DNA-PK inhibition sustains the antitumor innate immune response in Small Cell Lung Cancer

Small cell lung cancer (SCLC) is challenging to manage because of its high aggressiveness. Most SCLC patients show a good response to standard chemo-immunotherapy treatment, but they relapse after an initial response. Therefore, novel strategies to improve immune responsiveness are needed. Since the combination of DNA-damaging therapies with immunotherapy activates the stimulator of interferon genes (STING) pathway, we investigated whether the addition of DNA Damage Repair (DDR) inhibitors after chemotherapy could induce simultaneous activation of multiple innate immune sensors, thereby enhancing the antitumor immune response and reshaping the tumor microenvironment of SCLC. We explored the effect of DNA-PK inhibitor (DNA-PKi) on innate immune DNA/RNA sensors in three different models of SCLC: cell lines, patient derived peripheral blood mononuclear cells (PBMCs), 2D/3D cocultures of PBMCs and SCLC cells and in one ex vivo Malignant Pleural Effusion derived SCLC cells. We found that the sequential addition of DNA-PKi treatment to cisplatin activated CD8+ T cell and NK cell immune pathways, IFN-related pathways, and viral infections gene signatures, in SCLC cells and in patient derived PBMCs. We uncovered a novel DNA-PKi function in mediating the non-canonical STING translocation at mitochondria to interact with mitochondrial antiviral signalling protein (MAVS). DNA-PKi leads to acquisition of antitumor functions in patients-derived immune cells: metabolism modulation, M1 polarization, NK cell-mediated cytotoxicity and lymphocyte infiltration rate of 3D spheroids. Overall, this non-canonical pathway activation can enhance anti-cancer immune response in the various models of SCLC. These findings support a biological rational for DNA-PKi treatment as maintenance strategy after cisplatin with ability in sustaining an antitumor immune response in SCLC.