Selection of bispecific antibodies with optimal developability using FcRn‑Ph‑HPLC as an optimized FcRn affinity chromatography method

A challenge when developing therapeutic antibodies is the identification of candidates with favorable pharmacokinetics (PK) early in development. A key determinant of immunoglobulin (IgG) serum half‑life in vivo is the efficiency of pH-dependent binding to the neonatal Fc receptor (FcRn). Numerous studies have proposed techniques to assess FcRn binding of IgG-based therapeutics in vitro, enabling prediction of serum half-life prior to clinical assessment. FcRn high-performance liquid chromatography (HPLC) assays FcRn binding of therapeutic IgGs across a pH gradient, allowing the correlation of IgG column retention time to the half‑life of a therapeutic IgG in vivo. However, as FcRn retention time cannot be directly compared to an in vivo parameter, modifications to FcRn-HPLC are required to enable interpretation of the data within a physiological context, to provide more accurate estimations of serum half-life. This study presents an important modification to this method, FcRn-pH-HPLC, which reproducibly measures FcRn dissociation pH, allowing correlation with previously established half-lives of therapeutic antibodies. Furthermore, the influence of incorporating various antibody modifications, binding modules, and their orientations within IgGs and bispecifics on FcRn dissociation pH was evaluated using antibodies from the redirected optimized cell killing (ROCK®) platform. Target and effector antigen-binding domain sequences, their presentation format and orientation within a bispecific antibody alter FcRn retention; tested Fc domain modifications and incorporating stabilizing disulfide bonds had minimal effect. This study may inform the generation of mono-, bi- and multi-specific antibodies with tailored half-lives based on FcRn binding properties in vitro, to differentiate antibody-based therapeutic candidates with optimal developability.

Cryopreservation of Natural Killer Cells Pre-Complexed with Innate Cell Engagers

Innate cell engager (ICE^®) constructs are bispecific tetravalent antibodies targeting specific tumor antigens and simultaneously engaging natural killer (NK) cell and macrophage receptors for the destruction of tumor cells. Pre-complexing of ICE^® constructs with adoptive NK cells is a novel approach to enhance NK cell activity. The suitability of such complexes for cryopreservation, whilst retaining the biological activity and specificity, may enable the development of off-the-shelf NK cell products. This study investigates the binding affinity of ICE^® constructs targeting EpCAM and NK cell receptors CD16A, NKG2D, or NKp46 to the corresponding antigens, the ICE^® antitumor activity, and feasibility of cryopreservation. Cell surface retention assays using primary NK cells confirmed a substantially slower ICE^® construct dissociation kinetics compared with control molecules, suggesting the formation of durable complexes independently of the CD16A polymorphism. The high-affinity NK cell and EpCAM/CD16A ICE^® complexes were superior to those engaging NKG2D or NKp46 receptors when tested for the NK-cell-mediated elimination of EpCAM-expressing tumor cells. Moreover, the potency and efficacy of these complexes were unaffected after a single freeze–thaw cycle. CD16A-selective ICE^® drug candidates complexed with NK cells hold promise as novel cryopreserved off-the-shelf NK cell products with chimeric antigen receptor-like NK cell properties, capable of effective depletion of tumor cells.

A BCMA/CD16A bispecific innate cell engager for the treatment of multiple myeloma

Despite the recent progress, multiple myeloma (MM) is still essentially incurable and there is a need for additional effective treatments with good tolerability. RO7297089 is a novel bispecific BCMA/CD16A-directed innate cell engager (ICE^®) designed to induce BCMA+ MM cell lysis through high affinity binding of CD16A and retargeting of NK cell cytotoxicity and macrophage phagocytosis. Unlike conventional antibodies approved in MM, RO7297089 selectively targets CD16A with no binding of other Fcγ receptors, including CD16B on neutrophils, and irrespective of 158V/F polymorphism, and its activity is less affected by competing IgG suggesting activity in the presence of M-protein. Structural analysis revealed this is due to selective interaction with a single residue (Y140) uniquely present in CD16A opposite the Fc binding site. RO7297089 induced tumor cell killing more potently than conventional antibodies (wild-type and Fc-enhanced) and induced lysis of BCMA+ cells at very low effector-to-target ratios. Preclinical toxicology data suggested a favorable safety profile as in vitro cytokine release was minimal and no RO7297089-related mortalities or adverse events were observed in cynomolgus monkeys. These data suggest good tolerability and the potential of RO7297089 to be a novel effective treatment of MM patients.

Preclinical evaluation of AFM24, a novel CD16A-specific innate immune cell engager targeting EGFR-positive tumors

Epidermal growth factor receptor (EGFR)-targeted cancer therapy such as anti-EGFR monoclonal antibodies and tyrosine kinase inhibitors have demonstrated clinical efficacy. However, there remains a medical need addressing limitations of these therapies, which include a narrow therapeutic window mainly due to skin and organ toxicity, and primary and secondary resistance mechanisms of the EGFR-signaling cascade (e.g., RAS-mutated colorectal cancer). Using the redirected optimized cell killing (ROCK®) antibody platform, we have developed AFM24, a novel bispecific, IgG₁-scFv fusion antibody targeting CD16A on innate immune cells, and EGFR on tumor cells. We herein demonstrate binding of AFM24 to CD16A on natural killer (NK) cells and macrophages with K_D values in the low nanomolar range and to various EGFR-expressing tumor cells. AFM24 was highly potent and effective for antibody-dependent cell-mediated cytotoxicity via NK cells, and also mediated antibody-dependent cellular phagocytosis via macrophages in vitro. Importantly, AFM24 was effective toward a variety of EGFR-expressing tumor cells, regardless of EGFR expression level and KRAS/BRAF mutational status. In vivo, AFM24 was well tolerated up to the highest dose (75 mg/kg) when administered to cynomolgus monkeys once weekly for 28 days. Notably, skin and other toxicities were not observed. A transient elevation of interleukin-6 levels was detected at all dose levels, 2-4 hours post-dose, which returned to baseline levels after 24 hours. These results emphasize the promise of bispecific innate cell engagers as an alternative cancer therapy and demonstrate the potential for AFM24 to effectively target tumors expressing varying levels of EGFR, regardless of their mutational status.Abbreviations: ADA: antidrug antibody; ADCC: antibody-dependent cell-mediated cytotoxicity; ADCP: antibody-dependent cellular phagocytosis; AUC: area under the curve; CAR: chimeric-antigen receptor; CD: Cluster of differentiation; CRC :colorectal cancer; ECD: extracellular domain; EGF: epidermal growth factorEGFR epidermal growth factor receptor; ELISA: enzyme-linked immunosorbent assay; FACS: fluorescence-activated cell sorting; Fc: fragment, crystallizableFv variable fragment; HNSCC: head and neck squamous carcinomaIL interleukinm; Ab monoclonal antibody; MOA: mechanism of action; NK :natural killer; NSCLC: non-small cell lung cancer; PBMC: peripheral blood mononuclear cell; PBS: phosphate-buffered saline; PD: pharmacodynamic; ROCK: redirected optimized cell killing; RSV: respiratory syncytial virus; SABC: specific antibody binding capacity; SD: standard deviation; TAM: tumor-associated macrophage; TKI: tyrosine kinase inhibitor; WT: wildtype.

Abstract 5659: AFM24, a bispecific EGFR/CD16A innate cell engager with the potential to overcome resistance to current targeted treatments for EGFR-positive malignancies

The epidermal growth factor receptor (EGFR) is a prime target for cancer therapy across many solid tumor types, including CRC, NSCLC, breast, esophageal cancer, and SCCHN. Binding of EGFR by its ligand EGF induces cell proliferation, a process which is uncontrolled or constitutively active in many cancers. The development of anti-EGFR therapies such as monoclonal antibodies and tyrosine kinase inhibitors enabled clinicians to treat specific patient populations. Nevertheless, prognoses for patients remain unfavorable due to occurrence of intrinsic or acquired resistance via mutations of EGFR and/or downstream signaling factors such as KRAS and BRAF which are drivers of tumorigenesis. Inhibitors that target specific KRAS mutations, such as the G12C mutation (i.e. 14% of the most frequently observed in NSCLC and up to 5% in CRC), have shown early promising efficacy. While such drugs hold promise for specific mutations, there continues to be a need for new treatments with more differentiated and novel modes of action that utilize the power of the innate immune system, such as antibody dependent cellular cytotoxicity (ADCC) and antibody dependent cellular phagocytosis (ADCP).

