Abstract 699: Uterine serous papillary carcinomas overexpress human trophoblast-cell-surface marker (Trop-2) and are highly sensitive to immunotherapy with hRS7, a humanized monoclonal anti-Trop-2 antibody

Abstract

Abstract Purpose: To evaluate the expression of human trophoblast cell-surface marker (Trop-2) and the potential of hRS7, a humanized monoclonal anti-Trop-2 antibody, as a novel therapeutic strategy against Uterine Serous Papillary Carcinoma (USPC), a biologically aggressive and chemotherapy resistant variant of endometrial cancer. Methods: Trop-2 expression was evaluated by real time-PCR and flow cytometry in six primary uterine serous papillary carcinoma cell lines recently characterized in our laboratory. Sensitivity to hRS7 antibody-dependent-cellular-cytotoxicity (ADCC) was tested in standard 5-hrs 51Cr release-assays against primary USPC cell lines expressing different levels of Trop-2. Finally, to investigate the effect of interleukin-2 (IL-2) on hRS7-mediated ADCC, 5-hrs 51Cr assays were also conducted in the presence of low doses of IL-2 (i.e., 50-100 IU/ml). Results: Trop-2 mRNA transcript was significantly overexpressed in 3 out of 6 USPC primary cell lines when compared to normal human endometrial-cells (NEC) [p=0.005]. Consistent with RT-PCR data, high surface expression of Trop-2 was detected by flow cytometry in Trop-2 overexpressing cell lines [i.e., percentage of positive cells = 100% in all 3 positive cell lines, median (minimum-maximum) MFI (mean fluorescence intensity) of 184.2 (62.5-276.2)]. Importantly, while these USPC cell lines were found highly resistant to natural killer dependent cytotoxicity in the absence of the hRS7 antibody (range of killing 1.1% to 12.4%), they showed high sensitivity to hRS7-mediated ADCC in vitro (range of killing 28.2% to 64.4%) (P< 0.001). Incubation with IL-2 in addition to hRS7 further increased the cytotoxic activity against USPC cell lines overexpressing Trop-2 (p= 0.01). Conclusion: Primary USPC cell lines may overexpress Trop-2 at mRNA and protein level and are highly sensitive to hRS7-mediated cytotoxicity in vitro. hRS7 may represent a novel, potentially highly effective therapeutic strategy in patients harbouring advanced, recurrent or metastatic USPC refractory to standard treatment modalities. 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 699.