Department of Neurosurgery, University of Texas Health Science Center at Houston, Houston, Texas, USA.
Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
Neuro Oncol. 2021 Sep 1;23(9):1481-1493. doi: 10.1093/neuonc/noab014.
Despite multi-model therapy of maximal surgical resection, radiation, chemotherapy, and tumor-treating fields, the median survival of glioblastoma (GBM) patients is less than 15 months. Protein arginine methyltransferase 5 (PRMT5) catalyzes the symmetric dimethylation of arginine residues and is overexpressed in GBM. Inhibition of PRMT5 causes senescence in stem-like GBM tumor cells. LB100, a first-in-class small molecular inhibitor of protein phosphatase 2A (PP2A), can sensitize therapy-resistant tumor cells. Here, we tested the anti-GBM effect of concurrent PRMT5 and PP2A inhibition.
Patient-derived primary GBM neurospheres (GBMNS), transfected with PRMT5 target-specific siRNA, were treated with LB100 and subjected to in vitro assays including PP2A activity and western blot. The intracranial mouse xenograft model was used to test the in vivo antitumor efficacy of combination treatment.
We found that PRMT5 depletion increased PP2A activity in GBMNS. LB100 treatment significantly reduced the viability of PRMT5-depleted GBMNS compared to PRMT5-intact GBMNS. LB100 enhanced G1 cell cycle arrest induced by PRMT5 depletion. Combination therapy also increased the expression of phospho-MLKL. Necrostatin-1 rescued PRMT5-depleted cells from the cytotoxic effects of LB100, indicating that necroptosis caused the enhanced cytotoxicity of combination therapy. In the in vivo mouse tumor xenograft model, LB100 treatment combined with transient depletion of PRMT5 significantly decreased tumor size and prolonged survival, while LB100 treatment alone had no survival benefit.
Overall, combined PRMT5 and PP2A inhibition had significantly greater antitumor effects than PRMT5 inhibition alone.
尽管采用了最大程度的手术切除、放疗、化疗和肿瘤治疗电场等多模式治疗，胶质母细胞瘤（GBM）患者的中位生存期仍不足 15 个月。蛋白精氨酸甲基转移酶 5（PRMT5）催化精氨酸残基的对称二甲基化，在 GBM 中过度表达。抑制 PRMT5 会导致干细胞样 GBM 肿瘤细胞衰老。LB100 是一种首创的蛋白磷酸酶 2A（PP2A）小分子抑制剂，能够使耐药肿瘤细胞对治疗敏感。在此，我们检测了同时抑制 PRMT5 和 PP2A 的抗 GBM 效果。
用 PRMT5 靶向特异性 siRNA 转染的患者来源的原发性 GBM 神经球（GBMNS），用 LB100 处理并进行体外检测，包括 PP2A 活性和 Western blot。使用颅内小鼠异种移植模型检测联合治疗的体内抗肿瘤疗效。
我们发现 PRMT5 耗竭增加了 GBMNS 中的 PP2A 活性。与 PRMT5 完整的 GBMNS 相比，LB100 处理显著降低了 PRMT5 耗竭的 GBMNS 的活力。LB100 增强了 PRMT5 耗竭诱导的 G1 细胞周期停滞。联合治疗还增加了磷酸化 MLKL 的表达。坏死抑制剂-1 挽救了 LB100 耗竭的细胞免受细胞毒性的影响，表明坏死引起了联合治疗的增强细胞毒性。在体内小鼠肿瘤异种移植模型中，LB100 治疗联合 PRMT5 短暂耗竭显著减小肿瘤体积并延长生存期，而 LB100 单独治疗则没有生存获益。
总的来说，联合 PRMT5 和 PP2A 抑制的抗肿瘤效果明显强于单独抑制 PRMT5。