Affimed has engineered the tetravalent bispecific EGFR- and CD16A-binding antibody AFM24 to engage and redirect innate immune cells such as NK cells and macrophages to EGFR+ tumor cells. In contrast to currently available EGFR-targeted therapies (e.g. cetuximab), this innate cell engager has been designed to exhibit a significantly reduced inhibition of EGFR signaling aiming for an improved safety profile, i.e. avoiding skin and gastro-intestinal toxicities. In vitro, AFM24 demonstrated high affinity binding to immune cells regardless of CD16A variants and potent killing of multiple EGFR+ tumor cell lines, carrying relevant KRAS or BRAF mutations via a different mode of action, namely ADCC and ADCP, rather than EGFR signaling inhibition. It was shown that AFM24's activity is independent of both, the EGFR cell surface expression level and the cellular origin of the respective cell lines. Cynomolgus toxicity studies revealed a very good safety profile, and no toxicity was observed after repeated administration (q7x28d, in total 5 infusions) of AFM24 up to 75 mg/kg. In contrast, EGFR-targeting mAbs (e.g. cetuximab) exhibited severe toxicities particularly in skin in toxicology studies when investigated with a similar dosing schedule.

Due to its potent activation of innate immunity and its beneficial safety/tolerability profile, AFM24 has the potential to become a novel treatment option for patients suffering from EGFR-expressing cancers and to overcome limitations of available EGFR-targeted therapies such as resistance and/or associated toxicities. AFM24 has cleared the IND and clinical investigations are planned in patients with cancers known to express EGFR.

Citation Format: Uwe Reusch, Michael Damrat, Susanne Wingert, Stefan H.J. Knackmuss, Thomas Mueller, Ivica Fucek, Ute Schniegler-Mattox, Kristina Ellwanger, Torsten Haneke, Andras Strassz, Wolfgang Fischer, Erich Rajkovic, Michael Tesar. AFM24, a bispecific EGFR/CD16A innate cell engager with the potential to overcome resistance to current targeted treatments for EGFR-positive malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5659.

Redirected optimized cell killing (ROCK®): A highly versatile multispecific fit-for-purpose antibody platform for engaging innate immunity

Redirection of immune cells to efficiently eliminate tumor cells holds great promise. Natural killer cells (NK), macrophages, or T cells are specifically engaged with target cells expressing markers after infection or neoplastic transformation, resulting in their activation and subsequent killing of those targets. Multiple strategies to redirect immunity have been developed in the past two decades, but they have technical hurdles or cause undesirable side-effects, as exemplified by the T cell-based chimeric antigen receptor approaches (CAR-T therapies) or bispecific T cell engager platforms. Our first-in-class bispecific antibody redirecting innate immune cells to tumors (AFM13, a CD30/CD16A-specific innate immune cell engager) has shown signs of clinical efficacy in CD30-positive lymphomas and the potential to be safely administered, indicating a wider therapeutic window compared to T cell engaging therapies. AFM13 is the most advanced candidate from our fit-for-purpose redirected optimized cell killing (ROCK®) antibody platform, which comprises a plethora of CD16A-binding innate immune cell engagers with unique properties. Here, we discuss aspects of this modular platform, including the advantages of innate immune cell engagement over classical monoclonal antibodies and other engager concepts. We also present details on its potential to engineer a fit-for-purpose innate immune cell engager format that can be equipped with unique CD16A domains, modules that influence pharmacokinetic properties and molecular architectures that influence the activation of immune effectors, as well as tumor targeting. The ROCK® platform is aimed at the activation of innate immunity for the effective lysis of tumor cells and holds the promise of overcoming limitations of other approaches that redirect immune cells by widening the therapeutic window.

Abstract 2786: Pharmacokinetics and in vitro/in vivo characterization of high-affinity bispecific EGFR/CD16A NK cell engagers for the treatment of EGFR-expressing tumors

The epidermal growth factor receptor (EGFR) is a validated target for the treatment of several solid tumor types. Current EGFR-targeting monoclonal antibodies (mAbs) and tyrosine kinase inhibitors function mainly through blocking of signal-transduction. Moreover, treatment with these agents is dependent on the receptor's mutational status which may cause treatment resistance in a large number of patients. In addition, EGFR-targeting therapies have been associated with side effects considered to impact prescription rates, in particular in the U.S. A natural killer (NK) cell-based EGFR-targeting approach has the potential to widen the therapeutic window and overcome intrinsic and acquired resistance. Therefore, it offers a promising and well differentiated therapeutic option. We describe the engineering of different bispecific NK cell engagers designed to redirect NK cell-mediated killing to EGFR-positive tumors. Different bispecific EGFR/CD16A antibody constructs targeting human and cynomolgus EGFR and CD16A were designed using novel human Fv antibody binding domains from a toolbox of formats. The Fv domains were evaluated in terms of their pharmacokinetic (PK) properties. Furthermore, the antibody constructs were characterized in antigen and cell binding assays, as well as in in vitro cytotoxicity assays against tumor cell lines expressing Raswt or mutated Ras. PK parameters were determined in CD1 mice and in vivo efficacy of selected antibodies was investigated in an A-431 tumor model in humanized mice. We generated antibody constructs with varying half-lives, including antibodies with a PK profile which allows for dosing comparable to IgG-based antibodies, while aiming at an improved safety profile compared to other EGFR-targeting therapies. Different high affinity tetravalent, bispecific antibodies binding to CD16A and the extracellular domain of EGFR were characterized. While binding to CD16A of classical mAbs is impaired by serum IgG, no substantial changes in binding affinity of our constructs to NK cells were observed. The antibodies showed superior potency and efficacy compared to mAbs or Fc-enhanced antibodies when tested in cytotoxicity assays. In vivo efficacy of selected antibodies was demonstrated in an A-431 tumor model in humanized mice. We have successfully designed and characterized several novel, highly potent and differentiated tetravalent bispecific antibody constructs to redirect NK cell-mediated cell killing to EGFR-positive tumor cells. These drug candidates are suitable for the treatment of EGFR-expressing malignancies with the potential to overcome resistance to other EGFR-targeting agents and offering a potentially improved safety profile. These candidates are currently in development as monotherapy and are also explored in combination with immune activating agents.

Citation Format: Michael Kluge, Michael Tesar, Uwe Reusch, Stefan Knackmuss, Torsten Haneke, Kristina Ellwanger, Ivica Fucek, Thomas Mueller, Ute Schniegler-Mattox, Martin Treder. Pharmacokinetics and in vitro/in vivo characterization of high-affinity bispecific EGFR/CD16A NK cell engagers for the treatment of EGFR-expressing tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2786.

Trispecific antibodies for CD16A-directed NK cell engagement and dual-targeting of tumor cells

Bispecific antibodies that redirect the lytic activity of cytotoxic immune effector cells, such as T- and NK cells, onto tumor cells have emerged as a highly attractive and clinically validated treatment modality for hematological malignancies. Advancement of this therapeutic concept into solid tumor indications, however, is hampered by the scarcity of targetable antigens that are surface-expressed on tumor cells but demonstrate only limited expression on healthy tissues. To overcome this limitation, the concept of dual-targeting, i.e. the simultaneous targeting of two tumor-expressed surface antigens with limited co-expression on non-malignant cells, with multispecific antibodies has been proposed to increase tumor selectivity of antibody-induced effector cell cytotoxicity. Here, a novel CD16A (FcγRIIIa)-directed trispecific, tetravalent antibody format, termed aTriFlex, is described, that is capable of redirecting NK cell cytotoxicity to two surface-expressed antigens. Using a BCMA/CD200-based in vitro model system, the potential use of aTriFlex antibodies for dual-targeting and selective induction of NK cell-mediated target cell lysis was investigated. Bivalent bispecific target cell binding was found to result in significant avidity gains and up to 17-fold increased in vitro potency. These data suggest trispecific aTriFlex antibodies may support dual-targeting strategies to redirect NK cell cytotoxicity with increased selectivity to enable targeting of solid tumor antigens.

