Bispecific and bifunctional single chain recombinant antibodies

Engineered Bifunctional Proteins for Targeted Cancer Therapy: Prospects and Challenges

Bifunctional proteins (BFPs) are a class of therapeutic agents produced through genetic engineering and protein engineering, and are increasingly used to treat various human diseases, including cancer. These proteins usually have two or more biological functions-specifically recognizing different molecular targets to regulate the related signaling pathways, or mediating effector molecules/cells to kill tumor cells. Unlike conventional small-molecule or single-target drugs, BFPs possess stronger biological activity but lower systemic toxicity. Hence, BFPs are considered to offer many benefits for the treatment of heterogeneous tumors. In this review, the authors briefly describe the unique structural feature of BFP molecules and innovatively divide them into bispecific antibodies, cytokine-based BFPs (immunocytokines), and protein toxin-based BFPs (immunotoxins) according to their mode of action. In addition, the latest advances in the development of BFPs are discussed and the potential limitations or problems in clinical applications are outlined. Taken together, future studies need to be centered on understanding the characteristics of BFPs for optimizing and designing more effective such drugs.

Build-up functionalization of anti-EGFR × anti-CD3 bispecific diabodies by integrating high-affinity mutants and functional molecular formats

Designing non-natural antibody formats is a practical method for developing highly functional next-generation antibody drugs, particularly for improving the therapeutic efficacy of cancer treatments. One approach is constructing bispecific antibodies (bsAbs). We previously reported a functional humanized bispecific diabody (bsDb) that targeted epidermal growth factor receptor and CD3 (hEx3-Db). We enhanced its cytotoxicity by constructing an Fc fusion protein and rearranging order of the V domain. In this study, we created an additional functional bsAb, by integrating the molecular formats of bsAb and high-affinity mutants previously isolated by phage display in the form of Fv. Introducing the high-affinity mutations into bsDbs successfully increased their affinities and enhanced their cytotoxicity in vitro and in vivo. However, there were some limitations to affinity maturation of bsDb by integrating high-affinity Fv mutants, particularly in Fc-fused bsDb with intrinsic high affinity, because of their bivalency. The tetramers fractionated from the bsDb mutant exhibited the highest in vitro growth inhibition among the small bsAbs and was comparable to the in vivo anti-tumor effects of Fc-fused bsDbs. This molecule shows cost-efficient bacterial production and high therapeutic potential.

HIV-1 gp120-CD4-Induced Antibody Complex Elicits CD4 Binding Site-Specific Antibody Response in Mice

Elicitation of broadly neutralizing Ab (bNAb) responses toward the conserved HIV-1 envelope (Env) CD4 binding site (CD4bs) by vaccination is an important goal for vaccine development and yet to be achieved. The outcome of previous immunogenicity studies suggests that the limited accessibility of the CD4bs and the presence of predominant nonneutralizing determinants (nND) on Env may impede the elicitation of bNAbs and their precursors by vaccination. In this study, we designed a panel of novel immunogens that 1) preferentially expose the CD4bs by selective elimination of glycosylation sites flanking the CD4bs, and 2) minimize the nND immune response by engineering fusion proteins consisting of gp120 Core and one or two CD4-induced (CD4i) mAbs for masking nND epitopes, referred to as gp120-CD4i fusion proteins. As expected, the fusion proteins possess improved antigenicity with retained affinity for VRC01-class, CD4bs-directed bNAbs and dampened affinity for nonneutralizing Abs. We immunized C57BL/6 mice with these fusion proteins and found that overall the fusion proteins elicit more focused CD4bs Ab response than prototypical gp120 Core by serological analysis. Consistently, we found that mice immunized with selected gp120-CD4i fusion proteins have higher frequencies of germinal center-activated B cells and CD4bs-directed memory B cells than those inoculated with parental immunogens. We isolated three mAbs from mice immunized with selected gp120-CD4i fusion proteins and found that their footprints on Env are similar to VRC01-class bNAbs. Thus, using gp120-CD4i fusion proteins with selective glycan deletion as immunogens could focus Ab response toward CD4bs epitope.

Chemically Crosslinked Bispecific Antibodies for Cancer Therapy: Breaking from the Structural Restrictions of the Genetic Fusion Approach

Antibodies are composed of structurally and functionally independent domains that can be used as building blocks to construct different types of chimeric protein-format molecules. However, the generally used genetic fusion and chemical approaches restrict the types of structures that can be formed and do not give an ideal degree of homogeneity. In this study, we combined mutation techniques with chemical conjugation to construct a variety of homogeneous bivalent and bispecific antibodies. First, building modules without lysine residues—which can be chemical conjugation sites—were generated by means of genetic mutation. Specific mutated residues in the lysine-free modules were then re-mutated to lysine residues. Chemical conjugation at the recovered lysine sites enabled the construction of homogeneous bivalent and bispecific antibodies from block modules that could not have been so arranged by genetic fusion approaches. Molecular evolution and bioinformatics techniques assisted in finding viable alternatives to the lysine residues that did not deactivate the block modules. Multiple candidates for re-mutation positions offer a wide variety of possible steric arrangements of block modules, and appropriate linkages between block modules can generate highly bioactive bispecific antibodies. Here, we propose the effectiveness of the lysine-free block module design for site-specific chemical conjugation to form a variety of types of homogeneous chimeric protein-format molecule with a finely tuned structure and function.

