Radiation and tissue response

URPP Fellow: Stefanie Hiltbrunner

Radiotherapy is a standard therapy for cancer and site-directed ionizing radiation is used to specifically target solid cancer masses. Until recently, radiotherapy was given in multiple (e.g. 30-40) daily doses of 1.5-2 Gy each, but the development of stereotactic devices allows treatment with far fewer, high doses (10-40 Gy per dose). First data show that this so-called hypo-fractionated radiotherapy is at least as efficient with respect to clinical response as conventional, fractionated radiotherapy (Favaudon et al., 2014). The fact that patients can be treated in fewer sessions is a major advantage.

Induction of irreversible DNA-damage to tumor cells resulting in cell death is the main goal of radiotherapy. Recent data from us and others, however, show that the inflammatory and immune response elicited by radiation is an integral part of the therapeutic response (Formenti and Demaria, 2012; Gupta et al., 2012; Sharma et al., 2013). We recently identified radiotherapy-induced, local production of anaphylatoxins as an essential response with respect to boosting of tumor-specific immunity and to efficacy (Surace et al., 2015). This was unexpected as chronic complement activation was shown to be tumor-promoting (Elvington et al., 2014; Markiewski et al., 2008; Pio et al., 2014). Indeed, radiotherapy did not support tumor-specific immunity when given as multiple daily doses (Surace et al., 2015), suggesting that the radiotherapy-induced acute inflammatory response is beneficial, whereas a chronic inflammatory response is detrimental.

Localized radiotherapy of solid cancers induces a plethora of changes in the tumor, which collectively support intratumoral tumor-specific immune effector functions. We have seen this in both animal models and sarcoma patients. Moreover, the therapeutic efficacy of radiotherapy crucially depends on the concomitant activation of tumor-associated dendritic cells, local production of type I interferon and the presence of CD8+ T cells. Radiotherapy-induced immunostimulation seems a local event in most cases and as such confined to the irradiated site. However, evidence in mice and humans suggest that such immunostimulation can become systemic and result in control of (micro)metastases under CTLA-4 blockade. It is currently not known which mechanisms and pathways are involved in local and systemic radiation-induced immunostimulations.

We propose that deliberate interference with pathways that are affected by radiotherapy can improve therapeutic efficacy through stimulation of tumor-specific immunity. Virtually nothing is known about the tissue response to radiation and specifically, the differences between conventional and hypo-fractionated radiotherapy have not been investigated.

We therefore aim to perform an unbiased analysis of the tissue (tumor) response to different radiotherapy schedules and analyze inflammatory and immune parameters by flowcytometry and CyTOF as well as the type of cell death by electron microscopy and histology. Because the inflammatory response modifies the chromatin state and thereby the transcriptional activation or down-regulation of specific genes, different gene expression programs are established that either result in an acute inflammation or a tolerant/chronic state. It is the goal of this sub-project to identify the chromatin state that induces an immunosupportive character of the tumor microenvironment. We therefore will perform transcriptome analysis (RNA-sequencing, including micro-RNA) in tumors, proteome analysis in tumors, metabolite analysis (mass-spectrometry) in tumors and serum and epigenetic changes in tumors. Data will be analyzed using bioinformatics tools to identify pathways that change significantly upon hypo-fractionated and/or conventional fractionated radiotherapy. Subsequently, we will investigate the relevance of selected pathways to therapeutic response using selective blocking or knock out mice. Finally, we will validate our results using biopsies from patients with melanoma in situ taken before and after radiotherapy as well as serum samples from such patients and from patients with glioblastoma, who received a single high dose of radiotherapy.