Abstract 5671: AFM26 - A novel CD16A-directed bispecific TandAb targeting BCMA for multiple myeloma

Multiple myeloma (MM) is the second most common haematological cancer and is characterized by the accumulation of neoplastic plasma cells in the bone marrow and production of high levels of monoclonal immunoglobulin (M-protein). While historically considered incurable, recent approvals and ongoing clinical trials with monoclonal antibodies (mAbs) targeting surface antigens promise greatly improved outcomes and have heralded a new era of MM treatment in which immunotherapies are expected to take center stage. However, an unmet need remains as patients eventually relapse and/or become refractory to currently available treatments. Consequently, novel immunotherapeutic approaches are needed to provide improved treatment options to MM patients. Among the currently explored targets, B-cell maturation antigen (BCMA, CD269) is considered to be particularly attractive due to its limited expression on healthy tissues and almost universal expression on myeloma cells in the majority of patients.

Natural killer (NK) cells are cytotoxic effectors of the innate immune system capable of rapidly eradicating infected and transformed cells. The cytolytic activity of NK-cells can be used therapeutically to induce tumor cell lysis by direct engagement of the activating receptor CD16A (FcγRIIIa) using mAbs (ADCC). Despite similar mechanisms of target cell lysis, activation of NK-cells is not associated with the systemic symptoms of high level cytokine release as seen with direct T-cell engagement. Hence, it is considered a potent immunotherapeutic approach with reduced toxicity and a well-manageable safety profile. NK-cells readily infiltrate bone marrow and are thought to contribute to the efficacy of current myeloma treatments. Therefore, redirecting NK-cell cytotoxicity to malignant plasma cells appears to be a suitable therapeutic approach for MM.

Here we describe the characterization of AFM26, a novel tetravalent bispecific tandem diabody (TandAb) that specifically targets BCMA and CD16A with high affinity and induces potent and efficacious myeloma cell lysis. AFM26 incorporates an affinity-improved anti-CD16A domain and interacts bivalently with NK-cells, resulting in high avidity and prolonged cell surface retention that is largely unaffected by the presence of polyclonal IgG. Notably, AFM26 potently induces NK-cell-mediated in vitro lysis of target cells expressing low levels of BCMA at low effector:target ratios, even in presence of polyclonal IgG. This may suggest that AFM26, in contrast to classical mAbs, retains ADCC activity at low antibody concentrations in presence of serum IgG and despite high levels of IgG M-protein occurring in about half of MM patients. AFM26 exhibits high protein stability, full cross-reactivity with cynomolgus antigens (BCMA and CD16A) and does not bind APRIL and TACI, two functionally related receptors. These data suggest that TandAb AFM26 is a promising and highly potent drug candidate for MM treatment.

Citation Format: Thorsten Gantke, Uwe Reusch, Kristina Ellwanger, Ivica Fucek, Michael Weichel, Martin Treder. AFM26 - A novel CD16A-directed bispecific TandAb targeting BCMA for multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5671. doi:10.1158/1538-7445.AM2017-5671

Abstract 3753: Identification of antibodies against a novel tumor-associated MHC/peptide-target and generation of highly specific and potent HLA-A*02MMP1-003/CD3 TandAbs

Tumor-associated antigens for effective and safe T-cell engagement are very limited, leaving a need to open up the therapeutic target space. Targeting disease-specific MHC/peptide complexes with bispecific T-cell-recruiting antibodies is a highly attractive strategy to address this need, but so far, generation of antibodies against these peptides has been reported to be challenging. Immatics’ unique target discovery engine XPRESIDENT® holds the promise of identifying novel tumor-associated MHC/peptide complexes by providing direct and quantitative evidence for their presence on a large collection of primary human tumor and normal tissue specimens. By this approach, MMP1-003, an HLA-A*02-binding peptide originating from matrix metallopeptidase 1 (MMP1), was identified as a promising therapeutic target presented by several tumor types, including colorectal and lung cancer, but absent on normal tissues. These findings are underlined by RNAseq analysis of the source antigen which also points to MMP1 being a highly attractive tumor-associated target. Consequently, a fully human antibody phage display library was screened to identify highly specific single chain antibodies, which were shown to recognize the purified HLA-A*02/MMP1-003-complex in ELISA assays as well as on peptide-pulsed HLA-A*02+ T2 cells. The best candidates were reformatted into bispecific tetravalent TandAbs® through Affimed´s proprietary platform using a human/cyno-cross-reactive CD3-binding domain for T-cell engagement. Specific target recognition was confirmed for the TandAbs in binding and cytotoxicity assays on peptide-pulsed T2 cells. HLA-A*02/peptide-complexes selected from the broad normal tissue immunopeptidome with a high degree of sequence similarity to the HLA-A*02/MMP1-003-complex served as controls to confirm the specificity and hence the low risk of off-target binding. The most promising candidates were tested on a panel of endogenously target-expressing cancer cell lines covering MMP1 +/- and HLA-A*02 +/- expression profiles, as well as the source proteins for the most closely related control peptides. The lead TandAb showed excellent target specificity across a wide range of peptide-pulsed and endogenously expressing cell lines as well as potent cytotoxicity with picomolar EC50. In summary, we have identified a tumor-associated MMP1-derived peptide in an HLA-A*02 context by exploiting the knowledge of tumor and healthy tissue immunopeptidomes using XPRESIDENT®. Overcoming the existing barrier of developing antibodies targeting specific MHC/peptide complexes, we generated and characterized highly specific and potent T-cell-recruiting TandAbs. These hold the potential to open up the therapeutic target space for T-cell engagement by providing access to intracellular proteins that are presented in a disease-specific manner as MHC/peptide complexes.

Citation Format: Toni Weinschenk, Erich Rajkovic, Uwe Reusch, Michael Weichel, Kristina Ellwanger, Ivica Fucek, Michael Tesar, Dominik Hinz, Vera Molkenthin, Sebastian Bunk, Norbert Hilf, Oliver Schoor, Dominik Maurer, Kerstin Mock, Carsten Reinhardt, Martin Treder. Identification of antibodies against a novel tumor-associated MHC/peptide-target and generation of highly specific and potent HLA-A*02MMP1-003/CD3 TandAbs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3753. doi:10.1158/1538-7445.AM2017-3753

Abstract 3641: EGFR/CD16A TandAbs are efficacious NK-cell engagers with favorable biological properties which potently kill EGFR+ tumors with and without Ras mutation

Constitutive EGFR activation plays an important role in the pathophysiology of various solid cancers, such as colorectal cancer, non-small cell lung cancer or squamous cell carcinomas of the head and neck. Tyrosine kinase inhibitors (TKI) and monoclonal antibodies (mAbs), which interfere with signal transduction and activation of EGFR, are approved for treatment of such cancers. However, intrinsic or acquired resistance to these treatments has been described for many patients. Natural killer cells (NK-cells) are important effectors of innate immunity and NK-cell engagers have shown evidence of improved safety in patients compared to T-cell engagers. To specifically utilize the cytotoxic potential of NK-cells to eliminate EGFR-expressing tumors, we developed tetravalent bispecific EGFR/CD16A TandAbs comprising fully human Fv domains recognizing human and cynomolgus EGFR and CD16A. TandAbs recognizing epitopes in the extracellular domain of EGFR differing from epitopes targeted by other mAbs were characterized. Lead candidate AFM24 shows superior cytotoxicity in terms of ADCC (main mode of action) and reduced inhibition of EGFR-mediated phosphorylation compared to cetuximab. Importantly, inhibition of EGFR-signaling is believed to contribute to skin toxicity caused by therapeutic mAbs and TKI’s. AFM24’s cytotoxic activity was tested against EGFR+ tumor cell lines including some carrying a Ras mutation, which is a negative prognostic biomarker and renders cells less susceptible to cetuximab or panitumumab. The cetuximab-resistant CRC cell line HCT-116 or the NSCLC cell line A549 (both with Ras mutations) were efficiently killed with EGFR/CD16A TandAbs in vitro. In vivo data in the HCT-116 model indicate anti-tumor efficacy of AFM24, while no efficacy of cetuximab was seen. Importantly, AFM24 does not activate NK-cells without target cell binding and does not bind to any other members of the EGFR family. While binding and cytotoxic efficacy of many therapeutic mAbs are impaired by serum IgG, no substantial change in AFM24’s binding affinity to NK-cells was observed in the presence of high concentrations of human IgG. In calcein-release cytotoxicity assays with NK-cells as effectors, we showed that the presence of IgG had only little inhibitory effect on AFM24 efficacy compared to cetuximab. In addition, competition of an anti-CD16 mAb with AFM24 in cytotoxicity assays was substantially lower than with cetuximab. Taken together our data demonstrate that AFM24 is a highly potent human antibody displaying favorable biological properties over existing mAbs. This human/cynomolgus cross-reactive agent is currently in preclinical development to treat EGFR+ malignancies and has the potential to exhibit a favorable side effect profile and reduced toxicity and to overcome resistance to other targeted anti-EGFR therapeutic agents.

