Purification and characterization of a single-chain chimeric anti-p185 antibody expressed by CHO-GS system

Structural insight into a matured humanized monoclonal antibody HuA21 against HER2-overexpressing cancer cells

HER2, a member of the epidermal growth factor receptor (EGFR) family, has been associated with human breast, ovarian and gastric cancers. Anti-HER2 monoclonal antibodies (mAbs) have demonstrated clinical efficacy for HER2-overexpressing breast cancer. A chimeric antibody chA21 that specifically inhibits the growth of HER2-overexpressing cancer cells both in vitro and in vivo has previously been developed. To reduce a potential human anti-mouse immune response, the humanized antibody HuA21 was developed and was further subjected to affinity maturation by phage display on the basis of chA21. Here, the crystal structure of HuA21-scFv in complex with the extracellular domain of HER2 is reported, which demonstrates that HuA21 binds almost the same epitope as chA21 and also provides insight into how substitutions in HuA21 improve the binding affinity compared with chA21, which could facilitate structure-based optimization in the future. Furthermore, the effects of HuA21 variants with constant domains of different lengths were explored and it was noticed that the deletion of constant domain 1 could improve the inhibition efficacy in a cell-proliferation assay, possibly functioning via increased internalization, which might guide the design of other monoclonal antibodies.

Development and Characterization of a Humanized Anti-HER2 Antibody HuA21 with Potent Anti-Tumor Properties in Breast Cancer Cells

Human epidermal growth factor receptor 2 (HER2) is one of the most studied tumor-associated antigens for cancer immunotherapy. An engineered anti-HER-2 chimeric A21 antibody (chA21) is a chimeric antibody targeted to subdomain I of the HER2 extracellular domain. Here, we report the anti-tumor activity of the novel engineered monoclonal antibody humanized chA21 (HuA21) that targets HER2 on the basis of chA21, and we describe the underlying mechanisms. Our results reveal that HuA21 markedly inhibits the proliferation and migration of HER2-overexpressing breast cancer cells and causes enhanced antibody-dependent cell-mediated cytotoxicity potency against HER2-overexpressing tumor cells. In particular, HuA21, but not trastuzumab (Tra), markedly suppresses growth and enhances the internalization of the antibody in Tra-resistant BT-474 breast cancer cells. These characteristics are highly associated with the intrinsic ability of HuA21 to down-regulate HER2 activation and inhibit the extracellular signal-regulated kinase 1/2 (ERK1/2) and protein kinase B (Akt) signaling pathways. Furthermore, the combination of HuA21 with Tra synergistically enhances the anti-tumor effects in vitro and in vivo and inhibits HER2 activation and the ERK1/2 and Akt signaling pathways. Altogether, our results suggest that HuA21 may represent a unique anti-HER2 antibody with potential as a therapeutic candidate alone or in combination with other anti-HER2 reagents in cancer therapy.

Construction and evaluation of a novel humanized HER2-specific chimeric receptor

Introduction

The human epidermal growth factor receptor 2 (HER2) represents one of the most studied tumor-associated antigens (TAAs) for cancer immunotherapy. The monoclonal antibody (mAb) trastuzumab has improved the outcomes of patients with HER2+ breast cancer. However, a large number of HER2+ tumors are not responsive to, or become resistant to, trastuzumab-based therapy, and thus more effective therapies targeting HER2 are needed.

Methods

HER2-specific T cells were generated by the transfer of genes that encode chimeric antigen receptor (CAR). Using a multistep overlap extension PCR method, we constructed a novel, humanized HER2 CAR-containing, chA21 single-chain variable fragment (scFv) region of antigen-specific mAb and T-cell intracellular signaling chains made up of CD28 and CD3ζ. An interferon γ and interleukin 2 enzyme-linked immunosorbent assay and a chromium-51 release assay were used to evaluate the antitumor immune response of CAR T cells in coculture with tumor cells. Furthermore, SKBR3 tumor–bearing nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice were treated with HER2 CAR T cells to evaluate antitumor activity. Human CD3+ T cell accumulation in tumor xenograft was detected by immunohistochemistry.

Results

chA21-28z CAR was successfully constructed, and both CD4+ and CD8+ T cells were transduced. The expanded HER2 CAR T cells expressed a central memory phenotype and specifically reacted against HER2+ tumor cell lines. Furthermore, the SKBR3 tumor xenograft model revealed that HER2 CAR T cells significantly inhibited tumor growth in vivo. Immunohistochemical analysis showed robust accumulation of human CD3+ T cells in regressing SKBR3 lesions.

Conclusions

The results of this study show that novel chA21 scFv-based, HER2-specific CAR T cells not only recognized and killed HER2+ breast and ovarian cancer cells ex vivo but also induced regression of experimental breast cancer in vivo. Our data support further exploration of the HER2 CAR T-cell therapy for HER2-expressing cancers.

