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% radiochemica l purity and a specific activity of 370 MBq/mg employing a molar ratio of D TPA-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. P harmacokinetic data of Sm-153(III)DTPA-bis-biotin in normal mice showed tha t 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 ur ine. To have further evidence which could sustain that Sm-153(III)DTPA-bis- biotin is stable in solution as a real coordination complex, Sm-152(III)DTP A-bis-biotin was obtained in macroscopic quantities and its characterizatio n was done by IR, TGA, and conductivity measurements. The results indicated that the complex was chemically pure, where the Sm3+ 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 DT PA-bis-biotin and the Sm(III)DTPA-bis-biotin molecules were done. According ly, the coordination sphere of Sm(III) was totally satisfied with nitrogen and oxygen donors; the best coordination number was 9. The conformation geo metry of both compounds is presented.