Abstract 4819: Sacituzumab Govitecan (IMMU-132) in uterine serous carcinoma

Objective: Uterine serous carcinoma (USC) is an aggressive variant of endometrial cancer with poor prognosis. Sacituzumab govitecan (IMMU-132) is a novel antibody-drug conjugate (ADC) targeting trophoblast antigen 2 (Trop-2), a cell surface glycoprotein highly expressed in many epithelial tumors including USC, to deliver SN-38, the active metabolite of irinotecan. The objective of this study was to preclinically evaluate the efficacy of IMMU-132 against primary USC cell lines and xenografts. Methods: Trop-2 expression in primary tumor cell lines and USC cell viability after exposure to IMMU-132 ADC (hRS7-CL2A-SN-38), non-targeting control ADC (h679-CL2A-SN-38), and naked antibody hRS7 IgG were evaluated using RT-PCR and flow-cytometry-based-assays. Antibody-dependent-cell-cytotoxicity (ADCC) against Trop-2+ and Trop-2- USC cell lines was evaluated in vitro using 4 hr Chromium release assays. Finally, in vivo activity of Sacituzumab govitecan was tested against Trop-2+ USC xenografts by 3 twice-a-week retro-orbital injection of 500 μg of IMMU-132, control-ADC, and hRS7 naked-IgG. Results: Overexpression of Trop-2 was detected in 67% (8 out of 12) of primary USC cell lines. Primary tumors overexpressing Trop-2 were significantly more sensitive (ie, lower IC50) to IMMU-132 (hRS7-CL2A-SN-38) when compared to control ADC (h679-CL2A-SN-38). Both sacituzumab govitecan (IMMU-132) and the naked antibody hRS7 induced high level of ADCC against Trop2+ USC cell lines while no cytotoxicity was detected against Trop-2 negative tumors. In vivo experiments comparing IMMU-132 activity to control ADC and hRS7 showed a dramatically improved tumor suppression and increased survival in IMMU-132 treated mice when compared to controls (P = 0.0001 and P = 0.0002, respectively). Conclusion: IMMU-132 demonstrated remarkable antitumor activity against biologically aggressive USC overexpressing Trop-2. Our preclinical results combined with the dramatic clinical response recently reported in an USC patient treated with IMMU-132 (https://doi.org/10.1016/j.gore.2018.05.009) strongly supports further clinical development of sacituzumab govitecan in USC patients with advanced/recurrent disease. (ie, clinical trial IND 140394). Furthermore, due to a cleavable linker that can cause bystander effect, sacituzumab govitecan could be also effective in tumors with heterogenous TROP-2 expression. Citation Format: Salvatore Lopez, Chanhee Han, Burak Zeybek, Elena Bonazzoli, Anna Bianchi, Paola Manara, Stefania Bellone, Aranzazu Manzano, Emanuele Perrone, Luca Zammataro, Gary Altwerger, Alessandro D. Santin. Sacituzumab Govitecan (IMMU-132) in uterine serous carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4819.