Induction of tumour cell lysis by a bispecific antibody recognising epidermal growth factor receptor (EGFR) and CD3

High-throughput cytotoxicity and antigen-binding assay for screening small bispecific antibodies without purification

The cytotoxicity of T cell-recruiting antibodies with their potential to damage late-stage tumor masses is critically dependent on their structural and functional properties. Recently, we reported a semi-high-throughput process for screening highly cytotoxic small bispecific antibodies (i.e., diabodies). In the present study, we improved the high-throughput performance of this screening process by removing the protein purification stage and adding a stage for determining the concentrations of the diabodies in culture supernatant. The diabodies were constructed by using an Escherichia coli expression system, and each diabody contained tandemly arranged peptide tags at the C-terminus, which allowed the concentration of diabodies in the culture supernatant to be quantified by using a tag-sandwich enzyme-linked immunosorbent assay. When estimated diabody concentrations were used to determine the cytotoxicity of unpurified antibodies, results comparable to those of purified antibodies were obtained. In a surface plasmon resonance spectroscopy-based target-binding assay, contaminants in the culture supernatant prevented us from conducting a quantitative binding analysis; however, this approach did allow relative binding affinity to be determined, and the relative binding affinities of the unpurified diabodies were comparable to those of the purified antibodies. Thus, we present here an improved high-throughput process for the simultaneous screening and determination of the binding parameters of highly cytotoxic bispecific antibodies.

Development and characterization of a bispecific single-chain antibody directed against T cells and ovarian carcinoma

Bispecific antibodies with specificity for tumor antigen and CD3 have been shown to redirect the cytotoxicity of T cells against relevant tumor. Our objective was to generate single-chain bispecific antibodies (bsSCA) that could retarget mouse cytotoxic T lymphocytes (CTL) to destroy human ovarian carcinoma in a xenogeneic setting. A bsSCA, 2C11 x B43.13, was constructed by genetic engineering and expressed in mammalian cells. Molecular characteristics, binding properties, and ability to retarget CTL were studied. Western blot analysis showed that the product is a 65-kDa protein. Purification of antibodies could be done by single-step affinity chromatography using protein L-agarose with an unoptimized yield of 200 microg/L. BsSCA 2C11 x B43.13 was capable of binding to mouse CD3 and human CA125 as detected by FACS analysis of EL4 and OVCAR Nu3H2 cells, respectively. It could also bridge activated splenic T cells and human ovarian carcinoma as demonstrated by a bridge FACS assay. Redirected mouse CTL could mediate human target cell lysis in a 20-h 51Cr release assay despite that they are xenogeneic. Prolonged incubation of redirected CTL and tumor targets resulted in a dramatic reduction in tumor cell number. CD28 co-stimulation enhanced redirected CTL function in both types of assays. BsSCA 2C11 x B43.13 thus can be used as a preclinical immunotherapeutic model for human ovarian cancer in a xenogeneic setting.

Bispecific antibodies as novel bioconjugates

Bispecific antibodies are unique macromolecular heterobifunctional cross-linkers with two different binding specificities within a single molecule. As ideal bioconjugates, they can specifically glue any two different molecules together without the need for chemical conjugation. With this unique feature, they have immense potential in biological and immunological fields. Their applications range from immunohistochemistry, immunoassays, radioimmunodiagnosis, radioimmunotherapy, and immunotherapy. Recently, a new second generation of bispecific molecules, bispecific single chain Fv and diabodies, has been produced by DNA recombinant technology. They can be considered as the ultimate magic bullets for in vivo applications. They may theoretically improve tumor or pathogen targeting and minimize side effects, eventually replacing the full-length bispecific antibodies. Emphasizing on developmental methodology and clinical applications of bispecific antibodies, this review gives a bird's-eye view of these unique bioconjugates.

The inhibitory effect of an EGF receptor-specific tyrosine kinase inhibitor on pancreatic cancer cell lines was more potent than inhibitory antibodies against the receptors for EGF and IGF I

CONCLUSION

Epidermal growth factor (EGF) increased the cell number of the two pancreatic cancer cell lines, MiaPaCa-2 and LN-36, in vitro. A blockade of the EGF-R tyrosine kinase with tyrphostin was more efficient in reducing the cell number than inhibiting receptor antibodies. IGF-1 increased the cell number, and blockade of the IGF-1-R initially decreased the cell number that later was followed by an increase in LN-36.

BACKGROUND/AIM

The receptors and ligands of EGF and insulin-like growth factor-1 (IGF-1) are overexpressed in pancreatic cancer tissue. The aim of the present experiments was to study the effects of EGF and IGF-1 on the cell number in two pancreatic cancer cell lines.

MATERIAL AND METHODS

MiaPaCa-2 cells were grown in 0.2% fetal calf serum (FCS) and the newly established LN-36 cells in serum-free medium (SFM). The cell number was measured with the XTT method. The effects of EGF and IGF-1 were studied in combination with inhibiting receptor antibodies and an EGF-R-specific tyrosine kinase inhibitor, tyrphostin B56.

RESULTS

MiaPaCa-2 responded with increased cell number to stimulation with EGF, and at 10(-8) M or higher concentrations a dose-response pattern was seen. Administration of B56 to MiaPaCa-2 decreased the cell number by 87%. The inhibiting EGF-R-Ab only inhibited EGF-induced increase in cell number. IGF-1 doubled the cell number of MiaPaCa-2 and increased the cell growth induced by EGF. The inhibiting IGF-1-R-Ab reduced the cell number by 10%. The LN-36 cell line responded to EGF with an increased cell number with a maximum at 5 x 10(-9) M after 96 h. B56 reduced the cell number by 90% at 10(-5) M, with less effect during stimulation with EGF. In contrast to B56, the inhibiting EGF-R-Ab in the same experiment did not reduce the cell number. LN-36 responded to IGF-1 with an increased cell number, but EGF-stimulated growth was not influenced. The inhibiting IGF-1-R-Ab reduced the cell number and suppressed the IGF-1 stimulated increase after 24 h and later it induced an increased cell number.