Clostridium difficile infections are a major cause of antibiotic-associated diarrhea in hospital and care facility patients. In spite of the availability of effective antibiotic treatments, C. difficile infection (CDI) is still a major cause of patient suffering, death, and substantial health care costs. Clostridium difficile exerts its major pathological effects through the actions of two protein exotoxins, TcdA and TcdB, which bind to and disrupt gut tissue. Antibiotics target the infecting bacteria but not the exotoxins. Administering neutralizing antibodies against TcdA and TcdB to patients receiving antibiotic treatment might modulate the effects of the exotoxins directly. We have developed a mixture of three humanized IgG1 monoclonal antibodies (MAbs) which neutralize TcdA and TcdB to address three clinical needs: reduction of the severity and duration of diarrhea, reduction of death rates, and reduction of the rate of recurrence. The UCB MAb mixture showed higher potency in a variety of in vitro binding and neutralization assays (ϳ10-fold improvements), higher levels of protection in a hamster model of CDI (82% versus 18% at 28 days), and higher valencies of toxin binding (12 versus 2 for TcdA and 3 versus 2 for TcdB) than other agents in clinical development. Comparisons of the MAb properties also offered some insight into the potential relative importance of TcdA and TcdB in the disease process.

We generated an anti-albumin antibody, CA645, to link its Fv domain to an antigen-binding fragment (Fab), thereby extending the serum half-life of the Fab. CA645 was demonstrated to bind human, cynomolgus, and mouse serum albumin with similar affinity (1–7 nM), and to bind human serum albumin (HSA) when it is in complex with common known ligands. Importantly for half-life extension, CA645 binds HSA with similar affinity within the physiologically relevant range of pH 5.0 – pH 7.4, and does not have a deleterious effect on the binding of HSA to neonatal Fc receptor (FcRn). A crystal structure of humanized CA645 Fab in complex with HSA was solved and showed that CA645 Fab binds to domain II of HSA. Superimposition with the crystal structure of FcRn bound to HSA confirmed that CA645 does not block HSA binding to FcRn. In mice, the serum half-life of humanized CA645 Fab is 84.2 h. This is a significant extension in comparison with < 1 h for a non-HSA binding CA645 Fab variant. The Fab-HSA structure was used to design a series of mutants with reduced affinity to investigate the correlation between the affinity for albumin and serum half-life. Reduction in the affinity for MSA by 144-fold from 2.2 nM to 316 nM had no effect on serum half-life. Strikingly, despite a reduction in affinity to 62 µM, an extension in serum half-life of 26.4 h was still obtained. CA645 Fab and the CA645 Fab-HSA complex have been deposited in the Protein Data Bank (PDB) with accession codes, 5FUZ and 5FUO, respectively.

Increasingly diverse large molecule modalities have driven the need for complex bioanalysis and biotransformation assessment involving both traditional ligand-binding assays (LBA) and more recent hybrid immunoaffinity LC–MS platforms. Given the scientific expertise in LBA and LC–MS typically resides in different functions within the industry, this has presented operational challenges for an integrated approach for bioanalysis and biotransformation assessment. Encouragingly, over time, the industry has recognized the complementary value of the two platforms. This has not been an easy transition as organizational structures vary widely within the industry. However, there are tremendous benefits in adopting fully integrated strategies for biopharma. This IQ consortium paper presents current perspectives across the biopharma industry. It highlights the technical and operational challenges in current large molecule bioanalysis, the value of collaborations across LBA and LC–MS, and scientific expertise for fully integrated strategies for bioanalysis and biotransformation.

An antibody format, termed Fab-dsFv, has been designed for clinical indications that require monovalent target binding in the absence of direct Fc receptor (FcR) binding while retaining substantial serum presence. The variable fragment (Fv) domain of a humanized albumin-binding antibody was fused to the C-termini of Fab constant domains, such that the VL and VH domains were individually connected to the Cκ and CH1 domains by peptide linkers, respectively. The anti-albumin Fv was selected for properties thought to be desirable to ensure a durable serum half-life mediated via FcRn. The Fv domain was further stabilized by an inter-domain disulfide bond. The bispecific format was shown to be thermodynamically and biophysically stable, and retained good affinity and efficacy to both antigens simultaneously. In in vivo studies, the serum half-life of Fab-dsFv, 2.6 d in mice and 7.9 d in cynomolgus monkeys, was equivalent to Fab'-PEG.

ABSTRACT:The microsomal stability assay is commonly used to rank compounds according to their metabolic stability. Determination of the unbound intrinsic clearance (CL in,u ) is essential for the accurate comparison of compounds, since nonspecific binding to microsomes can lead to an underestimation of the microsomal clearance. In this study, a new method (linear extrapolation in the stability assay, LESA) was established, which allows direct calculation of CL in,u from microsomal stability data, without the need to independently determine the fraction of free (unbound) drug. The method was validated using nine drugs with different chemical structures and physicochemical properties. The CL in,u of these compounds was extrapolated from the intrinsic clearance values obtained at different concentrations of human liver microsomes and compared with that calculated by the conventional method, using microsomal intrinsic clearance values and the free fraction of drug determined by equilibrium dialysis, ultracentrifugation, or ultrafiltration. A good agreement was observed between the data generated by the LESA method and those determined by conventional procedures. The method was further evaluated using a published dataset for 10 additional drugs and found to yield intrinsic clearance data comparable to the previously reported values. LESA provides a convenient and rapid method to determine the influence of microsome binding on intrinsic clearance in a single assay.During the drug discovery process, in vitro drug metabolism data are widely used in the pharmaceutical industry as criteria to select new chemical entities for further development (Rodrigues, 1997). An important parameter that is used to rank compounds on the basis of their metabolic stability is the intrinsic clearance (CL in ), determined using hepatic microsomes (Obach, 1999;McGinnity and Riley, 2001). The metabolite formation method has been used for measurement of in vitro CL in (Madan et al., 2002;Jones and Houston, 2004). Here, the initial rate of metabolite production is measured using hepatic microsomes over a range of substrate concentrations under linear conditions with respect to protein concentration and time (Houston and Galetin, 2003). Alternatively, the substrate depletion approach has been adopted, where the consumption of the parent drug is monitored over time (Obach, 1999). This method is particularly popular in the pharmaceutical industry, since formal kinetic characterization of the enzymes involved and quantification of metabolites formed are not required, allowing rapid screening of compounds with automated and semiautomated methodologies. Normally at least 20% of the substrate must be metabolized within the incubation period, so that any substrate depletion can be distinguished from baseline variability (Jones and Houston, 2004). For this reason, higher microsome concentrations and longer incubation times are used than in studies utilizing the metabolite formation approach.Many drugs are lipophilic organic compounds that can bind nons...