Lock R B, Galperina O V, Feldhoff R C, Rhodes L J
J. Graham Brown Cancer Center, Department of Medicine, University of Louisville, Kentucky 40292.
Cancer Res. 1994 Sep 15;54(18):4933-9.
Morphological examination of HeLa cells exposed to etoposide for 1 h revealed two distinct modes of death: (a) within 6 h of drug removal, shrunken cells appeared which contained vacuolated cytoplasm and regions of intense chromatin staining, consistent with apoptosis; and (b) concomitant with release from G2 arrest, enlarged cells appeared which contained evenly staining nuclear fragments, consistent with mitotic death. The methylxanthine, caffeine, enhanced cytotoxicity in a concentration-dependent manner when applied for 24 h following etoposide exposure. One mM caffeine alleviated etoposide-induced G2 arrest and increased the incidence of mitotic death, accounting for the potentiation of cytotoxicity. Brief caffeine exposures (5 or 10 mM for 1-2 h) caused specific tyrosine dephosphorylation and activation of p34cdc2 kinase, and mitotic progression to a limited extent, in cells which were arrested in G2 following etoposide treatment. However, longer exposure times at a high caffeine concentration (10 mM) caused inhibition of both cell cycle progression and mitotic death, and the enhancement of etoposide cytotoxicity could be accounted for by up to a 3-fold increase in the proportion of morphologically apoptotic cells. Thus, caffeine potentiates etoposide cytotoxicity by two morphologically distinct mechanisms depending on its concentration.
对暴露于依托泊苷1小时的HeLa细胞进行形态学检查发现了两种不同的死亡模式：(a) 在去除药物后的6小时内，出现了皱缩的细胞，其细胞质有空泡化，染色质染色强烈，符合凋亡特征；(b) 与从G2期阻滞中释放同时发生，出现了增大的细胞，其含有均匀染色的核碎片，符合有丝分裂死亡特征。甲基黄嘌呤咖啡因在依托泊苷暴露后应用24小时时，以浓度依赖的方式增强了细胞毒性。1 mM咖啡因减轻了依托泊苷诱导的G2期阻滞，并增加了有丝分裂死亡的发生率，这解释了细胞毒性的增强。短暂暴露于咖啡因（5或10 mM，持续1 - 2小时）会导致在依托泊苷处理后停滞于G2期的细胞中p34cdc2激酶发生特异性酪氨酸去磷酸化并被激活，并在一定程度上促进有丝分裂进程。然而，在高咖啡因浓度（10 mM）下更长时间的暴露会导致细胞周期进程和有丝分裂死亡均受到抑制，依托泊苷细胞毒性的增强可归因于形态学上凋亡细胞比例增加高达3倍。因此，咖啡因根据其浓度通过两种形态学上不同的机制增强依托泊苷的细胞毒性。
