Preparation and pharmacokinetics of samarium(III)-153-labeled DTPA-bis-biotin. Characterization and theoretical studies of the samarium(III)-152 conjugate

The complex(153)Sm(III)DTPA-bis-biotin was prepared with a 99% radiochemical purity and a specific activity of 370 MBq/mg employing a molar ratio of DTPA-bis-biotin/Sm from 2 to 4 at pH 8.0. In vitro studies demonstrated that the complex is stable after dilution in saline and in human serum. Avidity of labeled biotin for avidin was not affected by the labeling procedure. Pharmacokinetic data of (153)Sm(III)DTPA-bis-biotin in normal mice showed that blood clearance is biexponential during the time interval from 0 to 24 h and that 3 h postinjection 92 +/- 4.32% of the dose is eliminated in the urine. To have further evidence which could sustain that (153)Sm(III)DTPA-bis-biotin is stable in solution as a real coordination complex, (152)Sm(III)DTPA-bis-biotin was obtained in macroscopic quantities and its characterization was done by IR, TGA, and conductivity measurements. The results indicated that the complex was chemically pure, where the Sm(3+) ion is neutralized by three carboxylate groups of the DTPA-bis-biotin ligand and coordinated to it. Using the Force Field method followed by ab initio calculations, the DTPA-bis-biotin and the Sm(III)DTPA-bis-biotin molecules were done. Accordingly, the coordination sphere of Sm(III) was totally satisfied with nitrogen and oxygen donors; the best coordination number was 9. The conformation geometry of both compounds is presented.

Preparation, biodistribution, and dosimetry of 188Re-labeled MoAb ior cea1 and its F(ab')2 fragments by avidin-biotin strategy

The biotinylated monoclonal antibody (MoAb) ior cea1 and its F(ab')2 fragments were labeled with Re-188 by combination of avidin-biotin strategy. 188Re-MoAb, 188Re-MoAb-biotin, 188Re-F(ab')2, and 188Re-F(ab')2-biotin preparations were produced for these studies with specific activities of 1.30+/-0.18 GBq/mg and from instant freeze-dried kit formulations using ethane-1-hydroxy-1,1-diphosphonic acid (EHDP) as a weak competing ligand. There were no significant differences (p > 0.05) between the biodistribution in mice of biotinylated and unbiotinylated 188Re-labeled immunoconjugates. When avidin was injected as a chase after injection of 188Re-MoAb-biotin or 188Re-F(ab')2-biotin, the blood radioactivity level decreased approximately 75% (cumulated activity) and the effective dose decreased almost 25% with respect to that of the radioimmunoconjugates in which the chase effect was not used. Our results suggest that 188Re-labeled biotinylated MoAb ior ceal and its F(ab')2 fragments prepared by this method are stable complexes in vivo.