Nrf-2/GSTs通路失活联合TKIs抑制CML干细胞肿瘤生成能力

Chronic myeloid leukemia (CML) is a disease of hematologic stem cells caused by the reciprocal translocation t (9:22) which leads to production of Bcr/Abl fusion protein. C-abl oncogene-targeted tyrosine kinase inhibitors (TKIs) such as imatinib mesylate have drastically improved the treatment of CML. However; these inhibitors do not target the leukemia stem cell (LSCs). Recent evidence suggests CML stem cells are insensitive to kinase inhibitors and responsible for minimal residual disease that regenerates Bcr/Abl-positive haemopoiesis. As a result, relapse occurs rapidly upon drug withdrawal. Identifying the mechanisms that support the persistence of LSCs is therefore of utmost importance for their eradication. Our recent efforts have focused on understanding why CML stem cells are resistant to STI-571 and on trying to find novel ways to disrupt the tumorigenic ability of this population. Our data indicated that the pathway involved in cellular anti-oxidation contributed largely to STI-571 resistance in CML stem cells. Firstly, the pathway was in hyperactive status. As a key molecular managing anti-oxidation, nuclear factor erythroid 2-related factor 2 (Nrf-2), was highly expressed in CML stem cells compared with HSC derived from healthy donors. Secondly, Nrf-2 mediated STI-571 resistance through rapid clearance of 4-hydroxynonenal (4-HNE) that generated during STI-571 treatment. Nrf-2 transactivated the expression of GST, which might in turn catalyse formation of GSH-4-HNE complex to assist in its export outward. Inhibition of Nrf-2 markedly increased the STI-571 sensitivity in CML stem cells. However, our present results are not sufficient to support that clearance of 4-HNE by Nrf-2/GST participated in tomorigenesis. We should further investigate whether combination of Nrf-2/GST inhibition with TKIs impair the long-term culture initiating ability of these cells in vitro and suppress leukemogenic potential in vivo.

特异性酪氨酸激酶抑制剂（TKIs）虽能控制慢性粒系白血病（CML）进展，然而复发始终无法克服。根源在于TKIs对耐药的CML干细胞杀伤效果欠佳。故阐明干细胞耐药机制是治愈疾病的关键。前期结果显示，CML干细胞中异常活化的抗氧化应激通路Nrf-2/GSTs可及时清除TKIs作用产生的毒性分子4-羟基壬烯醛而保护细胞。为了更清楚地证明Nrf-2/GSTs的功能，本项目将进一步在体外研究Nrf-2/GSTs联合TKIs对CML干细胞长期培养起始能力的影响。在体内， bcr/abl转化小鼠Lin-细胞并移植， Nrf-2/GSTs联合TKIs治疗，构建治疗模型以反映该处理对肿瘤的治疗效果；另，Nrf-2/GSTs联合TKIs预处理细胞后移植构建预防模型，反映该处理对肿瘤生成能力的影响；治疗模型中肿瘤细胞进行二次移植，反映治疗后干细胞经再次成瘤的能力。为临床克服疾病复发，治愈疾病提供潜在的治疗靶点。

特异性酪氨酸激酶抑制剂（TKIs）能够靶向失活 Bcr/Abl 融合蛋白，为慢性粒细胞白血病（CML）的治疗带来了革命性的突破，然而随之而来的耐药以及复发又成为该病治愈的新挑战。本项目旨在寻找能够有效杀伤CML肿瘤细胞的小分子化合物，以弥补单一使用TKIs治疗易耐药不足，为治愈CML提供新的靶点。以CML病人的骨髓单个核细胞作为研究对象，对43种小分子抑制剂（靶分子包括细胞周期激酶、DNA及组蛋白甲基化、乙酰化调节酶和蛋白酶体等）进行敏感性筛选，抑制剂Oprozomib能抑制泛素-蛋白酶体系统导致新合成肽链在加工折叠过程产生的错误折叠蛋白不能及时被清除而聚集。Oprozomib抑制β5i (LMP7 )亚基活性。作用后蛋白泛素化水平明显升高，细胞被成功诱导凋亡。通过蛋白组学方法进一步分析Oprozomib作用与细胞凋亡之间的分子联系，我们发现：Oprozomib作用可引起内质网应激反应，并启动未折叠蛋白（unfolded protein reaction，UPR）反应，延长作用的UPR可诱导细胞凋亡。Oprozomib能够诱导并延长PERK 及 IRE1α磷酸化，这两个分子作为UPR信号传递的枢纽，前者通过上调CHOP表达，最终抑制BCL-2诱导细胞凋亡；而后者则通过TRAF-ASK-JNK级联反应诱导细胞凋亡。同时我们还发现，Oprozomib能够调节Ca2+由内质网向胞浆中外流，通过Caspase-12诱导细胞凋亡。. 该研究的意义在于证实Oprozomib在体外对CML细胞具有明显的杀伤作用，且通过多条凋亡相关信号通路。肿瘤细胞的特点在于其活跃的增殖能力，而于此同时便更加依赖于强大的蛋白酶体系统以处理增殖过程中所产生的错误折叠蛋白。过度依赖便是可攻击的弱点，通过抑制肿瘤细胞蛋白酶体系统导致具有毒性的错误折叠蛋白聚集而诱发凋亡是治疗CML的新策略。