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A universal STING mimic boosts anti-tumor immunity

A universal STING mimic boosts anti-tumor immunity 

Stimulator of interferon genes (STING) represents an attractive oncology target due to its role in regulating anti-tumor immunity. However, the clinical potential of STING agonists is limited by factors including poor deliverability, downregulation of endogenous STING in the tumor microenvironment, and a complex balance between tumor control and progression. A universal STING mimic (uniSTING), reported in Nature Nanotechnology by researchers from the University of North Carolina at Chapel Hill, triggers STING signaling independently of endogenous STING expression and preferentially activates tumor control pathways. In vivo delivery of uniSTING-mRNA via lipid nanoparticles (LNPs) provides robust anti-tumor efficacy, which is enhanced by Wnt2 blockade with anti-Wnt2b antibodies. 



The cGAS-STING signaling pathway 

STING signaling is initiated when cyclic GMP-AMP synthase (cGAS) recognizes abnormal double-stranded DNA and generates 2′3′-cGAMP. This binds to STING, causing it to activate TANK-binding kinase 1 (TBK1) and inhibitor of κB kinases (IKKs), which respectively activate the transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor κB (NF-κB) to induce type I interferons (IFNs) and other inflammatory cytokines. Importantly, IRF3/IFN-I pathways are involved in tumor control, while NF-κB pathways are involved in tumor progression. 

UniSTING activates STING signaling in vitro, independent of endogenous STING levels 

To investigate uniSTING functionality in vitro, Wang et al. transfected a range of mammalian cell lines with expression vectors encoding uniSTING-FLAG, TBK1-GFP and IRF3-HA and performed confocal microscopy imaging, coimmunoprecipitation (co-IP), and RNA deep-sequencing. Immunofluorescence and co-IP showed all three proteins to co-localize in the cytosol, with IRF3 also observed in the nucleus, indicating its activated state. RNA deep-sequencing revealed over 200 differential expression genes to be elevated in uniSTING-treated cells, of which 80% were connected to IRF3/IFN-I signaling. 

In addition, Wang et al. treated STING-deleted bone-marrow-derived dendritic cells (BMDCs) with a cGAS inhibitor (Ru.521) and either uniSTING or 2′3′-cGAMP, prior to fluorescence-activated cell sorting and mRNA expression analysis. This revealed that only the uniSTING-treated cells retained the ability to activate IFNβ and CXCL10. Collectively, these data suggest that in the absence of endogenous STING, uniSTING selectively boosts the IRF3-dependent release of IFN-I. 

UniSTING-mRNA-LNPs exhibit anti-tumor effects in vivo 

UniSTING mRNA was in vitro transcribed using MEGAscript kits in the presence of CleanCap® AG, mRNA capping reagent, and encapsulated into LNPs for a series of in vivo studies. These included intratumoral injection of uniSTING-mRNA-LNPs into a selection of established tumors, which inhibited tumor growth and prolonged survival compared with soluble 2′3′-cGAMP or LNP-mock-mRNA. Additionally, intravenous injection of uniSTING-mRNA-LNPs effectively restrained several metastatic and orthotopic tumors, with immune cell profiling showing associated dendritic cell (DC) maturation and antigen-specific CD8+ T-cell responses. CleanCap® mCherry mRNA served as a control to confirm the effectiveness of the delivery system and define the cell types responsible for mRNA uptake and in vivo translation. 

Wnt2b blockade enhances the in vivo anti-tumor activity of uniSTING 

When Wang et al. incubated a dendritic cell line (DC2.4) with conditioned medium from uniSTING-mRNA treated tumor cells, they found that levels of IFNβ and CXCL10 mRNA were significantly increased, indicating the conditioned medium to contribute to DC activation. This increase was found to be modulated by exosomal miRNAs via downregulation of the Wnt2b immunosuppressor. Subsequently, dual treatment with uniSTING-mRNA-LNP and an anti-Wnt2b antibody was shown to enhance the anti-tumor efficacy of uniSTING in several cancer models. In conclusion, the use of uniSTING-mRNA-LNPs, either alone or combined with Wnt2b blockade, represents a promising therapeutic strategy for multiple cancer types, especially STING-deficient tumors. 


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Article reference: Wang Y, Li S, Hu M, et al. Universal STING mimic boosts antitumour immunity via preferential activation of tumour control signalling pathways. Nat Nanotechnol. (2024).