Abstract 4706: Spherical nucleic acids targeting toll-like receptor 9 enhance antitumor activity in combination with anti-PD-1 antibody in mouse tumor models

Abstract Of the several immunotherapy approaches being developed, checkpoint inhibitors (CPI) represent a breakthrough for the treatment of cancer. A T cell-inflamed tumor microenvironment (TME) is required for antitumor efficacy of CPI. However, the evidence suggests that 70% of tumors do not possess T cell-inflamed TME limiting the potential of CPI treatments to a smaller population of cancer patients. Immunotherapies that enable CPI effectiveness in patients with non-T cell-inflamed phenotype are being studied. Oligonucleotide-based TLR9 agonists induce potent CD8+ T cell and plasmacytoid dendritic cell activation and limit immune suppressor cell phenotypes in TME. Therefore, the combination of TLR9 agonists with CPI would be a rational approach for achieving higher rates of success in cancer treatment. However, TLR9 agonists were unsuccessful in previous cancer clinical trials. Spherical Nucleic Acids (SNAs) are a novel class of agents with oligonucleotides densely packed and radially oriented around spherical liposomal nanoparticles. SNAs overcome limitations of therapeutic oligonucleotides through increased uptake and nuclease stability. We have evaluated a TLR9 targeted SNA for anticancer activity as a monotherapy and in combination with an anti-PD-1 (a-PD-1) antibody in both a-PD-1 sensitive and insensitive mouse tumor models. Mice bearing a-PD-1 sensitive MC38 tumors were treated with intratumoral dosing of TLR9 agonist SNA, intraperitoneal (IP) dosing of a-PD-1 or the combination of both agents when average tumor volume was 100 mm3, with twice weekly dosing for a total of 5 doses. SNA alone showed dose-dependent tumor growth inhibition (TGI) of up to 87% and increased survival of mice. The combination of SNA and a-PD-1 greatly enhanced TGI (92% vs SNA, 74% or a-PD-1, 77%) and mice survival compared with either monotherapy. Moreover, once weekly dosing of SNA showed similar TGI compared with twice weekly dosing. In a-PD-1 insensitive EMT-6 model, mice were treated with intravenous dosing of TLR9 agonist SNA, IP dosing of a-PD-1 or the combination of both agents starting on day 3 following subcutaneous tumor cell inoculation. SNA alone showed potent dose-dependent TGI of up to 80% and increased mice survival. The combination of SNA and a-PD-1 showed a synergistic TGI (86% vs SNA, 64% or a-PD-1, no effect) and increased mice survival. Further, no tumor growth was observed in surviving mice after subsequent challenge with EMT-6 cells, suggesting development of tumor-specific memory responses in SNA treated animals. These data demonstrate that the TLR9 agonist SNA studied herein induces innate and adaptive immune responses in tumor-bearing mice and shows synergistic TGI with a-PD-1 in both a-PD-1 sensitive and insensitive tumor models. A TLR9 agonist SNA, AST-008, is currently in clinical development. Citation Format: SubbaRao Nallagatla, Bart R. Anderson, Sagar Anantatmula, Ekambar R. Kandimalla. Spherical nucleic acids targeting toll-like receptor 9 enhance antitumor activity in combination with anti-PD-1 antibody in mouse tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4706. doi:10.1158/1538-7445.AM2017-4706