Development of ¹¹¹In-DTPA-human polyclonal antibody complex for long-term inflammation/infection detection

Human polyclonal antibody (HIgG) was successively labeled with ¹¹¹In-indium chloride after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of solid DTPA-dianhydride (0.1-0.3 mg) to 100 μl of the HIgG solution (0.2-0.4 mg/ml) at pH = 6 in phosphate buffer media at 25°C with continuous stirring for 30 min. Radio-thin-layer chromatography showed an overall radiochemical yield of 96-99% at optimized conditions (specific activity = 300-500 MBq/mg, radiochemical purity >98%). The final isotonic ¹¹¹In-DTPA-HIgG complex was checked by radio-TLC to ensure the formation of only one species followed by filtration through a 0.22 μ filter. Preliminary long-term in vivo studies in turpentine-oil induced inflammation in rat model was performed to determine late complex distribution of the radioimmunoconjugate. The target/skin and target/blood ratios were 27 and 51 after 24 h, and 23 and 51 after 110 h, showing a high selectivity of the radiopharmaceutical for inflammatory lesions.