School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
Oncol Rep. 2011 May;25(5):1473-80. doi: 10.3892/or.2011.1187. Epub 2011 Feb 17.
The combination of paclitaxel (PTX) and topoisomerase I inhibitors such as camptothecin (CPT) constitutes a therapeutic strategy based on anticipated synergism. However, previous in vitro studies have generated contradictory findings for this strategy. The interaction between these drugs can be synergistic or antagonistic, depending on the cell type examined. To gain additional insight into this promising yet controversial strategy, we investigated the interaction between PTX and CPT in three different cell lines (PANC-1, MDA-MB-231 and HL-60) and explored possible underlying mechanisms of synergy or antagonism. Using a novel solubilizing natural compound, rubusoside, water-insoluble PTX and CPT were solubilized to enable the comparison of the effects of single drugs and their combination on cell viability. Intracellular drug concentrations were quantified to examine the effect of CPT on cellular uptake and accumulation of PTX. Flow cytometry and quantitative real-time PCR gene array analyses were used to explore the mechanisms behind the interaction between PTX and CPT. Our studies confirmed that rubusoside-solubilized PTX or CPT maintained cytotoxicity, causing significant reductions in cell viability. However, the efficacy of the combination of PTX and CPT produced varied results based on the cell line tested. CPT antagonistically reduced the cytotoxic activity of PTX in PANC-1 and MDA-MB-231 cells. The effect of CPT on the cytotoxicity of PTX was less pronounced in HL-60 cells, showing neither synergy nor antagonism. Analysis of apoptosis by flow cytometry revealed that upon co-treatment with CPT, apoptosis induced by PTX was attenuated in PANC-1 and MDA-MB-231 cells. In agreement with our cytotoxicity findings, no synergistic or antagonistic effects on apoptosis were observed in HL-60 cells. The antagonism in PANC-1 and MDA-MB-231 cells was not a result of reduced PTX uptake and accumulation because the amount of intracellular PTX was not altered upon co-treatment with CPT. Moreover, higher expression of anti-apoptosis-related transcripts (BCL2L10, CFLAR, HIP1 and TRADD) in PANC-1 cells was observed upon combination treatment over PTX treatment alone. Although exact underlying mechanisms are unknown, the suspected CPT-dependent reduction of intracellular PTX accumulation was ruled out. The findings of antagonism and increased anti-apoptotic gene transcription serve as a precaution to the design of combination drug strategies where a synergistic interaction may not exist.
紫杉醇（PTX）和拓扑异构酶 I 抑制剂（如喜树碱（CPT））的联合应用构成了一种基于预期协同作用的治疗策略。然而，之前的体外研究对这种策略产生了相互矛盾的结果。这些药物之间的相互作用可能是协同的，也可能是拮抗的，这取决于所研究的细胞类型。为了更深入地了解这一有前途但有争议的策略，我们研究了 PTX 和 CPT 在三种不同细胞系（PANC-1、MDA-MB-231 和 HL-60）中的相互作用，并探讨了协同或拮抗作用的潜在机制。我们使用一种新型可溶天然化合物——毛蕊花糖苷，将水不溶性的 PTX 和 CPT 溶解，以比较单药和联合用药对细胞活力的影响。定量检测细胞内药物浓度，以研究 CPT 对 PTX 细胞摄取和积累的影响。采用流式细胞术和实时定量 PCR 基因芯片分析，探讨 PTX 和 CPT 相互作用的机制。我们的研究证实，毛蕊花糖苷溶解的 PTX 或 CPT 保持细胞毒性，显著降低细胞活力。然而，PTX 和 CPT 联合用药的疗效因所测试的细胞系而异。CPT 在 PANC-1 和 MDA-MB-231 细胞中拮抗降低了 PTX 的细胞毒性活性。CPT 对 HL-60 细胞中 PTX 细胞毒性的影响不明显，既没有协同作用，也没有拮抗作用。流式细胞术分析凋亡结果显示，与 CPT 共同处理时，PTX 诱导的凋亡在 PANC-1 和 MDA-MB-231 细胞中减弱。与我们的细胞毒性结果一致，HL-60 细胞中未观察到协同或拮抗作用。PANC-1 和 MDA-MB-231 细胞中的拮抗作用不是由于 PTX 摄取和积累减少所致，因为与 CPT 共同处理后细胞内 PTX 的量没有改变。此外，在联合治疗时观察到 PANC-1 细胞中与抗凋亡相关的转录本（BCL2L10、CFLAR、HIP1 和 TRADD）的表达高于单独使用 PTX 治疗时。尽管确切的潜在机制尚不清楚，但可以排除 CPT 依赖性细胞内 PTX 积累减少的可能性。拮抗作用和增加的抗凋亡基因转录的发现为联合用药策略的设计提供了一个警示，在这种策略中，可能不存在协同作用。