A novel asymmetrical anti-HER2/CD3 bispecific antibody exhibits potent cytotoxicity for HER2-positive tumor cells

Background

Human epidermal growth factor receptor 2 (HER2) is overexpressed in multiple cancers, which is associated with poor prognosis. Herceptin and other agents targeting HER2 have potent antitumor efficacy in patients with HER2-positive cancers. However, the development of drug resistance adversely impacts the efficacy of these treatments. It is therefore urgent to develop new HER2-targeted therapies. Bispecific antibodies (BsAbs) could guide immune cells toward tumor cells, and produced remarkable effects in some cancers.

Methods

A BsAb named M802 that targets HER2 and CD3 was produced by introducing a salt bridge and knobs-into-holes (KIHs) packing into the structure. Flow cytometry was performed to determine its binding activity and cytotoxicity. CCK-8, Annexin V/PI staining, western blotting, and ELISA were utilized to study its effect on cell proliferation, apoptosis, the signaling pathways of tumor cells, and the secretion of cytokines by immune cells. Subcutaneous tumor mouse models were used to analyze the in vivo antitumor effects of M802.

Results

We generated a new format of BsAb, M802, consisting of a monovalent unit against HER2 and a single chain unit against CD3. Our in vitro and in vivo experiments indicated that M802 recruited CD3-positive immune cells and was more cytotoxic than Herceptin in cells with high expression of HER2, low expression of HER2, and Herceptin resistance. Although M802 showed weaker effects than Herceptin on the PI3K/AKT and MAPK pathways, it was more cytotoxic due to its specific recognition of HER2 and its ability to recruit effector cells via its anti-CD3 moiety.

Conclusions

Our results indicated that M802 exhibited potent antitumor efficacy in vitro and in vivo. M802 retained the function of Herceptin in antitumor signaling pathways, and also recruited CD3-positive immune cells to eliminate HER2-positive tumor cells. Therefore, M802 might be a promising HER2 targeted agent.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1354-1) contains supplementary material, which is available to authorized users.

Comprehensive study of domain rearrangements of single-chain bispecific antibodies to determine the best combination of configurations and microbial host cells

Small bispecific antibodies (bsAbs) are important therapeutic molecules and represent the first bsAb format approved by the United States Food and Drug Administration. Diabody (Db), a small bsAb format, has four possible domain orders; we previously reported the differences in the expression levels and cancer growth inhibition effects upon rearranging the domain order of this format. However, there have been no comprehensive reports on domain rearrangements of bispecific single-chain Db (scDb) and tandem single-chain Fv (taFv), which are widely used bsAb formats. In this study, we designed all possible domain orders for scDb and taFv (each with eight variants) with identical Fv pairs and individually expressed all 16 variants using Escherichia coli, Pichia pastoris, and Brevibacillus choshinensis. Comprehensive investigations showed that the intrinsic functions of the variants were similar to each other, regardless of the expression host system, but expression levels varied depending on the format as well as on the host cell. Among the 16 variants, we found a promising candidate that exhibited high activity and productivity. Furthermore, we determined that B. choshinensis is an attractive expression host because of its secretory production of recombinant proteins.

Rational design of a trispecific antibody targeting the HIV-1 Env with elevated anti-viral activity

HIV-1 broadly neutralizing antibodies (bNAbs) are being explored as passively administered therapeutic and preventative agents. However, the extensively diversified HIV-1 envelope glycoproteins (Env) rapidly acquire mutations to evade individual bNAbs in monotherapy regimens. The use of a "single" agent to simultaneously target distinct Env epitopes is desirable to overcome viral diversity. Here, we report the use of tandem single-chain variable fragment (ScFv) domains of two bNAbs, specific for the CD4-binding site and V3 glycan patch, to form anti-HIV-1 bispecific ScFvs (Bi-ScFvs). The optimal Bi-ScFv crosslinks adjacent protomers within one HIV-1 Env spike and has greater neutralization breadth than its parental bNAbs. Furthermore, the combination of this Bi-ScFv with a third bNAb recognizing the Env membrane proximal external region (MPER) results in a trispecific bNAb, which has nearly pan-isolate neutralization breadth and high potency. Thus, multispecific antibodies combining functional moieties of bNAbs could achieve outstanding neutralization capacity with augmented avidity.

A semi high-throughput method for screening small bispecific antibodies with high cytotoxicity

Small bispecific antibodies that induce T-cell-mediated cytotoxicity have the potential to damage late-stage tumor masses to a clinically relevant degree, but their cytotoxicity is critically dependent on their structural and functional properties. Here, we constructed an optimized procedure for identifying highly cytotoxic antibodies from a variety of the T-cell-recruiting antibodies engineered from a series of antibodies against cancer antigens of epidermal growth factor receptor family and T-cell receptors. By developing and applying a set of rapid operations for expression vector construction and protein preparation, we screened the cytotoxicity of 104 small antibodies with diabody format and identified some with 103-times higher cytotoxicity than that of previously reported active diabody. The results demonstrate that cytotoxicity is enhanced by synergistic effects between the target, epitope, binding affinity, and the order of heavy-chain and light-chain variable domains. We demonstrate the importance of screening to determine the critical rules for highly cytotoxic antibodies.

Are BiTEs the "missing link" in cancer therapy?

