In vitro studies on the immunosuppressive effect of 2',2'-difluorodeoxycytidine (dFdC) and its metabolite 2',2'-difluorodeoxyuridine (dFdU)

Effects of anticancer agents on cell viability, proliferative activity and cytokine production of peripheral blood mononuclear cells

We investigated the effects of anticancer agents on peripheral blood mononuclear cells for the purpose of providing data to support new translational chemoimmunotherapy regimens. Peripheral-blood mononuclear cells were treated with one of four anticancer agents (5-fluorouracil, irinotecan, cisplatin, and gemcitabine) for 2 h, after which cell viability was determined. For assessment of effects of each drug on proliferation and cytokine production, cells were stimulated with phytohemagglutinin for 48 h. As a result, the anticancer agents did not affect cell viability. Cell proliferation was unaffected by 5-fluorouracil and irinotecan but inhibited by cisplatin and gemcitabine. Treatment with gemcitabine enhanced the production of IFN-γ and decreased the number of regulatory T cells. gemcitabine treatment increased IFN-γ production among CD4 T cells but not among CD8 T cells. The results indicated that GEM had immunoregulatory properties that might support immune response against cancer. This finding has implications for designing chemoimmunotherapy strategies.

Deoxyuridine analog nucleotides in deoxycytidine analog treatment: secondary active metabolites?

Deoxycytidine analogs (dCa's) are nucleosides widely used in anticancer and anti (retro) viral therapies. Intracellularly phosphorylated dCa anabolites are considered to be their main active metabolites. This article reviews the literature on the formation and pharmacological activity of deaminated dCa nucleotides. Most dCa's are rapidly deaminated into deoxyuridine analogs (dUa's) which are only slowly phosphorylated and therefore relatively inactive. dUa nucleotides are, however, also formed via deamination of dCa monophosphates by deoxycytidine monophosphate deaminase (dCMPD). dUa-monophosphates can interact with thymidylate synthase (TS), whereas dUa-triphosphates are incorporated into nucleic acids and interfere with polymerases. Administration of dCa's as monophosphate prodrugs or co-administration of the cytidine deaminase inhibitor tetrahydrouridine (THU) does not prevent dUa nucleotide formation which is, on the other hand, influenced by the dose and dCMPD activity. Taken together, these observations show that the formation of dUa nucleotides is a common phenomenon in treatment with dCa's and these compounds may play a role in treatment outcome. We conclude that more attention should be given to these relatively unknown, but potentially important metabolites.

Combinatorial pharmacologic effects of gemcitabine and its metabolite dFdU

Recent evidence has shown that the gemcitabine metabolite, dFdU, is pharmacologically active. Though less potent, dFdU has a longer half-life and could potentiate or antagonize the activity of gemcitabine. Hence, studies were undertaken to evaluate the combined effects. Following chemical synthesis, an improved purification procedure for dFdU was developed (80 % yield; >99 % purity). Zebrafish phenotype-based embryo screens revealed no acute toxicity after gemcitabine or dFdU treatment. Only gemcitabine affected zebrafish development in a dose-dependent manner. Synergy or antagonism for the combination was not observed. Antitumor effects for dFdU were dose dependent. Antagonism was tumor cell-line dependent and did not depend on formation of the intracellular active metabolite of gemcitabine, suggesting that the drug-metabolite interaction occurs later. These studies highlight a platform for testing the pharmacologic activity for anticancer agent and metabolite combinations. Such analyses are expected to provide insight into the beneficial or harmful effect(s) of metabolites towards parent drug activity.

Pharmacokinetics of gemcitabine and metabolites in a patient with double-sided nephrectomy: a case report and review of the literature

CASE

A patient with complete renal failure as a result of urothelial cell carcinoma-related nephrectomy of both kidneys received palliative chemotherapy with carboplatin and gemcitabine.

TREATMENT

The patient received gemcitabine at 1,000 mg/m(2) followed by carboplatin at 100 mg. Shortly after, he underwent hemodialysis. The pharmacokinetics of gemcitabine and metabolites in plasma and in peripheral blood mononuclear cells were monitored.

RESULTS

Double-sided nephrectomy and hemodialysis had no influence on gemcitabine pharmacokinetics; however, a high exposure was seen for the main metabolite, difluordeoxyuridine (dFdU) (area under the concentration-time curve, 0-51 hours, 844 microg/ml.hour). During hemodialysis, plasma concentrations of dFdU were reduced by 50%. High concentrations of intracellular phosphorylated metabolites (gemcitabine triphosphate and dFdU triphosphate) were observed: 228 pmol/10(6) cells and 47 pmol/10(6) cells, respectively. The patient tolerated the regimen poorly; adverse events included grade 4 thrombocytopenia.

CONCLUSION

Hemodialysis effectively reduced plasma concentrations of dFdU. Furthermore, high concentrations of intracellular phosphorylated metabolites may be related to double-sided nephrectomy, resulting in poor tolerability of gemcitabine.

Combined chemoimmunotherapy of solid tumours: improving vaccines?

Cytotoxic chemotherapy not only affects the tumour but also targets dividing lymphocytes, the very cells required to develop an immune response. Hence, chemo- and immunotherapy have been seen as antagonistic. It is now clear that the way a chemotherapeutic drug kills a tumour cell determines how that dying cell interacts with the immune system and whether the interaction leads to an immune response. Chemotherapy also depletes regulatory T cells, potentially enhancing immune responses. Furthermore, lymphodepletion triggers homeostatic T cell reconstitution, creating new populations of pre-T cells that need education in the thymic environment. Post-chemotherapy immune system reconstitution may provide a unique opportunity for therapeutic intervention by shaping the repertoire towards reactivity to tumour antigens. An understanding of the underlying cellular and immunological events in both animal models and patients undergoing chemotherapy will guide decisions about which immunomodulatory approaches may be effective with different cytostatic drugs and hence to develop appropriate scheduling for integration of the treatment modalities.