Citation Format: Michael Kluge, Kristina Ellwanger, Uwe Reusch, Ivica Fucek, Michael Weichel, Torsten Haneke, Stefan Knackmus, Joachim Koch, Martin Treder. EGFR/CD16A TandAbs are efficacious NK-cell engagers with favorable biological properties which potently kill EGFR+ tumors with and without Ras mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3641. doi:10.1158/1538-7445.AM2017-3641

EGFR/CD16A tetravalent bispecific antibody AFM24 to engage NK-cells to kill EGFR expressing tumor cells and safety results in cynomolgus monkey studies

e14001

Background: The epidermal growth factor receptor is a target for the treatment of solid tumors, like CRC, HNSCC and NSCLC. Therapeutic success of EGFR-targeting agents depends on mutations defining resistance to these agents, thus an effective EGFR-targeting therapy overcoming resistance would offer an attractive new treatment option. Natural killer (NK-) cells play a central role in the innate immune system and can destroy cancer cells. NK-cell-engaging bispecific antibodies may offer a safe and effective therapy to target EGFR-expressing tumor cells irrespective of their mutational status. Methods: AFM24 was generated using proprietary human anti-EGFR and anti-CD16A variable domains and characterized for binding, stability, manufacturability, efficacy and safety in biophysical and functional assays in vitro and in vivo. Assays for binding to target/effector cells and cytotoxicity were performed in the presence of physiologically relevant IgG levels using EGFR+ tumor cell lines with and without RAS. The safety profile of AFM24 was investigated in vitro for off-target activity and in vivo in cynomolgus monkeys. Results: AFM24 showed excellent biophysical properties and picomolar EC50 values in cytotoxicity assays. It was more potent than cetuximab, or an antibody with cetuximab-derived anti-EGFR variable domain. Importantly, AFM24 was less prone to IgG interference and eliminated cell lines harboring negative predictive biomarkers in in vitro cytotoxicity assays, even in the presence of relevant serum IgG levels. AFM24 demonstrated in vivo efficacy in a humanized hu-NOG mouse model. Furthermore, AFM24 exhibited a favorable safety profile in cynomolgus monkeys. It was well tolerated up to 94 mg/kg in a single dose, maximum tolerated dose study (MTD) when administered as a 2 hour infusion. Conclusions: Our data suggest that AFM24 is a highly potent and potentially safer drug candidate suitable for the treatment of EGFR-expressing cancers with the potential to overcome resistance to other EGFR-targeting agents and to avoid toxic side effects seen with other anti-EGFR therapeutics.

AFM26 is a novel, highly potent BCMA/CD16A-directed bispecific antibody for high affinity NK-cell engagement in multiple myeloma

8045

Background: Despite recent advances in the treatment of multiple myeloma (MM), novel therapies are needed to achieve long-lasting remissions in a greater number of patients. Natural killer (NK) cells play a key role in the immune response to MM and have been implicated in the clinical efficacy of current standard of care interventions, including IMiDs, proteasome inhibitors, recently approved immunotherapies and autologous stem cell transplantation (ASCT). Numerous strategies are being developed to enhance the natural NK-cell cytotoxicity against myeloma cells, which is frequently dysregulated in MM. Approaches include modulation of activity, through cytokine stimulation or immune checkpoint targeting, and adoptive transfer of culture expanded NK-cells in ASCT-eligible MM. While highly attractive, these approaches are non-targeted, as they rely on the natural cytotoxicity of NK-cells, and may benefit from antigen-specific retargeting and effector activation. AFM26 is a novel tetravalent, bispecific antibody designed to specifically enhance NK-cell anti-MM activity by redirecting NK-cell lysis to BCMA, an antigen expressed on MM cells. Methods: NK-cell engagement and cytotoxicity of AFM26 towards MM cell lines and freshly isolated tumor cells from MM patients was characterized in vitro and compared with classical antibody formats. Results: AFM26 engages NK-cells with superior avidity ( KD: 1-2nM) through bivalent interaction with CD16A (FcγRIIIa) and demonstrates extended cell surface retention that is not affected by high level IgG, as is particularly relevant in MM. Importantly, AFM26 does not induce NK-cell depletion but selectively induces potent and efficacious lysis of MM cells in vitro. Conclusions: In summary, AFM26 is a promising candidate to enhance NK-cell activity and confer tumor-specificity to NK-cells in MM. Differentiation of AFM26 from classical antibody formats and its potential for combination with cellular NK-cell therapies is highlighted.

Highly Specific and Effective Targeting of EGFRvIII-Positive Tumors with TandAb Antibodies

To harness the cytotoxic capacity of immune cells for the treatment of solid tumors, we developed tetravalent, bispecific tandem diabody (TandAb) antibodies that recognize EGFRvIII, the deletion variant III of the epidermal growth factor receptor (EGFR), and CD3 on T-cells, thereby directing immune cells to eliminate EGFRvIII-positive tumor cells. Using phage display, we identified scFv antibodies selectively binding to EGFRvIII. These highly EGFRvIII-specific, fully human scFv were substantially improved by affinity maturation, achieving K_Ds in the picomolar range, and were used to construct a set of bispecific EGFRvIII-targeting TandAbs with a broad range of binding and cytotoxic properties. These antibodies exhibited an exquisite specificity for a distinguished epitope in the N-terminal portion of EGFRvIII, as shown on recombinant antigen in Western Blot, SPR, and ELISA, as well as on antigen-expressing cells in FACS assays, and did not bind to the wild-type EGFR. High-affinity EGFRvIII/CD3 TandAbs were most potent in killing assays, displaying cytotoxicity toward EGFRvIII-expressing CHO, F98 glioma, or human DK-MG cells with EC₅₀ values in the range of 1-10 pM in vitro. They also demonstrated dose-dependent growth control in vivo in an EGFRvIII-positive subcutaneous xenograft tumor model. Together with the tumor-exclusive expression of EGFRvIII, the EGFRvIII/CD3 TandAbs' high specificity and strictly target-dependent activation with no off-target activity provide an opportunity to target tumor cells and spare normal tissues, thereby reducing the side effects associated with other anti-EGFR therapies. In summary, EGFRvIII/CD3 TandAbs are highly attractive therapeutic antibody candidates for selective immunotherapy of EGFRvIII-positive tumors.

Abstract 580: Anti-EGFRvIII TandAbs recruiting either T or NK cells are highly specific and potent therapeutic antibody candidates for the treatment of EGFRvIII+ tumors

EGFRvIII is the most prevalent tumor-specific variant of the wild-type EGFR and represents an attractive tumor target in various solid tumors such as GMB, HNSCC or NSCLC. Despite the clinical successes achieved with EGFR targeting antibodies or small molecule inhibitors little therapeutic progress has been made with EGFRvIII. There is still a high medical need in such cancers and several agents are in development to address this notoriously difficult target: Celldex′ vaccine rindopepimut in combination with bevacizumab in late-stage development, or ADCs in early development by Amgen or Abbvie. However, despite the high tumor specificity of EGFRvIII expression, no potent T- or NK-cell engaging are currently in clinical development.

