Komata Tadashi, Kanzawa Takao, Nashimoto Takeo, Aoki Hiroshi, Endo Shin, Nameta Masaaki, Takahashi Hideaki, Yamamoto Tadashi, Kondo Seiji, Tanaka Ryuichi
Department of Neurosurgery, Brain Research Institute, Niigata University, Niigata, Japan.
J Neurooncol. 2004 Jun;68(2):101-11. doi: 10.1023/b:neon.0000027739.33842.6c.
Although hyperthermia has been used as a treatment of malignant brain tumors, it is not yet clear what is the mechanism of the cell growth inhibition by heat shock, especially by the temperature which has clinically been applied to tumor-brain border-zone, 42-43 degrees C. Therefore, we evaluated the change of U251-MG and U87-MG human malignant glioma cells after 43 degrees C-heat shock comparing with that of 45 degrees C. First, we observed that cell growth was transiently inhibited after 43 degrees C-heat shock for 3 or 5 days, in U251-MG or U87-MG cells, respectively, which was followed by regrowth. During the period of transient growth inhibition, mild G2/M arrest was observed. However, apoptosis was observed in only 2.7% or 1.5%, of 43 degrees C-heated cells, in U251-MG or U87-MG cells, respectively. Instead, transmission electron micrography showed the formation of vacuoles, degeneration of mitochondria, and autophagosomes. Moreover, in the both cell lines, flow-cytometric analysis with acridine orange revealed the induction of acidic vesicle organelles, which was blocked by 3-methyladenine (3-MA), suggesting the involvement of autophagy. Furthermore, while 3-MA did not increase the anti-tumor effect of 43 degrees C-heat shock, bafilomycin A1, another autophagy inhibitor, did significantly enhance the effect in U251-MG cells. Taken together, mild heat shock (43 degrees C for 2 h) causes autophagy and mild G2/M arrest, but does not induce apparent apoptosis in U251-MG and U87-MG glioma cells. Inhibition of autophagy with bafilomycin A1 may increase the anti-tumor efficacy of mild heat shock against some malignant glioma cells.
尽管热疗已被用于治疗恶性脑肿瘤，但热休克抑制细胞生长的机制仍不清楚，尤其是临床应用于肿瘤-脑交界区的42-43摄氏度的温度。因此，我们评估了43摄氏度热休克后U251-MG和U87-MG人恶性胶质瘤细胞的变化，并与45摄氏度热休克后的变化进行比较。首先，我们观察到，在U251-MG或U87-MG细胞中，43摄氏度热休克3天或5天后，细胞生长分别受到短暂抑制，随后恢复生长。在短暂生长抑制期间，观察到轻度的G2/M期阻滞。然而，在43摄氏度加热的细胞中，U251-MG细胞和U87-MG细胞中分别只有2.7%或1.5%的细胞发生凋亡。相反，透射电子显微镜显示有空泡形成、线粒体退化和自噬体。此外，在这两种细胞系中，吖啶橙流式细胞术分析显示酸性囊泡细胞器的诱导，这被3-甲基腺嘌呤（3-MA）阻断，提示自噬的参与。此外，虽然3-MA没有增加43摄氏度热休克的抗肿瘤作用，但另一种自噬抑制剂巴弗洛霉素A1在U251-MG细胞中确实显著增强了这种作用。综上所述，轻度热休克（43摄氏度，2小时）会导致自噬和轻度G2/M期阻滞，但不会在U251-MG和U87-MG胶质瘤细胞中诱导明显的凋亡。用巴弗洛霉素A1抑制自噬可能会增加轻度热休克对某些恶性胶质瘤细胞的抗肿瘤疗效。
