Keane Lily, Cheray Mathilde, Saidi Dalel, Kirby Caoimhe, Friess Lara, Gonzalez-Rodriguez Patricia, Gerdes Maren Elisabeth, Grabert Kathleen, McColl Barry W, Joseph Bertrand
Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
UK Dementia Research Institute, Center for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK.
Neurooncol Adv. 2021 Jul 5;3(1):vdab096. doi: 10.1093/noajnl/vdab096. eCollection 2021 Jan-Dec.
Diffuse intrinsic pontine gliomas (DIPG), within diffuse midline gliomas are aggressive pediatric brain tumors characterized by histone H3-K27M mutation. Small-molecule inhibitors for the EZH2-H3K27 histone methyltransferase have shown promise in preclinical animal models of DIPG, despite having little effect on DIPG cells . Therefore, we hypothesized that the effect of EZH2 inhibition could be mediated through targeting of this histone modifying enzyme in tumor-associated microglia.
Primary DIPG tissues, and cocultures between microglia and patient-derived DIPG or -pediatric high-grade glioma (pHGG) cell lines, were used to establish the H3-K27M status of each cell type. Antisense RNA strategies were used to target gene expression in both microglia and glioma cells. Microglia anti-tumoral properties were assessed by gene expression profile, tumor cell invasion capacity, microglial phagocytic activity, and associated tumor cell death.
In primary DIPG tissues, microglia do not carry the H3-K27M mutation, otherwise characteristic of the cancer cells. Activation of a microglial tumor-supportive phenotype by pHGG, independently of their H3-K27M status, is associated with a transient H3K27me3 downregulation. Repression of EZH2 in DIPG cells has no impact on tumor cell survival or their ability to activate microglia. However, repression of EZH2 in microglia induces an anti-tumor phenotype resulting in decreased cancer cell invasion capability, increased microglial phagocytosis, and tumor-related cell death.
These results indicate that microglia, beyond the tumor cells, contribute to the observed response of DIPG to EZH2 inhibition. Results highlight the potential importance of microglia as a new therapeutic avenue in DIPG.
弥漫性脑桥内在型胶质瘤（DIPG）属于弥漫性中线胶质瘤，是一种侵袭性儿童脑肿瘤，其特征为组蛋白H3-K27M突变。尽管EZH2-H3K27组蛋白甲基转移酶的小分子抑制剂对DIPG细胞几乎没有作用，但在DIPG临床前动物模型中已显示出前景。因此，我们推测EZH2抑制作用可能是通过靶向肿瘤相关小胶质细胞中的这种组蛋白修饰酶来介导的。
使用原发性DIPG组织，以及小胶质细胞与患者来源的DIPG或儿童高级别胶质瘤（pHGG）细胞系之间的共培养物，来确定每种细胞类型的H3-K27M状态。采用反义RNA策略靶向小胶质细胞和胶质瘤细胞中的基因表达。通过基因表达谱、肿瘤细胞侵袭能力、小胶质细胞吞噬活性和相关肿瘤细胞死亡来评估小胶质细胞的抗肿瘤特性。
在原发性DIPG组织中，小胶质细胞不携带H3-K27M突变，而这是癌细胞的特征。pHGG激活小胶质细胞的肿瘤支持表型，与其H3-K27M状态无关，这与H3K27me3的短暂下调有关。DIPG细胞中EZH2的抑制对肿瘤细胞存活或其激活小胶质细胞的能力没有影响。然而，小胶质细胞中EZH2的抑制会诱导抗肿瘤表型，导致癌细胞侵袭能力降低、小胶质细胞吞噬作用增强和肿瘤相关细胞死亡。
这些结果表明，小胶质细胞而非肿瘤细胞，促成了观察到的DIPG对EZH2抑制的反应。结果突出了小胶质细胞作为DIPG新治疗途径的潜在重要性。
