Targeted activation of the STimulator of INterferon Genes (STING) signaling pathway and the associated release of type I interferons can enhance the sensitivity of antigen presenting cells to neoantigens and promote their ability to prime T cell-based anti-cancer immune responses. This can lead to the establishment of T cell inflamed tumour microenvironments that are more susceptible to the anti-tumour effects of checkpoint blockade therapy. The Cancer Therapeutics CRC (CTx) is developing systemically delivered small molecule STING agonists to treat a range of cancers by triggering innate and adaptive anti-tumour immune responses. High throughput phenotypic screening of 415,000 compounds successfully led to the identification of direct STING agonists. Hits were deconvoluted by testing for STING dependent activity in THP-1 reporter cell lines and STING binding by SPR. CTx’s STING agonists bind both mouse and human STING and have cellular activity across both species. Cell-based activity has been demonstrated to be dependent upon STING (inactive in STING-/- cells), independent of cGAS (active in cGAS-/- cells) and could be blocked by TBK1 inhibitors. Compounds show activity in primary mouse and human cells across a range of STING variants. Dose-dependent in vivo PD biomarker responses in mice, including increased plasma IFN-β levels, were seen when administered intravenously (I.V) or intratumorally (I.T). In vivo, single agent efficacy of CTx STING agonists has been tested in multiple syngeneic mouse models of solid cancer. Treatment via I.T or I.V administration was well tolerated and evoked therapeutically beneficial immune-mediated anti-tumour responses. Successful induction of immunological memory, in response to STING agonist treatment was demonstrated in tumour-rechallenge experiments. In less responsive models, where intermediate efficacy was observed, increased tumour growth control could be achieved by co-treating mice with our STING agonist and anti-PD-1 antibody therapy. Overall, CTx has developed in vivo active systemically delivered small molecule STING agonists with excellent development potential which are clearly differentiated from the I.T delivered cyclic dinucleotide (CDN) compounds currently in clinical development.