High-dose radiation activates caspases in tumor cells to produce abundant DNA fragments for DNA sensing in antigen-presenting cells, but the intrinsic DNA sensing in tumor cells after radiation is rather limited. Here we demonstrate that irradiated tumor cells hijack caspase 9 signaling to suppress intrinsic DNA sensing. Instead of apoptotic genomic DNA, tumor-derived mitochondrial DNA triggers intrinsic DNA sensing. Specifically, loss of mitochondrial DNA sensing in Casp9−/− tumors abolishes the enhanced therapeutic effect of radiation. We demonstrated that combining emricasan, a pan-caspase inhibitor, with radiation generates synergistic therapeutic effects. Moreover, loss of CASP9 signaling in tumor cells led to adaptive resistance by upregulating programmed death-ligand 1 (PD-L1) and resulted in tumor relapse. Additional anti-PD-L1 blockade can further overcome this acquired immune resistance. Therefore, combining radiation with a caspase inhibitor and anti-PD-L1 can effectively control tumors by sequentially blocking both intrinsic and extrinsic inhibitory signaling.
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All data supporting the findings of this study are available within the article and its supplementary information files and from the corresponding author upon reasonable request. A reporting summary for this article is available as a Supplementary Information file.
Deng, L. et al. STING-dependent cytosolic DNA sensing promotes radiation-induced type I interferon-dependent antitumor immunity in immunogenic tumors. Immunity 41, 843–852 (2014).
Burnette, B. C. et al. The efficacy of radiotherapy relies upon induction of type I interferon-dependent innate and adaptive immunity. Cancer Res. 71, 2488–2496 (2011).
Vanpouille-Box, C. et al. DNA exonuclease Trex1 regulates radiotherapy-induced tumour immunogenicity. Nat. Commun. 8, 15618 (2017).
Harding, S. M. et al. Mitotic progression following DNA damage enables pattern recognition within micronuclei. Nature 548, 466 (2017).
Li, P. et al. Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptotic protease cascade. Cell 91, 479–489 (1997).
Maier, P., Hartmann, L., Wenz, F. & Herskind, C. Cellular pathways in response to ionizing radiation and their targetability for tumor radiosensitization. Int. J. Mol. Sci. 17, 102 (2016).
Gudkov, A. V. & Komarova, E. A. The role of p53 in determining sensitivity to radiotherapy. Nat. Rev. Cancer 3, 117 (2003).
Rongvaux, A. et al. Apoptotic caspases prevent the induction of type I interferons by mitochondrial DNA. Cell 159, 1563–1577 (2014).
White, M. J. et al. Apoptotic caspases suppress mtDNA-induced STING-mediated type I IFN production. Cell 159, 1549–1562 (2014).
McArthur, K. et al. BAK/BAX macropores facilitate mitochondrial herniation and mtDNA efflux during apoptosis. Science 359, eaao6047 (2018).
Lama, L. et al. Development of human cGAS-specific small-molecule inhibitors for repression of dsDNA-triggered interferon expression. Nat. Commun. 10, 2261 (2019).
Hauff, P., Gottwald, U. & Ocker, M. Early to phase II drugs currently under investigation for the treatment of liver fibrosis. Expert Opin. Investig. Drugs 24, 309–327 (2015).
Mehta, G. et al. A placebo-controlled, multicenter, double-blind, phase 2 randomized trial of the pan-caspase inhibitor Emricasan in patients with acutely decompensated cirrhosis. J. Clin. Exp. Hepatol. 8, 224–234 (2018).
Galluzzi, L., Buque, A., Kepp, O., Zitvogel, L. & Kroemer, G. Immunological effects of conventional chemotherapy and targeted anticancer agents. Cancer Cell 28, 690–714 (2015).
Liu, X. et al. CD47 blockade triggers T cell-mediated destruction of immunogenic tumors. Nat. Med. 21, 1209 (2015).
Stagg, J. et al. Anti-ErbB-2 mAb therapy requires type I and II interferons and synergizes with anti-PD-1 or anti-CD137 mAb therapy. Proc. Natl Acad. Sci. USA 108, 7142–7147 (2011).
Liu, Z. et al. Hypofractionated EGFR tyrosine kinase inhibitor limits tumor relapse through triggering innate and adaptive immunity. Sci. Immunol. 4, eaav6473 (2019).
Lee, Y. et al. Therapeutic effects of ablative radiation on local tumor require CD8+ T cells: changing strategies for cancer treatment. Blood 114, 589–595 (2009).
Lim, J. Y., Gerber, S. A., Murphy, S. P. & Lord, E. M. Type I interferons induced by radiation therapy mediate recruitment and effector function of CD8+ T cells. Cancer Immunol. Immunother. 63, 259–271 (2014).
Roberts, E. W. et al. Critical role for CD103+/CD141+ dendritic cells bearing CCR7 for tumor antigen trafficking and priming of T cell immunity in melanoma. Cancer Cell 30, 324–336 (2016).
Spranger, S., Dai, D., Horton, B. & Gajewski, T. F. Tumor-residing Batf3 dendritic cells are required for effector T cell trafficking and adoptive T cell therapy. Cancer Cell 31, 711–723. e714 (2017).
Hildner, K. et al. Batf3 deficiency reveals a critical role for CD8α+ dendritic cells in cytotoxic T cell immunity. Science 322, 1097–1100 (2008).
Dou, Z. et al. Cytoplasmic chromatin triggers inflammation in senescence and cancer. Nature 550, 402 (2017).
Mackenzie, K. J. et al. cGAS surveillance of micronuclei links genome instability to innate immunity. Nature 548, 461 (2017).
