Kinetic studies on 2',2'-difluorodeoxycytidine (Gemcitabine) with purified human deoxycytidine kinase and cytidine deaminase

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites, Antineoplastic / metabolism*
  • Azepines / pharmacology
  • Cytidine Deaminase / antagonists & inhibitors
  • Cytidine Deaminase / metabolism*
  • Deoxycytidine / analogs & derivatives*
  • Deoxycytidine / metabolism
  • Deoxycytidine / pharmacokinetics
  • Deoxycytidine Kinase / isolation & purification
  • Deoxycytidine Kinase / metabolism*
  • Deoxycytosine Nucleotides / pharmacology
  • Half-Life
  • Humans
  • Kinetics
  • Tetrahydrouridine / pharmacology


  • Antimetabolites, Antineoplastic
  • Azepines
  • Deoxycytosine Nucleotides
  • Deoxycytidine
  • Tetrahydrouridine
  • 2'-deoxycytidine 5'-triphosphate
  • diazepinone riboside
  • gemcitabine
  • Deoxycytidine Kinase
  • Cytidine Deaminase