Novel Selection Approaches to Identify Antibodies Targeting Neoepitopes on the C5b6 Intermediate Complex to Inhibit Membrane Attack Complex Formation.

The terminal pathway of complement is implicated in the pathology of multiple diseases and its inhibition is, therefore, an attractive therapeutic proposition. The practicalities of inhibiting this pathway, however, are challenging, as highlighted by the very few molecules in the clinic. The proteins are highly abundant, and assembly is mediated by high-affinity protein-protein interactions. One strategy is to target neoepitopes that are present transiently and only exist on active or intermediate complexes but not on the abundant native proteins. Here, we describe an antibody discovery campaign that generated neoepitope-specific mAbs against the C5b6 complex, a stable intermediate complex in terminal complement complex assembly. We used a highly diverse yeast-based antibody library of fully human IgGs to screen against soluble C5b6 antigen and successfully identified C5b6 neoepitope-specific antibodies. These antibodies were diverse, showed good binding to C5b6, and inhibited membrane attack complex (MAC) formation in a solution-based assay. However, when tested in a more physiologically relevant membrane-based assay these antibodies failed to inhibit MAC formation. Our data highlight the feasibility of identifying neoepitope binding mAbs, but also the technical challenges associated with the identification of functionally relevant, neoepitope-specific inhibitors of the terminal pathway.

'In-Format' screening of a novel bispecific antibody format reveals significant potency improvements relative to unformatted molecules.

Bispecific antibodies (BsAbs) are emerging as an important class of biopharmaceutical. The majority of BsAbs are created from conventional antibodies or fragments engineered into more complex configurations. A recurring challenge in their development, however, is the identification of components that are optimised for inclusion in the final format in order to deliver both efficacy and robust biophysical properties. Using a modular BsAb format, the mAb-dAb, we assessed whether an 'in-format' screening approach, designed to select format-compatible domain antibodies, could expedite lead discovery. Human nerve growth factor (NGF) was selected as an antigen to validate the approach; domain antibody (dAb) libraries were screened, panels of binders identified, and binding affinities and potencies compared for selected dAbs and corresponding mAb-dAbs. A number of dAbs that exhibited high potency (IC50) when assessed in-format were identified. In contrast, the corresponding dAb monomers had ∼1000-fold lower potency than the formatted dAbs; such dAb monomers would therefore have been omitted from further characterization. Subsequent stoichiometric analyses of mAb-dAbs bound to NGF, or an additional target antigen (vascular endothelial growth factor), suggested different target binding modes; this indicates that the observed potency improvements cannot be attributed simply to an avidity effect offered by the mAb-dAb format. We conclude that, for certain antigens, screening naïve selection outputs directly in-format enables the identification of a subset of format-compatible dAbs, and that this offers substantial benefits in terms of molecular properties and development time.

Novel Interaction Mechanism of a Domain Antibody-based Inhibitor of Human Vascular Endothelial Growth Factor with Greater Potency than Ranibizumab and Bevacizumab and Improved Capacity over Aflibercept.

A potent VEGF inhibitor with novel antibody architecture and antigen binding mode has been developed. The molecule, hereafter referred to as VEGF dual dAb (domain antibody), was evaluated in vitro for binding to VEGF and for potency in VEGF-driven models and compared with other anti-VEGF biologics that have been used in ocular anti-angiogenic therapeutic regimes. VEGF dual dAb is more potent than bevacizumab and ranibizumab for VEGF binding, inhibition of VEGF receptor binding assays (RBAs), and VEGF-driven in vitro models of angiogenesis and displays comparable inhibition to aflibercept (Eylea). VEGF dual dAb is dimeric, and each monomer contains two distinct anti-VEGF domain antibodies attached via linkers to a human IgG1 Fc domain. Mechanistically, the enhanced in vitro potency of VEGF dual dAb, in comparison to other anti-VEGF biologics, can be explained by increased binding stoichiometry. A consistent model of the target engagement has been built based on the x-ray complexes of each of the two isolated domain antibodies with the VEGF antigen.

Pharmacodynamics of DT-IgG, a dual-targeting antibody against VEGF-EGFR, in tumor xenografted mice.

