Cyclic diguanylate analogues: Facile synthesis, STING binding mode and anti-tumor immunity delivered by cytidinyl/cationic lipid.

Herein 2-cyanoethoxy-N,N,N',N'-tetraisopropyl-phosphorodiamidite(10, P ^III , 3.5 eq.) could synergistically react with 3',5'-dihydroxyl groups in a dinucleotide(P ^V ) at the cyclization step for the synthesis of cyclic dinucleotides (CDNs) (c-di-GMP, cGAMP etc.) and their phosphorothioated analogues. A dynamic P ^III -P ^V coordination mechanism has been proposed for the cyclization procedure which is confirmed by the variant ³¹ P NMR data and molecular simulation. Among the mono-phosphorothioated CDNs, two stereoisomers showed different capacity for STING activation and the reason was predicted by molecular modeling. While compound 12b ₁ showed most potent ability to elicit cytokines (IFNβ, IL-6, Cxcl9 and Cxcl10) induction compared to another stereoisomer. Also, 12b ₁ significantly inhibited the tumor growth in the EO771 model with both 0.1 μg (i.t.) and 2 μg (i.v.) administration through the aid of a Mix delivery system developed by our group, and achieved a 31% long-term survival rate of tumor-bearing mice. 12b ₁ /Mix significantly improved the percentage of CD8 ⁺ or CD4 ⁺ effector memory T (Tem, CD44 ^high CD62L ^low ) cells and CD8 ⁺ central memory T (Tcm, CD44 ^high CD62L ^high ) cells in the blood of EO771 mice, inducing the immune memory against EO771 tumor cells. Relatively lower dose regimens of 12b ₁ (0.1 μg)/Mix displayed better tumor suppression by more potent STING pathway activation and higher levels of cytokines induction in the tumor.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2022 Elsevier Masson SAS. All rights reserved.)