Targeting ErbB2 and ErbB3 with a bispecific single-chain Fv enhances targeting selectivity and induces a therapeutic effect in vitro

Bispecific antibodies

Bispecific antibodies (bsAbs) combine specificities of two antibodies and simultaneously address different antigens or epitopes. BsAbs with 'two-target' functionality can interfere with multiple surface receptors or ligands associated, for example with cancer, proliferation or inflammatory processes. BsAbs can also place targets into close proximity, either to support protein complex formation on one cell, or to trigger contacts between cells. Examples of 'forced-connection' functionalities are bsAbs that support protein complexation in the clotting cascade, or tumor-targeted immune cell recruiters and/or activators. Following years of research and development (R&D), the first bsAb was approved in 2009. Another bsAb entered the market in December 2014 and several more are in clinical trials. Here, we describe the potentials of bsAbs to become the next wave of antibody-based therapies, focusing on molecules in clinical development.

Targeting HER family in HER2-positive metastatic breast cancer: potential biomarkers and novel targeted therapies

HER2-targeted therapies have radically changed the prognosis of HER2-positive breast cancer over the last few years. However, resistance to these therapies has been a constant, leading to treatment-failure and new tumor progression. Recently, the kinase-impaired HER3 emerged as a pivotal player in oncogenic signaling, with an important role in both non-treated progression and treatment response. HER2/HER3 dimerization is required for full signaling potential and constitutes the key oncogenic unit. Also, when inhibiting PI3K/AKT pathway (as with anti-HER2 drugs) feedback mechanisms lead to a rebound in HER3 activity, which is one of the main roads to resistance. As current strategies to treat HER2-positive breast cancer are unable to inhibit this feedback response, two great promises emerged: the combination of targeted-therapies and drugs targeting HER3. In this article HER2 and HER3-targeted drugs and possible combinations between them, as well as the biomarkers to predict and monitor these drugs effect, are reviewed.

HER-3 peptide vaccines/mimics: Combined therapy with IGF-1R, HER-2, and HER-1 peptides induces synergistic antitumor effects against breast and pancreatic cancer cells

The human epidermal growth factor receptor 3 (HER-3/ErbB3) is a unique member of the human epidermal growth factor family of receptors, because it lacks intrinsic kinase activity and ability to heterodimerize with other members. HER-3 is frequently upregulated in cancers with epidermal growth factor receptor (EGFR/HER-1/ErbB1) or human epidermal growth factor receptor 2 (HER-2/ErBB2) overexpression, and targeting HER-3 may provide a route for overcoming resistance to agents that target EGFR or HER-2. We have previously developed vaccines and peptide mimics for HER-1, HER-2 and vascular endothelial growth factor (VEGF). In this study, we extend our studies by identifying and evaluating novel HER-3 peptide epitopes encompassing residues 99-122, 140-162, 237-269 and 461-479 of the HER-3 extracellular domain as putative B-cell epitopes for active immunotherapy against HER-3 positive cancers. We show that the HER-3 vaccine antibodies and HER-3 peptide mimics induced antitumor responses: inhibition of cancer cell proliferation, inhibition of receptor phosphorylation, induction of apoptosis and antibody dependent cellular cytotoxicity (ADCC). Two of the HER-3 epitopes 237-269 (domain II) and 461-479 (domain III) significantly inhibited growth of xenografts originating from both pancreatic (BxPC3) and breast (JIMT-1) cancers. Combined therapy of HER-3 (461-471) epitope with HER-2 (266-296), HER-2 (597-626), HER-1 (418-435) and insulin-like growth factor receptor type I (IGF-1R) (56-81) vaccine antibodies and peptide mimics show enhanced antitumor effects in breast and pancreatic cancer cells. This study establishes the hypothesis that combination immunotherapy targeting different signal transduction pathways can provide effective antitumor immunity and long-term control of HER-1 and HER-2 overexpressing cancers.

Combining anti-ERBB3 antibodies specific for domain I and domain III enhances the anti-tumor activity over the individual monoclonal antibodies

Background

Inappropriate signaling through the epidermal growth factor receptor family (EGFR1/ERBB1, ERBB2/HER2, ERBB3/HER3, and ERBB4/HER4) of receptor tyrosine kinases leads to unregulated activation of multiple downstream signaling pathways that are linked to cancer formation and progression. In particular, ERBB3 plays a critical role in linking ERBB signaling to the phosphoinositide 3-kinase and Akt signaling pathway and increased levels of ERBB3-dependent signaling is also increasingly recognized as a mechanism for acquired resistance to ERBB-targeted therapies.

Methods

We had previously reported the isolation of a panel of anti-ERBB3 single-chain Fv antibodies through use of phage-display technology. In the current study scFv specific for domain I (F4) and domain III (A5) were converted into human IgG1 formats and analyzed for efficacy.

Results

Treatment of cells with an oligoclonal mixture of the A5/F4 IgGs appeared more effective at blocking both ligand-induced and ligand-independent signaling through ERBB3 than either single IgG alone. This correlated with improved ability to inhibit the cell growth both as a single agent and in combination with other ERBB-targeted therapies. Treatment of NCI-N87 tumor xenografts with the A5/F4 oligoclonal led to a statistically significant decrease in tumor growth rate that was further enhanced in combination with trastuzumab.

Conclusion

These results suggest that an oligoclonal antibody mixture may be a more effective approach to downregulate ERBB3-dependent signaling.

A dual-targeting triplebody mediates preferential redirected lysis of antigen double-positive over single-positive leukemic cells

The single-chain triplebody HLA-ds16-hu19 consists of three single-chain Fv (scFv) antibody fragments connected in a single polypeptide chain. This protein with dual-targeting capacity mediated preferential lysis of antigen double positive(dp) over single-positive (sp) leukemic cells by recruitment of natural killer (NK) cells as effectors. The two distal scFv modules were specific for the histocompatibility protein HLA-DR and the lymphoid antigen CD19, the central one for the Fc gamma receptor CD16. In antibody-dependent cellular cytotoxicity (ADCC) experiments with a mixture of leukemic target cells comprising both HLA-DR sp HuT-78 or Kasumi-1 cells and (HLA-DR plus CD19) dp SEM cells, the triplebody mediated preferential lysis of the dp cells even when the sp cells were present in ≤ 20-fold numerical excess.The triplebody promoted equal lysis of SEM cells at 2.5-fold and 19.5-fold lower concentrations than the parental antibodies specific for HLA-DR and CD19, respectively. Finally, the triplebody also eliminated primary leukemic cells at lower concentrations than an equimolar mixture of bispecific single-chain Fv fragments (bsscFvs) separately addressing each target antigen (hu19-ds16 and HLA-ds16). The increased selectivity of targeting and the preferential lysis of dp over sp cells achieved by dual-targeting open attractive new perspectives for the use of dual-targeting agents in cancer therapy.

Tumor-antigen-binding bispecific antibodies for cancer treatment

Bi- and multispecific antibody derivatives (bsAbs) can be considered as the next generation of targeted biologics for cancer therapy. The general concept of bsAbs is a physical connection of recombinant antibody-derived entities with at least two binding specificities. This generates bsAbs that bind at least two antigens or epitopes, thus altering their binding functionalities and specificities in comparison to "normal" antibodies. Most bsAbs are produced as recombinant proteins, either as large IgG-like proteins that contain Fc regions, or as smaller entities with multiple antigen-binding regions but without Fc. Application of bsAbs in experimental cancer therapy currently includes molecules that bind different cell surface proteins to achieve more complete blockage of proliferative or angiogenesis-associated pathways. This approach of blocking more than one pathway component, or to simultaneously hit complementing pathways, also may limit potential escape mechanisms of cancer cells. BsAbs also are applied in the clinic as vehicles to deliver immune effector cells and/or cytokines to tumors.

