RECOMBINANT STAPHYLOKINASE VARIANTS WITH ALTERED IMMUNOREACTIVITY .4.IDENTIFICATION OF VARIANTS WITH REDUCED ANTIBODY INDUCTION BUT INTACTPOTENCY

Background The thrombolytic potency and antibody induction of selected variants of recombinant staphylokinase (SakSTAR), including SakSTAR(K -74) with Lys74, SakSTAR(E(75)) with Glu75, SakSTAR(EER) with Glu38, G lu75, and Arg77, and SakSTAR(K(74)ER) with Lys74, Glu75, and Arg77 rep laced by Ala, were studied. Methods and Results In rabbits, SakSTAR(K- 74) and SakSTAR(EER) elicited significantly less circulating neutraliz ing activity than SakSTAR and SakSTAR(E(75)) (P=.005 and P=.0002 versu s SakSTAR, respectively). In baboons, SakSTAR(K,,) in duced significan tly fewer antibodies than wild-type SakSTAR (P<.05). Intra-arterial ad ministration in patients with peripheral arterial occlusion of SakSTAR (K-74) (n=11) or SakSTAR(K(74)ER) (n=6) induced significantly fewer ci rculating neutralizing antibodies [median values and interquartile ran ges, 20 (3.8 to 26) and 2.4 (0.2 to 59) mu g compound neutralized/mL p lasma after 3 to 4 weeks (P=.01 and P=.035 versus SakSTAR, respectivel y)] than SakSTAR (n=9) [median value and interquartile range, 93 (24 t o 110) mu g compound neutralized/mL plasma]. Overt neutralizing antibo dy induction (>10 mu g compound neutralized/mL plasma) occurred in ail 9 patients given wild-type SakSTAR, in 6 of the 11 SakSTAR(K-74) pati ents (P=.038 versus SakSTAR), and in 2 of the 6 SakSTAR(K,,ER) patient s (P=.011 versus SakSTAR). Conclusions SakSTAR(K-74), a variant of rec ombinant staphylokinase with a single substitution of Lys74 with Ala, and SakSTAR(K(74)ER), with Lys74, Glu75, and Arg77 substituted with Al a, have intact thrombolytic potencies but induce significantly less an tibody formation in patients.