Targeting the STING-mediated DNA-sensing pathway to suppress autoimmunity and inflammageing

Inflammation is a key contributor to autoimmune and age-related disease, as well as the multimorbidity seen in both demographics. Activation of the cGAS-STING cell signalling pathway through DNA damage and cytoplasmic DNA causes downstream upregulation of interferons (IFNs) cytokines, producing an inflammatory response. This response is exacerbated in autoimmune disease and ageing, by persistent cytoplasmic DNA, overactivated signalling and elevated DNA damage. STING interacts with Transmembrane protein 203 (TMEM203), which regulates its lysosomal trafficking and downstream signalling upon activation. Previous research demonstrated that TMEM203 knockdown reduces IFN-β mRNA levels by approximately ~50%.
We hypothesized that targeting and inhibiting the STING-TMEM203 complex will dampen downstream inflammation associated with autoimmune disease and ageing (senescence phenotype). To test this, a protein-fragment complementation assay (PCA) was established and optimised for high throughput drug screening of a STING-targeted library of 1,574 small molecules, to identify inhibitors of the STING-TMEM203 complex. Several subsequent confirmation screens identified 18 compounds that consistently inhibited the STING-TMEM203 complex.
To evaluate whether these STING-TMEM203 inhibitors could dampen downstream inflammation, we tested the effect of the 18 small molecule inhibitors in the PCA using cGAMP-STING induced IFN-β production assays in human and mouse immune cells. Across three cell-based assays using human monocyte-derived macrophages (hMDMs), human peripheral blood mononuclear cells (hPBMCs), and mouse immortalized bone marrow-derived macrophages (iBMDMs), three compounds showed consistent IFN-β inhibition, two of which belonged to a similar chemical group.