Department of Experimental Immunology, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, The Netherlands.
Lymphoma and Myeloma Center Amsterdam (LYMMCARE), Amsterdam, The Netherlands.
Blood. 2020 Dec 17;136(25):2918-2926. doi: 10.1182/blood.2019004326.
Chronic lymphocytic leukemia (CLL) cells cycle between lymph node (LN) and peripheral blood (PB) and display major shifts in Bcl-2 family members between those compartments. Specifically, Bcl-XL and Mcl-1, which are not targeted by the Bcl-2 inhibitor venetoclax, are increased in the LN. Because ibrutinib forces CLL cells out of the LN, we hypothesized that ibrutinib may thereby affect expression of Bcl-XL and Mcl-1 and sensitize CLL cells to venetoclax. We investigated expression of Bcl-2 family members in patients under ibrutinib or venetoclax treatment, combined with dissecting functional interactions of Bcl-2 family members, in an in vitro model of venetoclax resistance. In the PB, recent LN emigrants had higher Bcl-XL and Mcl-1 expression than did cells immigrating back to the LN. Under ibrutinib treatment, this distinction collapsed; significantly, the pretreatment profile reappeared in patients who relapsed on ibrutinib. However, in response to venetoclax, Bcl-2 members displayed an early increase, underlining the different modes of action of these 2 drugs. Profiling by BH3 mimetics was performed in CLL cells fully resistant to venetoclax due to CD40-mediated induction of Bcl-XL, Mcl-1, and Bfl-1. Several dual or triple combinations of BH3 mimetics were highly synergistic in restoring killing of CLL cells. Lastly, we demonstrated that proapoptotic Bim interacts with antiapoptotic Bcl-2 members in a sequential manner: Bcl-2 > Bcl-XL > Mcl-1 > Bfl-1. Combined, the data indicate that Bcl-XL is more important in venetoclax resistance than is Mcl-1 and provide biological rationale for potential synergy between ibrutinib and venetoclax.
慢性淋巴细胞白血病（CLL）细胞在淋巴结（LN）和外周血（PB）之间循环，并在这些隔室之间显示 Bcl-2 家族成员的主要变化。具体来说，Bcl-XL 和 Mcl-1 不被 Bcl-2 抑制剂 venetoclax 靶向，在 LN 中增加。由于 ibrutinib 迫使 CLL 细胞离开 LN，我们假设 ibrutinib 可能因此影响 Bcl-XL 和 Mcl-1 的表达，并使 CLL 细胞对 venetoclax 敏感。我们研究了接受 ibrutinib 或 venetoclax 治疗的患者的 Bcl-2 家族成员的表达，同时在 venetoclax 耐药的体外模型中剖析了 Bcl-2 家族成员的功能相互作用。在 PB 中，最近从 LN 迁出的细胞比返回 LN 的细胞具有更高的 Bcl-XL 和 Mcl-1 表达。在 ibrutinib 治疗下，这种区别消失了；重要的是，在对 ibrutinib 复发的患者中，预处理谱再次出现。然而，对 venetoclax 的反应，Bcl-2 成员显示出早期增加，突出了这两种药物的不同作用模式。在由于 CD40 介导的 Bcl-XL、Mcl-1 和 Bfl-1 诱导而对 venetoclax 完全耐药的 CLL 细胞中进行 BH3 模拟物分析。几种 BH3 模拟物的双重或三重组合在恢复杀伤 CLL 细胞方面具有高度协同作用。最后，我们证明了促凋亡 Bim 以顺序方式与抗凋亡 Bcl-2 成员相互作用：Bcl-2 > Bcl-XL > Mcl-1 > Bfl-1。综合来看，这些数据表明 Bcl-XL 在 venetoclax 耐药中比 Mcl-1 更重要，并为 ibrutinib 和 venetoclax 之间可能的协同作用提供了生物学依据。
