Generation and characterization of a diabody targeting the αvβ6 integrin

Zirconium 89 and Copper 64 for ImmunoPET: From Antibody Bioconjugation and Radiolabeling to Molecular Imaging

Immunotherapy has transformed cancer treatment. Nevertheless, given the heterogeneity of clinical efficacy, the multiplicity of treatment options available and the possibility of serious adverse effects, selecting the most effective treatment has become the greatest challenge. Molecular imaging offers an attractive way for this purpose. ImmunoPET provides specific imaging with positron emission tomography (PET) using monoclonal antibodies (mAb) or its fragments as vector. By combining the high targeting specificity of mAb and the sensitivity of PET technique, immunoPET could noninvasively and dynamically reveal tumor antigens expression and provide theranostic tools of several types of malignancies. Because of their slow kinetics, mAbs require radioelements defined by a consistent half-life. Zirconium 89 (89Zr) and Copper 64 (64Cu) are radiometals with half-lives suitable for mAb labeling. Radiolabeling with a radiometal requires the prior use of a bifunctional chelate agent (BFCA) to functionalize mAb for radiometal chelation, in a second step. There are a number of BFCA available and much research is focused on antibody functionalization techniques or on developing the optimum chelating agent depending the selected radiometal. In this manuscript, we present a critical account of radiochemical techniques with radionuclides 89Zr and 64Cu and their applications in preclinical and clinical immuno-PET imaging.

Metal-Chelating Peptides Separation Using Immobilized Metal Ion Affinity Chromatography: Experimental Methodology and Simulation

Metal-Chelating Peptides (MCPs), obtained from protein hydrolysates, present various applications in the field of nutrition, pharmacy, cosmetic etc. The separation of MCPs from hydrolysates mixture is challenging, yet, techniques based on peptide-metal ion interactions such as Immobilized Metal Ion Affinity Chromatography (IMAC) seem to be efficient. However, separation processes are time consuming and expensive, therefore separation prediction using chromatography modelling and simulation should be necessary. Meanwhile, the obtention of sorption isotherm for chromatography modelling is a crucial step. Thus, Surface Plasmon Resonance (SPR), a biosensor method efficient to screen MCPs in hydrolysates and with similarities to IMAC might be a good option to acquire sorption isotherm. This review highlights IMAC experimental methodology to separate MCPs and how, IMAC chromatography can be modelled using transport dispersive model and input data obtained from SPR for peptides separation simulation.

Inhibitory effect of phenolic extract from squirting cucumber (Ecballium elaterium (L.) A. Rich) seed oil on integrin-mediated cell adhesion, migration and angiogenesis

Integrin targeted therapies by natural bioactive compounds have attracted attention in the field of oncology and cancer treatment. This study evaluates the potential of phenolic extract from the medicinal herb Ecballium elaterium L. seed oil (PEO) to inhibit the adhesion and migration of the highly invasive human fibrosarcoma cell line HT1080. At safe concentrations (up to 40 μg mL-1), results show that PEO dose-dependently inhibits adhesion and migration of HT1080 to fibronectin (IC50 = 18 μg mL-1) and fibrinogen (IC50 = 12.86 μg mL-1). These observations were associated with the reduction of cell motility and migration velocity as revealed in the Boyden chamber and random motility using two-dimensional assays, respectively. Additional experiments using integrin blocking antibodies showed that PEO at the highest safe concentration (40 μg mL-1) competitively inhibited the attachment of HT1080 cell to anti-αvβ3 (>98%), anti-α5β1 (>86%), and to a lesser extent anti-α2 (>50%) immobilized antibodies, suggesting that αvβ3 and α5β1 integrins were selectively targeted by PEO. Moreover, PEO specifically targeted these integrins in human microvascular endothelial cells (HMEC-1) and dose-dependently blocked the in vitro tubulogenesis. In the CAM model, PEO inhibited the VEGF-induced neoangiogenesis confirming its anti-angiogenic effect. Collectively, these results indicate that PEO holds promise for the development of natural integrin-targeted therapies against fibrosarcoma.

Integrin Alpha v Beta 6 (αvβ6) and Its Implications in Cancer Treatment

Integrins are necessary for cell adhesion, migration, and positioning. Essential for inducing signalling events for cell survival, proliferation, and differentiation, they also trigger a variety of signal transduction pathways involved in mediating invasion, metastasis, and squamous-cell carcinoma. Several recent studies have demonstrated that the up- and down-regulation of the expression of αv and other integrins can be a potent marker of malignant diseases and patient prognosis. This review focuses on an arginine-glycine-aspartic acid (RGD)-dependent integrin αVβ6, its biology, and its role in healthy humans. We examine the implications of αVβ6 in cancer progression and the promotion of epithelial-mesenchymal transition (EMT) by contributing to the activation of transforming growth factor beta TGF-β. Although αvβ6 is crucial for proper function in healthy people, it has also been validated as a target for cancer treatment. This review briefly considers aspects of targeting αVβ6 in the clinic via different therapeutic modalities.