The next generation of antibody drug conjugates

Antibody-drug conjugates (ADCs) represent a promising therapeutic modality for the clinical management of cancer. The recent approvals of brentuximab vedotin and ado-trastuzumab emtansine plus emerging data for many molecules in clinical trials highlight the potential for ADCs to offer new therapeutic options for patients. Currently, more than 30 ADCs are being evaluated in early- or late-stage clinical trials. Accordingly, much has been done to refine and transform the early-generation ADCs to the highly effective products that we now have in clinical development. These changes include a better understanding of optimal target selection, advances in antibody engineering, improvements in linker/payload conjugation strategies, and the generation of highly potent ADC payloads. In this review, we detail the current status of ADCs in both preclinical and clinical development, highlight technological advancements in ADC development, and speculate towards the future of this targeted therapeutic platform.

Functional expression of a single-chain antibody fragment against human epidermal growth factor receptor 2 (HER2) in Escherichia coli

The human epidermal growth factor receptor (HER) family plays an important role in cell growth and signaling and alteration of its function has been demonstrated in many different kinds of cancer. Receptor dimerization is necessary for the HER signal transduction pathway and tyrosine kinase activity. Recently, several monoclonal antibodies have been developed to directly interfere with ligand–HER receptor binding and receptor dimerization. A single chain variable fragment (ScFv) is a valuable alternative to an intact antibody. This report describes the production and purification of an ScFv specific for domain II of the HER2 receptor in Escherichia coli BL21 (DE3) cytoplasm. The majority of expressed of anti-her2his-ScFv protein was produced as inclusion bodies. A Ni-NTA affinity column was used to purify the anti-her2his-ScFv protein. The molecular weight of anti-her2his-ScFv protein was estimated to be approximately 27 kDa, as confirmed by SDS-PAGE and Western blotting assay. The anti-her2his-ScFv showed near 95 % purity and reached a yield of approximately 29 mg/l in flask fermentation. The purified anti-her2his-ScFv showed its biological activity by binding to HER2 receptor on the surface of BT-474 cells. This ScFv may be a potential pharmaceutical candidate for targeting tumour cells overexpressing HER2 receptor.

Design and applications of bispecific heterodimers: molecular imaging and beyond

Ligand-based molecular imaging probes have been designed with high affinity and specificity for monitoring biological process and responses. Single-target recognition by traditional probes can limit their applicability for disease detection and therapy because synergistic action between disease mediators and different receptors is often involved in disease progression. Consequently, probes that can recognize multiple targets should demonstrate higher targeting efficacy and specificity than their monospecific peers. This concept has been validated by multiple bispecific heterodimer-based imaging probes that have demonstrated promising results in several animal models. This review summarizes the design strategies for bispecific peptide- and antibody-based heterodimers and their applications in molecular targeting and imaging. The design and application of bispecific heterodimer-conjugated nanomaterials are also discussed.

Engineering of a bispecific affibody molecule towards HER2 and HER3 by addition of an albumin-binding domain allows for affinity purification and in vivo half-life extension

Emerging strategies in cancer biotherapy include the generation and application of bispecific antibodies, targeting two tumor-associated antigens for improved tumor selectivity and potency. Here, an alternative format for bispecific molecules was designed and investigated, in which two Affibody molecules were linked by an albumin-binding domain (ABD). Affibody molecules are small (6 kDa) affinity proteins and this new format allows for engineering of molecules with similar function as full-length bispecific antibodies, but in a dramatically smaller size (around eight-fold smaller). The ABD was intended to function both as a tag for affinity purification as well as for in vivo half-life extension in future preclinical and clinical investigations. Affinity-purified bispecific Affibody molecules, targeting HER2 and HER3, showed simultaneous binding to the three target proteins (HER2, HER3, and albumin) when investigated in biosensor assays. Moreover, simultaneous interactions with the receptors and albumin were demonstrated using flow cytometry on cancer cells. The bispecific Affibody molecules were also able to block ligand-induced phosphorylation of the HER receptors, indicating an anti-proliferative effect. We believe that this compact and flexible format has great potential for developing new potent bispecific affinity proteins in the future, as it combines the benefits of a small size (e.g. improved tissue penetration and reduced cost of goods) with a long circulatory half-life.

Imaging of HER3-expressing xenografts in mice using a (99m)Tc(CO) 3-HEHEHE-Z HER3:08699 affibody molecule

PURPOSE

Human epidermal growth factor receptor type 3 (HER3) is a transmembrane receptor tyrosine kinase belonging to the HER (ErbB) receptor family. Membranous expression of HER3 is associated with trastuzumab resistance in breast cancer and the transition to androgen independence in prostate cancer. Imaging of HER3 expression in malignant tumors may provide important diagnostic information that can influence patient management. Affibody molecules with low picomolar affinity to HER3 were recently selected. The aim of this study was to investigate the feasibility of HER3 imaging using radiolabeled Affibody molecules.

METHODS

A HER3-binding Affibody molecule, Z08699, with a HEHEHE-tag on N-terminus was labeled with (99m)Tc(CO)3 using an IsoLink kit. In vitro and in vivo binding specificity and the cellular processing of the labeled binder were evaluated. Biodistribution of (99m)Tc(CO)3-HEHEHE-Z08699 was studied over time in mice bearing HER3-expressing xenografts.

RESULTS

HEHEHE-Z08699 was labeled with (99m)Tc(CO)3 with an isolated yield of >80 % and a purity of >99 %. Binding of (99m)Tc(CO)3-HEHEHE-Z08699 was specific to BT474 and MCF7 (breast cancer), and LS174T (colon cancer) cells. Cellular processing showed rapid binding and relatively quick internalization of the receptor/Affibody molecule complex (70 % of cell-associated radioactivity was internalized after 24 h). The tumor targeting was receptor mediated and the excretion was predominantly renal. Receptor-mediated uptake was also found in the liver, lung, stomach, intestine, and salivary glands. At 4 h pi, tumor-to-blood ratios were 7 ± 3 for BT474, and 6 ± 2 for LS174T xenografts. LS174T tumors were visualized by microSPECT 4 h pi.

CONCLUSIONS

The results of this study suggest the feasibility of HER3-imaging in malignant tumors using Affibody molecules.