Conventional treatment for cancer routinely includes surgical resection and some combination of chemotherapy and radiation. These approaches are frequently accompanied by unintended and highly toxic collateral damage to healthy tissues, which are offset by only marginal prognostic improvements in patients with advanced cancers. This unfortunate balance has driven the development of novel therapies that aim to target tumors both safely and efficiently. Over the past decade, mounting evidence has supported the therapeutic utility of T-cell-centered cancer immunotherapy, which, in its various iterations, has been shown capable of eliciting highly precise and robust antitumor responses both in animal models and human trials. The identification of tumor-specific targets has further fueled a growing interest in T-cell therapies given their potential to circumvent the non-specific nature of traditional treatments. Of the several strategies geared toward achieving T-cell recognition of tumor, bispecific antibodies (bsAbs) represent a novel class of biologics that have garnered enthusiasm in recent years due to their versatility, specificity, safety, cost, and ease of production. Bispecific T-cell Engagers (BiTEs) are a subclass of bsAbs that are specific for CD3 on one arm and a tumor antigen on the second. As such, BiTEs function by recruiting and activating polyclonal populations of T-cells at tumor sites, and do so without the need for co-stimulation or conventional MHC recognition. Blinatumomab, a well-characterized BiTE, has emerged as a promising recombinant bscCD19×CD3 construct that has demonstrated remarkable antitumor activity in patients with B-cell malignancies. This clinical success has resulted in the rapid extension of BiTE technology against a greater repertoire of tumor antigens and the recent US Food and Drug Administration's (FDA) accelerated approval of blinatumomab for the treatment of a rare form of acute lymphoblastic leukemia (ALL). In this review, we dissect the role of T-cell therapeutics in the new era of cancer immunotherapy, appraise the value of CAR T-cells in the context of solid tumors, and discuss why the BiTE platform may rescue several of the apparent deficits and shortcomings of competing immunotherapies to support its widespread clinical application.

Bi-specific antibodies with high antigen-binding affinity identified by flow cytometry

Using conventional approaches, the antigen-binding affinity of a novel format of bi-specific antibody (BsAb) cannot be determined until purified BsAb is obtained. Here, we show that new lipoprotein A (NlpA)-based bacteria display technology, combined with flow cytometry (FCM), can be used to detect antigen-binding affinity of BsAbs, in the absence of expression and purification work. Two formats of BsAb, scFv2-CH/CL and Diabody-CH/CL, specific for human interleukin 1β (hIL-1β) and human interleukin 17A (hIL-17A), were constructed and displayed in Escherichia coli using NlpA-based bacteria display technology. Conversion of these cells to spheroplasts, and their incubation with fluorescently conjugated antigens resulted in the selective labeling of spheroplasts expressing BsAb; enabling their antigen-binding affinity to be analyzed with FCM. The association and dissociation of BsAbs for binding to hIL-1β and hIL-17A were analyzed using FCM-based assays. The results showed that antigen-binding affinity of Diabody-CH/CL was significantly higher than that of scFv2-CH/CL. To confirm these results of FCM-based assays, BsAbs were expressed, purified and subjected to relative affinity measurements, in vitro and in vivo bioactivity analysis. The results showed that Diabody-CH/CL had greater relative affinities for both antigens, resulting in better blocking bioactivities on cellular level and effects on alleviating joint inflammation, and cartilage destruction and bone damage in collagen induced arthritis (CIA) mice model. These results indicate that BsAbs with good antigen-binding affinity can be identified by FCM-based assays without expression and purification work, and the indentified BsAb can serve as a lead compound for further drug development.

Cloning, expression, purification and characterization of a bispecific single-chain diabody against fluoroquinolones and sulfonamides in Escherichia coli

A recombinant bispecific single-chain diabody (scDb), recognizing fluoroquinolones (FQs) and sulfonamides (SAs), was successfully constructed with two single-chain variable fragment antibodies (scFvs). The scDb gene was cloned into the expression vector pJB33, and 6×His-tagged scDb was expressed as soluble bodies in Escherichia coli RV308 host, then purified by one step affinity chromatography of immobilized metal ion affinity chromatography (IMAC). SDS-PAGE and Western blotting analysis of the purified scDb indicated that the prepared scDb was successfully expressed as a ∼60 kDa and the final purity of the scDb protein was up to 95% with yields of approximately 6 mg/L of bacterial culture. The scDb was further characterized by indirect competitive enzyme linked immunosorbent assay (icELISA), showing that the affinity and specificity of scDb were fully retained from the two parental scFvs, capable of simultaneously binding FQs and SAs. The 50% inhibition concentration (IC50) values of the optimized immunoassay were 0.45 ng mL(-1) for FQs and 0.75 ng mL(-1) for SAs, respectively. The scDb exhibited high affinity to 20 FQs and 14 SAs. Taken together, these findings suggested that the prepared scDb could be used to develop future novel immunoassay for simultaneous determination of 20 FQs and 14 SAs.

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.

Construction and expression of D-dimer and GPIIb/IIIa single-chain bispecific antibody

The aim of this study was to construct a plasmid expressing glycoprotein IIb-IIIa (GPIIb/IIIa) and D-dimer single-chain bispecific antibody for the targeted therapy of thrombosis. The phosphorylated gene encoding the anti-GPIIb/IIIa single-chain variable fragment (scFv) and the gene encoding the anti-D-dimer scFv were amplified by PCR and linked in tandem by blunt-end ligation. The recombinant plasmid was transfected into the competent cell line HB2151 and identified by PCR and DNA sequencing. Then, the soluble recombinant antibody in bacterial lysates was purified by an NTA column and molecular sieve chromatography in turn. Finally, the binding specificity of the purified antibody was tested by enzyme-linked immunosorbent assay (ELISA). Results demonstrated that the construction of the expression plasmid was successful and the purified recombinant protein, which had a molecular weight of ∼56 kDa, was specific to GPIIb/IIIa and D-dimer. In conclusion, a plasmid expressing a bispecific antibody was constructed by a new method of blunt-end ligation. The soluble recombinant protein is a promising platform for target-oriented thrombolytic therapy.

