细胞自噬调节AKT通路抑制剂在鼻咽癌中抗肿瘤作用的机制研究

Autophagy is an important homeostatic cellular recycling mechanism. Induction of autophagy in response to anticancer drugs can be viewed as having a prodeath or a prosurvival role in different cancer types. Our previous studies found, IC50 of AKT inhibitor achieved in our study was higher than the mean plasma concentration in human body, and this drug can not induce apoptosis in nasopharyngeal carcinoma (NPC) cell lines. Strategies for reinforcing the activity of the AKT inhibitors are needed. However, AKT inhibitor can induce autophagy. Furthermore, Phosphorylation levels of PRAS40 and S6, downstream of mTOR, were attenuated by the drug in a dose–dependent manner. It is reported that, suppression of the autophagy can promote apoptotic cell death and augment the cytotoxicity of AKT inhibitor and eEF-2 kinase, downstream of mTOR, may act as a controller in the crosstalk between autophagy and apoptosis. We therefore hypothesized that AKT inhibitors may affect the activity of eEF-2 kinase, and then induce protective autophagy, thus weakening its curative effect. On the contrary, inhibition autophagy may improve the efficacy of AKT inhibitors. In this study, first, we sought to determine whether autophagy inhibition drug can enhance the anti-tumor effect of AKT inhibitor in vitro and in vivo; second, we wanted to make sure whether autophagy inhibition caused by eEF-2 kinase inhibition was another way to improve efficacy of AKT inhibitor in molecular level. We hoped to provide a theoretical foundation and a new therapeutic method for the targeted therapy of NPC on the basis of this study.

自噬是一种重要的细胞自身再循环利用过程。抗肿瘤药物诱导产生的自噬，在不同肿瘤中可能产生抑制或者保护细胞两种相反的作用。我们前期研究发现，AKT抑制剂治疗鼻咽癌在体内达不到有效抑瘤浓度，不能诱导鼻咽癌细胞发生凋亡，需要进一步提高疗效；但该药物可以诱导鼻咽癌细胞自噬，并且抑制PI3K/AKT/mTOR通路下游的PRAS40和S6的磷酸化水平。文献报道抑制细胞保护性自噬能够增加细胞凋亡，而mTOR下游的eEF-2激酶可能是细胞发生自噬或凋亡的调定点。因此我们推测AKT抑制剂可能通过影响eEF-2激酶活性，诱导鼻咽癌细胞发生保护性自噬，进而削弱自身的疗效；反之抑制该自噬作用有可能提高疗效。本课题首先将从体内、体外观察联合自噬抑制药物后, AKT抑制剂抗肿瘤疗效的变化，其次明确通过eEF-2激酶抑制，抑制自噬，能否提高AKT抑制剂的疗效。本研究将为鼻咽癌的分子靶向治疗提供新的理论基础和治疗途径。

自噬是一种重要的细胞自身再循环利用过程。抗肿瘤药物诱导产生的自噬，在不同肿瘤中可能产生抑制或者保护细胞两种相反的作用。我们前期研究发现，AKT抑制剂治疗鼻咽癌在体内达不到有效抑瘤浓度，不能诱导鼻咽癌细胞发生凋亡，需要进一步提高疗效；但该药物可以诱导鼻咽癌细胞自噬，并且抑制PI3K/AKT/mTOR通路下游的PRAS40和S6的磷酸化水平。文献报道抑制细胞保护性自噬能够增加细胞凋亡，而mTOR下游的eEF-2激酶可能是细胞发生自噬或凋亡的调定点。我们的研究发现：MK-2206诱导鼻咽癌细胞株产生的自噬依赖eEF-2激酶。用shRNA敲除eEF-2激酶可以抑制MK-2206激活的自噬。与单用MK-2206相比，shRNA或NH125抑制eEF-2激酶，可以增强MK-2206对人鼻咽癌细胞的生长抑制作用。同时我们发现eEF-2激酶抑制剂和MK-2206的协同作用与羟氯喹和MK-2206的联合作用相似。此外，体内研究发现NH125与MK-2206具有良好的协同作用。结论：AKT抑制诱导的eEF-2激酶介导的自噬作用对鼻咽癌细胞具有保护作用。抑制eEF-2激酶可能是提高AKT抑制剂如MK-2206在鼻咽癌中的疗效的有效方法。