Priming anti-tumor immunity by radiotherapy: Dying tumor cell-derived DAMPs trigger endothelial cell activation and recruitment of myeloid cells

Abstract

The major goal of radiotherapy is the induction of tumor cell death. Additionally, radiotherapy can function as in situ cancer vaccination by exposing tumor antigens and providing adjuvants for anti-tumor immune priming. In this regard, the mode of tumor cell death and the repertoire of released damage-associated molecular patterns (DAMPs) are crucial. However, optimal dosing and fractionation of radiotherapy remain controversial. Here, we examined the initial steps of anti-tumor immune priming by different radiation regimens (20 Gy, 4 × 2 Gy, 2 Gy, 0 Gy) with cell lines of triple-negative breast cancer in vitro and in vivo. Previously, we have shown that especially high single doses (20 Gy) induce a delayed type of primary necrosis with characteristics of mitotic catastrophe and plasma membrane disintegration. Now, we provide evidence that protein DAMPs released by these dying cells stimulate sequential recruitment of neutrophils and monocytes in vivo. Key players in this regard appear to be endothelial cells revealing a distinct state of activation upon exposure to supernatants of irradiated tumor cells as characterized by high surface expression of adhesion molecules and production of a discrete cytokine/chemokine pattern. Furthermore, irradiated tumor cell-derived protein DAMPs enforced differentiation and maturation of dendritic cells as hallmarked by upregulation of co-stimulatory molecules and improved T cell-priming. Consistently, a recurring pattern was observed: The strongest effects were detected with 20 Gy-irradiated cells. Obviously, the initial steps of radiotherapy-induced anti-tumor immune priming are preferentially triggered by high single doses – at least in models of triple-negative breast cancer.

Clinically relevant radioresistant rhabdomyosarcoma cell lines: functional, molecular and immune-related characterization

“…CXCL5 acts as a protumor molecule in different cancer types and it is associated with neutrophil trafficking, cancer angiogenesis, progression and resistance to therapies [59]. Finally, CXCL12 [60] has shown to directly promote radioresistance of several cancer types by different mechanisms, including sustaining stemness and inhibiting immunoresponse.…”

Trial watch: STING agonists in cancer therapy

“…Similarly, Goldenticket mice -which harbor a single nucleotide polymorphism in Sting1 (T596A) that mimics the effects of a loss-of-function mutation -cannot establish efficient IFN-dependent immune responses against Listeria monocytogenes. 81,82 Subsequent works, however, suggested that STING signaling in neoplastic cells, responding to some chemotherapeutic agents and radiotherapy, when delivered according to optimal doses and fractionation schedules, [83][84][85][86] also contributes to anticancer immunity, at least in some settings. 46 In line with this model, the short-hairpin RNAmediated depletion of CGAS or STING in mouse mammary carcinoma cells exposed to hypofractionated radiation 87 abolishes their ability to establish a tumor-specific immune response with systemic outreach (so-called 'abscopal response') in the presence of an immunostimulatory agent.…”

Priming of Anti-tumor Immune Mechanisms by Radiotherapy Is Augmented by Inhibition of Heat Shock Protein 90

“…Apart from targeted radiosensitization, HSP90 inhibition may also enhance the priming of anti-tumor immune mechanisms that has been observed upon radiotherapy but appears to be restricted to higher single doses and strongly hypofractionated protocols (3 × 8 Gy) (7)(8)(9)(10)(11)42). Improved priming of anti-tumor immune mechanisms would be particularly desirable for patients with high-risk CRC whose tumors are prone to local failure as well as metastasis formation, and who receive radiotherapy in fractions of ≤ 5 Gy -for instance in combination with immunotherapeutic protocols (69)(70)(71).…”

“…With photon irradiation, higher single doses or strongly hypofractionated protocols, such as 3 × 8 Gy, seem to be beneficial for the stimulation of systemic anti-tumor immune mechanisms (7)(8)(9)(10). We and others have shown that DAMPs released from irradiated, dying tumor cells stimulate the activation of endothelial cells and the recruitment of antigen presenting cells (APCs) which then crossprime CD8 + T cells in a type I interferon-dependent manner involving the cGAS/STING axis (8,9,(11)(12)(13)(14).…”