Novel direct detection method for quantitative determination of intracellular nucleoside triphosphates using weak anion exchange liquid chromatography/tandem mass spectrometry

HIV-1 resistance profile of the novel nucleoside reverse transcriptase inhibitor beta-D-2',3'-dideoxy-2',3'-didehydro-5-fluorocytidine (Reverset)

Nucleoside reverse transcriptase inhibitors (NRTIs) represent the cornerstone of highly active antiretroviral therapy when combined with non-nucleoside reverse transcriptase inhibitors (NNRTIs) or HIV-1 protease inhibitors (PIs). Unlike the NNRTIs and PIs, NRTIs must be successively phosphorylated by cellular kinases to a triphosphate form, which represents the active metabolite possessing antiviral activity. Emergence of viral resistance to NRTIs has severely hampered treatment options for persons infected with HIV-1. As such, there is an urgent need to develop NRTIs capable of suppressing NRTI-resistant strains of HIV-1. We have recently reported that the cytidine analogue D-d4FC (DPC817, Reverset) effectively inhibits clinically prevalent resistant strains of HIV-1. In this report, we have extended these findings and now describe a detailed resistance profile for this novel NRTI. By examining a panel of 50 viruses carrying RTs derived from HIV-1 clinical isolates displaying a wide range of NRTI resistance mutations, we report that the median fold increase in effective antiviral concentration for such a panel of viruses is 3.2, which is comparable to tenofovir (2.8-fold) and didanosine (2.4-fold). D-d4FC is highly effective at inhibiting subsets of lamivudine- and zidovudine-resistant variants but, like other NRTIs, seems less potent against multi-NRTI-resistant viruses, particularly those carrying the Q151M complex of mutations. Finally, in vitro selections for HIV-1 mutants capable of replicating in the presence of D-d4FC yielded a mutant carrying the RT K65R mutation. This mutation confers 5.3- to 8.7-fold resistance to D-d4FC in vitro. These findings suggest that D-d4FC may represent an alternative NRTI for the treatment of individuals infected with lamivudine- and zidovudine-resistant strains of HIV-1.

Cellular pharmacology of D-d4FC, a nucleoside analogue active against drug-resistant HIV

The backbone of effective highly active antiretroviral therapy regimens for the treatment of HIV infections currently contains at least two nucleosides. Among the features that influence the potency of each component of a regimen and the overall efficacy of the combination are the cellular uptake and bioconversion of nucleoside analogues to their active triphosphate form, and the extent of possible interactions in these steps that might occur when more than one nucleoside is used in a regimen. D-d4FC (Reverset), a new cytidine analogue with the ability to inhibit many nucleoside-resistant viral variants, was examined for these parameters. In phytohemaglutinin-stimulated human peripheral blood mononuclear cells, D-d4FC was taken up in a rapid (8 h to 50% maximal value), saturable (plateau above 10 microM parent nucleoside concentration) process, resulting in levels of D-d4FC triphosphate that should provide potent antiviral activity against a variety of virus genotypes. Based on measurement of antiviral effects in cell culture, additive and in some cases, synergistic interactions were observed with protease inhibitors, non-nucleoside reverse transcriptase inhibitors or other nucleosides, including cytidine analogues.

Application of co-eluting structural analog internal standards for expanded linear dynamic range in liquid chromatography/electrospray mass spectrometry

Non-linear standard calibration curves occur frequently in liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), necessitating the use of non-linear regression curve fitting or a reduction in assay dynamic range. Non-linearity can be minimized by the use of stable isotope internal standards, if the cause of curve bending is ionization saturation. Unfortunately, stable isotope internal standards can be difficult or expensive to synthesize. Structural analog internal standards, if sufficiently close to analytes both in chemical structures and HPLC retention times, may mimic the effect of stable isotope internal standards. Tentative experimental evidence supporting this concept is presented in this paper.