Site-specific chelator-antibody conjugation for PET and SPECT imaging with radiometals

Antibodies and their derivatives radiolabelled with positron- and gamma-emitting radiometals enable sensitive and quantitative molecular Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) imaging of antibody distribution in vivo. Chelators that are covalently attached to antibodies allow radiolabelling with metallic PET and SPECT radioisotopes. Conventional strategies for chelator-protein conjugation generate heterogeneous mixtures of bioconjugates that can exhibit reduced affinity for their receptor targets, and undesirable biodistribution and pharmacokinetics. Recent advances in bioconjugation technology enable site-specific modification to generate well-defined constructs with superior properties. Herein we survey existing site-specific chelator-protein conjugation methods. These include chelator attachment to cysteines/disulfide bonds or the glycan region of the antibody, enzyme-mediated chelator conjugation, and incorporation of sequences of amino acids that chelate the radiometal. Such technology will allow better use of PET and SPECT imaging in the development of antibody-based therapies.

Site-Specifically Labeled Immunoconjugates for Molecular Imaging--Part 2: Peptide Tags and Unnatural Amino Acids

Molecular imaging using radioisotope- or fluorophore-labeled antibodies is increasingly becoming a critical component of modern precision medicine. Yet despite this promise, the vast majority of these immunoconjugates are synthesized via the random coupling of amine-reactive bifunctional probes to lysines within the antibody, a process that can result in heterogeneous and poorly defined constructs with suboptimal pharmacological properties. In an effort to circumvent these issues, the last 5 years have played witness to a great deal of research focused on the creation of effective strategies for the site-specific attachment of payloads to antibodies. These chemoselective modification methods yield immunoconjugates that are more homogenous and better defined than constructs created using traditional synthetic approaches. Moreover, site-specifically labeled immunoconjugates have also been shown to exhibit superior in vivo behavior compared to their randomly modified cousins. The over-arching goal of this two-part review is to provide a broad yet detailed account of the various site-specific bioconjugation approaches that have been used to create immunoconjugates for positron emission tomography (PET), single photon emission computed tomography (SPECT), and fluorescence imaging. In Part 1, we covered site-specific bioconjugation techniques based on the modification of cysteine residues and the chemoenzymatic manipulation of glycans. In Part 2, we will detail two families of bioconjugation approaches that leverage biochemical tools to achieve site-specificity. First, we will discuss modification methods that employ peptide tags either as sites for enzyme-catalyzed ligations or as radiometal coordination architectures. And second, we will examine bioconjugation strategies predicated on the incorporation of unnatural or non-canonical amino acids into antibodies via genetic engineering. Finally, we will compare the advantages and disadvantages of the modification strategies covered in both parts of the review and offer a brief discussion of the overall direction of the field.

Construction of a disulfide-stabilized diabody against fibroblast growth factor-2 and the inhibition activity in targeting breast cancer

Fibroblast growth factor‐2 (FGF‐2) is one of the most important angiogenic factors to promote tumor growth, progression and metastasis. Neutralizing antibodies against FGF‐2 may suppress the growth of tumor cells by blocking the FGF‐2 signaling pathway. In this study, a disulfide‐stabilized diabody (ds‐Diabody) that specifically targets FGF‐2 was designed. Compared to its parent antibody, the introduction of disulphide bonds in the diabody could significantly increase the stability of ds‐Diabody and maintain its antigen binding activity. The ds‐Diabody against FGF‐2 could effectively inhibit the tube formation and migration of vascular endothelial cells and block the proliferation and invasion of human breast cancer cells. In the mouse model of breast cancer xenograft tumors, the ds‐Diabody against FGF‐2 could significantly inhibit the growth of tumor cells. Moreover, the densities of microvessels stained with CD31 and lymphatic vessels stained with LYVE1 in tumors showed a significant decrease following treatment with the ds‐Diabody against FGF‐2. Our data indicated that the ds‐Diabody against FGF‐2 could inhibit tumor angiogenesis, lymphangiogenesis and tumor growth.