Engineering multivalent antibodies to target heregulin-induced HER3 signaling in breast cancer cells

The use of antibodies in therapy and diagnosis has undergone an unprecedented expansion during the past two decades. This is due in part to innovations in antibody engineering that now offer opportunities for the production of “second generation” antibodies with multiple specificities or altered valencies. The targeting of individual components of the human epidermal growth factor receptor (HER)3-PI3K signaling axis, including the preferred heterodimerization partner HER2, is known to have limited anti-tumor effects. The efficacy of antibodies or small molecule tyrosine kinase inhibitors (TKIs) in targeting this axis is further reduced by the presence of the HER3 ligand, heregulin. To address these shortcomings, we performed a comparative analysis of two distinct approaches toward reducing the proliferation and signaling in HER2 overexpressing tumor cells in the presence of heregulin. These strategies both involve the use of engineered antibodies in combination with the epidermal growth factor receptor (EGFR)/HER2 specific TKI, lapatinib. In the first approach, we generated a bispecific anti-HER2/HER3 antibody that, in the presence of lapatinib, is designed to sequester HER3 into inactive HER2-HER3 dimers that restrain HER3 interactions with other possible dimerization partners. The second approach involves the use of a tetravalent anti-HER3 antibody with the goal of inducing efficient HER3 internalization and degradation. In combination with lapatinib, we demonstrate that although the multivalent HER3 antibody is more effective than its bivalent counterpart in reducing heregulin-mediated signaling and growth, the bispecific HER2/HER3 antibody has increased inhibitory activity. Collectively, these observations provide support for the therapeutic use of bispecifics in combination with TKIs to recruit HER3 into complexes that are functionally inert.

Pharmacokinetics, pharmacodynamics and physiologically-based pharmacokinetic modelling of monoclonal antibodies

Development of monoclonal antibodies (mAbs) and their functional derivatives represents a growing segment of the development pipeline in the pharmaceutical industry. More than 25 mAbs and derivatives have been approved for a variety of therapeutic applications. In addition, around 500 mAbs and derivatives are currently in different stages of development. mAbs are considered to be large molecule therapeutics (in general, they are 2-3 orders of magnitude larger than small chemical molecule therapeutics), but they are not just big chemicals. These compounds demonstrate much more complex pharmacokinetic and pharmacodynamic behaviour than small molecules. Because of their large size and relatively poor membrane permeability and instability in the conditions of the gastrointestinal tract, parenteral administration is the most usual route of administration. The rate and extent of mAb distribution is very slow and depends on extravasation in tissue, distribution within the particular tissue, and degradation. Elimination primarily happens via catabolism to peptides and amino acids. Although not definitive, work has been published to define the human tissues mainly involved in the elimination of mAbs, and it seems that many cells throughout the body are involved. mAbs can be targeted against many soluble or membrane-bound targets, thus these compounds may act by a variety of mechanisms to achieve their pharmacological effect. mAbs targeting soluble antigen generally exhibit linear elimination, whereas those targeting membrane-bound antigen often exhibit non-linear elimination, mainly due to target-mediated drug disposition (TMDD). The high-affinity interaction of mAbs and their derivatives with the pharmacological target can often result in non-linear pharmacokinetics. Because of species differences (particularly due to differences in target affinity and abundance) in the pharmacokinetics and pharmacodynamics of mAbs, pharmacokinetic/pharmacodynamic modelling of mAbs has been used routinely to expedite the development of mAbs and their derivatives and has been utilized to help in the selection of appropriate dose regimens. Although modelling approaches have helped to explain variability in both pharmacokinetic and pharmacodynamic properties of these drugs, there is a clear need for more complex models to improve understanding of pharmacokinetic processes and pharmacodynamic interactions of mAbs with the immune system. There are different approaches applied to physiologically based pharmacokinetic (PBPK) modelling of mAbs and important differences between the models developed. Some key additional features that need to be accounted for in PBPK models of mAbs are neonatal Fc receptor (FcRn; an important salvage mechanism for antibodies) binding, TMDD and lymph flow. Several models have been described incorporating some or all of these features and the use of PBPK models are expected to expand over the next few years.

Monoclonal antibody against the ectodomain of E-cadherin (DECMA-1) suppresses breast carcinogenesis: involvement of the HER/PI3K/Akt/mTOR and IAP pathways

PURPOSE

Although targeted therapies against HER2 have been one of the most successful therapeutic strategies for breast cancer, patients eventually developed acquired resistance from compensatory upregulation of alternate HERs and mitogen-activated protein kinase-phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling. As we and others have shown that the soluble ectodomain fragment of E-cadherin exerts prooncogenic effects via HER1/2-mediated binding and activation of downstream prosurvival pathways, we explored whether targeting this ectodomain [DECMA-1 monoclonal antibody (mAb)] was effective in the treatment of HER2-positive (HER2(+)) breast cancers.

EXPERIMENTAL DESIGN

MMTV-PyMT transgenic mice and HER2(+)/E-cadherin-positive MCF-7 and BT474 trastuzumab-resistant (TtzmR) cells were treated with the DECMA-1 mAb. Antitumor responses were assessed by bromodeoxyuridine incorporation, apoptosis, and necrosis. The underlying intracellular prooncogenic pathways were explored using subcellular fractionation, immunoprecipitation, fluorescence microscopy, and immunoblotting.

RESULTS

Treatment with DECMA-1 mAb significantly delayed tumor onset and attenuated tumor burden in MMTV-PyMT mice by reducing tumor cell proliferation and inducing apoptosis without any detectable cytotoxicity to mice or end-organs. In vitro treatment of MCF-7 and BT474 TtzmR cells reduced proliferation and induced cancer cell apoptosis. Importantly, this inhibition of breast tumorigenesis was due to concomitant downregulation, via ubiquitin-mediated degradation through the lysosome and proteasome pathways, of all HER family members, components of downstream PI3K/Akt/mTOR prosurvival signaling and suppression of inhibitor of apoptosis proteins.

CONCLUSIONS

Our results establish that the E-cadherin ectodomain-specific mAb DECMA-1 inhibits Ecad(+)/HER2(+) breast cancers by hindering tumor growth and inducing apoptosis via downregulation of key oncogenic pathways involved in trastuzumab resistance, thereby establishing a novel therapeutic platform for the treatment of HER2(+) breast cancers.

Inhibiting HER3-mediated tumor cell growth with affibody molecules engineered to low picomolar affinity by position-directed error-prone PCR-like diversification

The HER3 receptor is implicated in the progression of various cancers as well as in resistance to several currently used drugs, and is hence a potential target for development of new therapies. We have previously generated Affibody molecules that inhibit heregulin-induced signaling of the HER3 pathways. The aim of this study was to improve the affinity of the binders to hopefully increase receptor inhibition efficacy and enable a high receptor-mediated uptake in tumors. We explored a novel strategy for affinity maturation of Affibody molecules that is based on alanine scanning followed by design of library diversification to mimic the result from an error-prone PCR reaction, but with full control over mutated positions and thus less biases. Using bacterial surface display and flow-cytometric sorting of the maturation library, the affinity for HER3 was improved more than 30-fold down to 21 pM. The affinity is among the higher that has been reported for Affibody molecules and we believe that the maturation strategy should be generally applicable for improvement of affinity proteins. The new binders also demonstrated an improved thermal stability as well as complete refolding after denaturation. Moreover, inhibition of ligand-induced proliferation of HER3-positive breast cancer cells was improved more than two orders of magnitude compared to the previously best-performing clone. Radiolabeled Affibody molecules showed specific targeting of a number of HER3-positive cell lines in vitro as well as targeting of HER3 in in vivo mouse models and represent promising candidates for future development of targeted therapies and diagnostics.

