Small Molecule TREX1 Inhibitors as Novel Immunotherapies

Mutations in the 3′ ‐> 5′ exonuclease TREX1 are associated with a spectrum of autoimmune phenotypes in humans and mice. In those affected, pathology is driven by persisting DNA which would normally be degraded by functional TREX1 enzyme. This undegraded DNA stimulates the nucleic acid sensing pathway, cGAS‐ STING, whose subsequent signaling generates a type‐I interferon response. This type‐I interferon response ultimately results in the chronic immune system activation typical of those affected. TREX1 and the cGAS‐ STING pathway have also been implicated in the tumor microenvironment, where TREX1 is believed to degrade tumor‐derived DNA destined to trigger cGAS‐STING signaling. If this tumor‐derived DNA is not degraded, the stimulated cGAS‐STING pathway promotes IFN‐dependent antitumor immunity. Consequently, small molecule stimulators of the cGAS‐STING pathway have shown promise as immunotherapies in animal models. Similarly, mice devoid of TREX1 exonuclease activity exhibit T‐cell dependent resistance to tumor growth. Collectively, these findings indicate that stimulation of the cGAS‐STING pathway activates the immune system, and that TREX1 inactivation represents a novel strategy for this purpose. Furthermore, they demonstrate the immunotherapy potential of such approaches. Thus, we hypothesize that small molecule inhibitors of TREX1 will activate the cGAS‐STING pathway. Studies described here identify small molecule inhibitors of TREX1, determine their mechanism of inhibition, and directly test the hypothesis that they can activate the cGAS‐STING pathway in murine cells. Findings from these studies will generate new structural insights into how TREX1 exonuclease activity may be affected, and have already identified several candidate chemotypes for development into novel immunotherapies. Support or Funding Information This work was supported by the NIH, NIAID, NIGMS, Lupus Research Alliance, Wake Forest Innovations, and a Sandy Lee Cowgill Memorial Scholarship. D18N mice display T‐cell dependent tumor resistance. 5×10 6 H31ml tumor cells were injected subcutaneously into WT and D18N mice, and tumor volume and survival tracked daily. Data in ‘B’ are separate study from ‘A’. For each study, eight to 16 mice were examined in two to four independent experiments. (A) D18N mice have decreased tumor growth in a mouse tumor model . (B) D18N model tumor‐resistance is T‐cell dependent. WT and D18N were treated with αCD8, αCD4, or isotype‐control antibodies. Arrows indicate D18N mice without treatment, or with CD8 + / CD4 + T‐cell depletion. Figure 1