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Antibodies have been widely used for cancer therapy owing to their ability to distinguish cancer cells by recognizing cancer-specific antigens. Epidermal growth factor receptor (EGFR) is a promising target for the cancer therapeutics, against which several antibody clones have been developed and brought into therapeutic use. Another antibody clone, 528, is an antagonistic anti-EGFR antibody, which has been the focus of our antibody engineering studies to develop cancer drugs. In this study, we explored the interaction of 528 with the extracellular region of EGFR (sEGFR) via binding analyses and structural studies. Dot blotting experiments with heat treated sEGFR and surface plasmon resonance binding experiments revealed that 528 recognizes the tertiary structure of sEGFR and exhibits competitive binding to sEGFR with EGF and cetuximab. Single particle analysis of the sEGFR-528 Fab complex via electron microscopy clearly showed the binding of 528 to domain III of sEGFR, the domain to which EGF and cetuximab bind, explaining its antagonistic activity. Comparison between the two-dimensional class average and the cetuximab/sEGFR crystal structure revealed that 528 binds to a site that is shifted from, rather than identical to, the cetuximab epitope, and may exclude known drug-resistant EGFR mutations.

Affinity maturation is one of the cardinal strategies for improving antibody function using in vitro evolutionary methods; one such well-established method is phage display. To minimise gene deletion, we previously developed an open sandwich (OS) method wherein selection was performed using only phage-displaying VH fragments after mixing with soluble VL fragments. The decrease in anti-EGFR antibody 528 affinity through humanization was successfully recovered by selecting VH mutants using this OS method. However, the affinity was not similar to that of parental 528. For further affinity maturation, we aimed to isolate VL mutants that act in synergy with VH mutants. However, the OS method could not be applied for selecting VL fragments because the preparation of soluble VH fragments was hampered by their instability and insolubility. Therefore, we initially designed a modified OS method based on domain-swapping of VH fragments, from added soluble Fv fragments to phage-displaying VL fragments. Using this novel Fv-added OS selection method, we successfully isolated VL mutants, and one of the Fv comprising VH and VL mutants showed affinity almost equivalent to that of parental 528. This method is applicable for engineering other VL fragments for affinity maturation.

The construction of antibody fragments has the potential to reduce the high cost of therapeutic antibody production, but the structures of these fragments, with monovalency and the lack of an Fc region, can lead to reduced function. Multimerization is one strategy for recovering function that also yields better tumor-to-blood ratios than IgGs or monomeric antibody fragments because of rapid tumor uptake and clearance. Here, we constructed single-chain variable fragment (scFv) multimers by modifying the linker length and domain order of humanized anti-(epidermal growth factor receptor) IgG 528 (h528) and tested their ability to inhibit tumor growth. h528 scFv multimers, expressed using a bacterial expression system, were successfully fractionated and inhibited cancer growth in a multimerization-dependent manner, whereas the h528 scFv monomer showed no inhibition. h528 scFv trimers with variable heavy-light domain order and no linkers showed the highest in vitro and in vivo antitumor effects, which were comparable with those of the approved anti-(epidermal growth factor receptor) therapeutic IgG Cetuximab and Panitumumab. The trimers were also structurally stable in vitro and in vivo, which may be attributable to a strong interaction between the variable heavy and variable light domains of h528 Fv. Thus, h528 scFv multimers, especially trimers, are attractive as the next generation of anti-(epidermal growth factor receptor) therapeutic IgG and offer the possibility of low-cost production., (© 2013 FEBS.)

The domains of bispecific diabodies (BsDbs) can be ordered in four different ways; however, the influence of domain order on the cytotoxicity of BsDbs that retarget immune cells against tumor cells had not been addressed. We previously reported the marked antitumor effects of a humanized BsDb that targets epidermal growth factor receptor and CD3 (hEx3-Db). Here, we rearranged the domains of hEx3-Db to examine the influence of domain order on the function of BsDbs. We successfully prepared homogenous dimers of hEx3-Db in all four domain configurations. Interestingly, all three rearranged hEx3s inhibited cancer growth more effectively than did the original hEx3-Db, in which both components were in variable heavy domain (VH)-variable light domain (VL) order (redesignated as hEx3-HL), and the highest effects were observed with hEx3-LH (hEx3-Db with both components in VL-VH order). In addition, hEx3-LH had comparable in vitro growth inhibitory effects to those of the tandem single-chain variable fragment (scFv) format of hEx3-Db (hEx3-tandem scFv (taFv)), which we previously showed to have greater cytotoxicity than does hEx3-HL. Flow cytometry suggested that the enhanced cytotoxicity of hEx3-LH is attributable to structural superiority for cross-linking, similar to that of hEx3-taFv. Furthermore, hEx3-LH inhibited cancer growth in mice more effectively than did hEx3-taFv; this difference may be due to differences in antibody stability. Our results show that merely rearranging the domain order of BsDbs can enhance their effects beyond those with structural format conversion.