It has been recognized that there may be more therapeutic potential with bi-specific antibodies recruiting immune effectors for targeted destruction of antigen-positive tumor cells. We developed tetravalent, bi-specific TandAbs that recognize EGFRvIII, and recruiting either T-cells or NK-cells by binding to the activating receptors CD3 and CD16A, respectively. This targeted antibody approach allows the selective destruction of EGFRvIII+ tumor cells employing highly potent and efficacious immune effector cells whilst sparing normal cells that are EGFRvIII- or cells presenting the ubiquitously expressed EGFR.

The selected EGFRvIII/CD3 and EGFRvIII/CD16A TandAbs exhibited exquisite specificity towards EGFRvIII in Western Blot, SPR, ELISA, and flow cytometric assays. No binding was observed to recombinant EGFR or to EGFR+ cells. They also displayed potent cytotoxicity towards EGFRvIII+ cell lines with EC50 values in the low picomolar range. No cytotoxicity was observed on EGFRvIII- target cells or cells expressing EGFR demonstrating the high selectivity of anti-EGFRvIII TandAbs. Importantly, in the absence of EGFRvIII+ target cells our TandAbs did not elicit T- or NK-cell activation and activation-induced immune cell proliferation suggesting an excellent safety profile. In vivo pharmacodynamics for anti-EGFRvIII TandAbs was demonstrated in a mouse xenograft model.

The clinical relevance of EGFRvIII as a tumor marker and the binding of our anti-EGFRvIII variable domains were evaluated by immunohistochemistry. Binding was shown in glioblastoma and other solid tumors, but no expression was detectable on healthy tissue.

In summary, the presented in vitro and in vivo studies qualify EGFRvIII/CD3 and EGFRvIII/CD16A TandAbs as highly attractive therapeutic antibody candidates and provides us with the possibility of employing both T-cell and NK-cell recruiting strategies for selective immunotherapy of EGFRvIII+ tumors. Due to tumor specific expression of EGFRvIII and the absence of off-target activity our TandAbs display an excellent safety profile reducing the risks of side effects associated with other anti-EGFRvIII therapies.

Citation Format: Kristina Ellwanger, Uwe Reusch, Ivica Fucek, Michael Weichel, Thorsten Gantke, Stefan Knackmuss, Martin Treder. Anti-EGFRvIII TandAbs recruiting either T or NK cells are highly specific and potent therapeutic antibody candidates for the treatment of EGFRvIII+ tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 580.

Abstract 593: Highly cytotoxic EGFR/CD16A TandAbs specifically recruit NK cells to potently kill various types of solid tumors

Constitutive EGFR activation through amplification or dysregulation plays an important role in the pathophysiology of numerous solid cancers, such as colorectal cancer (CRC), non-small cell lung cancer (NSCLC) or squamous cell carcinomas of the head and neck (SCCHN), thus providing a strong rationale for the development of therapeutic strategies targeting EGFR. Different therapeutic approaches have been approved for treatment of such cancers, including tyrosine kinase inhibitors that interfere with signal transduction by blocking the kinase domain or monoclonal antibodies (mAbs) that prevent EGFR ligand binding, dimerization and activation. However, despite demonstrated clinical efficacy, intrinsic or acquired resistance to such treatments has been described for a larger number of patients.

Natural killer cells (NK-cells) play a central role in the innate immune system and have the capacity to destroy virally-infected or neoplastic cells. To specifically utilize the cytotoxic potential of NK-cells for the elimination of EGFR+ cancer cells, we developed tetravalent bispecific EGFR/CD16A NK-cell TandAbs, with two binding sites for EGFR being expressed on tumor cells, and two binding sites for CD16A expressed on NK-cells.

Using antibody phage display technologies, we identified high affinity scFvs recognizing conformational epitopes in the extracellular domain of EGFR that were different to those targeted by other therapeutic antibodies. We engineered a set of bispecific EGFR/CD16A TandAbs and analysed their binding, thermostability and cytotoxic properties in a panel of in vitro assays. TandAbs containing our EGFR-specific domain 21 were highly potent in cytotoxicity assays towards endogenously EGFR-expressing tumor cell lines or transfected CHO cells with single digit picomolar or subpicomolar EC50 values. In contrast to comparator NK-cell recruiting TandAbs containing the Fv sequences from cetuximab, the TandAbs containing our EGFR-binding domain 21 did not exhibit any signs of temperature-induced instability or aggregation in thermostability studies.

Taken together, our data suggest that EGFR/CD16A TandAbs are novel, highly potent drug candidates suitable for the treatment of EGFR-overexpressing malignancies and overcoming resistance to other therapeutic agents.

Citation Format: Kristina Ellwanger, Uwe Reusch, Ivica Fucek, Michael Weichel, Erich Rajkovic, Martin Treder. Highly cytotoxic EGFR/CD16A TandAbs specifically recruit NK cells to potently kill various types of solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 593.

Characterization of CD33/CD3 Tetravalent Bispecific Tandem Diabodies (TandAbs) for the Treatment of Acute Myeloid Leukemia

PURPOSE

Randomized studies with gemtuzumab ozogamicin have validated CD33 as a target for antigen-specific immunotherapy of acute myelogenous leukemia (AML). Here, we investigated the potential of CD33/CD3-directed tandem diabodies (TandAbs) as novel treatment approach for AML. These tetravalent bispecific antibodies provide two binding sites for each antigen to maintain the avidity of a bivalent antibody and have a molecular weight exceeding the renal clearance threshold, thus offering a longer half-life compared to smaller antibody constructs.

EXPERIMENTAL DESIGN

We constructed a series of TandAbs composed of anti-CD33 and anti-CD3 variable domains of diverse binding affinities and profiled their functional properties in CD33⁺ human leukemia cell lines, xenograft models, and AML patient samples.

RESULTS

Our studies demonstrated that several CD33/CD3 TandAbs could induce potent, dose-dependent cytolysis of CD33⁺ AML cell lines. This effect was modulated by the effector-to-target cell ratio and strictly required the presence of T cells. Activation and proliferation of T cells and maximal AML cell cytolysis correlated with high avidity to both CD33 and CD3. High-avidity TandAbs were broadly active in primary specimens from patients with newly diagnosed or relapsed/refractory AML in vitro, with cytotoxic properties independent of CD33 receptor density and cytogenetic risk. Tumor growth delay and inhibition were observed in both prophylactic and established HL-60 xenograft models in immunodeficient mice.

CONCLUSIONS

Our data show high efficacy of CD33/CD3 TandAbs in various preclinical models of human AML. Together, these findings support further study of CD33/CD3 TandAbs as novel immunotherapeutics for patients with AML. Clin Cancer Res; 22(23); 5829-38. ©2016 AACR.

A tetravalent bispecific TandAb (CD19/CD3), AFM11, efficiently recruits T cells for the potent lysis of CD19(+) tumor cells

To harness the potent tumor-killing capacity of T cells for the treatment of CD19(+) malignancies, we constructed AFM11, a humanized tetravalent bispecific CD19/CD3 tandem diabody (TandAb) consisting solely of Fv domains. The molecule exhibits good manufacturability and stability properties. AFM11 has 2 binding sites for CD3 and 2 for CD19, an antigen that is expressed from early B cell development through differentiation into plasma cells, and is an attractive alternative to CD20 as a target for the development of therapeutic antibodies to treat B cell malignancies. Comparison of the binding and cytotoxicity of AFM11 with those of a tandem scFv bispecific T cell engager (BiTE) molecule targeting the same antigens revealed that AFM11 elicited more potent in vitro B cell lysis. Though possessing high affinity to CD3, the TandAb mediates serial-killing of CD19(+) cells with little dependence of potency or efficacy upon effector:target ratio, unlike the BiTE. The advantage of the TandAb over the BiTE was most pronounced at lower effector:target ratios. AFM11 mediated strictly target-dependent T cell activation evidenced by CD25 and CD69 induction, proliferation, and cytokine release, notwithstanding bivalent CD3 engagement. In a NOD/scid xenograft model, AFM11 induced dose-dependent growth inhibition of Raji tumors in vivo, and radiolabeled TandAb exhibited excellent localization to tumor but not to normal tissue. After intravenous administration in mice, half-life ranged from 18.4 to 22.9 h. In a human ex vivo B-cell chronic lymphocytic leukemia study, AFM11 exhibited substantial cytotoxic activity in an autologous setting. Thus, AFM11 may represent a promising therapeutic for treatment of CD19(+) malignancies with an advantageous safety risk profile and anticipated dosing regimen.

