Evaluation of 5'-deoxy-5'-[F-18]fluorothymidine as a tracer of intracellular thymidine phosphorylase activity
Evaluation of 5'-deoxy-5'-[F-18]fluorothymidine as a tracer of intracellular thymidine phosphorylase activity
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DOI：
10.1016/j.nucmedbio.2007.03.004
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发表时间：
2007-07-01
影响因子：
3.1
通讯作者：
Vesselle, Hubert
中科院分区：
文献类型：
--
作者：
Grierson, John R.;Brockenbrough, J. Scott;Vesselle, Hubert
用两株具有胞溶胸苷磷酸化酶（TP）活性的人细胞系（A549和U937）来评价5′-脱氧-5′-[F-18]氟胸苷（[F-） 8]DFT)作为胞内TP表达示踪剂的潜力。DFT的细胞代谢导致产生5-[F-18]氟-2,5-二脱氧核糖-1 α -磷酸（[F-18]FddR-IP），类似于胸腺嘧啶的代谢，产生2-脱氧核糖-1 α -磷酸（dR-1P）。A549细胞fdr - 1p的产率最高。A549细胞暴露于[F-18]DFT 40分钟后，细胞内[F-18] fdr - ip的相对浓度比培养液中的前体高7倍以上。在相同的时间内，在U937细胞中观察到两倍的浓度。然而，摄取率并不与细胞提取物中发现的TP活性相匹配[TP活性比(U937:A549)= 1.6]，这是用标记胸腺嘧啶/胸腺嘧啶裂解法独立测定的。TP活性比值的差异可追溯到fdr - ip在细胞中的不稳定性。这从细胞通过产生fdr - ip而积累放射性这一事实中可以明显看出，但当培养基随后不含示踪剂时，活性也会在1 h内从细胞中流出。细胞释放的显性标记分子为中性亲脂分子，推测为脱氧核苷。我们的研究结果表明[F- I 8]DFT不能有效成像TP表达，因为其初始代谢物会进一步转化为可扩散的次级代谢物，从而导致细胞活性丧失。(c) 2007爱思唯尔公司版权所有。
Two human cell lines (A549 and U937) with cytosotic thymidine phosphorylase (TP) activity were used to evaluate the potential of 5'- deoxy-5' -[F-18]fluorothymidine ([F-) 8]DFT) as a tracer of intracellular TP expression. Cellular metabolism of DFT led to the production of 5-[F-18]fluoro-2,5-dideoXy-D-ribose-1 alpha-phosphate ([F-18]FddR-IP), in analogy to the metabolism of thymidine, which produces 2-deoxyD-ribose-1 alpha-phosphate (dR-1P). A549 cells showed the highest production rate of FddR-1P. After A549 cells were exposed to [F-18]DFT for 40 min, the relative intracellular concentration of [F-18]FddR-IP was more than sevenfold higher in cells than its precursor in the incubating medium. For the same amount of time, a twofold concentration was seen in U937 cells. However, uptake ratios did not rank with the corresponding TP activities found in cell extracts [TP activity ratio (U937:A549)= 1.6] that were independently determined with a labeled thymidine/thymine cleavage assay.The discrepancy of TP activity ratios was traced to the instability of FddR-IP in cells. This was evident from the fact that cells accumulated radioactivity by producing FddR-IP, but activity also effluxed from cells over I h when the medium was subsequently made tracer free. The dominant labeled molecule released by cells was characterized as a neutral and lipophilic molecule, which was presumed to be a deoxynucleoside. Our results indicate that [F- I 8]DFT would not be effective for imaging TP expression because its initial metabolite undergoes further conversion to a diffusible secondary metabolite, allowing activity loss from cells. (c) 2007 Elsevier Inc. All rights reserved.