Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
Leukemia. 2022 Jul;36(7):1806-1817. doi: 10.1038/s41375-022-01595-0. Epub 2022 May 14.
Idelalisib targets PI3Kδ in the BCR pathway generating only a partial response in CLL patients, indicating that the leukemic cells may have evolved escape signals. Indeed, we detected increased activation of AKT accompanied by upregulation of MYC/BCL2 in post-therapy CLL cells from patients treated with idelalisib/ofatumumab. To unravel the mechanism of increased AKT-activation, we studied the impact of idelalisib on a CLL-derived cell line, MEC1, as a model. After an initial inhibition, AKT-activation level was restored in idelalisib-treated MEC1 cells in a time-dependent manner. As BCAP (B-cell adaptor for PI3K) and CD19 recruit PI3Kδ to activate AKT upon BCR-stimulation, we examined if idelalisib-treatment altered PI3Kδ-recruitment. Immunoprecipitation of BCAP/CD19 from idelalisib-treated MEC1 cells showed increased recruitment of PI3Kδ in association with PI3Kβ, but not PI3Kα or PI3Kγ and that, targeting both PI3Kδ with PI3Kβ inhibited AKT-reactivation. We detected similar, patient-specific recruitment pattern of PI3K-isoforms by BCAP/CD19 in post-idelalisib CLL cells with increased AKT-activation. Interestingly, a stronger inhibitory effect of idelalisib on P-AKT (T308) than S473 was discernible in idelalisib-treated cells despite increased recruitment of PI3Kδ/PI3Kβ and accumulation of phosphatidylinositol-3,4,5-triphosphate; which could be attributed to reduced PDK1 activity. Thus, administration of isoform-specific inhibitors may prove more effective strategy for treating CLL patients.
依鲁替尼靶向 B 细胞受体（BCR）通路中的 PI3Kδ，仅能使部分 CLL 患者产生部分缓解，这表明白血病细胞可能已经进化出逃逸信号。事实上，我们在接受依鲁替尼/奥法木单抗治疗的患者的治疗后 CLL 细胞中检测到 AKT 的活性增加，同时 MYC/BCL2 的表达上调。为了揭示 AKT 激活增加的机制，我们以 CLL 来源的细胞系 MEC1 作为模型研究了依鲁替尼的影响。在最初的抑制后，依鲁替尼处理的 MEC1 细胞中的 AKT 激活水平在时间依赖性方式下得以恢复。由于 BCAP（PI3K 的 B 细胞衔接子）和 CD19 在 BCR 刺激时将 PI3Kδ 募集到一起以激活 AKT，我们检查了依鲁替尼处理是否改变了 PI3Kδ 的募集。用依鲁替尼处理的 MEC1 细胞中的 BCAP/CD19 的免疫沉淀显示，PI3Kδ 与 PI3Kβ 一起的募集增加，但与 PI3Kα 或 PI3Kγ 一起没有募集，并且同时靶向 PI3Kδ 和 PI3Kβ 可抑制 AKT 的再激活。我们在依鲁替尼治疗后具有 AKT 激活增加的 CLL 细胞中检测到类似的、患者特异性的 PI3K 同工型募集模式。有趣的是，尽管 PI3Kδ/PI3Kβ 的募集增加和磷脂酰肌醇-3,4,5-三磷酸的积累，但依鲁替尼处理的细胞中对 P-AKT（T308）的抑制作用强于 S473，这可能归因于 PDK1 活性的降低。因此，施用同工型特异性抑制剂可能是治疗 CLL 患者的更有效策略。
