Fingert H J, Chang J D, Pardee A B
Cancer Res. 1986 May;46(5):2463-7.
Human tumor cells, like rodent cells, are sensitive to effects of methylxanthines (MEX) on lethality, cell cycle delays, and chromosome aberrations after DNA damage by anticancer drugs. Enhanced cytotoxicity of alkylating agents was observed when T24 human bladder tumor cells in culture were exposed to nontoxic concentrations of MEX such as caffeine or pentoxifylline. Tumor cell lethality was increased up to 10-fold by either caffeine or pentoxifylline (1 mM) present during the first cell cycle (16-24 h) after exposure to nitrogen mustard (HN2) or thiotepa. Cycloheximide, a protein synthesis inhibitor, abolished the enhanced lethality produced by MEX. In these synchronized human tumor cells further kinetic studies revealed that HN2 (0.5 microM X 1 h) delayed transit through S phase by about 1-2 h, and this delay was prevented by MEX. After completion of S phase, HN2-treated cells were delayed 3-6 h in G2, and MEX also prevented this delay, leading to mitoses at the rate of controls. Chromosome analysis of these mitotic cells revealed dramatic increases in aberrations induced by alkylator + MEX combinations. The greatest number of aberrations was seen in HN2-treated cells exposed briefly to MEX in late S-G2. In contrast, no increased chromosome damage was seen in cells exposed to MEX in mid-S phase. Taken together, our results are consistent with the model that MEX enhance lethality of alkylator-treated human tumor cells by preventing delays in cell cycle transit through G2, leading to chromosome aberrations which are lethal. G2 delays in human tumor cells may provide time for repair processes that are critical for survival after sublethal DNA damage by HN2 or other anticancer alkylating agents.
与啮齿动物细胞一样，人类肿瘤细胞对甲基黄嘌呤（MEX）在抗癌药物造成DNA损伤后对致死率、细胞周期延迟和染色体畸变的影响敏感。当培养的T24人膀胱肿瘤细胞暴露于无毒浓度的MEX（如咖啡因或己酮可可碱）时，可观察到烷化剂的细胞毒性增强。在暴露于氮芥（HN2）或噻替派后的第一个细胞周期（16 - 24小时）中，存在咖啡因或己酮可可碱（1 mM）时，肿瘤细胞致死率增加高达10倍。蛋白质合成抑制剂放线菌酮消除了MEX产生的增强致死率。在这些同步化的人类肿瘤细胞中，进一步的动力学研究表明，HN2（0.5 microM×1小时）使S期进程延迟约1 - 2小时，而MEX可防止这种延迟。S期完成后，经HN2处理的细胞在G2期延迟3 - 6小时，MEX也可防止这种延迟，使有丝分裂速率恢复到对照水平。对这些有丝分裂细胞的染色体分析显示，烷化剂+ MEX组合诱导的畸变显著增加。在S晚期 - G2期短暂暴露于MEX的HN2处理细胞中，畸变数量最多。相比之下，在S中期暴露于MEX的细胞中未观察到染色体损伤增加。综上所述，我们的结果与以下模型一致：MEX通过防止细胞周期在G2期的延迟来增强烷化剂处理的人类肿瘤细胞的致死率，导致致死性的染色体畸变。人类肿瘤细胞中的G2期延迟可能为亚致死性DNA损伤（由HN2或其他抗癌烷化剂引起）后的生存所必需的修复过程提供时间。