Ferguson, B. J., Mansur, D. S., Peters, N. E., Ren, H. & Smith, G. L. DNA-PK is a DNA sensor for IRF-3-dependent innate immunity. eLife 1, e00047 (2012).
Liu, H. et al. Nuclear cGAS suppresses DNA repair and promotes tumorigenesis. Nature 563, 131 (2018).
Yang, H., Wang, H., Ren, J., Chen, Q. & Chen, Z. J. cGAS is essential for cellular senescence. Proc. Natl Acad. Sci. USA 114, E4612–E4620 (2017).
Rodríguez-Ruiz, M. E., Vanpouille-Box, C., Melero, I., Formenti, S. C. & Demaria, S. Immunological mechanisms responsible for radiation-induced abscopal effect. Trends Immunol. 39, 644–655 (2018).
Dovedi, S. & Illidge, T. The antitumor immune response generated by fractionated radiation therapy may be limited by tumor cell adaptive resistance and can be circumvented by PD-L1 blockade. Oncoimmunology 4, e1016709 (2015).
Benci, J. L. et al. Tumor interferon signaling regulates a multigenic resistance program to immune checkpoint blockade. Cell 167, 1540–1554 (2016).
Deng, L., Liang, H., Burnette, B., weicheslbaum, r & Fu, Y.-X. Radiation and anti-PD-L1 antibody combinatorial therapy induces T cell-mediated depletion of myeloid-derived suppressor cells and tumor regression. Oncoimmunology 3, e28499 (2014).
Zou, W., Wolchok, J. D. & Chen, L. PD-L1 (B7-H1) and PD-1 pathway blockade for cancer therapy: mechanisms, response biomarkers, and combinations. Sci. Transl. Med. 8, 328rv324–328rv324 (2016).
Cai, X., Chiu, Y.-H. & Chen, Z. J. The cGAS-cGAMP-STING pathway of cytosolic DNA sensing and signaling. Mol. Cell 54, 289–296 (2014).
Wang, H. et al. cGAS is essential for the antitumor effect of immune checkpoint blockade. Proc. Nat. Acad. Sci. USA 114, 1637–1642 (2017).
Xu, M. M. et al. Dendritic cells but not macrophages sense tumor mitochondrial DNA for cross-priming through signal regulatory protein α signaling. Immunity 47, 363–373 (2017).
Glück, S. et al. Innate immune sensing of cytosolic chromatin fragments through cGAS promotes senescence. Nat. Cell Biol. 19, 1061 (2017).
Andreeva, L. et al. cGAS senses long and HMGB/TFAM-bound U-turn DNA by forming protein–DNA ladders. Nature 549, 394 (2017).
Kim, K. W., Moretti, L. & Lu, B. M867, a novel selective inhibitor of caspase-3 enhances cell death and extends tumor growth delay in irradiated lung cancer models. PLoS ONE 3, e2275 (2008).
Werthmöller, N., Frey, B., Wunderlich, R., Fietkau, R. & Gaipl, U. Modulation of radiochemoimmunotherapy-induced B16 melanoma cell death by the pan-caspase inhibitor zVAD-fmk induces anti-tumor immunity in a HMGB1-, nucleotide- and T cell-dependent manner. Cell Death Dis. 6, e1761 (2015).
Brumatti, G. et al. The caspase-8 inhibitor Emricasan combines with the SMAC mimetic birinapant to induce necroptosis and treat acute myeloid leukemia. Sci. Transl. Med. 8, 339ra369 (2016).
Giampazolias, E. et al. Mitochondrial permeabilization engages NF-κB-dependent anti-tumour activity under caspase deficiency. Nat. Cell Biol. 19, 1116 (2017).
Rodriguez-Ruiz, M. E. et al. Apoptotic caspases inhibit abscopal responses to radiation and identify a new prognostic biomarker for breast cancer patients. Oncoimmunology 8, e1655964 (2019).
Bai, M. et al. In vivo cell kinetics in breast carcinogenesis. Breast Cancer Res. 3, 276 (2001).
Huang, J.-S. et al. Caspase-3 expression in tumorigenesis and prognosis of buccal mucosa squamous cell carcinoma. Oncotarget 8, 84237 (2017).
Flanagan, L. et al. Low levels of caspase-3 predict favourable response to 5FU-based chemotherapy in advanced colorectal cancer: caspase-3 inhibition as a therapeutic approach. Cell Death Dis. 7, e2087 (2017).
Zhang, Z. et al. Increased HMGB1 and cleaved caspase-3 stimulate the proliferation of tumor cells and are correlated with the poor prognosis in colorectal cancer. J. Exp. Clin. Cancer Res. 34, 51 (2015).
Hu, Q. et al. Elevated cleaved caspase-3 is associated with shortened overall survival in several cancer types. Int. J. Clin. Exp. Pathol. 7, 5057 (2014).
We thank R. W. Welchselbaum for providing reagents and assisting with experiments and the UT southwestern Flow Cytometry Facility and Animal Resources Center. YXF holds the Mary Nell and Ralph B. Rogers Professorship in Immunology. This work was supported by NCI CA134563, Texas CPRIT grant RR150072 and RR180725 (established CPRIT scholar in cancer research) to Y.-X. F.
The authors declare no competing interests.
Editor recognition statement: Zoltan Fehervari was the primary editor on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.
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Han, C., Liu, Z., Zhang, Y. et al. Tumor cells suppress radiation-induced immunity by hijacking caspase 9 signaling. Nat Immunol 21, 546–554 (2020). https://doi.org/10.1038/s41590-020-0641-5
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