H3K27-altered Diffuse Midline Glioma (DMG) is a universally fatal paediatric brainstem tumour. The prevalent driver mutation H3K27M creates a unique epigenetic landscape that may also establish therapeutic vulnerabilities to epigenetic inhibitors. However, while HDAC, EZH2 and BET inhibitors have proven somewhat effective in pre-clinical models, none have translated into clinical benefit due to either poor blood–brain barrier penetration, lack of efficacy or toxicity. Thus, there remains an urgent need for new DMG treatments. Here, we performed wider screening of an epigenetic inhibitor library and identified inhibitors of protein arginine methyltransferases (PRMTs) among the top hits reducing DMG cell viability. Two of the most effective inhibitors, LLY-283 and GSK591, were targeted against PRMT5 using distinct binding mechanisms and reduced the viability of a subset of DMG cells expressing wild-type TP53 and mutant ACVR1. RNA-sequencing and phenotypic analyses revealed that LLY-283 could reduce the viability, clonogenicity and invasion of DMG cells in vitro, representing three clinically important phenotypes, but failed to prolong survival in an orthotopic xenograft model. Together, these data show the challenges of DMG treatment and highlight PRMT5 inhibitors for consideration in future studies of combination treatments.

H3K27 突变的弥漫性中线胶质瘤 （DMG） 是一种普遍致命的小儿脑干肿瘤。普遍的驱动突变 H3K27M 创造了一种独特的表观遗传学景观，也可能建立对表观遗传学抑制剂的治疗脆弱性。然而，虽然 HDAC、EZH2 和 BET 抑制剂在临床前模型中被证明具有一定的效果，但由于血脑屏障渗透性差、缺乏疗效或毒性，没有一种药物能转化为临床益处。因此，仍然迫切需要新的 DMG 治疗方法。在这里，我们对表观遗传学抑制剂库进行了更广泛的筛选，并在降低 DMG 细胞活力的热门命中中确定了蛋白精氨酸甲基转移酶 （PRMT） 的抑制剂。两种最有效的抑制剂 LLY-283 和 GSK591 使用不同的结合机制靶向 PRMT5，并降低了表达野生型 TP53 和突变型 ACVR1 的 DMG 细胞亚群的活力。RNA 测序和表型分析显示，LLY-283 可以在体外降低 DMG 细胞的活力、克隆形成性和侵袭性，代表 3 种临床重要表型，但未能延长原位异种移植模型的存活时间。总之，这些数据显示了 DMG 治疗的挑战，并突出了 PRMT5 抑制剂，供未来联合治疗研究考虑。