Introduction: Blockade of PD-1/PD-L1 has shown potent antitumor activity but these therapies are limited to certain diseases with higher intrinsic somatic mutation burden. A key research priority is now optimising response to these agents in diseases with limited clinical response. Activation of the cGAS-STING innate immune pathway has been identified as synergistic with anti-PD-1 therapy, and also a means of overcoming resistance to IO (immune-oncology therapy). We have reported activation of the cGAS-STING immune pathway as a result of cytosolic DNA released in response to intrinsic and extrinsic DNA damage, and that upregulation of PD-L1 in response to DNA damage is dependent on STING. Therefore, activating the STING pathway as a combination treatment with IO therapy could result in improved clinical responses. Experimental procedures: We perform qPCR analysis of the STING target genes, CXCL10/CCL5 after treatment with different classes of chemotherapy. We perform immunofluorescence to determine dsDNA translocation to the cytosol and the requirement of STING for this, an siRNA screening approach was used to identify the key nucleases involved in cytosolic dsDNA translocation and chemokines expression. Results: We observed increased expression of CXCL10/CCL5 gene expression following treatment with the topoisomerase I (irinotecan) and II (Doxorubicin and Etoposide) inhibitors. This chemokine expression was associated with increased expression of dsDNA in the cytosol. Using an siRNA approach, depletion of STING and the DNA nuclease MUS81 demonstrated abrogation of CXCL10/CCL5 expression following treatment with Doxorubicin. Conclusions: Here, we show that topoisomerase I and II inhibitors are the most potent chemotherapy at activating the cGAS-STING pathway and associated expression of interferon-dependent chemokines. We propose that combination therapies of topoisomerase I and II inhibitors with IO therapy will be effective in tumours which have had limited clinical response to single agent IO therapy.

Citation Format: Richard D. Wilkinson, David I. Johnston, Eileen E. Parkes, Nuala McCabe, Richard D. Kennedy. Exploring the effect of chemotherapies on STING-dependent cytokine release [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3787.