Bouffard D Y, Laliberté J, Momparler R L
Département de Pharmacologie, Université de Montréal, Québec, Canada.
Biochem Pharmacol. 1993 May 5;45(9):1857-61. doi: 10.1016/0006-2952(93)90444-2.
Phosphorylation of cytosine analogs by deoxycytidine kinase (dCK) and deamination by cytidine deaminase (CDA) are two important processes in the activation and elimination of these drugs. We have investigated the kinetic parameters of 2',2'-difluorodeoxycytidine (dFdC) using purified enzymes from human cells. Deoxycytidine (CdR) and dFdC had Km values of 1.5 and 4.6 microM for dCK, respectively. Feedback inhibition of dCK by deoxycytidine 5'-triphosphate (dCTP) was also studied. Our results show that dCTP produced a greater inhibition of the phosphorylation of dFdC than CdR with concentrations of dCTP ranging from 1 to 25 microM. dFdC was a good substrate for CDA. Kinetic studies with this enzyme gave Km values for CdR and dFdC of 46.3 and 95.7 microM, respectively. The effect of competitive inhibitors of CDA on the deamination of dFdC was also investigated. Diazepinone riboside was a more potent inhibitor than tetrahydrouridine using either CdR or dFdC as the substrate. Inhibitors of CDA could be useful in clinical trials in patients with cancer to increase the chemotherapeutic effectiveness of dFdC.
脱氧胞苷激酶（dCK）对胞嘧啶类似物的磷酸化作用以及胞苷脱氨酶（CDA）的脱氨作用是这些药物激活和消除过程中的两个重要环节。我们使用从人细胞中纯化得到的酶研究了2',2'-二氟脱氧胞苷（dFdC）的动力学参数。脱氧胞苷（CdR）和dFdC对dCK的Km值分别为1.5和4.6微摩尔。我们还研究了脱氧胞苷5'-三磷酸（dCTP）对dCK的反馈抑制作用。我们的结果表明，当dCTP浓度在1至25微摩尔范围内时，dCTP对dFdC磷酸化的抑制作用比对CdR的抑制作用更强。dFdC是CDA的良好底物。对该酶的动力学研究得出CdR和dFdC的Km值分别为46.3和95.7微摩尔。我们还研究了CDA竞争性抑制剂对dFdC脱氨作用的影响。以CdR或dFdC为底物时，二氮杂卓核苷比四氢尿苷是更有效的抑制剂。CDA抑制剂在癌症患者的临床试验中可能有助于提高dFdC的化疗效果。