Anti-HER-2 engineering antibody ChA21 inhibits growth and induces apoptosis of SK-OV-3 cells

Background and Aims

Anti-HER-2 antibodies targeting distinct epitopes have different biological functions on cancer cells. In a previous study, we demonstrated that anti-HER-2 engineering antibody ChA21 was able to bind to subdomain I of HER-2 extracellular domain. In this study, The effects of ChA21 on growth and apoptosis against ovarian carcinoma cell SK-OV-3 over-expressing HER-2 in vitro and in vivo were investigated.

Methods

Cell growth inhibition was evaluated by MTT assay. Apoptosis was detected by TUNEL stain, transmission electron microscopy and flow cytometry on cultured cells and tissue sections from nude mice xenografts. The apoptosis-related proteins Bax and Bcl-2 were assessed by immunohistochemistry.

Results

We found that treatment of ChA21 caused a dose-dependent decrease of cell proliferation in vitro and a significant inhibition of tumor growth in vivo. ChA21 therapy led to a significant increase in the induction of apoptosis, and up-regulated the expression of Bax, while the expression of Bcl-2 was down-regulated.

Conclusion

These data suggest that ChA21 inhibits the growth and induces apoptosis of SK-OV-3 via regulating the balance between Bax and Bcl-2.

Crystallization and preliminary crystallographic studies of the single-chain variable fragment of antibody chA21 in complex with an N-terminal fragment of ErbB2

ErbB2 is a transmembrane tyrosine kinase, the overexpression of which causes abnormality and disorder in cell signalling and leads to cell transformation. Previously, an anti-ErbB2 single-chain chimeric antibody chA21 that specifically inhibits the growth of ErbB2-overexpressing cancer cells in vitro and in vivo was developed. Here, an antibody-antigen complex consisting of the single-chain variable fragment (scFv) of chA21 and an N-terminal fragment (residues 1-192, named EP I) of the ErbB2 extracellular domain was crystallized using the sitting-drop vapour-diffusion method. An X-ray diffraction data set was collected to 2.45 A resolution from a single flash-cooled crystal; the crystal belonged to space group P2(1)2(1)2(1).

Epitope mapping and structural analysis of an anti‐ErbB2 antibody A21: Molecular basis for tumor inhibitory mechanism

Anti-ErbB2 antibodies targeting distinct epitopes can have different biological functions on cancer cells. A21 prepared by surface epitope masking (SEM) method is a tumor-inhibitory anti-ErbB2 monoclonal antibody. Previously we engineered a single chain chimeric antibody chA21 with potential for therapy of ErbB2-overexpressing tumors. Here, we mapped the A21 epitope on ErbB2 extracellular domain (ECD) by screening a combinatorial phage display peptide library, serial subdomain deletion, and mutagenesis scanning. X-ray crystal structure of the A21 scFv fragment at 2.1 A resolution was also determined. A molecular model of Ag-Ab complex was then constructed based on the crystal structures of the A21 scFv and ErbB2 ECD. Some of biological functions of the A21 mAb and its derivative antibodies including their tumor cell growth inhibition and effects on the expression, internalization, and phosphorylation of ErbB2 receptor were also investigated. The results showed that A21 recognized a conformational epitope comprising a large region mostly from ErbB2 extracellular subdomain I with several surface-exposed residues important for the binding affinity. These data provide unique functional properties of A21 that are quite different from two broadly used anti-ErbB2 mAbs, Herceptin and 2C4. It suggested that the A21 epitope may be another valuable target for designing new anti-ErbB2 therapeutics.

Codon optimization, expression, and characterization of an internalizing anti-ErbB2 single-chain antibody in Pichia pastoris

Anti-ErbB2 antibodies are used as convenient tools in exploration of ErbB2 functional mechanisms and in treatment of ErbB2-overexpressing tumors. When we employed the yeast Pichia pastoris to express an anti-ErbB2 single-chain antibody (scFv) derived from the tumor-inhibitory monoclonal antibody A21, the yield did not exceed 1-2 mg/L in shake flask cultures. As we considered that the poor codon usage bias may be one limiting factor leading to the inefficient translation and scFv production, we designed and synthesized the full-length scFv gene by choosing the P. pastoris preferred codons while keeping the G+C content at relatively low level. Codon optimization increased the scFv expression level 3- to 5-fold and up to 6-10 mg/L. Northern blotting further confirmed that the increase of scFv expression was mainly due to the enhancement of translation efficiency. Investigation of culture conditions revealed that the maximal cell growth and scFv expression were achieved at pH 6.5-7.0 with 2% casamino acids after 72 h methanol induction. Secreted scFv was easily purified (>95% homogeneous product) from culture supernatants in one step by using Ni2+ chelating affinity chromatography. The yield was approximately 10-15 mg/L. Functional studies showed that the A21 scFv could be internalized with high efficiency after binding to the ErbB2-overexpressing cells, suggesting this regent may prove especially useful for ErbB2-targeted immunotherapy.