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

Integrin β6 mediates epithelial-mesenchymal transition in diabetic kidney disease

The progression of diabetic kidney disease (DKD) is associated with increased fibronectin (FN) levels in proximal tubular epithelial cells. Bioinformatics analysis showed that integrin β6 and cell adhesion function were significantly changed in the cortices of db/db mice. Remodelling of cell adhesion is one of the core changes during epithelial-mesenchymal transition (EMT) in DKD. Integrin is a family of transmembrane proteins that regulates cell adhesion and migration, and extracellular FN is the major ligand of integrin β6. We found that the expression of integrin β6 was elevated in the proximal tubules of db/db mice and FN-induced renal proximal tubule cells. The levels of EMT were also significantly increased in vivo and in vitro. In addition, FN treatment activated the Fak/Src pathway, increased the expression of p-YAP, and then upregulated the Notch1 pathway in diabetic proximal tubules. Knockdown of integrin β6 or Notch1 attenuated reversed the EMT aggravation induced by FN. Furthermore, urinary integrin β6 was significantly increased in DKD patients. Our findings reveal a critical role of integrin β6 in regulating EMT in proximal tubular epithelial cells and identify a novel direction for the detection and treatment of DKD.

Development of brain-penetrable antibody radioligands for in vivo PET imaging of amyloid-β and tau

Introduction

Alzheimer's disease (AD) is characterized by the misfolding and aggregation of two major proteins: amyloid-beta (Aβ) and tau. Antibody-based PET radioligands are desirable due to their high specificity and affinity; however, antibody uptake in the brain is limited by the blood-brain barrier (BBB). Previously, we demonstrated that antibody transport across the BBB can be facilitated through interaction with the transferrin receptor (TfR), and the bispecific antibody-based PET ligands were capable of detecting Aβ aggregates via ex vivo imaging. Since tau accumulation in the brain is more closely correlated with neuronal death and cognition, we report here our strategies to prepare four F-18-labeled specifically engineered bispecific antibody probes for the selective detection of tau and Aβ aggregates to evaluate their feasibility and specificity, particularly for in vivo PET imaging.

Methods

We first created and evaluated (via both in vitro and ex vivo studies) four specifically engineered bispecific antibodies, by fusion of single-chain variable fragments (scFv) of a TfR antibody with either a full-size IgG antibody of Aβ or tau or with their respective scFv. Using [18F]SFB as the prosthetic group, all four 18F-labeled bispecific antibody probes were then prepared by conjugation of antibody and [18F]SFB in acetonitrile/0.1 M borate buffer solution (final pH ~ 8.5) with an incubation of 20 min at room temperature, followed by purification on a PD MiniTrap G-25 size exclusion gravity column.

Results

Based on both in vitro and ex vivo evaluation, the bispecific antibodies displayed much higher brain concentrations than the unmodified antibody, supporting our subsequent F18-radiolabeling. [18F]SFB was produced in high yields in 60 min (decay-corrected radiochemical yield (RCY) 46.7 ± 5.4) with radiochemical purities of >95%, confirmed by analytical high performance liquid chromatography (HPLC) and radio-TLC. Conjugation of [18F]SFB and bispecific antibodies showed a 65%-83% conversion efficiency with radiochemical purities of 95%-99% by radio-TLC.

Conclusions

We successfully labeled four novel and specifically engineered bispecific antibodies with [18F]SFB under mild conditions with a high RCY and purities. This study provides strategies to create brain-penetrable F-18 radiolabeled antibody probes for the selective detection of tau and Aβ aggregates in the brain of transgenic AD mice via in vivo PET imaging.

Evaluation and selection of a lead diabody for interferon-γ PET imaging

INTRODUCTION

Interferon-γ (IFN-γ) is an appealing target to evaluate immune response in cancer immunotherapy as it is a hallmark of an active immune system. Imaging and detection via immunopositron emission tomography (immunoPET) of this soluble cytokine has been made feasible using a ⁸⁹Zr-labeled (t _1/2 ~ 3.27 d) monoclonal antibody (mAb). Because of its size, using a full-length mAb as an imaging vector is not ideal for repeat serial imaging because of its prolonged blood pool residency and tumor accumulation resulting in lengthier wait times between administration and imaging. This consequently impacts the potential to image a dynamic immune response in real time. This work compares ⁸⁹Zr-labeled diabodies (Db) designed with variable linker lengths between the V_H and V_L regions with the goal of selecting a lead Db for future studies.

METHODS AND RESULTS

Four Db fragments with various linker lengths (HL-n, n = 7-13 amino acids) were each conjugated to desferrioxamine (DFO). The number of attached chelates was analyzed via mass spectrometry with all immunoconjugates exhibiting one unit of DFO attached. Db-DFO conjugates were subsequently radiolabeled with zirconium-89. All constructs radiolabeled with high yields. Each radioimmunoconjugate was tested for reactivity to IFN-γ. All tracers except for [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-9 exhibited comparable immunoreactivities (>90 %) to the radiolabeled parent mAb (95.8 %). At 24 h post-labeling, the IRF values were retained except for the HL-13 construct. Imaging scans and tissue distribution studies acquired in mice bearing CT26 syngeneic colorectal tumors between 1 and 24 h post-tracer administration demonstrated variable clearance kinetics and tumor localization of each radiotracer. HL-7 had higher binding in non-tumor tissues compared to HL-11 and HL-13 at 3 h p.i. Competitive binding studies versus unmodified parent mAb (AN-18) demonstrated blocking of radiolabeled HL-11 and HL-13. [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-7 was inadequately blocked.

