Abstract 4001: The anti-CD47 antibody Hu5F9-G4 activates macrophages and inhibits ovarian cancer xenografts, alone and in combination with chemotherapy or immunotherapy (2016)

Abstract Macrophage activation by inhibition of CD47 signaling is a new therapeutic approach to cancers. Binding of CD47 to its receptor SIRPα on macrophages initiates a signal cascade that inhibits phagocytosis. Blocking CD47 from interaction with SIRPα by the CD47 antibody Hu5F9-G4 results in phagocytosis of cancer cells, and anticancer activity in xenografts of human cancers. We developed taxane resistant variants from human ovarian carcinoma (OC) cell lines (ES-2, MES-OV and OVCAR-3) by step-wise exposure to paclitaxel (Ptx) and the transport inhibitor valspodar (6x resistance in ES-2/TP, 9x in MES-OV/TP, and 30x in OVCAR-3/TP). These 6 lines were transduced to establish stable luciferase expression for OC xenograft (OCX) imaging. All express CD47 by immunoblotting and flow cytometry, and all express calreticulin (CRT). CRT is a prophagocytic signal that promotes phagocytosis in the presence of CD47 blockade. CRT levels are lower in the Ptx-resistant variants (p&lt;0.01). We are assessing the efficacy of Hu5F9-G4: (1) as a single agent in drug sensitive and resistant OCX; (2) combined with Ptx and carboplatin (Carbo); and (3) combined with cetuximab (Cetux) or trastuzumab (Trastuz) in OCX that express EGFR and/or HER2. We found that EGFR and HER2 are highly expressed in the ovarian cancer TCGA database. All 6 OC lines express EGFR by immunoblotting, and 4 express HER2. Blocking CD47 in vitro induces phagocytosis of parental and drug-resistant OC cell lines by murine macrophages derived from NOD/SCIDgamma (NSG) mice. Hu5F9-G4 has single agent activity in MES-OV OCX, with 89% growth inhibition at 9 weeks (T/C 11%) vs untreated controls (p = 0.03). Ptx alone produced a T/C of 29%, and the combination of Ptx/Hu5F9-G4 3% (p = 0.03 vs Hu5F9-G4; p = 0.0002 vs Ptx). The Carbo experiment was terminated at 5 weeks because of toxicity in the Carbo groups, but at that time point the T/C for Carbo was 59%, Hu5F9-G4 20%, and the antibody combination/carboplatin combination 4% (p&lt;0.005 vs either single agent). In the combined antibody experiment, Hu5F9-G4 T/C was 23%, Cetux 84%, Trastuz 37%, Hu5F9-G4/Cetux 13%, and Hu5F9-G4/Trastuz 12% (p = 0.05 vs Hu5F9-G4 alone). Thus, Hu5F9-G4 has substantial efficacy in MES-OV OCX, and at least additive effects with chemotherapy (Ptx and Carbo) and immunotherapy (Cetux and Trastuz). Experiments with other xenografts are continuing. These results support CD47 as a therapeutic target in OC, and suggest that it may be successfully combined with chemotherapies and other antibodies. Citation Format: Rishil J. Kathawala, David C. Mundy, George E. Duran, Jens-Peter Volkmer, Kevin S. Kao, Yan C. Wang, Aditi Bellary, Irving L. Weissman, Branimir I. Sikic. The anti-CD47 antibody Hu5F9-G4 activates macrophages and inhibits ovarian cancer xenografts, alone and in combination with chemotherapy or immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4001.