Br J Clin Pharmacol. 2018;84:1279-1289. doi: 10.1111/bcp.13557.

Intracellular pharmacokinetics of gemcitabine, its deaminated metabolite 2′,2′-difluorodeoxyuridine and their nucleotides.

Derissen EJB 1,2, Huitema ADR 1,3, Rosing H 1, Schellens JHM 4,5, Beijnen JH 1,5.

  1. Department of Pharmacy & Pharmacology, Antoni van Leeuwenhoek Hospital – The Netherlands Cancer Institute and MC Slotervaart, Louwesweg, 6, 1066, EC, Amsterdam, The Netherlands.
  2. Department of Clinical Pharmacology and Pharmacy, VU University Medical Center, De Boelelaan 1117, 1081, HV, Amsterdam, The Netherlands.
  3. Department of Clinical Pharmacy, University Medical Center Utrecht, Heidelberglaan 100, 3584, CX, Utrecht, The Netherlands.
  4. Department of Clinical Pharmacology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066, CX, Amsterdam, The Netherlands.
  5. Science Faculty, Utrecht Institute for Pharmaceutical Sciences (UIPS), Division of Pharmaco-epidemiology & Clinical Pharmacology, Utrecht University, P.O. Box 80082, 3508, TB, Utrecht, The Netherlands.



AIMS: Gemcitabine (2′,2′-difluoro-2′-deoxycytidine; dFdC) is a prodrug that has to be phosphorylated within the tumour cell to become active. Intracellularly formed gemcitabine diphosphate (dFdCDP) and triphosphate (dFdCTP) are considered responsible for the antineoplastic effects of gemcitabine. However, a major part of gemcitabine is converted into 2′,2′-difluoro-2′-deoxyuridine (dFdU) by deamination. In the cell, dFdU can also be phosphorylated to its monophosphate (dFdUMP), diphosphate (dFdUDP) and triphosphate (dFdUTP). In vitro data suggest that these dFdU nucleotides might also contribute to the antitumour effects, although little is known about their intracellular pharmacokinetics (PK). Therefore, the objective of the present study was to gain insight into the intracellular PK of all dFdC and dFdU nucleotides formed during gemcitabine treatment.

METHODS: Peripheral blood mononuclear cell (PBMC) samples were collected from 38 patients receiving gemcitabine, at multiple time points after infusion. Gemcitabine, dFdU and their nucleotides were quantified in PBMCs. In addition, gemcitabine and dFdU plasma concentrations were monitored. The individual PK parameters in plasma and in PBMCs were determined.

RESULTS: Both in plasma and in PBMCs, dFdU was present in higher concentrations than gemcitabine [mean intracellular area under the concentration-time curve from time zero to 24 h (AUC0-24 h) 1650 vs. 95 μM*h]. However, the dFdUMP, dFdUDP and dFdUTP concentrations in PBMCs were much lower than the dFdCDP and dFdCTP concentrations. The mean AUC0-24 h for dFdUTP was 312 μM*h vs. 2640 μM*h for dFdCTP.

CONCLUSIONS: The study provides the first complete picture of all nucleotides that are formed intracellularly during gemcitabine treatment. Low intracellular dFdU nucleotide concentrations were found, which calls into question the relevance of these nucleotides for the cytotoxic effects of gemcitabine.

PMID: 29451684



This study demonstrated that dFdU is only phosphorylated to a very limited extent in PBMCs. Future studies should show whether dFdU is also hardly phosphorylated in tumour cells. If this is the case, dFdU is unlikely to contribute substantially to the cytotoxic effects of gemcitabine.

If dFdU does not substantially contribute to the cytotoxic effects of gemcitabine, it is rational to pay more attention to inter-individual differences in the deamination rate of gemcitabine to dFdU. Some clinical studies have shown that gemcitabine therapy was more effective and more toxic in patients with low cytidine deaminase (CDA) activity, i.e. a decreased deamination of gemcitabine to dFdU [1,2]. Conversely, Serdjebi et al. showed that gemcitabine was less active in pancreatic cancer patients with high CDA activity [3]. Future studies should prove whether individualization of the gemcitabine dose, based on the measured CDA activity, leads to better treatment results.



Figure 1. Gemcitabine metabolism and mechanisms of action.

dFdC, 2’,2’-difluorodeoxycytidine (gemcitabine); dFdCMP, 2’,2’-difluorodeoxycytidine 5’-monophosphate; dFdCDP, 2’,2’-difluorodeoxycytidine 5’-diphosphate; dFdCTP, 2’,2’-difluorodeoxycytidine 5’-triphosphate; dFdU, 2’,2’-difluorodeoxyuridine; dFdUMP, 2’,2’-difluorodeoxyuridine 5’-monophosphate; dFdUDP, 2’,2’-difluorodeoxyuridine 5’-diphosphate; dFdUTP, 2’,2’-difluorodeoxyuridine 5’-triphosphate; dCMP, deoxycytidine monophosphate; dCDP, deoxycytidine diphosphate; dCTP, deoxycytidine triphosphate; hNTs, human nucleoside transporters; UMP-CMP kinase, pyrimidine nucleoside monophosphate kinase. © 2018 The British Pharmacological Society.



[1] Tibaldi C, Giovannetti E, Vasile E, et al. Correlation of CDA, ERCC1, and XPD polymorphisms with response and survival in gemcitabine/cisplatin-treated advanced non-small cell lung cancer patients. Clin Cancer Res 2008; 14: 1797–1803.

[2] Tibaldi C, Giovannetti E, Tiseo M, et al. Correlation of cytidine deaminase polymorphisms and activity with clinical outcome in gemcitabine-/platinum-treated advanced non-small-cell lung cancer patients. Ann Oncol 2012; 23: 670–677.

[3] Serdjebi C, Seitz J-F, Ciccolini J, et al. Rapid deaminator status is associated with poor clinical outcome in pancreatic cancer patients treated with a gemcitabine-based regimen. Pharmacogenomics 2013; 14: 1047–51.