Pauwels Bea, Korst Annelies E C, Lambrechts Hilde A J, Pattyn Greet G O, de Pooter Christel M J, Lardon Filip, Vermorken Jan B
Laboratory of Cancer Research and Clinical Oncology, Department of Medical Oncology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
Cancer Chemother Pharmacol. 2006 Aug;58(2):219-28. doi: 10.1007/s00280-005-0158-5. Epub 2005 Dec 6.
Gemcitabine is an active antitumour agent with radiosensitising properties. Gemcitabine is rapidly metabolised, intracellularly as well as extracellularly, by deoxycytidine deaminase to difluorodeoxyuridine (dFdU), a compound with little antitumour activity. However, plasma concentrations are maintained for a prolonged period (>24 h) at levels known to cause growth inhibition. This is the first study that investigates the radiosensitising potential of dFdU in vitro.
ECV304 and H292, human cancer cells, were treated with different concentrations dFdU (0-100 microM) during 24 h before radiation treatment (RT). The schedule dependency of the radiosensitising effect was studied by varying the interval between dFdU and radiation treatment. In addition, the cell cycle effect of dFdU was investigated with flow cytometry, and the induction of apoptosis under radiosensitising conditions was determined by Annexin V staining and caspase 3 cleavage.
dFdU caused a clear concentration-dependent radiosensitising effect in both ECV304 and H292 cells. Dose enhancement factor (DEF) increased with an increasing concentration of dFdU: DEFs were 1.10, 1.60 and 2.17 after treatment with 10, 25 and 50 microM dFdU, respectively, in ECV304 cells and 1.08, 1.31 and 1.60 after treatment with 25, 50 and 100 microM, respectively, in H292 cells. DEFs decreased with an increasing interval of 0-24 h between dFdU treatment and radiation. Under radiosensitising conditions, the combination dFdU and radiation resulted in an increased induction of apoptosis. In addition, the cell cycle effect of dFdU, an arrest at the early S phase, is comparable with the cell cycle effect of gemcitabine.
dFdU, the main metabolite of gemcitabine, causes a concentration- and schedule- dependent radiosensitising effect in vitro. Since the metabolite is present in plasma for a long period (>24 h) after treatment with gemcitabine, it might be partly responsible for the interaction between radiotherapy and gemcitabine. This observation might have important consequences for the optimal schedules of the combination gemcitabine and radiation therapy.
吉西他滨是一种具有放射增敏特性的活性抗肿瘤药物。吉西他滨在细胞内和细胞外均能被脱氧胞苷脱氨酶迅速代谢为二氟脱氧尿苷（dFdU），后者几乎没有抗肿瘤活性。然而，血浆浓度能在已知可导致生长抑制的水平维持较长时间（>24小时）。这是第一项体外研究dFdU放射增敏潜力的研究。
在放射治疗（RT）前24小时，用不同浓度的dFdU（0 - 100微摩尔）处理人癌细胞ECV304和H292。通过改变dFdU与放射治疗之间的间隔时间，研究放射增敏作用的时间依赖性。此外，用流式细胞术研究dFdU对细胞周期的影响，并用膜联蛋白V染色和半胱天冬酶3切割来确定放射增敏条件下的细胞凋亡诱导情况。
dFdU在ECV304和H292细胞中均引起明显的浓度依赖性放射增敏作用。剂量增强因子（DEF）随dFdU浓度增加而升高：在ECV304细胞中，用10、25和50微摩尔dFdU处理后的DEF分别为1.10、1.60和2.17；在H292细胞中，用25、50和100微摩尔处理后的DEF分别为1.08、1.31和1.60。随着dFdU处理与放射之间间隔时间从0增加到24小时，DEF降低。在放射增敏条件下，dFdU与放射联合导致细胞凋亡诱导增加。此外，dFdU使细胞周期阻滞在早期S期的作用与吉西他滨的细胞周期作用相当。
吉西他滨的主要代谢产物dFdU在体外引起浓度和时间依赖性放射增敏作用。由于在用吉西他滨治疗后，该代谢产物在血浆中长时间存在（>24小时），它可能部分解释了放射治疗与吉西他滨之间的相互作用。这一观察结果可能对吉西他滨与放射治疗联合的最佳方案具有重要意义。
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