MicroSPECT/CT imaging of co-expressed HER2 and EGFR on subcutaneous human tumor xenografts in athymic mice using ¹¹¹In-labeled bispecific radioimmunoconjugates

Epidermal growth factor receptors (EGFR) form heterodimers with HER2 in breast cancer, and increased EGFR expression has been found in HER2-positive tumors resistant to trastuzumab (Herceptin). Our objective was to synthesize bispecific radioimmunoconjugates (bsRICs) that recognize HER2 and EGFR and evaluate their ability to image tumors in athymic mice that express one or both receptors by microSPECT/CT. Bispecific radioimmunoconjugates were constructed by conjugating maleimide-derivatized trastuzumab Fab fragments that bind HER2 to a thiolated form of EGF with an intervening 24 mer polyethylene glycol (PEG24) spacer. Bispecific radioimmunoconjugates were derivatized with diethylenetriaminepentaacetic acid for labeling with (111)In. The ability of (111)In-bsRICs to bind HER2 or EGFR was determined in competition assays using cells expressing one or both receptors. Tumor and normal tissue uptake were examined in CD1 athymic mice bearing subcutaneous tumor xenografts that expressed HER2, EGFR, or both receptors, with or without pre-administration of Fab or EGF to determine specificity. HER2 and EGFR binding and displacement of binding by competitors were found for (111)In-bsICs. The highest uptake of (111)In-bsRICs [7.3 ± 3.5 %ID/g] in 231-H2N human breast cancer xenografts (HER2+/EGFR+) occurred at 48 h post-injection. Pre-administration of trastuzumab Fab decreased uptake in SK-OV-3 (HER2+/EGFR-) human ovarian cancer xenografts from 7.1 ± 1.2 to 2.4 ± 1.5 %ID/g. Pre-administration of excess EGF decreased uptake in MDA-MB-231 (HER2-/EGFR+) human breast cancer xenografts from 5.9 ± 0.5 to 2.0 ± 0.1 %ID/g. All tumors were imaged by microSPECT/CT. We conclude that (111)In-bsRICs composed of trastuzumab Fab and EGF exhibited specific binding in vitro to tumor cells displaying HER2 or EGFR, and were taken up specifically in vivo in tumors expressing one or both receptors, permitting tumor visualization by microSPECT/CT. These agents may ultimately be useful for imaging heterodimerized HER2-EGFR complexes since their bivalent properties permit more avid binding to these complexes.

Self-assembled antibody multimers through peptide nucleic acid conjugation

With the recent clinical success of bispecific antibodies, a strategy to rapidly synthesize and evaluate bispecific or higher order multispecific molecules could facilitate the discovery of new therapeutic agents. Here, we show that unnatural amino acids (UAAs) with orthogonal chemical reactivity can be used to generate site-specific antibody-oligonucleotide conjugates. These constructs can then be self-assembled into multimeric complexes with defined composition, valency, and geometry. With this approach, we generated potent bispecific antibodies that recruit cytotoxic T lymphocytes to Her2 and CD20 positive cancer cells, as well as multimeric antibody fragments with enhanced activity. This strategy should accelerate the synthesis and in vitro characterization of antibody constructs with unique specificities and molecular architectures.

Small-animal SPECT/CT of HER2 and HER3 expression in tumor xenografts in athymic mice using trastuzumab Fab-heregulin bispecific radioimmunoconjugates

Heterodimerization of human epidermal growth factor receptor 2 (HER2) with HER3 initiates aberrant downstream growth-signaling pathways in tumors. Our objective was to construct bispecific radioimmunoconjugates (bsRICs) that recognize HER2 and HER3 and evaluate their ability to image tumors in athymic mice that express one or both receptors using small-animal SPECT/CT.

METHODS

bsRICs were constructed by reacting the maleimide-derivatized trastuzumab Fab fragments that bind HER2 with a thiolated form of the HER3-binding peptide of heregulin-β1 (HRG) with or without a 12- or 24 mer polyethylene glycol (PEG) spacer. bsRICs were derivatized with diethylenetriaminepentaacetic acid for labeling with (111)In. The ability of (111)In-bsRICs to bind HER2 or HER3 was determined in competition assays with unlabeled Fab or HRG on cells expressing one or both receptors. Tumor and normal-tissue uptake were examined in CD1 athymic mice bearing subcutaneous tumor xenografts that expressed HER2, HER3, or both receptors, with or without the preadministration of unlabeled Fab or HRG to determine the specificity of uptake.

RESULTS

Conjugation of Fab to HRG was confirmed by sodium dodecyl sulphate polyacrylamide gel electrophoresis-Western blot and size-exclusion high-performance liquid chromatography. Improved HER2 and HER3 binding and greater displacement of binding by competitors was found for (111)In-bsRICs that incorporated a PEG spacer, with the PEG(24) spacer being optimal. The highest uptake of (111)In-bsRICs (7.8% ± 2.1% injected dose per gram [%ID/g]) in BT-474 human breast cancer xenografts (HER2-positive/HER3-positive) occurred at 48 h after injection. The preadministration of trastuzumab Fab decreased uptake in SK-OV-3 (HER2-positive/HER3-negative) human ovarian cancer xenografts from 7.0 ± 1.2 to 2.6 ± 1.5 %ID/g (P < 0.001). The preadministration of an excess of HRG decreased uptake in MDA-MB-468 (HER2-negative/HER3-positive) human breast cancer xenografts from 4.4 ± 0.9 to 2.6 ± 0.5 %ID/g (P < 0.05). All tumors were imaged by small-animal SPECT/CT.

CONCLUSION

(111)In-bsRICs composed of trastuzumab Fab and HRG exhibited specific binding in vitro to tumor cells displaying HER2 or HER3 and were taken up specifically in vivo in tumors expressing one or both receptors, permitting tumor visualization by small-animal SPECT/CT. These agents could be useful for imaging heterodimerized HER2 and HER3 receptors because their bivalent properties may result in preferential binding to the heterodimerized forms. The approach may also be extended to constructing bsRICs for visualizing other peptide growth factor receptors.

Next generation of antibody therapy for cancer

Monoclonal antibodies (mAbs) have become a major class of therapeutic agents providing effective alternatives to treating various human diseases. To date, 15 mAbs have been approved by regulatory agencies in the world for clinical use in oncology indications. The selectivity and specificity, the unique pharmacokinetics, and the ability to engage and activate the host immune system differentiate these biologics from traditional small molecule anticancer drugs. mAb-based regimens have brought clinical benefits, including improvements in overall survival, to patients with a variety of cancers. Many challenges still remain, however, to fully realize the potential of these new medicines. With our further understanding of cancer biology, mechanism of antibody action, and advancement of antibody engineering technologies, many novel antibody formats or antibody-derived molecules are emerging as promising new generation therapeutics. Carefully designed and engineered, they retain the advantage of specificity and selectivity of original antibodies, but in the meantime acquire additional special features such as improved pharmacokinetics, increased selectivity, and enhanced anticancer efficacy. Promising clinical results are being generated with these newly improved antibody-based therapeutics.

