Abstract 4078: Enhanced anti-tumor activity through a combination of intravenous injectable TLR7 agonist, DSP-0509 and immune checkpoint inhibitors
Authors: Ota Yosuke , Otsubo Takeshi , Goto Masashi , Matsuki Yasushi 
Published: August 2019

Abstract
Toll-like receptors (TLRs) are a family of pattern-recognition receptors (PRR) that recognize pathogen-associated molecular patterns (PAMPs). TLR7 is mainly expressed in plasmacytoid dendritic cells (pDCs) and recognizes virus derived single-stranded RNA (ssRNA). TLR7 stimulation in pDCs induces type I interferon secretion, which results in innate immune activation. In this preclinical study, the characteristic changes in the tumor microenvironment (TME) after the combination treatment of DSP-0509 with immune checkpoint inhibitors (ICIs) in DSP-0509-responsive and -resistant tumors were assessed. Mutation rates of microsatellite loci were measured by 3130 xl Genetic Analyzer. Anti-tumor activity was evaluated in syngeneic mouse models along with flow cytometric analysis of tumor infiltrating lymphocytes (TILs). Gene expression profiles in tumor tissues were measured by qPCR arrays. Mutation rates of 5 microsatellite loci and basal levels of CD8+T cell infiltration were examined in tumor tissues derived from 10 syngeneic tumor-bearing mouse models. Intravenous administration of DSP-0509 significantly suppressed tumor growth in some tumor-bearing mouse models with high mutation rates and CD8+T cell infiltration including the CT26 (P&lt;0.05), but not in any models with low mutation rates and CD8+T cell infiltration including 4T1. Gene expression analysis revealed that the CT26 tumors highly expressed T cell inflamed genes including Ifng, Fasl and Il15 at the baseline, whereas the 4T1 tumors highly expressed immune suppressive genes including Il10 and Csf3. In contrast, the combination with anti-PD-1 antibody suppressed the tumor growth not only in the CT26 (P&lt;0.0001) but also in the 4T1-bearing model with immune suppressive TME (P&lt;0.05) and increased the expression of IFN-gamma signature genes including Ifng, Cxcl10 and Gzmb in both models. Similarly, the combination with anti-CTLA-4 antibody suppressed the tumor growth in both models and increased IFN-gamma signature genes. The frequency of PMN-MDSC (CD11b+Ly6g+) in 4T1 tumor was significantly decreased after the combination treatment of anti-PD-1 antibody (P&lt;0.05). Anti-tumor activity of DSP-0509 was associated with tumor mutation rates and the presence of CD8+ T cells within the tumor. The treatment of DSP-0509 in combination with anti-PD-1 antibody showed anti-tumor activity with increased expression of IFN-gamma signature genes and decreased PMN-MDSC even in the 4T1-bearing mouse model with immune suppressive TME (i.e., “cold”). In addition, the combination treatment with anti-CTLA-4 antibody also showed the anti-tumor activity with the increased IFN-gamma signature gene expression. These results suggest that combination of ICI with DSP-0509 resulted in anti-tumor activity by changing immunogenic “cold” to “hot” TME.
Citation Format: Yosuke Ota, Takeshi Otsubo, Masashi Goto, Yasushi Matsuki. Enhanced anti-tumor activity through a combination of intravenous injectable TLR7 agonist, DSP-0509 and immune checkpoint inhibitors [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 4078.