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Introduction In patients, a transient decrease in peripheral blood lymphocyte counts was observed following intraperitoneal administration of the trifunctional monoclonal antibody catumaxomab (anti-human EpCAM x anti-human CD3). The aim of this study was to clarify the observed effect in a preclinical mouse model and to analyse the related mechanism of action in vitro. Materials and methods A related antibody, BiLu (antihuman EpCAM x anti-mouse CD3), was administered to mice and blood leukocytes were analysed. In vitro studies measured activation and cytokine secretion from human peripheral blood mononuclear cells (PBMC). For the analysis of T cell adhesion, PBMC were preincubated with catumaxomab and then co-cultured with human endothelial cells (HUVEC); T cell adhesion was assessed in the presence or absence of endothelial cell preactivation by TNFα. Adherent T cells were determined by flow cytometry. Results Treatment of mice with BiLu resulted in a dosedependent transient decrease in CD3+ T cells (both CD4+ and CD8+) that returned to the normal range within 48 h. Catumaxomab physiologically activated T cells in vitro (increased CD69 expression) and induced cytokine release (TNFα, IFNγ). TNFα increased expression of adhesion molecules CD54 and CD62E on endothelial cells. Furthermore, catumaxomab dose-dependently enhanced adhesion of T cells to endothelial cells. Adhesion was further increased when endothelial cells were preactivated with TNFα. Conclusions Catumaxomab increases adhesion of T cells to endothelial cells due to antibody-mediated activation of T cells and production of T cell cytokines that up-regulate endothelial cell adhesion molecules. These results provide a mechanistic rationale for the transient, reversible decrease in lymphocyte counts observed following catumaxomab administration in patients, which is likely to be due to redistribution of lymphocytes.

Surgical intervention and radiotherapy still represent the gold standard in the therapy of head and neck squamous cell carcinoma (SCC), although often with unsatisfactory results. Radiation might induce the expression and secretion of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) by unknown mechanisms. These two highly active proangiogenic and cytoprotective factors might contribute to a limited therapeutic success by promoting revascularization and cytoprotection of the radiated tumor. The aim of the present study was to analyze the potential of the cyclooxygenase inhibitor flurbiprofen to reduce radiation-induced increase of VEGF and bFGF secretion of tumor cells. We analyzed the expression of VEGF and bFGF at 72 h after radiation with 30 Gy in four SCC cell lines (De-pt, Hun, Lau, and A549) in cell culture with or without added flurbiprofen. Controls were not exposed to radiation and were analyzed at the same time after culture in the same media. We observed increased VEGF levels in all and increased bFGF levels in three of four lines after radiation. In irradiated cultures with flurbiprofen, VEGF was reduced between 13% and 26% and bFGF was reduced between 84% and 93% compared with radiated cultures without flurbiprofen. We found no reduction of VEGF and bFGF secretion in the unirradiated cultures despite added flurbiprofen. We conclude that flurbiprofen is able to alter the radiation-induced secretion of these two growth factors and might be useful in decreasing the resistance of SCC to radiation.

Background For the development of biosimilar monoclonal antibodies or related substances containing the IgG Fc part it is mandatory to fully compare immunological properties between originator and biosimilar in a “comparability exercise” [1]. The important Fc associated functions to mediate antibody dependent cellular cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC) need to be characterized using both the active substance of the biosimilar and the comparator [2,3]. For testing anti TNFalpha antibodies target cells with stable expression of membrane TNFalpha (mTNFalpha) is required. Further prerequisites are test systems facilitating analysis with high precision and accuracy.

Monoclonal antibodies such as rituximab and alemtuzumab show considerable therapeutic efficacy in chronic lymphocytic leukaemia (CLL). Aiming to further improve antineoplastic efficacy, the trifunctional bispecific antibody FBTA05 was developed. FBTA05 is thought to function by simultaneously binding B cells and T cells by its variable regions and by recruiting FcγR-positive accessory immune cells by its intact Fc region. As it was previously shown that this antibody shows considerable cytotoxicity towards a spectrum of B-cell lymphoma cell lines, we here tested its potential efficacy ex vivo against malignant B-CLL cells. Therefore, we assessed the capacity of increasing concentrations of FBTA05 to bind to neoplastic cells, to induce cytotoxicity (comparing it with rituximab and alemtuzumab) and cytokine release. We evaluated the results with respect to the extent of CD20 expression, the effector:target cell ratio as well as with the patients' overall effector cell status. Thus, we show that, although FBTA05-elicited cytotoxicity was comparable with that induced by alemtuzumab, it considerably exceeded the antineoplastic effects of rituximab. Noteworthy, FBTA05 shows effective elimination of malignant B cells even if CD20 surface expression is low. Importantly, a high grade of cytotoxicity was associated with the induction of T-cell proliferation and the concomittant release of interferon-γ and interleukin-6, thus overcoming the detrimental effects of an unfavourable effector:target cell ratio. In conclusion, we here present novel evidence for the therapeutic efficacy of the trifunctional, bispecific antibody FBTA05 in CLL and provide evidence for the importance of immune-mediated mechanisms conveying the cytotoxic effects against malignant B lymphocytes.

