Radiosensitization by inhibition of Hsp90 and microenvironmental factors

已知磷脂酰肌醇3-激酶（PI 3 K）-Akt通路的活化诱导肿瘤放射抗性。在目前的研究中，我们检查了17-烯丙基氨基-17-去甲氧基格尔德霉素（17 AAG）的能力，它降低了Hsp 90客户端蛋白的水平，包括PI 3 K-Akt通路的组分，以敏感的放射抗性人鳞状细胞癌细胞X射线照射。17 AAG（0.2 μM）对放射抗性细胞SQ 20 B和SCC 13的放射增敏作用强于放射敏感细胞SCC 61。然而，在所有三种细胞系中，17 AAG通过降低表皮生长因子受体和ErbB-2的表达并抑制Akt的磷酸化来增加辐射诱导的细胞凋亡。此外，17 AAG（1 μM）使SQ 20 B球状体对辐射敏感，17 AAG抑制Akt活化增加了球状体中辐射诱导的凋亡。结果表明，17 AAG通过抑制PI 3 K-Akt通路有效地提高了辐射抵抗细胞对辐射的敏感性。我们还测试了GA和辐射联合对人肿瘤和正常细胞的存活、PI 3 K/Akt相关蛋白和凋亡诱导的影响。GA使肿瘤细胞优先于正常细胞对辐射敏感。此外，辐射和GA的组合废除Akt活性，并强烈增强依赖于Akt蛋白活性的细胞存活的肿瘤细胞中的细胞凋亡的诱导。目前的数据支持这一假设，即GA通过调节促有丝分裂，抗增殖和凋亡途径之间的平衡，使肿瘤细胞敏感。因此，靶向肿瘤细胞中的Hsp 90可能导致放射治疗中新的放射增敏策略的发展。

Activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway is known to induce tumor radioresistance. In the current studies, we examined the ability of 17-Allylamino-17-demethoxygeldanamycin (17AAG), which decreases the levels of Hsp90 client proteins including components of the PI3K-Akt pathway, to sensitize radioresistant human squamous cell carcinoma cells to X-irradiation. 17AAG (0.2 μM) enhanced the radiosensitivity more effectively in radioresistant SQ20B and SCC 13 cells than in radiosensitive SCC61 cells. However, in all three cell lines, 17AAG increased radiation-induced apoptosis by reducing the expression of the epidermal growth factor receptor and ErbB-2 and inhibiting the phosphorylation of Akt. Furthermore, 17AAG (1 μM) sensitized SQ20B spheroids to radiation, and inhibition of Akt activation by 17AAG increased radiation-induced apoptosis in spheroids. The findings suggest that 17AAG effectively sensitizes radioresistant cells to radiation by inhibiting the PI3K-Akt pathway.We also tested the effect of a combination of GA and radiation on cell survival, PI3K/Akt-related proteins and apoptosis induction in human tumor and normal cells. GA sensitized tumour cells in preference to normal cells to radiation. In addition, a combination of radiation and GA abolished Akt activities and strongly enhanced the induction of apoptosis in tumour cells which depend on Akt protein activities for cell survival. The present data support the hypothesis that GA sensitizes tumour cells by modulating the balance among mitogenic, antiproliferative and apoptotic pathways. Thus, targeting Hsp90 in tumour cells may lead to the development of new radiosensitizing strategies in radiotherapy.