Enhancement of 1-beta-D-arabinofuranosylcytosine accumulation within L1210 cells and increased cytotoxicity following thymidine exposure.
Enhancement of 1-beta-D-arabinofuranosylcytosine accumulation within L1210 cells and increased cytotoxicity following thymidine exposure.
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L1210 细胞内 1-β-D-阿拉伯呋喃糖基胞嘧啶积累增强，胸苷暴露后细胞毒性增加。
作者：
S. Grant;C. Lehman;E. Cadman
在对数生长期的L1210细胞悬浮培养中，研究了预先暴露于胸苷（dThd）对细胞内脱氧胞苷（dCyd）和1-β-d-阿拉伯呋喃糖基胞嘧啶（ara-C）积累以及细胞内脱氧核糖核苷酸库的影响。用0.1 mm dThd预处理5小时，导致细胞内dCyd掺入量从30 pmol dCyd/106个细胞增加至暴露于5 µm [3 H]dCyd 1小时后的220 pmol dCyd/106个细胞。在相同条件下，暴露于5 µm [3 H]-ara-C 1小时后，ara-C的细胞内掺入量从32 pmol ara-C/106细胞增加至120 pmol ara-C/106细胞。利用1小时的dThd暴露时间，以及dThd浓度为0.01和2毫米，导致细胞内增强dCyd和ara-C掺入。暴露于0.1 mm dThd 5小时后，[3 H]ara-C掺入RNA的量从0.21 pmol ara-C/µg d-核糖增加到0.48 pmol ara-C/µg脱氧核糖; DNA掺入量从0.70 pmol ara-C/µg脱氧核糖增加到3.50 pmol ara-C/µg脱氧核糖。此外，dThd预处理与1-β-d-阿拉伯呋喃糖基胞嘧啶5′-三磷酸产量增加8倍相关。
细胞内脱氧胞苷5′-三磷酸池的最大减少，从106 pmol/106细胞到25 pmol/106细胞，发生在0.1 mm dThd暴露5小时后。脱氧胞苷三磷酸池的减少与细胞内阿糖胞苷掺入的增强幅度呈负相关。0.1 mm dThd处理5小时，随后5 µm ara-C处理1小时的顺序导致L1210集落形成减少至对照值的3%，这代表了相对于单独给药或反向给药顺序的协同细胞杀伤。因此，dThd增强了阿糖胞苷C的细胞内和核酸掺入，最有可能是由于脱氧胞苷三磷酸池减少的结果，这是体外细胞毒性增强的可能生化解释。
The effect of prior exposure to thymidine (dThd) on the intracellular accumulation of deoxycytidine (dCyd) and 1-β-d-arabinofuranosylcytosine (ara-C), as well as intracellular deoxyribonucleotide pools, was studied in suspension cultures of L1210 cells during logarithmic growth. Pretreatment with 0.1 mm dThd for 5 hr resulted in an increase in intracellular dCyd incorporation from 30 pmol dCyd per 106 cells to 220 pmol dCyd per 106 cells following 1 hr exposure to 5 µm [3H]dCyd. Under the same conditions, the intracellular incorporation of ara-C was increased from 32 pmol ara-C per 106 cells to 120 pmol ara-C per 106 cells following 1 hr exposure to 5 µm [3H]-ara-C. Utilization of a 1-hr dThd exposure time, as well as dThd concentrations of 0.01 and 2 mm, resulted in less intracellular enhancement of dCyd and ara-C incorporation. Following a 5-hr exposure to 0.1 mm dThd, the incorporation of [3H]ara-C into RNA increased from 0.21 to 0.48 pmol ara-C per µg d-ribose; DNA incorporation increased from 0.70 to 3.50 pmol ara-C per µg deoxyribose. In addition, dThd pretreatment was associated with an 8-fold increase in 1-β-d-arabinofuranosylcytosine 5′-triphosphate production.
The maximum reduction of intracellular deoxycytidine 5′-triphosphate pools, from 106 pmol/106 cells to 25 pmol/106 cells, occurred after a 5-hr exposure of 0.1 mm dThd. This reduction in the deoxycytidine triphosphate pool was inversely correlated with the magnitude of the enhancement of intracellular ara-C incorporation. The sequence of 0.1 mm dThd for 5 hr followed by 5 µm ara-C for 1 hr resulted in a reduction in L1210 colony formation to 3% of control values, which represented synergistic cell killing relative to either drug given alone or the reverse drug sequence. Thus, dThd enhances the intracellular and nucleic acid incorporation of ara-C, most probably as a consequence of a reduction in deoxycytidine triphosphate pools, and this is the probable biochemical explanation for the enhanced in vitro cytotoxicity.