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We have designed and constructed a bacterial expression vector to produce a fusion protein of hapten-specific single-chain Fv (ScFv) and alkaline phosphatase (PhoA) in Escherichia coli. The ScFv gene was assembled using genes encoding the heavy and light chain variable domains of anti-NP (4-hydroxy-3-nitrophenyl acetyl) mouse monoclonal antibody. The ScFv gene was then fused to the 5' terminus of the E. coli PhoA coding region. The expressed fusion protein ScFv(NP)-PhoA was purified using an NP affinity column, and gel-filtration. Characterization of the fusion protein was then performed. The estimated molecular weight by gel filtration was approximately 151 kDa, suggesting the dimerization of the protein. Kinetic constants of ScFv(NP)-PhoA were calculated and compared with those of wild-type PhoA. The k(cat) values of ScFv(NP)-PhoA and wild-type PhoA were 103 (s(-1)) and 96.1 (s(-1)), respectively, showing that PhoA activity was somewhat increased by tethering the molecules. The equilibrium binding constant of ScFv(NP)-PhoA was determined using two different haptens, NP-capronate and NIP(3-iodo-4-hydroxy-5-nitrophenyl acetyl) by means of fluorescence quenching measurements. The obtained binding constants were 2.2 x 10(5) (M-1) for NP-capronate and 1.O x 10(6) (M(-1)) for NIP, respectively. No apparent difference in binding constants was seen between ScFv(NP) and ScFv(NP)-PhoA, showing that sufficient specificity and binding affinity were retained when ScFv(NP) was tethered to alkaline phosphatase. ScFv(NP)-PhoA can be used to detect nanogram concentrations of NP-BSA in ELISA without the use of chemically conjugated secondary antibodies.

Since it was recently reported that an antibody for proprotein convertase subtilisin/kexin type 9 (PCSK9) reduces the risk of cardiovascular events in a clinical context, PCSK9 inhibition is thought to be an attractive therapy for dyslipidemia. In the present study, we created a novel small biologic alternative to PCSK9 antibodies called DS-9001a, comprising an albumin binding domain fused to an artificial lipocalin mutein (ABD-fused Anticalin protein), which can be produced by a microbial production system. DS-9001a strongly interfered with PCSK9 binding to low-density-lipoprotein receptor (LDL-R) and PCSK9-mediated degradation of LDL-R. In cynomolgus monkeys, single DS-9001a administration significantly reduced the serum LDL-C level up to 21 days (62.4% reduction at the maximum). Moreover, DS-9001a reduced plasma non-high-density-lipoprotein cholesterol and oxidized LDL levels, and their further reductions were observed when atorvastatin and DS-9001a were administered in combination in human cholesteryl ester transfer protein/ApoB double transgenic mice. Additionally, their reductions on the combination of atorvastatin and DS-9001a were more pronounced than those on the combination of atorvastatin and anacetrapib. Besides its favorable pharmacologic profile, DS-9001a has a lower molecular weight (about 22 kDa), yielding a high stoichiometric drug concentration that might result in a smaller administration volume than that in existing antibody therapy. Since bacterial production systems are viewed as more suited to mass production at low cost, DS-9001a may provide a new therapeutic option to treat patients with dyslipidemia. In addition, considering the growing demand for antibody-like drugs, ABD-fused Anticalin proteins could represent a promising new class of small biologic molecules.

SummaryHemophilia A is a clotting disorder that is due to reduced or absent coagulation factor VIII (FVIII) activity. In approximately 25% of people with severe hemophilia A, standard treatment with intravenous plasma-derived or recombinant FVIII (rFVIII) induces anti-FVIII antibodies that inhibit FVIII activity (inhibitors). We describe the development of a rat model to study the formation of inhibitors. Immunization of rats with human rFVIII in adjuvant induced an anti-human rFVIII antibody response characteristic of an anti-FVIII inhibitor response in hemophilia A patients. The rats exhibited a rapid, polyclonal secondary antibody response to human rFVIII. These antibodies were reactive against epitopes located in the heavy and light chains. All the rFVIII-immunized rats developed antibodies against the FVIII C2 domain, a region of major reactivity in hemophilia A patients with inhibitors. Furthermore, competition ELISAs demonstrated that rat and human anti-FVIII antibodies recognized identical or overlapping epitopes of the FVIII molecule. The rat anti-FVIII antibodies also functioned as human FVIII inhibitors with titers ranging from 120 to 2048 Bethesda Units (B.U.). We propose that this rat model may be useful to investigate immune responses to FVIII and may lead to better therapies for FVIII inhibitors.