Abstract 2471: EGFRvIII T-cell TandAbs are specific and highly potent drug candidates for the treatment of a variety of solid tumors

To harness the cytotoxic capacity of immune effector cells for the treatment of several types of solid tumors, we developed tetravalent bifunctional antibodies that recognize EGFRvIII, the deletion variant III of EGFR. Their second functionality binds with high affinity to CD3, thereby directing T-cells to eliminate EGFRvIII+ cancer cells. The expression of EGFRvIII on various solid tumor types, and its absence from healthy tissues, provides an opportunity to develop cytotoxic antibodies that solely target cancer; these would spare normal tissues, and substantially reduce the side effects associated with EGFR therapy.

Using phage display, we identified scFvs that selectively bind to EGFRvIII but not to EGFR. The binding affinities of these highly EGFRvIII-specific antibodies were substantially improved, employing affinity maturation techniques, and achieved KDs in the 100pM range and lower.

We engineered a panel of bispecific EGFRvIII/CD3 TandAbs with a broad range of binding and cytotoxic properties. Mono- and bivalent binding, specificity for both EGFRvIII and CD3, T cell-mediated cytotoxic activity, and target-mediated T-cell activation were characterized in a panel of in vitro assays. EGFRvIII/CD3 TandAbs exhibit exquisite specificity towards the EGFRvIII antigen in Western Blot, SPR, ELISA, and FACS assays of EGFRvIII+ cells. No specific binding was observed to recombinant EGFR antigen or to EGFR-expressing cells. Apparent affinities of EGFRvIII/CD3 TandAbs to EGFRvIII were up to 25fold improved relative to the monovalently binding scFvs, and achieved a KD of 11pM for the best binding EGFRvIII/CD3 TandAb. Improvement of the binding affinities in the bivalent TandAb format was largely due to slower dissociation.

TandAbs with high affinity for EGFRvIII were most potent in killing assays, displaying cytotoxicity towards EGFRvIII-expressing F98 glioma and CHO cells with EC50 in the range of 1pM-10pM. No cytotoxicity was observed on EGFR+ cells or EGFRvIII- cells up to the maximally-evaluated TandAb concentration of 0.5μM (which is 100000 fold higher than the EC50) demonstrating the high selectivity of EGFRvIII/CD3 TandAbs for the tumor-specific EGFRvIII. High affinity binding to CD3 was necessary for efficacious T cell recruitment as shown by the correlation of CD3-binding and cytotoxic potency of EGFRvIII/CD3 TandAbs. Importantly, in the absence of EGFRvIII+ target cells in vitro, TandAbs did not elicit T cell activation, as demonstrated by their lack of proliferation: this specificity contributed to a good preclinical safety profile. Biophysical and pharmacological characterization of several candidates is currently ongoing, whereby the first EGFRvIII/CD3 TandAbs demonstrated a robust dose-dependent growth retardation of EGFRvIII+ subcutaneous xenograft tumors.

In summary, EGFRvIII/CD3 TandAbs are specific and highly potent drug candidates for the treatment of EGFRvIII+ malignancies.

Citation Format: Kristina Ellwanger, Uwe Reusch, Ivica Fucek, Michael Weichel, Carmen Herbrecht, Stefan Knackmuss, Erich Rajkovic, Vera Molkenthin, Eugene A. Zhukovsky. EGFRvIII T-cell TandAbs are specific and highly potent drug candidates for the treatment of a variety of solid tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2471. doi:10.1158/1538-7445.AM2015-2471

Fate Specification of Neural Plate Border by Canonical Wnt Signaling and Grhl3 is Crucial for Neural Tube Closure

During primary neurulation, the separation of a single-layered ectodermal sheet into the surface ectoderm (SE) and neural tube specifies SE and neural ectoderm (NE) cell fates. The mechanisms underlying fate specification in conjunction with neural tube closure are poorly understood. Here, by comparing expression profiles between SE and NE lineages, we observed that uncommitted progenitor cells, expressing stem cell markers, are present in the neural plate border/neural fold prior to neural tube closure. Our results also demonstrated that canonical Wnt and its antagonists, DKK1/KREMEN1, progressively specify these progenitors into SE or NE fates in accord with the progress of neural tube closure. Additionally, SE specification of the neural plate border via canonical Wnt signaling is directed by the grainyhead-like 3 (Grhl3) transcription factor. Thus, we propose that the fate specification of uncommitted progenitors in the neural plate border by canonical Wnt signaling and its downstream effector Grhl3 is crucial for neural tube closure. This study implicates that failure in critical genetic factors controlling fate specification of progenitor cells in the neural plate border/neural fold coordinated with neural tube closure may be potential causes of human neural tube defects.

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Neural plate border/neural fold possesses stem cell-like characters during primary neurulation.

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Canonical Wnt and its antagonists progressively specify progenitors into surface or neural fates upon neural tube closure.

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Fate specification into surface ectoderm in the neural fold is directed by the Grhl3 transcription factor.

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Fate specification of uncommitted progenitors in the neural plate border is intimately coupled to neural tube closure.

Abstract 2643: A highly cytotoxic EGFRvIII/CD3 TandAb recruits T cells to specifically and potently kill several types of solid tumor cancers

To harness the cytotoxic capacity of T cells for the treatment of EGFRvIII+ cancers, we developed a humanized bispecific tetravalent antibody, with two binding sites for CD3 (or CD16A) and EGFRvIII, the EGFRvIII/CD3 (and EGFRvIII/CD16A) RECRUIT-TandAb. EGFR dysregulation has been linked to numerous cancers, and both small molecules and EGFR targeting antibodies have successfully reached the clinic. The deletion variant III (EGFRvIII), the most common mutant form of EGFR is expressed exclusively in cancer tissues contributing to oncogenic transformation. The restricted EGFRvIII expression on various solid tumor types provides an opportunity to develop cytotoxic antibodies that solely target cancer, sparing normal tissues, and substantially reduce the side effects associated with EGFR therapy.

Using phage display libraries, we identified scFvs that selectively bound to the mutated and not the native form of EGFR. T cells are potent tumor-killing effector cells that cannot be recruited by native antibodies; hence we engineered a panel of bispecific EGFRvIII/CD3 TandAbs, capable of T cell-recruitment, with a broad range of binding and cytotoxic properties. The TandAbs' binding properties, T cell-mediated cytotoxic activity, and target-mediated T cell activation were characterized in a panel of in vitro assays. They exhibited exquisite specificity towards EGFRvIII in ELISA and FACS assays, with no wild-type EGFR binding observed, up to the maximally evaluated TandAb concentration of 1 μM. The most potent TandAbs displayed cytotoxicity towards EGFRvIII expressing F98 glioma and CHO cells with EC50 = 25 pM. We also assayed the cytotoxicity of these TandAbs towards EGFR+ cells as a more sensitive probe of residual binding to the native form. No cytotoxicity was observed up to the maximally evaluated TandAb concentration of 0.5 μM. The cytotoxic potency of the EGFRvIII/CD3 TandAb was higher than that of a comparator bivalent bispecific antibody, constructed from different anti-EGFRvIII/CD3 moieties or of EGFRvIII/CD16A TandAbs, which recruit NK cells instead of cytotoxic T cells. EGFRvIII/CD3 TandAbs with high affinity binding to CD3 were most efficacious for T cell recruitment and tumor cell killing and yet, in the absence of EGFRvIII+ target cells in vitro, TandAbs did not elicit T cell activation, as measured by their lack of proliferation, contributing to a good preclinical safety profile. In vivo EGFRvIII/CD3 TandAbs demonstrated a robust dose-dependent growth retardation of EGFRvIII+ subcutaneous Xenograft tumors in NOD/scid mice reconstituted with human PBMC; this tumor growth inhibition was more pronounced than that associated with cetuximab. In summary, our data demonstrate the strict specificity and high potency of the anti-tumor cytotoxicity mediated by the EGFRvIII/CD3 TandAb, a novel highly potent drug candidate for the treatment of EGFRvIII+ malignancies.

