GingisKHAN™ protease cleavage allows a high-throughput antibody to Fab conversion enabling direct functional assessment during lead identification of human monoclonal and bispecific IgG1 antibodies.

The determination of the binding strength of immunoglobulins (IgGs) to targets can be influenced by avidity when the targets are soluble di- or multimeric proteins, or associated to cell surfaces, including surfaces introduced from heterogeneous assays. However, for the understanding of the contribution of a second drug-to-target binding site in molecular design, or for ranking of monovalent binders during lead identification, affinity-based assessment of the binding strength is required. Typically, monovalent binders like antigen-binding fragments (Fabs) are generated by proteolytic cleavage with papain, which often results in a combination of under- and over-digestion, and requires specific optimization and chromatographic purification of the desired Fabs. Alternatively, the Fabs are produced by recombinant approaches. Here, we report a lean approach for the functional assessment of human IgG1s during lead identification based on an in-solution digestion with the GingisKHAN™ protease, generating a homogenous pool of intact Fabs and Fcs and enabling direct assaying of the Fab in the digestion mixture. The digest with GingisKHAN™ is highly specific and quantitative, does not require much optimization, and the protease does not interfere with methods typically applied for lead identification, such as surface plasmon resonance or cell-based assays. GingisKHAN™ is highly suited to differentiate between affinity and avidity driven binding of human IgG1 monoclonal and bispecific antibodies during lead identification.

Targeting key angiogenic pathways with a bispecific CrossMAb optimized for neovascular eye diseases.

Anti-angiogenic therapies using biological molecules that neutralize vascular endothelial growth factor-A (VEGF-A) have revolutionized treatment of retinal vascular diseases including age-related macular degeneration (AMD). This study reports preclinical assessment of a strategy to enhance anti-VEGF-A monotherapy efficacy by targeting both VEGF-A and angiopoietin-2 (ANG-2), a factor strongly upregulated in vitreous fluids of patients with retinal vascular disease and exerting some of its activities in concert with VEGF-A. Simultaneous VEGF-A and ANG-2 inhibition was found to reduce vessel lesion number, permeability, retinal edema, and neuron loss more effectively than either agent alone in a spontaneous choroidal neovascularization (CNV) model. We describe the generation of a bispecific domain-exchanged (crossed) monoclonal antibody (CrossMAb; RG7716) capable of binding, neutralizing, and depleting VEGF-A and ANG-2. RG7716 showed greater efficacy than anti-VEGF-A alone in a non-human primate laser-induced CNV model after intravitreal delivery. Modification of RG7716's FcRn and FcγR binding sites disabled the antibodies' Fc-mediated effector functions. This resulted in increased systemic, but not ocular, clearance. These properties make RG7716 a potential next-generation therapy for neovascular indications of the eye.

Combined inhibition of tumor necrosis factor α and interleukin-17 as a therapeutic opportunity in rheumatoid arthritis: development and characterization of a novel bispecific antibody.

OBJECTIVE: Rheumatoid arthritis therapies that are based on inhibition of a single cytokine, e.g., tumor necrosis factor α (TNFα) or interleukin-6 (IL-6), produce clinically meaningful responses in only about half of the treated patients. This study was undertaken to investigate whether combined inhibition of TNFα and IL-17 has additive or synergistic effects in the suppression of mesenchymal cell activation in vitro and inflammation and tissue destruction in arthritis in vivo. METHODS: Cultures of human fibroblast-like synoviocytes (FLS) were stimulated with TNFα, IL-17, or a combination of both. Single/combined neutralizing antibodies against TNFα and IL-17 were used to examine in vitro cytokine responses and in vivo development of arthritis and bone and cartilage destruction in TNFα-transgenic mice. Bispecific anti-TNFα/IL-17 antibodies were designed, and their potential to block cytokine responses in human FLS was tested. RESULTS: TNFα and IL-17 had additive/synergistic effects in promoting production of IL-6, IL-8, and granulocyte colony-stimulating factor, as well as matrix metalloproteinases, in FLS. Bispecific anti-TNFα/IL-17 antibodies showed superior efficacy in blocking cytokine and chemokine responses in vitro. Furthermore, dual versus single inhibition of both cytokines using neutralizing antibodies was more effective in inhibiting the development of inflammation and bone and cartilage destruction in arthritic mice. CONCLUSION: Combined blockade of TNFα and IL-17 was more effective than single blockade in inhibiting cytokine, chemokine, and matrix enzyme responses from human mesenchymal cells and in blocking tissue destruction associated with arthritis, and additionally showed a positive impact on rebalance of bone homeostasis. Bispecific anti-TNFα/IL-17 antibodies may have superior efficacy in the treatment of arthritis and may overcome the limited therapeutic responses obtained with single cytokine neutralization.

Differential roles of ArfGAP1, ArfGAP2, and ArfGAP3 in COPI trafficking.