Glioblastoma multiforme (GBM) remains an untreatable human brain malignancy. Despite promising preclinical studies using oncolytic herpes simplex virus (oHSV) vectors, efficacy in patients has been limited by inefficient virus replication in tumor cells. This disappointing outcome can be attributed in part to attenuating mutations engineered into these viruses to prevent replication in normal cells. Alternatively, retargeting of fully replication-competent HSV to tumor-associated receptors has the potential to achieve tumor specificity without impairment of oncolytic activity. Here, we report the establishment of an HSV retargeting system that relies on the combination of two engineered viral glycoproteins, gD and gB, to mediate highly efficient HSV infection exclusively through recognition of the abundantly expressed epidermal growth factor receptor (EGFR) on glioblastoma cells. We demonstrate efficacy in vitro and in a heterotopic tumor model in mice. Evidence for systemically administered virus homing to the tumor mass is presented. Treatment of orthotopic primary human GBM xenografts demonstrated prolonged survival with up to 73% of animals showing a complete response as confirmed by magnetic resonance imaging. Our study describes an approach to HSV retargeting that is effective in a glioma model and may be applicable to the treatment of a broad range of tumor types.

We showed previously that humanization of 528, a murine anti-epidermal growth factor receptor (EGFR) antibody, causes reduced affinity for its target. Here, to improve the affinity of the humanized antibody for use in cancer immunotherapy, we constructed phage display libraries focused on the complementarity-determining regions (CDRs) of the antibody and carried out affinity selection. Two-step selections using libraries constructed in a stepwise manner enabled a 32-fold affinity enhancement of humanized 528 (h528). Thermodynamic analysis of the interactions between the variable domain fragment of h528 (h528Fv) mutants and the soluble extracellular domain of EGFR indicated that the h528Fv mutants obtained from the first selection showed a large increase in negative enthalpy change due to binding, resulting in affinity enhancement. Furthermore, mutants from the second selection showed a decrease in entropy loss, which led to further affinity maturation. These results suggest that a single mutation in the heavy chain variable domain (i.e. Tyr(52) to Trp) enthalpically contributed for overcoming the energetic barrier to the antigen-antibody interaction, which was a major hurdle for the in vitro affinity maturation of h528. We reported previously that the humanized bispecific diabody hEx3 Db, which targets EGFR and CD3, shows strong anti-tumor activity. hEx3 Db mutants, in which the variable domains of h528 were replaced with those of the affinity-enhanced mutants, were prepared and characterized. In a growth inhibition assay of tumor cells, the hEx3 Db mutants showed stronger anti-tumor activity than that of hEx3 Db, suggesting that affinity enhancement of h528Fv enhances the anti-tumor activity of the bispecific diabody.

We previously reported the construction and activity of a humanized, bispecific diabody (hEx3) that recruited T cells towards an epidermal growth factor receptor (EGFR) positive tumor. Herein, we describe the construction of a second functional, fully humanized, anti-EGFR bispecific diabody that recruits another subset of lymphocyte effectors, the natural killer cells, to EGFR-expressing tumor cells. After we confirmed that an anti-EGFR × anti-CD16 bispecific diabody (Ex16) consisting of a previously humanized anti-EGFR variable fragment (Fv) and a mouse anti-CD16 Fv had growth inhibitory activity, we designed a humanized anti-CD16 Fv to construct the fully humanized Ex16 (hEx16). However, the humanized form had lower activity for inhibition of cancer growth. To restore its growth inhibitory activity, we introduced mutations into the Vernier zone, which is located near the complementarity-determining regions and is involved in their binding activity. We efficiently prepared 15 different hEx16 mutants by expressing each chimeric single-chain component for hEx16 separately. We then used our in vitro refolding system to select the most functional mutant, which had a growth inhibitory effect comparable with that of the commercially available chimeric anti-EGFR antibody, cetuximab. Our refolding system could aid in the efficient optimization of other proteins with heterodimeric structure., (© 2011 The Authors Journal compilation © 2011 FEBS.)