PURPOSE: DT-IgG is a fully humanized dual-target therapeutic antibody being developed to simultaneously target epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF), important signaling molecules for tumor growth. The antitumor pharmacodynamics (PD) of DT-IgG was studied in nude mice bearing human tumor xenografts with different EGFR and VEGF expressions and K-ras oncogene status and compared with bevacizumab, cetuximab and bevacizumab + cetuximab. METHODS: Mice bearing human oral squamous cell carcinoma (Tu212), lung adenocarcinoma (A549), or colon cancer (GEO) subcutaneous xenografts were administered with the antibodies intraperitoneally (i.p.), and tumor volumes were measured versus time. Nonlinear mixed effects modeling (NONMEM) was used to study drug potencies (IC(50)) and variations in tumor growth. RESULTS: The PD models adequately described tumor responses for the antibody dose regimens. In vivo IC(50) values varied with EGFR and K-ras status. DT-IgG had a similar serum t (1/2) as cetuximab (~1.7 vs. 1.5 day), was more rapid than bevacizumab (~6 day), and had the largest apparent distribution volume (DT-IgG > cetuximab > bevacizumab). The efficacy of DT-IgG was comparable to bevacizumab despite lower serum concentrations, but was less than bevacizumab + cetuximab. CONCLUSIONS: A lower IC(50) of DT-IgG partially compensated for lower serum concentrations than bevacizumab and cetuximab, but may require higher doses for comparable efficacy as the combination. The model adequately predicted variations of tumor response at the DT-IgG doses tested and could be used for targeting specific tumor efficacies for future testing.

A dual-targeting antibody against EGFR-VEGF for lung and head and neck cancer treatment.

An antibody simultaneously targeting epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF), two major tumor growth-driving machineries, may provide a novel effective strategy for optimizing tumor targeting and maximizing potential clinical benefits. Human domain antibodies selected against VEGF and EGFR were formatted into a fully human dual-targeting IgG (DT-IgG) to directly target both antigens in a single molecule. We evaluated the efficacy of DT-IgG in comparison with bevacizumab and cetuximab alone and in combination in the lung cancer cell line A549 (low EGFR expression and KRAS mutant) and the head and neck squamous cell carcinoma (HNSCC) cell line Tu212 (high EGFR expression and KRAS wild type) in vitro and in vivo. DT-IgG suppressed Tu212 and A549 cell growth, inhibited EGFR activation and induced apoptosis as effectively as cetuximab, and neutralized VEGF as effectively as bevacizumab. DT-IgG induced EGFR-dependent VEGF internalization, constituting a novel antiangiogenesis mechanism. In xenograft models with lung and head and neck cancer cell lines, DT-IgG displayed efficacy equivalent to bevacizumab in diminishing tumor growth despite its short serum half-life (36 hr in rats) and both agents may constitute preferable alternatives to cetuximab in KRAS-mutant tumors. Immunofluorescence staining revealed that localization of DT-IgG was similar to that of cetuximab, largely associated with EGFR+tumor cells. Our proof of principle study suggests a DT-IgG against EGFR and VEGF as an alternative therapeutic strategy with potentially enhanced clinical benefit.

Next generation immunotherapeutics--honing the magic bullet.

Most therapeutic antibodies in the clinic today are based on fully humanised immunoglobulins. They have proven to be outstandingly effective, especially for the treatment of cancer, autoimmune and inflammatory diseases where the target is a single, well-defined and accessible molecule. Many diseases however are complex, involving multiple mediators or signalling pathways that could be targeted simultaneously to maximise clinical benefit. There is also a wealth of validated intracellular and CNS-based targets which are currently inaccessible to monoclonal antibody therapy. A spectrum of next generation immunotherapeutics is in development to address these issues and a number of them have also entered clinical trials.

The crystal structure of human CD1b with a bound bacterial glycolipid.

The human MHC class I-like molecule CD1b is distinctive among CD1 alleles in that it is capable of presenting a set of glycolipid species that show a very broad range of variation in the lengths of their acyl chains. A structure of CD1b complexed with relatively short acyl chain glycolipids plus detergent suggested how an interlinked network of channels within the Ag-binding groove could accommodate acyl chain lengths of up to 80 carbons. The structure of CD1b complexed with glucose monomycolate, reported in this study, confirms this hypothesis and illustrates how the distinctive substituents of intracellular bacterial glycolipids can be accommodated. The Ag-binding groove of CD1b is, uniquely among CD1 alleles, partitioned into channels suitable for the compact accommodation of lengthy acyl chains. The current crystal structure illustrates for the first time the binding of a natural bacterial lipid Ag to CD1b and shows how its novel structural features fit this molecule for its role in the immune response to intracellular bacteria.

Structure of the snake-venom toxin convulxin.

Snake venoms contain a number of proteins that interact with components of the haemostatic system that promote or inhibit events leading to blood-clot formation. The snake-venom protein convulxin (Cvx) binds glycoprotein (GP) VI, the platelet receptor for collagen, and triggers signal transduction. Here, the 2.7 A resolution crystal structure of Cvx is presented. In common with other members of this snake-venom protein family, Cvx is an alphabeta-heterodimer and conforms to the C-type lectin-fold topology. Comparison with other family members allows a set of Cvx residues that form a concave surface to be putatively implicated in GPVI binding. Unlike other family members, with the exception of flavocetin-A (FL-A), Cvx forms an (alphabeta)(4) tetramer. This oligomeric structure is consistent with Cvx clustering GPVI molecules on the surface of platelets and as a result promoting signal transduction activity. The Cvx structure and the location of the putative binding sites suggest a model for this multimeric signalling assembly.