DZNep-mediated apoptosis in B-cell lymphoma is independent of the lymphoma type, EZH2 mutation status and MYC, BCL2 or BCL6 translocations

Enhancer of zeste homolog 2 (EZH2) tri-methylates histone 3 at position lysine 27 (H3K27me3). Overexpression and gain-of-function mutations in EZH2 are regarded as oncogenic drivers in lymphoma and other malignancies due to the silencing of tumor suppressors and differentiation genes. EZH2 inhibition is sought to represent a good strategy for tumor therapy. In this study, we treated Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) cell lines with 3-deazaneplanocin—A (DZNep), an indirect EZH2 inhibitor which possesses anticancer properties both in-vitro and in-vivo. We aimed to address the impact of the lymphoma type, EZH2 mutation status, as well as MYC, BCL2 and BCL6 translocations on the sensitivity of the lymphoma cell lines to DZNep-mediated apoptosis. We show that DZNep inhibits proliferation and induces apoptosis of these cell lines independent of the type of lymphoma, the EZH2 mutation status and the MYC, BCL2 and BCL6 rearrangement status. Furthermore, DZNep induced a much stronger apoptosis in majority of these cell lines at a lower concentration, and within a shorter period when compared with EPZ-6438, a direct EZH2 inhibitor currently in phase II clinical trials. Apoptosis induction by DZNep was both concentration-dependent and time-dependent, and was associated with the inhibition of EZH2 and subsequent downregulation of H3K27me3 in DZNep-sensitive cell lines. Although EZH2, MYC, BCL2 and BCL6 are important prognostic biomarkers for lymphomas, our study shows that they poorly influence the sensitivity of lymphoma cell lines to DZNep-mediated apoptosis.

zeste基因增强子同源物2（Enhancer of zeste homolog 2, EZH2）可对组蛋白H3第27位赖氨酸进行三甲基化修饰（H3K27me3）。EZH2的过表达与功能获得性突变，会通过沉默肿瘤抑制基因及分化相关基因，被视为淋巴瘤及其他恶性肿瘤的致癌驱动因素。靶向抑制EZH2被视作肿瘤治疗的良好策略。本研究采用间接EZH2抑制剂3-脱氮腺苷（3-deazaneplanocin—A, DZNep）处理伯基特淋巴瘤（Burkitt lymphoma, BL）与弥漫大B细胞淋巴瘤（diffuse large B-cell lymphoma, DLBCL）细胞系，该抑制剂在体外与体内均展现出抗癌活性。本研究旨在探讨淋巴瘤类型、EZH2突变状态，以及MYC、BCL2与BCL6基因易位对淋巴瘤细胞系对DZNep诱导细胞凋亡敏感性的影响。研究结果显示，DZNep可抑制上述细胞系的增殖并诱导其凋亡，且该效应不受淋巴瘤类型、EZH2突变状态，以及MYC、BCL2与BCL6基因重排状态的影响。此外，与目前处于Ⅱ期临床试验的直接EZH2抑制剂EPZ-6438相比，DZNep在更低浓度、更短时间内即可诱导多数细胞系发生更为显著的细胞凋亡。DZNep诱导的细胞凋亡兼具浓度依赖性与时间依赖性，且在DZNep敏感细胞系中，该效应与EZH2的抑制及后续H3K27me3的表达下调密切相关。尽管EZH2、MYC、BCL2及BCL6均为淋巴瘤重要的预后生物标志物，但本研究表明，上述因素对淋巴瘤细胞系的DZNep诱导细胞凋亡敏感性影响微弱。