Determination of the phosphorylated metabolites of gemcitabine and of difluorodeoxyuridine by LCMSMS

Does Intracellular Metabolism Render Gemcitabine Uptake Undetectable in Mass Spectrometry?

The ergothioneine transporter ETT (formerly OCTN1; human gene symbol SLC22A4) is a powerful and highly specific transporter for the uptake of ergothioneine (ET). Recently, Sparreboom et al. reported that the ETT would transport nucleosides and nucleoside analogues such as cytarabine and gemcitabine with the highest efficiency. In our assay system, we could not detect any such transport. Subsequently, Sparreboom suggested that the intracellular metabolization of the nucleosides occurs so fast that the original compounds cannot be detected by LC–MS/MS after inward transport. Our current experiments with 293 cells disprove this hypothesis. Uptake of gemcitabine was easily detected by LC–MS/MS measurements when we expressed the Na⁺/nucleoside cotransporter CNT3 (SLC28A3). Inward transport was 1280 times faster than the intracellular production of gemcitabine triphosphate. The deoxycytidine kinase inhibitor 2-thio-2′-deoxycytidine markedly blocked the production of gemcitabine triphosphate. There was no concomitant surge in intracellular gemcitabine, however. This does not fit the rapid phosphorylation of gemcitabine. Uptake of cytarabine was very slow, but detection by MS was still possible. When the ETT was expressed and incubated with gemcitabine, there was no increase in intracellular gemcitabine triphosphate. We conclude that the ETT does not transport nucleosides.

Sensitive liquid chromatography mass spectrometry (LC-MS) assay reveals novel insights on DNA methylation and incorporation of gemcitabine, its metabolite difluorodeoxyuridine, deoxyuridine, and RX-3117 into DNA

Antimetabolites are incorporated into DNA and RNA, affecting their function. Liquid-chromatography-mass-spectrometry (LC-MS-MS) permits the sensitive, selective analysis of normal nucleosides. The method was adapted to measure the incorporation of deoxyuridine, gemcitabine (difluorodeoxycytidine), its metabolite difluorodeoxyuridine (dFdU), and the novel compound fluorocyclopentenylcytosine (RX3117). DNA was degraded to its deoxynucleotides for quantification by LC-MS-MS, gradient chromatography on a Phenomenex prodigy-3-ODS with positive ionization. The range of deoxyuridine DNA-mis-incorporation varied nine-fold in 27 cell lines (leukemia, colon, ovarian, lung cancer). At low-folate conditions a 2.1-fold increase in deoxyuridine was observed. Global methylation (given as % 5-methyl-deoxycytidine) was comparable between the cell lines (4.6-6.5%). Exposure of A2780 cells to 1 μM gemcitabine (4 hours) resulted in 3.6 pmol gemcitabine/μg DNA, but in AG6000 cells (deoxycytidine-kinase-deficient) no incorporation was found. However, when A2780, AG6000, or CCRF-CEM cells were exposed to 100 μM dFdU we found it as gemcitabine, 20.5, 19.6, and 0.51 pmol gemcitabine/μg DNA, respectively. Preincubation of CCRF-CEM cells with cyclopentenyl-cytosine (a CTP-synthetase inhibitor) increased dFdU incorporation four-fold. Apparently dFdU is activated independently of deoxycytidine-kinase and possibly converted in-situ to dFdCMP. RX3117 was incorporated into both DNA and RNA (0.0037 and 0.00515 pmol/μg, respectively). In summary, a sensitive method to quantify the incorporation of gemcitabine, deoxyuridine, and RX-3117 was developed, which revealed that dFdU was incorporated into DNA as the parent compound gemcitabine.

Pharmacokinetics and pharmacogenetics of Gemcitabine as a mainstay in adult and pediatric oncology: an EORTC-PAMM perspective

Gemcitabine is an antimetabolite ranking among the most prescribed anticancer drugs worldwide. This nucleoside analog exerts its antiproliferative action after tumoral conversion into active triphosphorylated nucleotides interfering with DNA synthesis and targeting ribonucleotide reductase. Gemcitabine is a mainstay for treating pancreatic and lung cancers, alone or in combination with several cytotoxic drugs (nab-paclitaxel, cisplatin and oxaliplatin), and is an option in a variety of other solid or hematological cancers. Several determinants of response have been identified with gemcitabine, i.e., membrane transporters, activating and inactivating enzymes at the tumor level, or Hedgehog signaling pathway. More recent studies have investigated how germinal genetic polymorphisms affecting cytidine deaminase, the enzyme responsible for the liver disposition of gemcitabine, could act as well as a marker for clinical outcome (i.e., toxicity, efficacy) at the bedside. Besides, constant efforts have been made to develop alternative chemical derivatives or encapsulated forms of gemcitabine, as an attempt to improve its metabolism and pharmacokinetics profile. Overall, gemcitabine is a drug paradigmatic for constant searches of the scientific community to improve its administration through the development of personalized medicine in oncology.

Molecular mechanisms involved in the synergistic interaction of the EZH2 inhibitor 3-deazaneplanocin A with gemcitabine in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is characterized by overexpression of enhancer of Zeste homolog-2 (EZH2), which plays a pivotal role in cancer stem cell (CSC) self-renewal through methylation of histone H3 lysine-27 (H3K27me3). Against this background, EZH2 was identified as an attractive target, and we investigated the interaction of the EZH2 inhibitor DZNeP with gemcitabine. EZH2 expression was detected by quantitative PCR in 15 PDAC cells, including seven primary cell cultures, showing that expression values correlated with their originator tumors (Spearman R(2) = 0.89, P = 0.01). EZH2 expression in cancer cells was significantly higher than in normal ductal pancreatic cells and fibroblasts. The 3-deazaneplanocin A (DZNeP; 5 μmol/L, 72-hour exposure) modulated EZH2 and H3K27me3 protein expression and synergistically enhanced the antiproliferative activity of gemcitabine, with combination index values of 0.2 (PANC-1), 0.3 (MIA-PaCa-2), and 0.7 (LPC006). The drug combination reduced the percentages of cells in G(2)-M phase (e.g., from 27% to 19% in PANC-1, P < 0.05) and significantly increased apoptosis compared with gemcitabine alone. Moreover, DZNeP enhanced the mRNA and protein expression of the nucleoside transporters hENT1/hCNT1, possibly because of the significant reduction of deoxynucleotide content (e.g., 25% reduction of deoxycytidine nucleotides in PANC-1), as detected by liquid chromatography/tandem mass spectrometry. DZNeP decreased cell migration, which was additionally reduced by DZNeP/gemcitabine combination (-20% in LPC006, after 8-hour exposure, P < 0.05) and associated with increased E-cadherin mRNA and protein expression. Furthermore, DZNeP and DZNeP/gemcitabine combination significantly reduced the volume of PDAC spheroids growing in CSC-selective medium and decreased the proportion of CD133+ cells. All these molecular mechanisms underlying the synergism of DZNeP/gemcitabine combination support further studies on this novel therapeutic approach for treatment of PDACs.