Radioimmunoscintigraphy of experimental artery thrombi in rabbits with 99mTc labeled monoclonal anti-GPIII a antibody

Objectives To label monoclonal anti-GP III a antibody (SZ21) with ^99mTc and evaluate the value of ^99mTc-SZ21 for detecting thrombi in vivo.

Methods SZ21 was modified with 2-iminotholane and labeled with ^99mTc-GH and radiochemical purity was determined by ITLC-SG. Thrombi were induced in the right femoral arteries of 8 rabbits. ^99mTc-SZ21 was injected via ear edge vein in 5 rabbits. As control, ^99mTc-GH was administered in 3 rabbit. Static images with 500 Kcts per image were acquired in 256×256 matrix from 30min up to 3h after injection. Irregularly shaped ROIs were drawn on the images to encompass the area of thrombus. Similarly sized ROIs were applied to the adjacent background muscle area on the thrombus side (T/M) and to the area corresponding to thrombus area on the contralateral side (T/B). Vein blood was drawn at 2min, 5min, 10min, 30min and 1h-3h after injection in 2 rabbits so as to observe the blood clearance of ^99mTc-SZ21. Rabbits were sacrificed after 3h of imaging. The vessels including clots were harvested and imaged. Cardiac muscle, liver, spleen, lung, kidney, etc. were excised and weighed. Radioactivity counts were measured to calculate % ID/g.

Results The radiochemical purity of ^99mTc-SZ21 was beyond 90% and stable in vitro. Thrombi could be visualized at 30min after injection, and at 2h image of thrombi was clearly visualized, T/M (2.55±0.72) and T/B (1.94±0.51) ratios were high. In vitro imaging showed T/B was 4.43±1.5.

Conclusions ^99mTc-SZ21 has strong binding specificity to fresh thrombus with shorter imaging time in vivo, which shows ^99mTc-SZ21 is a potential agent for imaging diagnosis of thrombotic disease.