Department of Neurosurgery, Kumamoto University Hospital, 1-1-1 Honjo Chuo-ku, Kumamoto, 860-8556, Japan.
School of Medicine, Kumamoto University, Kumamoto, Japan.
Acta Neuropathol Commun. 2018 Feb 23;6(1):15. doi: 10.1186/s40478-018-0522-4.
The therapeutic response to high-dose methotrexate (HD-MTX) therapy for primary central nervous system lymphoma (PCNSL) varies. Polyglutamylation is a reversible protein modification with a high occurrence rate in tumor cells. MTX incorporated into cells is polyglutamylated and strongly binds to dihydrofolate reductase without competitive inhibition by leucovorin (LV). Tumor cells with high polyglutamylation levels are selectively killed, whereas normal cells with lower polyglutamylation are rescued by LV. We hypothesized that the extent of polyglutamylation in tumor cells determines treatment resistance. Here, we investigated the therapeutic response of PCNSL to HD-MTX therapy with LV rescue based on polyglutamylation status. Among 113 consecutive PCNSL patients who underwent HD-MTX therapy in our department between 2001 and 2014, polyglutamylation was evaluated by immunostaining in 82 cases, with relationships between polyglutamylation and therapeutic response retrospectively examined. Human malignant lymphoma lines were used for in vitro experiments, and folpolyglutamate synthetase (FPGS), which induces polyglutamylation, was knocked down with short-hairpin RNA, and a stable cell line with a low rate of polyglutamylation was established. Cell viability after MTX treatment with LV rescue was evaluated using sodium butyrate (NaBu), a histone-deacetylase inhibitor that induces polyglutamylation by elevating FPGS expression. The complete response rate was significantly higher in the group with polyglutamylation than in the non-polyglutamylation group [58.1% (25/43) and 33.3% (13/39), respectively] (p < 0.05), and progression-free survival was also significantly increased in the group with polyglutamylation (p < 0.01). In vitro, the relief effect of LV after MTX administration was significantly enhanced after FPGS knockdown in al cell lines, whereas enhancement of FPGS expression by NaBu treatment significantly reduced this relief effect. These findings suggested that polyglutamylation could be a predictor of therapeutic response to HD-MTX therapy with LV rescue in PCNSL. Combination therapy with HD-MTX and polyglutamylation-inducing agents might represent a promising strategy for PCNSL treatment.
原发性中枢神经系统淋巴瘤（PCNSL）患者接受大剂量甲氨蝶呤（HD-MTX）治疗的疗效存在差异。多聚谷氨酸化是一种具有高发生率的可逆蛋白修饰，肿瘤细胞中多聚谷氨酸化发生率很高。细胞内的 MTX 被多聚谷氨酸化，并与二氢叶酸还原酶结合，而不受甲酰四氢叶酸（LV）的竞争性抑制。具有高多聚谷氨酸化水平的肿瘤细胞被选择性杀死，而多聚谷氨酸化水平较低的正常细胞则被 LV 挽救。我们假设肿瘤细胞的多聚谷氨酸化程度决定了治疗的耐药性。在这里，我们根据多聚谷氨酸化状态研究了 PCNSL 患者接受 HD-MTX 联合 LV 解救治疗的疗效。在 2001 年至 2014 年间在我科接受 HD-MTX 治疗的 113 例连续 PCNSL 患者中，82 例通过免疫组化评估了多聚谷氨酸化，回顾性分析了多聚谷氨酸化与治疗反应之间的关系。使用人类恶性淋巴瘤细胞系进行体外实验，用短发夹 RNA 敲低 folpolyglutamate 合酶（FPGS），建立多聚谷氨酸化水平较低的稳定细胞系。用丁酸钠（NaBu）评估 LV 解救后 MTX 治疗的细胞活力，NaBu 通过提高 FPGS 表达诱导多聚谷氨酸化。多聚谷氨酸化组的完全缓解率显著高于非多聚谷氨酸化组[58.1%（25/43）和 33.3%（13/39）]（p<0.05），多聚谷氨酸化组的无进展生存期也显著延长（p<0.01）。在体外，FPGS 敲低后，所有细胞系中 MTX 给药后 LV 的缓解作用明显增强，而 NaBu 处理增强 FPGS 表达则显著降低了这种缓解作用。这些发现表明，多聚谷氨酸化可能是预测 PCNSL 患者接受 HD-MTX 联合 LV 解救治疗疗效的指标。HD-MTX 联合多聚谷氨酸化诱导剂的联合治疗可能是 PCNSL 治疗的一种有前途的策略。