Novel highly specific anti-periostin antibodies uncover the functional importance of the fascilin 1-1 domain and highlight preferential expression of periostin in aggressive breast cancer

Periostin (POSTN), a secreted homodimeric protein that binds integrins αvβ3, αvβ5, and α6β4, was originally found to be expressed in fetal tissues and in the adult upon injury particularly bone fractures due to its role in remodelling and repair. Recently it was found to be over-expressed in human breast cancer and a variety of other tumour types including head and neck squamous cell carcinoma, where its overexpression correlates with increased tumour invasion. Progress in studying its functional role in tumour pathogenesis has been hampered by the paucity of antibodies for its specific and sensitive detection. It has proven very difficult to obtain monoclonal antibodies (mAbs) against this highly conserved protein but we report here that combining infection of mice with lactate dehydrogenase elevating virus (LDV), a B cell activating arterivirus, with conjugation of human POSTN to ovalbumin as an immunogenic carrier, enabled us to develop six mAbs recognizing both human and mouse POSTN and inhibiting its binding to αvβ3 integrin. Two of the mAbs, MPB4B1 and MPC5B4, were tested and found to inhibit POSTN-induced migration of human endothelial colony forming cells. All six mAbs recognized amino acids 136-51 (APSNEAWDNLDSDIRR) within the POSTN fascilin (FAS) 1-1 domain revealing the functional importance of this motif; this was further highlighted by the ability of aa 136-151 peptide to inhibit integrin-mediated cell migration. Immunohistochemistry using MPC5B4, indicated that breast tumour cell POSTN expression was a strong prognostic indicator, along with tumour size, lymph node, and human epidermal growth factor receptor 2 (HER2) status.

Development and characterization of an αvβ6-specific diabody and a disulfide-stabilized αvβ6-specific cys-diabody

INTRODUCTION

This work describes the development and characterization of two antibody fragments that specifically target the α(v)β(6) integrin, a non-covalent diabody and a disulfide-stabilized cys-diabody. The diabodies were analyzed for their ability to bind both immobilized and cell surface-bound α(v)β(6). Radiolabeling was done using non-site-specific and site-specific conjugation approaches with N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]-SFB) and the bifunctional chelator 1,4,7-triazacyclononane-triacetic acid maleimide (NOTA-maleimide) and copper-64 ([(64)Cu]), respectively. The affects of each radiolabeling method on RCY, RCP, and immunoreactivity were analyzed for the [(18)F]-FB-α(v)β(6) diabody, [(18)F]-FB-α(v)β(6) cys-diabody, and the [(64)Cu]-NOTA-α(v)β(6) cys-diabody.

METHODS

Diabodies were constructed from the variable domains of the humanized 6.3G9 anti-α(v)β(6) intact antibody. The anti-α(v(β(6) cys-diabody was engineered with C-terminal cysteines to enable covalent dimerization and site-specific modification. Biochemical characterization included SDS-PAGE, Western blot, and electrospray ionization to confirm MW, and flow cytometry and ELISA experiments were used to determine binding affinity and specificity to α(v)β(6). The diabodies were radiolabeled with [(18)F]-SFB and in addition, the anti-α(v)β(6) cys-diabody was also radiolabeled site-specifically using NOTA-maleimide and [(64)Cu]. Immunoreactivities were confirmed using in vitro cell binding to DX3Puroβ(6) (α(v)β(6)+) and DX3Puro (α(v)β(6)-)cell lines.

RESULTS

The diabodies were purified from cell culture supernatants with purities >98%. Subnanomolar binding affinity towards αvβ6 was confirmed by ELISA (diabody IC(50)=0.8 nM, cys-diabody IC(50)=0.6 nM) and flow cytometry revealed high specificity only to the DX3Puroβ(6) cell line for both diabodies. RCYs were 22.6%±3.6% for the [(18)F]-FB-α(v)β(6) diabody, 8.3%±1.7% for the [(18)F]-FB-α(v)β(6) cys-diabody and 43.5%±5.5% for the [(64)Cu]-NOTA-α(v)β(6) cys-diabody. In vitro cell binding assays revealed excellent specificity and retention of immunoreactivity ([(18)F]-FB-α(v)β(6) diabody=58.7%±6.7%, [(18)F]-FB-α(v)β(6) cys-diabody=80.4%±4.4%, [(64)Cu]-NOTA-α(v)β(6) cys-diabody=59.4%±0.6%) regardless of the radiolabeling method used.

CONCLUSIONS

Two novel diabodies with excellent binding affinity and specificity for the α(v)β(6) integrin in vitro were developed. Radiolabeling of the diabodies with fluorine-18 ([(18)F]) and [(64)Cu] revealed advantages and disadvantages with regards to methodologies and RCYs, however immunoreactivities were well preserved regardless of radiolabeling approach.