Advances in bispecific biotherapeutics for the treatment of cancer

Conventional monoclonal antibody (mAb) therapeutics interfering with cellular signaling of their respective target antigens are frequently limited in their ability to induce significant anti-tumor activities when administered as single agents in patients with solid tumors. To overcome these limitations, several new technologies are being developed to empower biotherapeutics and to improve their anti-tumor activities, while maintaining their high tumor selectivity and superior safety profiles. The various efficacy enhancement technologies developed for mAbs can be divided broadly into two categories: First, technologies that improve the intrinsic anti-tumor activities of conventional immunoglobulin mAb formats, including the enhancement of effector cell functions and modulations of target binding properties, including interference with multiple signaling pathways. The second category of empowered biologics combines complementary anti-tumor modalities independent of the IgG format, including antibody drug conjugates (ADCs). In addition, bispecific compounds designed to recruit different subsets of inflammatory cells to the tumor environment, also belong to the mechanistic complementation strategy. This approach termed redirected immune cell killing, belongs to one the most promising new biotherapeutic platforms developed in oncology. Over 20 bispecific compounds are currently being developed pre-clinically, and several compounds are undergoing early stage clinical trials. In this report, we review the progress made in the development of bispecific biotherapeutics in the context of ADCs, redirected T- and B-cell killing and targeting of multiple signaling pathways. We also discuss the status of the clinical development of this class of compounds in oncology and the promises and challenges this field is currently facing.

The ERBB network: at last, cancer therapy meets systems biology

Although it is broadly agreed that the improved treatment of patients with cancer will depend on a deeper molecular understanding of the underlying pathogenesis, only a few examples are already available. This Timeline article focuses on the ERBB (also known as HER) network of receptor tyrosine kinases (RTKs), which exemplifies how a constant dialogue between basic research and medical oncology can translate into both a sustained pipeline of novel drugs and ways to overcome acquired treatment resistance in patients. We track the key early discoveries that linked this RTK family to oncogenesis, the course of pioneering clinical research and their merger into a systems-biology framework that is likely to inspire further generations of effective therapeutic strategies.

Hybrids of a genetically engineered antibody and a carbon nanotube transistor for detection of prostate cancer biomarkers

We developed a novel detection method for osteopontin (OPN), a new biomarker for prostate cancer, by attaching a genetically engineered single-chain variable fragment (scFv) protein with high binding affinity for OPN to a carbon nanotube field-effect transistor (NT-FET). Chemical functionalization using diazonium salts is used to covalently attach scFv to NT-FETs, as confirmed by atomic force microscopy, while preserving the activity of the biological binding site for OPN. Electron transport measurements indicate that functionalized NT-FET may be used to detect the binding of OPN to the complementary scFv protein. A concentration-dependent increase in the source-drain current is observed in the regime of clinical significance, with a detection limit of approximately 30 fM. The scFv-NT hybrid devices exhibit selectivity for OPN over other control proteins. These devices respond to the presence of OPN in a background of concentrated bovine serum albumin, without loss of signal. On the basis of these observations, the detection mechanism is attributed to changes in scattering at scFv protein-occupied defect sites on the carbon nanotube sidewall. The functionalization procedure described here is expected to be generalizable to any antibody containing an accessible amine group and to result in biosensors appropriate for detection of corresponding complementary proteins at fM concentrations.

A recombinant triplebody with specificity for CD19 and HLA-DR mediates preferential binding to antigen double-positive cells by dual-targeting

To test the hypothesis that dual-targeting confers the novel ability of selective binding to antigen double-positive over antigen single-positive cells, a single-chain triplebody (sctb), HLA-ds16-hu19, was produced and characterized. The molecule carries three single-chain Fv (scFv) antibody fragments in a single polypeptide chain, the two distal ones specific for the human histocompatibility protein HLA-DR and the B-lymphoid cell surface protein CD19, the central one for CD16, the human low affinity Fc-receptor FcγRIII. For comparison, the bispecific scFvs (bsscFv) hu19-ds16 and HLA-ds16 were also produced. All CD16 binding modules are disulfide-stabilized (ds). The sctb bound simultaneously to both CD19 and HLA-DR on the same cancer cell and, thus, showed functional dual-targeting. In a mixing-experiment with HLA-DR single-positive HUT-78 cells and (HLA-DR plus CD19) double-positive SEM cells, the triplebody showed preferential binding to the double-positive cells, even when the single-positive cells were present in a numerical excess of up to 20-fold. In antibody-dependent cellular cytotoxicity experiments with mononuclear cells as effector cells, the sctb promoted equal lysis of Raji cells, an antigen double-positive cell line, at 130-fold lower concentrations than the bsscFv hu19-ds16, indicating that both distal scFvs of the sctb contributed to tumor cell lysis. A panel of stably-transfected HEK293 cell lines was generated that included CD19- and HLA-DR single-positive and (HLA-DR plus CD19) double-positive lines with antigen-surface densities varying over a broad range. Using a pair of cell lines with matching densities, the sctb eliminated double-positive target cells preferentially single-positive cells. This ability of preferential or selective targeting of antigen double-positive over single-positive cells opens attractive new perspectives for the use of dual-targeting sctbs in cancer therapy.

Site-specific targeting of antibody activity in vivo mediated by disease-associated proteases

As a general strategy to selectively target antibody activity in vivo, a molecular architecture was designed to render binding activity dependent upon proteases in disease tissues. A protease-activated antibody (pro-antibody) targeting vascular cell adhesion molecule 1 (VCAM-1), a marker of atherosclerotic plaques, was constructed by tethering a binding site-masking peptide to the antibody via a matrix metalloprotease (MMP) susceptible linker. Pro-antibody activation in vitro by MMP-1 yielded a 200-fold increase in binding affinity and restored anti-VCAM-1 binding in tissue sections from ApoE⁻/⁻ mice ex vivo. The pro-antibody was efficiently activated by native proteases in aorta tissue extracts from ApoE⁻/⁻, but not from normal mice, and accumulated in aortic plaques in vivo with enhanced selectivity when compared to the unmodified antibody. Pro-antibody accumulation in aortic plaques was MMP-dependent, and significantly inhibited by a broad-spectrum MMP inhibitor. These results demonstrate that the activity of disease-associated proteases can be exploited to site-specifically target antibody activity in vivo.

Engineering antibodies for cancer therapy

The advent of modern antibody engineering has led to numerous successes in the application of these proteins for cancer therapy in the 13 years since the first Food and Drug Administration approval, which has stimulated active interest in developing more and better drugs based on these molecules. A wide range of tools for discovering and engineering antibodies has been brought to bear on this challenge in the past two decades. Here, we summarize mechanisms of monoclonal antibody therapeutic activity, challenges to effective antibody-based treatment, existing technologies for antibody engineering, and current concepts for engineering new antibody formats and antibody alternatives as next generation biopharmaceuticals for cancer treatment.

Antitumor activity of a novel bispecific antibody that targets the ErbB2/ErbB3 oncogenic unit and inhibits heregulin-induced activation of ErbB3

The prevalence of ErbB2 amplification in breast cancer has resulted in the heavy pursuit of ErbB2 as a therapeutic target. Although both the ErbB2 monoclonal antibody trastuzumab and ErbB1/ErbB2 dual kinase inhibitor lapatinib have met with success in the clinic, many patients fail to benefit. In addition, the majority of patients who initially respond will unfortunately ultimately progress on these therapies. Activation of ErbB3, the preferred dimerization partner of ErbB2, plays a key role in driving ErbB2-amplified tumor growth, but we have found that current ErbB2-directed therapies are poor inhibitors of ligand-induced activation. By simulating ErbB3 inhibition in a computational model of ErbB2/ErbB3 receptor signaling, we predicted that a bispecific antibody that docks onto ErbB2 and subsequently binds to ErbB3 and blocks ligand-induced receptor activation would be highly effective in ErbB2-amplified tumors, with superior activity to a monospecific ErbB3 inhibitor. We have developed a bispecific antibody suitable for both large scale production and systemic therapy by generating a single polypeptide fusion protein of two human scFv antibodies linked to modified human serum albumin. The resulting molecule, MM-111, forms a trimeric complex with ErbB2 and ErbB3, effectively inhibiting ErbB3 signaling and showing antitumor activity in preclinical models that is dependent on ErbB2 overexpression. MM-111 can be rationally combined with trastuzumab or lapatinib for increased antitumor activity and may in the future complement existing ErbB2-directed therapies to treat resistant tumors or deter relapse.

