Rapid quantitative determination of L-FMAU-TP from human peripheral-blood mononuclear cells of hepatitis B virus-infected patients treated with L-FMAU by ion-pairing, reverse-phase, liquid chromatography/electrospray tandem mass spectrometry

The purpose of this study was to develop an analytical method for the determination of 2'-fluoro-5-methyl-beta-l-arabinofuranosyl uracil triphosphate (L-FMAU-TP) in human peripheral blood mononuclear cells (PBMCs), and its application in the determination of cellular levels of L-FMAU-TP in PBMCs isolated from patients treated with 2'-fluoro-5-methyl-beta-l-arabinofuranosyl uracil (L-FMAU). An ion-pairing liquid chromatography (IPC) method, coupled with negative ion electrospray ionization tandem mass spectrometry (ESI-MS/MS), was developed for the accurate and repeatable detection of L-FMAU-TP, with a limit of detection of 1.6 pmol/10 cells. The calibration curve for L-FMAU-TP was linear over the concentration range 1.6 to 80 pmol/10(6) cells. The intra- and inter-day precision was lower than 11.2%, and the accuracy was between 97.1 and 106.9%. When applied to the determination of L-FMAU-TP in PBMCs isolated from HBV-infected patients undergoing L-FMAU treatment, the levels reached a steady state concentration 4 weeks after daily single oral administration of 20 mg L-FMAU, and these levels were maintained for up to 12 weeks, but then decreased 12 weeks after drug cessation. The terminal half-life of L-FMAU-TP in PBMCs after drug cessation was estimated to be 15.6 days.

Inhibitory activity of dioxolane purine analogs on wild-type and lamivudine-resistant mutants of hepadnaviruses

To design combination strategies for chronic hepatitis B therapy, we evaluated in vitro the inhibitory activity of 4 nucleoside analogs, (-)FTC, L-FMAU, DXG, and DAPD, in comparison with lamivudine (3TC) and PMEA. In a cell-free assay for the expression of wild-type duck hepatitis B virus (DHBV) reverse transcriptase, DAPD-TP was found to be the most active on viral minus strand DNA synthesis, including the priming reaction, followed by 3TC-TP, (-)FTC-TP, and DXG-TP, whereas L-FMAU-TP was a weak inhibitor. In cell culture experiments, important differences in drug concentration allowing a 50% inhibition of viral replication or polymerase activity (IC50s) were observed depending on the cell type used, showing that antiviral effect of nucleoside analogs may depend on their intracellular metabolism. IC50s obtained for wild-type DHBV replication in primary duck hepatocytes were much lower than with DHBV transfected LMH cells. IC50s were also significantly lower in the 2.2.1.5 and HepG2 cells compared with HBV transfected HuH7 cells. Moreover, L-FMAU inhibited preferentially HBV plus strand DNA synthesis in these cell lines. The antiviral effect of these inhibitors was also evaluated against 3TC-resistant mutants of the DHBV and HBV polymerases. These mutants were found to be cross resistant to (-)FTC. By contrast, the double DHBV polymerase mutant was sensitive to DXG-TP and DAPD-TP. Moreover, both purine analogs remained active against DHBV and HBV 3TC-resistant mutants in transfected LMH and HepG2 cells, respectively. In conclusion, the unique mechanism of action of these new inhibitors warrants further evaluation in experimental models to determine their capacity to delay or prevent the selection of drug resistant mutants.

Inhibition of the replication of the DNA polymerase M550V mutation variant of human hepatitis B virus by adefovir, tenofovir, L-FMAU, DAPD, penciclovir and lobucavir

Several nucleoside analogues (penciclovir, lobucavir, dioxalane guanine [DXG], 1-beta-2,6-diaminopurine dioxalane [DAPD], L-FMAU, lamivudine) and acyclic nucleoside phosphonate analogues (adefovir, tenofovir) that are in clinical use, in clinical trials or under preclinical development for the treatment of hepatitis B virus (HBV) infections, were evaluated for their inhibitory effect on the replication of a la- mivudine-resistant HBV variant containing the methionine --> valine substitution (M550V) in the polymerase nucleoside-binding domain. The antiviral activity was determined in the tetracycline-responsive HepAD38 and HepAD79 cells, which are stably transfected with either a cDNA copy of the wild-type pregenomic RNA or with cDNA containing the M550V mutation. As expected, lamivudine was much less ( approximately 200-fold) effective at inhibiting replication of the M550V mutant virus than the wild-type virus. In contrast, adefovir, tenofovir, lobucavir, L-FMAU, DXG and DAPD proved almost equally effective against both viruses. A second objective of this study was to directly compare the antiviral potency of the anti-HBV agents in HepG2 2.2.15 cells (which are routinely used for anti-HBV drug-screening purposes) with that in HepAD38 cells. HepAD38 cells produce much larger quantities of HBV than HepG2 2.2.15 cells, and thus allow drug screening in a multiwell plate format. All compounds were found to be almost equally effective at inhibiting HBV replication in HepAD38 cells (as in HepG2 2.2.15 cells), except for penciclovir, which was clearly less effective in HepAD38 cells.

