To generate a stable resource from which high affinity human antibodies to any given antigen can be rapidly isolated, functional V-gene segments from 43 non-immunized human donors were used to construct a repertoire of 1.4 x 10(10) single-chain Fv (scFv) fragments displayed on the surface of phage. Fragments were cloned in a phagemid vector, enabling both phage displayed and soluble scFv to be produced without subcloning. A hexahistidine tag has been incorporated to allow rapid purification of scFv by nickel chelate chromatography. This library format reduces the time needed to isolate monoclonal antibody fragments to under two weeks. All of the measured binding affinities show a Kd < 10 nM and off-rates of 10(-3) to 10(-4) s-1, properties usually associated with antibodies from a secondary immune response. The best of these scFvs, an anti-fluorescein antibody (0.3 nM) and an antibody directed against the hapten DTPA (0.8 nM), are the first antibodies with subnanomolar binding affinities to be isolated from a naive library. Antibodies to doxorubicin, which is both immunosuppressive and toxic, as well as a high affinity and high specificity antibody to the steroid hormone oestradiol have been isolated. This work shows that conventional hybridoma technology may be superseded by large phage libraries that are proving to be a stable and reliable source of specific, high affinity human monoclonal antibodies.

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We measured the concentration of calmodulin required to reverse inhibition by caldesmon of actin-activated myosin MgATPase activity, in a model smooth-muscle thin-filament system, reconstituted in vitro from purified vascular smooth-muscle actin, tropomyosin and caldesmon. At 37 degrees C in buffer containing 120 mM-KCl, 4 microM-Ca2+-calmodulin produced a half-maximal reversal of caldesmon inhibition, but more than 300 microM-Ca2+-calmodulin was necessary at 25 degrees C in buffer containing 60 mM-KCl. The binding affinity (K) of caldesmon for Ca2+-calmodulin was measured by a fluorescence-polarization method: K = 2.7 x 10(6) M-1 at 25 degrees C (60 mM-KCl); K = 1.4 x 10(6) M-1 at 37 degrees C in 70 mM-KCl-containing buffer; K = 0.35 x 10(6) M-1 at 37 degrees C in 120 mM-KCl- containing buffer (pH 7.0). At 37 degrees C/120 mM-KCl, but not at 25 degrees C/60 mM-KCl, Ca2+-calmodulin bound to caldesmon bound to actin-tropomyosin (K = 2.9 x 10(6) M-1). Ca2+ regulation in this system does not depend on a simple competition between Ca2+-calmodulin and actin for binding to caldesmon. Under conditions (37 degrees C/120 mM-KCl) where physiologically realistic concentrations of calmodulin can Ca2+-regulate synthetic thin filaments, Ca2+-calmodulin reverses caldesmon inhibition of actomyosin ATPase by forming a non-inhibited complex of Ca2+-calmodulin-caldesmon-(actin-tropomyosin).

Drug repositioning or repurposing has received much coverage in the scientific literature in recent years and has been responsible for the generation of both new intellectual property and investigational new drug submissions. The literature indicates a significant trend toward the use of computational-or informatics-based methods for generating initial repositioning hypotheses, followed by focused assessment of biological activity in phenotypic assays. Another viable method for drug repositioning is in vitro screening of known drugs or drug-like molecules, initially in disease-relevant phenotypic assays, to identify and validate candidates for repositioning. This approach can use large compound libraries or can focus on subsets of known drugs or drug-like molecules. In this short review, we focus on ways to generate and validate repositioning candidates in disease-related in vitro and phenotypic assays, and we discuss specific examples of this approach as applied to a variety of disease areas. We propose that in vitro screens offer several advantages over biochemical or in vivo methods as a starting point for drug repositioning.

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The recent determination of the genomic sequence of human caldesmon indicates that eight caldesmon mRNA species could be generated by selection of exon 1 or 1', exon 3a or 3ab and/or exon 4. We used reverse transcriptase PCR to determine which transcripts were produced in human, rabbit and sheep artery, vein, lung, intestine, kidney and liver. In all tissues the same three transcripts were present: exons 1'-2-3a-5-6...13, exons 1'-2-3a3b-5-6-...13 and exons 1'-2-3a3b-4-5-6...13. Exon 1 was not present and exon 4 was only present when exon 3b was also present. Three protein isoforms of caldesmon can be distinguished by electrophoresis on high-porosity 6% polyacrylamide gel: 130 kDa, 120 kDa and 70 kDa. The 70 kDa isoform lacks the sequence encoded by exon 3b. We investigated whether the two high-molecular-mass isoforms correspond to the presence and absence of exon 4 using an antiserum specific to the sequence encoded by exon 4. Western-blotting and immunoprecipitation experiments showed that both the 130 kDa and the 120 kDa isoforms were expressed with and without the exon 4 sequence. We therefore propose that the molecular-mass heterogeneity arises from additional first exons, possibly with separate promoter regions, which have not yet been characterized in the genomic sequence.

1. We have investigated the ability of bovine brain S.100, and of three related proteins from sheep aorta smooth muscle, to confer Ca(2+)-sensitivity on thin filaments reconstituted from smooth-muscle actin, tropomyosin and caldesmon. 2. At 37 degrees C in pH 7.0 buffer containing 120 mM-KCl, approximately stoichiometric amounts of S.100 reversed caldesmon's inhibition of the activation of myosin MgATPase by smooth-muscle actin-tropomyosin. The [S.100] which reversed by 50% the inhibition by caldesmon (the E.C.50) was 2.5 microM when [caldesmon] = 2-3 microM in the assay mixture. When [KCl] was decreased to 70 mM, E.C.50 = 11.5 microM; at 25 degrees C in 70 mM-KCl, up to 20 microM-S.100 had no effect. When skeletal-muscle actin rather than smooth-muscle actin was used to reconstitute thin filaments, 20 microM-S.100 did reverse inhibition by caldesmon, at 25 degrees C in buffer containing 70 mM-KCl. This dependence on conditions is also characteristic of the calmodulin-caldesmon interaction. 3. These results suggested that S.100 or a related protein might interact with caldesmon in smooth muscle. We therefore attempted to prepare such a protein from sheep aorta. Three proteins were purified: an Mr-17,000 protein (yield 16 mg/kg), an abundant Mr-11,000 protein (yield 48 mg/kg), and an Mr-9000 protein (yield 4 mg/kg). Neither of the last two low-Mr proteins had any effect on activation of myosin MgATPase by reconstituted thin filaments. The protein of Mr 17,000 had Ca(2+)-sensitizing activity, and behaved exactly like brain calmodulin in the assay system.