Rational engineering of antibody therapeutics targeting multiple oncogene pathways

Monoclonal antibodies have significantly advanced our ability to treat cancer, yet clinical studies have shown that many patients do not adequately respond to monospecific therapy. This is in part due to the multifactorial nature of the disease, where tumors rely on multiple and often redundant pathways for proliferation. Bi- or multi- specific antibodies capable of blocking multiple growth and survival pathways at once have a potential to better meet the challenge of blocking cancer growth, and indeed many of them are advancing in clinical development. ( 1) However, bispecific antibodies present significant design challenges mostly due to the increased number of variables to consider. In this perspective we describe an innovative integrated approach to the discovery of bispecific antibodies with optimal molecular properties, such as affinity, avidity, molecular format and stability. This approach combines simulations of potential inhibitors using mechanistic models of the disease-relevant biological system to reveal optimal inhibitor characteristics with antibody engineering techniques that yield manufacturable therapeutics with robust pharmaceutical properties. We illustrate how challenges of meeting the optimal design criteria and chemistry, manufacturing and control concerns can be addressed simultaneously in the context of an accelerated therapeutic design cycle. Finally, to demonstrate how this rational approach can be applied, we present a case study where the insights from mechanistic modeling were used to guide the engineering of an IgG-like bispecific antibody.

IBC's 21st Annual Antibody Engineering and 8th Annual Antibody Therapeutics International Conferences and 2010 Annual Meeting of the Antibody Society. December 5-9, 2010, San Diego, CA USA

The 21^st Annual Antibody Engineering and 8^th Annual Antibody Therapeutics international conferences, and the 2010 Annual Meeting of The Antibody Society, organized by IBC Life Sciences with contributions from The Antibody Society and two Scientific Advisory Boards, was held December 5–9, 2010 in San Diego, CA. The conferences featured over 100 presentations and 100 posters, and included a pre-conference workshop on deep-sequencing of antibody genes. The total number of delegates exceeded 800, which set a new attendance record for the conference.

The conferences were organized with a focus on antibody engineering only on the first day and a joint engineering/therapeutics session on the last day. Delegates could select from presentations that occurred in two simultaneous sessions on days 2 and 3. Day 1 included presentations on neutralizing antibodies and the identification of vaccine targets, as well as a historical overview of 20 years of phage display utilization. Topics presented in the Antibody Engineering sessions on day 2 and 3 included antibody biosynthesis, structure and stability; antibodies in a complex environment; antibody half-life; and targeted nanoparticle therapeutics. In the Antibody Therapeutics sessions on days 2 and 3, preclinical and early stage development and clinical updates of antibody therapeutics, including TRX518, SYM004, MM111, PRO140, CVX-241, ASG-5ME, U3-1287 (AMG888), R1507 and trastuzumab emtansine, were discussed and perspectives were provided on the development of biosimilar and biobetter antibodies, including coverage of regulatory and intellectual property issues. The joint engineering/therapeutics session on the last day focused on bispecific and next-generation antibodies. Summaries of most of the presentations are included here, but, due to the large number of speakers, it was not possible to include summaries for every presentation.

Delegates enjoyed the splendid views of the San Diego Bay and proximity to the Gaslamp Quarter provided by the venue. The 22^nd Annual Antibody Engineering and 9th Annual Antibody Therapeutics conferences, and the 2011 Annual Meeting of The Antibody Society, are planned for December 5–8, 2011 at the same location in San Diego, and will include two two-day short courses on Introduction to Antibody Engineering and Protein Characterization for Biotechnology Product Development.

Stable IgG-like bispecific antibodies directed toward the type I insulin-like growth factor receptor demonstrate enhanced ligand blockade and anti-tumor activity

Bispecific antibodies (BsAbs) target multiple epitopes on the same molecular target or different targets. Although interest in BsAbs has persisted for decades, production of stable and active BsAbs has hindered their clinical evaluation. Here, we describe the production and characterization of tetravalent IgG-like BsAbs that combine the activities of allosteric and competitive inhibitors of the type-I insulin-like growth factor receptor (IGF-1R). The BsAbs, which were engineered for thermal stability, express well, demonstrate favorable biophysical properties, and recognize both epitopes on IGF-1R. Only one BsAb with a unique geometry, denoted BIIB4-5scFv, was capable of engaging all four of its binding arms simultaneously. All the BsAbs (especially BIIB4-5scFv) demonstrated enhanced ligand blocking over the single monoclonal antibodies (mAbs), particularly at high ligand concentrations. The pharmacokinetic profiles of two IgG-like BsAbs were tested in nude mice and shown to be comparable with that of the parental mAbs. The BsAbs, especially BIIB4-5scFv, demonstrated an improved ability to reduce the growth of multiple tumor cell lines and to inhibit ligand-induced IGF-1R signaling in tumor cells over the parental mAbs. BIIB4-5scFv also led to superior tumor growth inhibition over its parental mAbs in vivo. In summary, BsAbs that bridge multiple inhibitory mechanisms against a single target may generally represent a more effective strategy for intervention in oncology or other indications compared with traditional mAb therapy.

Chemical generation of bispecific antibodies

Bispecific antibodies (BsAbs) are regarded as promising therapeutic agents due to their ability to simultaneously bind two different antigens. Several bispecific modalities have been developed, but their utility is limited due to problems with stability and manufacturing complexity. Here we report a versatile technology, based on a scaffold antibody and pharmacophore peptide heterodimers, that enables rapid generation and chemical optimization of bispecific antibodies, which are termed bispecific CovX-Bodies. Two different peptides are joined together using a branched azetidinone linker and fused to the scaffold antibody under mild conditions in a site-specific manner. Whereas the pharmacophores are responsible for functional activities, the antibody scaffold imparts long half-life and Ig-like distribution. The pharmacophores can be chemically optimized or replaced with other pharmacophores to generate optimized or unique bispecific antibodies. As a prototype, we developed a bispecific antibody that binds both vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang2) simultaneously, inhibits their function, shows efficacy in tumor xenograft studies, and greatly augments the antitumor effects of standard chemotherapy. This unique antiangiogenic bispecific antibody is in phase-1 clinical trials.

Research and development of next generation of antibody-based therapeutics

Monoclonal antibodies (mAb) are emerging as one of the major class of therapeutic agents in the treatment of many human diseases, in particular in cancer and immunological disorders. To date, 28 mAb have been approved by the United States Food and Drug Administration for clinical applications. In addition, several hundreds of mAb are being developed clinically by many biotech and pharmaceutical companies for various disease indications. Many challenges still remain, however, and the full potential of therapeutic antibodies has yet to be realized. With the advancement of antibody engineering technologies and our further understanding of disease biology as well as antibody mechanism of action, many classes of novel antibody formats or antibody derived molecules are emerging as promising new generation therapeutics. These new antibody formats or molecules are carefully designed and engineered to acquire special features, such as improved pharmacokinetics, increased selectivity, and enhanced efficacy. These new agents may have the potential to revolutionize both our thinking and practice in the efforts to research and develop next generation antibody-based therapeutics.

