Tumor-triggered DNA fragmentation with a nucleus-targeted nanodrug for precise cGAS-STING activation and enhanced cancer immunotherapy.

Abstract

Activation of the cGAS-STING pathway has emerged as a promising strategy in cancer immunotherapy due to the ability to trigger robust innate and adaptive immune response within the immunosuppressive tumor microenvironment. However, its clinical translation is restricted by multiple intractable challenges, particularly the severe inflammatory side effects caused by non-specific cGAS-STING activation. We herein developed a nucleus-targeted nanodrug with a unique characteristic of tumor-triggered DNA fragmentation and precise cGAS-STING activation. This nanodrug is engineered by encapsulating a protein (DNA fragmentation factor, DFF) and an agonist (procaspase-activating compound 1, PAC-1) into a nucleus-targeted nanoplatform. Using breast cancer (BCa) tumor models, we demonstrated this nanodrug could be efficiently internalized by BCa cells to achieve the cytosolic delivery of PAC-1 and nuclear delivery of DFF. Upon the activation of over-expressed procaspase-3 in BCa cells by PAC-1, the DNA degradation ability of DFF could be liberated, which could dramatically improve the cytosolic release of DNA fragments and thus enhance interferon-β (IFN-β) expression and secretion by activating the cGAS-STING pathway in BCa cells, ultimately inducing a significant inhibition of BCa tumor growth by enhancing the maturation of dendritic cells (DCs) and antitumor immunity of CD8⁺ T cells. STATEMENT OF SIGNIFICANCE: Activation of the cGAS-STING pathway has demonstrated the ability to reshape the immunosuppressive TME by triggering both the innate and adaptive immunity, but its clinical translation is restricted due to the severe inflammatory side effects caused by non-specific activation. We herein propose a concept of tumor-triggered cytosolic release of DNA fragments for precise cGAS-STING activation and enhanced cancer immunotherapy. To this end, a nanodrug is engineered by encapsulating DFF and PAC-1 into a nucleus-targeted nanoplatform. In this nanodrug, PAC-1 could induce the apoptosis of BCa cells by activating their over-expressed procaspase-3 into caspase-3, which could further trigger the DNA degradation ability of DFF to improve the cytosolic release of DNA fragments for precise cGAS-STING activation, thereby promoting IFN-β secretion from BCa cells to enhance the maturation of DCs and antitumor immunity of CD8⁺ T cells. The concept of tumor-triggered cytosolic release of DNA fragments demonstrated herein provides a potential immunotherapeutic strategy for tumor therapy, particularly the immune cold tumors with low response to immunotherapy.