We analysed the release of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) from squamous cell carcinoma (SCC) after irradiation and their potential contribution to radiation resistance. Three SCC cell lines were irradiated, and VEGF- and bFGF-release was quantified by Elisa-assay. Conditioned media (CM) were used in clonogenic assays for analysis of tumor cell survival. To evaluate the effect of tumor released VEGF and bFGF on survival, experiments with neutralizing monoclonal anti-VEGF and anti-bFGF antibodies were conducted in parallel. Cell cultures were irradiated with 2 Gy to analyse the effects of CM on tumor cell escape from radiation-induced death. We observed a marked increase in VEGF- and bFGF-release after irradiation by the surviving cells. Using these conditioned media, subsequently we observed an up to 10-fold increase in colony formation. The addition of anti-VEGF- and anti-bFGF-antibodies reduced colony formation, indicating that irradiation stimulates the release of growth promoting substances including VEGF and bFGF by the surviving cells. Additionally, irradiation of cells cultured with CM decreased colony formation about 50%, however, it was still increased 5-fold compared to the cultures without CM. The addition of VEGF- and/or bFGF-antibodies led to an additional 20% reduction of this radioprotective effect of the CM. This means, bFGF and VEGF contribute to a significant proportion of the survival stimulating activity. We thus show that irradiation might result in autologous protection of tumor cells from irradiation-induced cell death by the release of growth factors. These observations suggest that radiation might lead to unsuspected and undesired effects in tumorous tissue with possible clinical impact.

The contribution of VEGF (vascular endothelial growth factor) to angiogenesis and tumor aggressiveness has been shown in several tumor types, but no comparative data regarding the impact of the VEGF-subtypes on endothelial and tumor cell protection are available. Therefore, we analysed the cytoprotective effects of the two major soluble VEGF-subtypes, VEGF- 1 2 1 and - 1 6 5 , on HUVEC cell cultures (human umbilical vein endothelial cells) and squamous cell carcinoma (SCC) cell lines after ionizing radiation. We performed clonogenic analyses and proliferation assays for evaluation of cell survival and proliferative activity. Experiments were performed employing different intensities up to 8 Gy with or without added recombinant VEGF- 1 2 1 or - 1 6 5 and compared to non-irradiated cultures. To evaluate a possible contribution of the VEGF-receptors, we performed immunohistochemical stainings of VEGF-R1 (flt), -R2 (KDR,flk), and Neuropilin-1. In the SCC cell lines and HUVEC cultures, cell survival and proliferative activity were reduced in a dosage-dependent manner. The addition of VEGF- 1 2 1 yielded a significant increase of resistance from 1.2 to 2.7 Gy (+125%) for killing 50% of subjected cells, while VEGF- 1 6 5 was less effective in this regard (+83%). Conversely, in HUVEC cultures, 50%-survival was increased more strongly by VEGF- 1 6 5 compared to VEGF- 1 2 1 (+100% vs. +43%). Accordingly, proliferation was more intensely stimulated in HUVECs by VEGF- 1 6 5 than by VEGF- 1 2 1 . VEGF-receptors were expressed in all cell cultures analysed at comparable levels. We conclude that the two VEGF-subtypes differentially increase the survival of tumor and endothelial cells after irradiation in vitro. We hypothesise, that the release of VEGF by the tumor protects tumor cells and endothelium resulting in increased radiation resistance.

Background For the development of biosimilar monoclonal antibodies (mAb) or related substances containing the IgG Fc part it is mandatory to fully compare immunological properties between originator and biosimilar in a “comparability exercise” [1]. The most complex Fc associated function to mediate antibody dependent cellular cytotoxicity (ADCC) needs to be characterized using the active substance of the biosimilar and the comparator. From a regulatory point of view potency assays should reflect the proposed mode of action but in vitro ADCC assays are considered difficult to validate due to the variability of the primary effector cells [2,3]. The requirement to test for ADCC with high precision and accuracy is challenging. Design of cell lines to replace primary cells for effector or target cells is a solution to provide tools for standardized and extensive biosimilar testing.

