Validation of glypican-3-specific scFv isolated from paired display/secretory yeast display library

Preparation and Characterization of Anti-GPC3 Nanobody Against Hepatocellular Carcinoma

Background

Glypican-3 (GPC3) is a newly identified target molecule for the early diagnosis of hepatocellular carcinoma (HCC), while targeted inhibition of GPC3 signaling may help to control the proliferation and metastasis of HCC cells. The purpose of this study was to prepare the anti-GPC3 nanobody and to investigate the affinity of the anti-GPC3 nanobodies in vitro and the anticancer effects on hepatocellular carcinoma in vivo.

Methods

To screen for unknown anti-GPC3 antibodies, we constructed an antibody phage display library. After three rounds of panning, positive phage clones were identified by enzyme-linked immunosorbent assay (ELISA). Further, the nanobody fusion protein was expressed in E. coli BL21 cells and purified by affinity chromatography. Competitive ELISA and flow cytometry were conducted to confirm the affinity of the anti-GPC3 nanobodies in vitro. The antitumor effects of VHH_GPC3 were assessed in vivo.

Results

The results showed that the nanobody VHH_GPC3 had specific high-affinity binding to His-GPC3 antigen. Moreover, VHH_GPC3 exhibited specific binding to commercial human GPC3 and recognized the surface GPC3 protein of the hepatoma cell line HepG2. Importantly, in vivo study showed that GPC3 nanobody suppresses the growth of HepG2 and improves the survival rate of tumor mice.

Discussion

In summary, our new anti-GPC3 nanobody suggests a strong application potential for targeted therapy of liver cancer.

The Dual Role of the Liver in Nanomedicine as an Actor in the Elimination of Nanostructures or a Therapeutic Target

The development of nanostructures for therapeutic purpose is rapidly growing, following the results obtained in vivo in animal models and in the clinical trials. Unfortunately, the potential therapeutic efficacy is not completely exploited, yet. This is mainly due to the fast clearance of the nanostructures in the body. Nanoparticles and the liver have a unique interaction because the liver represents one of the major barriers for drug delivery. This interaction becomes even more relevant and complex when the drug delivery strategies employing nanostructures are proposed for the therapy of liver diseases, such as hepatocellular carcinoma (HCC). In this case, the selective delivery of therapeutic nanoparticles to the tumor microenvironment collides with the tendency of nanostructures to be quickly eliminated by the organ. The design of a new therapeutic approach based on nanoparticles to treat HCC has to particularly take into consideration passive and active mechanisms to avoid or delay liver elimination and to specifically address cancer cells or the cancer microenvironment. This review will analyze the different aspects concerning the dual role of the liver, both as an organ carrying out a clearance activity for the nanostructures and as target for therapeutic strategies for HCC treatment.

Generation of a Fully Human scFv that binds Tumor-Specific Glycoforms

Tumor-specific glycosylation changes are an attractive target for the development of diagnostic and therapeutic applications. Periostin is a glycoprotein with high expression in many tumors of epithelial origin including ovarian cancer. Strategies to target the peptide portion of periostin as a diagnostic or therapeutic biomarker for cancer are limited due to increased expression of periostin in non-cancerous inflammatory conditions. Here, we have screened for antibody fragments that recognize the tumor-specific glycosylation present on glycoforms of periostin containing bisecting N-glycans in ovarian cancer using a yeast-display library of antibody fragments, while subtracting those that bind to the periostin protein with glycoforms found in non-malignant cell types. We generated a biotinylated form of a fully human scFv antibody (scFvC9) that targets the bisecting N-glycans expressed by cancer cells. Validation studies in vitro and in vivo using scFvC9 indicate this antibody can be useful for the development of diagnostic, imaging, and therapeutic applications for cancers that express the antigen.

Efficient construct of a large and functional scFv yeast display library derived from the ascites B cells of ovarian cancer patients by three-fragment transformation-associated recombination

Over the past decade, yeast display technology has emerged as a powerful tool for the isolation of high-affinity immunoglobulin fragments with potential utility as clinical diagnostic and therapeutic reagents. Despite significant refinement of the various methodologies underpinning library construction and selections, certain aspects remain challenging and process limiting. We have sought to significantly improve the robustness of the single-chain Fv (scFv) library construction step by overcoming the technical inefficiencies frequently encountered during the PCR-mediated assembly of scFvs from the discrete heavy and light V-domain repertoires. Using a novel primer set designed to provide maximum amplification coverage of the known germ-line V-domain repertoire, we have exploited the potential of the in vivo homologous gap-repair apparatus of Saccharomyces cerevisiae to assemble intact scFvs directly from co-transformed PBMC-derived VH, VL, and linearized vector component fragments. We have successfully applied this three-fragment assembly strategy to construct a large (>10(9)) scFv yeast display library from the ascites immune repertoire of ovarian cancer patients and validated the approach by applying FACS-based sorting to readily isolate scFvs that recognize various tumor marker antigens (TMAs). It is expected that this simplified construction method may find general utility, both for de novo scFv library construction and for subsequent combinatorial affinity maturation manipulations that require more than two fragments.

Generation of recombinant antibodies to rat GABAA receptor subunits by affinity selection on synthetic peptides

The abundance and physiological importance of GABAA receptors in the central nervous system make this neurotransmitter receptor an attractive target for localizing diagnostic and therapeutic biomolecules. GABAA receptors are expressed within the retina and mediate synaptic signaling at multiple stages of the visual process. To generate monoclonal affinity reagents that can specifically recognize GABAA receptor subunits, we screened two bacteriophage M13 libraries, which displayed human scFvs, by affinity selection with synthetic peptides predicted to correspond to extracellular regions of the rat α1 and β2 GABAA subunits. We isolated three anti-β2 and one anti-α1 subunit specific scFvs. Fluorescence polarization measurements revealed all four scFvs to have low micromolar affinities with their cognate peptide targets. The scFvs were capable of detecting fully folded GABAA receptors heterologously expressed by Xenopus laevis oocytes, while preserving ligand-gated channel activity. Moreover, A10, the anti-α1 subunit-specific scFv, was capable of detecting native GABAA receptors in the mouse retina, as observed by immunofluorescence staining. In order to improve their apparent affinity via avidity, we dimerized the A10 scFv by fusing it to the Fc portion of the IgG. The resulting scFv-Fc construct had a Kd of ∼26 nM, which corresponds to an approximately 135-fold improvement in binding, and a lower detection limit in dot blots, compared to the monomeric scFv. These results strongly support the use of peptides as targets for generating affinity reagents to membrane proteins and encourage investigation of molecular conjugates that use scFvs as anchoring components to localize reagents of interest at GABAA receptors of retina and other neural tissues, for studies of receptor activation and subunit structure.