低剂量阿糖胞苷（LDAC）是不适合强化化疗的老年急性髓系白血病（AML）患者的标准疗法。虽然高剂量的阿糖胞苷会引起细胞毒性，但 LDAC 在 AML 中的精确作用机制仍不清楚。体外研究已证明 LDAC 诱导分化；然而，这种分化在体内很少观察到。我们假设这种差异可能归因于骨髓 (BM) 基质细胞对 AML 细胞的影响。因此，本研究旨在探讨 BM 基质细胞对 LDAC 诱导的 AML 细胞系和原代样本分化的影响。我们的结果表明，MS-5 基质细胞的存在阻止了 LDAC 诱导的细胞周期停滞、DNA 损伤信号传导以及 U937 和 MOLM-13 细胞系的分化。尽管转录组分析显示基质减少了参与细胞因子信号传导和氧化应激的基因表达，但用药理学抑制剂和中和抗体获得的数据并不支持 CXCL12、TGF-β1 或活性氧的作用。基质细胞的存在减少了 AML-M4 和骨髓增生异常综合征/AML 患者原始样本中 LDAC 诱导的分化。总之，我们的研究表明 BM 基质可减少 LDAC 诱导的 AML 分化。这些发现深入了解了 AML 患者中观察到的终末分化的有限发生，并为这一观察结果提出了可能的解释。版权所有 © 2023 Smoljo、Tomic、Lalic、Dembitz、Batinic、Bedalov 和 Visnjic。

Low-dose cytarabine (LDAC) is a standard therapy for elderly acute myeloid leukemia (AML) patients unfit for intensive chemotherapy. While high doses of cytarabine induce cytotoxicity, the precise mechanism of action of LDAC in AML remains elusive. In vitro studies have demonstrated LDAC-induced differentiation; however, such differentiation is seldom observed in vivo. We hypothesize that this discrepancy may be attributed to the influence of bone marrow (BM) stromal cells on AML cells. Thus, this study aimed to investigate the impact of BM stromal cells on LDAC-induced differentiation of AML cell lines and primary samples. Our results demonstrate that the presence of MS-5 stromal cells prevented LDAC-induced cell cycle arrest, DNA damage signaling and differentiation of U937 and MOLM-13 cell lines. Although transcriptomic analysis revealed that the stroma reduces the expression of genes involved in cytokine signaling and oxidative stress, data obtained with pharmacological inhibitors and neutralizing antibodies did not support the role for CXCL12, TGF-β1 or reactive oxygen species. The presence of stromal cells reduces LDAC-induced differentiation in primary samples from AML-M4 and myelodysplastic syndrome/AML patients. In conclusion, our study demonstrates that BM stroma reduces differentiation of AML induced by LDAC. These findings provide insights into the limited occurrence of terminal differentiation observed in AML patients, and suggest a potential explanation for this observation.Copyright © 2023 Smoljo, Tomic, Lalic, Dembitz, Batinic, Bedalov and Visnjic.