Besnard Thierry, Renée Nicole, Etienne-Grimaldi Marie-Christine, François Eric, Milano Gérard
Pharmacology Unit, Hôpital Pasteur, Nice, France.
J Chromatogr B Analyt Technol Biomed Life Sci. 2008 Jul 1;870(1):117-20. doi: 10.1016/j.jchromb.2008.05.040. Epub 2008 Jun 16.
The 5FU prodrug capecitabine undergoes a 3-step enzymatic conversion, including the conversion of 5'DFRC into 5'DFUR by cytidine deaminase (CDA). The presence of CDA activity in blood led us to analyze the possible ex vivo conversion of 5'DFCR into 5'DFUR in blood samples. We thus examined the impact of the addition of a CDA inhibitor (tetrahydrouridine (THU) 1 microM final) in blood. Blood samples from 3 healthy volunteers were taken on tubes containing or not THU. Blood was spiked with 5'DFCR (20 microM final) (T0) and was maintained at room temperature for 2 h. Plasma concentrations of 5'DFRC and 5'DFUR were analyzed with an optimized HPLC assay. In the absence of THU, 5'DFUR was detectable as early as T0. The percent of 5'DFUR produced relative to 5'DFCR increased over time, up to 7.7 % at 2h. In contrast, the presence of THU totally prevents the formation of 5'DFUR. The impact of THU for preventing the conversion of 5'DFCR was confirmed by the analysis of blood samples from 2 capecitabine-treated patients. Addition of THU in the sampling-tube before the introduction of blood is thus strongly recommended in order to guarantee accurate conditions for reliable measurement of capecitabine metabolites in plasma, and thus faithful pharmacokinetic data.
5-氟尿嘧啶前体药物卡培他滨经历三步酶促转化，包括胞苷脱氨酶（CDA）将5'-脱氧氟胞苷（5'DFCR）转化为5'-脱氧氟尿苷（5'DFUR）。血液中CDA活性的存在促使我们分析血样中5'DFCR在体外转化为5'DFUR的可能性。因此，我们研究了在血液中添加CDA抑制剂（四氢尿苷（THU），终浓度1微摩尔）的影响。从3名健康志愿者采集的血样分别置于含有或不含THU的试管中。血样加入5'DFCR（终浓度20微摩尔）（T0）后，在室温下保存2小时。采用优化的高效液相色谱法分析5'DFCR和5'DFUR的血浆浓度。在没有THU的情况下，早在T0时就可检测到5'DFUR。相对于5'DFCR产生的5'DFUR百分比随时间增加，2小时时高达7.7%。相反，THU的存在完全阻止了5'DFUR的形成。对2例接受卡培他滨治疗患者的血样分析证实了THU对阻止5'DFCR转化的作用。因此，强烈建议在采血前向采样管中加入THU，以确保在可靠测量血浆中卡培他滨代谢物的准确条件下，从而获得可靠的药代动力学数据。
