Recombinant staphylokinase variants with altered immunoreactivity. II: Thrombolytic properties and antibody induction

The substitution variants K35A,E38A,K74A, E75A,R77A (SakSTAR.M38) and K74A,E75A,R77A,E80A, D82A (SakSTAR.M89) of recombinant staphylokinase (SakSTAR) with reduced antibody reactivity were assayed for thrombolytic potency and antibody induction in animal models and in patients.

In a 125I-fibrin-labeled pulmonary embolism model in the hamster, the doses giving 50% clot lysis in 90 minutes were 25 micrograms/kg for SakSTAR, 85 micrograms/kg for SakSTAR.M38, and 90 micrograms/kg for SakSTAR.M89. In rabbits with 125I-fibrin-labeled plasma clots incorporated into extracorporeal arteriovenous loops, lysis within 2 hours was 76 +/- 18% (mean +/- SD, n = 28) with 400 micrograms/kg SakSTAR, 53 +/- 13% (n = 8) with 1000 micrograms/kg SakSTAR.M38, and 39 +/- 13% (n = 6) with 800 micrograms/kg SakSTAR.M89. When groups of eight rabbits were immunized by intravenous administration of 0.2 to 1.0 micrograms/kg compound followed by subcutaneous injection of 0.4 mg in Freund's adjuvant at 2, 3, and 5 weeks, SakSTAR.M38 and SakSTAR.M89 elicited markedly less circulating neutralizing activity, compared with SakSTAR, when determined at 6 weeks (neutralizing 6.1 +/- 3.0 and 4.9 +/- 1.3 micrograms compound/mL plasma, respectively, versus 20 +/- 17 micrograms/mL; P = .02 and P = .01, respectively) and induced significantly less resistance to thrombolysis (residual thrombolytic potency producing 59 +/- 25% and 39 +/- 12% lysis, respectively, versus 8.5 +/- 5.7%; P = .008 and P = .006, respectively). In patients with peripheral arterial occlusion, intra-arterial administration of SakSTAR.M38 (n = 4) or SakSTAR.M89 (n = 4) induced significantly fewer circulating neutralizing antibodies (P = .03) and specific IgG (P = .01) at 2 to 3 weeks than SakSTAR (n = 8).

SakSTAR.M38 and SakSTAR.M89 induce less antibody formation and might constitute preferred agents for thrombolytic therapy in humans.