ADU-S100 ammonium salt (ML RR-S2 CDA ammonium salt) is an activator of stimulator of interferon genes (STING). ADU-S100 ammonium salt leads to potent and systemic tumor regression and immunity.

ADU-S100 ammonium salt induces the highest expression of IFN-β and the pro-inflammatory cytokines TNF-α, IL-6, and MCP-1 on a molar equivalent basis, as compared to endogenous ML cGAMP and the TLR3 agonist poly I:C. ADU-S100 ammonium salt is also found to induce aggregation of STING and induce phosphorylation of TBK1 and IRF3 in mouse bone marrow macrophage. ADU-S100 ammonium salt induces significantly higher levels of IFN-α compared to ML cGAMP[1].

IT injection of ADU-S100 ammonium salt into one tumor in BALB/c mice bearing bilateral CT26 or 4T1 tumors also demonstrated significant regression of the contralateral, untreated tumor. IT injection with ADU-S100 ammonium salt eradicates multiple tumor types and primes an effective systemic CD8+ T cell immune response that significantly inhibits the growth of distal, untreated lesions[1].