rEVO Biologics (United States)

Metelimumab (CAT192) is a human IgG4 monoclonal antibody developed as a TGFβ1-specific antagonist. It was tested in clinical trials for the treatment of scleroderma but later terminated due to lack of efficacy. Subsequent characterization of CAT192 indicated that its TGFβ1 binding affinity was reduced by ∼50-fold upon conversion from the parental single-chain variable fragment (scFv) to IgG4. We hypothesized this result was due to decreased conformational flexibility of the IgG that could be altered via engineering. Therefore, we designed insertion mutants in the elbow region and screened for binding and potency. Our results indicated that increasing the elbow region linker length in each chain successfully restored the isoform-specific and high affinity binding of CAT192 to TGFβ1. The crystal structure of the high binding affinity mutant displays large conformational rearrangements of the variable domains compared to the wild-type antigen-binding fragment (Fab) and the low binding affinity mutants. Insertion of two glycines in both the heavy and light chain elbow regions provided sufficient flexibility for the variable domains to extend further apart than the wild-type Fab, and allow the CDR3s to make additional interactions not seen in the wild-type Fab structure. These interactions coupled with the dramatic conformational changes provide a possible explanation of how the scFv and elbow-engineered Fabs bind TGFβ1 with high affinity. This study demonstrates the benefits of re-examining both structure and function when converting scFv to IgG molecules, and highlights the potential of structure-based engineering to produce fully functional antibodies.

The purpose of this analysis was to evaluate the use of recombinant human antithrombin (rhAT) in preventing venous thromboembolism (VTE) in pregnant patients with hereditary AT deficiency (HATD). Data from two clinical trials were pooled. Dosing of rhAT was based on body weight and baseline AT activity, started up to 24 hours before scheduled induction or cesarean delivery, or at the onset of labor. A total of 21 pregnant HATD patients were enrolled. Mean rhAT therapy duration was 4.3 days and dose was 245.1 IU/kg/day. All patients achieved target mean AT activity (80-120% of normal) during rhAT therapy. There were no confirmed VTEs during rhAT treatment or within 7 ( ± 1) days after dosing. Two VTE events (one deep vein thrombosis and one pulmonary embolism) occurred 11 and 14 days after discontinuation of rhAT, in patients managed with prophylactic doses of heparin or low-molecular-weight heparin following delivery. rhAT was safe and effective in pregnant HATD patients when administered during the peripartum period, the period of highest VTE risk and a time when anticoagulation therapy is normally withheld. Pregnant HATD patients may benefit from therapeutic, rather than prophylactic, doses of anticoagulation after delivery to protect against postpartum VTE.

Antithrombin (AT) replacement has been described in patients with hereditary AT deficiency undergoing delivery; however, the kinetics of AT replacement in preeclampsia is not adequately understood. Therefore, the Prospective Randomized Evaluation of the Safety and Efficacy of Recombinant Antithrombin in Very Preterm Preeclampsia (PRESERVE-1) study has been proposed. Sixty women aged≥18 years at 24 0/7-28 0/7 weeks' gestation and with hypertension and proteinuria will be enrolled and randomly assigned to receive recombinant human AT or placebo until fetal and/or maternal indications cause cessation of expectant management or until 34 0/7 weeks' gestation. The primary endpoint is the increase in gestational age from randomization to delivery. Safety assessments and laboratory assays will also be performed. PRESERVE-1 study enrollment will begin during the second half of 2013. The PRESERVE-1 study will provide further insight into the pharmacokinetic activity and safety of AT therapy in preeclampsia.