Citation Format: Eugene A. Zhukovsky, Kristina Ellwanger, Uwe Reusch, Markus Eser, Fionnuala McAleese, Ivica Fucek, Carmen Burkhardt, Stefan Knackmuss. A highly cytotoxic EGFRvIII/CD3 TandAb recruits T cells to specifically and potently kill several types of solid tumor cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2643. doi:10.1158/1538-7445.AM2014-2643

Abstract C163: A highly cytotoxic EGFRvIII/CD3 TandAb recruits T cells to specifically and potently kill several types of solid tumor cancers

To harness the cytotoxic capacity of T cells for the treatment of EGFRvIII+ cancers, we developed a humanized bispecific tetravalent antibody, with two binding sites for CD3 and EGFRvIII, the EGFRvIII/CD3 RECRUIT-TandAb. EGFR dysregulation has been linked to numerous cancers, and both small molecules and EGFR targeting antibodies have successfully reached the clinic. However, the antibodies approved for clinical use, and those in development, all share a severe side effect profile due to the broad normal tissue-expression of EGFR. The deletion variant III of EGFR (EGFRvIII), with truncated extracellular domain and ensuing ligand-independent constitutive activity, is the most common mutant form associated with oncogenic transformation. EGFRvIII is expressed exclusively in cancer tissues and is associated with various solid tumor types. The restricted EGFRvIII expression on cancer cells provides an opportunity to develop cytotoxic antibodies that solely target cancer, sparing normal tissues, and substantially reduce the side effects associated with EGFR therapy. Using phage display libraries, we identified anti-EGFRvIII antibodies that selectively bound to the mutated and not the native form of EGFR. T cells are potent tumor-killing effector cells that cannot be recruited by native antibodies; hence we engineered a panel of bispecific EGFRvIII/CD3 TandAbs, capable of T cell-recruitment, with a broad range of binding and cytotoxic properties. The TandAbs’ binding properties, T cell-mediated cytotoxic activity, and target-mediated T cell activation were characterized in a panel of in vitro assays. They exhibited exquisite specificity towards EGFRvIII in ELISA and FACS assays, with no wild-type EGFR binding observed, up to the maximally evaluated TandAb concentration of 1 μM. The most potent TandAbs displayed cytotoxicity towards EGFRvIII expressing F98 glioma and CHO cells with EC50 = 25 pM. We also assayed the cytotoxicity of these TandAbs towards EGFR+ cells as a more sensitive probe of residual binding to the native form. No cytotoxicity was observed up to the maximally evaluated TandAb concentration of 0.5 μM. The cytotoxic potency of the EGFRvIII/CD3 TandAb was higher than that of a comparator bivalent bispecific antibody, constructed from different anti-EGFRvIII/CD3 moieties; moreover, the comparator was not strictly specific for EGFRvIII and had residual cytotoxicity, EC50 = 1 nM, towards EGFR+ cell lines. High affinity binding to CD3 was essential for efficacious T cell recruitment and yet, in the absence of EGFRvIII+ target cells in vitro, TandAbs did not elicit T cell activation, as measured by their lack of proliferation, contributing to a good preclinical safety profile. In summary, our data demonstrate the strict specificity and high potency of the anti-tumor cytotoxicity mediated by the EGFRvIII/CD3 TandAb, a novel highly potent drug candidate for the treatment of EGFRvIII+ malignancies.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C163.

Citation Format: Eugene A. Zhukovsky, Kristina Ellwanger, Uwe Reusch, Markus Eser, Ivica Fucek, Carmen Burkhardt. A highly cytotoxic EGFRvIII/CD3 TandAb recruits T cells to specifically and potently kill several types of solid tumor cancers. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C163.

Loss of Dickkopf-1 restores neurogenesis in old age and counteracts cognitive decline

Memory impairment has been associated with age-related decline in adult hippocampal neurogenesis. Although Notch, bone morphogenetic protein, and Wnt signaling pathways are known to regulate multiple aspects of adult neural stem cell function, the molecular basis of declining neurogenesis in the aging hippocampus remains unknown. Here, we show that expression of the Wnt antagonist Dickkopf-1 (Dkk1) increases with age and that its loss enhances neurogenesis in the hippocampus. Neural progenitors with inducible loss of Dkk1 increase their Wnt activity, which leads to enhanced self-renewal and increased generation of immature neurons. This Wnt-expanded progeny subsequently matures into glutamatergic granule neurons with increased dendritic complexity. As a result, mice deficient in Dkk1 exhibit enhanced spatial working memory and memory consolidation and also show improvements in affective behavior. Taken together, our findings show that upregulating Wnt signaling by reducing Dkk1 expression can counteract age-related decrease in neurogenesis and its associated cognitive decline.

AFM11, a CD19/CD3 bispecific tandab, to facilitate T-cell-mediated killing of CD19+ cells

3068

Background: CD19, due to broader expression on B cell subtypes, is an attractive alternative to CD20 as a target for treatment of B cell malignancies. T cells are potent tumor-killing effectors that cannot be recruited by full length antibodies, however TandAb technology harnesses their cytotoxic nature for oncology indications. The CD3 RECRUIT TandAb AFM11 enables T cells to potently and specifically kill CD19+ tumors and possesses advantageous PK properties enabling intravenous dosing. Methods: We constructed AFM11, a human bispecific tetravalent antibody with two binding sites for both CD3 and CD19. In vitro efficacy and safety were evaluated on CD19+ cell lines and primary tumors. In vivo efficacy was evaluated in a murine NOD/scid xenograft model reconstituted with human PBMC. Results: In vitro assays demonstrate higher potency and efficacy of target cell lysis by AFM11 relative to a bispecific tandem scFv. CD8+ T cells dominate early cytotoxicity (4 hrs) while after 24 hrs both CD4+ and CD8+ T cells equally contribute to tumor lysis with EC50 of 0.5 – 5 pM; cytotoxicity is independent of cell CD19 density. AFM11 exhibits similar cytotoxicity at Effector:Target ratios from 5:1 to 1:5 and facilitates T cell serial killing of its targets. AFM11 activates T cells only in the presence of CD19+ cells. In PBMC cultures AFM11 induces CD69 and CD25 expression, T cell proliferation, and production of IFN-γ, TNF-α, IL-2, IL-6, and IL-10. Depletion of CD19+ cells from PBMC abrogates these effects, and indicates strict CD19+ target-dependent T cell activation. Thus, AFM11 should not elicit the devastating cytokine release observed when full length antibodies bind CD3. Cell lysis by AFM11 is restricted to CD19+ targets asCD19- bystanders are not lysed in co-culture assays. Up to one week co-incubation with AFM11 does not inhibit T cell cytotoxicity and thus it does not induce anergy. In vivo AFM11 exhibits a dose-dependent growth inhibition of Raji tumors; a single dose of AFM11 exhibits similar efficacy as 5 daily injections. Conclusions: AFM11 is a highly efficacious novel drug candidate for the treatment of CD19+ malignancies with an advantageous safety profile and anticipated dosing regimen.

