title: New variant of human tissue plasminogen activator (TPA) with enhanced efficacy and lower incidence of bleeding compared with recombinant human TPA.
abstract: BACKGROUND
  The thrombolytic properties of a new variant of tissue plasminogen activator (TPA) (T103N, N117Q, KHRR 296-299 AAAA, or TNK-TPA) with longer plasma half-life, greater fibrin specificity, and increased resistance to inhibition by plasminogen activator inhibitor (PAI-1) were investigated in a rabbit thrombosed carotid artery model.
  
  
  RESULTS
  After 60 minutes of arterial occlusion, TPA (1.5, 3.0, 6.0, or 9.0 mg/kg as a front-loaded IV infusion for 90 minutes; n = 22) or TNK-TPA (0.38, 0.75, or 1.5 mg/kg as IV bolus; n = 16) was administered. Blood flow through the artery was monitored for an additional 120 minutes. Bleeding was assessed by weighing the amount of blood absorbed in a gauze pad placed in a subcutaneous muscular incision. Recanalization rates and duration of recanalization were dose dependent. The doses that produced > 80% recanalization rates with the longest duration of recanalization were 9.0 mg/kg for TPA and 1.5 mg/kg for TNK-TPA. At these doses, time to reperfusion (mean +/- SEM) was significantly faster (11 +/- 2 versus 23 +/- 7 minutes) and duration of recanalization longer (77 +/- 9 versus 51 +/- 18 minutes) for TNK-TPA compared with TPA (P < .025). Weights of the residual thrombi of the TPA group were greater than those of the TNK-TPA group (P = .004). Concentrations of fibrinogen, plasminogen, and alpha 2-antiplasmin at 120 minutes were significantly higher for TNK-TPA-treated animals compared with TPA-treated animals (P < .001). ANOVA of the blood loss data determined that there were significant differences between thrombolytic agents but not between doses. After correction for saline controls, total blood loss for pooled doses of TPA and TNK-TPA was 82 +/- 6 mg and 40 +/- 4 mg, respectively (P < .01).
  
  
  CONCLUSIONS
  From these data, we conclude that TNK-TPA, given as a bolus, produces faster and more complete recanalization of occluded arteries in a rabbit experimental model compared with TPA, without increasing systemic plasmin generation or peripheral bleeding. In addition, we observed that TNK-TPA, unlike TPA, did not potentiate collagen-induced aggregation of platelets obtained from human plasma. This lack of effect on platelet aggregation by TNK-TPA potentially could be associated with a decreased risk of reocclusion after successful thrombolysis.
authors.affiliation: Division of Cardiology, University of Texas Health Science Center, Houston 77030, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Benedict
authors.forename: C J
authors.initials: CJ
authors.lastname: Refino
authors.forename: B A
authors.initials: BA
authors.lastname: Keyt
authors.forename: R
authors.initials: R
authors.lastname: Pakala
authors.forename: N F
authors.initials: NF
authors.lastname: Paoni
authors.forename: G R
authors.initials: GR
authors.lastname: Thomas
authors.forename: W F
authors.initials: WF
authors.lastname: Bennett
mesh_terms: D000818:Animals; D002341:Carotid Artery Thrombosis / Q000188:drug therapy*; D005343:Fibrinolytic Agents / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use*; D006470:Hemorrhage / Q000139:chemically induced; D006801:Humans; D018082:Kringles; D008297:Male; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects; D011817:Rabbits; D010959:Tissue Plasminogen Activator / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use*
chemical_list: D005343:Fibrinolytic Agents; C083865:T103N; D010959:Tissue Plasminogen Activator