Departments of Hematology and Experimental Immunology, and Cell Biology and Histology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Clin Cancer Res. 2012 Jan 15;18(2):487-98. doi: 10.1158/1078-0432.CCR-11-1440. Epub 2011 Nov 29.
Chronic lymphocytic leukemia (CLL) cells in lymph nodes (LN), from which relapses are postulated to originate, display an antiapoptotic profile in contrast to CLL cells from peripheral blood (PB). The BH3 mimetic ABT-737 antagonizes the antiapoptotic proteins Bcl-X(L) and Bcl-2 but not Mcl-1 or Bfl-1. Previously, it was shown that CD40-stimulated CLL cells were resistant to ABT-737. We aimed to define which antiapoptotic proteins determine resistance to ABT-737 in CLL and whether combination of known antileukemia drugs and ABT-737 was able to induce apoptosis of CD40-stimulated CLL cells.
To mimic the LN microenvironment, PB lymphocytes of CLL patients were cultured on feeder cells expressing CD40L and treated with ABT-737 with or without various drugs. In addition, we carried out overexpression or knockdown of pro- and antiapoptotic proteins in immortalized primary B cells.
Upon CD40 stimulation patient-specific variations in ABT-737 sensitivity correlated with differences in levels of Mcl-1 and its antagonist Noxa. Knockdown of Noxa, as well as Mcl-1 overexpression, corroborated the importance of the Noxa/Mcl-1 ratio in determining the response to ABT-737. Inhibition of NF-κB resulted in increased Noxa levels and enhanced sensitivity to ABT-737. Interestingly, increasing the Noxa/Mcl-1 ratio, by decreasing Mcl-1 (dasatinib and roscovitine) or increasing Noxa levels (fludarabine and bortezomib), resulted in synergy with ABT-737.
Thus, the Noxa/Mcl-1 balance determines sensitivity to ABT-737 in CD40-stimulated CLL cells. These data provide a rationale to investigate the combination of drugs which enhance the Noxa/Mcl-1 balance with ABT-737 to eradicate CLL in chemoresistant niches.
与外周血（PB）中的 CLL 细胞相比，淋巴结（LN）中的 CLL 细胞显示出抗凋亡特征，据推测复发是由此起源的。BH3 模拟物 ABT-737 拮抗抗凋亡蛋白 Bcl-X(L)和 Bcl-2，但不拮抗 Mcl-1 或 Bfl-1。此前已表明，CD40 刺激的 CLL 细胞对 ABT-737 具有抗性。我们旨在确定哪些抗凋亡蛋白决定了 CLL 对 ABT-737 的抗性，以及是否可以将已知的抗白血病药物与 ABT-737 联合使用来诱导 CD40 刺激的 CLL 细胞凋亡。
为了模拟 LN 微环境，将 CLL 患者的 PB 淋巴细胞在表达 CD40L 的饲养细胞上培养，并在有或没有各种药物的情况下用 ABT-737 处理。此外，我们在永生化原代 B 细胞中过表达或敲低促凋亡和抗凋亡蛋白。
在 CD40 刺激下，患者对 ABT-737 的敏感性存在个体差异，这与 Mcl-1 及其拮抗剂 Noxa 的水平差异有关。Noxa 的敲低以及 Mcl-1 的过表达证实了 Noxa/Mcl-1 比值在决定对 ABT-737 的反应中的重要性。抑制 NF-κB 导致 Noxa 水平升高，并增强对 ABT-737 的敏感性。有趣的是，通过降低 Mcl-1（达沙替尼和罗西维林）或增加 Noxa 水平（氟达拉滨和硼替佐米）来增加 Noxa/Mcl-1 比值，与 ABT-737 产生协同作用。
因此，Noxa/Mcl-1 平衡决定了 CD40 刺激的 CLL 细胞对 ABT-737 的敏感性。这些数据为研究增强 Noxa/Mcl-1 平衡与 ABT-737 联合使用以根除化学耐药性龛中的 CLL 的药物组合提供了依据。
