Antibody-enhanced thrombolysis: targeting of tissue plasminogen activator in vivo

Tissue plasminogen activator (tPA) was modified by the unidirectional crosslinking reagent N-succinimidyl 3-(2-pyridyldithio)propionate and coupled to iminothiolane-modified anti-fibrin antibody 59D8 by the formation of disulfide bonds at neutral pH. Purification by two affinity-chromatography steps yielded tPA-anti-fibrin antibody conjugate (tPA-59D8) possessing both tPA and anti-fibrin antibody activities. In a quantitative rabbit thrombolysis model, the activity of the purified conjugate was compared with that of tPA alone and that of a conjugate between tPA and a digoxin-specific monoclonal antibody. After correction for spontaneous lysis (10.9 +/- 2.5%), tPA-59D8 was shown to be 2.8-9.6 times more potent than tPA alone. Unconjugated tPA and tPA-digoxin were equipotent. At equivalent thrombolytic concentrations, tPA-59D8 degraded less fibrinogen and consumed less alpha 2-antiplasmin than did tPA alone. This suggests that tPA can be efficiently directed to the site of a thrombus by conjugation to an anti-fibrin monoclonal antibody, resulting in both more potent and more selective thrombolysis.