We report a scanning electrochemical microscopy (SECM)-based receptor-mediated endocytosis detection method. Epidermal growth factor receptor (EGFR), which is one of the key membrane proteins associated with cancer, was used as a model for receptor-mediated endocytosis. EGFR molecules on the outer cell membrane were detected by SECM by using alkaline phosphatase (ALP) as a labeling enzyme. Since SECM detected the ALP activity on the outer membrane, the procedure helped discriminate the EGFR on the outer membrane from the intracellular EGFR involved in endocytosis. SECM showed a marked decrease in the current responses generated due to ALP activity by 93% on addition of the epidermal growth factor, indicating clearly that EGF triggered the endocytosis, which led to the withdrawal of most EGFRs from the outer membrane.

We performed in vitro and in vivo experiments of the anti-epidermal growth factor receptor (EGFR) x anti-CD3 bispecific diabody (hEx3-Db) with the IgG-like bispecific antibodies (BsAbs) (hEx3-scFv-Fc and hEx3-scDb-Fc) and the anti-EGFR therapeutic antibody cetuximab to assess the effect of BsAbs on cancer growth inhibition. In vitro, efficacy of the BsAbs and cetuximab were compared by growth inhibition assays of human cell lines of bile duct (TFK-1, HuCC-T1, OCUCh-LM1), epidermoid (A431), gastric (Kato-III), colon (DLD-1, SW480), and breast (SK-BR-3, MCF-7) cancer. In vivo, in three mouse models, we evaluated the anti-tumor activity of hEx3-Db and cetuximab, assessed the effect of hEx3-Db alone, and compared the antitumor activity of hEx3-Db with the IgG-like BsAbs. In vitro, hEx3-scFv-Fc showed nearly 100% killing activity for all cell lines. Both in vitro and in vivo, hEx3-Db needed CD3-positive phenotypes to induce a growth inhibitory effect. In contrast, IgG-like BsAbs showed monotherapeutic effects in vivo by inducing antibody-dependent cellular cytotoxicity (ADCC) similar to cetuximab. However, enhancement was not observed when lymphokine-activated killer cells with the T-cell phenotype were co-injected. Results suggest that IgG-like BsAbs could not efficiently direct T lymphocytes toward tumor cells to induce ADCC due to steric hindrance on binding to CD3- and Fc-receptor-positive phenotypes. Although hEx3-scFv-Fc showed high cytotoxicity in vitro, its high molecular weight limits its usefulness. With an in vivo effect comparable to hEx3-scFv-Fc and its realistic molecular weight, hEx3-scDb-Fc shows promise as a novel recombinant therapeutic antibody and may be modified to enhance its potency by prevention of steric hindrance.

Herpes simplex virus entry into cells requires the binding of envelope glycoprotein D (gD) to an entry receptor. Depending on the cell, entry occurs by different mechanisms, including fusion at the cell surface or endocytosis. Here we examined the entry mechanism through a non-HSV receptor mediated by a soluble bi-specific adapter protein composed of recognition elements for gD and the EGF receptor (EGFR). Virus entered into endosomes using either EGF or an EGFR-specific single chain antibody (scFv) for receptor recognition. Infection was less efficient with the EGF adapter which could be attributed to its weaker binding to a viral gD. Infection mediated by the scFv adapter was pH sensitive, indicating that gD-EGFR bridging alone was insufficient for capsid release from endosomes. We also show that the scFv adapter enhanced infection of EGFR-expressing tumor tissue in vivo. Our results indicate that adapters may retarget HSV infection without drastically changing the entry mechanism., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Diabodies (Dbs) and tandem single-chain variable fragments (taFv) are the most widely used recombinant formats for constructing small bispecific antibodies. However, only a few studies have compared these formats, and none have discussed their binding kinetics and cross-linking ability. We previously reported the usefulness for cancer immunotherapy of a humanized bispecific Db (hEx3-Db) and its single-chain format (hEx3-scDb) that target epidermal growth factor receptor and CD3. Here, we converted hEx3-Db into a taFv format to investigate how format affects the function of a small bispecific antibody; our investigation included a cytotoxicity assay, surface plasmon resonance spectroscopy, thermodynamic analysis, and flow cytometry. The prepared taFv (hEx3-taFv) showed an enhanced cytotoxicity, which may be attributable to a structural superiority to the diabody format in cross-linking target cells but not to differences in the binding affinities of the formats. Comparable cross-linking ability for soluble antigens was observed among hEx3-Db, hEx3-scDb, and hEx3-taFv with surface plasmon resonance spectroscopy. Furthermore, drastic increases in cytotoxicity were found in the dimeric form of hEx3-taFv, especially when the two hEx3-taFv were covalently linked. Our results show that converting the format of small bispecific antibodies can improve their function. In particular, for small bispecific antibodies that target tumor and immune cells, a functional orientation that avoids steric hindrance in cross-linking two target cells may be important in enhancing the growth inhibition effect.

