Design, Synthesis, and Biological Evaluation of Novel Cyclic Adenosine–Inosine Monophosphate (cAIMP) Analogs That Activate Stimulator of Interferon Genes (STING)

We describe novel STING-activating
cyclic dinucleotides whose constituent
nucleosides are adenosine and inosine and that vary by ribose substitution,
internucleotide linkage position, and phosphate modification. In mammalian
cells in vitro, some of these cAIMP
analogs induce greater STING-dependent IRF and NF-κB pathway
signaling than do the reference agonists for murine (DMXAA) or human
(2′,3′-cGAMP) STING. In human blood ex vivo, they induce
type I interferons (IFNs) and proinflammatory cytokines: for the former,
3′,3′-cAIMP (9; EC50 of 6.4
μM) and analogs 52–56 (EC50 of 0.4–4.7 μM), which contain one or two 2′-fluoro-2′-deoxyriboses
and/or bis-phosphorothioate linkages, are more potent than 2′,3′-cGAMP
(EC50 of 19.6 μM). Interestingly, 9 induces
type I IFNs more strongly than do its linkage isomers 2′,3′-cAIMP
(10), 3′,2′-cAIMP (23), and
2′,2′-cAIMP (27). Lastly, some of the cAIMP
analogs are more resistant than 2′,3′-cGAMP to enzymatic
cleavage in vitro. We hope to exploit our findings to develop STING-targeted
immunotherapies.