Aziz S M, Gillespie M N, Crooks P A, Tofiq S F, Tsuboi C P, Olson J W, Gosland M P
Division of Pharmacology and Experimental Therapeutics, College of Pharmacy, A.B. Chandler Medical Center, University of Kentucky, Lexington, USA.
J Pharmacol Exp Ther. 1996 Jul;278(1):185-92.
The polyamines, putrescine (PUT), spermidine (SPD) and spermine (SPM), are a family of low molecular weight organic cations that are essential for cell growth, differentiation and neoplastic transformation. The marked compensatory increase in extracellular polyamine influx may be a reason for the unsatisfactory clinical chemotherapeutic effect of polyamine synthesis blockers like difluoromethylornithine (DFMO). In this study, a polymeric conjugate of SPM (poly-SPM) that blocks the import of polyamines into mammalian cells was used to test the potential therapeutic exploitation of the polyamine transport system in anticancer therapy. Our results indicate that a temperature-dependent polyamine transport system is expressed in two human cancer cell lines, MES-SA uterine sarcoma cells, K562 leukemic cells and their respective multiple drug resistance (MDR) positive counterparts, Dx5 and K562/R7 cells. The V(max) values for 14C-PUT and 14C-SPD uptake were significantly higher in MES-SA than in Dx5 cells, whereas the respective Km values were significantly lower. Addition of 20 microM poly-SPM reduced both the uptake of 14C-polyamines and the cellular polyamine contents in both cancer cell lines. In addition, the poly-SPM conjugate evoked a concentration-dependent cytotoxicity in MES-SA and K562 cells and their MDR-positive variants. Presence of aminoguanidine, an amine oxidase blocker, failed to alter the IC50 values generated with poly-SPM, which indicates that this polymer is not a substrate for amine oxidase. Moreover, coadministration of 25 microM SPD reversed the cytotoxic effect exerted by poly-SPM on both the MES-SA and Dx5 cells as reflected by an increase in their IC50 values. Relative to parental cells, the MDR-positive variants exhibited a lower 14C-polyamine uptake rate and were more resistant to the cytotoxic effect of poly-SPM. Pretreatment with 1 mM DFMO for 24 hr significantly increased polyamine transport, but failed to reduce intracellular SPM contents or exert a cytotoxic effect in both cancer cell lines. On other hand, the combination of DFMO and poly-SPM produced a greater depletion of polyamine content accompanied by a higher cytotoxicity than either agent alone. These results provide the first direct evidence that pharmacologic interruption of polyamine uptake may be an effective approach to cancer therapy. In addition, it appears that expression of MDR influences polyamine transport and renders cells more resistant to the cytotoxic effects of SPM polymer.
多胺，如腐胺（PUT）、亚精胺（SPD）和精胺（SPM），是一类低分子量有机阳离子，对细胞生长、分化和肿瘤转化至关重要。细胞外多胺流入的显著代偿性增加可能是像二氟甲基鸟氨酸（DFMO）这样的多胺合成阻滞剂临床化疗效果不理想的一个原因。在本研究中，一种能阻断多胺进入哺乳动物细胞的SPM聚合物共轭物（聚-SPM）被用于测试多胺转运系统在抗癌治疗中的潜在治疗应用。我们的结果表明，一种温度依赖性多胺转运系统在两种人类癌细胞系中表达，即MES-SA子宫肉瘤细胞、K562白血病细胞及其各自的多药耐药（MDR）阳性对应细胞系Dx5和K562/R7细胞。MES-SA细胞中14C-PUT和14C-SPD摄取的V(max)值显著高于Dx5细胞，而各自的Km值则显著更低。添加20微摩尔的聚-SPM可降低两种癌细胞系中14C-多胺的摄取以及细胞内多胺含量。此外，聚-SPM共轭物在MES-SA和K562细胞及其MDR阳性变体中引发浓度依赖性细胞毒性。胺氧化酶阻滞剂氨基胍的存在未能改变聚-SPM产生的IC50值，这表明该聚合物不是胺氧化酶的底物。此外，共同给予25微摩尔的SPD可逆转聚-SPM对MES-SA和Dx5细胞的细胞毒性作用，这表现为它们的IC50值增加。相对于亲代细胞，MDR阳性变体表现出较低的14C-多胺摄取率，并且对聚-SPM的细胞毒性作用更具抗性。用1毫摩尔的DFMO预处理24小时可显著增加多胺转运，但未能降低两种癌细胞系中的细胞内SPM含量或发挥细胞毒性作用。另一方面，DFMO和聚-SPM的联合使用比单独使用任何一种药物都能使多胺含量消耗得更多，并伴有更高的细胞毒性。这些结果提供了首个直接证据，表明多胺摄取的药理学阻断可能是一种有效的癌症治疗方法。此外，似乎MDR的表达会影响多胺转运，并使细胞对SPM聚合物的细胞毒性作用更具抗性。
