Preparation & Evaluation of [201Tl](III)-DTPA-HIgG for Inflammation Detection

Background: Radiolabeled polyclonal human immunoglubins are useful in the detection of inflammations. In this work a novel approach has been presented to use thallium-201 as a comlexed nuclide for the development of radioimmunoconjugates. Materials and Methods: Thallium-201 (T1/2=3.04 d) in Tl+ form was converted to Tl3+ cation in presence of O3 in 6M HCl, controlled by RTLC/gel electrophoresis methods and used in the labeling of human polyclonal antibody (HIgG) after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a HIgG pharmaceutical solution (5 mg/ml, in phosphate buffer, pH=7) to a glass tube, which was pre-coated with DTPA-dianhydride (0.01 mg) at 25C with continuous mild stirring for 30 min. Results: The final isotonic [201Tl](III)-DTPA-HIgG complex was checked by radio-TLC using several solvent systems to ensure the formation of only one species, and it was followed by filtration through a 0.22 µm filter (specific activity= 33.7 TBq/mM, radiochemical purity95%). Preliminary bio-distribution studies in normal and inflammation-bearing rats were performed. The target/skin and target/blood ratios were 4 and 6 after 28h, respectively, showing the selectivity of the radiopharmaceutical for the inflammatory lesions. Conclusion: The incorporation of Tl(III) cation into a immunoconjugate was performed using the known methods. The biodistribution of the immunocomplex was shown to be consistent with a stable complex for the detection of inflammations. Significant inflammation detection was observed for the final complex in rats with turpentine oil-induced inflammation.