Cyclic di-IMP (sodium salt) (c-di-IMP) is a synthetic second messenger structurally related to the bacterial second messengers cyclic di-GMP and cyclic di-AMP . C-di-IMP has adjuvant properties when co-administered with antigens in vitro and by mucosal routes in vivo. C-di-IMP enriches the population of MHC class I and II, CD80, CD86, CD40, and CD54 positive dendritic cells derived from murine bone marrow. It also stimulates macrophages at 500 ng ml. Mice immunized with β-galactosidase (β-gal) plus c-di-IMP through the intranasal route show a humoral immune response, evidenced by an increase in IgG titers up to 2-fold compared to mice immunized with β-gal alone. Mice immunized with β-gal plus c-di-IMP also exhibit a Th1 Th2 response, indicating that the adjuvant activity of c-di-IMP leads to a cellular immune response as well.
M04 acts as a stimulator of interferon genes (STING) agonist, effectively inducing IFN reporter gene expression in HEK293T cells equipped with wild-type human STING. Its activity is specific, not affecting HEK293T cells with the R71H-G230A-R293Q (HAQ) human STING variant or mouse RAW 264.7 cells, showcasing allelic- and species-dependent effects at a concentration of 75 µM. This compound also stimulates the production of TNF-α, IL-10, IL-1β, and IL-12p70 in human peripheral blood mononuclear cells (PBMCs). At 50 µM, M04 enhances human monocyte-derived dendritic cells' expression of HLA-DR (MHC class II receptor) and co-stimulatory molecules CD40, CD80, and CD86, improving T cell cross-priming in an ex vivo assay.