DNA-dependent protein kinase (DNA-PK) has a central role in the repair of DNA damage induced by radiotherapy of cancer. As such, the combination of DNA-PK inhibitors and radiotherapy are under investigation in cancer clinical trials. While much of this efficacy is attributed to cancer-cell intrinsic mechanisms, little is known about the immunological ramifications. This thesis evaluates the immunological effects of a novel inhibitor of DNA-PK, M3814 (peposertib), in combination with radiotherapy.
Here, M3814 is shown to radiosensitise a panel of cancer cell lines. Furthermore, in KP.B6.F1 cells, a murine non-small cell lung carcinoma model, this cell death is accompanied by markers of immunogenic cell death including translocation of calreticulin to the cell-surface membrane and release of high mobility group box 1 (HMGB1). Additionally, treatment with radiotherapy and M3814 in MC38 cells increased expression of Interferon-β (Ifnβ), an anti-viral cytokine induced by the cGAS-STING pathway. In contrast, KP.B6.F1 cells failed to express IFNβ, despite evidence of increase formation of cGAS positive micronuclei following combination treatment. This was found to be due to a deficiency of STING which could be restored by the hypomethylating agent decitabine.
In a syngeneic murine tumour model, addition of decitabine to combination treatment improved KP.B6.F1 tumour control and increased survival. Analysis of the immune compartments of KP.B6.F1 tumours determined increased infiltration of active T effector cells, active CD8+ T cells, inflammatory monocytes and M1 macrophages in mice treated with a combination of decitabine, M3814 radiotherapy.
Together, this work demonstrates that addition of M3814 to radiotherapy not only increases cancer cell death but also increases the immunogenicity of tumour cells. Furthermore, it provides a potential therapeutic strategy to overcome cGAS-STING downregulation in cancer.