Imaging Experimental Pulmonary Embolism In Dogs Using ～(99m)Tc-labeled SZ51-F(ab)₂

1. Preparing a kit of ^99mTc-labeled anti-P-Selectin McAb (SZ51)for radioimmunoimaging of thrombiObjective To establish a new method for preparing a kit of ^99mTc-labeled anti-P-Selectin McAb (SZ51) for radioimmunoimaging of thrombi. Methods SZ51 was modified with 2-iminotholane and labeled with ^99mTc-GH. Labeling yield, radiochemical purity and immunoreactivity were determined by ITLC-SG, Sephadex G-25 column chromatography and ELISA, respectively. The kit was prepared in the best label conditions. Results The McAb was modified at the best ratio, and the number of free thiol groups per antibody molecule was 13. The radiolabeling rate was 90%⁹5%. The results of ELISA showed that antibody reactivity was not affected. The stability of the kit could be maintained at 4℃ for more than 3 months. Conclusion The labeling method using a commercial kit is relatively simple and quick. ^99mTc-SZ51 could be a useful tool agent for imaging diagnosis of thrombotic disease.2. Preparation of ^99mTc -labeled SZ51 for radioimmunoimagingin dogs with pulmonary embolismObjective To evaluate the value of ^99mTc-SZ51 in detecting pulmonary embolism and distinguishing the fresh and old thrombi. Methods SZ51 was modified with 2-iminotholane and labeled with ^99mTc-GH. Labeling yield, radiochemical purity and immunoreactivity were determined by ITLC-SG, Sephadex G 25 column chromatography and ELISA, respectively. The 8 dogs with pulmonary embolism were used for radioimaging. Results Using the best ratio modified McAb, 90%⁹5% radiolabeling yield was obtained. The results of ELISA showed that antibody reactivity was not affected. Radioimaging results showed that ^99mTc-SZ51 concentrated in the pulmonary embolism 1 hour after injection, and more clearly gradually within 3 hours.Quantitative analysis showed the ratios of radioactive uptake between the thrombus and surrounding lung were 5.3±0.5 in vivo imaging and 7.0±1.2 in vitro. The higher uptake was found in fresh pulmonary thrombus than in old thrombus, the ratio of them was 2.65. Conclusion 99mTc-SZ51 was an available imaging agent for detecting experimental pulmonary embolism and distinguishing the fresh and old thrombus.3. Imaging experimental pulmonary embolism in dogs using99mTc-labeled SZ51-F(ab)2Objective Using 99mTc-labeled F(ab)2 fragment of anti P-selectin monoclonal antibody (McAb) SZ51 to image experimental pulmonary embolism in dogs and to assess its value in distinguishing the fresh from old thrombi. Methods SZ51-F(ab)2 fragment was prepared from McAb SZ51 using pre-activated papain digestion and then modified with 2-iminotholane and labeled with 99rTTc-GH using ligand exchange method. Labeling yield and immunoreactivity were determined by instant thin-layer chromatography (ITLC) and enzyme linked immunosorbent assay (ELISA), respectively. Four dogs with pulmonary embolism were used for imaging. Results The yield of F(ab)2 fragment was 46.7% and radiolabeling yield was 90%⁹5%. As shown in ELISA, radio-labeled antibody retained P-selectin binding activity. One hour following intravenous injection of 99nTc-SZ51-F(ab)2, the agent appeared in the pulmonary embolism and became more clearly within 3 hours. The ratio of radioactive uptake between the thrombus and surrounding lung at 3 hours was 2.7±0.5. The uptake in fresh pulmonary thrombus (1 day old ) was higher than that in old thrombus (7 day old), and the ratio of them was 2.47. Conclusion 99mTc- SZ51-F(ab)2was an available imaging agent for detecting pulmonary embolism and distinguishing the fresh and old thrombus.