Mixed immunoassay design for multiple chemical residues detection

In this research, a mixed immunoassay design for multiple chemical residues detection based on combined reverse competitive enzyme-linked immunosorbent assay (ELISA) procedure was developed. This method integrated two reverse ELISA reactions in one assay by labeling horseradish peroxidase to deoxynivalenol (DON) and orbifloxacin. Within this method, IC50 of the two mAbs for each analyte we produced ranged from 23~68 ng mL(-1) for DONs and 4.1~49 ng mL(-1) for quinolones (QNs). The limit of detection measured by IC10 was achieved at 0.45-1.3 ng mL(-1) for DONs and 0.59-6.9 ng mL(-1) for QNs, which was lower than the maximum residue levels. Recoveries in negative samples spiked at concentrations of 100, 200, and 500 ng mL(-1) ranged from 91.3 to 102.2 % for DONs and 88.7-98.05 % for QNs with relative standard deviation less than 9.88 and 12.67 %. The results demonstrated that this developed immunoassay was suitable for screening of low molecular weight contaminants.

Generation of single-chain bispecific green fluorescent protein fusion antibodies for imaging of antibody-induced T cell synapses

There is growing interest in the development of novel single-chain bispecific antibodies for retargeting of immune effector T cells to tumor cells. Until today, functional fusion constructs consisting of a single-chain bispecific antibody and a fluorescent protein were not reported. Such molecules could be useful for an in vivo visualization of this retargeting process. Recently, we established two novel single-chain bispecific antibodies. One is capable of retargeting T cells to CD33, and the other is capable of retargeting T cells to the prostate stem cell antigen (PSCA). CD33 is an attractive immunotarget on the surface of tumor cells from patients with acute myeloid leukemia (AML). The PSCA is a potential target on prostate cancer cells. Flanking the reading frame encoding the green fluorescent protein (GFP) with a recently described novel helical linker element allowed us to establish novel single-chain bispecific fusion antibodies. These fluorescent fusion antibodies were useful to efficiently retarget T cells to the respective tumor cells and visualize the formation of immune synapses between effector and target cells.

Production of bispecific antibodies: diabodies and tandem scFv

Recombinant bispecific antibodies have many different applications; especially promising is their therapeutic potential due to their ability to retarget an effector molecule or a cell to a disease-related target structure. In the last years, many formats have been developed: two commonly used are the bispecific diabody and the tandem scFv. In this chapter, the cloning, bacterial production, purification, and characterization of the two antibody formats are described in detail.

Construction and humanization of a functional bispecific EGFR × CD16 diabody using a refolding system

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.

Unexpected recombinations in single chain bispecific anti-CD3-anti-CD33 antibodies can be avoided by a novel linker module

CD33 is an attractive immunotarget on the surface of tumor cells from patients with acute myeloid leukemia (AML). In a first attempt for immunotargeting of AML blasts we constructed two bispecific antibodies in the single chain bispecific diabody (scBsDb) format by fusing the variable domains of monoclonal antibodies directed against CD3 and CD33. Unfortunately, protein expression of both scBsDbs resulted in varying mixtures of fragmented and full length proteins. As the non-functional fragments competed with the functional full length antibodies we tried to understand the reason for the fragmentation. We found that the anti-CD3 and anti-CD33 antibody genes show striking sequence homologies: during B cell development the same V(h) J558 heavy and V(l) kk4 light chain genes were selected. Moreover, the closely related D genes DSP2 (9 and 11) were combined with the same JH4 gene. And finally, during VJ recombination of the light chain the same JK5 element was selected. These homologies between the two monoclonal antibodies were the reason for recombinations in the cell lines generated for expression of the scBsDbs. Finally, we solved this problem by (i) rearranging the order of the heavy and light chains of the anti-CD3 and anti-CD33 domains, and (ii) a replacement of one of the commonly used glycine serine linkers with a novel linker domain. The resulting bispecific antibody in a single chain bispecific tandem format (scBsTaFv) was stable and capable of redirecting T cells to CD33-positive tumor cells including AML blasts of patients.

Retargeting of T cells to prostate stem cell antigen expressing tumor cells: comparison of different antibody formats

BACKGROUND

Prostate cancer (PCa) is the most common malignant disease in men. Novel treatment options are needed for patients after development of metastatic, hormone-refractory disease or for those who have failed a local treatment. The prostate stem cell antigen (PSCA) is expressed in >80% of primary PCa samples and bone metastases. Its expression is increased both in androgen-dependent and independent prostate tumors, particularly in carcinomas of high stages and Gleason scores. Therefore, PSCA is an attractive target for immunotherapy of PCa by retargeting of T cells to tumor cells.

METHODS

A series of different bispecific antibody formats for retargeting of T cells to tumor cells were described but, only very limited data obtained by side by side comparison of the different antibody formats are available. We established two novel bispecific antibodies in different formats. The functionality of both constructs was analyzed by FACS and chromium release assays. In parallel, the release of pro-inflammatory cytokines was determined by ELISA.

