Abstract A190: Colon tumor cells expressing CD24 have oncogenic properties and are inhibited by monoclonal antibody immunotherapy.

Abstract

Abstract CD24 is a heavily glycosylated glycosylphosphatidylinositol- anchored protein that is overexpressed in many different tumor types, including colon cancer (>80 %), and has been shown to correlate with shortened patient survival. CD24 plays a role in regulating cancer cell proliferation and tumor microenvironment interactions. The mechanism by which CD24 regulates cell survival and proliferation is not very well understood. What is better known is that CD24 modulates cancer cell adhesion to the vasculature wall and cancer cell-platelet thrombi formation by its binding to P-selectin expressed on activated platelets and endothelial cells. CD24 was also reported to be a functional marker for liver, colon and pancreatic cancer stem cells. All of these functions may contribute to tumor growth and metastasis. The aim of this study was to investigate the function of CD24 as a target for colon cancer therapy. In order to confirm that CD24 expressing cells acquire oncogenic properties, we transfected the CD24 gene into the CD24− colon cancer line SW480. We confirmed that CD24 overexpression induces SW480 tumor growth in vivo. In order to understand the mechanism by which CD24 promotes tumorigenesis, we found that CD24 overexpression activates several oncogenic pathways. Previous publications have shown that CD24 increases expression of p-Raf, p-ERK, and p-JNK in SW480CD24+ cells. Here, using a reporter assay, we show that CD24 expression activates not only ERK and JNK but also the Wnt pathway. It was also shown in the past that treatment of HT-29 colon cancer cells with the antiproliferative anti-CD24 mAb SWA11 caused a decrease in hypoxia and VEGF pathways. We show here that CD24 induced VEGF as well as FGF-2, IL-10, and MMP2 expression and activation of the hypoxia pathway. Finally, we have tested the tumor inhibitory effect of two different anti-CD24 antibodies, SWA11 (mouse IgG2a) and ALB9 (mouse IgG1). Results suggest that both antibodies bind specifically to the CD24 protein core as shown by competition assays with CD24 Fc and binding assays to the deglycosylated CD24. We show that SWA11 significantly inhibited both HT-29 and SW480CD24+ tumor growth in vivo while ALB9 inhibited SW480CD24+ tumor growth only. SWA11 didn't show any neutralizing activity in vitro in inhibiting cell proliferation or CD24 expression but showed effector function activity that may account for its mechanism of action in vivo. ALB9 mechanism of action was not explored in this study, but as it is a mouse IgG1 antibody, ADCC activity is not likely to be part of its mechanism of action. Together, these results provide support for the hypothesis that CD24 has oncogenic properties and that CD24-expressing tumor can be inhibited with antibody immunotherapy. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A190. Citation Format: Luciana F. Macedo, Elizabeth Kaiser, Haiyan Jiang, Hillary Millar, Diana Wiley, Adam Cotty, Fred Kaplan, Barry Morse, Jill M. Carton, Michael F. Naso, Randall Brezski, Allison Oberholtze, E. Christine Pietsch, Li Yingzhe, Debbie Marshall, Linda A. Snyder. Colon tumor cells expressing CD24 have oncogenic properties and are inhibited by monoclonal antibody immunotherapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A190.