursor and reacting it with the antibody in pH 8.5 borate buffer. Quality control procedures consisted of methanol precipitation, size-exclusion high-performance liquid chromatography (HPLC), and pyrogen and sterility assays, as well as determination of the immunoreactive fraction by a rapid procedure using a recombinant tenascin fragment coupled to magnetic beads.


RESULTS
A total of 16 antibody labeling runs were performed. Using beam currents of 50-60 microA alpha-particles and irradiation times of 1.5-4.5 h, the mean (211)At production yield was 27.75 +/- 2.59 MBq/microA.h, and the maximum level of (211)At produced was 6.59 GBq after a 4-h irradiation at 55 microA. The decay-corrected distillation yield was 67% +/- 16%. The yield for the coupling of the (211)At-labeled active ester to the antibody was 76% +/- 8%. The fraction of (211)At activity that eluted with a retention time corresponding to intact IgG on HPLC was 96.0% +/- 2.5%. All preparations had a pyrogen level of <0.125 EU/mL and were determined to be sterile. The mean immunoreactive fraction for these 16 preparations was 83.3% +/- 5.3%. Radiolysis did not interfere with labeling chemistry or the quality of the labeled antibody product.


CONCLUSIONS
These results show that it is feasible to produce clinically relevant activities of (211)At-labeled antibodies and have permitted the initiation of a phase I trial of (211)At-labeled chimeric 81C6 administered directly into the tumor resection cavities of brain tumor patients.
Zalutsky
M R
MR
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Zhao
X G
XG
Alston
K L
KL
Bigner
D
D
D000512:Alpha Particles; D000911:Antibodies, Monoclonal; D001246:Astatine; D018796:Immunoconjugates / Q000627:therapeutic use; D007553:Isotope Labeling; D016499:Radioimmunotherapy; D011993:Recombinant Fusion Proteins / Q000276:immunology; D019063:Tenascin / Q000276:immunology
D000911:Antibodies, Monoclonal; D018796:Immunoconjugates; D011993:Recombinant Fusion Proteins; D019063:Tenascin; D001246:Astatine