Unravelling the effects of proton irradiation on macrophages in cancer

Résumé

In addition to be one of the most abundant constituents of the tumor microenvironment, tumor-associated macrophages (TAMs) influence key processes in tumor progression, including angiogenesis, immunosuppression, invasion and metastasis. For a long time, TAMs have been associated to a M2-like phenotype, characterized by anti-inflammatory properties and pro-tumoral functions. This alternative activation state of macrophages contrasts with the classical activation state, also referred to as the M1 phenotype. M1-like macrophages are associated to pro-inflammatory, phagocytic and anti-tumoral roles. Interestingly, microenvironmental changes in tumor may easily switch the phenotype from M2 to M1, or inversely. Therefore, re-educating TAMs with treatment modalities represents a promising therapeutic strategy to elicit tumor regression. Several chemotherapies and immunotherapies have successfully triggered a reprogramming of TAMs and a concomitant tumor regression. However, these therapies are not localized and could thus trigger a systemic inflammatory response. For this reason, local radiotherapy represents an attractive alternative. Until now, X-rays and γ-rays have not succeeded to reprogram TAM. As radiotherapy is a continuously evolving field, new types of advanced radiotherapy have emerged, such as protontherapy. By presenting several physical advantages over conventional radiotherapy, protontherapy is a powerful therapeutic tool used to precisely target the tumor. Interestingly, proton beam therapy has demonstrated different radiobiological effects on tumors. Therefore, understanding the effect of proton irradiation on macrophages, and more specifically on their reprogramming, could allow to re-evaluate the use rate of protontherapy for cancer treatment.

In this work, we demonstrated that M1 macrophages are the most radioresistant phenotype to moderate doses of proton irradiation. This radioresistance is probably due to a different kinetic of DNA damage detection and repair. Interestingly, the evaluation of heterochromatin level before irradiation cannot explain the radioresistance of M1 macrophages. However, this phenotype better faces reactive oxygen species (ROS) exposure compared to M0 and M2 macrophages to proton irradiation. A better ROS management could thereby contribute to the radioresistance of M1 macrophages. The present study also determined, at least in part, how moderate doses (5 and 10 Gy) of proton irradiation, but not X-ray radiation, triggered macrophage reprogramming in unpolarized (M0) and M2-like macrophages. By targeting NFκB p65, proton irradiation educated M0 macrophages to adopt a M1-like phenotype and reprogramed M2 macrophages to acquire a mixed M1/M2 phenotype. These results were confirmed by the use of an IKK inhibitor (Bay-117082) in combination with proton irradiation. When nuclear translocation of NFκB was prevented, proton irradiation failed to induce macrophage reprogramming. As DNA damage and oxidative stress are intimately correlated to NFκB p50 – p65 activation, we suggested that proton irradiation induces a stronger NFκB activation compared to X-rays, thereby explaining the effective macrophage reprogramming. Finally, we set-up experiments for co-culture between M2 macrophages and A549 cancer cells. Our preliminary results revealed that proton-induced macrophage reprogramming is not influenced by the presence of cancer cells. Exposure to 10 Gy of protons also triggered cytosolic DNA-sensing pathway (cGAS/STING) in M2 macrophages co-cultured with cancer cells. In other reports, this signaling pathway was shown to be essential for triggering immune antitumor responses, initiated by TAMs.

Despite further investigations are needed to fully identify the molecular mechanisms by which proton radiation induces macrophage reprogramming and despite the need for validation of our results by in vivo experiments, this study further underpins the huge potential of protontherapy for targeting TAMs in tumors.

la date de réponse	30 mai 2018
langue originale	Anglais
L'institution diplômante	Universite de Namur
Sponsors	FRS-FNRS-Télévie
Superviseur	Carine Michiels (Promoteur), Anne-Catherine Heuskin (Président), Stephane Lucas (Jury), Yves Poumay (Jury), Olivier Feron (Jury) & Peter E. Huber (Jury)