Abstract 1243: Bispecific TandAbs: a safe and potent platform for T cell-mediated killing of CD19+ cells

CD19 is expressed from early B cell development through differentiation into plasma cells, and is an attractive alternative to CD20 as a target for therapeutic antibodies that treat B cell malignancies. T cells are potent tumor-killing effector cells that cannot be recruited by native antibodies. The TandAb technology enables the development of bispecific antibody therapeutics for oncology indications that harness the cytotoxic nature of T cells. The CD3 RECRUIT-TandAb AFM11, a human bispecific tetravalent antibody with two binding sites for both CD3 and CD19, exhibits highly potent cytotoxic activity and possesses pharmacokinetic properties that are considerably improved relative to alternative bispecific formats. In vitro assays demonstrate high affinity binding of AFM11 to CD3+ and CD19+ cells leading to higher potency and efficacy of T cell recruitment and target cell lysis relative to alternative bispecific antibody formats(tandem scFv, diabody). Cytotoxicity assays show that AFM11 mediates target cell lysis by CD4+ and CD8+ T cells with EC50 values in the low to sub-picomolar range that is independent of the target cell CD19 density. AFM11 exhibits nearly identical cytotoxicity across a broad range of effector-to-target ratios, from 5:1 to 1:5, and facilitates serial target cell killing by T cells. Binding of antibodies to CD3 on T cells may elicit devastating cytokine release if it results in systemic rather than target-specific activation of T cells. Indeed, the anti-CD3 antibody OKT3 exhibits high toxicity in humans due to non-specific activation of T cells. Thus, in vitro assays were used to assess AFM11 off-target activity. AFM11 activates T cells inly in the presence of CD19+ cells, resulting in induction of CD69 and CD25 expression and the on-target release of IFN-γ, TNF-α, IL-2, and IL-6. However, depletion of CD19+ cells from PBMC cultures completely abrogates AFM11-mediated activation marker expression, T cell proliferation, and cytokine release, and supports strict CD19+ target-dependent T cell activation. Conversely, OKT3, produced cytokine release and T cell proliferation in all cultures except purified T cells. AFM11-mediated target cell lysis is specific for and restricted to CD19+ target cells since CD19− bystanders were not lysed in assays with mixed target populations. Binding of AFM11 to CD3 also did not induce anergy since its incubation with T cells for several days did not inhibit their potent cytotoxicity. AFM11 demonstrated a robust dose-dependent inhibition of growth of Raji tumor xenografts in NOD/scid mice reconstituted with human PBMC. Moreover, a single dose of AFM11 resulted in tumor growth inhibition similar to that produced by 5 daily injections. Altogether, these data suggest that AFM11 is a highly efficacious novel drug candidate for the treatment of hematological malignancies with advantages in both safety profile and anticipated dosing regimen.

Citation Format: Eugene A. Zhukovsky, Uwe Reusch, Carmen Burkhardt, Stefan Knackmuss, Ivica Fucek, Markus Eser, Fionnuala McAleese, Kristina Ellwanger. Bispecific TandAbs: a safe and potent platform for T cell-mediated killing of CD19+ cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1243. doi:10.1158/1538-7445.AM2013-1243

High affinity CD3 RECRUIT TandAb for T cell-mediated lysis of CD19+ tumor B cells

8059

Background: CD19 is expressed from early B cell development to the differentiation into plasma cells and is an attractive target for B cell malignancies either lacking CD20 expression or refractory to anti-CD20 antibody therapies. T cells are potent tumor killing effector cells that are not recruited by native antibodies. The CD3 RECRUIT-TandAb AFM11, a human bispecific tetravalent antibody with two binding sites for both CD3 and CD19, is a novel therapeutic for the treatment of NHL that harnesses the cytotoxic nature of T cells. Methods: A bispecific anti-CD19/anti-CD3 tetravalent TandAb with humanized and affinity matured variable domains was constructed. The TandAb’s binding, T-cell mediated cytotoxic activity, and cytokine release were characterized in a panel of in vitro assays. In vivo efficacy was evaluated in a murine NOD/scid xenograft model reconstituted with human PBMC. Results: AFM11 mediates highly potent target tumor cell lysis in cytotoxicity assays: EC50 values are low to sub-picomolar range in a panel of CD19+ cell lines and primary B-CLL tumor cells. The cytotoxic activity of tetravalent AFM11 is superior to that of alternative bivalent antibody formats possessing only a single binding site for both CD19 and CD3. High affinity binding of AFM11 to CD19, and more so to CD3 (low to sub-nanomolar Kd), is essential for efficacious T cell recruitment. The high affinity bivalent binding of AFM11 to CD3 does not trigger T cell activation in the absence of CD19+ target cells in functional in vitro assays. AFM11 activates T cells only in the presence of its targets and mediates lysis while sparing antigen-negative bystanders. AFM11 induces down-modulation of the CD3/TCR complex in the absence of target cells and at high concentrations. Also, AFM11-treated T cells can be re-engaged for target cell lysis. These features of AFM11-induced T cell activation may contribute additional safety with no compromise of efficacy. Finally, AFM11 demonstrates a robust dose-dependent inhibition of subcutaneous Raji tumors in mice. Conclusions: AFM11 is a novel highly efficacious drug candidate for the treatment of B cell malignancies with an advantageous safety profile.

Dkk1 regulates ventral midbrain dopaminergic differentiation and morphogenesis

Dickkopf1 (Dkk1) is a Wnt/β-catenin inhibitor that participates in many processes during embryonic development. One of its roles during embryogenesis is to induce head formation, since Dkk1-null mice lack head structures anterior to midbrain. The Wnt/β-catenin pathway is also known to regulate different aspects of ventral midbrain (VM) dopaminergic (DA) neuron development and, in vitro, Dkk1-mediated inhibition of the Wnt/β-catenin pathway improves the DA differentiation in mouse embryonic stem cells (mESC). However, the in vivo function of Dkk1 on the development of midbrain DA neurons remains to be elucidated. Here we examined Dkk1^+/− embryos and found that Dkk1 is required for the differentiation of DA precursors/neuroblasts into DA neurons at E13.5. This deficit persisted until E17.5, when a defect in the number and distribution of VM DA neurons was detected. Furthermore, analysis of the few Dkk1^−/− embryos that survived until E17.5 revealed a more severe loss of midbrain DA neurons and morphogenesis defects. Our results thus show that Dkk1 is required for midbrain DA differentiation and morphogenesis.

Negative regulation of bone formation by the transmembrane Wnt antagonist Kremen-2

Wnt signalling is a key pathway controlling bone formation in mice and humans. One of the regulators of this pathway is Dkk1, which antagonizes Wnt signalling through the formation of a ternary complex with the transmembrane receptors Krm1/2 and Lrp5/6, thereby blocking the induction of Wnt signalling by the latter ones. Here we show that Kremen-2 (Krm2) is predominantly expressed in bone, and that its osteoblast-specific over-expression in transgenic mice (Col1a1-Krm2) results in severe osteoporosis. Histomorphometric analysis revealed that osteoblast maturation and bone formation are disturbed in Col1a1-Krm2 mice, whereas bone resorption is increased. In line with these findings, primary osteoblasts derived from Col1a1-Krm2 mice display a cell-autonomous differentiation defect, impaired canonical Wnt signalling and decreased production of the osteoclast inhibitory factor Opg. To determine whether the observed effects of Krm2 on bone remodeling are physiologically relevant, we analyzed the skeletal phenotype of 24 weeks old Krm2-deficient mice and observed high bone mass caused by a more than three-fold increase in bone formation. Taken together, these data identify Krm2 as a regulator of bone remodeling and raise the possibility that antagonizing KRM2 might prove beneficial in patients with bone loss disorders.

Neural crests are actively precluded from the anterior neural fold by a novel inhibitory mechanism dependent on Dickkopf1 secreted by the prechordal mesoderm

It is known the interactions between the neural plate and epidermis generate neural crest (NC), but it is unknown why the NC develops only at the lateral border of the neural plate and not in the anterior fold. Using grafting experiments we show that there is a previously unidentified mechanism that precludes NC from the anterior region. We identify prechordal mesoderm as the tissue that inhibits NC in the anterior territory and show that the Wnt/beta-catenin antagonist Dkk1, secreted by this tissue, is sufficient to mimic this NC inhibition. We show that Dkk1 is required for preventing the formation of NC in the anterior neural folds as loss-of-function experiments using a Dkk1 blocking antibody in Xenopus as well as the analysis of Dkk1-null mouse embryos transform the anterior neural fold into NC. This can be mimicked by Wnt/beta-catenin signaling activation without affecting the anterior posterior patterning of the neural plate, or placodal specification. Finally, we show that the NC cells induced at the anterior neural fold are able to migrate and differentiate as normal NC. These results demonstrate that anterior regions of the embryo lack NC because of a mechanism, conserved from fish to mammals, that suppresses Wnt/beta-catenin signaling via Dkk1.