1154 Crystalized cyclic dinucleotide-manganese nanoparticles potentiate systemic STING activation across different species

Background Activation of the STING (stimulator of interferon genes) pathway boosts both innate and adaptive antitumor immune responses via the production of type-I interferons (IFN-I). However, 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. Methods Various metal ions were screened for synergy with CDNs in eliciting IFN-I response from bone marrow-derived dendritic cells. Lipid nanoparticles carrying CDNs and manganese ions (Mn2+) (termed CMP) were synthesized. Mice bearing syngenetic tumors (including CT26 and B16F10) as well as genetically engineered mouse models were treated by intravenous administration of CMP, followed by tumor monitoring and immune profiling of the tumor microenvironment. White New Zealand rabbits bearing VX2 tumors, healthy Beagle dogs, as well as non-human primates (NHPs) were treated with CMP and investigated. Lastly, human tumor biopsies derived from head and neck squamous cell carcinoma (HNSCC) patients were incubated with CMP or soluble STING agonists and analyzed for STING activation. Results We identified that Mn2+ could synergize with CDN STING agonists for inducing IFN-I production. Intravenous administration of CMP led to robust IFN-I response, reversed the immunosuppressive tumor microenvironment, and expanded anti-tumor CD8+ T cells. Systemic CMP therapy resulted in robust anti-tumor efficacy in multiple murine tumor models, including CT26, B16F10, and a genetically engineered mouse model of MMTV-PyMT triple-negative breast cancer. CMP also suppressed primary and metastatic tumor burden in VX2 squamous carcinomas bearing rabbits. In addition, CMP elicited systemic STING activation in healthy dogs and NHPs safely in a dose-dependent manner. Mechanistically, the efficacy of CMP therapy was dependent on the host STING expression but independent of the tumor STING expression. In addition, the anti-tumor efficacy of CMP 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, CMP treatment led to robust IFN-I responses from fresh human tumor biopsies derived from HNSCC patients. Conclusions CMP underscores the importance of harnessing nanoparticle design to potentiate systemic STING activation across multiple preclinical species, unleashing the therapeutic potential of targeting cGAS-STING pathway for cancer immunotherapy. Acknowledgements This work was supported by NIH (R01AI127070, R01CA210273, U01CA210152, R01DK108901, R01DE026728, R01DE030691, R01DE031951) and the University of Michigan Frankel Innovation Initiatives.