Metallo-nanoassemblies potentiate systemic STING activation across different species

Introduction: : Activation of STING initiates interferon (IFN) regulatory factor 3 (IRF3) and nuclear factor (NF-kb) pathways to generate type I IFN (IFN-I) and proinflammatory cytokines/chemokines, essential for establishing innate and adaptive antitumor immune responses. However, therapeutic targeting of STING for cancer immunotherapy faces considerable challenges. Most cyclic-dinucleotide (CDN) STING agonists are administered intratumorally because of their undesirable pharmacological properties, limiting their utility against advanced cancer. Here, we report the development of a new nanoparticle platform for the systemic delivery of CDN STING agonists with potent efficacy, favorable pharmaceutical properties, and acceptable safety profiles.

Materials and

Methods: : Various metal ions were screened for synergy with CDNs in eliciting IFN-I response from bone marrow-derived dendritic cells. Lipid nanoparticles carrying structurally ordered CDNs and manganese ions (Mn2+) nanoassembles (termed CRYSTAL) were synthesized. Mice bearing syngenetic tumors (including CT26 and MB49) as well as genetically engineered mouse models were treated by intravenous administration of CRYSTAL, followed by tumor monitoring and immune profiling of the tumor microenvironment. White New Zealand rabbits bearing VX2 tumors, as well as non-human primates (NHPs) were treated with CRYSTAL and investigated. Lastly, human tumor biopsies derived from head and neck squamous cell carcinoma (HNSCC) patients were incubated with CRYSTAL or soluble STING agonists and analyzed for STING activation.

Results, Conclusions, and Discussions:: Apart from amplifying the IFN-I responses of STING agonists via Mn2+, we identified that Mn2+ intercalated with cyclic-dinucleotides (CDNs) to form structurally ordered metallo-nanoassemblies (Figure 1a). The self-limited one-pot assembling process of CRYSTAL enables scalability, synthetic reproducibility, and computational predictability of their structures. Intravenous administration of CRYSTAL led to robust IFN-I response, reversed the immunosuppressive tumor microenvironment, and expanded anti-tumor CD8+ T cells. Systemic CRYSTAL therapy resulted in robust anti-tumor efficacy in multiple murine tumor models, including CT26, MB49, and a genetically engineered mouse model of MMTV-PyMT triple-negative breast cancer (Figure 1c-e). CRYSTAL also suppressed primary and metastatic tumor burden in VX2 squamous carcinomas bearing rabbits (Figure 1f). In addition, CRYSTAL elicited systemic STING activation in NHPs safely in a dose-dependent manner (Figure 1g). Mechanistically, the efficacy of CRYSTAL therapy was dependent on the host STING expression but independent of the tumor STING expression. In addition, the anti-tumor efficacy of CRYSTAL was decreased in mice lacking Ifnar1 or Ifngr1 expression in the B16F10 melanoma model, showing the crucial effects of IFN-I and IFN-II responses. Moreover, CRYSTAL treatment led to robust IFN-I responses from fresh human tumor biopsies derived from HNSCC patients.
CRYSTAL underscores the critical role of engineering structurally ordered metallo-nanoassemblies in targeting the cGAS-STING pathway for cancer immunotherapy, opening doors for incorporating such design strategies in future metalloimmunotherapies.

Acknowledgements and/or References (Optional):: This work was supported by NIH (R01AI127070, R01CA210273, U01CA210152, R01DK108901, R01DE026728, R01DE030691, R01DE031951) and the University of Michigan Frankel Innovation Initiatives.