Yves Laroche

Improved Generation of Germline-Competent Embryonic Stem Cell Lines from Inbred Mouse Strains

Genetically altered mice may exhibit highly variable phenotypes due to the variation in genetic background, which can only be circumvented by generation of inbred, isogenic gene‐targeted and control mice. Here we report that an embryonic stem (ES) cell culture medium conditioned by a rabbit fibroblast cell line transduced with genomic rabbit leukemia inhibitory factor allows efficient derivation and maintenance of ES cell lines from all of 10 inbred mouse strains tested, including some that were presumed to be nonpermissive for ES cell derivation (129/SvEv, 129/SvJ, C57BL/6N, C57BL/6JOla, CBA/CaOla, DBA/2N, DBA/1Ola, C3H/HeN, BALB/c, and FVB/N). Germline transmission was established by blastocyst injection of established ES cell lines after 10 or more passages from all of seven strains tested (129/SvJ, C57BL/6N, C57BL/6JOla, DBA/2N, DBA/1Ola, BALB/c, and FVB/N), by diploid aggregation of ES cell lines from all of four strains tested (129/SvEv, C57BL/6N, CBA/ CaOla, and FVB/N), or by tetraploid aggregation of ES cell lines from all of three strains tested (129/SvEv, C57BL/6N, and CBA/CaOla). Thus, these inbred ES cell lines may constitute useful tools to derive gene‐targeted mice and isogenic controls in selected genetic backgrounds.

Recombinant human microplasmin: production and potential therapeutic properties

Summary.  The effect of recombinant human microplasmin was studied in ischemic stroke models in mice and in an extracorporeal loop thrombosis model in rabbits. Human microplasminogen (µPlg), which lacks the five ‘kringle’ domains of plasminogen was expressed with high yield in Pichia pastoris. It was purified, converted to microplasmin (µPli) and equilibrated with 5 mmol L−1 citrate, pH 3.1, yielding a stable preparation. In mice with middle cerebral artery (MCA) ligation, an intravenous (i.v.) bolus of 5.0 mg kg−1µPli reduced infarct size at 24 h from 27 (26–30) to 25 (21–28) mm3 (median and range, n= 16 each, P= 0.0001), whereas 4.0 mg kg−1 rt‐PA and 40 mg kg−1µPlg had no effect. Infarct reduction was observed with administration at 4 h after occlusion. In mice with MCA, infarct size at 24 h was reduced from 20 (14–30) to 9.1 (3.1–25) mm3 with 5.0 mg kg−1µPli (n = 15 each, P < 0.002) and to 11 (5.2–27) mm3 with 4.0 mg kg−1 rt‐PA (n = 6; P= 0.02). Infarct reduction was still observed at 10 h after occlusion with µPli but not with t‐PA. In rabbits with radiolabeled clots in an extracorporeal arteriovenous loop, local infusion of 2.5 mg kg−1µPli over 2 h, induced 51 ± 15% lysis (mean ± SD, n= 11) vs. a control value of 23 ± 5.5%. µPli did not prolong template bleeding times, whereas equipotent doses of rt‐PA were associated with extensive rebleeding. The potency of µPli in both models was similar to that of intact plasmin. These findings indicate that recombinant µPli may be useful for treatment of ischemic stroke and arterial thrombosis.

Recombinant staphylokinase variants with altered immunoreactivity. I: Construction and characterization

BACKGROUND Recombinant staphylokinase offers promise for thrombolytic therapy in acute myocardial infarction, but it is immunogenic. Although reduced immunogenicity of heterologous proteinaceous drugs by protein engineering has not previously been reported, an attempt was made to achieve this in staphylokinase by site-specific mutagenesis. METHODS AND RESULTS Biospecific interaction analysis of a panel of 17 murine monoclonal antibodies against recombinant staphylokinase (SakSTAR variant) identified three nonoverlapping immunodominant epitopes, two of which could be eliminated by substitution mutagenesis of clusters of two or three charged amino acids with alanine. Circulating anti-staphylokinase antibodies elceted in patients by treatment with SakSTAR were incompletely (< 90%) absorbed by these mutants. Therefore, the combination variants K35A,E38A,K74A,E75A,R77A (SakSTAR.M38) and K74A,E75A,R77A,E80A,D82A (SakSTAR.M89) were constructed, expressed in Escherichia coli, highly purified by ion-exchange and hydrophobic interaction chromatography, and characterized. These variants had specific activities that were approximately half that of SakSTAR, and they combined the reduced reactivity with the panels of monoclonal antibodies of their parent molecules. Absorption of circulating antibodies elicited in patients by treatment with SakSTAR was incomplete in 13 of 16 patients (median values, 68% and 65% with SakSTAR.M38 and SakSTAR.M89, respectively). CONCLUSIONS SakSTAR contains three immunodominant epitopes, two of which were eliminated by site-directed mutagenesis, yielding combination mutants with relatively maintained specific activities that were not recognized by a significant fraction of the antibodies elicited in patients by treatment with wildtype SakSTAR. These mutants appear to be suitable for more detailed investigation of their thrombolytic and antigenic properties.

Polyethylene Glycol–Derivatized Cysteine-Substitution Variants of Recombinant Staphylokinase for Single-Bolus Treatment of Acute Myocardial Infarction

BackgroundThrombolytic therapy of acute myocardial infarction (AMI) is evolving toward bolus administration. Derivatization of proteins with polyethylene glycol (PEG) may reduce their clearance. Methods and ResultsA staphylokinase (SakSTAR) variant with 12 amino acid substitutions to reduce its antigenicity, SakSTAR (K35A, E65Q, K74R, E80A, D82A, T90A, E99D, T101S, E108A, K109A, K130T, K135R), and with Ser in position 3 mutated into Cys (code SY161), was derivatized with maleimide-PEG with Mr of 5000 (P5), 10 000 (P10), or 20 000 (P20). The PEGylated variants recognized only one third of the antibodies elicited with wild-type SakSTAR in AMI patients. In experimental animals, plasma clearances were reduced 2.5- to 5-fold with P5, 5- to 20-fold with P10, and 20-fold with P20, and bolus injection induced pulmonary plasma clot lysis at doses inversely related to their clearance. Intravenous bolus injection of 5 mg of the P5, P10, or P20 variants in AMI patients was associated with plasma half-lives (t1/2&agr;) of 13, 30, and 120 minutes and clearances of 75, 43, and 8 mL/min, respectively, compared with 3 minutes and 360 mL/min for SakSTAR. Injection of 5 mg P5 variant restored TIMI-3 flow within 60 minutes in 14 of 18 AMI patients (78%, 95% CI 55% to 91%) and of 2.5 mg in 7 of 11 patients (63%, 95% CI 35% to 85%), both in the absence of fibrinogen degradation. The immunogenicity of the variants was significantly (P <0.002) reduced. ConclusionsThe staphylokinase variant SY161-P5, derivatized with one linear polyethylene glycol molecule of Mr 5000, is a promising fibrin-selective agent for single-bolus coronary thrombolysis.