BCL6 mediates Chemoresistance in Acute Myeloid Leukemia. BCL6 mediates Chemoresistance in Acute Myeloid Leukemia

BCL6 is a transcription repressor that plays a crucial role in germinal center formation and lymphomagenesis. However, its role in myeloid malignancies remains unclear. Here, we explored the role of BCL6 in acute myeloid leukemia (AML). Heterogeneous levels of BCL6 were found across AML cell lines and primary AML samples. Cells with higher levels of BCL6 were indeed sensitive to treatment with BCL6 inhibitors. Gene expression profiling of AML cells treated with BCL6 inhibitor revealed a subset of target genes that are common with lymphoma cells. Ex vivo treatment of primary AML cells with BCL6 peptide inhibitor (BPI) induced apoptosis and decrease colony forming capacity which correlated with the levels of BCL6 expression . Importantly, inhibition of BCL6 in primary AML cells with either BPI or BCL6 siRNA resulted in significant reduction of leukemia initiating capacity using immunodeficient mice, suggesting ablation of leukemia stem cells (LSC). Such anti-LSC activity was also observed as downregulation of LSC gene signatures using gene expression analyses of cells treated with a BCL6 inhibitor. Importantly, treatment with cytarabine (AraC) induced BCL6 expression, and the levels of BCL6 induction were correlated with resistance to AraC. Treatment of AML primary derived xenografts (PDX) revealed that when AraC was combined with BCL6 inhibitor, inhibition of BCL6 significantly potentiated the efficacy of AraC and improved cytotoxic effects by interfering with the leukemia initiating capacity of AML cells. This suggests that pharmacological inhibition of BCL6 might provide a novel therapeutic strategy for ablation of LSCs and overcome chemoresistance in AML. Overall design: Nine samples total: AML37 primary cell (three experimental replicates) treated with FX1, DMSO, and untreated for 12 hours after CD34 positive selection using FACS. Cells were treated for 12 hours using EC50 concentration for the same primary cell.

BCL6是一种转录抑制因子（transcription repressor），在生发中心形成与淋巴瘤发生过程中发挥关键作用。然而其在髓系恶性肿瘤中的作用仍未明确。本研究探究了BCL6在急性髓系白血病（acute myeloid leukemia, AML）中的作用。研究发现，不同AML细胞系及原代AML样本中，BCL6的表达水平存在异质性。BCL6高表达的细胞确实对BCL6抑制剂治疗敏感。对经BCL6抑制剂处理的AML细胞进行基因表达谱分析，可发现一组与淋巴瘤细胞共有的靶基因。采用BCL6肽类抑制剂（BCL6 peptide inhibitor, BPI）对原代AML细胞进行离体处理，可诱导细胞凋亡并降低其集落形成能力，该效应与BCL6的表达水平相关。值得注意的是，采用BPI或BCL6小干扰RNA（small interfering RNA, siRNA）抑制原代AML细胞中的BCL6后，通过免疫缺陷小鼠实验证实，白血病起始能力显著降低，提示可清除白血病干细胞（leukemia stem cells, LSC）。通过对BCL6抑制剂处理后的细胞进行基因表达分析，发现LSC基因特征表达下调，同样可观察到上述抗LSC活性。重要的是，阿糖胞苷（cytarabine, AraC）处理可诱导BCL6表达，且BCL6的诱导水平与AraC耐药性呈正相关。对AML患者来源移植瘤（patient-derived xenografts, PDX）模型的处理实验显示，当AraC与BCL6抑制剂联合使用时，抑制BCL6可显著增强AraC的疗效，并通过干扰AML细胞的白血病起始能力提升细胞毒效应。上述结果表明，通过药理学手段抑制BCL6或许可为清除AML中的LSC提供全新的治疗策略，并克服AML的化疗耐药性。总体实验设计：共包含9份样本：经荧光激活细胞分选（fluorescence-activated cell sorting, FACS）纯化CD34阳性的AML37原代细胞（3次实验重复），分别经FX1、二甲基亚砜（dimethyl sulfoxide, DMSO）处理及设置未处理组，处理时长为12小时；采用对应该原代细胞的半数最大效应浓度（half maximal effective concentration, EC50）处理细胞12小时。