Clark Amy S, West Kip, Streicher Samantha, Dennis Phillip A
Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20889, USA.
Mol Cancer Ther. 2002 Jul;1(9):707-17.
To evaluate the role of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in breast cancer cell survival and therapeutic resistance, we analyzed a panel of six breast cancer cell lines that varied in erbB2 and estrogen receptor status. Akt activity was constitutive in four cell lines and was associated with either PTEN mutations or erbB2 overexpression. Akt promoted breast cancer cell survival because a PI3K inhibitor, LY294002, or transient transfection of a dominant-negative Akt mutant inhibited Akt activity and increased apoptosis. When combined with therapies commonly used in breast cancer treatment, LY294002 potentiated apoptosis caused by doxorubicin, trastuzumab, paclitaxel, or etoposide. Potentiation of apoptosis by LY294002 correlated with induction of Akt by doxorubicin or trastuzumab alone that occurred before the onset of apoptosis. Similar results were observed with tamoxifen. Combining LY294002 with tamoxifen in estrogen receptor-positive cells greatly potentiated apoptosis, which was correlated with tamoxifen-induced Akt phosphorylation that preceded apoptosis. To confirm that the effects of LY294002 on chemotherapy-induced apoptosis were attributable to inhibition of Akt, we transiently transfected breast cancer cells with dominant-negative Akt and observed increased doxorubicin-induced apoptosis. Conversely, stably transfecting cells with constitutively active Akt increased Akt activity and attenuated doxorubicin-induced apoptosis. These studies show that endogenous Akt activity promotes breast cancer cell survival and therapeutic resistance, and that induction of Akt by chemotherapy, trastuzumab, or tamoxifen might be an early compensatory mechanism that could be exploited to increase the efficacy of these therapies.
为了评估磷脂酰肌醇3激酶（PI3K）/Akt信号通路在乳腺癌细胞存活及治疗抵抗中的作用，我们分析了一组六种乳腺癌细胞系，这些细胞系在erbB2和雌激素受体状态方面存在差异。Akt活性在四种细胞系中呈组成性，且与PTEN突变或erbB2过表达相关。Akt促进乳腺癌细胞存活，因为PI3K抑制剂LY294002或显性负性Akt突变体的瞬时转染可抑制Akt活性并增加细胞凋亡。当与乳腺癌治疗中常用的疗法联合使用时，LY294002可增强阿霉素、曲妥珠单抗、紫杉醇或依托泊苷诱导的细胞凋亡。LY294002增强细胞凋亡与阿霉素或曲妥珠单抗单独诱导的Akt在细胞凋亡开始前的上调有关。他莫昔芬也观察到类似结果。在雌激素受体阳性细胞中将LY294002与他莫昔芬联合使用可极大地增强细胞凋亡，这与他莫昔芬诱导的在细胞凋亡之前的Akt磷酸化相关。为了证实LY294002对化疗诱导的细胞凋亡的作用归因于对Akt的抑制，我们用显性负性Akt瞬时转染乳腺癌细胞，并观察到阿霉素诱导的细胞凋亡增加。相反，用组成型活性Akt稳定转染细胞可增加Akt活性并减弱阿霉素诱导的细胞凋亡。这些研究表明内源性Akt活性促进乳腺癌细胞存活和治疗抵抗，并且化疗、曲妥珠单抗或他莫昔芬诱导的Akt可能是一种早期补偿机制，可利用该机制来提高这些疗法的疗效。