RESULTS AND CONCLUSIONS

Irrespective of the underlying antibody format, both novel bispecific antibodies cause an efficient killing of PSCA-positive tumor cells by pre- and non-pre-activated T cells. Killing and release of pro-inflammatory cytokines requires an antigen specific cross-linkage of the T cells with the target cells.

Cytotoxic enhancement of a bispecific diabody by format conversion to tandem single-chain variable fragment (taFv): the case of the hEx3 diabody

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.

A bispecific antibody effectively inhibits tumor growth and metastasis by simultaneous blocking vascular endothelial growth factor A and osteopontin

Both vascular endothelial growth factor A (VEGF) and osteopontin (OPN) can directly induce tumor angiogenesis, which is essential for the growth and metastasis of solid tumors. Here we engineered a bispecific antibody (VEGF/OPN-BsAb) using the anti-VEGF-A antibody bevacizumab and the anti-OPN antibody hu1A12. Compared with hu1A12 alone and bevacizumab alone, VEGF/OPN-BsAb was significantly more effective in inhibiting tumor angiogenesis in a highly metastatic human hepatocellular carcinoma nude mouse model. Further study demonstrated that VEGF/OPN-BsAb could effectively suppress primary tumor growth and metastasis to lungs, suggesting that it might be a promising therapeutic agent for treatment of metastatic cancer.

Multiple signaling pathways induced by hexavalent, monospecific, anti-CD20 and hexavalent, bispecific, anti-CD20/CD22 humanized antibodies correlate with enhanced toxicity to B-cell lymphomas and leukemias

We have generated hexavalent antibodies (HexAbs) comprising 6 Fabs tethered to one Fc of human IgG1. Three such constructs, 20-20, a monospecific HexAb comprising 6 Fabs of veltuzumab (humanized anti-CD20 immunoglobulin G1κ [IgG1κ]), 20-22, a bispecific HexAb comprising veltuzumab and 4 Fabs of epratuzumab (humanized anti-CD22 IgG1κ), and 22-20, a bispecific HexAb comprising epratuzumab and 4 Fabs of veltuzumab, were previously shown to inhibit pro-liferation of several lymphoma cell lines at nanomolar concentrations in the absence of a crosslinking antibody. We now report an in-depth analysis of the apoptotic and survival signals induced by the 3 HexAbs in Burkitt lymphomas and provide in vitro cytotoxicity data for additional lymphoma cell lines and also chronic lymphocytic leukemia patient specimens. Among the key findings are the significant increase in the levels of phosphorylated p38 and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) by all 3 HexAbs and the notable differences in the signaling events triggered by the HexAbs from those incurred by crosslinking veltuzumab or rituximab with a secondary antibody. Thus, the greatly enhanced direct toxicity of these HexAbs correlates with their ability to alter the basal expression of various intracellular proteins involved in regulating cell growth, survival, and apoptosis, with the net outcome leading to cell death.

Engineered proteins pull double duty

Myriad bi-specific proteins have been developed that recognize two different clinical targets, with the goal of achieving enhanced therapeutic effects as compared with proteins that interact with only one target. These engineered proteins are starting to enter clinical testing for a variety of biomedical applications, particularly cancer treatment.

Development of a two-part strategy to identify a therapeutic human bispecific antibody that inhibits IgE receptor signaling

The development of bispecific antibodies as therapeutic agents for human diseases has great clinical potential, but broad application has been hindered by the difficulty of identifying bispecific antibody formats that exhibit favorable pharmacokinetic properties and ease of large-scale manufacturing. Previously, the development of an antibody technology utilizing heavy chain knobs-into-holes mutations and a single common light chain enabled the small-scale generation of human full-length bispecific antibodies. Here we have extended the technology by developing a two-part bispecific antibody discovery strategy that facilitates proof-of-concept studies and clinical candidate antibody generation. Our scheme consists of the efficient small-scale generation of bispecific antibodies lacking a common light chain and the hinge disulfides for proof-of-concept studies coupled with the identification of a common light chain bispecific antibody for large-scale production with high purity and yield. We have applied this technology to generate a bispecific antibody suitable for development as a human therapeutic. This antibody directly inhibits the activation of the high affinity IgE receptor FcϵRI on mast cells and basophils by cross-linking FcϵRI with the inhibitory receptor FcγRIIb, an approach that has strong therapeutic potential for asthma and other allergic diseases. Our approach for producing human bispecific full-length antibodies enables the clinical application of bispecific antibodies to a validated therapeutic pathway in asthma.

Highly enhanced cytotoxicity of a dimeric bispecific diabody, the hEx3 tetrabody

We previously reported the utility for cancer immunotherapy of a humanized bispecific diabody (hEx3) that targets epidermal growth factor receptor and CD3. Here, we used dynamic and static light scattering measurements to show that the multimer fraction observed in hEx3 in solution is a monodisperse tetramer. The multimerization into tetramers increased the inhibition of cancer cell growth by the hEx3 diabody. Furthermore, 1:2 stoichiometric binding for both antigens was observed in a thermodynamic analysis, indicating that the tetramer has bivalent binding activity for each target, and the structure may be in a circular configuration, as is the case for the single-chain Fv tetrabody. In addition to enhanced cytotoxicity, the functional affinity and stability of the hEx3 tetrabody were superior to those of the hEx3 diabody. The increase in molecular weight is also expected to improve the pharmacokinetics of the bispecific diabody, making the hEx3 tetrabody attractive as a therapeutic antibody fragment for cancer immunotherapy.

