Imaging of vascular injury with ^99mTc-labeled monoclonal antiplatelet antibody S12: Preliminary experience in human percutaneous transluminal angioplasty

Background. To evaluate the in vivo safety, biodistribution, and diagnostic accuracy of a monoclonal Fab' antibody (S12) that is specific for the platelet membrane glycoprotein (GMP-140) expressed during platelet activation at vascular injury sites, 11 peripheral percutaneous transluminal angioplasty (PTA) patients (age, 61±8 years) with severe vascular disease had serial ^99mTc S12 radionuclide imaging at 5 and 90 minutes, 4-6 hours, and 20-24 hours after a total of 23 angiographically successful PTA procedures. No acute allergic reactions or hematologic toxicity occurred. Methods and Results. The average PTA percent angiographic diameter stenosis (DS) at all 23 sites decreased from 85±12% to 12±11%, with a mean before-to-after-PTA change of 73±14% (p<0.01). The mean radionuclide image-derived ratio of ^99mTc S12 activity in PTA versus contralateral non-PTA arterial segments for all angioplasty sites was 1.6±0.5. Vascular ^99mTc S12 antibody activity was qualitatively evident in the majority (78%) of PTA sites at 4-6 hours after injection. ^99mTc S12 target-to-background (muscle) ratio equaled 2.3±0.6 at PTA sites. Nine PTA sites (39%) had residual ^99mTc S12 activity at 24 hours after injection (mean PTA site-to-contralateral artery ratio, 1.5±0.4). The mean vascular ^99mTc S12 activity ratios in 10 procedurally complicated (defined as extensive dilation [>2 cm] or grade I or greater arterial dissection) and 13 uncomplicated PTA segments were 1.9±0.5 versus 1.2±0.1, respectively (p<0.01). The associated before-to-after-PTA angiographic improvement was significantly less in procedurally complicated PTA sites (66±12% versus 80±12% DS; p<0.01). Conclusions. ^99mTc S12 activity is significantly increased at angiographically patent PTA sites that are procedurally complicated and are associated with less significant before-to-after-PTA angiographic improvement. ^99mTc S12 monoclonal Fab' antibody imaging permits noninvasive identification of local vascular platelet activation resulting from angioplasty balloon injury in humans.