Background: Dihydroorotate Dehydrogenase (DHODH) is a key enzyme of the de novo pyrimidine biosynthesis, whose inhibition was recently found to induce differentiation and apoptosis in acute myeloid leukemia (AML). DHODH inhibitors were previously investigated in solid tumors, where they showed promising antiproliferative activity, both in vitro and in vivo. However, their effectiveness was not confirmed in clinical trials, probably due to the pyrimidine salvage pathway that cancer cells could exploit to survive. In this study we investigated the pro-apoptotic activity of MEDS433, the DHODH inhibitor developed by our group, against AML. Learning from previous failures, we challenged our model mimicking in vivo conditions, and looked for synergic combination to boost apoptosis. Methods: We evaluated the apoptotic rate of multiple AML cell lines and AML primary cells treated with MEDS433 or other DHODH inhibitors, alone and in combination with classical antileukemic drugs or with dipyridamole, a blocker of the pyrimidine salvage pathway. Experiments were also performed mimicking in vivo conditions, i.e., in the presence of physiological uridine plasma levels (5 μM). Results: MEDS433 showed a strong apoptotic effect against multiple AML cell lines, which was at least partially independent from the differentiation process. Its combination with classical antileukemic agents resulted in a further increase of the apoptotic rate. However, when MEDS433 was tested in the presence of 5 μM uridine and/or in primary AML cells, results were less impressive. On the contrary, the combination of MEDS433 with dipyridamole resulted in an outstanding synergistic effect, with a dramatic increase of the apoptotic rate both in AML cell lines and AML primary cells, which was unaffected by physiological uridine concentrations. Preliminary analyses show that the toxicity of this treatment should be limited to proliferating cells. Conclusions: The combination of a DHODH inhibitor and dipyridamole is characterized by differentiating and pro-apoptotic features and induces metabolic lethality on a wide variety of AMLs with different genetic backgrounds.

中文翻译：

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DHODH抑制剂与双嘧达莫之间的协同作用导致急性髓样白血病的代谢致死性。

背景：二氢乳清酸脱氢酶（DHODH）是从头进行嘧啶生物合成的关键酶，最近发现其抑制作用可诱导急性髓样白血病（AML）分化和凋亡。以前曾在实体瘤中研究过DHODH抑制剂，在体外和体内，它们均显示出有希望的抗增殖活性。但是，它们的有效性在临床试验中尚未得到证实，这可能是由于嘧啶的挽救途径可以使癌细胞得以存活。在这项研究中，我们研究了我们小组开发的DHODH抑制剂MEDS433对AML的促凋亡活性。从先前的失败中吸取教训，我们挑战了模仿体内条件的模型，并寻找协同组合来增强细胞凋亡。方法：我们评估了单独或与经典抗白血病药物或与嘧啶挽救途径的阻断剂双嘧达莫联合使用MEDS433或其他DHODH抑制剂治疗的多种AML细胞系和AML原代细胞的凋亡率。还模拟了体内条件，即在生理尿苷血浆水平（5μM）存在下进行了实验。结果：MEDS433对多种AML细胞株显示出强凋亡作用，至少部分独立于分化过程。它与经典抗白血病药物的组合导致凋亡率进一步提高。但是，当在5μM尿苷存在下和/或在原代AML细胞中测试MEDS433时，结果不那么令人印象深刻。反之，MEDS433与双嘧达莫的组合产生了显着的协同作用，AML细胞系和AML原代细胞的凋亡率均显着增加，不受生理尿苷浓度的影响。初步分析表明，这种治疗方法的毒性应限于增殖细胞。结论：DHODH抑制剂和双嘧达莫的组合具有分化和促凋亡的特征，并在具有不同遗传背景的多种AML中诱导代谢致死性。