EXTRACORPOREAL IMMUNOADSORPTION COMPARED TO AVIDIN CHASE - ENHANCEMENT OF TUMOR-TO-NORMAL TISSUE RATIO FOR BIOTINYLATED RHENIUM-188-CHIMERIC BR96

Based on the biodistribution and kinetics of biotinylated Re-188-chime ric BR96 (chiBR96), the enhancement of the tumor-to-normal tissue (T/N ) radioactivity ratio using extracorporeal immunoadsorption (ECIA) was evaluated and compared with that of avidin ''chase'' in colon carcino ma-isografted Brown Norwegian rats. Methods: Extracorporeal immunoadso rption (ECIA) was performed 6 or 12 hr after intravenous administratio n of biotinylated Re-188-chiBR96. Radioactivity redistribution was inv estigated just after ECIA [8 or 14 hr postinjection of the antibody] a nd 40 or 34 hr after ECIA performance (48 hr postinjection). Avidin wa s administered intraperitoneally at 6 hr postinjection. Tumor radioact ivity uptake and T/N activity ratios of biotinylated Re-188-chiBR96 we re compared using ECIA and avidin chase and were also compared with co ntrols. Results: Both ECIA and avidin chase can rapidly increase the r adioactivity tumor-to-blood ratio without significantly interfering wi th the tumor uptake. ECIA at 8 hr postinjection increased the T/N rati os in blood-rich tissues, such as liver and bone marrow, from 6 and 8 to 10 and 18, respectively. Corresponding T/N ratios at 14 hr increase d from 9 and 10 to 24 and 36, In contrast, when avidin chase was used, there were no T/N improvements, except in blood. Moreover, avidin cha se caused a significant accumulation of radioactivity in the liver. Co nclusion: The ECIA approach, with direct removal of unbound circulatin g biotinylated Re-188-chiBR96, thus can rapidly improve and maintain T /N ratios without overloading the liver with radioactivity, in contras t to avidin chase.