The anti-hepatitis B virus activities, cytotoxicities, and anabolic profiles of the (-) and (+) enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine

Abstract

The anti-hepatitis B (anti-HBV) activities of the (-) and (+) enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine (2'-deoxy-3'-thia-5-fluorocytosine [FTC]) were studied by using an HBVtransfected cell line (HepG2 derivative 2.2.15, subclone P5A). The (-) isomer was found to be a potent inhibitor of viral replication, with an apparent 50% inhibitory concentration of 10 nM, whfle the (+) isomer was found to be considerably less active. Both isomers showed miimal toxicity to HepG2 cells (50% inhibitory concentration, >200 a.M) and showed minimal toxicity in the human bone marrow progenitor cell assay. In accord with the cellular antiviral activity data, the 5'-triphosphate of (-)-FIC inhibited viral DNA synthesis in an endogenous HBV DNA polymerase assay, while the 5'-triphosphate of the (+) isomer was inactive.Unphosphorylated (-)-FTC did not inhibit product formation in the endogenous assay, souggestng that the antiviral activity of the compound is dependent on anabolism to the 5'-triphosphate. Both (-)-and (+)-FTC were anabolized to the corresponding 5'-triphosphates in chronically HBV-infected HepG2 celLs. The rate of accumulation and the steady-state concentration of the 5'-triphosphate of (-)-FTC were greater. Also, (-)-FTC was not a substrate for cytidine deaminase and, therefore, is not subject to d tion and conversion to an inactive uridine analog. The (+) isomer is, however, a good substrate for cytidine deaminase.Hepatitis B virus (HBV), the causative agent of acute and chronic hepatitis, directly affects about 5% of the world's population. Chronic carriers of HBV are at an increased risk of liver damage that, in the worst cases, can lead to cirrhosis of the liver and/or to hepatocellular carcinoma. Vaccination against HBV is one way to effectively prevent HBV infection. However, vaccination is not an effective therapy for the estimated 200 million chronic carriers. Although several antiviral agents such as alpha interferon, adenine arabinoside monophosphate, and acyclovir have been tested as therapeutic agents, only alpha interferon has demonstrated some promise (7,8,9,17,23,25).The replication cycle of hepadnaviruses includes the reverse transcription of an RNA template (6). This process is catalyzed by a polymerase that shares significant sequence homology with the reverse transcriptase from retroviruses (17). As a consequence, it has been demonstrated that a number of compounds that inhibit human immunodeficiency virus (HIV) replication in vitro (for example, 2',3'-dideoxycytidine) also inhibit HBV replication in vitro (4,14,15,18,24). These agents await further study to determine their usefulness as therapeutic agents for the treatment of HBV infections.Here we report the anti-HBV activities, cytotoxicities, and anabolism of the resolved enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine (FTC) (Fig. 1). The anti-HBV activity of the racemic material has been reported previously (4). Our results show that the * Corresponding authors. antiviral activ...

Cellular and molecular events leading to mitochondrial toxicity of 1-(2-deoxy-2-fluoro-1-beta-D-arabinofuranosyl)-5-iodouracil in human liver cells.

“…These studies emphasize the importance of such biochemical studies in the development of novel entities for the treatment of viral infections and underlines the potential role of metabolites such as FMAU in a possible synergistic toxicity with the parent drug. The absence of such mitochondria effects with 3TC (Table II) and (-)-2',3'-dideoxy-5-fluoro-3'-thiacytidine (39), two nucleoside analogs being developed for the treatment of HIV and HBV infections (40)(41)(42) demonstrate that each nucleoside should be considered as a unique entity and further emphasizes the usefulness of that class of compound to treat such viral infections.…”

The Enantioselectivity of Enzymes Involved in Current Antiviral Therapy Using Nucleoside Analogues: A New Strategy?

“…This is likely in view of the fact that both D-and L-FTCMP are substrates of calf thymus dCMPK with a preference for the L-enantiomer (E L/D =8.1) (Furman et al, 1992). No study of the interaction of dCMPK with β-ddCMP or β-FddCMP has been reported.…”

“…Thus, the β-L-enantiomer of dC, or the α-L-and β-L-enantiomers of riboC, araC, xyloC and lyxoC were resistant to human CDA (Shafiee et al, 1998). Similarly, the β-L-enantiomers of 3TC (Chang et al, 1992a), FTC (Furman et al, 1992), FddC (Martin et al, 1997) and Fd4C were not substrates or weak substrates of CDA, contrary to the corresponding β-D-enantiomers. E. coli CDA has been used to develop a process for the production of β-L-3TC in multikilogram amounts, which is based on the exclusive deamination of the D-enantiomer from the racemic mixture (Mahmoudian et al, 1993) (Figure 10).…”

Antiviral β-L-nucleosides specific for hepatitis B virus infection

“…Furthermore, the 5Ј-triphosphates of L-dC, L-dT, and L-dA each inhibited WHV DNA polymerase with a 50% inhibitory concentration of 0.24 to 1.82 M. In addition, exposure of HepG2 cells to L-dC led to a second 5Ј-triphosphate derivative, i.e., ␤-L-2Ј-dUTP (LdUTP) which also inhibited WHV DNA polymerase, with a 50% inhibitory concentration of 5. (4,19,31,51), L-dC was not a substrate for cytosolic cytidine deaminase, which suggested that the 5Ј-monophosphate metabolite of L-dC may be susceptible to deamination through deoxycytidylate deaminase. The inhibition of HBV replication by these ␤-L-2Ј-deoxynucleosides and inhibition of hepadnaviral polymerase by their corresponding 5Ј-triphosphates suggested that, like most nucleoside analogs, L-dC, L-dT, and L-dA may act by inhibiting the reverse transcription of HBV pregenomic RNA.…”