Unique inhibitory effect of 1-(2'-deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil 5'-triphosphate on Epstein-Barr virus and human DNA polymerases

1-(2'-Deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil (L-FMAU) was shown to have potent antiviral activity against Epstein-Barr virus (EBV) without any cellular toxicity at concentrations up to 200 microM (Yao et al., Biochem Pharmacol 51: 941-947, 1996). The 5'-triphosphate of L-FMAU was not a substrate for EBV or cellular DNA polymerases, but could inhibit the elongation reaction, 3'-to-5' exonuclease activity, and nucleotide turnover catalyzed by EBV DNA polymerase. DNA synthesis catalyzed by human DNA polymerases was inhibited to a lesser extent. The inhibition pattern of EBV DNA polymerase by L-FMAU-5'-triphosphate (L-FMAU-TP) was consistent with an uncompetitive mechanism when dNTP or template-primer were used as the variable substrates. The Ki values were 38+/-10 microM for the elongation reaction, and about 50+/-10 microM for both nucleotide exchange and 3'-to-5' exonuclease reactions, values that were 10-20 times less than that for GMP. L-FMAU-TP is the first nucleoside 5'-triphosphate shown to have such unique behavior toward DNA polymerases. EBV DNA polymerase could be one of the targets for the inhibitory effect of L-FMAU-TP on EBV replication.

Human cytomegalovirus-induced DNA polymerase and its interaction with the triphosphates of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil, -5-iodocytosine, and -5-methylcytosine

Human cytomegalovirus-induced DNA polymerase and cellular DNA polymerase alpha were purified by successive chromatography on DEAE-cellulose, phosphocellulose, heparin agarose, and single-stranded DNA agarose columns. The purified virus-induced DNA polymerase was resolved to consist of two polypeptides corresponding to molecular weights of 140,000 and 58,000, as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Virus-induced DNA polymerase and cellular alpha polymerase were examined for their sensitivities to the triphosphates of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAUTP), -5-iodocytosine (FIACTP), and -5-methylcytosine (FMACTP). The inhibitive effects of these triphosphates on the DNA polymerases were competitive with regard to the natural substrates; thus FMAUTP competes with dTTP, and FIACTP and FMACTP compete with dCTP. The inhibition constants (Ki) for FMAUTP, FIACTP, and FMACTP of virus-induced DNA polymerase are 0.06, 0.30, and 0.47 microM, respectively. Cellular DNA polymerase alpha is much less sensitive to these inhibitors, and its Ki values for FMAUTP, FIACTP, and FMACTP are 0.45, 3.10, and 2.90 microM, respectively. In addition, human cytomegalovirus-induced DNA polymerase, but not cellular DNA polymerase alpha, can utilize these analog triphosphates as alternate substrates for their corresponding natural deoxyribonucleoside triphosphates in in vitro DNA synthesis.

Studies on biologically active nucleosides and nucleotides. 5. Synthesis and antitumor activity of some 2,2'-anhydro-1-(3',5'-di-O-acyl-beta-D-arabinofuranosyl)cytosine salts and 2,2'-anhydro-1-(3'-O-acyl-beta-D-arabinofuranoxyl)cytosine 5'-phosphates

A series of 3',5'-diesters of a 2,2'-anhydro-1-(beta-D-arabinofuranosyl)cytosine salt bearing functional substituents on the ester side chains (4--16) have been synthesized. The synthesis of these diesters involved the reaction between cytidine and the corresponding acid anhydride or acid chloride in the presence of boron trifluoride etherate. Similar reaction of bis(cytidine 5'-)suberate (21) with pivaloyl chloride gave bis[2,2'-anhydro-1-(3'-O-pivaloyl-beta-D-arabinofuranosyl)cytosine 5'-]suberate dihydrochloride (22). The reaction could also be extended to a one-step synthesis of 3'-esters of 2,2'-anhydro-1-(beta-D-arabinofuranosyl)cytosine 5'-phosphate (24) from 5'-cytidylic acid. These compounds have been examined for antitumor activity against L1210 leukemia in BDF1 mice. The diesters with a long-chain carboxylic acid (4c, 7c, 12, and 24d) showed high activity when administered intraperitoneally. The compound 24d exhibited moderate activity when administered orally.