Recent advances in the understanding of immune tolerance has led to the targeting of various checkpoints for the treatment of cancer. Several independent clinical studies have pointed out a strong correlation between the clinical activity of checkpoint inhibitors and tumor checkpoint expression. These findings highlight an opportunity to improve cancer immunotherapy by combining checkpoint inhibitors with an immunostimulatory agent that modulates the tumor microenvironment.
Our objective was to modulate the tumor microenvironment by activating Toll-like receptor (TLR) 9, a pathogen-associated molecular pattern recognition receptor. In preclinical studies, administration of IMO-2125, a novel TLR9 agonist, led to maturation of dendritic cells and induction of IFN-alpha. We hypothesized that immune activation by a TLR9 agonist administered intratumorally (i.t.) will lead to modulation of immune checkpoints in the tumor microenvironment, allowing these tumors to be targeted with a checkpoint inhibitor.
To evaluate the potential of i.t. IMO-2125 therapy and its effect on checkpoint gene expression, we employed three different tumor models: CT26 colon carcinoma, A20 lymphoma, and B16 melanoma mouse models. IMO-2125 was administered at a dose of 50 mcg per treatment, either as a single dose or as multiple doses into a targeted tumor nodule. Blood samples were collected post-dosing for analysis of the cytokine profile. Anti-tumor activity was evaluated by measuring the growth of the injected tumor as well as the distant tumor. Tumor nodules were homogenized to analyze gene expression of selected checkpoints by qPCR.
Results showed that a single i.t. injection of IMO-2125 in a CT26 colon carcinoma model induced systemic Th1 type cytokines, and resulted in tumor growth inhibition. Two days post IMO-2125 administration, analysis of gene expression of the treated tumor showed upregulation of IDO1 (13 fold) and PDL1 (2.7 fold), and no changes in expression of PD1 and OX40. Increased IDO1 gene expression correlated with increased IDO protein levels in the treated tumor nodules. In contrast, subcutaneous administration of IMO-2125 showed no substantial anti-tumor effect and no significant changes in checkpoint gene expression despite an induction of similar levels of systemic cytokines as the i.t. treatment. Multiple i.t. injections of IMO-2125 led to inhibition of tumor growth of the injected tumor and the distant tumor in all three tumor models. Tumor growth was correlated with increased CD3+ cells in treated as well as distant tumors. Analysis of the checkpoint gene expression at treated and distant tumor sites was conducted at 1-2 weeks post treatment. There was a significant upregulation of IDO1 and PDL1 gene expression in the treated tumors as well as in distant tumors. In addition to IDO1 and PDL1, depending on the tumor model, other immune checkpoints, including PD1, TIM3, BTLA, LAG3, OX40, and CTLA4, were also modulated.
In conclusion, IMO-2125 i.t. treatment led to modulation of the tumor microenvironment by inducing local and systemic Th1 type immune responses, which impacted the levels of checkpoint gene expression. Increased expression of some of these checkpoints may allow tumors to be targeted broadly by checkpoint inhibitor therapy.
Citation Format: Wayne Jiang, Daqing Wang, Fugang Zhu, Lakshmi Bhagat, Jillian DiMuzio, Sudhir Agrawal. Modulation of checkpoint expression in tumor microenvironment by intratumoral administration of a novel TLR9 agonist: Rationale for combination therapy. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B159.
- ©2016 American Association for Cancer Research.