Division of Stem Cell and Molecular Medicine, Center for Stem Cell Biology and Regenerative Medicine, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.
Department of Endocrinology, Hematology and Gerontology, Chiba University Graduate School of Medicine, Chiba, Japan.
Blood Adv. 2021 Jan 26;5(2):438-450. doi: 10.1182/bloodadvances.2020001461.
Dihydroorotate dehydrogenase (DHODH) catalyzes a rate-limiting step in de novo pyrimidine nucleotide synthesis. DHODH inhibition has recently been recognized as a potential new approach for treating acute myeloid leukemia (AML) by inducing differentiation. We investigated the efficacy of PTC299, a novel DHODH inhibitor, for myelodysplastic syndrome (MDS). PTC299 inhibited the proliferation of MDS cell lines, and this was rescued by exogenous uridine, which bypasses de novo pyrimidine synthesis. In contrast to AML cells, PTC299 was inefficient at inhibiting growth and inducing the differentiation of MDS cells, but synergized with hypomethylating agents, such as decitabine, to inhibit the growth of MDS cells. This synergistic effect was confirmed in primary MDS samples. As a single agent, PTC299 prolonged the survival of mice in xenograft models using MDS cell lines, and was more potent in combination with decitabine. Mechanistically, a treatment with PTC299 induced intra-S-phase arrest followed by apoptotic cell death. Of interest, PTC299 enhanced the incorporation of decitabine, an analog of cytidine, into DNA by inhibiting pyrimidine production, thereby enhancing the cytotoxic effects of decitabine. RNA-seq data revealed the marked downregulation of MYC target gene sets with PTC299 exposure. Transfection of MDS cell lines with MYC largely attenuated the growth inhibitory effects of PTC299, suggesting MYC as one of the major targets of PTC299. Our results indicate that the DHODH inhibitor PTC299 suppresses the growth of MDS cells and acts in a synergistic manner with decitabine. This combination therapy may be a new therapeutic option for the treatment of MDS.
二氢乳清酸脱氢酶（DHODH）催化从头合成嘧啶核苷酸合成的限速步骤。DHODH 抑制已被最近被认为是通过诱导分化治疗急性髓系白血病（AML）的一种潜在的新方法。我们研究了新型 DHODH 抑制剂 PTC299 对骨髓增生异常综合征（MDS）的疗效。PTC299 抑制 MDS 细胞系的增殖，这可被外源性尿嘧啶挽救，尿嘧啶绕过从头嘧啶合成。与 AML 细胞不同，PTC299 不能有效地抑制 MDS 细胞的生长和诱导分化，但与低甲基化剂（如地西他滨）协同抑制 MDS 细胞的生长。这一协同作用在原发性 MDS 样本中得到了证实。作为单一药物，PTC299 在使用 MDS 细胞系的异种移植模型中延长了小鼠的存活时间，并且与地西他滨联合使用更为有效。在机制上，PTC299 诱导细胞内 S 期停滞，随后发生细胞凋亡。有趣的是，PTC299 通过抑制嘧啶合成，增强了胞嘧啶类似物地西他滨掺入 DNA 的作用，从而增强了地西他滨的细胞毒性作用。RNA-seq 数据显示，PTC299 暴露后 MYC 靶基因集明显下调。MDS 细胞系中转染 MYC 可显著减弱 PTC299 的生长抑制作用，表明 MYC 是 PTC299 的主要靶点之一。我们的研究结果表明，DHODH 抑制剂 PTC299 抑制 MDS 细胞的生长，并与地西他滨协同作用。这种联合治疗可能是治疗 MDS 的一种新的治疗选择。