The trifunctional bispecific antibodies catumaxomab (anti-EpCAM x anti-CD3) and ertumaxomab (anti-HER-2/neu x anti-CD3) exert their mechanism of action by simultaneous recruitment and activation of two different types of immune effector cells at the tumor site. The interaction of different immune effector cells results in efficient elimination of tumor cells by several killing mechanisms including T-cell cytotoxic responses and direct effects mediated by accessory cells. Effective treatment of cancer is essentially based on cytotoxic drugs that kill tumor cells or inhibit their proliferation. However, the commonly observed hematotoxicity of chemotherapeutics is regularly associated with some degree of immunosuppression. On the other hand, some of these chemotherapeutic agents are reported to support or even enhance the anti-tumoral effect of immunotherapeutic drugs in certain doses. A largely intact immune system is the key for trifunctional antibodies to exhibit their full mode of action. Since chemotherapy might impact the number and function of immune effector cells, we evaluated in different preclinical in vitro models whether the efficacy of trifunctional bispecific antibodies would be influenced when combined with chemotherapeutic drugs (5-FU and cisplatin). The preclinical studies performed included in vitro cytotoxicity assays with established tumor cell lines evaluating potential synergy by using the method of Chou and Talalay. Furthermore, results from 3D tumor spheroids and from an autologous human ex vivo setting are presented. In addition, immune cells from cancer patients were obtained at different time points during and after chemotherapy and were assessed for their in vitro cytotoxicity mediated by trifunctional antibodies. So far the results from the different in vitro assay systems used indicate synergy for the combination of the trifunctional antibodies with 5-FU and cisplatin. Furthermore, no negative influence of these chemotherapeutic drugs was observed on the trifunctional mode of action in vitro. These results provide a basis for the possible combination of these drugs with trifunctional antibodies in the clinical setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3481.

Catumaxomab is a trifunctional, bispecific antibody targeting EpCAM and CD3 which redirects T-cells to EpCAM expressing tumor cells and is able to evoke T-cell cytotoxic responses. The hybrid Fc region of catumaxomab provides a third functional binding site, which is able to bind and activate Fcγ receptor (FcγR)-positive accessory cells. In clinical trials a transient decrease in peripheral blood lymphocyte counts was observed following i.p. administration of catumaxomab. Lymphocyte decrease may be a result of either decreased production or increased destruction of lymphocytes, redistribution of lymphocytes or various unknown / multifactorial pathogeneses. We determined whether the observed transient decrease in patients might be due to antibody induced adhesion of lymphocytes to endothelial cells or to migration of lymphocytes into the tissue. Therefore, we investigated the influence of catumaxomab on adhesion of human T cells to endothelial cells in vitro. Catumaxomab physiologically activated T-cells by increasing expression of the activation marker CD69 and induced the release of cytokines, including TNFα and IFNγ. TNFα increased expression of adhesion molecules CD54 and CD62E on endothelial cells. Furthermore, catumaxomab dose-dependently increased adhesion of T cells to endothelial cells, and the adhesion was further increased when the endothelial cells were preactivated with TNFα. Thus, catumaxomab increases adhesion of T-cells to endothelial cells, which is due to antibody mediated upregulation of adhesion molecules on T-cells and production of cytokines that upregulate endothelial cell adhesion molecules. Furthermore, we showed that treatment of BALB/c mice with the related trifunctional antibody BiLu (anti-human EpCAM x anti-mouse CD3), that binds to mouse CD3, also resulted in a dose-dependent transient decrease in CD3+ T-cells (both CD4+ and CD8+) that returned to the normal range within 48 h. These results provide a rationale for the transient and reversible decrease in peripheral lymphocyte counts observed following catumaxomab administration in clinical studies, which is likely to be due to redistribution of lymphocytes and not due to depletion of circulating lymphocytes or stem cells. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2447.

BACKGROUND Trifunctional antibodies, such as catumaxomab (anti-EpCAM×anti-CD3) and ertumaxomab (anti- HER-2/neu×anti-CD3), transiently link immune effector cells to tumour cells, which results in cellular cytotoxicity towards the tumour cells. A functional immune system is therefore essential for effective anti-tumour activity. However, the commonly observed haematotoxicity of chemotherapeutics and radiation therapy may be associated with some degree of immunosuppression. Combining chemotherapy and trifunctional antibodies in cancer treatment requires understanding of the impact of chemotherapeutics on immune cell function and, thus, on the activity of trifunctional antibodies. METHODS The effect of chemotherapeutic treatment on trifunctional antibody-mediated anti-tumour activity was assessed in vitro. Blood samples were collected from 12 head and neck squamous cell carcinoma patients after chemotherapy (5-fluorouracil, cisplatin) and radiotherapy, and from one healthy control donor. The immune cell status was analysed and mononuclear cells (MNC) were isolated. The potency of catumaxomab and ertumaxomab was assessed in a cytotoxicity assay using MNC isolated from each patient sample in co-culture with a tumour target cell line. The release of infl ammatory cytokines was also monitored in the cell culture supernatant. RESULTS Most patients included in this study had decreased immune cell counts during the course of chemotherapy. Nonetheless, an effective and concentration-dependent anti- tumour activity mediated by trifunctional antibodies was demonstrated using these patient immune effector cells. The immune response activity of the patient immune cells was not impaired one week after cisplatin administration or even three days after the last 5-fluorouracil treatment. CONCLUSION This study shows for the first time that immune effector cells from cancer patients undergoing standard chemotherapy and radiotherapy can be activated by trifunctional antibodies for efficient killing of tumour cells.