Abstract 2487: The antitumor efficacy of anti-BST2 antibody is significantly increased in combination with CpG oligodeoxynucleotide in endometrial cancer

Abstract

Abstract Background: CpG oligodeoxynucleotides (ODN) has been shown to exhibit a potent immunostimulatory activity. Therefore, CpG ODN has been considered to be a promising material for enhancing the therapeutic effect of anticancer monoclonal antibody with antibody-dependent cell-mediated cytotoxicity (ADCC) activity. We have previously identified bone marrow stromal antigen 2 (BST2) as a therapeutic target of endometrial cancer cells and also demonstrated that an anti-BST2 antibody showed a potent anti-tumor effect by ADCC and complement-dependent cytotoxicity (CDC) activities against BST2 positive cells. The aim of this study was to evaluate the synergistic anti-tumor effect by combination of anti-BST2 antibody and CpG ODN, and to clarify the mechanisms of its anti-tumor effect, using xenograft model of BST2 positive endometrial cancer cells. Material and Method: We implanted 7-8 week-old female SCID mice with 5×106 HEC-88 nu endometrial cancer cells subcutaneously. Mice with tumor were treated by intra-peritoneal injection of an anti-BST2 mAb alone (12.5 and 200 μg/mouse, twice a week for four weeks), intra-tumoral injection of CpG ODN alone (10 μg/mouse, twice a week for four weeks) or combination therapy (12.5 μg/mouse of anti-BST2 mAb and 10 μg/mouse of CpG ODN). Anti-tumor effect was evaluated by monitoring the changes of tumor volume. Finally, population of NK cells and macrophages infiltrated into the tumor were analyzed by the FACS analysis, how CpG ODN induces immunopotentiative action. Results: Intraperitoneal treatment by anti-BST2 antibody showed a significant anti-tumor effect, dose dependently. The combination therapy of anti-BST2 antibody and CpG ODN was more effective than the single-agent therapy (p = 0.0002). In addition, the combination therapy also resulted high population of NK cells and macrophages in tumor significantly (p = 0.00018). Conclusion: We showed that CpG ODN increases the efficacy of anti-tumor effect of anti-BST2 mAb induced ADCC activity via potentiating NK cells and macrophages mediated cancer cell injury. Combination of GpG ODN would be a promising approach for enhancing the activity of ADCC based monoclonal antibodies, which targeting anti-tumor antigen. Citation Format: Yusuke Takahashi, Satoshi Serada, Kosuke Hiramatsu, Kouji Kobiyama, Minoru Fujimoto, Ken Ishii, Tetsuji Naka. The antitumor efficacy of anti-BST2 antibody is significantly increased in combination with CpG oligodeoxynucleotide in endometrial cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2487. doi:10.1158/1538-7445.AM2015-2487