Use of uteroglobin for the engineering of polyvalent, polyspecific fusion proteins

We report a novel strategy to engineer and express stable and soluble human recombinant polyvalent/polyspecific fusion proteins. The procedure is based on the use of a central skeleton of uteroglobin, a small and very soluble covalently linked homodimeric protein that is very resistant to proteolytic enzymes and to pH variations. Using a human recombinant antibody (scFv) specific for the angiogenesis marker domain B of fibronectin, interleukin 2, and an scFv able to neutralize tumor necrosis factor-alpha, we expressed various biologically active uteroglobin fusion proteins. The results demonstrate the possibility to generate monospecific divalent and tetravalent antibodies, immunocytokines, and dual specificity tetravalent antibodies. Furthermore, compared with similar fusion proteins in which uteroglobin was not used, the use of uteroglobin improved properties of solubility and stability. Indeed, in the reported cases it was possible to vacuum dry and reconstitute the proteins without any aggregation or loss in protein and biological activity.

Hexavalent bispecific antibodies represent a new class of anticancer therapeutics: 1. Properties of anti-CD20/CD22 antibodies in lymphoma

The dock and lock (DNL) method is a new technology for generating multivalent antibodies. Here, we report in vitro and in vivo characterizations of 20-22 and 22-20, a pair of humanized hexavalent anti-CD20/22 bispecific antibodies (bsAbs) derived from veltuzumab (v-mab) and epratuzumab (e-mab). The 22-20 was made by site-specific conjugation of e-mab to 4 Fabs of v-mab; 20-22 is of the opposite configuration, composing v-mab and 4 Fabs of e-mab. Each bsAb translocates both CD22 and CD20 into lipid rafts, induces apoptosis and growth inhibition without second-antibody crosslinking, and is significantly more potent in killing lymphoma cells in vitro than their parental antibodies. Although both bsAbs triggered antibody-dependent cellular toxicity, neither displayed complement-dependent cytotoxicity. Intriguingly, 22-20 and 20-22 killed human lymphoma cells in preference to normal B cells ex vivo, whereas the parental v-mab depleted malignant and normal B cells equally. In vivo studies in Daudi tumors revealed 20-22, despite having a shorter serum half-life, had antitumor efficacy comparable with equimolar v-mab; 22-20 was less potent than 20-22 but more effective than e-mab and control bsAbs. These results indicate multiple advantages of hexavalent anti-CD20/22 bsAbs over the individual parental antibodies and suggest that these may represent a new class of cancer therapeutics.

Humanization of the bispecific epidermal growth factor receptor x CD3 diabody and its efficacy as a potential clinical reagent

PURPOSE

Bispecific antibodies (BsAb) have been exploited as both cancer immunodiagnostics and cancer therapeutics and show promise in clinical trials of cancer imaging and therapy. For development of BsAbs as clinical reagents, we have focused on construction of small recombinant BsAbs, called bispecific diabodies. Here, we constructed and characterized a humanized bispecific diabody.

EXPERIMENTAL DESIGN

We have reported significant antitumor activity of an anti-epidermal growth factor receptor (EGFR) x anti-CD3 bispecific diabody (Ex3) in in vitro cytotoxicity assays and in vivo. We humanized the Ex3 diabody (hEx3) by grafting the complementarity-determining region and compared its biological properties with those of Ex3. We also tested its physiologic stability and ability to alter survival in xenografted mice.

RESULTS

The final yield of hEx3 was 10 times that of Ex3, and refolded hEx3 and Ex3 showed identical binding profiles in EGFR-positive cell lines and EGFR-transfected Chinese hamster ovary cells. hEx3 showed dose-dependent cytotoxicity to EGFR-positive cell lines, which could be specifically inhibited by parental monoclonal antibody IgGs against EGFR or CD3 antigens. The heterodimeric structure was retained in PBS for 6 months, and growth inhibition was maintained after incubation under physiologic conditions. Coadministration of hEx3 with T-LAK cells and interleukin-2 prolonged the survival of nude mice with human colon carcinoma.

CONCLUSIONS

The humanized diabody hEx3 is an attractive molecule for cancer therapy and may provide important insights into the development of EGFR-based cancer-targeting reagents.

Simultaneous targeting of multiple disease mediators by a dual-variable-domain immunoglobulin

For complex diseases in which multiple mediators contribute to overall disease pathogenesis by distinct or redundant mechanisms, simultaneous blockade of multiple targets may yield better therapeutic efficacy than inhibition of a single target. However, developing two separate monoclonal antibodies for clinical use as combination therapy is impractical, owing to regulatory hurdles and cost. Multi-specific, antibody-based molecules have been investigated; however, their therapeutic use has been hampered by poor pharmacokinetics, stability and manufacturing feasibility. Here, we describe a generally applicable model of a dual-specific, tetravalent immunoglobulin G (IgG)-like molecule--termed dual-variable-domain immunoglobulin (DVD-Ig)--that can be engineered from any two monoclonal antibodies while preserving activities of the parental antibodies. This molecule can be efficiently produced from mammalian cells and exhibits good physicochemical and pharmacokinetic properties. Preclinical studies of a DVD-Ig protein in an animal disease model demonstrate its potential for therapeutic application in human diseases.

Construction of miniantibodies for the in vivo study of human autoimmune diseases in animal models

Background

Phage display antibody libraries have been made from the lymphocytes of patients suffering from autoimmune diseases in which the antibodies are known to play a role in the pathogenesis or are important for the diagnosis of the disease. In the case of Celiac Disease, the immune response is directed against the autoantigen tissue transglutaminase. However, despite numerous studies, the role of these antibodies in the pathogenesis of this disease has not been elucidated.

