ESTRO 2020 Abstract Book

S1012 ESTRO 2020

than patient 2. Even during the first progression period following ICB initiation and the first ineffective SBRT, T cells specific for differentiation antigens and neoepitopes were detected in the blood of patient 2. Conclusion Our data suggest that oligometastatic patients, where a large proportion of the tumor mass can be irradiated, are good candidates to improve ICB responses by RT, even in the case of an unfavorable pretreatment immune signature, after progression on long-term anti-PD-1, and despite advanced age. Additional immunotherapies (e.g., epitope-based vaccination) may prolong antitumor responses and may be particularly beneficial for patients with unfavorable pretreatment tumor immune signature. PO-1815 Radiotherapy combined to Duox1 inhibition in macrophages enhances their anti-tumor effect L. Meziani 1 1 Institut Gustave Roussy, INSERM U1030, Villejuif, France Purpose or Objective The role of tumor-associated macrophages (TAM) in response to anticancer therapies is well defined, notably in response to radiotherapy (RT, Klug et al ., 2013). The efficacy of RT can be compromised by the occurrence of side effects in the healthy tissues surrounding the tumor by inducing a chronic oxidative stress and a chronic inflammation leading in some case to tumor development. It has been shown that reactive oxygen species (ROS) produced by NADPH oxidase (NOX) are involved in genomic instability of irradiated cells (Ameziani-El-Hassani et al ., 2015). We have previously demonstrated that chronic inflammatory response, mediated by anti-inflammatory macrophages (displaying the same activation profile as TAM) promote the development of radiation-induced tissue toxicity (Meziani et al ., 2018). These data suggest a link between NADPH oxidase and macrophage in the tissue response to radiotherapy. The role of several NOXs in macrophage response to radiotherapy, such as NOX2, has been reported (Wu et al ., 2017; Xu et al ., 2016). However, the role of DUOX1 (a dual NADPH oxidase, and a member of the NOX family) in macrophage activation and response to radiotherapy is poorly known. Material and Methods We evaluated the role of DUOX1 in macrophage activation in vitro and then we evaluated the anti-tumor effect of activated DUOX1 KO macrophages. Results We showed that DUOX1 plays a pivotal role in macrophage differentiation/activation. Interestingly, we showed that DUOX1 controls in vitro macrophage secretion of IFNγ and CCL4. Furthermore, we showed that DUOX1 is involved in macrophage phagocytosis and controls Src phosphorylation in activated macrophages. Interestingly, it has been shown that Src promotes anti-inflammatory macrophage generation (Hu et a., 2018) and plays a pro-tumoral role in several tumor models (Lamar et al., 2019). We have then evaluated the in vivo relevance of DUOX1 in macrophage activation and in the tumor response to radiotherapy. To this end, we have performed intra-tumor injection of macrophages derived from WT or Duox1 KO mice. Bone marrow derived macrophages (BMDMs) from both WT and KO mice were activated in vitro with GM-CSF to induce pro-inflammatory (anti-tumor) profile, and then injected intra-tumorally in subcutaneous MC38 tumours. Intra- tumor injection of WT BMDMs induced a limited delay in tumor growth. Interestingly, injection of Duox1 -/- BMDMs resulted significantly enhanced a significant tumor growth delay when compared with the injection of WT BMDMs. More interestingly, a 8 Gy tumor irradiation one day before BMDM injection enhanced the anti-tumor effect of injected DUOX1 KO BMDMs. This anti-tumor effect seems to be mediated by an IFNg response. Conclusion

Herein, we demonstrate that inhibition of DUOX1 represents a promising approach to modulate macrophage response/polarization in order to enhance their anti- tumoral activity. PO-1816 Impact of radiotherapy in immunological parameters in brain metastases by SRS A. Gonzalez-Pose 1 , A. Garcia-Perez 1 , M. Gonzalez- Rodriguez 2 , A. Lopez Medina 1 , S. Mirete Bachiller 3 , V. Ochagavia 2 , I. Nieto 2 , F.J. Salvador 1 , V.M. Muñoz Garzón 2 1 Hospital do Meixoeiro, Medical Physics, Vigo Pontevedra, Spain ; 2 Hospital do Meixoeiro, Radiation Oncology, Vigo, Spain ; 3 Hospital do Meixoeiro, Inmulogía, Vigo, Spain Purpose or Objective The aim of this study was to observe how fractionation affects immunity system in patients with brain metastases. Ionizing radiation liberates antigens from within the tumor that can activate an antitumor immune response through attraction, invasion and priming of CD8 T cells in the tumor microenvironment. Higher doses induce more T-cell infiltration in the tumor, and also in its microenvironment, as well as, antigen-presenting cells in draining lymph nodes. Additionally, antitumor responses are reduced due to the presence of PD1 proteins. Material and Methods Eleven patients, recruited to HeNeBra Project, with brain metastases, treated with stereotactic radiosurgery (SRS) and different fractionation schedules (5 x 4 Gy (n = 1), 5 x 5 Gy (n = 2), 3 x 7 Gy (n = 2), 3 x 8 Gy (n = 2), 3 x 9 Gy (n = 1), 1 x 21 Gy (n = 2), 1 x 25 Gy (n = 1)) were choosen to analyze their immunological parameters. The variation of different types of lymphocytes and the PD1 protein in peripheral blood were measured before treatment and one month after completion. These lymphocytes were CD3 (encompassing all T lymphocytes with antitumor activity), CD4 (take part in cellular immunity), CD8 or cytotoxic T- cells; and Natural Killer cells (NK) (cytotoxic cells without T cell receptor). Patients were grouped into two samples depending on fractionation schedule: fractionated or single dose. Results Figure 1 shows the variation in lymphocytes population because radiotherapy treatment (before and one month after treatment). CD3, CD4 and NK cells levels in the peripheral blood of patients who received fractionated treatment were decreased while CD8 cell levels remain practically constant. However, variations of CD3, CD4, CD8 and NK in patients treated with a single dose show a substantial increase between pre-treatment and one month post-radiotherapy. Figure 2 displays the concentration of PD1 in peripheral blood before and after the treatment. The standard deviation of PD1 concentration of patients treated by single-dose scheme decreases from 17.9 pg/ml to 2.9 pg/ml, and the average value changes from 42.2 pg/ml to 17.1 pg/ml, while these values don't change significantly in fractionated schemes. These results (increase in CD8, in NK, and decrease in PD1 for single dose treatment) suggest immune response is enhanced by radiotherapy for one- session treatments.