Nanoparticle STING Agonist Reprograms the Bone Marrow to an Antitumor Phenotype and Protects Against Bone Destruction.

When breast cancer metastasizes to bone, treatment options are limited. Failure to treat bone metastases is thought to be due to therapy-resistant features of the bone marrow microenvironment. Using a murine model of bone metastatic mammary carcinoma, we demonstrate that systemic delivery of polymer nanoparticles loaded with cyclic dinucleotide (CDN) agonists of stimulator of interferon genes (STING) inhibited tumor growth and bone destruction after 7 days of treatment. Each dose of STING-activating nanoparticles trafficked to the bone marrow compartment and was retained within the tumor microenvironment for over 24 hours, enhancing antitumor immunity through proinflammatory cytokine production and early T-cell activation. While acquired resistance mechanisms, including increased levels of immunosuppressive cytokines and the infiltration of regulatory T cells, ultimately limited antitumor efficacy after 2 weeks of treatment, bone protective effects remained. Overall, these studies demonstrate that STING pathway activation, here enabled using a nanomedicine approach to enhance CDN delivery to bone metastatic sites, can reprogram the immune contexture of the bone marrow to an antitumor phenotype that inhibits bone colonization of metastatic breast cancer cells and protects from tumor-mediated bone destruction.
Significance: Bone metastases are difficult to treat due to the inaccessibility of the bone marrow compartment and the immunosuppressive microenvironment that protects resident stem cells. Packaging a STING agonist into a nanoparticle that enables systemic administration and drug accumulation at tumor sites overcomes both barriers to stymie metastatic breast cancer growth.
Competing Interests: N.E. Bennett reports grants from NIH during the conduct of the study. A.R. Merkel reports grants from Verteran's Administration and non-financial support from Vanderbilt University Medical Center during the conduct of the study; grants from NIH Clinical and Translational Science Award and National Center for Advancing Translational Sciences outside the submitted work. M.A. Fischer reports grants from Incyte Corporation during the conduct of the study. M.R. Savona reports grants from ALX Oncology, Astex, Incyte, Takeda, TG Therapeutics; personal fees from BMS, CTI, Forma, Geron, Novartis, Sierra Oncology, Taiho; personal fees and other from Ryvu and Karyopharm outside the submitted work. J.A. Rhoades reports grants from Veterans Administration during the conduct of the study. S.A. Guelcher reports grants from Incyte Corporation during the conduct of the study. J.T. Wilson reports a patent to 10,696,985 issued and a patent to PCT/US2019/058945 pending. No disclosures were reported by the other authors.
(© 2023 The Authors; Published by the American Association for Cancer Research.)