Results

We were able to engineer specific anti-transglutaminase antibody fragments in the form called "miniantibody". These are produced by genetic fusion of anti-tTG scFv to Human, Mouse or Rat Fc domains, making them suitable for in vivo expression. The results obtained here indicate that the miniantibody molecule is efficiently secreted, and that the reactivity to the antigen is retained even after fusion to heterologous Fc domains. Further analysis demonstrate that the molecule is secreted as homodimeric, mimicking original antibody structure. Finally, the in vivo expression in mice leads to detectable serum levels with no apparent gross immune response by the host.

Conclusion

In this work we demonstrated the usefulness of a method for the in vivo expression of miniantibodies specific to transglutaminase, corresponding to the autoimmune specificity of Celiac Disease. This can be proposed as a general method to study the pathogenic role of autoimmune antibodies in autoimmune diseases.

Self-assembled "dock and lock" system for linking payloads to targeting proteins

Random conjugation of therapeutic or diagnostic payloads to targeting proteins generates functionally heterogeneous products. Conjugation of payloads to an adapter that binds to a peptide tag engineered into a targeting protein provides an alternative strategy. To progress into clinical development, an adapter/docking tag system should include humanized components and be stable in circulation. We describe here an adapter/docking tag system based on mutated fragments of human RNase I that spontaneously bind to each other and form a conjugate with a disulfide bond between complimentary cysteine residues. This self-assembled "dock and lock" system utilizes the previously described fusion C-tag, a 1-15 aa fragment of human RNase I with the R4C amino acid substitution, and a newly engineered adapter protein (Ad-C), a 21-127-aa fragment of human RNase I with the V118C substitution. Two vastly different C-tagged recombinant proteins, human vascular endothelial growth factor (VEGF) and a 254-aa long N-terminal fragment of anthrax lethal factor (LFn), retain functional activities after spontaneous conjugation of Ad-C to N-terminal or C-terminal C-tag, respectively. Ad-C modified with pegylated phospolipid and inserted into the lipid membrane of drug-loaded liposomes (Doxil) retained the ability to conjugate C-tagged proteins, yielding targeted liposomes decorated with functionally active proteins. To further optimize the system, we engineered an adapter with an additional cysteine residue at position 88 for site-specific modification, conjugated it to C-tagged VEGF, and labeled with a near-infrared fluorescent dye Cy5.5, yielding a unique functionally active probe for in vivo molecular imaging. We expect that this self-assembled "dock and lock" system will provide new opportunities for using functionally active proteins for biomedical purposes.

Recombinant antibodies: from the laboratory to the clinic

The development of recombinant antibodies has facilitated the exploitation of the Ab-Ag interaction specificity for targeted therapies. A fully human antibody, with custom integrated designs, can be obtained in one-third the time, compared to development of antibodies by hybridoma technology. Recombinant antibodies can be tailored for specific applications, "armed" with cytotoxic agents in a controllable fashion, and used for extracellular and intracellular targeting. Multitargeted and combination therapies are rapidly evolving for the treatment of cancer. Antibody therapeutics, costly to develop and produce, have proven beneficial in the clinic.

Ligand-Targeted Delivery of Therapeutic siRNA

RNA interference (RNAi) is a post-transcriptional gene-silencing phenomenon that is triggered by double-stranded RNA (dsRNA). Since many diseases are associated with the inappropriate production of specific proteins, attempts are being made to exploit RNAi in a clinical settings. However, before RNAi can be exploited as therapeutically, several obstacles must be overcome. For example, small interfering RNA (siRNA) is unstable in the blood stream so any effects of injected siRNA are only transient. Accordingly, methods must be developed to prolong its activity. Furthermore, the efficient and safe delivery of siRNA into target tissues and cells is critical for successful therapy. Any useful delivery method should be designed to target siRNA to specific cells and to promote gene-silencing activity once the siRNA is inside the cells. Recent chemical modifications of siRNA have overcome problems associated with the instability of siRNA, and various ligands, including glycosylated molecules, peptides, proteins, antibodies and engineered antibody fragments, appear to be very useful or have considerable potential for the targeted delivery of siRNA. The use of such ligands improves the efficiency, specificity and, as a consequence, the safety of the corresponding delivery systems.

Antibodies for targeted cancer therapy -- technical aspects and clinical perspectives

The efficacy of traditional anti-cancer agents comes with the price of toxicity to normal cells, which limits the success of therapy. In the past 2 decades, greater understanding of the molecular differences between malignant and normal cells has led to the development of therapies that more specifically target human tumors. These include new anti-cancer agents directed against intracellular targets associated with malignant alterations, such as increased proliferation, impaired apoptosis or angiogenesis. In addition, antibodies have been developed that are directed towards tumor-associated antigens and provide tailor-made effector functions by inhibiting cell growth, inducing apoptosis or constituting cytotoxic drug delivery systems. Since the targeted approach of anti-cancer therapies increases the exposure of malignant cells and at the same time reduces the exposure of normal tissues, it offers the promise of enhanced efficacy and lower side effects. Antibodies, immunoconjugates and liposomal drug delivery systems derived thereof are now mainstream cancer therapeutics, and by the end of 2003 17 marketed antibody-based products generated several billion in combined annual sales. This study highlights the most recent breakthroughs in antibody technology and summarizes major achievements in antibody-based cancer therapy in oncology trials.