A recombinant trispecific single-chain Fv derivative directed against CD123 and CD33 mediates effective elimination of acute myeloid leukaemia cells by dual targeting

Two trivalent constructs consisting of single-chain Fv antibody fragments (scFvs) specific for the interleukin-3 receptor alpha chain (CD123), CD33 and the Fcgamma-receptor III (CD16) were designed and characterized for the elimination of acute myeloid leukaemia (AML) cells. The dual targeting single-chain Fv triplebody (sctb) [123 x ds16 x 33] and the mono targeting sctb [123 x ds16 x 123] both specifically bound their respective target antigens and were stable in human serum at 37 degrees C for at least 5 d. Both constructs induced potent antibody-dependent cellular cytotoxicity (ADCC) of two different AML-derived CD33- and CD123 double-positive cell lines in the low picomolar range using isolated mononuclear cells (MNCs) as effector cells. In these experiments the dual targeting molecule produced significantly stronger lysis than the mono targeting agent. In addition, the sctbs showed a high potency in mediating ADCC of primary leukaemia cells isolated from peripheral blood or bone marrow of seven AML patients. Hence, these novel molecules displayed potent anti-leukaemic effects against AML cells in vitro and represent attractive candidates for further preclinical development.

Antitumor effects and normal-tissue toxicity of 111In-nuclear localization sequence-trastuzumab in athymic mice bearing HER-positive human breast cancer xenografts

(111)In-nuclear localization sequence-trastuzumab is a radioimmunotherapeutic agent consisting of trastuzumab modified with NLS peptides (CGYGPKKKRKVGG) and labeled with the Auger electron emitter (111)In. Our objectives were to evaluate the tumor growth-inhibitory properties and normal-tissue toxicity of (111)In-NLS-trastuzumab in mice after intraperitoneal administration.

METHODS

The pharmacokinetics of (111)In-NLS-trastuzumab after intravenous (tail vein) or intraperitoneal injection in BALB/c mice were compared. Normal-tissue toxicity was determined in BALB/c mice at 2 wk after intraperitoneal injection of 3.7-18.5 MBq (4 mg/kg) of (111)In-NLS-trastuzumab by monitoring body weight, histopathologic examination of tissues, and hematology (white blood cell, platelet, red blood cell, and hemoglobin) or clinical biochemistry (alanine transaminase and creatinine) parameters. A no-observable-adverse-effect-level (NOAEL) dose was defined. Athymic mice bearing subcutaneous MDA-MB-361 or MDA-MB-231 human breast cancer xenografts (5.0 x 10(5) or 0.5 x 10(5) HER2/cell, respectively) were treated with a single NOAEL dose or 2 doses administered intraperitoneally and separated by 2 wk. Control groups were administered (111)In-trastuzumab, trastuzumab, nonspecific (111)In-NLS-human IgG (hIgG), or normal saline.

RESULTS

The bioavailability of (111)In-NLS-trastuzumab after intraperitoneal injection was 0.7. The NOAEL dose was 9.25 MBq (4 mg/kg); doses greater than or equal to 18.5 MBq decreased white blood cell or platelet counts, and doses of 27.7 MBq decreased red blood cell counts. There was no increase in alanine transaminase or creatinine at any doses tested. There were no morphologic changes to the liver, kidneys, heart, or spleen or loss of body weight. A single dose of (111)In-NLS-trastuzumab (9.25 MBq)-compared with mice receiving (111)In-trastuzumab, trastuzumab, (111)In-NLS-hIgG, or normal saline-significantly slowed the rate of growth of MDA-MB-361 tumors over 60 d (0.014 d(-1) vs. 0.033 d(-1), 0.046 d(-1), 0.030 d(-1), and 0.061 d(-1), respectively; P < 0.05). (111)In-NLS-trastuzumab had no effect on the growth of MDA-MB-231 tumors. Two doses of (111)In-NLS-trastuzumab (9.25 MBq; 4 mg/kg) separated by 2 wk increased the survival of mice with MDA-MB-361 tumors, compared with mice treated with trastuzumab or normal saline (>140 d vs. 96 and 84 d, respectively; P < 0.001 or 0.027, respectively).

CONCLUSION

(111)In-NLS-trastuzumab is a promising radioimmunotherapeutic agent that could be effective for treatment of HER2-overexpressing breast cancer in humans.

Generation and characterization of anti-alpha-enolase single-chain antibodies in chicken

It was previously reported that up-regulation of α-enolase protein was detected in 65% of patients with non-small cell lung cancers (NSCLC). Moreover, a high titer of anti-α-enolase antibodies was developed in a smaller proportion (7.4%) of these patients than in non-tumor-associated patients and healthy subjects. In the present study, we characterized polyclonal and single-chain variable fragment (scFv) anti-α-enolase antibodies from immunized chickens. The E. coli-derived recombinant α-enolase protein was purified to its high homogenicity as verified by SDS-PAGE. After the 4th immunization, a high titer of specific polyclonal anti-α-enolase antibodies was elicited in immunized chickens and specifically recognized the purified human α-enolase antigen as determined by Western blot and ELISA. The expressed heavy and light chain variable genes (VH and VL) were isolated from spleen B cells and amplified to construct phage antibody libraries containing scFv molecules. After four rounds of panning selection, the scFv antibodies of randomly chosen clones were expressed and their binding specificity to α-enolase protein was verified using competitive ELISA, flow cytometry and immunofluorescence staining. Nucleotide sequence analysis from 10 α-enolase binding clones showed that 3 (30%) clones used identical heavy and light genes for scFv antibody expression, as represented by EnL5. Notably, amino acid changes in complementarity-determining regions (CDRs) were more frequently observed than those in framework regions (FRs) in all clones, indicating a strong affinity selection through mutations. All together, it is believed that these polyclonal and scFv IgY antibodies may be helpful in the development of molecular diagnostic and therapeutic agents for lung cancers in the future.

A bispecific enediyne-energized fusion protein containing ligand-based and antibody-based oligopeptides against epidermal growth factor receptor and human epidermal growth factor receptor 2 shows potent antitumor activity

PURPOSE

The cooverexpression of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) observed in many human tumors and their synergistic interaction in the transformation of cells make these receptors important targets for the development of new targeted therapeutics. Targeting of EGFR and HER2 simultaneously has been pursued as a strategy with which to potentially increase efficiency and selectivity in therapy of certain cancers. This study was set to construct a bispecific energized fusion protein (Ec-LDP-Hr-AE) consisting of two oligopeptides against EGFR and HER2, and lidamycin, and investigate its antitumor efficacy.

EXPERIMENTAL DESIGN

In vitro experiments measured the binding and internalization of bispecific Ec-LDP-Hr fusion protein. The potency of energized fusion proteins was also done in which the bispecific Ec-LDP-Hr-AE was compared with lidamycin (LDM) and its monospecific counterparts, Ec-LDP-AE and LDP-Hr-AE. In vivo, Ec-LDP-Hr-AE was given i.v. to nude mice bearing human ovarian carcinoma SK-OV-3 xenografts.