CONCLUSION

Despite nuanced differences in linker lengths, our data demonstrates that [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-11 exhibited the best radiotracer properties for the assessment of IFN-γ production in vivo. Work is currently underway to test the potential of using shorter-lived isotopes, like copper-64 (t_1/2 ~ 12.7 h) to match pharmacokinetics and half-lives.

Antibody Fragment and Affibody ImmunoPET Imaging Agents: Radiolabelling Strategies and Applications

Antibodies have long been recognised as potent vectors for carrying diagnostic medical radionuclides, contrast agents and optical probes to diseased tissue for imaging. The area of ImmunoPET combines the use of positron emission tomography (PET) imaging with antibodies to improve the diagnosis, staging and monitoring of diseases. Recent developments in antibody engineering and PET radiochemistry have led to a new wave of experimental ImmunoPET imaging agents that are based on a range of antibody fragments and affibodies. In contrast to full antibodies, engineered affibody proteins and antibody fragments such as minibodies, diabodies, single-chain variable region fragments (scFvs), and nanobodies are much smaller but retain the essential specificities and affinities of full antibodies in addition to more desirable pharmacokinetics for imaging. Herein, recent key developments in the PET radiolabelling strategies of antibody fragments and related affibody molecules are highlighted, along with the main PET imaging applications of overexpressed antigen-associated tumours and immune cells.

Identification of a Novel ITGαvβ6-Binding Peptide Using Protein Separation and Phage Display

Purpose: Targeted therapies are regarded as promising approaches to increase 5-year survival rate of head and neck squamous cell carcinoma (HNSCC) patients.Experimental design: For the selection of carcinoma-specific peptides membrane proteome of HNO97 tumor cells fractionated by the ProteomeLab PF2D system and corresponding HNO97 cells were deployed for an alternating biopanning using a sunflower trypsin inhibitor1-based phage display (SFTI8Ph) library. Stability, binding properties and affinity of novel candidates were assessed in vitro using radio-HPLC, binding experiments and surface plasmon resonance assay (SPR), respectively. Subsequently, the affinity of the peptide was verified in situ by using peptide histochemistry, in vitro using flow cytometry, and in vivo by positron emissions tomography (PET/CT).Results: We identified a novel ITGα_vβ₆ binding peptide (SFITGv6) containing the amino acid sequence FRGDLMQL. SFITGv6 provides stability over a period of 24 hours and demonstrates high affinity (K_D = 14.8 nmol/L) for ITGα_vβ₆ In HNO97 cells, a maximal uptake and internalization of up to 37.3% and 37.5%, respectively, was measured. Small-animal PET imaging and biodistribution studies of HNO97 xenografted Balb/c nu/nu mice showed tumor-specific accumulation of ⁶⁸Ga- and ¹⁷⁷Lu-labeled DOTA-SFITGv6, respectively, 30 to 60 minutes after injection. Moreover, peptide histochemistry revealed a strong and homogenous binding of biotin-labeled SFITGv6 to HNSCC tumors and breast- and lung cancer-derived brain metastases. Finally, first PET/CT scans of HNSCC and NSCLC patients displayed SFITGv6 accumulation specifically in tumors, but not in inflammatory lesions.Conclusions: Thus, SFITGv6 represents a novel powerful tracer for imaging and possibly for endoradiotherapy of ITGα_vβ₆-positive carcinoma. Clin Cancer Res; 23(15); 4170-80. ©2017 AACR.

Photoacoustic and Fluorescence Imaging of Cutaneous Squamous Cell Carcinoma in Living Subjects Using a Probe Targeting Integrin αvβ6

Cutaneous squamous cell carcinoma (cSCC) is the second most common non-melanoma skin cancer worldwide. Today, cSCC is diagnosed by visual inspection followed by invasive skin biopsy. There is a need to develop non-invasive diagnostic tools to achieve early and accurate detection. Photoacoustic imaging (PAI) possesses high ultrasonic resolution and strong optical contrast at new depths (<1-5 cm). Together with exogenous contrast agents, PAI has found promising use in various tumors in living subjects. The expression of integrin α_vβ₆ is significantly up-regulated in cSCC. We fabricated an anti-integrin α_vβ₆ antibody and labeled it with indocyanine green (ICG) to form an ICG-α_vβ₆ antibody. The results showed that the ICG-α_vβ₆ antibody probe could be used to detect cSCC with high specificity (3-fold over the control by PAI) and deep penetration (approximately 1 cm) by PAI. This suggests that the ICG-α_vβ₆ antibody is a promising probe targeting the integrin α_vβ₆ for detection of cSCC tumors by PAI and fluorescence imaging. It may find clinical application in the early diagnosis of cSCC as well as in intraoperative navigation.