Antiangiogenic peptides and proteins: from experimental tools to clinical drugs

The formation of a 'tumor-associated vasculature', a process referred to as tumor angiogenesis, is a stromal reaction essential for tumor progression. Inhibition of tumor angiogenesis suppresses tumor growth in many experimental models, thereby indicating that tumor-associated vasculature may be a relevant target to inhibit tumor progression. Among the antiangiogenic molecules reported to date many are peptides and proteins. They include cytokines, chemokines, antibodies to vascular growth factors and growth factor receptors, soluble receptors, fragments derived from extracellular matrix proteins and small synthetic peptides. The polypeptide tumor necrosis factor (TNF, Beromun) was the first drug registered for the regional treatment of human cancer, whose mechanisms of action involved selective disruption of the tumor vasculature. More recently, bevacizumab (Avastin), an antibody against vascular endothelial growth factor (VEGF)-A, was approved as the first systemic antiangiogenic drug that had a significant impact on the survival of patients with advanced colorectal cancer, in combination with chemotherapy. Several additional peptides and antibodies with antiangiogenic activity are currently tested in clinical trials for their therapeutic efficacy. Thus, peptides, polypeptides and antibodies are emerging as leading molecules among the plethora of compounds with antiangiogenic activity. In this article, we will review some of these molecules and discuss their mechanism of action and their potential therapeutic use as anticancer agents in humans.

Eradication of tumors from a human colon cancer cell line and from ovarian cancer metastases in immunodeficient mice by a single-chain Ep-CAM-/CD3-bispecific antibody construct

Bispecific T-cell engager (BiTE) are a class of bispecific single-chain antibodies that can very effectively redirect cytotoxic T cells for killing of tumor target cells. Here, we have assessed the in vivo efficacy of one representative, called bscEp-CAMxCD3, with specificity for tumors overexpressing epithelial cell adhesion molecule (Ep-CAM) in human xenograft models. Cells of the human colon carcinoma line SW480 were mixed at a 1:1 ratio with unstimulated human peripheral mononuclear cells, s.c. injected in nonobese diabetes/severe combined immunodeficiency (NOD/SCID) mice, and animals were treated with bscEp-CAMxCD3. Five daily i.v. injections of as little as 100 ng per mouse of bscEp-CAMxCD3 completely prevented tumor outgrowth when treatment was started at the day of tumor cell inoculation. BscEp-CAMxCD3 was also efficacious when administered up to 8 days after xenograft injection. Established tumors could be eradicated in all animals by five 10 microg doses given between days 8 and 12 after tumor cell inoculation. To test the efficacy of bscEp-CAMxCD3 in a more physiologic model, pieces of primary metastatic tumor tissue from ovarian cancer patients were implanted in NOD/SCID mice. Partial tumor engraftment and growth was observed with four of six patient samples. Treatment of established tumors with daily 5 microg doses led to a significant reduction and, in some cases, eradication of human tumor tissue. These effects obviously relied on the tumor-resident T cells reactivated by bscEp-CAMxCD3. Our data show that the class of single-chain bispecific antibodies has very high antitumor efficacy in vivo and can use previously unstimulated T cells at low effector-to-target ratios.

Recombinant bispecific antibodies for cancer therapy

Bispecific antibodies can serve as mediators to retarget effector mechanisms to disease-associated sites. Studies over the past two decades have revealed the potentials but also the limitations of conventional bispecific antibodies. The development of recombinant antibody formats has opened up the possibility of generating bispecific molecules with improved properties. This review summarizes recent developments in the field of recombinant bispecific antibodies and discusses further requirements for clinical development.

Bispecific single-chain diabody-mediated killing of endoglin-positive endothelial cells by cytotoxic T lymphocytes

We present a novel vascular tumor therapy approach based on lysing endothelial cells by cytotoxic T lymphocytes (CTLs). Retargeting of CTLs is achieved by a recombinant bispecific antibody molecule (bispecific single-chain diabody) directed against human endoglin (CD105, EDG) and the T-cell coreceptor CD3 (scDb EDGCD3). Bacterially expressed scDb EDGCD3 was able to bind to endoglin-expressing endothelial cells as well as CD3-expressing T lymphocytes. The single-chain diabody mediated killing of endothelial cells (HUVEC, HMEC) by activated cytotoxic T lymphocytes at picomolar concentrations, and cells not expressing endoglin were not affected. Because endoglin is up-regulated in the vasculature of many solid tumors, this antibody molecule should be capable of lysing tumor endothelial cells and thus destroying the vascular bed of the tumor.

Integrating molecular detection and response to create self-signalling antibodies

Monoclonal antibodies are reproducible, specific, and cost-effective molecular probes; use outside the laboratory is, however, restricted by technical limitations. Addressing these constraints, the first self-signalling antibodies are now described, where specific antigen binding causes release of bound reporter from bispecific antibodies (BsAb) to generate a detectable signal. The report examines the concept that two different antibody binding sites in close proximity can promote interaction between molecules recognised by these sites, generating a signal by molecular crowding. Signal strength is found to increase with increasing homogeneity for a BsAb reactive with multimeric surfactant antigen; signal response is linear for a BsAb reactive with univalent small analyte deoxypyridinoline. Self-signalling is consistent with intramolecular steric hindrance. This is the first report detailing integration of two different functions, molecular detection and signal response, into BsAbs and with detection of large and small analytes, has generic application to antibody-based systems.