Disease relevance of dFdCTP

• This study shows that sequential treatment of two neuroblastoma cell lines with BL1521, an HDACi, and dFdC resulted in strong antagonism despite a minor increase of dFdCTP incorporation into the DNA of one cell line [1].
• Both sensitivity to dFdC and accumulation of dFdCTP were clearly cell line-dependent: in this panel of cell lines, the head and neck cancer (HNSCC) cell line 22B appeared to be the most sensitive, whereas the small cell lung cancer (SCLC) cell lines were the least sensitive to dFdC [2].

High impact information on dFdCTP

• Gemcitabine is activated by dCyd kinase (dCK) and interferes, as its triphosphate dFdCTP, with tumor growth through incorporation into DNA [3].
• Paclitaxel did not affect the pharmacokinetics of gemcitabine, nor did gemcitabine affect the pharmacokinetics of paclitaxel, but paclitaxel increased dFdCTP accumulation [4].
• The results demonstrated that dFdCyd rapidly accumulated as the 5'-triphosphate dFdCTP in HT-29 cells, which was eliminated slowly in the absence of dFdCyd with a half-life of > 12 h [5].
• PURPOSE: Phase I clinical and in vitro studies of gemcitabine (2',2'-difluorodeoxycytidine; dFdC) have demonstrated that the accumulation rate of dFdC 5'-triphosphate (dFdCTP) in mononuclear and leukemia cells is saturated when plasma or extracellular dFdC levels exceed 15 to 20 mumol/L [6].
• We examined the values for elimination kinetics of cellular dFdCTP and found they were dependent on cellular concentration after incubation of CCRF-CEM cells with dFdC and washing into drug-free medium [7].

Biological context of dFdCTP

• The deamination product 2',2'-difluorodeoxyuridine was the predominant extracellular catabolite at low cellular dFdCTP concentrations, whereas at high dFdCTP concentrations dFdC was the major excretion product [7].
• In addition, dFdCTP inhibited partially purified dCMP deaminase with a 50% inhibitory concentration of 0.46 mM [7].
• In contrast, a CHO mutant deficient in deoxycytidine kinase, and thus unable to accumulate dFdCTP, maintained its CTP pools under identical conditions, suggesting that the CTP pool depletion was dependent on dFdC phosphorylation [8].
• Incorporation of dFdCTP into DNA is most likely the major mechanism by which gemcitabine causes cell death [9].
• Mean plasma Cmax(gemcitabine) and mean dFdCTP AUC in arm A was 20.8 microM +/- 17.2 microM and 35,079 +/- 18,216 microM*min respectively and in arm B, 41.2 +/- 13.9 microM and 32 249 +/- 11 267 microM*min respectively. dFdCTP saturation was reached in Arm B but not in Arm A [10].

Anatomical context of dFdCTP

• In all cell lines, CDDP failed to increase dFdCTP accumulation at 4- or 24-h exposure to dFdC; in two cell lines, CDDP even tended to decrease dFdCTP accumulation [11].
• By treating KB cells with radiolabeled-Gem following HU treatment, we further confirmed that the incorporation of dFdCTP into DNA increased 6-fold over control reactions under these conditions [12].
• The concentration of the active metabolite of gemcitabine, gemcitabine triphosphate (dFdCTP) in peripheral white blood cells, ranged between 37 and 283 pmol/10(6) cells at the end of infusion on day 1 and 35 and 115 pmol/10(6) cells on day 15 [13].
• The stability of dFdCTP in intact mononuclear blood cells on ice is strongly limited (half-life approximately 100 min) and after freezing the half-life of the analyte in the cellular lysate is approximately 30 min [14].

Associations of dFdCTP with other chemical compounds

• In vitro DNA primer extension assays demonstrated that dFdC 5'-triphosphate (dFdCTP) competed with deoxycytidine triphosphate for incorporation into the C sites of the growing DNA strand [15].
• Gemcitabine (dFdC) is a new cytidine analogue which is active mainly by the incorporation of its triphosphate (dFdCTP) into DNA, leading to cell death [16].

Gene context of dFdCTP

• In addition, the increased CTP, ATP, and UTP pools in the MDR variants might explain the increased ara-CTP and dFdCTP accumulation [17].
• In order to determine whether lack of dCK affected the formation of the active triphosphate of the deoxycytidine analog dFdC, dFdCTP accumulation and retention was measured in H9 parental and AZT-resistant cells after exposure to 1 and 10 microM dFdC [18].
• In Colon 26-G, dCK activity was 1.7-fold decreased; dCDA and DNA polymerase were not changed; and Colon 26-G accumulated 1.5-fold less dFdCTP, 6 hours after a gemcitabine injection, than the parental tumor [3].
• The apparent Ki values of dFdCTP were 11.2 microM for DNA polymerase alpha and 14.4 microM for polymerase epsilon [15].
• Initial studies of the mechanism of interaction concentrated on the effect of CDDP on dFdCTP accumulation and DNA strand break formation [11].

Analytical, diagnostic and therapeutic context of dFdCTP

• Conversely, no dFdCTP could be detected in the control xenografts 14 h postinjection [19].
• To test this hypothesis, we examined dFdCyd/dFdCTP uptake and clearance in HT-29 human colon carcinoma xenografts in nude mice by high-performance liquid chromatography (HPLC) and fluorine-19 magnetic resonance spectroscopy (F-19 MRS) [19].
• RESULTS: HPLC experiments revealed an increased tumor accumulation of dFdCTP in xenografts overexpressing dCK compared with wild-type controls (P < or = 0.05). dFdCTP in the dCK-infected tumors was easily identified at 24 h postinjection [19].
• Furthermore, the UTP levels and the CTP/UTP ratio after treatment were related to dFdCTP accumulation [2].
• Intracellular dFdCTP is the critical determinant for dFdC cytotoxicity, so therapeutic drug monitoring or in vitro testing of the capability of cancer cells to accumulate dFdCTP may be informative for optimizing dFdC administration [20].

References