Stefania Bellone, Jonathan Black, Diana P. English, Carlton L. Schwab, Salvatore Lopez, Emiliano Cocco, Elena Bonazzoli, Federica Predolini, Francesca Ferrari, Elena Ratner, Dan-Arin Silasi, Masoud Azodi, Peter E. Schwartz, Alessandro D. Santin

Uterine serous carcinoma (USC) is an aggressive form of endometrial cancer which carries an extremely poor prognosis. Solitomab is a novel bispecific single-chain antibody construct which targets epithelial-cell-adhesion-molecule (EpCAM) on tumor cells and also contains a CD3 binding region. We evaluated the expression levels of EpCAM and the in vitro activity of solitomab against primary USC cell lines in vitro and ex-vivo in the ascites of USC patients. To determine the frequency of expression of EpCAM on uterine serous carcinoma cell lines as well as the ability of solitomab to modulate immune responses (T-cell proliferation, activation, cytokine production, and tumor killing) to tumor cells when it is combined with lymphocytes and EpCAM positive cell lines or EpCAM positive acitic fluid in vitro. EpCAM expression was evaluated by flow cytometry in a total of 14 primary USC cell lines. Sensitivity to solitomab-dependent-cellular-cytotoxicity (ADCC) was tested against a panel of primary USC cell lines expressing different levels of EpCAM in standard 4h (51)Cr release-assays. The proliferative activity, activation, cytokine secretion (i.e., Type I vs Type II) and cytotoxicity of solitomab in autologous tumor-associated-T cells (TAL) in the ascitic fluid of USC patients was also evaluated by CFSE and flow-cytometry assays. Differences in EpCAM expression, ADCC levels were analyzed using upaired t test. T-cell activation marker increase and cytokine release were analyzed by paired t test. Surface expression of EpCAM was found in 85.7% (12 out of 14) of the USC cell lines tested by flow cytometry. EpCAM positive cell lines were found resistant to NK or T-cell-mediated killing after exposure to peripheral blood lymphocytes (PBL) in 4-hour chromium-release assays (mean killing ± SEM, 2.7 ± 3.1% after incubation of EpCAM positive cell lines with control BiTE®). In contrast, after incubation with solitomab, EpCAM positive USC cells became highly sensitive to T cell cytotoxicity (mean killing ± SEM of 25.7 ± 4.5%; P < 0.0001) by PBL. Ex vivo incubation of autologous tumor associated lymphocytes (TAL) with EpCAM expressing malignant cells in ascites with solitomab, resulted in a significant increase in T-cell proliferation in both CD4+ and CD8+ T cells, increase in T-cell activation markers (i.e., CD25 and HLA-DR), and a reduction in number of viable USC cells in ascites (P < 0.001). Solitomab induces robust immunologic responses in vitro resulting in increased T-cell activation, proliferation, production of cytokines, and direct killing of tumor cells. These finding suggest that solitomab may represent a novel, potentially effective agent for treatment of recurrent/metastatic and/or chemo-resistant USC overexpressing EpCAM.