We report the preparation and functional characterization of an Escherichia coli-expressed recombinant fusion protein, 528scFv-TRAIL, specific for the human epidermal growth factor receptor (EGFR) and empowered by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The 528scFv-TRAIL, expressed as insoluble inclusion bodies in E. coli, was solubilized and then refolded by using a modified stepwise dialysis method. Treatment with 528scFv-TRAIL resulted in the specific binding to the cell surface of EGFR-positive cells with concomitant deployment of the TRAIL moiety to DR-5 receptor in a manner comparable to a commercially available form of recombinant TRAIL (cTRAIL). 528scFv-TRAIL, prepared by either of three refolding processes described herein, showed potent cytotoxic activity against EGFR-positive TFK-1 cell line and was superior to its parental 528scFv; a recombinant variable fragment with single specificity against human EGFR. Narrow variations in the cytotoxic potential of 528scFv-TRAIL were ascribed to manipulation of redox conditions during the refolding process. Together, our findings point to the potential value of 528scFv-TRAIL for treatment of EGFR-expressing cancers. Furthermore, preparation of 528scFv-TRAIL from insoluble aggregates in a prokaryotic cell based expression system by means of in vitro refolding introduces a feasible cost-benefit, time-efficient approach for industrial-scale production.

A membrane protein on the surface of a single living mammalian cell was imaged by scanning electrochemical microscopy (SECM). The epidermal growth factor receptor (EGFR) is one of the key membrane proteins associated with cancer. It elicits a wide range of cell-type-specific responses, leading to cell proliferation, differentiation, apoptosis, and migration. To estimate EGFR expression levels by SECM, EGFR was labeled with alkaline phosphatase (ALP) via an antibody. The oxidation current of PAP (p-aminophenol) produced by the ALP-catalyzed reaction was monitored to estimate the density of cell surface EGFR. EGFR measurement by SECM has three advantages. First, a single adhesion cell can be measured without peeling it from the culture dish; second, it is possible to optimize labeling antibody concentrations by using living cells because detection of faradaic current is suitable for quantitative estimation in situ; and third, SECM measurements afford information on the expression state at the cell membrane at the single-cell level. In this study, we optimized the concentration of labeling antibody for EGFR at the cell surface and confirmed distinct differences in EGFR expression levels among three types of cells. SECM measurements were compatible with the results of flow cytometry.

We report the utility of in vitro refolding in the preparation of monomorphous hEx3 bispecific diabodies with epidermal growth factor receptor and CD3 retargeting from insoluble aggregates in Escherichia coli. Appropriate interaction between cognate variable heavy and light chains led to the formation of functional hEx3 heterodimers in a diabody format rather than inactive homodimers. The refolded hEx3 was found to exhibit almost the equivalent activity to the hEx3 and single-chain hEx3 (hEx3-scDb) prepared in a mammalian secretion system. We suggest that the preparation of hEx3 from bacterial insoluble material by means of in vitro refolding would be useful for industrial-scale production of the diabody for its potential use in clinical studies.

Recently, recombinant antibodies have been dissected into antigen-binding regions and rebuilt into multivalent high-avidity formats. These new structural designs are expected to improve in vivo pharmacokinetics and efficacy in clinical use. Here, we designed effective recombinant bispecific antibody (BsAb) formats based on hEx3, a humanized bispecific diabody with epidermal growth factor receptor and CD3 retargeting. The bispecific and bivalent IgG-like antibodies engineered from hEx3 (or its single-chain form, hEx3-scDb) and the human Fc region showed stronger binding to each target cell than did monovalent diabody formats, and their affinity was identical to that of the corresponding parent IgG. The bivalent effect of the constructed IgG-like BsAbs resulted in cell cytotoxicity 10 times that of monovalent diabodies, and further, the fusion of Fc portion contributed intense cytotoxicity in peripheral blood mononuclear cells by the induction of the antibody-dependent cellular cytotoxicity. The growth-inhibition effects of IgG-like BsAbs were superior to those of the approved therapeutic antibody cetuximab, which recognizes the same epidermal growth factor receptor antigen, even when peripheral blood mononuclear cells were used as effector cells. We thus demonstrated a critical improvement in the effect of hEx3 by the bottom-up construction of IgG-like BsAbs; in adoptive immunotherapy, monotherapy without supplemental molecules may be able to induce antibody-dependent cellular cytotoxicity.