The formation of coat protein complex I (COPI)-coated vesicles is regulated by the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor 1 (Arf1), which in its GTP-bound form recruits coatomer to the Golgi membrane. Arf GTPase-activating protein (GAP) catalyzed GTP hydrolysis in Arf1 triggers uncoating and is required for uptake of cargo molecules into vesicles. Three mammalian ArfGAPs are involved in COPI vesicle trafficking; however, their individual functions remain obscure. ArfGAP1 binds to membranes depending on their curvature. In this study, we show that ArfGAP2 and ArfGAP3 do not bind directly to membranes but are recruited via interactions with coatomer. In the presence of coatomer, ArfGAP2 and ArfGAP3 activities are comparable with or even higher than ArfGAP1 activity. Although previously speculated, our results now demonstrate a function for coatomer in ArfGAP-catalyzed GTP hydrolysis by Arf1. We suggest that ArfGAP2 and ArfGAP3 are coat protein-dependent ArfGAPs, whereas ArfGAP1 has a more general function.

Differential localization of coatomer complex isoforms within the Golgi apparatus.

Coatomer, the coat protein of coat protein complex (COP)I-vesicles, is a soluble protein complex made up of seven subunits, alpha-, beta-, beta'-, gamma-, delta-, epsilon-, and zeta-COP. Higher eukaryotes have two paralogous versions of the gamma- and zeta- subunits, termed gamma1- and gamma2-COP and zeta1- and zeta2-COP. Different combinations of these subunits are known to exist within coatomer complexes, and gamma1/zeta1-, gamma1/zeta2-, and gamma2/zeta1-COP represent the major coatomer populations in mammals. The role of COPI vesicles in the early secretory pathway is the subject of considerable debate. To help to resolve this discussion, we used quantitative immunoelectron microscopy and found that significant localization differences for COPI-isoforms do exist, with a preference for gamma1zeta1- and gamma1zeta2-coatomer in the early Golgi apparatus and gamma2zeta1-coatomer in the late Golgi apparatus. These differences suggest distinct functions for coatomer isoforms in a manner similar to clathrin/adaptor vesicles, where different adaptor proteins serve particular transport routes.

Discriminatory aptamer reveals serum response element transcription regulated by cytohesin-2.

Cytohesins are a family of highly homologous guanine nucleotide exchange factors (GEFs) that act on ADP-ribosylation factors (ARFs). The small ARF-GEFs are involved in integrin signaling, actin cytoskeleton remodeling, and vesicle transport. Here, we selected and applied a specific inhibitor for ARF nucleotide-binding site opener (ARNO)/cytohesin-2, an RNA aptamer that clearly discriminates between cytohesin-1 and cytohesin-2. This reagent bound to an N-terminal segment of cytohesin-2 and did not inhibit ARF-GEF function in vitro. When transfected into HeLa cells, it persisted for at least 6 h without requiring stabilization. Its effect in vivo was to down-regulate gene expression mediated through the serum-response element and knockdown mitogen-activated protein kinase activation, indicating that cytohesin-2 acts by means of mitogen-activated protein kinase signaling. We conclude that the N-terminal coiled-coil and parts of the Sec7 domain of cytohesin-2 are required for serum-mediated transcriptional activation in nonimmune cells, whereas cytohesin-1 is not. Our results indicate that intramer technology can be used not only for assigning novel biological functions to proteins or protein domains but also to prove nonredundancy of highly homologous proteins.

The tyrosine kinase Pyk2 regulates Arf1 activity by phosphorylation and inhibition of the Arf-GTPase-activating protein ASAP1.

Proline-rich tyrosine kinase 2 (Pyk2), a non-receptor tyrosine kinase structurally related to focal adhesion kinase, has been implicated in the regulation of mitogen-activated protein kinase cascades and ion channels, the induction of apoptosis, and in the modulation of the cytoskeleton. In order to understand how Pyk2 signaling mediates these diverse cellular functions, we performed a yeast two-hybrid screening using the C-terminal part of Pyk2 that contains potential protein-protein interaction sites as bait. A prominent binder of Pyk2 identified by this method was the Arf-GTPase-activating protein ASAP1. Pyk2-ASAP1 interaction was confirmed in pull-down as well as in co-immunoprecipitation experiments, and contact sites were mapped to the proline-rich regions of Pyk2 and the SH3 domain of ASAP1. Pyk2 directly phosphorylates ASAP1 on tyrosine residues in vitro and increases ASAP1 tyrosine phosphorylation when co-expressed in HEK293T cells. Phosphorylation of tyrosine 308 and 782 affects the phosphoinositide binding profile of ASAP1, and fluorimetric Arf-GTPase assays with purified proteins revealed an inhibition of ASAP1 GTPase-activating protein activity by Pyk2-mediated tyrosine phosphorylation. We therefore provide evidence for a functional interaction between Pyk2 and ASAP1 and a regulation of ASAP1 and hence Arf1 activity by Pyk2-mediated tyrosine phosphorylation.