RESULTS

Binding and internalization studies showed that bispecific fusion protein Ec-LDP-Hr bound to carcinoma cells specifically and then were internalized into the cytoplasm. Bispecific Ec-LDP-Hr-AE was more potent and selective in its cytotoxicity against different carcinoma cell lines than corresponding momospecific agents and LDM in vitro. In addition, Ec-LDP-Hr-AE significantly inhibited the growth of SK-OV-3 xenografts in nude mouse model. In vivo imaging study showed that FITC-labeled Ec-LDP-Hr was targeted and accumulated in the tumors.

CONCLUSION

A ligand-based and an antibody-based oligopeptide fused to the enediyne antibiotic LDM created a new bispecific fusion protein with low molecular weight and more potent in vitro and in vivo antitumor activity (than momospecific fusion proteins).

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

SEEDbodies: fusion proteins based on strand-exchange engineered domain (SEED) CH3 heterodimers in an Fc analogue platform for asymmetric binders or immunofusions and bispecific antibodies

Bispecific antibodies and asymmetric Fc fusion proteins offer opportunities for important advances in therapeutics. Bivalent IgG depends upon in vivo dimerization of its heavy chains, mediated by homodimeric association of its C(H)3 domains. We have developed a heterodimeric Fc platform that supports the design of bispecific and asymmetric fusion proteins by devising strand-exchange engineered domain (SEED) C(H)3 heterodimers. These derivatives of human IgG and IgA C(H)3 domains create complementary human SEED C(H)3 heterodimers that are composed of alternating segments of human IgA and IgG C(H)3 sequences. The resulting pair of SEED C(H)3 domains preferentially associates to form heterodimers when expressed in mammalian cells. SEEDbody (Sb) fusion proteins consist of [IgG1 hinge]-C(H)2-[SEED C(H)3], that may be genetically linked to one or more fusion partners. This investigation reports on the generation of mono-Fab-Sb and Sb-IL2 monocytokine as models. They were expressed at high levels in NS/0 cells, purified on recombinant protein A resin and were well-behaved in solution. When administered intravenously to mice, Sb pharmacokinetics exhibited the long serum half-life extensions typical of comparable Fc-containing immunofusion and IgG1 controls.

[Bispecific antibodies: what future?]

Monoclonal antibodies have emerged as a very successful class of therapeutic agents. In their native format, monoclonal antibodies are monospecific in that they recognize only one epitope, but their Fc domain also binds to FcfR-expressing cells. Attempts to improve the cytotoxicity of antibodies, particularly in the cancer field, have led to the design of bispecific antibodies: this can occur through various strategies, such as quadroma, thioether-linked Fab' gamma fragments or genetic engineering. Such bispecific antibodies have been developped to enhance immunotherapy, by bridging tumor cells and T cells, or radioimmunotherapy by combining bispecific antibodies and radiolabeled bivalent haptens that bind cooperatively to target cells. Multiple further applications can be envisaged such as targeting two different antigens on the same cell, or two epitopes of the same antigen. Although progresses have been slowed by technical constraints, there is little doubt that this class of novel antibodies derivatives will experience a promising development.

Engineering and characterization of a bispecific HER2 x EGFR-binding affibody molecule

HER2 (human epidermal-growth-factor receptor-2; ErbB2) and EGFR (epidermal-growth-factor receptor) are overexpressed in various forms of cancer, and the co-expression of both HER2 and EGFR has been reported in a number of studies. The simultaneous targeting of HER2 and EGFR has been discussed as a strategy with which to potentially increase efficiency and selectivity in molecular imaging and therapy of certain cancers. In an effort to generate a molecule capable of bispecifically targeting HER2 and EGFR, a gene fragment encoding a bivalent HER2-binding affibody molecule was genetically fused in-frame with a bivalent EGFR-binding affibody molecule via a (G4S)3 [(Gly4-Ser)3]-encoding gene fragment. The encoded 30 kDa affibody construct (ZHER2)2-(G4S)3-(ZEGFR)2, with potential for bs (bispecific) binding to HER2 and EGFR, was expressed in Escherichia coli and characterized in terms of its binding capabilities. The retained ability to bind HER2 and EGFR separately was demonstrated using both biosensor technology and flow-cytometric analysis, the latter using HER2- and EGFR-overexpressing cells. Furthermore, simultaneous binding to HER2 and EGFR was demonstrated in: (i) a sandwich format employing real-time biospecific interaction analysis where the bs affibody molecule bound immobilized EGFR and soluble HER2; (ii) immunofluorescence microscopy, where the bs affibody molecule bound EGFR-overexpressing cells and soluble HER2; and (iii) a cell-cell interaction analysis where the bs affibody molecule bound HER2-overexpressing SKBR-3 cells and EGFR-overexpressing A-431 cells. This is, to our knowledge, the first reported bs affinity protein with potential ability for the simultaneous targeting of HER2 and EGFR. The potential future use of this and similar constructs, capable of bs targeting of receptors to increase the efficacy and selectivity in imaging and therapy, is discussed.

Affinity and avidity in antibody-based tumor targeting

Many factors contribute to successful tumor targeting by antibodies. Besides properties of the tumor tissue and general antibody pharmacology, a relationship exists between an antibody and its antigen that can shape penetration, catabolism, specificity, and efficacy. The affinity and avidity of the binding interactions play critical roles in these dynamics. In this work, we review the principles that guide models predicting tumor penetration and cellular internalization while providing a critical overview of studies aimed at experimentally determining the specific role of affinity and avidity in these processes. One should gain the perspective that binding affinity can, in part, dictate the localization of antibodies in tumors, leading to high concentrations in the perivascular space or low concentrations diffused throughout the tumor. These patterns can be simply due to the diminution of available dose by binding antigen and are complicated by internalization and degradation stemming from slow rates of dissociation. As opposed to the trend of simply increasing affinity to increase efficacy, novel strategies that increase avidity and broaden specificity have made significant progress in tumor targeting.

Targeting the EGFR and the PKB pathway in cancer

The EGFR and PKB pathways are frequently activated in cancer, so are prime targets for cancer therapy. To this end, new inhibitors are being tested. EGFR inhibitors as single therapy have little benefit, although therapies that evoke an antitumor immune response are more effective. Resistance mutations within the EGFR are common, as is activation of the antiapoptotic PKB pathway via alternative tyrosine kinase receptors, especially other EGFR family members or IGF1R. To combat resistance, multitargeted EGFR inhibitors and combined inhibition of the EGFR and PKB are being investigated. Inhibition of the EGFR and PKB pathways also sensitizes cancer cells to chemotherapy. Thus, EGFR and PI3K/PKB inhibitors will be most effective when used in rational combinations of targeted inhibitors and traditional chemotherapy.

Tumour vascularisation: a druggable target

Tumour growth, spreading and metastasis require the development of a local vasculature. There have been great advances in the understanding of how this new vasculature arises, particularly in our increased knowledge of the process of angiogenesis, Although, a vast number of pro-angiogenic and anti-angiogenic mediators have been identified, one of the key signalling processes in the development of the tumour vasculature is the hypoxia-induced stimulation of vascular endothelial cell growth factors (VEGFs) production. Anti-VEGF therapy therefore not only provides a new paradigm for limiting tumour growth via targeting angiogenesis, but also provides prototypic agents to test the hypothesis that by controlling the development of the tumour vasculature we are able to limit, and potentially stop, tumour growth and spreading.