To investigate the role of Vernier zone residues, which are comprised in the framework regions and underlie the complementarity-determining regions (CDRs) of antibodies, in the specific, high affinity interactions of antibodies with their targets, we focused on the variable domain fragment of murine anti-human epidermal growth factor receptor antibody 528 (m528Fv). Grafting of the CDRs of m528Fv onto a selected framework region of human antibodies, referred to as humanization, reduced the antibody's affinity for its target by a factor of 1/40. The reduction in affinity was due to a substantial reduction in the negative enthalpy change associated with binding. Crystal structures of the ligand-free antibody fragments showed no noteworthy conformational changes due to humanization, and the loop structures of the CDRs of the humanized antibodies were identical to those of the parent antibodies. Several mutants of the CDR-grafted (humanized) variable domain fragment (h528Fv), in which some of the Vernier zone residues in the heavy chain were replaced with the parental murine residues, were constructed and prepared using a bacterial expression system. Thermodynamic analyses of the interactions between the mutants and the soluble extracellular domain of epidermal growth factor receptor showed that several single mutations and a double mutation increased the negative enthalpy and heat capacity changes. Combination of these mutations, however, led to somewhat reduced negative enthalpy and heat capacity changes. The affinity of each mutant for the target was within the range for the wild-type h528Fv, and this similarity was due to enthalpy-entropy compensation. These results suggest that Vernier zone residues make enthalpic contributions to antigen binding and that the regulation of conformational entropy changes upon humanization of murine antibodies must be carefully considered and optimized.

Herpes simplex virus 1 (HSV-1) enters cells via initial binding of envelope glycoproteins (g) C and B to cell-surface glycosaminoglycans (GAGs) and subsequent membrane fusion involving envelope gD, gB, and gH/gL. Current insights suggest that the fusion process is initiated by interaction of gD with a cognate cellular receptor, such as the widely distributed cell adhesion molecule nectin-1. To redirect the tropism of HSV-1, we have generated a soluble adapter protein (P-V528LH) comprising the gD-binding variable domain of nectin-1 fused to a single-chain antibody (528LH) recognizing the EGF receptor. The adapter molecule enabled HSV-1 entry into naturally nonpermissive CHO cells expressing the human EGF receptor, but not into CHO cells lacking the receptor, and entry was not observed when the antibody portion of the adapter was replaced with an antibody of different specificity. Adapter-mediated entry increased with the viral dose and was nearly as efficient as direct viral entry into nectin-1-bearing CHO cells. Entry depended on viral gD and was diminished in the absence of cellular GAGs. These experiments represent the first demonstration that a soluble molecule can direct HSV infection via a new receptor, supporting the possible utility of this approach for HSV retargeting.

Purpose: In the field of cancer immunotherapy research, the targeting of effector cells with specific antibodies is a very promising approach. Recent advances in genetic engineering have made it possible to prepare immunoglobulin fragments consisting of variable domains using bacterial expression systems., Methods: We have produced an anti-epidermal growth-factor receptor (EGFR) x anti-CD3 bispecific diabody (Ex3 diabody) in an Escherichia coli (E. coli) expression system with refolding method. The Ex3 diabody targets lymphokine-activated killer cells with a T-cell phenotype (T-LAK cells) to EGFR positive bile duct carcinoma cells with dramatic enhancement of cytotoxicity in vitro. This specific killing of EGFR-positive cells was completely inhibited by parental mAb IgGs directed to EGFR and the CD3 antigen., Results: When T-LAK cells were cultured with EGFR-positive tumor cells in the presence of Ex3 diabody, they produced much higher levels of IFN-gamma, GM-CSF, and TNF-alpha than in its absence, this being a possible mechanism underlying specific antitumor activity. The Ex3 diabody showed good stability when tested at 37 degrees C for 48 h, and also markedly inhibited tumor growth of bile duct carcinoma xenografts in severe combined immunodeficient (SCID) mice. When Ex3 diabody (20 microg/mouse) was administrated intravenously, together with T-LAK cells and interleukin-2 (IL-2), complete cure of tumors were observed in three of six mice, and the other three showed marked retardation of tumor growth., Conclusion: The Ex3 diabody can be considered a highly promising reagent for study of specific targeting immunotherapy against bile duct and other EGFR-positive carcinomas.