Papel do receptor P2X7 e da enzima CD39/NTPDASE1 na resposta à radioterapia em gliomas

Abstract

Gliomas represent the most common class of malignant tumors of the central nervous system being the most aggressive, and lethal brain tumors in primary brain tumors. Among the treatments, radiation is one of the most used therapies, but the intrinsic radioresistance of these tumors remains a critical problem in the management of these patients. Currently it is known that the effect of radiation extends beyond the directly cytotoxicity caused in tumor cells. Radiation therapy appears to induce an immunogenic cell death that among the features is ATP release. The ATP can cause cytotoxicity via P2X7 receptor and also acts as a sign of damage activating the immune system. The ATP can be hydrolyzed by enzymes of the purinergic system, among them the ectonucleotidase CD39, to adenosine, which has an opposite effect to ATP, causing immunosuppression. The radiation-induced ATP release and the ability of this nucleotide in modulate immune responses raised the hypothesis about the purinergic signaling participation in the tumor and immune cells response to radiation. Therefore, this study investigated: i) the role of ectonucleotidase CD39/NTPDase1 in the radiation-induced immune response in gliomas, ii) the importance of ATP-P2X7 receptor in the gliomas response to radiotherapy. Using knockout mice for CD39/NTPDase1, we observed that the deletion of this enzyme combined with radiotherapy significantly reduced the immunosuppressive cells Tregs in the tumor and spleen, attenuated the infiltration of myeloid derived suppressor cells caused by radiation and increased CCR7 expression in splenic dendritic cells and macrophages, indicating the presence of freshly mobilized antigen presenting cells available to differentiate in immune-effector cells that sustain a more prolonged antigen-specific T-cell–mediated immune response. Thereby, showing that blocking the activity of CD39/NTPDase1 can control immunosuppressive mechanisms generated by the tumor and promises to improve the radiotherapy response. Furthermore, in this study we observed that radiation actives the P2X7 receptor and by silencing this receptor on the GL261 glioma cell line, we have shown that radiotherapy is less efficient in vivo when compared with mice injected with GL261 WT cells, which constitutively express the P2X7 receptor. We also showed that patients with glioma that overexpress the P2X7 receptor, showed a better response to radiotherapy, revealing the importance of the expression of this receptor on glioma cells as a useful marker to analyze the tumor sensitivity to radiation and a successful radiotherapy response. In summary, our data shed light on the purinergic signaling for modulating the radiotherapy response in gliomas.