目的:肿瘤对辐射的反应被认为依赖于肿瘤细胞的直接杀伤。我们的实验室对此提出了质疑。首先,我们展示了宿主的生物学,特别是酸性鞘磷脂酶(ASMase)的内皮表达,在确定肿瘤的放射稳定性方面至关重要。其次,我们已经证明,免疫系统可以通过在半照射的肿瘤中完全控制肿瘤来增强辐射反应。在本文中,我们专注于这两个发现的整合。
方法:我们使用Lewis肺癌(LLC)细胞,在以下任一者的侧腹注射:(i)ASMase敲除或(ii)匹配背景的WT(sv129xBl/6)或(iii)C57Bl/6小鼠。放射治疗(RT)递送至LLC肿瘤体积的50%或100%。肿瘤反应,免疫浸润(CD8+T细胞),测量ICAM-1和STING活化。放射治疗还与甲基环糊精联合使用,以抑制ASMase介导的富含神经酰胺的脂筏的形成。
结果:我们概括了我们之前的发现,即在LLC/C57Bl/6模型中,肿瘤半照射足以控制肿瘤。然而,在ASMaseKO小鼠中,半照射无效。同样,ASMase的药理抑制作用显着降低了肿瘤对半照射的反应。Further,我们证实ICAM-1表达升高,CD8+T细胞水平升高,在C57Bl/6小鼠中生长的肿瘤中ICAM-1和STING激活,以及ASMaseWT菌株。然而,在ASMaseKO小鼠中生长的肿瘤中未观察到此类变化。
结论:ASMase和神经酰胺的产生是通过STING激活介导辐射诱导的抗肿瘤免疫应答所必需的。
OBJECTIVE: Tumor response to radiation is thought to depend on the direct killing of tumor cells. Our laboratory has called this into question. Firstly, we showed that the biology of the host, specifically the endothelial expression of acid sphingomyelinase (ASMase), was critical in determining tumor radiocurability. Secondly, we have shown that the immune system can enhance radiation response by allowing a complete tumor control in hemi-irradiated tumors. In this paper, we focus on the integration of these two findings.
METHODS: We used Lewis Lung Carcinoma (LLC) cells, injected in the flank of either: (i) ASMase knockout or (ii) WT of matched background (sv129xBl/6) or (iii) C57Bl/6 mice. Radiation therapy (RT) was delivered to 50% or 100% of the LLC tumor volume. Tumor response, immune infiltration (CD8+ T cells), ICAM-1, and STING activation were measured. Radiotherapy was also combined with methyl-cyclodextrin, to inhibit the ASMase-mediated formation of ceramide-enriched lipid rafts.
RESULTS: We recapitulated our previous finding, namely that tumor hemi-irradiation was sufficient for tumor control in the LLC/C57Bl/6 model. However, in ASMase KO mice hemi-irradiation was ineffective. Likewise, pharmacological inhibition of ASMase significantly reduced the tumor response to hemi-irradiation. Further, we demonstrated elevated ICAM-1 expression, increased levels of CD8+ T cells, ICAM-1, and STING activation in tumors growing in C57Bl/6 mice, as well as the ASMase WT strain. However, no such changes were seen in tumors growing in ASMase KO mice.
CONCLUSIONS: ASMase and ceramide generation are necessary to mediate a radiation-induced anti-tumor immune response via STING activation.