Ionizing radiation modulates human macrophages towards a pro-inflammatory phenotype preserving their pro-invasive and pro-angiogenic capacities

In order to improve the efficacy of conventional radiotherapy, attention has been paid to immune cells, which not only modulate cancer cell response to therapy but are also highly recruited to tumours after irradiation. Particularly, the effect of ionizing radiation on macrophages, using therapeutically relevant doses, is not well understood. To evaluate how radiotherapy affects macrophage behaviour and macrophage-mediated cancer cell activity, human monocyte derived-macrophages were subjected, for a week, to cumulative ionizing radiation doses, as used during cancer treatment (2Gy/fraction/day). Irradiated macrophages remained viable and metabolically active, despite DNA damage. NF-kappaB transcription activation and increased Bcl-xL expression evidenced the promotion of pro-survival activity. A significant increase of pro-inflammatory macrophage markers CD80, CD86 and HLA-DR, but not CCR7, TNF and IL1B was observed after 10Gy cumulative doses, while anti-inflammatory markers CD163, MRC1, VCAN and IL-10 expression decreased, suggesting the modulation towards a more proinflammatory phenotype. Moreover, ionizing radiation induced macrophage morphological alterations and increased their phagocytic rate, without affecting matrix metalloproteases (MMP)2 and MMP9 activity. Importantly, irradiated macrophages promoted cancer cell-invasion and cancer cell-induced angiogenesis. Our work highlights macrophage ability to sustain cancer cell activities as a major concern that needs to be addressed to improve radiotherapy efficacy

Human Monocytes Undergo Excessive Apoptosis following Temozolomide Activating the ATM/ATR Pathway While Dendritic Cells and Macrophages Are Resistant

Immunodeficiency is a severe therapy-limiting side effect of anticancer chemotherapy resulting from sensitivity of immunocompetent cells to DNA damaging agents. A central role in the immune system is played by monocytes that differentiate into macrophages and dendritic cells (DCs). In this study we compared human monocytes isolated from peripheral blood and cytokine matured macrophages and DCs derived from them and assessed the mechanism of toxicity of the DNA methylating anticancer drug temozolomide (TMZ) in these cell populations. We observed that monocytes, but not DCs and macrophages, were highly sensitive to the killing effect of TMZ. Studies on DNA damage and repair revealed that the initial DNA incision was efficient in monocytes while the re-ligation step of base excision repair (BER) can not be accomplished, resulting in an accumulation of DNA single-strand breaks (SSBs). Furthermore, monocytes accumulated DNA double-strand breaks (DSBs) following TMZ treatment, while DCs and macrophages were able to repair DSBs. Monocytes lack the DNA repair proteins XRCC1, ligase IIIα and PARP-1 whose expression is restored during differentiation into macrophages and DCs following treatment with GM-CSF and GM-CSF plus IL-4, respectively. These proteins play a key role both in BER and DSB repair by B-NHEJ, which explains the accumulation of DNA breaks in monocytes following TMZ treatment. Although TMZ provoked an upregulation of XRCC1 and ligase IIIα, BER was not enhanced likely because PARP-1 was not upregulated. Accordingly, inhibition of PARP-1 did not sensitize monocytes, but monocyte-derived DCs in which strong PARP activation was observed. TMZ induced in monocytes the DNA damage response pathways ATM-Chk2 and ATR-Chk1 resulting in p53 activation. Finally, upon activation of the Fas-receptor and the mitochondrial pathway apoptosis was executed in a caspase-dependent manner. The downregulation of DNA repair in monocytes, resulting in their selective killing by TMZ, might impact on the immune response during cancer chemotherapy

Supplementary Material for: Compromised DNA Repair and Signalling in Human Granulocytes

In previous studies, we showed impaired DNA repair in human monocytes. Here, we addressed the question of whether human neutrophilic granulocytes that arise from the same precursor as monocytes exhibit a similar phenotype and are impaired in repairing their DNA. We show that neutrophilic granulocytes isolated from peripheral blood display a lack of the same repair proteins that are missing in monocytes and do not show repair of their DNA when damaged by ionising radiation (IR) or chemical ROS. Contrary to T cells, we observed no decline in the number of single-strand breaks following γ-radiation. Also, granulocytes did not show γH2AX foci formation while T cells and peripheral blood lymphocytes (PBL) responded. In comparison to PBL, XRCC1, PARP-1 and ligase III were not expressed and there was also no discernible signal for key damage response proteins ATM, ATR and DNA-PKCS as well as γH2AX in neutrophils. Time course and dose-response experiments confirmed the absence of H2AX phosphorylation after radiation treatment although an accumulation of double-strand breaks was detected in the neutral Comet assay. Overall, the data indicate that terminally differentiated neutrophilic granulocytes in the peripheral blood display strong downregulation of DNA repair and DNA damage response factors, which should be taken into account if studies with whole peripheral blood containing granulocytes are performed, causing a significant intra-experimental variation in the cellular repair capacity